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/mm_inline.h>
19 #include <linux/mmu_notifier.h>
20 #include <linux/poll.h>
21 #include <linux/slab.h>
22 #include <linux/seq_file.h>
23 #include <linux/file.h>
24 #include <linux/bug.h>
25 #include <linux/anon_inodes.h>
26 #include <linux/syscalls.h>
27 #include <linux/userfaultfd_k.h>
28 #include <linux/mempolicy.h>
29 #include <linux/ioctl.h>
30 #include <linux/security.h>
31 #include <linux/hugetlb.h>
32 #include <linux/swapops.h>
33 #include <linux/miscdevice.h>
34
35 int sysctl_unprivileged_userfaultfd __read_mostly;
36
37 static struct kmem_cache *userfaultfd_ctx_cachep __read_mostly;
38
39 /*
40 * Start with fault_pending_wqh and fault_wqh so they're more likely
41 * to be in the same cacheline.
42 *
43 * Locking order:
44 * fd_wqh.lock
45 * fault_pending_wqh.lock
46 * fault_wqh.lock
47 * event_wqh.lock
48 *
49 * To avoid deadlocks, IRQs must be disabled when taking any of the above locks,
50 * since fd_wqh.lock is taken by aio_poll() while it's holding a lock that's
51 * also taken in IRQ context.
52 */
53 struct userfaultfd_ctx {
54 /* waitqueue head for the pending (i.e. not read) userfaults */
55 wait_queue_head_t fault_pending_wqh;
56 /* waitqueue head for the userfaults */
57 wait_queue_head_t fault_wqh;
58 /* waitqueue head for the pseudo fd to wakeup poll/read */
59 wait_queue_head_t fd_wqh;
60 /* waitqueue head for events */
61 wait_queue_head_t event_wqh;
62 /* a refile sequence protected by fault_pending_wqh lock */
63 seqcount_spinlock_t refile_seq;
64 /* pseudo fd refcounting */
65 refcount_t refcount;
66 /* userfaultfd syscall flags */
67 unsigned int flags;
68 /* features requested from the userspace */
69 unsigned int features;
70 /* released */
71 bool released;
72 /* memory mappings are changing because of non-cooperative event */
73 atomic_t mmap_changing;
74 /* mm with one ore more vmas attached to this userfaultfd_ctx */
75 struct mm_struct *mm;
76 };
77
78 struct userfaultfd_fork_ctx {
79 struct userfaultfd_ctx *orig;
80 struct userfaultfd_ctx *new;
81 struct list_head list;
82 };
83
84 struct userfaultfd_unmap_ctx {
85 struct userfaultfd_ctx *ctx;
86 unsigned long start;
87 unsigned long end;
88 struct list_head list;
89 };
90
91 struct userfaultfd_wait_queue {
92 struct uffd_msg msg;
93 wait_queue_entry_t wq;
94 struct userfaultfd_ctx *ctx;
95 bool waken;
96 };
97
98 struct userfaultfd_wake_range {
99 unsigned long start;
100 unsigned long len;
101 };
102
103 /* internal indication that UFFD_API ioctl was successfully executed */
104 #define UFFD_FEATURE_INITIALIZED (1u << 31)
105
userfaultfd_is_initialized(struct userfaultfd_ctx * ctx)106 static bool userfaultfd_is_initialized(struct userfaultfd_ctx *ctx)
107 {
108 return ctx->features & UFFD_FEATURE_INITIALIZED;
109 }
110
userfaultfd_wake_function(wait_queue_entry_t * wq,unsigned mode,int wake_flags,void * key)111 static int userfaultfd_wake_function(wait_queue_entry_t *wq, unsigned mode,
112 int wake_flags, void *key)
113 {
114 struct userfaultfd_wake_range *range = key;
115 int ret;
116 struct userfaultfd_wait_queue *uwq;
117 unsigned long start, len;
118
119 uwq = container_of(wq, struct userfaultfd_wait_queue, wq);
120 ret = 0;
121 /* len == 0 means wake all */
122 start = range->start;
123 len = range->len;
124 if (len && (start > uwq->msg.arg.pagefault.address ||
125 start + len <= uwq->msg.arg.pagefault.address))
126 goto out;
127 WRITE_ONCE(uwq->waken, true);
128 /*
129 * The Program-Order guarantees provided by the scheduler
130 * ensure uwq->waken is visible before the task is woken.
131 */
132 ret = wake_up_state(wq->private, mode);
133 if (ret) {
134 /*
135 * Wake only once, autoremove behavior.
136 *
137 * After the effect of list_del_init is visible to the other
138 * CPUs, the waitqueue may disappear from under us, see the
139 * !list_empty_careful() in handle_userfault().
140 *
141 * try_to_wake_up() has an implicit smp_mb(), and the
142 * wq->private is read before calling the extern function
143 * "wake_up_state" (which in turns calls try_to_wake_up).
144 */
145 list_del_init(&wq->entry);
146 }
147 out:
148 return ret;
149 }
150
151 /**
152 * userfaultfd_ctx_get - Acquires a reference to the internal userfaultfd
153 * context.
154 * @ctx: [in] Pointer to the userfaultfd context.
155 */
userfaultfd_ctx_get(struct userfaultfd_ctx * ctx)156 static void userfaultfd_ctx_get(struct userfaultfd_ctx *ctx)
157 {
158 refcount_inc(&ctx->refcount);
159 }
160
161 /**
162 * userfaultfd_ctx_put - Releases a reference to the internal userfaultfd
163 * context.
164 * @ctx: [in] Pointer to userfaultfd context.
165 *
166 * The userfaultfd context reference must have been previously acquired either
167 * with userfaultfd_ctx_get() or userfaultfd_ctx_fdget().
168 */
userfaultfd_ctx_put(struct userfaultfd_ctx * ctx)169 static void userfaultfd_ctx_put(struct userfaultfd_ctx *ctx)
170 {
171 if (refcount_dec_and_test(&ctx->refcount)) {
172 VM_BUG_ON(spin_is_locked(&ctx->fault_pending_wqh.lock));
173 VM_BUG_ON(waitqueue_active(&ctx->fault_pending_wqh));
174 VM_BUG_ON(spin_is_locked(&ctx->fault_wqh.lock));
175 VM_BUG_ON(waitqueue_active(&ctx->fault_wqh));
176 VM_BUG_ON(spin_is_locked(&ctx->event_wqh.lock));
177 VM_BUG_ON(waitqueue_active(&ctx->event_wqh));
178 VM_BUG_ON(spin_is_locked(&ctx->fd_wqh.lock));
179 VM_BUG_ON(waitqueue_active(&ctx->fd_wqh));
180 mmdrop(ctx->mm);
181 kmem_cache_free(userfaultfd_ctx_cachep, ctx);
182 }
183 }
184
msg_init(struct uffd_msg * msg)185 static inline void msg_init(struct uffd_msg *msg)
186 {
187 BUILD_BUG_ON(sizeof(struct uffd_msg) != 32);
188 /*
189 * Must use memset to zero out the paddings or kernel data is
190 * leaked to userland.
191 */
192 memset(msg, 0, sizeof(struct uffd_msg));
193 }
194
userfault_msg(unsigned long address,unsigned long real_address,unsigned int flags,unsigned long reason,unsigned int features)195 static inline struct uffd_msg userfault_msg(unsigned long address,
196 unsigned long real_address,
197 unsigned int flags,
198 unsigned long reason,
199 unsigned int features)
200 {
201 struct uffd_msg msg;
202
203 msg_init(&msg);
204 msg.event = UFFD_EVENT_PAGEFAULT;
205
206 msg.arg.pagefault.address = (features & UFFD_FEATURE_EXACT_ADDRESS) ?
207 real_address : address;
208
209 /*
210 * These flags indicate why the userfault occurred:
211 * - UFFD_PAGEFAULT_FLAG_WP indicates a write protect fault.
212 * - UFFD_PAGEFAULT_FLAG_MINOR indicates a minor fault.
213 * - Neither of these flags being set indicates a MISSING fault.
214 *
215 * Separately, UFFD_PAGEFAULT_FLAG_WRITE indicates it was a write
216 * fault. Otherwise, it was a read fault.
217 */
218 if (flags & FAULT_FLAG_WRITE)
219 msg.arg.pagefault.flags |= UFFD_PAGEFAULT_FLAG_WRITE;
220 if (reason & VM_UFFD_WP)
221 msg.arg.pagefault.flags |= UFFD_PAGEFAULT_FLAG_WP;
222 if (reason & VM_UFFD_MINOR)
223 msg.arg.pagefault.flags |= UFFD_PAGEFAULT_FLAG_MINOR;
224 if (features & UFFD_FEATURE_THREAD_ID)
225 msg.arg.pagefault.feat.ptid = task_pid_vnr(current);
226 return msg;
227 }
228
229 #ifdef CONFIG_HUGETLB_PAGE
230 /*
231 * Same functionality as userfaultfd_must_wait below with modifications for
232 * hugepmd ranges.
233 */
userfaultfd_huge_must_wait(struct userfaultfd_ctx * ctx,struct vm_area_struct * vma,unsigned long address,unsigned long flags,unsigned long reason)234 static inline bool userfaultfd_huge_must_wait(struct userfaultfd_ctx *ctx,
235 struct vm_area_struct *vma,
236 unsigned long address,
237 unsigned long flags,
238 unsigned long reason)
239 {
240 struct mm_struct *mm = ctx->mm;
241 pte_t *ptep, pte;
242 bool ret = true;
243
244 mmap_assert_locked(mm);
245
246 ptep = huge_pte_offset(mm, address, vma_mmu_pagesize(vma));
247
248 if (!ptep)
249 goto out;
250
251 ret = false;
252 pte = huge_ptep_get(ptep);
253
254 /*
255 * Lockless access: we're in a wait_event so it's ok if it
256 * changes under us. PTE markers should be handled the same as none
257 * ptes here.
258 */
259 if (huge_pte_none_mostly(pte))
260 ret = true;
261 if (!huge_pte_write(pte) && (reason & VM_UFFD_WP))
262 ret = true;
263 out:
264 return ret;
265 }
266 #else
userfaultfd_huge_must_wait(struct userfaultfd_ctx * ctx,struct vm_area_struct * vma,unsigned long address,unsigned long flags,unsigned long reason)267 static inline bool userfaultfd_huge_must_wait(struct userfaultfd_ctx *ctx,
268 struct vm_area_struct *vma,
269 unsigned long address,
270 unsigned long flags,
271 unsigned long reason)
272 {
273 return false; /* should never get here */
274 }
275 #endif /* CONFIG_HUGETLB_PAGE */
276
277 /*
278 * Verify the pagetables are still not ok after having reigstered into
279 * the fault_pending_wqh to avoid userland having to UFFDIO_WAKE any
280 * userfault that has already been resolved, if userfaultfd_read and
281 * UFFDIO_COPY|ZEROPAGE are being run simultaneously on two different
282 * threads.
283 */
userfaultfd_must_wait(struct userfaultfd_ctx * ctx,unsigned long address,unsigned long flags,unsigned long reason)284 static inline bool userfaultfd_must_wait(struct userfaultfd_ctx *ctx,
285 unsigned long address,
286 unsigned long flags,
287 unsigned long reason)
288 {
289 struct mm_struct *mm = ctx->mm;
290 pgd_t *pgd;
291 p4d_t *p4d;
292 pud_t *pud;
293 pmd_t *pmd, _pmd;
294 pte_t *pte;
295 bool ret = true;
296
297 mmap_assert_locked(mm);
298
299 pgd = pgd_offset(mm, address);
300 if (!pgd_present(*pgd))
301 goto out;
302 p4d = p4d_offset(pgd, address);
303 if (!p4d_present(*p4d))
304 goto out;
305 pud = pud_offset(p4d, address);
306 if (!pud_present(*pud))
307 goto out;
308 pmd = pmd_offset(pud, address);
309 /*
310 * READ_ONCE must function as a barrier with narrower scope
311 * and it must be equivalent to:
312 * _pmd = *pmd; barrier();
313 *
314 * This is to deal with the instability (as in
315 * pmd_trans_unstable) of the pmd.
316 */
317 _pmd = READ_ONCE(*pmd);
318 if (pmd_none(_pmd))
319 goto out;
320
321 ret = false;
322 if (!pmd_present(_pmd))
323 goto out;
324
325 if (pmd_trans_huge(_pmd)) {
326 if (!pmd_write(_pmd) && (reason & VM_UFFD_WP))
327 ret = true;
328 goto out;
329 }
330
331 /*
332 * the pmd is stable (as in !pmd_trans_unstable) so we can re-read it
333 * and use the standard pte_offset_map() instead of parsing _pmd.
334 */
335 pte = pte_offset_map(pmd, address);
336 /*
337 * Lockless access: we're in a wait_event so it's ok if it
338 * changes under us. PTE markers should be handled the same as none
339 * ptes here.
340 */
341 if (pte_none_mostly(*pte))
342 ret = true;
343 if (!pte_write(*pte) && (reason & VM_UFFD_WP))
344 ret = true;
345 pte_unmap(pte);
346
347 out:
348 return ret;
349 }
350
userfaultfd_get_blocking_state(unsigned int flags)351 static inline unsigned int userfaultfd_get_blocking_state(unsigned int flags)
352 {
353 if (flags & FAULT_FLAG_INTERRUPTIBLE)
354 return TASK_INTERRUPTIBLE;
355
356 if (flags & FAULT_FLAG_KILLABLE)
357 return TASK_KILLABLE;
358
359 return TASK_UNINTERRUPTIBLE;
360 }
361
362 /*
363 * The locking rules involved in returning VM_FAULT_RETRY depending on
364 * FAULT_FLAG_ALLOW_RETRY, FAULT_FLAG_RETRY_NOWAIT and
365 * FAULT_FLAG_KILLABLE are not straightforward. The "Caution"
366 * recommendation in __lock_page_or_retry is not an understatement.
367 *
368 * If FAULT_FLAG_ALLOW_RETRY is set, the mmap_lock must be released
369 * before returning VM_FAULT_RETRY only if FAULT_FLAG_RETRY_NOWAIT is
370 * not set.
371 *
372 * If FAULT_FLAG_ALLOW_RETRY is set but FAULT_FLAG_KILLABLE is not
373 * set, VM_FAULT_RETRY can still be returned if and only if there are
374 * fatal_signal_pending()s, and the mmap_lock must be released before
375 * returning it.
376 */
handle_userfault(struct vm_fault * vmf,unsigned long reason)377 vm_fault_t handle_userfault(struct vm_fault *vmf, unsigned long reason)
378 {
379 struct mm_struct *mm = vmf->vma->vm_mm;
380 struct userfaultfd_ctx *ctx;
381 struct userfaultfd_wait_queue uwq;
382 vm_fault_t ret = VM_FAULT_SIGBUS;
383 bool must_wait;
384 unsigned int blocking_state;
385
386 /*
387 * We don't do userfault handling for the final child pid update.
388 *
389 * We also don't do userfault handling during
390 * coredumping. hugetlbfs has the special
391 * follow_hugetlb_page() to skip missing pages in the
392 * FOLL_DUMP case, anon memory also checks for FOLL_DUMP with
393 * the no_page_table() helper in follow_page_mask(), but the
394 * shmem_vm_ops->fault method is invoked even during
395 * coredumping without mmap_lock and it ends up here.
396 */
397 if (current->flags & (PF_EXITING|PF_DUMPCORE))
398 goto out;
399
400 /*
401 * Coredumping runs without mmap_lock so we can only check that
402 * the mmap_lock is held, if PF_DUMPCORE was not set.
403 */
404 mmap_assert_locked(mm);
405
406 ctx = vmf->vma->vm_userfaultfd_ctx.ctx;
407 if (!ctx)
408 goto out;
409
410 BUG_ON(ctx->mm != mm);
411
412 /* Any unrecognized flag is a bug. */
413 VM_BUG_ON(reason & ~__VM_UFFD_FLAGS);
414 /* 0 or > 1 flags set is a bug; we expect exactly 1. */
415 VM_BUG_ON(!reason || (reason & (reason - 1)));
416
417 if (ctx->features & UFFD_FEATURE_SIGBUS)
418 goto out;
419 if (!(vmf->flags & FAULT_FLAG_USER) && (ctx->flags & UFFD_USER_MODE_ONLY))
420 goto out;
421
422 /*
423 * If it's already released don't get it. This avoids to loop
424 * in __get_user_pages if userfaultfd_release waits on the
425 * caller of handle_userfault to release the mmap_lock.
426 */
427 if (unlikely(READ_ONCE(ctx->released))) {
428 /*
429 * Don't return VM_FAULT_SIGBUS in this case, so a non
430 * cooperative manager can close the uffd after the
431 * last UFFDIO_COPY, without risking to trigger an
432 * involuntary SIGBUS if the process was starting the
433 * userfaultfd while the userfaultfd was still armed
434 * (but after the last UFFDIO_COPY). If the uffd
435 * wasn't already closed when the userfault reached
436 * this point, that would normally be solved by
437 * userfaultfd_must_wait returning 'false'.
438 *
439 * If we were to return VM_FAULT_SIGBUS here, the non
440 * cooperative manager would be instead forced to
441 * always call UFFDIO_UNREGISTER before it can safely
442 * close the uffd.
443 */
444 ret = VM_FAULT_NOPAGE;
445 goto out;
446 }
447
448 /*
449 * Check that we can return VM_FAULT_RETRY.
450 *
451 * NOTE: it should become possible to return VM_FAULT_RETRY
452 * even if FAULT_FLAG_TRIED is set without leading to gup()
453 * -EBUSY failures, if the userfaultfd is to be extended for
454 * VM_UFFD_WP tracking and we intend to arm the userfault
455 * without first stopping userland access to the memory. For
456 * VM_UFFD_MISSING userfaults this is enough for now.
457 */
458 if (unlikely(!(vmf->flags & FAULT_FLAG_ALLOW_RETRY))) {
459 /*
460 * Validate the invariant that nowait must allow retry
461 * to be sure not to return SIGBUS erroneously on
462 * nowait invocations.
463 */
464 BUG_ON(vmf->flags & FAULT_FLAG_RETRY_NOWAIT);
465 #ifdef CONFIG_DEBUG_VM
466 if (printk_ratelimit()) {
467 printk(KERN_WARNING
468 "FAULT_FLAG_ALLOW_RETRY missing %x\n",
469 vmf->flags);
470 dump_stack();
471 }
472 #endif
473 goto out;
474 }
475
476 /*
477 * Handle nowait, not much to do other than tell it to retry
478 * and wait.
479 */
480 ret = VM_FAULT_RETRY;
481 if (vmf->flags & FAULT_FLAG_RETRY_NOWAIT)
482 goto out;
483
484 /* take the reference before dropping the mmap_lock */
485 userfaultfd_ctx_get(ctx);
486
487 init_waitqueue_func_entry(&uwq.wq, userfaultfd_wake_function);
488 uwq.wq.private = current;
489 uwq.msg = userfault_msg(vmf->address, vmf->real_address, vmf->flags,
490 reason, ctx->features);
491 uwq.ctx = ctx;
492 uwq.waken = false;
493
494 blocking_state = userfaultfd_get_blocking_state(vmf->flags);
495
496 spin_lock_irq(&ctx->fault_pending_wqh.lock);
497 /*
498 * After the __add_wait_queue the uwq is visible to userland
499 * through poll/read().
500 */
501 __add_wait_queue(&ctx->fault_pending_wqh, &uwq.wq);
502 /*
503 * The smp_mb() after __set_current_state prevents the reads
504 * following the spin_unlock to happen before the list_add in
505 * __add_wait_queue.
506 */
507 set_current_state(blocking_state);
508 spin_unlock_irq(&ctx->fault_pending_wqh.lock);
509
510 if (!is_vm_hugetlb_page(vmf->vma))
511 must_wait = userfaultfd_must_wait(ctx, vmf->address, vmf->flags,
512 reason);
513 else
514 must_wait = userfaultfd_huge_must_wait(ctx, vmf->vma,
515 vmf->address,
516 vmf->flags, reason);
517 mmap_read_unlock(mm);
518
519 if (likely(must_wait && !READ_ONCE(ctx->released))) {
520 wake_up_poll(&ctx->fd_wqh, EPOLLIN);
521 schedule();
522 }
523
524 __set_current_state(TASK_RUNNING);
525
526 /*
527 * Here we race with the list_del; list_add in
528 * userfaultfd_ctx_read(), however because we don't ever run
529 * list_del_init() to refile across the two lists, the prev
530 * and next pointers will never point to self. list_add also
531 * would never let any of the two pointers to point to
532 * self. So list_empty_careful won't risk to see both pointers
533 * pointing to self at any time during the list refile. The
534 * only case where list_del_init() is called is the full
535 * removal in the wake function and there we don't re-list_add
536 * and it's fine not to block on the spinlock. The uwq on this
537 * kernel stack can be released after the list_del_init.
538 */
539 if (!list_empty_careful(&uwq.wq.entry)) {
540 spin_lock_irq(&ctx->fault_pending_wqh.lock);
541 /*
542 * No need of list_del_init(), the uwq on the stack
543 * will be freed shortly anyway.
544 */
545 list_del(&uwq.wq.entry);
546 spin_unlock_irq(&ctx->fault_pending_wqh.lock);
547 }
548
549 /*
550 * ctx may go away after this if the userfault pseudo fd is
551 * already released.
552 */
553 userfaultfd_ctx_put(ctx);
554
555 out:
556 return ret;
557 }
558
userfaultfd_event_wait_completion(struct userfaultfd_ctx * ctx,struct userfaultfd_wait_queue * ewq)559 static void userfaultfd_event_wait_completion(struct userfaultfd_ctx *ctx,
560 struct userfaultfd_wait_queue *ewq)
561 {
562 struct userfaultfd_ctx *release_new_ctx;
563
564 if (WARN_ON_ONCE(current->flags & PF_EXITING))
565 goto out;
566
567 ewq->ctx = ctx;
568 init_waitqueue_entry(&ewq->wq, current);
569 release_new_ctx = NULL;
570
571 spin_lock_irq(&ctx->event_wqh.lock);
572 /*
573 * After the __add_wait_queue the uwq is visible to userland
574 * through poll/read().
575 */
576 __add_wait_queue(&ctx->event_wqh, &ewq->wq);
577 for (;;) {
578 set_current_state(TASK_KILLABLE);
579 if (ewq->msg.event == 0)
580 break;
581 if (READ_ONCE(ctx->released) ||
582 fatal_signal_pending(current)) {
583 /*
584 * &ewq->wq may be queued in fork_event, but
585 * __remove_wait_queue ignores the head
586 * parameter. It would be a problem if it
587 * didn't.
588 */
589 __remove_wait_queue(&ctx->event_wqh, &ewq->wq);
590 if (ewq->msg.event == UFFD_EVENT_FORK) {
591 struct userfaultfd_ctx *new;
592
593 new = (struct userfaultfd_ctx *)
594 (unsigned long)
595 ewq->msg.arg.reserved.reserved1;
596 release_new_ctx = new;
597 }
598 break;
599 }
600
601 spin_unlock_irq(&ctx->event_wqh.lock);
602
603 wake_up_poll(&ctx->fd_wqh, EPOLLIN);
604 schedule();
605
606 spin_lock_irq(&ctx->event_wqh.lock);
607 }
608 __set_current_state(TASK_RUNNING);
609 spin_unlock_irq(&ctx->event_wqh.lock);
610
611 if (release_new_ctx) {
612 struct vm_area_struct *vma;
613 struct mm_struct *mm = release_new_ctx->mm;
614 VMA_ITERATOR(vmi, mm, 0);
615
616 /* the various vma->vm_userfaultfd_ctx still points to it */
617 mmap_write_lock(mm);
618 for_each_vma(vmi, vma) {
619 if (vma->vm_userfaultfd_ctx.ctx == release_new_ctx) {
620 vma->vm_userfaultfd_ctx = NULL_VM_UFFD_CTX;
621 vma->vm_flags &= ~__VM_UFFD_FLAGS;
622 }
623 }
624 mmap_write_unlock(mm);
625
626 userfaultfd_ctx_put(release_new_ctx);
627 }
628
629 /*
630 * ctx may go away after this if the userfault pseudo fd is
631 * already released.
632 */
633 out:
634 atomic_dec(&ctx->mmap_changing);
635 VM_BUG_ON(atomic_read(&ctx->mmap_changing) < 0);
636 userfaultfd_ctx_put(ctx);
637 }
638
userfaultfd_event_complete(struct userfaultfd_ctx * ctx,struct userfaultfd_wait_queue * ewq)639 static void userfaultfd_event_complete(struct userfaultfd_ctx *ctx,
640 struct userfaultfd_wait_queue *ewq)
641 {
642 ewq->msg.event = 0;
643 wake_up_locked(&ctx->event_wqh);
644 __remove_wait_queue(&ctx->event_wqh, &ewq->wq);
645 }
646
dup_userfaultfd(struct vm_area_struct * vma,struct list_head * fcs)647 int dup_userfaultfd(struct vm_area_struct *vma, struct list_head *fcs)
648 {
649 struct userfaultfd_ctx *ctx = NULL, *octx;
650 struct userfaultfd_fork_ctx *fctx;
651
652 octx = vma->vm_userfaultfd_ctx.ctx;
653 if (!octx || !(octx->features & UFFD_FEATURE_EVENT_FORK)) {
654 vma->vm_userfaultfd_ctx = NULL_VM_UFFD_CTX;
655 vma->vm_flags &= ~__VM_UFFD_FLAGS;
656 return 0;
657 }
658
659 list_for_each_entry(fctx, fcs, list)
660 if (fctx->orig == octx) {
661 ctx = fctx->new;
662 break;
663 }
664
665 if (!ctx) {
666 fctx = kmalloc(sizeof(*fctx), GFP_KERNEL);
667 if (!fctx)
668 return -ENOMEM;
669
670 ctx = kmem_cache_alloc(userfaultfd_ctx_cachep, GFP_KERNEL);
671 if (!ctx) {
672 kfree(fctx);
673 return -ENOMEM;
674 }
675
676 refcount_set(&ctx->refcount, 1);
677 ctx->flags = octx->flags;
678 ctx->features = octx->features;
679 ctx->released = false;
680 atomic_set(&ctx->mmap_changing, 0);
681 ctx->mm = vma->vm_mm;
682 mmgrab(ctx->mm);
683
684 userfaultfd_ctx_get(octx);
685 atomic_inc(&octx->mmap_changing);
686 fctx->orig = octx;
687 fctx->new = ctx;
688 list_add_tail(&fctx->list, fcs);
689 }
690
691 vma->vm_userfaultfd_ctx.ctx = ctx;
692 return 0;
693 }
694
dup_fctx(struct userfaultfd_fork_ctx * fctx)695 static void dup_fctx(struct userfaultfd_fork_ctx *fctx)
696 {
697 struct userfaultfd_ctx *ctx = fctx->orig;
698 struct userfaultfd_wait_queue ewq;
699
700 msg_init(&ewq.msg);
701
702 ewq.msg.event = UFFD_EVENT_FORK;
703 ewq.msg.arg.reserved.reserved1 = (unsigned long)fctx->new;
704
705 userfaultfd_event_wait_completion(ctx, &ewq);
706 }
707
dup_userfaultfd_complete(struct list_head * fcs)708 void dup_userfaultfd_complete(struct list_head *fcs)
709 {
710 struct userfaultfd_fork_ctx *fctx, *n;
711
712 list_for_each_entry_safe(fctx, n, fcs, list) {
713 dup_fctx(fctx);
714 list_del(&fctx->list);
715 kfree(fctx);
716 }
717 }
718
mremap_userfaultfd_prep(struct vm_area_struct * vma,struct vm_userfaultfd_ctx * vm_ctx)719 void mremap_userfaultfd_prep(struct vm_area_struct *vma,
720 struct vm_userfaultfd_ctx *vm_ctx)
721 {
722 struct userfaultfd_ctx *ctx;
723
724 ctx = vma->vm_userfaultfd_ctx.ctx;
725
726 if (!ctx)
727 return;
728
729 if (ctx->features & UFFD_FEATURE_EVENT_REMAP) {
730 vm_ctx->ctx = ctx;
731 userfaultfd_ctx_get(ctx);
732 atomic_inc(&ctx->mmap_changing);
733 } else {
734 /* Drop uffd context if remap feature not enabled */
735 vma->vm_userfaultfd_ctx = NULL_VM_UFFD_CTX;
736 vma->vm_flags &= ~__VM_UFFD_FLAGS;
737 }
738 }
739
mremap_userfaultfd_complete(struct vm_userfaultfd_ctx * vm_ctx,unsigned long from,unsigned long to,unsigned long len)740 void mremap_userfaultfd_complete(struct vm_userfaultfd_ctx *vm_ctx,
741 unsigned long from, unsigned long to,
742 unsigned long len)
743 {
744 struct userfaultfd_ctx *ctx = vm_ctx->ctx;
745 struct userfaultfd_wait_queue ewq;
746
747 if (!ctx)
748 return;
749
750 if (to & ~PAGE_MASK) {
751 userfaultfd_ctx_put(ctx);
752 return;
753 }
754
755 msg_init(&ewq.msg);
756
757 ewq.msg.event = UFFD_EVENT_REMAP;
758 ewq.msg.arg.remap.from = from;
759 ewq.msg.arg.remap.to = to;
760 ewq.msg.arg.remap.len = len;
761
762 userfaultfd_event_wait_completion(ctx, &ewq);
763 }
764
userfaultfd_remove(struct vm_area_struct * vma,unsigned long start,unsigned long end)765 bool userfaultfd_remove(struct vm_area_struct *vma,
766 unsigned long start, unsigned long end)
767 {
768 struct mm_struct *mm = vma->vm_mm;
769 struct userfaultfd_ctx *ctx;
770 struct userfaultfd_wait_queue ewq;
771
772 ctx = vma->vm_userfaultfd_ctx.ctx;
773 if (!ctx || !(ctx->features & UFFD_FEATURE_EVENT_REMOVE))
774 return true;
775
776 userfaultfd_ctx_get(ctx);
777 atomic_inc(&ctx->mmap_changing);
778 mmap_read_unlock(mm);
779
780 msg_init(&ewq.msg);
781
782 ewq.msg.event = UFFD_EVENT_REMOVE;
783 ewq.msg.arg.remove.start = start;
784 ewq.msg.arg.remove.end = end;
785
786 userfaultfd_event_wait_completion(ctx, &ewq);
787
788 return false;
789 }
790
has_unmap_ctx(struct userfaultfd_ctx * ctx,struct list_head * unmaps,unsigned long start,unsigned long end)791 static bool has_unmap_ctx(struct userfaultfd_ctx *ctx, struct list_head *unmaps,
792 unsigned long start, unsigned long end)
793 {
794 struct userfaultfd_unmap_ctx *unmap_ctx;
795
796 list_for_each_entry(unmap_ctx, unmaps, list)
797 if (unmap_ctx->ctx == ctx && unmap_ctx->start == start &&
798 unmap_ctx->end == end)
799 return true;
800
801 return false;
802 }
803
userfaultfd_unmap_prep(struct mm_struct * mm,unsigned long start,unsigned long end,struct list_head * unmaps)804 int userfaultfd_unmap_prep(struct mm_struct *mm, unsigned long start,
805 unsigned long end, struct list_head *unmaps)
806 {
807 VMA_ITERATOR(vmi, mm, start);
808 struct vm_area_struct *vma;
809
810 for_each_vma_range(vmi, vma, end) {
811 struct userfaultfd_unmap_ctx *unmap_ctx;
812 struct userfaultfd_ctx *ctx = vma->vm_userfaultfd_ctx.ctx;
813
814 if (!ctx || !(ctx->features & UFFD_FEATURE_EVENT_UNMAP) ||
815 has_unmap_ctx(ctx, unmaps, start, end))
816 continue;
817
818 unmap_ctx = kzalloc(sizeof(*unmap_ctx), GFP_KERNEL);
819 if (!unmap_ctx)
820 return -ENOMEM;
821
822 userfaultfd_ctx_get(ctx);
823 atomic_inc(&ctx->mmap_changing);
824 unmap_ctx->ctx = ctx;
825 unmap_ctx->start = start;
826 unmap_ctx->end = end;
827 list_add_tail(&unmap_ctx->list, unmaps);
828 }
829
830 return 0;
831 }
832
userfaultfd_unmap_complete(struct mm_struct * mm,struct list_head * uf)833 void userfaultfd_unmap_complete(struct mm_struct *mm, struct list_head *uf)
834 {
835 struct userfaultfd_unmap_ctx *ctx, *n;
836 struct userfaultfd_wait_queue ewq;
837
838 list_for_each_entry_safe(ctx, n, uf, list) {
839 msg_init(&ewq.msg);
840
841 ewq.msg.event = UFFD_EVENT_UNMAP;
842 ewq.msg.arg.remove.start = ctx->start;
843 ewq.msg.arg.remove.end = ctx->end;
844
845 userfaultfd_event_wait_completion(ctx->ctx, &ewq);
846
847 list_del(&ctx->list);
848 kfree(ctx);
849 }
850 }
851
userfaultfd_release(struct inode * inode,struct file * file)852 static int userfaultfd_release(struct inode *inode, struct file *file)
853 {
854 struct userfaultfd_ctx *ctx = file->private_data;
855 struct mm_struct *mm = ctx->mm;
856 struct vm_area_struct *vma, *prev;
857 /* len == 0 means wake all */
858 struct userfaultfd_wake_range range = { .len = 0, };
859 unsigned long new_flags;
860 MA_STATE(mas, &mm->mm_mt, 0, 0);
861
862 WRITE_ONCE(ctx->released, true);
863
864 if (!mmget_not_zero(mm))
865 goto wakeup;
866
867 /*
868 * Flush page faults out of all CPUs. NOTE: all page faults
869 * must be retried without returning VM_FAULT_SIGBUS if
870 * userfaultfd_ctx_get() succeeds but vma->vma_userfault_ctx
871 * changes while handle_userfault released the mmap_lock. So
872 * it's critical that released is set to true (above), before
873 * taking the mmap_lock for writing.
874 */
875 mmap_write_lock(mm);
876 prev = NULL;
877 mas_for_each(&mas, vma, ULONG_MAX) {
878 cond_resched();
879 BUG_ON(!!vma->vm_userfaultfd_ctx.ctx ^
880 !!(vma->vm_flags & __VM_UFFD_FLAGS));
881 if (vma->vm_userfaultfd_ctx.ctx != ctx) {
882 prev = vma;
883 continue;
884 }
885 new_flags = vma->vm_flags & ~__VM_UFFD_FLAGS;
886 prev = vma_merge(mm, prev, vma->vm_start, vma->vm_end,
887 new_flags, vma->anon_vma,
888 vma->vm_file, vma->vm_pgoff,
889 vma_policy(vma),
890 NULL_VM_UFFD_CTX, anon_vma_name(vma));
891 if (prev) {
892 mas_pause(&mas);
893 vma = prev;
894 } else {
895 prev = vma;
896 }
897
898 vma->vm_flags = new_flags;
899 vma->vm_userfaultfd_ctx = NULL_VM_UFFD_CTX;
900 }
901 mmap_write_unlock(mm);
902 mmput(mm);
903 wakeup:
904 /*
905 * After no new page faults can wait on this fault_*wqh, flush
906 * the last page faults that may have been already waiting on
907 * the fault_*wqh.
908 */
909 spin_lock_irq(&ctx->fault_pending_wqh.lock);
910 __wake_up_locked_key(&ctx->fault_pending_wqh, TASK_NORMAL, &range);
911 __wake_up(&ctx->fault_wqh, TASK_NORMAL, 1, &range);
912 spin_unlock_irq(&ctx->fault_pending_wqh.lock);
913
914 /* Flush pending events that may still wait on event_wqh */
915 wake_up_all(&ctx->event_wqh);
916
917 wake_up_poll(&ctx->fd_wqh, EPOLLHUP);
918 userfaultfd_ctx_put(ctx);
919 return 0;
920 }
921
922 /* fault_pending_wqh.lock must be hold by the caller */
find_userfault_in(wait_queue_head_t * wqh)923 static inline struct userfaultfd_wait_queue *find_userfault_in(
924 wait_queue_head_t *wqh)
925 {
926 wait_queue_entry_t *wq;
927 struct userfaultfd_wait_queue *uwq;
928
929 lockdep_assert_held(&wqh->lock);
930
931 uwq = NULL;
932 if (!waitqueue_active(wqh))
933 goto out;
934 /* walk in reverse to provide FIFO behavior to read userfaults */
935 wq = list_last_entry(&wqh->head, typeof(*wq), entry);
936 uwq = container_of(wq, struct userfaultfd_wait_queue, wq);
937 out:
938 return uwq;
939 }
940
find_userfault(struct userfaultfd_ctx * ctx)941 static inline struct userfaultfd_wait_queue *find_userfault(
942 struct userfaultfd_ctx *ctx)
943 {
944 return find_userfault_in(&ctx->fault_pending_wqh);
945 }
946
find_userfault_evt(struct userfaultfd_ctx * ctx)947 static inline struct userfaultfd_wait_queue *find_userfault_evt(
948 struct userfaultfd_ctx *ctx)
949 {
950 return find_userfault_in(&ctx->event_wqh);
951 }
952
userfaultfd_poll(struct file * file,poll_table * wait)953 static __poll_t userfaultfd_poll(struct file *file, poll_table *wait)
954 {
955 struct userfaultfd_ctx *ctx = file->private_data;
956 __poll_t ret;
957
958 poll_wait(file, &ctx->fd_wqh, wait);
959
960 if (!userfaultfd_is_initialized(ctx))
961 return EPOLLERR;
962
963 /*
964 * poll() never guarantees that read won't block.
965 * userfaults can be waken before they're read().
966 */
967 if (unlikely(!(file->f_flags & O_NONBLOCK)))
968 return EPOLLERR;
969 /*
970 * lockless access to see if there are pending faults
971 * __pollwait last action is the add_wait_queue but
972 * the spin_unlock would allow the waitqueue_active to
973 * pass above the actual list_add inside
974 * add_wait_queue critical section. So use a full
975 * memory barrier to serialize the list_add write of
976 * add_wait_queue() with the waitqueue_active read
977 * below.
978 */
979 ret = 0;
980 smp_mb();
981 if (waitqueue_active(&ctx->fault_pending_wqh))
982 ret = EPOLLIN;
983 else if (waitqueue_active(&ctx->event_wqh))
984 ret = EPOLLIN;
985
986 return ret;
987 }
988
989 static const struct file_operations userfaultfd_fops;
990
resolve_userfault_fork(struct userfaultfd_ctx * new,struct inode * inode,struct uffd_msg * msg)991 static int resolve_userfault_fork(struct userfaultfd_ctx *new,
992 struct inode *inode,
993 struct uffd_msg *msg)
994 {
995 int fd;
996
997 fd = anon_inode_getfd_secure("[userfaultfd]", &userfaultfd_fops, new,
998 O_RDONLY | (new->flags & UFFD_SHARED_FCNTL_FLAGS), inode);
999 if (fd < 0)
1000 return fd;
1001
1002 msg->arg.reserved.reserved1 = 0;
1003 msg->arg.fork.ufd = fd;
1004 return 0;
1005 }
1006
userfaultfd_ctx_read(struct userfaultfd_ctx * ctx,int no_wait,struct uffd_msg * msg,struct inode * inode)1007 static ssize_t userfaultfd_ctx_read(struct userfaultfd_ctx *ctx, int no_wait,
1008 struct uffd_msg *msg, struct inode *inode)
1009 {
1010 ssize_t ret;
1011 DECLARE_WAITQUEUE(wait, current);
1012 struct userfaultfd_wait_queue *uwq;
1013 /*
1014 * Handling fork event requires sleeping operations, so
1015 * we drop the event_wqh lock, then do these ops, then
1016 * lock it back and wake up the waiter. While the lock is
1017 * dropped the ewq may go away so we keep track of it
1018 * carefully.
1019 */
1020 LIST_HEAD(fork_event);
1021 struct userfaultfd_ctx *fork_nctx = NULL;
1022
1023 /* always take the fd_wqh lock before the fault_pending_wqh lock */
1024 spin_lock_irq(&ctx->fd_wqh.lock);
1025 __add_wait_queue(&ctx->fd_wqh, &wait);
1026 for (;;) {
1027 set_current_state(TASK_INTERRUPTIBLE);
1028 spin_lock(&ctx->fault_pending_wqh.lock);
1029 uwq = find_userfault(ctx);
1030 if (uwq) {
1031 /*
1032 * Use a seqcount to repeat the lockless check
1033 * in wake_userfault() to avoid missing
1034 * wakeups because during the refile both
1035 * waitqueue could become empty if this is the
1036 * only userfault.
1037 */
1038 write_seqcount_begin(&ctx->refile_seq);
1039
1040 /*
1041 * The fault_pending_wqh.lock prevents the uwq
1042 * to disappear from under us.
1043 *
1044 * Refile this userfault from
1045 * fault_pending_wqh to fault_wqh, it's not
1046 * pending anymore after we read it.
1047 *
1048 * Use list_del() by hand (as
1049 * userfaultfd_wake_function also uses
1050 * list_del_init() by hand) to be sure nobody
1051 * changes __remove_wait_queue() to use
1052 * list_del_init() in turn breaking the
1053 * !list_empty_careful() check in
1054 * handle_userfault(). The uwq->wq.head list
1055 * must never be empty at any time during the
1056 * refile, or the waitqueue could disappear
1057 * from under us. The "wait_queue_head_t"
1058 * parameter of __remove_wait_queue() is unused
1059 * anyway.
1060 */
1061 list_del(&uwq->wq.entry);
1062 add_wait_queue(&ctx->fault_wqh, &uwq->wq);
1063
1064 write_seqcount_end(&ctx->refile_seq);
1065
1066 /* careful to always initialize msg if ret == 0 */
1067 *msg = uwq->msg;
1068 spin_unlock(&ctx->fault_pending_wqh.lock);
1069 ret = 0;
1070 break;
1071 }
1072 spin_unlock(&ctx->fault_pending_wqh.lock);
1073
1074 spin_lock(&ctx->event_wqh.lock);
1075 uwq = find_userfault_evt(ctx);
1076 if (uwq) {
1077 *msg = uwq->msg;
1078
1079 if (uwq->msg.event == UFFD_EVENT_FORK) {
1080 fork_nctx = (struct userfaultfd_ctx *)
1081 (unsigned long)
1082 uwq->msg.arg.reserved.reserved1;
1083 list_move(&uwq->wq.entry, &fork_event);
1084 /*
1085 * fork_nctx can be freed as soon as
1086 * we drop the lock, unless we take a
1087 * reference on it.
1088 */
1089 userfaultfd_ctx_get(fork_nctx);
1090 spin_unlock(&ctx->event_wqh.lock);
1091 ret = 0;
1092 break;
1093 }
1094
1095 userfaultfd_event_complete(ctx, uwq);
1096 spin_unlock(&ctx->event_wqh.lock);
1097 ret = 0;
1098 break;
1099 }
1100 spin_unlock(&ctx->event_wqh.lock);
1101
1102 if (signal_pending(current)) {
1103 ret = -ERESTARTSYS;
1104 break;
1105 }
1106 if (no_wait) {
1107 ret = -EAGAIN;
1108 break;
1109 }
1110 spin_unlock_irq(&ctx->fd_wqh.lock);
1111 schedule();
1112 spin_lock_irq(&ctx->fd_wqh.lock);
1113 }
1114 __remove_wait_queue(&ctx->fd_wqh, &wait);
1115 __set_current_state(TASK_RUNNING);
1116 spin_unlock_irq(&ctx->fd_wqh.lock);
1117
1118 if (!ret && msg->event == UFFD_EVENT_FORK) {
1119 ret = resolve_userfault_fork(fork_nctx, inode, msg);
1120 spin_lock_irq(&ctx->event_wqh.lock);
1121 if (!list_empty(&fork_event)) {
1122 /*
1123 * The fork thread didn't abort, so we can
1124 * drop the temporary refcount.
1125 */
1126 userfaultfd_ctx_put(fork_nctx);
1127
1128 uwq = list_first_entry(&fork_event,
1129 typeof(*uwq),
1130 wq.entry);
1131 /*
1132 * If fork_event list wasn't empty and in turn
1133 * the event wasn't already released by fork
1134 * (the event is allocated on fork kernel
1135 * stack), put the event back to its place in
1136 * the event_wq. fork_event head will be freed
1137 * as soon as we return so the event cannot
1138 * stay queued there no matter the current
1139 * "ret" value.
1140 */
1141 list_del(&uwq->wq.entry);
1142 __add_wait_queue(&ctx->event_wqh, &uwq->wq);
1143
1144 /*
1145 * Leave the event in the waitqueue and report
1146 * error to userland if we failed to resolve
1147 * the userfault fork.
1148 */
1149 if (likely(!ret))
1150 userfaultfd_event_complete(ctx, uwq);
1151 } else {
1152 /*
1153 * Here the fork thread aborted and the
1154 * refcount from the fork thread on fork_nctx
1155 * has already been released. We still hold
1156 * the reference we took before releasing the
1157 * lock above. If resolve_userfault_fork
1158 * failed we've to drop it because the
1159 * fork_nctx has to be freed in such case. If
1160 * it succeeded we'll hold it because the new
1161 * uffd references it.
1162 */
1163 if (ret)
1164 userfaultfd_ctx_put(fork_nctx);
1165 }
1166 spin_unlock_irq(&ctx->event_wqh.lock);
1167 }
1168
1169 return ret;
1170 }
1171
userfaultfd_read(struct file * file,char __user * buf,size_t count,loff_t * ppos)1172 static ssize_t userfaultfd_read(struct file *file, char __user *buf,
1173 size_t count, loff_t *ppos)
1174 {
1175 struct userfaultfd_ctx *ctx = file->private_data;
1176 ssize_t _ret, ret = 0;
1177 struct uffd_msg msg;
1178 int no_wait = file->f_flags & O_NONBLOCK;
1179 struct inode *inode = file_inode(file);
1180
1181 if (!userfaultfd_is_initialized(ctx))
1182 return -EINVAL;
1183
1184 for (;;) {
1185 if (count < sizeof(msg))
1186 return ret ? ret : -EINVAL;
1187 _ret = userfaultfd_ctx_read(ctx, no_wait, &msg, inode);
1188 if (_ret < 0)
1189 return ret ? ret : _ret;
1190 if (copy_to_user((__u64 __user *) buf, &msg, sizeof(msg)))
1191 return ret ? ret : -EFAULT;
1192 ret += sizeof(msg);
1193 buf += sizeof(msg);
1194 count -= sizeof(msg);
1195 /*
1196 * Allow to read more than one fault at time but only
1197 * block if waiting for the very first one.
1198 */
1199 no_wait = O_NONBLOCK;
1200 }
1201 }
1202
__wake_userfault(struct userfaultfd_ctx * ctx,struct userfaultfd_wake_range * range)1203 static void __wake_userfault(struct userfaultfd_ctx *ctx,
1204 struct userfaultfd_wake_range *range)
1205 {
1206 spin_lock_irq(&ctx->fault_pending_wqh.lock);
1207 /* wake all in the range and autoremove */
1208 if (waitqueue_active(&ctx->fault_pending_wqh))
1209 __wake_up_locked_key(&ctx->fault_pending_wqh, TASK_NORMAL,
1210 range);
1211 if (waitqueue_active(&ctx->fault_wqh))
1212 __wake_up(&ctx->fault_wqh, TASK_NORMAL, 1, range);
1213 spin_unlock_irq(&ctx->fault_pending_wqh.lock);
1214 }
1215
wake_userfault(struct userfaultfd_ctx * ctx,struct userfaultfd_wake_range * range)1216 static __always_inline void wake_userfault(struct userfaultfd_ctx *ctx,
1217 struct userfaultfd_wake_range *range)
1218 {
1219 unsigned seq;
1220 bool need_wakeup;
1221
1222 /*
1223 * To be sure waitqueue_active() is not reordered by the CPU
1224 * before the pagetable update, use an explicit SMP memory
1225 * barrier here. PT lock release or mmap_read_unlock(mm) still
1226 * have release semantics that can allow the
1227 * waitqueue_active() to be reordered before the pte update.
1228 */
1229 smp_mb();
1230
1231 /*
1232 * Use waitqueue_active because it's very frequent to
1233 * change the address space atomically even if there are no
1234 * userfaults yet. So we take the spinlock only when we're
1235 * sure we've userfaults to wake.
1236 */
1237 do {
1238 seq = read_seqcount_begin(&ctx->refile_seq);
1239 need_wakeup = waitqueue_active(&ctx->fault_pending_wqh) ||
1240 waitqueue_active(&ctx->fault_wqh);
1241 cond_resched();
1242 } while (read_seqcount_retry(&ctx->refile_seq, seq));
1243 if (need_wakeup)
1244 __wake_userfault(ctx, range);
1245 }
1246
validate_range(struct mm_struct * mm,__u64 start,__u64 len)1247 static __always_inline int validate_range(struct mm_struct *mm,
1248 __u64 start, __u64 len)
1249 {
1250 __u64 task_size = mm->task_size;
1251
1252 if (start & ~PAGE_MASK)
1253 return -EINVAL;
1254 if (len & ~PAGE_MASK)
1255 return -EINVAL;
1256 if (!len)
1257 return -EINVAL;
1258 if (start < mmap_min_addr)
1259 return -EINVAL;
1260 if (start >= task_size)
1261 return -EINVAL;
1262 if (len > task_size - start)
1263 return -EINVAL;
1264 return 0;
1265 }
1266
userfaultfd_register(struct userfaultfd_ctx * ctx,unsigned long arg)1267 static int userfaultfd_register(struct userfaultfd_ctx *ctx,
1268 unsigned long arg)
1269 {
1270 struct mm_struct *mm = ctx->mm;
1271 struct vm_area_struct *vma, *prev, *cur;
1272 int ret;
1273 struct uffdio_register uffdio_register;
1274 struct uffdio_register __user *user_uffdio_register;
1275 unsigned long vm_flags, new_flags;
1276 bool found;
1277 bool basic_ioctls;
1278 unsigned long start, end, vma_end;
1279 MA_STATE(mas, &mm->mm_mt, 0, 0);
1280
1281 user_uffdio_register = (struct uffdio_register __user *) arg;
1282
1283 ret = -EFAULT;
1284 if (copy_from_user(&uffdio_register, user_uffdio_register,
1285 sizeof(uffdio_register)-sizeof(__u64)))
1286 goto out;
1287
1288 ret = -EINVAL;
1289 if (!uffdio_register.mode)
1290 goto out;
1291 if (uffdio_register.mode & ~UFFD_API_REGISTER_MODES)
1292 goto out;
1293 vm_flags = 0;
1294 if (uffdio_register.mode & UFFDIO_REGISTER_MODE_MISSING)
1295 vm_flags |= VM_UFFD_MISSING;
1296 if (uffdio_register.mode & UFFDIO_REGISTER_MODE_WP) {
1297 #ifndef CONFIG_HAVE_ARCH_USERFAULTFD_WP
1298 goto out;
1299 #endif
1300 vm_flags |= VM_UFFD_WP;
1301 }
1302 if (uffdio_register.mode & UFFDIO_REGISTER_MODE_MINOR) {
1303 #ifndef CONFIG_HAVE_ARCH_USERFAULTFD_MINOR
1304 goto out;
1305 #endif
1306 vm_flags |= VM_UFFD_MINOR;
1307 }
1308
1309 ret = validate_range(mm, uffdio_register.range.start,
1310 uffdio_register.range.len);
1311 if (ret)
1312 goto out;
1313
1314 start = uffdio_register.range.start;
1315 end = start + uffdio_register.range.len;
1316
1317 ret = -ENOMEM;
1318 if (!mmget_not_zero(mm))
1319 goto out;
1320
1321 mmap_write_lock(mm);
1322 mas_set(&mas, start);
1323 vma = mas_find(&mas, ULONG_MAX);
1324 if (!vma)
1325 goto out_unlock;
1326
1327 /* check that there's at least one vma in the range */
1328 ret = -EINVAL;
1329 if (vma->vm_start >= end)
1330 goto out_unlock;
1331
1332 /*
1333 * If the first vma contains huge pages, make sure start address
1334 * is aligned to huge page size.
1335 */
1336 if (is_vm_hugetlb_page(vma)) {
1337 unsigned long vma_hpagesize = vma_kernel_pagesize(vma);
1338
1339 if (start & (vma_hpagesize - 1))
1340 goto out_unlock;
1341 }
1342
1343 /*
1344 * Search for not compatible vmas.
1345 */
1346 found = false;
1347 basic_ioctls = false;
1348 for (cur = vma; cur; cur = mas_next(&mas, end - 1)) {
1349 cond_resched();
1350
1351 BUG_ON(!!cur->vm_userfaultfd_ctx.ctx ^
1352 !!(cur->vm_flags & __VM_UFFD_FLAGS));
1353
1354 /* check not compatible vmas */
1355 ret = -EINVAL;
1356 if (!vma_can_userfault(cur, vm_flags))
1357 goto out_unlock;
1358
1359 /*
1360 * UFFDIO_COPY will fill file holes even without
1361 * PROT_WRITE. This check enforces that if this is a
1362 * MAP_SHARED, the process has write permission to the backing
1363 * file. If VM_MAYWRITE is set it also enforces that on a
1364 * MAP_SHARED vma: there is no F_WRITE_SEAL and no further
1365 * F_WRITE_SEAL can be taken until the vma is destroyed.
1366 */
1367 ret = -EPERM;
1368 if (unlikely(!(cur->vm_flags & VM_MAYWRITE)))
1369 goto out_unlock;
1370
1371 /*
1372 * If this vma contains ending address, and huge pages
1373 * check alignment.
1374 */
1375 if (is_vm_hugetlb_page(cur) && end <= cur->vm_end &&
1376 end > cur->vm_start) {
1377 unsigned long vma_hpagesize = vma_kernel_pagesize(cur);
1378
1379 ret = -EINVAL;
1380
1381 if (end & (vma_hpagesize - 1))
1382 goto out_unlock;
1383 }
1384 if ((vm_flags & VM_UFFD_WP) && !(cur->vm_flags & VM_MAYWRITE))
1385 goto out_unlock;
1386
1387 /*
1388 * Check that this vma isn't already owned by a
1389 * different userfaultfd. We can't allow more than one
1390 * userfaultfd to own a single vma simultaneously or we
1391 * wouldn't know which one to deliver the userfaults to.
1392 */
1393 ret = -EBUSY;
1394 if (cur->vm_userfaultfd_ctx.ctx &&
1395 cur->vm_userfaultfd_ctx.ctx != ctx)
1396 goto out_unlock;
1397
1398 /*
1399 * Note vmas containing huge pages
1400 */
1401 if (is_vm_hugetlb_page(cur))
1402 basic_ioctls = true;
1403
1404 found = true;
1405 }
1406 BUG_ON(!found);
1407
1408 mas_set(&mas, start);
1409 prev = mas_prev(&mas, 0);
1410 if (prev != vma)
1411 mas_next(&mas, ULONG_MAX);
1412
1413 ret = 0;
1414 do {
1415 cond_resched();
1416
1417 BUG_ON(!vma_can_userfault(vma, vm_flags));
1418 BUG_ON(vma->vm_userfaultfd_ctx.ctx &&
1419 vma->vm_userfaultfd_ctx.ctx != ctx);
1420 WARN_ON(!(vma->vm_flags & VM_MAYWRITE));
1421
1422 /*
1423 * Nothing to do: this vma is already registered into this
1424 * userfaultfd and with the right tracking mode too.
1425 */
1426 if (vma->vm_userfaultfd_ctx.ctx == ctx &&
1427 (vma->vm_flags & vm_flags) == vm_flags)
1428 goto skip;
1429
1430 if (vma->vm_start > start)
1431 start = vma->vm_start;
1432 vma_end = min(end, vma->vm_end);
1433
1434 new_flags = (vma->vm_flags & ~__VM_UFFD_FLAGS) | vm_flags;
1435 prev = vma_merge(mm, prev, start, vma_end, new_flags,
1436 vma->anon_vma, vma->vm_file, vma->vm_pgoff,
1437 vma_policy(vma),
1438 ((struct vm_userfaultfd_ctx){ ctx }),
1439 anon_vma_name(vma));
1440 if (prev) {
1441 /* vma_merge() invalidated the mas */
1442 mas_pause(&mas);
1443 vma = prev;
1444 goto next;
1445 }
1446 if (vma->vm_start < start) {
1447 ret = split_vma(mm, vma, start, 1);
1448 if (ret)
1449 break;
1450 /* split_vma() invalidated the mas */
1451 mas_pause(&mas);
1452 }
1453 if (vma->vm_end > end) {
1454 ret = split_vma(mm, vma, end, 0);
1455 if (ret)
1456 break;
1457 /* split_vma() invalidated the mas */
1458 mas_pause(&mas);
1459 }
1460 next:
1461 /*
1462 * In the vma_merge() successful mprotect-like case 8:
1463 * the next vma was merged into the current one and
1464 * the current one has not been updated yet.
1465 */
1466 vma->vm_flags = new_flags;
1467 vma->vm_userfaultfd_ctx.ctx = ctx;
1468
1469 if (is_vm_hugetlb_page(vma) && uffd_disable_huge_pmd_share(vma))
1470 hugetlb_unshare_all_pmds(vma);
1471
1472 skip:
1473 prev = vma;
1474 start = vma->vm_end;
1475 vma = mas_next(&mas, end - 1);
1476 } while (vma);
1477 out_unlock:
1478 mmap_write_unlock(mm);
1479 mmput(mm);
1480 if (!ret) {
1481 __u64 ioctls_out;
1482
1483 ioctls_out = basic_ioctls ? UFFD_API_RANGE_IOCTLS_BASIC :
1484 UFFD_API_RANGE_IOCTLS;
1485
1486 /*
1487 * Declare the WP ioctl only if the WP mode is
1488 * specified and all checks passed with the range
1489 */
1490 if (!(uffdio_register.mode & UFFDIO_REGISTER_MODE_WP))
1491 ioctls_out &= ~((__u64)1 << _UFFDIO_WRITEPROTECT);
1492
1493 /* CONTINUE ioctl is only supported for MINOR ranges. */
1494 if (!(uffdio_register.mode & UFFDIO_REGISTER_MODE_MINOR))
1495 ioctls_out &= ~((__u64)1 << _UFFDIO_CONTINUE);
1496
1497 /*
1498 * Now that we scanned all vmas we can already tell
1499 * userland which ioctls methods are guaranteed to
1500 * succeed on this range.
1501 */
1502 if (put_user(ioctls_out, &user_uffdio_register->ioctls))
1503 ret = -EFAULT;
1504 }
1505 out:
1506 return ret;
1507 }
1508
userfaultfd_unregister(struct userfaultfd_ctx * ctx,unsigned long arg)1509 static int userfaultfd_unregister(struct userfaultfd_ctx *ctx,
1510 unsigned long arg)
1511 {
1512 struct mm_struct *mm = ctx->mm;
1513 struct vm_area_struct *vma, *prev, *cur;
1514 int ret;
1515 struct uffdio_range uffdio_unregister;
1516 unsigned long new_flags;
1517 bool found;
1518 unsigned long start, end, vma_end;
1519 const void __user *buf = (void __user *)arg;
1520 MA_STATE(mas, &mm->mm_mt, 0, 0);
1521
1522 ret = -EFAULT;
1523 if (copy_from_user(&uffdio_unregister, buf, sizeof(uffdio_unregister)))
1524 goto out;
1525
1526 ret = validate_range(mm, uffdio_unregister.start,
1527 uffdio_unregister.len);
1528 if (ret)
1529 goto out;
1530
1531 start = uffdio_unregister.start;
1532 end = start + uffdio_unregister.len;
1533
1534 ret = -ENOMEM;
1535 if (!mmget_not_zero(mm))
1536 goto out;
1537
1538 mmap_write_lock(mm);
1539 mas_set(&mas, start);
1540 vma = mas_find(&mas, ULONG_MAX);
1541 if (!vma)
1542 goto out_unlock;
1543
1544 /* check that there's at least one vma in the range */
1545 ret = -EINVAL;
1546 if (vma->vm_start >= end)
1547 goto out_unlock;
1548
1549 /*
1550 * If the first vma contains huge pages, make sure start address
1551 * is aligned to huge page size.
1552 */
1553 if (is_vm_hugetlb_page(vma)) {
1554 unsigned long vma_hpagesize = vma_kernel_pagesize(vma);
1555
1556 if (start & (vma_hpagesize - 1))
1557 goto out_unlock;
1558 }
1559
1560 /*
1561 * Search for not compatible vmas.
1562 */
1563 found = false;
1564 ret = -EINVAL;
1565 for (cur = vma; cur; cur = mas_next(&mas, end - 1)) {
1566 cond_resched();
1567
1568 BUG_ON(!!cur->vm_userfaultfd_ctx.ctx ^
1569 !!(cur->vm_flags & __VM_UFFD_FLAGS));
1570
1571 /*
1572 * Check not compatible vmas, not strictly required
1573 * here as not compatible vmas cannot have an
1574 * userfaultfd_ctx registered on them, but this
1575 * provides for more strict behavior to notice
1576 * unregistration errors.
1577 */
1578 if (!vma_can_userfault(cur, cur->vm_flags))
1579 goto out_unlock;
1580
1581 found = true;
1582 }
1583 BUG_ON(!found);
1584
1585 mas_set(&mas, start);
1586 prev = mas_prev(&mas, 0);
1587 if (prev != vma)
1588 mas_next(&mas, ULONG_MAX);
1589
1590 ret = 0;
1591 do {
1592 cond_resched();
1593
1594 BUG_ON(!vma_can_userfault(vma, vma->vm_flags));
1595
1596 /*
1597 * Nothing to do: this vma is already registered into this
1598 * userfaultfd and with the right tracking mode too.
1599 */
1600 if (!vma->vm_userfaultfd_ctx.ctx)
1601 goto skip;
1602
1603 WARN_ON(!(vma->vm_flags & VM_MAYWRITE));
1604
1605 if (vma->vm_start > start)
1606 start = vma->vm_start;
1607 vma_end = min(end, vma->vm_end);
1608
1609 if (userfaultfd_missing(vma)) {
1610 /*
1611 * Wake any concurrent pending userfault while
1612 * we unregister, so they will not hang
1613 * permanently and it avoids userland to call
1614 * UFFDIO_WAKE explicitly.
1615 */
1616 struct userfaultfd_wake_range range;
1617 range.start = start;
1618 range.len = vma_end - start;
1619 wake_userfault(vma->vm_userfaultfd_ctx.ctx, &range);
1620 }
1621
1622 /* Reset ptes for the whole vma range if wr-protected */
1623 if (userfaultfd_wp(vma))
1624 uffd_wp_range(mm, vma, start, vma_end - start, false);
1625
1626 new_flags = vma->vm_flags & ~__VM_UFFD_FLAGS;
1627 prev = vma_merge(mm, prev, start, vma_end, new_flags,
1628 vma->anon_vma, vma->vm_file, vma->vm_pgoff,
1629 vma_policy(vma),
1630 NULL_VM_UFFD_CTX, anon_vma_name(vma));
1631 if (prev) {
1632 vma = prev;
1633 mas_pause(&mas);
1634 goto next;
1635 }
1636 if (vma->vm_start < start) {
1637 ret = split_vma(mm, vma, start, 1);
1638 if (ret)
1639 break;
1640 mas_pause(&mas);
1641 }
1642 if (vma->vm_end > end) {
1643 ret = split_vma(mm, vma, end, 0);
1644 if (ret)
1645 break;
1646 mas_pause(&mas);
1647 }
1648 next:
1649 /*
1650 * In the vma_merge() successful mprotect-like case 8:
1651 * the next vma was merged into the current one and
1652 * the current one has not been updated yet.
1653 */
1654 vma->vm_flags = new_flags;
1655 vma->vm_userfaultfd_ctx = NULL_VM_UFFD_CTX;
1656
1657 skip:
1658 prev = vma;
1659 start = vma->vm_end;
1660 vma = mas_next(&mas, end - 1);
1661 } while (vma);
1662 out_unlock:
1663 mmap_write_unlock(mm);
1664 mmput(mm);
1665 out:
1666 return ret;
1667 }
1668
1669 /*
1670 * userfaultfd_wake may be used in combination with the
1671 * UFFDIO_*_MODE_DONTWAKE to wakeup userfaults in batches.
1672 */
userfaultfd_wake(struct userfaultfd_ctx * ctx,unsigned long arg)1673 static int userfaultfd_wake(struct userfaultfd_ctx *ctx,
1674 unsigned long arg)
1675 {
1676 int ret;
1677 struct uffdio_range uffdio_wake;
1678 struct userfaultfd_wake_range range;
1679 const void __user *buf = (void __user *)arg;
1680
1681 ret = -EFAULT;
1682 if (copy_from_user(&uffdio_wake, buf, sizeof(uffdio_wake)))
1683 goto out;
1684
1685 ret = validate_range(ctx->mm, uffdio_wake.start, uffdio_wake.len);
1686 if (ret)
1687 goto out;
1688
1689 range.start = uffdio_wake.start;
1690 range.len = uffdio_wake.len;
1691
1692 /*
1693 * len == 0 means wake all and we don't want to wake all here,
1694 * so check it again to be sure.
1695 */
1696 VM_BUG_ON(!range.len);
1697
1698 wake_userfault(ctx, &range);
1699 ret = 0;
1700
1701 out:
1702 return ret;
1703 }
1704
userfaultfd_copy(struct userfaultfd_ctx * ctx,unsigned long arg)1705 static int userfaultfd_copy(struct userfaultfd_ctx *ctx,
1706 unsigned long arg)
1707 {
1708 __s64 ret;
1709 struct uffdio_copy uffdio_copy;
1710 struct uffdio_copy __user *user_uffdio_copy;
1711 struct userfaultfd_wake_range range;
1712
1713 user_uffdio_copy = (struct uffdio_copy __user *) arg;
1714
1715 ret = -EAGAIN;
1716 if (atomic_read(&ctx->mmap_changing))
1717 goto out;
1718
1719 ret = -EFAULT;
1720 if (copy_from_user(&uffdio_copy, user_uffdio_copy,
1721 /* don't copy "copy" last field */
1722 sizeof(uffdio_copy)-sizeof(__s64)))
1723 goto out;
1724
1725 ret = validate_range(ctx->mm, uffdio_copy.dst, uffdio_copy.len);
1726 if (ret)
1727 goto out;
1728 /*
1729 * double check for wraparound just in case. copy_from_user()
1730 * will later check uffdio_copy.src + uffdio_copy.len to fit
1731 * in the userland range.
1732 */
1733 ret = -EINVAL;
1734 if (uffdio_copy.src + uffdio_copy.len <= uffdio_copy.src)
1735 goto out;
1736 if (uffdio_copy.mode & ~(UFFDIO_COPY_MODE_DONTWAKE|UFFDIO_COPY_MODE_WP))
1737 goto out;
1738 if (mmget_not_zero(ctx->mm)) {
1739 ret = mcopy_atomic(ctx->mm, uffdio_copy.dst, uffdio_copy.src,
1740 uffdio_copy.len, &ctx->mmap_changing,
1741 uffdio_copy.mode);
1742 mmput(ctx->mm);
1743 } else {
1744 return -ESRCH;
1745 }
1746 if (unlikely(put_user(ret, &user_uffdio_copy->copy)))
1747 return -EFAULT;
1748 if (ret < 0)
1749 goto out;
1750 BUG_ON(!ret);
1751 /* len == 0 would wake all */
1752 range.len = ret;
1753 if (!(uffdio_copy.mode & UFFDIO_COPY_MODE_DONTWAKE)) {
1754 range.start = uffdio_copy.dst;
1755 wake_userfault(ctx, &range);
1756 }
1757 ret = range.len == uffdio_copy.len ? 0 : -EAGAIN;
1758 out:
1759 return ret;
1760 }
1761
userfaultfd_zeropage(struct userfaultfd_ctx * ctx,unsigned long arg)1762 static int userfaultfd_zeropage(struct userfaultfd_ctx *ctx,
1763 unsigned long arg)
1764 {
1765 __s64 ret;
1766 struct uffdio_zeropage uffdio_zeropage;
1767 struct uffdio_zeropage __user *user_uffdio_zeropage;
1768 struct userfaultfd_wake_range range;
1769
1770 user_uffdio_zeropage = (struct uffdio_zeropage __user *) arg;
1771
1772 ret = -EAGAIN;
1773 if (atomic_read(&ctx->mmap_changing))
1774 goto out;
1775
1776 ret = -EFAULT;
1777 if (copy_from_user(&uffdio_zeropage, user_uffdio_zeropage,
1778 /* don't copy "zeropage" last field */
1779 sizeof(uffdio_zeropage)-sizeof(__s64)))
1780 goto out;
1781
1782 ret = validate_range(ctx->mm, uffdio_zeropage.range.start,
1783 uffdio_zeropage.range.len);
1784 if (ret)
1785 goto out;
1786 ret = -EINVAL;
1787 if (uffdio_zeropage.mode & ~UFFDIO_ZEROPAGE_MODE_DONTWAKE)
1788 goto out;
1789
1790 if (mmget_not_zero(ctx->mm)) {
1791 ret = mfill_zeropage(ctx->mm, uffdio_zeropage.range.start,
1792 uffdio_zeropage.range.len,
1793 &ctx->mmap_changing);
1794 mmput(ctx->mm);
1795 } else {
1796 return -ESRCH;
1797 }
1798 if (unlikely(put_user(ret, &user_uffdio_zeropage->zeropage)))
1799 return -EFAULT;
1800 if (ret < 0)
1801 goto out;
1802 /* len == 0 would wake all */
1803 BUG_ON(!ret);
1804 range.len = ret;
1805 if (!(uffdio_zeropage.mode & UFFDIO_ZEROPAGE_MODE_DONTWAKE)) {
1806 range.start = uffdio_zeropage.range.start;
1807 wake_userfault(ctx, &range);
1808 }
1809 ret = range.len == uffdio_zeropage.range.len ? 0 : -EAGAIN;
1810 out:
1811 return ret;
1812 }
1813
userfaultfd_writeprotect(struct userfaultfd_ctx * ctx,unsigned long arg)1814 static int userfaultfd_writeprotect(struct userfaultfd_ctx *ctx,
1815 unsigned long arg)
1816 {
1817 int ret;
1818 struct uffdio_writeprotect uffdio_wp;
1819 struct uffdio_writeprotect __user *user_uffdio_wp;
1820 struct userfaultfd_wake_range range;
1821 bool mode_wp, mode_dontwake;
1822
1823 if (atomic_read(&ctx->mmap_changing))
1824 return -EAGAIN;
1825
1826 user_uffdio_wp = (struct uffdio_writeprotect __user *) arg;
1827
1828 if (copy_from_user(&uffdio_wp, user_uffdio_wp,
1829 sizeof(struct uffdio_writeprotect)))
1830 return -EFAULT;
1831
1832 ret = validate_range(ctx->mm, uffdio_wp.range.start,
1833 uffdio_wp.range.len);
1834 if (ret)
1835 return ret;
1836
1837 if (uffdio_wp.mode & ~(UFFDIO_WRITEPROTECT_MODE_DONTWAKE |
1838 UFFDIO_WRITEPROTECT_MODE_WP))
1839 return -EINVAL;
1840
1841 mode_wp = uffdio_wp.mode & UFFDIO_WRITEPROTECT_MODE_WP;
1842 mode_dontwake = uffdio_wp.mode & UFFDIO_WRITEPROTECT_MODE_DONTWAKE;
1843
1844 if (mode_wp && mode_dontwake)
1845 return -EINVAL;
1846
1847 if (mmget_not_zero(ctx->mm)) {
1848 ret = mwriteprotect_range(ctx->mm, uffdio_wp.range.start,
1849 uffdio_wp.range.len, mode_wp,
1850 &ctx->mmap_changing);
1851 mmput(ctx->mm);
1852 } else {
1853 return -ESRCH;
1854 }
1855
1856 if (ret)
1857 return ret;
1858
1859 if (!mode_wp && !mode_dontwake) {
1860 range.start = uffdio_wp.range.start;
1861 range.len = uffdio_wp.range.len;
1862 wake_userfault(ctx, &range);
1863 }
1864 return ret;
1865 }
1866
userfaultfd_continue(struct userfaultfd_ctx * ctx,unsigned long arg)1867 static int userfaultfd_continue(struct userfaultfd_ctx *ctx, unsigned long arg)
1868 {
1869 __s64 ret;
1870 struct uffdio_continue uffdio_continue;
1871 struct uffdio_continue __user *user_uffdio_continue;
1872 struct userfaultfd_wake_range range;
1873
1874 user_uffdio_continue = (struct uffdio_continue __user *)arg;
1875
1876 ret = -EAGAIN;
1877 if (atomic_read(&ctx->mmap_changing))
1878 goto out;
1879
1880 ret = -EFAULT;
1881 if (copy_from_user(&uffdio_continue, user_uffdio_continue,
1882 /* don't copy the output fields */
1883 sizeof(uffdio_continue) - (sizeof(__s64))))
1884 goto out;
1885
1886 ret = validate_range(ctx->mm, uffdio_continue.range.start,
1887 uffdio_continue.range.len);
1888 if (ret)
1889 goto out;
1890
1891 ret = -EINVAL;
1892 /* double check for wraparound just in case. */
1893 if (uffdio_continue.range.start + uffdio_continue.range.len <=
1894 uffdio_continue.range.start) {
1895 goto out;
1896 }
1897 if (uffdio_continue.mode & ~UFFDIO_CONTINUE_MODE_DONTWAKE)
1898 goto out;
1899
1900 if (mmget_not_zero(ctx->mm)) {
1901 ret = mcopy_continue(ctx->mm, uffdio_continue.range.start,
1902 uffdio_continue.range.len,
1903 &ctx->mmap_changing);
1904 mmput(ctx->mm);
1905 } else {
1906 return -ESRCH;
1907 }
1908
1909 if (unlikely(put_user(ret, &user_uffdio_continue->mapped)))
1910 return -EFAULT;
1911 if (ret < 0)
1912 goto out;
1913
1914 /* len == 0 would wake all */
1915 BUG_ON(!ret);
1916 range.len = ret;
1917 if (!(uffdio_continue.mode & UFFDIO_CONTINUE_MODE_DONTWAKE)) {
1918 range.start = uffdio_continue.range.start;
1919 wake_userfault(ctx, &range);
1920 }
1921 ret = range.len == uffdio_continue.range.len ? 0 : -EAGAIN;
1922
1923 out:
1924 return ret;
1925 }
1926
uffd_ctx_features(__u64 user_features)1927 static inline unsigned int uffd_ctx_features(__u64 user_features)
1928 {
1929 /*
1930 * For the current set of features the bits just coincide. Set
1931 * UFFD_FEATURE_INITIALIZED to mark the features as enabled.
1932 */
1933 return (unsigned int)user_features | UFFD_FEATURE_INITIALIZED;
1934 }
1935
1936 /*
1937 * userland asks for a certain API version and we return which bits
1938 * and ioctl commands are implemented in this kernel for such API
1939 * version or -EINVAL if unknown.
1940 */
userfaultfd_api(struct userfaultfd_ctx * ctx,unsigned long arg)1941 static int userfaultfd_api(struct userfaultfd_ctx *ctx,
1942 unsigned long arg)
1943 {
1944 struct uffdio_api uffdio_api;
1945 void __user *buf = (void __user *)arg;
1946 unsigned int ctx_features;
1947 int ret;
1948 __u64 features;
1949
1950 ret = -EFAULT;
1951 if (copy_from_user(&uffdio_api, buf, sizeof(uffdio_api)))
1952 goto out;
1953 /* Ignore unsupported features (userspace built against newer kernel) */
1954 features = uffdio_api.features & UFFD_API_FEATURES;
1955 ret = -EPERM;
1956 if ((features & UFFD_FEATURE_EVENT_FORK) && !capable(CAP_SYS_PTRACE))
1957 goto err_out;
1958 /* report all available features and ioctls to userland */
1959 uffdio_api.features = UFFD_API_FEATURES;
1960 #ifndef CONFIG_HAVE_ARCH_USERFAULTFD_MINOR
1961 uffdio_api.features &=
1962 ~(UFFD_FEATURE_MINOR_HUGETLBFS | UFFD_FEATURE_MINOR_SHMEM);
1963 #endif
1964 #ifndef CONFIG_HAVE_ARCH_USERFAULTFD_WP
1965 uffdio_api.features &= ~UFFD_FEATURE_PAGEFAULT_FLAG_WP;
1966 #endif
1967 #ifndef CONFIG_PTE_MARKER_UFFD_WP
1968 uffdio_api.features &= ~UFFD_FEATURE_WP_HUGETLBFS_SHMEM;
1969 #endif
1970 uffdio_api.ioctls = UFFD_API_IOCTLS;
1971 ret = -EFAULT;
1972 if (copy_to_user(buf, &uffdio_api, sizeof(uffdio_api)))
1973 goto out;
1974
1975 /* only enable the requested features for this uffd context */
1976 ctx_features = uffd_ctx_features(features);
1977 ret = -EINVAL;
1978 if (cmpxchg(&ctx->features, 0, ctx_features) != 0)
1979 goto err_out;
1980
1981 ret = 0;
1982 out:
1983 return ret;
1984 err_out:
1985 memset(&uffdio_api, 0, sizeof(uffdio_api));
1986 if (copy_to_user(buf, &uffdio_api, sizeof(uffdio_api)))
1987 ret = -EFAULT;
1988 goto out;
1989 }
1990
userfaultfd_ioctl(struct file * file,unsigned cmd,unsigned long arg)1991 static long userfaultfd_ioctl(struct file *file, unsigned cmd,
1992 unsigned long arg)
1993 {
1994 int ret = -EINVAL;
1995 struct userfaultfd_ctx *ctx = file->private_data;
1996
1997 if (cmd != UFFDIO_API && !userfaultfd_is_initialized(ctx))
1998 return -EINVAL;
1999
2000 switch(cmd) {
2001 case UFFDIO_API:
2002 ret = userfaultfd_api(ctx, arg);
2003 break;
2004 case UFFDIO_REGISTER:
2005 ret = userfaultfd_register(ctx, arg);
2006 break;
2007 case UFFDIO_UNREGISTER:
2008 ret = userfaultfd_unregister(ctx, arg);
2009 break;
2010 case UFFDIO_WAKE:
2011 ret = userfaultfd_wake(ctx, arg);
2012 break;
2013 case UFFDIO_COPY:
2014 ret = userfaultfd_copy(ctx, arg);
2015 break;
2016 case UFFDIO_ZEROPAGE:
2017 ret = userfaultfd_zeropage(ctx, arg);
2018 break;
2019 case UFFDIO_WRITEPROTECT:
2020 ret = userfaultfd_writeprotect(ctx, arg);
2021 break;
2022 case UFFDIO_CONTINUE:
2023 ret = userfaultfd_continue(ctx, arg);
2024 break;
2025 }
2026 return ret;
2027 }
2028
2029 #ifdef CONFIG_PROC_FS
userfaultfd_show_fdinfo(struct seq_file * m,struct file * f)2030 static void userfaultfd_show_fdinfo(struct seq_file *m, struct file *f)
2031 {
2032 struct userfaultfd_ctx *ctx = f->private_data;
2033 wait_queue_entry_t *wq;
2034 unsigned long pending = 0, total = 0;
2035
2036 spin_lock_irq(&ctx->fault_pending_wqh.lock);
2037 list_for_each_entry(wq, &ctx->fault_pending_wqh.head, entry) {
2038 pending++;
2039 total++;
2040 }
2041 list_for_each_entry(wq, &ctx->fault_wqh.head, entry) {
2042 total++;
2043 }
2044 spin_unlock_irq(&ctx->fault_pending_wqh.lock);
2045
2046 /*
2047 * If more protocols will be added, there will be all shown
2048 * separated by a space. Like this:
2049 * protocols: aa:... bb:...
2050 */
2051 seq_printf(m, "pending:\t%lu\ntotal:\t%lu\nAPI:\t%Lx:%x:%Lx\n",
2052 pending, total, UFFD_API, ctx->features,
2053 UFFD_API_IOCTLS|UFFD_API_RANGE_IOCTLS);
2054 }
2055 #endif
2056
2057 static const struct file_operations userfaultfd_fops = {
2058 #ifdef CONFIG_PROC_FS
2059 .show_fdinfo = userfaultfd_show_fdinfo,
2060 #endif
2061 .release = userfaultfd_release,
2062 .poll = userfaultfd_poll,
2063 .read = userfaultfd_read,
2064 .unlocked_ioctl = userfaultfd_ioctl,
2065 .compat_ioctl = compat_ptr_ioctl,
2066 .llseek = noop_llseek,
2067 };
2068
init_once_userfaultfd_ctx(void * mem)2069 static void init_once_userfaultfd_ctx(void *mem)
2070 {
2071 struct userfaultfd_ctx *ctx = (struct userfaultfd_ctx *) mem;
2072
2073 init_waitqueue_head(&ctx->fault_pending_wqh);
2074 init_waitqueue_head(&ctx->fault_wqh);
2075 init_waitqueue_head(&ctx->event_wqh);
2076 init_waitqueue_head(&ctx->fd_wqh);
2077 seqcount_spinlock_init(&ctx->refile_seq, &ctx->fault_pending_wqh.lock);
2078 }
2079
new_userfaultfd(int flags)2080 static int new_userfaultfd(int flags)
2081 {
2082 struct userfaultfd_ctx *ctx;
2083 int fd;
2084
2085 BUG_ON(!current->mm);
2086
2087 /* Check the UFFD_* constants for consistency. */
2088 BUILD_BUG_ON(UFFD_USER_MODE_ONLY & UFFD_SHARED_FCNTL_FLAGS);
2089 BUILD_BUG_ON(UFFD_CLOEXEC != O_CLOEXEC);
2090 BUILD_BUG_ON(UFFD_NONBLOCK != O_NONBLOCK);
2091
2092 if (flags & ~(UFFD_SHARED_FCNTL_FLAGS | UFFD_USER_MODE_ONLY))
2093 return -EINVAL;
2094
2095 ctx = kmem_cache_alloc(userfaultfd_ctx_cachep, GFP_KERNEL);
2096 if (!ctx)
2097 return -ENOMEM;
2098
2099 refcount_set(&ctx->refcount, 1);
2100 ctx->flags = flags;
2101 ctx->features = 0;
2102 ctx->released = false;
2103 atomic_set(&ctx->mmap_changing, 0);
2104 ctx->mm = current->mm;
2105 /* prevent the mm struct to be freed */
2106 mmgrab(ctx->mm);
2107
2108 fd = anon_inode_getfd_secure("[userfaultfd]", &userfaultfd_fops, ctx,
2109 O_RDONLY | (flags & UFFD_SHARED_FCNTL_FLAGS), NULL);
2110 if (fd < 0) {
2111 mmdrop(ctx->mm);
2112 kmem_cache_free(userfaultfd_ctx_cachep, ctx);
2113 }
2114 return fd;
2115 }
2116
userfaultfd_syscall_allowed(int flags)2117 static inline bool userfaultfd_syscall_allowed(int flags)
2118 {
2119 /* Userspace-only page faults are always allowed */
2120 if (flags & UFFD_USER_MODE_ONLY)
2121 return true;
2122
2123 /*
2124 * The user is requesting a userfaultfd which can handle kernel faults.
2125 * Privileged users are always allowed to do this.
2126 */
2127 if (capable(CAP_SYS_PTRACE))
2128 return true;
2129
2130 /* Otherwise, access to kernel fault handling is sysctl controlled. */
2131 return sysctl_unprivileged_userfaultfd;
2132 }
2133
SYSCALL_DEFINE1(userfaultfd,int,flags)2134 SYSCALL_DEFINE1(userfaultfd, int, flags)
2135 {
2136 if (!userfaultfd_syscall_allowed(flags))
2137 return -EPERM;
2138
2139 return new_userfaultfd(flags);
2140 }
2141
userfaultfd_dev_ioctl(struct file * file,unsigned int cmd,unsigned long flags)2142 static long userfaultfd_dev_ioctl(struct file *file, unsigned int cmd, unsigned long flags)
2143 {
2144 if (cmd != USERFAULTFD_IOC_NEW)
2145 return -EINVAL;
2146
2147 return new_userfaultfd(flags);
2148 }
2149
2150 static const struct file_operations userfaultfd_dev_fops = {
2151 .unlocked_ioctl = userfaultfd_dev_ioctl,
2152 .compat_ioctl = userfaultfd_dev_ioctl,
2153 .owner = THIS_MODULE,
2154 .llseek = noop_llseek,
2155 };
2156
2157 static struct miscdevice userfaultfd_misc = {
2158 .minor = MISC_DYNAMIC_MINOR,
2159 .name = "userfaultfd",
2160 .fops = &userfaultfd_dev_fops
2161 };
2162
userfaultfd_init(void)2163 static int __init userfaultfd_init(void)
2164 {
2165 int ret;
2166
2167 ret = misc_register(&userfaultfd_misc);
2168 if (ret)
2169 return ret;
2170
2171 userfaultfd_ctx_cachep = kmem_cache_create("userfaultfd_ctx_cache",
2172 sizeof(struct userfaultfd_ctx),
2173 0,
2174 SLAB_HWCACHE_ALIGN|SLAB_PANIC,
2175 init_once_userfaultfd_ctx);
2176 return 0;
2177 }
2178 __initcall(userfaultfd_init);
2179
