2d8c2d848668076111daf445098fdf182aa6c9e6
[sfrench/cifs-2.6.git] / fs / userfaultfd.c
1 /*
2  *  fs/userfaultfd.c
3  *
4  *  Copyright (C) 2007  Davide Libenzi <davidel@xmailserver.org>
5  *  Copyright (C) 2008-2009 Red Hat, Inc.
6  *  Copyright (C) 2015  Red Hat, Inc.
7  *
8  *  This work is licensed under the terms of the GNU GPL, version 2. See
9  *  the COPYING file in the top-level directory.
10  *
11  *  Some part derived from fs/eventfd.c (anon inode setup) and
12  *  mm/ksm.c (mm hashing).
13  */
14
15 #include <linux/list.h>
16 #include <linux/hashtable.h>
17 #include <linux/sched/signal.h>
18 #include <linux/sched/mm.h>
19 #include <linux/mm.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
33 static struct kmem_cache *userfaultfd_ctx_cachep __read_mostly;
34
35 enum userfaultfd_state {
36         UFFD_STATE_WAIT_API,
37         UFFD_STATE_RUNNING,
38 };
39
40 /*
41  * Start with fault_pending_wqh and fault_wqh so they're more likely
42  * to be in the same cacheline.
43  */
44 struct userfaultfd_ctx {
45         /* waitqueue head for the pending (i.e. not read) userfaults */
46         wait_queue_head_t fault_pending_wqh;
47         /* waitqueue head for the userfaults */
48         wait_queue_head_t fault_wqh;
49         /* waitqueue head for the pseudo fd to wakeup poll/read */
50         wait_queue_head_t fd_wqh;
51         /* waitqueue head for events */
52         wait_queue_head_t event_wqh;
53         /* a refile sequence protected by fault_pending_wqh lock */
54         struct seqcount refile_seq;
55         /* pseudo fd refcounting */
56         atomic_t refcount;
57         /* userfaultfd syscall flags */
58         unsigned int flags;
59         /* features requested from the userspace */
60         unsigned int features;
61         /* state machine */
62         enum userfaultfd_state state;
63         /* released */
64         bool released;
65         /* mm with one ore more vmas attached to this userfaultfd_ctx */
66         struct mm_struct *mm;
67 };
68
69 struct userfaultfd_fork_ctx {
70         struct userfaultfd_ctx *orig;
71         struct userfaultfd_ctx *new;
72         struct list_head list;
73 };
74
75 struct userfaultfd_unmap_ctx {
76         struct userfaultfd_ctx *ctx;
77         unsigned long start;
78         unsigned long end;
79         struct list_head list;
80 };
81
82 struct userfaultfd_wait_queue {
83         struct uffd_msg msg;
84         wait_queue_entry_t wq;
85         struct userfaultfd_ctx *ctx;
86         bool waken;
87 };
88
89 struct userfaultfd_wake_range {
90         unsigned long start;
91         unsigned long len;
92 };
93
94 static int userfaultfd_wake_function(wait_queue_entry_t *wq, unsigned mode,
95                                      int wake_flags, void *key)
96 {
97         struct userfaultfd_wake_range *range = key;
98         int ret;
99         struct userfaultfd_wait_queue *uwq;
100         unsigned long start, len;
101
102         uwq = container_of(wq, struct userfaultfd_wait_queue, wq);
103         ret = 0;
104         /* len == 0 means wake all */
105         start = range->start;
106         len = range->len;
107         if (len && (start > uwq->msg.arg.pagefault.address ||
108                     start + len <= uwq->msg.arg.pagefault.address))
109                 goto out;
110         WRITE_ONCE(uwq->waken, true);
111         /*
112          * The implicit smp_mb__before_spinlock in try_to_wake_up()
113          * renders uwq->waken visible to other CPUs before the task is
114          * waken.
115          */
116         ret = wake_up_state(wq->private, mode);
117         if (ret)
118                 /*
119                  * Wake only once, autoremove behavior.
120                  *
121                  * After the effect of list_del_init is visible to the
122                  * other CPUs, the waitqueue may disappear from under
123                  * us, see the !list_empty_careful() in
124                  * handle_userfault(). try_to_wake_up() has an
125                  * implicit smp_mb__before_spinlock, and the
126                  * wq->private is read before calling the extern
127                  * function "wake_up_state" (which in turns calls
128                  * try_to_wake_up). While the spin_lock;spin_unlock;
129                  * wouldn't be enough, the smp_mb__before_spinlock is
130                  * enough to avoid an explicit smp_mb() here.
131                  */
132                 list_del_init(&wq->entry);
133 out:
134         return ret;
135 }
136
137 /**
138  * userfaultfd_ctx_get - Acquires a reference to the internal userfaultfd
139  * context.
140  * @ctx: [in] Pointer to the userfaultfd context.
141  */
142 static void userfaultfd_ctx_get(struct userfaultfd_ctx *ctx)
143 {
144         if (!atomic_inc_not_zero(&ctx->refcount))
145                 BUG();
146 }
147
148 /**
149  * userfaultfd_ctx_put - Releases a reference to the internal userfaultfd
150  * context.
151  * @ctx: [in] Pointer to userfaultfd context.
152  *
153  * The userfaultfd context reference must have been previously acquired either
154  * with userfaultfd_ctx_get() or userfaultfd_ctx_fdget().
155  */
156 static void userfaultfd_ctx_put(struct userfaultfd_ctx *ctx)
157 {
158         if (atomic_dec_and_test(&ctx->refcount)) {
159                 VM_BUG_ON(spin_is_locked(&ctx->fault_pending_wqh.lock));
160                 VM_BUG_ON(waitqueue_active(&ctx->fault_pending_wqh));
161                 VM_BUG_ON(spin_is_locked(&ctx->fault_wqh.lock));
162                 VM_BUG_ON(waitqueue_active(&ctx->fault_wqh));
163                 VM_BUG_ON(spin_is_locked(&ctx->event_wqh.lock));
164                 VM_BUG_ON(waitqueue_active(&ctx->event_wqh));
165                 VM_BUG_ON(spin_is_locked(&ctx->fd_wqh.lock));
166                 VM_BUG_ON(waitqueue_active(&ctx->fd_wqh));
167                 mmdrop(ctx->mm);
168                 kmem_cache_free(userfaultfd_ctx_cachep, ctx);
169         }
170 }
171
172 static inline void msg_init(struct uffd_msg *msg)
173 {
174         BUILD_BUG_ON(sizeof(struct uffd_msg) != 32);
175         /*
176          * Must use memset to zero out the paddings or kernel data is
177          * leaked to userland.
178          */
179         memset(msg, 0, sizeof(struct uffd_msg));
180 }
181
182 static inline struct uffd_msg userfault_msg(unsigned long address,
183                                             unsigned int flags,
184                                             unsigned long reason)
185 {
186         struct uffd_msg msg;
187         msg_init(&msg);
188         msg.event = UFFD_EVENT_PAGEFAULT;
189         msg.arg.pagefault.address = address;
190         if (flags & FAULT_FLAG_WRITE)
191                 /*
192                  * If UFFD_FEATURE_PAGEFAULT_FLAG_WP was set in the
193                  * uffdio_api.features and UFFD_PAGEFAULT_FLAG_WRITE
194                  * was not set in a UFFD_EVENT_PAGEFAULT, it means it
195                  * was a read fault, otherwise if set it means it's
196                  * a write fault.
197                  */
198                 msg.arg.pagefault.flags |= UFFD_PAGEFAULT_FLAG_WRITE;
199         if (reason & VM_UFFD_WP)
200                 /*
201                  * If UFFD_FEATURE_PAGEFAULT_FLAG_WP was set in the
202                  * uffdio_api.features and UFFD_PAGEFAULT_FLAG_WP was
203                  * not set in a UFFD_EVENT_PAGEFAULT, it means it was
204                  * a missing fault, otherwise if set it means it's a
205                  * write protect fault.
206                  */
207                 msg.arg.pagefault.flags |= UFFD_PAGEFAULT_FLAG_WP;
208         return msg;
209 }
210
211 #ifdef CONFIG_HUGETLB_PAGE
212 /*
213  * Same functionality as userfaultfd_must_wait below with modifications for
214  * hugepmd ranges.
215  */
216 static inline bool userfaultfd_huge_must_wait(struct userfaultfd_ctx *ctx,
217                                          struct vm_area_struct *vma,
218                                          unsigned long address,
219                                          unsigned long flags,
220                                          unsigned long reason)
221 {
222         struct mm_struct *mm = ctx->mm;
223         pte_t *pte;
224         bool ret = true;
225
226         VM_BUG_ON(!rwsem_is_locked(&mm->mmap_sem));
227
228         pte = huge_pte_offset(mm, address, vma_mmu_pagesize(vma));
229         if (!pte)
230                 goto out;
231
232         ret = false;
233
234         /*
235          * Lockless access: we're in a wait_event so it's ok if it
236          * changes under us.
237          */
238         if (huge_pte_none(*pte))
239                 ret = true;
240         if (!huge_pte_write(*pte) && (reason & VM_UFFD_WP))
241                 ret = true;
242 out:
243         return ret;
244 }
245 #else
246 static inline bool userfaultfd_huge_must_wait(struct userfaultfd_ctx *ctx,
247                                          struct vm_area_struct *vma,
248                                          unsigned long address,
249                                          unsigned long flags,
250                                          unsigned long reason)
251 {
252         return false;   /* should never get here */
253 }
254 #endif /* CONFIG_HUGETLB_PAGE */
255
256 /*
257  * Verify the pagetables are still not ok after having reigstered into
258  * the fault_pending_wqh to avoid userland having to UFFDIO_WAKE any
259  * userfault that has already been resolved, if userfaultfd_read and
260  * UFFDIO_COPY|ZEROPAGE are being run simultaneously on two different
261  * threads.
262  */
263 static inline bool userfaultfd_must_wait(struct userfaultfd_ctx *ctx,
264                                          unsigned long address,
265                                          unsigned long flags,
266                                          unsigned long reason)
267 {
268         struct mm_struct *mm = ctx->mm;
269         pgd_t *pgd;
270         p4d_t *p4d;
271         pud_t *pud;
272         pmd_t *pmd, _pmd;
273         pte_t *pte;
274         bool ret = true;
275
276         VM_BUG_ON(!rwsem_is_locked(&mm->mmap_sem));
277
278         pgd = pgd_offset(mm, address);
279         if (!pgd_present(*pgd))
280                 goto out;
281         p4d = p4d_offset(pgd, address);
282         if (!p4d_present(*p4d))
283                 goto out;
284         pud = pud_offset(p4d, address);
285         if (!pud_present(*pud))
286                 goto out;
287         pmd = pmd_offset(pud, address);
288         /*
289          * READ_ONCE must function as a barrier with narrower scope
290          * and it must be equivalent to:
291          *      _pmd = *pmd; barrier();
292          *
293          * This is to deal with the instability (as in
294          * pmd_trans_unstable) of the pmd.
295          */
296         _pmd = READ_ONCE(*pmd);
297         if (!pmd_present(_pmd))
298                 goto out;
299
300         ret = false;
301         if (pmd_trans_huge(_pmd))
302                 goto out;
303
304         /*
305          * the pmd is stable (as in !pmd_trans_unstable) so we can re-read it
306          * and use the standard pte_offset_map() instead of parsing _pmd.
307          */
308         pte = pte_offset_map(pmd, address);
309         /*
310          * Lockless access: we're in a wait_event so it's ok if it
311          * changes under us.
312          */
313         if (pte_none(*pte))
314                 ret = true;
315         pte_unmap(pte);
316
317 out:
318         return ret;
319 }
320
321 /*
322  * The locking rules involved in returning VM_FAULT_RETRY depending on
323  * FAULT_FLAG_ALLOW_RETRY, FAULT_FLAG_RETRY_NOWAIT and
324  * FAULT_FLAG_KILLABLE are not straightforward. The "Caution"
325  * recommendation in __lock_page_or_retry is not an understatement.
326  *
327  * If FAULT_FLAG_ALLOW_RETRY is set, the mmap_sem must be released
328  * before returning VM_FAULT_RETRY only if FAULT_FLAG_RETRY_NOWAIT is
329  * not set.
330  *
331  * If FAULT_FLAG_ALLOW_RETRY is set but FAULT_FLAG_KILLABLE is not
332  * set, VM_FAULT_RETRY can still be returned if and only if there are
333  * fatal_signal_pending()s, and the mmap_sem must be released before
334  * returning it.
335  */
336 int handle_userfault(struct vm_fault *vmf, unsigned long reason)
337 {
338         struct mm_struct *mm = vmf->vma->vm_mm;
339         struct userfaultfd_ctx *ctx;
340         struct userfaultfd_wait_queue uwq;
341         int ret;
342         bool must_wait, return_to_userland;
343         long blocking_state;
344
345         ret = VM_FAULT_SIGBUS;
346
347         /*
348          * We don't do userfault handling for the final child pid update.
349          *
350          * We also don't do userfault handling during
351          * coredumping. hugetlbfs has the special
352          * follow_hugetlb_page() to skip missing pages in the
353          * FOLL_DUMP case, anon memory also checks for FOLL_DUMP with
354          * the no_page_table() helper in follow_page_mask(), but the
355          * shmem_vm_ops->fault method is invoked even during
356          * coredumping without mmap_sem and it ends up here.
357          */
358         if (current->flags & (PF_EXITING|PF_DUMPCORE))
359                 goto out;
360
361         /*
362          * Coredumping runs without mmap_sem so we can only check that
363          * the mmap_sem is held, if PF_DUMPCORE was not set.
364          */
365         WARN_ON_ONCE(!rwsem_is_locked(&mm->mmap_sem));
366
367         ctx = vmf->vma->vm_userfaultfd_ctx.ctx;
368         if (!ctx)
369                 goto out;
370
371         BUG_ON(ctx->mm != mm);
372
373         VM_BUG_ON(reason & ~(VM_UFFD_MISSING|VM_UFFD_WP));
374         VM_BUG_ON(!(reason & VM_UFFD_MISSING) ^ !!(reason & VM_UFFD_WP));
375
376         /*
377          * If it's already released don't get it. This avoids to loop
378          * in __get_user_pages if userfaultfd_release waits on the
379          * caller of handle_userfault to release the mmap_sem.
380          */
381         if (unlikely(ACCESS_ONCE(ctx->released)))
382                 goto out;
383
384         /*
385          * Check that we can return VM_FAULT_RETRY.
386          *
387          * NOTE: it should become possible to return VM_FAULT_RETRY
388          * even if FAULT_FLAG_TRIED is set without leading to gup()
389          * -EBUSY failures, if the userfaultfd is to be extended for
390          * VM_UFFD_WP tracking and we intend to arm the userfault
391          * without first stopping userland access to the memory. For
392          * VM_UFFD_MISSING userfaults this is enough for now.
393          */
394         if (unlikely(!(vmf->flags & FAULT_FLAG_ALLOW_RETRY))) {
395                 /*
396                  * Validate the invariant that nowait must allow retry
397                  * to be sure not to return SIGBUS erroneously on
398                  * nowait invocations.
399                  */
400                 BUG_ON(vmf->flags & FAULT_FLAG_RETRY_NOWAIT);
401 #ifdef CONFIG_DEBUG_VM
402                 if (printk_ratelimit()) {
403                         printk(KERN_WARNING
404                                "FAULT_FLAG_ALLOW_RETRY missing %x\n",
405                                vmf->flags);
406                         dump_stack();
407                 }
408 #endif
409                 goto out;
410         }
411
412         /*
413          * Handle nowait, not much to do other than tell it to retry
414          * and wait.
415          */
416         ret = VM_FAULT_RETRY;
417         if (vmf->flags & FAULT_FLAG_RETRY_NOWAIT)
418                 goto out;
419
420         /* take the reference before dropping the mmap_sem */
421         userfaultfd_ctx_get(ctx);
422
423         init_waitqueue_func_entry(&uwq.wq, userfaultfd_wake_function);
424         uwq.wq.private = current;
425         uwq.msg = userfault_msg(vmf->address, vmf->flags, reason);
426         uwq.ctx = ctx;
427         uwq.waken = false;
428
429         return_to_userland =
430                 (vmf->flags & (FAULT_FLAG_USER|FAULT_FLAG_KILLABLE)) ==
431                 (FAULT_FLAG_USER|FAULT_FLAG_KILLABLE);
432         blocking_state = return_to_userland ? TASK_INTERRUPTIBLE :
433                          TASK_KILLABLE;
434
435         spin_lock(&ctx->fault_pending_wqh.lock);
436         /*
437          * After the __add_wait_queue the uwq is visible to userland
438          * through poll/read().
439          */
440         __add_wait_queue(&ctx->fault_pending_wqh, &uwq.wq);
441         /*
442          * The smp_mb() after __set_current_state prevents the reads
443          * following the spin_unlock to happen before the list_add in
444          * __add_wait_queue.
445          */
446         set_current_state(blocking_state);
447         spin_unlock(&ctx->fault_pending_wqh.lock);
448
449         if (!is_vm_hugetlb_page(vmf->vma))
450                 must_wait = userfaultfd_must_wait(ctx, vmf->address, vmf->flags,
451                                                   reason);
452         else
453                 must_wait = userfaultfd_huge_must_wait(ctx, vmf->vma,
454                                                        vmf->address,
455                                                        vmf->flags, reason);
456         up_read(&mm->mmap_sem);
457
458         if (likely(must_wait && !ACCESS_ONCE(ctx->released) &&
459                    (return_to_userland ? !signal_pending(current) :
460                     !fatal_signal_pending(current)))) {
461                 wake_up_poll(&ctx->fd_wqh, POLLIN);
462                 schedule();
463                 ret |= VM_FAULT_MAJOR;
464
465                 /*
466                  * False wakeups can orginate even from rwsem before
467                  * up_read() however userfaults will wait either for a
468                  * targeted wakeup on the specific uwq waitqueue from
469                  * wake_userfault() or for signals or for uffd
470                  * release.
471                  */
472                 while (!READ_ONCE(uwq.waken)) {
473                         /*
474                          * This needs the full smp_store_mb()
475                          * guarantee as the state write must be
476                          * visible to other CPUs before reading
477                          * uwq.waken from other CPUs.
478                          */
479                         set_current_state(blocking_state);
480                         if (READ_ONCE(uwq.waken) ||
481                             READ_ONCE(ctx->released) ||
482                             (return_to_userland ? signal_pending(current) :
483                              fatal_signal_pending(current)))
484                                 break;
485                         schedule();
486                 }
487         }
488
489         __set_current_state(TASK_RUNNING);
490
491         if (return_to_userland) {
492                 if (signal_pending(current) &&
493                     !fatal_signal_pending(current)) {
494                         /*
495                          * If we got a SIGSTOP or SIGCONT and this is
496                          * a normal userland page fault, just let
497                          * userland return so the signal will be
498                          * handled and gdb debugging works.  The page
499                          * fault code immediately after we return from
500                          * this function is going to release the
501                          * mmap_sem and it's not depending on it
502                          * (unlike gup would if we were not to return
503                          * VM_FAULT_RETRY).
504                          *
505                          * If a fatal signal is pending we still take
506                          * the streamlined VM_FAULT_RETRY failure path
507                          * and there's no need to retake the mmap_sem
508                          * in such case.
509                          */
510                         down_read(&mm->mmap_sem);
511                         ret = VM_FAULT_NOPAGE;
512                 }
513         }
514
515         /*
516          * Here we race with the list_del; list_add in
517          * userfaultfd_ctx_read(), however because we don't ever run
518          * list_del_init() to refile across the two lists, the prev
519          * and next pointers will never point to self. list_add also
520          * would never let any of the two pointers to point to
521          * self. So list_empty_careful won't risk to see both pointers
522          * pointing to self at any time during the list refile. The
523          * only case where list_del_init() is called is the full
524          * removal in the wake function and there we don't re-list_add
525          * and it's fine not to block on the spinlock. The uwq on this
526          * kernel stack can be released after the list_del_init.
527          */
528         if (!list_empty_careful(&uwq.wq.entry)) {
529                 spin_lock(&ctx->fault_pending_wqh.lock);
530                 /*
531                  * No need of list_del_init(), the uwq on the stack
532                  * will be freed shortly anyway.
533                  */
534                 list_del(&uwq.wq.entry);
535                 spin_unlock(&ctx->fault_pending_wqh.lock);
536         }
537
538         /*
539          * ctx may go away after this if the userfault pseudo fd is
540          * already released.
541          */
542         userfaultfd_ctx_put(ctx);
543
544 out:
545         return ret;
546 }
547
548 static void userfaultfd_event_wait_completion(struct userfaultfd_ctx *ctx,
549                                               struct userfaultfd_wait_queue *ewq)
550 {
551         if (WARN_ON_ONCE(current->flags & PF_EXITING))
552                 goto out;
553
554         ewq->ctx = ctx;
555         init_waitqueue_entry(&ewq->wq, current);
556
557         spin_lock(&ctx->event_wqh.lock);
558         /*
559          * After the __add_wait_queue the uwq is visible to userland
560          * through poll/read().
561          */
562         __add_wait_queue(&ctx->event_wqh, &ewq->wq);
563         for (;;) {
564                 set_current_state(TASK_KILLABLE);
565                 if (ewq->msg.event == 0)
566                         break;
567                 if (ACCESS_ONCE(ctx->released) ||
568                     fatal_signal_pending(current)) {
569                         __remove_wait_queue(&ctx->event_wqh, &ewq->wq);
570                         if (ewq->msg.event == UFFD_EVENT_FORK) {
571                                 struct userfaultfd_ctx *new;
572
573                                 new = (struct userfaultfd_ctx *)
574                                         (unsigned long)
575                                         ewq->msg.arg.reserved.reserved1;
576
577                                 userfaultfd_ctx_put(new);
578                         }
579                         break;
580                 }
581
582                 spin_unlock(&ctx->event_wqh.lock);
583
584                 wake_up_poll(&ctx->fd_wqh, POLLIN);
585                 schedule();
586
587                 spin_lock(&ctx->event_wqh.lock);
588         }
589         __set_current_state(TASK_RUNNING);
590         spin_unlock(&ctx->event_wqh.lock);
591
592         /*
593          * ctx may go away after this if the userfault pseudo fd is
594          * already released.
595          */
596 out:
597         userfaultfd_ctx_put(ctx);
598 }
599
600 static void userfaultfd_event_complete(struct userfaultfd_ctx *ctx,
601                                        struct userfaultfd_wait_queue *ewq)
602 {
603         ewq->msg.event = 0;
604         wake_up_locked(&ctx->event_wqh);
605         __remove_wait_queue(&ctx->event_wqh, &ewq->wq);
606 }
607
608 int dup_userfaultfd(struct vm_area_struct *vma, struct list_head *fcs)
609 {
610         struct userfaultfd_ctx *ctx = NULL, *octx;
611         struct userfaultfd_fork_ctx *fctx;
612
613         octx = vma->vm_userfaultfd_ctx.ctx;
614         if (!octx || !(octx->features & UFFD_FEATURE_EVENT_FORK)) {
615                 vma->vm_userfaultfd_ctx = NULL_VM_UFFD_CTX;
616                 vma->vm_flags &= ~(VM_UFFD_WP | VM_UFFD_MISSING);
617                 return 0;
618         }
619
620         list_for_each_entry(fctx, fcs, list)
621                 if (fctx->orig == octx) {
622                         ctx = fctx->new;
623                         break;
624                 }
625
626         if (!ctx) {
627                 fctx = kmalloc(sizeof(*fctx), GFP_KERNEL);
628                 if (!fctx)
629                         return -ENOMEM;
630
631                 ctx = kmem_cache_alloc(userfaultfd_ctx_cachep, GFP_KERNEL);
632                 if (!ctx) {
633                         kfree(fctx);
634                         return -ENOMEM;
635                 }
636
637                 atomic_set(&ctx->refcount, 1);
638                 ctx->flags = octx->flags;
639                 ctx->state = UFFD_STATE_RUNNING;
640                 ctx->features = octx->features;
641                 ctx->released = false;
642                 ctx->mm = vma->vm_mm;
643                 atomic_inc(&ctx->mm->mm_count);
644
645                 userfaultfd_ctx_get(octx);
646                 fctx->orig = octx;
647                 fctx->new = ctx;
648                 list_add_tail(&fctx->list, fcs);
649         }
650
651         vma->vm_userfaultfd_ctx.ctx = ctx;
652         return 0;
653 }
654
655 static void dup_fctx(struct userfaultfd_fork_ctx *fctx)
656 {
657         struct userfaultfd_ctx *ctx = fctx->orig;
658         struct userfaultfd_wait_queue ewq;
659
660         msg_init(&ewq.msg);
661
662         ewq.msg.event = UFFD_EVENT_FORK;
663         ewq.msg.arg.reserved.reserved1 = (unsigned long)fctx->new;
664
665         userfaultfd_event_wait_completion(ctx, &ewq);
666 }
667
668 void dup_userfaultfd_complete(struct list_head *fcs)
669 {
670         struct userfaultfd_fork_ctx *fctx, *n;
671
672         list_for_each_entry_safe(fctx, n, fcs, list) {
673                 dup_fctx(fctx);
674                 list_del(&fctx->list);
675                 kfree(fctx);
676         }
677 }
678
679 void mremap_userfaultfd_prep(struct vm_area_struct *vma,
680                              struct vm_userfaultfd_ctx *vm_ctx)
681 {
682         struct userfaultfd_ctx *ctx;
683
684         ctx = vma->vm_userfaultfd_ctx.ctx;
685         if (ctx && (ctx->features & UFFD_FEATURE_EVENT_REMAP)) {
686                 vm_ctx->ctx = ctx;
687                 userfaultfd_ctx_get(ctx);
688         }
689 }
690
691 void mremap_userfaultfd_complete(struct vm_userfaultfd_ctx *vm_ctx,
692                                  unsigned long from, unsigned long to,
693                                  unsigned long len)
694 {
695         struct userfaultfd_ctx *ctx = vm_ctx->ctx;
696         struct userfaultfd_wait_queue ewq;
697
698         if (!ctx)
699                 return;
700
701         if (to & ~PAGE_MASK) {
702                 userfaultfd_ctx_put(ctx);
703                 return;
704         }
705
706         msg_init(&ewq.msg);
707
708         ewq.msg.event = UFFD_EVENT_REMAP;
709         ewq.msg.arg.remap.from = from;
710         ewq.msg.arg.remap.to = to;
711         ewq.msg.arg.remap.len = len;
712
713         userfaultfd_event_wait_completion(ctx, &ewq);
714 }
715
716 bool userfaultfd_remove(struct vm_area_struct *vma,
717                         unsigned long start, unsigned long end)
718 {
719         struct mm_struct *mm = vma->vm_mm;
720         struct userfaultfd_ctx *ctx;
721         struct userfaultfd_wait_queue ewq;
722
723         ctx = vma->vm_userfaultfd_ctx.ctx;
724         if (!ctx || !(ctx->features & UFFD_FEATURE_EVENT_REMOVE))
725                 return true;
726
727         userfaultfd_ctx_get(ctx);
728         up_read(&mm->mmap_sem);
729
730         msg_init(&ewq.msg);
731
732         ewq.msg.event = UFFD_EVENT_REMOVE;
733         ewq.msg.arg.remove.start = start;
734         ewq.msg.arg.remove.end = end;
735
736         userfaultfd_event_wait_completion(ctx, &ewq);
737
738         return false;
739 }
740
741 static bool has_unmap_ctx(struct userfaultfd_ctx *ctx, struct list_head *unmaps,
742                           unsigned long start, unsigned long end)
743 {
744         struct userfaultfd_unmap_ctx *unmap_ctx;
745
746         list_for_each_entry(unmap_ctx, unmaps, list)
747                 if (unmap_ctx->ctx == ctx && unmap_ctx->start == start &&
748                     unmap_ctx->end == end)
749                         return true;
750
751         return false;
752 }
753
754 int userfaultfd_unmap_prep(struct vm_area_struct *vma,
755                            unsigned long start, unsigned long end,
756                            struct list_head *unmaps)
757 {
758         for ( ; vma && vma->vm_start < end; vma = vma->vm_next) {
759                 struct userfaultfd_unmap_ctx *unmap_ctx;
760                 struct userfaultfd_ctx *ctx = vma->vm_userfaultfd_ctx.ctx;
761
762                 if (!ctx || !(ctx->features & UFFD_FEATURE_EVENT_UNMAP) ||
763                     has_unmap_ctx(ctx, unmaps, start, end))
764                         continue;
765
766                 unmap_ctx = kzalloc(sizeof(*unmap_ctx), GFP_KERNEL);
767                 if (!unmap_ctx)
768                         return -ENOMEM;
769
770                 userfaultfd_ctx_get(ctx);
771                 unmap_ctx->ctx = ctx;
772                 unmap_ctx->start = start;
773                 unmap_ctx->end = end;
774                 list_add_tail(&unmap_ctx->list, unmaps);
775         }
776
777         return 0;
778 }
779
780 void userfaultfd_unmap_complete(struct mm_struct *mm, struct list_head *uf)
781 {
782         struct userfaultfd_unmap_ctx *ctx, *n;
783         struct userfaultfd_wait_queue ewq;
784
785         list_for_each_entry_safe(ctx, n, uf, list) {
786                 msg_init(&ewq.msg);
787
788                 ewq.msg.event = UFFD_EVENT_UNMAP;
789                 ewq.msg.arg.remove.start = ctx->start;
790                 ewq.msg.arg.remove.end = ctx->end;
791
792                 userfaultfd_event_wait_completion(ctx->ctx, &ewq);
793
794                 list_del(&ctx->list);
795                 kfree(ctx);
796         }
797 }
798
799 static int userfaultfd_release(struct inode *inode, struct file *file)
800 {
801         struct userfaultfd_ctx *ctx = file->private_data;
802         struct mm_struct *mm = ctx->mm;
803         struct vm_area_struct *vma, *prev;
804         /* len == 0 means wake all */
805         struct userfaultfd_wake_range range = { .len = 0, };
806         unsigned long new_flags;
807
808         ACCESS_ONCE(ctx->released) = true;
809
810         if (!mmget_not_zero(mm))
811                 goto wakeup;
812
813         /*
814          * Flush page faults out of all CPUs. NOTE: all page faults
815          * must be retried without returning VM_FAULT_SIGBUS if
816          * userfaultfd_ctx_get() succeeds but vma->vma_userfault_ctx
817          * changes while handle_userfault released the mmap_sem. So
818          * it's critical that released is set to true (above), before
819          * taking the mmap_sem for writing.
820          */
821         down_write(&mm->mmap_sem);
822         prev = NULL;
823         for (vma = mm->mmap; vma; vma = vma->vm_next) {
824                 cond_resched();
825                 BUG_ON(!!vma->vm_userfaultfd_ctx.ctx ^
826                        !!(vma->vm_flags & (VM_UFFD_MISSING | VM_UFFD_WP)));
827                 if (vma->vm_userfaultfd_ctx.ctx != ctx) {
828                         prev = vma;
829                         continue;
830                 }
831                 new_flags = vma->vm_flags & ~(VM_UFFD_MISSING | VM_UFFD_WP);
832                 prev = vma_merge(mm, prev, vma->vm_start, vma->vm_end,
833                                  new_flags, vma->anon_vma,
834                                  vma->vm_file, vma->vm_pgoff,
835                                  vma_policy(vma),
836                                  NULL_VM_UFFD_CTX);
837                 if (prev)
838                         vma = prev;
839                 else
840                         prev = vma;
841                 vma->vm_flags = new_flags;
842                 vma->vm_userfaultfd_ctx = NULL_VM_UFFD_CTX;
843         }
844         up_write(&mm->mmap_sem);
845         mmput(mm);
846 wakeup:
847         /*
848          * After no new page faults can wait on this fault_*wqh, flush
849          * the last page faults that may have been already waiting on
850          * the fault_*wqh.
851          */
852         spin_lock(&ctx->fault_pending_wqh.lock);
853         __wake_up_locked_key(&ctx->fault_pending_wqh, TASK_NORMAL, &range);
854         __wake_up_locked_key(&ctx->fault_wqh, TASK_NORMAL, &range);
855         spin_unlock(&ctx->fault_pending_wqh.lock);
856
857         wake_up_poll(&ctx->fd_wqh, POLLHUP);
858         userfaultfd_ctx_put(ctx);
859         return 0;
860 }
861
862 /* fault_pending_wqh.lock must be hold by the caller */
863 static inline struct userfaultfd_wait_queue *find_userfault_in(
864                 wait_queue_head_t *wqh)
865 {
866         wait_queue_entry_t *wq;
867         struct userfaultfd_wait_queue *uwq;
868
869         VM_BUG_ON(!spin_is_locked(&wqh->lock));
870
871         uwq = NULL;
872         if (!waitqueue_active(wqh))
873                 goto out;
874         /* walk in reverse to provide FIFO behavior to read userfaults */
875         wq = list_last_entry(&wqh->head, typeof(*wq), entry);
876         uwq = container_of(wq, struct userfaultfd_wait_queue, wq);
877 out:
878         return uwq;
879 }
880
881 static inline struct userfaultfd_wait_queue *find_userfault(
882                 struct userfaultfd_ctx *ctx)
883 {
884         return find_userfault_in(&ctx->fault_pending_wqh);
885 }
886
887 static inline struct userfaultfd_wait_queue *find_userfault_evt(
888                 struct userfaultfd_ctx *ctx)
889 {
890         return find_userfault_in(&ctx->event_wqh);
891 }
892
893 static unsigned int userfaultfd_poll(struct file *file, poll_table *wait)
894 {
895         struct userfaultfd_ctx *ctx = file->private_data;
896         unsigned int ret;
897
898         poll_wait(file, &ctx->fd_wqh, wait);
899
900         switch (ctx->state) {
901         case UFFD_STATE_WAIT_API:
902                 return POLLERR;
903         case UFFD_STATE_RUNNING:
904                 /*
905                  * poll() never guarantees that read won't block.
906                  * userfaults can be waken before they're read().
907                  */
908                 if (unlikely(!(file->f_flags & O_NONBLOCK)))
909                         return POLLERR;
910                 /*
911                  * lockless access to see if there are pending faults
912                  * __pollwait last action is the add_wait_queue but
913                  * the spin_unlock would allow the waitqueue_active to
914                  * pass above the actual list_add inside
915                  * add_wait_queue critical section. So use a full
916                  * memory barrier to serialize the list_add write of
917                  * add_wait_queue() with the waitqueue_active read
918                  * below.
919                  */
920                 ret = 0;
921                 smp_mb();
922                 if (waitqueue_active(&ctx->fault_pending_wqh))
923                         ret = POLLIN;
924                 else if (waitqueue_active(&ctx->event_wqh))
925                         ret = POLLIN;
926
927                 return ret;
928         default:
929                 WARN_ON_ONCE(1);
930                 return POLLERR;
931         }
932 }
933
934 static const struct file_operations userfaultfd_fops;
935
936 static int resolve_userfault_fork(struct userfaultfd_ctx *ctx,
937                                   struct userfaultfd_ctx *new,
938                                   struct uffd_msg *msg)
939 {
940         int fd;
941         struct file *file;
942         unsigned int flags = new->flags & UFFD_SHARED_FCNTL_FLAGS;
943
944         fd = get_unused_fd_flags(flags);
945         if (fd < 0)
946                 return fd;
947
948         file = anon_inode_getfile("[userfaultfd]", &userfaultfd_fops, new,
949                                   O_RDWR | flags);
950         if (IS_ERR(file)) {
951                 put_unused_fd(fd);
952                 return PTR_ERR(file);
953         }
954
955         fd_install(fd, file);
956         msg->arg.reserved.reserved1 = 0;
957         msg->arg.fork.ufd = fd;
958
959         return 0;
960 }
961
962 static ssize_t userfaultfd_ctx_read(struct userfaultfd_ctx *ctx, int no_wait,
963                                     struct uffd_msg *msg)
964 {
965         ssize_t ret;
966         DECLARE_WAITQUEUE(wait, current);
967         struct userfaultfd_wait_queue *uwq;
968         /*
969          * Handling fork event requires sleeping operations, so
970          * we drop the event_wqh lock, then do these ops, then
971          * lock it back and wake up the waiter. While the lock is
972          * dropped the ewq may go away so we keep track of it
973          * carefully.
974          */
975         LIST_HEAD(fork_event);
976         struct userfaultfd_ctx *fork_nctx = NULL;
977
978         /* always take the fd_wqh lock before the fault_pending_wqh lock */
979         spin_lock(&ctx->fd_wqh.lock);
980         __add_wait_queue(&ctx->fd_wqh, &wait);
981         for (;;) {
982                 set_current_state(TASK_INTERRUPTIBLE);
983                 spin_lock(&ctx->fault_pending_wqh.lock);
984                 uwq = find_userfault(ctx);
985                 if (uwq) {
986                         /*
987                          * Use a seqcount to repeat the lockless check
988                          * in wake_userfault() to avoid missing
989                          * wakeups because during the refile both
990                          * waitqueue could become empty if this is the
991                          * only userfault.
992                          */
993                         write_seqcount_begin(&ctx->refile_seq);
994
995                         /*
996                          * The fault_pending_wqh.lock prevents the uwq
997                          * to disappear from under us.
998                          *
999                          * Refile this userfault from
1000                          * fault_pending_wqh to fault_wqh, it's not
1001                          * pending anymore after we read it.
1002                          *
1003                          * Use list_del() by hand (as
1004                          * userfaultfd_wake_function also uses
1005                          * list_del_init() by hand) to be sure nobody
1006                          * changes __remove_wait_queue() to use
1007                          * list_del_init() in turn breaking the
1008                          * !list_empty_careful() check in
1009                          * handle_userfault(). The uwq->wq.head list
1010                          * must never be empty at any time during the
1011                          * refile, or the waitqueue could disappear
1012                          * from under us. The "wait_queue_head_t"
1013                          * parameter of __remove_wait_queue() is unused
1014                          * anyway.
1015                          */
1016                         list_del(&uwq->wq.entry);
1017                         __add_wait_queue(&ctx->fault_wqh, &uwq->wq);
1018
1019                         write_seqcount_end(&ctx->refile_seq);
1020
1021                         /* careful to always initialize msg if ret == 0 */
1022                         *msg = uwq->msg;
1023                         spin_unlock(&ctx->fault_pending_wqh.lock);
1024                         ret = 0;
1025                         break;
1026                 }
1027                 spin_unlock(&ctx->fault_pending_wqh.lock);
1028
1029                 spin_lock(&ctx->event_wqh.lock);
1030                 uwq = find_userfault_evt(ctx);
1031                 if (uwq) {
1032                         *msg = uwq->msg;
1033
1034                         if (uwq->msg.event == UFFD_EVENT_FORK) {
1035                                 fork_nctx = (struct userfaultfd_ctx *)
1036                                         (unsigned long)
1037                                         uwq->msg.arg.reserved.reserved1;
1038                                 list_move(&uwq->wq.entry, &fork_event);
1039                                 spin_unlock(&ctx->event_wqh.lock);
1040                                 ret = 0;
1041                                 break;
1042                         }
1043
1044                         userfaultfd_event_complete(ctx, uwq);
1045                         spin_unlock(&ctx->event_wqh.lock);
1046                         ret = 0;
1047                         break;
1048                 }
1049                 spin_unlock(&ctx->event_wqh.lock);
1050
1051                 if (signal_pending(current)) {
1052                         ret = -ERESTARTSYS;
1053                         break;
1054                 }
1055                 if (no_wait) {
1056                         ret = -EAGAIN;
1057                         break;
1058                 }
1059                 spin_unlock(&ctx->fd_wqh.lock);
1060                 schedule();
1061                 spin_lock(&ctx->fd_wqh.lock);
1062         }
1063         __remove_wait_queue(&ctx->fd_wqh, &wait);
1064         __set_current_state(TASK_RUNNING);
1065         spin_unlock(&ctx->fd_wqh.lock);
1066
1067         if (!ret && msg->event == UFFD_EVENT_FORK) {
1068                 ret = resolve_userfault_fork(ctx, fork_nctx, msg);
1069
1070                 if (!ret) {
1071                         spin_lock(&ctx->event_wqh.lock);
1072                         if (!list_empty(&fork_event)) {
1073                                 uwq = list_first_entry(&fork_event,
1074                                                        typeof(*uwq),
1075                                                        wq.entry);
1076                                 list_del(&uwq->wq.entry);
1077                                 __add_wait_queue(&ctx->event_wqh, &uwq->wq);
1078                                 userfaultfd_event_complete(ctx, uwq);
1079                         }
1080                         spin_unlock(&ctx->event_wqh.lock);
1081                 }
1082         }
1083
1084         return ret;
1085 }
1086
1087 static ssize_t userfaultfd_read(struct file *file, char __user *buf,
1088                                 size_t count, loff_t *ppos)
1089 {
1090         struct userfaultfd_ctx *ctx = file->private_data;
1091         ssize_t _ret, ret = 0;
1092         struct uffd_msg msg;
1093         int no_wait = file->f_flags & O_NONBLOCK;
1094
1095         if (ctx->state == UFFD_STATE_WAIT_API)
1096                 return -EINVAL;
1097
1098         for (;;) {
1099                 if (count < sizeof(msg))
1100                         return ret ? ret : -EINVAL;
1101                 _ret = userfaultfd_ctx_read(ctx, no_wait, &msg);
1102                 if (_ret < 0)
1103                         return ret ? ret : _ret;
1104                 if (copy_to_user((__u64 __user *) buf, &msg, sizeof(msg)))
1105                         return ret ? ret : -EFAULT;
1106                 ret += sizeof(msg);
1107                 buf += sizeof(msg);
1108                 count -= sizeof(msg);
1109                 /*
1110                  * Allow to read more than one fault at time but only
1111                  * block if waiting for the very first one.
1112                  */
1113                 no_wait = O_NONBLOCK;
1114         }
1115 }
1116
1117 static void __wake_userfault(struct userfaultfd_ctx *ctx,
1118                              struct userfaultfd_wake_range *range)
1119 {
1120         spin_lock(&ctx->fault_pending_wqh.lock);
1121         /* wake all in the range and autoremove */
1122         if (waitqueue_active(&ctx->fault_pending_wqh))
1123                 __wake_up_locked_key(&ctx->fault_pending_wqh, TASK_NORMAL,
1124                                      range);
1125         if (waitqueue_active(&ctx->fault_wqh))
1126                 __wake_up_locked_key(&ctx->fault_wqh, TASK_NORMAL, range);
1127         spin_unlock(&ctx->fault_pending_wqh.lock);
1128 }
1129
1130 static __always_inline void wake_userfault(struct userfaultfd_ctx *ctx,
1131                                            struct userfaultfd_wake_range *range)
1132 {
1133         unsigned seq;
1134         bool need_wakeup;
1135
1136         /*
1137          * To be sure waitqueue_active() is not reordered by the CPU
1138          * before the pagetable update, use an explicit SMP memory
1139          * barrier here. PT lock release or up_read(mmap_sem) still
1140          * have release semantics that can allow the
1141          * waitqueue_active() to be reordered before the pte update.
1142          */
1143         smp_mb();
1144
1145         /*
1146          * Use waitqueue_active because it's very frequent to
1147          * change the address space atomically even if there are no
1148          * userfaults yet. So we take the spinlock only when we're
1149          * sure we've userfaults to wake.
1150          */
1151         do {
1152                 seq = read_seqcount_begin(&ctx->refile_seq);
1153                 need_wakeup = waitqueue_active(&ctx->fault_pending_wqh) ||
1154                         waitqueue_active(&ctx->fault_wqh);
1155                 cond_resched();
1156         } while (read_seqcount_retry(&ctx->refile_seq, seq));
1157         if (need_wakeup)
1158                 __wake_userfault(ctx, range);
1159 }
1160
1161 static __always_inline int validate_range(struct mm_struct *mm,
1162                                           __u64 start, __u64 len)
1163 {
1164         __u64 task_size = mm->task_size;
1165
1166         if (start & ~PAGE_MASK)
1167                 return -EINVAL;
1168         if (len & ~PAGE_MASK)
1169                 return -EINVAL;
1170         if (!len)
1171                 return -EINVAL;
1172         if (start < mmap_min_addr)
1173                 return -EINVAL;
1174         if (start >= task_size)
1175                 return -EINVAL;
1176         if (len > task_size - start)
1177                 return -EINVAL;
1178         return 0;
1179 }
1180
1181 static inline bool vma_can_userfault(struct vm_area_struct *vma)
1182 {
1183         return vma_is_anonymous(vma) || is_vm_hugetlb_page(vma) ||
1184                 vma_is_shmem(vma);
1185 }
1186
1187 static int userfaultfd_register(struct userfaultfd_ctx *ctx,
1188                                 unsigned long arg)
1189 {
1190         struct mm_struct *mm = ctx->mm;
1191         struct vm_area_struct *vma, *prev, *cur;
1192         int ret;
1193         struct uffdio_register uffdio_register;
1194         struct uffdio_register __user *user_uffdio_register;
1195         unsigned long vm_flags, new_flags;
1196         bool found;
1197         bool non_anon_pages;
1198         unsigned long start, end, vma_end;
1199
1200         user_uffdio_register = (struct uffdio_register __user *) arg;
1201
1202         ret = -EFAULT;
1203         if (copy_from_user(&uffdio_register, user_uffdio_register,
1204                            sizeof(uffdio_register)-sizeof(__u64)))
1205                 goto out;
1206
1207         ret = -EINVAL;
1208         if (!uffdio_register.mode)
1209                 goto out;
1210         if (uffdio_register.mode & ~(UFFDIO_REGISTER_MODE_MISSING|
1211                                      UFFDIO_REGISTER_MODE_WP))
1212                 goto out;
1213         vm_flags = 0;
1214         if (uffdio_register.mode & UFFDIO_REGISTER_MODE_MISSING)
1215                 vm_flags |= VM_UFFD_MISSING;
1216         if (uffdio_register.mode & UFFDIO_REGISTER_MODE_WP) {
1217                 vm_flags |= VM_UFFD_WP;
1218                 /*
1219                  * FIXME: remove the below error constraint by
1220                  * implementing the wprotect tracking mode.
1221                  */
1222                 ret = -EINVAL;
1223                 goto out;
1224         }
1225
1226         ret = validate_range(mm, uffdio_register.range.start,
1227                              uffdio_register.range.len);
1228         if (ret)
1229                 goto out;
1230
1231         start = uffdio_register.range.start;
1232         end = start + uffdio_register.range.len;
1233
1234         ret = -ENOMEM;
1235         if (!mmget_not_zero(mm))
1236                 goto out;
1237
1238         down_write(&mm->mmap_sem);
1239         vma = find_vma_prev(mm, start, &prev);
1240         if (!vma)
1241                 goto out_unlock;
1242
1243         /* check that there's at least one vma in the range */
1244         ret = -EINVAL;
1245         if (vma->vm_start >= end)
1246                 goto out_unlock;
1247
1248         /*
1249          * If the first vma contains huge pages, make sure start address
1250          * is aligned to huge page size.
1251          */
1252         if (is_vm_hugetlb_page(vma)) {
1253                 unsigned long vma_hpagesize = vma_kernel_pagesize(vma);
1254
1255                 if (start & (vma_hpagesize - 1))
1256                         goto out_unlock;
1257         }
1258
1259         /*
1260          * Search for not compatible vmas.
1261          */
1262         found = false;
1263         non_anon_pages = false;
1264         for (cur = vma; cur && cur->vm_start < end; cur = cur->vm_next) {
1265                 cond_resched();
1266
1267                 BUG_ON(!!cur->vm_userfaultfd_ctx.ctx ^
1268                        !!(cur->vm_flags & (VM_UFFD_MISSING | VM_UFFD_WP)));
1269
1270                 /* check not compatible vmas */
1271                 ret = -EINVAL;
1272                 if (!vma_can_userfault(cur))
1273                         goto out_unlock;
1274                 /*
1275                  * If this vma contains ending address, and huge pages
1276                  * check alignment.
1277                  */
1278                 if (is_vm_hugetlb_page(cur) && end <= cur->vm_end &&
1279                     end > cur->vm_start) {
1280                         unsigned long vma_hpagesize = vma_kernel_pagesize(cur);
1281
1282                         ret = -EINVAL;
1283
1284                         if (end & (vma_hpagesize - 1))
1285                                 goto out_unlock;
1286                 }
1287
1288                 /*
1289                  * Check that this vma isn't already owned by a
1290                  * different userfaultfd. We can't allow more than one
1291                  * userfaultfd to own a single vma simultaneously or we
1292                  * wouldn't know which one to deliver the userfaults to.
1293                  */
1294                 ret = -EBUSY;
1295                 if (cur->vm_userfaultfd_ctx.ctx &&
1296                     cur->vm_userfaultfd_ctx.ctx != ctx)
1297                         goto out_unlock;
1298
1299                 /*
1300                  * Note vmas containing huge pages
1301                  */
1302                 if (is_vm_hugetlb_page(cur) || vma_is_shmem(cur))
1303                         non_anon_pages = true;
1304
1305                 found = true;
1306         }
1307         BUG_ON(!found);
1308
1309         if (vma->vm_start < start)
1310                 prev = vma;
1311
1312         ret = 0;
1313         do {
1314                 cond_resched();
1315
1316                 BUG_ON(!vma_can_userfault(vma));
1317                 BUG_ON(vma->vm_userfaultfd_ctx.ctx &&
1318                        vma->vm_userfaultfd_ctx.ctx != ctx);
1319
1320                 /*
1321                  * Nothing to do: this vma is already registered into this
1322                  * userfaultfd and with the right tracking mode too.
1323                  */
1324                 if (vma->vm_userfaultfd_ctx.ctx == ctx &&
1325                     (vma->vm_flags & vm_flags) == vm_flags)
1326                         goto skip;
1327
1328                 if (vma->vm_start > start)
1329                         start = vma->vm_start;
1330                 vma_end = min(end, vma->vm_end);
1331
1332                 new_flags = (vma->vm_flags & ~vm_flags) | vm_flags;
1333                 prev = vma_merge(mm, prev, start, vma_end, new_flags,
1334                                  vma->anon_vma, vma->vm_file, vma->vm_pgoff,
1335                                  vma_policy(vma),
1336                                  ((struct vm_userfaultfd_ctx){ ctx }));
1337                 if (prev) {
1338                         vma = prev;
1339                         goto next;
1340                 }
1341                 if (vma->vm_start < start) {
1342                         ret = split_vma(mm, vma, start, 1);
1343                         if (ret)
1344                                 break;
1345                 }
1346                 if (vma->vm_end > end) {
1347                         ret = split_vma(mm, vma, end, 0);
1348                         if (ret)
1349                                 break;
1350                 }
1351         next:
1352                 /*
1353                  * In the vma_merge() successful mprotect-like case 8:
1354                  * the next vma was merged into the current one and
1355                  * the current one has not been updated yet.
1356                  */
1357                 vma->vm_flags = new_flags;
1358                 vma->vm_userfaultfd_ctx.ctx = ctx;
1359
1360         skip:
1361                 prev = vma;
1362                 start = vma->vm_end;
1363                 vma = vma->vm_next;
1364         } while (vma && vma->vm_start < end);
1365 out_unlock:
1366         up_write(&mm->mmap_sem);
1367         mmput(mm);
1368         if (!ret) {
1369                 /*
1370                  * Now that we scanned all vmas we can already tell
1371                  * userland which ioctls methods are guaranteed to
1372                  * succeed on this range.
1373                  */
1374                 if (put_user(non_anon_pages ? UFFD_API_RANGE_IOCTLS_BASIC :
1375                              UFFD_API_RANGE_IOCTLS,
1376                              &user_uffdio_register->ioctls))
1377                         ret = -EFAULT;
1378         }
1379 out:
1380         return ret;
1381 }
1382
1383 static int userfaultfd_unregister(struct userfaultfd_ctx *ctx,
1384                                   unsigned long arg)
1385 {
1386         struct mm_struct *mm = ctx->mm;
1387         struct vm_area_struct *vma, *prev, *cur;
1388         int ret;
1389         struct uffdio_range uffdio_unregister;
1390         unsigned long new_flags;
1391         bool found;
1392         unsigned long start, end, vma_end;
1393         const void __user *buf = (void __user *)arg;
1394
1395         ret = -EFAULT;
1396         if (copy_from_user(&uffdio_unregister, buf, sizeof(uffdio_unregister)))
1397                 goto out;
1398
1399         ret = validate_range(mm, uffdio_unregister.start,
1400                              uffdio_unregister.len);
1401         if (ret)
1402                 goto out;
1403
1404         start = uffdio_unregister.start;
1405         end = start + uffdio_unregister.len;
1406
1407         ret = -ENOMEM;
1408         if (!mmget_not_zero(mm))
1409                 goto out;
1410
1411         down_write(&mm->mmap_sem);
1412         vma = find_vma_prev(mm, start, &prev);
1413         if (!vma)
1414                 goto out_unlock;
1415
1416         /* check that there's at least one vma in the range */
1417         ret = -EINVAL;
1418         if (vma->vm_start >= end)
1419                 goto out_unlock;
1420
1421         /*
1422          * If the first vma contains huge pages, make sure start address
1423          * is aligned to huge page size.
1424          */
1425         if (is_vm_hugetlb_page(vma)) {
1426                 unsigned long vma_hpagesize = vma_kernel_pagesize(vma);
1427
1428                 if (start & (vma_hpagesize - 1))
1429                         goto out_unlock;
1430         }
1431
1432         /*
1433          * Search for not compatible vmas.
1434          */
1435         found = false;
1436         ret = -EINVAL;
1437         for (cur = vma; cur && cur->vm_start < end; cur = cur->vm_next) {
1438                 cond_resched();
1439
1440                 BUG_ON(!!cur->vm_userfaultfd_ctx.ctx ^
1441                        !!(cur->vm_flags & (VM_UFFD_MISSING | VM_UFFD_WP)));
1442
1443                 /*
1444                  * Check not compatible vmas, not strictly required
1445                  * here as not compatible vmas cannot have an
1446                  * userfaultfd_ctx registered on them, but this
1447                  * provides for more strict behavior to notice
1448                  * unregistration errors.
1449                  */
1450                 if (!vma_can_userfault(cur))
1451                         goto out_unlock;
1452
1453                 found = true;
1454         }
1455         BUG_ON(!found);
1456
1457         if (vma->vm_start < start)
1458                 prev = vma;
1459
1460         ret = 0;
1461         do {
1462                 cond_resched();
1463
1464                 BUG_ON(!vma_can_userfault(vma));
1465
1466                 /*
1467                  * Nothing to do: this vma is already registered into this
1468                  * userfaultfd and with the right tracking mode too.
1469                  */
1470                 if (!vma->vm_userfaultfd_ctx.ctx)
1471                         goto skip;
1472
1473                 if (vma->vm_start > start)
1474                         start = vma->vm_start;
1475                 vma_end = min(end, vma->vm_end);
1476
1477                 if (userfaultfd_missing(vma)) {
1478                         /*
1479                          * Wake any concurrent pending userfault while
1480                          * we unregister, so they will not hang
1481                          * permanently and it avoids userland to call
1482                          * UFFDIO_WAKE explicitly.
1483                          */
1484                         struct userfaultfd_wake_range range;
1485                         range.start = start;
1486                         range.len = vma_end - start;
1487                         wake_userfault(vma->vm_userfaultfd_ctx.ctx, &range);
1488                 }
1489
1490                 new_flags = vma->vm_flags & ~(VM_UFFD_MISSING | VM_UFFD_WP);
1491                 prev = vma_merge(mm, prev, start, vma_end, new_flags,
1492                                  vma->anon_vma, vma->vm_file, vma->vm_pgoff,
1493                                  vma_policy(vma),
1494                                  NULL_VM_UFFD_CTX);
1495                 if (prev) {
1496                         vma = prev;
1497                         goto next;
1498                 }
1499                 if (vma->vm_start < start) {
1500                         ret = split_vma(mm, vma, start, 1);
1501                         if (ret)
1502                                 break;
1503                 }
1504                 if (vma->vm_end > end) {
1505                         ret = split_vma(mm, vma, end, 0);
1506                         if (ret)
1507                                 break;
1508                 }
1509         next:
1510                 /*
1511                  * In the vma_merge() successful mprotect-like case 8:
1512                  * the next vma was merged into the current one and
1513                  * the current one has not been updated yet.
1514                  */
1515                 vma->vm_flags = new_flags;
1516                 vma->vm_userfaultfd_ctx = NULL_VM_UFFD_CTX;
1517
1518         skip:
1519                 prev = vma;
1520                 start = vma->vm_end;
1521                 vma = vma->vm_next;
1522         } while (vma && vma->vm_start < end);
1523 out_unlock:
1524         up_write(&mm->mmap_sem);
1525         mmput(mm);
1526 out:
1527         return ret;
1528 }
1529
1530 /*
1531  * userfaultfd_wake may be used in combination with the
1532  * UFFDIO_*_MODE_DONTWAKE to wakeup userfaults in batches.
1533  */
1534 static int userfaultfd_wake(struct userfaultfd_ctx *ctx,
1535                             unsigned long arg)
1536 {
1537         int ret;
1538         struct uffdio_range uffdio_wake;
1539         struct userfaultfd_wake_range range;
1540         const void __user *buf = (void __user *)arg;
1541
1542         ret = -EFAULT;
1543         if (copy_from_user(&uffdio_wake, buf, sizeof(uffdio_wake)))
1544                 goto out;
1545
1546         ret = validate_range(ctx->mm, uffdio_wake.start, uffdio_wake.len);
1547         if (ret)
1548                 goto out;
1549
1550         range.start = uffdio_wake.start;
1551         range.len = uffdio_wake.len;
1552
1553         /*
1554          * len == 0 means wake all and we don't want to wake all here,
1555          * so check it again to be sure.
1556          */
1557         VM_BUG_ON(!range.len);
1558
1559         wake_userfault(ctx, &range);
1560         ret = 0;
1561
1562 out:
1563         return ret;
1564 }
1565
1566 static int userfaultfd_copy(struct userfaultfd_ctx *ctx,
1567                             unsigned long arg)
1568 {
1569         __s64 ret;
1570         struct uffdio_copy uffdio_copy;
1571         struct uffdio_copy __user *user_uffdio_copy;
1572         struct userfaultfd_wake_range range;
1573
1574         user_uffdio_copy = (struct uffdio_copy __user *) arg;
1575
1576         ret = -EFAULT;
1577         if (copy_from_user(&uffdio_copy, user_uffdio_copy,
1578                            /* don't copy "copy" last field */
1579                            sizeof(uffdio_copy)-sizeof(__s64)))
1580                 goto out;
1581
1582         ret = validate_range(ctx->mm, uffdio_copy.dst, uffdio_copy.len);
1583         if (ret)
1584                 goto out;
1585         /*
1586          * double check for wraparound just in case. copy_from_user()
1587          * will later check uffdio_copy.src + uffdio_copy.len to fit
1588          * in the userland range.
1589          */
1590         ret = -EINVAL;
1591         if (uffdio_copy.src + uffdio_copy.len <= uffdio_copy.src)
1592                 goto out;
1593         if (uffdio_copy.mode & ~UFFDIO_COPY_MODE_DONTWAKE)
1594                 goto out;
1595         if (mmget_not_zero(ctx->mm)) {
1596                 ret = mcopy_atomic(ctx->mm, uffdio_copy.dst, uffdio_copy.src,
1597                                    uffdio_copy.len);
1598                 mmput(ctx->mm);
1599         } else {
1600                 return -ENOSPC;
1601         }
1602         if (unlikely(put_user(ret, &user_uffdio_copy->copy)))
1603                 return -EFAULT;
1604         if (ret < 0)
1605                 goto out;
1606         BUG_ON(!ret);
1607         /* len == 0 would wake all */
1608         range.len = ret;
1609         if (!(uffdio_copy.mode & UFFDIO_COPY_MODE_DONTWAKE)) {
1610                 range.start = uffdio_copy.dst;
1611                 wake_userfault(ctx, &range);
1612         }
1613         ret = range.len == uffdio_copy.len ? 0 : -EAGAIN;
1614 out:
1615         return ret;
1616 }
1617
1618 static int userfaultfd_zeropage(struct userfaultfd_ctx *ctx,
1619                                 unsigned long arg)
1620 {
1621         __s64 ret;
1622         struct uffdio_zeropage uffdio_zeropage;
1623         struct uffdio_zeropage __user *user_uffdio_zeropage;
1624         struct userfaultfd_wake_range range;
1625
1626         user_uffdio_zeropage = (struct uffdio_zeropage __user *) arg;
1627
1628         ret = -EFAULT;
1629         if (copy_from_user(&uffdio_zeropage, user_uffdio_zeropage,
1630                            /* don't copy "zeropage" last field */
1631                            sizeof(uffdio_zeropage)-sizeof(__s64)))
1632                 goto out;
1633
1634         ret = validate_range(ctx->mm, uffdio_zeropage.range.start,
1635                              uffdio_zeropage.range.len);
1636         if (ret)
1637                 goto out;
1638         ret = -EINVAL;
1639         if (uffdio_zeropage.mode & ~UFFDIO_ZEROPAGE_MODE_DONTWAKE)
1640                 goto out;
1641
1642         if (mmget_not_zero(ctx->mm)) {
1643                 ret = mfill_zeropage(ctx->mm, uffdio_zeropage.range.start,
1644                                      uffdio_zeropage.range.len);
1645                 mmput(ctx->mm);
1646         } else {
1647                 return -ENOSPC;
1648         }
1649         if (unlikely(put_user(ret, &user_uffdio_zeropage->zeropage)))
1650                 return -EFAULT;
1651         if (ret < 0)
1652                 goto out;
1653         /* len == 0 would wake all */
1654         BUG_ON(!ret);
1655         range.len = ret;
1656         if (!(uffdio_zeropage.mode & UFFDIO_ZEROPAGE_MODE_DONTWAKE)) {
1657                 range.start = uffdio_zeropage.range.start;
1658                 wake_userfault(ctx, &range);
1659         }
1660         ret = range.len == uffdio_zeropage.range.len ? 0 : -EAGAIN;
1661 out:
1662         return ret;
1663 }
1664
1665 static inline unsigned int uffd_ctx_features(__u64 user_features)
1666 {
1667         /*
1668          * For the current set of features the bits just coincide
1669          */
1670         return (unsigned int)user_features;
1671 }
1672
1673 /*
1674  * userland asks for a certain API version and we return which bits
1675  * and ioctl commands are implemented in this kernel for such API
1676  * version or -EINVAL if unknown.
1677  */
1678 static int userfaultfd_api(struct userfaultfd_ctx *ctx,
1679                            unsigned long arg)
1680 {
1681         struct uffdio_api uffdio_api;
1682         void __user *buf = (void __user *)arg;
1683         int ret;
1684         __u64 features;
1685
1686         ret = -EINVAL;
1687         if (ctx->state != UFFD_STATE_WAIT_API)
1688                 goto out;
1689         ret = -EFAULT;
1690         if (copy_from_user(&uffdio_api, buf, sizeof(uffdio_api)))
1691                 goto out;
1692         features = uffdio_api.features;
1693         if (uffdio_api.api != UFFD_API || (features & ~UFFD_API_FEATURES)) {
1694                 memset(&uffdio_api, 0, sizeof(uffdio_api));
1695                 if (copy_to_user(buf, &uffdio_api, sizeof(uffdio_api)))
1696                         goto out;
1697                 ret = -EINVAL;
1698                 goto out;
1699         }
1700         /* report all available features and ioctls to userland */
1701         uffdio_api.features = UFFD_API_FEATURES;
1702         uffdio_api.ioctls = UFFD_API_IOCTLS;
1703         ret = -EFAULT;
1704         if (copy_to_user(buf, &uffdio_api, sizeof(uffdio_api)))
1705                 goto out;
1706         ctx->state = UFFD_STATE_RUNNING;
1707         /* only enable the requested features for this uffd context */
1708         ctx->features = uffd_ctx_features(features);
1709         ret = 0;
1710 out:
1711         return ret;
1712 }
1713
1714 static long userfaultfd_ioctl(struct file *file, unsigned cmd,
1715                               unsigned long arg)
1716 {
1717         int ret = -EINVAL;
1718         struct userfaultfd_ctx *ctx = file->private_data;
1719
1720         if (cmd != UFFDIO_API && ctx->state == UFFD_STATE_WAIT_API)
1721                 return -EINVAL;
1722
1723         switch(cmd) {
1724         case UFFDIO_API:
1725                 ret = userfaultfd_api(ctx, arg);
1726                 break;
1727         case UFFDIO_REGISTER:
1728                 ret = userfaultfd_register(ctx, arg);
1729                 break;
1730         case UFFDIO_UNREGISTER:
1731                 ret = userfaultfd_unregister(ctx, arg);
1732                 break;
1733         case UFFDIO_WAKE:
1734                 ret = userfaultfd_wake(ctx, arg);
1735                 break;
1736         case UFFDIO_COPY:
1737                 ret = userfaultfd_copy(ctx, arg);
1738                 break;
1739         case UFFDIO_ZEROPAGE:
1740                 ret = userfaultfd_zeropage(ctx, arg);
1741                 break;
1742         }
1743         return ret;
1744 }
1745
1746 #ifdef CONFIG_PROC_FS
1747 static void userfaultfd_show_fdinfo(struct seq_file *m, struct file *f)
1748 {
1749         struct userfaultfd_ctx *ctx = f->private_data;
1750         wait_queue_entry_t *wq;
1751         struct userfaultfd_wait_queue *uwq;
1752         unsigned long pending = 0, total = 0;
1753
1754         spin_lock(&ctx->fault_pending_wqh.lock);
1755         list_for_each_entry(wq, &ctx->fault_pending_wqh.head, entry) {
1756                 uwq = container_of(wq, struct userfaultfd_wait_queue, wq);
1757                 pending++;
1758                 total++;
1759         }
1760         list_for_each_entry(wq, &ctx->fault_wqh.head, entry) {
1761                 uwq = container_of(wq, struct userfaultfd_wait_queue, wq);
1762                 total++;
1763         }
1764         spin_unlock(&ctx->fault_pending_wqh.lock);
1765
1766         /*
1767          * If more protocols will be added, there will be all shown
1768          * separated by a space. Like this:
1769          *      protocols: aa:... bb:...
1770          */
1771         seq_printf(m, "pending:\t%lu\ntotal:\t%lu\nAPI:\t%Lx:%x:%Lx\n",
1772                    pending, total, UFFD_API, ctx->features,
1773                    UFFD_API_IOCTLS|UFFD_API_RANGE_IOCTLS);
1774 }
1775 #endif
1776
1777 static const struct file_operations userfaultfd_fops = {
1778 #ifdef CONFIG_PROC_FS
1779         .show_fdinfo    = userfaultfd_show_fdinfo,
1780 #endif
1781         .release        = userfaultfd_release,
1782         .poll           = userfaultfd_poll,
1783         .read           = userfaultfd_read,
1784         .unlocked_ioctl = userfaultfd_ioctl,
1785         .compat_ioctl   = userfaultfd_ioctl,
1786         .llseek         = noop_llseek,
1787 };
1788
1789 static void init_once_userfaultfd_ctx(void *mem)
1790 {
1791         struct userfaultfd_ctx *ctx = (struct userfaultfd_ctx *) mem;
1792
1793         init_waitqueue_head(&ctx->fault_pending_wqh);
1794         init_waitqueue_head(&ctx->fault_wqh);
1795         init_waitqueue_head(&ctx->event_wqh);
1796         init_waitqueue_head(&ctx->fd_wqh);
1797         seqcount_init(&ctx->refile_seq);
1798 }
1799
1800 /**
1801  * userfaultfd_file_create - Creates a userfaultfd file pointer.
1802  * @flags: Flags for the userfaultfd file.
1803  *
1804  * This function creates a userfaultfd file pointer, w/out installing
1805  * it into the fd table. This is useful when the userfaultfd file is
1806  * used during the initialization of data structures that require
1807  * extra setup after the userfaultfd creation. So the userfaultfd
1808  * creation is split into the file pointer creation phase, and the
1809  * file descriptor installation phase.  In this way races with
1810  * userspace closing the newly installed file descriptor can be
1811  * avoided.  Returns a userfaultfd file pointer, or a proper error
1812  * pointer.
1813  */
1814 static struct file *userfaultfd_file_create(int flags)
1815 {
1816         struct file *file;
1817         struct userfaultfd_ctx *ctx;
1818
1819         BUG_ON(!current->mm);
1820
1821         /* Check the UFFD_* constants for consistency.  */
1822         BUILD_BUG_ON(UFFD_CLOEXEC != O_CLOEXEC);
1823         BUILD_BUG_ON(UFFD_NONBLOCK != O_NONBLOCK);
1824
1825         file = ERR_PTR(-EINVAL);
1826         if (flags & ~UFFD_SHARED_FCNTL_FLAGS)
1827                 goto out;
1828
1829         file = ERR_PTR(-ENOMEM);
1830         ctx = kmem_cache_alloc(userfaultfd_ctx_cachep, GFP_KERNEL);
1831         if (!ctx)
1832                 goto out;
1833
1834         atomic_set(&ctx->refcount, 1);
1835         ctx->flags = flags;
1836         ctx->features = 0;
1837         ctx->state = UFFD_STATE_WAIT_API;
1838         ctx->released = false;
1839         ctx->mm = current->mm;
1840         /* prevent the mm struct to be freed */
1841         mmgrab(ctx->mm);
1842
1843         file = anon_inode_getfile("[userfaultfd]", &userfaultfd_fops, ctx,
1844                                   O_RDWR | (flags & UFFD_SHARED_FCNTL_FLAGS));
1845         if (IS_ERR(file)) {
1846                 mmdrop(ctx->mm);
1847                 kmem_cache_free(userfaultfd_ctx_cachep, ctx);
1848         }
1849 out:
1850         return file;
1851 }
1852
1853 SYSCALL_DEFINE1(userfaultfd, int, flags)
1854 {
1855         int fd, error;
1856         struct file *file;
1857
1858         error = get_unused_fd_flags(flags & UFFD_SHARED_FCNTL_FLAGS);
1859         if (error < 0)
1860                 return error;
1861         fd = error;
1862
1863         file = userfaultfd_file_create(flags);
1864         if (IS_ERR(file)) {
1865                 error = PTR_ERR(file);
1866                 goto err_put_unused_fd;
1867         }
1868         fd_install(fd, file);
1869
1870         return fd;
1871
1872 err_put_unused_fd:
1873         put_unused_fd(fd);
1874
1875         return error;
1876 }
1877
1878 static int __init userfaultfd_init(void)
1879 {
1880         userfaultfd_ctx_cachep = kmem_cache_create("userfaultfd_ctx_cache",
1881                                                 sizeof(struct userfaultfd_ctx),
1882                                                 0,
1883                                                 SLAB_HWCACHE_ALIGN|SLAB_PANIC,
1884                                                 init_once_userfaultfd_ctx);
1885         return 0;
1886 }
1887 __initcall(userfaultfd_init);