1 // SPDX-License-Identifier: GPL-2.0-only
2 /*
3 * fs/userfaultfd.c
4 *
5 * Copyright (C) 2007 Davide Libenzi <davidel@xmailserver.org>
6 * Copyright (C) 2008-2009 Red Hat, Inc.
7 * Copyright (C) 2015 Red Hat, Inc.
8 *
9 * Some part derived from fs/eventfd.c (anon inode setup) and
10 * mm/ksm.c (mm hashing).
11 */
12
13 #include <linux/list.h>
14 #include <linux/hashtable.h>
15 #include <linux/sched/signal.h>
16 #include <linux/sched/mm.h>
17 #include <linux/mm.h>
18 #include <linux/mmu_notifier.h>
19 #include <linux/poll.h>
20 #include <linux/slab.h>
21 #include <linux/seq_file.h>
22 #include <linux/file.h>
23 #include <linux/bug.h>
24 #include <linux/anon_inodes.h>
25 #include <linux/syscalls.h>
26 #include <linux/userfaultfd_k.h>
27 #include <linux/mempolicy.h>
28 #include <linux/ioctl.h>
29 #include <linux/security.h>
30 #include <linux/hugetlb.h>
31
32 int sysctl_unprivileged_userfaultfd __read_mostly;
33
34 static struct kmem_cache *userfaultfd_ctx_cachep __read_mostly;
35
36 /*
37 * Start with fault_pending_wqh and fault_wqh so they're more likely
38 * to be in the same cacheline.
39 *
40 * Locking order:
41 * fd_wqh.lock
42 * fault_pending_wqh.lock
43 * fault_wqh.lock
44 * event_wqh.lock
45 *
46 * To avoid deadlocks, IRQs must be disabled when taking any of the above locks,
47 * since fd_wqh.lock is taken by aio_poll() while it's holding a lock that's
48 * also taken in IRQ context.
49 */
50 struct userfaultfd_ctx {
51 /* waitqueue head for the pending (i.e. not read) userfaults */
52 wait_queue_head_t fault_pending_wqh;
53 /* waitqueue head for the userfaults */
54 wait_queue_head_t fault_wqh;
55 /* waitqueue head for the pseudo fd to wakeup poll/read */
56 wait_queue_head_t fd_wqh;
57 /* waitqueue head for events */
58 wait_queue_head_t event_wqh;
59 /* a refile sequence protected by fault_pending_wqh lock */
60 seqcount_spinlock_t refile_seq;
61 /* pseudo fd refcounting */
62 refcount_t refcount;
63 /* userfaultfd syscall flags */
64 unsigned int flags;
65 /* features requested from the userspace */
66 unsigned int features;
67 /* released */
68 bool released;
69 /* memory mappings are changing because of non-cooperative event */
70 atomic_t mmap_changing;
71 /* mm with one ore more vmas attached to this userfaultfd_ctx */
72 struct mm_struct *mm;
73 };
74
75 struct userfaultfd_fork_ctx {
76 struct userfaultfd_ctx *orig;
77 struct userfaultfd_ctx *new;
78 struct list_head list;
79 };
80
81 struct userfaultfd_unmap_ctx {
82 struct userfaultfd_ctx *ctx;
83 unsigned long start;
84 unsigned long end;
85 struct list_head list;
86 };
87
88 struct userfaultfd_wait_queue {
89 struct uffd_msg msg;
90 wait_queue_entry_t wq;
91 struct userfaultfd_ctx *ctx;
92 bool waken;
93 };
94
95 struct userfaultfd_wake_range {
96 unsigned long start;
97 unsigned long len;
98 };
99
100 /* internal indication that UFFD_API ioctl was successfully executed */
101 #define UFFD_FEATURE_INITIALIZED (1u << 31)
102
userfaultfd_is_initialized(struct userfaultfd_ctx * ctx)103 static bool userfaultfd_is_initialized(struct userfaultfd_ctx *ctx)
104 {
105 return ctx->features & UFFD_FEATURE_INITIALIZED;
106 }
107
userfaultfd_wake_function(wait_queue_entry_t * wq,unsigned mode,int wake_flags,void * key)108 static int userfaultfd_wake_function(wait_queue_entry_t *wq, unsigned mode,
109 int wake_flags, void *key)
110 {
111 struct userfaultfd_wake_range *range = key;
112 int ret;
113 struct userfaultfd_wait_queue *uwq;
114 unsigned long start, len;
115
116 uwq = container_of(wq, struct userfaultfd_wait_queue, wq);
117 ret = 0;
118 /* len == 0 means wake all */
119 start = range->start;
120 len = range->len;
121 if (len && (start > uwq->msg.arg.pagefault.address ||
122 start + len <= uwq->msg.arg.pagefault.address))
123 goto out;
124 WRITE_ONCE(uwq->waken, true);
125 /*
126 * The Program-Order guarantees provided by the scheduler
127 * ensure uwq->waken is visible before the task is woken.
128 */
129 ret = wake_up_state(wq->private, mode);
130 if (ret) {
131 /*
132 * Wake only once, autoremove behavior.
133 *
134 * After the effect of list_del_init is visible to the other
135 * CPUs, the waitqueue may disappear from under us, see the
136 * !list_empty_careful() in handle_userfault().
137 *
138 * try_to_wake_up() has an implicit smp_mb(), and the
139 * wq->private is read before calling the extern function
140 * "wake_up_state" (which in turns calls try_to_wake_up).
141 */
142 list_del_init(&wq->entry);
143 }
144 out:
145 return ret;
146 }
147
148 /**
149 * userfaultfd_ctx_get - Acquires a reference to the internal userfaultfd
150 * context.
151 * @ctx: [in] Pointer to the userfaultfd context.
152 */
userfaultfd_ctx_get(struct userfaultfd_ctx * ctx)153 static void userfaultfd_ctx_get(struct userfaultfd_ctx *ctx)
154 {
155 refcount_inc(&ctx->refcount);
156 }
157
158 /**
159 * userfaultfd_ctx_put - Releases a reference to the internal userfaultfd
160 * context.
161 * @ctx: [in] Pointer to userfaultfd context.
162 *
163 * The userfaultfd context reference must have been previously acquired either
164 * with userfaultfd_ctx_get() or userfaultfd_ctx_fdget().
165 */
userfaultfd_ctx_put(struct userfaultfd_ctx * ctx)166 static void userfaultfd_ctx_put(struct userfaultfd_ctx *ctx)
167 {
168 if (refcount_dec_and_test(&ctx->refcount)) {
169 VM_BUG_ON(spin_is_locked(&ctx->fault_pending_wqh.lock));
170 VM_BUG_ON(waitqueue_active(&ctx->fault_pending_wqh));
171 VM_BUG_ON(spin_is_locked(&ctx->fault_wqh.lock));
172 VM_BUG_ON(waitqueue_active(&ctx->fault_wqh));
173 VM_BUG_ON(spin_is_locked(&ctx->event_wqh.lock));
174 VM_BUG_ON(waitqueue_active(&ctx->event_wqh));
175 VM_BUG_ON(spin_is_locked(&ctx->fd_wqh.lock));
176 VM_BUG_ON(waitqueue_active(&ctx->fd_wqh));
177 mmdrop(ctx->mm);
178 kmem_cache_free(userfaultfd_ctx_cachep, ctx);
179 }
180 }
181
msg_init(struct uffd_msg * msg)182 static inline void msg_init(struct uffd_msg *msg)
183 {
184 BUILD_BUG_ON(sizeof(struct uffd_msg) != 32);
185 /*
186 * Must use memset to zero out the paddings or kernel data is
187 * leaked to userland.
188 */
189 memset(msg, 0, sizeof(struct uffd_msg));
190 }
191
userfault_msg(unsigned long address,unsigned int flags,unsigned long reason,unsigned int features)192 static inline struct uffd_msg userfault_msg(unsigned long address,
193 unsigned int flags,
194 unsigned long reason,
195 unsigned int features)
196 {
197 struct uffd_msg msg;
198 msg_init(&msg);
199 msg.event = UFFD_EVENT_PAGEFAULT;
200 msg.arg.pagefault.address = address;
201 /*
202 * These flags indicate why the userfault occurred:
203 * - UFFD_PAGEFAULT_FLAG_WP indicates a write protect fault.
204 * - UFFD_PAGEFAULT_FLAG_MINOR indicates a minor fault.
205 * - Neither of these flags being set indicates a MISSING fault.
206 *
207 * Separately, UFFD_PAGEFAULT_FLAG_WRITE indicates it was a write
208 * fault. Otherwise, it was a read fault.
209 */
210 if (flags & FAULT_FLAG_WRITE)
211 msg.arg.pagefault.flags |= UFFD_PAGEFAULT_FLAG_WRITE;
212 if (reason & VM_UFFD_WP)
213 msg.arg.pagefault.flags |= UFFD_PAGEFAULT_FLAG_WP;
214 if (reason & VM_UFFD_MINOR)
215 msg.arg.pagefault.flags |= UFFD_PAGEFAULT_FLAG_MINOR;
216 if (features & UFFD_FEATURE_THREAD_ID)
217 msg.arg.pagefault.feat.ptid = task_pid_vnr(current);
218 return msg;
219 }
220
221 #ifdef CONFIG_HUGETLB_PAGE
222 /*
223 * Same functionality as userfaultfd_must_wait below with modifications for
224 * hugepmd ranges.
225 */
userfaultfd_huge_must_wait(struct userfaultfd_ctx * ctx,struct vm_area_struct * vma,unsigned long address,unsigned long flags,unsigned long reason)226 static inline bool userfaultfd_huge_must_wait(struct userfaultfd_ctx *ctx,
227 struct vm_area_struct *vma,
228 unsigned long address,
229 unsigned long flags,
230 unsigned long reason)
231 {
232 struct mm_struct *mm = ctx->mm;
233 pte_t *ptep, pte;
234 bool ret = true;
235
236 mmap_assert_locked(mm);
237
238 ptep = huge_pte_offset(mm, address, vma_mmu_pagesize(vma));
239
240 if (!ptep)
241 goto out;
242
243 ret = false;
244 pte = huge_ptep_get(ptep);
245
246 /*
247 * Lockless access: we're in a wait_event so it's ok if it
248 * changes under us.
249 */
250 if (huge_pte_none(pte))
251 ret = true;
252 if (!huge_pte_write(pte) && (reason & VM_UFFD_WP))
253 ret = true;
254 out:
255 return ret;
256 }
257 #else
userfaultfd_huge_must_wait(struct userfaultfd_ctx * ctx,struct vm_area_struct * vma,unsigned long address,unsigned long flags,unsigned long reason)258 static inline bool userfaultfd_huge_must_wait(struct userfaultfd_ctx *ctx,
259 struct vm_area_struct *vma,
260 unsigned long address,
261 unsigned long flags,
262 unsigned long reason)
263 {
264 return false; /* should never get here */
265 }
266 #endif /* CONFIG_HUGETLB_PAGE */
267
268 /*
269 * Verify the pagetables are still not ok after having reigstered into
270 * the fault_pending_wqh to avoid userland having to UFFDIO_WAKE any
271 * userfault that has already been resolved, if userfaultfd_read and
272 * UFFDIO_COPY|ZEROPAGE are being run simultaneously on two different
273 * threads.
274 */
userfaultfd_must_wait(struct userfaultfd_ctx * ctx,unsigned long address,unsigned long flags,unsigned long reason)275 static inline bool userfaultfd_must_wait(struct userfaultfd_ctx *ctx,
276 unsigned long address,
277 unsigned long flags,
278 unsigned long reason)
279 {
280 struct mm_struct *mm = ctx->mm;
281 pgd_t *pgd;
282 p4d_t *p4d;
283 pud_t *pud;
284 pmd_t *pmd, _pmd;
285 pte_t *pte;
286 bool ret = true;
287
288 mmap_assert_locked(mm);
289
290 pgd = pgd_offset(mm, address);
291 if (!pgd_present(*pgd))
292 goto out;
293 p4d = p4d_offset(pgd, address);
294 if (!p4d_present(*p4d))
295 goto out;
296 pud = pud_offset(p4d, address);
297 if (!pud_present(*pud))
298 goto out;
299 pmd = pmd_offset(pud, address);
300 /*
301 * READ_ONCE must function as a barrier with narrower scope
302 * and it must be equivalent to:
303 * _pmd = *pmd; barrier();
304 *
305 * This is to deal with the instability (as in
306 * pmd_trans_unstable) of the pmd.
307 */
308 _pmd = READ_ONCE(*pmd);
309 if (pmd_none(_pmd))
310 goto out;
311
312 ret = false;
313 if (!pmd_present(_pmd))
314 goto out;
315
316 if (pmd_trans_huge(_pmd)) {
317 if (!pmd_write(_pmd) && (reason & VM_UFFD_WP))
318 ret = true;
319 goto out;
320 }
321
322 /*
323 * the pmd is stable (as in !pmd_trans_unstable) so we can re-read it
324 * and use the standard pte_offset_map() instead of parsing _pmd.
325 */
326 pte = pte_offset_map(pmd, address);
327 /*
328 * Lockless access: we're in a wait_event so it's ok if it
329 * changes under us.
330 */
331 if (pte_none(*pte))
332 ret = true;
333 if (!pte_write(*pte) && (reason & VM_UFFD_WP))
334 ret = true;
335 pte_unmap(pte);
336
337 out:
338 return ret;
339 }
340
userfaultfd_get_blocking_state(unsigned int flags)341 static inline unsigned int userfaultfd_get_blocking_state(unsigned int flags)
342 {
343 if (flags & FAULT_FLAG_INTERRUPTIBLE)
344 return TASK_INTERRUPTIBLE;
345
346 if (flags & FAULT_FLAG_KILLABLE)
347 return TASK_KILLABLE;
348
349 return TASK_UNINTERRUPTIBLE;
350 }
351
352 /*
353 * The locking rules involved in returning VM_FAULT_RETRY depending on
354 * FAULT_FLAG_ALLOW_RETRY, FAULT_FLAG_RETRY_NOWAIT and
355 * FAULT_FLAG_KILLABLE are not straightforward. The "Caution"
356 * recommendation in __lock_page_or_retry is not an understatement.
357 *
358 * If FAULT_FLAG_ALLOW_RETRY is set, the mmap_lock must be released
359 * before returning VM_FAULT_RETRY only if FAULT_FLAG_RETRY_NOWAIT is
360 * not set.
361 *
362 * If FAULT_FLAG_ALLOW_RETRY is set but FAULT_FLAG_KILLABLE is not
363 * set, VM_FAULT_RETRY can still be returned if and only if there are
364 * fatal_signal_pending()s, and the mmap_lock must be released before
365 * returning it.
366 */
handle_userfault(struct vm_fault * vmf,unsigned long reason)367 vm_fault_t handle_userfault(struct vm_fault *vmf, unsigned long reason)
368 {
369 struct mm_struct *mm = vmf->vma->vm_mm;
370 struct userfaultfd_ctx *ctx;
371 struct userfaultfd_wait_queue uwq;
372 vm_fault_t ret = VM_FAULT_SIGBUS;
373 bool must_wait;
374 unsigned int blocking_state;
375
376 /*
377 * We don't do userfault handling for the final child pid update.
378 *
379 * We also don't do userfault handling during
380 * coredumping. hugetlbfs has the special
381 * follow_hugetlb_page() to skip missing pages in the
382 * FOLL_DUMP case, anon memory also checks for FOLL_DUMP with
383 * the no_page_table() helper in follow_page_mask(), but the
384 * shmem_vm_ops->fault method is invoked even during
385 * coredumping without mmap_lock and it ends up here.
386 */
387 if (current->flags & (PF_EXITING|PF_DUMPCORE))
388 goto out;
389
390 /*
391 * Coredumping runs without mmap_lock so we can only check that
392 * the mmap_lock is held, if PF_DUMPCORE was not set.
393 */
394 mmap_assert_locked(mm);
395
396 ctx = vmf->vma->vm_userfaultfd_ctx.ctx;
397 if (!ctx)
398 goto out;
399
400 BUG_ON(ctx->mm != mm);
401
402 /* Any unrecognized flag is a bug. */
403 VM_BUG_ON(reason & ~__VM_UFFD_FLAGS);
404 /* 0 or > 1 flags set is a bug; we expect exactly 1. */
405 VM_BUG_ON(!reason || (reason & (reason - 1)));
406
407 if (ctx->features & UFFD_FEATURE_SIGBUS)
408 goto out;
409 if ((vmf->flags & FAULT_FLAG_USER) == 0 &&
410 ctx->flags & UFFD_USER_MODE_ONLY) {
411 printk_once(KERN_WARNING "uffd: Set unprivileged_userfaultfd "
412 "sysctl knob to 1 if kernel faults must be handled "
413 "without obtaining CAP_SYS_PTRACE capability\n");
414 goto out;
415 }
416
417 /*
418 * If it's already released don't get it. This avoids to loop
419 * in __get_user_pages if userfaultfd_release waits on the
420 * caller of handle_userfault to release the mmap_lock.
421 */
422 if (unlikely(READ_ONCE(ctx->released))) {
423 /*
424 * Don't return VM_FAULT_SIGBUS in this case, so a non
425 * cooperative manager can close the uffd after the
426 * last UFFDIO_COPY, without risking to trigger an
427 * involuntary SIGBUS if the process was starting the
428 * userfaultfd while the userfaultfd was still armed
429 * (but after the last UFFDIO_COPY). If the uffd
430 * wasn't already closed when the userfault reached
431 * this point, that would normally be solved by
432 * userfaultfd_must_wait returning 'false'.
433 *
434 * If we were to return VM_FAULT_SIGBUS here, the non
435 * cooperative manager would be instead forced to
436 * always call UFFDIO_UNREGISTER before it can safely
437 * close the uffd.
438 */
439 ret = VM_FAULT_NOPAGE;
440 goto out;
441 }
442
443 /*
444 * Check that we can return VM_FAULT_RETRY.
445 *
446 * NOTE: it should become possible to return VM_FAULT_RETRY
447 * even if FAULT_FLAG_TRIED is set without leading to gup()
448 * -EBUSY failures, if the userfaultfd is to be extended for
449 * VM_UFFD_WP tracking and we intend to arm the userfault
450 * without first stopping userland access to the memory. For
451 * VM_UFFD_MISSING userfaults this is enough for now.
452 */
453 if (unlikely(!(vmf->flags & FAULT_FLAG_ALLOW_RETRY))) {
454 /*
455 * Validate the invariant that nowait must allow retry
456 * to be sure not to return SIGBUS erroneously on
457 * nowait invocations.
458 */
459 BUG_ON(vmf->flags & FAULT_FLAG_RETRY_NOWAIT);
460 #ifdef CONFIG_DEBUG_VM
461 if (printk_ratelimit()) {
462 printk(KERN_WARNING
463 "FAULT_FLAG_ALLOW_RETRY missing %x\n",
464 vmf->flags);
465 dump_stack();
466 }
467 #endif
468 goto out;
469 }
470
471 /*
472 * Handle nowait, not much to do other than tell it to retry
473 * and wait.
474 */
475 ret = VM_FAULT_RETRY;
476 if (vmf->flags & FAULT_FLAG_RETRY_NOWAIT)
477 goto out;
478
479 /* take the reference before dropping the mmap_lock */
480 userfaultfd_ctx_get(ctx);
481
482 init_waitqueue_func_entry(&uwq.wq, userfaultfd_wake_function);
483 uwq.wq.private = current;
484 uwq.msg = userfault_msg(vmf->address, vmf->flags, reason,
485 ctx->features);
486 uwq.ctx = ctx;
487 uwq.waken = false;
488
489 blocking_state = userfaultfd_get_blocking_state(vmf->flags);
490
491 spin_lock_irq(&ctx->fault_pending_wqh.lock);
492 /*
493 * After the __add_wait_queue the uwq is visible to userland
494 * through poll/read().
495 */
496 __add_wait_queue(&ctx->fault_pending_wqh, &uwq.wq);
497 /*
498 * The smp_mb() after __set_current_state prevents the reads
499 * following the spin_unlock to happen before the list_add in
500 * __add_wait_queue.
501 */
502 set_current_state(blocking_state);
503 spin_unlock_irq(&ctx->fault_pending_wqh.lock);
504
505 if (!is_vm_hugetlb_page(vmf->vma))
506 must_wait = userfaultfd_must_wait(ctx, vmf->address, vmf->flags,
507 reason);
508 else
509 must_wait = userfaultfd_huge_must_wait(ctx, vmf->vma,
510 vmf->address,
511 vmf->flags, reason);
512 mmap_read_unlock(mm);
513
514 if (likely(must_wait && !READ_ONCE(ctx->released))) {
515 wake_up_poll(&ctx->fd_wqh, EPOLLIN);
516 schedule();
517 }
518
519 __set_current_state(TASK_RUNNING);
520
521 /*
522 * Here we race with the list_del; list_add in
523 * userfaultfd_ctx_read(), however because we don't ever run
524 * list_del_init() to refile across the two lists, the prev
525 * and next pointers will never point to self. list_add also
526 * would never let any of the two pointers to point to
527 * self. So list_empty_careful won't risk to see both pointers
528 * pointing to self at any time during the list refile. The
529 * only case where list_del_init() is called is the full
530 * removal in the wake function and there we don't re-list_add
531 * and it's fine not to block on the spinlock. The uwq on this
532 * kernel stack can be released after the list_del_init.
533 */
534 if (!list_empty_careful(&uwq.wq.entry)) {
535 spin_lock_irq(&ctx->fault_pending_wqh.lock);
536 /*
537 * No need of list_del_init(), the uwq on the stack
538 * will be freed shortly anyway.
539 */
540 list_del(&uwq.wq.entry);
541 spin_unlock_irq(&ctx->fault_pending_wqh.lock);
542 }
543
544 /*
545 * ctx may go away after this if the userfault pseudo fd is
546 * already released.
547 */
548 userfaultfd_ctx_put(ctx);
549
550 out:
551 return ret;
552 }
553
userfaultfd_event_wait_completion(struct userfaultfd_ctx * ctx,struct userfaultfd_wait_queue * ewq)554 static void userfaultfd_event_wait_completion(struct userfaultfd_ctx *ctx,
555 struct userfaultfd_wait_queue *ewq)
556 {
557 struct userfaultfd_ctx *release_new_ctx;
558
559 if (WARN_ON_ONCE(current->flags & PF_EXITING))
560 goto out;
561
562 ewq->ctx = ctx;
563 init_waitqueue_entry(&ewq->wq, current);
564 release_new_ctx = NULL;
565
566 spin_lock_irq(&ctx->event_wqh.lock);
567 /*
568 * After the __add_wait_queue the uwq is visible to userland
569 * through poll/read().
570 */
571 __add_wait_queue(&ctx->event_wqh, &ewq->wq);
572 for (;;) {
573 set_current_state(TASK_KILLABLE);
574 if (ewq->msg.event == 0)
575 break;
576 if (READ_ONCE(ctx->released) ||
577 fatal_signal_pending(current)) {
578 /*
579 * &ewq->wq may be queued in fork_event, but
580 * __remove_wait_queue ignores the head
581 * parameter. It would be a problem if it
582 * didn't.
583 */
584 __remove_wait_queue(&ctx->event_wqh, &ewq->wq);
585 if (ewq->msg.event == UFFD_EVENT_FORK) {
586 struct userfaultfd_ctx *new;
587
588 new = (struct userfaultfd_ctx *)
589 (unsigned long)
590 ewq->msg.arg.reserved.reserved1;
591 release_new_ctx = new;
592 }
593 break;
594 }
595
596 spin_unlock_irq(&ctx->event_wqh.lock);
597
598 wake_up_poll(&ctx->fd_wqh, EPOLLIN);
599 schedule();
600
601 spin_lock_irq(&ctx->event_wqh.lock);
602 }
603 __set_current_state(TASK_RUNNING);
604 spin_unlock_irq(&ctx->event_wqh.lock);
605
606 if (release_new_ctx) {
607 struct vm_area_struct *vma;
608 struct mm_struct *mm = release_new_ctx->mm;
609
610 /* the various vma->vm_userfaultfd_ctx still points to it */
611 mmap_write_lock(mm);
612 for (vma = mm->mmap; vma; vma = vma->vm_next)
613 if (vma->vm_userfaultfd_ctx.ctx == release_new_ctx) {
614 vma->vm_userfaultfd_ctx = NULL_VM_UFFD_CTX;
615 vma->vm_flags &= ~__VM_UFFD_FLAGS;
616 }
617 mmap_write_unlock(mm);
618
619 userfaultfd_ctx_put(release_new_ctx);
620 }
621
622 /*
623 * ctx may go away after this if the userfault pseudo fd is
624 * already released.
625 */
626 out:
627 atomic_dec(&ctx->mmap_changing);
628 VM_BUG_ON(atomic_read(&ctx->mmap_changing) < 0);
629 userfaultfd_ctx_put(ctx);
630 }
631
userfaultfd_event_complete(struct userfaultfd_ctx * ctx,struct userfaultfd_wait_queue * ewq)632 static void userfaultfd_event_complete(struct userfaultfd_ctx *ctx,
633 struct userfaultfd_wait_queue *ewq)
634 {
635 ewq->msg.event = 0;
636 wake_up_locked(&ctx->event_wqh);
637 __remove_wait_queue(&ctx->event_wqh, &ewq->wq);
638 }
639
dup_userfaultfd(struct vm_area_struct * vma,struct list_head * fcs)640 int dup_userfaultfd(struct vm_area_struct *vma, struct list_head *fcs)
641 {
642 struct userfaultfd_ctx *ctx = NULL, *octx;
643 struct userfaultfd_fork_ctx *fctx;
644
645 octx = vma->vm_userfaultfd_ctx.ctx;
646 if (!octx || !(octx->features & UFFD_FEATURE_EVENT_FORK)) {
647 vma->vm_userfaultfd_ctx = NULL_VM_UFFD_CTX;
648 vma->vm_flags &= ~__VM_UFFD_FLAGS;
649 return 0;
650 }
651
652 list_for_each_entry(fctx, fcs, list)
653 if (fctx->orig == octx) {
654 ctx = fctx->new;
655 break;
656 }
657
658 if (!ctx) {
659 fctx = kmalloc(sizeof(*fctx), GFP_KERNEL);
660 if (!fctx)
661 return -ENOMEM;
662
663 ctx = kmem_cache_alloc(userfaultfd_ctx_cachep, GFP_KERNEL);
664 if (!ctx) {
665 kfree(fctx);
666 return -ENOMEM;
667 }
668
669 refcount_set(&ctx->refcount, 1);
670 ctx->flags = octx->flags;
671 ctx->features = octx->features;
672 ctx->released = false;
673 atomic_set(&ctx->mmap_changing, 0);
674 ctx->mm = vma->vm_mm;
675 mmgrab(ctx->mm);
676
677 userfaultfd_ctx_get(octx);
678 atomic_inc(&octx->mmap_changing);
679 fctx->orig = octx;
680 fctx->new = ctx;
681 list_add_tail(&fctx->list, fcs);
682 }
683
684 vma->vm_userfaultfd_ctx.ctx = ctx;
685 return 0;
686 }
687
dup_fctx(struct userfaultfd_fork_ctx * fctx)688 static void dup_fctx(struct userfaultfd_fork_ctx *fctx)
689 {
690 struct userfaultfd_ctx *ctx = fctx->orig;
691 struct userfaultfd_wait_queue ewq;
692
693 msg_init(&ewq.msg);
694
695 ewq.msg.event = UFFD_EVENT_FORK;
696 ewq.msg.arg.reserved.reserved1 = (unsigned long)fctx->new;
697
698 userfaultfd_event_wait_completion(ctx, &ewq);
699 }
700
dup_userfaultfd_complete(struct list_head * fcs)701 void dup_userfaultfd_complete(struct list_head *fcs)
702 {
703 struct userfaultfd_fork_ctx *fctx, *n;
704
705 list_for_each_entry_safe(fctx, n, fcs, list) {
706 dup_fctx(fctx);
707 list_del(&fctx->list);
708 kfree(fctx);
709 }
710 }
711
mremap_userfaultfd_prep(struct vm_area_struct * vma,struct vm_userfaultfd_ctx * vm_ctx)712 void mremap_userfaultfd_prep(struct vm_area_struct *vma,
713 struct vm_userfaultfd_ctx *vm_ctx)
714 {
715 struct userfaultfd_ctx *ctx;
716
717 ctx = vma->vm_userfaultfd_ctx.ctx;
718
719 if (!ctx)
720 return;
721
722 if (ctx->features & UFFD_FEATURE_EVENT_REMAP) {
723 vm_ctx->ctx = ctx;
724 userfaultfd_ctx_get(ctx);
725 atomic_inc(&ctx->mmap_changing);
726 } else {
727 /* Drop uffd context if remap feature not enabled */
728 vma->vm_userfaultfd_ctx = NULL_VM_UFFD_CTX;
729 vma->vm_flags &= ~__VM_UFFD_FLAGS;
730 }
731 }
732
mremap_userfaultfd_complete(struct vm_userfaultfd_ctx * vm_ctx,unsigned long from,unsigned long to,unsigned long len)733 void mremap_userfaultfd_complete(struct vm_userfaultfd_ctx *vm_ctx,
734 unsigned long from, unsigned long to,
735 unsigned long len)
736 {
737 struct userfaultfd_ctx *ctx = vm_ctx->ctx;
738 struct userfaultfd_wait_queue ewq;
739
740 if (!ctx)
741 return;
742
743 if (to & ~PAGE_MASK) {
744 userfaultfd_ctx_put(ctx);
745 return;
746 }
747
748 msg_init(&ewq.msg);
749
750 ewq.msg.event = UFFD_EVENT_REMAP;
751 ewq.msg.arg.remap.from = from;
752 ewq.msg.arg.remap.to = to;
753 ewq.msg.arg.remap.len = len;
754
755 userfaultfd_event_wait_completion(ctx, &ewq);
756 }
757
userfaultfd_remove(struct vm_area_struct * vma,unsigned long start,unsigned long end)758 bool userfaultfd_remove(struct vm_area_struct *vma,
759 unsigned long start, unsigned long end)
760 {
761 struct mm_struct *mm = vma->vm_mm;
762 struct userfaultfd_ctx *ctx;
763 struct userfaultfd_wait_queue ewq;
764
765 ctx = vma->vm_userfaultfd_ctx.ctx;
766 if (!ctx || !(ctx->features & UFFD_FEATURE_EVENT_REMOVE))
767 return true;
768
769 userfaultfd_ctx_get(ctx);
770 atomic_inc(&ctx->mmap_changing);
771 mmap_read_unlock(mm);
772
773 msg_init(&ewq.msg);
774
775 ewq.msg.event = UFFD_EVENT_REMOVE;
776 ewq.msg.arg.remove.start = start;
777 ewq.msg.arg.remove.end = end;
778
779 userfaultfd_event_wait_completion(ctx, &ewq);
780
781 return false;
782 }
783
has_unmap_ctx(struct userfaultfd_ctx * ctx,struct list_head * unmaps,unsigned long start,unsigned long end)784 static bool has_unmap_ctx(struct userfaultfd_ctx *ctx, struct list_head *unmaps,
785 unsigned long start, unsigned long end)
786 {
787 struct userfaultfd_unmap_ctx *unmap_ctx;
788
789 list_for_each_entry(unmap_ctx, unmaps, list)
790 if (unmap_ctx->ctx == ctx && unmap_ctx->start == start &&
791 unmap_ctx->end == end)
792 return true;
793
794 return false;
795 }
796
userfaultfd_unmap_prep(struct vm_area_struct * vma,unsigned long start,unsigned long end,struct list_head * unmaps)797 int userfaultfd_unmap_prep(struct vm_area_struct *vma,
798 unsigned long start, unsigned long end,
799 struct list_head *unmaps)
800 {
801 for ( ; vma && vma->vm_start < end; vma = vma->vm_next) {
802 struct userfaultfd_unmap_ctx *unmap_ctx;
803 struct userfaultfd_ctx *ctx = vma->vm_userfaultfd_ctx.ctx;
804
805 if (!ctx || !(ctx->features & UFFD_FEATURE_EVENT_UNMAP) ||
806 has_unmap_ctx(ctx, unmaps, start, end))
807 continue;
808
809 unmap_ctx = kzalloc(sizeof(*unmap_ctx), GFP_KERNEL);
810 if (!unmap_ctx)
811 return -ENOMEM;
812
813 userfaultfd_ctx_get(ctx);
814 atomic_inc(&ctx->mmap_changing);
815 unmap_ctx->ctx = ctx;
816 unmap_ctx->start = start;
817 unmap_ctx->end = end;
818 list_add_tail(&unmap_ctx->list, unmaps);
819 }
820
821 return 0;
822 }
823
userfaultfd_unmap_complete(struct mm_struct * mm,struct list_head * uf)824 void userfaultfd_unmap_complete(struct mm_struct *mm, struct list_head *uf)
825 {
826 struct userfaultfd_unmap_ctx *ctx, *n;
827 struct userfaultfd_wait_queue ewq;
828
829 list_for_each_entry_safe(ctx, n, uf, list) {
830 msg_init(&ewq.msg);
831
832 ewq.msg.event = UFFD_EVENT_UNMAP;
833 ewq.msg.arg.remove.start = ctx->start;
834 ewq.msg.arg.remove.end = ctx->end;
835
836 userfaultfd_event_wait_completion(ctx->ctx, &ewq);
837
838 list_del(&ctx->list);
839 kfree(ctx);
840 }
841 }
842
userfaultfd_release(struct inode * inode,struct file * file)843 static int userfaultfd_release(struct inode *inode, struct file *file)
844 {
845 struct userfaultfd_ctx *ctx = file->private_data;
846 struct mm_struct *mm = ctx->mm;
847 struct vm_area_struct *vma, *prev;
848 /* len == 0 means wake all */
849 struct userfaultfd_wake_range range = { .len = 0, };
850 unsigned long new_flags;
851
852 WRITE_ONCE(ctx->released, true);
853
854 if (!mmget_not_zero(mm))
855 goto wakeup;
856
857 /*
858 * Flush page faults out of all CPUs. NOTE: all page faults
859 * must be retried without returning VM_FAULT_SIGBUS if
860 * userfaultfd_ctx_get() succeeds but vma->vma_userfault_ctx
861 * changes while handle_userfault released the mmap_lock. So
862 * it's critical that released is set to true (above), before
863 * taking the mmap_lock for writing.
864 */
865 mmap_write_lock(mm);
866 prev = NULL;
867 for (vma = mm->mmap; vma; vma = vma->vm_next) {
868 cond_resched();
869 BUG_ON(!!vma->vm_userfaultfd_ctx.ctx ^
870 !!(vma->vm_flags & __VM_UFFD_FLAGS));
871 if (vma->vm_userfaultfd_ctx.ctx != ctx) {
872 prev = vma;
873 continue;
874 }
875 new_flags = vma->vm_flags & ~__VM_UFFD_FLAGS;
876 prev = vma_merge(mm, prev, vma->vm_start, vma->vm_end,
877 new_flags, vma->anon_vma,
878 vma->vm_file, vma->vm_pgoff,
879 vma_policy(vma),
880 NULL_VM_UFFD_CTX);
881 if (prev)
882 vma = prev;
883 else
884 prev = vma;
885 vma->vm_flags = new_flags;
886 vma->vm_userfaultfd_ctx = NULL_VM_UFFD_CTX;
887 }
888 mmap_write_unlock(mm);
889 mmput(mm);
890 wakeup:
891 /*
892 * After no new page faults can wait on this fault_*wqh, flush
893 * the last page faults that may have been already waiting on
894 * the fault_*wqh.
895 */
896 spin_lock_irq(&ctx->fault_pending_wqh.lock);
897 __wake_up_locked_key(&ctx->fault_pending_wqh, TASK_NORMAL, &range);
898 __wake_up(&ctx->fault_wqh, TASK_NORMAL, 1, &range);
899 spin_unlock_irq(&ctx->fault_pending_wqh.lock);
900
901 /* Flush pending events that may still wait on event_wqh */
902 wake_up_all(&ctx->event_wqh);
903
904 wake_up_poll(&ctx->fd_wqh, EPOLLHUP);
905 userfaultfd_ctx_put(ctx);
906 return 0;
907 }
908
909 /* fault_pending_wqh.lock must be hold by the caller */
find_userfault_in(wait_queue_head_t * wqh)910 static inline struct userfaultfd_wait_queue *find_userfault_in(
911 wait_queue_head_t *wqh)
912 {
913 wait_queue_entry_t *wq;
914 struct userfaultfd_wait_queue *uwq;
915
916 lockdep_assert_held(&wqh->lock);
917
918 uwq = NULL;
919 if (!waitqueue_active(wqh))
920 goto out;
921 /* walk in reverse to provide FIFO behavior to read userfaults */
922 wq = list_last_entry(&wqh->head, typeof(*wq), entry);
923 uwq = container_of(wq, struct userfaultfd_wait_queue, wq);
924 out:
925 return uwq;
926 }
927
find_userfault(struct userfaultfd_ctx * ctx)928 static inline struct userfaultfd_wait_queue *find_userfault(
929 struct userfaultfd_ctx *ctx)
930 {
931 return find_userfault_in(&ctx->fault_pending_wqh);
932 }
933
find_userfault_evt(struct userfaultfd_ctx * ctx)934 static inline struct userfaultfd_wait_queue *find_userfault_evt(
935 struct userfaultfd_ctx *ctx)
936 {
937 return find_userfault_in(&ctx->event_wqh);
938 }
939
userfaultfd_poll(struct file * file,poll_table * wait)940 static __poll_t userfaultfd_poll(struct file *file, poll_table *wait)
941 {
942 struct userfaultfd_ctx *ctx = file->private_data;
943 __poll_t ret;
944
945 poll_wait(file, &ctx->fd_wqh, wait);
946
947 if (!userfaultfd_is_initialized(ctx))
948 return EPOLLERR;
949
950 /*
951 * poll() never guarantees that read won't block.
952 * userfaults can be waken before they're read().
953 */
954 if (unlikely(!(file->f_flags & O_NONBLOCK)))
955 return EPOLLERR;
956 /*
957 * lockless access to see if there are pending faults
958 * __pollwait last action is the add_wait_queue but
959 * the spin_unlock would allow the waitqueue_active to
960 * pass above the actual list_add inside
961 * add_wait_queue critical section. So use a full
962 * memory barrier to serialize the list_add write of
963 * add_wait_queue() with the waitqueue_active read
964 * below.
965 */
966 ret = 0;
967 smp_mb();
968 if (waitqueue_active(&ctx->fault_pending_wqh))
969 ret = EPOLLIN;
970 else if (waitqueue_active(&ctx->event_wqh))
971 ret = EPOLLIN;
972
973 return ret;
974 }
975
976 static const struct file_operations userfaultfd_fops;
977
resolve_userfault_fork(struct userfaultfd_ctx * new,struct inode * inode,struct uffd_msg * msg)978 static int resolve_userfault_fork(struct userfaultfd_ctx *new,
979 struct inode *inode,
980 struct uffd_msg *msg)
981 {
982 int fd;
983
984 fd = anon_inode_getfd_secure("[userfaultfd]", &userfaultfd_fops, new,
985 O_RDWR | (new->flags & UFFD_SHARED_FCNTL_FLAGS), inode);
986 if (fd < 0)
987 return fd;
988
989 msg->arg.reserved.reserved1 = 0;
990 msg->arg.fork.ufd = fd;
991 return 0;
992 }
993
userfaultfd_ctx_read(struct userfaultfd_ctx * ctx,int no_wait,struct uffd_msg * msg,struct inode * inode)994 static ssize_t userfaultfd_ctx_read(struct userfaultfd_ctx *ctx, int no_wait,
995 struct uffd_msg *msg, struct inode *inode)
996 {
997 ssize_t ret;
998 DECLARE_WAITQUEUE(wait, current);
999 struct userfaultfd_wait_queue *uwq;
1000 /*
1001 * Handling fork event requires sleeping operations, so
1002 * we drop the event_wqh lock, then do these ops, then
1003 * lock it back and wake up the waiter. While the lock is
1004 * dropped the ewq may go away so we keep track of it
1005 * carefully.
1006 */
1007 LIST_HEAD(fork_event);
1008 struct userfaultfd_ctx *fork_nctx = NULL;
1009
1010 /* always take the fd_wqh lock before the fault_pending_wqh lock */
1011 spin_lock_irq(&ctx->fd_wqh.lock);
1012 __add_wait_queue(&ctx->fd_wqh, &wait);
1013 for (;;) {
1014 set_current_state(TASK_INTERRUPTIBLE);
1015 spin_lock(&ctx->fault_pending_wqh.lock);
1016 uwq = find_userfault(ctx);
1017 if (uwq) {
1018 /*
1019 * Use a seqcount to repeat the lockless check
1020 * in wake_userfault() to avoid missing
1021 * wakeups because during the refile both
1022 * waitqueue could become empty if this is the
1023 * only userfault.
1024 */
1025 write_seqcount_begin(&ctx->refile_seq);
1026
1027 /*
1028 * The fault_pending_wqh.lock prevents the uwq
1029 * to disappear from under us.
1030 *
1031 * Refile this userfault from
1032 * fault_pending_wqh to fault_wqh, it's not
1033 * pending anymore after we read it.
1034 *
1035 * Use list_del() by hand (as
1036 * userfaultfd_wake_function also uses
1037 * list_del_init() by hand) to be sure nobody
1038 * changes __remove_wait_queue() to use
1039 * list_del_init() in turn breaking the
1040 * !list_empty_careful() check in
1041 * handle_userfault(). The uwq->wq.head list
1042 * must never be empty at any time during the
1043 * refile, or the waitqueue could disappear
1044 * from under us. The "wait_queue_head_t"
1045 * parameter of __remove_wait_queue() is unused
1046 * anyway.
1047 */
1048 list_del(&uwq->wq.entry);
1049 add_wait_queue(&ctx->fault_wqh, &uwq->wq);
1050
1051 write_seqcount_end(&ctx->refile_seq);
1052
1053 /* careful to always initialize msg if ret == 0 */
1054 *msg = uwq->msg;
1055 spin_unlock(&ctx->fault_pending_wqh.lock);
1056 ret = 0;
1057 break;
1058 }
1059 spin_unlock(&ctx->fault_pending_wqh.lock);
1060
1061 spin_lock(&ctx->event_wqh.lock);
1062 uwq = find_userfault_evt(ctx);
1063 if (uwq) {
1064 *msg = uwq->msg;
1065
1066 if (uwq->msg.event == UFFD_EVENT_FORK) {
1067 fork_nctx = (struct userfaultfd_ctx *)
1068 (unsigned long)
1069 uwq->msg.arg.reserved.reserved1;
1070 list_move(&uwq->wq.entry, &fork_event);
1071 /*
1072 * fork_nctx can be freed as soon as
1073 * we drop the lock, unless we take a
1074 * reference on it.
1075 */
1076 userfaultfd_ctx_get(fork_nctx);
1077 spin_unlock(&ctx->event_wqh.lock);
1078 ret = 0;
1079 break;
1080 }
1081
1082 userfaultfd_event_complete(ctx, uwq);
1083 spin_unlock(&ctx->event_wqh.lock);
1084 ret = 0;
1085 break;
1086 }
1087 spin_unlock(&ctx->event_wqh.lock);
1088
1089 if (signal_pending(current)) {
1090 ret = -ERESTARTSYS;
1091 break;
1092 }
1093 if (no_wait) {
1094 ret = -EAGAIN;
1095 break;
1096 }
1097 spin_unlock_irq(&ctx->fd_wqh.lock);
1098 schedule();
1099 spin_lock_irq(&ctx->fd_wqh.lock);
1100 }
1101 __remove_wait_queue(&ctx->fd_wqh, &wait);
1102 __set_current_state(TASK_RUNNING);
1103 spin_unlock_irq(&ctx->fd_wqh.lock);
1104
1105 if (!ret && msg->event == UFFD_EVENT_FORK) {
1106 ret = resolve_userfault_fork(fork_nctx, inode, msg);
1107 spin_lock_irq(&ctx->event_wqh.lock);
1108 if (!list_empty(&fork_event)) {
1109 /*
1110 * The fork thread didn't abort, so we can
1111 * drop the temporary refcount.
1112 */
1113 userfaultfd_ctx_put(fork_nctx);
1114
1115 uwq = list_first_entry(&fork_event,
1116 typeof(*uwq),
1117 wq.entry);
1118 /*
1119 * If fork_event list wasn't empty and in turn
1120 * the event wasn't already released by fork
1121 * (the event is allocated on fork kernel
1122 * stack), put the event back to its place in
1123 * the event_wq. fork_event head will be freed
1124 * as soon as we return so the event cannot
1125 * stay queued there no matter the current
1126 * "ret" value.
1127 */
1128 list_del(&uwq->wq.entry);
1129 __add_wait_queue(&ctx->event_wqh, &uwq->wq);
1130
1131 /*
1132 * Leave the event in the waitqueue and report
1133 * error to userland if we failed to resolve
1134 * the userfault fork.
1135 */
1136 if (likely(!ret))
1137 userfaultfd_event_complete(ctx, uwq);
1138 } else {
1139 /*
1140 * Here the fork thread aborted and the
1141 * refcount from the fork thread on fork_nctx
1142 * has already been released. We still hold
1143 * the reference we took before releasing the
1144 * lock above. If resolve_userfault_fork
1145 * failed we've to drop it because the
1146 * fork_nctx has to be freed in such case. If
1147 * it succeeded we'll hold it because the new
1148 * uffd references it.
1149 */
1150 if (ret)
1151 userfaultfd_ctx_put(fork_nctx);
1152 }
1153 spin_unlock_irq(&ctx->event_wqh.lock);
1154 }
1155
1156 return ret;
1157 }
1158
userfaultfd_read(struct file * file,char __user * buf,size_t count,loff_t * ppos)1159 static ssize_t userfaultfd_read(struct file *file, char __user *buf,
1160 size_t count, loff_t *ppos)
1161 {
1162 struct userfaultfd_ctx *ctx = file->private_data;
1163 ssize_t _ret, ret = 0;
1164 struct uffd_msg msg;
1165 int no_wait = file->f_flags & O_NONBLOCK;
1166 struct inode *inode = file_inode(file);
1167
1168 if (!userfaultfd_is_initialized(ctx))
1169 return -EINVAL;
1170
1171 for (;;) {
1172 if (count < sizeof(msg))
1173 return ret ? ret : -EINVAL;
1174 _ret = userfaultfd_ctx_read(ctx, no_wait, &msg, inode);
1175 if (_ret < 0)
1176 return ret ? ret : _ret;
1177 if (copy_to_user((__u64 __user *) buf, &msg, sizeof(msg)))
1178 return ret ? ret : -EFAULT;
1179 ret += sizeof(msg);
1180 buf += sizeof(msg);
1181 count -= sizeof(msg);
1182 /*
1183 * Allow to read more than one fault at time but only
1184 * block if waiting for the very first one.
1185 */
1186 no_wait = O_NONBLOCK;
1187 }
1188 }
1189
__wake_userfault(struct userfaultfd_ctx * ctx,struct userfaultfd_wake_range * range)1190 static void __wake_userfault(struct userfaultfd_ctx *ctx,
1191 struct userfaultfd_wake_range *range)
1192 {
1193 spin_lock_irq(&ctx->fault_pending_wqh.lock);
1194 /* wake all in the range and autoremove */
1195 if (waitqueue_active(&ctx->fault_pending_wqh))
1196 __wake_up_locked_key(&ctx->fault_pending_wqh, TASK_NORMAL,
1197 range);
1198 if (waitqueue_active(&ctx->fault_wqh))
1199 __wake_up(&ctx->fault_wqh, TASK_NORMAL, 1, range);
1200 spin_unlock_irq(&ctx->fault_pending_wqh.lock);
1201 }
1202
wake_userfault(struct userfaultfd_ctx * ctx,struct userfaultfd_wake_range * range)1203 static __always_inline void wake_userfault(struct userfaultfd_ctx *ctx,
1204 struct userfaultfd_wake_range *range)
1205 {
1206 unsigned seq;
1207 bool need_wakeup;
1208
1209 /*
1210 * To be sure waitqueue_active() is not reordered by the CPU
1211 * before the pagetable update, use an explicit SMP memory
1212 * barrier here. PT lock release or mmap_read_unlock(mm) still
1213 * have release semantics that can allow the
1214 * waitqueue_active() to be reordered before the pte update.
1215 */
1216 smp_mb();
1217
1218 /*
1219 * Use waitqueue_active because it's very frequent to
1220 * change the address space atomically even if there are no
1221 * userfaults yet. So we take the spinlock only when we're
1222 * sure we've userfaults to wake.
1223 */
1224 do {
1225 seq = read_seqcount_begin(&ctx->refile_seq);
1226 need_wakeup = waitqueue_active(&ctx->fault_pending_wqh) ||
1227 waitqueue_active(&ctx->fault_wqh);
1228 cond_resched();
1229 } while (read_seqcount_retry(&ctx->refile_seq, seq));
1230 if (need_wakeup)
1231 __wake_userfault(ctx, range);
1232 }
1233
validate_range(struct mm_struct * mm,__u64 start,__u64 len)1234 static __always_inline int validate_range(struct mm_struct *mm,
1235 __u64 start, __u64 len)
1236 {
1237 __u64 task_size = mm->task_size;
1238
1239 if (start & ~PAGE_MASK)
1240 return -EINVAL;
1241 if (len & ~PAGE_MASK)
1242 return -EINVAL;
1243 if (!len)
1244 return -EINVAL;
1245 if (start < mmap_min_addr)
1246 return -EINVAL;
1247 if (start >= task_size)
1248 return -EINVAL;
1249 if (len > task_size - start)
1250 return -EINVAL;
1251 return 0;
1252 }
1253
vma_can_userfault(struct vm_area_struct * vma,unsigned long vm_flags)1254 static inline bool vma_can_userfault(struct vm_area_struct *vma,
1255 unsigned long vm_flags)
1256 {
1257 /* FIXME: add WP support to hugetlbfs and shmem */
1258 if (vm_flags & VM_UFFD_WP) {
1259 if (is_vm_hugetlb_page(vma) || vma_is_shmem(vma))
1260 return false;
1261 }
1262
1263 if (vm_flags & VM_UFFD_MINOR) {
1264 if (!(is_vm_hugetlb_page(vma) || vma_is_shmem(vma)))
1265 return false;
1266 }
1267
1268 return vma_is_anonymous(vma) || is_vm_hugetlb_page(vma) ||
1269 vma_is_shmem(vma);
1270 }
1271
userfaultfd_register(struct userfaultfd_ctx * ctx,unsigned long arg)1272 static int userfaultfd_register(struct userfaultfd_ctx *ctx,
1273 unsigned long arg)
1274 {
1275 struct mm_struct *mm = ctx->mm;
1276 struct vm_area_struct *vma, *prev, *cur;
1277 int ret;
1278 struct uffdio_register uffdio_register;
1279 struct uffdio_register __user *user_uffdio_register;
1280 unsigned long vm_flags, new_flags;
1281 bool found;
1282 bool basic_ioctls;
1283 unsigned long start, end, vma_end;
1284
1285 user_uffdio_register = (struct uffdio_register __user *) arg;
1286
1287 ret = -EFAULT;
1288 if (copy_from_user(&uffdio_register, user_uffdio_register,
1289 sizeof(uffdio_register)-sizeof(__u64)))
1290 goto out;
1291
1292 ret = -EINVAL;
1293 if (!uffdio_register.mode)
1294 goto out;
1295 if (uffdio_register.mode & ~UFFD_API_REGISTER_MODES)
1296 goto out;
1297 vm_flags = 0;
1298 if (uffdio_register.mode & UFFDIO_REGISTER_MODE_MISSING)
1299 vm_flags |= VM_UFFD_MISSING;
1300 if (uffdio_register.mode & UFFDIO_REGISTER_MODE_WP) {
1301 #ifndef CONFIG_HAVE_ARCH_USERFAULTFD_WP
1302 goto out;
1303 #endif
1304 vm_flags |= VM_UFFD_WP;
1305 }
1306 if (uffdio_register.mode & UFFDIO_REGISTER_MODE_MINOR) {
1307 #ifndef CONFIG_HAVE_ARCH_USERFAULTFD_MINOR
1308 goto out;
1309 #endif
1310 vm_flags |= VM_UFFD_MINOR;
1311 }
1312
1313 ret = validate_range(mm, uffdio_register.range.start,
1314 uffdio_register.range.len);
1315 if (ret)
1316 goto out;
1317
1318 start = uffdio_register.range.start;
1319 end = start + uffdio_register.range.len;
1320
1321 ret = -ENOMEM;
1322 if (!mmget_not_zero(mm))
1323 goto out;
1324
1325 mmap_write_lock(mm);
1326 vma = find_vma_prev(mm, start, &prev);
1327 if (!vma)
1328 goto out_unlock;
1329
1330 /* check that there's at least one vma in the range */
1331 ret = -EINVAL;
1332 if (vma->vm_start >= end)
1333 goto out_unlock;
1334
1335 /*
1336 * If the first vma contains huge pages, make sure start address
1337 * is aligned to huge page size.
1338 */
1339 if (is_vm_hugetlb_page(vma)) {
1340 unsigned long vma_hpagesize = vma_kernel_pagesize(vma);
1341
1342 if (start & (vma_hpagesize - 1))
1343 goto out_unlock;
1344 }
1345
1346 /*
1347 * Search for not compatible vmas.
1348 */
1349 found = false;
1350 basic_ioctls = false;
1351 for (cur = vma; cur && cur->vm_start < end; cur = cur->vm_next) {
1352 cond_resched();
1353
1354 BUG_ON(!!cur->vm_userfaultfd_ctx.ctx ^
1355 !!(cur->vm_flags & __VM_UFFD_FLAGS));
1356
1357 /* check not compatible vmas */
1358 ret = -EINVAL;
1359 if (!vma_can_userfault(cur, vm_flags))
1360 goto out_unlock;
1361
1362 /*
1363 * UFFDIO_COPY will fill file holes even without
1364 * PROT_WRITE. This check enforces that if this is a
1365 * MAP_SHARED, the process has write permission to the backing
1366 * file. If VM_MAYWRITE is set it also enforces that on a
1367 * MAP_SHARED vma: there is no F_WRITE_SEAL and no further
1368 * F_WRITE_SEAL can be taken until the vma is destroyed.
1369 */
1370 ret = -EPERM;
1371 if (unlikely(!(cur->vm_flags & VM_MAYWRITE)))
1372 goto out_unlock;
1373
1374 /*
1375 * If this vma contains ending address, and huge pages
1376 * check alignment.
1377 */
1378 if (is_vm_hugetlb_page(cur) && end <= cur->vm_end &&
1379 end > cur->vm_start) {
1380 unsigned long vma_hpagesize = vma_kernel_pagesize(cur);
1381
1382 ret = -EINVAL;
1383
1384 if (end & (vma_hpagesize - 1))
1385 goto out_unlock;
1386 }
1387 if ((vm_flags & VM_UFFD_WP) && !(cur->vm_flags & VM_MAYWRITE))
1388 goto out_unlock;
1389
1390 /*
1391 * Check that this vma isn't already owned by a
1392 * different userfaultfd. We can't allow more than one
1393 * userfaultfd to own a single vma simultaneously or we
1394 * wouldn't know which one to deliver the userfaults to.
1395 */
1396 ret = -EBUSY;
1397 if (cur->vm_userfaultfd_ctx.ctx &&
1398 cur->vm_userfaultfd_ctx.ctx != ctx)
1399 goto out_unlock;
1400
1401 /*
1402 * Note vmas containing huge pages
1403 */
1404 if (is_vm_hugetlb_page(cur))
1405 basic_ioctls = true;
1406
1407 found = true;
1408 }
1409 BUG_ON(!found);
1410
1411 if (vma->vm_start < start)
1412 prev = vma;
1413
1414 ret = 0;
1415 do {
1416 cond_resched();
1417
1418 BUG_ON(!vma_can_userfault(vma, vm_flags));
1419 BUG_ON(vma->vm_userfaultfd_ctx.ctx &&
1420 vma->vm_userfaultfd_ctx.ctx != ctx);
1421 WARN_ON(!(vma->vm_flags & VM_MAYWRITE));
1422
1423 /*
1424 * Nothing to do: this vma is already registered into this
1425 * userfaultfd and with the right tracking mode too.
1426 */
1427 if (vma->vm_userfaultfd_ctx.ctx == ctx &&
1428 (vma->vm_flags & vm_flags) == vm_flags)
1429 goto skip;
1430
1431 if (vma->vm_start > start)
1432 start = vma->vm_start;
1433 vma_end = min(end, vma->vm_end);
1434
1435 new_flags = (vma->vm_flags & ~__VM_UFFD_FLAGS) | vm_flags;
1436 prev = vma_merge(mm, prev, start, vma_end, new_flags,
1437 vma->anon_vma, vma->vm_file, vma->vm_pgoff,
1438 vma_policy(vma),
1439 ((struct vm_userfaultfd_ctx){ ctx }));
1440 if (prev) {
1441 vma = prev;
1442 goto next;
1443 }
1444 if (vma->vm_start < start) {
1445 ret = split_vma(mm, vma, start, 1);
1446 if (ret)
1447 break;
1448 }
1449 if (vma->vm_end > end) {
1450 ret = split_vma(mm, vma, end, 0);
1451 if (ret)
1452 break;
1453 }
1454 next:
1455 /*
1456 * In the vma_merge() successful mprotect-like case 8:
1457 * the next vma was merged into the current one and
1458 * the current one has not been updated yet.
1459 */
1460 vma->vm_flags = new_flags;
1461 vma->vm_userfaultfd_ctx.ctx = ctx;
1462
1463 if (is_vm_hugetlb_page(vma) && uffd_disable_huge_pmd_share(vma))
1464 hugetlb_unshare_all_pmds(vma);
1465
1466 skip:
1467 prev = vma;
1468 start = vma->vm_end;
1469 vma = vma->vm_next;
1470 } while (vma && vma->vm_start < end);
1471 out_unlock:
1472 mmap_write_unlock(mm);
1473 mmput(mm);
1474 if (!ret) {
1475 __u64 ioctls_out;
1476
1477 ioctls_out = basic_ioctls ? UFFD_API_RANGE_IOCTLS_BASIC :
1478 UFFD_API_RANGE_IOCTLS;
1479
1480 /*
1481 * Declare the WP ioctl only if the WP mode is
1482 * specified and all checks passed with the range
1483 */
1484 if (!(uffdio_register.mode & UFFDIO_REGISTER_MODE_WP))
1485 ioctls_out &= ~((__u64)1 << _UFFDIO_WRITEPROTECT);
1486
1487 /* CONTINUE ioctl is only supported for MINOR ranges. */
1488 if (!(uffdio_register.mode & UFFDIO_REGISTER_MODE_MINOR))
1489 ioctls_out &= ~((__u64)1 << _UFFDIO_CONTINUE);
1490
1491 /*
1492 * Now that we scanned all vmas we can already tell
1493 * userland which ioctls methods are guaranteed to
1494 * succeed on this range.
1495 */
1496 if (put_user(ioctls_out, &user_uffdio_register->ioctls))
1497 ret = -EFAULT;
1498 }
1499 out:
1500 return ret;
1501 }
1502
userfaultfd_unregister(struct userfaultfd_ctx * ctx,unsigned long arg)1503 static int userfaultfd_unregister(struct userfaultfd_ctx *ctx,
1504 unsigned long arg)
1505 {
1506 struct mm_struct *mm = ctx->mm;
1507 struct vm_area_struct *vma, *prev, *cur;
1508 int ret;
1509 struct uffdio_range uffdio_unregister;
1510 unsigned long new_flags;
1511 bool found;
1512 unsigned long start, end, vma_end;
1513 const void __user *buf = (void __user *)arg;
1514
1515 ret = -EFAULT;
1516 if (copy_from_user(&uffdio_unregister, buf, sizeof(uffdio_unregister)))
1517 goto out;
1518
1519 ret = validate_range(mm, uffdio_unregister.start,
1520 uffdio_unregister.len);
1521 if (ret)
1522 goto out;
1523
1524 start = uffdio_unregister.start;
1525 end = start + uffdio_unregister.len;
1526
1527 ret = -ENOMEM;
1528 if (!mmget_not_zero(mm))
1529 goto out;
1530
1531 mmap_write_lock(mm);
1532 vma = find_vma_prev(mm, start, &prev);
1533 if (!vma)
1534 goto out_unlock;
1535
1536 /* check that there's at least one vma in the range */
1537 ret = -EINVAL;
1538 if (vma->vm_start >= end)
1539 goto out_unlock;
1540
1541 /*
1542 * If the first vma contains huge pages, make sure start address
1543 * is aligned to huge page size.
1544 */
1545 if (is_vm_hugetlb_page(vma)) {
1546 unsigned long vma_hpagesize = vma_kernel_pagesize(vma);
1547
1548 if (start & (vma_hpagesize - 1))
1549 goto out_unlock;
1550 }
1551
1552 /*
1553 * Search for not compatible vmas.
1554 */
1555 found = false;
1556 ret = -EINVAL;
1557 for (cur = vma; cur && cur->vm_start < end; cur = cur->vm_next) {
1558 cond_resched();
1559
1560 BUG_ON(!!cur->vm_userfaultfd_ctx.ctx ^
1561 !!(cur->vm_flags & __VM_UFFD_FLAGS));
1562
1563 /*
1564 * Check not compatible vmas, not strictly required
1565 * here as not compatible vmas cannot have an
1566 * userfaultfd_ctx registered on them, but this
1567 * provides for more strict behavior to notice
1568 * unregistration errors.
1569 */
1570 if (!vma_can_userfault(cur, cur->vm_flags))
1571 goto out_unlock;
1572
1573 found = true;
1574 }
1575 BUG_ON(!found);
1576
1577 if (vma->vm_start < start)
1578 prev = vma;
1579
1580 ret = 0;
1581 do {
1582 cond_resched();
1583
1584 BUG_ON(!vma_can_userfault(vma, vma->vm_flags));
1585
1586 /*
1587 * Nothing to do: this vma is already registered into this
1588 * userfaultfd and with the right tracking mode too.
1589 */
1590 if (!vma->vm_userfaultfd_ctx.ctx)
1591 goto skip;
1592
1593 WARN_ON(!(vma->vm_flags & VM_MAYWRITE));
1594
1595 if (vma->vm_start > start)
1596 start = vma->vm_start;
1597 vma_end = min(end, vma->vm_end);
1598
1599 if (userfaultfd_missing(vma)) {
1600 /*
1601 * Wake any concurrent pending userfault while
1602 * we unregister, so they will not hang
1603 * permanently and it avoids userland to call
1604 * UFFDIO_WAKE explicitly.
1605 */
1606 struct userfaultfd_wake_range range;
1607 range.start = start;
1608 range.len = vma_end - start;
1609 wake_userfault(vma->vm_userfaultfd_ctx.ctx, &range);
1610 }
1611
1612 new_flags = vma->vm_flags & ~__VM_UFFD_FLAGS;
1613 prev = vma_merge(mm, prev, start, vma_end, new_flags,
1614 vma->anon_vma, vma->vm_file, vma->vm_pgoff,
1615 vma_policy(vma),
1616 NULL_VM_UFFD_CTX);
1617 if (prev) {
1618 vma = prev;
1619 goto next;
1620 }
1621 if (vma->vm_start < start) {
1622 ret = split_vma(mm, vma, start, 1);
1623 if (ret)
1624 break;
1625 }
1626 if (vma->vm_end > end) {
1627 ret = split_vma(mm, vma, end, 0);
1628 if (ret)
1629 break;
1630 }
1631 next:
1632 /*
1633 * In the vma_merge() successful mprotect-like case 8:
1634 * the next vma was merged into the current one and
1635 * the current one has not been updated yet.
1636 */
1637 vma->vm_flags = new_flags;
1638 vma->vm_userfaultfd_ctx = NULL_VM_UFFD_CTX;
1639
1640 skip:
1641 prev = vma;
1642 start = vma->vm_end;
1643 vma = vma->vm_next;
1644 } while (vma && vma->vm_start < end);
1645 out_unlock:
1646 mmap_write_unlock(mm);
1647 mmput(mm);
1648 out:
1649 return ret;
1650 }
1651
1652 /*
1653 * userfaultfd_wake may be used in combination with the
1654 * UFFDIO_*_MODE_DONTWAKE to wakeup userfaults in batches.
1655 */
userfaultfd_wake(struct userfaultfd_ctx * ctx,unsigned long arg)1656 static int userfaultfd_wake(struct userfaultfd_ctx *ctx,
1657 unsigned long arg)
1658 {
1659 int ret;
1660 struct uffdio_range uffdio_wake;
1661 struct userfaultfd_wake_range range;
1662 const void __user *buf = (void __user *)arg;
1663
1664 ret = -EFAULT;
1665 if (copy_from_user(&uffdio_wake, buf, sizeof(uffdio_wake)))
1666 goto out;
1667
1668 ret = validate_range(ctx->mm, uffdio_wake.start, uffdio_wake.len);
1669 if (ret)
1670 goto out;
1671
1672 range.start = uffdio_wake.start;
1673 range.len = uffdio_wake.len;
1674
1675 /*
1676 * len == 0 means wake all and we don't want to wake all here,
1677 * so check it again to be sure.
1678 */
1679 VM_BUG_ON(!range.len);
1680
1681 wake_userfault(ctx, &range);
1682 ret = 0;
1683
1684 out:
1685 return ret;
1686 }
1687
userfaultfd_copy(struct userfaultfd_ctx * ctx,unsigned long arg)1688 static int userfaultfd_copy(struct userfaultfd_ctx *ctx,
1689 unsigned long arg)
1690 {
1691 __s64 ret;
1692 struct uffdio_copy uffdio_copy;
1693 struct uffdio_copy __user *user_uffdio_copy;
1694 struct userfaultfd_wake_range range;
1695
1696 user_uffdio_copy = (struct uffdio_copy __user *) arg;
1697
1698 ret = -EAGAIN;
1699 if (atomic_read(&ctx->mmap_changing))
1700 goto out;
1701
1702 ret = -EFAULT;
1703 if (copy_from_user(&uffdio_copy, user_uffdio_copy,
1704 /* don't copy "copy" last field */
1705 sizeof(uffdio_copy)-sizeof(__s64)))
1706 goto out;
1707
1708 ret = validate_range(ctx->mm, uffdio_copy.dst, uffdio_copy.len);
1709 if (ret)
1710 goto out;
1711 /*
1712 * double check for wraparound just in case. copy_from_user()
1713 * will later check uffdio_copy.src + uffdio_copy.len to fit
1714 * in the userland range.
1715 */
1716 ret = -EINVAL;
1717 if (uffdio_copy.src + uffdio_copy.len <= uffdio_copy.src)
1718 goto out;
1719 if (uffdio_copy.mode & ~(UFFDIO_COPY_MODE_DONTWAKE|UFFDIO_COPY_MODE_WP))
1720 goto out;
1721 if (mmget_not_zero(ctx->mm)) {
1722 ret = mcopy_atomic(ctx->mm, uffdio_copy.dst, uffdio_copy.src,
1723 uffdio_copy.len, &ctx->mmap_changing,
1724 uffdio_copy.mode);
1725 mmput(ctx->mm);
1726 } else {
1727 return -ESRCH;
1728 }
1729 if (unlikely(put_user(ret, &user_uffdio_copy->copy)))
1730 return -EFAULT;
1731 if (ret < 0)
1732 goto out;
1733 BUG_ON(!ret);
1734 /* len == 0 would wake all */
1735 range.len = ret;
1736 if (!(uffdio_copy.mode & UFFDIO_COPY_MODE_DONTWAKE)) {
1737 range.start = uffdio_copy.dst;
1738 wake_userfault(ctx, &range);
1739 }
1740 ret = range.len == uffdio_copy.len ? 0 : -EAGAIN;
1741 out:
1742 return ret;
1743 }
1744
userfaultfd_zeropage(struct userfaultfd_ctx * ctx,unsigned long arg)1745 static int userfaultfd_zeropage(struct userfaultfd_ctx *ctx,
1746 unsigned long arg)
1747 {
1748 __s64 ret;
1749 struct uffdio_zeropage uffdio_zeropage;
1750 struct uffdio_zeropage __user *user_uffdio_zeropage;
1751 struct userfaultfd_wake_range range;
1752
1753 user_uffdio_zeropage = (struct uffdio_zeropage __user *) arg;
1754
1755 ret = -EAGAIN;
1756 if (atomic_read(&ctx->mmap_changing))
1757 goto out;
1758
1759 ret = -EFAULT;
1760 if (copy_from_user(&uffdio_zeropage, user_uffdio_zeropage,
1761 /* don't copy "zeropage" last field */
1762 sizeof(uffdio_zeropage)-sizeof(__s64)))
1763 goto out;
1764
1765 ret = validate_range(ctx->mm, uffdio_zeropage.range.start,
1766 uffdio_zeropage.range.len);
1767 if (ret)
1768 goto out;
1769 ret = -EINVAL;
1770 if (uffdio_zeropage.mode & ~UFFDIO_ZEROPAGE_MODE_DONTWAKE)
1771 goto out;
1772
1773 if (mmget_not_zero(ctx->mm)) {
1774 ret = mfill_zeropage(ctx->mm, uffdio_zeropage.range.start,
1775 uffdio_zeropage.range.len,
1776 &ctx->mmap_changing);
1777 mmput(ctx->mm);
1778 } else {
1779 return -ESRCH;
1780 }
1781 if (unlikely(put_user(ret, &user_uffdio_zeropage->zeropage)))
1782 return -EFAULT;
1783 if (ret < 0)
1784 goto out;
1785 /* len == 0 would wake all */
1786 BUG_ON(!ret);
1787 range.len = ret;
1788 if (!(uffdio_zeropage.mode & UFFDIO_ZEROPAGE_MODE_DONTWAKE)) {
1789 range.start = uffdio_zeropage.range.start;
1790 wake_userfault(ctx, &range);
1791 }
1792 ret = range.len == uffdio_zeropage.range.len ? 0 : -EAGAIN;
1793 out:
1794 return ret;
1795 }
1796
userfaultfd_writeprotect(struct userfaultfd_ctx * ctx,unsigned long arg)1797 static int userfaultfd_writeprotect(struct userfaultfd_ctx *ctx,
1798 unsigned long arg)
1799 {
1800 int ret;
1801 struct uffdio_writeprotect uffdio_wp;
1802 struct uffdio_writeprotect __user *user_uffdio_wp;
1803 struct userfaultfd_wake_range range;
1804 bool mode_wp, mode_dontwake;
1805
1806 if (atomic_read(&ctx->mmap_changing))
1807 return -EAGAIN;
1808
1809 user_uffdio_wp = (struct uffdio_writeprotect __user *) arg;
1810
1811 if (copy_from_user(&uffdio_wp, user_uffdio_wp,
1812 sizeof(struct uffdio_writeprotect)))
1813 return -EFAULT;
1814
1815 ret = validate_range(ctx->mm, uffdio_wp.range.start,
1816 uffdio_wp.range.len);
1817 if (ret)
1818 return ret;
1819
1820 if (uffdio_wp.mode & ~(UFFDIO_WRITEPROTECT_MODE_DONTWAKE |
1821 UFFDIO_WRITEPROTECT_MODE_WP))
1822 return -EINVAL;
1823
1824 mode_wp = uffdio_wp.mode & UFFDIO_WRITEPROTECT_MODE_WP;
1825 mode_dontwake = uffdio_wp.mode & UFFDIO_WRITEPROTECT_MODE_DONTWAKE;
1826
1827 if (mode_wp && mode_dontwake)
1828 return -EINVAL;
1829
1830 if (mmget_not_zero(ctx->mm)) {
1831 ret = mwriteprotect_range(ctx->mm, uffdio_wp.range.start,
1832 uffdio_wp.range.len, mode_wp,
1833 &ctx->mmap_changing);
1834 mmput(ctx->mm);
1835 } else {
1836 return -ESRCH;
1837 }
1838
1839 if (ret)
1840 return ret;
1841
1842 if (!mode_wp && !mode_dontwake) {
1843 range.start = uffdio_wp.range.start;
1844 range.len = uffdio_wp.range.len;
1845 wake_userfault(ctx, &range);
1846 }
1847 return ret;
1848 }
1849
userfaultfd_continue(struct userfaultfd_ctx * ctx,unsigned long arg)1850 static int userfaultfd_continue(struct userfaultfd_ctx *ctx, unsigned long arg)
1851 {
1852 __s64 ret;
1853 struct uffdio_continue uffdio_continue;
1854 struct uffdio_continue __user *user_uffdio_continue;
1855 struct userfaultfd_wake_range range;
1856
1857 user_uffdio_continue = (struct uffdio_continue __user *)arg;
1858
1859 ret = -EAGAIN;
1860 if (atomic_read(&ctx->mmap_changing))
1861 goto out;
1862
1863 ret = -EFAULT;
1864 if (copy_from_user(&uffdio_continue, user_uffdio_continue,
1865 /* don't copy the output fields */
1866 sizeof(uffdio_continue) - (sizeof(__s64))))
1867 goto out;
1868
1869 ret = validate_range(ctx->mm, uffdio_continue.range.start,
1870 uffdio_continue.range.len);
1871 if (ret)
1872 goto out;
1873
1874 ret = -EINVAL;
1875 /* double check for wraparound just in case. */
1876 if (uffdio_continue.range.start + uffdio_continue.range.len <=
1877 uffdio_continue.range.start) {
1878 goto out;
1879 }
1880 if (uffdio_continue.mode & ~UFFDIO_CONTINUE_MODE_DONTWAKE)
1881 goto out;
1882
1883 if (mmget_not_zero(ctx->mm)) {
1884 ret = mcopy_continue(ctx->mm, uffdio_continue.range.start,
1885 uffdio_continue.range.len,
1886 &ctx->mmap_changing);
1887 mmput(ctx->mm);
1888 } else {
1889 return -ESRCH;
1890 }
1891
1892 if (unlikely(put_user(ret, &user_uffdio_continue->mapped)))
1893 return -EFAULT;
1894 if (ret < 0)
1895 goto out;
1896
1897 /* len == 0 would wake all */
1898 BUG_ON(!ret);
1899 range.len = ret;
1900 if (!(uffdio_continue.mode & UFFDIO_CONTINUE_MODE_DONTWAKE)) {
1901 range.start = uffdio_continue.range.start;
1902 wake_userfault(ctx, &range);
1903 }
1904 ret = range.len == uffdio_continue.range.len ? 0 : -EAGAIN;
1905
1906 out:
1907 return ret;
1908 }
1909
uffd_ctx_features(__u64 user_features)1910 static inline unsigned int uffd_ctx_features(__u64 user_features)
1911 {
1912 /*
1913 * For the current set of features the bits just coincide. Set
1914 * UFFD_FEATURE_INITIALIZED to mark the features as enabled.
1915 */
1916 return (unsigned int)user_features | UFFD_FEATURE_INITIALIZED;
1917 }
1918
1919 /*
1920 * userland asks for a certain API version and we return which bits
1921 * and ioctl commands are implemented in this kernel for such API
1922 * version or -EINVAL if unknown.
1923 */
userfaultfd_api(struct userfaultfd_ctx * ctx,unsigned long arg)1924 static int userfaultfd_api(struct userfaultfd_ctx *ctx,
1925 unsigned long arg)
1926 {
1927 struct uffdio_api uffdio_api;
1928 void __user *buf = (void __user *)arg;
1929 unsigned int ctx_features;
1930 int ret;
1931 __u64 features;
1932
1933 ret = -EFAULT;
1934 if (copy_from_user(&uffdio_api, buf, sizeof(uffdio_api)))
1935 goto out;
1936 features = uffdio_api.features;
1937 ret = -EINVAL;
1938 if (uffdio_api.api != UFFD_API || (features & ~UFFD_API_FEATURES))
1939 goto err_out;
1940 ret = -EPERM;
1941 if ((features & UFFD_FEATURE_EVENT_FORK) && !capable(CAP_SYS_PTRACE))
1942 goto err_out;
1943 /* report all available features and ioctls to userland */
1944 uffdio_api.features = UFFD_API_FEATURES;
1945 #ifndef CONFIG_HAVE_ARCH_USERFAULTFD_MINOR
1946 uffdio_api.features &=
1947 ~(UFFD_FEATURE_MINOR_HUGETLBFS | UFFD_FEATURE_MINOR_SHMEM);
1948 #endif
1949 #ifndef CONFIG_HAVE_ARCH_USERFAULTFD_WP
1950 uffdio_api.features &= ~UFFD_FEATURE_PAGEFAULT_FLAG_WP;
1951 #endif
1952 uffdio_api.ioctls = UFFD_API_IOCTLS;
1953 ret = -EFAULT;
1954 if (copy_to_user(buf, &uffdio_api, sizeof(uffdio_api)))
1955 goto out;
1956
1957 /* only enable the requested features for this uffd context */
1958 ctx_features = uffd_ctx_features(features);
1959 ret = -EINVAL;
1960 if (cmpxchg(&ctx->features, 0, ctx_features) != 0)
1961 goto err_out;
1962
1963 ret = 0;
1964 out:
1965 return ret;
1966 err_out:
1967 memset(&uffdio_api, 0, sizeof(uffdio_api));
1968 if (copy_to_user(buf, &uffdio_api, sizeof(uffdio_api)))
1969 ret = -EFAULT;
1970 goto out;
1971 }
1972
userfaultfd_ioctl(struct file * file,unsigned cmd,unsigned long arg)1973 static long userfaultfd_ioctl(struct file *file, unsigned cmd,
1974 unsigned long arg)
1975 {
1976 int ret = -EINVAL;
1977 struct userfaultfd_ctx *ctx = file->private_data;
1978
1979 if (cmd != UFFDIO_API && !userfaultfd_is_initialized(ctx))
1980 return -EINVAL;
1981
1982 switch(cmd) {
1983 case UFFDIO_API:
1984 ret = userfaultfd_api(ctx, arg);
1985 break;
1986 case UFFDIO_REGISTER:
1987 ret = userfaultfd_register(ctx, arg);
1988 break;
1989 case UFFDIO_UNREGISTER:
1990 ret = userfaultfd_unregister(ctx, arg);
1991 break;
1992 case UFFDIO_WAKE:
1993 ret = userfaultfd_wake(ctx, arg);
1994 break;
1995 case UFFDIO_COPY:
1996 ret = userfaultfd_copy(ctx, arg);
1997 break;
1998 case UFFDIO_ZEROPAGE:
1999 ret = userfaultfd_zeropage(ctx, arg);
2000 break;
2001 case UFFDIO_WRITEPROTECT:
2002 ret = userfaultfd_writeprotect(ctx, arg);
2003 break;
2004 case UFFDIO_CONTINUE:
2005 ret = userfaultfd_continue(ctx, arg);
2006 break;
2007 }
2008 return ret;
2009 }
2010
2011 #ifdef CONFIG_PROC_FS
userfaultfd_show_fdinfo(struct seq_file * m,struct file * f)2012 static void userfaultfd_show_fdinfo(struct seq_file *m, struct file *f)
2013 {
2014 struct userfaultfd_ctx *ctx = f->private_data;
2015 wait_queue_entry_t *wq;
2016 unsigned long pending = 0, total = 0;
2017
2018 spin_lock_irq(&ctx->fault_pending_wqh.lock);
2019 list_for_each_entry(wq, &ctx->fault_pending_wqh.head, entry) {
2020 pending++;
2021 total++;
2022 }
2023 list_for_each_entry(wq, &ctx->fault_wqh.head, entry) {
2024 total++;
2025 }
2026 spin_unlock_irq(&ctx->fault_pending_wqh.lock);
2027
2028 /*
2029 * If more protocols will be added, there will be all shown
2030 * separated by a space. Like this:
2031 * protocols: aa:... bb:...
2032 */
2033 seq_printf(m, "pending:\t%lu\ntotal:\t%lu\nAPI:\t%Lx:%x:%Lx\n",
2034 pending, total, UFFD_API, ctx->features,
2035 UFFD_API_IOCTLS|UFFD_API_RANGE_IOCTLS);
2036 }
2037 #endif
2038
2039 static const struct file_operations userfaultfd_fops = {
2040 #ifdef CONFIG_PROC_FS
2041 .show_fdinfo = userfaultfd_show_fdinfo,
2042 #endif
2043 .release = userfaultfd_release,
2044 .poll = userfaultfd_poll,
2045 .read = userfaultfd_read,
2046 .unlocked_ioctl = userfaultfd_ioctl,
2047 .compat_ioctl = compat_ptr_ioctl,
2048 .llseek = noop_llseek,
2049 };
2050
init_once_userfaultfd_ctx(void * mem)2051 static void init_once_userfaultfd_ctx(void *mem)
2052 {
2053 struct userfaultfd_ctx *ctx = (struct userfaultfd_ctx *) mem;
2054
2055 init_waitqueue_head(&ctx->fault_pending_wqh);
2056 init_waitqueue_head(&ctx->fault_wqh);
2057 init_waitqueue_head(&ctx->event_wqh);
2058 init_waitqueue_head(&ctx->fd_wqh);
2059 seqcount_spinlock_init(&ctx->refile_seq, &ctx->fault_pending_wqh.lock);
2060 }
2061
SYSCALL_DEFINE1(userfaultfd,int,flags)2062 SYSCALL_DEFINE1(userfaultfd, int, flags)
2063 {
2064 struct userfaultfd_ctx *ctx;
2065 int fd;
2066
2067 if (!sysctl_unprivileged_userfaultfd &&
2068 (flags & UFFD_USER_MODE_ONLY) == 0 &&
2069 !capable(CAP_SYS_PTRACE)) {
2070 printk_once(KERN_WARNING "uffd: Set unprivileged_userfaultfd "
2071 "sysctl knob to 1 if kernel faults must be handled "
2072 "without obtaining CAP_SYS_PTRACE capability\n");
2073 return -EPERM;
2074 }
2075
2076 BUG_ON(!current->mm);
2077
2078 /* Check the UFFD_* constants for consistency. */
2079 BUILD_BUG_ON(UFFD_USER_MODE_ONLY & UFFD_SHARED_FCNTL_FLAGS);
2080 BUILD_BUG_ON(UFFD_CLOEXEC != O_CLOEXEC);
2081 BUILD_BUG_ON(UFFD_NONBLOCK != O_NONBLOCK);
2082
2083 if (flags & ~(UFFD_SHARED_FCNTL_FLAGS | UFFD_USER_MODE_ONLY))
2084 return -EINVAL;
2085
2086 ctx = kmem_cache_alloc(userfaultfd_ctx_cachep, GFP_KERNEL);
2087 if (!ctx)
2088 return -ENOMEM;
2089
2090 refcount_set(&ctx->refcount, 1);
2091 ctx->flags = flags;
2092 ctx->features = 0;
2093 ctx->released = false;
2094 atomic_set(&ctx->mmap_changing, 0);
2095 ctx->mm = current->mm;
2096 /* prevent the mm struct to be freed */
2097 mmgrab(ctx->mm);
2098
2099 fd = anon_inode_getfd_secure("[userfaultfd]", &userfaultfd_fops, ctx,
2100 O_RDWR | (flags & UFFD_SHARED_FCNTL_FLAGS), NULL);
2101 if (fd < 0) {
2102 mmdrop(ctx->mm);
2103 kmem_cache_free(userfaultfd_ctx_cachep, ctx);
2104 }
2105 return fd;
2106 }
2107
userfaultfd_init(void)2108 static int __init userfaultfd_init(void)
2109 {
2110 userfaultfd_ctx_cachep = kmem_cache_create("userfaultfd_ctx_cache",
2111 sizeof(struct userfaultfd_ctx),
2112 0,
2113 SLAB_HWCACHE_ALIGN|SLAB_PANIC,
2114 init_once_userfaultfd_ctx);
2115 return 0;
2116 }
2117 __initcall(userfaultfd_init);
2118
