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1/*
2 * memfd_create system call and file sealing support
3 *
4 * Code was originally included in shmem.c, and broken out to facilitate
5 * use by hugetlbfs as well as tmpfs.
6 *
7 * This file is released under the GPL.
8 */
9
10#include <linux/fs.h>
11#include <linux/vfs.h>
12#include <linux/pagemap.h>
13#include <linux/file.h>
14#include <linux/mm.h>
15#include <linux/sched/signal.h>
16#include <linux/khugepaged.h>
17#include <linux/syscalls.h>
18#include <linux/hugetlb.h>
19#include <linux/shmem_fs.h>
20#include <linux/memfd.h>
21#include <uapi/linux/memfd.h>
22
23/*
24 * We need a tag: a new tag would expand every xa_node by 8 bytes,
25 * so reuse a tag which we firmly believe is never set or cleared on tmpfs
26 * or hugetlbfs because they are memory only filesystems.
27 */
28#define MEMFD_TAG_PINNED PAGECACHE_TAG_TOWRITE
29#define LAST_SCAN 4 /* about 150ms max */
30
31static void memfd_tag_pins(struct xa_state *xas)
32{
33 struct page *page;
34 unsigned int tagged = 0;
35
36 lru_add_drain();
37
38 xas_lock_irq(xas);
39 xas_for_each(xas, page, ULONG_MAX) {
40 if (xa_is_value(page))
41 continue;
42 page = find_subpage(page, xas->xa_index);
43 if (page_count(page) - page_mapcount(page) > 1)
44 xas_set_mark(xas, MEMFD_TAG_PINNED);
45
46 if (++tagged % XA_CHECK_SCHED)
47 continue;
48
49 xas_pause(xas);
50 xas_unlock_irq(xas);
51 cond_resched();
52 xas_lock_irq(xas);
53 }
54 xas_unlock_irq(xas);
55}
56
57/*
58 * Setting SEAL_WRITE requires us to verify there's no pending writer. However,
59 * via get_user_pages(), drivers might have some pending I/O without any active
60 * user-space mappings (eg., direct-IO, AIO). Therefore, we look at all pages
61 * and see whether it has an elevated ref-count. If so, we tag them and wait for
62 * them to be dropped.
63 * The caller must guarantee that no new user will acquire writable references
64 * to those pages to avoid races.
65 */
66static int memfd_wait_for_pins(struct address_space *mapping)
67{
68 XA_STATE(xas, &mapping->i_pages, 0);
69 struct page *page;
70 int error, scan;
71
72 memfd_tag_pins(&xas);
73
74 error = 0;
75 for (scan = 0; scan <= LAST_SCAN; scan++) {
76 unsigned int tagged = 0;
77
78 if (!xas_marked(&xas, MEMFD_TAG_PINNED))
79 break;
80
81 if (!scan)
82 lru_add_drain_all();
83 else if (schedule_timeout_killable((HZ << scan) / 200))
84 scan = LAST_SCAN;
85
86 xas_set(&xas, 0);
87 xas_lock_irq(&xas);
88 xas_for_each_marked(&xas, page, ULONG_MAX, MEMFD_TAG_PINNED) {
89 bool clear = true;
90 if (xa_is_value(page))
91 continue;
92 page = find_subpage(page, xas.xa_index);
93 if (page_count(page) - page_mapcount(page) != 1) {
94 /*
95 * On the last scan, we clean up all those tags
96 * we inserted; but make a note that we still
97 * found pages pinned.
98 */
99 if (scan == LAST_SCAN)
100 error = -EBUSY;
101 else
102 clear = false;
103 }
104 if (clear)
105 xas_clear_mark(&xas, MEMFD_TAG_PINNED);
106 if (++tagged % XA_CHECK_SCHED)
107 continue;
108
109 xas_pause(&xas);
110 xas_unlock_irq(&xas);
111 cond_resched();
112 xas_lock_irq(&xas);
113 }
114 xas_unlock_irq(&xas);
115 }
116
117 return error;
118}
119
120static unsigned int *memfd_file_seals_ptr(struct file *file)
121{
122 if (shmem_file(file))
123 return &SHMEM_I(file_inode(file))->seals;
124
125#ifdef CONFIG_HUGETLBFS
126 if (is_file_hugepages(file))
127 return &HUGETLBFS_I(file_inode(file))->seals;
128#endif
129
130 return NULL;
131}
132
133#define F_ALL_SEALS (F_SEAL_SEAL | \
134 F_SEAL_SHRINK | \
135 F_SEAL_GROW | \
136 F_SEAL_WRITE | \
137 F_SEAL_FUTURE_WRITE)
138
139static int memfd_add_seals(struct file *file, unsigned int seals)
140{
141 struct inode *inode = file_inode(file);
142 unsigned int *file_seals;
143 int error;
144
145 /*
146 * SEALING
147 * Sealing allows multiple parties to share a tmpfs or hugetlbfs file
148 * but restrict access to a specific subset of file operations. Seals
149 * can only be added, but never removed. This way, mutually untrusted
150 * parties can share common memory regions with a well-defined policy.
151 * A malicious peer can thus never perform unwanted operations on a
152 * shared object.
153 *
154 * Seals are only supported on special tmpfs or hugetlbfs files and
155 * always affect the whole underlying inode. Once a seal is set, it
156 * may prevent some kinds of access to the file. Currently, the
157 * following seals are defined:
158 * SEAL_SEAL: Prevent further seals from being set on this file
159 * SEAL_SHRINK: Prevent the file from shrinking
160 * SEAL_GROW: Prevent the file from growing
161 * SEAL_WRITE: Prevent write access to the file
162 *
163 * As we don't require any trust relationship between two parties, we
164 * must prevent seals from being removed. Therefore, sealing a file
165 * only adds a given set of seals to the file, it never touches
166 * existing seals. Furthermore, the "setting seals"-operation can be
167 * sealed itself, which basically prevents any further seal from being
168 * added.
169 *
170 * Semantics of sealing are only defined on volatile files. Only
171 * anonymous tmpfs and hugetlbfs files support sealing. More
172 * importantly, seals are never written to disk. Therefore, there's
173 * no plan to support it on other file types.
174 */
175
176 if (!(file->f_mode & FMODE_WRITE))
177 return -EPERM;
178 if (seals & ~(unsigned int)F_ALL_SEALS)
179 return -EINVAL;
180
181 inode_lock(inode);
182
183 file_seals = memfd_file_seals_ptr(file);
184 if (!file_seals) {
185 error = -EINVAL;
186 goto unlock;
187 }
188
189 if (*file_seals & F_SEAL_SEAL) {
190 error = -EPERM;
191 goto unlock;
192 }
193
194 if ((seals & F_SEAL_WRITE) && !(*file_seals & F_SEAL_WRITE)) {
195 error = mapping_deny_writable(file->f_mapping);
196 if (error)
197 goto unlock;
198
199 error = memfd_wait_for_pins(file->f_mapping);
200 if (error) {
201 mapping_allow_writable(file->f_mapping);
202 goto unlock;
203 }
204 }
205
206 *file_seals |= seals;
207 error = 0;
208
209unlock:
210 inode_unlock(inode);
211 return error;
212}
213
214static int memfd_get_seals(struct file *file)
215{
216 unsigned int *seals = memfd_file_seals_ptr(file);
217
218 return seals ? *seals : -EINVAL;
219}
220
221long memfd_fcntl(struct file *file, unsigned int cmd, unsigned long arg)
222{
223 long error;
224
225 switch (cmd) {
226 case F_ADD_SEALS:
227 /* disallow upper 32bit */
228 if (arg > UINT_MAX)
229 return -EINVAL;
230
231 error = memfd_add_seals(file, arg);
232 break;
233 case F_GET_SEALS:
234 error = memfd_get_seals(file);
235 break;
236 default:
237 error = -EINVAL;
238 break;
239 }
240
241 return error;
242}
243
244#define MFD_NAME_PREFIX "memfd:"
245#define MFD_NAME_PREFIX_LEN (sizeof(MFD_NAME_PREFIX) - 1)
246#define MFD_NAME_MAX_LEN (NAME_MAX - MFD_NAME_PREFIX_LEN)
247
248#define MFD_ALL_FLAGS (MFD_CLOEXEC | MFD_ALLOW_SEALING | MFD_HUGETLB)
249
250SYSCALL_DEFINE2(memfd_create,
251 const char __user *, uname,
252 unsigned int, flags)
253{
254 unsigned int *file_seals;
255 struct file *file;
256 int fd, error;
257 char *name;
258 long len;
259
260 if (!(flags & MFD_HUGETLB)) {
261 if (flags & ~(unsigned int)MFD_ALL_FLAGS)
262 return -EINVAL;
263 } else {
264 /* Allow huge page size encoding in flags. */
265 if (flags & ~(unsigned int)(MFD_ALL_FLAGS |
266 (MFD_HUGE_MASK << MFD_HUGE_SHIFT)))
267 return -EINVAL;
268 }
269
270 /* length includes terminating zero */
271 len = strnlen_user(uname, MFD_NAME_MAX_LEN + 1);
272 if (len <= 0)
273 return -EFAULT;
274 if (len > MFD_NAME_MAX_LEN + 1)
275 return -EINVAL;
276
277 name = kmalloc(len + MFD_NAME_PREFIX_LEN, GFP_KERNEL);
278 if (!name)
279 return -ENOMEM;
280
281 strcpy(name, MFD_NAME_PREFIX);
282 if (copy_from_user(&name[MFD_NAME_PREFIX_LEN], uname, len)) {
283 error = -EFAULT;
284 goto err_name;
285 }
286
287 /* terminating-zero may have changed after strnlen_user() returned */
288 if (name[len + MFD_NAME_PREFIX_LEN - 1]) {
289 error = -EFAULT;
290 goto err_name;
291 }
292
293 fd = get_unused_fd_flags((flags & MFD_CLOEXEC) ? O_CLOEXEC : 0);
294 if (fd < 0) {
295 error = fd;
296 goto err_name;
297 }
298
299 if (flags & MFD_HUGETLB) {
300 struct user_struct *user = NULL;
301
302 file = hugetlb_file_setup(name, 0, VM_NORESERVE, &user,
303 HUGETLB_ANONHUGE_INODE,
304 (flags >> MFD_HUGE_SHIFT) &
305 MFD_HUGE_MASK);
306 } else
307 file = shmem_file_setup(name, 0, VM_NORESERVE);
308 if (IS_ERR(file)) {
309 error = PTR_ERR(file);
310 goto err_fd;
311 }
312 file->f_mode |= FMODE_LSEEK | FMODE_PREAD | FMODE_PWRITE;
313 file->f_flags |= O_LARGEFILE;
314
315 if (flags & MFD_ALLOW_SEALING) {
316 file_seals = memfd_file_seals_ptr(file);
317 *file_seals &= ~F_SEAL_SEAL;
318 }
319
320 fd_install(fd, file);
321 kfree(name);
322 return fd;
323
324err_fd:
325 put_unused_fd(fd);
326err_name:
327 kfree(name);
328 return error;
329}
1/*
2 * memfd_create system call and file sealing support
3 *
4 * Code was originally included in shmem.c, and broken out to facilitate
5 * use by hugetlbfs as well as tmpfs.
6 *
7 * This file is released under the GPL.
8 */
9
10#include <linux/fs.h>
11#include <linux/vfs.h>
12#include <linux/pagemap.h>
13#include <linux/file.h>
14#include <linux/mm.h>
15#include <linux/sched/signal.h>
16#include <linux/khugepaged.h>
17#include <linux/syscalls.h>
18#include <linux/hugetlb.h>
19#include <linux/shmem_fs.h>
20#include <linux/memfd.h>
21#include <linux/pid_namespace.h>
22#include <uapi/linux/memfd.h>
23
24/*
25 * We need a tag: a new tag would expand every xa_node by 8 bytes,
26 * so reuse a tag which we firmly believe is never set or cleared on tmpfs
27 * or hugetlbfs because they are memory only filesystems.
28 */
29#define MEMFD_TAG_PINNED PAGECACHE_TAG_TOWRITE
30#define LAST_SCAN 4 /* about 150ms max */
31
32static void memfd_tag_pins(struct xa_state *xas)
33{
34 struct page *page;
35 int latency = 0;
36 int cache_count;
37
38 lru_add_drain();
39
40 xas_lock_irq(xas);
41 xas_for_each(xas, page, ULONG_MAX) {
42 cache_count = 1;
43 if (!xa_is_value(page) &&
44 PageTransHuge(page) && !PageHuge(page))
45 cache_count = HPAGE_PMD_NR;
46
47 if (!xa_is_value(page) &&
48 page_count(page) - total_mapcount(page) != cache_count)
49 xas_set_mark(xas, MEMFD_TAG_PINNED);
50 if (cache_count != 1)
51 xas_set(xas, page->index + cache_count);
52
53 latency += cache_count;
54 if (latency < XA_CHECK_SCHED)
55 continue;
56 latency = 0;
57
58 xas_pause(xas);
59 xas_unlock_irq(xas);
60 cond_resched();
61 xas_lock_irq(xas);
62 }
63 xas_unlock_irq(xas);
64}
65
66/*
67 * Setting SEAL_WRITE requires us to verify there's no pending writer. However,
68 * via get_user_pages(), drivers might have some pending I/O without any active
69 * user-space mappings (eg., direct-IO, AIO). Therefore, we look at all pages
70 * and see whether it has an elevated ref-count. If so, we tag them and wait for
71 * them to be dropped.
72 * The caller must guarantee that no new user will acquire writable references
73 * to those pages to avoid races.
74 */
75static int memfd_wait_for_pins(struct address_space *mapping)
76{
77 XA_STATE(xas, &mapping->i_pages, 0);
78 struct page *page;
79 int error, scan;
80
81 memfd_tag_pins(&xas);
82
83 error = 0;
84 for (scan = 0; scan <= LAST_SCAN; scan++) {
85 int latency = 0;
86 int cache_count;
87
88 if (!xas_marked(&xas, MEMFD_TAG_PINNED))
89 break;
90
91 if (!scan)
92 lru_add_drain_all();
93 else if (schedule_timeout_killable((HZ << scan) / 200))
94 scan = LAST_SCAN;
95
96 xas_set(&xas, 0);
97 xas_lock_irq(&xas);
98 xas_for_each_marked(&xas, page, ULONG_MAX, MEMFD_TAG_PINNED) {
99 bool clear = true;
100
101 cache_count = 1;
102 if (!xa_is_value(page) &&
103 PageTransHuge(page) && !PageHuge(page))
104 cache_count = HPAGE_PMD_NR;
105
106 if (!xa_is_value(page) && cache_count !=
107 page_count(page) - total_mapcount(page)) {
108 /*
109 * On the last scan, we clean up all those tags
110 * we inserted; but make a note that we still
111 * found pages pinned.
112 */
113 if (scan == LAST_SCAN)
114 error = -EBUSY;
115 else
116 clear = false;
117 }
118 if (clear)
119 xas_clear_mark(&xas, MEMFD_TAG_PINNED);
120
121 latency += cache_count;
122 if (latency < XA_CHECK_SCHED)
123 continue;
124 latency = 0;
125
126 xas_pause(&xas);
127 xas_unlock_irq(&xas);
128 cond_resched();
129 xas_lock_irq(&xas);
130 }
131 xas_unlock_irq(&xas);
132 }
133
134 return error;
135}
136
137static unsigned int *memfd_file_seals_ptr(struct file *file)
138{
139 if (shmem_file(file))
140 return &SHMEM_I(file_inode(file))->seals;
141
142#ifdef CONFIG_HUGETLBFS
143 if (is_file_hugepages(file))
144 return &HUGETLBFS_I(file_inode(file))->seals;
145#endif
146
147 return NULL;
148}
149
150#define F_ALL_SEALS (F_SEAL_SEAL | \
151 F_SEAL_EXEC | \
152 F_SEAL_SHRINK | \
153 F_SEAL_GROW | \
154 F_SEAL_WRITE | \
155 F_SEAL_FUTURE_WRITE)
156
157static int memfd_add_seals(struct file *file, unsigned int seals)
158{
159 struct inode *inode = file_inode(file);
160 unsigned int *file_seals;
161 int error;
162
163 /*
164 * SEALING
165 * Sealing allows multiple parties to share a tmpfs or hugetlbfs file
166 * but restrict access to a specific subset of file operations. Seals
167 * can only be added, but never removed. This way, mutually untrusted
168 * parties can share common memory regions with a well-defined policy.
169 * A malicious peer can thus never perform unwanted operations on a
170 * shared object.
171 *
172 * Seals are only supported on special tmpfs or hugetlbfs files and
173 * always affect the whole underlying inode. Once a seal is set, it
174 * may prevent some kinds of access to the file. Currently, the
175 * following seals are defined:
176 * SEAL_SEAL: Prevent further seals from being set on this file
177 * SEAL_SHRINK: Prevent the file from shrinking
178 * SEAL_GROW: Prevent the file from growing
179 * SEAL_WRITE: Prevent write access to the file
180 * SEAL_EXEC: Prevent modification of the exec bits in the file mode
181 *
182 * As we don't require any trust relationship between two parties, we
183 * must prevent seals from being removed. Therefore, sealing a file
184 * only adds a given set of seals to the file, it never touches
185 * existing seals. Furthermore, the "setting seals"-operation can be
186 * sealed itself, which basically prevents any further seal from being
187 * added.
188 *
189 * Semantics of sealing are only defined on volatile files. Only
190 * anonymous tmpfs and hugetlbfs files support sealing. More
191 * importantly, seals are never written to disk. Therefore, there's
192 * no plan to support it on other file types.
193 */
194
195 if (!(file->f_mode & FMODE_WRITE))
196 return -EPERM;
197 if (seals & ~(unsigned int)F_ALL_SEALS)
198 return -EINVAL;
199
200 inode_lock(inode);
201
202 file_seals = memfd_file_seals_ptr(file);
203 if (!file_seals) {
204 error = -EINVAL;
205 goto unlock;
206 }
207
208 if (*file_seals & F_SEAL_SEAL) {
209 error = -EPERM;
210 goto unlock;
211 }
212
213 if ((seals & F_SEAL_WRITE) && !(*file_seals & F_SEAL_WRITE)) {
214 error = mapping_deny_writable(file->f_mapping);
215 if (error)
216 goto unlock;
217
218 error = memfd_wait_for_pins(file->f_mapping);
219 if (error) {
220 mapping_allow_writable(file->f_mapping);
221 goto unlock;
222 }
223 }
224
225 /*
226 * SEAL_EXEC implys SEAL_WRITE, making W^X from the start.
227 */
228 if (seals & F_SEAL_EXEC && inode->i_mode & 0111)
229 seals |= F_SEAL_SHRINK|F_SEAL_GROW|F_SEAL_WRITE|F_SEAL_FUTURE_WRITE;
230
231 *file_seals |= seals;
232 error = 0;
233
234unlock:
235 inode_unlock(inode);
236 return error;
237}
238
239static int memfd_get_seals(struct file *file)
240{
241 unsigned int *seals = memfd_file_seals_ptr(file);
242
243 return seals ? *seals : -EINVAL;
244}
245
246long memfd_fcntl(struct file *file, unsigned int cmd, unsigned int arg)
247{
248 long error;
249
250 switch (cmd) {
251 case F_ADD_SEALS:
252 error = memfd_add_seals(file, arg);
253 break;
254 case F_GET_SEALS:
255 error = memfd_get_seals(file);
256 break;
257 default:
258 error = -EINVAL;
259 break;
260 }
261
262 return error;
263}
264
265#define MFD_NAME_PREFIX "memfd:"
266#define MFD_NAME_PREFIX_LEN (sizeof(MFD_NAME_PREFIX) - 1)
267#define MFD_NAME_MAX_LEN (NAME_MAX - MFD_NAME_PREFIX_LEN)
268
269#define MFD_ALL_FLAGS (MFD_CLOEXEC | MFD_ALLOW_SEALING | MFD_HUGETLB | MFD_NOEXEC_SEAL | MFD_EXEC)
270
271static int check_sysctl_memfd_noexec(unsigned int *flags)
272{
273#ifdef CONFIG_SYSCTL
274 struct pid_namespace *ns = task_active_pid_ns(current);
275 int sysctl = pidns_memfd_noexec_scope(ns);
276
277 if (!(*flags & (MFD_EXEC | MFD_NOEXEC_SEAL))) {
278 if (sysctl >= MEMFD_NOEXEC_SCOPE_NOEXEC_SEAL)
279 *flags |= MFD_NOEXEC_SEAL;
280 else
281 *flags |= MFD_EXEC;
282 }
283
284 if (!(*flags & MFD_NOEXEC_SEAL) && sysctl >= MEMFD_NOEXEC_SCOPE_NOEXEC_ENFORCED) {
285 pr_err_ratelimited(
286 "%s[%d]: memfd_create() requires MFD_NOEXEC_SEAL with vm.memfd_noexec=%d\n",
287 current->comm, task_pid_nr(current), sysctl);
288 return -EACCES;
289 }
290#endif
291 return 0;
292}
293
294SYSCALL_DEFINE2(memfd_create,
295 const char __user *, uname,
296 unsigned int, flags)
297{
298 unsigned int *file_seals;
299 struct file *file;
300 int fd, error;
301 char *name;
302 long len;
303
304 if (!(flags & MFD_HUGETLB)) {
305 if (flags & ~(unsigned int)MFD_ALL_FLAGS)
306 return -EINVAL;
307 } else {
308 /* Allow huge page size encoding in flags. */
309 if (flags & ~(unsigned int)(MFD_ALL_FLAGS |
310 (MFD_HUGE_MASK << MFD_HUGE_SHIFT)))
311 return -EINVAL;
312 }
313
314 /* Invalid if both EXEC and NOEXEC_SEAL are set.*/
315 if ((flags & MFD_EXEC) && (flags & MFD_NOEXEC_SEAL))
316 return -EINVAL;
317
318 error = check_sysctl_memfd_noexec(&flags);
319 if (error < 0)
320 return error;
321
322 /* length includes terminating zero */
323 len = strnlen_user(uname, MFD_NAME_MAX_LEN + 1);
324 if (len <= 0)
325 return -EFAULT;
326 if (len > MFD_NAME_MAX_LEN + 1)
327 return -EINVAL;
328
329 name = kmalloc(len + MFD_NAME_PREFIX_LEN, GFP_KERNEL);
330 if (!name)
331 return -ENOMEM;
332
333 strcpy(name, MFD_NAME_PREFIX);
334 if (copy_from_user(&name[MFD_NAME_PREFIX_LEN], uname, len)) {
335 error = -EFAULT;
336 goto err_name;
337 }
338
339 /* terminating-zero may have changed after strnlen_user() returned */
340 if (name[len + MFD_NAME_PREFIX_LEN - 1]) {
341 error = -EFAULT;
342 goto err_name;
343 }
344
345 fd = get_unused_fd_flags((flags & MFD_CLOEXEC) ? O_CLOEXEC : 0);
346 if (fd < 0) {
347 error = fd;
348 goto err_name;
349 }
350
351 if (flags & MFD_HUGETLB) {
352 file = hugetlb_file_setup(name, 0, VM_NORESERVE,
353 HUGETLB_ANONHUGE_INODE,
354 (flags >> MFD_HUGE_SHIFT) &
355 MFD_HUGE_MASK);
356 } else
357 file = shmem_file_setup(name, 0, VM_NORESERVE);
358 if (IS_ERR(file)) {
359 error = PTR_ERR(file);
360 goto err_fd;
361 }
362 file->f_mode |= FMODE_LSEEK | FMODE_PREAD | FMODE_PWRITE;
363 file->f_flags |= O_LARGEFILE;
364
365 if (flags & MFD_NOEXEC_SEAL) {
366 struct inode *inode = file_inode(file);
367
368 inode->i_mode &= ~0111;
369 file_seals = memfd_file_seals_ptr(file);
370 if (file_seals) {
371 *file_seals &= ~F_SEAL_SEAL;
372 *file_seals |= F_SEAL_EXEC;
373 }
374 } else if (flags & MFD_ALLOW_SEALING) {
375 /* MFD_EXEC and MFD_ALLOW_SEALING are set */
376 file_seals = memfd_file_seals_ptr(file);
377 if (file_seals)
378 *file_seals &= ~F_SEAL_SEAL;
379 }
380
381 fd_install(fd, file);
382 kfree(name);
383 return fd;
384
385err_fd:
386 put_unused_fd(fd);
387err_name:
388 kfree(name);
389 return error;
390}