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 static int sysctl_unprivileged_userfaultfd __read_mostly;
36
37 #ifdef CONFIG_SYSCTL
38 static struct ctl_table vm_userfaultfd_table[] = {
39 {
40 .procname = "unprivileged_userfaultfd",
41 .data = &sysctl_unprivileged_userfaultfd,
42 .maxlen = sizeof(sysctl_unprivileged_userfaultfd),
43 .mode = 0644,
44 .proc_handler = proc_dointvec_minmax,
45 .extra1 = SYSCTL_ZERO,
46 .extra2 = SYSCTL_ONE,
47 },
48 { }
49 };
50 #endif
51
52 static struct kmem_cache *userfaultfd_ctx_cachep __read_mostly;
53
54 struct userfaultfd_fork_ctx {
55 struct userfaultfd_ctx *orig;
56 struct userfaultfd_ctx *new;
57 struct list_head list;
58 };
59
60 struct userfaultfd_unmap_ctx {
61 struct userfaultfd_ctx *ctx;
62 unsigned long start;
63 unsigned long end;
64 struct list_head list;
65 };
66
67 struct userfaultfd_wait_queue {
68 struct uffd_msg msg;
69 wait_queue_entry_t wq;
70 struct userfaultfd_ctx *ctx;
71 bool waken;
72 };
73
74 struct userfaultfd_wake_range {
75 unsigned long start;
76 unsigned long len;
77 };
78
79 /* internal indication that UFFD_API ioctl was successfully executed */
80 #define UFFD_FEATURE_INITIALIZED (1u << 31)
81
userfaultfd_is_initialized(struct userfaultfd_ctx * ctx)82 static bool userfaultfd_is_initialized(struct userfaultfd_ctx *ctx)
83 {
84 return ctx->features & UFFD_FEATURE_INITIALIZED;
85 }
86
87 /*
88 * Whether WP_UNPOPULATED is enabled on the uffd context. It is only
89 * meaningful when userfaultfd_wp()==true on the vma and when it's
90 * anonymous.
91 */
userfaultfd_wp_unpopulated(struct vm_area_struct * vma)92 bool userfaultfd_wp_unpopulated(struct vm_area_struct *vma)
93 {
94 struct userfaultfd_ctx *ctx = vma->vm_userfaultfd_ctx.ctx;
95
96 if (!ctx)
97 return false;
98
99 return ctx->features & UFFD_FEATURE_WP_UNPOPULATED;
100 }
101
userfaultfd_set_vm_flags(struct vm_area_struct * vma,vm_flags_t flags)102 static void userfaultfd_set_vm_flags(struct vm_area_struct *vma,
103 vm_flags_t flags)
104 {
105 const bool uffd_wp_changed = (vma->vm_flags ^ flags) & VM_UFFD_WP;
106
107 vm_flags_reset(vma, flags);
108 /*
109 * For shared mappings, we want to enable writenotify while
110 * userfaultfd-wp is enabled (see vma_wants_writenotify()). We'll simply
111 * recalculate vma->vm_page_prot whenever userfaultfd-wp changes.
112 */
113 if ((vma->vm_flags & VM_SHARED) && uffd_wp_changed)
114 vma_set_page_prot(vma);
115 }
116
userfaultfd_wake_function(wait_queue_entry_t * wq,unsigned mode,int wake_flags,void * key)117 static int userfaultfd_wake_function(wait_queue_entry_t *wq, unsigned mode,
118 int wake_flags, void *key)
119 {
120 struct userfaultfd_wake_range *range = key;
121 int ret;
122 struct userfaultfd_wait_queue *uwq;
123 unsigned long start, len;
124
125 uwq = container_of(wq, struct userfaultfd_wait_queue, wq);
126 ret = 0;
127 /* len == 0 means wake all */
128 start = range->start;
129 len = range->len;
130 if (len && (start > uwq->msg.arg.pagefault.address ||
131 start + len <= uwq->msg.arg.pagefault.address))
132 goto out;
133 WRITE_ONCE(uwq->waken, true);
134 /*
135 * The Program-Order guarantees provided by the scheduler
136 * ensure uwq->waken is visible before the task is woken.
137 */
138 ret = wake_up_state(wq->private, mode);
139 if (ret) {
140 /*
141 * Wake only once, autoremove behavior.
142 *
143 * After the effect of list_del_init is visible to the other
144 * CPUs, the waitqueue may disappear from under us, see the
145 * !list_empty_careful() in handle_userfault().
146 *
147 * try_to_wake_up() has an implicit smp_mb(), and the
148 * wq->private is read before calling the extern function
149 * "wake_up_state" (which in turns calls try_to_wake_up).
150 */
151 list_del_init(&wq->entry);
152 }
153 out:
154 return ret;
155 }
156
157 /**
158 * userfaultfd_ctx_get - Acquires a reference to the internal userfaultfd
159 * context.
160 * @ctx: [in] Pointer to the userfaultfd context.
161 */
userfaultfd_ctx_get(struct userfaultfd_ctx * ctx)162 static void userfaultfd_ctx_get(struct userfaultfd_ctx *ctx)
163 {
164 refcount_inc(&ctx->refcount);
165 }
166
167 /**
168 * userfaultfd_ctx_put - Releases a reference to the internal userfaultfd
169 * context.
170 * @ctx: [in] Pointer to userfaultfd context.
171 *
172 * The userfaultfd context reference must have been previously acquired either
173 * with userfaultfd_ctx_get() or userfaultfd_ctx_fdget().
174 */
userfaultfd_ctx_put(struct userfaultfd_ctx * ctx)175 static void userfaultfd_ctx_put(struct userfaultfd_ctx *ctx)
176 {
177 if (refcount_dec_and_test(&ctx->refcount)) {
178 VM_BUG_ON(spin_is_locked(&ctx->fault_pending_wqh.lock));
179 VM_BUG_ON(waitqueue_active(&ctx->fault_pending_wqh));
180 VM_BUG_ON(spin_is_locked(&ctx->fault_wqh.lock));
181 VM_BUG_ON(waitqueue_active(&ctx->fault_wqh));
182 VM_BUG_ON(spin_is_locked(&ctx->event_wqh.lock));
183 VM_BUG_ON(waitqueue_active(&ctx->event_wqh));
184 VM_BUG_ON(spin_is_locked(&ctx->fd_wqh.lock));
185 VM_BUG_ON(waitqueue_active(&ctx->fd_wqh));
186 mmdrop(ctx->mm);
187 kmem_cache_free(userfaultfd_ctx_cachep, ctx);
188 }
189 }
190
msg_init(struct uffd_msg * msg)191 static inline void msg_init(struct uffd_msg *msg)
192 {
193 BUILD_BUG_ON(sizeof(struct uffd_msg) != 32);
194 /*
195 * Must use memset to zero out the paddings or kernel data is
196 * leaked to userland.
197 */
198 memset(msg, 0, sizeof(struct uffd_msg));
199 }
200
userfault_msg(unsigned long address,unsigned long real_address,unsigned int flags,unsigned long reason,unsigned int features)201 static inline struct uffd_msg userfault_msg(unsigned long address,
202 unsigned long real_address,
203 unsigned int flags,
204 unsigned long reason,
205 unsigned int features)
206 {
207 struct uffd_msg msg;
208
209 msg_init(&msg);
210 msg.event = UFFD_EVENT_PAGEFAULT;
211
212 msg.arg.pagefault.address = (features & UFFD_FEATURE_EXACT_ADDRESS) ?
213 real_address : address;
214
215 /*
216 * These flags indicate why the userfault occurred:
217 * - UFFD_PAGEFAULT_FLAG_WP indicates a write protect fault.
218 * - UFFD_PAGEFAULT_FLAG_MINOR indicates a minor fault.
219 * - Neither of these flags being set indicates a MISSING fault.
220 *
221 * Separately, UFFD_PAGEFAULT_FLAG_WRITE indicates it was a write
222 * fault. Otherwise, it was a read fault.
223 */
224 if (flags & FAULT_FLAG_WRITE)
225 msg.arg.pagefault.flags |= UFFD_PAGEFAULT_FLAG_WRITE;
226 if (reason & VM_UFFD_WP)
227 msg.arg.pagefault.flags |= UFFD_PAGEFAULT_FLAG_WP;
228 if (reason & VM_UFFD_MINOR)
229 msg.arg.pagefault.flags |= UFFD_PAGEFAULT_FLAG_MINOR;
230 if (features & UFFD_FEATURE_THREAD_ID)
231 msg.arg.pagefault.feat.ptid = task_pid_vnr(current);
232 return msg;
233 }
234
235 #ifdef CONFIG_HUGETLB_PAGE
236 /*
237 * Same functionality as userfaultfd_must_wait below with modifications for
238 * hugepmd ranges.
239 */
userfaultfd_huge_must_wait(struct userfaultfd_ctx * ctx,struct vm_fault * vmf,unsigned long reason)240 static inline bool userfaultfd_huge_must_wait(struct userfaultfd_ctx *ctx,
241 struct vm_fault *vmf,
242 unsigned long reason)
243 {
244 struct vm_area_struct *vma = vmf->vma;
245 pte_t *ptep, pte;
246 bool ret = true;
247
248 assert_fault_locked(vmf);
249
250 ptep = hugetlb_walk(vma, vmf->address, vma_mmu_pagesize(vma));
251 if (!ptep)
252 goto out;
253
254 ret = false;
255 pte = huge_ptep_get(ptep);
256
257 /*
258 * Lockless access: we're in a wait_event so it's ok if it
259 * changes under us. PTE markers should be handled the same as none
260 * ptes here.
261 */
262 if (huge_pte_none_mostly(pte))
263 ret = true;
264 if (!huge_pte_write(pte) && (reason & VM_UFFD_WP))
265 ret = true;
266 out:
267 return ret;
268 }
269 #else
userfaultfd_huge_must_wait(struct userfaultfd_ctx * ctx,struct vm_fault * vmf,unsigned long reason)270 static inline bool userfaultfd_huge_must_wait(struct userfaultfd_ctx *ctx,
271 struct vm_fault *vmf,
272 unsigned long reason)
273 {
274 return false; /* should never get here */
275 }
276 #endif /* CONFIG_HUGETLB_PAGE */
277
278 /*
279 * Verify the pagetables are still not ok after having reigstered into
280 * the fault_pending_wqh to avoid userland having to UFFDIO_WAKE any
281 * userfault that has already been resolved, if userfaultfd_read and
282 * UFFDIO_COPY|ZEROPAGE are being run simultaneously on two different
283 * threads.
284 */
userfaultfd_must_wait(struct userfaultfd_ctx * ctx,struct vm_fault * vmf,unsigned long reason)285 static inline bool userfaultfd_must_wait(struct userfaultfd_ctx *ctx,
286 struct vm_fault *vmf,
287 unsigned long reason)
288 {
289 struct mm_struct *mm = ctx->mm;
290 unsigned long address = vmf->address;
291 pgd_t *pgd;
292 p4d_t *p4d;
293 pud_t *pud;
294 pmd_t *pmd, _pmd;
295 pte_t *pte;
296 pte_t ptent;
297 bool ret = true;
298
299 assert_fault_locked(vmf);
300
301 pgd = pgd_offset(mm, address);
302 if (!pgd_present(*pgd))
303 goto out;
304 p4d = p4d_offset(pgd, address);
305 if (!p4d_present(*p4d))
306 goto out;
307 pud = pud_offset(p4d, address);
308 if (!pud_present(*pud))
309 goto out;
310 pmd = pmd_offset(pud, address);
311 again:
312 _pmd = pmdp_get_lockless(pmd);
313 if (pmd_none(_pmd))
314 goto out;
315
316 ret = false;
317 if (!pmd_present(_pmd) || pmd_devmap(_pmd))
318 goto out;
319
320 if (pmd_trans_huge(_pmd)) {
321 if (!pmd_write(_pmd) && (reason & VM_UFFD_WP))
322 ret = true;
323 goto out;
324 }
325
326 pte = pte_offset_map(pmd, address);
327 if (!pte) {
328 ret = true;
329 goto again;
330 }
331 /*
332 * Lockless access: we're in a wait_event so it's ok if it
333 * changes under us. PTE markers should be handled the same as none
334 * ptes here.
335 */
336 ptent = ptep_get(pte);
337 if (pte_none_mostly(ptent))
338 ret = true;
339 if (!pte_write(ptent) && (reason & VM_UFFD_WP))
340 ret = true;
341 pte_unmap(pte);
342
343 out:
344 return ret;
345 }
346
userfaultfd_get_blocking_state(unsigned int flags)347 static inline unsigned int userfaultfd_get_blocking_state(unsigned int flags)
348 {
349 if (flags & FAULT_FLAG_INTERRUPTIBLE)
350 return TASK_INTERRUPTIBLE;
351
352 if (flags & FAULT_FLAG_KILLABLE)
353 return TASK_KILLABLE;
354
355 return TASK_UNINTERRUPTIBLE;
356 }
357
358 /*
359 * The locking rules involved in returning VM_FAULT_RETRY depending on
360 * FAULT_FLAG_ALLOW_RETRY, FAULT_FLAG_RETRY_NOWAIT and
361 * FAULT_FLAG_KILLABLE are not straightforward. The "Caution"
362 * recommendation in __lock_page_or_retry is not an understatement.
363 *
364 * If FAULT_FLAG_ALLOW_RETRY is set, the mmap_lock must be released
365 * before returning VM_FAULT_RETRY only if FAULT_FLAG_RETRY_NOWAIT is
366 * not set.
367 *
368 * If FAULT_FLAG_ALLOW_RETRY is set but FAULT_FLAG_KILLABLE is not
369 * set, VM_FAULT_RETRY can still be returned if and only if there are
370 * fatal_signal_pending()s, and the mmap_lock must be released before
371 * returning it.
372 */
handle_userfault(struct vm_fault * vmf,unsigned long reason)373 vm_fault_t handle_userfault(struct vm_fault *vmf, unsigned long reason)
374 {
375 struct vm_area_struct *vma = vmf->vma;
376 struct mm_struct *mm = vma->vm_mm;
377 struct userfaultfd_ctx *ctx;
378 struct userfaultfd_wait_queue uwq;
379 vm_fault_t ret = VM_FAULT_SIGBUS;
380 bool must_wait;
381 unsigned int blocking_state;
382
383 /*
384 * We don't do userfault handling for the final child pid update.
385 *
386 * We also don't do userfault handling during
387 * coredumping. hugetlbfs has the special
388 * hugetlb_follow_page_mask() to skip missing pages in the
389 * FOLL_DUMP case, anon memory also checks for FOLL_DUMP with
390 * the no_page_table() helper in follow_page_mask(), but the
391 * shmem_vm_ops->fault method is invoked even during
392 * coredumping and it ends up here.
393 */
394 if (current->flags & (PF_EXITING|PF_DUMPCORE))
395 goto out;
396
397 assert_fault_locked(vmf);
398
399 ctx = vma->vm_userfaultfd_ctx.ctx;
400 if (!ctx)
401 goto out;
402
403 BUG_ON(ctx->mm != mm);
404
405 /* Any unrecognized flag is a bug. */
406 VM_BUG_ON(reason & ~__VM_UFFD_FLAGS);
407 /* 0 or > 1 flags set is a bug; we expect exactly 1. */
408 VM_BUG_ON(!reason || (reason & (reason - 1)));
409
410 if (ctx->features & UFFD_FEATURE_SIGBUS)
411 goto out;
412 if (!(vmf->flags & FAULT_FLAG_USER) && (ctx->flags & UFFD_USER_MODE_ONLY))
413 goto out;
414
415 /*
416 * If it's already released don't get it. This avoids to loop
417 * in __get_user_pages if userfaultfd_release waits on the
418 * caller of handle_userfault to release the mmap_lock.
419 */
420 if (unlikely(READ_ONCE(ctx->released))) {
421 /*
422 * Don't return VM_FAULT_SIGBUS in this case, so a non
423 * cooperative manager can close the uffd after the
424 * last UFFDIO_COPY, without risking to trigger an
425 * involuntary SIGBUS if the process was starting the
426 * userfaultfd while the userfaultfd was still armed
427 * (but after the last UFFDIO_COPY). If the uffd
428 * wasn't already closed when the userfault reached
429 * this point, that would normally be solved by
430 * userfaultfd_must_wait returning 'false'.
431 *
432 * If we were to return VM_FAULT_SIGBUS here, the non
433 * cooperative manager would be instead forced to
434 * always call UFFDIO_UNREGISTER before it can safely
435 * close the uffd.
436 */
437 ret = VM_FAULT_NOPAGE;
438 goto out;
439 }
440
441 /*
442 * Check that we can return VM_FAULT_RETRY.
443 *
444 * NOTE: it should become possible to return VM_FAULT_RETRY
445 * even if FAULT_FLAG_TRIED is set without leading to gup()
446 * -EBUSY failures, if the userfaultfd is to be extended for
447 * VM_UFFD_WP tracking and we intend to arm the userfault
448 * without first stopping userland access to the memory. For
449 * VM_UFFD_MISSING userfaults this is enough for now.
450 */
451 if (unlikely(!(vmf->flags & FAULT_FLAG_ALLOW_RETRY))) {
452 /*
453 * Validate the invariant that nowait must allow retry
454 * to be sure not to return SIGBUS erroneously on
455 * nowait invocations.
456 */
457 BUG_ON(vmf->flags & FAULT_FLAG_RETRY_NOWAIT);
458 #ifdef CONFIG_DEBUG_VM
459 if (printk_ratelimit()) {
460 printk(KERN_WARNING
461 "FAULT_FLAG_ALLOW_RETRY missing %x\n",
462 vmf->flags);
463 dump_stack();
464 }
465 #endif
466 goto out;
467 }
468
469 /*
470 * Handle nowait, not much to do other than tell it to retry
471 * and wait.
472 */
473 ret = VM_FAULT_RETRY;
474 if (vmf->flags & FAULT_FLAG_RETRY_NOWAIT)
475 goto out;
476
477 /* take the reference before dropping the mmap_lock */
478 userfaultfd_ctx_get(ctx);
479
480 init_waitqueue_func_entry(&uwq.wq, userfaultfd_wake_function);
481 uwq.wq.private = current;
482 uwq.msg = userfault_msg(vmf->address, vmf->real_address, vmf->flags,
483 reason, ctx->features);
484 uwq.ctx = ctx;
485 uwq.waken = false;
486
487 blocking_state = userfaultfd_get_blocking_state(vmf->flags);
488
489 /*
490 * Take the vma lock now, in order to safely call
491 * userfaultfd_huge_must_wait() later. Since acquiring the
492 * (sleepable) vma lock can modify the current task state, that
493 * must be before explicitly calling set_current_state().
494 */
495 if (is_vm_hugetlb_page(vma))
496 hugetlb_vma_lock_read(vma);
497
498 spin_lock_irq(&ctx->fault_pending_wqh.lock);
499 /*
500 * After the __add_wait_queue the uwq is visible to userland
501 * through poll/read().
502 */
503 __add_wait_queue(&ctx->fault_pending_wqh, &uwq.wq);
504 /*
505 * The smp_mb() after __set_current_state prevents the reads
506 * following the spin_unlock to happen before the list_add in
507 * __add_wait_queue.
508 */
509 set_current_state(blocking_state);
510 spin_unlock_irq(&ctx->fault_pending_wqh.lock);
511
512 if (!is_vm_hugetlb_page(vma))
513 must_wait = userfaultfd_must_wait(ctx, vmf, reason);
514 else
515 must_wait = userfaultfd_huge_must_wait(ctx, vmf, reason);
516 if (is_vm_hugetlb_page(vma))
517 hugetlb_vma_unlock_read(vma);
518 release_fault_lock(vmf);
519
520 if (likely(must_wait && !READ_ONCE(ctx->released))) {
521 wake_up_poll(&ctx->fd_wqh, EPOLLIN);
522 schedule();
523 }
524
525 __set_current_state(TASK_RUNNING);
526
527 /*
528 * Here we race with the list_del; list_add in
529 * userfaultfd_ctx_read(), however because we don't ever run
530 * list_del_init() to refile across the two lists, the prev
531 * and next pointers will never point to self. list_add also
532 * would never let any of the two pointers to point to
533 * self. So list_empty_careful won't risk to see both pointers
534 * pointing to self at any time during the list refile. The
535 * only case where list_del_init() is called is the full
536 * removal in the wake function and there we don't re-list_add
537 * and it's fine not to block on the spinlock. The uwq on this
538 * kernel stack can be released after the list_del_init.
539 */
540 if (!list_empty_careful(&uwq.wq.entry)) {
541 spin_lock_irq(&ctx->fault_pending_wqh.lock);
542 /*
543 * No need of list_del_init(), the uwq on the stack
544 * will be freed shortly anyway.
545 */
546 list_del(&uwq.wq.entry);
547 spin_unlock_irq(&ctx->fault_pending_wqh.lock);
548 }
549
550 /*
551 * ctx may go away after this if the userfault pseudo fd is
552 * already released.
553 */
554 userfaultfd_ctx_put(ctx);
555
556 out:
557 return ret;
558 }
559
userfaultfd_event_wait_completion(struct userfaultfd_ctx * ctx,struct userfaultfd_wait_queue * ewq)560 static void userfaultfd_event_wait_completion(struct userfaultfd_ctx *ctx,
561 struct userfaultfd_wait_queue *ewq)
562 {
563 struct userfaultfd_ctx *release_new_ctx;
564
565 if (WARN_ON_ONCE(current->flags & PF_EXITING))
566 goto out;
567
568 ewq->ctx = ctx;
569 init_waitqueue_entry(&ewq->wq, current);
570 release_new_ctx = NULL;
571
572 spin_lock_irq(&ctx->event_wqh.lock);
573 /*
574 * After the __add_wait_queue the uwq is visible to userland
575 * through poll/read().
576 */
577 __add_wait_queue(&ctx->event_wqh, &ewq->wq);
578 for (;;) {
579 set_current_state(TASK_KILLABLE);
580 if (ewq->msg.event == 0)
581 break;
582 if (READ_ONCE(ctx->released) ||
583 fatal_signal_pending(current)) {
584 /*
585 * &ewq->wq may be queued in fork_event, but
586 * __remove_wait_queue ignores the head
587 * parameter. It would be a problem if it
588 * didn't.
589 */
590 __remove_wait_queue(&ctx->event_wqh, &ewq->wq);
591 if (ewq->msg.event == UFFD_EVENT_FORK) {
592 struct userfaultfd_ctx *new;
593
594 new = (struct userfaultfd_ctx *)
595 (unsigned long)
596 ewq->msg.arg.reserved.reserved1;
597 release_new_ctx = new;
598 }
599 break;
600 }
601
602 spin_unlock_irq(&ctx->event_wqh.lock);
603
604 wake_up_poll(&ctx->fd_wqh, EPOLLIN);
605 schedule();
606
607 spin_lock_irq(&ctx->event_wqh.lock);
608 }
609 __set_current_state(TASK_RUNNING);
610 spin_unlock_irq(&ctx->event_wqh.lock);
611
612 if (release_new_ctx) {
613 struct vm_area_struct *vma;
614 struct mm_struct *mm = release_new_ctx->mm;
615 VMA_ITERATOR(vmi, mm, 0);
616
617 /* the various vma->vm_userfaultfd_ctx still points to it */
618 mmap_write_lock(mm);
619 for_each_vma(vmi, vma) {
620 if (vma->vm_userfaultfd_ctx.ctx == release_new_ctx) {
621 vma_start_write(vma);
622 vma->vm_userfaultfd_ctx = NULL_VM_UFFD_CTX;
623 userfaultfd_set_vm_flags(vma,
624 vma->vm_flags & ~__VM_UFFD_FLAGS);
625 }
626 }
627 mmap_write_unlock(mm);
628
629 userfaultfd_ctx_put(release_new_ctx);
630 }
631
632 /*
633 * ctx may go away after this if the userfault pseudo fd is
634 * already released.
635 */
636 out:
637 atomic_dec(&ctx->mmap_changing);
638 VM_BUG_ON(atomic_read(&ctx->mmap_changing) < 0);
639 userfaultfd_ctx_put(ctx);
640 }
641
userfaultfd_event_complete(struct userfaultfd_ctx * ctx,struct userfaultfd_wait_queue * ewq)642 static void userfaultfd_event_complete(struct userfaultfd_ctx *ctx,
643 struct userfaultfd_wait_queue *ewq)
644 {
645 ewq->msg.event = 0;
646 wake_up_locked(&ctx->event_wqh);
647 __remove_wait_queue(&ctx->event_wqh, &ewq->wq);
648 }
649
dup_userfaultfd(struct vm_area_struct * vma,struct list_head * fcs)650 int dup_userfaultfd(struct vm_area_struct *vma, struct list_head *fcs)
651 {
652 struct userfaultfd_ctx *ctx = NULL, *octx;
653 struct userfaultfd_fork_ctx *fctx;
654
655 octx = vma->vm_userfaultfd_ctx.ctx;
656 if (!octx || !(octx->features & UFFD_FEATURE_EVENT_FORK)) {
657 vma_start_write(vma);
658 vma->vm_userfaultfd_ctx = NULL_VM_UFFD_CTX;
659 userfaultfd_set_vm_flags(vma, vma->vm_flags & ~__VM_UFFD_FLAGS);
660 return 0;
661 }
662
663 list_for_each_entry(fctx, fcs, list)
664 if (fctx->orig == octx) {
665 ctx = fctx->new;
666 break;
667 }
668
669 if (!ctx) {
670 fctx = kmalloc(sizeof(*fctx), GFP_KERNEL);
671 if (!fctx)
672 return -ENOMEM;
673
674 ctx = kmem_cache_alloc(userfaultfd_ctx_cachep, GFP_KERNEL);
675 if (!ctx) {
676 kfree(fctx);
677 return -ENOMEM;
678 }
679
680 refcount_set(&ctx->refcount, 1);
681 ctx->flags = octx->flags;
682 ctx->features = octx->features;
683 ctx->released = false;
684 init_rwsem(&ctx->map_changing_lock);
685 atomic_set(&ctx->mmap_changing, 0);
686 ctx->mm = vma->vm_mm;
687 mmgrab(ctx->mm);
688
689 userfaultfd_ctx_get(octx);
690 down_write(&octx->map_changing_lock);
691 atomic_inc(&octx->mmap_changing);
692 up_write(&octx->map_changing_lock);
693 fctx->orig = octx;
694 fctx->new = ctx;
695 list_add_tail(&fctx->list, fcs);
696 }
697
698 vma->vm_userfaultfd_ctx.ctx = ctx;
699 return 0;
700 }
701
dup_fctx(struct userfaultfd_fork_ctx * fctx)702 static void dup_fctx(struct userfaultfd_fork_ctx *fctx)
703 {
704 struct userfaultfd_ctx *ctx = fctx->orig;
705 struct userfaultfd_wait_queue ewq;
706
707 msg_init(&ewq.msg);
708
709 ewq.msg.event = UFFD_EVENT_FORK;
710 ewq.msg.arg.reserved.reserved1 = (unsigned long)fctx->new;
711
712 userfaultfd_event_wait_completion(ctx, &ewq);
713 }
714
dup_userfaultfd_complete(struct list_head * fcs)715 void dup_userfaultfd_complete(struct list_head *fcs)
716 {
717 struct userfaultfd_fork_ctx *fctx, *n;
718
719 list_for_each_entry_safe(fctx, n, fcs, list) {
720 dup_fctx(fctx);
721 list_del(&fctx->list);
722 kfree(fctx);
723 }
724 }
725
mremap_userfaultfd_prep(struct vm_area_struct * vma,struct vm_userfaultfd_ctx * vm_ctx)726 void mremap_userfaultfd_prep(struct vm_area_struct *vma,
727 struct vm_userfaultfd_ctx *vm_ctx)
728 {
729 struct userfaultfd_ctx *ctx;
730
731 ctx = vma->vm_userfaultfd_ctx.ctx;
732
733 if (!ctx)
734 return;
735
736 if (ctx->features & UFFD_FEATURE_EVENT_REMAP) {
737 vm_ctx->ctx = ctx;
738 userfaultfd_ctx_get(ctx);
739 down_write(&ctx->map_changing_lock);
740 atomic_inc(&ctx->mmap_changing);
741 up_write(&ctx->map_changing_lock);
742 } else {
743 /* Drop uffd context if remap feature not enabled */
744 vma_start_write(vma);
745 vma->vm_userfaultfd_ctx = NULL_VM_UFFD_CTX;
746 userfaultfd_set_vm_flags(vma, vma->vm_flags & ~__VM_UFFD_FLAGS);
747 }
748 }
749
mremap_userfaultfd_complete(struct vm_userfaultfd_ctx * vm_ctx,unsigned long from,unsigned long to,unsigned long len)750 void mremap_userfaultfd_complete(struct vm_userfaultfd_ctx *vm_ctx,
751 unsigned long from, unsigned long to,
752 unsigned long len)
753 {
754 struct userfaultfd_ctx *ctx = vm_ctx->ctx;
755 struct userfaultfd_wait_queue ewq;
756
757 if (!ctx)
758 return;
759
760 if (to & ~PAGE_MASK) {
761 userfaultfd_ctx_put(ctx);
762 return;
763 }
764
765 msg_init(&ewq.msg);
766
767 ewq.msg.event = UFFD_EVENT_REMAP;
768 ewq.msg.arg.remap.from = from;
769 ewq.msg.arg.remap.to = to;
770 ewq.msg.arg.remap.len = len;
771
772 userfaultfd_event_wait_completion(ctx, &ewq);
773 }
774
userfaultfd_remove(struct vm_area_struct * vma,unsigned long start,unsigned long end)775 bool userfaultfd_remove(struct vm_area_struct *vma,
776 unsigned long start, unsigned long end)
777 {
778 struct mm_struct *mm = vma->vm_mm;
779 struct userfaultfd_ctx *ctx;
780 struct userfaultfd_wait_queue ewq;
781
782 ctx = vma->vm_userfaultfd_ctx.ctx;
783 if (!ctx || !(ctx->features & UFFD_FEATURE_EVENT_REMOVE))
784 return true;
785
786 userfaultfd_ctx_get(ctx);
787 down_write(&ctx->map_changing_lock);
788 atomic_inc(&ctx->mmap_changing);
789 up_write(&ctx->map_changing_lock);
790 mmap_read_unlock(mm);
791
792 msg_init(&ewq.msg);
793
794 ewq.msg.event = UFFD_EVENT_REMOVE;
795 ewq.msg.arg.remove.start = start;
796 ewq.msg.arg.remove.end = end;
797
798 userfaultfd_event_wait_completion(ctx, &ewq);
799
800 return false;
801 }
802
has_unmap_ctx(struct userfaultfd_ctx * ctx,struct list_head * unmaps,unsigned long start,unsigned long end)803 static bool has_unmap_ctx(struct userfaultfd_ctx *ctx, struct list_head *unmaps,
804 unsigned long start, unsigned long end)
805 {
806 struct userfaultfd_unmap_ctx *unmap_ctx;
807
808 list_for_each_entry(unmap_ctx, unmaps, list)
809 if (unmap_ctx->ctx == ctx && unmap_ctx->start == start &&
810 unmap_ctx->end == end)
811 return true;
812
813 return false;
814 }
815
userfaultfd_unmap_prep(struct vm_area_struct * vma,unsigned long start,unsigned long end,struct list_head * unmaps)816 int userfaultfd_unmap_prep(struct vm_area_struct *vma, unsigned long start,
817 unsigned long end, struct list_head *unmaps)
818 {
819 struct userfaultfd_unmap_ctx *unmap_ctx;
820 struct userfaultfd_ctx *ctx = vma->vm_userfaultfd_ctx.ctx;
821
822 if (!ctx || !(ctx->features & UFFD_FEATURE_EVENT_UNMAP) ||
823 has_unmap_ctx(ctx, unmaps, start, end))
824 return 0;
825
826 unmap_ctx = kzalloc(sizeof(*unmap_ctx), GFP_KERNEL);
827 if (!unmap_ctx)
828 return -ENOMEM;
829
830 userfaultfd_ctx_get(ctx);
831 down_write(&ctx->map_changing_lock);
832 atomic_inc(&ctx->mmap_changing);
833 up_write(&ctx->map_changing_lock);
834 unmap_ctx->ctx = ctx;
835 unmap_ctx->start = start;
836 unmap_ctx->end = end;
837 list_add_tail(&unmap_ctx->list, unmaps);
838
839 return 0;
840 }
841
userfaultfd_unmap_complete(struct mm_struct * mm,struct list_head * uf)842 void userfaultfd_unmap_complete(struct mm_struct *mm, struct list_head *uf)
843 {
844 struct userfaultfd_unmap_ctx *ctx, *n;
845 struct userfaultfd_wait_queue ewq;
846
847 list_for_each_entry_safe(ctx, n, uf, list) {
848 msg_init(&ewq.msg);
849
850 ewq.msg.event = UFFD_EVENT_UNMAP;
851 ewq.msg.arg.remove.start = ctx->start;
852 ewq.msg.arg.remove.end = ctx->end;
853
854 userfaultfd_event_wait_completion(ctx->ctx, &ewq);
855
856 list_del(&ctx->list);
857 kfree(ctx);
858 }
859 }
860
userfaultfd_release(struct inode * inode,struct file * file)861 static int userfaultfd_release(struct inode *inode, struct file *file)
862 {
863 struct userfaultfd_ctx *ctx = file->private_data;
864 struct mm_struct *mm = ctx->mm;
865 struct vm_area_struct *vma, *prev;
866 /* len == 0 means wake all */
867 struct userfaultfd_wake_range range = { .len = 0, };
868 unsigned long new_flags;
869 VMA_ITERATOR(vmi, mm, 0);
870
871 WRITE_ONCE(ctx->released, true);
872
873 if (!mmget_not_zero(mm))
874 goto wakeup;
875
876 /*
877 * Flush page faults out of all CPUs. NOTE: all page faults
878 * must be retried without returning VM_FAULT_SIGBUS if
879 * userfaultfd_ctx_get() succeeds but vma->vma_userfault_ctx
880 * changes while handle_userfault released the mmap_lock. So
881 * it's critical that released is set to true (above), before
882 * taking the mmap_lock for writing.
883 */
884 mmap_write_lock(mm);
885 prev = NULL;
886 for_each_vma(vmi, vma) {
887 cond_resched();
888 BUG_ON(!!vma->vm_userfaultfd_ctx.ctx ^
889 !!(vma->vm_flags & __VM_UFFD_FLAGS));
890 if (vma->vm_userfaultfd_ctx.ctx != ctx) {
891 prev = vma;
892 continue;
893 }
894 /* Reset ptes for the whole vma range if wr-protected */
895 if (userfaultfd_wp(vma))
896 uffd_wp_range(vma, vma->vm_start,
897 vma->vm_end - vma->vm_start, false);
898 new_flags = vma->vm_flags & ~__VM_UFFD_FLAGS;
899 prev = vma_merge(&vmi, mm, prev, vma->vm_start, vma->vm_end,
900 new_flags, vma->anon_vma,
901 vma->vm_file, vma->vm_pgoff,
902 vma_policy(vma),
903 NULL_VM_UFFD_CTX, anon_vma_name(vma));
904 if (prev) {
905 vma = prev;
906 } else {
907 prev = vma;
908 }
909
910 vma_start_write(vma);
911 userfaultfd_set_vm_flags(vma, new_flags);
912 vma->vm_userfaultfd_ctx = NULL_VM_UFFD_CTX;
913 }
914 mmap_write_unlock(mm);
915 mmput(mm);
916 wakeup:
917 /*
918 * After no new page faults can wait on this fault_*wqh, flush
919 * the last page faults that may have been already waiting on
920 * the fault_*wqh.
921 */
922 spin_lock_irq(&ctx->fault_pending_wqh.lock);
923 __wake_up_locked_key(&ctx->fault_pending_wqh, TASK_NORMAL, &range);
924 __wake_up(&ctx->fault_wqh, TASK_NORMAL, 1, &range);
925 spin_unlock_irq(&ctx->fault_pending_wqh.lock);
926
927 /* Flush pending events that may still wait on event_wqh */
928 wake_up_all(&ctx->event_wqh);
929
930 wake_up_poll(&ctx->fd_wqh, EPOLLHUP);
931 userfaultfd_ctx_put(ctx);
932 return 0;
933 }
934
935 /* fault_pending_wqh.lock must be hold by the caller */
find_userfault_in(wait_queue_head_t * wqh)936 static inline struct userfaultfd_wait_queue *find_userfault_in(
937 wait_queue_head_t *wqh)
938 {
939 wait_queue_entry_t *wq;
940 struct userfaultfd_wait_queue *uwq;
941
942 lockdep_assert_held(&wqh->lock);
943
944 uwq = NULL;
945 if (!waitqueue_active(wqh))
946 goto out;
947 /* walk in reverse to provide FIFO behavior to read userfaults */
948 wq = list_last_entry(&wqh->head, typeof(*wq), entry);
949 uwq = container_of(wq, struct userfaultfd_wait_queue, wq);
950 out:
951 return uwq;
952 }
953
find_userfault(struct userfaultfd_ctx * ctx)954 static inline struct userfaultfd_wait_queue *find_userfault(
955 struct userfaultfd_ctx *ctx)
956 {
957 return find_userfault_in(&ctx->fault_pending_wqh);
958 }
959
find_userfault_evt(struct userfaultfd_ctx * ctx)960 static inline struct userfaultfd_wait_queue *find_userfault_evt(
961 struct userfaultfd_ctx *ctx)
962 {
963 return find_userfault_in(&ctx->event_wqh);
964 }
965
userfaultfd_poll(struct file * file,poll_table * wait)966 static __poll_t userfaultfd_poll(struct file *file, poll_table *wait)
967 {
968 struct userfaultfd_ctx *ctx = file->private_data;
969 __poll_t ret;
970
971 poll_wait(file, &ctx->fd_wqh, wait);
972
973 if (!userfaultfd_is_initialized(ctx))
974 return EPOLLERR;
975
976 /*
977 * poll() never guarantees that read won't block.
978 * userfaults can be waken before they're read().
979 */
980 if (unlikely(!(file->f_flags & O_NONBLOCK)))
981 return EPOLLERR;
982 /*
983 * lockless access to see if there are pending faults
984 * __pollwait last action is the add_wait_queue but
985 * the spin_unlock would allow the waitqueue_active to
986 * pass above the actual list_add inside
987 * add_wait_queue critical section. So use a full
988 * memory barrier to serialize the list_add write of
989 * add_wait_queue() with the waitqueue_active read
990 * below.
991 */
992 ret = 0;
993 smp_mb();
994 if (waitqueue_active(&ctx->fault_pending_wqh))
995 ret = EPOLLIN;
996 else if (waitqueue_active(&ctx->event_wqh))
997 ret = EPOLLIN;
998
999 return ret;
1000 }
1001
1002 static const struct file_operations userfaultfd_fops;
1003
resolve_userfault_fork(struct userfaultfd_ctx * new,struct inode * inode,struct uffd_msg * msg)1004 static int resolve_userfault_fork(struct userfaultfd_ctx *new,
1005 struct inode *inode,
1006 struct uffd_msg *msg)
1007 {
1008 int fd;
1009
1010 fd = anon_inode_getfd_secure("[userfaultfd]", &userfaultfd_fops, new,
1011 O_RDONLY | (new->flags & UFFD_SHARED_FCNTL_FLAGS), inode);
1012 if (fd < 0)
1013 return fd;
1014
1015 msg->arg.reserved.reserved1 = 0;
1016 msg->arg.fork.ufd = fd;
1017 return 0;
1018 }
1019
userfaultfd_ctx_read(struct userfaultfd_ctx * ctx,int no_wait,struct uffd_msg * msg,struct inode * inode)1020 static ssize_t userfaultfd_ctx_read(struct userfaultfd_ctx *ctx, int no_wait,
1021 struct uffd_msg *msg, struct inode *inode)
1022 {
1023 ssize_t ret;
1024 DECLARE_WAITQUEUE(wait, current);
1025 struct userfaultfd_wait_queue *uwq;
1026 /*
1027 * Handling fork event requires sleeping operations, so
1028 * we drop the event_wqh lock, then do these ops, then
1029 * lock it back and wake up the waiter. While the lock is
1030 * dropped the ewq may go away so we keep track of it
1031 * carefully.
1032 */
1033 LIST_HEAD(fork_event);
1034 struct userfaultfd_ctx *fork_nctx = NULL;
1035
1036 /* always take the fd_wqh lock before the fault_pending_wqh lock */
1037 spin_lock_irq(&ctx->fd_wqh.lock);
1038 __add_wait_queue(&ctx->fd_wqh, &wait);
1039 for (;;) {
1040 set_current_state(TASK_INTERRUPTIBLE);
1041 spin_lock(&ctx->fault_pending_wqh.lock);
1042 uwq = find_userfault(ctx);
1043 if (uwq) {
1044 /*
1045 * Use a seqcount to repeat the lockless check
1046 * in wake_userfault() to avoid missing
1047 * wakeups because during the refile both
1048 * waitqueue could become empty if this is the
1049 * only userfault.
1050 */
1051 write_seqcount_begin(&ctx->refile_seq);
1052
1053 /*
1054 * The fault_pending_wqh.lock prevents the uwq
1055 * to disappear from under us.
1056 *
1057 * Refile this userfault from
1058 * fault_pending_wqh to fault_wqh, it's not
1059 * pending anymore after we read it.
1060 *
1061 * Use list_del() by hand (as
1062 * userfaultfd_wake_function also uses
1063 * list_del_init() by hand) to be sure nobody
1064 * changes __remove_wait_queue() to use
1065 * list_del_init() in turn breaking the
1066 * !list_empty_careful() check in
1067 * handle_userfault(). The uwq->wq.head list
1068 * must never be empty at any time during the
1069 * refile, or the waitqueue could disappear
1070 * from under us. The "wait_queue_head_t"
1071 * parameter of __remove_wait_queue() is unused
1072 * anyway.
1073 */
1074 list_del(&uwq->wq.entry);
1075 add_wait_queue(&ctx->fault_wqh, &uwq->wq);
1076
1077 write_seqcount_end(&ctx->refile_seq);
1078
1079 /* careful to always initialize msg if ret == 0 */
1080 *msg = uwq->msg;
1081 spin_unlock(&ctx->fault_pending_wqh.lock);
1082 ret = 0;
1083 break;
1084 }
1085 spin_unlock(&ctx->fault_pending_wqh.lock);
1086
1087 spin_lock(&ctx->event_wqh.lock);
1088 uwq = find_userfault_evt(ctx);
1089 if (uwq) {
1090 *msg = uwq->msg;
1091
1092 if (uwq->msg.event == UFFD_EVENT_FORK) {
1093 fork_nctx = (struct userfaultfd_ctx *)
1094 (unsigned long)
1095 uwq->msg.arg.reserved.reserved1;
1096 list_move(&uwq->wq.entry, &fork_event);
1097 /*
1098 * fork_nctx can be freed as soon as
1099 * we drop the lock, unless we take a
1100 * reference on it.
1101 */
1102 userfaultfd_ctx_get(fork_nctx);
1103 spin_unlock(&ctx->event_wqh.lock);
1104 ret = 0;
1105 break;
1106 }
1107
1108 userfaultfd_event_complete(ctx, uwq);
1109 spin_unlock(&ctx->event_wqh.lock);
1110 ret = 0;
1111 break;
1112 }
1113 spin_unlock(&ctx->event_wqh.lock);
1114
1115 if (signal_pending(current)) {
1116 ret = -ERESTARTSYS;
1117 break;
1118 }
1119 if (no_wait) {
1120 ret = -EAGAIN;
1121 break;
1122 }
1123 spin_unlock_irq(&ctx->fd_wqh.lock);
1124 schedule();
1125 spin_lock_irq(&ctx->fd_wqh.lock);
1126 }
1127 __remove_wait_queue(&ctx->fd_wqh, &wait);
1128 __set_current_state(TASK_RUNNING);
1129 spin_unlock_irq(&ctx->fd_wqh.lock);
1130
1131 if (!ret && msg->event == UFFD_EVENT_FORK) {
1132 ret = resolve_userfault_fork(fork_nctx, inode, msg);
1133 spin_lock_irq(&ctx->event_wqh.lock);
1134 if (!list_empty(&fork_event)) {
1135 /*
1136 * The fork thread didn't abort, so we can
1137 * drop the temporary refcount.
1138 */
1139 userfaultfd_ctx_put(fork_nctx);
1140
1141 uwq = list_first_entry(&fork_event,
1142 typeof(*uwq),
1143 wq.entry);
1144 /*
1145 * If fork_event list wasn't empty and in turn
1146 * the event wasn't already released by fork
1147 * (the event is allocated on fork kernel
1148 * stack), put the event back to its place in
1149 * the event_wq. fork_event head will be freed
1150 * as soon as we return so the event cannot
1151 * stay queued there no matter the current
1152 * "ret" value.
1153 */
1154 list_del(&uwq->wq.entry);
1155 __add_wait_queue(&ctx->event_wqh, &uwq->wq);
1156
1157 /*
1158 * Leave the event in the waitqueue and report
1159 * error to userland if we failed to resolve
1160 * the userfault fork.
1161 */
1162 if (likely(!ret))
1163 userfaultfd_event_complete(ctx, uwq);
1164 } else {
1165 /*
1166 * Here the fork thread aborted and the
1167 * refcount from the fork thread on fork_nctx
1168 * has already been released. We still hold
1169 * the reference we took before releasing the
1170 * lock above. If resolve_userfault_fork
1171 * failed we've to drop it because the
1172 * fork_nctx has to be freed in such case. If
1173 * it succeeded we'll hold it because the new
1174 * uffd references it.
1175 */
1176 if (ret)
1177 userfaultfd_ctx_put(fork_nctx);
1178 }
1179 spin_unlock_irq(&ctx->event_wqh.lock);
1180 }
1181
1182 return ret;
1183 }
1184
userfaultfd_read(struct file * file,char __user * buf,size_t count,loff_t * ppos)1185 static ssize_t userfaultfd_read(struct file *file, char __user *buf,
1186 size_t count, loff_t *ppos)
1187 {
1188 struct userfaultfd_ctx *ctx = file->private_data;
1189 ssize_t _ret, ret = 0;
1190 struct uffd_msg msg;
1191 int no_wait = file->f_flags & O_NONBLOCK;
1192 struct inode *inode = file_inode(file);
1193
1194 if (!userfaultfd_is_initialized(ctx))
1195 return -EINVAL;
1196
1197 for (;;) {
1198 if (count < sizeof(msg))
1199 return ret ? ret : -EINVAL;
1200 _ret = userfaultfd_ctx_read(ctx, no_wait, &msg, inode);
1201 if (_ret < 0)
1202 return ret ? ret : _ret;
1203 if (copy_to_user((__u64 __user *) buf, &msg, sizeof(msg)))
1204 return ret ? ret : -EFAULT;
1205 ret += sizeof(msg);
1206 buf += sizeof(msg);
1207 count -= sizeof(msg);
1208 /*
1209 * Allow to read more than one fault at time but only
1210 * block if waiting for the very first one.
1211 */
1212 no_wait = O_NONBLOCK;
1213 }
1214 }
1215
__wake_userfault(struct userfaultfd_ctx * ctx,struct userfaultfd_wake_range * range)1216 static void __wake_userfault(struct userfaultfd_ctx *ctx,
1217 struct userfaultfd_wake_range *range)
1218 {
1219 spin_lock_irq(&ctx->fault_pending_wqh.lock);
1220 /* wake all in the range and autoremove */
1221 if (waitqueue_active(&ctx->fault_pending_wqh))
1222 __wake_up_locked_key(&ctx->fault_pending_wqh, TASK_NORMAL,
1223 range);
1224 if (waitqueue_active(&ctx->fault_wqh))
1225 __wake_up(&ctx->fault_wqh, TASK_NORMAL, 1, range);
1226 spin_unlock_irq(&ctx->fault_pending_wqh.lock);
1227 }
1228
wake_userfault(struct userfaultfd_ctx * ctx,struct userfaultfd_wake_range * range)1229 static __always_inline void wake_userfault(struct userfaultfd_ctx *ctx,
1230 struct userfaultfd_wake_range *range)
1231 {
1232 unsigned seq;
1233 bool need_wakeup;
1234
1235 /*
1236 * To be sure waitqueue_active() is not reordered by the CPU
1237 * before the pagetable update, use an explicit SMP memory
1238 * barrier here. PT lock release or mmap_read_unlock(mm) still
1239 * have release semantics that can allow the
1240 * waitqueue_active() to be reordered before the pte update.
1241 */
1242 smp_mb();
1243
1244 /*
1245 * Use waitqueue_active because it's very frequent to
1246 * change the address space atomically even if there are no
1247 * userfaults yet. So we take the spinlock only when we're
1248 * sure we've userfaults to wake.
1249 */
1250 do {
1251 seq = read_seqcount_begin(&ctx->refile_seq);
1252 need_wakeup = waitqueue_active(&ctx->fault_pending_wqh) ||
1253 waitqueue_active(&ctx->fault_wqh);
1254 cond_resched();
1255 } while (read_seqcount_retry(&ctx->refile_seq, seq));
1256 if (need_wakeup)
1257 __wake_userfault(ctx, range);
1258 }
1259
validate_unaligned_range(struct mm_struct * mm,__u64 start,__u64 len)1260 static __always_inline int validate_unaligned_range(
1261 struct mm_struct *mm, __u64 start, __u64 len)
1262 {
1263 __u64 task_size = mm->task_size;
1264
1265 if (len & ~PAGE_MASK)
1266 return -EINVAL;
1267 if (!len)
1268 return -EINVAL;
1269 if (start < mmap_min_addr)
1270 return -EINVAL;
1271 if (start >= task_size)
1272 return -EINVAL;
1273 if (len > task_size - start)
1274 return -EINVAL;
1275 if (start + len <= start)
1276 return -EINVAL;
1277 return 0;
1278 }
1279
validate_range(struct mm_struct * mm,__u64 start,__u64 len)1280 static __always_inline int validate_range(struct mm_struct *mm,
1281 __u64 start, __u64 len)
1282 {
1283 if (start & ~PAGE_MASK)
1284 return -EINVAL;
1285
1286 return validate_unaligned_range(mm, start, len);
1287 }
1288
userfaultfd_register(struct userfaultfd_ctx * ctx,unsigned long arg)1289 static int userfaultfd_register(struct userfaultfd_ctx *ctx,
1290 unsigned long arg)
1291 {
1292 struct mm_struct *mm = ctx->mm;
1293 struct vm_area_struct *vma, *prev, *cur;
1294 int ret;
1295 struct uffdio_register uffdio_register;
1296 struct uffdio_register __user *user_uffdio_register;
1297 unsigned long vm_flags, new_flags;
1298 bool found;
1299 bool basic_ioctls;
1300 unsigned long start, end, vma_end;
1301 struct vma_iterator vmi;
1302 pgoff_t pgoff;
1303
1304 user_uffdio_register = (struct uffdio_register __user *) arg;
1305
1306 ret = -EFAULT;
1307 if (copy_from_user(&uffdio_register, user_uffdio_register,
1308 sizeof(uffdio_register)-sizeof(__u64)))
1309 goto out;
1310
1311 ret = -EINVAL;
1312 if (!uffdio_register.mode)
1313 goto out;
1314 if (uffdio_register.mode & ~UFFD_API_REGISTER_MODES)
1315 goto out;
1316 vm_flags = 0;
1317 if (uffdio_register.mode & UFFDIO_REGISTER_MODE_MISSING)
1318 vm_flags |= VM_UFFD_MISSING;
1319 if (uffdio_register.mode & UFFDIO_REGISTER_MODE_WP) {
1320 #ifndef CONFIG_HAVE_ARCH_USERFAULTFD_WP
1321 goto out;
1322 #endif
1323 vm_flags |= VM_UFFD_WP;
1324 }
1325 if (uffdio_register.mode & UFFDIO_REGISTER_MODE_MINOR) {
1326 #ifndef CONFIG_HAVE_ARCH_USERFAULTFD_MINOR
1327 goto out;
1328 #endif
1329 vm_flags |= VM_UFFD_MINOR;
1330 }
1331
1332 ret = validate_range(mm, uffdio_register.range.start,
1333 uffdio_register.range.len);
1334 if (ret)
1335 goto out;
1336
1337 start = uffdio_register.range.start;
1338 end = start + uffdio_register.range.len;
1339
1340 ret = -ENOMEM;
1341 if (!mmget_not_zero(mm))
1342 goto out;
1343
1344 ret = -EINVAL;
1345 mmap_write_lock(mm);
1346 vma_iter_init(&vmi, mm, start);
1347 vma = vma_find(&vmi, end);
1348 if (!vma)
1349 goto out_unlock;
1350
1351 /*
1352 * If the first vma contains huge pages, make sure start address
1353 * is aligned to huge page size.
1354 */
1355 if (is_vm_hugetlb_page(vma)) {
1356 unsigned long vma_hpagesize = vma_kernel_pagesize(vma);
1357
1358 if (start & (vma_hpagesize - 1))
1359 goto out_unlock;
1360 }
1361
1362 /*
1363 * Search for not compatible vmas.
1364 */
1365 found = false;
1366 basic_ioctls = false;
1367 cur = vma;
1368 do {
1369 cond_resched();
1370
1371 BUG_ON(!!cur->vm_userfaultfd_ctx.ctx ^
1372 !!(cur->vm_flags & __VM_UFFD_FLAGS));
1373
1374 /* check not compatible vmas */
1375 ret = -EINVAL;
1376 if (!vma_can_userfault(cur, vm_flags))
1377 goto out_unlock;
1378
1379 /*
1380 * UFFDIO_COPY will fill file holes even without
1381 * PROT_WRITE. This check enforces that if this is a
1382 * MAP_SHARED, the process has write permission to the backing
1383 * file. If VM_MAYWRITE is set it also enforces that on a
1384 * MAP_SHARED vma: there is no F_WRITE_SEAL and no further
1385 * F_WRITE_SEAL can be taken until the vma is destroyed.
1386 */
1387 ret = -EPERM;
1388 if (unlikely(!(cur->vm_flags & VM_MAYWRITE)))
1389 goto out_unlock;
1390
1391 /*
1392 * If this vma contains ending address, and huge pages
1393 * check alignment.
1394 */
1395 if (is_vm_hugetlb_page(cur) && end <= cur->vm_end &&
1396 end > cur->vm_start) {
1397 unsigned long vma_hpagesize = vma_kernel_pagesize(cur);
1398
1399 ret = -EINVAL;
1400
1401 if (end & (vma_hpagesize - 1))
1402 goto out_unlock;
1403 }
1404 if ((vm_flags & VM_UFFD_WP) && !(cur->vm_flags & VM_MAYWRITE))
1405 goto out_unlock;
1406
1407 /*
1408 * Check that this vma isn't already owned by a
1409 * different userfaultfd. We can't allow more than one
1410 * userfaultfd to own a single vma simultaneously or we
1411 * wouldn't know which one to deliver the userfaults to.
1412 */
1413 ret = -EBUSY;
1414 if (cur->vm_userfaultfd_ctx.ctx &&
1415 cur->vm_userfaultfd_ctx.ctx != ctx)
1416 goto out_unlock;
1417
1418 /*
1419 * Note vmas containing huge pages
1420 */
1421 if (is_vm_hugetlb_page(cur))
1422 basic_ioctls = true;
1423
1424 found = true;
1425 } for_each_vma_range(vmi, cur, end);
1426 BUG_ON(!found);
1427
1428 vma_iter_set(&vmi, start);
1429 prev = vma_prev(&vmi);
1430 if (vma->vm_start < start)
1431 prev = vma;
1432
1433 ret = 0;
1434 for_each_vma_range(vmi, vma, end) {
1435 cond_resched();
1436
1437 BUG_ON(!vma_can_userfault(vma, vm_flags));
1438 BUG_ON(vma->vm_userfaultfd_ctx.ctx &&
1439 vma->vm_userfaultfd_ctx.ctx != ctx);
1440 WARN_ON(!(vma->vm_flags & VM_MAYWRITE));
1441
1442 /*
1443 * Nothing to do: this vma is already registered into this
1444 * userfaultfd and with the right tracking mode too.
1445 */
1446 if (vma->vm_userfaultfd_ctx.ctx == ctx &&
1447 (vma->vm_flags & vm_flags) == vm_flags)
1448 goto skip;
1449
1450 if (vma->vm_start > start)
1451 start = vma->vm_start;
1452 vma_end = min(end, vma->vm_end);
1453
1454 new_flags = (vma->vm_flags & ~__VM_UFFD_FLAGS) | vm_flags;
1455 pgoff = vma->vm_pgoff + ((start - vma->vm_start) >> PAGE_SHIFT);
1456 prev = vma_merge(&vmi, mm, prev, start, vma_end, new_flags,
1457 vma->anon_vma, vma->vm_file, pgoff,
1458 vma_policy(vma),
1459 ((struct vm_userfaultfd_ctx){ ctx }),
1460 anon_vma_name(vma));
1461 if (prev) {
1462 /* vma_merge() invalidated the mas */
1463 vma = prev;
1464 goto next;
1465 }
1466 if (vma->vm_start < start) {
1467 ret = split_vma(&vmi, vma, start, 1);
1468 if (ret)
1469 break;
1470 }
1471 if (vma->vm_end > end) {
1472 ret = split_vma(&vmi, vma, end, 0);
1473 if (ret)
1474 break;
1475 }
1476 next:
1477 /*
1478 * In the vma_merge() successful mprotect-like case 8:
1479 * the next vma was merged into the current one and
1480 * the current one has not been updated yet.
1481 */
1482 vma_start_write(vma);
1483 userfaultfd_set_vm_flags(vma, new_flags);
1484 vma->vm_userfaultfd_ctx.ctx = ctx;
1485
1486 if (is_vm_hugetlb_page(vma) && uffd_disable_huge_pmd_share(vma))
1487 hugetlb_unshare_all_pmds(vma);
1488
1489 skip:
1490 prev = vma;
1491 start = vma->vm_end;
1492 }
1493
1494 out_unlock:
1495 mmap_write_unlock(mm);
1496 mmput(mm);
1497 if (!ret) {
1498 __u64 ioctls_out;
1499
1500 ioctls_out = basic_ioctls ? UFFD_API_RANGE_IOCTLS_BASIC :
1501 UFFD_API_RANGE_IOCTLS;
1502
1503 /*
1504 * Declare the WP ioctl only if the WP mode is
1505 * specified and all checks passed with the range
1506 */
1507 if (!(uffdio_register.mode & UFFDIO_REGISTER_MODE_WP))
1508 ioctls_out &= ~((__u64)1 << _UFFDIO_WRITEPROTECT);
1509
1510 /* CONTINUE ioctl is only supported for MINOR ranges. */
1511 if (!(uffdio_register.mode & UFFDIO_REGISTER_MODE_MINOR))
1512 ioctls_out &= ~((__u64)1 << _UFFDIO_CONTINUE);
1513
1514 /*
1515 * Now that we scanned all vmas we can already tell
1516 * userland which ioctls methods are guaranteed to
1517 * succeed on this range.
1518 */
1519 if (put_user(ioctls_out, &user_uffdio_register->ioctls))
1520 ret = -EFAULT;
1521 }
1522 out:
1523 return ret;
1524 }
1525
userfaultfd_unregister(struct userfaultfd_ctx * ctx,unsigned long arg)1526 static int userfaultfd_unregister(struct userfaultfd_ctx *ctx,
1527 unsigned long arg)
1528 {
1529 struct mm_struct *mm = ctx->mm;
1530 struct vm_area_struct *vma, *prev, *cur;
1531 int ret;
1532 struct uffdio_range uffdio_unregister;
1533 unsigned long new_flags;
1534 bool found;
1535 unsigned long start, end, vma_end;
1536 const void __user *buf = (void __user *)arg;
1537 struct vma_iterator vmi;
1538 pgoff_t pgoff;
1539
1540 ret = -EFAULT;
1541 if (copy_from_user(&uffdio_unregister, buf, sizeof(uffdio_unregister)))
1542 goto out;
1543
1544 ret = validate_range(mm, uffdio_unregister.start,
1545 uffdio_unregister.len);
1546 if (ret)
1547 goto out;
1548
1549 start = uffdio_unregister.start;
1550 end = start + uffdio_unregister.len;
1551
1552 ret = -ENOMEM;
1553 if (!mmget_not_zero(mm))
1554 goto out;
1555
1556 mmap_write_lock(mm);
1557 ret = -EINVAL;
1558 vma_iter_init(&vmi, mm, start);
1559 vma = vma_find(&vmi, end);
1560 if (!vma)
1561 goto out_unlock;
1562
1563 /*
1564 * If the first vma contains huge pages, make sure start address
1565 * is aligned to huge page size.
1566 */
1567 if (is_vm_hugetlb_page(vma)) {
1568 unsigned long vma_hpagesize = vma_kernel_pagesize(vma);
1569
1570 if (start & (vma_hpagesize - 1))
1571 goto out_unlock;
1572 }
1573
1574 /*
1575 * Search for not compatible vmas.
1576 */
1577 found = false;
1578 cur = vma;
1579 do {
1580 cond_resched();
1581
1582 BUG_ON(!!cur->vm_userfaultfd_ctx.ctx ^
1583 !!(cur->vm_flags & __VM_UFFD_FLAGS));
1584
1585 /*
1586 * Check not compatible vmas, not strictly required
1587 * here as not compatible vmas cannot have an
1588 * userfaultfd_ctx registered on them, but this
1589 * provides for more strict behavior to notice
1590 * unregistration errors.
1591 */
1592 if (!vma_can_userfault(cur, cur->vm_flags))
1593 goto out_unlock;
1594
1595 found = true;
1596 } for_each_vma_range(vmi, cur, end);
1597 BUG_ON(!found);
1598
1599 vma_iter_set(&vmi, start);
1600 prev = vma_prev(&vmi);
1601 if (vma->vm_start < start)
1602 prev = vma;
1603
1604 ret = 0;
1605 for_each_vma_range(vmi, vma, end) {
1606 cond_resched();
1607
1608 BUG_ON(!vma_can_userfault(vma, vma->vm_flags));
1609
1610 /*
1611 * Nothing to do: this vma is already registered into this
1612 * userfaultfd and with the right tracking mode too.
1613 */
1614 if (!vma->vm_userfaultfd_ctx.ctx)
1615 goto skip;
1616
1617 WARN_ON(!(vma->vm_flags & VM_MAYWRITE));
1618
1619 if (vma->vm_start > start)
1620 start = vma->vm_start;
1621 vma_end = min(end, vma->vm_end);
1622
1623 if (userfaultfd_missing(vma)) {
1624 /*
1625 * Wake any concurrent pending userfault while
1626 * we unregister, so they will not hang
1627 * permanently and it avoids userland to call
1628 * UFFDIO_WAKE explicitly.
1629 */
1630 struct userfaultfd_wake_range range;
1631 range.start = start;
1632 range.len = vma_end - start;
1633 wake_userfault(vma->vm_userfaultfd_ctx.ctx, &range);
1634 }
1635
1636 /* Reset ptes for the whole vma range if wr-protected */
1637 if (userfaultfd_wp(vma))
1638 uffd_wp_range(vma, start, vma_end - start, false);
1639
1640 new_flags = vma->vm_flags & ~__VM_UFFD_FLAGS;
1641 pgoff = vma->vm_pgoff + ((start - vma->vm_start) >> PAGE_SHIFT);
1642 prev = vma_merge(&vmi, mm, prev, start, vma_end, new_flags,
1643 vma->anon_vma, vma->vm_file, pgoff,
1644 vma_policy(vma),
1645 NULL_VM_UFFD_CTX, anon_vma_name(vma));
1646 if (prev) {
1647 vma = prev;
1648 goto next;
1649 }
1650 if (vma->vm_start < start) {
1651 ret = split_vma(&vmi, vma, start, 1);
1652 if (ret)
1653 break;
1654 }
1655 if (vma->vm_end > end) {
1656 ret = split_vma(&vmi, vma, end, 0);
1657 if (ret)
1658 break;
1659 }
1660 next:
1661 /*
1662 * In the vma_merge() successful mprotect-like case 8:
1663 * the next vma was merged into the current one and
1664 * the current one has not been updated yet.
1665 */
1666 vma_start_write(vma);
1667 userfaultfd_set_vm_flags(vma, new_flags);
1668 vma->vm_userfaultfd_ctx = NULL_VM_UFFD_CTX;
1669
1670 skip:
1671 prev = vma;
1672 start = vma->vm_end;
1673 }
1674
1675 out_unlock:
1676 mmap_write_unlock(mm);
1677 mmput(mm);
1678 out:
1679 return ret;
1680 }
1681
1682 /*
1683 * userfaultfd_wake may be used in combination with the
1684 * UFFDIO_*_MODE_DONTWAKE to wakeup userfaults in batches.
1685 */
userfaultfd_wake(struct userfaultfd_ctx * ctx,unsigned long arg)1686 static int userfaultfd_wake(struct userfaultfd_ctx *ctx,
1687 unsigned long arg)
1688 {
1689 int ret;
1690 struct uffdio_range uffdio_wake;
1691 struct userfaultfd_wake_range range;
1692 const void __user *buf = (void __user *)arg;
1693
1694 ret = -EFAULT;
1695 if (copy_from_user(&uffdio_wake, buf, sizeof(uffdio_wake)))
1696 goto out;
1697
1698 ret = validate_range(ctx->mm, uffdio_wake.start, uffdio_wake.len);
1699 if (ret)
1700 goto out;
1701
1702 range.start = uffdio_wake.start;
1703 range.len = uffdio_wake.len;
1704
1705 /*
1706 * len == 0 means wake all and we don't want to wake all here,
1707 * so check it again to be sure.
1708 */
1709 VM_BUG_ON(!range.len);
1710
1711 wake_userfault(ctx, &range);
1712 ret = 0;
1713
1714 out:
1715 return ret;
1716 }
1717
userfaultfd_copy(struct userfaultfd_ctx * ctx,unsigned long arg)1718 static int userfaultfd_copy(struct userfaultfd_ctx *ctx,
1719 unsigned long arg)
1720 {
1721 __s64 ret;
1722 struct uffdio_copy uffdio_copy;
1723 struct uffdio_copy __user *user_uffdio_copy;
1724 struct userfaultfd_wake_range range;
1725 uffd_flags_t flags = 0;
1726
1727 user_uffdio_copy = (struct uffdio_copy __user *) arg;
1728
1729 ret = -EAGAIN;
1730 if (atomic_read(&ctx->mmap_changing))
1731 goto out;
1732
1733 ret = -EFAULT;
1734 if (copy_from_user(&uffdio_copy, user_uffdio_copy,
1735 /* don't copy "copy" last field */
1736 sizeof(uffdio_copy)-sizeof(__s64)))
1737 goto out;
1738
1739 ret = validate_unaligned_range(ctx->mm, uffdio_copy.src,
1740 uffdio_copy.len);
1741 if (ret)
1742 goto out;
1743 ret = validate_range(ctx->mm, uffdio_copy.dst, uffdio_copy.len);
1744 if (ret)
1745 goto out;
1746
1747 ret = -EINVAL;
1748 if (uffdio_copy.mode & ~(UFFDIO_COPY_MODE_DONTWAKE|UFFDIO_COPY_MODE_WP))
1749 goto out;
1750 if (uffdio_copy.mode & UFFDIO_COPY_MODE_WP)
1751 flags |= MFILL_ATOMIC_WP;
1752 if (mmget_not_zero(ctx->mm)) {
1753 ret = mfill_atomic_copy(ctx, uffdio_copy.dst, uffdio_copy.src,
1754 uffdio_copy.len, flags);
1755 mmput(ctx->mm);
1756 } else {
1757 return -ESRCH;
1758 }
1759 if (unlikely(put_user(ret, &user_uffdio_copy->copy)))
1760 return -EFAULT;
1761 if (ret < 0)
1762 goto out;
1763 BUG_ON(!ret);
1764 /* len == 0 would wake all */
1765 range.len = ret;
1766 if (!(uffdio_copy.mode & UFFDIO_COPY_MODE_DONTWAKE)) {
1767 range.start = uffdio_copy.dst;
1768 wake_userfault(ctx, &range);
1769 }
1770 ret = range.len == uffdio_copy.len ? 0 : -EAGAIN;
1771 out:
1772 return ret;
1773 }
1774
userfaultfd_zeropage(struct userfaultfd_ctx * ctx,unsigned long arg)1775 static int userfaultfd_zeropage(struct userfaultfd_ctx *ctx,
1776 unsigned long arg)
1777 {
1778 __s64 ret;
1779 struct uffdio_zeropage uffdio_zeropage;
1780 struct uffdio_zeropage __user *user_uffdio_zeropage;
1781 struct userfaultfd_wake_range range;
1782
1783 user_uffdio_zeropage = (struct uffdio_zeropage __user *) arg;
1784
1785 ret = -EAGAIN;
1786 if (atomic_read(&ctx->mmap_changing))
1787 goto out;
1788
1789 ret = -EFAULT;
1790 if (copy_from_user(&uffdio_zeropage, user_uffdio_zeropage,
1791 /* don't copy "zeropage" last field */
1792 sizeof(uffdio_zeropage)-sizeof(__s64)))
1793 goto out;
1794
1795 ret = validate_range(ctx->mm, uffdio_zeropage.range.start,
1796 uffdio_zeropage.range.len);
1797 if (ret)
1798 goto out;
1799 ret = -EINVAL;
1800 if (uffdio_zeropage.mode & ~UFFDIO_ZEROPAGE_MODE_DONTWAKE)
1801 goto out;
1802
1803 if (mmget_not_zero(ctx->mm)) {
1804 ret = mfill_atomic_zeropage(ctx, uffdio_zeropage.range.start,
1805 uffdio_zeropage.range.len);
1806 mmput(ctx->mm);
1807 } else {
1808 return -ESRCH;
1809 }
1810 if (unlikely(put_user(ret, &user_uffdio_zeropage->zeropage)))
1811 return -EFAULT;
1812 if (ret < 0)
1813 goto out;
1814 /* len == 0 would wake all */
1815 BUG_ON(!ret);
1816 range.len = ret;
1817 if (!(uffdio_zeropage.mode & UFFDIO_ZEROPAGE_MODE_DONTWAKE)) {
1818 range.start = uffdio_zeropage.range.start;
1819 wake_userfault(ctx, &range);
1820 }
1821 ret = range.len == uffdio_zeropage.range.len ? 0 : -EAGAIN;
1822 out:
1823 return ret;
1824 }
1825
userfaultfd_writeprotect(struct userfaultfd_ctx * ctx,unsigned long arg)1826 static int userfaultfd_writeprotect(struct userfaultfd_ctx *ctx,
1827 unsigned long arg)
1828 {
1829 int ret;
1830 struct uffdio_writeprotect uffdio_wp;
1831 struct uffdio_writeprotect __user *user_uffdio_wp;
1832 struct userfaultfd_wake_range range;
1833 bool mode_wp, mode_dontwake;
1834
1835 if (atomic_read(&ctx->mmap_changing))
1836 return -EAGAIN;
1837
1838 user_uffdio_wp = (struct uffdio_writeprotect __user *) arg;
1839
1840 if (copy_from_user(&uffdio_wp, user_uffdio_wp,
1841 sizeof(struct uffdio_writeprotect)))
1842 return -EFAULT;
1843
1844 ret = validate_range(ctx->mm, uffdio_wp.range.start,
1845 uffdio_wp.range.len);
1846 if (ret)
1847 return ret;
1848
1849 if (uffdio_wp.mode & ~(UFFDIO_WRITEPROTECT_MODE_DONTWAKE |
1850 UFFDIO_WRITEPROTECT_MODE_WP))
1851 return -EINVAL;
1852
1853 mode_wp = uffdio_wp.mode & UFFDIO_WRITEPROTECT_MODE_WP;
1854 mode_dontwake = uffdio_wp.mode & UFFDIO_WRITEPROTECT_MODE_DONTWAKE;
1855
1856 if (mode_wp && mode_dontwake)
1857 return -EINVAL;
1858
1859 if (mmget_not_zero(ctx->mm)) {
1860 ret = mwriteprotect_range(ctx, uffdio_wp.range.start,
1861 uffdio_wp.range.len, mode_wp);
1862 mmput(ctx->mm);
1863 } else {
1864 return -ESRCH;
1865 }
1866
1867 if (ret)
1868 return ret;
1869
1870 if (!mode_wp && !mode_dontwake) {
1871 range.start = uffdio_wp.range.start;
1872 range.len = uffdio_wp.range.len;
1873 wake_userfault(ctx, &range);
1874 }
1875 return ret;
1876 }
1877
userfaultfd_continue(struct userfaultfd_ctx * ctx,unsigned long arg)1878 static int userfaultfd_continue(struct userfaultfd_ctx *ctx, unsigned long arg)
1879 {
1880 __s64 ret;
1881 struct uffdio_continue uffdio_continue;
1882 struct uffdio_continue __user *user_uffdio_continue;
1883 struct userfaultfd_wake_range range;
1884 uffd_flags_t flags = 0;
1885
1886 user_uffdio_continue = (struct uffdio_continue __user *)arg;
1887
1888 ret = -EAGAIN;
1889 if (atomic_read(&ctx->mmap_changing))
1890 goto out;
1891
1892 ret = -EFAULT;
1893 if (copy_from_user(&uffdio_continue, user_uffdio_continue,
1894 /* don't copy the output fields */
1895 sizeof(uffdio_continue) - (sizeof(__s64))))
1896 goto out;
1897
1898 ret = validate_range(ctx->mm, uffdio_continue.range.start,
1899 uffdio_continue.range.len);
1900 if (ret)
1901 goto out;
1902
1903 ret = -EINVAL;
1904 if (uffdio_continue.mode & ~(UFFDIO_CONTINUE_MODE_DONTWAKE |
1905 UFFDIO_CONTINUE_MODE_WP))
1906 goto out;
1907 if (uffdio_continue.mode & UFFDIO_CONTINUE_MODE_WP)
1908 flags |= MFILL_ATOMIC_WP;
1909
1910 if (mmget_not_zero(ctx->mm)) {
1911 ret = mfill_atomic_continue(ctx, uffdio_continue.range.start,
1912 uffdio_continue.range.len, flags);
1913 mmput(ctx->mm);
1914 } else {
1915 return -ESRCH;
1916 }
1917
1918 if (unlikely(put_user(ret, &user_uffdio_continue->mapped)))
1919 return -EFAULT;
1920 if (ret < 0)
1921 goto out;
1922
1923 /* len == 0 would wake all */
1924 BUG_ON(!ret);
1925 range.len = ret;
1926 if (!(uffdio_continue.mode & UFFDIO_CONTINUE_MODE_DONTWAKE)) {
1927 range.start = uffdio_continue.range.start;
1928 wake_userfault(ctx, &range);
1929 }
1930 ret = range.len == uffdio_continue.range.len ? 0 : -EAGAIN;
1931
1932 out:
1933 return ret;
1934 }
1935
userfaultfd_poison(struct userfaultfd_ctx * ctx,unsigned long arg)1936 static inline int userfaultfd_poison(struct userfaultfd_ctx *ctx, unsigned long arg)
1937 {
1938 __s64 ret;
1939 struct uffdio_poison uffdio_poison;
1940 struct uffdio_poison __user *user_uffdio_poison;
1941 struct userfaultfd_wake_range range;
1942
1943 user_uffdio_poison = (struct uffdio_poison __user *)arg;
1944
1945 ret = -EAGAIN;
1946 if (atomic_read(&ctx->mmap_changing))
1947 goto out;
1948
1949 ret = -EFAULT;
1950 if (copy_from_user(&uffdio_poison, user_uffdio_poison,
1951 /* don't copy the output fields */
1952 sizeof(uffdio_poison) - (sizeof(__s64))))
1953 goto out;
1954
1955 ret = validate_range(ctx->mm, uffdio_poison.range.start,
1956 uffdio_poison.range.len);
1957 if (ret)
1958 goto out;
1959
1960 ret = -EINVAL;
1961 if (uffdio_poison.mode & ~UFFDIO_POISON_MODE_DONTWAKE)
1962 goto out;
1963
1964 if (mmget_not_zero(ctx->mm)) {
1965 ret = mfill_atomic_poison(ctx, uffdio_poison.range.start,
1966 uffdio_poison.range.len, 0);
1967 mmput(ctx->mm);
1968 } else {
1969 return -ESRCH;
1970 }
1971
1972 if (unlikely(put_user(ret, &user_uffdio_poison->updated)))
1973 return -EFAULT;
1974 if (ret < 0)
1975 goto out;
1976
1977 /* len == 0 would wake all */
1978 BUG_ON(!ret);
1979 range.len = ret;
1980 if (!(uffdio_poison.mode & UFFDIO_POISON_MODE_DONTWAKE)) {
1981 range.start = uffdio_poison.range.start;
1982 wake_userfault(ctx, &range);
1983 }
1984 ret = range.len == uffdio_poison.range.len ? 0 : -EAGAIN;
1985
1986 out:
1987 return ret;
1988 }
1989
uffd_ctx_features(__u64 user_features)1990 static inline unsigned int uffd_ctx_features(__u64 user_features)
1991 {
1992 /*
1993 * For the current set of features the bits just coincide. Set
1994 * UFFD_FEATURE_INITIALIZED to mark the features as enabled.
1995 */
1996 return (unsigned int)user_features | UFFD_FEATURE_INITIALIZED;
1997 }
1998
userfaultfd_move(struct userfaultfd_ctx * ctx,unsigned long arg)1999 static int userfaultfd_move(struct userfaultfd_ctx *ctx,
2000 unsigned long arg)
2001 {
2002 __s64 ret;
2003 struct uffdio_move uffdio_move;
2004 struct uffdio_move __user *user_uffdio_move;
2005 struct userfaultfd_wake_range range;
2006 struct mm_struct *mm = ctx->mm;
2007
2008 user_uffdio_move = (struct uffdio_move __user *) arg;
2009
2010 if (atomic_read(&ctx->mmap_changing))
2011 return -EAGAIN;
2012
2013 if (copy_from_user(&uffdio_move, user_uffdio_move,
2014 /* don't copy "move" last field */
2015 sizeof(uffdio_move)-sizeof(__s64)))
2016 return -EFAULT;
2017
2018 /* Do not allow cross-mm moves. */
2019 if (mm != current->mm)
2020 return -EINVAL;
2021
2022 ret = validate_range(mm, uffdio_move.dst, uffdio_move.len);
2023 if (ret)
2024 return ret;
2025
2026 ret = validate_range(mm, uffdio_move.src, uffdio_move.len);
2027 if (ret)
2028 return ret;
2029
2030 if (uffdio_move.mode & ~(UFFDIO_MOVE_MODE_ALLOW_SRC_HOLES|
2031 UFFDIO_MOVE_MODE_DONTWAKE))
2032 return -EINVAL;
2033
2034 if (mmget_not_zero(mm)) {
2035 ret = move_pages(ctx, uffdio_move.dst, uffdio_move.src,
2036 uffdio_move.len, uffdio_move.mode);
2037 mmput(mm);
2038 } else {
2039 return -ESRCH;
2040 }
2041
2042 if (unlikely(put_user(ret, &user_uffdio_move->move)))
2043 return -EFAULT;
2044 if (ret < 0)
2045 goto out;
2046
2047 /* len == 0 would wake all */
2048 VM_WARN_ON(!ret);
2049 range.len = ret;
2050 if (!(uffdio_move.mode & UFFDIO_MOVE_MODE_DONTWAKE)) {
2051 range.start = uffdio_move.dst;
2052 wake_userfault(ctx, &range);
2053 }
2054 ret = range.len == uffdio_move.len ? 0 : -EAGAIN;
2055
2056 out:
2057 return ret;
2058 }
2059
2060 /*
2061 * userland asks for a certain API version and we return which bits
2062 * and ioctl commands are implemented in this kernel for such API
2063 * version or -EINVAL if unknown.
2064 */
userfaultfd_api(struct userfaultfd_ctx * ctx,unsigned long arg)2065 static int userfaultfd_api(struct userfaultfd_ctx *ctx,
2066 unsigned long arg)
2067 {
2068 struct uffdio_api uffdio_api;
2069 void __user *buf = (void __user *)arg;
2070 unsigned int ctx_features;
2071 int ret;
2072 __u64 features;
2073
2074 ret = -EFAULT;
2075 if (copy_from_user(&uffdio_api, buf, sizeof(uffdio_api)))
2076 goto out;
2077 features = uffdio_api.features;
2078 ret = -EINVAL;
2079 if (uffdio_api.api != UFFD_API)
2080 goto err_out;
2081 ret = -EPERM;
2082 if ((features & UFFD_FEATURE_EVENT_FORK) && !capable(CAP_SYS_PTRACE))
2083 goto err_out;
2084 /* report all available features and ioctls to userland */
2085 uffdio_api.features = UFFD_API_FEATURES;
2086 #ifndef CONFIG_HAVE_ARCH_USERFAULTFD_MINOR
2087 uffdio_api.features &=
2088 ~(UFFD_FEATURE_MINOR_HUGETLBFS | UFFD_FEATURE_MINOR_SHMEM);
2089 #endif
2090 #ifndef CONFIG_HAVE_ARCH_USERFAULTFD_WP
2091 uffdio_api.features &= ~UFFD_FEATURE_PAGEFAULT_FLAG_WP;
2092 #endif
2093 #ifndef CONFIG_PTE_MARKER_UFFD_WP
2094 uffdio_api.features &= ~UFFD_FEATURE_WP_HUGETLBFS_SHMEM;
2095 uffdio_api.features &= ~UFFD_FEATURE_WP_UNPOPULATED;
2096 #endif
2097
2098 ret = -EINVAL;
2099 if (features & ~uffdio_api.features)
2100 goto err_out;
2101
2102 uffdio_api.ioctls = UFFD_API_IOCTLS;
2103 ret = -EFAULT;
2104 if (copy_to_user(buf, &uffdio_api, sizeof(uffdio_api)))
2105 goto out;
2106
2107 /* only enable the requested features for this uffd context */
2108 ctx_features = uffd_ctx_features(features);
2109 ret = -EINVAL;
2110 if (cmpxchg(&ctx->features, 0, ctx_features) != 0)
2111 goto err_out;
2112
2113 ret = 0;
2114 out:
2115 return ret;
2116 err_out:
2117 memset(&uffdio_api, 0, sizeof(uffdio_api));
2118 if (copy_to_user(buf, &uffdio_api, sizeof(uffdio_api)))
2119 ret = -EFAULT;
2120 goto out;
2121 }
2122
userfaultfd_ioctl(struct file * file,unsigned cmd,unsigned long arg)2123 static long userfaultfd_ioctl(struct file *file, unsigned cmd,
2124 unsigned long arg)
2125 {
2126 int ret = -EINVAL;
2127 struct userfaultfd_ctx *ctx = file->private_data;
2128
2129 if (cmd != UFFDIO_API && !userfaultfd_is_initialized(ctx))
2130 return -EINVAL;
2131
2132 switch(cmd) {
2133 case UFFDIO_API:
2134 ret = userfaultfd_api(ctx, arg);
2135 break;
2136 case UFFDIO_REGISTER:
2137 ret = userfaultfd_register(ctx, arg);
2138 break;
2139 case UFFDIO_UNREGISTER:
2140 ret = userfaultfd_unregister(ctx, arg);
2141 break;
2142 case UFFDIO_WAKE:
2143 ret = userfaultfd_wake(ctx, arg);
2144 break;
2145 case UFFDIO_COPY:
2146 ret = userfaultfd_copy(ctx, arg);
2147 break;
2148 case UFFDIO_ZEROPAGE:
2149 ret = userfaultfd_zeropage(ctx, arg);
2150 break;
2151 case UFFDIO_MOVE:
2152 ret = userfaultfd_move(ctx, arg);
2153 break;
2154 case UFFDIO_WRITEPROTECT:
2155 ret = userfaultfd_writeprotect(ctx, arg);
2156 break;
2157 case UFFDIO_CONTINUE:
2158 ret = userfaultfd_continue(ctx, arg);
2159 break;
2160 case UFFDIO_POISON:
2161 ret = userfaultfd_poison(ctx, arg);
2162 break;
2163 }
2164 return ret;
2165 }
2166
2167 #ifdef CONFIG_PROC_FS
userfaultfd_show_fdinfo(struct seq_file * m,struct file * f)2168 static void userfaultfd_show_fdinfo(struct seq_file *m, struct file *f)
2169 {
2170 struct userfaultfd_ctx *ctx = f->private_data;
2171 wait_queue_entry_t *wq;
2172 unsigned long pending = 0, total = 0;
2173
2174 spin_lock_irq(&ctx->fault_pending_wqh.lock);
2175 list_for_each_entry(wq, &ctx->fault_pending_wqh.head, entry) {
2176 pending++;
2177 total++;
2178 }
2179 list_for_each_entry(wq, &ctx->fault_wqh.head, entry) {
2180 total++;
2181 }
2182 spin_unlock_irq(&ctx->fault_pending_wqh.lock);
2183
2184 /*
2185 * If more protocols will be added, there will be all shown
2186 * separated by a space. Like this:
2187 * protocols: aa:... bb:...
2188 */
2189 seq_printf(m, "pending:\t%lu\ntotal:\t%lu\nAPI:\t%Lx:%x:%Lx\n",
2190 pending, total, UFFD_API, ctx->features,
2191 UFFD_API_IOCTLS|UFFD_API_RANGE_IOCTLS);
2192 }
2193 #endif
2194
2195 static const struct file_operations userfaultfd_fops = {
2196 #ifdef CONFIG_PROC_FS
2197 .show_fdinfo = userfaultfd_show_fdinfo,
2198 #endif
2199 .release = userfaultfd_release,
2200 .poll = userfaultfd_poll,
2201 .read = userfaultfd_read,
2202 .unlocked_ioctl = userfaultfd_ioctl,
2203 .compat_ioctl = compat_ptr_ioctl,
2204 .llseek = noop_llseek,
2205 };
2206
init_once_userfaultfd_ctx(void * mem)2207 static void init_once_userfaultfd_ctx(void *mem)
2208 {
2209 struct userfaultfd_ctx *ctx = (struct userfaultfd_ctx *) mem;
2210
2211 init_waitqueue_head(&ctx->fault_pending_wqh);
2212 init_waitqueue_head(&ctx->fault_wqh);
2213 init_waitqueue_head(&ctx->event_wqh);
2214 init_waitqueue_head(&ctx->fd_wqh);
2215 seqcount_spinlock_init(&ctx->refile_seq, &ctx->fault_pending_wqh.lock);
2216 }
2217
new_userfaultfd(int flags)2218 static int new_userfaultfd(int flags)
2219 {
2220 struct userfaultfd_ctx *ctx;
2221 int fd;
2222
2223 BUG_ON(!current->mm);
2224
2225 /* Check the UFFD_* constants for consistency. */
2226 BUILD_BUG_ON(UFFD_USER_MODE_ONLY & UFFD_SHARED_FCNTL_FLAGS);
2227 BUILD_BUG_ON(UFFD_CLOEXEC != O_CLOEXEC);
2228 BUILD_BUG_ON(UFFD_NONBLOCK != O_NONBLOCK);
2229
2230 if (flags & ~(UFFD_SHARED_FCNTL_FLAGS | UFFD_USER_MODE_ONLY))
2231 return -EINVAL;
2232
2233 ctx = kmem_cache_alloc(userfaultfd_ctx_cachep, GFP_KERNEL);
2234 if (!ctx)
2235 return -ENOMEM;
2236
2237 refcount_set(&ctx->refcount, 1);
2238 ctx->flags = flags;
2239 ctx->features = 0;
2240 ctx->released = false;
2241 init_rwsem(&ctx->map_changing_lock);
2242 atomic_set(&ctx->mmap_changing, 0);
2243 ctx->mm = current->mm;
2244 /* prevent the mm struct to be freed */
2245 mmgrab(ctx->mm);
2246
2247 fd = anon_inode_getfd_secure("[userfaultfd]", &userfaultfd_fops, ctx,
2248 O_RDONLY | (flags & UFFD_SHARED_FCNTL_FLAGS), NULL);
2249 if (fd < 0) {
2250 mmdrop(ctx->mm);
2251 kmem_cache_free(userfaultfd_ctx_cachep, ctx);
2252 }
2253 return fd;
2254 }
2255
userfaultfd_syscall_allowed(int flags)2256 static inline bool userfaultfd_syscall_allowed(int flags)
2257 {
2258 /* Userspace-only page faults are always allowed */
2259 if (flags & UFFD_USER_MODE_ONLY)
2260 return true;
2261
2262 /*
2263 * The user is requesting a userfaultfd which can handle kernel faults.
2264 * Privileged users are always allowed to do this.
2265 */
2266 if (capable(CAP_SYS_PTRACE))
2267 return true;
2268
2269 /* Otherwise, access to kernel fault handling is sysctl controlled. */
2270 return sysctl_unprivileged_userfaultfd;
2271 }
2272
SYSCALL_DEFINE1(userfaultfd,int,flags)2273 SYSCALL_DEFINE1(userfaultfd, int, flags)
2274 {
2275 if (!userfaultfd_syscall_allowed(flags))
2276 return -EPERM;
2277
2278 return new_userfaultfd(flags);
2279 }
2280
userfaultfd_dev_ioctl(struct file * file,unsigned int cmd,unsigned long flags)2281 static long userfaultfd_dev_ioctl(struct file *file, unsigned int cmd, unsigned long flags)
2282 {
2283 if (cmd != USERFAULTFD_IOC_NEW)
2284 return -EINVAL;
2285
2286 return new_userfaultfd(flags);
2287 }
2288
2289 static const struct file_operations userfaultfd_dev_fops = {
2290 .unlocked_ioctl = userfaultfd_dev_ioctl,
2291 .compat_ioctl = userfaultfd_dev_ioctl,
2292 .owner = THIS_MODULE,
2293 .llseek = noop_llseek,
2294 };
2295
2296 static struct miscdevice userfaultfd_misc = {
2297 .minor = MISC_DYNAMIC_MINOR,
2298 .name = "userfaultfd",
2299 .fops = &userfaultfd_dev_fops
2300 };
2301
userfaultfd_init(void)2302 static int __init userfaultfd_init(void)
2303 {
2304 int ret;
2305
2306 ret = misc_register(&userfaultfd_misc);
2307 if (ret)
2308 return ret;
2309
2310 userfaultfd_ctx_cachep = kmem_cache_create("userfaultfd_ctx_cache",
2311 sizeof(struct userfaultfd_ctx),
2312 0,
2313 SLAB_HWCACHE_ALIGN|SLAB_PANIC,
2314 init_once_userfaultfd_ctx);
2315 #ifdef CONFIG_SYSCTL
2316 register_sysctl_init("vm", vm_userfaultfd_table);
2317 #endif
2318 return 0;
2319 }
2320 __initcall(userfaultfd_init);
2321