2 * Copyright (c) 2006 Robert N. M. Watson
5 * Redistribution and use in source and binary forms, with or without
6 * modification, are permitted provided that the following conditions
8 * 1. Redistributions of source code must retain the above copyright
9 * notice, this list of conditions and the following disclaimer.
10 * 2. Redistributions in binary form must reproduce the above copyright
11 * notice, this list of conditions and the following disclaimer in the
12 * documentation and/or other materials provided with the distribution.
14 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
15 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
16 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
17 * ARE DISCLAIMED. IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
18 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
19 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
20 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
21 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
22 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
23 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
28 * Support for shared swap-backed anonymous memory objects via
29 * shm_open(2) and shm_unlink(2). While most of the implementation is
30 * here, vm_mmap.c contains mapping logic changes.
34 * (2) Need to export data to a userland tool via a sysctl. Should ipcs(1)
35 * and ipcrm(1) be expanded or should new tools to manage both POSIX
36 * kernel semaphores and POSIX shared memory be written?
38 * (3) Add support for this file type to fstat(1).
40 * (4) Resource limits? Does this need its own resource limits or are the
41 * existing limits in mmap(2) sufficient?
43 * (5) Partial page truncation. vnode_pager_setsize() will zero any parts
44 * of a partially mapped page as a result of ftruncate(2)/truncate(2).
45 * We can do the same (with the same pmap evil), but do we need to
46 * worry about the bits on disk if the page is swapped out or will the
47 * swapper zero the parts of a page that are invalid if the page is
48 * swapped back in for us?
50 * (6) Add MAC support in mac_biba(4) and mac_mls(4).
52 * (7) Add a MAC check_create() hook for creating new named objects.
55 #include <sys/cdefs.h>
56 __FBSDID("$FreeBSD$");
58 #include <sys/param.h>
59 #include <sys/fcntl.h>
61 #include <sys/filedesc.h>
62 #include <sys/fnv_hash.h>
63 #include <sys/kernel.h>
65 #include <sys/malloc.h>
67 #include <sys/mutex.h>
69 #include <sys/refcount.h>
70 #include <sys/resourcevar.h>
72 #include <sys/sysctl.h>
73 #include <sys/sysproto.h>
74 #include <sys/systm.h>
77 #include <sys/vnode.h>
79 #include <security/mac/mac_framework.h>
82 #include <vm/vm_param.h>
84 #include <vm/vm_map.h>
85 #include <vm/vm_object.h>
86 #include <vm/vm_page.h>
87 #include <vm/vm_pager.h>
88 #include <vm/swap_pager.h>
93 struct shmfd *sm_shmfd;
94 LIST_ENTRY(shm_mapping) sm_link;
97 static MALLOC_DEFINE(M_SHMFD, "shmfd", "shared memory file descriptor");
98 static LIST_HEAD(, shm_mapping) *shm_dictionary;
99 static struct sx shm_dict_lock;
100 static struct mtx shm_timestamp_lock;
101 static u_long shm_hash;
103 #define SHM_HASH(fnv) (&shm_dictionary[(fnv) & shm_hash])
105 static int shm_access(struct shmfd *shmfd, struct ucred *ucred, int flags);
106 static struct shmfd *shm_alloc(struct ucred *ucred, mode_t mode);
107 static void shm_dict_init(void *arg);
108 static void shm_drop(struct shmfd *shmfd);
109 static struct shmfd *shm_hold(struct shmfd *shmfd);
110 static void shm_insert(char *path, Fnv32_t fnv, struct shmfd *shmfd);
111 static struct shmfd *shm_lookup(char *path, Fnv32_t fnv);
112 static int shm_remove(char *path, Fnv32_t fnv, struct ucred *ucred);
113 static int shm_dotruncate(struct shmfd *shmfd, off_t length);
115 static fo_rdwr_t shm_read;
116 static fo_rdwr_t shm_write;
117 static fo_truncate_t shm_truncate;
118 static fo_ioctl_t shm_ioctl;
119 static fo_poll_t shm_poll;
120 static fo_kqfilter_t shm_kqfilter;
121 static fo_stat_t shm_stat;
122 static fo_close_t shm_close;
124 /* File descriptor operations. */
125 static struct fileops shm_ops = {
127 .fo_write = shm_write,
128 .fo_truncate = shm_truncate,
129 .fo_ioctl = shm_ioctl,
131 .fo_kqfilter = shm_kqfilter,
133 .fo_close = shm_close,
134 .fo_flags = DFLAG_PASSABLE
137 FEATURE(posix_shm, "POSIX shared memory");
140 shm_read(struct file *fp, struct uio *uio, struct ucred *active_cred,
141 int flags, struct thread *td)
148 shm_write(struct file *fp, struct uio *uio, struct ucred *active_cred,
149 int flags, struct thread *td)
156 shm_truncate(struct file *fp, off_t length, struct ucred *active_cred,
166 error = mac_posixshm_check_truncate(active_cred, fp->f_cred, shmfd);
170 return (shm_dotruncate(shmfd, length));
174 shm_ioctl(struct file *fp, u_long com, void *data,
175 struct ucred *active_cred, struct thread *td)
182 shm_poll(struct file *fp, int events, struct ucred *active_cred,
190 shm_kqfilter(struct file *fp, struct knote *kn)
197 shm_stat(struct file *fp, struct stat *sb, struct ucred *active_cred,
208 error = mac_posixshm_check_stat(active_cred, fp->f_cred, shmfd);
214 * Attempt to return sanish values for fstat() on a memory file
217 bzero(sb, sizeof(*sb));
218 sb->st_mode = S_IFREG | shmfd->shm_mode; /* XXX */
219 sb->st_blksize = PAGE_SIZE;
220 sb->st_size = shmfd->shm_size;
221 sb->st_blocks = (sb->st_size + sb->st_blksize - 1) / sb->st_blksize;
222 sb->st_atim = shmfd->shm_atime;
223 sb->st_ctim = shmfd->shm_ctime;
224 sb->st_mtim = shmfd->shm_mtime;
225 sb->st_birthtim = shmfd->shm_birthtime;
226 sb->st_uid = shmfd->shm_uid;
227 sb->st_gid = shmfd->shm_gid;
233 shm_close(struct file *fp, struct thread *td)
245 shm_dotruncate(struct shmfd *shmfd, off_t length)
249 vm_pindex_t nobjsize;
252 object = shmfd->shm_object;
253 VM_OBJECT_LOCK(object);
254 if (length == shmfd->shm_size) {
255 VM_OBJECT_UNLOCK(object);
258 nobjsize = OFF_TO_IDX(length + PAGE_MASK);
260 /* Are we shrinking? If so, trim the end. */
261 if (length < shmfd->shm_size) {
262 delta = ptoa(object->size - nobjsize);
264 /* Toss in memory pages. */
265 if (nobjsize < object->size)
266 vm_object_page_remove(object, nobjsize, object->size,
269 /* Toss pages from swap. */
270 if (object->type == OBJT_SWAP)
271 swap_pager_freespace(object, nobjsize, delta);
273 /* Free the swap accounted for shm */
274 swap_release_by_cred(delta, object->cred);
275 object->charge -= delta;
278 * If the last page is partially mapped, then zero out
279 * the garbage at the end of the page. See comments
280 * in vnode_pager_setsize() for more details.
282 * XXXJHB: This handles in memory pages, but what about
283 * a page swapped out to disk?
285 if ((length & PAGE_MASK) &&
286 (m = vm_page_lookup(object, OFF_TO_IDX(length))) != NULL &&
288 int base = (int)length & PAGE_MASK;
289 int size = PAGE_SIZE - base;
291 pmap_zero_page_area(m, base, size);
294 * Update the valid bits to reflect the blocks that
295 * have been zeroed. Some of these valid bits may
296 * have already been set.
298 vm_page_set_valid(m, base, size);
301 * Round "base" to the next block boundary so that the
302 * dirty bit for a partially zeroed block is not
305 base = roundup2(base, DEV_BSIZE);
307 vm_page_clear_dirty(m, base, PAGE_SIZE - base);
308 } else if ((length & PAGE_MASK) &&
309 __predict_false(object->cache != NULL)) {
310 vm_page_cache_free(object, OFF_TO_IDX(length),
315 /* Attempt to reserve the swap */
316 delta = ptoa(nobjsize - object->size);
317 if (!swap_reserve_by_cred(delta, object->cred)) {
318 VM_OBJECT_UNLOCK(object);
321 object->charge += delta;
323 shmfd->shm_size = length;
324 mtx_lock(&shm_timestamp_lock);
325 vfs_timestamp(&shmfd->shm_ctime);
326 shmfd->shm_mtime = shmfd->shm_ctime;
327 mtx_unlock(&shm_timestamp_lock);
328 object->size = nobjsize;
329 VM_OBJECT_UNLOCK(object);
334 * shmfd object management including creation and reference counting
337 static struct shmfd *
338 shm_alloc(struct ucred *ucred, mode_t mode)
342 shmfd = malloc(sizeof(*shmfd), M_SHMFD, M_WAITOK | M_ZERO);
344 shmfd->shm_uid = ucred->cr_uid;
345 shmfd->shm_gid = ucred->cr_gid;
346 shmfd->shm_mode = mode;
347 shmfd->shm_object = vm_pager_allocate(OBJT_DEFAULT, NULL,
348 shmfd->shm_size, VM_PROT_DEFAULT, 0, ucred);
349 KASSERT(shmfd->shm_object != NULL, ("shm_create: vm_pager_allocate"));
350 VM_OBJECT_LOCK(shmfd->shm_object);
351 vm_object_clear_flag(shmfd->shm_object, OBJ_ONEMAPPING);
352 vm_object_set_flag(shmfd->shm_object, OBJ_NOSPLIT);
353 VM_OBJECT_UNLOCK(shmfd->shm_object);
354 vfs_timestamp(&shmfd->shm_birthtime);
355 shmfd->shm_atime = shmfd->shm_mtime = shmfd->shm_ctime =
356 shmfd->shm_birthtime;
357 refcount_init(&shmfd->shm_refs, 1);
359 mac_posixshm_init(shmfd);
360 mac_posixshm_create(ucred, shmfd);
366 static struct shmfd *
367 shm_hold(struct shmfd *shmfd)
370 refcount_acquire(&shmfd->shm_refs);
375 shm_drop(struct shmfd *shmfd)
378 if (refcount_release(&shmfd->shm_refs)) {
380 mac_posixshm_destroy(shmfd);
382 vm_object_deallocate(shmfd->shm_object);
383 free(shmfd, M_SHMFD);
388 * Determine if the credentials have sufficient permissions for a
389 * specified combination of FREAD and FWRITE.
392 shm_access(struct shmfd *shmfd, struct ucred *ucred, int flags)
401 return (vaccess(VREG, shmfd->shm_mode, shmfd->shm_uid, shmfd->shm_gid,
402 accmode, ucred, NULL));
406 * Dictionary management. We maintain an in-kernel dictionary to map
407 * paths to shmfd objects. We use the FNV hash on the path to store
408 * the mappings in a hash table.
411 shm_dict_init(void *arg)
414 mtx_init(&shm_timestamp_lock, "shm timestamps", NULL, MTX_DEF);
415 sx_init(&shm_dict_lock, "shm dictionary");
416 shm_dictionary = hashinit(1024, M_SHMFD, &shm_hash);
418 SYSINIT(shm_dict_init, SI_SUB_SYSV_SHM, SI_ORDER_ANY, shm_dict_init, NULL);
420 static struct shmfd *
421 shm_lookup(char *path, Fnv32_t fnv)
423 struct shm_mapping *map;
425 LIST_FOREACH(map, SHM_HASH(fnv), sm_link) {
426 if (map->sm_fnv != fnv)
428 if (strcmp(map->sm_path, path) == 0)
429 return (map->sm_shmfd);
436 shm_insert(char *path, Fnv32_t fnv, struct shmfd *shmfd)
438 struct shm_mapping *map;
440 map = malloc(sizeof(struct shm_mapping), M_SHMFD, M_WAITOK);
443 map->sm_shmfd = shm_hold(shmfd);
444 LIST_INSERT_HEAD(SHM_HASH(fnv), map, sm_link);
448 shm_remove(char *path, Fnv32_t fnv, struct ucred *ucred)
450 struct shm_mapping *map;
453 LIST_FOREACH(map, SHM_HASH(fnv), sm_link) {
454 if (map->sm_fnv != fnv)
456 if (strcmp(map->sm_path, path) == 0) {
458 error = mac_posixshm_check_unlink(ucred, map->sm_shmfd);
462 error = shm_access(map->sm_shmfd, ucred,
466 LIST_REMOVE(map, sm_link);
467 shm_drop(map->sm_shmfd);
468 free(map->sm_path, M_SHMFD);
479 shm_open(struct thread *td, struct shm_open_args *uap)
481 struct filedesc *fdp;
489 if ((uap->flags & O_ACCMODE) != O_RDONLY &&
490 (uap->flags & O_ACCMODE) != O_RDWR)
493 if ((uap->flags & ~(O_ACCMODE | O_CREAT | O_EXCL | O_TRUNC)) != 0)
496 fdp = td->td_proc->p_fd;
497 cmode = (uap->mode & ~fdp->fd_cmask) & ACCESSPERMS;
499 error = falloc(td, &fp, &fd);
503 /* A SHM_ANON path pointer creates an anonymous object. */
504 if (uap->path == SHM_ANON) {
505 /* A read-only anonymous object is pointless. */
506 if ((uap->flags & O_ACCMODE) == O_RDONLY) {
507 fdclose(fdp, fp, fd, td);
511 shmfd = shm_alloc(td->td_ucred, cmode);
513 path = malloc(MAXPATHLEN, M_SHMFD, M_WAITOK);
514 error = copyinstr(uap->path, path, MAXPATHLEN, NULL);
516 /* Require paths to start with a '/' character. */
517 if (error == 0 && path[0] != '/')
520 fdclose(fdp, fp, fd, td);
526 fnv = fnv_32_str(path, FNV1_32_INIT);
527 sx_xlock(&shm_dict_lock);
528 shmfd = shm_lookup(path, fnv);
530 /* Object does not yet exist, create it if requested. */
531 if (uap->flags & O_CREAT) {
532 shmfd = shm_alloc(td->td_ucred, cmode);
533 shm_insert(path, fnv, shmfd);
540 * Object already exists, obtain a new
541 * reference if requested and permitted.
544 if ((uap->flags & (O_CREAT | O_EXCL)) ==
549 error = mac_posixshm_check_open(td->td_ucred,
553 error = shm_access(shmfd, td->td_ucred,
554 FFLAGS(uap->flags & O_ACCMODE));
558 * Truncate the file back to zero length if
559 * O_TRUNC was specified and the object was
560 * opened with read/write.
563 (uap->flags & (O_ACCMODE | O_TRUNC)) ==
564 (O_RDWR | O_TRUNC)) {
566 error = mac_posixshm_check_truncate(
567 td->td_ucred, fp->f_cred, shmfd);
570 shm_dotruncate(shmfd, 0);
575 sx_xunlock(&shm_dict_lock);
578 fdclose(fdp, fp, fd, td);
584 finit(fp, FFLAGS(uap->flags & O_ACCMODE), DTYPE_SHM, shmfd, &shm_ops);
587 if (fdp->fd_ofiles[fd] == fp)
588 fdp->fd_ofileflags[fd] |= UF_EXCLOSE;
589 FILEDESC_XUNLOCK(fdp);
590 td->td_retval[0] = fd;
597 shm_unlink(struct thread *td, struct shm_unlink_args *uap)
603 path = malloc(MAXPATHLEN, M_TEMP, M_WAITOK);
604 error = copyinstr(uap->path, path, MAXPATHLEN, NULL);
610 fnv = fnv_32_str(path, FNV1_32_INIT);
611 sx_xlock(&shm_dict_lock);
612 error = shm_remove(path, fnv, td->td_ucred);
613 sx_xunlock(&shm_dict_lock);
620 * mmap() helper to validate mmap() requests against shm object state
621 * and give mmap() the vm_object to use for the mapping.
624 shm_mmap(struct shmfd *shmfd, vm_size_t objsize, vm_ooffset_t foff,
629 * XXXRW: This validation is probably insufficient, and subject to
630 * sign errors. It should be fixed.
632 if (foff >= shmfd->shm_size ||
633 foff + objsize > round_page(shmfd->shm_size))
636 mtx_lock(&shm_timestamp_lock);
637 vfs_timestamp(&shmfd->shm_atime);
638 mtx_unlock(&shm_timestamp_lock);
639 vm_object_reference(shmfd->shm_object);
640 *obj = shmfd->shm_object;