userfaultfd_release: always remove uffd flags and clear vm_userfaultfd_ctx
[sfrench/cifs-2.6.git] / fs / userfaultfd.c
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/poll.h>
19 #include <linux/slab.h>
20 #include <linux/seq_file.h>
21 #include <linux/file.h>
22 #include <linux/bug.h>
23 #include <linux/anon_inodes.h>
24 #include <linux/syscalls.h>
25 #include <linux/userfaultfd_k.h>
26 #include <linux/mempolicy.h>
27 #include <linux/ioctl.h>
28 #include <linux/security.h>
29 #include <linux/hugetlb.h>
30
31 int sysctl_unprivileged_userfaultfd __read_mostly = 1;
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  * Locking order:
45  *      fd_wqh.lock
46  *              fault_pending_wqh.lock
47  *                      fault_wqh.lock
48  *              event_wqh.lock
49  *
50  * To avoid deadlocks, IRQs must be disabled when taking any of the above locks,
51  * since fd_wqh.lock is taken by aio_poll() while it's holding a lock that's
52  * also taken in IRQ context.
53  */
54 struct userfaultfd_ctx {
55         /* waitqueue head for the pending (i.e. not read) userfaults */
56         wait_queue_head_t fault_pending_wqh;
57         /* waitqueue head for the userfaults */
58         wait_queue_head_t fault_wqh;
59         /* waitqueue head for the pseudo fd to wakeup poll/read */
60         wait_queue_head_t fd_wqh;
61         /* waitqueue head for events */
62         wait_queue_head_t event_wqh;
63         /* a refile sequence protected by fault_pending_wqh lock */
64         struct seqcount refile_seq;
65         /* pseudo fd refcounting */
66         refcount_t refcount;
67         /* userfaultfd syscall flags */
68         unsigned int flags;
69         /* features requested from the userspace */
70         unsigned int features;
71         /* state machine */
72         enum userfaultfd_state state;
73         /* released */
74         bool released;
75         /* memory mappings are changing because of non-cooperative event */
76         bool mmap_changing;
77         /* mm with one ore more vmas attached to this userfaultfd_ctx */
78         struct mm_struct *mm;
79 };
80
81 struct userfaultfd_fork_ctx {
82         struct userfaultfd_ctx *orig;
83         struct userfaultfd_ctx *new;
84         struct list_head list;
85 };
86
87 struct userfaultfd_unmap_ctx {
88         struct userfaultfd_ctx *ctx;
89         unsigned long start;
90         unsigned long end;
91         struct list_head list;
92 };
93
94 struct userfaultfd_wait_queue {
95         struct uffd_msg msg;
96         wait_queue_entry_t wq;
97         struct userfaultfd_ctx *ctx;
98         bool waken;
99 };
100
101 struct userfaultfd_wake_range {
102         unsigned long start;
103         unsigned long len;
104 };
105
106 static int userfaultfd_wake_function(wait_queue_entry_t *wq, unsigned mode,
107                                      int wake_flags, void *key)
108 {
109         struct userfaultfd_wake_range *range = key;
110         int ret;
111         struct userfaultfd_wait_queue *uwq;
112         unsigned long start, len;
113
114         uwq = container_of(wq, struct userfaultfd_wait_queue, wq);
115         ret = 0;
116         /* len == 0 means wake all */
117         start = range->start;
118         len = range->len;
119         if (len && (start > uwq->msg.arg.pagefault.address ||
120                     start + len <= uwq->msg.arg.pagefault.address))
121                 goto out;
122         WRITE_ONCE(uwq->waken, true);
123         /*
124          * The Program-Order guarantees provided by the scheduler
125          * ensure uwq->waken is visible before the task is woken.
126          */
127         ret = wake_up_state(wq->private, mode);
128         if (ret) {
129                 /*
130                  * Wake only once, autoremove behavior.
131                  *
132                  * After the effect of list_del_init is visible to the other
133                  * CPUs, the waitqueue may disappear from under us, see the
134                  * !list_empty_careful() in handle_userfault().
135                  *
136                  * try_to_wake_up() has an implicit smp_mb(), and the
137                  * wq->private is read before calling the extern function
138                  * "wake_up_state" (which in turns calls try_to_wake_up).
139                  */
140                 list_del_init(&wq->entry);
141         }
142 out:
143         return ret;
144 }
145
146 /**
147  * userfaultfd_ctx_get - Acquires a reference to the internal userfaultfd
148  * context.
149  * @ctx: [in] Pointer to the userfaultfd context.
150  */
151 static void userfaultfd_ctx_get(struct userfaultfd_ctx *ctx)
152 {
153         refcount_inc(&ctx->refcount);
154 }
155
156 /**
157  * userfaultfd_ctx_put - Releases a reference to the internal userfaultfd
158  * context.
159  * @ctx: [in] Pointer to userfaultfd context.
160  *
161  * The userfaultfd context reference must have been previously acquired either
162  * with userfaultfd_ctx_get() or userfaultfd_ctx_fdget().
163  */
164 static void userfaultfd_ctx_put(struct userfaultfd_ctx *ctx)
165 {
166         if (refcount_dec_and_test(&ctx->refcount)) {
167                 VM_BUG_ON(spin_is_locked(&ctx->fault_pending_wqh.lock));
168                 VM_BUG_ON(waitqueue_active(&ctx->fault_pending_wqh));
169                 VM_BUG_ON(spin_is_locked(&ctx->fault_wqh.lock));
170                 VM_BUG_ON(waitqueue_active(&ctx->fault_wqh));
171                 VM_BUG_ON(spin_is_locked(&ctx->event_wqh.lock));
172                 VM_BUG_ON(waitqueue_active(&ctx->event_wqh));
173                 VM_BUG_ON(spin_is_locked(&ctx->fd_wqh.lock));
174                 VM_BUG_ON(waitqueue_active(&ctx->fd_wqh));
175                 mmdrop(ctx->mm);
176                 kmem_cache_free(userfaultfd_ctx_cachep, ctx);
177         }
178 }
179
180 static inline void msg_init(struct uffd_msg *msg)
181 {
182         BUILD_BUG_ON(sizeof(struct uffd_msg) != 32);
183         /*
184          * Must use memset to zero out the paddings or kernel data is
185          * leaked to userland.
186          */
187         memset(msg, 0, sizeof(struct uffd_msg));
188 }
189
190 static inline struct uffd_msg userfault_msg(unsigned long address,
191                                             unsigned int flags,
192                                             unsigned long reason,
193                                             unsigned int features)
194 {
195         struct uffd_msg msg;
196         msg_init(&msg);
197         msg.event = UFFD_EVENT_PAGEFAULT;
198         msg.arg.pagefault.address = address;
199         if (flags & FAULT_FLAG_WRITE)
200                 /*
201                  * If UFFD_FEATURE_PAGEFAULT_FLAG_WP was set in the
202                  * uffdio_api.features and UFFD_PAGEFAULT_FLAG_WRITE
203                  * was not set in a UFFD_EVENT_PAGEFAULT, it means it
204                  * was a read fault, otherwise if set it means it's
205                  * a write fault.
206                  */
207                 msg.arg.pagefault.flags |= UFFD_PAGEFAULT_FLAG_WRITE;
208         if (reason & VM_UFFD_WP)
209                 /*
210                  * If UFFD_FEATURE_PAGEFAULT_FLAG_WP was set in the
211                  * uffdio_api.features and UFFD_PAGEFAULT_FLAG_WP was
212                  * not set in a UFFD_EVENT_PAGEFAULT, it means it was
213                  * a missing fault, otherwise if set it means it's a
214                  * write protect fault.
215                  */
216                 msg.arg.pagefault.flags |= UFFD_PAGEFAULT_FLAG_WP;
217         if (features & UFFD_FEATURE_THREAD_ID)
218                 msg.arg.pagefault.feat.ptid = task_pid_vnr(current);
219         return msg;
220 }
221
222 #ifdef CONFIG_HUGETLB_PAGE
223 /*
224  * Same functionality as userfaultfd_must_wait below with modifications for
225  * hugepmd ranges.
226  */
227 static inline bool userfaultfd_huge_must_wait(struct userfaultfd_ctx *ctx,
228                                          struct vm_area_struct *vma,
229                                          unsigned long address,
230                                          unsigned long flags,
231                                          unsigned long reason)
232 {
233         struct mm_struct *mm = ctx->mm;
234         pte_t *ptep, pte;
235         bool ret = true;
236
237         VM_BUG_ON(!rwsem_is_locked(&mm->mmap_sem));
238
239         ptep = huge_pte_offset(mm, address, vma_mmu_pagesize(vma));
240
241         if (!ptep)
242                 goto out;
243
244         ret = false;
245         pte = huge_ptep_get(ptep);
246
247         /*
248          * Lockless access: we're in a wait_event so it's ok if it
249          * changes under us.
250          */
251         if (huge_pte_none(pte))
252                 ret = true;
253         if (!huge_pte_write(pte) && (reason & VM_UFFD_WP))
254                 ret = true;
255 out:
256         return ret;
257 }
258 #else
259 static inline bool userfaultfd_huge_must_wait(struct userfaultfd_ctx *ctx,
260                                          struct vm_area_struct *vma,
261                                          unsigned long address,
262                                          unsigned long flags,
263                                          unsigned long reason)
264 {
265         return false;   /* should never get here */
266 }
267 #endif /* CONFIG_HUGETLB_PAGE */
268
269 /*
270  * Verify the pagetables are still not ok after having reigstered into
271  * the fault_pending_wqh to avoid userland having to UFFDIO_WAKE any
272  * userfault that has already been resolved, if userfaultfd_read and
273  * UFFDIO_COPY|ZEROPAGE are being run simultaneously on two different
274  * threads.
275  */
276 static inline bool userfaultfd_must_wait(struct userfaultfd_ctx *ctx,
277                                          unsigned long address,
278                                          unsigned long flags,
279                                          unsigned long reason)
280 {
281         struct mm_struct *mm = ctx->mm;
282         pgd_t *pgd;
283         p4d_t *p4d;
284         pud_t *pud;
285         pmd_t *pmd, _pmd;
286         pte_t *pte;
287         bool ret = true;
288
289         VM_BUG_ON(!rwsem_is_locked(&mm->mmap_sem));
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         /*
302          * READ_ONCE must function as a barrier with narrower scope
303          * and it must be equivalent to:
304          *      _pmd = *pmd; barrier();
305          *
306          * This is to deal with the instability (as in
307          * pmd_trans_unstable) of the pmd.
308          */
309         _pmd = READ_ONCE(*pmd);
310         if (pmd_none(_pmd))
311                 goto out;
312
313         ret = false;
314         if (!pmd_present(_pmd))
315                 goto out;
316
317         if (pmd_trans_huge(_pmd))
318                 goto out;
319
320         /*
321          * the pmd is stable (as in !pmd_trans_unstable) so we can re-read it
322          * and use the standard pte_offset_map() instead of parsing _pmd.
323          */
324         pte = pte_offset_map(pmd, address);
325         /*
326          * Lockless access: we're in a wait_event so it's ok if it
327          * changes under us.
328          */
329         if (pte_none(*pte))
330                 ret = true;
331         pte_unmap(pte);
332
333 out:
334         return ret;
335 }
336
337 /*
338  * The locking rules involved in returning VM_FAULT_RETRY depending on
339  * FAULT_FLAG_ALLOW_RETRY, FAULT_FLAG_RETRY_NOWAIT and
340  * FAULT_FLAG_KILLABLE are not straightforward. The "Caution"
341  * recommendation in __lock_page_or_retry is not an understatement.
342  *
343  * If FAULT_FLAG_ALLOW_RETRY is set, the mmap_sem must be released
344  * before returning VM_FAULT_RETRY only if FAULT_FLAG_RETRY_NOWAIT is
345  * not set.
346  *
347  * If FAULT_FLAG_ALLOW_RETRY is set but FAULT_FLAG_KILLABLE is not
348  * set, VM_FAULT_RETRY can still be returned if and only if there are
349  * fatal_signal_pending()s, and the mmap_sem must be released before
350  * returning it.
351  */
352 vm_fault_t handle_userfault(struct vm_fault *vmf, unsigned long reason)
353 {
354         struct mm_struct *mm = vmf->vma->vm_mm;
355         struct userfaultfd_ctx *ctx;
356         struct userfaultfd_wait_queue uwq;
357         vm_fault_t ret = VM_FAULT_SIGBUS;
358         bool must_wait, return_to_userland;
359         long blocking_state;
360
361         /*
362          * We don't do userfault handling for the final child pid update.
363          *
364          * We also don't do userfault handling during
365          * coredumping. hugetlbfs has the special
366          * follow_hugetlb_page() to skip missing pages in the
367          * FOLL_DUMP case, anon memory also checks for FOLL_DUMP with
368          * the no_page_table() helper in follow_page_mask(), but the
369          * shmem_vm_ops->fault method is invoked even during
370          * coredumping without mmap_sem and it ends up here.
371          */
372         if (current->flags & (PF_EXITING|PF_DUMPCORE))
373                 goto out;
374
375         /*
376          * Coredumping runs without mmap_sem so we can only check that
377          * the mmap_sem is held, if PF_DUMPCORE was not set.
378          */
379         WARN_ON_ONCE(!rwsem_is_locked(&mm->mmap_sem));
380
381         ctx = vmf->vma->vm_userfaultfd_ctx.ctx;
382         if (!ctx)
383                 goto out;
384
385         BUG_ON(ctx->mm != mm);
386
387         VM_BUG_ON(reason & ~(VM_UFFD_MISSING|VM_UFFD_WP));
388         VM_BUG_ON(!(reason & VM_UFFD_MISSING) ^ !!(reason & VM_UFFD_WP));
389
390         if (ctx->features & UFFD_FEATURE_SIGBUS)
391                 goto out;
392
393         /*
394          * If it's already released don't get it. This avoids to loop
395          * in __get_user_pages if userfaultfd_release waits on the
396          * caller of handle_userfault to release the mmap_sem.
397          */
398         if (unlikely(READ_ONCE(ctx->released))) {
399                 /*
400                  * Don't return VM_FAULT_SIGBUS in this case, so a non
401                  * cooperative manager can close the uffd after the
402                  * last UFFDIO_COPY, without risking to trigger an
403                  * involuntary SIGBUS if the process was starting the
404                  * userfaultfd while the userfaultfd was still armed
405                  * (but after the last UFFDIO_COPY). If the uffd
406                  * wasn't already closed when the userfault reached
407                  * this point, that would normally be solved by
408                  * userfaultfd_must_wait returning 'false'.
409                  *
410                  * If we were to return VM_FAULT_SIGBUS here, the non
411                  * cooperative manager would be instead forced to
412                  * always call UFFDIO_UNREGISTER before it can safely
413                  * close the uffd.
414                  */
415                 ret = VM_FAULT_NOPAGE;
416                 goto out;
417         }
418
419         /*
420          * Check that we can return VM_FAULT_RETRY.
421          *
422          * NOTE: it should become possible to return VM_FAULT_RETRY
423          * even if FAULT_FLAG_TRIED is set without leading to gup()
424          * -EBUSY failures, if the userfaultfd is to be extended for
425          * VM_UFFD_WP tracking and we intend to arm the userfault
426          * without first stopping userland access to the memory. For
427          * VM_UFFD_MISSING userfaults this is enough for now.
428          */
429         if (unlikely(!(vmf->flags & FAULT_FLAG_ALLOW_RETRY))) {
430                 /*
431                  * Validate the invariant that nowait must allow retry
432                  * to be sure not to return SIGBUS erroneously on
433                  * nowait invocations.
434                  */
435                 BUG_ON(vmf->flags & FAULT_FLAG_RETRY_NOWAIT);
436 #ifdef CONFIG_DEBUG_VM
437                 if (printk_ratelimit()) {
438                         printk(KERN_WARNING
439                                "FAULT_FLAG_ALLOW_RETRY missing %x\n",
440                                vmf->flags);
441                         dump_stack();
442                 }
443 #endif
444                 goto out;
445         }
446
447         /*
448          * Handle nowait, not much to do other than tell it to retry
449          * and wait.
450          */
451         ret = VM_FAULT_RETRY;
452         if (vmf->flags & FAULT_FLAG_RETRY_NOWAIT)
453                 goto out;
454
455         /* take the reference before dropping the mmap_sem */
456         userfaultfd_ctx_get(ctx);
457
458         init_waitqueue_func_entry(&uwq.wq, userfaultfd_wake_function);
459         uwq.wq.private = current;
460         uwq.msg = userfault_msg(vmf->address, vmf->flags, reason,
461                         ctx->features);
462         uwq.ctx = ctx;
463         uwq.waken = false;
464
465         return_to_userland =
466                 (vmf->flags & (FAULT_FLAG_USER|FAULT_FLAG_KILLABLE)) ==
467                 (FAULT_FLAG_USER|FAULT_FLAG_KILLABLE);
468         blocking_state = return_to_userland ? TASK_INTERRUPTIBLE :
469                          TASK_KILLABLE;
470
471         spin_lock_irq(&ctx->fault_pending_wqh.lock);
472         /*
473          * After the __add_wait_queue the uwq is visible to userland
474          * through poll/read().
475          */
476         __add_wait_queue(&ctx->fault_pending_wqh, &uwq.wq);
477         /*
478          * The smp_mb() after __set_current_state prevents the reads
479          * following the spin_unlock to happen before the list_add in
480          * __add_wait_queue.
481          */
482         set_current_state(blocking_state);
483         spin_unlock_irq(&ctx->fault_pending_wqh.lock);
484
485         if (!is_vm_hugetlb_page(vmf->vma))
486                 must_wait = userfaultfd_must_wait(ctx, vmf->address, vmf->flags,
487                                                   reason);
488         else
489                 must_wait = userfaultfd_huge_must_wait(ctx, vmf->vma,
490                                                        vmf->address,
491                                                        vmf->flags, reason);
492         up_read(&mm->mmap_sem);
493
494         if (likely(must_wait && !READ_ONCE(ctx->released) &&
495                    (return_to_userland ? !signal_pending(current) :
496                     !fatal_signal_pending(current)))) {
497                 wake_up_poll(&ctx->fd_wqh, EPOLLIN);
498                 schedule();
499                 ret |= VM_FAULT_MAJOR;
500
501                 /*
502                  * False wakeups can orginate even from rwsem before
503                  * up_read() however userfaults will wait either for a
504                  * targeted wakeup on the specific uwq waitqueue from
505                  * wake_userfault() or for signals or for uffd
506                  * release.
507                  */
508                 while (!READ_ONCE(uwq.waken)) {
509                         /*
510                          * This needs the full smp_store_mb()
511                          * guarantee as the state write must be
512                          * visible to other CPUs before reading
513                          * uwq.waken from other CPUs.
514                          */
515                         set_current_state(blocking_state);
516                         if (READ_ONCE(uwq.waken) ||
517                             READ_ONCE(ctx->released) ||
518                             (return_to_userland ? signal_pending(current) :
519                              fatal_signal_pending(current)))
520                                 break;
521                         schedule();
522                 }
523         }
524
525         __set_current_state(TASK_RUNNING);
526
527         if (return_to_userland) {
528                 if (signal_pending(current) &&
529                     !fatal_signal_pending(current)) {
530                         /*
531                          * If we got a SIGSTOP or SIGCONT and this is
532                          * a normal userland page fault, just let
533                          * userland return so the signal will be
534                          * handled and gdb debugging works.  The page
535                          * fault code immediately after we return from
536                          * this function is going to release the
537                          * mmap_sem and it's not depending on it
538                          * (unlike gup would if we were not to return
539                          * VM_FAULT_RETRY).
540                          *
541                          * If a fatal signal is pending we still take
542                          * the streamlined VM_FAULT_RETRY failure path
543                          * and there's no need to retake the mmap_sem
544                          * in such case.
545                          */
546                         down_read(&mm->mmap_sem);
547                         ret = VM_FAULT_NOPAGE;
548                 }
549         }
550
551         /*
552          * Here we race with the list_del; list_add in
553          * userfaultfd_ctx_read(), however because we don't ever run
554          * list_del_init() to refile across the two lists, the prev
555          * and next pointers will never point to self. list_add also
556          * would never let any of the two pointers to point to
557          * self. So list_empty_careful won't risk to see both pointers
558          * pointing to self at any time during the list refile. The
559          * only case where list_del_init() is called is the full
560          * removal in the wake function and there we don't re-list_add
561          * and it's fine not to block on the spinlock. The uwq on this
562          * kernel stack can be released after the list_del_init.
563          */
564         if (!list_empty_careful(&uwq.wq.entry)) {
565                 spin_lock_irq(&ctx->fault_pending_wqh.lock);
566                 /*
567                  * No need of list_del_init(), the uwq on the stack
568                  * will be freed shortly anyway.
569                  */
570                 list_del(&uwq.wq.entry);
571                 spin_unlock_irq(&ctx->fault_pending_wqh.lock);
572         }
573
574         /*
575          * ctx may go away after this if the userfault pseudo fd is
576          * already released.
577          */
578         userfaultfd_ctx_put(ctx);
579
580 out:
581         return ret;
582 }
583
584 static void userfaultfd_event_wait_completion(struct userfaultfd_ctx *ctx,
585                                               struct userfaultfd_wait_queue *ewq)
586 {
587         struct userfaultfd_ctx *release_new_ctx;
588
589         if (WARN_ON_ONCE(current->flags & PF_EXITING))
590                 goto out;
591
592         ewq->ctx = ctx;
593         init_waitqueue_entry(&ewq->wq, current);
594         release_new_ctx = NULL;
595
596         spin_lock_irq(&ctx->event_wqh.lock);
597         /*
598          * After the __add_wait_queue the uwq is visible to userland
599          * through poll/read().
600          */
601         __add_wait_queue(&ctx->event_wqh, &ewq->wq);
602         for (;;) {
603                 set_current_state(TASK_KILLABLE);
604                 if (ewq->msg.event == 0)
605                         break;
606                 if (READ_ONCE(ctx->released) ||
607                     fatal_signal_pending(current)) {
608                         /*
609                          * &ewq->wq may be queued in fork_event, but
610                          * __remove_wait_queue ignores the head
611                          * parameter. It would be a problem if it
612                          * didn't.
613                          */
614                         __remove_wait_queue(&ctx->event_wqh, &ewq->wq);
615                         if (ewq->msg.event == UFFD_EVENT_FORK) {
616                                 struct userfaultfd_ctx *new;
617
618                                 new = (struct userfaultfd_ctx *)
619                                         (unsigned long)
620                                         ewq->msg.arg.reserved.reserved1;
621                                 release_new_ctx = new;
622                         }
623                         break;
624                 }
625
626                 spin_unlock_irq(&ctx->event_wqh.lock);
627
628                 wake_up_poll(&ctx->fd_wqh, EPOLLIN);
629                 schedule();
630
631                 spin_lock_irq(&ctx->event_wqh.lock);
632         }
633         __set_current_state(TASK_RUNNING);
634         spin_unlock_irq(&ctx->event_wqh.lock);
635
636         if (release_new_ctx) {
637                 struct vm_area_struct *vma;
638                 struct mm_struct *mm = release_new_ctx->mm;
639
640                 /* the various vma->vm_userfaultfd_ctx still points to it */
641                 down_write(&mm->mmap_sem);
642                 /* no task can run (and in turn coredump) yet */
643                 VM_WARN_ON(!mmget_still_valid(mm));
644                 for (vma = mm->mmap; vma; vma = vma->vm_next)
645                         if (vma->vm_userfaultfd_ctx.ctx == release_new_ctx) {
646                                 vma->vm_userfaultfd_ctx = NULL_VM_UFFD_CTX;
647                                 vma->vm_flags &= ~(VM_UFFD_WP | VM_UFFD_MISSING);
648                         }
649                 up_write(&mm->mmap_sem);
650
651                 userfaultfd_ctx_put(release_new_ctx);
652         }
653
654         /*
655          * ctx may go away after this if the userfault pseudo fd is
656          * already released.
657          */
658 out:
659         WRITE_ONCE(ctx->mmap_changing, false);
660         userfaultfd_ctx_put(ctx);
661 }
662
663 static void userfaultfd_event_complete(struct userfaultfd_ctx *ctx,
664                                        struct userfaultfd_wait_queue *ewq)
665 {
666         ewq->msg.event = 0;
667         wake_up_locked(&ctx->event_wqh);
668         __remove_wait_queue(&ctx->event_wqh, &ewq->wq);
669 }
670
671 int dup_userfaultfd(struct vm_area_struct *vma, struct list_head *fcs)
672 {
673         struct userfaultfd_ctx *ctx = NULL, *octx;
674         struct userfaultfd_fork_ctx *fctx;
675
676         octx = vma->vm_userfaultfd_ctx.ctx;
677         if (!octx || !(octx->features & UFFD_FEATURE_EVENT_FORK)) {
678                 vma->vm_userfaultfd_ctx = NULL_VM_UFFD_CTX;
679                 vma->vm_flags &= ~(VM_UFFD_WP | VM_UFFD_MISSING);
680                 return 0;
681         }
682
683         list_for_each_entry(fctx, fcs, list)
684                 if (fctx->orig == octx) {
685                         ctx = fctx->new;
686                         break;
687                 }
688
689         if (!ctx) {
690                 fctx = kmalloc(sizeof(*fctx), GFP_KERNEL);
691                 if (!fctx)
692                         return -ENOMEM;
693
694                 ctx = kmem_cache_alloc(userfaultfd_ctx_cachep, GFP_KERNEL);
695                 if (!ctx) {
696                         kfree(fctx);
697                         return -ENOMEM;
698                 }
699
700                 refcount_set(&ctx->refcount, 1);
701                 ctx->flags = octx->flags;
702                 ctx->state = UFFD_STATE_RUNNING;
703                 ctx->features = octx->features;
704                 ctx->released = false;
705                 ctx->mmap_changing = false;
706                 ctx->mm = vma->vm_mm;
707                 mmgrab(ctx->mm);
708
709                 userfaultfd_ctx_get(octx);
710                 WRITE_ONCE(octx->mmap_changing, true);
711                 fctx->orig = octx;
712                 fctx->new = ctx;
713                 list_add_tail(&fctx->list, fcs);
714         }
715
716         vma->vm_userfaultfd_ctx.ctx = ctx;
717         return 0;
718 }
719
720 static void dup_fctx(struct userfaultfd_fork_ctx *fctx)
721 {
722         struct userfaultfd_ctx *ctx = fctx->orig;
723         struct userfaultfd_wait_queue ewq;
724
725         msg_init(&ewq.msg);
726
727         ewq.msg.event = UFFD_EVENT_FORK;
728         ewq.msg.arg.reserved.reserved1 = (unsigned long)fctx->new;
729
730         userfaultfd_event_wait_completion(ctx, &ewq);
731 }
732
733 void dup_userfaultfd_complete(struct list_head *fcs)
734 {
735         struct userfaultfd_fork_ctx *fctx, *n;
736
737         list_for_each_entry_safe(fctx, n, fcs, list) {
738                 dup_fctx(fctx);
739                 list_del(&fctx->list);
740                 kfree(fctx);
741         }
742 }
743
744 void mremap_userfaultfd_prep(struct vm_area_struct *vma,
745                              struct vm_userfaultfd_ctx *vm_ctx)
746 {
747         struct userfaultfd_ctx *ctx;
748
749         ctx = vma->vm_userfaultfd_ctx.ctx;
750
751         if (!ctx)
752                 return;
753
754         if (ctx->features & UFFD_FEATURE_EVENT_REMAP) {
755                 vm_ctx->ctx = ctx;
756                 userfaultfd_ctx_get(ctx);
757                 WRITE_ONCE(ctx->mmap_changing, true);
758         } else {
759                 /* Drop uffd context if remap feature not enabled */
760                 vma->vm_userfaultfd_ctx = NULL_VM_UFFD_CTX;
761                 vma->vm_flags &= ~(VM_UFFD_WP | VM_UFFD_MISSING);
762         }
763 }
764
765 void mremap_userfaultfd_complete(struct vm_userfaultfd_ctx *vm_ctx,
766                                  unsigned long from, unsigned long to,
767                                  unsigned long len)
768 {
769         struct userfaultfd_ctx *ctx = vm_ctx->ctx;
770         struct userfaultfd_wait_queue ewq;
771
772         if (!ctx)
773                 return;
774
775         if (to & ~PAGE_MASK) {
776                 userfaultfd_ctx_put(ctx);
777                 return;
778         }
779
780         msg_init(&ewq.msg);
781
782         ewq.msg.event = UFFD_EVENT_REMAP;
783         ewq.msg.arg.remap.from = from;
784         ewq.msg.arg.remap.to = to;
785         ewq.msg.arg.remap.len = len;
786
787         userfaultfd_event_wait_completion(ctx, &ewq);
788 }
789
790 bool userfaultfd_remove(struct vm_area_struct *vma,
791                         unsigned long start, unsigned long end)
792 {
793         struct mm_struct *mm = vma->vm_mm;
794         struct userfaultfd_ctx *ctx;
795         struct userfaultfd_wait_queue ewq;
796
797         ctx = vma->vm_userfaultfd_ctx.ctx;
798         if (!ctx || !(ctx->features & UFFD_FEATURE_EVENT_REMOVE))
799                 return true;
800
801         userfaultfd_ctx_get(ctx);
802         WRITE_ONCE(ctx->mmap_changing, true);
803         up_read(&mm->mmap_sem);
804
805         msg_init(&ewq.msg);
806
807         ewq.msg.event = UFFD_EVENT_REMOVE;
808         ewq.msg.arg.remove.start = start;
809         ewq.msg.arg.remove.end = end;
810
811         userfaultfd_event_wait_completion(ctx, &ewq);
812
813         return false;
814 }
815
816 static bool has_unmap_ctx(struct userfaultfd_ctx *ctx, struct list_head *unmaps,
817                           unsigned long start, unsigned long end)
818 {
819         struct userfaultfd_unmap_ctx *unmap_ctx;
820
821         list_for_each_entry(unmap_ctx, unmaps, list)
822                 if (unmap_ctx->ctx == ctx && unmap_ctx->start == start &&
823                     unmap_ctx->end == end)
824                         return true;
825
826         return false;
827 }
828
829 int userfaultfd_unmap_prep(struct vm_area_struct *vma,
830                            unsigned long start, unsigned long end,
831                            struct list_head *unmaps)
832 {
833         for ( ; vma && vma->vm_start < end; vma = vma->vm_next) {
834                 struct userfaultfd_unmap_ctx *unmap_ctx;
835                 struct userfaultfd_ctx *ctx = vma->vm_userfaultfd_ctx.ctx;
836
837                 if (!ctx || !(ctx->features & UFFD_FEATURE_EVENT_UNMAP) ||
838                     has_unmap_ctx(ctx, unmaps, start, end))
839                         continue;
840
841                 unmap_ctx = kzalloc(sizeof(*unmap_ctx), GFP_KERNEL);
842                 if (!unmap_ctx)
843                         return -ENOMEM;
844
845                 userfaultfd_ctx_get(ctx);
846                 WRITE_ONCE(ctx->mmap_changing, true);
847                 unmap_ctx->ctx = ctx;
848                 unmap_ctx->start = start;
849                 unmap_ctx->end = end;
850                 list_add_tail(&unmap_ctx->list, unmaps);
851         }
852
853         return 0;
854 }
855
856 void userfaultfd_unmap_complete(struct mm_struct *mm, struct list_head *uf)
857 {
858         struct userfaultfd_unmap_ctx *ctx, *n;
859         struct userfaultfd_wait_queue ewq;
860
861         list_for_each_entry_safe(ctx, n, uf, list) {
862                 msg_init(&ewq.msg);
863
864                 ewq.msg.event = UFFD_EVENT_UNMAP;
865                 ewq.msg.arg.remove.start = ctx->start;
866                 ewq.msg.arg.remove.end = ctx->end;
867
868                 userfaultfd_event_wait_completion(ctx->ctx, &ewq);
869
870                 list_del(&ctx->list);
871                 kfree(ctx);
872         }
873 }
874
875 static int userfaultfd_release(struct inode *inode, struct file *file)
876 {
877         struct userfaultfd_ctx *ctx = file->private_data;
878         struct mm_struct *mm = ctx->mm;
879         struct vm_area_struct *vma, *prev;
880         /* len == 0 means wake all */
881         struct userfaultfd_wake_range range = { .len = 0, };
882         unsigned long new_flags;
883         bool still_valid;
884
885         WRITE_ONCE(ctx->released, true);
886
887         if (!mmget_not_zero(mm))
888                 goto wakeup;
889
890         /*
891          * Flush page faults out of all CPUs. NOTE: all page faults
892          * must be retried without returning VM_FAULT_SIGBUS if
893          * userfaultfd_ctx_get() succeeds but vma->vma_userfault_ctx
894          * changes while handle_userfault released the mmap_sem. So
895          * it's critical that released is set to true (above), before
896          * taking the mmap_sem for writing.
897          */
898         down_write(&mm->mmap_sem);
899         still_valid = mmget_still_valid(mm);
900         prev = NULL;
901         for (vma = mm->mmap; vma; vma = vma->vm_next) {
902                 cond_resched();
903                 BUG_ON(!!vma->vm_userfaultfd_ctx.ctx ^
904                        !!(vma->vm_flags & (VM_UFFD_MISSING | VM_UFFD_WP)));
905                 if (vma->vm_userfaultfd_ctx.ctx != ctx) {
906                         prev = vma;
907                         continue;
908                 }
909                 new_flags = vma->vm_flags & ~(VM_UFFD_MISSING | VM_UFFD_WP);
910                 if (still_valid) {
911                         prev = vma_merge(mm, prev, vma->vm_start, vma->vm_end,
912                                          new_flags, vma->anon_vma,
913                                          vma->vm_file, vma->vm_pgoff,
914                                          vma_policy(vma),
915                                          NULL_VM_UFFD_CTX);
916                         if (prev)
917                                 vma = prev;
918                         else
919                                 prev = vma;
920                 }
921                 vma->vm_flags = new_flags;
922                 vma->vm_userfaultfd_ctx = NULL_VM_UFFD_CTX;
923         }
924         up_write(&mm->mmap_sem);
925         mmput(mm);
926 wakeup:
927         /*
928          * After no new page faults can wait on this fault_*wqh, flush
929          * the last page faults that may have been already waiting on
930          * the fault_*wqh.
931          */
932         spin_lock_irq(&ctx->fault_pending_wqh.lock);
933         __wake_up_locked_key(&ctx->fault_pending_wqh, TASK_NORMAL, &range);
934         __wake_up(&ctx->fault_wqh, TASK_NORMAL, 1, &range);
935         spin_unlock_irq(&ctx->fault_pending_wqh.lock);
936
937         /* Flush pending events that may still wait on event_wqh */
938         wake_up_all(&ctx->event_wqh);
939
940         wake_up_poll(&ctx->fd_wqh, EPOLLHUP);
941         userfaultfd_ctx_put(ctx);
942         return 0;
943 }
944
945 /* fault_pending_wqh.lock must be hold by the caller */
946 static inline struct userfaultfd_wait_queue *find_userfault_in(
947                 wait_queue_head_t *wqh)
948 {
949         wait_queue_entry_t *wq;
950         struct userfaultfd_wait_queue *uwq;
951
952         lockdep_assert_held(&wqh->lock);
953
954         uwq = NULL;
955         if (!waitqueue_active(wqh))
956                 goto out;
957         /* walk in reverse to provide FIFO behavior to read userfaults */
958         wq = list_last_entry(&wqh->head, typeof(*wq), entry);
959         uwq = container_of(wq, struct userfaultfd_wait_queue, wq);
960 out:
961         return uwq;
962 }
963
964 static inline struct userfaultfd_wait_queue *find_userfault(
965                 struct userfaultfd_ctx *ctx)
966 {
967         return find_userfault_in(&ctx->fault_pending_wqh);
968 }
969
970 static inline struct userfaultfd_wait_queue *find_userfault_evt(
971                 struct userfaultfd_ctx *ctx)
972 {
973         return find_userfault_in(&ctx->event_wqh);
974 }
975
976 static __poll_t userfaultfd_poll(struct file *file, poll_table *wait)
977 {
978         struct userfaultfd_ctx *ctx = file->private_data;
979         __poll_t ret;
980
981         poll_wait(file, &ctx->fd_wqh, wait);
982
983         switch (ctx->state) {
984         case UFFD_STATE_WAIT_API:
985                 return EPOLLERR;
986         case UFFD_STATE_RUNNING:
987                 /*
988                  * poll() never guarantees that read won't block.
989                  * userfaults can be waken before they're read().
990                  */
991                 if (unlikely(!(file->f_flags & O_NONBLOCK)))
992                         return EPOLLERR;
993                 /*
994                  * lockless access to see if there are pending faults
995                  * __pollwait last action is the add_wait_queue but
996                  * the spin_unlock would allow the waitqueue_active to
997                  * pass above the actual list_add inside
998                  * add_wait_queue critical section. So use a full
999                  * memory barrier to serialize the list_add write of
1000                  * add_wait_queue() with the waitqueue_active read
1001                  * below.
1002                  */
1003                 ret = 0;
1004                 smp_mb();
1005                 if (waitqueue_active(&ctx->fault_pending_wqh))
1006                         ret = EPOLLIN;
1007                 else if (waitqueue_active(&ctx->event_wqh))
1008                         ret = EPOLLIN;
1009
1010                 return ret;
1011         default:
1012                 WARN_ON_ONCE(1);
1013                 return EPOLLERR;
1014         }
1015 }
1016
1017 static const struct file_operations userfaultfd_fops;
1018
1019 static int resolve_userfault_fork(struct userfaultfd_ctx *ctx,
1020                                   struct userfaultfd_ctx *new,
1021                                   struct uffd_msg *msg)
1022 {
1023         int fd;
1024
1025         fd = anon_inode_getfd("[userfaultfd]", &userfaultfd_fops, new,
1026                               O_RDWR | (new->flags & UFFD_SHARED_FCNTL_FLAGS));
1027         if (fd < 0)
1028                 return fd;
1029
1030         msg->arg.reserved.reserved1 = 0;
1031         msg->arg.fork.ufd = fd;
1032         return 0;
1033 }
1034
1035 static ssize_t userfaultfd_ctx_read(struct userfaultfd_ctx *ctx, int no_wait,
1036                                     struct uffd_msg *msg)
1037 {
1038         ssize_t ret;
1039         DECLARE_WAITQUEUE(wait, current);
1040         struct userfaultfd_wait_queue *uwq;
1041         /*
1042          * Handling fork event requires sleeping operations, so
1043          * we drop the event_wqh lock, then do these ops, then
1044          * lock it back and wake up the waiter. While the lock is
1045          * dropped the ewq may go away so we keep track of it
1046          * carefully.
1047          */
1048         LIST_HEAD(fork_event);
1049         struct userfaultfd_ctx *fork_nctx = NULL;
1050
1051         /* always take the fd_wqh lock before the fault_pending_wqh lock */
1052         spin_lock_irq(&ctx->fd_wqh.lock);
1053         __add_wait_queue(&ctx->fd_wqh, &wait);
1054         for (;;) {
1055                 set_current_state(TASK_INTERRUPTIBLE);
1056                 spin_lock(&ctx->fault_pending_wqh.lock);
1057                 uwq = find_userfault(ctx);
1058                 if (uwq) {
1059                         /*
1060                          * Use a seqcount to repeat the lockless check
1061                          * in wake_userfault() to avoid missing
1062                          * wakeups because during the refile both
1063                          * waitqueue could become empty if this is the
1064                          * only userfault.
1065                          */
1066                         write_seqcount_begin(&ctx->refile_seq);
1067
1068                         /*
1069                          * The fault_pending_wqh.lock prevents the uwq
1070                          * to disappear from under us.
1071                          *
1072                          * Refile this userfault from
1073                          * fault_pending_wqh to fault_wqh, it's not
1074                          * pending anymore after we read it.
1075                          *
1076                          * Use list_del() by hand (as
1077                          * userfaultfd_wake_function also uses
1078                          * list_del_init() by hand) to be sure nobody
1079                          * changes __remove_wait_queue() to use
1080                          * list_del_init() in turn breaking the
1081                          * !list_empty_careful() check in
1082                          * handle_userfault(). The uwq->wq.head list
1083                          * must never be empty at any time during the
1084                          * refile, or the waitqueue could disappear
1085                          * from under us. The "wait_queue_head_t"
1086                          * parameter of __remove_wait_queue() is unused
1087                          * anyway.
1088                          */
1089                         list_del(&uwq->wq.entry);
1090                         add_wait_queue(&ctx->fault_wqh, &uwq->wq);
1091
1092                         write_seqcount_end(&ctx->refile_seq);
1093
1094                         /* careful to always initialize msg if ret == 0 */
1095                         *msg = uwq->msg;
1096                         spin_unlock(&ctx->fault_pending_wqh.lock);
1097                         ret = 0;
1098                         break;
1099                 }
1100                 spin_unlock(&ctx->fault_pending_wqh.lock);
1101
1102                 spin_lock(&ctx->event_wqh.lock);
1103                 uwq = find_userfault_evt(ctx);
1104                 if (uwq) {
1105                         *msg = uwq->msg;
1106
1107                         if (uwq->msg.event == UFFD_EVENT_FORK) {
1108                                 fork_nctx = (struct userfaultfd_ctx *)
1109                                         (unsigned long)
1110                                         uwq->msg.arg.reserved.reserved1;
1111                                 list_move(&uwq->wq.entry, &fork_event);
1112                                 /*
1113                                  * fork_nctx can be freed as soon as
1114                                  * we drop the lock, unless we take a
1115                                  * reference on it.
1116                                  */
1117                                 userfaultfd_ctx_get(fork_nctx);
1118                                 spin_unlock(&ctx->event_wqh.lock);
1119                                 ret = 0;
1120                                 break;
1121                         }
1122
1123                         userfaultfd_event_complete(ctx, uwq);
1124                         spin_unlock(&ctx->event_wqh.lock);
1125                         ret = 0;
1126                         break;
1127                 }
1128                 spin_unlock(&ctx->event_wqh.lock);
1129
1130                 if (signal_pending(current)) {
1131                         ret = -ERESTARTSYS;
1132                         break;
1133                 }
1134                 if (no_wait) {
1135                         ret = -EAGAIN;
1136                         break;
1137                 }
1138                 spin_unlock_irq(&ctx->fd_wqh.lock);
1139                 schedule();
1140                 spin_lock_irq(&ctx->fd_wqh.lock);
1141         }
1142         __remove_wait_queue(&ctx->fd_wqh, &wait);
1143         __set_current_state(TASK_RUNNING);
1144         spin_unlock_irq(&ctx->fd_wqh.lock);
1145
1146         if (!ret && msg->event == UFFD_EVENT_FORK) {
1147                 ret = resolve_userfault_fork(ctx, fork_nctx, msg);
1148                 spin_lock_irq(&ctx->event_wqh.lock);
1149                 if (!list_empty(&fork_event)) {
1150                         /*
1151                          * The fork thread didn't abort, so we can
1152                          * drop the temporary refcount.
1153                          */
1154                         userfaultfd_ctx_put(fork_nctx);
1155
1156                         uwq = list_first_entry(&fork_event,
1157                                                typeof(*uwq),
1158                                                wq.entry);
1159                         /*
1160                          * If fork_event list wasn't empty and in turn
1161                          * the event wasn't already released by fork
1162                          * (the event is allocated on fork kernel
1163                          * stack), put the event back to its place in
1164                          * the event_wq. fork_event head will be freed
1165                          * as soon as we return so the event cannot
1166                          * stay queued there no matter the current
1167                          * "ret" value.
1168                          */
1169                         list_del(&uwq->wq.entry);
1170                         __add_wait_queue(&ctx->event_wqh, &uwq->wq);
1171
1172                         /*
1173                          * Leave the event in the waitqueue and report
1174                          * error to userland if we failed to resolve
1175                          * the userfault fork.
1176                          */
1177                         if (likely(!ret))
1178                                 userfaultfd_event_complete(ctx, uwq);
1179                 } else {
1180                         /*
1181                          * Here the fork thread aborted and the
1182                          * refcount from the fork thread on fork_nctx
1183                          * has already been released. We still hold
1184                          * the reference we took before releasing the
1185                          * lock above. If resolve_userfault_fork
1186                          * failed we've to drop it because the
1187                          * fork_nctx has to be freed in such case. If
1188                          * it succeeded we'll hold it because the new
1189                          * uffd references it.
1190                          */
1191                         if (ret)
1192                                 userfaultfd_ctx_put(fork_nctx);
1193                 }
1194                 spin_unlock_irq(&ctx->event_wqh.lock);
1195         }
1196
1197         return ret;
1198 }
1199
1200 static ssize_t userfaultfd_read(struct file *file, char __user *buf,
1201                                 size_t count, loff_t *ppos)
1202 {
1203         struct userfaultfd_ctx *ctx = file->private_data;
1204         ssize_t _ret, ret = 0;
1205         struct uffd_msg msg;
1206         int no_wait = file->f_flags & O_NONBLOCK;
1207
1208         if (ctx->state == UFFD_STATE_WAIT_API)
1209                 return -EINVAL;
1210
1211         for (;;) {
1212                 if (count < sizeof(msg))
1213                         return ret ? ret : -EINVAL;
1214                 _ret = userfaultfd_ctx_read(ctx, no_wait, &msg);
1215                 if (_ret < 0)
1216                         return ret ? ret : _ret;
1217                 if (copy_to_user((__u64 __user *) buf, &msg, sizeof(msg)))
1218                         return ret ? ret : -EFAULT;
1219                 ret += sizeof(msg);
1220                 buf += sizeof(msg);
1221                 count -= sizeof(msg);
1222                 /*
1223                  * Allow to read more than one fault at time but only
1224                  * block if waiting for the very first one.
1225                  */
1226                 no_wait = O_NONBLOCK;
1227         }
1228 }
1229
1230 static void __wake_userfault(struct userfaultfd_ctx *ctx,
1231                              struct userfaultfd_wake_range *range)
1232 {
1233         spin_lock_irq(&ctx->fault_pending_wqh.lock);
1234         /* wake all in the range and autoremove */
1235         if (waitqueue_active(&ctx->fault_pending_wqh))
1236                 __wake_up_locked_key(&ctx->fault_pending_wqh, TASK_NORMAL,
1237                                      range);
1238         if (waitqueue_active(&ctx->fault_wqh))
1239                 __wake_up(&ctx->fault_wqh, TASK_NORMAL, 1, range);
1240         spin_unlock_irq(&ctx->fault_pending_wqh.lock);
1241 }
1242
1243 static __always_inline void wake_userfault(struct userfaultfd_ctx *ctx,
1244                                            struct userfaultfd_wake_range *range)
1245 {
1246         unsigned seq;
1247         bool need_wakeup;
1248
1249         /*
1250          * To be sure waitqueue_active() is not reordered by the CPU
1251          * before the pagetable update, use an explicit SMP memory
1252          * barrier here. PT lock release or up_read(mmap_sem) still
1253          * have release semantics that can allow the
1254          * waitqueue_active() to be reordered before the pte update.
1255          */
1256         smp_mb();
1257
1258         /*
1259          * Use waitqueue_active because it's very frequent to
1260          * change the address space atomically even if there are no
1261          * userfaults yet. So we take the spinlock only when we're
1262          * sure we've userfaults to wake.
1263          */
1264         do {
1265                 seq = read_seqcount_begin(&ctx->refile_seq);
1266                 need_wakeup = waitqueue_active(&ctx->fault_pending_wqh) ||
1267                         waitqueue_active(&ctx->fault_wqh);
1268                 cond_resched();
1269         } while (read_seqcount_retry(&ctx->refile_seq, seq));
1270         if (need_wakeup)
1271                 __wake_userfault(ctx, range);
1272 }
1273
1274 static __always_inline int validate_range(struct mm_struct *mm,
1275                                           __u64 start, __u64 len)
1276 {
1277         __u64 task_size = mm->task_size;
1278
1279         if (start & ~PAGE_MASK)
1280                 return -EINVAL;
1281         if (len & ~PAGE_MASK)
1282                 return -EINVAL;
1283         if (!len)
1284                 return -EINVAL;
1285         if (start < mmap_min_addr)
1286                 return -EINVAL;
1287         if (start >= task_size)
1288                 return -EINVAL;
1289         if (len > task_size - start)
1290                 return -EINVAL;
1291         return 0;
1292 }
1293
1294 static inline bool vma_can_userfault(struct vm_area_struct *vma)
1295 {
1296         return vma_is_anonymous(vma) || is_vm_hugetlb_page(vma) ||
1297                 vma_is_shmem(vma);
1298 }
1299
1300 static int userfaultfd_register(struct userfaultfd_ctx *ctx,
1301                                 unsigned long arg)
1302 {
1303         struct mm_struct *mm = ctx->mm;
1304         struct vm_area_struct *vma, *prev, *cur;
1305         int ret;
1306         struct uffdio_register uffdio_register;
1307         struct uffdio_register __user *user_uffdio_register;
1308         unsigned long vm_flags, new_flags;
1309         bool found;
1310         bool basic_ioctls;
1311         unsigned long start, end, vma_end;
1312
1313         user_uffdio_register = (struct uffdio_register __user *) arg;
1314
1315         ret = -EFAULT;
1316         if (copy_from_user(&uffdio_register, user_uffdio_register,
1317                            sizeof(uffdio_register)-sizeof(__u64)))
1318                 goto out;
1319
1320         ret = -EINVAL;
1321         if (!uffdio_register.mode)
1322                 goto out;
1323         if (uffdio_register.mode & ~(UFFDIO_REGISTER_MODE_MISSING|
1324                                      UFFDIO_REGISTER_MODE_WP))
1325                 goto out;
1326         vm_flags = 0;
1327         if (uffdio_register.mode & UFFDIO_REGISTER_MODE_MISSING)
1328                 vm_flags |= VM_UFFD_MISSING;
1329         if (uffdio_register.mode & UFFDIO_REGISTER_MODE_WP) {
1330                 vm_flags |= VM_UFFD_WP;
1331                 /*
1332                  * FIXME: remove the below error constraint by
1333                  * implementing the wprotect tracking mode.
1334                  */
1335                 ret = -EINVAL;
1336                 goto out;
1337         }
1338
1339         ret = validate_range(mm, uffdio_register.range.start,
1340                              uffdio_register.range.len);
1341         if (ret)
1342                 goto out;
1343
1344         start = uffdio_register.range.start;
1345         end = start + uffdio_register.range.len;
1346
1347         ret = -ENOMEM;
1348         if (!mmget_not_zero(mm))
1349                 goto out;
1350
1351         down_write(&mm->mmap_sem);
1352         if (!mmget_still_valid(mm))
1353                 goto out_unlock;
1354         vma = find_vma_prev(mm, start, &prev);
1355         if (!vma)
1356                 goto out_unlock;
1357
1358         /* check that there's at least one vma in the range */
1359         ret = -EINVAL;
1360         if (vma->vm_start >= end)
1361                 goto out_unlock;
1362
1363         /*
1364          * If the first vma contains huge pages, make sure start address
1365          * is aligned to huge page size.
1366          */
1367         if (is_vm_hugetlb_page(vma)) {
1368                 unsigned long vma_hpagesize = vma_kernel_pagesize(vma);
1369
1370                 if (start & (vma_hpagesize - 1))
1371                         goto out_unlock;
1372         }
1373
1374         /*
1375          * Search for not compatible vmas.
1376          */
1377         found = false;
1378         basic_ioctls = false;
1379         for (cur = vma; cur && cur->vm_start < end; cur = cur->vm_next) {
1380                 cond_resched();
1381
1382                 BUG_ON(!!cur->vm_userfaultfd_ctx.ctx ^
1383                        !!(cur->vm_flags & (VM_UFFD_MISSING | VM_UFFD_WP)));
1384
1385                 /* check not compatible vmas */
1386                 ret = -EINVAL;
1387                 if (!vma_can_userfault(cur))
1388                         goto out_unlock;
1389
1390                 /*
1391                  * UFFDIO_COPY will fill file holes even without
1392                  * PROT_WRITE. This check enforces that if this is a
1393                  * MAP_SHARED, the process has write permission to the backing
1394                  * file. If VM_MAYWRITE is set it also enforces that on a
1395                  * MAP_SHARED vma: there is no F_WRITE_SEAL and no further
1396                  * F_WRITE_SEAL can be taken until the vma is destroyed.
1397                  */
1398                 ret = -EPERM;
1399                 if (unlikely(!(cur->vm_flags & VM_MAYWRITE)))
1400                         goto out_unlock;
1401
1402                 /*
1403                  * If this vma contains ending address, and huge pages
1404                  * check alignment.
1405                  */
1406                 if (is_vm_hugetlb_page(cur) && end <= cur->vm_end &&
1407                     end > cur->vm_start) {
1408                         unsigned long vma_hpagesize = vma_kernel_pagesize(cur);
1409
1410                         ret = -EINVAL;
1411
1412                         if (end & (vma_hpagesize - 1))
1413                                 goto out_unlock;
1414                 }
1415
1416                 /*
1417                  * Check that this vma isn't already owned by a
1418                  * different userfaultfd. We can't allow more than one
1419                  * userfaultfd to own a single vma simultaneously or we
1420                  * wouldn't know which one to deliver the userfaults to.
1421                  */
1422                 ret = -EBUSY;
1423                 if (cur->vm_userfaultfd_ctx.ctx &&
1424                     cur->vm_userfaultfd_ctx.ctx != ctx)
1425                         goto out_unlock;
1426
1427                 /*
1428                  * Note vmas containing huge pages
1429                  */
1430                 if (is_vm_hugetlb_page(cur))
1431                         basic_ioctls = true;
1432
1433                 found = true;
1434         }
1435         BUG_ON(!found);
1436
1437         if (vma->vm_start < start)
1438                 prev = vma;
1439
1440         ret = 0;
1441         do {
1442                 cond_resched();
1443
1444                 BUG_ON(!vma_can_userfault(vma));
1445                 BUG_ON(vma->vm_userfaultfd_ctx.ctx &&
1446                        vma->vm_userfaultfd_ctx.ctx != ctx);
1447                 WARN_ON(!(vma->vm_flags & VM_MAYWRITE));
1448
1449                 /*
1450                  * Nothing to do: this vma is already registered into this
1451                  * userfaultfd and with the right tracking mode too.
1452                  */
1453                 if (vma->vm_userfaultfd_ctx.ctx == ctx &&
1454                     (vma->vm_flags & vm_flags) == vm_flags)
1455                         goto skip;
1456
1457                 if (vma->vm_start > start)
1458                         start = vma->vm_start;
1459                 vma_end = min(end, vma->vm_end);
1460
1461                 new_flags = (vma->vm_flags & ~vm_flags) | vm_flags;
1462                 prev = vma_merge(mm, prev, start, vma_end, new_flags,
1463                                  vma->anon_vma, vma->vm_file, vma->vm_pgoff,
1464                                  vma_policy(vma),
1465                                  ((struct vm_userfaultfd_ctx){ ctx }));
1466                 if (prev) {
1467                         vma = prev;
1468                         goto next;
1469                 }
1470                 if (vma->vm_start < start) {
1471                         ret = split_vma(mm, vma, start, 1);
1472                         if (ret)
1473                                 break;
1474                 }
1475                 if (vma->vm_end > end) {
1476                         ret = split_vma(mm, vma, end, 0);
1477                         if (ret)
1478                                 break;
1479                 }
1480         next:
1481                 /*
1482                  * In the vma_merge() successful mprotect-like case 8:
1483                  * the next vma was merged into the current one and
1484                  * the current one has not been updated yet.
1485                  */
1486                 vma->vm_flags = new_flags;
1487                 vma->vm_userfaultfd_ctx.ctx = ctx;
1488
1489         skip:
1490                 prev = vma;
1491                 start = vma->vm_end;
1492                 vma = vma->vm_next;
1493         } while (vma && vma->vm_start < end);
1494 out_unlock:
1495         up_write(&mm->mmap_sem);
1496         mmput(mm);
1497         if (!ret) {
1498                 /*
1499                  * Now that we scanned all vmas we can already tell
1500                  * userland which ioctls methods are guaranteed to
1501                  * succeed on this range.
1502                  */
1503                 if (put_user(basic_ioctls ? UFFD_API_RANGE_IOCTLS_BASIC :
1504                              UFFD_API_RANGE_IOCTLS,
1505                              &user_uffdio_register->ioctls))
1506                         ret = -EFAULT;
1507         }
1508 out:
1509         return ret;
1510 }
1511
1512 static int userfaultfd_unregister(struct userfaultfd_ctx *ctx,
1513                                   unsigned long arg)
1514 {
1515         struct mm_struct *mm = ctx->mm;
1516         struct vm_area_struct *vma, *prev, *cur;
1517         int ret;
1518         struct uffdio_range uffdio_unregister;
1519         unsigned long new_flags;
1520         bool found;
1521         unsigned long start, end, vma_end;
1522         const void __user *buf = (void __user *)arg;
1523
1524         ret = -EFAULT;
1525         if (copy_from_user(&uffdio_unregister, buf, sizeof(uffdio_unregister)))
1526                 goto out;
1527
1528         ret = validate_range(mm, uffdio_unregister.start,
1529                              uffdio_unregister.len);
1530         if (ret)
1531                 goto out;
1532
1533         start = uffdio_unregister.start;
1534         end = start + uffdio_unregister.len;
1535
1536         ret = -ENOMEM;
1537         if (!mmget_not_zero(mm))
1538                 goto out;
1539
1540         down_write(&mm->mmap_sem);
1541         if (!mmget_still_valid(mm))
1542                 goto out_unlock;
1543         vma = find_vma_prev(mm, start, &prev);
1544         if (!vma)
1545                 goto out_unlock;
1546
1547         /* check that there's at least one vma in the range */
1548         ret = -EINVAL;
1549         if (vma->vm_start >= end)
1550                 goto out_unlock;
1551
1552         /*
1553          * If the first vma contains huge pages, make sure start address
1554          * is aligned to huge page size.
1555          */
1556         if (is_vm_hugetlb_page(vma)) {
1557                 unsigned long vma_hpagesize = vma_kernel_pagesize(vma);
1558
1559                 if (start & (vma_hpagesize - 1))
1560                         goto out_unlock;
1561         }
1562
1563         /*
1564          * Search for not compatible vmas.
1565          */
1566         found = false;
1567         ret = -EINVAL;
1568         for (cur = vma; cur && cur->vm_start < end; cur = cur->vm_next) {
1569                 cond_resched();
1570
1571                 BUG_ON(!!cur->vm_userfaultfd_ctx.ctx ^
1572                        !!(cur->vm_flags & (VM_UFFD_MISSING | VM_UFFD_WP)));
1573
1574                 /*
1575                  * Check not compatible vmas, not strictly required
1576                  * here as not compatible vmas cannot have an
1577                  * userfaultfd_ctx registered on them, but this
1578                  * provides for more strict behavior to notice
1579                  * unregistration errors.
1580                  */
1581                 if (!vma_can_userfault(cur))
1582                         goto out_unlock;
1583
1584                 found = true;
1585         }
1586         BUG_ON(!found);
1587
1588         if (vma->vm_start < start)
1589                 prev = vma;
1590
1591         ret = 0;
1592         do {
1593                 cond_resched();
1594
1595                 BUG_ON(!vma_can_userfault(vma));
1596
1597                 /*
1598                  * Nothing to do: this vma is already registered into this
1599                  * userfaultfd and with the right tracking mode too.
1600                  */
1601                 if (!vma->vm_userfaultfd_ctx.ctx)
1602                         goto skip;
1603
1604                 WARN_ON(!(vma->vm_flags & VM_MAYWRITE));
1605
1606                 if (vma->vm_start > start)
1607                         start = vma->vm_start;
1608                 vma_end = min(end, vma->vm_end);
1609
1610                 if (userfaultfd_missing(vma)) {
1611                         /*
1612                          * Wake any concurrent pending userfault while
1613                          * we unregister, so they will not hang
1614                          * permanently and it avoids userland to call
1615                          * UFFDIO_WAKE explicitly.
1616                          */
1617                         struct userfaultfd_wake_range range;
1618                         range.start = start;
1619                         range.len = vma_end - start;
1620                         wake_userfault(vma->vm_userfaultfd_ctx.ctx, &range);
1621                 }
1622
1623                 new_flags = vma->vm_flags & ~(VM_UFFD_MISSING | VM_UFFD_WP);
1624                 prev = vma_merge(mm, prev, start, vma_end, new_flags,
1625                                  vma->anon_vma, vma->vm_file, vma->vm_pgoff,
1626                                  vma_policy(vma),
1627                                  NULL_VM_UFFD_CTX);
1628                 if (prev) {
1629                         vma = prev;
1630                         goto next;
1631                 }
1632                 if (vma->vm_start < start) {
1633                         ret = split_vma(mm, vma, start, 1);
1634                         if (ret)
1635                                 break;
1636                 }
1637                 if (vma->vm_end > end) {
1638                         ret = split_vma(mm, vma, end, 0);
1639                         if (ret)
1640                                 break;
1641                 }
1642         next:
1643                 /*
1644                  * In the vma_merge() successful mprotect-like case 8:
1645                  * the next vma was merged into the current one and
1646                  * the current one has not been updated yet.
1647                  */
1648                 vma->vm_flags = new_flags;
1649                 vma->vm_userfaultfd_ctx = NULL_VM_UFFD_CTX;
1650
1651         skip:
1652                 prev = vma;
1653                 start = vma->vm_end;
1654                 vma = vma->vm_next;
1655         } while (vma && vma->vm_start < end);
1656 out_unlock:
1657         up_write(&mm->mmap_sem);
1658         mmput(mm);
1659 out:
1660         return ret;
1661 }
1662
1663 /*
1664  * userfaultfd_wake may be used in combination with the
1665  * UFFDIO_*_MODE_DONTWAKE to wakeup userfaults in batches.
1666  */
1667 static int userfaultfd_wake(struct userfaultfd_ctx *ctx,
1668                             unsigned long arg)
1669 {
1670         int ret;
1671         struct uffdio_range uffdio_wake;
1672         struct userfaultfd_wake_range range;
1673         const void __user *buf = (void __user *)arg;
1674
1675         ret = -EFAULT;
1676         if (copy_from_user(&uffdio_wake, buf, sizeof(uffdio_wake)))
1677                 goto out;
1678
1679         ret = validate_range(ctx->mm, uffdio_wake.start, uffdio_wake.len);
1680         if (ret)
1681                 goto out;
1682
1683         range.start = uffdio_wake.start;
1684         range.len = uffdio_wake.len;
1685
1686         /*
1687          * len == 0 means wake all and we don't want to wake all here,
1688          * so check it again to be sure.
1689          */
1690         VM_BUG_ON(!range.len);
1691
1692         wake_userfault(ctx, &range);
1693         ret = 0;
1694
1695 out:
1696         return ret;
1697 }
1698
1699 static int userfaultfd_copy(struct userfaultfd_ctx *ctx,
1700                             unsigned long arg)
1701 {
1702         __s64 ret;
1703         struct uffdio_copy uffdio_copy;
1704         struct uffdio_copy __user *user_uffdio_copy;
1705         struct userfaultfd_wake_range range;
1706
1707         user_uffdio_copy = (struct uffdio_copy __user *) arg;
1708
1709         ret = -EAGAIN;
1710         if (READ_ONCE(ctx->mmap_changing))
1711                 goto out;
1712
1713         ret = -EFAULT;
1714         if (copy_from_user(&uffdio_copy, user_uffdio_copy,
1715                            /* don't copy "copy" last field */
1716                            sizeof(uffdio_copy)-sizeof(__s64)))
1717                 goto out;
1718
1719         ret = validate_range(ctx->mm, uffdio_copy.dst, uffdio_copy.len);
1720         if (ret)
1721                 goto out;
1722         /*
1723          * double check for wraparound just in case. copy_from_user()
1724          * will later check uffdio_copy.src + uffdio_copy.len to fit
1725          * in the userland range.
1726          */
1727         ret = -EINVAL;
1728         if (uffdio_copy.src + uffdio_copy.len <= uffdio_copy.src)
1729                 goto out;
1730         if (uffdio_copy.mode & ~UFFDIO_COPY_MODE_DONTWAKE)
1731                 goto out;
1732         if (mmget_not_zero(ctx->mm)) {
1733                 ret = mcopy_atomic(ctx->mm, uffdio_copy.dst, uffdio_copy.src,
1734                                    uffdio_copy.len, &ctx->mmap_changing);
1735                 mmput(ctx->mm);
1736         } else {
1737                 return -ESRCH;
1738         }
1739         if (unlikely(put_user(ret, &user_uffdio_copy->copy)))
1740                 return -EFAULT;
1741         if (ret < 0)
1742                 goto out;
1743         BUG_ON(!ret);
1744         /* len == 0 would wake all */
1745         range.len = ret;
1746         if (!(uffdio_copy.mode & UFFDIO_COPY_MODE_DONTWAKE)) {
1747                 range.start = uffdio_copy.dst;
1748                 wake_userfault(ctx, &range);
1749         }
1750         ret = range.len == uffdio_copy.len ? 0 : -EAGAIN;
1751 out:
1752         return ret;
1753 }
1754
1755 static int userfaultfd_zeropage(struct userfaultfd_ctx *ctx,
1756                                 unsigned long arg)
1757 {
1758         __s64 ret;
1759         struct uffdio_zeropage uffdio_zeropage;
1760         struct uffdio_zeropage __user *user_uffdio_zeropage;
1761         struct userfaultfd_wake_range range;
1762
1763         user_uffdio_zeropage = (struct uffdio_zeropage __user *) arg;
1764
1765         ret = -EAGAIN;
1766         if (READ_ONCE(ctx->mmap_changing))
1767                 goto out;
1768
1769         ret = -EFAULT;
1770         if (copy_from_user(&uffdio_zeropage, user_uffdio_zeropage,
1771                            /* don't copy "zeropage" last field */
1772                            sizeof(uffdio_zeropage)-sizeof(__s64)))
1773                 goto out;
1774
1775         ret = validate_range(ctx->mm, uffdio_zeropage.range.start,
1776                              uffdio_zeropage.range.len);
1777         if (ret)
1778                 goto out;
1779         ret = -EINVAL;
1780         if (uffdio_zeropage.mode & ~UFFDIO_ZEROPAGE_MODE_DONTWAKE)
1781                 goto out;
1782
1783         if (mmget_not_zero(ctx->mm)) {
1784                 ret = mfill_zeropage(ctx->mm, uffdio_zeropage.range.start,
1785                                      uffdio_zeropage.range.len,
1786                                      &ctx->mmap_changing);
1787                 mmput(ctx->mm);
1788         } else {
1789                 return -ESRCH;
1790         }
1791         if (unlikely(put_user(ret, &user_uffdio_zeropage->zeropage)))
1792                 return -EFAULT;
1793         if (ret < 0)
1794                 goto out;
1795         /* len == 0 would wake all */
1796         BUG_ON(!ret);
1797         range.len = ret;
1798         if (!(uffdio_zeropage.mode & UFFDIO_ZEROPAGE_MODE_DONTWAKE)) {
1799                 range.start = uffdio_zeropage.range.start;
1800                 wake_userfault(ctx, &range);
1801         }
1802         ret = range.len == uffdio_zeropage.range.len ? 0 : -EAGAIN;
1803 out:
1804         return ret;
1805 }
1806
1807 static inline unsigned int uffd_ctx_features(__u64 user_features)
1808 {
1809         /*
1810          * For the current set of features the bits just coincide
1811          */
1812         return (unsigned int)user_features;
1813 }
1814
1815 /*
1816  * userland asks for a certain API version and we return which bits
1817  * and ioctl commands are implemented in this kernel for such API
1818  * version or -EINVAL if unknown.
1819  */
1820 static int userfaultfd_api(struct userfaultfd_ctx *ctx,
1821                            unsigned long arg)
1822 {
1823         struct uffdio_api uffdio_api;
1824         void __user *buf = (void __user *)arg;
1825         int ret;
1826         __u64 features;
1827
1828         ret = -EINVAL;
1829         if (ctx->state != UFFD_STATE_WAIT_API)
1830                 goto out;
1831         ret = -EFAULT;
1832         if (copy_from_user(&uffdio_api, buf, sizeof(uffdio_api)))
1833                 goto out;
1834         features = uffdio_api.features;
1835         if (uffdio_api.api != UFFD_API || (features & ~UFFD_API_FEATURES)) {
1836                 memset(&uffdio_api, 0, sizeof(uffdio_api));
1837                 if (copy_to_user(buf, &uffdio_api, sizeof(uffdio_api)))
1838                         goto out;
1839                 ret = -EINVAL;
1840                 goto out;
1841         }
1842         /* report all available features and ioctls to userland */
1843         uffdio_api.features = UFFD_API_FEATURES;
1844         uffdio_api.ioctls = UFFD_API_IOCTLS;
1845         ret = -EFAULT;
1846         if (copy_to_user(buf, &uffdio_api, sizeof(uffdio_api)))
1847                 goto out;
1848         ctx->state = UFFD_STATE_RUNNING;
1849         /* only enable the requested features for this uffd context */
1850         ctx->features = uffd_ctx_features(features);
1851         ret = 0;
1852 out:
1853         return ret;
1854 }
1855
1856 static long userfaultfd_ioctl(struct file *file, unsigned cmd,
1857                               unsigned long arg)
1858 {
1859         int ret = -EINVAL;
1860         struct userfaultfd_ctx *ctx = file->private_data;
1861
1862         if (cmd != UFFDIO_API && ctx->state == UFFD_STATE_WAIT_API)
1863                 return -EINVAL;
1864
1865         switch(cmd) {
1866         case UFFDIO_API:
1867                 ret = userfaultfd_api(ctx, arg);
1868                 break;
1869         case UFFDIO_REGISTER:
1870                 ret = userfaultfd_register(ctx, arg);
1871                 break;
1872         case UFFDIO_UNREGISTER:
1873                 ret = userfaultfd_unregister(ctx, arg);
1874                 break;
1875         case UFFDIO_WAKE:
1876                 ret = userfaultfd_wake(ctx, arg);
1877                 break;
1878         case UFFDIO_COPY:
1879                 ret = userfaultfd_copy(ctx, arg);
1880                 break;
1881         case UFFDIO_ZEROPAGE:
1882                 ret = userfaultfd_zeropage(ctx, arg);
1883                 break;
1884         }
1885         return ret;
1886 }
1887
1888 #ifdef CONFIG_PROC_FS
1889 static void userfaultfd_show_fdinfo(struct seq_file *m, struct file *f)
1890 {
1891         struct userfaultfd_ctx *ctx = f->private_data;
1892         wait_queue_entry_t *wq;
1893         unsigned long pending = 0, total = 0;
1894
1895         spin_lock_irq(&ctx->fault_pending_wqh.lock);
1896         list_for_each_entry(wq, &ctx->fault_pending_wqh.head, entry) {
1897                 pending++;
1898                 total++;
1899         }
1900         list_for_each_entry(wq, &ctx->fault_wqh.head, entry) {
1901                 total++;
1902         }
1903         spin_unlock_irq(&ctx->fault_pending_wqh.lock);
1904
1905         /*
1906          * If more protocols will be added, there will be all shown
1907          * separated by a space. Like this:
1908          *      protocols: aa:... bb:...
1909          */
1910         seq_printf(m, "pending:\t%lu\ntotal:\t%lu\nAPI:\t%Lx:%x:%Lx\n",
1911                    pending, total, UFFD_API, ctx->features,
1912                    UFFD_API_IOCTLS|UFFD_API_RANGE_IOCTLS);
1913 }
1914 #endif
1915
1916 static const struct file_operations userfaultfd_fops = {
1917 #ifdef CONFIG_PROC_FS
1918         .show_fdinfo    = userfaultfd_show_fdinfo,
1919 #endif
1920         .release        = userfaultfd_release,
1921         .poll           = userfaultfd_poll,
1922         .read           = userfaultfd_read,
1923         .unlocked_ioctl = userfaultfd_ioctl,
1924         .compat_ioctl   = userfaultfd_ioctl,
1925         .llseek         = noop_llseek,
1926 };
1927
1928 static void init_once_userfaultfd_ctx(void *mem)
1929 {
1930         struct userfaultfd_ctx *ctx = (struct userfaultfd_ctx *) mem;
1931
1932         init_waitqueue_head(&ctx->fault_pending_wqh);
1933         init_waitqueue_head(&ctx->fault_wqh);
1934         init_waitqueue_head(&ctx->event_wqh);
1935         init_waitqueue_head(&ctx->fd_wqh);
1936         seqcount_init(&ctx->refile_seq);
1937 }
1938
1939 SYSCALL_DEFINE1(userfaultfd, int, flags)
1940 {
1941         struct userfaultfd_ctx *ctx;
1942         int fd;
1943
1944         if (!sysctl_unprivileged_userfaultfd && !capable(CAP_SYS_PTRACE))
1945                 return -EPERM;
1946
1947         BUG_ON(!current->mm);
1948
1949         /* Check the UFFD_* constants for consistency.  */
1950         BUILD_BUG_ON(UFFD_CLOEXEC != O_CLOEXEC);
1951         BUILD_BUG_ON(UFFD_NONBLOCK != O_NONBLOCK);
1952
1953         if (flags & ~UFFD_SHARED_FCNTL_FLAGS)
1954                 return -EINVAL;
1955
1956         ctx = kmem_cache_alloc(userfaultfd_ctx_cachep, GFP_KERNEL);
1957         if (!ctx)
1958                 return -ENOMEM;
1959
1960         refcount_set(&ctx->refcount, 1);
1961         ctx->flags = flags;
1962         ctx->features = 0;
1963         ctx->state = UFFD_STATE_WAIT_API;
1964         ctx->released = false;
1965         ctx->mmap_changing = false;
1966         ctx->mm = current->mm;
1967         /* prevent the mm struct to be freed */
1968         mmgrab(ctx->mm);
1969
1970         fd = anon_inode_getfd("[userfaultfd]", &userfaultfd_fops, ctx,
1971                               O_RDWR | (flags & UFFD_SHARED_FCNTL_FLAGS));
1972         if (fd < 0) {
1973                 mmdrop(ctx->mm);
1974                 kmem_cache_free(userfaultfd_ctx_cachep, ctx);
1975         }
1976         return fd;
1977 }
1978
1979 static int __init userfaultfd_init(void)
1980 {
1981         userfaultfd_ctx_cachep = kmem_cache_create("userfaultfd_ctx_cache",
1982                                                 sizeof(struct userfaultfd_ctx),
1983                                                 0,
1984                                                 SLAB_HWCACHE_ALIGN|SLAB_PANIC,
1985                                                 init_once_userfaultfd_ctx);
1986         return 0;
1987 }
1988 __initcall(userfaultfd_init);