xnu-7195.50.7.100.1.tar.gz

[apple/xnu.git] / bsd / kern / kern_guarded.c

/*
 * Copyright (c) 2018 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 <sys/param.h>
#include <sys/systm.h>
#include <sys/filedesc.h>
#include <sys/kernel.h>
#include <sys/file_internal.h>
#include <kern/exc_guard.h>
#include <sys/guarded.h>
#include <kern/kalloc.h>
#include <sys/sysproto.h>
#include <sys/vnode.h>
#include <sys/vnode_internal.h>
#include <sys/uio_internal.h>
#include <sys/ubc_internal.h>
#include <vfs/vfs_support.h>
#include <security/audit/audit.h>
#include <sys/syscall.h>
#include <sys/kauth.h>
#include <sys/kdebug.h>
#include <stdbool.h>
#include <vm/vm_protos.h>
#include <libkern/section_keywords.h>
#if CONFIG_MACF && CONFIG_VNGUARD
#include <security/mac.h>
#include <security/mac_framework.h>
#include <security/mac_policy.h>
#include <pexpert/pexpert.h>
#include <sys/sysctl.h>
#include <sys/reason.h>
#endif


#define f_flag fp_glob->fg_flag
extern int dofilewrite(vfs_context_t ctx, struct fileproc *fp,
    user_addr_t bufp, user_size_t nbyte, off_t offset,
    int flags, user_ssize_t *retval );
extern int do_uiowrite(struct proc *p, struct fileproc *fp, uio_t uio, int flags, user_ssize_t *retval);

/*
 * Experimental guarded file descriptor support.
 */

kern_return_t task_exception_notify(exception_type_t exception,
    mach_exception_data_type_t code, mach_exception_data_type_t subcode);
kern_return_t task_violated_guard(mach_exception_code_t, mach_exception_subcode_t, void *);

/*
 * Most fd's have an underlying fileproc struct; but some may be
 * guarded_fileproc structs which implement guarded fds.  The latter
 * struct (below) embeds the former.
 *
 * The two types should be distinguished by the "type" portion of fp_flags.
 * There's also a magic number to help catch misuse and bugs.
 *
 * This is a bit unpleasant, but results from the desire to allow
 * alternate file behaviours for a few file descriptors without
 * growing the fileproc data structure.
 */

struct guarded_fileproc {
        struct fileproc gf_fileproc;
        u_int           gf_magic;
        u_int           gf_attrs;
        guardid_t       gf_guard;
};

const size_t sizeof_guarded_fileproc = sizeof(struct guarded_fileproc);

#define FP_TO_GFP(fp)   ((struct guarded_fileproc *)(fp))
#define GFP_TO_FP(gfp)  (&(gfp)->gf_fileproc)

#define GUARDED_FILEPROC_MAGIC  0x29083

struct gfp_crarg {
        guardid_t gca_guard;
        u_int gca_attrs;
};

static struct fileproc *
guarded_fileproc_alloc_init(void *crarg)
{
        struct gfp_crarg *aarg = crarg;
        struct guarded_fileproc *gfp;

        if ((gfp = kalloc(sizeof(*gfp))) == NULL) {
                return NULL;
        }

        bzero(gfp, sizeof(*gfp));

        struct fileproc *fp = &gfp->gf_fileproc;
        os_ref_init(&fp->fp_iocount, &f_refgrp);
        fp->fp_flags = FTYPE_GUARDED;

        gfp->gf_magic = GUARDED_FILEPROC_MAGIC;
        gfp->gf_guard = aarg->gca_guard;
        gfp->gf_attrs = aarg->gca_attrs;

        return GFP_TO_FP(gfp);
}

void
guarded_fileproc_free(struct fileproc *fp)
{
        struct guarded_fileproc *gfp = FP_TO_GFP(fp);

        if (FILEPROC_TYPE(fp) != FTYPE_GUARDED ||
            GUARDED_FILEPROC_MAGIC != gfp->gf_magic) {
                panic("%s: corrupt fp %p flags %x", __func__, fp, fp->fp_flags);
        }

        kfree(gfp, sizeof(*gfp));
}

static int
fp_lookup_guarded(proc_t p, int fd, guardid_t guard,
    struct guarded_fileproc **gfpp, int locked)
{
        struct fileproc *fp;
        int error;

        if ((error = fp_lookup(p, fd, &fp, locked)) != 0) {
                return error;
        }
        if (FILEPROC_TYPE(fp) != FTYPE_GUARDED) {
                (void) fp_drop(p, fd, fp, locked);
                return EINVAL;
        }
        struct guarded_fileproc *gfp = FP_TO_GFP(fp);

        if (GUARDED_FILEPROC_MAGIC != gfp->gf_magic) {
                panic("%s: corrupt fp %p", __func__, fp);
        }

        if (guard != gfp->gf_guard) {
                (void) fp_drop(p, fd, fp, locked);
                return EPERM; /* *not* a mismatch exception */
        }
        if (gfpp) {
                *gfpp = gfp;
        }
        return 0;
}

/*
 * Expected use pattern:
 *
 * if (FP_ISGUARDED(fp, GUARD_CLOSE)) {
 *      error = fp_guard_exception(p, fd, fp, kGUARD_EXC_CLOSE);
 *      proc_fdunlock(p);
 *      return error;
 * }
 */

int
fp_isguarded(struct fileproc *fp, u_int attrs)
{
        if (FILEPROC_TYPE(fp) == FTYPE_GUARDED) {
                struct guarded_fileproc *gfp = FP_TO_GFP(fp);

                if (GUARDED_FILEPROC_MAGIC != gfp->gf_magic) {
                        panic("%s: corrupt gfp %p flags %x",
                            __func__, gfp, fp->fp_flags);
                }
                return (attrs & gfp->gf_attrs) == attrs;
        }
        return 0;
}

extern char *proc_name_address(void *p);

int
fp_guard_exception(proc_t p, int fd, struct fileproc *fp, u_int flavor)
{
        if (FILEPROC_TYPE(fp) != FTYPE_GUARDED) {
                panic("%s corrupt fp %p flags %x", __func__, fp, fp->fp_flags);
        }

        struct guarded_fileproc *gfp = FP_TO_GFP(fp);
        /* all gfd fields protected via proc_fdlock() */
        proc_fdlock_assert(p, LCK_MTX_ASSERT_OWNED);

        mach_exception_code_t code = 0;
        EXC_GUARD_ENCODE_TYPE(code, GUARD_TYPE_FD);
        EXC_GUARD_ENCODE_FLAVOR(code, flavor);
        EXC_GUARD_ENCODE_TARGET(code, fd);
        mach_exception_subcode_t subcode = gfp->gf_guard;

        thread_t t = current_thread();
        thread_guard_violation(t, code, subcode, TRUE);
        return EPERM;
}

/*
 * (Invoked before returning to userland from the syscall handler.)
 */
void
fd_guard_ast(
        thread_t __unused t,
        mach_exception_code_t code,
        mach_exception_subcode_t subcode)
{
        task_exception_notify(EXC_GUARD, code, subcode);
        proc_t p = current_proc();
        psignal(p, SIGKILL);
}

/*
 * Experimental guarded file descriptor SPIs
 */

/*
 * int guarded_open_np(const char *pathname, int flags,
 *     const guardid_t *guard, u_int guardflags, ...);
 *
 * In this initial implementation, GUARD_DUP must be specified.
 * GUARD_CLOSE, GUARD_SOCKET_IPC and GUARD_FILEPORT are optional.
 *
 * If GUARD_DUP wasn't specified, then we'd have to do the (extra) work
 * to allow dup-ing a descriptor to inherit the guard onto the new
 * descriptor.  (Perhaps GUARD_DUP behaviours should just always be true
 * for a guarded fd?  Or, more sanely, all the dup operations should
 * just always propagate the guard?)
 *
 * Guarded descriptors are always close-on-exec, and GUARD_CLOSE
 * requires close-on-fork; O_CLOEXEC must be set in flags.
 * This setting is immutable; attempts to clear the flag will
 * cause a guard exception.
 *
 * XXX  It's somewhat broken that change_fdguard_np() can completely
 *      remove the guard and thus revoke down the immutability
 *      promises above.  Ick.
 */
int
guarded_open_np(proc_t p, struct guarded_open_np_args *uap, int32_t *retval)
{
        if ((uap->flags & O_CLOEXEC) == 0) {
                return EINVAL;
        }

#define GUARD_REQUIRED (GUARD_DUP)
#define GUARD_ALL      (GUARD_REQUIRED |        \
                        (GUARD_CLOSE | GUARD_SOCKET_IPC | GUARD_FILEPORT | GUARD_WRITE))

        if (((uap->guardflags & GUARD_REQUIRED) != GUARD_REQUIRED) ||
            ((uap->guardflags & ~GUARD_ALL) != 0)) {
                return EINVAL;
        }

        int error;
        struct gfp_crarg crarg = {
                .gca_attrs = uap->guardflags
        };

        if ((error = copyin(uap->guard,
            &(crarg.gca_guard), sizeof(crarg.gca_guard))) != 0) {
                return error;
        }

        /*
         * Disallow certain guard values -- is zero enough?
         */
        if (crarg.gca_guard == 0) {
                return EINVAL;
        }

        struct filedesc *fdp = p->p_fd;
        struct vnode_attr va;
        struct nameidata nd;
        vfs_context_t ctx = vfs_context_current();
        int cmode;

        VATTR_INIT(&va);
        cmode = ((uap->mode & ~fdp->fd_cmask) & ALLPERMS) & ~S_ISTXT;
        VATTR_SET(&va, va_mode, cmode & ACCESSPERMS);

        NDINIT(&nd, LOOKUP, OP_OPEN, FOLLOW | AUDITVNPATH1, UIO_USERSPACE,
            uap->path, ctx);

        return open1(ctx, &nd, uap->flags | O_CLOFORK, &va,
                   guarded_fileproc_alloc_init, &crarg, retval);
}

/*
 * int guarded_open_dprotected_np(const char *pathname, int flags,
 *     const guardid_t *guard, u_int guardflags, int dpclass, int dpflags, ...);
 *
 * This SPI is extension of guarded_open_np() to include dataprotection class on creation
 * in "dpclass" and dataprotection flags 'dpflags'. Otherwise behaviors are same as in
 * guarded_open_np()
 */
int
guarded_open_dprotected_np(proc_t p, struct guarded_open_dprotected_np_args *uap, int32_t *retval)
{
        if ((uap->flags & O_CLOEXEC) == 0) {
                return EINVAL;
        }

        if (((uap->guardflags & GUARD_REQUIRED) != GUARD_REQUIRED) ||
            ((uap->guardflags & ~GUARD_ALL) != 0)) {
                return EINVAL;
        }

        int error;
        struct gfp_crarg crarg = {
                .gca_attrs = uap->guardflags
        };

        if ((error = copyin(uap->guard,
            &(crarg.gca_guard), sizeof(crarg.gca_guard))) != 0) {
                return error;
        }

        /*
         * Disallow certain guard values -- is zero enough?
         */
        if (crarg.gca_guard == 0) {
                return EINVAL;
        }

        struct filedesc *fdp = p->p_fd;
        struct vnode_attr va;
        struct nameidata nd;
        vfs_context_t ctx = vfs_context_current();
        int cmode;

        VATTR_INIT(&va);
        cmode = ((uap->mode & ~fdp->fd_cmask) & ALLPERMS) & ~S_ISTXT;
        VATTR_SET(&va, va_mode, cmode & ACCESSPERMS);

        NDINIT(&nd, LOOKUP, OP_OPEN, FOLLOW | AUDITVNPATH1, UIO_USERSPACE,
            uap->path, ctx);

        /*
         * Initialize the extra fields in vnode_attr to pass down dataprotection
         * extra fields.
         * 1. target cprotect class.
         * 2. set a flag to mark it as requiring open-raw-encrypted semantics.
         */
        if (uap->flags & O_CREAT) {
                VATTR_SET(&va, va_dataprotect_class, uap->dpclass);
        }

        if (uap->dpflags & (O_DP_GETRAWENCRYPTED | O_DP_GETRAWUNENCRYPTED)) {
                if (uap->flags & (O_RDWR | O_WRONLY)) {
                        /* Not allowed to write raw encrypted bytes */
                        return EINVAL;
                }
                if (uap->dpflags & O_DP_GETRAWENCRYPTED) {
                        VATTR_SET(&va, va_dataprotect_flags, VA_DP_RAWENCRYPTED);
                }
                if (uap->dpflags & O_DP_GETRAWUNENCRYPTED) {
                        VATTR_SET(&va, va_dataprotect_flags, VA_DP_RAWUNENCRYPTED);
                }
        }

        return open1(ctx, &nd, uap->flags | O_CLOFORK, &va,
                   guarded_fileproc_alloc_init, &crarg, retval);
}

/*
 * int guarded_kqueue_np(const guardid_t *guard, u_int guardflags);
 *
 * Create a guarded kqueue descriptor with guardid and guardflags.
 *
 * Same restrictions on guardflags as for guarded_open_np().
 * All kqueues are -always- close-on-exec and close-on-fork by themselves
 * and are not sendable.
 */
int
guarded_kqueue_np(proc_t p, struct guarded_kqueue_np_args *uap, int32_t *retval)
{
        if (((uap->guardflags & GUARD_REQUIRED) != GUARD_REQUIRED) ||
            ((uap->guardflags & ~GUARD_ALL) != 0)) {
                return EINVAL;
        }

        int error;
        struct gfp_crarg crarg = {
                .gca_attrs = uap->guardflags
        };

        if ((error = copyin(uap->guard,
            &(crarg.gca_guard), sizeof(crarg.gca_guard))) != 0) {
                return error;
        }

        if (crarg.gca_guard == 0) {
                return EINVAL;
        }

        return kqueue_internal(p, guarded_fileproc_alloc_init, &crarg, retval);
}

/*
 * int guarded_close_np(int fd, const guardid_t *guard);
 */
int
guarded_close_np(proc_t p, struct guarded_close_np_args *uap,
    __unused int32_t *retval)
{
        struct guarded_fileproc *gfp;
        int fd = uap->fd;
        int error;
        guardid_t uguard;

        AUDIT_SYSCLOSE(p, fd);

        if ((error = copyin(uap->guard, &uguard, sizeof(uguard))) != 0) {
                return error;
        }

        proc_fdlock(p);
        if ((error = fp_lookup_guarded(p, fd, uguard, &gfp, 1)) != 0) {
                proc_fdunlock(p);
                return error;
        }
        fp_drop(p, fd, GFP_TO_FP(gfp), 1);
        return fp_close_and_unlock(p, fd, GFP_TO_FP(gfp), 0);
}

/*
 * int
 * change_fdguard_np(int fd, const guardid_t *guard, u_int guardflags,
 *    const guardid_t *nguard, u_int nguardflags, int *fdflagsp);
 *
 * Given a file descriptor, atomically exchange <guard, guardflags> for
 * a new guard <nguard, nguardflags>, returning the previous fd
 * flags (see fcntl:F_SETFD) in *fdflagsp.
 *
 * This syscall can be used to either (a) add a new guard to an existing
 * unguarded file descriptor (b) remove the old guard from an existing
 * guarded file descriptor or (c) change the guard (guardid and/or
 * guardflags) on a guarded file descriptor.
 *
 * If 'guard' is NULL, fd must be unguarded at entry. If the call completes
 * successfully the fd will be guarded with <nguard, nguardflags>.
 *
 * Guarding a file descriptor has some side-effects on the "fdflags"
 * associated with the descriptor - in particular FD_CLOEXEC is
 * forced ON unconditionally, and FD_CLOFORK is forced ON by GUARD_CLOSE.
 * Callers who wish to subsequently restore the state of the fd should save
 * the value of *fdflagsp after a successful invocation.
 *
 * If 'nguard' is NULL, fd must be guarded at entry, <guard, guardflags>
 * must match with what's already guarding the descriptor, and the
 * result will be to completely remove the guard.  Note also that the
 * fdflags are copied to the descriptor from the incoming *fdflagsp argument.
 *
 * If the descriptor is guarded, and neither 'guard' nor 'nguard' is NULL
 * and <guard, guardflags> matches what's already guarding the descriptor,
 * then <nguard, nguardflags> becomes the new guard.  In this case, even if
 * the GUARD_CLOSE flag is being cleared, it is still possible to continue
 * to keep FD_CLOFORK on the descriptor by passing FD_CLOFORK via fdflagsp.
 *
 * (File descriptors whose underlying fileglobs are marked FG_CONFINED are
 * still close-on-fork, regardless of the setting of FD_CLOFORK.)
 *
 * Example 1: Guard an unguarded descriptor during a set of operations,
 * then restore the original state of the descriptor.
 *
 * int sav_flags = 0;
 * change_fdguard_np(fd, NULL, 0, &myguard, GUARD_CLOSE, &sav_flags);
 * // do things with now guarded 'fd'
 * change_fdguard_np(fd, &myguard, GUARD_CLOSE, NULL, 0, &sav_flags);
 * // fd now unguarded.
 *
 * Example 2: Change the guard of a guarded descriptor during a set of
 * operations, then restore the original state of the descriptor.
 *
 * int sav_flags = (gdflags & GUARD_CLOSE) ? FD_CLOFORK : 0;
 * change_fdguard_np(fd, &gd, gdflags, &myguard, GUARD_CLOSE, &sav_flags);
 * // do things with 'fd' with a different guard
 * change_fdguard_np(fd, &myg, GUARD_CLOSE, &gd, gdflags, &sav_flags);
 * // back to original guarded state
 *
 * XXX  This SPI is too much of a chainsaw and should be revised.
 */

int
change_fdguard_np(proc_t p, struct change_fdguard_np_args *uap,
    __unused int32_t *retval)
{
        struct fileproc *fp;
        int fd = uap->fd;
        int error;
        guardid_t oldg = 0, newg = 0;
        int nfdflags = 0;

        if (0 != uap->guard &&
            0 != (error = copyin(uap->guard, &oldg, sizeof(oldg)))) {
                return error; /* can't copyin current guard */
        }
        if (0 != uap->nguard &&
            0 != (error = copyin(uap->nguard, &newg, sizeof(newg)))) {
                return error; /* can't copyin new guard */
        }
        if (0 != uap->fdflagsp &&
            0 != (error = copyin(uap->fdflagsp, &nfdflags, sizeof(nfdflags)))) {
                return error; /* can't copyin new fdflags */
        }
        proc_fdlock(p);
restart:
        if ((error = fp_lookup(p, fd, &fp, 1)) != 0) {
                proc_fdunlock(p);
                return error;
        }

        if (0 != uap->fdflagsp) {
                int ofdflags = FDFLAGS_GET(p, fd);
                int ofl = ((ofdflags & UF_EXCLOSE) ? FD_CLOEXEC : 0) |
                    ((ofdflags & UF_FORKCLOSE) ? FD_CLOFORK : 0);
                proc_fdunlock(p);
                if (0 != (error = copyout(&ofl, uap->fdflagsp, sizeof(ofl)))) {
                        proc_fdlock(p);
                        goto dropout; /* can't copyout old fdflags */
                }
                proc_fdlock(p);
        }

        if (FILEPROC_TYPE(fp) == FTYPE_GUARDED) {
                if (0 == uap->guard || 0 == uap->guardflags) {
                        error = EINVAL; /* missing guard! */
                } else if (0 == oldg) {
                        error = EPERM; /* guardids cannot be zero */
                }
        } else {
                if (0 != uap->guard || 0 != uap->guardflags) {
                        error = EINVAL; /* guard provided, but none needed! */
                }
        }

        if (0 != error) {
                goto dropout;
        }

        if (0 != uap->nguard) {
                /*
                 * There's a new guard in town.
                 */
                if (0 == newg) {
                        error = EINVAL; /* guards cannot contain zero */
                } else if (((uap->nguardflags & GUARD_REQUIRED) != GUARD_REQUIRED) ||
                    ((uap->nguardflags & ~GUARD_ALL) != 0)) {
                        error = EINVAL; /* must have valid attributes too */
                }
                if (0 != error) {
                        goto dropout;
                }

                if (FILEPROC_TYPE(fp) == FTYPE_GUARDED) {
                        /*
                         * Replace old guard with new guard
                         */
                        struct guarded_fileproc *gfp = FP_TO_GFP(fp);

                        if (GUARDED_FILEPROC_MAGIC != gfp->gf_magic) {
                                panic("%s: corrupt gfp %p flags %x",
                                    __func__, gfp, fp->fp_flags);
                        }

                        if (oldg == gfp->gf_guard &&
                            uap->guardflags == gfp->gf_attrs) {
                                /*
                                 * Must match existing guard + attributes
                                 * before we'll swap them to new ones, managing
                                 * fdflags "side-effects" as we go.   Note that
                                 * userland can request FD_CLOFORK semantics.
                                 */
                                if (gfp->gf_attrs & GUARD_CLOSE) {
                                        FDFLAGS_CLR(p, fd, UF_FORKCLOSE);
                                }
                                gfp->gf_guard = newg;
                                gfp->gf_attrs = uap->nguardflags;
                                if (gfp->gf_attrs & GUARD_CLOSE) {
                                        FDFLAGS_SET(p, fd, UF_FORKCLOSE);
                                }
                                FDFLAGS_SET(p, fd,
                                    (nfdflags & FD_CLOFORK) ? UF_FORKCLOSE : 0);
                                /* FG_CONFINED enforced regardless */
                        } else {
                                error = EPERM;
                        }
                        goto dropout;
                } else {
                        /*
                         * Add a guard to a previously unguarded descriptor
                         */
                        switch (FILEGLOB_DTYPE(fp->fp_glob)) {
                        case DTYPE_VNODE:
                        case DTYPE_PIPE:
                        case DTYPE_SOCKET:
                        case DTYPE_KQUEUE:
                        case DTYPE_NETPOLICY:
                                break;
                        default:
                                error = ENOTSUP;
                                goto dropout;
                        }

                        proc_fdunlock(p);

                        struct gfp_crarg crarg = {
                                .gca_guard = newg,
                                .gca_attrs = uap->nguardflags
                        };
                        struct fileproc *nfp =
                            guarded_fileproc_alloc_init(&crarg);
                        struct guarded_fileproc *gfp;

                        proc_fdlock(p);

                        switch (error = fp_tryswap(p, fd, nfp)) {
                        case 0: /* success; guarded-ness comes with side-effects */
                                fp = NULL;
                                gfp = FP_TO_GFP(nfp);
                                if (gfp->gf_attrs & GUARD_CLOSE) {
                                        FDFLAGS_SET(p, fd, UF_FORKCLOSE);
                                }
                                FDFLAGS_SET(p, fd, UF_EXCLOSE);
                                (void) fp_drop(p, fd, nfp, 1);
                                break;
                        case EKEEPLOOKING: /* fp_iocount indicates a collision */
                                (void) fp_drop(p, fd, fp, 1);
                                fileproc_free(nfp);
                                goto restart;
                        default:
                                (void) fp_drop(p, fd, fp, 1);
                                fileproc_free(nfp);
                                break;
                        }
                        proc_fdunlock(p);
                        return error;
                }
        } else {
                /*
                 * No new guard.
                 */
                if (FILEPROC_TYPE(fp) == FTYPE_GUARDED) {
                        /*
                         * Remove the guard altogether.
                         */
                        struct guarded_fileproc *gfp = FP_TO_GFP(fp);

                        if (0 != uap->nguardflags) {
                                error = EINVAL;
                                goto dropout;
                        }

                        if (GUARDED_FILEPROC_MAGIC != gfp->gf_magic) {
                                panic("%s: corrupt gfp %p flags %x",
                                    __func__, gfp, fp->fp_flags);
                        }

                        if (oldg != gfp->gf_guard ||
                            uap->guardflags != gfp->gf_attrs) {
                                error = EPERM;
                                goto dropout;
                        }

                        proc_fdunlock(p);
                        struct fileproc *nfp = fileproc_alloc_init(NULL);
                        proc_fdlock(p);

                        switch (error = fp_tryswap(p, fd, nfp)) {
                        case 0: /* success; undo side-effects of guarded-ness */
                                fp = NULL;
                                FDFLAGS_CLR(p, fd, UF_FORKCLOSE | UF_EXCLOSE);
                                FDFLAGS_SET(p, fd,
                                    (nfdflags & FD_CLOFORK) ? UF_FORKCLOSE : 0);
                                /* FG_CONFINED enforced regardless */
                                FDFLAGS_SET(p, fd,
                                    (nfdflags & FD_CLOEXEC) ? UF_EXCLOSE : 0);
                                (void) fp_drop(p, fd, nfp, 1);
                                break;
                        case EKEEPLOOKING: /* fp_iocount indicates collision */
                                (void) fp_drop(p, fd, fp, 1);
                                fileproc_free(nfp);
                                goto restart;
                        default:
                                (void) fp_drop(p, fd, fp, 1);
                                fileproc_free(nfp);
                                break;
                        }
                        proc_fdunlock(p);
                        return error;
                } else {
                        /*
                         * Not already guarded, and no new guard?
                         */
                        error = EINVAL;
                }
        }

dropout:
        (void) fp_drop(p, fd, fp, 1);
        proc_fdunlock(p);
        return error;
}

/*
 * user_ssize_t guarded_write_np(int fd, const guardid_t *guard,
 *                          user_addr_t cbuf, user_ssize_t nbyte);
 *
 * Initial implementation of guarded writes.
 */
int
guarded_write_np(struct proc *p, struct guarded_write_np_args *uap, user_ssize_t *retval)
{
        int error;
        int fd = uap->fd;
        guardid_t uguard;
        struct fileproc *fp;
        struct guarded_fileproc *gfp;

        AUDIT_ARG(fd, fd);

        if ((error = copyin(uap->guard, &uguard, sizeof(uguard))) != 0) {
                return error;
        }

        error = fp_lookup_guarded(p, fd, uguard, &gfp, 0);
        if (error) {
                return error;
        }

        fp = GFP_TO_FP(gfp);
        if ((fp->f_flag & FWRITE) == 0) {
                error = EBADF;
        } else {
                struct vfs_context context = *(vfs_context_current());
                context.vc_ucred = fp->fp_glob->fg_cred;

                error = dofilewrite(&context, fp, uap->cbuf, uap->nbyte,
                    (off_t)-1, 0, retval);
        }

        fp_drop(p, fd, fp, 0);

        return error;
}

/*
 * user_ssize_t guarded_pwrite_np(int fd, const guardid_t *guard,
 *                        user_addr_t buf, user_size_t nbyte, off_t offset);
 *
 * Initial implementation of guarded pwrites.
 */
int
guarded_pwrite_np(struct proc *p, struct guarded_pwrite_np_args *uap, user_ssize_t *retval)
{
        struct fileproc *fp;
        int error;
        int fd = uap->fd;
        vnode_t vp  = (vnode_t)0;
        guardid_t uguard;
        struct guarded_fileproc *gfp;

        AUDIT_ARG(fd, fd);

        if ((error = copyin(uap->guard, &uguard, sizeof(uguard))) != 0) {
                return error;
        }

        error = fp_lookup_guarded(p, fd, uguard, &gfp, 0);
        if (error) {
                return error;
        }

        fp = GFP_TO_FP(gfp);
        if ((fp->f_flag & FWRITE) == 0) {
                error = EBADF;
        } else {
                struct vfs_context context = *vfs_context_current();
                context.vc_ucred = fp->fp_glob->fg_cred;

                if (FILEGLOB_DTYPE(fp->fp_glob) != DTYPE_VNODE) {
                        error = ESPIPE;
                        goto errout;
                }
                vp = (vnode_t)fp->fp_glob->fg_data;
                if (vnode_isfifo(vp)) {
                        error = ESPIPE;
                        goto errout;
                }
                if ((vp->v_flag & VISTTY)) {
                        error = ENXIO;
                        goto errout;
                }
                if (uap->offset == (off_t)-1) {
                        error = EINVAL;
                        goto errout;
                }

                error = dofilewrite(&context, fp, uap->buf, uap->nbyte,
                    uap->offset, FOF_OFFSET, retval);
        }
errout:
        fp_drop(p, fd, fp, 0);

        KERNEL_DEBUG_CONSTANT((BSDDBG_CODE(DBG_BSD_SC_EXTENDED_INFO, SYS_guarded_pwrite_np) | DBG_FUNC_NONE),
            uap->fd, uap->nbyte, (unsigned int)((uap->offset >> 32)), (unsigned int)(uap->offset), 0);

        return error;
}

/*
 * user_ssize_t guarded_writev_np(int fd, const guardid_t *guard,
 *                                   struct iovec *iovp, u_int iovcnt);
 *
 * Initial implementation of guarded writev.
 *
 */
int
guarded_writev_np(struct proc *p, struct guarded_writev_np_args *uap, user_ssize_t *retval)
{
        uio_t auio = NULL;
        int error;
        struct fileproc *fp;
        struct user_iovec *iovp;
        guardid_t uguard;
        struct guarded_fileproc *gfp;

        AUDIT_ARG(fd, uap->fd);

        /* Verify range bedfore calling uio_create() */
        if (uap->iovcnt <= 0 || uap->iovcnt > UIO_MAXIOV) {
                return EINVAL;
        }

        /* allocate a uio large enough to hold the number of iovecs passed */
        auio = uio_create(uap->iovcnt, 0,
            (IS_64BIT_PROCESS(p) ? UIO_USERSPACE64 : UIO_USERSPACE32),
            UIO_WRITE);

        /* get location of iovecs within the uio.  then copyin the iovecs from
         * user space.
         */
        iovp = uio_iovsaddr(auio);
        if (iovp == NULL) {
                error = ENOMEM;
                goto ExitThisRoutine;
        }
        error = copyin_user_iovec_array(uap->iovp,
            IS_64BIT_PROCESS(p) ? UIO_USERSPACE64 : UIO_USERSPACE32,
            uap->iovcnt, iovp);
        if (error) {
                goto ExitThisRoutine;
        }

        /* finalize uio_t for use and do the IO
         */
        error = uio_calculateresid(auio);
        if (error) {
                goto ExitThisRoutine;
        }

        if ((error = copyin(uap->guard, &uguard, sizeof(uguard))) != 0) {
                goto ExitThisRoutine;
        }

        error = fp_lookup_guarded(p, uap->fd, uguard, &gfp, 0);
        if (error) {
                goto ExitThisRoutine;
        }

        fp = GFP_TO_FP(gfp);
        if ((fp->f_flag & FWRITE) == 0) {
                error = EBADF;
        } else {
                error = do_uiowrite(p, fp, auio, 0, retval);
        }

        fp_drop(p, uap->fd, fp, 0);
ExitThisRoutine:
        if (auio != NULL) {
                uio_free(auio);
        }
        return error;
}

/*
 * int falloc_guarded(struct proc *p, struct fileproc **fp, int *fd,
 *     vfs_context_t ctx, const guardid_t *guard, u_int attrs);
 *
 * This SPI is the guarded variant of falloc().  It borrows the same
 * restrictions as those used by the rest of the guarded_* routines.
 */
int
falloc_guarded(struct proc *p, struct fileproc **fp, int *fd,
    vfs_context_t ctx, const guardid_t *guard, u_int attrs)
{
        struct gfp_crarg crarg;

        if (((attrs & GUARD_REQUIRED) != GUARD_REQUIRED) ||
            ((attrs & ~GUARD_ALL) != 0) || (*guard == 0)) {
                return EINVAL;
        }

        bzero(&crarg, sizeof(crarg));
        crarg.gca_guard = *guard;
        crarg.gca_attrs = attrs;

        return falloc_withalloc(p, fp, fd, ctx, guarded_fileproc_alloc_init,
                   &crarg);
}

#if CONFIG_MACF && CONFIG_VNGUARD

/*
 * Guarded vnodes
 *
 * Uses MAC hooks to guard operations on vnodes in the system. Given an fd,
 * add data to the label on the fileglob and the vnode it points at.
 * The data contains a pointer to the fileglob, the set of attributes to
 * guard, a guard value for uniquification, and the pid of the process
 * who set the guard up in the first place.
 *
 * The fd must have been opened read/write, and the underlying
 * fileglob is FG_CONFINED so that there's no ambiguity about the
 * owning process.
 *
 * When there's a callback for a vnode operation of interest (rename, unlink,
 * etc.) check to see if the guard permits that operation, and if not
 * take an action e.g. log a message or generate a crash report.
 *
 * The label is removed from the vnode and the fileglob when the fileglob
 * is closed.
 *
 * The initial action to be taken can be specified by a boot arg (vnguard=0x42)
 * and change via the "kern.vnguard.flags" sysctl.
 */

struct vng_owner;

struct vng_info { /* lives on the vnode label */
        guardid_t vgi_guard;
        unsigned vgi_attrs;
        TAILQ_HEAD(, vng_owner) vgi_owners;
};

struct vng_owner { /* lives on the fileglob label */
        proc_t vgo_p;
        struct fileglob *vgo_fg;
        struct vng_info *vgo_vgi;
        TAILQ_ENTRY(vng_owner) vgo_link;
};

static struct vng_info *
new_vgi(unsigned attrs, guardid_t guard)
{
        struct vng_info *vgi = kalloc(sizeof(*vgi));
        vgi->vgi_guard = guard;
        vgi->vgi_attrs = attrs;
        TAILQ_INIT(&vgi->vgi_owners);
        return vgi;
}

static struct vng_owner *
new_vgo(proc_t p, struct fileglob *fg)
{
        struct vng_owner *vgo = kalloc(sizeof(*vgo));
        memset(vgo, 0, sizeof(*vgo));
        vgo->vgo_p = p;
        vgo->vgo_fg = fg;
        return vgo;
}

static void
vgi_add_vgo(struct vng_info *vgi, struct vng_owner *vgo)
{
        vgo->vgo_vgi = vgi;
        TAILQ_INSERT_HEAD(&vgi->vgi_owners, vgo, vgo_link);
}

static boolean_t
vgi_remove_vgo(struct vng_info *vgi, struct vng_owner *vgo)
{
        TAILQ_REMOVE(&vgi->vgi_owners, vgo, vgo_link);
        vgo->vgo_vgi = NULL;
        return TAILQ_EMPTY(&vgi->vgi_owners);
}

static void
free_vgi(struct vng_info *vgi)
{
        assert(TAILQ_EMPTY(&vgi->vgi_owners));
#if DEVELOP || DEBUG
        memset(vgi, 0xbeadfade, sizeof(*vgi));
#endif
        kfree(vgi, sizeof(*vgi));
}

static void
free_vgo(struct vng_owner *vgo)
{
#if DEVELOP || DEBUG
        memset(vgo, 0x2bedf1d0, sizeof(*vgo));
#endif
        kfree(vgo, sizeof(*vgo));
}

static int label_slot;
static lck_rw_t llock;
static lck_grp_t *llock_grp;

static __inline void *
vng_lbl_get(struct label *label)
{
        lck_rw_assert(&llock, LCK_RW_ASSERT_HELD);
        void *data;
        if (NULL == label) {
                data = NULL;
        } else {
                data = (void *)mac_label_get(label, label_slot);
        }
        return data;
}

static __inline struct vng_info *
vng_lbl_get_withattr(struct label *label, unsigned attrmask)
{
        struct vng_info *vgi = vng_lbl_get(label);
        assert(NULL == vgi || (vgi->vgi_attrs & ~VNG_ALL) == 0);
        if (NULL != vgi && 0 == (vgi->vgi_attrs & attrmask)) {
                vgi = NULL;
        }
        return vgi;
}

static __inline void
vng_lbl_set(struct label *label, void *data)
{
        assert(NULL != label);
        lck_rw_assert(&llock, LCK_RW_ASSERT_EXCLUSIVE);
        mac_label_set(label, label_slot, (intptr_t)data);
}

static int
vnguard_sysc_getguardattr(proc_t p, struct vnguard_getattr *vga)
{
        const int fd = vga->vga_fd;

        if (0 == vga->vga_guard) {
                return EINVAL;
        }

        int error;
        struct fileproc *fp;
        if (0 != (error = fp_lookup(p, fd, &fp, 0))) {
                return error;
        }
        do {
                struct fileglob *fg = fp->fp_glob;
                if (FILEGLOB_DTYPE(fg) != DTYPE_VNODE) {
                        error = EBADF;
                        break;
                }
                struct vnode *vp = fg->fg_data;
                if (!vnode_isreg(vp) || NULL == vp->v_mount) {
                        error = EBADF;
                        break;
                }
                error = vnode_getwithref(vp);
                if (0 != error) {
                        break;
                }

                vga->vga_attrs = 0;

                lck_rw_lock_shared(&llock);

                if (NULL != vp->v_label) {
                        const struct vng_info *vgi = vng_lbl_get(vp->v_label);
                        if (NULL != vgi) {
                                if (vgi->vgi_guard != vga->vga_guard) {
                                        error = EPERM;
                                } else {
                                        vga->vga_attrs = vgi->vgi_attrs;
                                }
                        }
                }

                lck_rw_unlock_shared(&llock);
                vnode_put(vp);
        } while (0);

        fp_drop(p, fd, fp, 0);
        return error;
}

static int
vnguard_sysc_setguard(proc_t p, const struct vnguard_set *vns)
{
        const int fd = vns->vns_fd;

        if ((vns->vns_attrs & ~VNG_ALL) != 0 ||
            0 == vns->vns_attrs || 0 == vns->vns_guard) {
                return EINVAL;
        }

        int error;
        struct fileproc *fp;
        if (0 != (error = fp_lookup(p, fd, &fp, 0))) {
                return error;
        }
        do {
                /*
                 * To avoid trivial DoS, insist that the caller
                 * has read/write access to the file.
                 */
                if ((FREAD | FWRITE) != (fp->f_flag & (FREAD | FWRITE))) {
                        error = EBADF;
                        break;
                }
                struct fileglob *fg = fp->fp_glob;
                if (FILEGLOB_DTYPE(fg) != DTYPE_VNODE) {
                        error = EBADF;
                        break;
                }
                /*
                 * Confinement means there's only one fd pointing at
                 * this fileglob, and will always be associated with
                 * this pid.
                 */
                if (0 == (FG_CONFINED & fg->fg_lflags)) {
                        error = EBADF;
                        break;
                }
                struct vnode *vp = fg->fg_data;
                if (!vnode_isreg(vp) || NULL == vp->v_mount) {
                        error = EBADF;
                        break;
                }
                error = vnode_getwithref(vp);
                if (0 != error) {
                        break;
                }

                /* Ensure the target vnode -has- a label */
                struct vfs_context *ctx = vfs_context_current();
                mac_vnode_label_update(ctx, vp, NULL);

                struct vng_info *nvgi = new_vgi(vns->vns_attrs, vns->vns_guard);
                struct vng_owner *nvgo = new_vgo(p, fg);

                lck_rw_lock_exclusive(&llock);

                do {
                        /*
                         * A vnode guard is associated with one or more
                         * fileglobs in one or more processes.
                         */
                        struct vng_info *vgi = vng_lbl_get(vp->v_label);
                        struct vng_owner *vgo = vng_lbl_get(fg->fg_label);

                        if (NULL == vgi) {
                                /* vnode unguarded, add the first guard */
                                if (NULL != vgo) {
                                        panic("vnguard label on fileglob "
                                            "but not vnode");
                                }
                                /* add a kusecount so we can unlabel later */
                                error = vnode_ref_ext(vp, O_EVTONLY, 0);
                                if (0 == error) {
                                        /* add the guard */
                                        vgi_add_vgo(nvgi, nvgo);
                                        vng_lbl_set(vp->v_label, nvgi);
                                        vng_lbl_set(fg->fg_label, nvgo);
                                } else {
                                        free_vgo(nvgo);
                                        free_vgi(nvgi);
                                }
                        } else {
                                /* vnode already guarded */
                                free_vgi(nvgi);
                                if (vgi->vgi_guard != vns->vns_guard) {
                                        error = EPERM; /* guard mismatch */
                                } else if (vgi->vgi_attrs != vns->vns_attrs) {
                                        /*
                                         * Temporary workaround for older versions of SQLite:
                                         * allow newer guard attributes to be silently cleared.
                                         */
                                        const unsigned mask = ~(VNG_WRITE_OTHER | VNG_TRUNC_OTHER);
                                        if ((vgi->vgi_attrs & mask) == (vns->vns_attrs & mask)) {
                                                vgi->vgi_attrs &= vns->vns_attrs;
                                        } else {
                                                error = EACCES; /* attr mismatch */
                                        }
                                }
                                if (0 != error || NULL != vgo) {
                                        free_vgo(nvgo);
                                        break;
                                }
                                /* record shared ownership */
                                vgi_add_vgo(vgi, nvgo);
                                vng_lbl_set(fg->fg_label, nvgo);
                        }
                } while (0);

                lck_rw_unlock_exclusive(&llock);
                vnode_put(vp);
        } while (0);

        fp_drop(p, fd, fp, 0);
        return error;
}

static int
vng_policy_syscall(proc_t p, int cmd, user_addr_t arg)
{
        int error = EINVAL;

        switch (cmd) {
        case VNG_SYSC_PING:
                if (0 == arg) {
                        error = 0;
                }
                break;
        case VNG_SYSC_SET_GUARD: {
                struct vnguard_set vns;
                error = copyin(arg, (void *)&vns, sizeof(vns));
                if (error) {
                        break;
                }
                error = vnguard_sysc_setguard(p, &vns);
                break;
        }
        case VNG_SYSC_GET_ATTR: {
                struct vnguard_getattr vga;
                error = copyin(arg, (void *)&vga, sizeof(vga));
                if (error) {
                        break;
                }
                error = vnguard_sysc_getguardattr(p, &vga);
                if (error) {
                        break;
                }
                error = copyout((void *)&vga, arg, sizeof(vga));
                break;
        }
        default:
                break;
        }
        return error;
}

/*
 * This is called just before the fileglob disappears in fg_free().
 * Take the exclusive lock: no other thread can add or remove
 * a vng_info to any vnode in the system.
 */
static void
vng_file_label_destroy(struct label *label)
{
        lck_rw_lock_exclusive(&llock);
        struct vng_owner *lvgo = vng_lbl_get(label);
        if (lvgo) {
                vng_lbl_set(label, 0);
                struct vng_info *vgi = lvgo->vgo_vgi;
                assert(vgi);
                if (vgi_remove_vgo(vgi, lvgo)) {
                        /* that was the last reference */
                        vgi->vgi_attrs = 0;
                        struct fileglob *fg = lvgo->vgo_fg;
                        assert(fg);
                        if (DTYPE_VNODE == FILEGLOB_DTYPE(fg)) {
                                struct vnode *vp = fg->fg_data;
                                int error = vnode_getwithref(vp);
                                if (0 == error) {
                                        vng_lbl_set(vp->v_label, 0);
                                        lck_rw_unlock_exclusive(&llock);
                                        /* may trigger VNOP_INACTIVE */
                                        vnode_rele_ext(vp, O_EVTONLY, 0);
                                        vnode_put(vp);
                                        free_vgi(vgi);
                                        free_vgo(lvgo);
                                        return;
                                }
                        }
                }
                free_vgo(lvgo);
        }
        lck_rw_unlock_exclusive(&llock);
}

static os_reason_t
vng_reason_from_pathname(const char *path, uint32_t pathlen)
{
        os_reason_t r = os_reason_create(OS_REASON_GUARD, GUARD_REASON_VNODE);
        if (NULL == r) {
                return r;
        }
        /*
         * If the pathname is very long, just keep the trailing part
         */
        const uint32_t pathmax = 3 * EXIT_REASON_USER_DESC_MAX_LEN / 4;
        if (pathlen > pathmax) {
                path += (pathlen - pathmax);
                pathlen = pathmax;
        }
        uint32_t rsize = kcdata_estimate_required_buffer_size(1, pathlen);
        if (0 == os_reason_alloc_buffer(r, rsize)) {
                struct kcdata_descriptor *kcd = &r->osr_kcd_descriptor;
                mach_vm_address_t addr;
                if (kcdata_get_memory_addr(kcd,
                    EXIT_REASON_USER_DESC, pathlen, &addr) == KERN_SUCCESS) {
                        kcdata_memcpy(kcd, addr, path, pathlen);
                        return r;
                }
        }
        os_reason_free(r);
        return OS_REASON_NULL;
}

static int vng_policy_flags;

/*
 * Note: if an EXC_GUARD is generated, llock will be dropped and
 * subsequently reacquired by this routine. Data derived from
 * any label in the caller should be regenerated.
 */
static int
vng_guard_violation(const struct vng_info *vgi,
    unsigned opval, vnode_t vp)
{
        int retval = 0;

        if (vng_policy_flags & kVNG_POLICY_EPERM) {
                /* deny the operation */
                retval = EPERM;
        }

        if (vng_policy_flags & (kVNG_POLICY_LOGMSG | kVNG_POLICY_UPRINTMSG)) {
                /* log a message */
                const char *op;
                switch (opval) {
                case VNG_RENAME_FROM:
                        op = "rename-from";
                        break;
                case VNG_RENAME_TO:
                        op = "rename-to";
                        break;
                case VNG_UNLINK:
                        op = "unlink";
                        break;
                case VNG_LINK:
                        op = "link";
                        break;
                case VNG_EXCHDATA:
                        op = "exchdata";
                        break;
                case VNG_WRITE_OTHER:
                        op = "write";
                        break;
                case VNG_TRUNC_OTHER:
                        op = "truncate";
                        break;
                default:
                        op = "(unknown)";
                        break;
                }

                const char *nm = vnode_getname(vp);
                proc_t p = current_proc();
                const struct vng_owner *vgo;
                TAILQ_FOREACH(vgo, &vgi->vgi_owners, vgo_link) {
                        const char fmt[] =
                            "%s[%d]: %s%s: '%s' guarded by %s[%d] (0x%llx)\n";

                        if (vng_policy_flags & kVNG_POLICY_LOGMSG) {
                                printf(fmt,
                                    proc_name_address(p), proc_pid(p), op,
                                    0 != retval ? " denied" : "",
                                    NULL != nm ? nm : "(unknown)",
                                    proc_name_address(vgo->vgo_p),
                                    proc_pid(vgo->vgo_p), vgi->vgi_guard);
                        }
                        if (vng_policy_flags & kVNG_POLICY_UPRINTMSG) {
                                uprintf(fmt,
                                    proc_name_address(p), proc_pid(p), op,
                                    0 != retval ? " denied" : "",
                                    NULL != nm ? nm : "(unknown)",
                                    proc_name_address(vgo->vgo_p),
                                    proc_pid(vgo->vgo_p), vgi->vgi_guard);
                        }
                }
                if (NULL != nm) {
                        vnode_putname(nm);
                }
        }

        if (vng_policy_flags & (kVNG_POLICY_EXC | kVNG_POLICY_EXC_CORPSE)) {
                /* EXC_GUARD exception */
                const struct vng_owner *vgo = TAILQ_FIRST(&vgi->vgi_owners);
                pid_t pid = vgo ? proc_pid(vgo->vgo_p) : 0;
                mach_exception_code_t code;
                mach_exception_subcode_t subcode;

                code = 0;
                EXC_GUARD_ENCODE_TYPE(code, GUARD_TYPE_VN);
                EXC_GUARD_ENCODE_FLAVOR(code, opval);
                EXC_GUARD_ENCODE_TARGET(code, pid);
                subcode = vgi->vgi_guard;

                lck_rw_unlock_shared(&llock);

                if (vng_policy_flags & kVNG_POLICY_EXC_CORPSE) {
                        char *path;
                        int len = MAXPATHLEN;
                        MALLOC(path, char *, len, M_TEMP, M_WAITOK);
                        os_reason_t r = NULL;
                        if (NULL != path) {
                                vn_getpath(vp, path, &len);
                                if (*path && len) {
                                        r = vng_reason_from_pathname(path, len);
                                }
                        }
                        task_violated_guard(code, subcode, r); /* not fatal */
                        if (NULL != r) {
                                os_reason_free(r);
                        }
                        if (NULL != path) {
                                FREE(path, M_TEMP);
                        }
                } else {
                        thread_t t = current_thread();
                        thread_guard_violation(t, code, subcode, TRUE);
                }

                lck_rw_lock_shared(&llock);
        } else if (vng_policy_flags & kVNG_POLICY_SIGKILL) {
                proc_t p = current_proc();
                psignal(p, SIGKILL);
        }

        return retval;
}

/*
 * A fatal vnode guard was tripped on this thread.
 *
 * (Invoked before returning to userland from the syscall handler.)
 */
void
vn_guard_ast(thread_t __unused t,
    mach_exception_data_type_t code, mach_exception_data_type_t subcode)
{
        task_exception_notify(EXC_GUARD, code, subcode);
        proc_t p = current_proc();
        psignal(p, SIGKILL);
}

/*
 * vnode callbacks
 */

static int
vng_vnode_check_rename(kauth_cred_t __unused cred,
    struct vnode *__unused dvp, struct label *__unused dlabel,
    struct vnode *vp, struct label *label,
    struct componentname *__unused cnp,
    struct vnode *__unused tdvp, struct label *__unused tdlabel,
    struct vnode *tvp, struct label *tlabel,
    struct componentname *__unused tcnp)
{
        int error = 0;
        if (NULL != label || NULL != tlabel) {
                lck_rw_lock_shared(&llock);
                const struct vng_info *vgi =
                    vng_lbl_get_withattr(label, VNG_RENAME_FROM);
                if (NULL != vgi) {
                        error = vng_guard_violation(vgi, VNG_RENAME_FROM, vp);
                }
                if (0 == error) {
                        vgi = vng_lbl_get_withattr(tlabel, VNG_RENAME_TO);
                        if (NULL != vgi) {
                                error = vng_guard_violation(vgi,
                                    VNG_RENAME_TO, tvp);
                        }
                }
                lck_rw_unlock_shared(&llock);
        }
        return error;
}

static int
vng_vnode_check_link(kauth_cred_t __unused cred,
    struct vnode *__unused dvp, struct label *__unused dlabel,
    struct vnode *vp, struct label *label, struct componentname *__unused cnp)
{
        int error = 0;
        if (NULL != label) {
                lck_rw_lock_shared(&llock);
                const struct vng_info *vgi =
                    vng_lbl_get_withattr(label, VNG_LINK);
                if (vgi) {
                        error = vng_guard_violation(vgi, VNG_LINK, vp);
                }
                lck_rw_unlock_shared(&llock);
        }
        return error;
}

static int
vng_vnode_check_unlink(kauth_cred_t __unused cred,
    struct vnode *__unused dvp, struct label *__unused dlabel,
    struct vnode *vp, struct label *label, struct componentname *__unused cnp)
{
        int error = 0;
        if (NULL != label) {
                lck_rw_lock_shared(&llock);
                const struct vng_info *vgi =
                    vng_lbl_get_withattr(label, VNG_UNLINK);
                if (vgi) {
                        error = vng_guard_violation(vgi, VNG_UNLINK, vp);
                }
                lck_rw_unlock_shared(&llock);
        }
        return error;
}

/*
 * Only check violations for writes performed by "other processes"
 */
static int
vng_vnode_check_write(kauth_cred_t __unused actv_cred,
    kauth_cred_t __unused file_cred, struct vnode *vp, struct label *label)
{
        int error = 0;
        if (NULL != label) {
                lck_rw_lock_shared(&llock);
                const struct vng_info *vgi =
                    vng_lbl_get_withattr(label, VNG_WRITE_OTHER);
                if (vgi) {
                        proc_t p = current_proc();
                        const struct vng_owner *vgo;
                        TAILQ_FOREACH(vgo, &vgi->vgi_owners, vgo_link) {
                                if (vgo->vgo_p == p) {
                                        goto done;
                                }
                        }
                        error = vng_guard_violation(vgi, VNG_WRITE_OTHER, vp);
                }
done:
                lck_rw_unlock_shared(&llock);
        }
        return error;
}

/*
 * Only check violations for truncates performed by "other processes"
 */
static int
vng_vnode_check_truncate(kauth_cred_t __unused actv_cred,
    kauth_cred_t __unused file_cred, struct vnode *vp,
    struct label *label)
{
        int error = 0;
        if (NULL != label) {
                lck_rw_lock_shared(&llock);
                const struct vng_info *vgi =
                    vng_lbl_get_withattr(label, VNG_TRUNC_OTHER);
                if (vgi) {
                        proc_t p = current_proc();
                        const struct vng_owner *vgo;
                        TAILQ_FOREACH(vgo, &vgi->vgi_owners, vgo_link) {
                                if (vgo->vgo_p == p) {
                                        goto done;
                                }
                        }
                        error = vng_guard_violation(vgi, VNG_TRUNC_OTHER, vp);
                }
done:
                lck_rw_unlock_shared(&llock);
        }
        return error;
}

static int
vng_vnode_check_exchangedata(kauth_cred_t __unused cred,
    struct vnode *fvp, struct label *flabel,
    struct vnode *svp, struct label *slabel)
{
        int error = 0;
        if (NULL != flabel || NULL != slabel) {
                lck_rw_lock_shared(&llock);
                const struct vng_info *vgi =
                    vng_lbl_get_withattr(flabel, VNG_EXCHDATA);
                if (NULL != vgi) {
                        error = vng_guard_violation(vgi, VNG_EXCHDATA, fvp);
                }
                if (0 == error) {
                        vgi = vng_lbl_get_withattr(slabel, VNG_EXCHDATA);
                        if (NULL != vgi) {
                                error = vng_guard_violation(vgi,
                                    VNG_EXCHDATA, svp);
                        }
                }
                lck_rw_unlock_shared(&llock);
        }
        return error;
}

/* Intercept open-time truncations (by "other") of a guarded vnode */

static int
vng_vnode_check_open(kauth_cred_t cred,
    struct vnode *vp, struct label *label, int acc_mode)
{
        if (0 == (acc_mode & O_TRUNC)) {
                return 0;
        }
        return vng_vnode_check_truncate(cred, NULL, vp, label);
}

/*
 * Configuration gorp
 */

static void
vng_init(struct mac_policy_conf *mpc)
{
        llock_grp = lck_grp_alloc_init(mpc->mpc_name, LCK_GRP_ATTR_NULL);
        lck_rw_init(&llock, llock_grp, LCK_ATTR_NULL);
}

SECURITY_READ_ONLY_EARLY(static struct mac_policy_ops) vng_policy_ops = {
        .mpo_file_label_destroy = vng_file_label_destroy,

        .mpo_vnode_check_link = vng_vnode_check_link,
        .mpo_vnode_check_unlink = vng_vnode_check_unlink,
        .mpo_vnode_check_rename = vng_vnode_check_rename,
        .mpo_vnode_check_write = vng_vnode_check_write,
        .mpo_vnode_check_truncate = vng_vnode_check_truncate,
        .mpo_vnode_check_exchangedata = vng_vnode_check_exchangedata,
        .mpo_vnode_check_open = vng_vnode_check_open,

        .mpo_policy_syscall = vng_policy_syscall,
        .mpo_policy_init = vng_init,
};

static const char *vng_labelnames[] = {
        "vnguard",
};

#define ACOUNT(arr) ((unsigned)(sizeof (arr) / sizeof (arr[0])))

SECURITY_READ_ONLY_LATE(static struct mac_policy_conf) vng_policy_conf = {
        .mpc_name = VNG_POLICY_NAME,
        .mpc_fullname = "Guarded vnode policy",
        .mpc_field_off = &label_slot,
        .mpc_labelnames = vng_labelnames,
        .mpc_labelname_count = ACOUNT(vng_labelnames),
        .mpc_ops = &vng_policy_ops,
        .mpc_loadtime_flags = 0,
        .mpc_runtime_flags = 0
};

SECURITY_READ_ONLY_LATE(static mac_policy_handle_t) vng_policy_handle;

void
vnguard_policy_init(void)
{
        if (0 == PE_i_can_has_debugger(NULL)) {
                return;
        }
        vng_policy_flags = kVNG_POLICY_LOGMSG |
            kVNG_POLICY_EXC_CORPSE | kVNG_POLICY_UPRINTMSG;
        PE_parse_boot_argn("vnguard", &vng_policy_flags, sizeof(vng_policy_flags));
        if (vng_policy_flags) {
                mac_policy_register(&vng_policy_conf, &vng_policy_handle, NULL);
        }
}

#if DEBUG || DEVELOPMENT
#include <sys/sysctl.h>

SYSCTL_DECL(_kern_vnguard);
SYSCTL_NODE(_kern, OID_AUTO, vnguard, CTLFLAG_RW | CTLFLAG_LOCKED, 0, "vnguard");
SYSCTL_INT(_kern_vnguard, OID_AUTO, flags, CTLFLAG_RW | CTLFLAG_LOCKED,
    &vng_policy_flags, 0, "vnguard policy flags");
#endif

#endif /* CONFIG_MACF && CONFIG_VNGUARD */