uipc_shm.c

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/*-
 * SPDX-License-Identifier: BSD-2-Clause-FreeBSD
 *
 * Copyright (c) 2006, 2011, 2016-2017 Robert N. M. Watson
 * Copyright 2020 The FreeBSD Foundation
 * All rights reserved.
 *
 * Portions of this software were developed by BAE Systems, the University of
 * Cambridge Computer Laboratory, and Memorial University under DARPA/AFRL
 * contract FA8650-15-C-7558 ("CADETS"), as part of the DARPA Transparent
 * Computing (TC) research program.
 *
 * Portions of this software were developed by Konstantin Belousov
 * under sponsorship from the FreeBSD Foundation.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer.
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in the
 *    documentation and/or other materials provided with the distribution.
 *
 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
 * ARE DISCLAIMED.  IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
 * SUCH DAMAGE.
 */
 
/*
 * Support for shared swap-backed anonymous memory objects via
 * shm_open(2), shm_rename(2), and shm_unlink(2).
 * While most of the implementation is here, vm_mmap.c contains
 * mapping logic changes.
 *
 * posixshmcontrol(1) allows users to inspect the state of the memory
 * objects.  Per-uid swap resource limit controls total amount of
 * memory that user can consume for anonymous objects, including
 * shared.
 */
 
#include <sys/cdefs.h>
__FBSDID("$FreeBSD$");
 
#include "opt_capsicum.h"
#include "opt_ktrace.h"
 
#include <sys/param.h>
#include <sys/capsicum.h>
#include <sys/conf.h>
#include <sys/fcntl.h>
#include <sys/file.h>
#include <sys/filedesc.h>
#include <sys/filio.h>
#include <sys/fnv_hash.h>
#include <sys/kernel.h>
#include <sys/limits.h>
#include <sys/uio.h>
#include <sys/signal.h>
#include <sys/jail.h>
#include <sys/ktrace.h>
#include <sys/lock.h>
#include <sys/malloc.h>
#include <sys/mman.h>
#include <sys/mutex.h>
#include <sys/priv.h>
#include <sys/proc.h>
#include <sys/refcount.h>
#include <sys/resourcevar.h>
#include <sys/rwlock.h>
#include <sys/sbuf.h>
#include <sys/stat.h>
#include <sys/syscallsubr.h>
#include <sys/sysctl.h>
#include <sys/sysproto.h>
#include <sys/systm.h>
#include <sys/sx.h>
#include <sys/time.h>
#include <sys/vmmeter.h>
#include <sys/vnode.h>
#include <sys/unistd.h>
#include <sys/user.h>
 
#include <security/audit/audit.h>
#include <security/mac/mac_framework.h>
 
#include <vm/vm.h>
#include <vm/vm_param.h>
#include <vm/pmap.h>
#include <vm/vm_extern.h>
#include <vm/vm_map.h>
#include <vm/vm_kern.h>
#include <vm/vm_object.h>
#include <vm/vm_page.h>
#include <vm/vm_pageout.h>
#include <vm/vm_pager.h>
#include <vm/swap_pager.h>
 
struct shm_mapping {
        char            *sm_path;
        Fnv32_t         sm_fnv;
        struct shmfd    *sm_shmfd;
        LIST_ENTRY(shm_mapping) sm_link;
};
 
static MALLOC_DEFINE(M_SHMFD, "shmfd", "shared memory file descriptor");
static LIST_HEAD(, shm_mapping) *shm_dictionary;
static struct sx shm_dict_lock;
static struct mtx shm_timestamp_lock;
static u_long shm_hash;
static struct unrhdr64 shm_ino_unr;
static dev_t shm_dev_ino;
 
#define SHM_HASH(fnv)   (&shm_dictionary[(fnv) & shm_hash])
 
static void     shm_init(void *arg);
static void     shm_insert(char *path, Fnv32_t fnv, struct shmfd *shmfd);
static struct shmfd *shm_lookup(char *path, Fnv32_t fnv);
static int      shm_remove(char *path, Fnv32_t fnv, struct ucred *ucred);
static int      shm_dotruncate_cookie(struct shmfd *shmfd, off_t length,
    void *rl_cookie);
static int      shm_dotruncate_locked(struct shmfd *shmfd, off_t length,
    void *rl_cookie);
static int      shm_copyin_path(struct thread *td, const char *userpath_in,
    char **path_out);
static int      shm_deallocate(struct shmfd *shmfd, off_t *offset,
    off_t *length, int flags);
 
static fo_rdwr_t        shm_read;
static fo_rdwr_t        shm_write;
static fo_truncate_t    shm_truncate;
static fo_ioctl_t       shm_ioctl;
static fo_stat_t        shm_stat;
static fo_close_t       shm_close;
static fo_chmod_t       shm_chmod;
static fo_chown_t       shm_chown;
static fo_seek_t        shm_seek;
static fo_fill_kinfo_t  shm_fill_kinfo;
static fo_mmap_t        shm_mmap;
static fo_get_seals_t   shm_get_seals;
static fo_add_seals_t   shm_add_seals;
static fo_fallocate_t   shm_fallocate;
static fo_fspacectl_t   shm_fspacectl;
 
/* File descriptor operations. */
struct fileops shm_ops = {
        .fo_read = shm_read,
        .fo_write = shm_write,
        .fo_truncate = shm_truncate,
        .fo_ioctl = shm_ioctl,
        .fo_poll = invfo_poll,
        .fo_kqfilter = invfo_kqfilter,
        .fo_stat = shm_stat,
        .fo_close = shm_close,
        .fo_chmod = shm_chmod,
        .fo_chown = shm_chown,
        .fo_sendfile = vn_sendfile,
        .fo_seek = shm_seek,
        .fo_fill_kinfo = shm_fill_kinfo,
        .fo_mmap = shm_mmap,
        .fo_get_seals = shm_get_seals,
        .fo_add_seals = shm_add_seals,
        .fo_fallocate = shm_fallocate,
        .fo_fspacectl = shm_fspacectl,
        .fo_flags = DFLAG_PASSABLE | DFLAG_SEEKABLE,
};
 
FEATURE(posix_shm, "POSIX shared memory");
 
static SYSCTL_NODE(_vm, OID_AUTO, largepages, CTLFLAG_RD | CTLFLAG_MPSAFE, 0,
    "");
 
static int largepage_reclaim_tries = 1;
SYSCTL_INT(_vm_largepages, OID_AUTO, reclaim_tries,
    CTLFLAG_RWTUN, &largepage_reclaim_tries, 0,
    "Number of contig reclaims before giving up for default alloc policy");
 
static int
uiomove_object_page(vm_object_t obj, size_t len, struct uio *uio)
{
        vm_page_t m;
        vm_pindex_t idx;
        size_t tlen;
        int error, offset, rv;
 
        idx = OFF_TO_IDX(uio->uio_offset);
        offset = uio->uio_offset & PAGE_MASK;
        tlen = MIN(PAGE_SIZE - offset, len);
 
        rv = vm_page_grab_valid_unlocked(&m, obj, idx,
            VM_ALLOC_SBUSY | VM_ALLOC_IGN_SBUSY | VM_ALLOC_NOCREAT);
        if (rv == VM_PAGER_OK)
                goto found;
 
        /*
         * Read I/O without either a corresponding resident page or swap
         * page: use zero_region.  This is intended to avoid instantiating
         * pages on read from a sparse region.
         */
        VM_OBJECT_WLOCK(obj);
        m = vm_page_lookup(obj, idx);
        if (uio->uio_rw == UIO_READ && m == NULL &&
            !vm_pager_has_page(obj, idx, NULL, NULL)) {
                VM_OBJECT_WUNLOCK(obj);
                return (uiomove(__DECONST(void *, zero_region), tlen, uio));
        }
 
        /*
         * Although the tmpfs vnode lock is held here, it is
         * nonetheless safe to sleep waiting for a free page.  The
         * pageout daemon does not need to acquire the tmpfs vnode
         * lock to page out tobj's pages because tobj is a OBJT_SWAP
         * type object.
         */
        rv = vm_page_grab_valid(&m, obj, idx,
            VM_ALLOC_NORMAL | VM_ALLOC_SBUSY | VM_ALLOC_IGN_SBUSY);
        if (rv != VM_PAGER_OK) {
                VM_OBJECT_WUNLOCK(obj);
                printf("uiomove_object: vm_obj %p idx %jd pager error %d\n",
                    obj, idx, rv);
                return (EIO);
        }
        VM_OBJECT_WUNLOCK(obj);
 
found:
        error = uiomove_fromphys(&m, offset, tlen, uio);
        if (uio->uio_rw == UIO_WRITE && error == 0)
                vm_page_set_dirty(m);
        vm_page_activate(m);
        vm_page_sunbusy(m);
 
        return (error);
}
 
int
uiomove_object(vm_object_t obj, off_t obj_size, struct uio *uio)
{
        ssize_t resid;
        size_t len;
        int error;
 
        error = 0;
        while ((resid = uio->uio_resid) > 0) {
                if (obj_size <= uio->uio_offset)
                        break;
                len = MIN(obj_size - uio->uio_offset, resid);
                if (len == 0)
                        break;
                error = uiomove_object_page(obj, len, uio);
                if (error != 0 || resid == uio->uio_resid)
                        break;
        }
        return (error);
}
 
static u_long count_largepages[MAXPAGESIZES];
 
static int
shm_largepage_phys_populate(vm_object_t object, vm_pindex_t pidx,
    int fault_type, vm_prot_t max_prot, vm_pindex_t *first, vm_pindex_t *last)
{
        vm_page_t m __diagused;
        int psind;
 
        psind = object->un_pager.phys.data_val;
        if (psind == 0 || pidx >= object->size)
                return (VM_PAGER_FAIL);
        *first = rounddown2(pidx, pagesizes[psind] / PAGE_SIZE);
 
        /*
         * We only busy the first page in the superpage run.  It is
         * useless to busy whole run since we only remove full
         * superpage, and it takes too long to busy e.g. 512 * 512 ==
         * 262144 pages constituing 1G amd64 superage.
         */
        m = vm_page_grab(object, *first, VM_ALLOC_NORMAL | VM_ALLOC_NOCREAT);
        MPASS(m != NULL);
 
        *last = *first + atop(pagesizes[psind]) - 1;
        return (VM_PAGER_OK);
}
 
static boolean_t
shm_largepage_phys_haspage(vm_object_t object, vm_pindex_t pindex,
    int *before, int *after)
{
        int psind;
 
        psind = object->un_pager.phys.data_val;
        if (psind == 0 || pindex >= object->size)
                return (FALSE);
        if (before != NULL) {
                *before = pindex - rounddown2(pindex, pagesizes[psind] /
                    PAGE_SIZE);
        }
        if (after != NULL) {
                *after = roundup2(pindex, pagesizes[psind] / PAGE_SIZE) -
                    pindex;
        }
        return (TRUE);
}
 
static void
shm_largepage_phys_ctor(vm_object_t object, vm_prot_t prot,
    vm_ooffset_t foff, struct ucred *cred)
{
}
 
static void
shm_largepage_phys_dtor(vm_object_t object)
{
        int psind;
 
        psind = object->un_pager.phys.data_val;
        if (psind != 0) {
                atomic_subtract_long(&count_largepages[psind],
                    object->size / (pagesizes[psind] / PAGE_SIZE));
                vm_wire_sub(object->size);
        } else {
                KASSERT(object->size == 0,
                    ("largepage phys obj %p not initialized bit size %#jx > 0",
                    object, (uintmax_t)object->size));
        }
}
 
static const struct phys_pager_ops shm_largepage_phys_ops = {
        .phys_pg_populate =     shm_largepage_phys_populate,
        .phys_pg_haspage =      shm_largepage_phys_haspage,
        .phys_pg_ctor =         shm_largepage_phys_ctor,
        .phys_pg_dtor =         shm_largepage_phys_dtor,
};
 
bool
shm_largepage(struct shmfd *shmfd)
{
        return (shmfd->shm_object->type == OBJT_PHYS);
}
 
static int
shm_seek(struct file *fp, off_t offset, int whence, struct thread *td)
{
        struct shmfd *shmfd;
        off_t foffset;
        int error;
 
        shmfd = fp->f_data;
        foffset = foffset_lock(fp, 0);
        error = 0;
        switch (whence) {
        case L_INCR:
                if (foffset < 0 ||
                    (offset > 0 && foffset > OFF_MAX - offset)) {
                        error = EOVERFLOW;
                        break;
                }
                offset += foffset;
                break;
        case L_XTND:
                if (offset > 0 && shmfd->shm_size > OFF_MAX - offset) {
                        error = EOVERFLOW;
                        break;
                }
                offset += shmfd->shm_size;
                break;
        case L_SET:
                break;
        default:
                error = EINVAL;
        }
        if (error == 0) {
                if (offset < 0 || offset > shmfd->shm_size)
                        error = EINVAL;
                else
                        td->td_uretoff.tdu_off = offset;
        }
        foffset_unlock(fp, offset, error != 0 ? FOF_NOUPDATE : 0);
        return (error);
}
 
static int
shm_read(struct file *fp, struct uio *uio, struct ucred *active_cred,
    int flags, struct thread *td)
{
        struct shmfd *shmfd;
        void *rl_cookie;
        int error;
 
        shmfd = fp->f_data;
#ifdef MAC
        error = mac_posixshm_check_read(active_cred, fp->f_cred, shmfd);
        if (error)
                return (error);
#endif
        foffset_lock_uio(fp, uio, flags);
        rl_cookie = rangelock_rlock(&shmfd->shm_rl, uio->uio_offset,
            uio->uio_offset + uio->uio_resid, &shmfd->shm_mtx);
        error = uiomove_object(shmfd->shm_object, shmfd->shm_size, uio);
        rangelock_unlock(&shmfd->shm_rl, rl_cookie, &shmfd->shm_mtx);
        foffset_unlock_uio(fp, uio, flags);
        return (error);
}
 
static int
shm_write(struct file *fp, struct uio *uio, struct ucred *active_cred,
    int flags, struct thread *td)
{
        struct shmfd *shmfd;
        void *rl_cookie;
        int error;
        off_t size;
 
        shmfd = fp->f_data;
#ifdef MAC
        error = mac_posixshm_check_write(active_cred, fp->f_cred, shmfd);
        if (error)
                return (error);
#endif
        if (shm_largepage(shmfd) && shmfd->shm_lp_psind == 0)
                return (EINVAL);
        foffset_lock_uio(fp, uio, flags);
        if (uio->uio_resid > OFF_MAX - uio->uio_offset) {
                /*
                 * Overflow is only an error if we're supposed to expand on
                 * write.  Otherwise, we'll just truncate the write to the
                 * size of the file, which can only grow up to OFF_MAX.
                 */
                if ((shmfd->shm_flags & SHM_GROW_ON_WRITE) != 0) {
                        foffset_unlock_uio(fp, uio, flags);
                        return (EFBIG);
                }
 
                size = shmfd->shm_size;
        } else {
                size = uio->uio_offset + uio->uio_resid;
        }
        if ((flags & FOF_OFFSET) == 0) {
                rl_cookie = rangelock_wlock(&shmfd->shm_rl, 0, OFF_MAX,
                    &shmfd->shm_mtx);
        } else {
                rl_cookie = rangelock_wlock(&shmfd->shm_rl, uio->uio_offset,
                    size, &shmfd->shm_mtx);
        }
        if ((shmfd->shm_seals & F_SEAL_WRITE) != 0) {
                error = EPERM;
        } else {
                error = 0;
                if ((shmfd->shm_flags & SHM_GROW_ON_WRITE) != 0 &&
                    size > shmfd->shm_size) {
                        error = shm_dotruncate_cookie(shmfd, size, rl_cookie);
                }
                if (error == 0)
                        error = uiomove_object(shmfd->shm_object,
                            shmfd->shm_size, uio);
        }
        rangelock_unlock(&shmfd->shm_rl, rl_cookie, &shmfd->shm_mtx);
        foffset_unlock_uio(fp, uio, flags);
        return (error);
}
 
static int
shm_truncate(struct file *fp, off_t length, struct ucred *active_cred,
    struct thread *td)
{
        struct shmfd *shmfd;
#ifdef MAC
        int error;
#endif
 
        shmfd = fp->f_data;
#ifdef MAC
        error = mac_posixshm_check_truncate(active_cred, fp->f_cred, shmfd);
        if (error)
                return (error);
#endif
        return (shm_dotruncate(shmfd, length));
}
 
int
shm_ioctl(struct file *fp, u_long com, void *data, struct ucred *active_cred,
    struct thread *td)
{
        struct shmfd *shmfd;
        struct shm_largepage_conf *conf;
        void *rl_cookie;
 
        shmfd = fp->f_data;
        switch (com) {
        case FIONBIO:
        case FIOASYNC:
                /*
                 * Allow fcntl(fd, F_SETFL, O_NONBLOCK) to work,
                 * just like it would on an unlinked regular file
                 */
                return (0);
        case FIOSSHMLPGCNF:
                if (!shm_largepage(shmfd))
                        return (ENOTTY);
                conf = data;
                if (shmfd->shm_lp_psind != 0 &&
                    conf->psind != shmfd->shm_lp_psind)
                        return (EINVAL);
                if (conf->psind <= 0 || conf->psind >= MAXPAGESIZES ||
                    pagesizes[conf->psind] == 0)
                        return (EINVAL);
                if (conf->alloc_policy != SHM_LARGEPAGE_ALLOC_DEFAULT &&
                    conf->alloc_policy != SHM_LARGEPAGE_ALLOC_NOWAIT &&
                    conf->alloc_policy != SHM_LARGEPAGE_ALLOC_HARD)
                        return (EINVAL);
 
                rl_cookie = rangelock_wlock(&shmfd->shm_rl, 0, OFF_MAX,
                    &shmfd->shm_mtx);
                shmfd->shm_lp_psind = conf->psind;
                shmfd->shm_lp_alloc_policy = conf->alloc_policy;
                shmfd->shm_object->un_pager.phys.data_val = conf->psind;
                rangelock_unlock(&shmfd->shm_rl, rl_cookie, &shmfd->shm_mtx);
                return (0);
        case FIOGSHMLPGCNF:
                if (!shm_largepage(shmfd))
                        return (ENOTTY);
                conf = data;
                rl_cookie = rangelock_rlock(&shmfd->shm_rl, 0, OFF_MAX,
                    &shmfd->shm_mtx);
                conf->psind = shmfd->shm_lp_psind;
                conf->alloc_policy = shmfd->shm_lp_alloc_policy;
                rangelock_unlock(&shmfd->shm_rl, rl_cookie, &shmfd->shm_mtx);
                return (0);
        default:
                return (ENOTTY);
        }
}
 
static int
shm_stat(struct file *fp, struct stat *sb, struct ucred *active_cred)
{
        struct shmfd *shmfd;
#ifdef MAC
        int error;
#endif
 
        shmfd = fp->f_data;
 
#ifdef MAC
        error = mac_posixshm_check_stat(active_cred, fp->f_cred, shmfd);
        if (error)
                return (error);
#endif
 
        /*
         * Attempt to return sanish values for fstat() on a memory file
         * descriptor.
         */
        bzero(sb, sizeof(*sb));
        sb->st_blksize = PAGE_SIZE;
        sb->st_size = shmfd->shm_size;
        sb->st_blocks = howmany(sb->st_size, sb->st_blksize);
        mtx_lock(&shm_timestamp_lock);
        sb->st_atim = shmfd->shm_atime;
        sb->st_ctim = shmfd->shm_ctime;
        sb->st_mtim = shmfd->shm_mtime;
        sb->st_birthtim = shmfd->shm_birthtime;
        sb->st_mode = S_IFREG | shmfd->shm_mode;                /* XXX */
        sb->st_uid = shmfd->shm_uid;
        sb->st_gid = shmfd->shm_gid;
        mtx_unlock(&shm_timestamp_lock);
        sb->st_dev = shm_dev_ino;
        sb->st_ino = shmfd->shm_ino;
        sb->st_nlink = shmfd->shm_object->ref_count;
        sb->st_blocks = shmfd->shm_object->size /
            (pagesizes[shmfd->shm_lp_psind] >> PAGE_SHIFT);
 
        return (0);
}
 
static int
shm_close(struct file *fp, struct thread *td)
{
        struct shmfd *shmfd;
 
        shmfd = fp->f_data;
        fp->f_data = NULL;
        shm_drop(shmfd);
 
        return (0);
}
 
static int
shm_copyin_path(struct thread *td, const char *userpath_in, char **path_out) {
        int error;
        char *path;
        const char *pr_path;
        size_t pr_pathlen;
 
        path = malloc(MAXPATHLEN, M_SHMFD, M_WAITOK);
        pr_path = td->td_ucred->cr_prison->pr_path;
 
        /* Construct a full pathname for jailed callers. */
        pr_pathlen = strcmp(pr_path, "/") ==
            0 ? 0 : strlcpy(path, pr_path, MAXPATHLEN);
        error = copyinstr(userpath_in, path + pr_pathlen,
            MAXPATHLEN - pr_pathlen, NULL);
        if (error != 0)
                goto out;
 
#ifdef KTRACE
        if (KTRPOINT(curthread, KTR_NAMEI))
                ktrnamei(path);
#endif
 
        /* Require paths to start with a '/' character. */
        if (path[pr_pathlen] != '/') {
                error = EINVAL;
                goto out;
        }
 
        *path_out = path;
 
out:
        if (error != 0)
                free(path, M_SHMFD);
 
        return (error);
}
 
static int
shm_partial_page_invalidate(vm_object_t object, vm_pindex_t idx, int base,
    int end)
{
        vm_page_t m;
        int rv;
 
        VM_OBJECT_ASSERT_WLOCKED(object);
        KASSERT(base >= 0, ("%s: base %d", __func__, base));
        KASSERT(end - base <= PAGE_SIZE, ("%s: base %d end %d", __func__, base,
            end));
 
retry:
        m = vm_page_grab(object, idx, VM_ALLOC_NOCREAT);
        if (m != NULL) {
                MPASS(vm_page_all_valid(m));
        } else if (vm_pager_has_page(object, idx, NULL, NULL)) {
                m = vm_page_alloc(object, idx,
                    VM_ALLOC_NORMAL | VM_ALLOC_WAITFAIL);
                if (m == NULL)
                        goto retry;
                vm_object_pip_add(object, 1);
                VM_OBJECT_WUNLOCK(object);
                rv = vm_pager_get_pages(object, &m, 1, NULL, NULL);
                VM_OBJECT_WLOCK(object);
                vm_object_pip_wakeup(object);
                if (rv == VM_PAGER_OK) {
                        /*
                         * Since the page was not resident, and therefore not
                         * recently accessed, immediately enqueue it for
                         * asynchronous laundering.  The current operation is
                         * not regarded as an access.
                         */
                        vm_page_launder(m);
                } else {
                        vm_page_free(m);
                        VM_OBJECT_WUNLOCK(object);
                        return (EIO);
                }
        }
        if (m != NULL) {
                pmap_zero_page_area(m, base, end - base);
                KASSERT(vm_page_all_valid(m), ("%s: page %p is invalid",
                    __func__, m));
                vm_page_set_dirty(m);
                vm_page_xunbusy(m);
        }
 
        return (0);
}
 
static int
shm_dotruncate_locked(struct shmfd *shmfd, off_t length, void *rl_cookie)
{
        vm_object_t object;
        vm_pindex_t nobjsize;
        vm_ooffset_t delta;
        int base, error;
 
        KASSERT(length >= 0, ("shm_dotruncate: length < 0"));
        object = shmfd->shm_object;
        VM_OBJECT_ASSERT_WLOCKED(object);
        rangelock_cookie_assert(rl_cookie, RA_WLOCKED);
        if (length == shmfd->shm_size)
                return (0);
        nobjsize = OFF_TO_IDX(length + PAGE_MASK);
 
        /* Are we shrinking?  If so, trim the end. */
        if (length < shmfd->shm_size) {
                if ((shmfd->shm_seals & F_SEAL_SHRINK) != 0)
                        return (EPERM);
 
                /*
                 * Disallow any requests to shrink the size if this
                 * object is mapped into the kernel.
                 */
                if (shmfd->shm_kmappings > 0)
                        return (EBUSY);
 
                /*
                 * Zero the truncated part of the last page.
                 */
                base = length & PAGE_MASK;
                if (base != 0) {
                        error = shm_partial_page_invalidate(object,
                            OFF_TO_IDX(length), base, PAGE_SIZE);
                        if (error)
                                return (error);
                }
                delta = IDX_TO_OFF(object->size - nobjsize);
 
                if (nobjsize < object->size)
                        vm_object_page_remove(object, nobjsize, object->size,
                            0);
 
                /* Free the swap accounted for shm */
                swap_release_by_cred(delta, object->cred);
                object->charge -= delta;
        } else {
                if ((shmfd->shm_seals & F_SEAL_GROW) != 0)
                        return (EPERM);
 
                /* Try to reserve additional swap space. */
                delta = IDX_TO_OFF(nobjsize - object->size);
                if (!swap_reserve_by_cred(delta, object->cred))
                        return (ENOMEM);
                object->charge += delta;
        }
        shmfd->shm_size = length;
        mtx_lock(&shm_timestamp_lock);
        vfs_timestamp(&shmfd->shm_ctime);
        shmfd->shm_mtime = shmfd->shm_ctime;
        mtx_unlock(&shm_timestamp_lock);
        object->size = nobjsize;
        return (0);
}
 
static int
shm_dotruncate_largepage(struct shmfd *shmfd, off_t length, void *rl_cookie)
{
        vm_object_t object;
        vm_page_t m;
        vm_pindex_t newobjsz;
        vm_pindex_t oldobjsz __unused;
        int aflags, error, i, psind, try;
 
        KASSERT(length >= 0, ("shm_dotruncate: length < 0"));
        object = shmfd->shm_object;
        VM_OBJECT_ASSERT_WLOCKED(object);
        rangelock_cookie_assert(rl_cookie, RA_WLOCKED);
 
        oldobjsz = object->size;
        newobjsz = OFF_TO_IDX(length);
        if (length == shmfd->shm_size)
                return (0);
        psind = shmfd->shm_lp_psind;
        if (psind == 0 && length != 0)
                return (EINVAL);
        if ((length & (pagesizes[psind] - 1)) != 0)
                return (EINVAL);
 
        if (length < shmfd->shm_size) {
                if ((shmfd->shm_seals & F_SEAL_SHRINK) != 0)
                        return (EPERM);
                if (shmfd->shm_kmappings > 0)
                        return (EBUSY);
                return (ENOTSUP);       /* Pages are unmanaged. */
#if 0
                vm_object_page_remove(object, newobjsz, oldobjsz, 0);
                object->size = newobjsz;
                shmfd->shm_size = length;
                return (0);
#endif
        }
 
        if ((shmfd->shm_seals & F_SEAL_GROW) != 0)
                return (EPERM);
 
        aflags = VM_ALLOC_NORMAL | VM_ALLOC_ZERO;
        if (shmfd->shm_lp_alloc_policy == SHM_LARGEPAGE_ALLOC_NOWAIT)
                aflags |= VM_ALLOC_WAITFAIL;
        try = 0;
 
        /*
         * Extend shmfd and object, keeping all already fully
         * allocated large pages intact even on error, because dropped
         * object lock might allowed mapping of them.
         */
        while (object->size < newobjsz) {
                m = vm_page_alloc_contig(object, object->size, aflags,
                    pagesizes[psind] / PAGE_SIZE, 0, ~0,
                    pagesizes[psind], 0,
                    VM_MEMATTR_DEFAULT);
                if (m == NULL) {
                        VM_OBJECT_WUNLOCK(object);
                        if (shmfd->shm_lp_alloc_policy ==
                            SHM_LARGEPAGE_ALLOC_NOWAIT ||
                            (shmfd->shm_lp_alloc_policy ==
                            SHM_LARGEPAGE_ALLOC_DEFAULT &&
                            try >= largepage_reclaim_tries)) {
                                VM_OBJECT_WLOCK(object);
                                return (ENOMEM);
                        }
                        error = vm_page_reclaim_contig(aflags,
                            pagesizes[psind] / PAGE_SIZE, 0, ~0,
                            pagesizes[psind], 0) ? 0 :
                            vm_wait_intr(object);
                        if (error != 0) {
                                VM_OBJECT_WLOCK(object);
                                return (error);
                        }
                        try++;
                        VM_OBJECT_WLOCK(object);
                        continue;
                }
                try = 0;
                for (i = 0; i < pagesizes[psind] / PAGE_SIZE; i++) {
                        if ((m[i].flags & PG_ZERO) == 0)
                                pmap_zero_page(&m[i]);
                        vm_page_valid(&m[i]);
                        vm_page_xunbusy(&m[i]);
                }
                object->size += OFF_TO_IDX(pagesizes[psind]);
                shmfd->shm_size += pagesizes[psind];
                atomic_add_long(&count_largepages[psind], 1);
                vm_wire_add(atop(pagesizes[psind]));
        }
        return (0);
}
 
static int
shm_dotruncate_cookie(struct shmfd *shmfd, off_t length, void *rl_cookie)
{
        int error;
 
        VM_OBJECT_WLOCK(shmfd->shm_object);
        error = shm_largepage(shmfd) ? shm_dotruncate_largepage(shmfd,
            length, rl_cookie) : shm_dotruncate_locked(shmfd, length,
            rl_cookie);
        VM_OBJECT_WUNLOCK(shmfd->shm_object);
        return (error);
}
 
int
shm_dotruncate(struct shmfd *shmfd, off_t length)
{
        void *rl_cookie;
        int error;
 
        rl_cookie = rangelock_wlock(&shmfd->shm_rl, 0, OFF_MAX,
            &shmfd->shm_mtx);
        error = shm_dotruncate_cookie(shmfd, length, rl_cookie);
        rangelock_unlock(&shmfd->shm_rl, rl_cookie, &shmfd->shm_mtx);
        return (error);
}
 
/*
 * shmfd object management including creation and reference counting
 * routines.
 */
struct shmfd *
shm_alloc(struct ucred *ucred, mode_t mode, bool largepage)
{
        struct shmfd *shmfd;
 
        shmfd = malloc(sizeof(*shmfd), M_SHMFD, M_WAITOK | M_ZERO);
        shmfd->shm_size = 0;
        shmfd->shm_uid = ucred->cr_uid;
        shmfd->shm_gid = ucred->cr_gid;
        shmfd->shm_mode = mode;
        if (largepage) {
                shmfd->shm_object = phys_pager_allocate(NULL,
                    &shm_largepage_phys_ops, NULL, shmfd->shm_size,
                    VM_PROT_DEFAULT, 0, ucred);
                shmfd->shm_lp_alloc_policy = SHM_LARGEPAGE_ALLOC_DEFAULT;
        } else {
                shmfd->shm_object = vm_pager_allocate(OBJT_SWAP, NULL,
                    shmfd->shm_size, VM_PROT_DEFAULT, 0, ucred);
        }
        KASSERT(shmfd->shm_object != NULL, ("shm_create: vm_pager_allocate"));
        vfs_timestamp(&shmfd->shm_birthtime);
        shmfd->shm_atime = shmfd->shm_mtime = shmfd->shm_ctime =
            shmfd->shm_birthtime;
        shmfd->shm_ino = alloc_unr64(&shm_ino_unr);
        refcount_init(&shmfd->shm_refs, 1);
        mtx_init(&shmfd->shm_mtx, "shmrl", NULL, MTX_DEF);
        rangelock_init(&shmfd->shm_rl);
#ifdef MAC
        mac_posixshm_init(shmfd);
        mac_posixshm_create(ucred, shmfd);
#endif
 
        return (shmfd);
}
 
struct shmfd *
shm_hold(struct shmfd *shmfd)
{
 
        refcount_acquire(&shmfd->shm_refs);
        return (shmfd);
}
 
void
shm_drop(struct shmfd *shmfd)
{
 
        if (refcount_release(&shmfd->shm_refs)) {
#ifdef MAC
                mac_posixshm_destroy(shmfd);
#endif
                rangelock_destroy(&shmfd->shm_rl);
                mtx_destroy(&shmfd->shm_mtx);
                vm_object_deallocate(shmfd->shm_object);
                free(shmfd, M_SHMFD);
        }
}
 
/*
 * Determine if the credentials have sufficient permissions for a
 * specified combination of FREAD and FWRITE.
 */
int
shm_access(struct shmfd *shmfd, struct ucred *ucred, int flags)
{
        accmode_t accmode;
        int error;
 
        accmode = 0;
        if (flags & FREAD)
                accmode |= VREAD;
        if (flags & FWRITE)
                accmode |= VWRITE;
        mtx_lock(&shm_timestamp_lock);
        error = vaccess(VREG, shmfd->shm_mode, shmfd->shm_uid, shmfd->shm_gid,
            accmode, ucred);
        mtx_unlock(&shm_timestamp_lock);
        return (error);
}
 
static void
shm_init(void *arg)
{
        char name[32];
        int i;
 
        mtx_init(&shm_timestamp_lock, "shm timestamps", NULL, MTX_DEF);
        sx_init(&shm_dict_lock, "shm dictionary");
        shm_dictionary = hashinit(1024, M_SHMFD, &shm_hash);
        new_unrhdr64(&shm_ino_unr, 1);
        shm_dev_ino = devfs_alloc_cdp_inode();
        KASSERT(shm_dev_ino > 0, ("shm dev inode not initialized"));
 
        for (i = 1; i < MAXPAGESIZES; i++) {
                if (pagesizes[i] == 0)
                        break;
#define M       (1024 * 1024)
#define G       (1024 * M)
                if (pagesizes[i] >= G)
                        snprintf(name, sizeof(name), "%luG", pagesizes[i] / G);
                else if (pagesizes[i] >= M)
                        snprintf(name, sizeof(name), "%luM", pagesizes[i] / M);
                else
                        snprintf(name, sizeof(name), "%lu", pagesizes[i]);
#undef G
#undef M
                SYSCTL_ADD_ULONG(NULL, SYSCTL_STATIC_CHILDREN(_vm_largepages),
                    OID_AUTO, name, CTLFLAG_RD, &count_largepages[i],
                    "number of non-transient largepages allocated");
        }
}
SYSINIT(shm_init, SI_SUB_SYSV_SHM, SI_ORDER_ANY, shm_init, NULL);
 
/*
 * Dictionary management.  We maintain an in-kernel dictionary to map
 * paths to shmfd objects.  We use the FNV hash on the path to store
 * the mappings in a hash table.
 */
static struct shmfd *
shm_lookup(char *path, Fnv32_t fnv)
{
        struct shm_mapping *map;
 
        LIST_FOREACH(map, SHM_HASH(fnv), sm_link) {
                if (map->sm_fnv != fnv)
                        continue;
                if (strcmp(map->sm_path, path) == 0)
                        return (map->sm_shmfd);
        }
 
        return (NULL);
}
 
static void
shm_insert(char *path, Fnv32_t fnv, struct shmfd *shmfd)
{
        struct shm_mapping *map;
 
        map = malloc(sizeof(struct shm_mapping), M_SHMFD, M_WAITOK);
        map->sm_path = path;
        map->sm_fnv = fnv;
        map->sm_shmfd = shm_hold(shmfd);
        shmfd->shm_path = path;
        LIST_INSERT_HEAD(SHM_HASH(fnv), map, sm_link);
}
 
static int
shm_remove(char *path, Fnv32_t fnv, struct ucred *ucred)
{
        struct shm_mapping *map;
        int error;
 
        LIST_FOREACH(map, SHM_HASH(fnv), sm_link) {
                if (map->sm_fnv != fnv)
                        continue;
                if (strcmp(map->sm_path, path) == 0) {
#ifdef MAC
                        error = mac_posixshm_check_unlink(ucred, map->sm_shmfd);
                        if (error)
                                return (error);
#endif
                        error = shm_access(map->sm_shmfd, ucred,
                            FREAD | FWRITE);
                        if (error)
                                return (error);
                        map->sm_shmfd->shm_path = NULL;
                        LIST_REMOVE(map, sm_link);
                        shm_drop(map->sm_shmfd);
                        free(map->sm_path, M_SHMFD);
                        free(map, M_SHMFD);
                        return (0);
                }
        }
 
        return (ENOENT);
}
 
int
kern_shm_open2(struct thread *td, const char *userpath, int flags, mode_t mode,
    int shmflags, struct filecaps *fcaps, const char *name __unused)
{
        struct pwddesc *pdp;
        struct shmfd *shmfd;
        struct file *fp;
        char *path;
        void *rl_cookie;
        Fnv32_t fnv;
        mode_t cmode;
        int error, fd, initial_seals;
        bool largepage;
 
        if ((shmflags & ~(SHM_ALLOW_SEALING | SHM_GROW_ON_WRITE |
            SHM_LARGEPAGE)) != 0)
                return (EINVAL);
 
        initial_seals = F_SEAL_SEAL;
        if ((shmflags & SHM_ALLOW_SEALING) != 0)
                initial_seals &= ~F_SEAL_SEAL;
 
#ifdef CAPABILITY_MODE
        /*
         * shm_open(2) is only allowed for anonymous objects.
         */
        if (IN_CAPABILITY_MODE(td) && (userpath != SHM_ANON))
                return (ECAPMODE);
#endif
 
        AUDIT_ARG_FFLAGS(flags);
        AUDIT_ARG_MODE(mode);
 
        if ((flags & O_ACCMODE) != O_RDONLY && (flags & O_ACCMODE) != O_RDWR)
                return (EINVAL);
 
        if ((flags & ~(O_ACCMODE | O_CREAT | O_EXCL | O_TRUNC | O_CLOEXEC)) != 0)
                return (EINVAL);
 
        largepage = (shmflags & SHM_LARGEPAGE) != 0;
        if (largepage && !PMAP_HAS_LARGEPAGES)
                return (ENOTTY);
 
        /*
         * Currently only F_SEAL_SEAL may be set when creating or opening shmfd.
         * If the decision is made later to allow additional seals, care must be
         * taken below to ensure that the seals are properly set if the shmfd
         * already existed -- this currently assumes that only F_SEAL_SEAL can
         * be set and doesn't take further precautions to ensure the validity of
         * the seals being added with respect to current mappings.
         */
        if ((initial_seals & ~F_SEAL_SEAL) != 0)
                return (EINVAL);
 
        pdp = td->td_proc->p_pd;
        cmode = (mode & ~pdp->pd_cmask) & ACCESSPERMS;
 
        /*
         * shm_open(2) created shm should always have O_CLOEXEC set, as mandated
         * by POSIX.  We allow it to be unset here so that an in-kernel
         * interface may be written as a thin layer around shm, optionally not
         * setting CLOEXEC.  For shm_open(2), O_CLOEXEC is set unconditionally
         * in sys_shm_open() to keep this implementation compliant.
         */
        error = falloc_caps(td, &fp, &fd, flags & O_CLOEXEC, fcaps);
        if (error)
                return (error);
 
        /* A SHM_ANON path pointer creates an anonymous object. */
        if (userpath == SHM_ANON) {
                /* A read-only anonymous object is pointless. */
                if ((flags & O_ACCMODE) == O_RDONLY) {
                        fdclose(td, fp, fd);
                        fdrop(fp, td);
                        return (EINVAL);
                }
                shmfd = shm_alloc(td->td_ucred, cmode, largepage);
                shmfd->shm_seals = initial_seals;
                shmfd->shm_flags = shmflags;
        } else {
                error = shm_copyin_path(td, userpath, &path);
                if (error != 0) {
                        fdclose(td, fp, fd);
                        fdrop(fp, td);
                        return (error);
                }
 
                AUDIT_ARG_UPATH1_CANON(path);
                fnv = fnv_32_str(path, FNV1_32_INIT);
                sx_xlock(&shm_dict_lock);
                shmfd = shm_lookup(path, fnv);
                if (shmfd == NULL) {
                        /* Object does not yet exist, create it if requested. */
                        if (flags & O_CREAT) {
#ifdef MAC
                                error = mac_posixshm_check_create(td->td_ucred,
                                    path);
                                if (error == 0) {
#endif
                                        shmfd = shm_alloc(td->td_ucred, cmode,
                                            largepage);
                                        shmfd->shm_seals = initial_seals;
                                        shmfd->shm_flags = shmflags;
                                        shm_insert(path, fnv, shmfd);
#ifdef MAC
                                }
#endif
                        } else {
                                free(path, M_SHMFD);
                                error = ENOENT;
                        }
                } else {
                        rl_cookie = rangelock_wlock(&shmfd->shm_rl, 0, OFF_MAX,
                            &shmfd->shm_mtx);
 
                        /*
                         * kern_shm_open() likely shouldn't ever error out on
                         * trying to set a seal that already exists, unlike
                         * F_ADD_SEALS.  This would break terribly as
                         * shm_open(2) actually sets F_SEAL_SEAL to maintain
                         * historical behavior where the underlying file could
                         * not be sealed.
                         */
                        initial_seals &= ~shmfd->shm_seals;
 
                        /*
                         * Object already exists, obtain a new
                         * reference if requested and permitted.
                         */
                        free(path, M_SHMFD);
 
                        /*
                         * initial_seals can't set additional seals if we've
                         * already been set F_SEAL_SEAL.  If F_SEAL_SEAL is set,
                         * then we've already removed that one from
                         * initial_seals.  This is currently redundant as we
                         * only allow setting F_SEAL_SEAL at creation time, but
                         * it's cheap to check and decreases the effort required
                         * to allow additional seals.
                         */
                        if ((shmfd->shm_seals & F_SEAL_SEAL) != 0 &&
                            initial_seals != 0)
                                error = EPERM;
                        else if ((flags & (O_CREAT | O_EXCL)) ==
                            (O_CREAT | O_EXCL))
                                error = EEXIST;
                        else if (shmflags != 0 && shmflags != shmfd->shm_flags)
                                error = EINVAL;
                        else {
#ifdef MAC
                                error = mac_posixshm_check_open(td->td_ucred,
                                    shmfd, FFLAGS(flags & O_ACCMODE));
                                if (error == 0)
#endif
                                error = shm_access(shmfd, td->td_ucred,
                                    FFLAGS(flags & O_ACCMODE));
                        }
 
                        /*
                         * Truncate the file back to zero length if
                         * O_TRUNC was specified and the object was
                         * opened with read/write.
                         */
                        if (error == 0 &&
                            (flags & (O_ACCMODE | O_TRUNC)) ==
                            (O_RDWR | O_TRUNC)) {
                                VM_OBJECT_WLOCK(shmfd->shm_object);
#ifdef MAC
                                error = mac_posixshm_check_truncate(
                                        td->td_ucred, fp->f_cred, shmfd);
                                if (error == 0)
#endif
                                        error = shm_dotruncate_locked(shmfd, 0,
                                            rl_cookie);
                                VM_OBJECT_WUNLOCK(shmfd->shm_object);
                        }
                        if (error == 0) {
                                /*
                                 * Currently we only allow F_SEAL_SEAL to be
                                 * set initially.  As noted above, this would
                                 * need to be reworked should that change.
                                 */
                                shmfd->shm_seals |= initial_seals;
                                shm_hold(shmfd);
                        }
                        rangelock_unlock(&shmfd->shm_rl, rl_cookie,
                            &shmfd->shm_mtx);
                }
                sx_xunlock(&shm_dict_lock);
 
                if (error) {
                        fdclose(td, fp, fd);
                        fdrop(fp, td);
                        return (error);
                }
        }
 
        finit(fp, FFLAGS(flags & O_ACCMODE), DTYPE_SHM, shmfd, &shm_ops);
 
        td->td_retval[0] = fd;
        fdrop(fp, td);
 
        return (0);
}
 
/* System calls. */
#ifdef COMPAT_FREEBSD12
int
freebsd12_shm_open(struct thread *td, struct freebsd12_shm_open_args *uap)
{
 
        return (kern_shm_open(td, uap->path, uap->flags | O_CLOEXEC,
            uap->mode, NULL));
}
#endif
 
int
sys_shm_unlink(struct thread *td, struct shm_unlink_args *uap)
{
        char *path;
        Fnv32_t fnv;
        int error;
 
        error = shm_copyin_path(td, uap->path, &path);
        if (error != 0)
                return (error);
 
        AUDIT_ARG_UPATH1_CANON(path);
        fnv = fnv_32_str(path, FNV1_32_INIT);
        sx_xlock(&shm_dict_lock);
        error = shm_remove(path, fnv, td->td_ucred);
        sx_xunlock(&shm_dict_lock);
        free(path, M_SHMFD);
 
        return (error);
}
 
int
sys_shm_rename(struct thread *td, struct shm_rename_args *uap)
{
        char *path_from = NULL, *path_to = NULL;
        Fnv32_t fnv_from, fnv_to;
        struct shmfd *fd_from;
        struct shmfd *fd_to;
        int error;
        int flags;
 
        flags = uap->flags;
        AUDIT_ARG_FFLAGS(flags);
 
        /*
         * Make sure the user passed only valid flags.
         * If you add a new flag, please add a new term here.
         */
        if ((flags & ~(
            SHM_RENAME_NOREPLACE |
            SHM_RENAME_EXCHANGE
            )) != 0) {
                error = EINVAL;
                goto out;
        }
 
        /*
         * EXCHANGE and NOREPLACE don't quite make sense together. Let's
         * force the user to choose one or the other.
         */
        if ((flags & SHM_RENAME_NOREPLACE) != 0 &&
            (flags & SHM_RENAME_EXCHANGE) != 0) {
                error = EINVAL;
                goto out;
        }
 
        /* Renaming to or from anonymous makes no sense */
        if (uap->path_from == SHM_ANON || uap->path_to == SHM_ANON) {
                error = EINVAL;
                goto out;
        }
 
        error = shm_copyin_path(td, uap->path_from, &path_from);
        if (error != 0)
                goto out;
 
        error = shm_copyin_path(td, uap->path_to, &path_to);
        if (error != 0)
                goto out;
 
        AUDIT_ARG_UPATH1_CANON(path_from);
        AUDIT_ARG_UPATH2_CANON(path_to);
 
        /* Rename with from/to equal is a no-op */
        if (strcmp(path_from, path_to) == 0)
                goto out;
 
        fnv_from = fnv_32_str(path_from, FNV1_32_INIT);
        fnv_to = fnv_32_str(path_to, FNV1_32_INIT);
 
        sx_xlock(&shm_dict_lock);
 
        fd_from = shm_lookup(path_from, fnv_from);
        if (fd_from == NULL) {
                error = ENOENT;
                goto out_locked;
        }
 
        fd_to = shm_lookup(path_to, fnv_to);
        if ((flags & SHM_RENAME_NOREPLACE) != 0 && fd_to != NULL) {
                error = EEXIST;
                goto out_locked;
        }
 
        /*
         * Unconditionally prevents shm_remove from invalidating the 'from'
         * shm's state.
         */
        shm_hold(fd_from);
        error = shm_remove(path_from, fnv_from, td->td_ucred);
 
        /*
         * One of my assumptions failed if ENOENT (e.g. locking didn't
         * protect us)
         */
        KASSERT(error != ENOENT, ("Our shm disappeared during shm_rename: %s",
            path_from));
        if (error != 0) {
                shm_drop(fd_from);
                goto out_locked;
        }
 
        /*
         * If we are exchanging, we need to ensure the shm_remove below
         * doesn't invalidate the dest shm's state.
         */
        if ((flags & SHM_RENAME_EXCHANGE) != 0 && fd_to != NULL)
                shm_hold(fd_to);
 
        /*
         * NOTE: if path_to is not already in the hash, c'est la vie;
         * it simply means we have nothing already at path_to to unlink.
         * That is the ENOENT case.
         *
         * If we somehow don't have access to unlink this guy, but
         * did for the shm at path_from, then relink the shm to path_from
         * and abort with EACCES.
         *
         * All other errors: that is weird; let's relink and abort the
         * operation.
         */
        error = shm_remove(path_to, fnv_to, td->td_ucred);
        if (error != 0 && error != ENOENT) {
                shm_insert(path_from, fnv_from, fd_from);
                shm_drop(fd_from);
                /* Don't free path_from now, since the hash references it */
                path_from = NULL;
                goto out_locked;
        }
 
        error = 0;
 
        shm_insert(path_to, fnv_to, fd_from);
 
        /* Don't free path_to now, since the hash references it */
        path_to = NULL;
 
        /* We kept a ref when we removed, and incremented again in insert */
        shm_drop(fd_from);
        KASSERT(fd_from->shm_refs > 0, ("Expected >0 refs; got: %d\n",
            fd_from->shm_refs));
 
        if ((flags & SHM_RENAME_EXCHANGE) != 0 && fd_to != NULL) {
                shm_insert(path_from, fnv_from, fd_to);
                path_from = NULL;
                shm_drop(fd_to);
                KASSERT(fd_to->shm_refs > 0, ("Expected >0 refs; got: %d\n",
                    fd_to->shm_refs));
        }
 
out_locked:
        sx_xunlock(&shm_dict_lock);
 
out:
        free(path_from, M_SHMFD);
        free(path_to, M_SHMFD);
        return (error);
}
 
static int
shm_mmap_large(struct shmfd *shmfd, vm_map_t map, vm_offset_t *addr,
    vm_size_t size, vm_prot_t prot, vm_prot_t max_prot, int flags,
    vm_ooffset_t foff, struct thread *td)
{
        struct vmspace *vms;
        vm_map_entry_t next_entry, prev_entry;
        vm_offset_t align, mask, maxaddr;
        int docow, error, rv, try;
        bool curmap;
 
        if (shmfd->shm_lp_psind == 0)
                return (EINVAL);
 
        /* MAP_PRIVATE is disabled */
        if ((flags & ~(MAP_SHARED | MAP_FIXED | MAP_EXCL |
            MAP_NOCORE |
#ifdef MAP_32BIT
            MAP_32BIT |
#endif
            MAP_ALIGNMENT_MASK)) != 0)
                return (EINVAL);
 
        vms = td->td_proc->p_vmspace;
        curmap = map == &vms->vm_map;
        if (curmap) {
                error = kern_mmap_racct_check(td, map, size);
                if (error != 0)
                        return (error);
        }
 
        docow = shmfd->shm_lp_psind << MAP_SPLIT_BOUNDARY_SHIFT;
        docow |= MAP_INHERIT_SHARE;
        if ((flags & MAP_NOCORE) != 0)
                docow |= MAP_DISABLE_COREDUMP;
 
        mask = pagesizes[shmfd->shm_lp_psind] - 1;
        if ((foff & mask) != 0)
                return (EINVAL);
        maxaddr = vm_map_max(map);
#ifdef MAP_32BIT
        if ((flags & MAP_32BIT) != 0 && maxaddr > MAP_32BIT_MAX_ADDR)
                maxaddr = MAP_32BIT_MAX_ADDR;
#endif
        if (size == 0 || (size & mask) != 0 ||
            (*addr != 0 && ((*addr & mask) != 0 ||
            *addr + size < *addr || *addr + size > maxaddr)))
                return (EINVAL);
 
        align = flags & MAP_ALIGNMENT_MASK;
        if (align == 0) {
                align = pagesizes[shmfd->shm_lp_psind];
        } else if (align == MAP_ALIGNED_SUPER) {
                if (shmfd->shm_lp_psind != 1)
                        return (EINVAL);
                align = pagesizes[1];
        } else {
                align >>= MAP_ALIGNMENT_SHIFT;
                align = 1ULL << align;
                /* Also handles overflow. */
                if (align < pagesizes[shmfd->shm_lp_psind])
                        return (EINVAL);
        }
 
        vm_map_lock(map);
        if ((flags & MAP_FIXED) == 0) {
                try = 1;
                if (curmap && (*addr == 0 ||
                    (*addr >= round_page((vm_offset_t)vms->vm_taddr) &&
                    *addr < round_page((vm_offset_t)vms->vm_daddr +
                    lim_max(td, RLIMIT_DATA))))) {
                        *addr = roundup2((vm_offset_t)vms->vm_daddr +
                            lim_max(td, RLIMIT_DATA),
                            pagesizes[shmfd->shm_lp_psind]);
                }
again:
                rv = vm_map_find_aligned(map, addr, size, maxaddr, align);
                if (rv != KERN_SUCCESS) {
                        if (try == 1) {
                                try = 2;
                                *addr = vm_map_min(map);
                                if ((*addr & mask) != 0)
                                        *addr = (*addr + mask) & mask;
                                goto again;
                        }
                        goto fail1;
                }
        } else if ((flags & MAP_EXCL) == 0) {
                rv = vm_map_delete(map, *addr, *addr + size);
                if (rv != KERN_SUCCESS)
                        goto fail1;
        } else {
                error = ENOSPC;
                if (vm_map_lookup_entry(map, *addr, &prev_entry))
                        goto fail;
                next_entry = vm_map_entry_succ(prev_entry);
                if (next_entry->start < *addr + size)
                        goto fail;
        }
 
        rv = vm_map_insert(map, shmfd->shm_object, foff, *addr, *addr + size,
            prot, max_prot, docow);
fail1:
        error = vm_mmap_to_errno(rv);
fail:
        vm_map_unlock(map);
        return (error);
}
 
static int
shm_mmap(struct file *fp, vm_map_t map, vm_offset_t *addr, vm_size_t objsize,
    vm_prot_t prot, vm_prot_t cap_maxprot, int flags,
    vm_ooffset_t foff, struct thread *td)
{
        struct shmfd *shmfd;
        vm_prot_t maxprot;
        int error;
        bool writecnt;
        void *rl_cookie;
 
        shmfd = fp->f_data;
        maxprot = VM_PROT_NONE;
 
        rl_cookie = rangelock_rlock(&shmfd->shm_rl, 0, objsize,
            &shmfd->shm_mtx);
        /* FREAD should always be set. */
        if ((fp->f_flag & FREAD) != 0)
                maxprot |= VM_PROT_EXECUTE | VM_PROT_READ;
 
        /*
         * If FWRITE's set, we can allow VM_PROT_WRITE unless it's a shared
         * mapping with a write seal applied.  Private mappings are always
         * writeable.
         */
        if ((flags & MAP_SHARED) == 0) {
                cap_maxprot |= VM_PROT_WRITE;
                maxprot |= VM_PROT_WRITE;
                writecnt = false;
        } else {
                if ((fp->f_flag & FWRITE) != 0 &&
                    (shmfd->shm_seals & F_SEAL_WRITE) == 0)
                        maxprot |= VM_PROT_WRITE;
 
                /*
                 * Any mappings from a writable descriptor may be upgraded to
                 * VM_PROT_WRITE with mprotect(2), unless a write-seal was
                 * applied between the open and subsequent mmap(2).  We want to
                 * reject application of a write seal as long as any such
                 * mapping exists so that the seal cannot be trivially bypassed.
                 */
                writecnt = (maxprot & VM_PROT_WRITE) != 0;
                if (!writecnt && (prot & VM_PROT_WRITE) != 0) {
                        error = EACCES;
                        goto out;
                }
        }
        maxprot &= cap_maxprot;
 
        /* See comment in vn_mmap(). */
        if (
#ifdef _LP64
            objsize > OFF_MAX ||
#endif
            foff > OFF_MAX - objsize) {
                error = EINVAL;
                goto out;
        }
 
#ifdef MAC
        error = mac_posixshm_check_mmap(td->td_ucred, shmfd, prot, flags);
        if (error != 0)
                goto out;
#endif
 
        mtx_lock(&shm_timestamp_lock);
        vfs_timestamp(&shmfd->shm_atime);
        mtx_unlock(&shm_timestamp_lock);
        vm_object_reference(shmfd->shm_object);
 
        if (shm_largepage(shmfd)) {
                writecnt = false;
                error = shm_mmap_large(shmfd, map, addr, objsize, prot,
                    maxprot, flags, foff, td);
        } else {
                if (writecnt) {
                        vm_pager_update_writecount(shmfd->shm_object, 0,
                            objsize);
                }
                error = vm_mmap_object(map, addr, objsize, prot, maxprot, flags,
                    shmfd->shm_object, foff, writecnt, td);
        }
        if (error != 0) {
                if (writecnt)
                        vm_pager_release_writecount(shmfd->shm_object, 0,
                            objsize);
                vm_object_deallocate(shmfd->shm_object);
        }
out:
        rangelock_unlock(&shmfd->shm_rl, rl_cookie, &shmfd->shm_mtx);
        return (error);
}
 
static int
shm_chmod(struct file *fp, mode_t mode, struct ucred *active_cred,
    struct thread *td)
{
        struct shmfd *shmfd;
        int error;
 
        error = 0;
        shmfd = fp->f_data;
        mtx_lock(&shm_timestamp_lock);
        /*
         * SUSv4 says that x bits of permission need not be affected.
         * Be consistent with our shm_open there.
         */
#ifdef MAC
        error = mac_posixshm_check_setmode(active_cred, shmfd, mode);
        if (error != 0)
                goto out;
#endif
        error = vaccess(VREG, shmfd->shm_mode, shmfd->shm_uid, shmfd->shm_gid,
            VADMIN, active_cred);
        if (error != 0)
                goto out;
        shmfd->shm_mode = mode & ACCESSPERMS;
out:
        mtx_unlock(&shm_timestamp_lock);
        return (error);
}
 
static int
shm_chown(struct file *fp, uid_t uid, gid_t gid, struct ucred *active_cred,
    struct thread *td)
{
        struct shmfd *shmfd;
        int error;
 
        error = 0;
        shmfd = fp->f_data;
        mtx_lock(&shm_timestamp_lock);
#ifdef MAC
        error = mac_posixshm_check_setowner(active_cred, shmfd, uid, gid);
        if (error != 0)
                goto out;
#endif
        if (uid == (uid_t)-1)
                uid = shmfd->shm_uid;
        if (gid == (gid_t)-1)
                 gid = shmfd->shm_gid;
        if (((uid != shmfd->shm_uid && uid != active_cred->cr_uid) ||
            (gid != shmfd->shm_gid && !groupmember(gid, active_cred))) &&
            (error = priv_check_cred(active_cred, PRIV_VFS_CHOWN)))
                goto out;
        shmfd->shm_uid = uid;
        shmfd->shm_gid = gid;
out:
        mtx_unlock(&shm_timestamp_lock);
        return (error);
}
 
/*
 * Helper routines to allow the backing object of a shared memory file
 * descriptor to be mapped in the kernel.
 */
int
shm_map(struct file *fp, size_t size, off_t offset, void **memp)
{
        struct shmfd *shmfd;
        vm_offset_t kva, ofs;
        vm_object_t obj;
        int rv;
 
        if (fp->f_type != DTYPE_SHM)
                return (EINVAL);
        shmfd = fp->f_data;
        obj = shmfd->shm_object;
        VM_OBJECT_WLOCK(obj);
        /*
         * XXXRW: This validation is probably insufficient, and subject to
         * sign errors.  It should be fixed.
         */
        if (offset >= shmfd->shm_size ||
            offset + size > round_page(shmfd->shm_size)) {
                VM_OBJECT_WUNLOCK(obj);
                return (EINVAL);
        }
 
        shmfd->shm_kmappings++;
        vm_object_reference_locked(obj);
        VM_OBJECT_WUNLOCK(obj);
 
        /* Map the object into the kernel_map and wire it. */
        kva = vm_map_min(kernel_map);
        ofs = offset & PAGE_MASK;
        offset = trunc_page(offset);
        size = round_page(size + ofs);
        rv = vm_map_find(kernel_map, obj, offset, &kva, size, 0,
            VMFS_OPTIMAL_SPACE, VM_PROT_READ | VM_PROT_WRITE,
            VM_PROT_READ | VM_PROT_WRITE, 0);
        if (rv == KERN_SUCCESS) {
                rv = vm_map_wire(kernel_map, kva, kva + size,
                    VM_MAP_WIRE_SYSTEM | VM_MAP_WIRE_NOHOLES);
                if (rv == KERN_SUCCESS) {
                        *memp = (void *)(kva + ofs);
                        return (0);
                }
                vm_map_remove(kernel_map, kva, kva + size);
        } else
                vm_object_deallocate(obj);
 
        /* On failure, drop our mapping reference. */
        VM_OBJECT_WLOCK(obj);
        shmfd->shm_kmappings--;
        VM_OBJECT_WUNLOCK(obj);
 
        return (vm_mmap_to_errno(rv));
}
 
/*
 * We require the caller to unmap the entire entry.  This allows us to
 * safely decrement shm_kmappings when a mapping is removed.
 */
int
shm_unmap(struct file *fp, void *mem, size_t size)
{
        struct shmfd *shmfd;
        vm_map_entry_t entry;
        vm_offset_t kva, ofs;
        vm_object_t obj;
        vm_pindex_t pindex;
        vm_prot_t prot;
        boolean_t wired;
        vm_map_t map;
        int rv;
 
        if (fp->f_type != DTYPE_SHM)
                return (EINVAL);
        shmfd = fp->f_data;
        kva = (vm_offset_t)mem;
        ofs = kva & PAGE_MASK;
        kva = trunc_page(kva);
        size = round_page(size + ofs);
        map = kernel_map;
        rv = vm_map_lookup(&map, kva, VM_PROT_READ | VM_PROT_WRITE, &entry,
            &obj, &pindex, &prot, &wired);
        if (rv != KERN_SUCCESS)
                return (EINVAL);
        if (entry->start != kva || entry->end != kva + size) {
                vm_map_lookup_done(map, entry);
                return (EINVAL);
        }
        vm_map_lookup_done(map, entry);
        if (obj != shmfd->shm_object)
                return (EINVAL);
        vm_map_remove(map, kva, kva + size);
        VM_OBJECT_WLOCK(obj);
        KASSERT(shmfd->shm_kmappings > 0, ("shm_unmap: object not mapped"));
        shmfd->shm_kmappings--;
        VM_OBJECT_WUNLOCK(obj);
        return (0);
}
 
static int
shm_fill_kinfo_locked(struct shmfd *shmfd, struct kinfo_file *kif, bool list)
{
        const char *path, *pr_path;
        size_t pr_pathlen;
        bool visible;
 
        sx_assert(&shm_dict_lock, SA_LOCKED);
        kif->kf_type = KF_TYPE_SHM;
        kif->kf_un.kf_file.kf_file_mode = S_IFREG | shmfd->shm_mode;
        kif->kf_un.kf_file.kf_file_size = shmfd->shm_size;
        if (shmfd->shm_path != NULL) {
                if (shmfd->shm_path != NULL) {
                        path = shmfd->shm_path;
                        pr_path = curthread->td_ucred->cr_prison->pr_path;
                        if (strcmp(pr_path, "/") != 0) {
                                /* Return the jail-rooted pathname. */
                                pr_pathlen = strlen(pr_path);
                                visible = strncmp(path, pr_path, pr_pathlen)
                                    == 0 && path[pr_pathlen] == '/';
                                if (list && !visible)
                                        return (EPERM);
                                if (visible)
                                        path += pr_pathlen;
                        }
                        strlcpy(kif->kf_path, path, sizeof(kif->kf_path));
                }
        }
        return (0);
}
 
static int
shm_fill_kinfo(struct file *fp, struct kinfo_file *kif,
    struct filedesc *fdp __unused)
{
        int res;
 
        sx_slock(&shm_dict_lock);
        res = shm_fill_kinfo_locked(fp->f_data, kif, false);
        sx_sunlock(&shm_dict_lock);
        return (res);
}
 
static int
shm_add_seals(struct file *fp, int seals)
{
        struct shmfd *shmfd;
        void *rl_cookie;
        vm_ooffset_t writemappings;
        int error, nseals;
 
        error = 0;
        shmfd = fp->f_data;
        rl_cookie = rangelock_wlock(&shmfd->shm_rl, 0, OFF_MAX,
            &shmfd->shm_mtx);
 
        /* Even already-set seals should result in EPERM. */
        if ((shmfd->shm_seals & F_SEAL_SEAL) != 0) {
                error = EPERM;
                goto out;
        }
        nseals = seals & ~shmfd->shm_seals;
        if ((nseals & F_SEAL_WRITE) != 0) {
                if (shm_largepage(shmfd)) {
                        error = ENOTSUP;
                        goto out;
                }
 
                /*
                 * The rangelock above prevents writable mappings from being
                 * added after we've started applying seals.  The RLOCK here
                 * is to avoid torn reads on ILP32 arches as unmapping/reducing
                 * writemappings will be done without a rangelock.
                 */
                VM_OBJECT_RLOCK(shmfd->shm_object);
                writemappings = shmfd->shm_object->un_pager.swp.writemappings;
                VM_OBJECT_RUNLOCK(shmfd->shm_object);
                /* kmappings are also writable */
                if (writemappings > 0) {
                        error = EBUSY;
                        goto out;
                }
        }
        shmfd->shm_seals |= nseals;
out:
        rangelock_unlock(&shmfd->shm_rl, rl_cookie, &shmfd->shm_mtx);
        return (error);
}
 
static int
shm_get_seals(struct file *fp, int *seals)
{
        struct shmfd *shmfd;
 
        shmfd = fp->f_data;
        *seals = shmfd->shm_seals;
        return (0);
}
 
static int
shm_deallocate(struct shmfd *shmfd, off_t *offset, off_t *length, int flags)
{
        vm_object_t object;
        vm_pindex_t pistart, pi, piend;
        vm_ooffset_t off, len;
        int startofs, endofs, end;
        int error;
 
        off = *offset;
        len = *length;
        KASSERT(off + len <= (vm_ooffset_t)OFF_MAX, ("off + len overflows"));
        if (off + len > shmfd->shm_size)
                len = shmfd->shm_size - off;
        object = shmfd->shm_object;
        startofs = off & PAGE_MASK;
        endofs = (off + len) & PAGE_MASK;
        pistart = OFF_TO_IDX(off);
        piend = OFF_TO_IDX(off + len);
        pi = OFF_TO_IDX(off + PAGE_MASK);
        error = 0;
 
        /* Handle the case when offset is on or beyond shm size. */
        if ((off_t)len <= 0) {
                *length = 0;
                return (0);
        }
 
        VM_OBJECT_WLOCK(object);
 
        if (startofs != 0) {
                end = pistart != piend ? PAGE_SIZE : endofs;
                error = shm_partial_page_invalidate(object, pistart, startofs,
                    end);
                if (error)
                        goto out;
                off += end - startofs;
                len -= end - startofs;
        }
 
        if (pi < piend) {
                vm_object_page_remove(object, pi, piend, 0);
                off += IDX_TO_OFF(piend - pi);
                len -= IDX_TO_OFF(piend - pi);
        }
 
        if (endofs != 0 && pistart != piend) {
                error = shm_partial_page_invalidate(object, piend, 0, endofs);
                if (error)
                        goto out;
                off += endofs;
                len -= endofs;
        }
 
out:
        VM_OBJECT_WUNLOCK(shmfd->shm_object);
        *offset = off;
        *length = len;
        return (error);
}
 
static int
shm_fspacectl(struct file *fp, int cmd, off_t *offset, off_t *length, int flags,
    struct ucred *active_cred, struct thread *td)
{
        void *rl_cookie;
        struct shmfd *shmfd;
        off_t off, len;
        int error;
 
        /* This assumes that the caller already checked for overflow. */
        error = EINVAL;
        shmfd = fp->f_data;
        off = *offset;
        len = *length;
 
        if (cmd != SPACECTL_DEALLOC || off < 0 || len <= 0 ||
            len > OFF_MAX - off || flags != 0)
                return (EINVAL);
 
        rl_cookie = rangelock_wlock(&shmfd->shm_rl, off, off + len,
            &shmfd->shm_mtx);
        switch (cmd) {
        case SPACECTL_DEALLOC:
                if ((shmfd->shm_seals & F_SEAL_WRITE) != 0) {
                        error = EPERM;
                        break;
                }
                error = shm_deallocate(shmfd, &off, &len, flags);
                *offset = off;
                *length = len;
                break;
        default:
                __assert_unreachable();
        }
        rangelock_unlock(&shmfd->shm_rl, rl_cookie, &shmfd->shm_mtx);
        return (error);
}
 
 
static int
shm_fallocate(struct file *fp, off_t offset, off_t len, struct thread *td)
{
        void *rl_cookie;
        struct shmfd *shmfd;
        size_t size;
        int error;
 
        /* This assumes that the caller already checked for overflow. */
        error = 0;
        shmfd = fp->f_data;
        size = offset + len;
 
        /*
         * Just grab the rangelock for the range that we may be attempting to
         * grow, rather than blocking read/write for regions we won't be
         * touching while this (potential) resize is in progress.  Other
         * attempts to resize the shmfd will have to take a write lock from 0 to
         * OFF_MAX, so this being potentially beyond the current usable range of
         * the shmfd is not necessarily a concern.  If other mechanisms are
         * added to grow a shmfd, this may need to be re-evaluated.
         */
        rl_cookie = rangelock_wlock(&shmfd->shm_rl, offset, size,
            &shmfd->shm_mtx);
        if (size > shmfd->shm_size)
                error = shm_dotruncate_cookie(shmfd, size, rl_cookie);
        rangelock_unlock(&shmfd->shm_rl, rl_cookie, &shmfd->shm_mtx);
        /* Translate to posix_fallocate(2) return value as needed. */
        if (error == ENOMEM)
                error = ENOSPC;
        return (error);
}
 
static int
sysctl_posix_shm_list(SYSCTL_HANDLER_ARGS)
{
        struct shm_mapping *shmm;
        struct sbuf sb;
        struct kinfo_file kif;
        u_long i;
        int error, error2;
 
        sbuf_new_for_sysctl(&sb, NULL, sizeof(struct kinfo_file) * 5, req);
        sbuf_clear_flags(&sb, SBUF_INCLUDENUL);
        error = 0;
        sx_slock(&shm_dict_lock);
        for (i = 0; i < shm_hash + 1; i++) {
                LIST_FOREACH(shmm, &shm_dictionary[i], sm_link) {
                        error = shm_fill_kinfo_locked(shmm->sm_shmfd,
                            &kif, true);
                        if (error == EPERM) {
                                error = 0;
                                continue;
                        }
                        if (error != 0)
                                break;
                        pack_kinfo(&kif);
                        error = sbuf_bcat(&sb, &kif, kif.kf_structsize) == 0 ?
                            0 : ENOMEM;
                        if (error != 0)
                                break;
                }
        }
        sx_sunlock(&shm_dict_lock);
        error2 = sbuf_finish(&sb);
        sbuf_delete(&sb);
        return (error != 0 ? error : error2);
}
 
SYSCTL_PROC(_kern_ipc, OID_AUTO, posix_shm_list,
    CTLFLAG_RD | CTLFLAG_PRISON | CTLFLAG_MPSAFE | CTLTYPE_OPAQUE,
    NULL, 0, sysctl_posix_shm_list, "",
    "POSIX SHM list");
 
int
kern_shm_open(struct thread *td, const char *path, int flags, mode_t mode,
    struct filecaps *caps)
{
 
        return (kern_shm_open2(td, path, flags, mode, 0, caps, NULL));
}
 
/*
 * This version of the shm_open() interface leaves CLOEXEC behavior up to the
 * caller, and libc will enforce it for the traditional shm_open() call.  This
 * allows other consumers, like memfd_create(), to opt-in for CLOEXEC.  This
 * interface also includes a 'name' argument that is currently unused, but could
 * potentially be exported later via some interface for debugging purposes.
 * From the kernel's perspective, it is optional.  Individual consumers like
 * memfd_create() may require it in order to be compatible with other systems
 * implementing the same function.
 */
int
sys_shm_open2(struct thread *td, struct shm_open2_args *uap)
{
 
        return (kern_shm_open2(td, uap->path, uap->flags, uap->mode,
            uap->shmflags, NULL, uap->name));
}