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 #include <linux/uio.h>
35
36 static int sysctl_unprivileged_userfaultfd __read_mostly;
37
38 #ifdef CONFIG_SYSCTL
39 static struct ctl_table vm_userfaultfd_table[] = {
40 {
41 .procname = "unprivileged_userfaultfd",
42 .data = &sysctl_unprivileged_userfaultfd,
43 .maxlen = sizeof(sysctl_unprivileged_userfaultfd),
44 .mode = 0644,
45 .proc_handler = proc_dointvec_minmax,
46 .extra1 = SYSCTL_ZERO,
47 .extra2 = SYSCTL_ONE,
48 },
49 };
50 #endif
51
52 static struct kmem_cache *userfaultfd_ctx_cachep __ro_after_init;
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
userfaultfd_wp_async_ctx(struct userfaultfd_ctx * ctx)87 static bool userfaultfd_wp_async_ctx(struct userfaultfd_ctx *ctx)
88 {
89 return ctx && (ctx->features & UFFD_FEATURE_WP_ASYNC);
90 }
91
92 /*
93 * Whether WP_UNPOPULATED is enabled on the uffd context. It is only
94 * meaningful when userfaultfd_wp()==true on the vma and when it's
95 * anonymous.
96 */
userfaultfd_wp_unpopulated(struct vm_area_struct * vma)97 bool userfaultfd_wp_unpopulated(struct vm_area_struct *vma)
98 {
99 struct userfaultfd_ctx *ctx = vma->vm_userfaultfd_ctx.ctx;
100
101 if (!ctx)
102 return false;
103
104 return ctx->features & UFFD_FEATURE_WP_UNPOPULATED;
105 }
106
userfaultfd_wake_function(wait_queue_entry_t * wq,unsigned mode,int wake_flags,void * key)107 static int userfaultfd_wake_function(wait_queue_entry_t *wq, unsigned mode,
108 int wake_flags, void *key)
109 {
110 struct userfaultfd_wake_range *range = key;
111 int ret;
112 struct userfaultfd_wait_queue *uwq;
113 unsigned long start, len;
114
115 uwq = container_of(wq, struct userfaultfd_wait_queue, wq);
116 ret = 0;
117 /* len == 0 means wake all */
118 start = range->start;
119 len = range->len;
120 if (len && (start > uwq->msg.arg.pagefault.address ||
121 start + len <= uwq->msg.arg.pagefault.address))
122 goto out;
123 WRITE_ONCE(uwq->waken, true);
124 /*
125 * The Program-Order guarantees provided by the scheduler
126 * ensure uwq->waken is visible before the task is woken.
127 */
128 ret = wake_up_state(wq->private, mode);
129 if (ret) {
130 /*
131 * Wake only once, autoremove behavior.
132 *
133 * After the effect of list_del_init is visible to the other
134 * CPUs, the waitqueue may disappear from under us, see the
135 * !list_empty_careful() in handle_userfault().
136 *
137 * try_to_wake_up() has an implicit smp_mb(), and the
138 * wq->private is read before calling the extern function
139 * "wake_up_state" (which in turns calls try_to_wake_up).
140 */
141 list_del_init(&wq->entry);
142 }
143 out:
144 return ret;
145 }
146
147 /**
148 * userfaultfd_ctx_get - Acquires a reference to the internal userfaultfd
149 * context.
150 * @ctx: [in] Pointer to the userfaultfd context.
151 */
userfaultfd_ctx_get(struct userfaultfd_ctx * ctx)152 static void userfaultfd_ctx_get(struct userfaultfd_ctx *ctx)
153 {
154 refcount_inc(&ctx->refcount);
155 }
156
157 /**
158 * userfaultfd_ctx_put - Releases a reference to the internal userfaultfd
159 * context.
160 * @ctx: [in] Pointer to userfaultfd context.
161 *
162 * The userfaultfd context reference must have been previously acquired either
163 * with userfaultfd_ctx_get() or userfaultfd_ctx_fdget().
164 */
userfaultfd_ctx_put(struct userfaultfd_ctx * ctx)165 static void userfaultfd_ctx_put(struct userfaultfd_ctx *ctx)
166 {
167 if (refcount_dec_and_test(&ctx->refcount)) {
168 VM_BUG_ON(spin_is_locked(&ctx->fault_pending_wqh.lock));
169 VM_BUG_ON(waitqueue_active(&ctx->fault_pending_wqh));
170 VM_BUG_ON(spin_is_locked(&ctx->fault_wqh.lock));
171 VM_BUG_ON(waitqueue_active(&ctx->fault_wqh));
172 VM_BUG_ON(spin_is_locked(&ctx->event_wqh.lock));
173 VM_BUG_ON(waitqueue_active(&ctx->event_wqh));
174 VM_BUG_ON(spin_is_locked(&ctx->fd_wqh.lock));
175 VM_BUG_ON(waitqueue_active(&ctx->fd_wqh));
176 mmdrop(ctx->mm);
177 kmem_cache_free(userfaultfd_ctx_cachep, ctx);
178 }
179 }
180
msg_init(struct uffd_msg * msg)181 static inline void msg_init(struct uffd_msg *msg)
182 {
183 BUILD_BUG_ON(sizeof(struct uffd_msg) != 32);
184 /*
185 * Must use memset to zero out the paddings or kernel data is
186 * leaked to userland.
187 */
188 memset(msg, 0, sizeof(struct uffd_msg));
189 }
190
userfault_msg(unsigned long address,unsigned long real_address,unsigned int flags,unsigned long reason,unsigned int features)191 static inline struct uffd_msg userfault_msg(unsigned long address,
192 unsigned long real_address,
193 unsigned int flags,
194 unsigned long reason,
195 unsigned int features)
196 {
197 struct uffd_msg msg;
198
199 msg_init(&msg);
200 msg.event = UFFD_EVENT_PAGEFAULT;
201
202 msg.arg.pagefault.address = (features & UFFD_FEATURE_EXACT_ADDRESS) ?
203 real_address : address;
204
205 /*
206 * These flags indicate why the userfault occurred:
207 * - UFFD_PAGEFAULT_FLAG_WP indicates a write protect fault.
208 * - UFFD_PAGEFAULT_FLAG_MINOR indicates a minor fault.
209 * - Neither of these flags being set indicates a MISSING fault.
210 *
211 * Separately, UFFD_PAGEFAULT_FLAG_WRITE indicates it was a write
212 * fault. Otherwise, it was a read fault.
213 */
214 if (flags & FAULT_FLAG_WRITE)
215 msg.arg.pagefault.flags |= UFFD_PAGEFAULT_FLAG_WRITE;
216 if (reason & VM_UFFD_WP)
217 msg.arg.pagefault.flags |= UFFD_PAGEFAULT_FLAG_WP;
218 if (reason & VM_UFFD_MINOR)
219 msg.arg.pagefault.flags |= UFFD_PAGEFAULT_FLAG_MINOR;
220 if (features & UFFD_FEATURE_THREAD_ID)
221 msg.arg.pagefault.feat.ptid = task_pid_vnr(current);
222 return msg;
223 }
224
225 #ifdef CONFIG_HUGETLB_PAGE
226 /*
227 * Same functionality as userfaultfd_must_wait below with modifications for
228 * hugepmd ranges.
229 */
userfaultfd_huge_must_wait(struct userfaultfd_ctx * ctx,struct vm_fault * vmf,unsigned long reason)230 static inline bool userfaultfd_huge_must_wait(struct userfaultfd_ctx *ctx,
231 struct vm_fault *vmf,
232 unsigned long reason)
233 {
234 struct vm_area_struct *vma = vmf->vma;
235 pte_t *ptep, pte;
236 bool ret = true;
237
238 assert_fault_locked(vmf);
239
240 ptep = hugetlb_walk(vma, vmf->address, vma_mmu_pagesize(vma));
241 if (!ptep)
242 goto out;
243
244 ret = false;
245 pte = huge_ptep_get(vma->vm_mm, vmf->address, ptep);
246
247 /*
248 * Lockless access: we're in a wait_event so it's ok if it
249 * changes under us. PTE markers should be handled the same as none
250 * ptes here.
251 */
252 if (huge_pte_none_mostly(pte))
253 ret = true;
254 if (!huge_pte_write(pte) && (reason & VM_UFFD_WP))
255 ret = true;
256 out:
257 return ret;
258 }
259 #else
userfaultfd_huge_must_wait(struct userfaultfd_ctx * ctx,struct vm_fault * vmf,unsigned long reason)260 static inline bool userfaultfd_huge_must_wait(struct userfaultfd_ctx *ctx,
261 struct vm_fault *vmf,
262 unsigned long reason)
263 {
264 return false; /* should never get here */
265 }
266 #endif /* CONFIG_HUGETLB_PAGE */
267
268 /*
269 * Verify the pagetables are still not ok after having reigstered into
270 * the fault_pending_wqh to avoid userland having to UFFDIO_WAKE any
271 * userfault that has already been resolved, if userfaultfd_read_iter and
272 * UFFDIO_COPY|ZEROPAGE are being run simultaneously on two different
273 * threads.
274 */
userfaultfd_must_wait(struct userfaultfd_ctx * ctx,struct vm_fault * vmf,unsigned long reason)275 static inline bool userfaultfd_must_wait(struct userfaultfd_ctx *ctx,
276 struct vm_fault *vmf,
277 unsigned long reason)
278 {
279 struct mm_struct *mm = ctx->mm;
280 unsigned long address = vmf->address;
281 pgd_t *pgd;
282 p4d_t *p4d;
283 pud_t *pud;
284 pmd_t *pmd, _pmd;
285 pte_t *pte;
286 pte_t ptent;
287 bool ret = true;
288
289 assert_fault_locked(vmf);
290
291 pgd = pgd_offset(mm, address);
292 if (!pgd_present(*pgd))
293 goto out;
294 p4d = p4d_offset(pgd, address);
295 if (!p4d_present(*p4d))
296 goto out;
297 pud = pud_offset(p4d, address);
298 if (!pud_present(*pud))
299 goto out;
300 pmd = pmd_offset(pud, address);
301 again:
302 _pmd = pmdp_get_lockless(pmd);
303 if (pmd_none(_pmd))
304 goto out;
305
306 ret = false;
307 if (!pmd_present(_pmd) || pmd_devmap(_pmd))
308 goto out;
309
310 if (pmd_trans_huge(_pmd)) {
311 if (!pmd_write(_pmd) && (reason & VM_UFFD_WP))
312 ret = true;
313 goto out;
314 }
315
316 pte = pte_offset_map(pmd, address);
317 if (!pte) {
318 ret = true;
319 goto again;
320 }
321 /*
322 * Lockless access: we're in a wait_event so it's ok if it
323 * changes under us. PTE markers should be handled the same as none
324 * ptes here.
325 */
326 ptent = ptep_get(pte);
327 if (pte_none_mostly(ptent))
328 ret = true;
329 if (!pte_write(ptent) && (reason & VM_UFFD_WP))
330 ret = true;
331 pte_unmap(pte);
332
333 out:
334 return ret;
335 }
336
userfaultfd_get_blocking_state(unsigned int flags)337 static inline unsigned int userfaultfd_get_blocking_state(unsigned int flags)
338 {
339 if (flags & FAULT_FLAG_INTERRUPTIBLE)
340 return TASK_INTERRUPTIBLE;
341
342 if (flags & FAULT_FLAG_KILLABLE)
343 return TASK_KILLABLE;
344
345 return TASK_UNINTERRUPTIBLE;
346 }
347
348 /*
349 * The locking rules involved in returning VM_FAULT_RETRY depending on
350 * FAULT_FLAG_ALLOW_RETRY, FAULT_FLAG_RETRY_NOWAIT and
351 * FAULT_FLAG_KILLABLE are not straightforward. The "Caution"
352 * recommendation in __lock_page_or_retry is not an understatement.
353 *
354 * If FAULT_FLAG_ALLOW_RETRY is set, the mmap_lock must be released
355 * before returning VM_FAULT_RETRY only if FAULT_FLAG_RETRY_NOWAIT is
356 * not set.
357 *
358 * If FAULT_FLAG_ALLOW_RETRY is set but FAULT_FLAG_KILLABLE is not
359 * set, VM_FAULT_RETRY can still be returned if and only if there are
360 * fatal_signal_pending()s, and the mmap_lock must be released before
361 * returning it.
362 */
handle_userfault(struct vm_fault * vmf,unsigned long reason)363 vm_fault_t handle_userfault(struct vm_fault *vmf, unsigned long reason)
364 {
365 struct vm_area_struct *vma = vmf->vma;
366 struct mm_struct *mm = vma->vm_mm;
367 struct userfaultfd_ctx *ctx;
368 struct userfaultfd_wait_queue uwq;
369 vm_fault_t ret = VM_FAULT_SIGBUS;
370 bool must_wait;
371 unsigned int blocking_state;
372
373 /*
374 * We don't do userfault handling for the final child pid update
375 * and when coredumping (faults triggered by get_dump_page()).
376 */
377 if (current->flags & (PF_EXITING|PF_DUMPCORE))
378 goto out;
379
380 assert_fault_locked(vmf);
381
382 ctx = vma->vm_userfaultfd_ctx.ctx;
383 if (!ctx)
384 goto out;
385
386 BUG_ON(ctx->mm != mm);
387
388 /* Any unrecognized flag is a bug. */
389 VM_BUG_ON(reason & ~__VM_UFFD_FLAGS);
390 /* 0 or > 1 flags set is a bug; we expect exactly 1. */
391 VM_BUG_ON(!reason || (reason & (reason - 1)));
392
393 if (ctx->features & UFFD_FEATURE_SIGBUS)
394 goto out;
395 if (!(vmf->flags & FAULT_FLAG_USER) && (ctx->flags & UFFD_USER_MODE_ONLY))
396 goto out;
397
398 /*
399 * If it's already released don't get it. This avoids to loop
400 * in __get_user_pages if userfaultfd_release waits on the
401 * caller of handle_userfault to release the mmap_lock.
402 */
403 if (unlikely(READ_ONCE(ctx->released))) {
404 /*
405 * Don't return VM_FAULT_SIGBUS in this case, so a non
406 * cooperative manager can close the uffd after the
407 * last UFFDIO_COPY, without risking to trigger an
408 * involuntary SIGBUS if the process was starting the
409 * userfaultfd while the userfaultfd was still armed
410 * (but after the last UFFDIO_COPY). If the uffd
411 * wasn't already closed when the userfault reached
412 * this point, that would normally be solved by
413 * userfaultfd_must_wait returning 'false'.
414 *
415 * If we were to return VM_FAULT_SIGBUS here, the non
416 * cooperative manager would be instead forced to
417 * always call UFFDIO_UNREGISTER before it can safely
418 * close the uffd.
419 */
420 ret = VM_FAULT_NOPAGE;
421 goto out;
422 }
423
424 /*
425 * Check that we can return VM_FAULT_RETRY.
426 *
427 * NOTE: it should become possible to return VM_FAULT_RETRY
428 * even if FAULT_FLAG_TRIED is set without leading to gup()
429 * -EBUSY failures, if the userfaultfd is to be extended for
430 * VM_UFFD_WP tracking and we intend to arm the userfault
431 * without first stopping userland access to the memory. For
432 * VM_UFFD_MISSING userfaults this is enough for now.
433 */
434 if (unlikely(!(vmf->flags & FAULT_FLAG_ALLOW_RETRY))) {
435 /*
436 * Validate the invariant that nowait must allow retry
437 * to be sure not to return SIGBUS erroneously on
438 * nowait invocations.
439 */
440 BUG_ON(vmf->flags & FAULT_FLAG_RETRY_NOWAIT);
441 #ifdef CONFIG_DEBUG_VM
442 if (printk_ratelimit()) {
443 printk(KERN_WARNING
444 "FAULT_FLAG_ALLOW_RETRY missing %x\n",
445 vmf->flags);
446 dump_stack();
447 }
448 #endif
449 goto out;
450 }
451
452 /*
453 * Handle nowait, not much to do other than tell it to retry
454 * and wait.
455 */
456 ret = VM_FAULT_RETRY;
457 if (vmf->flags & FAULT_FLAG_RETRY_NOWAIT)
458 goto out;
459
460 /* take the reference before dropping the mmap_lock */
461 userfaultfd_ctx_get(ctx);
462
463 init_waitqueue_func_entry(&uwq.wq, userfaultfd_wake_function);
464 uwq.wq.private = current;
465 uwq.msg = userfault_msg(vmf->address, vmf->real_address, vmf->flags,
466 reason, ctx->features);
467 uwq.ctx = ctx;
468 uwq.waken = false;
469
470 blocking_state = userfaultfd_get_blocking_state(vmf->flags);
471
472 /*
473 * Take the vma lock now, in order to safely call
474 * userfaultfd_huge_must_wait() later. Since acquiring the
475 * (sleepable) vma lock can modify the current task state, that
476 * must be before explicitly calling set_current_state().
477 */
478 if (is_vm_hugetlb_page(vma))
479 hugetlb_vma_lock_read(vma);
480
481 spin_lock_irq(&ctx->fault_pending_wqh.lock);
482 /*
483 * After the __add_wait_queue the uwq is visible to userland
484 * through poll/read().
485 */
486 __add_wait_queue(&ctx->fault_pending_wqh, &uwq.wq);
487 /*
488 * The smp_mb() after __set_current_state prevents the reads
489 * following the spin_unlock to happen before the list_add in
490 * __add_wait_queue.
491 */
492 set_current_state(blocking_state);
493 spin_unlock_irq(&ctx->fault_pending_wqh.lock);
494
495 if (!is_vm_hugetlb_page(vma))
496 must_wait = userfaultfd_must_wait(ctx, vmf, reason);
497 else
498 must_wait = userfaultfd_huge_must_wait(ctx, vmf, reason);
499 if (is_vm_hugetlb_page(vma))
500 hugetlb_vma_unlock_read(vma);
501 release_fault_lock(vmf);
502
503 if (likely(must_wait && !READ_ONCE(ctx->released))) {
504 wake_up_poll(&ctx->fd_wqh, EPOLLIN);
505 schedule();
506 }
507
508 __set_current_state(TASK_RUNNING);
509
510 /*
511 * Here we race with the list_del; list_add in
512 * userfaultfd_ctx_read(), however because we don't ever run
513 * list_del_init() to refile across the two lists, the prev
514 * and next pointers will never point to self. list_add also
515 * would never let any of the two pointers to point to
516 * self. So list_empty_careful won't risk to see both pointers
517 * pointing to self at any time during the list refile. The
518 * only case where list_del_init() is called is the full
519 * removal in the wake function and there we don't re-list_add
520 * and it's fine not to block on the spinlock. The uwq on this
521 * kernel stack can be released after the list_del_init.
522 */
523 if (!list_empty_careful(&uwq.wq.entry)) {
524 spin_lock_irq(&ctx->fault_pending_wqh.lock);
525 /*
526 * No need of list_del_init(), the uwq on the stack
527 * will be freed shortly anyway.
528 */
529 list_del(&uwq.wq.entry);
530 spin_unlock_irq(&ctx->fault_pending_wqh.lock);
531 }
532
533 /*
534 * ctx may go away after this if the userfault pseudo fd is
535 * already released.
536 */
537 userfaultfd_ctx_put(ctx);
538
539 out:
540 return ret;
541 }
542
userfaultfd_event_wait_completion(struct userfaultfd_ctx * ctx,struct userfaultfd_wait_queue * ewq)543 static void userfaultfd_event_wait_completion(struct userfaultfd_ctx *ctx,
544 struct userfaultfd_wait_queue *ewq)
545 {
546 struct userfaultfd_ctx *release_new_ctx;
547
548 if (WARN_ON_ONCE(current->flags & PF_EXITING))
549 goto out;
550
551 ewq->ctx = ctx;
552 init_waitqueue_entry(&ewq->wq, current);
553 release_new_ctx = NULL;
554
555 spin_lock_irq(&ctx->event_wqh.lock);
556 /*
557 * After the __add_wait_queue the uwq is visible to userland
558 * through poll/read().
559 */
560 __add_wait_queue(&ctx->event_wqh, &ewq->wq);
561 for (;;) {
562 set_current_state(TASK_KILLABLE);
563 if (ewq->msg.event == 0)
564 break;
565 if (READ_ONCE(ctx->released) ||
566 fatal_signal_pending(current)) {
567 /*
568 * &ewq->wq may be queued in fork_event, but
569 * __remove_wait_queue ignores the head
570 * parameter. It would be a problem if it
571 * didn't.
572 */
573 __remove_wait_queue(&ctx->event_wqh, &ewq->wq);
574 if (ewq->msg.event == UFFD_EVENT_FORK) {
575 struct userfaultfd_ctx *new;
576
577 new = (struct userfaultfd_ctx *)
578 (unsigned long)
579 ewq->msg.arg.reserved.reserved1;
580 release_new_ctx = new;
581 }
582 break;
583 }
584
585 spin_unlock_irq(&ctx->event_wqh.lock);
586
587 wake_up_poll(&ctx->fd_wqh, EPOLLIN);
588 schedule();
589
590 spin_lock_irq(&ctx->event_wqh.lock);
591 }
592 __set_current_state(TASK_RUNNING);
593 spin_unlock_irq(&ctx->event_wqh.lock);
594
595 if (release_new_ctx) {
596 userfaultfd_release_new(release_new_ctx);
597 userfaultfd_ctx_put(release_new_ctx);
598 }
599
600 /*
601 * ctx may go away after this if the userfault pseudo fd is
602 * already released.
603 */
604 out:
605 atomic_dec(&ctx->mmap_changing);
606 VM_BUG_ON(atomic_read(&ctx->mmap_changing) < 0);
607 userfaultfd_ctx_put(ctx);
608 }
609
userfaultfd_event_complete(struct userfaultfd_ctx * ctx,struct userfaultfd_wait_queue * ewq)610 static void userfaultfd_event_complete(struct userfaultfd_ctx *ctx,
611 struct userfaultfd_wait_queue *ewq)
612 {
613 ewq->msg.event = 0;
614 wake_up_locked(&ctx->event_wqh);
615 __remove_wait_queue(&ctx->event_wqh, &ewq->wq);
616 }
617
dup_userfaultfd(struct vm_area_struct * vma,struct list_head * fcs)618 int dup_userfaultfd(struct vm_area_struct *vma, struct list_head *fcs)
619 {
620 struct userfaultfd_ctx *ctx = NULL, *octx;
621 struct userfaultfd_fork_ctx *fctx;
622
623 octx = vma->vm_userfaultfd_ctx.ctx;
624 if (!octx)
625 return 0;
626
627 if (!(octx->features & UFFD_FEATURE_EVENT_FORK)) {
628 userfaultfd_reset_ctx(vma);
629 return 0;
630 }
631
632 list_for_each_entry(fctx, fcs, list)
633 if (fctx->orig == octx) {
634 ctx = fctx->new;
635 break;
636 }
637
638 if (!ctx) {
639 fctx = kmalloc(sizeof(*fctx), GFP_KERNEL);
640 if (!fctx)
641 return -ENOMEM;
642
643 ctx = kmem_cache_alloc(userfaultfd_ctx_cachep, GFP_KERNEL);
644 if (!ctx) {
645 kfree(fctx);
646 return -ENOMEM;
647 }
648
649 refcount_set(&ctx->refcount, 1);
650 ctx->flags = octx->flags;
651 ctx->features = octx->features;
652 ctx->released = false;
653 init_rwsem(&ctx->map_changing_lock);
654 atomic_set(&ctx->mmap_changing, 0);
655 ctx->mm = vma->vm_mm;
656 mmgrab(ctx->mm);
657
658 userfaultfd_ctx_get(octx);
659 down_write(&octx->map_changing_lock);
660 atomic_inc(&octx->mmap_changing);
661 up_write(&octx->map_changing_lock);
662 fctx->orig = octx;
663 fctx->new = ctx;
664 list_add_tail(&fctx->list, fcs);
665 }
666
667 vma->vm_userfaultfd_ctx.ctx = ctx;
668 return 0;
669 }
670
dup_fctx(struct userfaultfd_fork_ctx * fctx)671 static void dup_fctx(struct userfaultfd_fork_ctx *fctx)
672 {
673 struct userfaultfd_ctx *ctx = fctx->orig;
674 struct userfaultfd_wait_queue ewq;
675
676 msg_init(&ewq.msg);
677
678 ewq.msg.event = UFFD_EVENT_FORK;
679 ewq.msg.arg.reserved.reserved1 = (unsigned long)fctx->new;
680
681 userfaultfd_event_wait_completion(ctx, &ewq);
682 }
683
dup_userfaultfd_complete(struct list_head * fcs)684 void dup_userfaultfd_complete(struct list_head *fcs)
685 {
686 struct userfaultfd_fork_ctx *fctx, *n;
687
688 list_for_each_entry_safe(fctx, n, fcs, list) {
689 dup_fctx(fctx);
690 list_del(&fctx->list);
691 kfree(fctx);
692 }
693 }
694
dup_userfaultfd_fail(struct list_head * fcs)695 void dup_userfaultfd_fail(struct list_head *fcs)
696 {
697 struct userfaultfd_fork_ctx *fctx, *n;
698
699 /*
700 * An error has occurred on fork, we will tear memory down, but have
701 * allocated memory for fctx's and raised reference counts for both the
702 * original and child contexts (and on the mm for each as a result).
703 *
704 * These would ordinarily be taken care of by a user handling the event,
705 * but we are no longer doing so, so manually clean up here.
706 *
707 * mm tear down will take care of cleaning up VMA contexts.
708 */
709 list_for_each_entry_safe(fctx, n, fcs, list) {
710 struct userfaultfd_ctx *octx = fctx->orig;
711 struct userfaultfd_ctx *ctx = fctx->new;
712
713 atomic_dec(&octx->mmap_changing);
714 VM_BUG_ON(atomic_read(&octx->mmap_changing) < 0);
715 userfaultfd_ctx_put(octx);
716 userfaultfd_ctx_put(ctx);
717
718 list_del(&fctx->list);
719 kfree(fctx);
720 }
721 }
722
mremap_userfaultfd_prep(struct vm_area_struct * vma,struct vm_userfaultfd_ctx * vm_ctx)723 void mremap_userfaultfd_prep(struct vm_area_struct *vma,
724 struct vm_userfaultfd_ctx *vm_ctx)
725 {
726 struct userfaultfd_ctx *ctx;
727
728 ctx = vma->vm_userfaultfd_ctx.ctx;
729
730 if (!ctx)
731 return;
732
733 if (ctx->features & UFFD_FEATURE_EVENT_REMAP) {
734 vm_ctx->ctx = ctx;
735 userfaultfd_ctx_get(ctx);
736 down_write(&ctx->map_changing_lock);
737 atomic_inc(&ctx->mmap_changing);
738 up_write(&ctx->map_changing_lock);
739 } else {
740 /* Drop uffd context if remap feature not enabled */
741 userfaultfd_reset_ctx(vma);
742 }
743 }
744
mremap_userfaultfd_complete(struct vm_userfaultfd_ctx * vm_ctx,unsigned long from,unsigned long to,unsigned long len)745 void mremap_userfaultfd_complete(struct vm_userfaultfd_ctx *vm_ctx,
746 unsigned long from, unsigned long to,
747 unsigned long len)
748 {
749 struct userfaultfd_ctx *ctx = vm_ctx->ctx;
750 struct userfaultfd_wait_queue ewq;
751
752 if (!ctx)
753 return;
754
755 if (to & ~PAGE_MASK) {
756 userfaultfd_ctx_put(ctx);
757 return;
758 }
759
760 msg_init(&ewq.msg);
761
762 ewq.msg.event = UFFD_EVENT_REMAP;
763 ewq.msg.arg.remap.from = from;
764 ewq.msg.arg.remap.to = to;
765 ewq.msg.arg.remap.len = len;
766
767 userfaultfd_event_wait_completion(ctx, &ewq);
768 }
769
userfaultfd_remove(struct vm_area_struct * vma,unsigned long start,unsigned long end)770 bool userfaultfd_remove(struct vm_area_struct *vma,
771 unsigned long start, unsigned long end)
772 {
773 struct mm_struct *mm = vma->vm_mm;
774 struct userfaultfd_ctx *ctx;
775 struct userfaultfd_wait_queue ewq;
776
777 ctx = vma->vm_userfaultfd_ctx.ctx;
778 if (!ctx || !(ctx->features & UFFD_FEATURE_EVENT_REMOVE))
779 return true;
780
781 userfaultfd_ctx_get(ctx);
782 down_write(&ctx->map_changing_lock);
783 atomic_inc(&ctx->mmap_changing);
784 up_write(&ctx->map_changing_lock);
785 mmap_read_unlock(mm);
786
787 msg_init(&ewq.msg);
788
789 ewq.msg.event = UFFD_EVENT_REMOVE;
790 ewq.msg.arg.remove.start = start;
791 ewq.msg.arg.remove.end = end;
792
793 userfaultfd_event_wait_completion(ctx, &ewq);
794
795 return false;
796 }
797
has_unmap_ctx(struct userfaultfd_ctx * ctx,struct list_head * unmaps,unsigned long start,unsigned long end)798 static bool has_unmap_ctx(struct userfaultfd_ctx *ctx, struct list_head *unmaps,
799 unsigned long start, unsigned long end)
800 {
801 struct userfaultfd_unmap_ctx *unmap_ctx;
802
803 list_for_each_entry(unmap_ctx, unmaps, list)
804 if (unmap_ctx->ctx == ctx && unmap_ctx->start == start &&
805 unmap_ctx->end == end)
806 return true;
807
808 return false;
809 }
810
userfaultfd_unmap_prep(struct vm_area_struct * vma,unsigned long start,unsigned long end,struct list_head * unmaps)811 int userfaultfd_unmap_prep(struct vm_area_struct *vma, unsigned long start,
812 unsigned long end, struct list_head *unmaps)
813 {
814 struct userfaultfd_unmap_ctx *unmap_ctx;
815 struct userfaultfd_ctx *ctx = vma->vm_userfaultfd_ctx.ctx;
816
817 if (!ctx || !(ctx->features & UFFD_FEATURE_EVENT_UNMAP) ||
818 has_unmap_ctx(ctx, unmaps, start, end))
819 return 0;
820
821 unmap_ctx = kzalloc(sizeof(*unmap_ctx), GFP_KERNEL);
822 if (!unmap_ctx)
823 return -ENOMEM;
824
825 userfaultfd_ctx_get(ctx);
826 down_write(&ctx->map_changing_lock);
827 atomic_inc(&ctx->mmap_changing);
828 up_write(&ctx->map_changing_lock);
829 unmap_ctx->ctx = ctx;
830 unmap_ctx->start = start;
831 unmap_ctx->end = end;
832 list_add_tail(&unmap_ctx->list, unmaps);
833
834 return 0;
835 }
836
userfaultfd_unmap_complete(struct mm_struct * mm,struct list_head * uf)837 void userfaultfd_unmap_complete(struct mm_struct *mm, struct list_head *uf)
838 {
839 struct userfaultfd_unmap_ctx *ctx, *n;
840 struct userfaultfd_wait_queue ewq;
841
842 list_for_each_entry_safe(ctx, n, uf, list) {
843 msg_init(&ewq.msg);
844
845 ewq.msg.event = UFFD_EVENT_UNMAP;
846 ewq.msg.arg.remove.start = ctx->start;
847 ewq.msg.arg.remove.end = ctx->end;
848
849 userfaultfd_event_wait_completion(ctx->ctx, &ewq);
850
851 list_del(&ctx->list);
852 kfree(ctx);
853 }
854 }
855
userfaultfd_release(struct inode * inode,struct file * file)856 static int userfaultfd_release(struct inode *inode, struct file *file)
857 {
858 struct userfaultfd_ctx *ctx = file->private_data;
859 struct mm_struct *mm = ctx->mm;
860 /* len == 0 means wake all */
861 struct userfaultfd_wake_range range = { .len = 0, };
862
863 WRITE_ONCE(ctx->released, true);
864
865 userfaultfd_release_all(mm, ctx);
866
867 /*
868 * After no new page faults can wait on this fault_*wqh, flush
869 * the last page faults that may have been already waiting on
870 * the fault_*wqh.
871 */
872 spin_lock_irq(&ctx->fault_pending_wqh.lock);
873 __wake_up_locked_key(&ctx->fault_pending_wqh, TASK_NORMAL, &range);
874 __wake_up(&ctx->fault_wqh, TASK_NORMAL, 1, &range);
875 spin_unlock_irq(&ctx->fault_pending_wqh.lock);
876
877 /* Flush pending events that may still wait on event_wqh */
878 wake_up_all(&ctx->event_wqh);
879
880 wake_up_poll(&ctx->fd_wqh, EPOLLHUP);
881 userfaultfd_ctx_put(ctx);
882 return 0;
883 }
884
885 /* fault_pending_wqh.lock must be hold by the caller */
find_userfault_in(wait_queue_head_t * wqh)886 static inline struct userfaultfd_wait_queue *find_userfault_in(
887 wait_queue_head_t *wqh)
888 {
889 wait_queue_entry_t *wq;
890 struct userfaultfd_wait_queue *uwq;
891
892 lockdep_assert_held(&wqh->lock);
893
894 uwq = NULL;
895 if (!waitqueue_active(wqh))
896 goto out;
897 /* walk in reverse to provide FIFO behavior to read userfaults */
898 wq = list_last_entry(&wqh->head, typeof(*wq), entry);
899 uwq = container_of(wq, struct userfaultfd_wait_queue, wq);
900 out:
901 return uwq;
902 }
903
find_userfault(struct userfaultfd_ctx * ctx)904 static inline struct userfaultfd_wait_queue *find_userfault(
905 struct userfaultfd_ctx *ctx)
906 {
907 return find_userfault_in(&ctx->fault_pending_wqh);
908 }
909
find_userfault_evt(struct userfaultfd_ctx * ctx)910 static inline struct userfaultfd_wait_queue *find_userfault_evt(
911 struct userfaultfd_ctx *ctx)
912 {
913 return find_userfault_in(&ctx->event_wqh);
914 }
915
userfaultfd_poll(struct file * file,poll_table * wait)916 static __poll_t userfaultfd_poll(struct file *file, poll_table *wait)
917 {
918 struct userfaultfd_ctx *ctx = file->private_data;
919 __poll_t ret;
920
921 poll_wait(file, &ctx->fd_wqh, wait);
922
923 if (!userfaultfd_is_initialized(ctx))
924 return EPOLLERR;
925
926 /*
927 * poll() never guarantees that read won't block.
928 * userfaults can be waken before they're read().
929 */
930 if (unlikely(!(file->f_flags & O_NONBLOCK)))
931 return EPOLLERR;
932 /*
933 * lockless access to see if there are pending faults
934 * __pollwait last action is the add_wait_queue but
935 * the spin_unlock would allow the waitqueue_active to
936 * pass above the actual list_add inside
937 * add_wait_queue critical section. So use a full
938 * memory barrier to serialize the list_add write of
939 * add_wait_queue() with the waitqueue_active read
940 * below.
941 */
942 ret = 0;
943 smp_mb();
944 if (waitqueue_active(&ctx->fault_pending_wqh))
945 ret = EPOLLIN;
946 else if (waitqueue_active(&ctx->event_wqh))
947 ret = EPOLLIN;
948
949 return ret;
950 }
951
952 static const struct file_operations userfaultfd_fops;
953
resolve_userfault_fork(struct userfaultfd_ctx * new,struct inode * inode,struct uffd_msg * msg)954 static int resolve_userfault_fork(struct userfaultfd_ctx *new,
955 struct inode *inode,
956 struct uffd_msg *msg)
957 {
958 int fd;
959
960 fd = anon_inode_create_getfd("[userfaultfd]", &userfaultfd_fops, new,
961 O_RDONLY | (new->flags & UFFD_SHARED_FCNTL_FLAGS), inode);
962 if (fd < 0)
963 return fd;
964
965 msg->arg.reserved.reserved1 = 0;
966 msg->arg.fork.ufd = fd;
967 return 0;
968 }
969
userfaultfd_ctx_read(struct userfaultfd_ctx * ctx,int no_wait,struct uffd_msg * msg,struct inode * inode)970 static ssize_t userfaultfd_ctx_read(struct userfaultfd_ctx *ctx, int no_wait,
971 struct uffd_msg *msg, struct inode *inode)
972 {
973 ssize_t ret;
974 DECLARE_WAITQUEUE(wait, current);
975 struct userfaultfd_wait_queue *uwq;
976 /*
977 * Handling fork event requires sleeping operations, so
978 * we drop the event_wqh lock, then do these ops, then
979 * lock it back and wake up the waiter. While the lock is
980 * dropped the ewq may go away so we keep track of it
981 * carefully.
982 */
983 LIST_HEAD(fork_event);
984 struct userfaultfd_ctx *fork_nctx = NULL;
985
986 /* always take the fd_wqh lock before the fault_pending_wqh lock */
987 spin_lock_irq(&ctx->fd_wqh.lock);
988 __add_wait_queue(&ctx->fd_wqh, &wait);
989 for (;;) {
990 set_current_state(TASK_INTERRUPTIBLE);
991 spin_lock(&ctx->fault_pending_wqh.lock);
992 uwq = find_userfault(ctx);
993 if (uwq) {
994 /*
995 * Use a seqcount to repeat the lockless check
996 * in wake_userfault() to avoid missing
997 * wakeups because during the refile both
998 * waitqueue could become empty if this is the
999 * only userfault.
1000 */
1001 write_seqcount_begin(&ctx->refile_seq);
1002
1003 /*
1004 * The fault_pending_wqh.lock prevents the uwq
1005 * to disappear from under us.
1006 *
1007 * Refile this userfault from
1008 * fault_pending_wqh to fault_wqh, it's not
1009 * pending anymore after we read it.
1010 *
1011 * Use list_del() by hand (as
1012 * userfaultfd_wake_function also uses
1013 * list_del_init() by hand) to be sure nobody
1014 * changes __remove_wait_queue() to use
1015 * list_del_init() in turn breaking the
1016 * !list_empty_careful() check in
1017 * handle_userfault(). The uwq->wq.head list
1018 * must never be empty at any time during the
1019 * refile, or the waitqueue could disappear
1020 * from under us. The "wait_queue_head_t"
1021 * parameter of __remove_wait_queue() is unused
1022 * anyway.
1023 */
1024 list_del(&uwq->wq.entry);
1025 add_wait_queue(&ctx->fault_wqh, &uwq->wq);
1026
1027 write_seqcount_end(&ctx->refile_seq);
1028
1029 /* careful to always initialize msg if ret == 0 */
1030 *msg = uwq->msg;
1031 spin_unlock(&ctx->fault_pending_wqh.lock);
1032 ret = 0;
1033 break;
1034 }
1035 spin_unlock(&ctx->fault_pending_wqh.lock);
1036
1037 spin_lock(&ctx->event_wqh.lock);
1038 uwq = find_userfault_evt(ctx);
1039 if (uwq) {
1040 *msg = uwq->msg;
1041
1042 if (uwq->msg.event == UFFD_EVENT_FORK) {
1043 fork_nctx = (struct userfaultfd_ctx *)
1044 (unsigned long)
1045 uwq->msg.arg.reserved.reserved1;
1046 list_move(&uwq->wq.entry, &fork_event);
1047 /*
1048 * fork_nctx can be freed as soon as
1049 * we drop the lock, unless we take a
1050 * reference on it.
1051 */
1052 userfaultfd_ctx_get(fork_nctx);
1053 spin_unlock(&ctx->event_wqh.lock);
1054 ret = 0;
1055 break;
1056 }
1057
1058 userfaultfd_event_complete(ctx, uwq);
1059 spin_unlock(&ctx->event_wqh.lock);
1060 ret = 0;
1061 break;
1062 }
1063 spin_unlock(&ctx->event_wqh.lock);
1064
1065 if (signal_pending(current)) {
1066 ret = -ERESTARTSYS;
1067 break;
1068 }
1069 if (no_wait) {
1070 ret = -EAGAIN;
1071 break;
1072 }
1073 spin_unlock_irq(&ctx->fd_wqh.lock);
1074 schedule();
1075 spin_lock_irq(&ctx->fd_wqh.lock);
1076 }
1077 __remove_wait_queue(&ctx->fd_wqh, &wait);
1078 __set_current_state(TASK_RUNNING);
1079 spin_unlock_irq(&ctx->fd_wqh.lock);
1080
1081 if (!ret && msg->event == UFFD_EVENT_FORK) {
1082 ret = resolve_userfault_fork(fork_nctx, inode, msg);
1083 spin_lock_irq(&ctx->event_wqh.lock);
1084 if (!list_empty(&fork_event)) {
1085 /*
1086 * The fork thread didn't abort, so we can
1087 * drop the temporary refcount.
1088 */
1089 userfaultfd_ctx_put(fork_nctx);
1090
1091 uwq = list_first_entry(&fork_event,
1092 typeof(*uwq),
1093 wq.entry);
1094 /*
1095 * If fork_event list wasn't empty and in turn
1096 * the event wasn't already released by fork
1097 * (the event is allocated on fork kernel
1098 * stack), put the event back to its place in
1099 * the event_wq. fork_event head will be freed
1100 * as soon as we return so the event cannot
1101 * stay queued there no matter the current
1102 * "ret" value.
1103 */
1104 list_del(&uwq->wq.entry);
1105 __add_wait_queue(&ctx->event_wqh, &uwq->wq);
1106
1107 /*
1108 * Leave the event in the waitqueue and report
1109 * error to userland if we failed to resolve
1110 * the userfault fork.
1111 */
1112 if (likely(!ret))
1113 userfaultfd_event_complete(ctx, uwq);
1114 } else {
1115 /*
1116 * Here the fork thread aborted and the
1117 * refcount from the fork thread on fork_nctx
1118 * has already been released. We still hold
1119 * the reference we took before releasing the
1120 * lock above. If resolve_userfault_fork
1121 * failed we've to drop it because the
1122 * fork_nctx has to be freed in such case. If
1123 * it succeeded we'll hold it because the new
1124 * uffd references it.
1125 */
1126 if (ret)
1127 userfaultfd_ctx_put(fork_nctx);
1128 }
1129 spin_unlock_irq(&ctx->event_wqh.lock);
1130 }
1131
1132 return ret;
1133 }
1134
userfaultfd_read_iter(struct kiocb * iocb,struct iov_iter * to)1135 static ssize_t userfaultfd_read_iter(struct kiocb *iocb, struct iov_iter *to)
1136 {
1137 struct file *file = iocb->ki_filp;
1138 struct userfaultfd_ctx *ctx = file->private_data;
1139 ssize_t _ret, ret = 0;
1140 struct uffd_msg msg;
1141 struct inode *inode = file_inode(file);
1142 bool no_wait;
1143
1144 if (!userfaultfd_is_initialized(ctx))
1145 return -EINVAL;
1146
1147 no_wait = file->f_flags & O_NONBLOCK || iocb->ki_flags & IOCB_NOWAIT;
1148 for (;;) {
1149 if (iov_iter_count(to) < sizeof(msg))
1150 return ret ? ret : -EINVAL;
1151 _ret = userfaultfd_ctx_read(ctx, no_wait, &msg, inode);
1152 if (_ret < 0)
1153 return ret ? ret : _ret;
1154 _ret = !copy_to_iter_full(&msg, sizeof(msg), to);
1155 if (_ret)
1156 return ret ? ret : -EFAULT;
1157 ret += sizeof(msg);
1158 /*
1159 * Allow to read more than one fault at time but only
1160 * block if waiting for the very first one.
1161 */
1162 no_wait = true;
1163 }
1164 }
1165
__wake_userfault(struct userfaultfd_ctx * ctx,struct userfaultfd_wake_range * range)1166 static void __wake_userfault(struct userfaultfd_ctx *ctx,
1167 struct userfaultfd_wake_range *range)
1168 {
1169 spin_lock_irq(&ctx->fault_pending_wqh.lock);
1170 /* wake all in the range and autoremove */
1171 if (waitqueue_active(&ctx->fault_pending_wqh))
1172 __wake_up_locked_key(&ctx->fault_pending_wqh, TASK_NORMAL,
1173 range);
1174 if (waitqueue_active(&ctx->fault_wqh))
1175 __wake_up(&ctx->fault_wqh, TASK_NORMAL, 1, range);
1176 spin_unlock_irq(&ctx->fault_pending_wqh.lock);
1177 }
1178
wake_userfault(struct userfaultfd_ctx * ctx,struct userfaultfd_wake_range * range)1179 static __always_inline void wake_userfault(struct userfaultfd_ctx *ctx,
1180 struct userfaultfd_wake_range *range)
1181 {
1182 unsigned seq;
1183 bool need_wakeup;
1184
1185 /*
1186 * To be sure waitqueue_active() is not reordered by the CPU
1187 * before the pagetable update, use an explicit SMP memory
1188 * barrier here. PT lock release or mmap_read_unlock(mm) still
1189 * have release semantics that can allow the
1190 * waitqueue_active() to be reordered before the pte update.
1191 */
1192 smp_mb();
1193
1194 /*
1195 * Use waitqueue_active because it's very frequent to
1196 * change the address space atomically even if there are no
1197 * userfaults yet. So we take the spinlock only when we're
1198 * sure we've userfaults to wake.
1199 */
1200 do {
1201 seq = read_seqcount_begin(&ctx->refile_seq);
1202 need_wakeup = waitqueue_active(&ctx->fault_pending_wqh) ||
1203 waitqueue_active(&ctx->fault_wqh);
1204 cond_resched();
1205 } while (read_seqcount_retry(&ctx->refile_seq, seq));
1206 if (need_wakeup)
1207 __wake_userfault(ctx, range);
1208 }
1209
validate_unaligned_range(struct mm_struct * mm,__u64 start,__u64 len)1210 static __always_inline int validate_unaligned_range(
1211 struct mm_struct *mm, __u64 start, __u64 len)
1212 {
1213 __u64 task_size = mm->task_size;
1214
1215 if (len & ~PAGE_MASK)
1216 return -EINVAL;
1217 if (!len)
1218 return -EINVAL;
1219 if (start < mmap_min_addr)
1220 return -EINVAL;
1221 if (start >= task_size)
1222 return -EINVAL;
1223 if (len > task_size - start)
1224 return -EINVAL;
1225 if (start + len <= start)
1226 return -EINVAL;
1227 return 0;
1228 }
1229
validate_range(struct mm_struct * mm,__u64 start,__u64 len)1230 static __always_inline int validate_range(struct mm_struct *mm,
1231 __u64 start, __u64 len)
1232 {
1233 if (start & ~PAGE_MASK)
1234 return -EINVAL;
1235
1236 return validate_unaligned_range(mm, start, len);
1237 }
1238
userfaultfd_register(struct userfaultfd_ctx * ctx,unsigned long arg)1239 static int userfaultfd_register(struct userfaultfd_ctx *ctx,
1240 unsigned long arg)
1241 {
1242 struct mm_struct *mm = ctx->mm;
1243 struct vm_area_struct *vma, *cur;
1244 int ret;
1245 struct uffdio_register uffdio_register;
1246 struct uffdio_register __user *user_uffdio_register;
1247 unsigned long vm_flags;
1248 bool found;
1249 bool basic_ioctls;
1250 unsigned long start, end;
1251 struct vma_iterator vmi;
1252 bool wp_async = userfaultfd_wp_async_ctx(ctx);
1253
1254 user_uffdio_register = (struct uffdio_register __user *) arg;
1255
1256 ret = -EFAULT;
1257 if (copy_from_user(&uffdio_register, user_uffdio_register,
1258 sizeof(uffdio_register)-sizeof(__u64)))
1259 goto out;
1260
1261 ret = -EINVAL;
1262 if (!uffdio_register.mode)
1263 goto out;
1264 if (uffdio_register.mode & ~UFFD_API_REGISTER_MODES)
1265 goto out;
1266 vm_flags = 0;
1267 if (uffdio_register.mode & UFFDIO_REGISTER_MODE_MISSING)
1268 vm_flags |= VM_UFFD_MISSING;
1269 if (uffdio_register.mode & UFFDIO_REGISTER_MODE_WP) {
1270 #ifndef CONFIG_HAVE_ARCH_USERFAULTFD_WP
1271 goto out;
1272 #endif
1273 vm_flags |= VM_UFFD_WP;
1274 }
1275 if (uffdio_register.mode & UFFDIO_REGISTER_MODE_MINOR) {
1276 #ifndef CONFIG_HAVE_ARCH_USERFAULTFD_MINOR
1277 goto out;
1278 #endif
1279 vm_flags |= VM_UFFD_MINOR;
1280 }
1281
1282 ret = validate_range(mm, uffdio_register.range.start,
1283 uffdio_register.range.len);
1284 if (ret)
1285 goto out;
1286
1287 start = uffdio_register.range.start;
1288 end = start + uffdio_register.range.len;
1289
1290 ret = -ENOMEM;
1291 if (!mmget_not_zero(mm))
1292 goto out;
1293
1294 ret = -EINVAL;
1295 mmap_write_lock(mm);
1296 vma_iter_init(&vmi, mm, start);
1297 vma = vma_find(&vmi, end);
1298 if (!vma)
1299 goto out_unlock;
1300
1301 /*
1302 * If the first vma contains huge pages, make sure start address
1303 * is aligned to huge page size.
1304 */
1305 if (is_vm_hugetlb_page(vma)) {
1306 unsigned long vma_hpagesize = vma_kernel_pagesize(vma);
1307
1308 if (start & (vma_hpagesize - 1))
1309 goto out_unlock;
1310 }
1311
1312 /*
1313 * Search for not compatible vmas.
1314 */
1315 found = false;
1316 basic_ioctls = false;
1317 cur = vma;
1318 do {
1319 cond_resched();
1320
1321 BUG_ON(!!cur->vm_userfaultfd_ctx.ctx ^
1322 !!(cur->vm_flags & __VM_UFFD_FLAGS));
1323
1324 /* check not compatible vmas */
1325 ret = -EINVAL;
1326 if (!vma_can_userfault(cur, vm_flags, wp_async))
1327 goto out_unlock;
1328
1329 /*
1330 * UFFDIO_COPY will fill file holes even without
1331 * PROT_WRITE. This check enforces that if this is a
1332 * MAP_SHARED, the process has write permission to the backing
1333 * file. If VM_MAYWRITE is set it also enforces that on a
1334 * MAP_SHARED vma: there is no F_WRITE_SEAL and no further
1335 * F_WRITE_SEAL can be taken until the vma is destroyed.
1336 */
1337 ret = -EPERM;
1338 if (unlikely(!(cur->vm_flags & VM_MAYWRITE)))
1339 goto out_unlock;
1340
1341 /*
1342 * If this vma contains ending address, and huge pages
1343 * check alignment.
1344 */
1345 if (is_vm_hugetlb_page(cur) && end <= cur->vm_end &&
1346 end > cur->vm_start) {
1347 unsigned long vma_hpagesize = vma_kernel_pagesize(cur);
1348
1349 ret = -EINVAL;
1350
1351 if (end & (vma_hpagesize - 1))
1352 goto out_unlock;
1353 }
1354 if ((vm_flags & VM_UFFD_WP) && !(cur->vm_flags & VM_MAYWRITE))
1355 goto out_unlock;
1356
1357 /*
1358 * Check that this vma isn't already owned by a
1359 * different userfaultfd. We can't allow more than one
1360 * userfaultfd to own a single vma simultaneously or we
1361 * wouldn't know which one to deliver the userfaults to.
1362 */
1363 ret = -EBUSY;
1364 if (cur->vm_userfaultfd_ctx.ctx &&
1365 cur->vm_userfaultfd_ctx.ctx != ctx)
1366 goto out_unlock;
1367
1368 /*
1369 * Note vmas containing huge pages
1370 */
1371 if (is_vm_hugetlb_page(cur))
1372 basic_ioctls = true;
1373
1374 found = true;
1375 } for_each_vma_range(vmi, cur, end);
1376 BUG_ON(!found);
1377
1378 ret = userfaultfd_register_range(ctx, vma, vm_flags, start, end,
1379 wp_async);
1380
1381 out_unlock:
1382 mmap_write_unlock(mm);
1383 mmput(mm);
1384 if (!ret) {
1385 __u64 ioctls_out;
1386
1387 ioctls_out = basic_ioctls ? UFFD_API_RANGE_IOCTLS_BASIC :
1388 UFFD_API_RANGE_IOCTLS;
1389
1390 /*
1391 * Declare the WP ioctl only if the WP mode is
1392 * specified and all checks passed with the range
1393 */
1394 if (!(uffdio_register.mode & UFFDIO_REGISTER_MODE_WP))
1395 ioctls_out &= ~((__u64)1 << _UFFDIO_WRITEPROTECT);
1396
1397 /* CONTINUE ioctl is only supported for MINOR ranges. */
1398 if (!(uffdio_register.mode & UFFDIO_REGISTER_MODE_MINOR))
1399 ioctls_out &= ~((__u64)1 << _UFFDIO_CONTINUE);
1400
1401 /*
1402 * Now that we scanned all vmas we can already tell
1403 * userland which ioctls methods are guaranteed to
1404 * succeed on this range.
1405 */
1406 if (put_user(ioctls_out, &user_uffdio_register->ioctls))
1407 ret = -EFAULT;
1408 }
1409 out:
1410 return ret;
1411 }
1412
userfaultfd_unregister(struct userfaultfd_ctx * ctx,unsigned long arg)1413 static int userfaultfd_unregister(struct userfaultfd_ctx *ctx,
1414 unsigned long arg)
1415 {
1416 struct mm_struct *mm = ctx->mm;
1417 struct vm_area_struct *vma, *prev, *cur;
1418 int ret;
1419 struct uffdio_range uffdio_unregister;
1420 bool found;
1421 unsigned long start, end, vma_end;
1422 const void __user *buf = (void __user *)arg;
1423 struct vma_iterator vmi;
1424 bool wp_async = userfaultfd_wp_async_ctx(ctx);
1425
1426 ret = -EFAULT;
1427 if (copy_from_user(&uffdio_unregister, buf, sizeof(uffdio_unregister)))
1428 goto out;
1429
1430 ret = validate_range(mm, uffdio_unregister.start,
1431 uffdio_unregister.len);
1432 if (ret)
1433 goto out;
1434
1435 start = uffdio_unregister.start;
1436 end = start + uffdio_unregister.len;
1437
1438 ret = -ENOMEM;
1439 if (!mmget_not_zero(mm))
1440 goto out;
1441
1442 mmap_write_lock(mm);
1443 ret = -EINVAL;
1444 vma_iter_init(&vmi, mm, start);
1445 vma = vma_find(&vmi, end);
1446 if (!vma)
1447 goto out_unlock;
1448
1449 /*
1450 * If the first vma contains huge pages, make sure start address
1451 * is aligned to huge page size.
1452 */
1453 if (is_vm_hugetlb_page(vma)) {
1454 unsigned long vma_hpagesize = vma_kernel_pagesize(vma);
1455
1456 if (start & (vma_hpagesize - 1))
1457 goto out_unlock;
1458 }
1459
1460 /*
1461 * Search for not compatible vmas.
1462 */
1463 found = false;
1464 cur = vma;
1465 do {
1466 cond_resched();
1467
1468 BUG_ON(!!cur->vm_userfaultfd_ctx.ctx ^
1469 !!(cur->vm_flags & __VM_UFFD_FLAGS));
1470
1471 /*
1472 * Check not compatible vmas, not strictly required
1473 * here as not compatible vmas cannot have an
1474 * userfaultfd_ctx registered on them, but this
1475 * provides for more strict behavior to notice
1476 * unregistration errors.
1477 */
1478 if (!vma_can_userfault(cur, cur->vm_flags, wp_async))
1479 goto out_unlock;
1480
1481 found = true;
1482 } for_each_vma_range(vmi, cur, end);
1483 BUG_ON(!found);
1484
1485 vma_iter_set(&vmi, start);
1486 prev = vma_prev(&vmi);
1487 if (vma->vm_start < start)
1488 prev = vma;
1489
1490 ret = 0;
1491 for_each_vma_range(vmi, vma, end) {
1492 cond_resched();
1493
1494 BUG_ON(!vma_can_userfault(vma, vma->vm_flags, wp_async));
1495
1496 /*
1497 * Nothing to do: this vma is already registered into this
1498 * userfaultfd and with the right tracking mode too.
1499 */
1500 if (!vma->vm_userfaultfd_ctx.ctx)
1501 goto skip;
1502
1503 WARN_ON(!(vma->vm_flags & VM_MAYWRITE));
1504
1505 if (vma->vm_start > start)
1506 start = vma->vm_start;
1507 vma_end = min(end, vma->vm_end);
1508
1509 if (userfaultfd_missing(vma)) {
1510 /*
1511 * Wake any concurrent pending userfault while
1512 * we unregister, so they will not hang
1513 * permanently and it avoids userland to call
1514 * UFFDIO_WAKE explicitly.
1515 */
1516 struct userfaultfd_wake_range range;
1517 range.start = start;
1518 range.len = vma_end - start;
1519 wake_userfault(vma->vm_userfaultfd_ctx.ctx, &range);
1520 }
1521
1522 vma = userfaultfd_clear_vma(&vmi, prev, vma,
1523 start, vma_end);
1524 if (IS_ERR(vma)) {
1525 ret = PTR_ERR(vma);
1526 break;
1527 }
1528
1529 skip:
1530 prev = vma;
1531 start = vma->vm_end;
1532 }
1533
1534 out_unlock:
1535 mmap_write_unlock(mm);
1536 mmput(mm);
1537 out:
1538 return ret;
1539 }
1540
1541 /*
1542 * userfaultfd_wake may be used in combination with the
1543 * UFFDIO_*_MODE_DONTWAKE to wakeup userfaults in batches.
1544 */
userfaultfd_wake(struct userfaultfd_ctx * ctx,unsigned long arg)1545 static int userfaultfd_wake(struct userfaultfd_ctx *ctx,
1546 unsigned long arg)
1547 {
1548 int ret;
1549 struct uffdio_range uffdio_wake;
1550 struct userfaultfd_wake_range range;
1551 const void __user *buf = (void __user *)arg;
1552
1553 ret = -EFAULT;
1554 if (copy_from_user(&uffdio_wake, buf, sizeof(uffdio_wake)))
1555 goto out;
1556
1557 ret = validate_range(ctx->mm, uffdio_wake.start, uffdio_wake.len);
1558 if (ret)
1559 goto out;
1560
1561 range.start = uffdio_wake.start;
1562 range.len = uffdio_wake.len;
1563
1564 /*
1565 * len == 0 means wake all and we don't want to wake all here,
1566 * so check it again to be sure.
1567 */
1568 VM_BUG_ON(!range.len);
1569
1570 wake_userfault(ctx, &range);
1571 ret = 0;
1572
1573 out:
1574 return ret;
1575 }
1576
userfaultfd_copy(struct userfaultfd_ctx * ctx,unsigned long arg)1577 static int userfaultfd_copy(struct userfaultfd_ctx *ctx,
1578 unsigned long arg)
1579 {
1580 __s64 ret;
1581 struct uffdio_copy uffdio_copy;
1582 struct uffdio_copy __user *user_uffdio_copy;
1583 struct userfaultfd_wake_range range;
1584 uffd_flags_t flags = 0;
1585
1586 user_uffdio_copy = (struct uffdio_copy __user *) arg;
1587
1588 ret = -EAGAIN;
1589 if (atomic_read(&ctx->mmap_changing))
1590 goto out;
1591
1592 ret = -EFAULT;
1593 if (copy_from_user(&uffdio_copy, user_uffdio_copy,
1594 /* don't copy "copy" last field */
1595 sizeof(uffdio_copy)-sizeof(__s64)))
1596 goto out;
1597
1598 ret = validate_unaligned_range(ctx->mm, uffdio_copy.src,
1599 uffdio_copy.len);
1600 if (ret)
1601 goto out;
1602 ret = validate_range(ctx->mm, uffdio_copy.dst, uffdio_copy.len);
1603 if (ret)
1604 goto out;
1605
1606 ret = -EINVAL;
1607 if (uffdio_copy.mode & ~(UFFDIO_COPY_MODE_DONTWAKE|UFFDIO_COPY_MODE_WP))
1608 goto out;
1609 if (uffdio_copy.mode & UFFDIO_COPY_MODE_WP)
1610 flags |= MFILL_ATOMIC_WP;
1611 if (mmget_not_zero(ctx->mm)) {
1612 ret = mfill_atomic_copy(ctx, uffdio_copy.dst, uffdio_copy.src,
1613 uffdio_copy.len, flags);
1614 mmput(ctx->mm);
1615 } else {
1616 return -ESRCH;
1617 }
1618 if (unlikely(put_user(ret, &user_uffdio_copy->copy)))
1619 return -EFAULT;
1620 if (ret < 0)
1621 goto out;
1622 BUG_ON(!ret);
1623 /* len == 0 would wake all */
1624 range.len = ret;
1625 if (!(uffdio_copy.mode & UFFDIO_COPY_MODE_DONTWAKE)) {
1626 range.start = uffdio_copy.dst;
1627 wake_userfault(ctx, &range);
1628 }
1629 ret = range.len == uffdio_copy.len ? 0 : -EAGAIN;
1630 out:
1631 return ret;
1632 }
1633
userfaultfd_zeropage(struct userfaultfd_ctx * ctx,unsigned long arg)1634 static int userfaultfd_zeropage(struct userfaultfd_ctx *ctx,
1635 unsigned long arg)
1636 {
1637 __s64 ret;
1638 struct uffdio_zeropage uffdio_zeropage;
1639 struct uffdio_zeropage __user *user_uffdio_zeropage;
1640 struct userfaultfd_wake_range range;
1641
1642 user_uffdio_zeropage = (struct uffdio_zeropage __user *) arg;
1643
1644 ret = -EAGAIN;
1645 if (atomic_read(&ctx->mmap_changing))
1646 goto out;
1647
1648 ret = -EFAULT;
1649 if (copy_from_user(&uffdio_zeropage, user_uffdio_zeropage,
1650 /* don't copy "zeropage" last field */
1651 sizeof(uffdio_zeropage)-sizeof(__s64)))
1652 goto out;
1653
1654 ret = validate_range(ctx->mm, uffdio_zeropage.range.start,
1655 uffdio_zeropage.range.len);
1656 if (ret)
1657 goto out;
1658 ret = -EINVAL;
1659 if (uffdio_zeropage.mode & ~UFFDIO_ZEROPAGE_MODE_DONTWAKE)
1660 goto out;
1661
1662 if (mmget_not_zero(ctx->mm)) {
1663 ret = mfill_atomic_zeropage(ctx, uffdio_zeropage.range.start,
1664 uffdio_zeropage.range.len);
1665 mmput(ctx->mm);
1666 } else {
1667 return -ESRCH;
1668 }
1669 if (unlikely(put_user(ret, &user_uffdio_zeropage->zeropage)))
1670 return -EFAULT;
1671 if (ret < 0)
1672 goto out;
1673 /* len == 0 would wake all */
1674 BUG_ON(!ret);
1675 range.len = ret;
1676 if (!(uffdio_zeropage.mode & UFFDIO_ZEROPAGE_MODE_DONTWAKE)) {
1677 range.start = uffdio_zeropage.range.start;
1678 wake_userfault(ctx, &range);
1679 }
1680 ret = range.len == uffdio_zeropage.range.len ? 0 : -EAGAIN;
1681 out:
1682 return ret;
1683 }
1684
userfaultfd_writeprotect(struct userfaultfd_ctx * ctx,unsigned long arg)1685 static int userfaultfd_writeprotect(struct userfaultfd_ctx *ctx,
1686 unsigned long arg)
1687 {
1688 int ret;
1689 struct uffdio_writeprotect uffdio_wp;
1690 struct uffdio_writeprotect __user *user_uffdio_wp;
1691 struct userfaultfd_wake_range range;
1692 bool mode_wp, mode_dontwake;
1693
1694 if (atomic_read(&ctx->mmap_changing))
1695 return -EAGAIN;
1696
1697 user_uffdio_wp = (struct uffdio_writeprotect __user *) arg;
1698
1699 if (copy_from_user(&uffdio_wp, user_uffdio_wp,
1700 sizeof(struct uffdio_writeprotect)))
1701 return -EFAULT;
1702
1703 ret = validate_range(ctx->mm, uffdio_wp.range.start,
1704 uffdio_wp.range.len);
1705 if (ret)
1706 return ret;
1707
1708 if (uffdio_wp.mode & ~(UFFDIO_WRITEPROTECT_MODE_DONTWAKE |
1709 UFFDIO_WRITEPROTECT_MODE_WP))
1710 return -EINVAL;
1711
1712 mode_wp = uffdio_wp.mode & UFFDIO_WRITEPROTECT_MODE_WP;
1713 mode_dontwake = uffdio_wp.mode & UFFDIO_WRITEPROTECT_MODE_DONTWAKE;
1714
1715 if (mode_wp && mode_dontwake)
1716 return -EINVAL;
1717
1718 if (mmget_not_zero(ctx->mm)) {
1719 ret = mwriteprotect_range(ctx, uffdio_wp.range.start,
1720 uffdio_wp.range.len, mode_wp);
1721 mmput(ctx->mm);
1722 } else {
1723 return -ESRCH;
1724 }
1725
1726 if (ret)
1727 return ret;
1728
1729 if (!mode_wp && !mode_dontwake) {
1730 range.start = uffdio_wp.range.start;
1731 range.len = uffdio_wp.range.len;
1732 wake_userfault(ctx, &range);
1733 }
1734 return ret;
1735 }
1736
userfaultfd_continue(struct userfaultfd_ctx * ctx,unsigned long arg)1737 static int userfaultfd_continue(struct userfaultfd_ctx *ctx, unsigned long arg)
1738 {
1739 __s64 ret;
1740 struct uffdio_continue uffdio_continue;
1741 struct uffdio_continue __user *user_uffdio_continue;
1742 struct userfaultfd_wake_range range;
1743 uffd_flags_t flags = 0;
1744
1745 user_uffdio_continue = (struct uffdio_continue __user *)arg;
1746
1747 ret = -EAGAIN;
1748 if (atomic_read(&ctx->mmap_changing))
1749 goto out;
1750
1751 ret = -EFAULT;
1752 if (copy_from_user(&uffdio_continue, user_uffdio_continue,
1753 /* don't copy the output fields */
1754 sizeof(uffdio_continue) - (sizeof(__s64))))
1755 goto out;
1756
1757 ret = validate_range(ctx->mm, uffdio_continue.range.start,
1758 uffdio_continue.range.len);
1759 if (ret)
1760 goto out;
1761
1762 ret = -EINVAL;
1763 if (uffdio_continue.mode & ~(UFFDIO_CONTINUE_MODE_DONTWAKE |
1764 UFFDIO_CONTINUE_MODE_WP))
1765 goto out;
1766 if (uffdio_continue.mode & UFFDIO_CONTINUE_MODE_WP)
1767 flags |= MFILL_ATOMIC_WP;
1768
1769 if (mmget_not_zero(ctx->mm)) {
1770 ret = mfill_atomic_continue(ctx, uffdio_continue.range.start,
1771 uffdio_continue.range.len, flags);
1772 mmput(ctx->mm);
1773 } else {
1774 return -ESRCH;
1775 }
1776
1777 if (unlikely(put_user(ret, &user_uffdio_continue->mapped)))
1778 return -EFAULT;
1779 if (ret < 0)
1780 goto out;
1781
1782 /* len == 0 would wake all */
1783 BUG_ON(!ret);
1784 range.len = ret;
1785 if (!(uffdio_continue.mode & UFFDIO_CONTINUE_MODE_DONTWAKE)) {
1786 range.start = uffdio_continue.range.start;
1787 wake_userfault(ctx, &range);
1788 }
1789 ret = range.len == uffdio_continue.range.len ? 0 : -EAGAIN;
1790
1791 out:
1792 return ret;
1793 }
1794
userfaultfd_poison(struct userfaultfd_ctx * ctx,unsigned long arg)1795 static inline int userfaultfd_poison(struct userfaultfd_ctx *ctx, unsigned long arg)
1796 {
1797 __s64 ret;
1798 struct uffdio_poison uffdio_poison;
1799 struct uffdio_poison __user *user_uffdio_poison;
1800 struct userfaultfd_wake_range range;
1801
1802 user_uffdio_poison = (struct uffdio_poison __user *)arg;
1803
1804 ret = -EAGAIN;
1805 if (atomic_read(&ctx->mmap_changing))
1806 goto out;
1807
1808 ret = -EFAULT;
1809 if (copy_from_user(&uffdio_poison, user_uffdio_poison,
1810 /* don't copy the output fields */
1811 sizeof(uffdio_poison) - (sizeof(__s64))))
1812 goto out;
1813
1814 ret = validate_range(ctx->mm, uffdio_poison.range.start,
1815 uffdio_poison.range.len);
1816 if (ret)
1817 goto out;
1818
1819 ret = -EINVAL;
1820 if (uffdio_poison.mode & ~UFFDIO_POISON_MODE_DONTWAKE)
1821 goto out;
1822
1823 if (mmget_not_zero(ctx->mm)) {
1824 ret = mfill_atomic_poison(ctx, uffdio_poison.range.start,
1825 uffdio_poison.range.len, 0);
1826 mmput(ctx->mm);
1827 } else {
1828 return -ESRCH;
1829 }
1830
1831 if (unlikely(put_user(ret, &user_uffdio_poison->updated)))
1832 return -EFAULT;
1833 if (ret < 0)
1834 goto out;
1835
1836 /* len == 0 would wake all */
1837 BUG_ON(!ret);
1838 range.len = ret;
1839 if (!(uffdio_poison.mode & UFFDIO_POISON_MODE_DONTWAKE)) {
1840 range.start = uffdio_poison.range.start;
1841 wake_userfault(ctx, &range);
1842 }
1843 ret = range.len == uffdio_poison.range.len ? 0 : -EAGAIN;
1844
1845 out:
1846 return ret;
1847 }
1848
userfaultfd_wp_async(struct vm_area_struct * vma)1849 bool userfaultfd_wp_async(struct vm_area_struct *vma)
1850 {
1851 return userfaultfd_wp_async_ctx(vma->vm_userfaultfd_ctx.ctx);
1852 }
1853
uffd_ctx_features(__u64 user_features)1854 static inline unsigned int uffd_ctx_features(__u64 user_features)
1855 {
1856 /*
1857 * For the current set of features the bits just coincide. Set
1858 * UFFD_FEATURE_INITIALIZED to mark the features as enabled.
1859 */
1860 return (unsigned int)user_features | UFFD_FEATURE_INITIALIZED;
1861 }
1862
userfaultfd_move(struct userfaultfd_ctx * ctx,unsigned long arg)1863 static int userfaultfd_move(struct userfaultfd_ctx *ctx,
1864 unsigned long arg)
1865 {
1866 __s64 ret;
1867 struct uffdio_move uffdio_move;
1868 struct uffdio_move __user *user_uffdio_move;
1869 struct userfaultfd_wake_range range;
1870 struct mm_struct *mm = ctx->mm;
1871
1872 user_uffdio_move = (struct uffdio_move __user *) arg;
1873
1874 if (atomic_read(&ctx->mmap_changing))
1875 return -EAGAIN;
1876
1877 if (copy_from_user(&uffdio_move, user_uffdio_move,
1878 /* don't copy "move" last field */
1879 sizeof(uffdio_move)-sizeof(__s64)))
1880 return -EFAULT;
1881
1882 /* Do not allow cross-mm moves. */
1883 if (mm != current->mm)
1884 return -EINVAL;
1885
1886 ret = validate_range(mm, uffdio_move.dst, uffdio_move.len);
1887 if (ret)
1888 return ret;
1889
1890 ret = validate_range(mm, uffdio_move.src, uffdio_move.len);
1891 if (ret)
1892 return ret;
1893
1894 if (uffdio_move.mode & ~(UFFDIO_MOVE_MODE_ALLOW_SRC_HOLES|
1895 UFFDIO_MOVE_MODE_DONTWAKE))
1896 return -EINVAL;
1897
1898 if (mmget_not_zero(mm)) {
1899 ret = move_pages(ctx, uffdio_move.dst, uffdio_move.src,
1900 uffdio_move.len, uffdio_move.mode);
1901 mmput(mm);
1902 } else {
1903 return -ESRCH;
1904 }
1905
1906 if (unlikely(put_user(ret, &user_uffdio_move->move)))
1907 return -EFAULT;
1908 if (ret < 0)
1909 goto out;
1910
1911 /* len == 0 would wake all */
1912 VM_WARN_ON(!ret);
1913 range.len = ret;
1914 if (!(uffdio_move.mode & UFFDIO_MOVE_MODE_DONTWAKE)) {
1915 range.start = uffdio_move.dst;
1916 wake_userfault(ctx, &range);
1917 }
1918 ret = range.len == uffdio_move.len ? 0 : -EAGAIN;
1919
1920 out:
1921 return ret;
1922 }
1923
1924 /*
1925 * userland asks for a certain API version and we return which bits
1926 * and ioctl commands are implemented in this kernel for such API
1927 * version or -EINVAL if unknown.
1928 */
userfaultfd_api(struct userfaultfd_ctx * ctx,unsigned long arg)1929 static int userfaultfd_api(struct userfaultfd_ctx *ctx,
1930 unsigned long arg)
1931 {
1932 struct uffdio_api uffdio_api;
1933 void __user *buf = (void __user *)arg;
1934 unsigned int ctx_features;
1935 int ret;
1936 __u64 features;
1937
1938 ret = -EFAULT;
1939 if (copy_from_user(&uffdio_api, buf, sizeof(uffdio_api)))
1940 goto out;
1941 features = uffdio_api.features;
1942 ret = -EINVAL;
1943 if (uffdio_api.api != UFFD_API)
1944 goto err_out;
1945 ret = -EPERM;
1946 if ((features & UFFD_FEATURE_EVENT_FORK) && !capable(CAP_SYS_PTRACE))
1947 goto err_out;
1948
1949 /* WP_ASYNC relies on WP_UNPOPULATED, choose it unconditionally */
1950 if (features & UFFD_FEATURE_WP_ASYNC)
1951 features |= UFFD_FEATURE_WP_UNPOPULATED;
1952
1953 /* report all available features and ioctls to userland */
1954 uffdio_api.features = UFFD_API_FEATURES;
1955 #ifndef CONFIG_HAVE_ARCH_USERFAULTFD_MINOR
1956 uffdio_api.features &=
1957 ~(UFFD_FEATURE_MINOR_HUGETLBFS | UFFD_FEATURE_MINOR_SHMEM);
1958 #endif
1959 #ifndef CONFIG_HAVE_ARCH_USERFAULTFD_WP
1960 uffdio_api.features &= ~UFFD_FEATURE_PAGEFAULT_FLAG_WP;
1961 #endif
1962 #ifndef CONFIG_PTE_MARKER_UFFD_WP
1963 uffdio_api.features &= ~UFFD_FEATURE_WP_HUGETLBFS_SHMEM;
1964 uffdio_api.features &= ~UFFD_FEATURE_WP_UNPOPULATED;
1965 uffdio_api.features &= ~UFFD_FEATURE_WP_ASYNC;
1966 #endif
1967
1968 ret = -EINVAL;
1969 if (features & ~uffdio_api.features)
1970 goto err_out;
1971
1972 uffdio_api.ioctls = UFFD_API_IOCTLS;
1973 ret = -EFAULT;
1974 if (copy_to_user(buf, &uffdio_api, sizeof(uffdio_api)))
1975 goto out;
1976
1977 /* only enable the requested features for this uffd context */
1978 ctx_features = uffd_ctx_features(features);
1979 ret = -EINVAL;
1980 if (cmpxchg(&ctx->features, 0, ctx_features) != 0)
1981 goto err_out;
1982
1983 ret = 0;
1984 out:
1985 return ret;
1986 err_out:
1987 memset(&uffdio_api, 0, sizeof(uffdio_api));
1988 if (copy_to_user(buf, &uffdio_api, sizeof(uffdio_api)))
1989 ret = -EFAULT;
1990 goto out;
1991 }
1992
userfaultfd_ioctl(struct file * file,unsigned cmd,unsigned long arg)1993 static long userfaultfd_ioctl(struct file *file, unsigned cmd,
1994 unsigned long arg)
1995 {
1996 int ret = -EINVAL;
1997 struct userfaultfd_ctx *ctx = file->private_data;
1998
1999 if (cmd != UFFDIO_API && !userfaultfd_is_initialized(ctx))
2000 return -EINVAL;
2001
2002 switch(cmd) {
2003 case UFFDIO_API:
2004 ret = userfaultfd_api(ctx, arg);
2005 break;
2006 case UFFDIO_REGISTER:
2007 ret = userfaultfd_register(ctx, arg);
2008 break;
2009 case UFFDIO_UNREGISTER:
2010 ret = userfaultfd_unregister(ctx, arg);
2011 break;
2012 case UFFDIO_WAKE:
2013 ret = userfaultfd_wake(ctx, arg);
2014 break;
2015 case UFFDIO_COPY:
2016 ret = userfaultfd_copy(ctx, arg);
2017 break;
2018 case UFFDIO_ZEROPAGE:
2019 ret = userfaultfd_zeropage(ctx, arg);
2020 break;
2021 case UFFDIO_MOVE:
2022 ret = userfaultfd_move(ctx, arg);
2023 break;
2024 case UFFDIO_WRITEPROTECT:
2025 ret = userfaultfd_writeprotect(ctx, arg);
2026 break;
2027 case UFFDIO_CONTINUE:
2028 ret = userfaultfd_continue(ctx, arg);
2029 break;
2030 case UFFDIO_POISON:
2031 ret = userfaultfd_poison(ctx, arg);
2032 break;
2033 }
2034 return ret;
2035 }
2036
2037 #ifdef CONFIG_PROC_FS
userfaultfd_show_fdinfo(struct seq_file * m,struct file * f)2038 static void userfaultfd_show_fdinfo(struct seq_file *m, struct file *f)
2039 {
2040 struct userfaultfd_ctx *ctx = f->private_data;
2041 wait_queue_entry_t *wq;
2042 unsigned long pending = 0, total = 0;
2043
2044 spin_lock_irq(&ctx->fault_pending_wqh.lock);
2045 list_for_each_entry(wq, &ctx->fault_pending_wqh.head, entry) {
2046 pending++;
2047 total++;
2048 }
2049 list_for_each_entry(wq, &ctx->fault_wqh.head, entry) {
2050 total++;
2051 }
2052 spin_unlock_irq(&ctx->fault_pending_wqh.lock);
2053
2054 /*
2055 * If more protocols will be added, there will be all shown
2056 * separated by a space. Like this:
2057 * protocols: aa:... bb:...
2058 */
2059 seq_printf(m, "pending:\t%lu\ntotal:\t%lu\nAPI:\t%Lx:%x:%Lx\n",
2060 pending, total, UFFD_API, ctx->features,
2061 UFFD_API_IOCTLS|UFFD_API_RANGE_IOCTLS);
2062 }
2063 #endif
2064
2065 static const struct file_operations userfaultfd_fops = {
2066 #ifdef CONFIG_PROC_FS
2067 .show_fdinfo = userfaultfd_show_fdinfo,
2068 #endif
2069 .release = userfaultfd_release,
2070 .poll = userfaultfd_poll,
2071 .read_iter = userfaultfd_read_iter,
2072 .unlocked_ioctl = userfaultfd_ioctl,
2073 .compat_ioctl = compat_ptr_ioctl,
2074 .llseek = noop_llseek,
2075 };
2076
init_once_userfaultfd_ctx(void * mem)2077 static void init_once_userfaultfd_ctx(void *mem)
2078 {
2079 struct userfaultfd_ctx *ctx = (struct userfaultfd_ctx *) mem;
2080
2081 init_waitqueue_head(&ctx->fault_pending_wqh);
2082 init_waitqueue_head(&ctx->fault_wqh);
2083 init_waitqueue_head(&ctx->event_wqh);
2084 init_waitqueue_head(&ctx->fd_wqh);
2085 seqcount_spinlock_init(&ctx->refile_seq, &ctx->fault_pending_wqh.lock);
2086 }
2087
new_userfaultfd(int flags)2088 static int new_userfaultfd(int flags)
2089 {
2090 struct userfaultfd_ctx *ctx;
2091 struct file *file;
2092 int fd;
2093
2094 BUG_ON(!current->mm);
2095
2096 /* Check the UFFD_* constants for consistency. */
2097 BUILD_BUG_ON(UFFD_USER_MODE_ONLY & UFFD_SHARED_FCNTL_FLAGS);
2098 BUILD_BUG_ON(UFFD_CLOEXEC != O_CLOEXEC);
2099 BUILD_BUG_ON(UFFD_NONBLOCK != O_NONBLOCK);
2100
2101 if (flags & ~(UFFD_SHARED_FCNTL_FLAGS | UFFD_USER_MODE_ONLY))
2102 return -EINVAL;
2103
2104 ctx = kmem_cache_alloc(userfaultfd_ctx_cachep, GFP_KERNEL);
2105 if (!ctx)
2106 return -ENOMEM;
2107
2108 refcount_set(&ctx->refcount, 1);
2109 ctx->flags = flags;
2110 ctx->features = 0;
2111 ctx->released = false;
2112 init_rwsem(&ctx->map_changing_lock);
2113 atomic_set(&ctx->mmap_changing, 0);
2114 ctx->mm = current->mm;
2115
2116 fd = get_unused_fd_flags(flags & UFFD_SHARED_FCNTL_FLAGS);
2117 if (fd < 0)
2118 goto err_out;
2119
2120 /* Create a new inode so that the LSM can block the creation. */
2121 file = anon_inode_create_getfile("[userfaultfd]", &userfaultfd_fops, ctx,
2122 O_RDONLY | (flags & UFFD_SHARED_FCNTL_FLAGS), NULL);
2123 if (IS_ERR(file)) {
2124 put_unused_fd(fd);
2125 fd = PTR_ERR(file);
2126 goto err_out;
2127 }
2128 /* prevent the mm struct to be freed */
2129 mmgrab(ctx->mm);
2130 file->f_mode |= FMODE_NOWAIT;
2131 fd_install(fd, file);
2132 return fd;
2133 err_out:
2134 kmem_cache_free(userfaultfd_ctx_cachep, ctx);
2135 return fd;
2136 }
2137
userfaultfd_syscall_allowed(int flags)2138 static inline bool userfaultfd_syscall_allowed(int flags)
2139 {
2140 /* Userspace-only page faults are always allowed */
2141 if (flags & UFFD_USER_MODE_ONLY)
2142 return true;
2143
2144 /*
2145 * The user is requesting a userfaultfd which can handle kernel faults.
2146 * Privileged users are always allowed to do this.
2147 */
2148 if (capable(CAP_SYS_PTRACE))
2149 return true;
2150
2151 /* Otherwise, access to kernel fault handling is sysctl controlled. */
2152 return sysctl_unprivileged_userfaultfd;
2153 }
2154
SYSCALL_DEFINE1(userfaultfd,int,flags)2155 SYSCALL_DEFINE1(userfaultfd, int, flags)
2156 {
2157 if (!userfaultfd_syscall_allowed(flags))
2158 return -EPERM;
2159
2160 return new_userfaultfd(flags);
2161 }
2162
userfaultfd_dev_ioctl(struct file * file,unsigned int cmd,unsigned long flags)2163 static long userfaultfd_dev_ioctl(struct file *file, unsigned int cmd, unsigned long flags)
2164 {
2165 if (cmd != USERFAULTFD_IOC_NEW)
2166 return -EINVAL;
2167
2168 return new_userfaultfd(flags);
2169 }
2170
2171 static const struct file_operations userfaultfd_dev_fops = {
2172 .unlocked_ioctl = userfaultfd_dev_ioctl,
2173 .compat_ioctl = userfaultfd_dev_ioctl,
2174 .owner = THIS_MODULE,
2175 .llseek = noop_llseek,
2176 };
2177
2178 static struct miscdevice userfaultfd_misc = {
2179 .minor = MISC_DYNAMIC_MINOR,
2180 .name = "userfaultfd",
2181 .fops = &userfaultfd_dev_fops
2182 };
2183
userfaultfd_init(void)2184 static int __init userfaultfd_init(void)
2185 {
2186 int ret;
2187
2188 ret = misc_register(&userfaultfd_misc);
2189 if (ret)
2190 return ret;
2191
2192 userfaultfd_ctx_cachep = kmem_cache_create("userfaultfd_ctx_cache",
2193 sizeof(struct userfaultfd_ctx),
2194 0,
2195 SLAB_HWCACHE_ALIGN|SLAB_PANIC,
2196 init_once_userfaultfd_ctx);
2197 #ifdef CONFIG_SYSCTL
2198 register_sysctl_init("vm", vm_userfaultfd_table);
2199 #endif
2200 return 0;
2201 }
2202 __initcall(userfaultfd_init);
2203