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

/*
 * Copyright (c) 2012 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 <sys/guarded.h>
#include <kern/kalloc.h>
#include <sys/sysproto.h>
#include <sys/vnode.h>
#include <vfs/vfs_support.h>
#include <security/audit/audit.h>

/*
 * 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);

/*
 * 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 f_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;
        thread_t        gf_thread;
        guardid_t       gf_guard;
        int             gf_exc_fd;
        u_int           gf_exc_code;
};

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));
        gfp->gf_fileproc.f_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->f_flags);

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

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

        if ((error = fp_lookup(p, fd, &fp, 1)) != 0)
                return (error);
        if (FILEPROC_TYPE(fp) != FTYPE_GUARDED) {
                (void) fp_drop(p, fd, fp, 1);
                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, 1);
                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->f_flags);
                return ((attrs & gfp->gf_attrs) ? 1 : 0);
        }
        return (0);
}

extern char *proc_name_address(void *p);

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

        struct guarded_fileproc *gfp = FP_TO_GFP(fp);

        /* all gfd fields protected via proc_fdlock() */
        proc_fdlock_assert(p, LCK_MTX_ASSERT_OWNED);

        if (NULL == gfp->gf_thread) {
                thread_t t = current_thread();
                gfp->gf_thread = t;
                gfp->gf_exc_fd = fd;
                gfp->gf_exc_code = code;

                /*
                 * This thread was the first to attempt the
                 * operation that violated the guard on this fd;
                 * generate an exception.
                 */
                printf("%s: guarded fd exception: "
                    "fd %d code 0x%x guard 0x%llx\n",
                    proc_name_address(p), gfp->gf_exc_fd,
                    gfp->gf_exc_code, gfp->gf_guard);

                thread_guard_violation(t, GUARD_TYPE_FD);
        } else {
                /*
                 * We already recorded a violation on this fd for a
                 * different thread, so posting an exception is
                 * already in progress.  We could pause for a bit
                 * and check again, or we could panic (though that seems
                 * heavy handed), or we could just press on with the
                 * error return alone.  For now, resort to printf.
                 */
                printf("%s: guarded fd exception+: "
                    "fd %d code 0x%x guard 0x%llx\n",
                    proc_name_address(p), gfp->gf_exc_fd,
                    gfp->gf_exc_code, gfp->gf_guard);
        }

        return (EPERM);
}

/*
 * (Invoked before returning to userland from the syscall handler.)
 */
void
fd_guard_ast(thread_t t)
{
        proc_t p = current_proc();
        struct filedesc *fdp = p->p_fd;
        int i;

        proc_fdlock(p);
        for (i = fdp->fd_lastfile; i >= 0; i--) {
                struct fileproc *fp = fdp->fd_ofiles[i];

                if (fp == NULL ||
                    FILEPROC_TYPE(fp) != FTYPE_GUARDED)
                        continue;

                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->f_flags);

                if (gfp->gf_thread == t) {
                        mach_exception_data_type_t code, subcode;

                        gfp->gf_thread = NULL;

                        /*
                         * EXC_GUARD exception code namespace.
                         *
                         * code:
                         * +-------------------------------------------------+
                         * | [63:61] guard type | [60:0] guard-specific data |
                         * +-------------------------------------------------+
                         *
                         * subcode:
                         * +-------------------------------------------------+
                         * |       [63:0] guard-specific data                |
                         * +-------------------------------------------------+
                         *
                         * At the moment, we have just one guard type: file
                         * descriptor guards.
                         *
                         * File descriptor guards use the exception codes like
                         * so:
                         *
                         * code:                         
                         * +--------------------------------------------------+
                         * |[63:61] GUARD_TYPE_FD | [60:32] flavor | [31:0] fd|
                         * +--------------------------------------------------+
                         *
                         * subcode:
                         * +--------------------------------------------------+
                         * |       [63:0] guard value                         |
                         * +--------------------------------------------------+
                         */
                        code = (((uint64_t)GUARD_TYPE_FD) << 61) |
                               (((uint64_t)gfp->gf_exc_code) << 32) |
                               ((uint64_t)gfp->gf_exc_fd);
                        subcode = gfp->gf_guard;
                        proc_fdunlock(p);

                        (void) task_exception_notify(EXC_GUARD, code, subcode);
                        psignal(p, SIGKILL);

                        return;
                }
        }
        proc_fdunlock(p);
}

/*
 * 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.
 */
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))

        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_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.
 *
 * XXX  Is it ever sensible to allow a kqueue fd (guarded or not) to
 *      be sent to another process via a fileport or socket?
 */
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_body(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)) != 0) {
                proc_fdunlock(p);
                return (error);
        }
        error = close_internal_locked(p, fd, GFP_TO_FP(gfp), 0);
        proc_fdunlock(p);
        return (error);
}

/*
 * 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.
 *
 * 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
 */

#define FDFLAGS_GET(p, fd) (*fdflags(p, fd) & (UF_EXCLOSE|UF_FORKCLOSE))
#define FDFLAGS_SET(p, fd, bits) \
           (*fdflags(p, fd) |= ((bits) & (UF_EXCLOSE|UF_FORKCLOSE)))
#define FDFLAGS_CLR(p, fd, bits) \
           (*fdflags(p, fd) &= ~((bits) & (UF_EXCLOSE|UF_FORKCLOSE)))

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 (0 == uap->nguardflags)
                        error = EINVAL; /* attributes cannot be zero */
                else if (((uap->nguardflags & GUARD_REQUIRED) != GUARD_REQUIRED) ||
                    ((uap->guardflags & ~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->f_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);
                        } else {
                                error = EPERM;
                        }
                        goto dropout;
                } else {
                        /*
                         * Add a guard to a previously unguarded descriptor
                         */
                        switch (FILEGLOB_DTYPE(fp->f_fglob)) {
                        case DTYPE_VNODE:
                        case DTYPE_PIPE:
                        case DTYPE_SOCKET:
                        case DTYPE_KQUEUE:
                                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);

                        proc_fdlock(p);

                        switch (error = fp_tryswap(p, fd, nfp)) {
                                struct guarded_fileproc *gfp;

                        case 0: /* guarded-ness comes with side-effects */
                                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);
                                fileproc_free(fp);
                                break;
                        case EKEEPLOOKING: /* f_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->f_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: /* undo side-effects of guarded-ness */
                                FDFLAGS_CLR(p, fd, UF_FORKCLOSE | UF_EXCLOSE);
                                FDFLAGS_SET(p, fd,
                                    (nfdflags & FD_CLOFORK) ? UF_FORKCLOSE : 0);
                                FDFLAGS_SET(p, fd,
                                    (nfdflags & FD_CLOEXEC) ? UF_EXCLOSE : 0);
                                (void) fp_drop(p, fd, nfp, 1);
                                fileproc_free(fp);
                                break;
                        case EKEEPLOOKING: /* f_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);
}