xnu-3248.30.4.tar.gz

[apple/xnu.git] / osfmk / ipc / ipc_voucher.c

/*
 * Copyright (c) 2013 Apple Inc. All rights reserved.
 *
 * @APPLE_OSREFERENCE_LICENSE_HEADER_START@
 *
 * This file contains Original Code and/or Modifications of Original Code
 * as defined in and that are subject to the Apple Public Source License
 * Version 2.0 (the 'License'). You may not use this file except in
 * compliance with the License. The rights granted to you under the License
 * may not be used to create, or enable the creation or redistribution of,
 * unlawful or unlicensed copies of an Apple operating system, or to
 * circumvent, violate, or enable the circumvention or violation of, any
 * terms of an Apple operating system software license agreement.
 *
 * Please obtain a copy of the License at
 * http://www.opensource.apple.com/apsl/ and read it before using this file.
 *
 * The Original Code and all software distributed under the License are
 * distributed on an 'AS IS' basis, WITHOUT WARRANTY OF ANY KIND, EITHER
 * EXPRESS OR IMPLIED, AND APPLE HEREBY DISCLAIMS ALL SUCH WARRANTIES,
 * INCLUDING WITHOUT LIMITATION, ANY WARRANTIES OF MERCHANTABILITY,
 * FITNESS FOR A PARTICULAR PURPOSE, QUIET ENJOYMENT OR NON-INFRINGEMENT.
 * Please see the License for the specific language governing rights and
 * limitations under the License.
 *
 * @APPLE_OSREFERENCE_LICENSE_HEADER_END@
 */

#include <mach/mach_types.h>
#include <mach/notify.h>
#include <ipc/ipc_types.h>
#include <ipc/ipc_port.h>
#include <ipc/ipc_voucher.h>
#include <kern/ipc_kobject.h>
#include <kern/ipc_tt.h>
#include <kern/mach_param.h>
#include <kern/kalloc.h>
#include <kern/zalloc.h>

#include <libkern/OSAtomic.h>

#include <mach/mach_voucher_server.h>
#include <mach/mach_voucher_attr_control_server.h>
#include <mach/mach_host_server.h>

/*
 * Sysctl variable; enable and disable tracing of voucher contents
 */
uint32_t ipc_voucher_trace_contents = 0;

static zone_t ipc_voucher_zone;
static zone_t ipc_voucher_attr_control_zone;

/*
 * Voucher hash table
 */
#define IV_HASH_BUCKETS 127
#define IV_HASH_BUCKET(x) ((x) % IV_HASH_BUCKETS)

static queue_head_t ivht_bucket[IV_HASH_BUCKETS];
static lck_spin_t ivht_lock_data;
static uint32_t ivht_count = 0;

#define ivht_lock_init() \
        lck_spin_init(&ivht_lock_data, &ipc_lck_grp, &ipc_lck_attr)
#define ivht_lock_destroy() \
        lck_spin_destroy(&ivht_lock_data, &ipc_lck_grp)
#define ivht_lock() \
        lck_spin_lock(&ivht_lock_data)
#define ivht_lock_try() \
        lck_spin_try_lock(&ivht_lock_data)
#define ivht_unlock() \
        lck_spin_unlock(&ivht_lock_data)

/*
 * Global table of resource manager registrations
 *
 * NOTE: For now, limited to well-known resource managers
 * eventually, will include dynamic allocations requiring
 * table growth and hashing by key.
 */
static iv_index_t ivgt_keys_in_use = MACH_VOUCHER_ATTR_KEY_NUM_WELL_KNOWN;
static ipc_voucher_global_table_element iv_global_table[MACH_VOUCHER_ATTR_KEY_NUM_WELL_KNOWN];
static lck_spin_t ivgt_lock_data; 

#define ivgt_lock_init() \
        lck_spin_init(&ivgt_lock_data, &ipc_lck_grp, &ipc_lck_attr)
#define ivgt_lock_destroy() \
        lck_spin_destroy(&ivgt_lock_data, &ipc_lck_grp)
#define ivgt_lock() \
        lck_spin_lock(&ivgt_lock_data)
#define ivgt_lock_try() \
        lck_spin_try_lock(&ivgt_lock_data)
#define ivgt_unlock() \
        lck_spin_unlock(&ivgt_lock_data)

ipc_voucher_t iv_alloc(iv_index_t entries);
void iv_dealloc(ipc_voucher_t iv, boolean_t unhash);

static inline iv_refs_t
iv_reference(ipc_voucher_t iv)
{
        iv_refs_t refs;

        refs = hw_atomic_add(&iv->iv_refs, 1);
        return refs;
}

static inline void
iv_release(ipc_voucher_t iv)
{
        iv_refs_t refs;

        assert(0 < iv->iv_refs);
        refs = hw_atomic_sub(&iv->iv_refs, 1);
        if (0 == refs)
                iv_dealloc(iv, TRUE);
}

/*
 * freelist helper macros
 */
#define IV_FREELIST_END ((iv_index_t) 0)

/*
 * Attribute value hashing helper macros
 */
#define IV_HASH_END UINT32_MAX
#define IV_HASH_VAL(sz, val) \
        (((val) >> 3) % (sz))

static inline iv_index_t
iv_hash_value(
        iv_index_t key_index,
        mach_voucher_attr_value_handle_t value)
{
        ipc_voucher_attr_control_t ivac;

        ivac = iv_global_table[key_index].ivgte_control;
        assert(IVAC_NULL != ivac);
        return IV_HASH_VAL(ivac->ivac_init_table_size, value);
}

/*
 * Convert a key to an index.  This key-index is used to both index
 * into the voucher table of attribute cache indexes and also the
 * table of resource managers by key.
 *
 * For now, well-known keys have a one-to-one mapping of indexes
 * into these tables.  But as time goes on, that may not always
 * be the case (sparse use over time).  This isolates the code from
 * having to change in these cases - yet still lets us keep a densely
 * packed set of tables.
 */
static inline iv_index_t
iv_key_to_index(mach_voucher_attr_key_t key)
{
        if (MACH_VOUCHER_ATTR_KEY_ALL == key ||
            MACH_VOUCHER_ATTR_KEY_NUM_WELL_KNOWN < key)
                return IV_UNUSED_KEYINDEX;
        return (iv_index_t)key - 1;
}

static inline mach_voucher_attr_key_t
iv_index_to_key(iv_index_t key_index)
{
        if (MACH_VOUCHER_ATTR_KEY_NUM_WELL_KNOWN > key_index)
                return iv_global_table[key_index].ivgte_key;
        return MACH_VOUCHER_ATTR_KEY_NONE;
                
}

static void ivace_release(iv_index_t key_index, iv_index_t value_index);
static void ivace_lookup_values(iv_index_t key_index, iv_index_t value_index, 
                                mach_voucher_attr_value_handle_array_t  values,
                                mach_voucher_attr_value_handle_array_size_t *count);

static iv_index_t iv_lookup(ipc_voucher_t, iv_index_t);

                                
static void ivgt_lookup(iv_index_t,
                        boolean_t,
                        ipc_voucher_attr_manager_t *,
                        ipc_voucher_attr_control_t *);


#if defined(MACH_VOUCHER_ATTR_KEY_USER_DATA) || defined(MACH_VOUCHER_ATTR_KEY_TEST)
void user_data_attr_manager_init(void);
#endif 

void
ipc_voucher_init(void)
{
        natural_t ipc_voucher_max = (task_max + thread_max) * 2;
        natural_t attr_manager_max = MACH_VOUCHER_ATTR_KEY_NUM_WELL_KNOWN;
        iv_index_t i;

        ipc_voucher_zone = zinit(sizeof(struct ipc_voucher),
                                 ipc_voucher_max * sizeof(struct ipc_voucher),
                                 sizeof(struct ipc_voucher),
                                 "ipc vouchers");
        zone_change(ipc_voucher_zone, Z_NOENCRYPT, TRUE);

        ipc_voucher_attr_control_zone = zinit(sizeof(struct ipc_voucher_attr_control),
                                 attr_manager_max * sizeof(struct ipc_voucher_attr_control),
                                 sizeof(struct ipc_voucher_attr_control),
                                 "ipc voucher attr controls");
        zone_change(ipc_voucher_attr_control_zone, Z_NOENCRYPT, TRUE);

        /* initialize voucher hash */
        ivht_lock_init();
        for (i = 0; i < IV_HASH_BUCKETS; i++)
                queue_init(&ivht_bucket[i]);

        /* initialize global table locking */
        ivgt_lock_init();

#if defined(MACH_VOUCHER_ATTR_KEY_USER_DATA) || defined(MACH_VOUCHER_ATTR_KEY_TEST)
        user_data_attr_manager_init();
#endif
}

ipc_voucher_t
iv_alloc(iv_index_t entries)
{
        ipc_voucher_t iv;
        iv_index_t i;


        iv = (ipc_voucher_t)zalloc(ipc_voucher_zone);
        if (IV_NULL == iv)
                return IV_NULL;
                
        iv->iv_refs = 1;
        iv->iv_sum = 0;
        iv->iv_hash = 0;
        iv->iv_port = IP_NULL;

        if (entries > IV_ENTRIES_INLINE) {
                iv_entry_t table;

                /* TODO - switch to ipc_table method of allocation */
                table = (iv_entry_t) kalloc(sizeof(*table) * entries);
                if (IVE_NULL == table) {
                        zfree(ipc_voucher_zone, iv);
                        return IV_NULL;
                }
                iv->iv_table = table;
                iv->iv_table_size = entries;
        } else {
                iv->iv_table = iv->iv_inline_table;
                iv->iv_table_size = IV_ENTRIES_INLINE;
        }

        /* initialize the table entries */
        for (i=0; i < iv->iv_table_size; i++)
                iv->iv_table[i] = IV_UNUSED_VALINDEX;
                
        return (iv);
}

/*
 *      Routine:        iv_set
 *      Purpose:
 *              Set the voucher's value index for a given key index.
 *      Conditions:
 *              This is only called during voucher creation, as
 *              they are immutable once references are distributed.
 */
static void
iv_set(ipc_voucher_t iv, 
       iv_index_t key_index,
       iv_index_t value_index)
{
        assert(key_index < iv->iv_table_size);
        iv->iv_table[key_index] = value_index;
}

void
iv_dealloc(ipc_voucher_t iv, boolean_t unhash)
{
        ipc_port_t port = iv->iv_port;
        natural_t i;

        /*
         * Do we have to remove it from the hash?
         */
        if (unhash) {
                ivht_lock();
                assert(0 == iv->iv_refs);
                assert(IV_HASH_BUCKETS > iv->iv_hash);
                queue_remove(&ivht_bucket[iv->iv_hash], iv, ipc_voucher_t, iv_hash_link);
                ivht_count--;
                ivht_unlock();

                KERNEL_DEBUG_CONSTANT(MACHDBG_CODE(DBG_MACH_IPC,MACH_IPC_VOUCHER_DESTROY) | DBG_FUNC_NONE,
                                      VM_KERNEL_ADDRPERM((uintptr_t)iv), 0, ivht_count, 0, 0);

        } else
                assert(0 == --iv->iv_refs);

        /*
         * if a port was allocated for this voucher,
         * it must not have any remaining send rights,
         * because the port's reference on the voucher
         * is gone.  We can just discard it now.
         */
        if (IP_VALID(port)) {
                assert(ip_active(port));
                assert(port->ip_srights == 0);

                ipc_port_dealloc_kernel(port);
        }

        /* release the attribute references held by this voucher */
        for (i = 0; i < iv->iv_table_size; i++) {
                ivace_release(i, iv->iv_table[i]);
#if MACH_ASSERT
                iv_set(iv, i, ~0);
#endif
        }
                        
        if (iv->iv_table != iv->iv_inline_table)
                kfree(iv->iv_table, 
                      iv->iv_table_size * sizeof(*iv->iv_table));

        zfree(ipc_voucher_zone, iv);
}

/*
 *      Routine:        iv_lookup
 *      Purpose:
 *              Find the voucher's value index for a given key_index
 *      Conditions:
 *              Vouchers are immutable, so no locking required to do
 *              a lookup.
 */
static inline iv_index_t
iv_lookup(ipc_voucher_t iv, iv_index_t key_index)
{
        if (key_index < iv->iv_table_size)
                return iv->iv_table[key_index];
        return IV_UNUSED_VALINDEX;
}

/*
 *      Routine:        unsafe_convert_port_to_voucher
 *      Purpose:
 *              Unsafe conversion of a port to a voucher.
 *              Intended only for use by trace and debugging
 *              code. Consumes nothing, validates very little,
 *              produces an unreferenced voucher, which you
 *              MAY NOT use as a voucher, only log as an
 *              address.
 *      Conditions:
 *              Caller has a send-right reference to port.
 *              Port may or may not be locked.
 */
uintptr_t
unsafe_convert_port_to_voucher(
        ipc_port_t      port)
{
        if (IP_VALID(port)) {
                uintptr_t voucher = (uintptr_t) port->ip_kobject;

                /*
                 * No need to lock because we have a reference on the
                 * port, and if it is a true voucher port, that reference
                 * keeps the voucher bound to the port (and active).
                 */
                if (ip_kotype(port) == IKOT_VOUCHER)
                        return (voucher);
        }
        return (uintptr_t)IV_NULL;
}

/*
 *      Routine:        convert_port_to_voucher
 *      Purpose:
 *              Convert from a port to a voucher.
 *              Doesn't consume the port [send-right] ref;
 *              produces a voucher ref, which may be null.
 *      Conditions:
 *              Caller has a send-right reference to port.
 *              Port may or may not be locked.
 */
ipc_voucher_t
convert_port_to_voucher(
        ipc_port_t      port)
{
        if (IP_VALID(port)) {
                ipc_voucher_t voucher = (ipc_voucher_t) port->ip_kobject;

                /*
                 * No need to lock because we have a reference on the
                 * port, and if it is a true voucher port, that reference
                 * keeps the voucher bound to the port (and active).
                 */
                if (ip_kotype(port) != IKOT_VOUCHER)
                        return IV_NULL;

                assert(ip_active(port));

                ipc_voucher_reference(voucher);
                return (voucher);
        }
        return IV_NULL;
}

/*
 *      Routine:        convert_port_name_to_voucher
 *      Purpose:
 *              Convert from a port name in the current space to a voucher.
 *              Produces a voucher ref, which may be null.
 *      Conditions:
 *              Nothing locked.
 */

ipc_voucher_t
convert_port_name_to_voucher(
        mach_port_name_t        voucher_name)
{
        ipc_voucher_t iv;
        kern_return_t kr;
        ipc_port_t port;

        if (MACH_PORT_VALID(voucher_name)) {
                kr = ipc_port_translate_send(current_space(), voucher_name, &port);
                if (KERN_SUCCESS != kr)
                        return IV_NULL;

                iv = convert_port_to_voucher(port);
                ip_unlock(port);
                return iv;
        }
        return IV_NULL;
}


void
ipc_voucher_reference(ipc_voucher_t voucher)
{
        iv_refs_t refs;

        if (IPC_VOUCHER_NULL == voucher)
                return;

        refs = iv_reference(voucher);
        assert(1 < refs);
}

void
ipc_voucher_release(ipc_voucher_t voucher)
{
        if (IPC_VOUCHER_NULL != voucher)
                iv_release(voucher);
}

/*
 * Routine:     ipc_voucher_notify
 * Purpose:
 *      Called whenever the Mach port system detects no-senders
 *      on the voucher port.
 *
 *      Each time the send-right count goes positive, a no-senders 
 *      notification is armed (and a voucher reference is donated).
 *      So, each notification that comes in must release a voucher
 *      reference.  If more send rights have been added since it
 *      fired (asynchronously), they will be protected by a different
 *      reference hold.
 */
void
ipc_voucher_notify(mach_msg_header_t *msg)
{
        mach_no_senders_notification_t *notification = (void *)msg;
        ipc_port_t port = notification->not_header.msgh_remote_port;
        ipc_voucher_t iv;

        assert(ip_active(port));
        assert(IKOT_VOUCHER == ip_kotype(port));
        iv = (ipc_voucher_t)port->ip_kobject;

        ipc_voucher_release(iv);
}

/*
 * Convert a voucher to a port.
 */
ipc_port_t
convert_voucher_to_port(ipc_voucher_t voucher)
{
        ipc_port_t      port, send;

        if (IV_NULL == voucher)
                return (IP_NULL);

        assert(0 < voucher->iv_refs);

        /* create a port if needed */
        port = voucher->iv_port;
        if (!IP_VALID(port)) {
                port = ipc_port_alloc_kernel();
                assert(IP_VALID(port));
                ipc_kobject_set_atomically(port, (ipc_kobject_t) voucher, IKOT_VOUCHER);

                /* If we lose the race, deallocate and pick up the other guy's port */
                if (!OSCompareAndSwapPtr(IP_NULL, port, &voucher->iv_port)) {
                        ipc_port_dealloc_kernel(port);
                        port = voucher->iv_port;
                        assert(ip_kotype(port) == IKOT_VOUCHER);
                        assert(port->ip_kobject == (ipc_kobject_t)voucher);
                }
        }
        
        ip_lock(port);
        assert(ip_active(port));
        send = ipc_port_make_send_locked(port);

        if (1 == port->ip_srights) {
                ipc_port_t old_notify;

                /* transfer our ref to the port, and arm the no-senders notification */
                assert(IP_NULL == port->ip_nsrequest);
                ipc_port_nsrequest(port, port->ip_mscount, ipc_port_make_sonce_locked(port), &old_notify);
                /* port unlocked */
                assert(IP_NULL == old_notify);
        } else {
                /* piggyback on the existing port reference, so consume ours */
                ip_unlock(port);
                ipc_voucher_release(voucher);
        }
        return (send);
}

#define ivace_reset_data(ivace_elem, next_index) {       \
        (ivace_elem)->ivace_value = 0xDEADC0DEDEADC0DE;  \
        (ivace_elem)->ivace_refs = 0;                    \
        (ivace_elem)->ivace_made = 0;                    \
        (ivace_elem)->ivace_free = TRUE;                 \
        (ivace_elem)->ivace_releasing = FALSE;           \
        (ivace_elem)->ivace_layered = 0;                 \
        (ivace_elem)->ivace_index = IV_HASH_END;         \
        (ivace_elem)->ivace_next = (next_index);         \
}

#define ivace_copy_data(ivace_src_elem, ivace_dst_elem) {  \
        (ivace_dst_elem)->ivace_value = (ivace_src_elem)->ivace_value; \
        (ivace_dst_elem)->ivace_refs = (ivace_src_elem)->ivace_refs;   \
        (ivace_dst_elem)->ivace_made = (ivace_src_elem)->ivace_made;   \
        (ivace_dst_elem)->ivace_free = (ivace_src_elem)->ivace_free;   \
        (ivace_dst_elem)->ivace_layered = (ivace_src_elem)->ivace_layered;   \
        (ivace_dst_elem)->ivace_releasing = (ivace_src_elem)->ivace_releasing; \
        (ivace_dst_elem)->ivace_index = (ivace_src_elem)->ivace_index; \
        (ivace_dst_elem)->ivace_next = (ivace_src_elem)->ivace_next; \
}

ipc_voucher_attr_control_t
ivac_alloc(iv_index_t key_index)
{
        ipc_voucher_attr_control_t ivac;
        ivac_entry_t table;
        natural_t i;


        ivac = (ipc_voucher_attr_control_t)zalloc(ipc_voucher_attr_control_zone);
        if (IVAC_NULL == ivac)
                return IVAC_NULL;
                
        ivac->ivac_refs = 1;
        ivac->ivac_is_growing = FALSE;
        ivac->ivac_port = IP_NULL;

        /* start with just the inline table */
        table = (ivac_entry_t) kalloc(IVAC_ENTRIES_MIN * sizeof(ivac_entry));
        ivac->ivac_table = table;
        ivac->ivac_table_size = IVAC_ENTRIES_MIN;
        ivac->ivac_init_table_size = IVAC_ENTRIES_MIN;
        for (i = 0; i < ivac->ivac_table_size; i++) {
                ivace_reset_data(&table[i], i+1);
        }

        /* the default table entry is never on freelist */
        table[0].ivace_next = IV_HASH_END;
        table[0].ivace_free = FALSE;
        table[i-1].ivace_next = IV_FREELIST_END;
        ivac->ivac_freelist = 1;
        ivac_lock_init(ivac);
        ivac->ivac_key_index = key_index;
        return (ivac);
}
        

void
ivac_dealloc(ipc_voucher_attr_control_t ivac)
{
        ipc_voucher_attr_manager_t ivam = IVAM_NULL;
        iv_index_t key_index = ivac->ivac_key_index;
        ipc_port_t port = ivac->ivac_port;
        natural_t i;

        /*
         * If the control is in the global table, we
         * have to remove it from there before we (re)confirm
         * that the reference count is still zero.
         */
        ivgt_lock();
        if (ivac->ivac_refs > 0) {
                ivgt_unlock();
                return;
        }

        /* take it out of the global table */
        if (iv_global_table[key_index].ivgte_control == ivac) {
                ivam = iv_global_table[key_index].ivgte_manager;
                iv_global_table[key_index].ivgte_manager = IVAM_NULL;
                iv_global_table[key_index].ivgte_control = IVAC_NULL;
                iv_global_table[key_index].ivgte_key = MACH_VOUCHER_ATTR_KEY_NONE;
        }
        ivgt_unlock();

        /* release the reference held on the resource manager */
        if (IVAM_NULL != ivam)
                (ivam->ivam_release)(ivam);

        /*
         * if a port was allocated for this voucher,
         * it must not have any remaining send rights,
         * because the port's reference on the voucher
         * is gone.  We can just discard it now.
         */
        if (IP_VALID(port)) {
                assert(ip_active(port));
                assert(port->ip_srights == 0);

                ipc_port_dealloc_kernel(port);
        }

        /*
         * the resource manager's control reference and all references
         * held by the specific value caches are gone, so free the
         * table.
         */
#ifdef MACH_DEBUG
        for (i = 0; i < ivac->ivac_table_size; i++)
                if (ivac->ivac_table[i].ivace_refs != 0)
                        panic("deallocing a resource manager with live refs to its attr values\n");
#endif
        kfree(ivac->ivac_table, ivac->ivac_table_size * sizeof(*ivac->ivac_table));
        ivac_lock_destroy(ivac);
        zfree(ipc_voucher_attr_control_zone, ivac);
}

void
ipc_voucher_attr_control_reference(ipc_voucher_attr_control_t control)
{
        ivac_reference(control);
}

void
ipc_voucher_attr_control_release(ipc_voucher_attr_control_t control)
{
        ivac_release(control);
}

/*
 *      Routine:        convert_port_to_voucher_attr_control reference
 *      Purpose:
 *              Convert from a port to a voucher attribute control.
 *              Doesn't consume the port ref; produces a voucher ref,
 *              which may be null.
 *      Conditions:
 *              Nothing locked.
 */
ipc_voucher_attr_control_t
convert_port_to_voucher_attr_control(
        ipc_port_t      port)
{
        if (IP_VALID(port)) {
                ipc_voucher_attr_control_t ivac = (ipc_voucher_attr_control_t) port->ip_kobject;

                /*
                 * No need to lock because we have a reference on the
                 * port, and if it is a true voucher control port,
                 * that reference keeps the voucher bound to the port
                 * (and active).
                 */
                if (ip_kotype(port) != IKOT_VOUCHER_ATTR_CONTROL)
                        return IVAC_NULL;

                assert(ip_active(port));

                ivac_reference(ivac);
                return (ivac);
        }
        return IVAC_NULL;
}

void
ipc_voucher_attr_control_notify(mach_msg_header_t *msg)
{
        mach_no_senders_notification_t *notification = (void *)msg;
        ipc_port_t port = notification->not_header.msgh_remote_port;
        ipc_voucher_attr_control_t ivac;

        assert(IKOT_VOUCHER_ATTR_CONTROL == ip_kotype(port));
        ip_lock(port);
        assert(ip_active(port));

        /* if no new send rights, drop a control reference */
        if (port->ip_mscount == notification->not_count) {
                ivac = (ipc_voucher_attr_control_t)port->ip_kobject;
                ip_unlock(port);

                ivac_release(ivac);
        }
        ip_unlock(port);
}

/*
 * Convert a voucher attr control to a port.
 */
ipc_port_t
convert_voucher_attr_control_to_port(ipc_voucher_attr_control_t control)
{
        ipc_port_t      port, send;

        if (IVAC_NULL == control)
                return (IP_NULL);

        /* create a port if needed */
        port = control->ivac_port;
        if (!IP_VALID(port)) {
                port = ipc_port_alloc_kernel();
                assert(IP_VALID(port));
                if (OSCompareAndSwapPtr(IP_NULL, port, &control->ivac_port)) {
                        ip_lock(port);
                        ipc_kobject_set_atomically(port, (ipc_kobject_t) control, IKOT_VOUCHER_ATTR_CONTROL);
                } else {
                        ipc_port_dealloc_kernel(port);
                        port = control->ivac_port;
                        ip_lock(port);
                        assert(ip_kotype(port) == IKOT_VOUCHER_ATTR_CONTROL);
                        assert(port->ip_kobject == (ipc_kobject_t)control);
                }
        } else 
                ip_lock(port);

        assert(ip_active(port));
        send = ipc_port_make_send_locked(port);

        if (1 == port->ip_srights) {
                ipc_port_t old_notify;

                /* transfer our ref to the port, and arm the no-senders notification */
                assert(IP_NULL == port->ip_nsrequest);
                ipc_port_nsrequest(port, port->ip_mscount, ipc_port_make_sonce_locked(port), &old_notify);
                assert(IP_NULL == old_notify);
                ip_unlock(port);
        } else {
                /* piggyback on the existing port reference, so consume ours */
                ip_unlock(port);
                ivac_release(control);
        }
        return (send);
}

/*
 * Look up the values for a given <key, index> pair.
 */
static void
ivace_lookup_values(
        iv_index_t                              key_index,
        iv_index_t                              value_index,
        mach_voucher_attr_value_handle_array_t          values,
        mach_voucher_attr_value_handle_array_size_t     *count)
{
        ipc_voucher_attr_control_t ivac;
        ivac_entry_t ivace;

        if (IV_UNUSED_VALINDEX == value_index ||
            MACH_VOUCHER_ATTR_KEY_NUM_WELL_KNOWN <= key_index) {
                *count = 0;
                return;
        }

        ivac = iv_global_table[key_index].ivgte_control;
        assert(IVAC_NULL != ivac);

        /*
         * Get the entry and then the linked values.
         */
        ivac_lock(ivac);
        assert(value_index < ivac->ivac_table_size);
        ivace = &ivac->ivac_table[value_index];

        /*
         * TODO: support chained values (for effective vouchers).
         */
        assert(ivace->ivace_refs > 0);
        values[0] = ivace->ivace_value;
        ivac_unlock(ivac);
        *count = 1;
}

/*
 *  ivac_grow_table - Allocate a bigger table of attribute values
 *
 *  Conditions: ivac is locked on entry and again on return
 */
static void
ivac_grow_table(ipc_voucher_attr_control_t ivac)
{
        iv_index_t i = 0;

        /* NOTE: do not modify *_table and *_size values once set */
        ivac_entry_t new_table = NULL, old_table = NULL;
        iv_index_t new_size, old_size;

        if (ivac->ivac_is_growing) {
                ivac_sleep(ivac);
                return;
        }

        ivac->ivac_is_growing = 1;
        if (ivac->ivac_table_size >= IVAC_ENTRIES_MAX) {
                panic("Cannot grow ipc space beyond IVAC_ENTRIES_MAX. Some process is leaking vouchers");
                return;
        }

        old_size = ivac->ivac_table_size;
        ivac_unlock(ivac);

        new_size = old_size * 2;

        assert(new_size > old_size);
        assert(new_size < IVAC_ENTRIES_MAX);

        new_table = kalloc(sizeof(ivac_entry) * new_size);
        if (!new_table){
                panic("Failed to grow ivac table to size %d\n", new_size);
                return;
        }

        /* setup the free list for new entries */
        for (i = old_size; i < new_size; i++) {
                ivace_reset_data(&new_table[i], i+1);
        }

        ivac_lock(ivac);
        
        for (i = 0; i < ivac->ivac_table_size; i++){
                ivace_copy_data(&ivac->ivac_table[i], &new_table[i]);
        }

        old_table = ivac->ivac_table;

        ivac->ivac_table = new_table;
        ivac->ivac_table_size = new_size;
        
        /* adding new free entries at head of freelist */
        ivac->ivac_table[new_size - 1].ivace_next = ivac->ivac_freelist;
        ivac->ivac_freelist = old_size;
        ivac->ivac_is_growing = 0;
        ivac_wakeup(ivac);

        if (old_table){
                ivac_unlock(ivac);
                kfree(old_table, old_size * sizeof(ivac_entry));
                ivac_lock(ivac);
        }
}

/*
 * ivace_reference_by_index
 *
 * Take an additional reference on the <key_index, val_index>
 * cached value. It is assumed the caller already holds a
 * reference to the same cached key-value pair.
 */
static void
ivace_reference_by_index(
        iv_index_t      key_index,
        iv_index_t      val_index)
{
        ipc_voucher_attr_control_t ivac;
        ivac_entry_t ivace;

        if (IV_UNUSED_VALINDEX == val_index)
                return;

        ivgt_lookup(key_index, FALSE, NULL, &ivac);
        assert(IVAC_NULL != ivac);

        ivac_lock(ivac);
        assert(val_index < ivac->ivac_table_size);
        ivace = &ivac->ivac_table[val_index];

        assert(0xdeadc0dedeadc0de != ivace->ivace_value);
        assert(0 < ivace->ivace_refs);
        assert(!ivace->ivace_free);
        ivace->ivace_refs++;
        ivac_unlock(ivac);
}


/*
 * Look up the values for a given <key, index> pair.
 *
 * Consumes a reference on the passed voucher control.
 * Either it is donated to a newly-created value cache
 * or it is released (if we piggy back on an existing
 * value cache entry).
 */
static iv_index_t
ivace_reference_by_value(
        ipc_voucher_attr_control_t      ivac,
        mach_voucher_attr_value_handle_t        value)
{
        ivac_entry_t ivace = IVACE_NULL;
        iv_index_t hash_index;
        iv_index_t index;

        if (IVAC_NULL == ivac) {
                return IV_UNUSED_VALINDEX;
        }

        ivac_lock(ivac);
restart:
        hash_index = IV_HASH_VAL(ivac->ivac_init_table_size, value);
        index = ivac->ivac_table[hash_index].ivace_index;
        while (index != IV_HASH_END) {
                assert(index < ivac->ivac_table_size);
                ivace = &ivac->ivac_table[index];
                assert(!ivace->ivace_free);

                if (ivace->ivace_value == value)
                        break;

                assert(ivace->ivace_next != index);
                index = ivace->ivace_next;
        }

        /* found it? */
        if (index != IV_HASH_END) { 
                /* only add reference on non-default value */
                if (IV_UNUSED_VALINDEX != index) {
                        ivace->ivace_refs++;
                        ivace->ivace_made++;
                }

                ivac_unlock(ivac);
                ivac_release(ivac);
                return index;
        }

        /* insert new entry in the table */
        index = ivac->ivac_freelist;
        if (IV_FREELIST_END == index) {
                /* freelist empty */
                ivac_grow_table(ivac);
                goto restart;
        }

        /* take the entry off the freelist */
        ivace = &ivac->ivac_table[index];
        ivac->ivac_freelist = ivace->ivace_next;

        /* initialize the new entry */
        ivace->ivace_value = value;
        ivace->ivace_refs = 1;
        ivace->ivace_made = 1;
        ivace->ivace_free = FALSE;

        /* insert the new entry in the proper hash chain */
        ivace->ivace_next = ivac->ivac_table[hash_index].ivace_index;
        ivac->ivac_table[hash_index].ivace_index = index;
        ivac_unlock(ivac);

        /* donated passed in ivac reference to new entry */

        return index;
}

/*
 * Release a reference on the given <key_index, value_index> pair.
 *
 * Conditions:  called with nothing locked, as it may cause
 *              callouts and/or messaging to the resource 
 *              manager.
 */
static void ivace_release(
        iv_index_t key_index,     
        iv_index_t value_index)
{
        ipc_voucher_attr_control_t ivac;
        ipc_voucher_attr_manager_t ivam;
        mach_voucher_attr_value_handle_t value;
        mach_voucher_attr_value_reference_t made;
        mach_voucher_attr_key_t key;
        iv_index_t hash_index;
        ivac_entry_t ivace;
        kern_return_t kr;

        /* cant release the default value */
        if (IV_UNUSED_VALINDEX == value_index)
                return;

        ivgt_lookup(key_index, FALSE, &ivam, &ivac);
        assert(IVAC_NULL != ivac);
        assert(IVAM_NULL != ivam);

        ivac_lock(ivac);
        assert(value_index < ivac->ivac_table_size);
        ivace = &ivac->ivac_table[value_index];

        assert(0 < ivace->ivace_refs);

        if (0 < --ivace->ivace_refs) {
                ivac_unlock(ivac);
                return;
        }

        key = iv_index_to_key(key_index);
        assert(MACH_VOUCHER_ATTR_KEY_NONE != key);

        /*
         * if last return reply is still pending,
         * let it handle this later return when
         * the previous reply comes in.
         */
        if (ivace->ivace_releasing) {
                ivac_unlock(ivac);
                return;
        }

        /* claim releasing */
        ivace->ivace_releasing = TRUE;
        value = ivace->ivace_value;

 redrive:
        assert(value == ivace->ivace_value);
        assert(!ivace->ivace_free);
        made = ivace->ivace_made;
        ivac_unlock(ivac);

        /* callout to manager's release_value */
        kr = (ivam->ivam_release_value)(ivam, key, value, made);

        /* recalculate entry address as table may have changed */
        ivac_lock(ivac);
        ivace = &ivac->ivac_table[value_index];
        assert(value == ivace->ivace_value);

        /*
         * new made values raced with this return.  If the
         * manager OK'ed the prior release, we have to start
         * the made numbering over again (pretend the race
         * didn't happen). If the entry has zero refs again,
         * re-drive the release.
         */
        if (ivace->ivace_made != made) {
                assert(made < ivace->ivace_made);

                if (KERN_SUCCESS == kr)
                        ivace->ivace_made -= made;

                if (0 == ivace->ivace_refs)
                        goto redrive;

                ivace->ivace_releasing = FALSE;
                ivac_unlock(ivac);
                return;
        } else {
                /*
                 * If the manager returned FAILURE, someone took a 
                 * reference on the value but have not updated the ivace,
                 * release the lock and return since thread who got
                 * the new reference will update the ivace and will have
                 * non-zero reference on the value.
                 */
                if (KERN_SUCCESS != kr) {
                        ivace->ivace_releasing = FALSE;
                        ivac_unlock(ivac);
                        return;
                }
        }

        assert(0 == ivace->ivace_refs);

        /*
         * going away - remove entry from its hash
         * If its at the head of the hash bucket list (common), unchain
         * at the head. Otherwise walk the chain until the next points
         * at this entry, and remove it from the the list there.
         */
        hash_index = iv_hash_value(key_index, value);
        if (ivac->ivac_table[hash_index].ivace_index == value_index) {
                ivac->ivac_table[hash_index].ivace_index = ivace->ivace_next;
        } else {
                hash_index = ivac->ivac_table[hash_index].ivace_index;
                assert(IV_HASH_END != hash_index);
                while (ivac->ivac_table[hash_index].ivace_next != value_index) {
                        hash_index = ivac->ivac_table[hash_index].ivace_next;
                        assert(IV_HASH_END != hash_index);
                }
                ivac->ivac_table[hash_index].ivace_next = ivace->ivace_next;
        }

        /* Put this entry on the freelist */
        ivace->ivace_value = 0xdeadc0dedeadc0de;
        ivace->ivace_releasing = FALSE;
        ivace->ivace_free = TRUE;
        ivace->ivace_made = 0;
        ivace->ivace_next = ivac->ivac_freelist;
        ivac->ivac_freelist = value_index;
        ivac_unlock(ivac);

        /* release the reference this value held on its cache control */
        ivac_release(ivac);

        return;
}


/*
 * ivgt_looup
 *
 * Lookup an entry in the global table from the context of a manager
 * registration.  Adds a reference to the control to keep the results
 * around (if needed).
 *
 * Because of the calling point, we can't be sure the manager is
 * [fully] registered yet.  So, we must hold the global table lock
 * during the lookup to synchronize with in-parallel registrations
 * (and possible table growth).
 */
static void
ivgt_lookup(iv_index_t key_index,
            boolean_t take_reference,
            ipc_voucher_attr_manager_t *manager,
            ipc_voucher_attr_control_t *control)
{
        ipc_voucher_attr_control_t ivac;

        if (key_index < MACH_VOUCHER_ATTR_KEY_NUM_WELL_KNOWN) {
                ivgt_lock();
                if (NULL != manager)
                        *manager = iv_global_table[key_index].ivgte_manager;
                ivac = iv_global_table[key_index].ivgte_control;
                if (IVAC_NULL != ivac) {
                        assert(key_index == ivac->ivac_key_index);
                        if (take_reference) {
                                assert(NULL != control);
                                ivac_reference(ivac);
                        }
                }
                ivgt_unlock();
                if (NULL != control)
                        *control = ivac;
        } else {
                if (NULL != manager)
                        *manager = IVAM_NULL;
                if (NULL != control)
                        *control = IVAC_NULL;
        }
}

/*
 *      Routine:        ipc_replace_voucher_value
 *      Purpose:
 *              Replace the <voucher, key> value with the results of
 *              running the supplied command through the resource
 *              manager's get-value callback.
 *      Conditions:
 *              Nothing locked (may invoke user-space repeatedly).
 *              Caller holds references on voucher and previous voucher.
 */
static kern_return_t
ipc_replace_voucher_value(
        ipc_voucher_t                           voucher,
        mach_voucher_attr_key_t                 key,
        mach_voucher_attr_recipe_command_t      command,
        ipc_voucher_t                           prev_voucher,
        mach_voucher_attr_content_t             content,
        mach_voucher_attr_content_size_t        content_size)
{
        mach_voucher_attr_value_handle_t previous_vals[MACH_VOUCHER_ATTR_VALUE_MAX_NESTED];
        mach_voucher_attr_value_handle_array_size_t previous_vals_count;
        mach_voucher_attr_value_handle_t new_value;
        ipc_voucher_t new_value_voucher;
        ipc_voucher_attr_manager_t ivam;
        ipc_voucher_attr_control_t ivac;
        iv_index_t prev_val_index;
        iv_index_t save_val_index;
        iv_index_t val_index;
        iv_index_t key_index;
        kern_return_t kr;
        
        /*
         * Get the manager for this key_index.
         * Returns a reference on the control.
         */
        key_index = iv_key_to_index(key);
        ivgt_lookup(key_index, TRUE, &ivam, &ivac);
        if (IVAM_NULL == ivam)
                return KERN_INVALID_ARGUMENT;

        /* save the current value stored in the forming voucher */
        save_val_index = iv_lookup(voucher, key_index);

        /*
         * Get the previous value(s) for this key creation.
         * If a previous voucher is specified, they come from there.
         * Otherwise, they come from the intermediate values already
         * in the forming voucher.
         */
        prev_val_index = (IV_NULL != prev_voucher) ?
                         iv_lookup(prev_voucher, key_index) :
                         save_val_index;
        ivace_lookup_values(key_index, prev_val_index,
                            previous_vals, &previous_vals_count);

        /* Call out to resource manager to get new value */
        new_value_voucher = IV_NULL;
        kr = (ivam->ivam_get_value)(
                                    ivam, key, command,
                                    previous_vals, previous_vals_count,
                                    content, content_size,
                                    &new_value, &new_value_voucher);
        if (KERN_SUCCESS != kr) {
                ivac_release(ivac);
                return kr;
        }

        /* TODO: value insertion from returned voucher */
        if (IV_NULL != new_value_voucher)
                iv_release(new_value_voucher);

        /*
         * Find or create a slot in the table associated
         * with this attribute value.  The ivac reference
         * is transferred to a new value, or consumed if
         * we find a matching existing value.
         */
        val_index = ivace_reference_by_value(ivac, new_value);
        iv_set(voucher, key_index, val_index);

        /*
         * release saved old value from the newly forming voucher
         * This is saved until the end to avoid churning the
         * release logic in cases where the same value is returned
         * as was there before.
         */
        ivace_release(key_index, save_val_index);
        
        return KERN_SUCCESS;
}

/*
 *      Routine:        ipc_directly_replace_voucher_value
 *      Purpose:
 *              Replace the <voucher, key> value with the value-handle
 *              supplied directly by the attribute manager.
 *      Conditions:
 *              Nothing locked.
 *              Caller holds references on voucher.
 *              A made reference to the value-handle is donated by the caller.
 */
static kern_return_t
ipc_directly_replace_voucher_value(
        ipc_voucher_t                           voucher,
        mach_voucher_attr_key_t                 key,
        mach_voucher_attr_value_handle_t        new_value)
{
        ipc_voucher_attr_manager_t ivam;
        ipc_voucher_attr_control_t ivac;
        iv_index_t save_val_index;
        iv_index_t val_index;
        iv_index_t key_index;
        
        /*
         * Get the manager for this key_index.
         * Returns a reference on the control.
         */
        key_index = iv_key_to_index(key);
        ivgt_lookup(key_index, TRUE, &ivam, &ivac);
        if (IVAM_NULL == ivam)
                return KERN_INVALID_ARGUMENT;

        /* save the current value stored in the forming voucher */
        save_val_index = iv_lookup(voucher, key_index);

        /*
         * Find or create a slot in the table associated
         * with this attribute value.  The ivac reference
         * is transferred to a new value, or consumed if
         * we find a matching existing value.
         */
        val_index = ivace_reference_by_value(ivac, new_value);
        iv_set(voucher, key_index, val_index);

        /*
         * release saved old value from the newly forming voucher
         * This is saved until the end to avoid churning the
         * release logic in cases where the same value is returned
         * as was there before.
         */
        ivace_release(key_index, save_val_index);
        
        return KERN_SUCCESS;
}

static kern_return_t
ipc_execute_voucher_recipe_command(
        ipc_voucher_t                           voucher,
        mach_voucher_attr_key_t                 key,
        mach_voucher_attr_recipe_command_t      command,
        ipc_voucher_t                           prev_iv,
        mach_voucher_attr_content_t             content,
        mach_voucher_attr_content_size_t        content_size,
        boolean_t                               key_priv)
{
        iv_index_t prev_val_index;
        iv_index_t val_index;
        kern_return_t kr;

        switch (command) {

        /*
         * MACH_VOUCHER_ATTR_COPY
         *      Copy the attribute(s) from the previous voucher to the new
         *      one.  A wildcard key is an acceptable value - indicating a
         *      desire to copy all the attribute values from the previous
         *      voucher.
         */
        case MACH_VOUCHER_ATTR_COPY:
                
                /* no recipe data on a copy */
                if (0 < content_size)
                        return KERN_INVALID_ARGUMENT;

                /* nothing to copy from? - done */
                if (IV_NULL == prev_iv)
                        return KERN_SUCCESS;

                if (MACH_VOUCHER_ATTR_KEY_ALL == key) {
                        iv_index_t limit, j;

                        /* reconcile possible difference in voucher sizes */
                        limit = (prev_iv->iv_table_size < voucher->iv_table_size) ?
                                prev_iv->iv_table_size :
                                voucher->iv_table_size;

                        /* wildcard matching */
                        for (j = 0; j < limit; j++) {
                                /* release old value being replaced */
                                val_index = iv_lookup(voucher, j);
                                ivace_release(j, val_index);

                                /* replace with reference to prev voucher's value */
                                prev_val_index = iv_lookup(prev_iv, j);
                                ivace_reference_by_index(j, prev_val_index);
                                iv_set(voucher, j, prev_val_index);
                        }
                } else {
                        iv_index_t key_index;

                        /* copy just one key */
                        key_index = iv_key_to_index(key);
                        if (ivgt_keys_in_use < key_index)
                                return KERN_INVALID_ARGUMENT;

                        /* release old value being replaced */
                        val_index = iv_lookup(voucher, key_index);
                        ivace_release(key_index, val_index);

                        /* replace with reference to prev voucher's value */
                        prev_val_index = iv_lookup(prev_iv, key_index);
                        ivace_reference_by_index(key_index, prev_val_index);
                        iv_set(voucher, key_index, prev_val_index);
                }
                break;

        /*
         * MACH_VOUCHER_ATTR_REMOVE
         *      Remove the attribute(s) from the under construction voucher.
         *      A wildcard key is an acceptable value - indicating a desire
         *      to remove all the attribute values set up so far in the voucher.
         *      If a previous voucher is specified, only remove the value it
         *      it matches the value in the previous voucher.
         */
        case MACH_VOUCHER_ATTR_REMOVE:
                /* no recipe data on a remove */
                if (0 < content_size)
                        return KERN_INVALID_ARGUMENT;

                if (MACH_VOUCHER_ATTR_KEY_ALL == key) {
                        iv_index_t limit, j;

                        /* reconcile possible difference in voucher sizes */
                        limit = (IV_NULL == prev_iv) ? voucher->iv_table_size :
                                ((prev_iv->iv_table_size < voucher->iv_table_size) ?
                                 prev_iv->iv_table_size : voucher->iv_table_size);

                        /* wildcard matching */
                        for (j = 0; j < limit; j++) {
                                val_index = iv_lookup(voucher, j);

                                /* If not matched in previous, skip */
                                if (IV_NULL != prev_iv) {
                                        prev_val_index = iv_lookup(prev_iv, j);
                                        if (val_index != prev_val_index)
                                                continue;
                                }
                                /* release and clear */
                                ivace_release(j, val_index);
                                iv_set(voucher, j, IV_UNUSED_VALINDEX);
                        }
                } else {
                        iv_index_t key_index;

                        /* copy just one key */
                        key_index = iv_key_to_index(key);
                        if (ivgt_keys_in_use < key_index)
                                return KERN_INVALID_ARGUMENT;

                        val_index = iv_lookup(voucher, key_index);

                        /* If not matched in previous, skip */
                        if (IV_NULL != prev_iv) {
                                prev_val_index = iv_lookup(prev_iv, key_index);
                                if (val_index != prev_val_index)
                                        break;
                        }

                        /* release and clear */
                        ivace_release(key_index, val_index);
                        iv_set(voucher, key_index, IV_UNUSED_VALINDEX);
                }
                break;

        /*
         * MACH_VOUCHER_ATTR_SET_VALUE_HANDLE
         *      Use key-privilege to set a value handle for the attribute directly,
         *      rather than triggering a callback into the attribute manager to
         *      interpret a recipe to generate the value handle.
         */
        case MACH_VOUCHER_ATTR_SET_VALUE_HANDLE:
                if (key_priv) {
                        mach_voucher_attr_value_handle_t new_value;

                        if (sizeof(mach_voucher_attr_value_handle_t) != content_size)
                                return KERN_INVALID_ARGUMENT;
                        
                        new_value = *(mach_voucher_attr_value_handle_t *)(void *)content;
                        kr = ipc_directly_replace_voucher_value(voucher,
                                                                key,
                                                                new_value);
                        if (KERN_SUCCESS != kr)
                                return kr;
                } else
                        return KERN_INVALID_CAPABILITY;
                break;

        /*
         * MACH_VOUCHER_ATTR_REDEEM
         *      Redeem the attribute(s) from the previous voucher for a possibly
         *      new value in the new voucher. A wildcard key is an acceptable value,
         *      indicating a desire to redeem all the values.
         */     
        case MACH_VOUCHER_ATTR_REDEEM:

                if (MACH_VOUCHER_ATTR_KEY_ALL == key) {
                        iv_index_t limit, j;

                        /* reconcile possible difference in voucher sizes */
                        if (IV_NULL != prev_iv)
                                limit = (prev_iv->iv_table_size < voucher->iv_table_size) ?
                                        prev_iv->iv_table_size :
                                        voucher->iv_table_size;
                        else
                                limit = voucher->iv_table_size;

                        /* wildcard matching */
                        for (j = 0; j < limit; j++) {
                                mach_voucher_attr_key_t j_key;

                                j_key = iv_index_to_key(j);

                                /* skip non-existent managers */
                                if (MACH_VOUCHER_ATTR_KEY_NONE == j_key)
                                        continue;

                                /* get the new value from redeem (skip empty previous) */
                                kr = ipc_replace_voucher_value(voucher,
                                                               j_key,
                                                               command,
                                                               prev_iv,
                                                               content,
                                                               content_size);
                                if (KERN_SUCCESS != kr)
                                        return kr;
                        }
                        break;
                }
                /* fall thru for single key redemption */

        /*
         * DEFAULT:
         *      Replace the current value for the <voucher, key> pair with whatever
         *      value the resource manager returns for the command and recipe
         *      combination provided.
         */
        default:
                kr = ipc_replace_voucher_value(voucher,
                                               key,
                                               command,
                                               prev_iv,
                                               content,
                                               content_size);
                if (KERN_SUCCESS != kr)
                        return kr;

                break;
        }
        return KERN_SUCCESS;
}

/*
 *      Routine:        iv_checksum
 *      Purpose:
 *              Compute the voucher sum.  This is more position-
 *              relevant than many other checksums - important for
 *              vouchers (arrays of low, oft-reused, indexes).
 */
static inline iv_index_t
iv_checksum(ipc_voucher_t voucher, boolean_t *emptyp)
{
        iv_index_t c = 0;

        boolean_t empty = TRUE;
        if (0 < voucher->iv_table_size) {
                iv_index_t i = voucher->iv_table_size - 1;
        
                do {
                        iv_index_t v = voucher->iv_table[i];
                        c = c << 3 | c >> (32 - 3);             /* rotate */
                        c = ~c;                                 /* invert */
                        if (0 < v) {
                                c += v;                         /* add in */
                                empty = FALSE;
                        }
                } while (0 < i--);
        }
        *emptyp = empty;
        return c;
}

/*
 *      Routine:        iv_dedup
 *      Purpose:
 *              See if the set of values represented by this new voucher
 *              already exist in another voucher.  If so return a reference
 *              to the existing voucher and deallocate the voucher provided.
 *              Otherwise, insert this one in the hash and return it.
 *      Conditions:
 *              A voucher reference is donated on entry.
 *      Returns:
 *              A voucher reference (may be different than on entry).
 */
static ipc_voucher_t
iv_dedup(ipc_voucher_t new_iv)
{
        boolean_t empty;
        iv_index_t sum; 
        iv_index_t hash;
        ipc_voucher_t iv;

        sum = iv_checksum(new_iv, &empty);

        /* If all values are default, that's the empty (NULL) voucher */
        if (empty) {
                iv_dealloc(new_iv, FALSE);
                return IV_NULL;
        }

        hash = IV_HASH_BUCKET(sum);

        ivht_lock();
        queue_iterate(&ivht_bucket[hash], iv, ipc_voucher_t, iv_hash_link) {
                assert(iv->iv_hash == hash);

                /* if not already deallocating and sums match... */
                if (0 < iv->iv_refs && iv->iv_sum == sum) {
                        iv_refs_t refs;
                        iv_index_t i;

                        assert(iv->iv_table_size <= new_iv->iv_table_size);
                
                        /* and common entries match... */
                        for (i = 0; i < iv->iv_table_size; i++)
                                if (iv->iv_table[i] != new_iv->iv_table[i])
                                        break;
                        if (i < iv->iv_table_size)
                                continue;

                        /* and all extra entries in new one are unused... */
                        while (i < new_iv->iv_table_size)
                                if (new_iv->iv_table[i++] != IV_UNUSED_VALINDEX)
                                        break;
                        if (i < new_iv->iv_table_size)
                                continue;

                        /* ... we found a match... */

                        /* can we get a ref before it hits 0
                         *
                         * This is thread safe. The reference is just an atomic
                         * add. If the reference count is zero when we adjust it,
                         * no other thread can have a reference to the voucher.
                         * The dealloc code requires holding the ivht_lock, so
                         * the voucher cannot be yanked out from under us.
                         */
                        refs = iv_reference(iv);
                        if (1 == refs) {
                                /* drats! going away. Put back to zero */
                                iv->iv_refs = 0;
                                continue;
                        }

                        ivht_unlock();

                        /* referenced previous, so deallocate the new one */
                        iv_dealloc(new_iv, FALSE);
                        return iv;
                }
        }

        /* add the new voucher to the hash, and return it */
        new_iv->iv_sum = sum;
        new_iv->iv_hash = hash;
        queue_enter(&ivht_bucket[hash], new_iv, ipc_voucher_t, iv_hash_link);
        ivht_count++;
        ivht_unlock();

        /*
         * This code is disabled for KDEBUG_LEVEL_IST and KDEBUG_LEVEL_NONE
         */
#if (KDEBUG_LEVEL >= KDEBUG_LEVEL_STANDARD)
        if (kdebug_enable & ~KDEBUG_ENABLE_PPT) {
                uintptr_t voucher_addr = VM_KERNEL_ADDRPERM((uintptr_t)new_iv);
                uintptr_t attr_tracepoints_needed = 0;

                if (ipc_voucher_trace_contents) {
                        /*
                         * voucher_contents sizing is a bit more constrained
                         * than might be obvious.
                         *
                         * This is typically a uint8_t typed array. However,
                         * we want to access it as a uintptr_t to efficiently
                         * copyout the data in tracepoints.
                         *
                         * This constrains the size to uintptr_t bytes, and
                         * adds a minimimum alignment requirement equivalent
                         * to a uintptr_t.
                         *
                         * Further constraining the size is the fact that it
                         * is copied out 4 uintptr_t chunks at a time. We do
                         * NOT want to run off the end of the array and copyout
                         * random stack data.
                         *
                         * So the minimum size is 4 * sizeof(uintptr_t), and
                         * the minimum alignment is uintptr_t aligned.
                         */

#define PAYLOAD_PER_TRACEPOINT (4 * sizeof(uintptr_t))
#define PAYLOAD_SIZE 1024

                        _Static_assert(PAYLOAD_SIZE % PAYLOAD_PER_TRACEPOINT == 0, "size invariant violated");

                        mach_voucher_attr_raw_recipe_array_size_t payload_size = PAYLOAD_SIZE;
                        uintptr_t payload[PAYLOAD_SIZE / sizeof(uintptr_t)];
                        kern_return_t kr;

                        kr = mach_voucher_extract_all_attr_recipes(new_iv, (mach_voucher_attr_raw_recipe_array_t)payload, &payload_size);
                        if (KERN_SUCCESS == kr) {
                                attr_tracepoints_needed = (payload_size + PAYLOAD_PER_TRACEPOINT - 1) / PAYLOAD_PER_TRACEPOINT;

                                /*
                                 * To prevent leaking data from the stack, we
                                 * need to zero data to the end of a tracepoint
                                 * payload.
                                 */
                                size_t remainder = payload_size % PAYLOAD_PER_TRACEPOINT;
                                if (remainder) {
                                        bzero((uint8_t*)payload + payload_size,
                                              PAYLOAD_PER_TRACEPOINT - remainder);
                                }
                        }

                        KERNEL_DEBUG_CONSTANT(MACHDBG_CODE(DBG_MACH_IPC,MACH_IPC_VOUCHER_CREATE) | DBG_FUNC_NONE,
                                              voucher_addr,
                                              new_iv->iv_table_size, ivht_count, payload_size, 0);

                        uintptr_t index = 0;
                        while (attr_tracepoints_needed--) {
                                KERNEL_DEBUG_CONSTANT1(MACHDBG_CODE(DBG_MACH_IPC,MACH_IPC_VOUCHER_CREATE_ATTR_DATA) | DBG_FUNC_NONE,
                                                       payload[index],
                                                       payload[index+1],
                                                       payload[index+2],
                                                       payload[index+3],
                                                       voucher_addr);
                                index += 4;
                        }
                } else {
                        KERNEL_DEBUG_CONSTANT(MACHDBG_CODE(DBG_MACH_IPC,MACH_IPC_VOUCHER_CREATE) | DBG_FUNC_NONE,
                                              voucher_addr,
                                              new_iv->iv_table_size, ivht_count, 0, 0);
                }
        }
#endif /* KDEBUG_LEVEL >= KDEBUG_LEVEL_STANDARD */

        return new_iv;
}

/*
 *      Routine:        ipc_create_mach_voucher
 *      Purpose:
 *              Create a new mach voucher and initialize it with the
 *              value(s) created by having the appropriate resource
 *              managers interpret the supplied recipe commands and
 *              data.
 *      Conditions:
 *              Nothing locked (may invoke user-space repeatedly).
 *              Caller holds references on previous vouchers.
 *              Previous vouchers are passed as voucher indexes.
 */
kern_return_t
ipc_create_mach_voucher(
        ipc_voucher_attr_raw_recipe_array_t             recipes,
        ipc_voucher_attr_raw_recipe_array_size_t        recipe_size,
        ipc_voucher_t                                   *new_voucher)
{
        ipc_voucher_attr_recipe_t sub_recipe;
        ipc_voucher_attr_recipe_size_t recipe_used = 0;
        ipc_voucher_t voucher;
        kern_return_t kr = KERN_SUCCESS;

        /* if nothing to do ... */
        if (0 == recipe_size) {
                *new_voucher = IV_NULL;
                return KERN_SUCCESS;
        }

        /* allocate a voucher */
        voucher = iv_alloc(ivgt_keys_in_use);
        if (IV_NULL == voucher)
                return KERN_RESOURCE_SHORTAGE;

        /* iterate over the recipe items */
        while (0 < recipe_size - recipe_used) {

                if (recipe_size - recipe_used < sizeof(*sub_recipe)) {
                        kr = KERN_INVALID_ARGUMENT;
                        break;
                }

                /* find the next recipe */
                sub_recipe = (ipc_voucher_attr_recipe_t)(void *)&recipes[recipe_used];
                if (recipe_size - recipe_used - sizeof(*sub_recipe) < sub_recipe->content_size) {
                        kr = KERN_INVALID_ARGUMENT;
                        break;
                }
                recipe_used += sizeof(*sub_recipe) + sub_recipe->content_size;

                kr = ipc_execute_voucher_recipe_command(voucher,
                                                        sub_recipe->key,
                                                        sub_recipe->command,
                                                        sub_recipe->previous_voucher,
                                                        sub_recipe->content,
                                                        sub_recipe->content_size,
                                                        FALSE);
                if (KERN_SUCCESS != kr)
                        break;
        }

        if (KERN_SUCCESS == kr) {
                *new_voucher = iv_dedup(voucher);
        } else {
                iv_dealloc(voucher, FALSE);
                *new_voucher = IV_NULL;
        }
        return kr;
}

/*
 *      Routine:        ipc_voucher_attr_control_create_mach_voucher
 *      Purpose:
 *              Create a new mach voucher and initialize it with the
 *              value(s) created by having the appropriate resource
 *              managers interpret the supplied recipe commands and
 *              data.
 *
 *              The resource manager control's privilege over its
 *              particular key value is reflected on to the execution
 *              code, allowing internal commands (like setting a
 *              key value handle directly, rather than having to
 *              create a recipe, that will generate a callback just
 *              to get the value.
 *
 *      Conditions:
 *              Nothing locked (may invoke user-space repeatedly).
 *              Caller holds references on previous vouchers.
 *              Previous vouchers are passed as voucher indexes.
 */
kern_return_t
ipc_voucher_attr_control_create_mach_voucher(
        ipc_voucher_attr_control_t                      control,
        ipc_voucher_attr_raw_recipe_array_t             recipes,
        ipc_voucher_attr_raw_recipe_array_size_t        recipe_size,
        ipc_voucher_t                                   *new_voucher)
{
        mach_voucher_attr_key_t control_key;
        ipc_voucher_attr_recipe_t sub_recipe;
        ipc_voucher_attr_recipe_size_t recipe_used = 0;
        ipc_voucher_t voucher = IV_NULL;
        kern_return_t kr = KERN_SUCCESS;

        if (IPC_VOUCHER_ATTR_CONTROL_NULL == control)
                return KERN_INVALID_CAPABILITY;

        /* if nothing to do ... */
        if (0 == recipe_size) {
                *new_voucher = IV_NULL;
                return KERN_SUCCESS;
        }

        /* allocate new voucher */
        voucher = iv_alloc(ivgt_keys_in_use);
        if (IV_NULL == voucher)
                return KERN_RESOURCE_SHORTAGE;

        control_key = iv_index_to_key(control->ivac_key_index);

        /* iterate over the recipe items */
        while (0 < recipe_size - recipe_used) {

                if (recipe_size - recipe_used < sizeof(*sub_recipe)) {
                        kr = KERN_INVALID_ARGUMENT;
                        break;
                }

                /* find the next recipe */
                sub_recipe = (ipc_voucher_attr_recipe_t)(void *)&recipes[recipe_used];
                if (recipe_size - recipe_used - sizeof(*sub_recipe) < sub_recipe->content_size) {
                        kr = KERN_INVALID_ARGUMENT;
                        break;
                }
                recipe_used += sizeof(*sub_recipe) + sub_recipe->content_size;

                kr = ipc_execute_voucher_recipe_command(voucher,
                                                        sub_recipe->key,
                                                        sub_recipe->command,
                                                        sub_recipe->previous_voucher,
                                                        sub_recipe->content,
                                                        sub_recipe->content_size,
                                                        (sub_recipe->key == control_key));
                if (KERN_SUCCESS != kr)
                        break;
        }

        if (KERN_SUCCESS == kr) {
                *new_voucher = iv_dedup(voucher);
        } else {
                *new_voucher = IV_NULL;
                iv_dealloc(voucher, FALSE);
        }
        return kr;
}

/*
 *      ipc_register_well_known_mach_voucher_attr_manager
 *
 *      Register the resource manager responsible for a given key value.
 */
kern_return_t
ipc_register_well_known_mach_voucher_attr_manager(
        ipc_voucher_attr_manager_t manager,
        mach_voucher_attr_value_handle_t default_value,
        mach_voucher_attr_key_t key,
        ipc_voucher_attr_control_t *control)
{
        ipc_voucher_attr_control_t new_control;
        iv_index_t key_index;
        iv_index_t hash_index;

        if (IVAM_NULL == manager)
                return KERN_INVALID_ARGUMENT;

        key_index = iv_key_to_index(key);
        if (IV_UNUSED_KEYINDEX == key_index)
                return KERN_INVALID_ARGUMENT;

        new_control = ivac_alloc(key_index);
        if (IVAC_NULL == new_control)
                return KERN_RESOURCE_SHORTAGE;

        /* insert the default value into slot 0 */
        new_control->ivac_table[IV_UNUSED_VALINDEX].ivace_value = default_value;
        new_control->ivac_table[IV_UNUSED_VALINDEX].ivace_refs = IVACE_REFS_MAX;
        new_control->ivac_table[IV_UNUSED_VALINDEX].ivace_made = IVACE_REFS_MAX;
        assert(IV_HASH_END == new_control->ivac_table[IV_UNUSED_VALINDEX].ivace_next);

        ivgt_lock();
        if (IVAM_NULL != iv_global_table[key_index].ivgte_manager) {
                ivgt_unlock();
                ivac_release(new_control);
                return KERN_INVALID_ARGUMENT;
        }

        /* fill in the global table slot for this key */
        iv_global_table[key_index].ivgte_manager = manager;
        iv_global_table[key_index].ivgte_control = new_control;
        iv_global_table[key_index].ivgte_key = key;

        /* insert the default value into the hash (in case it is returned later) */
        hash_index = iv_hash_value(key_index, default_value);
        assert(IV_HASH_END == new_control->ivac_table[hash_index].ivace_index);
        new_control->ivac_table[hash_index].ivace_index = IV_UNUSED_VALINDEX;

        ivgt_unlock();
        
        /* return the reference on the new cache control to the caller */
        *control = new_control;

        return KERN_SUCCESS;
}

/*
 *      Routine:        mach_voucher_extract_attr_content
 *      Purpose:
 *              Extract the content for a given <voucher, key> pair.
 *
 *              If a value other than the default is present for this
 *              <voucher,key> pair, we need to contact the resource
 *              manager to extract the content/meaning of the value(s)
 *              present.  Otherwise, return success (but no data).
 *
 *      Conditions:
 *              Nothing locked - as it may upcall to user-space.
 *              The caller holds a reference on the voucher.
 */
kern_return_t
mach_voucher_extract_attr_content(
        ipc_voucher_t                           voucher,
        mach_voucher_attr_key_t                 key,
        mach_voucher_attr_content_t             content,
        mach_voucher_attr_content_size_t        *in_out_size)
{
        mach_voucher_attr_value_handle_t vals[MACH_VOUCHER_ATTR_VALUE_MAX_NESTED];
        mach_voucher_attr_value_handle_array_size_t vals_count;
        mach_voucher_attr_recipe_command_t command;
        ipc_voucher_attr_manager_t manager;
        iv_index_t value_index;
        iv_index_t key_index;
        kern_return_t kr;


        if (IV_NULL == voucher)
                return KERN_INVALID_ARGUMENT;

        key_index = iv_key_to_index(key);

        value_index = iv_lookup(voucher, key_index);
        if (IV_UNUSED_VALINDEX == value_index) {
                *in_out_size = 0;
                return KERN_SUCCESS;
        }

        /*
         * Get the manager for this key_index.  The
         * existence of a non-default value for this
         * slot within our voucher will keep the
         * manager referenced during the callout.
         */
        ivgt_lookup(key_index, FALSE, &manager, NULL);
        if (IVAM_NULL == manager) {
                return KERN_INVALID_ARGUMENT;
        }

        /*
         * Get the value(s) to pass to the manager
         * for this value_index.
         */
        ivace_lookup_values(key_index, value_index,
                            vals, &vals_count);
        assert(0 < vals_count);

        /* callout to manager */
        
        kr = (manager->ivam_extract_content)(manager, key, 
                                             vals, vals_count,
                                             &command,
                                             content, in_out_size);
        return kr;
}

/*
 *      Routine:        mach_voucher_extract_attr_recipe
 *      Purpose:
 *              Extract a recipe for a given <voucher, key> pair.
 *
 *              If a value other than the default is present for this
 *              <voucher,key> pair, we need to contact the resource
 *              manager to extract the content/meaning of the value(s)
 *              present.  Otherwise, return success (but no data).
 *
 *      Conditions:
 *              Nothing locked - as it may upcall to user-space.
 *              The caller holds a reference on the voucher.
 */
kern_return_t
mach_voucher_extract_attr_recipe(
        ipc_voucher_t                           voucher,
        mach_voucher_attr_key_t                 key,
        mach_voucher_attr_raw_recipe_t          raw_recipe,
        mach_voucher_attr_raw_recipe_size_t     *in_out_size)
{
        mach_voucher_attr_value_handle_t vals[MACH_VOUCHER_ATTR_VALUE_MAX_NESTED];
        mach_voucher_attr_value_handle_array_size_t vals_count;
        ipc_voucher_attr_manager_t manager;
        mach_voucher_attr_recipe_t recipe;
        iv_index_t value_index;
        iv_index_t key_index;
        kern_return_t kr;


        if (IV_NULL == voucher)
                return KERN_INVALID_ARGUMENT;

        key_index = iv_key_to_index(key);

        value_index = iv_lookup(voucher, key_index);
        if (IV_UNUSED_VALINDEX == value_index) {
                *in_out_size = 0;
                return KERN_SUCCESS;
        }

        if (*in_out_size < sizeof(*recipe))
                return KERN_NO_SPACE;

        recipe = (mach_voucher_attr_recipe_t)(void *)raw_recipe;
        recipe->key = key;
        recipe->command = MACH_VOUCHER_ATTR_NOOP;
        recipe->previous_voucher = MACH_VOUCHER_NAME_NULL;
        recipe->content_size = *in_out_size - sizeof(*recipe);

        /*
         * Get the manager for this key_index.  The
         * existence of a non-default value for this
         * slot within our voucher will keep the
         * manager referenced during the callout.
         */
        ivgt_lookup(key_index, FALSE, &manager, NULL);
        if (IVAM_NULL == manager) {
                return KERN_INVALID_ARGUMENT;
        }

        /*
         * Get the value(s) to pass to the manager
         * for this value_index.
         */
        ivace_lookup_values(key_index, value_index,
                            vals, &vals_count);
        assert(0 < vals_count);

        /* callout to manager */
        kr = (manager->ivam_extract_content)(manager, key, 
                                             vals, vals_count,
                                             &recipe->command,
                                             recipe->content, &recipe->content_size);
        if (KERN_SUCCESS == kr) {
          assert(*in_out_size - sizeof(*recipe) >= recipe->content_size);
          *in_out_size = sizeof(*recipe) + recipe->content_size;
        }

        return kr;
}



/*
 *      Routine:        mach_voucher_extract_all_attr_recipes
 *      Purpose:
 *              Extract all the (non-default) contents for a given voucher,
 *              building up a recipe that could be provided to a future 
 *              voucher creation call.
 *      Conditions:             
 *              Nothing locked (may invoke user-space).
 *              Caller holds a reference on the supplied voucher.
 */
kern_return_t
mach_voucher_extract_all_attr_recipes(
        ipc_voucher_t                                   voucher,
        mach_voucher_attr_raw_recipe_array_t            recipes,
        mach_voucher_attr_raw_recipe_array_size_t       *in_out_size)
{
        mach_voucher_attr_recipe_size_t recipe_size = *in_out_size;
        mach_voucher_attr_recipe_size_t recipe_used = 0;
        iv_index_t key_index;

        if (IV_NULL == voucher)
                return KERN_INVALID_ARGUMENT;

        for (key_index = 0; key_index < voucher->iv_table_size; key_index++) {
                mach_voucher_attr_value_handle_t vals[MACH_VOUCHER_ATTR_VALUE_MAX_NESTED];
                mach_voucher_attr_value_handle_array_size_t vals_count;
                mach_voucher_attr_content_size_t content_size;
                ipc_voucher_attr_manager_t manager;
                mach_voucher_attr_recipe_t recipe;
                mach_voucher_attr_key_t key;
                iv_index_t value_index;
                kern_return_t kr;

                /* don't output anything for a default value */
                value_index = iv_lookup(voucher, key_index);
                if (IV_UNUSED_VALINDEX == value_index)
                        continue;

                if (recipe_size - recipe_used < sizeof(*recipe))
                        return KERN_NO_SPACE;

                /*
                 * Get the manager for this key_index.  The
                 * existence of a non-default value for this
                 * slot within our voucher will keep the
                 * manager referenced during the callout.
                 */
                ivgt_lookup(key_index, FALSE, &manager, NULL);
                assert(IVAM_NULL != manager);
                if (IVAM_NULL == manager) {
                        continue;
                }

                recipe = (mach_voucher_attr_recipe_t)(void *)&recipes[recipe_used];
                content_size = recipe_size - recipe_used - sizeof(*recipe);

                /*
                 * Get the value(s) to pass to the manager
                 * for this value_index.
                 */
                ivace_lookup_values(key_index, value_index,
                                    vals, &vals_count);
                assert(0 < vals_count);

                key = iv_index_to_key(key_index);

                recipe->key = key;
                recipe->command = MACH_VOUCHER_ATTR_NOOP;
                recipe->content_size = content_size;

                /* callout to manager */
                kr = (manager->ivam_extract_content)(manager, key, 
                                             vals, vals_count,
                                             &recipe->command,
                                             recipe->content, &recipe->content_size);
                if (KERN_SUCCESS != kr)
                        return kr;

                assert(recipe->content_size <= content_size);
                recipe_used += sizeof(*recipe) + recipe->content_size;
        }

        *in_out_size = recipe_used;
        return KERN_SUCCESS;
}

/*
 *      Routine:        mach_voucher_debug_info
 *      Purpose:
 *              Extract all the (non-default) contents for a given mach port name,
 *              building up a recipe that could be provided to a future 
 *              voucher creation call.
 *      Conditions:
 *              Nothing locked (may invoke user-space).
 *              Caller may not hold a reference on the supplied voucher.
 */
#if !(DEVELOPMENT || DEBUG)
kern_return_t
mach_voucher_debug_info(
        ipc_space_t                                     __unused space,
        mach_port_name_t                                __unused voucher_name,
        mach_voucher_attr_raw_recipe_array_t            __unused recipes,
        mach_voucher_attr_raw_recipe_array_size_t       __unused *in_out_size)
{
        return KERN_NOT_SUPPORTED;
}
#else
kern_return_t
mach_voucher_debug_info(
        ipc_space_t                                     space,
        mach_port_name_t                                voucher_name,
        mach_voucher_attr_raw_recipe_array_t            recipes,
        mach_voucher_attr_raw_recipe_array_size_t       *in_out_size)
{
        ipc_voucher_t voucher = IPC_VOUCHER_NULL;
        kern_return_t kr;
        ipc_port_t port = MACH_PORT_NULL;

        if (!MACH_PORT_VALID(voucher_name)) {
                return KERN_INVALID_ARGUMENT;
        }

        kr = ipc_port_translate_send(space, voucher_name, &port);
        if (KERN_SUCCESS != kr)
                return KERN_INVALID_ARGUMENT;

        voucher = convert_port_to_voucher(port);
        ip_unlock(port);

        if (voucher) {
                kr = mach_voucher_extract_all_attr_recipes(voucher, recipes, in_out_size);
                ipc_voucher_release(voucher);
                return kr;
        }

        return KERN_FAILURE;
}
#endif

/*
 *      Routine:        mach_voucher_attr_command
 *      Purpose:
 *              Invoke an attribute-specific command through this voucher.
 *
 *              The voucher layout, membership, etc... is not altered
 *              through the execution of this command.
 *
 *      Conditions:
 *              Nothing locked - as it may upcall to user-space.
 *              The caller holds a reference on the voucher.
 */
kern_return_t
mach_voucher_attr_command(
        ipc_voucher_t                                           voucher,
        mach_voucher_attr_key_t                         key,
        mach_voucher_attr_command_t                     command,
        mach_voucher_attr_content_t                     in_content,
        mach_voucher_attr_content_size_t        in_content_size,
        mach_voucher_attr_content_t                     out_content,
        mach_voucher_attr_content_size_t        *out_content_size)
{
        mach_voucher_attr_value_handle_t vals[MACH_VOUCHER_ATTR_VALUE_MAX_NESTED];
        mach_voucher_attr_value_handle_array_size_t vals_count;
        ipc_voucher_attr_manager_t manager;
        ipc_voucher_attr_control_t control;
        iv_index_t value_index;
        iv_index_t key_index;
        kern_return_t kr;


        if (IV_NULL == voucher)
                return KERN_INVALID_ARGUMENT;

        key_index = iv_key_to_index(key);

        /*
         * Get the manager for this key_index.
         * Allowing commands against the default value
         * for an attribute means that we have to hold
         * reference on the attribute manager control
         * to keep the manager around during the command
         * execution.
         */
        ivgt_lookup(key_index, TRUE, &manager, &control);
        if (IVAM_NULL == manager) {
                return KERN_INVALID_ARGUMENT;
        }

        /*
         * Get the values for this <voucher, key> pair
         * to pass to the attribute manager.  It is still
         * permissible to execute a command against the
         * default value (empty value array).
         */
        value_index = iv_lookup(voucher, key_index);
        ivace_lookup_values(key_index, value_index,
                            vals, &vals_count);

        /* callout to manager */
        kr = (manager->ivam_command)(manager, key, 
                                     vals, vals_count,
                                     command,
                                     in_content, in_content_size,
                                     out_content, out_content_size);

        /* release reference on control */
        ivac_release(control);

        return kr;
}

/*
 *      Routine:        mach_voucher_attr_control_get_values
 *      Purpose:
 *              For a given voucher, get the value handle associated with the
 *              specified attribute manager.
 */
kern_return_t
mach_voucher_attr_control_get_values(
        ipc_voucher_attr_control_t control,
        ipc_voucher_t voucher,
        mach_voucher_attr_value_handle_array_t out_values,
        mach_voucher_attr_value_handle_array_size_t *in_out_size)
{
        iv_index_t key_index, value_index;

        if (IPC_VOUCHER_ATTR_CONTROL_NULL == control)
                return KERN_INVALID_CAPABILITY;

        if (IV_NULL == voucher)
                return KERN_INVALID_ARGUMENT;

        if (0 == *in_out_size)
                return KERN_SUCCESS;

        key_index = control->ivac_key_index;

        assert(0 < voucher->iv_refs);
        value_index = iv_lookup(voucher, key_index);
        ivace_lookup_values(key_index, value_index,
                            out_values, in_out_size);
        return KERN_SUCCESS;
}


/*
 *      Routine:        mach_voucher_attr_control_create_mach_voucher
 *      Purpose:
 *              Create a new mach voucher and initialize it by processing the
 *              supplied recipe(s).
 *
 *              Coming in on the attribute control port denotes special privileges
 *              over they key associated with the control port.
 *
 *              Coming in from user-space, each recipe item will have a previous
 *              recipe port name that needs to be converted to a voucher.  Because
 *              we can't rely on the port namespace to hold a reference on each
 *              previous voucher port for the duration of processing that command,
 *              we have to convert the name to a voucher reference and release it
 *              after the command processing is done.
 */
kern_return_t
mach_voucher_attr_control_create_mach_voucher(
        ipc_voucher_attr_control_t control,
        mach_voucher_attr_raw_recipe_array_t recipes,
        mach_voucher_attr_raw_recipe_size_t recipe_size,
        ipc_voucher_t *new_voucher)
{
        mach_voucher_attr_key_t control_key;
        mach_voucher_attr_recipe_t sub_recipe;
        mach_voucher_attr_recipe_size_t recipe_used = 0;
        ipc_voucher_t voucher = IV_NULL;
        kern_return_t kr = KERN_SUCCESS;

        if (IPC_VOUCHER_ATTR_CONTROL_NULL == control)
                return KERN_INVALID_CAPABILITY;

        /* if nothing to do ... */
        if (0 == recipe_size) {
                *new_voucher = IV_NULL;
                return KERN_SUCCESS;
        }

        /* allocate new voucher */
        voucher = iv_alloc(ivgt_keys_in_use);
        if (IV_NULL == voucher)
                return KERN_RESOURCE_SHORTAGE;

        control_key = iv_index_to_key(control->ivac_key_index);

        /* iterate over the recipe items */
        while (0 < recipe_size - recipe_used) {
                ipc_voucher_t prev_iv;

                if (recipe_size - recipe_used < sizeof(*sub_recipe)) {
                        kr = KERN_INVALID_ARGUMENT;
                        break;
                }

                /* find the next recipe */
                sub_recipe = (mach_voucher_attr_recipe_t)(void *)&recipes[recipe_used];
                if (recipe_size - recipe_used - sizeof(*sub_recipe) < sub_recipe->content_size) {
                        kr = KERN_INVALID_ARGUMENT;
                        break;
                }
                recipe_used += sizeof(*sub_recipe) + sub_recipe->content_size;

                /* convert voucher port name (current space) into a voucher reference */
                prev_iv = convert_port_name_to_voucher(sub_recipe->previous_voucher);
                if (MACH_PORT_NULL != sub_recipe->previous_voucher && IV_NULL == prev_iv) {
                        kr = KERN_INVALID_CAPABILITY;
                        break;
                }

                kr = ipc_execute_voucher_recipe_command(voucher,
                                                        sub_recipe->key,
                                                        sub_recipe->command,
                                                        prev_iv,
                                                        sub_recipe->content,
                                                        sub_recipe->content_size,
                                                        (sub_recipe->key == control_key));
                ipc_voucher_release(prev_iv);

                if (KERN_SUCCESS != kr)
                        break;
        }

        if (KERN_SUCCESS == kr) {
                *new_voucher = iv_dedup(voucher);
        } else {
                *new_voucher = IV_NULL;
                iv_dealloc(voucher, FALSE);
        }
        return kr;
}

/*
 *      Routine:        host_create_mach_voucher
 *      Purpose:
 *              Create a new mach voucher and initialize it by processing the
 *              supplied recipe(s).
 *
 *              Comming in from user-space, each recipe item will have a previous
 *              recipe port name that needs to be converted to a voucher.  Because
 *              we can't rely on the port namespace to hold a reference on each
 *              previous voucher port for the duration of processing that command,
 *              we have to convert the name to a voucher reference and release it
 *              after the command processing is done.
 */
kern_return_t
host_create_mach_voucher(
        host_t host,
        mach_voucher_attr_raw_recipe_array_t recipes,
        mach_voucher_attr_raw_recipe_size_t recipe_size,
        ipc_voucher_t *new_voucher)
{
        mach_voucher_attr_recipe_t sub_recipe;
        mach_voucher_attr_recipe_size_t recipe_used = 0;
        ipc_voucher_t voucher = IV_NULL;
        kern_return_t kr = KERN_SUCCESS;

        if (host == HOST_NULL)
                return KERN_INVALID_ARGUMENT;

        /* if nothing to do ... */
        if (0 == recipe_size) {
                *new_voucher = IV_NULL;
                return KERN_SUCCESS;
        }

        /* allocate new voucher */
        voucher = iv_alloc(ivgt_keys_in_use);
        if (IV_NULL == voucher)
                return KERN_RESOURCE_SHORTAGE;

        /* iterate over the recipe items */
        while (0 < recipe_size - recipe_used) {
                ipc_voucher_t prev_iv;

                if (recipe_size - recipe_used < sizeof(*sub_recipe)) {
                        kr = KERN_INVALID_ARGUMENT;
                        break;
                }

                /* find the next recipe */
                sub_recipe = (mach_voucher_attr_recipe_t)(void *)&recipes[recipe_used];
                if (recipe_size - recipe_used - sizeof(*sub_recipe) < sub_recipe->content_size) {
                        kr = KERN_INVALID_ARGUMENT;
                        break;
                }
                recipe_used += sizeof(*sub_recipe) + sub_recipe->content_size;

                /* convert voucher port name (current space) into a voucher reference */
                prev_iv = convert_port_name_to_voucher(sub_recipe->previous_voucher);
                if (MACH_PORT_NULL != sub_recipe->previous_voucher && IV_NULL == prev_iv) {
                        kr = KERN_INVALID_CAPABILITY;
                        break;
                }

                kr = ipc_execute_voucher_recipe_command(voucher,
                                                        sub_recipe->key,
                                                        sub_recipe->command,
                                                        prev_iv,
                                                        sub_recipe->content,
                                                        sub_recipe->content_size,
                                                        FALSE);
                ipc_voucher_release(prev_iv);

                if (KERN_SUCCESS != kr)
                        break;
        }

        if (KERN_SUCCESS == kr) {
                *new_voucher = iv_dedup(voucher);
        } else {
                *new_voucher = IV_NULL;
                iv_dealloc(voucher, FALSE);
        }
        return kr;
}

/*
 *      Routine:        host_register_well_known_mach_voucher_attr_manager
 *      Purpose:
 *              Register the user-level resource manager responsible for a given
 *              key value.  
 *      Conditions:
 *              The manager port passed in has to be converted/wrapped
 *              in an ipc_voucher_attr_manager_t structure and then call the
 *              internal variant.  We have a generic ipc voucher manager
 *              type that implements a MIG proxy out to user-space just for
 *              this purpose.
 */
kern_return_t
host_register_well_known_mach_voucher_attr_manager(
        host_t host,
        mach_voucher_attr_manager_t __unused manager,
        mach_voucher_attr_value_handle_t __unused default_value,
        mach_voucher_attr_key_t __unused key,
        ipc_voucher_attr_control_t __unused *control)
{
        if (HOST_NULL == host)
                return KERN_INVALID_HOST;

#if 1
        return KERN_NOT_SUPPORTED;
#else
        /*
         * Allocate a mig_voucher_attr_manager_t that provides the
         * MIG proxy functions for the three manager callbacks and
         * store the port right in there.
         *
         * If the user-space manager dies, we'll detect it on our
         * next upcall, and cleanup the proxy at that point.
         */
        mig_voucher_attr_manager_t proxy;
        kern_return_t kr;

        proxy = mvam_alloc(manager);

        kr = ipc_register_well_known_mach_voucher_attr_manager(&proxy->mvam_manager,
                                                               default_value,
                                                               key,
                                                               control);
        if (KERN_SUCCESS != kr)
                mvam_release(proxy);

        return kr;
#endif
}

/*
 *      Routine:        host_register_mach_voucher_attr_manager
 *      Purpose:
 *              Register the user-space resource manager and return a
 *              dynamically allocated key.
 *      Conditions:
 *              Wrap the supplied port with the MIG proxy ipc
 *              voucher resource manager, and then call the internal
 *              variant.
 */
kern_return_t
host_register_mach_voucher_attr_manager(
        host_t host,
        mach_voucher_attr_manager_t __unused manager,
        mach_voucher_attr_value_handle_t __unused default_value,
        mach_voucher_attr_key_t __unused *key,
        ipc_voucher_attr_control_t __unused *control)
{
        if (HOST_NULL == host)
                return KERN_INVALID_HOST;

        return KERN_NOT_SUPPORTED;
}


#if defined(MACH_VOUCHER_ATTR_KEY_USER_DATA) || defined(MACH_VOUCHER_ATTR_KEY_TEST)

/*
 * Build-in a simple User Data Resource Manager
 */
#define USER_DATA_MAX_DATA      (16*1024)

struct user_data_value_element {
        mach_voucher_attr_value_reference_t     e_made;
        mach_voucher_attr_content_size_t        e_size;
        iv_index_t                              e_sum;
        iv_index_t                              e_hash;
        queue_chain_t                           e_hash_link;
        uint8_t                                 e_data[];
};

typedef struct user_data_value_element *user_data_element_t;

/*
 * User Data Voucher Hash Table
 */
#define USER_DATA_HASH_BUCKETS 127
#define USER_DATA_HASH_BUCKET(x) ((x) % USER_DATA_HASH_BUCKETS)

static queue_head_t user_data_bucket[USER_DATA_HASH_BUCKETS];
static lck_spin_t user_data_lock_data;

#define user_data_lock_init() \
        lck_spin_init(&user_data_lock_data, &ipc_lck_grp, &ipc_lck_attr)
#define user_data_lock_destroy() \
        lck_spin_destroy(&user_data_lock_data, &ipc_lck_grp)
#define user_data_lock() \
        lck_spin_lock(&user_data_lock_data)
#define user_data_lock_try() \
        lck_spin_try_lock(&user_data_lock_data)
#define user_data_unlock() \
        lck_spin_unlock(&user_data_lock_data)

static kern_return_t
user_data_release_value(
        ipc_voucher_attr_manager_t              manager,
        mach_voucher_attr_key_t                 key,
        mach_voucher_attr_value_handle_t        value,
        mach_voucher_attr_value_reference_t     sync);

static kern_return_t
user_data_get_value(
        ipc_voucher_attr_manager_t                      manager,
        mach_voucher_attr_key_t                         key,
        mach_voucher_attr_recipe_command_t              command,
        mach_voucher_attr_value_handle_array_t          prev_values,
        mach_voucher_attr_value_handle_array_size_t     prev_value_count,
        mach_voucher_attr_content_t                     content,
        mach_voucher_attr_content_size_t                content_size,
        mach_voucher_attr_value_handle_t                *out_value,
        ipc_voucher_t                                   *out_value_voucher);

static kern_return_t
user_data_extract_content(
        ipc_voucher_attr_manager_t                      manager,
        mach_voucher_attr_key_t                         key,
        mach_voucher_attr_value_handle_array_t          values,
        mach_voucher_attr_value_handle_array_size_t     value_count,
        mach_voucher_attr_recipe_command_t              *out_command,
        mach_voucher_attr_content_t                     out_content,
        mach_voucher_attr_content_size_t                *in_out_content_size);

static kern_return_t
user_data_command(
        ipc_voucher_attr_manager_t                              manager,
        mach_voucher_attr_key_t                                 key,
        mach_voucher_attr_value_handle_array_t  values,
        mach_msg_type_number_t                                  value_count,
        mach_voucher_attr_command_t                             command,
        mach_voucher_attr_content_t                             in_content,
        mach_voucher_attr_content_size_t                in_content_size,
        mach_voucher_attr_content_t                             out_content,
        mach_voucher_attr_content_size_t                *out_content_size);

static void
user_data_release(
        ipc_voucher_attr_manager_t              manager);

struct ipc_voucher_attr_manager user_data_manager = {
        .ivam_release_value =   user_data_release_value,
        .ivam_get_value =       user_data_get_value,
        .ivam_extract_content = user_data_extract_content,
        .ivam_command =         user_data_command,
        .ivam_release =         user_data_release,
};

ipc_voucher_attr_control_t user_data_control;
ipc_voucher_attr_control_t test_control;

#if defined(MACH_VOUCHER_ATTR_KEY_USER_DATA) && defined(MACH_VOUCHER_ATTR_KEY_TEST)
#define USER_DATA_ASSERT_KEY(key)                               \
        assert(MACH_VOUCHER_ATTR_KEY_USER_DATA == (key) ||      \
               MACH_VOUCHER_ATTR_KEY_TEST == (key));
#elif defined(MACH_VOUCHER_ATTR_KEY_USER_DATA)
#define USER_DATA_ASSERT_KEY(key) assert(MACH_VOUCHER_ATTR_KEY_USER_DATA == (key))
#else
#define USER_DATA_ASSERT_KEY(key) assert(MACH_VOUCHER_ATTR_KEY_TEST == (key))
#endif

/*
 *      Routine:        user_data_release_value
 *      Purpose:
 *              Release a made reference on a specific value managed by
 *              this voucher attribute manager.
 *      Conditions:
 *              Must remove the element associated with this value from
 *              the hash if this is the last know made reference.
 */
static kern_return_t
user_data_release_value(
        ipc_voucher_attr_manager_t              __assert_only manager,
        mach_voucher_attr_key_t                 __assert_only key,
        mach_voucher_attr_value_handle_t        value,
        mach_voucher_attr_value_reference_t     sync)
{
        user_data_element_t elem;
        iv_index_t hash;

        assert (&user_data_manager == manager);
        USER_DATA_ASSERT_KEY(key);

        elem = (user_data_element_t)value;
        hash = elem->e_hash;

        user_data_lock();
        if (sync == elem->e_made) {
                queue_remove(&user_data_bucket[hash], elem, user_data_element_t, e_hash_link);
                user_data_unlock();
                kfree(elem, sizeof(*elem) + elem->e_size);
                return KERN_SUCCESS;
        }
        assert(sync < elem->e_made);
        user_data_unlock();

        return KERN_FAILURE;
}

/*
 *      Routine:        user_data_checksum
 *      Purpose:
 *              Provide a rudimentary checksum for the data presented
 *              to these voucher attribute managers.
 */
static iv_index_t
user_data_checksum(
        mach_voucher_attr_content_t                     content,
        mach_voucher_attr_content_size_t                content_size)
{
        mach_voucher_attr_content_size_t i;
        iv_index_t cksum = 0;

        for(i = 0; i < content_size; i++, content++) {
                cksum = (cksum << 8) ^ (cksum + *(unsigned char *)content);
        }

        return (~cksum);
}

/*
 *      Routine:        user_data_dedup
 *      Purpose:
 *              See if the content represented by this request already exists
 *              in another user data element.  If so return a made reference
 *              to the existing element.  Otherwise, create a new element and
 *              return that (after inserting it in the hash).
 *      Conditions:
 *              Nothing locked.
 *      Returns:
 *              A made reference on the user_data_element_t
 */
static user_data_element_t
user_data_dedup(
        mach_voucher_attr_content_t                     content,
        mach_voucher_attr_content_size_t                content_size)
{
        iv_index_t sum; 
        iv_index_t hash;
        user_data_element_t elem;
        user_data_element_t alloc = NULL;

        sum = user_data_checksum(content, content_size);
        hash = USER_DATA_HASH_BUCKET(sum);

 retry:
        user_data_lock();
        queue_iterate(&user_data_bucket[hash], elem, user_data_element_t, e_hash_link) {
                assert(elem->e_hash == hash);

                /* if sums match... */
                if (elem->e_sum == sum && elem->e_size == content_size) {
                        iv_index_t i;

                        /* and all data matches */
                        for (i = 0; i < content_size; i++)
                                if (elem->e_data[i] != content[i])
                                        break;
                        if (i < content_size)
                                continue;

                        /* ... we found a match... */

                        elem->e_made++;
                        user_data_unlock();

                        if (NULL != alloc)
                                kfree(alloc, sizeof(*alloc) + content_size);

                        return elem;
                }
        }

        if (NULL == alloc) {
                user_data_unlock();

                alloc = (user_data_element_t)kalloc(sizeof(*alloc) + content_size);
                alloc->e_made = 1;
                alloc->e_size = content_size;
                alloc->e_sum = sum;
                alloc->e_hash = hash;
                memcpy(alloc->e_data, content, content_size);
                goto retry;
        }

        queue_enter(&user_data_bucket[hash], alloc, user_data_element_t, e_hash_link);
        user_data_unlock();

        return alloc;
}

static kern_return_t
user_data_get_value(
        ipc_voucher_attr_manager_t                      __assert_only manager,
        mach_voucher_attr_key_t                         __assert_only key,
        mach_voucher_attr_recipe_command_t              command,
        mach_voucher_attr_value_handle_array_t          prev_values,
        mach_voucher_attr_value_handle_array_size_t     prev_value_count,
        mach_voucher_attr_content_t                     content,
        mach_voucher_attr_content_size_t                content_size,
        mach_voucher_attr_value_handle_t                *out_value,
        ipc_voucher_t                                   *out_value_voucher)
{
        user_data_element_t elem;

        assert (&user_data_manager == manager);
        USER_DATA_ASSERT_KEY(key);

        /* never an out voucher */
        *out_value_voucher = IPC_VOUCHER_NULL;

        switch (command) {

        case MACH_VOUCHER_ATTR_REDEEM:

                /* redeem of previous values is the value */
                if (0 < prev_value_count) {
                        elem = (user_data_element_t)prev_values[0];
                        assert(0 < elem->e_made);
                        elem->e_made++;
                        *out_value = prev_values[0];
                        return KERN_SUCCESS;
                }

                /* redeem of default is default */
                *out_value = 0;
                return KERN_SUCCESS;

        case MACH_VOUCHER_ATTR_USER_DATA_STORE:
                if (USER_DATA_MAX_DATA < content_size)
                        return KERN_RESOURCE_SHORTAGE;

                /* empty is the default */
                if (0 == content_size) {
                        *out_value = 0;
                        return KERN_SUCCESS;
                }

                elem = user_data_dedup(content, content_size);
                *out_value = (mach_voucher_attr_value_handle_t)elem;
                return KERN_SUCCESS;

        default:
                /* every other command is unknown */
                return KERN_INVALID_ARGUMENT;
        }
}

static kern_return_t
user_data_extract_content(
        ipc_voucher_attr_manager_t                      __assert_only manager,
        mach_voucher_attr_key_t                         __assert_only key,
        mach_voucher_attr_value_handle_array_t          values,
        mach_voucher_attr_value_handle_array_size_t     value_count,
        mach_voucher_attr_recipe_command_t              *out_command,
        mach_voucher_attr_content_t                     out_content,
        mach_voucher_attr_content_size_t                *in_out_content_size)
{
        mach_voucher_attr_content_size_t size = 0;
        user_data_element_t elem;
        unsigned int i;

        assert (&user_data_manager == manager);
        USER_DATA_ASSERT_KEY(key);

        /* concatenate the stored data items */
        for (i = 0; i < value_count ; i++) {
                elem = (user_data_element_t)values[i];
                assert(USER_DATA_MAX_DATA >= elem->e_size);

                if (size + elem->e_size > *in_out_content_size)
                        return KERN_NO_SPACE;

                memcpy(&out_content[size], elem->e_data, elem->e_size);
                size += elem->e_size;
        }
        *out_command = MACH_VOUCHER_ATTR_BITS_STORE;
        *in_out_content_size = size;
        return KERN_SUCCESS;
}

static kern_return_t
user_data_command(
        ipc_voucher_attr_manager_t                              __assert_only manager,
        mach_voucher_attr_key_t                                 __assert_only key,
        mach_voucher_attr_value_handle_array_t  __unused values,
        mach_msg_type_number_t                                  __unused value_count,
        mach_voucher_attr_command_t                             __unused command,
        mach_voucher_attr_content_t                             __unused in_content,
        mach_voucher_attr_content_size_t                __unused in_content_size,
        mach_voucher_attr_content_t                             __unused out_content,
        mach_voucher_attr_content_size_t                __unused *out_content_size)
{
        assert (&user_data_manager == manager);
        USER_DATA_ASSERT_KEY(key);
        return KERN_FAILURE;
}

static void
user_data_release(
        ipc_voucher_attr_manager_t              manager)
{
        if (manager != &user_data_manager)
                return;

        panic("Voucher user-data manager released");
}

static int user_data_manager_inited = 0;

void
user_data_attr_manager_init()
{
        kern_return_t kr;

#if defined(MACH_VOUCHER_ATTR_KEY_USER_DATA)    
        if ((user_data_manager_inited & 0x1) != 0x1) {
                kr = ipc_register_well_known_mach_voucher_attr_manager(&user_data_manager,
                                                (mach_voucher_attr_value_handle_t)0,
                                                MACH_VOUCHER_ATTR_KEY_USER_DATA,
                                                &user_data_control);
                if (KERN_SUCCESS != kr)
                        printf("Voucher user-data manager register(USER-DATA) returned %d", kr);
                else
                        user_data_manager_inited |= 0x1;
        }
#endif
#if defined(MACH_VOUCHER_ATTR_KEY_TEST)
        if ((user_data_manager_inited & 0x2) != 0x2) {
                kr = ipc_register_well_known_mach_voucher_attr_manager(&user_data_manager,
                                                (mach_voucher_attr_value_handle_t)0,
                                                MACH_VOUCHER_ATTR_KEY_TEST,
                                                &test_control);
                if (KERN_SUCCESS != kr)
                        printf("Voucher user-data manager register(TEST) returned %d", kr);
                else
                        user_data_manager_inited |= 0x2;
        }
#endif
#if defined(MACH_VOUCHER_ATTR_KEY_USER_DATA) || defined(MACH_VOUCHER_ATTR_KEY_TEST)
        int i;

        for (i=0; i < USER_DATA_HASH_BUCKETS; i++)
                queue_init(&user_data_bucket[i]);

        user_data_lock_init();
#endif
}

#endif /* MACH_DEBUG */