blob: 66cdb44616d5a0ba79a04f60de5fd835805b6e56 [file] [log] [blame]
Andrea Arcangeli86039bd2015-09-04 15:46:31 -07001/*
2 * fs/userfaultfd.c
3 *
4 * Copyright (C) 2007 Davide Libenzi <davidel@xmailserver.org>
5 * Copyright (C) 2008-2009 Red Hat, Inc.
6 * Copyright (C) 2015 Red Hat, Inc.
7 *
8 * This work is licensed under the terms of the GNU GPL, version 2. See
9 * the COPYING file in the top-level directory.
10 *
11 * Some part derived from fs/eventfd.c (anon inode setup) and
12 * mm/ksm.c (mm hashing).
13 */
14
15#include <linux/hashtable.h>
16#include <linux/sched.h>
17#include <linux/mm.h>
18#include <linux/poll.h>
19#include <linux/slab.h>
20#include <linux/seq_file.h>
21#include <linux/file.h>
22#include <linux/bug.h>
23#include <linux/anon_inodes.h>
24#include <linux/syscalls.h>
25#include <linux/userfaultfd_k.h>
26#include <linux/mempolicy.h>
27#include <linux/ioctl.h>
28#include <linux/security.h>
29
Andrea Arcangeli3004ec92015-09-04 15:46:48 -070030static struct kmem_cache *userfaultfd_ctx_cachep __read_mostly;
31
Andrea Arcangeli86039bd2015-09-04 15:46:31 -070032enum userfaultfd_state {
33 UFFD_STATE_WAIT_API,
34 UFFD_STATE_RUNNING,
35};
36
Andrea Arcangeli3004ec92015-09-04 15:46:48 -070037/*
38 * Start with fault_pending_wqh and fault_wqh so they're more likely
39 * to be in the same cacheline.
40 */
Andrea Arcangeli86039bd2015-09-04 15:46:31 -070041struct userfaultfd_ctx {
Andrea Arcangeli15b726e2015-09-04 15:46:44 -070042 /* waitqueue head for the pending (i.e. not read) userfaults */
43 wait_queue_head_t fault_pending_wqh;
44 /* waitqueue head for the userfaults */
Andrea Arcangeli86039bd2015-09-04 15:46:31 -070045 wait_queue_head_t fault_wqh;
46 /* waitqueue head for the pseudo fd to wakeup poll/read */
47 wait_queue_head_t fd_wqh;
Andrea Arcangeli2c5b7e12015-09-04 15:47:23 -070048 /* a refile sequence protected by fault_pending_wqh lock */
49 struct seqcount refile_seq;
Andrea Arcangeli3004ec92015-09-04 15:46:48 -070050 /* pseudo fd refcounting */
51 atomic_t refcount;
Andrea Arcangeli86039bd2015-09-04 15:46:31 -070052 /* userfaultfd syscall flags */
53 unsigned int flags;
54 /* state machine */
55 enum userfaultfd_state state;
56 /* released */
57 bool released;
58 /* mm with one ore more vmas attached to this userfaultfd_ctx */
59 struct mm_struct *mm;
60};
61
62struct userfaultfd_wait_queue {
Andrea Arcangelia9b85f92015-09-04 15:46:37 -070063 struct uffd_msg msg;
Andrea Arcangeli86039bd2015-09-04 15:46:31 -070064 wait_queue_t wq;
Andrea Arcangeli86039bd2015-09-04 15:46:31 -070065 struct userfaultfd_ctx *ctx;
66};
67
68struct userfaultfd_wake_range {
69 unsigned long start;
70 unsigned long len;
71};
72
73static int userfaultfd_wake_function(wait_queue_t *wq, unsigned mode,
74 int wake_flags, void *key)
75{
76 struct userfaultfd_wake_range *range = key;
77 int ret;
78 struct userfaultfd_wait_queue *uwq;
79 unsigned long start, len;
80
81 uwq = container_of(wq, struct userfaultfd_wait_queue, wq);
82 ret = 0;
Andrea Arcangeli86039bd2015-09-04 15:46:31 -070083 /* len == 0 means wake all */
84 start = range->start;
85 len = range->len;
Andrea Arcangelia9b85f92015-09-04 15:46:37 -070086 if (len && (start > uwq->msg.arg.pagefault.address ||
87 start + len <= uwq->msg.arg.pagefault.address))
Andrea Arcangeli86039bd2015-09-04 15:46:31 -070088 goto out;
89 ret = wake_up_state(wq->private, mode);
90 if (ret)
91 /*
92 * Wake only once, autoremove behavior.
93 *
94 * After the effect of list_del_init is visible to the
95 * other CPUs, the waitqueue may disappear from under
96 * us, see the !list_empty_careful() in
97 * handle_userfault(). try_to_wake_up() has an
98 * implicit smp_mb__before_spinlock, and the
99 * wq->private is read before calling the extern
100 * function "wake_up_state" (which in turns calls
101 * try_to_wake_up). While the spin_lock;spin_unlock;
102 * wouldn't be enough, the smp_mb__before_spinlock is
103 * enough to avoid an explicit smp_mb() here.
104 */
105 list_del_init(&wq->task_list);
106out:
107 return ret;
108}
109
110/**
111 * userfaultfd_ctx_get - Acquires a reference to the internal userfaultfd
112 * context.
113 * @ctx: [in] Pointer to the userfaultfd context.
114 *
115 * Returns: In case of success, returns not zero.
116 */
117static void userfaultfd_ctx_get(struct userfaultfd_ctx *ctx)
118{
119 if (!atomic_inc_not_zero(&ctx->refcount))
120 BUG();
121}
122
123/**
124 * userfaultfd_ctx_put - Releases a reference to the internal userfaultfd
125 * context.
126 * @ctx: [in] Pointer to userfaultfd context.
127 *
128 * The userfaultfd context reference must have been previously acquired either
129 * with userfaultfd_ctx_get() or userfaultfd_ctx_fdget().
130 */
131static void userfaultfd_ctx_put(struct userfaultfd_ctx *ctx)
132{
133 if (atomic_dec_and_test(&ctx->refcount)) {
134 VM_BUG_ON(spin_is_locked(&ctx->fault_pending_wqh.lock));
135 VM_BUG_ON(waitqueue_active(&ctx->fault_pending_wqh));
136 VM_BUG_ON(spin_is_locked(&ctx->fault_wqh.lock));
137 VM_BUG_ON(waitqueue_active(&ctx->fault_wqh));
138 VM_BUG_ON(spin_is_locked(&ctx->fd_wqh.lock));
139 VM_BUG_ON(waitqueue_active(&ctx->fd_wqh));
140 mmput(ctx->mm);
Andrea Arcangeli3004ec92015-09-04 15:46:48 -0700141 kmem_cache_free(userfaultfd_ctx_cachep, ctx);
Andrea Arcangeli86039bd2015-09-04 15:46:31 -0700142 }
143}
144
Andrea Arcangelia9b85f92015-09-04 15:46:37 -0700145static inline void msg_init(struct uffd_msg *msg)
Andrea Arcangeli86039bd2015-09-04 15:46:31 -0700146{
Andrea Arcangelia9b85f92015-09-04 15:46:37 -0700147 BUILD_BUG_ON(sizeof(struct uffd_msg) != 32);
148 /*
149 * Must use memset to zero out the paddings or kernel data is
150 * leaked to userland.
151 */
152 memset(msg, 0, sizeof(struct uffd_msg));
153}
154
155static inline struct uffd_msg userfault_msg(unsigned long address,
156 unsigned int flags,
157 unsigned long reason)
158{
159 struct uffd_msg msg;
160 msg_init(&msg);
161 msg.event = UFFD_EVENT_PAGEFAULT;
162 msg.arg.pagefault.address = address;
Andrea Arcangeli86039bd2015-09-04 15:46:31 -0700163 if (flags & FAULT_FLAG_WRITE)
164 /*
Andrea Arcangelia9b85f92015-09-04 15:46:37 -0700165 * If UFFD_FEATURE_PAGEFAULT_FLAG_WRITE was set in the
166 * uffdio_api.features and UFFD_PAGEFAULT_FLAG_WRITE
167 * was not set in a UFFD_EVENT_PAGEFAULT, it means it
168 * was a read fault, otherwise if set it means it's
169 * a write fault.
Andrea Arcangeli86039bd2015-09-04 15:46:31 -0700170 */
Andrea Arcangelia9b85f92015-09-04 15:46:37 -0700171 msg.arg.pagefault.flags |= UFFD_PAGEFAULT_FLAG_WRITE;
Andrea Arcangeli86039bd2015-09-04 15:46:31 -0700172 if (reason & VM_UFFD_WP)
173 /*
Andrea Arcangelia9b85f92015-09-04 15:46:37 -0700174 * If UFFD_FEATURE_PAGEFAULT_FLAG_WP was set in the
175 * uffdio_api.features and UFFD_PAGEFAULT_FLAG_WP was
176 * not set in a UFFD_EVENT_PAGEFAULT, it means it was
177 * a missing fault, otherwise if set it means it's a
178 * write protect fault.
Andrea Arcangeli86039bd2015-09-04 15:46:31 -0700179 */
Andrea Arcangelia9b85f92015-09-04 15:46:37 -0700180 msg.arg.pagefault.flags |= UFFD_PAGEFAULT_FLAG_WP;
181 return msg;
Andrea Arcangeli86039bd2015-09-04 15:46:31 -0700182}
183
184/*
Andrea Arcangeli8d2afd92015-09-04 15:46:51 -0700185 * Verify the pagetables are still not ok after having reigstered into
186 * the fault_pending_wqh to avoid userland having to UFFDIO_WAKE any
187 * userfault that has already been resolved, if userfaultfd_read and
188 * UFFDIO_COPY|ZEROPAGE are being run simultaneously on two different
189 * threads.
190 */
191static inline bool userfaultfd_must_wait(struct userfaultfd_ctx *ctx,
192 unsigned long address,
193 unsigned long flags,
194 unsigned long reason)
195{
196 struct mm_struct *mm = ctx->mm;
197 pgd_t *pgd;
198 pud_t *pud;
199 pmd_t *pmd, _pmd;
200 pte_t *pte;
201 bool ret = true;
202
203 VM_BUG_ON(!rwsem_is_locked(&mm->mmap_sem));
204
205 pgd = pgd_offset(mm, address);
206 if (!pgd_present(*pgd))
207 goto out;
208 pud = pud_offset(pgd, address);
209 if (!pud_present(*pud))
210 goto out;
211 pmd = pmd_offset(pud, address);
212 /*
213 * READ_ONCE must function as a barrier with narrower scope
214 * and it must be equivalent to:
215 * _pmd = *pmd; barrier();
216 *
217 * This is to deal with the instability (as in
218 * pmd_trans_unstable) of the pmd.
219 */
220 _pmd = READ_ONCE(*pmd);
221 if (!pmd_present(_pmd))
222 goto out;
223
224 ret = false;
225 if (pmd_trans_huge(_pmd))
226 goto out;
227
228 /*
229 * the pmd is stable (as in !pmd_trans_unstable) so we can re-read it
230 * and use the standard pte_offset_map() instead of parsing _pmd.
231 */
232 pte = pte_offset_map(pmd, address);
233 /*
234 * Lockless access: we're in a wait_event so it's ok if it
235 * changes under us.
236 */
237 if (pte_none(*pte))
238 ret = true;
239 pte_unmap(pte);
240
241out:
242 return ret;
243}
244
245/*
Andrea Arcangeli86039bd2015-09-04 15:46:31 -0700246 * The locking rules involved in returning VM_FAULT_RETRY depending on
247 * FAULT_FLAG_ALLOW_RETRY, FAULT_FLAG_RETRY_NOWAIT and
248 * FAULT_FLAG_KILLABLE are not straightforward. The "Caution"
249 * recommendation in __lock_page_or_retry is not an understatement.
250 *
251 * If FAULT_FLAG_ALLOW_RETRY is set, the mmap_sem must be released
252 * before returning VM_FAULT_RETRY only if FAULT_FLAG_RETRY_NOWAIT is
253 * not set.
254 *
255 * If FAULT_FLAG_ALLOW_RETRY is set but FAULT_FLAG_KILLABLE is not
256 * set, VM_FAULT_RETRY can still be returned if and only if there are
257 * fatal_signal_pending()s, and the mmap_sem must be released before
258 * returning it.
259 */
260int handle_userfault(struct vm_area_struct *vma, unsigned long address,
261 unsigned int flags, unsigned long reason)
262{
263 struct mm_struct *mm = vma->vm_mm;
264 struct userfaultfd_ctx *ctx;
265 struct userfaultfd_wait_queue uwq;
Andrea Arcangeliba85c702015-09-04 15:46:41 -0700266 int ret;
Andrea Arcangelidfa37dc2015-09-04 15:47:18 -0700267 bool must_wait, return_to_userland;
Andrea Arcangeli86039bd2015-09-04 15:46:31 -0700268
269 BUG_ON(!rwsem_is_locked(&mm->mmap_sem));
270
Andrea Arcangeliba85c702015-09-04 15:46:41 -0700271 ret = VM_FAULT_SIGBUS;
Andrea Arcangeli86039bd2015-09-04 15:46:31 -0700272 ctx = vma->vm_userfaultfd_ctx.ctx;
273 if (!ctx)
Andrea Arcangeliba85c702015-09-04 15:46:41 -0700274 goto out;
Andrea Arcangeli86039bd2015-09-04 15:46:31 -0700275
276 BUG_ON(ctx->mm != mm);
277
278 VM_BUG_ON(reason & ~(VM_UFFD_MISSING|VM_UFFD_WP));
279 VM_BUG_ON(!(reason & VM_UFFD_MISSING) ^ !!(reason & VM_UFFD_WP));
280
281 /*
282 * If it's already released don't get it. This avoids to loop
283 * in __get_user_pages if userfaultfd_release waits on the
284 * caller of handle_userfault to release the mmap_sem.
285 */
286 if (unlikely(ACCESS_ONCE(ctx->released)))
Andrea Arcangeliba85c702015-09-04 15:46:41 -0700287 goto out;
Andrea Arcangeli86039bd2015-09-04 15:46:31 -0700288
289 /*
Linus Torvalds39680f52016-03-01 11:56:22 -0800290 * We don't do userfault handling for the final child pid update.
291 */
292 if (current->flags & PF_EXITING)
293 goto out;
294
295 /*
Andrea Arcangeli86039bd2015-09-04 15:46:31 -0700296 * Check that we can return VM_FAULT_RETRY.
297 *
298 * NOTE: it should become possible to return VM_FAULT_RETRY
299 * even if FAULT_FLAG_TRIED is set without leading to gup()
300 * -EBUSY failures, if the userfaultfd is to be extended for
301 * VM_UFFD_WP tracking and we intend to arm the userfault
302 * without first stopping userland access to the memory. For
303 * VM_UFFD_MISSING userfaults this is enough for now.
304 */
305 if (unlikely(!(flags & FAULT_FLAG_ALLOW_RETRY))) {
306 /*
307 * Validate the invariant that nowait must allow retry
308 * to be sure not to return SIGBUS erroneously on
309 * nowait invocations.
310 */
311 BUG_ON(flags & FAULT_FLAG_RETRY_NOWAIT);
312#ifdef CONFIG_DEBUG_VM
313 if (printk_ratelimit()) {
314 printk(KERN_WARNING
315 "FAULT_FLAG_ALLOW_RETRY missing %x\n", flags);
316 dump_stack();
317 }
318#endif
Andrea Arcangeliba85c702015-09-04 15:46:41 -0700319 goto out;
Andrea Arcangeli86039bd2015-09-04 15:46:31 -0700320 }
321
322 /*
323 * Handle nowait, not much to do other than tell it to retry
324 * and wait.
325 */
Andrea Arcangeliba85c702015-09-04 15:46:41 -0700326 ret = VM_FAULT_RETRY;
Andrea Arcangeli86039bd2015-09-04 15:46:31 -0700327 if (flags & FAULT_FLAG_RETRY_NOWAIT)
Andrea Arcangeliba85c702015-09-04 15:46:41 -0700328 goto out;
Andrea Arcangeli86039bd2015-09-04 15:46:31 -0700329
330 /* take the reference before dropping the mmap_sem */
331 userfaultfd_ctx_get(ctx);
332
Andrea Arcangeli86039bd2015-09-04 15:46:31 -0700333 init_waitqueue_func_entry(&uwq.wq, userfaultfd_wake_function);
334 uwq.wq.private = current;
Andrea Arcangelia9b85f92015-09-04 15:46:37 -0700335 uwq.msg = userfault_msg(address, flags, reason);
Andrea Arcangeli86039bd2015-09-04 15:46:31 -0700336 uwq.ctx = ctx;
337
Andrea Arcangelidfa37dc2015-09-04 15:47:18 -0700338 return_to_userland = (flags & (FAULT_FLAG_USER|FAULT_FLAG_KILLABLE)) ==
339 (FAULT_FLAG_USER|FAULT_FLAG_KILLABLE);
340
Andrea Arcangeli15b726e2015-09-04 15:46:44 -0700341 spin_lock(&ctx->fault_pending_wqh.lock);
Andrea Arcangeli86039bd2015-09-04 15:46:31 -0700342 /*
343 * After the __add_wait_queue the uwq is visible to userland
344 * through poll/read().
345 */
Andrea Arcangeli15b726e2015-09-04 15:46:44 -0700346 __add_wait_queue(&ctx->fault_pending_wqh, &uwq.wq);
347 /*
348 * The smp_mb() after __set_current_state prevents the reads
349 * following the spin_unlock to happen before the list_add in
350 * __add_wait_queue.
351 */
Andrea Arcangelidfa37dc2015-09-04 15:47:18 -0700352 set_current_state(return_to_userland ? TASK_INTERRUPTIBLE :
353 TASK_KILLABLE);
Andrea Arcangeli15b726e2015-09-04 15:46:44 -0700354 spin_unlock(&ctx->fault_pending_wqh.lock);
Andrea Arcangeli86039bd2015-09-04 15:46:31 -0700355
Andrea Arcangeli8d2afd92015-09-04 15:46:51 -0700356 must_wait = userfaultfd_must_wait(ctx, address, flags, reason);
357 up_read(&mm->mmap_sem);
358
359 if (likely(must_wait && !ACCESS_ONCE(ctx->released) &&
Andrea Arcangelidfa37dc2015-09-04 15:47:18 -0700360 (return_to_userland ? !signal_pending(current) :
361 !fatal_signal_pending(current)))) {
Andrea Arcangeli86039bd2015-09-04 15:46:31 -0700362 wake_up_poll(&ctx->fd_wqh, POLLIN);
363 schedule();
Andrea Arcangeliba85c702015-09-04 15:46:41 -0700364 ret |= VM_FAULT_MAJOR;
Andrea Arcangeli86039bd2015-09-04 15:46:31 -0700365 }
Andrea Arcangeliba85c702015-09-04 15:46:41 -0700366
Andrea Arcangeli86039bd2015-09-04 15:46:31 -0700367 __set_current_state(TASK_RUNNING);
Andrea Arcangeli15b726e2015-09-04 15:46:44 -0700368
Andrea Arcangelidfa37dc2015-09-04 15:47:18 -0700369 if (return_to_userland) {
370 if (signal_pending(current) &&
371 !fatal_signal_pending(current)) {
372 /*
373 * If we got a SIGSTOP or SIGCONT and this is
374 * a normal userland page fault, just let
375 * userland return so the signal will be
376 * handled and gdb debugging works. The page
377 * fault code immediately after we return from
378 * this function is going to release the
379 * mmap_sem and it's not depending on it
380 * (unlike gup would if we were not to return
381 * VM_FAULT_RETRY).
382 *
383 * If a fatal signal is pending we still take
384 * the streamlined VM_FAULT_RETRY failure path
385 * and there's no need to retake the mmap_sem
386 * in such case.
387 */
388 down_read(&mm->mmap_sem);
389 ret = 0;
390 }
391 }
392
Andrea Arcangeli15b726e2015-09-04 15:46:44 -0700393 /*
394 * Here we race with the list_del; list_add in
395 * userfaultfd_ctx_read(), however because we don't ever run
396 * list_del_init() to refile across the two lists, the prev
397 * and next pointers will never point to self. list_add also
398 * would never let any of the two pointers to point to
399 * self. So list_empty_careful won't risk to see both pointers
400 * pointing to self at any time during the list refile. The
401 * only case where list_del_init() is called is the full
402 * removal in the wake function and there we don't re-list_add
403 * and it's fine not to block on the spinlock. The uwq on this
404 * kernel stack can be released after the list_del_init.
405 */
Andrea Arcangeliba85c702015-09-04 15:46:41 -0700406 if (!list_empty_careful(&uwq.wq.task_list)) {
Andrea Arcangeli15b726e2015-09-04 15:46:44 -0700407 spin_lock(&ctx->fault_pending_wqh.lock);
408 /*
409 * No need of list_del_init(), the uwq on the stack
410 * will be freed shortly anyway.
411 */
412 list_del(&uwq.wq.task_list);
413 spin_unlock(&ctx->fault_pending_wqh.lock);
Andrea Arcangeliba85c702015-09-04 15:46:41 -0700414 }
Andrea Arcangeli86039bd2015-09-04 15:46:31 -0700415
416 /*
417 * ctx may go away after this if the userfault pseudo fd is
418 * already released.
419 */
420 userfaultfd_ctx_put(ctx);
421
Andrea Arcangeliba85c702015-09-04 15:46:41 -0700422out:
423 return ret;
Andrea Arcangeli86039bd2015-09-04 15:46:31 -0700424}
425
426static int userfaultfd_release(struct inode *inode, struct file *file)
427{
428 struct userfaultfd_ctx *ctx = file->private_data;
429 struct mm_struct *mm = ctx->mm;
430 struct vm_area_struct *vma, *prev;
431 /* len == 0 means wake all */
432 struct userfaultfd_wake_range range = { .len = 0, };
433 unsigned long new_flags;
434
435 ACCESS_ONCE(ctx->released) = true;
436
437 /*
438 * Flush page faults out of all CPUs. NOTE: all page faults
439 * must be retried without returning VM_FAULT_SIGBUS if
440 * userfaultfd_ctx_get() succeeds but vma->vma_userfault_ctx
441 * changes while handle_userfault released the mmap_sem. So
442 * it's critical that released is set to true (above), before
443 * taking the mmap_sem for writing.
444 */
445 down_write(&mm->mmap_sem);
446 prev = NULL;
447 for (vma = mm->mmap; vma; vma = vma->vm_next) {
448 cond_resched();
449 BUG_ON(!!vma->vm_userfaultfd_ctx.ctx ^
450 !!(vma->vm_flags & (VM_UFFD_MISSING | VM_UFFD_WP)));
451 if (vma->vm_userfaultfd_ctx.ctx != ctx) {
452 prev = vma;
453 continue;
454 }
455 new_flags = vma->vm_flags & ~(VM_UFFD_MISSING | VM_UFFD_WP);
456 prev = vma_merge(mm, prev, vma->vm_start, vma->vm_end,
457 new_flags, vma->anon_vma,
458 vma->vm_file, vma->vm_pgoff,
459 vma_policy(vma),
460 NULL_VM_UFFD_CTX);
461 if (prev)
462 vma = prev;
463 else
464 prev = vma;
465 vma->vm_flags = new_flags;
466 vma->vm_userfaultfd_ctx = NULL_VM_UFFD_CTX;
467 }
468 up_write(&mm->mmap_sem);
469
470 /*
Andrea Arcangeli15b726e2015-09-04 15:46:44 -0700471 * After no new page faults can wait on this fault_*wqh, flush
Andrea Arcangeli86039bd2015-09-04 15:46:31 -0700472 * the last page faults that may have been already waiting on
Andrea Arcangeli15b726e2015-09-04 15:46:44 -0700473 * the fault_*wqh.
Andrea Arcangeli86039bd2015-09-04 15:46:31 -0700474 */
Andrea Arcangeli15b726e2015-09-04 15:46:44 -0700475 spin_lock(&ctx->fault_pending_wqh.lock);
Andrea Arcangeliac5be6b2015-09-22 14:58:49 -0700476 __wake_up_locked_key(&ctx->fault_pending_wqh, TASK_NORMAL, &range);
477 __wake_up_locked_key(&ctx->fault_wqh, TASK_NORMAL, &range);
Andrea Arcangeli15b726e2015-09-04 15:46:44 -0700478 spin_unlock(&ctx->fault_pending_wqh.lock);
Andrea Arcangeli86039bd2015-09-04 15:46:31 -0700479
480 wake_up_poll(&ctx->fd_wqh, POLLHUP);
481 userfaultfd_ctx_put(ctx);
482 return 0;
483}
484
Andrea Arcangeli15b726e2015-09-04 15:46:44 -0700485/* fault_pending_wqh.lock must be hold by the caller */
486static inline struct userfaultfd_wait_queue *find_userfault(
487 struct userfaultfd_ctx *ctx)
Andrea Arcangeli86039bd2015-09-04 15:46:31 -0700488{
489 wait_queue_t *wq;
Andrea Arcangeli15b726e2015-09-04 15:46:44 -0700490 struct userfaultfd_wait_queue *uwq;
Andrea Arcangeli86039bd2015-09-04 15:46:31 -0700491
Andrea Arcangeli15b726e2015-09-04 15:46:44 -0700492 VM_BUG_ON(!spin_is_locked(&ctx->fault_pending_wqh.lock));
Andrea Arcangeli86039bd2015-09-04 15:46:31 -0700493
Andrea Arcangeli15b726e2015-09-04 15:46:44 -0700494 uwq = NULL;
495 if (!waitqueue_active(&ctx->fault_pending_wqh))
496 goto out;
497 /* walk in reverse to provide FIFO behavior to read userfaults */
498 wq = list_last_entry(&ctx->fault_pending_wqh.task_list,
499 typeof(*wq), task_list);
500 uwq = container_of(wq, struct userfaultfd_wait_queue, wq);
501out:
502 return uwq;
Andrea Arcangeli86039bd2015-09-04 15:46:31 -0700503}
504
505static unsigned int userfaultfd_poll(struct file *file, poll_table *wait)
506{
507 struct userfaultfd_ctx *ctx = file->private_data;
508 unsigned int ret;
509
510 poll_wait(file, &ctx->fd_wqh, wait);
511
512 switch (ctx->state) {
513 case UFFD_STATE_WAIT_API:
514 return POLLERR;
515 case UFFD_STATE_RUNNING:
Andrea Arcangeliba85c702015-09-04 15:46:41 -0700516 /*
517 * poll() never guarantees that read won't block.
518 * userfaults can be waken before they're read().
519 */
520 if (unlikely(!(file->f_flags & O_NONBLOCK)))
521 return POLLERR;
Andrea Arcangeli15b726e2015-09-04 15:46:44 -0700522 /*
523 * lockless access to see if there are pending faults
524 * __pollwait last action is the add_wait_queue but
525 * the spin_unlock would allow the waitqueue_active to
526 * pass above the actual list_add inside
527 * add_wait_queue critical section. So use a full
528 * memory barrier to serialize the list_add write of
529 * add_wait_queue() with the waitqueue_active read
530 * below.
531 */
532 ret = 0;
533 smp_mb();
534 if (waitqueue_active(&ctx->fault_pending_wqh))
535 ret = POLLIN;
Andrea Arcangeli86039bd2015-09-04 15:46:31 -0700536 return ret;
537 default:
538 BUG();
539 }
540}
541
542static ssize_t userfaultfd_ctx_read(struct userfaultfd_ctx *ctx, int no_wait,
Andrea Arcangelia9b85f92015-09-04 15:46:37 -0700543 struct uffd_msg *msg)
Andrea Arcangeli86039bd2015-09-04 15:46:31 -0700544{
545 ssize_t ret;
546 DECLARE_WAITQUEUE(wait, current);
Andrea Arcangeli15b726e2015-09-04 15:46:44 -0700547 struct userfaultfd_wait_queue *uwq;
Andrea Arcangeli86039bd2015-09-04 15:46:31 -0700548
Andrea Arcangeli15b726e2015-09-04 15:46:44 -0700549 /* always take the fd_wqh lock before the fault_pending_wqh lock */
Andrea Arcangeli86039bd2015-09-04 15:46:31 -0700550 spin_lock(&ctx->fd_wqh.lock);
551 __add_wait_queue(&ctx->fd_wqh, &wait);
552 for (;;) {
553 set_current_state(TASK_INTERRUPTIBLE);
Andrea Arcangeli15b726e2015-09-04 15:46:44 -0700554 spin_lock(&ctx->fault_pending_wqh.lock);
555 uwq = find_userfault(ctx);
556 if (uwq) {
Andrea Arcangeli86039bd2015-09-04 15:46:31 -0700557 /*
Andrea Arcangeli2c5b7e12015-09-04 15:47:23 -0700558 * Use a seqcount to repeat the lockless check
559 * in wake_userfault() to avoid missing
560 * wakeups because during the refile both
561 * waitqueue could become empty if this is the
562 * only userfault.
563 */
564 write_seqcount_begin(&ctx->refile_seq);
565
566 /*
Andrea Arcangeli15b726e2015-09-04 15:46:44 -0700567 * The fault_pending_wqh.lock prevents the uwq
568 * to disappear from under us.
569 *
570 * Refile this userfault from
571 * fault_pending_wqh to fault_wqh, it's not
572 * pending anymore after we read it.
573 *
574 * Use list_del() by hand (as
575 * userfaultfd_wake_function also uses
576 * list_del_init() by hand) to be sure nobody
577 * changes __remove_wait_queue() to use
578 * list_del_init() in turn breaking the
579 * !list_empty_careful() check in
580 * handle_userfault(). The uwq->wq.task_list
581 * must never be empty at any time during the
582 * refile, or the waitqueue could disappear
583 * from under us. The "wait_queue_head_t"
584 * parameter of __remove_wait_queue() is unused
585 * anyway.
Andrea Arcangeli86039bd2015-09-04 15:46:31 -0700586 */
Andrea Arcangeli15b726e2015-09-04 15:46:44 -0700587 list_del(&uwq->wq.task_list);
588 __add_wait_queue(&ctx->fault_wqh, &uwq->wq);
589
Andrea Arcangeli2c5b7e12015-09-04 15:47:23 -0700590 write_seqcount_end(&ctx->refile_seq);
591
Andrea Arcangelia9b85f92015-09-04 15:46:37 -0700592 /* careful to always initialize msg if ret == 0 */
593 *msg = uwq->msg;
Andrea Arcangeli15b726e2015-09-04 15:46:44 -0700594 spin_unlock(&ctx->fault_pending_wqh.lock);
Andrea Arcangeli86039bd2015-09-04 15:46:31 -0700595 ret = 0;
596 break;
597 }
Andrea Arcangeli15b726e2015-09-04 15:46:44 -0700598 spin_unlock(&ctx->fault_pending_wqh.lock);
Andrea Arcangeli86039bd2015-09-04 15:46:31 -0700599 if (signal_pending(current)) {
600 ret = -ERESTARTSYS;
601 break;
602 }
603 if (no_wait) {
604 ret = -EAGAIN;
605 break;
606 }
607 spin_unlock(&ctx->fd_wqh.lock);
608 schedule();
609 spin_lock(&ctx->fd_wqh.lock);
610 }
611 __remove_wait_queue(&ctx->fd_wqh, &wait);
612 __set_current_state(TASK_RUNNING);
613 spin_unlock(&ctx->fd_wqh.lock);
614
615 return ret;
616}
617
618static ssize_t userfaultfd_read(struct file *file, char __user *buf,
619 size_t count, loff_t *ppos)
620{
621 struct userfaultfd_ctx *ctx = file->private_data;
622 ssize_t _ret, ret = 0;
Andrea Arcangelia9b85f92015-09-04 15:46:37 -0700623 struct uffd_msg msg;
Andrea Arcangeli86039bd2015-09-04 15:46:31 -0700624 int no_wait = file->f_flags & O_NONBLOCK;
625
626 if (ctx->state == UFFD_STATE_WAIT_API)
627 return -EINVAL;
Andrea Arcangeli86039bd2015-09-04 15:46:31 -0700628
629 for (;;) {
Andrea Arcangelia9b85f92015-09-04 15:46:37 -0700630 if (count < sizeof(msg))
Andrea Arcangeli86039bd2015-09-04 15:46:31 -0700631 return ret ? ret : -EINVAL;
Andrea Arcangelia9b85f92015-09-04 15:46:37 -0700632 _ret = userfaultfd_ctx_read(ctx, no_wait, &msg);
Andrea Arcangeli86039bd2015-09-04 15:46:31 -0700633 if (_ret < 0)
634 return ret ? ret : _ret;
Andrea Arcangelia9b85f92015-09-04 15:46:37 -0700635 if (copy_to_user((__u64 __user *) buf, &msg, sizeof(msg)))
Andrea Arcangeli86039bd2015-09-04 15:46:31 -0700636 return ret ? ret : -EFAULT;
Andrea Arcangelia9b85f92015-09-04 15:46:37 -0700637 ret += sizeof(msg);
638 buf += sizeof(msg);
639 count -= sizeof(msg);
Andrea Arcangeli86039bd2015-09-04 15:46:31 -0700640 /*
641 * Allow to read more than one fault at time but only
642 * block if waiting for the very first one.
643 */
644 no_wait = O_NONBLOCK;
645 }
646}
647
648static void __wake_userfault(struct userfaultfd_ctx *ctx,
649 struct userfaultfd_wake_range *range)
650{
651 unsigned long start, end;
652
653 start = range->start;
654 end = range->start + range->len;
655
Andrea Arcangeli15b726e2015-09-04 15:46:44 -0700656 spin_lock(&ctx->fault_pending_wqh.lock);
Andrea Arcangeli86039bd2015-09-04 15:46:31 -0700657 /* wake all in the range and autoremove */
Andrea Arcangeli15b726e2015-09-04 15:46:44 -0700658 if (waitqueue_active(&ctx->fault_pending_wqh))
Andrea Arcangeliac5be6b2015-09-22 14:58:49 -0700659 __wake_up_locked_key(&ctx->fault_pending_wqh, TASK_NORMAL,
Andrea Arcangeli15b726e2015-09-04 15:46:44 -0700660 range);
661 if (waitqueue_active(&ctx->fault_wqh))
Andrea Arcangeliac5be6b2015-09-22 14:58:49 -0700662 __wake_up_locked_key(&ctx->fault_wqh, TASK_NORMAL, range);
Andrea Arcangeli15b726e2015-09-04 15:46:44 -0700663 spin_unlock(&ctx->fault_pending_wqh.lock);
Andrea Arcangeli86039bd2015-09-04 15:46:31 -0700664}
665
666static __always_inline void wake_userfault(struct userfaultfd_ctx *ctx,
667 struct userfaultfd_wake_range *range)
668{
Andrea Arcangeli2c5b7e12015-09-04 15:47:23 -0700669 unsigned seq;
670 bool need_wakeup;
671
Andrea Arcangeli86039bd2015-09-04 15:46:31 -0700672 /*
673 * To be sure waitqueue_active() is not reordered by the CPU
674 * before the pagetable update, use an explicit SMP memory
675 * barrier here. PT lock release or up_read(mmap_sem) still
676 * have release semantics that can allow the
677 * waitqueue_active() to be reordered before the pte update.
678 */
679 smp_mb();
680
681 /*
682 * Use waitqueue_active because it's very frequent to
683 * change the address space atomically even if there are no
684 * userfaults yet. So we take the spinlock only when we're
685 * sure we've userfaults to wake.
686 */
Andrea Arcangeli2c5b7e12015-09-04 15:47:23 -0700687 do {
688 seq = read_seqcount_begin(&ctx->refile_seq);
689 need_wakeup = waitqueue_active(&ctx->fault_pending_wqh) ||
690 waitqueue_active(&ctx->fault_wqh);
691 cond_resched();
692 } while (read_seqcount_retry(&ctx->refile_seq, seq));
693 if (need_wakeup)
Andrea Arcangeli86039bd2015-09-04 15:46:31 -0700694 __wake_userfault(ctx, range);
695}
696
697static __always_inline int validate_range(struct mm_struct *mm,
698 __u64 start, __u64 len)
699{
700 __u64 task_size = mm->task_size;
701
702 if (start & ~PAGE_MASK)
703 return -EINVAL;
704 if (len & ~PAGE_MASK)
705 return -EINVAL;
706 if (!len)
707 return -EINVAL;
708 if (start < mmap_min_addr)
709 return -EINVAL;
710 if (start >= task_size)
711 return -EINVAL;
712 if (len > task_size - start)
713 return -EINVAL;
714 return 0;
715}
716
717static int userfaultfd_register(struct userfaultfd_ctx *ctx,
718 unsigned long arg)
719{
720 struct mm_struct *mm = ctx->mm;
721 struct vm_area_struct *vma, *prev, *cur;
722 int ret;
723 struct uffdio_register uffdio_register;
724 struct uffdio_register __user *user_uffdio_register;
725 unsigned long vm_flags, new_flags;
726 bool found;
727 unsigned long start, end, vma_end;
728
729 user_uffdio_register = (struct uffdio_register __user *) arg;
730
731 ret = -EFAULT;
732 if (copy_from_user(&uffdio_register, user_uffdio_register,
733 sizeof(uffdio_register)-sizeof(__u64)))
734 goto out;
735
736 ret = -EINVAL;
737 if (!uffdio_register.mode)
738 goto out;
739 if (uffdio_register.mode & ~(UFFDIO_REGISTER_MODE_MISSING|
740 UFFDIO_REGISTER_MODE_WP))
741 goto out;
742 vm_flags = 0;
743 if (uffdio_register.mode & UFFDIO_REGISTER_MODE_MISSING)
744 vm_flags |= VM_UFFD_MISSING;
745 if (uffdio_register.mode & UFFDIO_REGISTER_MODE_WP) {
746 vm_flags |= VM_UFFD_WP;
747 /*
748 * FIXME: remove the below error constraint by
749 * implementing the wprotect tracking mode.
750 */
751 ret = -EINVAL;
752 goto out;
753 }
754
755 ret = validate_range(mm, uffdio_register.range.start,
756 uffdio_register.range.len);
757 if (ret)
758 goto out;
759
760 start = uffdio_register.range.start;
761 end = start + uffdio_register.range.len;
762
763 down_write(&mm->mmap_sem);
764 vma = find_vma_prev(mm, start, &prev);
765
766 ret = -ENOMEM;
767 if (!vma)
768 goto out_unlock;
769
770 /* check that there's at least one vma in the range */
771 ret = -EINVAL;
772 if (vma->vm_start >= end)
773 goto out_unlock;
774
775 /*
776 * Search for not compatible vmas.
777 *
778 * FIXME: this shall be relaxed later so that it doesn't fail
779 * on tmpfs backed vmas (in addition to the current allowance
780 * on anonymous vmas).
781 */
782 found = false;
783 for (cur = vma; cur && cur->vm_start < end; cur = cur->vm_next) {
784 cond_resched();
785
786 BUG_ON(!!cur->vm_userfaultfd_ctx.ctx ^
787 !!(cur->vm_flags & (VM_UFFD_MISSING | VM_UFFD_WP)));
788
789 /* check not compatible vmas */
790 ret = -EINVAL;
791 if (cur->vm_ops)
792 goto out_unlock;
793
794 /*
795 * Check that this vma isn't already owned by a
796 * different userfaultfd. We can't allow more than one
797 * userfaultfd to own a single vma simultaneously or we
798 * wouldn't know which one to deliver the userfaults to.
799 */
800 ret = -EBUSY;
801 if (cur->vm_userfaultfd_ctx.ctx &&
802 cur->vm_userfaultfd_ctx.ctx != ctx)
803 goto out_unlock;
804
805 found = true;
806 }
807 BUG_ON(!found);
808
809 if (vma->vm_start < start)
810 prev = vma;
811
812 ret = 0;
813 do {
814 cond_resched();
815
816 BUG_ON(vma->vm_ops);
817 BUG_ON(vma->vm_userfaultfd_ctx.ctx &&
818 vma->vm_userfaultfd_ctx.ctx != ctx);
819
820 /*
821 * Nothing to do: this vma is already registered into this
822 * userfaultfd and with the right tracking mode too.
823 */
824 if (vma->vm_userfaultfd_ctx.ctx == ctx &&
825 (vma->vm_flags & vm_flags) == vm_flags)
826 goto skip;
827
828 if (vma->vm_start > start)
829 start = vma->vm_start;
830 vma_end = min(end, vma->vm_end);
831
832 new_flags = (vma->vm_flags & ~vm_flags) | vm_flags;
833 prev = vma_merge(mm, prev, start, vma_end, new_flags,
834 vma->anon_vma, vma->vm_file, vma->vm_pgoff,
835 vma_policy(vma),
836 ((struct vm_userfaultfd_ctx){ ctx }));
837 if (prev) {
838 vma = prev;
839 goto next;
840 }
841 if (vma->vm_start < start) {
842 ret = split_vma(mm, vma, start, 1);
843 if (ret)
844 break;
845 }
846 if (vma->vm_end > end) {
847 ret = split_vma(mm, vma, end, 0);
848 if (ret)
849 break;
850 }
851 next:
852 /*
853 * In the vma_merge() successful mprotect-like case 8:
854 * the next vma was merged into the current one and
855 * the current one has not been updated yet.
856 */
857 vma->vm_flags = new_flags;
858 vma->vm_userfaultfd_ctx.ctx = ctx;
859
860 skip:
861 prev = vma;
862 start = vma->vm_end;
863 vma = vma->vm_next;
864 } while (vma && vma->vm_start < end);
865out_unlock:
866 up_write(&mm->mmap_sem);
867 if (!ret) {
868 /*
869 * Now that we scanned all vmas we can already tell
870 * userland which ioctls methods are guaranteed to
871 * succeed on this range.
872 */
873 if (put_user(UFFD_API_RANGE_IOCTLS,
874 &user_uffdio_register->ioctls))
875 ret = -EFAULT;
876 }
877out:
878 return ret;
879}
880
881static int userfaultfd_unregister(struct userfaultfd_ctx *ctx,
882 unsigned long arg)
883{
884 struct mm_struct *mm = ctx->mm;
885 struct vm_area_struct *vma, *prev, *cur;
886 int ret;
887 struct uffdio_range uffdio_unregister;
888 unsigned long new_flags;
889 bool found;
890 unsigned long start, end, vma_end;
891 const void __user *buf = (void __user *)arg;
892
893 ret = -EFAULT;
894 if (copy_from_user(&uffdio_unregister, buf, sizeof(uffdio_unregister)))
895 goto out;
896
897 ret = validate_range(mm, uffdio_unregister.start,
898 uffdio_unregister.len);
899 if (ret)
900 goto out;
901
902 start = uffdio_unregister.start;
903 end = start + uffdio_unregister.len;
904
905 down_write(&mm->mmap_sem);
906 vma = find_vma_prev(mm, start, &prev);
907
908 ret = -ENOMEM;
909 if (!vma)
910 goto out_unlock;
911
912 /* check that there's at least one vma in the range */
913 ret = -EINVAL;
914 if (vma->vm_start >= end)
915 goto out_unlock;
916
917 /*
918 * Search for not compatible vmas.
919 *
920 * FIXME: this shall be relaxed later so that it doesn't fail
921 * on tmpfs backed vmas (in addition to the current allowance
922 * on anonymous vmas).
923 */
924 found = false;
925 ret = -EINVAL;
926 for (cur = vma; cur && cur->vm_start < end; cur = cur->vm_next) {
927 cond_resched();
928
929 BUG_ON(!!cur->vm_userfaultfd_ctx.ctx ^
930 !!(cur->vm_flags & (VM_UFFD_MISSING | VM_UFFD_WP)));
931
932 /*
933 * Check not compatible vmas, not strictly required
934 * here as not compatible vmas cannot have an
935 * userfaultfd_ctx registered on them, but this
936 * provides for more strict behavior to notice
937 * unregistration errors.
938 */
939 if (cur->vm_ops)
940 goto out_unlock;
941
942 found = true;
943 }
944 BUG_ON(!found);
945
946 if (vma->vm_start < start)
947 prev = vma;
948
949 ret = 0;
950 do {
951 cond_resched();
952
953 BUG_ON(vma->vm_ops);
954
955 /*
956 * Nothing to do: this vma is already registered into this
957 * userfaultfd and with the right tracking mode too.
958 */
959 if (!vma->vm_userfaultfd_ctx.ctx)
960 goto skip;
961
962 if (vma->vm_start > start)
963 start = vma->vm_start;
964 vma_end = min(end, vma->vm_end);
965
966 new_flags = vma->vm_flags & ~(VM_UFFD_MISSING | VM_UFFD_WP);
967 prev = vma_merge(mm, prev, start, vma_end, new_flags,
968 vma->anon_vma, vma->vm_file, vma->vm_pgoff,
969 vma_policy(vma),
970 NULL_VM_UFFD_CTX);
971 if (prev) {
972 vma = prev;
973 goto next;
974 }
975 if (vma->vm_start < start) {
976 ret = split_vma(mm, vma, start, 1);
977 if (ret)
978 break;
979 }
980 if (vma->vm_end > end) {
981 ret = split_vma(mm, vma, end, 0);
982 if (ret)
983 break;
984 }
985 next:
986 /*
987 * In the vma_merge() successful mprotect-like case 8:
988 * the next vma was merged into the current one and
989 * the current one has not been updated yet.
990 */
991 vma->vm_flags = new_flags;
992 vma->vm_userfaultfd_ctx = NULL_VM_UFFD_CTX;
993
994 skip:
995 prev = vma;
996 start = vma->vm_end;
997 vma = vma->vm_next;
998 } while (vma && vma->vm_start < end);
999out_unlock:
1000 up_write(&mm->mmap_sem);
1001out:
1002 return ret;
1003}
1004
1005/*
Andrea Arcangeliba85c702015-09-04 15:46:41 -07001006 * userfaultfd_wake may be used in combination with the
1007 * UFFDIO_*_MODE_DONTWAKE to wakeup userfaults in batches.
Andrea Arcangeli86039bd2015-09-04 15:46:31 -07001008 */
1009static int userfaultfd_wake(struct userfaultfd_ctx *ctx,
1010 unsigned long arg)
1011{
1012 int ret;
1013 struct uffdio_range uffdio_wake;
1014 struct userfaultfd_wake_range range;
1015 const void __user *buf = (void __user *)arg;
1016
1017 ret = -EFAULT;
1018 if (copy_from_user(&uffdio_wake, buf, sizeof(uffdio_wake)))
1019 goto out;
1020
1021 ret = validate_range(ctx->mm, uffdio_wake.start, uffdio_wake.len);
1022 if (ret)
1023 goto out;
1024
1025 range.start = uffdio_wake.start;
1026 range.len = uffdio_wake.len;
1027
1028 /*
1029 * len == 0 means wake all and we don't want to wake all here,
1030 * so check it again to be sure.
1031 */
1032 VM_BUG_ON(!range.len);
1033
1034 wake_userfault(ctx, &range);
1035 ret = 0;
1036
1037out:
1038 return ret;
1039}
1040
Andrea Arcangeliad465ca2015-09-04 15:47:11 -07001041static int userfaultfd_copy(struct userfaultfd_ctx *ctx,
1042 unsigned long arg)
1043{
1044 __s64 ret;
1045 struct uffdio_copy uffdio_copy;
1046 struct uffdio_copy __user *user_uffdio_copy;
1047 struct userfaultfd_wake_range range;
1048
1049 user_uffdio_copy = (struct uffdio_copy __user *) arg;
1050
1051 ret = -EFAULT;
1052 if (copy_from_user(&uffdio_copy, user_uffdio_copy,
1053 /* don't copy "copy" last field */
1054 sizeof(uffdio_copy)-sizeof(__s64)))
1055 goto out;
1056
1057 ret = validate_range(ctx->mm, uffdio_copy.dst, uffdio_copy.len);
1058 if (ret)
1059 goto out;
1060 /*
1061 * double check for wraparound just in case. copy_from_user()
1062 * will later check uffdio_copy.src + uffdio_copy.len to fit
1063 * in the userland range.
1064 */
1065 ret = -EINVAL;
1066 if (uffdio_copy.src + uffdio_copy.len <= uffdio_copy.src)
1067 goto out;
1068 if (uffdio_copy.mode & ~UFFDIO_COPY_MODE_DONTWAKE)
1069 goto out;
1070
1071 ret = mcopy_atomic(ctx->mm, uffdio_copy.dst, uffdio_copy.src,
1072 uffdio_copy.len);
1073 if (unlikely(put_user(ret, &user_uffdio_copy->copy)))
1074 return -EFAULT;
1075 if (ret < 0)
1076 goto out;
1077 BUG_ON(!ret);
1078 /* len == 0 would wake all */
1079 range.len = ret;
1080 if (!(uffdio_copy.mode & UFFDIO_COPY_MODE_DONTWAKE)) {
1081 range.start = uffdio_copy.dst;
1082 wake_userfault(ctx, &range);
1083 }
1084 ret = range.len == uffdio_copy.len ? 0 : -EAGAIN;
1085out:
1086 return ret;
1087}
1088
1089static int userfaultfd_zeropage(struct userfaultfd_ctx *ctx,
1090 unsigned long arg)
1091{
1092 __s64 ret;
1093 struct uffdio_zeropage uffdio_zeropage;
1094 struct uffdio_zeropage __user *user_uffdio_zeropage;
1095 struct userfaultfd_wake_range range;
1096
1097 user_uffdio_zeropage = (struct uffdio_zeropage __user *) arg;
1098
1099 ret = -EFAULT;
1100 if (copy_from_user(&uffdio_zeropage, user_uffdio_zeropage,
1101 /* don't copy "zeropage" last field */
1102 sizeof(uffdio_zeropage)-sizeof(__s64)))
1103 goto out;
1104
1105 ret = validate_range(ctx->mm, uffdio_zeropage.range.start,
1106 uffdio_zeropage.range.len);
1107 if (ret)
1108 goto out;
1109 ret = -EINVAL;
1110 if (uffdio_zeropage.mode & ~UFFDIO_ZEROPAGE_MODE_DONTWAKE)
1111 goto out;
1112
1113 ret = mfill_zeropage(ctx->mm, uffdio_zeropage.range.start,
1114 uffdio_zeropage.range.len);
1115 if (unlikely(put_user(ret, &user_uffdio_zeropage->zeropage)))
1116 return -EFAULT;
1117 if (ret < 0)
1118 goto out;
1119 /* len == 0 would wake all */
1120 BUG_ON(!ret);
1121 range.len = ret;
1122 if (!(uffdio_zeropage.mode & UFFDIO_ZEROPAGE_MODE_DONTWAKE)) {
1123 range.start = uffdio_zeropage.range.start;
1124 wake_userfault(ctx, &range);
1125 }
1126 ret = range.len == uffdio_zeropage.range.len ? 0 : -EAGAIN;
1127out:
1128 return ret;
1129}
1130
Andrea Arcangeli86039bd2015-09-04 15:46:31 -07001131/*
1132 * userland asks for a certain API version and we return which bits
1133 * and ioctl commands are implemented in this kernel for such API
1134 * version or -EINVAL if unknown.
1135 */
1136static int userfaultfd_api(struct userfaultfd_ctx *ctx,
1137 unsigned long arg)
1138{
1139 struct uffdio_api uffdio_api;
1140 void __user *buf = (void __user *)arg;
1141 int ret;
1142
1143 ret = -EINVAL;
1144 if (ctx->state != UFFD_STATE_WAIT_API)
1145 goto out;
1146 ret = -EFAULT;
Andrea Arcangelia9b85f92015-09-04 15:46:37 -07001147 if (copy_from_user(&uffdio_api, buf, sizeof(uffdio_api)))
Andrea Arcangeli86039bd2015-09-04 15:46:31 -07001148 goto out;
Andrea Arcangelia9b85f92015-09-04 15:46:37 -07001149 if (uffdio_api.api != UFFD_API || uffdio_api.features) {
Andrea Arcangeli86039bd2015-09-04 15:46:31 -07001150 memset(&uffdio_api, 0, sizeof(uffdio_api));
1151 if (copy_to_user(buf, &uffdio_api, sizeof(uffdio_api)))
1152 goto out;
1153 ret = -EINVAL;
1154 goto out;
1155 }
Pavel Emelyanov3f602d22015-09-04 15:46:34 -07001156 uffdio_api.features = UFFD_API_FEATURES;
Andrea Arcangeli86039bd2015-09-04 15:46:31 -07001157 uffdio_api.ioctls = UFFD_API_IOCTLS;
1158 ret = -EFAULT;
1159 if (copy_to_user(buf, &uffdio_api, sizeof(uffdio_api)))
1160 goto out;
1161 ctx->state = UFFD_STATE_RUNNING;
1162 ret = 0;
1163out:
1164 return ret;
1165}
1166
1167static long userfaultfd_ioctl(struct file *file, unsigned cmd,
1168 unsigned long arg)
1169{
1170 int ret = -EINVAL;
1171 struct userfaultfd_ctx *ctx = file->private_data;
1172
Andrea Arcangelie6485a42015-09-04 15:47:15 -07001173 if (cmd != UFFDIO_API && ctx->state == UFFD_STATE_WAIT_API)
1174 return -EINVAL;
1175
Andrea Arcangeli86039bd2015-09-04 15:46:31 -07001176 switch(cmd) {
1177 case UFFDIO_API:
1178 ret = userfaultfd_api(ctx, arg);
1179 break;
1180 case UFFDIO_REGISTER:
1181 ret = userfaultfd_register(ctx, arg);
1182 break;
1183 case UFFDIO_UNREGISTER:
1184 ret = userfaultfd_unregister(ctx, arg);
1185 break;
1186 case UFFDIO_WAKE:
1187 ret = userfaultfd_wake(ctx, arg);
1188 break;
Andrea Arcangeliad465ca2015-09-04 15:47:11 -07001189 case UFFDIO_COPY:
1190 ret = userfaultfd_copy(ctx, arg);
1191 break;
1192 case UFFDIO_ZEROPAGE:
1193 ret = userfaultfd_zeropage(ctx, arg);
1194 break;
Andrea Arcangeli86039bd2015-09-04 15:46:31 -07001195 }
1196 return ret;
1197}
1198
1199#ifdef CONFIG_PROC_FS
1200static void userfaultfd_show_fdinfo(struct seq_file *m, struct file *f)
1201{
1202 struct userfaultfd_ctx *ctx = f->private_data;
1203 wait_queue_t *wq;
1204 struct userfaultfd_wait_queue *uwq;
1205 unsigned long pending = 0, total = 0;
1206
Andrea Arcangeli15b726e2015-09-04 15:46:44 -07001207 spin_lock(&ctx->fault_pending_wqh.lock);
1208 list_for_each_entry(wq, &ctx->fault_pending_wqh.task_list, task_list) {
Andrea Arcangeli86039bd2015-09-04 15:46:31 -07001209 uwq = container_of(wq, struct userfaultfd_wait_queue, wq);
Andrea Arcangeli15b726e2015-09-04 15:46:44 -07001210 pending++;
Andrea Arcangeli86039bd2015-09-04 15:46:31 -07001211 total++;
1212 }
Andrea Arcangeli15b726e2015-09-04 15:46:44 -07001213 list_for_each_entry(wq, &ctx->fault_wqh.task_list, task_list) {
1214 uwq = container_of(wq, struct userfaultfd_wait_queue, wq);
1215 total++;
1216 }
1217 spin_unlock(&ctx->fault_pending_wqh.lock);
Andrea Arcangeli86039bd2015-09-04 15:46:31 -07001218
1219 /*
1220 * If more protocols will be added, there will be all shown
1221 * separated by a space. Like this:
1222 * protocols: aa:... bb:...
1223 */
1224 seq_printf(m, "pending:\t%lu\ntotal:\t%lu\nAPI:\t%Lx:%x:%Lx\n",
Pavel Emelyanov3f602d22015-09-04 15:46:34 -07001225 pending, total, UFFD_API, UFFD_API_FEATURES,
Andrea Arcangeli86039bd2015-09-04 15:46:31 -07001226 UFFD_API_IOCTLS|UFFD_API_RANGE_IOCTLS);
1227}
1228#endif
1229
1230static const struct file_operations userfaultfd_fops = {
1231#ifdef CONFIG_PROC_FS
1232 .show_fdinfo = userfaultfd_show_fdinfo,
1233#endif
1234 .release = userfaultfd_release,
1235 .poll = userfaultfd_poll,
1236 .read = userfaultfd_read,
1237 .unlocked_ioctl = userfaultfd_ioctl,
1238 .compat_ioctl = userfaultfd_ioctl,
1239 .llseek = noop_llseek,
1240};
1241
Andrea Arcangeli3004ec92015-09-04 15:46:48 -07001242static void init_once_userfaultfd_ctx(void *mem)
1243{
1244 struct userfaultfd_ctx *ctx = (struct userfaultfd_ctx *) mem;
1245
1246 init_waitqueue_head(&ctx->fault_pending_wqh);
1247 init_waitqueue_head(&ctx->fault_wqh);
1248 init_waitqueue_head(&ctx->fd_wqh);
Andrea Arcangeli2c5b7e12015-09-04 15:47:23 -07001249 seqcount_init(&ctx->refile_seq);
Andrea Arcangeli3004ec92015-09-04 15:46:48 -07001250}
1251
Andrea Arcangeli86039bd2015-09-04 15:46:31 -07001252/**
1253 * userfaultfd_file_create - Creates an userfaultfd file pointer.
1254 * @flags: Flags for the userfaultfd file.
1255 *
1256 * This function creates an userfaultfd file pointer, w/out installing
1257 * it into the fd table. This is useful when the userfaultfd file is
1258 * used during the initialization of data structures that require
1259 * extra setup after the userfaultfd creation. So the userfaultfd
1260 * creation is split into the file pointer creation phase, and the
1261 * file descriptor installation phase. In this way races with
1262 * userspace closing the newly installed file descriptor can be
1263 * avoided. Returns an userfaultfd file pointer, or a proper error
1264 * pointer.
1265 */
1266static struct file *userfaultfd_file_create(int flags)
1267{
1268 struct file *file;
1269 struct userfaultfd_ctx *ctx;
1270
1271 BUG_ON(!current->mm);
1272
1273 /* Check the UFFD_* constants for consistency. */
1274 BUILD_BUG_ON(UFFD_CLOEXEC != O_CLOEXEC);
1275 BUILD_BUG_ON(UFFD_NONBLOCK != O_NONBLOCK);
1276
1277 file = ERR_PTR(-EINVAL);
1278 if (flags & ~UFFD_SHARED_FCNTL_FLAGS)
1279 goto out;
1280
1281 file = ERR_PTR(-ENOMEM);
Andrea Arcangeli3004ec92015-09-04 15:46:48 -07001282 ctx = kmem_cache_alloc(userfaultfd_ctx_cachep, GFP_KERNEL);
Andrea Arcangeli86039bd2015-09-04 15:46:31 -07001283 if (!ctx)
1284 goto out;
1285
1286 atomic_set(&ctx->refcount, 1);
Andrea Arcangeli86039bd2015-09-04 15:46:31 -07001287 ctx->flags = flags;
1288 ctx->state = UFFD_STATE_WAIT_API;
1289 ctx->released = false;
1290 ctx->mm = current->mm;
1291 /* prevent the mm struct to be freed */
1292 atomic_inc(&ctx->mm->mm_users);
1293
1294 file = anon_inode_getfile("[userfaultfd]", &userfaultfd_fops, ctx,
1295 O_RDWR | (flags & UFFD_SHARED_FCNTL_FLAGS));
Eric Biggersc03e9462015-09-17 16:01:54 -07001296 if (IS_ERR(file)) {
1297 mmput(ctx->mm);
Andrea Arcangeli3004ec92015-09-04 15:46:48 -07001298 kmem_cache_free(userfaultfd_ctx_cachep, ctx);
Eric Biggersc03e9462015-09-17 16:01:54 -07001299 }
Andrea Arcangeli86039bd2015-09-04 15:46:31 -07001300out:
1301 return file;
1302}
1303
1304SYSCALL_DEFINE1(userfaultfd, int, flags)
1305{
1306 int fd, error;
1307 struct file *file;
1308
1309 error = get_unused_fd_flags(flags & UFFD_SHARED_FCNTL_FLAGS);
1310 if (error < 0)
1311 return error;
1312 fd = error;
1313
1314 file = userfaultfd_file_create(flags);
1315 if (IS_ERR(file)) {
1316 error = PTR_ERR(file);
1317 goto err_put_unused_fd;
1318 }
1319 fd_install(fd, file);
1320
1321 return fd;
1322
1323err_put_unused_fd:
1324 put_unused_fd(fd);
1325
1326 return error;
1327}
Andrea Arcangeli3004ec92015-09-04 15:46:48 -07001328
1329static int __init userfaultfd_init(void)
1330{
1331 userfaultfd_ctx_cachep = kmem_cache_create("userfaultfd_ctx_cache",
1332 sizeof(struct userfaultfd_ctx),
1333 0,
1334 SLAB_HWCACHE_ALIGN|SLAB_PANIC,
1335 init_once_userfaultfd_ctx);
1336 return 0;
1337}
1338__initcall(userfaultfd_init);