[mirror_ubuntu-jammy-kernel.git] / mm / memfd.c

/*
 * memfd_create system call and file sealing support
 *
 * Code was originally included in shmem.c, and broken out to facilitate
 * use by hugetlbfs as well as tmpfs.
 *
 * This file is released under the GPL.
 */

#include <linux/fs.h>
#include <linux/vfs.h>
#include <linux/pagemap.h>
#include <linux/file.h>
#include <linux/mm.h>
#include <linux/sched/signal.h>
#include <linux/khugepaged.h>
#include <linux/syscalls.h>
#include <linux/hugetlb.h>
#include <linux/shmem_fs.h>
#include <linux/memfd.h>
#include <uapi/linux/memfd.h>

/*
 * We need a tag: a new tag would expand every xa_node by 8 bytes,
 * so reuse a tag which we firmly believe is never set or cleared on tmpfs
 * or hugetlbfs because they are memory only filesystems.
 */
#define MEMFD_TAG_PINNED        PAGECACHE_TAG_TOWRITE
#define LAST_SCAN               4       /* about 150ms max */

static void memfd_tag_pins(struct xa_state *xas)
{
	struct page *page;
	int latency = 0;
	int cache_count;

	lru_add_drain();

	xas_lock_irq(xas);
	xas_for_each(xas, page, ULONG_MAX) {
		cache_count = 1;
		if (!xa_is_value(page) &&
		    PageTransHuge(page) && !PageHuge(page))
			cache_count = HPAGE_PMD_NR;

		if (!xa_is_value(page) &&
		    page_count(page) - total_mapcount(page) != cache_count)
			xas_set_mark(xas, MEMFD_TAG_PINNED);
		if (cache_count != 1)
			xas_set(xas, page->index + cache_count);

		latency += cache_count;
		if (latency < XA_CHECK_SCHED)
			continue;
		latency = 0;

		xas_pause(xas);
		xas_unlock_irq(xas);
		cond_resched();
		xas_lock_irq(xas);
	}
	xas_unlock_irq(xas);
}

/*
 * Setting SEAL_WRITE requires us to verify there's no pending writer. However,
 * via get_user_pages(), drivers might have some pending I/O without any active
 * user-space mappings (eg., direct-IO, AIO). Therefore, we look at all pages
 * and see whether it has an elevated ref-count. If so, we tag them and wait for
 * them to be dropped.
 * The caller must guarantee that no new user will acquire writable references
 * to those pages to avoid races.
 */
static int memfd_wait_for_pins(struct address_space *mapping)
{
	XA_STATE(xas, &mapping->i_pages, 0);
	struct page *page;
	int error, scan;

	memfd_tag_pins(&xas);

	error = 0;
	for (scan = 0; scan <= LAST_SCAN; scan++) {
		int latency = 0;
		int cache_count;

		if (!xas_marked(&xas, MEMFD_TAG_PINNED))
			break;

		if (!scan)
			lru_add_drain_all();
		else if (schedule_timeout_killable((HZ << scan) / 200))
			scan = LAST_SCAN;

		xas_set(&xas, 0);
		xas_lock_irq(&xas);
		xas_for_each_marked(&xas, page, ULONG_MAX, MEMFD_TAG_PINNED) {
			bool clear = true;

			cache_count = 1;
			if (!xa_is_value(page) &&
			    PageTransHuge(page) && !PageHuge(page))
				cache_count = HPAGE_PMD_NR;

			if (!xa_is_value(page) && cache_count !=
			    page_count(page) - total_mapcount(page)) {
				/*
				 * On the last scan, we clean up all those tags
				 * we inserted; but make a note that we still
				 * found pages pinned.
				 */
				if (scan == LAST_SCAN)
					error = -EBUSY;
				else
					clear = false;
			}
			if (clear)
				xas_clear_mark(&xas, MEMFD_TAG_PINNED);

			latency += cache_count;
			if (latency < XA_CHECK_SCHED)
				continue;
			latency = 0;

			xas_pause(&xas);
			xas_unlock_irq(&xas);
			cond_resched();
			xas_lock_irq(&xas);
		}
		xas_unlock_irq(&xas);
	}

	return error;
}

static unsigned int *memfd_file_seals_ptr(struct file *file)
{
	if (shmem_file(file))
		return &SHMEM_I(file_inode(file))->seals;

#ifdef CONFIG_HUGETLBFS
	if (is_file_hugepages(file))
		return &HUGETLBFS_I(file_inode(file))->seals;
#endif

	return NULL;
}

#define F_ALL_SEALS (F_SEAL_SEAL | \
		     F_SEAL_SHRINK | \
		     F_SEAL_GROW | \
		     F_SEAL_WRITE | \
		     F_SEAL_FUTURE_WRITE)

static int memfd_add_seals(struct file *file, unsigned int seals)
{
	struct inode *inode = file_inode(file);
	unsigned int *file_seals;
	int error;

	/*
	 * SEALING
	 * Sealing allows multiple parties to share a tmpfs or hugetlbfs file
	 * but restrict access to a specific subset of file operations. Seals
	 * can only be added, but never removed. This way, mutually untrusted
	 * parties can share common memory regions with a well-defined policy.
	 * A malicious peer can thus never perform unwanted operations on a
	 * shared object.
	 *
	 * Seals are only supported on special tmpfs or hugetlbfs files and
	 * always affect the whole underlying inode. Once a seal is set, it
	 * may prevent some kinds of access to the file. Currently, the
	 * following seals are defined:
	 *   SEAL_SEAL: Prevent further seals from being set on this file
	 *   SEAL_SHRINK: Prevent the file from shrinking
	 *   SEAL_GROW: Prevent the file from growing
	 *   SEAL_WRITE: Prevent write access to the file
	 *
	 * As we don't require any trust relationship between two parties, we
	 * must prevent seals from being removed. Therefore, sealing a file
	 * only adds a given set of seals to the file, it never touches
	 * existing seals. Furthermore, the "setting seals"-operation can be
	 * sealed itself, which basically prevents any further seal from being
	 * added.
	 *
	 * Semantics of sealing are only defined on volatile files. Only
	 * anonymous tmpfs and hugetlbfs files support sealing. More
	 * importantly, seals are never written to disk. Therefore, there's
	 * no plan to support it on other file types.
	 */

	if (!(file->f_mode & FMODE_WRITE))
		return -EPERM;
	if (seals & ~(unsigned int)F_ALL_SEALS)
		return -EINVAL;

	inode_lock(inode);

	file_seals = memfd_file_seals_ptr(file);
	if (!file_seals) {
		error = -EINVAL;
		goto unlock;
	}

	if (*file_seals & F_SEAL_SEAL) {
		error = -EPERM;
		goto unlock;
	}

	if ((seals & F_SEAL_WRITE) && !(*file_seals & F_SEAL_WRITE)) {
		error = mapping_deny_writable(file->f_mapping);
		if (error)
			goto unlock;

		error = memfd_wait_for_pins(file->f_mapping);
		if (error) {
			mapping_allow_writable(file->f_mapping);
			goto unlock;
		}
	}

	*file_seals |= seals;
	error = 0;

unlock:
	inode_unlock(inode);
	return error;
}

static int memfd_get_seals(struct file *file)
{
	unsigned int *seals = memfd_file_seals_ptr(file);

	return seals ? *seals : -EINVAL;
}

long memfd_fcntl(struct file *file, unsigned int cmd, unsigned long arg)
{
	long error;

	switch (cmd) {
	case F_ADD_SEALS:
		/* disallow upper 32bit */
		if (arg > UINT_MAX)
			return -EINVAL;

		error = memfd_add_seals(file, arg);
		break;
	case F_GET_SEALS:
		error = memfd_get_seals(file);
		break;
	default:
		error = -EINVAL;
		break;
	}

	return error;
}

#define MFD_NAME_PREFIX "memfd:"
#define MFD_NAME_PREFIX_LEN (sizeof(MFD_NAME_PREFIX) - 1)
#define MFD_NAME_MAX_LEN (NAME_MAX - MFD_NAME_PREFIX_LEN)

#define MFD_ALL_FLAGS (MFD_CLOEXEC | MFD_ALLOW_SEALING | MFD_HUGETLB)

SYSCALL_DEFINE2(memfd_create,
		const char __user *, uname,
		unsigned int, flags)
{
	unsigned int *file_seals;
	struct file *file;
	int fd, error;
	char *name;
	long len;

	if (!(flags & MFD_HUGETLB)) {
		if (flags & ~(unsigned int)MFD_ALL_FLAGS)
			return -EINVAL;
	} else {
		/* Allow huge page size encoding in flags. */
		if (flags & ~(unsigned int)(MFD_ALL_FLAGS |
				(MFD_HUGE_MASK << MFD_HUGE_SHIFT)))
			return -EINVAL;
	}

	/* length includes terminating zero */
	len = strnlen_user(uname, MFD_NAME_MAX_LEN + 1);
	if (len <= 0)
		return -EFAULT;
	if (len > MFD_NAME_MAX_LEN + 1)
		return -EINVAL;

	name = kmalloc(len + MFD_NAME_PREFIX_LEN, GFP_KERNEL);
	if (!name)
		return -ENOMEM;

	strcpy(name, MFD_NAME_PREFIX);
	if (copy_from_user(&name[MFD_NAME_PREFIX_LEN], uname, len)) {
		error = -EFAULT;
		goto err_name;
	}

	/* terminating-zero may have changed after strnlen_user() returned */
	if (name[len + MFD_NAME_PREFIX_LEN - 1]) {
		error = -EFAULT;
		goto err_name;
	}

	fd = get_unused_fd_flags((flags & MFD_CLOEXEC) ? O_CLOEXEC : 0);
	if (fd < 0) {
		error = fd;
		goto err_name;
	}

	if (flags & MFD_HUGETLB) {
		struct ucounts *ucounts = NULL;

		file = hugetlb_file_setup(name, 0, VM_NORESERVE, &ucounts,
					HUGETLB_ANONHUGE_INODE,
					(flags >> MFD_HUGE_SHIFT) &
					MFD_HUGE_MASK);
	} else
		file = shmem_file_setup(name, 0, VM_NORESERVE);
	if (IS_ERR(file)) {
		error = PTR_ERR(file);
		goto err_fd;
	}
	file->f_mode |= FMODE_LSEEK | FMODE_PREAD | FMODE_PWRITE;
	file->f_flags |= O_LARGEFILE;

	if (flags & MFD_ALLOW_SEALING) {
		file_seals = memfd_file_seals_ptr(file);
		*file_seals &= ~F_SEAL_SEAL;
	}

	fd_install(fd, file);
	kfree(name);
	return fd;

err_fd:
	put_unused_fd(fd);
err_name:
	kfree(name);
	return error;
}
Commit	Line	Data
5d752600 MK	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	/*
2313216f	24	* We need a tag: a new tag would expand every xa_node by 8 bytes,
5d752600 MK	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
ef3038a5	31	static void memfd_tag_pins(struct xa_state *xas)
5d752600	32	{
5d752600	33	struct page *page;
78389d7c HD	34	int latency = 0;
78389d7c HD	35	int cache_count;
5d752600 MK	36
5d752600 MK	37	lru_add_drain();
5d752600	38
ef3038a5 MW	39	xas_lock_irq(xas);
ef3038a5 MW	40	xas_for_each(xas, page, ULONG_MAX) {
78389d7c HD	41	cache_count = 1;
	42	if (!xa_is_value(page) &&
	43	PageTransHuge(page) && !PageHuge(page))
	44	cache_count = HPAGE_PMD_NR;
	45
	46	if (!xa_is_value(page) &&
	47	page_count(page) - total_mapcount(page) != cache_count)
ef3038a5	48	xas_set_mark(xas, MEMFD_TAG_PINNED);
78389d7c HD	49	if (cache_count != 1)
78389d7c HD	50	xas_set(xas, page->index + cache_count);
5d752600	51
78389d7c HD	52	latency += cache_count;
78389d7c HD	53	if (latency < XA_CHECK_SCHED)
ef3038a5	54	continue;
78389d7c	55	latency = 0;
ef3038a5 MW	56
	57	xas_pause(xas);
	58	xas_unlock_irq(xas);
	59	cond_resched();
	60	xas_lock_irq(xas);
5d752600	61	}
ef3038a5	62	xas_unlock_irq(xas);
5d752600 MK	63	}
	64
	65	/*
	66	* Setting SEAL_WRITE requires us to verify there's no pending writer. However,
	67	* via get_user_pages(), drivers might have some pending I/O without any active
	68	* user-space mappings (eg., direct-IO, AIO). Therefore, we look at all pages
	69	* and see whether it has an elevated ref-count. If so, we tag them and wait for
	70	* them to be dropped.
	71	* The caller must guarantee that no new user will acquire writable references
	72	* to those pages to avoid races.
	73	*/
	74	static int memfd_wait_for_pins(struct address_space *mapping)
	75	{
2313216f	76	XA_STATE(xas, &mapping->i_pages, 0);
5d752600 MK	77	struct page *page;
	78	int error, scan;
	79
ef3038a5	80	memfd_tag_pins(&xas);
5d752600 MK	81
	82	error = 0;
	83	for (scan = 0; scan <= LAST_SCAN; scan++) {
78389d7c HD	84	int latency = 0;
78389d7c HD	85	int cache_count;
2313216f MW	86
2313216f MW	87	if (!xas_marked(&xas, MEMFD_TAG_PINNED))
5d752600 MK	88	break;
	89
	90	if (!scan)
	91	lru_add_drain_all();
	92	else if (schedule_timeout_killable((HZ << scan) / 200))
	93	scan = LAST_SCAN;
	94
2313216f MW	95	xas_set(&xas, 0);
	96	xas_lock_irq(&xas);
	97	xas_for_each_marked(&xas, page, ULONG_MAX, MEMFD_TAG_PINNED) {
	98	bool clear = true;
78389d7c HD	99
	100	cache_count = 1;
	101	if (!xa_is_value(page) &&
	102	PageTransHuge(page) && !PageHuge(page))
	103	cache_count = HPAGE_PMD_NR;
	104
	105	if (!xa_is_value(page) && cache_count !=
	106	page_count(page) - total_mapcount(page)) {
5d752600 MK	107	/*
	108	* On the last scan, we clean up all those tags
	109	* we inserted; but make a note that we still
	110	* found pages pinned.
	111	*/
2313216f MW	112	if (scan == LAST_SCAN)
	113	error = -EBUSY;
	114	else
	115	clear = false;
5d752600	116	}
2313216f MW	117	if (clear)
2313216f MW	118	xas_clear_mark(&xas, MEMFD_TAG_PINNED);
78389d7c HD	119
	120	latency += cache_count;
	121	if (latency < XA_CHECK_SCHED)
2313216f	122	continue;
78389d7c	123	latency = 0;
5d752600	124
2313216f MW	125	xas_pause(&xas);
	126	xas_unlock_irq(&xas);
	127	cond_resched();
	128	xas_lock_irq(&xas);
5d752600	129	}
2313216f	130	xas_unlock_irq(&xas);
5d752600 MK	131	}
	132
	133	return error;
	134	}
	135
	136	static unsigned int memfd_file_seals_ptr(struct file file)
	137	{
	138	if (shmem_file(file))
	139	return &SHMEM_I(file_inode(file))->seals;
	140
	141	#ifdef CONFIG_HUGETLBFS
	142	if (is_file_hugepages(file))
	143	return &HUGETLBFS_I(file_inode(file))->seals;
	144	#endif
	145
	146	return NULL;
	147	}
	148
	149	#define F_ALL_SEALS (F_SEAL_SEAL \| \
	150	F_SEAL_SHRINK \| \
	151	F_SEAL_GROW \| \
ab3948f5 JFG	152	F_SEAL_WRITE \| \
ab3948f5 JFG	153	F_SEAL_FUTURE_WRITE)
5d752600 MK	154
	155	static int memfd_add_seals(struct file *file, unsigned int seals)
	156	{
	157	struct inode *inode = file_inode(file);
	158	unsigned int *file_seals;
	159	int error;
	160
	161	/*
	162	* SEALING
	163	* Sealing allows multiple parties to share a tmpfs or hugetlbfs file
	164	* but restrict access to a specific subset of file operations. Seals
	165	* can only be added, but never removed. This way, mutually untrusted
	166	* parties can share common memory regions with a well-defined policy.
	167	* A malicious peer can thus never perform unwanted operations on a
	168	* shared object.
	169	*
	170	* Seals are only supported on special tmpfs or hugetlbfs files and
	171	* always affect the whole underlying inode. Once a seal is set, it
	172	* may prevent some kinds of access to the file. Currently, the
	173	* following seals are defined:
	174	* SEAL_SEAL: Prevent further seals from being set on this file
	175	* SEAL_SHRINK: Prevent the file from shrinking
	176	* SEAL_GROW: Prevent the file from growing
	177	* SEAL_WRITE: Prevent write access to the file
	178	*
	179	* As we don't require any trust relationship between two parties, we
	180	* must prevent seals from being removed. Therefore, sealing a file
	181	* only adds a given set of seals to the file, it never touches
	182	* existing seals. Furthermore, the "setting seals"-operation can be
	183	* sealed itself, which basically prevents any further seal from being
	184	* added.
	185	*
	186	* Semantics of sealing are only defined on volatile files. Only
	187	* anonymous tmpfs and hugetlbfs files support sealing. More
	188	* importantly, seals are never written to disk. Therefore, there's
	189	* no plan to support it on other file types.
	190	*/
	191
	192	if (!(file->f_mode & FMODE_WRITE))
	193	return -EPERM;
	194	if (seals & ~(unsigned int)F_ALL_SEALS)
	195	return -EINVAL;
	196
	197	inode_lock(inode);
	198
	199	file_seals = memfd_file_seals_ptr(file);
	200	if (!file_seals) {
	201	error = -EINVAL;
	202	goto unlock;
	203	}
	204
	205	if (*file_seals & F_SEAL_SEAL) {
	206	error = -EPERM;
	207	goto unlock;
	208	}
	209
	210	if ((seals & F_SEAL_WRITE) && !(*file_seals & F_SEAL_WRITE)) {
	211	error = mapping_deny_writable(file->f_mapping);
	212	if (error)
	213	goto unlock;
	214
	215	error = memfd_wait_for_pins(file->f_mapping);
	216	if (error) {
	217	mapping_allow_writable(file->f_mapping);
218	goto unlock;
219	}
220	}
221
222	*file_seals \|= seals;
223	error = 0;
224
225	unlock:
226	inode_unlock(inode);
227	return error;
228	}
229
230	static int memfd_get_seals(struct file *file)
231	{
232	unsigned int *seals = memfd_file_seals_ptr(file);
233
234	return seals ? *seals : -EINVAL;
235	}
236
237	long memfd_fcntl(struct file *file, unsigned int cmd, unsigned long arg)
238	{
239	long error;
240
241	switch (cmd) {
242	case F_ADD_SEALS:
243	/* disallow upper 32bit */
244	if (arg > UINT_MAX)
245	return -EINVAL;
246
247	error = memfd_add_seals(file, arg);
248	break;
249	case F_GET_SEALS:
250	error = memfd_get_seals(file);
251	break;
252	default:
253	error = -EINVAL;
254	break;
255	}
256
257	return error;
258	}
259
260	#define MFD_NAME_PREFIX "memfd:"
261	#define MFD_NAME_PREFIX_LEN (sizeof(MFD_NAME_PREFIX) - 1)
262	#define MFD_NAME_MAX_LEN (NAME_MAX - MFD_NAME_PREFIX_LEN)
263
264	#define MFD_ALL_FLAGS (MFD_CLOEXEC \| MFD_ALLOW_SEALING \| MFD_HUGETLB)
265
266	SYSCALL_DEFINE2(memfd_create,
267	const char __user *, uname,
268	unsigned int, flags)
269	{
270	unsigned int *file_seals;
271	struct file *file;
272	int fd, error;
273	char *name;
274	long len;
275
276	if (!(flags & MFD_HUGETLB)) {
277	if (flags & ~(unsigned int)MFD_ALL_FLAGS)
278	return -EINVAL;
279	} else {
280	/* Allow huge page size encoding in flags. */
281	if (flags & ~(unsigned int)(MFD_ALL_FLAGS \|
282	(MFD_HUGE_MASK << MFD_HUGE_SHIFT)))
283	return -EINVAL;
284	}
285
286	/* length includes terminating zero */
287	len = strnlen_user(uname, MFD_NAME_MAX_LEN + 1);
288	if (len <= 0)
289	return -EFAULT;
290	if (len > MFD_NAME_MAX_LEN + 1)
291	return -EINVAL;
292
293	name = kmalloc(len + MFD_NAME_PREFIX_LEN, GFP_KERNEL);
294	if (!name)
295	return -ENOMEM;
296
297	strcpy(name, MFD_NAME_PREFIX);
298	if (copy_from_user(&name[MFD_NAME_PREFIX_LEN], uname, len)) {
299	error = -EFAULT;
300	goto err_name;
301	}
302
303	/* terminating-zero may have changed after strnlen_user() returned */
304	if (name[len + MFD_NAME_PREFIX_LEN - 1]) {
305	error = -EFAULT;
306	goto err_name;
307	}
308
309	fd = get_unused_fd_flags((flags & MFD_CLOEXEC) ? O_CLOEXEC : 0);
310	if (fd < 0) {
311	error = fd;
312	goto err_name;
313	}
314
315	if (flags & MFD_HUGETLB) {
d7c9e99a	316	struct ucounts *ucounts = NULL;
5d752600	317
d7c9e99a	318	file = hugetlb_file_setup(name, 0, VM_NORESERVE, &ucounts,
5d752600 MK	319	HUGETLB_ANONHUGE_INODE,
	320	(flags >> MFD_HUGE_SHIFT) &
	321	MFD_HUGE_MASK);
	322	} else
	323	file = shmem_file_setup(name, 0, VM_NORESERVE);
	324	if (IS_ERR(file)) {
	325	error = PTR_ERR(file);
	326	goto err_fd;
	327	}
	328	file->f_mode \|= FMODE_LSEEK \| FMODE_PREAD \| FMODE_PWRITE;
c9c554f2	329	file->f_flags \|= O_LARGEFILE;
5d752600 MK	330
	331	if (flags & MFD_ALLOW_SEALING) {
	332	file_seals = memfd_file_seals_ptr(file);
	333	*file_seals &= ~F_SEAL_SEAL;
	334	}
	335
	336	fd_install(fd, file);
	337	kfree(name);
	338	return fd;
	339
	340	err_fd:
	341	put_unused_fd(fd);
	342	err_name:
	343	kfree(name);
	344	return error;
	345	}