Merge tag 'trace-rtla-v6.0' of git://git.kernel.org/pub/scm/linux/kernel/git/rostedt...
[platform/kernel/linux-starfive.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/mm_inline.h>
19 #include <linux/mmu_notifier.h>
20 #include <linux/poll.h>
21 #include <linux/slab.h>
22 #include <linux/seq_file.h>
23 #include <linux/file.h>
24 #include <linux/bug.h>
25 #include <linux/anon_inodes.h>
26 #include <linux/syscalls.h>
27 #include <linux/userfaultfd_k.h>
28 #include <linux/mempolicy.h>
29 #include <linux/ioctl.h>
30 #include <linux/security.h>
31 #include <linux/hugetlb.h>
32 #include <linux/swapops.h>
33
34 int sysctl_unprivileged_userfaultfd __read_mostly;
35
36 static struct kmem_cache *userfaultfd_ctx_cachep __read_mostly;
37
38 /*
39  * Start with fault_pending_wqh and fault_wqh so they're more likely
40  * to be in the same cacheline.
41  *
42  * Locking order:
43  *      fd_wqh.lock
44  *              fault_pending_wqh.lock
45  *                      fault_wqh.lock
46  *              event_wqh.lock
47  *
48  * To avoid deadlocks, IRQs must be disabled when taking any of the above locks,
49  * since fd_wqh.lock is taken by aio_poll() while it's holding a lock that's
50  * also taken in IRQ context.
51  */
52 struct userfaultfd_ctx {
53         /* waitqueue head for the pending (i.e. not read) userfaults */
54         wait_queue_head_t fault_pending_wqh;
55         /* waitqueue head for the userfaults */
56         wait_queue_head_t fault_wqh;
57         /* waitqueue head for the pseudo fd to wakeup poll/read */
58         wait_queue_head_t fd_wqh;
59         /* waitqueue head for events */
60         wait_queue_head_t event_wqh;
61         /* a refile sequence protected by fault_pending_wqh lock */
62         seqcount_spinlock_t refile_seq;
63         /* pseudo fd refcounting */
64         refcount_t refcount;
65         /* userfaultfd syscall flags */
66         unsigned int flags;
67         /* features requested from the userspace */
68         unsigned int features;
69         /* released */
70         bool released;
71         /* memory mappings are changing because of non-cooperative event */
72         atomic_t mmap_changing;
73         /* mm with one ore more vmas attached to this userfaultfd_ctx */
74         struct mm_struct *mm;
75 };
76
77 struct userfaultfd_fork_ctx {
78         struct userfaultfd_ctx *orig;
79         struct userfaultfd_ctx *new;
80         struct list_head list;
81 };
82
83 struct userfaultfd_unmap_ctx {
84         struct userfaultfd_ctx *ctx;
85         unsigned long start;
86         unsigned long end;
87         struct list_head list;
88 };
89
90 struct userfaultfd_wait_queue {
91         struct uffd_msg msg;
92         wait_queue_entry_t wq;
93         struct userfaultfd_ctx *ctx;
94         bool waken;
95 };
96
97 struct userfaultfd_wake_range {
98         unsigned long start;
99         unsigned long len;
100 };
101
102 /* internal indication that UFFD_API ioctl was successfully executed */
103 #define UFFD_FEATURE_INITIALIZED                (1u << 31)
104
105 static bool userfaultfd_is_initialized(struct userfaultfd_ctx *ctx)
106 {
107         return ctx->features & UFFD_FEATURE_INITIALIZED;
108 }
109
110 static int userfaultfd_wake_function(wait_queue_entry_t *wq, unsigned mode,
111                                      int wake_flags, void *key)
112 {
113         struct userfaultfd_wake_range *range = key;
114         int ret;
115         struct userfaultfd_wait_queue *uwq;
116         unsigned long start, len;
117
118         uwq = container_of(wq, struct userfaultfd_wait_queue, wq);
119         ret = 0;
120         /* len == 0 means wake all */
121         start = range->start;
122         len = range->len;
123         if (len && (start > uwq->msg.arg.pagefault.address ||
124                     start + len <= uwq->msg.arg.pagefault.address))
125                 goto out;
126         WRITE_ONCE(uwq->waken, true);
127         /*
128          * The Program-Order guarantees provided by the scheduler
129          * ensure uwq->waken is visible before the task is woken.
130          */
131         ret = wake_up_state(wq->private, mode);
132         if (ret) {
133                 /*
134                  * Wake only once, autoremove behavior.
135                  *
136                  * After the effect of list_del_init is visible to the other
137                  * CPUs, the waitqueue may disappear from under us, see the
138                  * !list_empty_careful() in handle_userfault().
139                  *
140                  * try_to_wake_up() has an implicit smp_mb(), and the
141                  * wq->private is read before calling the extern function
142                  * "wake_up_state" (which in turns calls try_to_wake_up).
143                  */
144                 list_del_init(&wq->entry);
145         }
146 out:
147         return ret;
148 }
149
150 /**
151  * userfaultfd_ctx_get - Acquires a reference to the internal userfaultfd
152  * context.
153  * @ctx: [in] Pointer to the userfaultfd context.
154  */
155 static void userfaultfd_ctx_get(struct userfaultfd_ctx *ctx)
156 {
157         refcount_inc(&ctx->refcount);
158 }
159
160 /**
161  * userfaultfd_ctx_put - Releases a reference to the internal userfaultfd
162  * context.
163  * @ctx: [in] Pointer to userfaultfd context.
164  *
165  * The userfaultfd context reference must have been previously acquired either
166  * with userfaultfd_ctx_get() or userfaultfd_ctx_fdget().
167  */
168 static void userfaultfd_ctx_put(struct userfaultfd_ctx *ctx)
169 {
170         if (refcount_dec_and_test(&ctx->refcount)) {
171                 VM_BUG_ON(spin_is_locked(&ctx->fault_pending_wqh.lock));
172                 VM_BUG_ON(waitqueue_active(&ctx->fault_pending_wqh));
173                 VM_BUG_ON(spin_is_locked(&ctx->fault_wqh.lock));
174                 VM_BUG_ON(waitqueue_active(&ctx->fault_wqh));
175                 VM_BUG_ON(spin_is_locked(&ctx->event_wqh.lock));
176                 VM_BUG_ON(waitqueue_active(&ctx->event_wqh));
177                 VM_BUG_ON(spin_is_locked(&ctx->fd_wqh.lock));
178                 VM_BUG_ON(waitqueue_active(&ctx->fd_wqh));
179                 mmdrop(ctx->mm);
180                 kmem_cache_free(userfaultfd_ctx_cachep, ctx);
181         }
182 }
183
184 static inline void msg_init(struct uffd_msg *msg)
185 {
186         BUILD_BUG_ON(sizeof(struct uffd_msg) != 32);
187         /*
188          * Must use memset to zero out the paddings or kernel data is
189          * leaked to userland.
190          */
191         memset(msg, 0, sizeof(struct uffd_msg));
192 }
193
194 static inline struct uffd_msg userfault_msg(unsigned long address,
195                                             unsigned long real_address,
196                                             unsigned int flags,
197                                             unsigned long reason,
198                                             unsigned int features)
199 {
200         struct uffd_msg msg;
201
202         msg_init(&msg);
203         msg.event = UFFD_EVENT_PAGEFAULT;
204
205         msg.arg.pagefault.address = (features & UFFD_FEATURE_EXACT_ADDRESS) ?
206                                     real_address : address;
207
208         /*
209          * These flags indicate why the userfault occurred:
210          * - UFFD_PAGEFAULT_FLAG_WP indicates a write protect fault.
211          * - UFFD_PAGEFAULT_FLAG_MINOR indicates a minor fault.
212          * - Neither of these flags being set indicates a MISSING fault.
213          *
214          * Separately, UFFD_PAGEFAULT_FLAG_WRITE indicates it was a write
215          * fault. Otherwise, it was a read fault.
216          */
217         if (flags & FAULT_FLAG_WRITE)
218                 msg.arg.pagefault.flags |= UFFD_PAGEFAULT_FLAG_WRITE;
219         if (reason & VM_UFFD_WP)
220                 msg.arg.pagefault.flags |= UFFD_PAGEFAULT_FLAG_WP;
221         if (reason & VM_UFFD_MINOR)
222                 msg.arg.pagefault.flags |= UFFD_PAGEFAULT_FLAG_MINOR;
223         if (features & UFFD_FEATURE_THREAD_ID)
224                 msg.arg.pagefault.feat.ptid = task_pid_vnr(current);
225         return msg;
226 }
227
228 #ifdef CONFIG_HUGETLB_PAGE
229 /*
230  * Same functionality as userfaultfd_must_wait below with modifications for
231  * hugepmd ranges.
232  */
233 static inline bool userfaultfd_huge_must_wait(struct userfaultfd_ctx *ctx,
234                                          struct vm_area_struct *vma,
235                                          unsigned long address,
236                                          unsigned long flags,
237                                          unsigned long reason)
238 {
239         struct mm_struct *mm = ctx->mm;
240         pte_t *ptep, pte;
241         bool ret = true;
242
243         mmap_assert_locked(mm);
244
245         ptep = huge_pte_offset(mm, address, vma_mmu_pagesize(vma));
246
247         if (!ptep)
248                 goto out;
249
250         ret = false;
251         pte = huge_ptep_get(ptep);
252
253         /*
254          * Lockless access: we're in a wait_event so it's ok if it
255          * changes under us.  PTE markers should be handled the same as none
256          * ptes here.
257          */
258         if (huge_pte_none_mostly(pte))
259                 ret = true;
260         if (!huge_pte_write(pte) && (reason & VM_UFFD_WP))
261                 ret = true;
262 out:
263         return ret;
264 }
265 #else
266 static inline bool userfaultfd_huge_must_wait(struct userfaultfd_ctx *ctx,
267                                          struct vm_area_struct *vma,
268                                          unsigned long address,
269                                          unsigned long flags,
270                                          unsigned long reason)
271 {
272         return false;   /* should never get here */
273 }
274 #endif /* CONFIG_HUGETLB_PAGE */
275
276 /*
277  * Verify the pagetables are still not ok after having reigstered into
278  * the fault_pending_wqh to avoid userland having to UFFDIO_WAKE any
279  * userfault that has already been resolved, if userfaultfd_read and
280  * UFFDIO_COPY|ZEROPAGE are being run simultaneously on two different
281  * threads.
282  */
283 static inline bool userfaultfd_must_wait(struct userfaultfd_ctx *ctx,
284                                          unsigned long address,
285                                          unsigned long flags,
286                                          unsigned long reason)
287 {
288         struct mm_struct *mm = ctx->mm;
289         pgd_t *pgd;
290         p4d_t *p4d;
291         pud_t *pud;
292         pmd_t *pmd, _pmd;
293         pte_t *pte;
294         bool ret = true;
295
296         mmap_assert_locked(mm);
297
298         pgd = pgd_offset(mm, address);
299         if (!pgd_present(*pgd))
300                 goto out;
301         p4d = p4d_offset(pgd, address);
302         if (!p4d_present(*p4d))
303                 goto out;
304         pud = pud_offset(p4d, address);
305         if (!pud_present(*pud))
306                 goto out;
307         pmd = pmd_offset(pud, address);
308         /*
309          * READ_ONCE must function as a barrier with narrower scope
310          * and it must be equivalent to:
311          *      _pmd = *pmd; barrier();
312          *
313          * This is to deal with the instability (as in
314          * pmd_trans_unstable) of the pmd.
315          */
316         _pmd = READ_ONCE(*pmd);
317         if (pmd_none(_pmd))
318                 goto out;
319
320         ret = false;
321         if (!pmd_present(_pmd))
322                 goto out;
323
324         if (pmd_trans_huge(_pmd)) {
325                 if (!pmd_write(_pmd) && (reason & VM_UFFD_WP))
326                         ret = true;
327                 goto out;
328         }
329
330         /*
331          * the pmd is stable (as in !pmd_trans_unstable) so we can re-read it
332          * and use the standard pte_offset_map() instead of parsing _pmd.
333          */
334         pte = pte_offset_map(pmd, address);
335         /*
336          * Lockless access: we're in a wait_event so it's ok if it
337          * changes under us.  PTE markers should be handled the same as none
338          * ptes here.
339          */
340         if (pte_none_mostly(*pte))
341                 ret = true;
342         if (!pte_write(*pte) && (reason & VM_UFFD_WP))
343                 ret = true;
344         pte_unmap(pte);
345
346 out:
347         return ret;
348 }
349
350 static inline unsigned int userfaultfd_get_blocking_state(unsigned int flags)
351 {
352         if (flags & FAULT_FLAG_INTERRUPTIBLE)
353                 return TASK_INTERRUPTIBLE;
354
355         if (flags & FAULT_FLAG_KILLABLE)
356                 return TASK_KILLABLE;
357
358         return TASK_UNINTERRUPTIBLE;
359 }
360
361 /*
362  * The locking rules involved in returning VM_FAULT_RETRY depending on
363  * FAULT_FLAG_ALLOW_RETRY, FAULT_FLAG_RETRY_NOWAIT and
364  * FAULT_FLAG_KILLABLE are not straightforward. The "Caution"
365  * recommendation in __lock_page_or_retry is not an understatement.
366  *
367  * If FAULT_FLAG_ALLOW_RETRY is set, the mmap_lock must be released
368  * before returning VM_FAULT_RETRY only if FAULT_FLAG_RETRY_NOWAIT is
369  * not set.
370  *
371  * If FAULT_FLAG_ALLOW_RETRY is set but FAULT_FLAG_KILLABLE is not
372  * set, VM_FAULT_RETRY can still be returned if and only if there are
373  * fatal_signal_pending()s, and the mmap_lock must be released before
374  * returning it.
375  */
376 vm_fault_t handle_userfault(struct vm_fault *vmf, unsigned long reason)
377 {
378         struct mm_struct *mm = vmf->vma->vm_mm;
379         struct userfaultfd_ctx *ctx;
380         struct userfaultfd_wait_queue uwq;
381         vm_fault_t ret = VM_FAULT_SIGBUS;
382         bool must_wait;
383         unsigned int blocking_state;
384
385         /*
386          * We don't do userfault handling for the final child pid update.
387          *
388          * We also don't do userfault handling during
389          * coredumping. hugetlbfs has the special
390          * follow_hugetlb_page() to skip missing pages in the
391          * FOLL_DUMP case, anon memory also checks for FOLL_DUMP with
392          * the no_page_table() helper in follow_page_mask(), but the
393          * shmem_vm_ops->fault method is invoked even during
394          * coredumping without mmap_lock and it ends up here.
395          */
396         if (current->flags & (PF_EXITING|PF_DUMPCORE))
397                 goto out;
398
399         /*
400          * Coredumping runs without mmap_lock so we can only check that
401          * the mmap_lock is held, if PF_DUMPCORE was not set.
402          */
403         mmap_assert_locked(mm);
404
405         ctx = vmf->vma->vm_userfaultfd_ctx.ctx;
406         if (!ctx)
407                 goto out;
408
409         BUG_ON(ctx->mm != mm);
410
411         /* Any unrecognized flag is a bug. */
412         VM_BUG_ON(reason & ~__VM_UFFD_FLAGS);
413         /* 0 or > 1 flags set is a bug; we expect exactly 1. */
414         VM_BUG_ON(!reason || (reason & (reason - 1)));
415
416         if (ctx->features & UFFD_FEATURE_SIGBUS)
417                 goto out;
418         if ((vmf->flags & FAULT_FLAG_USER) == 0 &&
419             ctx->flags & UFFD_USER_MODE_ONLY) {
420                 printk_once(KERN_WARNING "uffd: Set unprivileged_userfaultfd "
421                         "sysctl knob to 1 if kernel faults must be handled "
422                         "without obtaining CAP_SYS_PTRACE capability\n");
423                 goto out;
424         }
425
426         /*
427          * If it's already released don't get it. This avoids to loop
428          * in __get_user_pages if userfaultfd_release waits on the
429          * caller of handle_userfault to release the mmap_lock.
430          */
431         if (unlikely(READ_ONCE(ctx->released))) {
432                 /*
433                  * Don't return VM_FAULT_SIGBUS in this case, so a non
434                  * cooperative manager can close the uffd after the
435                  * last UFFDIO_COPY, without risking to trigger an
436                  * involuntary SIGBUS if the process was starting the
437                  * userfaultfd while the userfaultfd was still armed
438                  * (but after the last UFFDIO_COPY). If the uffd
439                  * wasn't already closed when the userfault reached
440                  * this point, that would normally be solved by
441                  * userfaultfd_must_wait returning 'false'.
442                  *
443                  * If we were to return VM_FAULT_SIGBUS here, the non
444                  * cooperative manager would be instead forced to
445                  * always call UFFDIO_UNREGISTER before it can safely
446                  * close the uffd.
447                  */
448                 ret = VM_FAULT_NOPAGE;
449                 goto out;
450         }
451
452         /*
453          * Check that we can return VM_FAULT_RETRY.
454          *
455          * NOTE: it should become possible to return VM_FAULT_RETRY
456          * even if FAULT_FLAG_TRIED is set without leading to gup()
457          * -EBUSY failures, if the userfaultfd is to be extended for
458          * VM_UFFD_WP tracking and we intend to arm the userfault
459          * without first stopping userland access to the memory. For
460          * VM_UFFD_MISSING userfaults this is enough for now.
461          */
462         if (unlikely(!(vmf->flags & FAULT_FLAG_ALLOW_RETRY))) {
463                 /*
464                  * Validate the invariant that nowait must allow retry
465                  * to be sure not to return SIGBUS erroneously on
466                  * nowait invocations.
467                  */
468                 BUG_ON(vmf->flags & FAULT_FLAG_RETRY_NOWAIT);
469 #ifdef CONFIG_DEBUG_VM
470                 if (printk_ratelimit()) {
471                         printk(KERN_WARNING
472                                "FAULT_FLAG_ALLOW_RETRY missing %x\n",
473                                vmf->flags);
474                         dump_stack();
475                 }
476 #endif
477                 goto out;
478         }
479
480         /*
481          * Handle nowait, not much to do other than tell it to retry
482          * and wait.
483          */
484         ret = VM_FAULT_RETRY;
485         if (vmf->flags & FAULT_FLAG_RETRY_NOWAIT)
486                 goto out;
487
488         /* take the reference before dropping the mmap_lock */
489         userfaultfd_ctx_get(ctx);
490
491         init_waitqueue_func_entry(&uwq.wq, userfaultfd_wake_function);
492         uwq.wq.private = current;
493         uwq.msg = userfault_msg(vmf->address, vmf->real_address, vmf->flags,
494                                 reason, ctx->features);
495         uwq.ctx = ctx;
496         uwq.waken = false;
497
498         blocking_state = userfaultfd_get_blocking_state(vmf->flags);
499
500         spin_lock_irq(&ctx->fault_pending_wqh.lock);
501         /*
502          * After the __add_wait_queue the uwq is visible to userland
503          * through poll/read().
504          */
505         __add_wait_queue(&ctx->fault_pending_wqh, &uwq.wq);
506         /*
507          * The smp_mb() after __set_current_state prevents the reads
508          * following the spin_unlock to happen before the list_add in
509          * __add_wait_queue.
510          */
511         set_current_state(blocking_state);
512         spin_unlock_irq(&ctx->fault_pending_wqh.lock);
513
514         if (!is_vm_hugetlb_page(vmf->vma))
515                 must_wait = userfaultfd_must_wait(ctx, vmf->address, vmf->flags,
516                                                   reason);
517         else
518                 must_wait = userfaultfd_huge_must_wait(ctx, vmf->vma,
519                                                        vmf->address,
520                                                        vmf->flags, reason);
521         mmap_read_unlock(mm);
522
523         if (likely(must_wait && !READ_ONCE(ctx->released))) {
524                 wake_up_poll(&ctx->fd_wqh, EPOLLIN);
525                 schedule();
526         }
527
528         __set_current_state(TASK_RUNNING);
529
530         /*
531          * Here we race with the list_del; list_add in
532          * userfaultfd_ctx_read(), however because we don't ever run
533          * list_del_init() to refile across the two lists, the prev
534          * and next pointers will never point to self. list_add also
535          * would never let any of the two pointers to point to
536          * self. So list_empty_careful won't risk to see both pointers
537          * pointing to self at any time during the list refile. The
538          * only case where list_del_init() is called is the full
539          * removal in the wake function and there we don't re-list_add
540          * and it's fine not to block on the spinlock. The uwq on this
541          * kernel stack can be released after the list_del_init.
542          */
543         if (!list_empty_careful(&uwq.wq.entry)) {
544                 spin_lock_irq(&ctx->fault_pending_wqh.lock);
545                 /*
546                  * No need of list_del_init(), the uwq on the stack
547                  * will be freed shortly anyway.
548                  */
549                 list_del(&uwq.wq.entry);
550                 spin_unlock_irq(&ctx->fault_pending_wqh.lock);
551         }
552
553         /*
554          * ctx may go away after this if the userfault pseudo fd is
555          * already released.
556          */
557         userfaultfd_ctx_put(ctx);
558
559 out:
560         return ret;
561 }
562
563 static void userfaultfd_event_wait_completion(struct userfaultfd_ctx *ctx,
564                                               struct userfaultfd_wait_queue *ewq)
565 {
566         struct userfaultfd_ctx *release_new_ctx;
567
568         if (WARN_ON_ONCE(current->flags & PF_EXITING))
569                 goto out;
570
571         ewq->ctx = ctx;
572         init_waitqueue_entry(&ewq->wq, current);
573         release_new_ctx = NULL;
574
575         spin_lock_irq(&ctx->event_wqh.lock);
576         /*
577          * After the __add_wait_queue the uwq is visible to userland
578          * through poll/read().
579          */
580         __add_wait_queue(&ctx->event_wqh, &ewq->wq);
581         for (;;) {
582                 set_current_state(TASK_KILLABLE);
583                 if (ewq->msg.event == 0)
584                         break;
585                 if (READ_ONCE(ctx->released) ||
586                     fatal_signal_pending(current)) {
587                         /*
588                          * &ewq->wq may be queued in fork_event, but
589                          * __remove_wait_queue ignores the head
590                          * parameter. It would be a problem if it
591                          * didn't.
592                          */
593                         __remove_wait_queue(&ctx->event_wqh, &ewq->wq);
594                         if (ewq->msg.event == UFFD_EVENT_FORK) {
595                                 struct userfaultfd_ctx *new;
596
597                                 new = (struct userfaultfd_ctx *)
598                                         (unsigned long)
599                                         ewq->msg.arg.reserved.reserved1;
600                                 release_new_ctx = new;
601                         }
602                         break;
603                 }
604
605                 spin_unlock_irq(&ctx->event_wqh.lock);
606
607                 wake_up_poll(&ctx->fd_wqh, EPOLLIN);
608                 schedule();
609
610                 spin_lock_irq(&ctx->event_wqh.lock);
611         }
612         __set_current_state(TASK_RUNNING);
613         spin_unlock_irq(&ctx->event_wqh.lock);
614
615         if (release_new_ctx) {
616                 struct vm_area_struct *vma;
617                 struct mm_struct *mm = release_new_ctx->mm;
618
619                 /* the various vma->vm_userfaultfd_ctx still points to it */
620                 mmap_write_lock(mm);
621                 for (vma = mm->mmap; vma; vma = vma->vm_next)
622                         if (vma->vm_userfaultfd_ctx.ctx == release_new_ctx) {
623                                 vma->vm_userfaultfd_ctx = NULL_VM_UFFD_CTX;
624                                 vma->vm_flags &= ~__VM_UFFD_FLAGS;
625                         }
626                 mmap_write_unlock(mm);
627
628                 userfaultfd_ctx_put(release_new_ctx);
629         }
630
631         /*
632          * ctx may go away after this if the userfault pseudo fd is
633          * already released.
634          */
635 out:
636         atomic_dec(&ctx->mmap_changing);
637         VM_BUG_ON(atomic_read(&ctx->mmap_changing) < 0);
638         userfaultfd_ctx_put(ctx);
639 }
640
641 static void userfaultfd_event_complete(struct userfaultfd_ctx *ctx,
642                                        struct userfaultfd_wait_queue *ewq)
643 {
644         ewq->msg.event = 0;
645         wake_up_locked(&ctx->event_wqh);
646         __remove_wait_queue(&ctx->event_wqh, &ewq->wq);
647 }
648
649 int dup_userfaultfd(struct vm_area_struct *vma, struct list_head *fcs)
650 {
651         struct userfaultfd_ctx *ctx = NULL, *octx;
652         struct userfaultfd_fork_ctx *fctx;
653
654         octx = vma->vm_userfaultfd_ctx.ctx;
655         if (!octx || !(octx->features & UFFD_FEATURE_EVENT_FORK)) {
656                 vma->vm_userfaultfd_ctx = NULL_VM_UFFD_CTX;
657                 vma->vm_flags &= ~__VM_UFFD_FLAGS;
658                 return 0;
659         }
660
661         list_for_each_entry(fctx, fcs, list)
662                 if (fctx->orig == octx) {
663                         ctx = fctx->new;
664                         break;
665                 }
666
667         if (!ctx) {
668                 fctx = kmalloc(sizeof(*fctx), GFP_KERNEL);
669                 if (!fctx)
670                         return -ENOMEM;
671
672                 ctx = kmem_cache_alloc(userfaultfd_ctx_cachep, GFP_KERNEL);
673                 if (!ctx) {
674                         kfree(fctx);
675                         return -ENOMEM;
676                 }
677
678                 refcount_set(&ctx->refcount, 1);
679                 ctx->flags = octx->flags;
680                 ctx->features = octx->features;
681                 ctx->released = false;
682                 atomic_set(&ctx->mmap_changing, 0);
683                 ctx->mm = vma->vm_mm;
684                 mmgrab(ctx->mm);
685
686                 userfaultfd_ctx_get(octx);
687                 atomic_inc(&octx->mmap_changing);
688                 fctx->orig = octx;
689                 fctx->new = ctx;
690                 list_add_tail(&fctx->list, fcs);
691         }
692
693         vma->vm_userfaultfd_ctx.ctx = ctx;
694         return 0;
695 }
696
697 static void dup_fctx(struct userfaultfd_fork_ctx *fctx)
698 {
699         struct userfaultfd_ctx *ctx = fctx->orig;
700         struct userfaultfd_wait_queue ewq;
701
702         msg_init(&ewq.msg);
703
704         ewq.msg.event = UFFD_EVENT_FORK;
705         ewq.msg.arg.reserved.reserved1 = (unsigned long)fctx->new;
706
707         userfaultfd_event_wait_completion(ctx, &ewq);
708 }
709
710 void dup_userfaultfd_complete(struct list_head *fcs)
711 {
712         struct userfaultfd_fork_ctx *fctx, *n;
713
714         list_for_each_entry_safe(fctx, n, fcs, list) {
715                 dup_fctx(fctx);
716                 list_del(&fctx->list);
717                 kfree(fctx);
718         }
719 }
720
721 void mremap_userfaultfd_prep(struct vm_area_struct *vma,
722                              struct vm_userfaultfd_ctx *vm_ctx)
723 {
724         struct userfaultfd_ctx *ctx;
725
726         ctx = vma->vm_userfaultfd_ctx.ctx;
727
728         if (!ctx)
729                 return;
730
731         if (ctx->features & UFFD_FEATURE_EVENT_REMAP) {
732                 vm_ctx->ctx = ctx;
733                 userfaultfd_ctx_get(ctx);
734                 atomic_inc(&ctx->mmap_changing);
735         } else {
736                 /* Drop uffd context if remap feature not enabled */
737                 vma->vm_userfaultfd_ctx = NULL_VM_UFFD_CTX;
738                 vma->vm_flags &= ~__VM_UFFD_FLAGS;
739         }
740 }
741
742 void mremap_userfaultfd_complete(struct vm_userfaultfd_ctx *vm_ctx,
743                                  unsigned long from, unsigned long to,
744                                  unsigned long len)
745 {
746         struct userfaultfd_ctx *ctx = vm_ctx->ctx;
747         struct userfaultfd_wait_queue ewq;
748
749         if (!ctx)
750                 return;
751
752         if (to & ~PAGE_MASK) {
753                 userfaultfd_ctx_put(ctx);
754                 return;
755         }
756
757         msg_init(&ewq.msg);
758
759         ewq.msg.event = UFFD_EVENT_REMAP;
760         ewq.msg.arg.remap.from = from;
761         ewq.msg.arg.remap.to = to;
762         ewq.msg.arg.remap.len = len;
763
764         userfaultfd_event_wait_completion(ctx, &ewq);
765 }
766
767 bool userfaultfd_remove(struct vm_area_struct *vma,
768                         unsigned long start, unsigned long end)
769 {
770         struct mm_struct *mm = vma->vm_mm;
771         struct userfaultfd_ctx *ctx;
772         struct userfaultfd_wait_queue ewq;
773
774         ctx = vma->vm_userfaultfd_ctx.ctx;
775         if (!ctx || !(ctx->features & UFFD_FEATURE_EVENT_REMOVE))
776                 return true;
777
778         userfaultfd_ctx_get(ctx);
779         atomic_inc(&ctx->mmap_changing);
780         mmap_read_unlock(mm);
781
782         msg_init(&ewq.msg);
783
784         ewq.msg.event = UFFD_EVENT_REMOVE;
785         ewq.msg.arg.remove.start = start;
786         ewq.msg.arg.remove.end = end;
787
788         userfaultfd_event_wait_completion(ctx, &ewq);
789
790         return false;
791 }
792
793 static bool has_unmap_ctx(struct userfaultfd_ctx *ctx, struct list_head *unmaps,
794                           unsigned long start, unsigned long end)
795 {
796         struct userfaultfd_unmap_ctx *unmap_ctx;
797
798         list_for_each_entry(unmap_ctx, unmaps, list)
799                 if (unmap_ctx->ctx == ctx && unmap_ctx->start == start &&
800                     unmap_ctx->end == end)
801                         return true;
802
803         return false;
804 }
805
806 int userfaultfd_unmap_prep(struct vm_area_struct *vma,
807                            unsigned long start, unsigned long end,
808                            struct list_head *unmaps)
809 {
810         for ( ; vma && vma->vm_start < end; vma = vma->vm_next) {
811                 struct userfaultfd_unmap_ctx *unmap_ctx;
812                 struct userfaultfd_ctx *ctx = vma->vm_userfaultfd_ctx.ctx;
813
814                 if (!ctx || !(ctx->features & UFFD_FEATURE_EVENT_UNMAP) ||
815                     has_unmap_ctx(ctx, unmaps, start, end))
816                         continue;
817
818                 unmap_ctx = kzalloc(sizeof(*unmap_ctx), GFP_KERNEL);
819                 if (!unmap_ctx)
820                         return -ENOMEM;
821
822                 userfaultfd_ctx_get(ctx);
823                 atomic_inc(&ctx->mmap_changing);
824                 unmap_ctx->ctx = ctx;
825                 unmap_ctx->start = start;
826                 unmap_ctx->end = end;
827                 list_add_tail(&unmap_ctx->list, unmaps);
828         }
829
830         return 0;
831 }
832
833 void userfaultfd_unmap_complete(struct mm_struct *mm, struct list_head *uf)
834 {
835         struct userfaultfd_unmap_ctx *ctx, *n;
836         struct userfaultfd_wait_queue ewq;
837
838         list_for_each_entry_safe(ctx, n, uf, list) {
839                 msg_init(&ewq.msg);
840
841                 ewq.msg.event = UFFD_EVENT_UNMAP;
842                 ewq.msg.arg.remove.start = ctx->start;
843                 ewq.msg.arg.remove.end = ctx->end;
844
845                 userfaultfd_event_wait_completion(ctx->ctx, &ewq);
846
847                 list_del(&ctx->list);
848                 kfree(ctx);
849         }
850 }
851
852 static int userfaultfd_release(struct inode *inode, struct file *file)
853 {
854         struct userfaultfd_ctx *ctx = file->private_data;
855         struct mm_struct *mm = ctx->mm;
856         struct vm_area_struct *vma, *prev;
857         /* len == 0 means wake all */
858         struct userfaultfd_wake_range range = { .len = 0, };
859         unsigned long new_flags;
860
861         WRITE_ONCE(ctx->released, true);
862
863         if (!mmget_not_zero(mm))
864                 goto wakeup;
865
866         /*
867          * Flush page faults out of all CPUs. NOTE: all page faults
868          * must be retried without returning VM_FAULT_SIGBUS if
869          * userfaultfd_ctx_get() succeeds but vma->vma_userfault_ctx
870          * changes while handle_userfault released the mmap_lock. So
871          * it's critical that released is set to true (above), before
872          * taking the mmap_lock for writing.
873          */
874         mmap_write_lock(mm);
875         prev = NULL;
876         for (vma = mm->mmap; vma; vma = vma->vm_next) {
877                 cond_resched();
878                 BUG_ON(!!vma->vm_userfaultfd_ctx.ctx ^
879                        !!(vma->vm_flags & __VM_UFFD_FLAGS));
880                 if (vma->vm_userfaultfd_ctx.ctx != ctx) {
881                         prev = vma;
882                         continue;
883                 }
884                 new_flags = vma->vm_flags & ~__VM_UFFD_FLAGS;
885                 prev = vma_merge(mm, prev, vma->vm_start, vma->vm_end,
886                                  new_flags, vma->anon_vma,
887                                  vma->vm_file, vma->vm_pgoff,
888                                  vma_policy(vma),
889                                  NULL_VM_UFFD_CTX, anon_vma_name(vma));
890                 if (prev)
891                         vma = prev;
892                 else
893                         prev = vma;
894                 vma->vm_flags = new_flags;
895                 vma->vm_userfaultfd_ctx = NULL_VM_UFFD_CTX;
896         }
897         mmap_write_unlock(mm);
898         mmput(mm);
899 wakeup:
900         /*
901          * After no new page faults can wait on this fault_*wqh, flush
902          * the last page faults that may have been already waiting on
903          * the fault_*wqh.
904          */
905         spin_lock_irq(&ctx->fault_pending_wqh.lock);
906         __wake_up_locked_key(&ctx->fault_pending_wqh, TASK_NORMAL, &range);
907         __wake_up(&ctx->fault_wqh, TASK_NORMAL, 1, &range);
908         spin_unlock_irq(&ctx->fault_pending_wqh.lock);
909
910         /* Flush pending events that may still wait on event_wqh */
911         wake_up_all(&ctx->event_wqh);
912
913         wake_up_poll(&ctx->fd_wqh, EPOLLHUP);
914         userfaultfd_ctx_put(ctx);
915         return 0;
916 }
917
918 /* fault_pending_wqh.lock must be hold by the caller */
919 static inline struct userfaultfd_wait_queue *find_userfault_in(
920                 wait_queue_head_t *wqh)
921 {
922         wait_queue_entry_t *wq;
923         struct userfaultfd_wait_queue *uwq;
924
925         lockdep_assert_held(&wqh->lock);
926
927         uwq = NULL;
928         if (!waitqueue_active(wqh))
929                 goto out;
930         /* walk in reverse to provide FIFO behavior to read userfaults */
931         wq = list_last_entry(&wqh->head, typeof(*wq), entry);
932         uwq = container_of(wq, struct userfaultfd_wait_queue, wq);
933 out:
934         return uwq;
935 }
936
937 static inline struct userfaultfd_wait_queue *find_userfault(
938                 struct userfaultfd_ctx *ctx)
939 {
940         return find_userfault_in(&ctx->fault_pending_wqh);
941 }
942
943 static inline struct userfaultfd_wait_queue *find_userfault_evt(
944                 struct userfaultfd_ctx *ctx)
945 {
946         return find_userfault_in(&ctx->event_wqh);
947 }
948
949 static __poll_t userfaultfd_poll(struct file *file, poll_table *wait)
950 {
951         struct userfaultfd_ctx *ctx = file->private_data;
952         __poll_t ret;
953
954         poll_wait(file, &ctx->fd_wqh, wait);
955
956         if (!userfaultfd_is_initialized(ctx))
957                 return EPOLLERR;
958
959         /*
960          * poll() never guarantees that read won't block.
961          * userfaults can be waken before they're read().
962          */
963         if (unlikely(!(file->f_flags & O_NONBLOCK)))
964                 return EPOLLERR;
965         /*
966          * lockless access to see if there are pending faults
967          * __pollwait last action is the add_wait_queue but
968          * the spin_unlock would allow the waitqueue_active to
969          * pass above the actual list_add inside
970          * add_wait_queue critical section. So use a full
971          * memory barrier to serialize the list_add write of
972          * add_wait_queue() with the waitqueue_active read
973          * below.
974          */
975         ret = 0;
976         smp_mb();
977         if (waitqueue_active(&ctx->fault_pending_wqh))
978                 ret = EPOLLIN;
979         else if (waitqueue_active(&ctx->event_wqh))
980                 ret = EPOLLIN;
981
982         return ret;
983 }
984
985 static const struct file_operations userfaultfd_fops;
986
987 static int resolve_userfault_fork(struct userfaultfd_ctx *new,
988                                   struct inode *inode,
989                                   struct uffd_msg *msg)
990 {
991         int fd;
992
993         fd = anon_inode_getfd_secure("[userfaultfd]", &userfaultfd_fops, new,
994                         O_RDWR | (new->flags & UFFD_SHARED_FCNTL_FLAGS), inode);
995         if (fd < 0)
996                 return fd;
997
998         msg->arg.reserved.reserved1 = 0;
999         msg->arg.fork.ufd = fd;
1000         return 0;
1001 }
1002
1003 static ssize_t userfaultfd_ctx_read(struct userfaultfd_ctx *ctx, int no_wait,
1004                                     struct uffd_msg *msg, struct inode *inode)
1005 {
1006         ssize_t ret;
1007         DECLARE_WAITQUEUE(wait, current);
1008         struct userfaultfd_wait_queue *uwq;
1009         /*
1010          * Handling fork event requires sleeping operations, so
1011          * we drop the event_wqh lock, then do these ops, then
1012          * lock it back and wake up the waiter. While the lock is
1013          * dropped the ewq may go away so we keep track of it
1014          * carefully.
1015          */
1016         LIST_HEAD(fork_event);
1017         struct userfaultfd_ctx *fork_nctx = NULL;
1018
1019         /* always take the fd_wqh lock before the fault_pending_wqh lock */
1020         spin_lock_irq(&ctx->fd_wqh.lock);
1021         __add_wait_queue(&ctx->fd_wqh, &wait);
1022         for (;;) {
1023                 set_current_state(TASK_INTERRUPTIBLE);
1024                 spin_lock(&ctx->fault_pending_wqh.lock);
1025                 uwq = find_userfault(ctx);
1026                 if (uwq) {
1027                         /*
1028                          * Use a seqcount to repeat the lockless check
1029                          * in wake_userfault() to avoid missing
1030                          * wakeups because during the refile both
1031                          * waitqueue could become empty if this is the
1032                          * only userfault.
1033                          */
1034                         write_seqcount_begin(&ctx->refile_seq);
1035
1036                         /*
1037                          * The fault_pending_wqh.lock prevents the uwq
1038                          * to disappear from under us.
1039                          *
1040                          * Refile this userfault from
1041                          * fault_pending_wqh to fault_wqh, it's not
1042                          * pending anymore after we read it.
1043                          *
1044                          * Use list_del() by hand (as
1045                          * userfaultfd_wake_function also uses
1046                          * list_del_init() by hand) to be sure nobody
1047                          * changes __remove_wait_queue() to use
1048                          * list_del_init() in turn breaking the
1049                          * !list_empty_careful() check in
1050                          * handle_userfault(). The uwq->wq.head list
1051                          * must never be empty at any time during the
1052                          * refile, or the waitqueue could disappear
1053                          * from under us. The "wait_queue_head_t"
1054                          * parameter of __remove_wait_queue() is unused
1055                          * anyway.
1056                          */
1057                         list_del(&uwq->wq.entry);
1058                         add_wait_queue(&ctx->fault_wqh, &uwq->wq);
1059
1060                         write_seqcount_end(&ctx->refile_seq);
1061
1062                         /* careful to always initialize msg if ret == 0 */
1063                         *msg = uwq->msg;
1064                         spin_unlock(&ctx->fault_pending_wqh.lock);
1065                         ret = 0;
1066                         break;
1067                 }
1068                 spin_unlock(&ctx->fault_pending_wqh.lock);
1069
1070                 spin_lock(&ctx->event_wqh.lock);
1071                 uwq = find_userfault_evt(ctx);
1072                 if (uwq) {
1073                         *msg = uwq->msg;
1074
1075                         if (uwq->msg.event == UFFD_EVENT_FORK) {
1076                                 fork_nctx = (struct userfaultfd_ctx *)
1077                                         (unsigned long)
1078                                         uwq->msg.arg.reserved.reserved1;
1079                                 list_move(&uwq->wq.entry, &fork_event);
1080                                 /*
1081                                  * fork_nctx can be freed as soon as
1082                                  * we drop the lock, unless we take a
1083                                  * reference on it.
1084                                  */
1085                                 userfaultfd_ctx_get(fork_nctx);
1086                                 spin_unlock(&ctx->event_wqh.lock);
1087                                 ret = 0;
1088                                 break;
1089                         }
1090
1091                         userfaultfd_event_complete(ctx, uwq);
1092                         spin_unlock(&ctx->event_wqh.lock);
1093                         ret = 0;
1094                         break;
1095                 }
1096                 spin_unlock(&ctx->event_wqh.lock);
1097
1098                 if (signal_pending(current)) {
1099                         ret = -ERESTARTSYS;
1100                         break;
1101                 }
1102                 if (no_wait) {
1103                         ret = -EAGAIN;
1104                         break;
1105                 }
1106                 spin_unlock_irq(&ctx->fd_wqh.lock);
1107                 schedule();
1108                 spin_lock_irq(&ctx->fd_wqh.lock);
1109         }
1110         __remove_wait_queue(&ctx->fd_wqh, &wait);
1111         __set_current_state(TASK_RUNNING);
1112         spin_unlock_irq(&ctx->fd_wqh.lock);
1113
1114         if (!ret && msg->event == UFFD_EVENT_FORK) {
1115                 ret = resolve_userfault_fork(fork_nctx, inode, msg);
1116                 spin_lock_irq(&ctx->event_wqh.lock);
1117                 if (!list_empty(&fork_event)) {
1118                         /*
1119                          * The fork thread didn't abort, so we can
1120                          * drop the temporary refcount.
1121                          */
1122                         userfaultfd_ctx_put(fork_nctx);
1123
1124                         uwq = list_first_entry(&fork_event,
1125                                                typeof(*uwq),
1126                                                wq.entry);
1127                         /*
1128                          * If fork_event list wasn't empty and in turn
1129                          * the event wasn't already released by fork
1130                          * (the event is allocated on fork kernel
1131                          * stack), put the event back to its place in
1132                          * the event_wq. fork_event head will be freed
1133                          * as soon as we return so the event cannot
1134                          * stay queued there no matter the current
1135                          * "ret" value.
1136                          */
1137                         list_del(&uwq->wq.entry);
1138                         __add_wait_queue(&ctx->event_wqh, &uwq->wq);
1139
1140                         /*
1141                          * Leave the event in the waitqueue and report
1142                          * error to userland if we failed to resolve
1143                          * the userfault fork.
1144                          */
1145                         if (likely(!ret))
1146                                 userfaultfd_event_complete(ctx, uwq);
1147                 } else {
1148                         /*
1149                          * Here the fork thread aborted and the
1150                          * refcount from the fork thread on fork_nctx
1151                          * has already been released. We still hold
1152                          * the reference we took before releasing the
1153                          * lock above. If resolve_userfault_fork
1154                          * failed we've to drop it because the
1155                          * fork_nctx has to be freed in such case. If
1156                          * it succeeded we'll hold it because the new
1157                          * uffd references it.
1158                          */
1159                         if (ret)
1160                                 userfaultfd_ctx_put(fork_nctx);
1161                 }
1162                 spin_unlock_irq(&ctx->event_wqh.lock);
1163         }
1164
1165         return ret;
1166 }
1167
1168 static ssize_t userfaultfd_read(struct file *file, char __user *buf,
1169                                 size_t count, loff_t *ppos)
1170 {
1171         struct userfaultfd_ctx *ctx = file->private_data;
1172         ssize_t _ret, ret = 0;
1173         struct uffd_msg msg;
1174         int no_wait = file->f_flags & O_NONBLOCK;
1175         struct inode *inode = file_inode(file);
1176
1177         if (!userfaultfd_is_initialized(ctx))
1178                 return -EINVAL;
1179
1180         for (;;) {
1181                 if (count < sizeof(msg))
1182                         return ret ? ret : -EINVAL;
1183                 _ret = userfaultfd_ctx_read(ctx, no_wait, &msg, inode);
1184                 if (_ret < 0)
1185                         return ret ? ret : _ret;
1186                 if (copy_to_user((__u64 __user *) buf, &msg, sizeof(msg)))
1187                         return ret ? ret : -EFAULT;
1188                 ret += sizeof(msg);
1189                 buf += sizeof(msg);
1190                 count -= sizeof(msg);
1191                 /*
1192                  * Allow to read more than one fault at time but only
1193                  * block if waiting for the very first one.
1194                  */
1195                 no_wait = O_NONBLOCK;
1196         }
1197 }
1198
1199 static void __wake_userfault(struct userfaultfd_ctx *ctx,
1200                              struct userfaultfd_wake_range *range)
1201 {
1202         spin_lock_irq(&ctx->fault_pending_wqh.lock);
1203         /* wake all in the range and autoremove */
1204         if (waitqueue_active(&ctx->fault_pending_wqh))
1205                 __wake_up_locked_key(&ctx->fault_pending_wqh, TASK_NORMAL,
1206                                      range);
1207         if (waitqueue_active(&ctx->fault_wqh))
1208                 __wake_up(&ctx->fault_wqh, TASK_NORMAL, 1, range);
1209         spin_unlock_irq(&ctx->fault_pending_wqh.lock);
1210 }
1211
1212 static __always_inline void wake_userfault(struct userfaultfd_ctx *ctx,
1213                                            struct userfaultfd_wake_range *range)
1214 {
1215         unsigned seq;
1216         bool need_wakeup;
1217
1218         /*
1219          * To be sure waitqueue_active() is not reordered by the CPU
1220          * before the pagetable update, use an explicit SMP memory
1221          * barrier here. PT lock release or mmap_read_unlock(mm) still
1222          * have release semantics that can allow the
1223          * waitqueue_active() to be reordered before the pte update.
1224          */
1225         smp_mb();
1226
1227         /*
1228          * Use waitqueue_active because it's very frequent to
1229          * change the address space atomically even if there are no
1230          * userfaults yet. So we take the spinlock only when we're
1231          * sure we've userfaults to wake.
1232          */
1233         do {
1234                 seq = read_seqcount_begin(&ctx->refile_seq);
1235                 need_wakeup = waitqueue_active(&ctx->fault_pending_wqh) ||
1236                         waitqueue_active(&ctx->fault_wqh);
1237                 cond_resched();
1238         } while (read_seqcount_retry(&ctx->refile_seq, seq));
1239         if (need_wakeup)
1240                 __wake_userfault(ctx, range);
1241 }
1242
1243 static __always_inline int validate_range(struct mm_struct *mm,
1244                                           __u64 start, __u64 len)
1245 {
1246         __u64 task_size = mm->task_size;
1247
1248         if (start & ~PAGE_MASK)
1249                 return -EINVAL;
1250         if (len & ~PAGE_MASK)
1251                 return -EINVAL;
1252         if (!len)
1253                 return -EINVAL;
1254         if (start < mmap_min_addr)
1255                 return -EINVAL;
1256         if (start >= task_size)
1257                 return -EINVAL;
1258         if (len > task_size - start)
1259                 return -EINVAL;
1260         return 0;
1261 }
1262
1263 static int userfaultfd_register(struct userfaultfd_ctx *ctx,
1264                                 unsigned long arg)
1265 {
1266         struct mm_struct *mm = ctx->mm;
1267         struct vm_area_struct *vma, *prev, *cur;
1268         int ret;
1269         struct uffdio_register uffdio_register;
1270         struct uffdio_register __user *user_uffdio_register;
1271         unsigned long vm_flags, new_flags;
1272         bool found;
1273         bool basic_ioctls;
1274         unsigned long start, end, vma_end;
1275
1276         user_uffdio_register = (struct uffdio_register __user *) arg;
1277
1278         ret = -EFAULT;
1279         if (copy_from_user(&uffdio_register, user_uffdio_register,
1280                            sizeof(uffdio_register)-sizeof(__u64)))
1281                 goto out;
1282
1283         ret = -EINVAL;
1284         if (!uffdio_register.mode)
1285                 goto out;
1286         if (uffdio_register.mode & ~UFFD_API_REGISTER_MODES)
1287                 goto out;
1288         vm_flags = 0;
1289         if (uffdio_register.mode & UFFDIO_REGISTER_MODE_MISSING)
1290                 vm_flags |= VM_UFFD_MISSING;
1291         if (uffdio_register.mode & UFFDIO_REGISTER_MODE_WP) {
1292 #ifndef CONFIG_HAVE_ARCH_USERFAULTFD_WP
1293                 goto out;
1294 #endif
1295                 vm_flags |= VM_UFFD_WP;
1296         }
1297         if (uffdio_register.mode & UFFDIO_REGISTER_MODE_MINOR) {
1298 #ifndef CONFIG_HAVE_ARCH_USERFAULTFD_MINOR
1299                 goto out;
1300 #endif
1301                 vm_flags |= VM_UFFD_MINOR;
1302         }
1303
1304         ret = validate_range(mm, uffdio_register.range.start,
1305                              uffdio_register.range.len);
1306         if (ret)
1307                 goto out;
1308
1309         start = uffdio_register.range.start;
1310         end = start + uffdio_register.range.len;
1311
1312         ret = -ENOMEM;
1313         if (!mmget_not_zero(mm))
1314                 goto out;
1315
1316         mmap_write_lock(mm);
1317         vma = find_vma_prev(mm, start, &prev);
1318         if (!vma)
1319                 goto out_unlock;
1320
1321         /* check that there's at least one vma in the range */
1322         ret = -EINVAL;
1323         if (vma->vm_start >= end)
1324                 goto out_unlock;
1325
1326         /*
1327          * If the first vma contains huge pages, make sure start address
1328          * is aligned to huge page size.
1329          */
1330         if (is_vm_hugetlb_page(vma)) {
1331                 unsigned long vma_hpagesize = vma_kernel_pagesize(vma);
1332
1333                 if (start & (vma_hpagesize - 1))
1334                         goto out_unlock;
1335         }
1336
1337         /*
1338          * Search for not compatible vmas.
1339          */
1340         found = false;
1341         basic_ioctls = false;
1342         for (cur = vma; cur && cur->vm_start < end; cur = cur->vm_next) {
1343                 cond_resched();
1344
1345                 BUG_ON(!!cur->vm_userfaultfd_ctx.ctx ^
1346                        !!(cur->vm_flags & __VM_UFFD_FLAGS));
1347
1348                 /* check not compatible vmas */
1349                 ret = -EINVAL;
1350                 if (!vma_can_userfault(cur, vm_flags))
1351                         goto out_unlock;
1352
1353                 /*
1354                  * UFFDIO_COPY will fill file holes even without
1355                  * PROT_WRITE. This check enforces that if this is a
1356                  * MAP_SHARED, the process has write permission to the backing
1357                  * file. If VM_MAYWRITE is set it also enforces that on a
1358                  * MAP_SHARED vma: there is no F_WRITE_SEAL and no further
1359                  * F_WRITE_SEAL can be taken until the vma is destroyed.
1360                  */
1361                 ret = -EPERM;
1362                 if (unlikely(!(cur->vm_flags & VM_MAYWRITE)))
1363                         goto out_unlock;
1364
1365                 /*
1366                  * If this vma contains ending address, and huge pages
1367                  * check alignment.
1368                  */
1369                 if (is_vm_hugetlb_page(cur) && end <= cur->vm_end &&
1370                     end > cur->vm_start) {
1371                         unsigned long vma_hpagesize = vma_kernel_pagesize(cur);
1372
1373                         ret = -EINVAL;
1374
1375                         if (end & (vma_hpagesize - 1))
1376                                 goto out_unlock;
1377                 }
1378                 if ((vm_flags & VM_UFFD_WP) && !(cur->vm_flags & VM_MAYWRITE))
1379                         goto out_unlock;
1380
1381                 /*
1382                  * Check that this vma isn't already owned by a
1383                  * different userfaultfd. We can't allow more than one
1384                  * userfaultfd to own a single vma simultaneously or we
1385                  * wouldn't know which one to deliver the userfaults to.
1386                  */
1387                 ret = -EBUSY;
1388                 if (cur->vm_userfaultfd_ctx.ctx &&
1389                     cur->vm_userfaultfd_ctx.ctx != ctx)
1390                         goto out_unlock;
1391
1392                 /*
1393                  * Note vmas containing huge pages
1394                  */
1395                 if (is_vm_hugetlb_page(cur))
1396                         basic_ioctls = true;
1397
1398                 found = true;
1399         }
1400         BUG_ON(!found);
1401
1402         if (vma->vm_start < start)
1403                 prev = vma;
1404
1405         ret = 0;
1406         do {
1407                 cond_resched();
1408
1409                 BUG_ON(!vma_can_userfault(vma, vm_flags));
1410                 BUG_ON(vma->vm_userfaultfd_ctx.ctx &&
1411                        vma->vm_userfaultfd_ctx.ctx != ctx);
1412                 WARN_ON(!(vma->vm_flags & VM_MAYWRITE));
1413
1414                 /*
1415                  * Nothing to do: this vma is already registered into this
1416                  * userfaultfd and with the right tracking mode too.
1417                  */
1418                 if (vma->vm_userfaultfd_ctx.ctx == ctx &&
1419                     (vma->vm_flags & vm_flags) == vm_flags)
1420                         goto skip;
1421
1422                 if (vma->vm_start > start)
1423                         start = vma->vm_start;
1424                 vma_end = min(end, vma->vm_end);
1425
1426                 new_flags = (vma->vm_flags & ~__VM_UFFD_FLAGS) | vm_flags;
1427                 prev = vma_merge(mm, prev, start, vma_end, new_flags,
1428                                  vma->anon_vma, vma->vm_file, vma->vm_pgoff,
1429                                  vma_policy(vma),
1430                                  ((struct vm_userfaultfd_ctx){ ctx }),
1431                                  anon_vma_name(vma));
1432                 if (prev) {
1433                         vma = prev;
1434                         goto next;
1435                 }
1436                 if (vma->vm_start < start) {
1437                         ret = split_vma(mm, vma, start, 1);
1438                         if (ret)
1439                                 break;
1440                 }
1441                 if (vma->vm_end > end) {
1442                         ret = split_vma(mm, vma, end, 0);
1443                         if (ret)
1444                                 break;
1445                 }
1446         next:
1447                 /*
1448                  * In the vma_merge() successful mprotect-like case 8:
1449                  * the next vma was merged into the current one and
1450                  * the current one has not been updated yet.
1451                  */
1452                 vma->vm_flags = new_flags;
1453                 vma->vm_userfaultfd_ctx.ctx = ctx;
1454
1455                 if (is_vm_hugetlb_page(vma) && uffd_disable_huge_pmd_share(vma))
1456                         hugetlb_unshare_all_pmds(vma);
1457
1458         skip:
1459                 prev = vma;
1460                 start = vma->vm_end;
1461                 vma = vma->vm_next;
1462         } while (vma && vma->vm_start < end);
1463 out_unlock:
1464         mmap_write_unlock(mm);
1465         mmput(mm);
1466         if (!ret) {
1467                 __u64 ioctls_out;
1468
1469                 ioctls_out = basic_ioctls ? UFFD_API_RANGE_IOCTLS_BASIC :
1470                     UFFD_API_RANGE_IOCTLS;
1471
1472                 /*
1473                  * Declare the WP ioctl only if the WP mode is
1474                  * specified and all checks passed with the range
1475                  */
1476                 if (!(uffdio_register.mode & UFFDIO_REGISTER_MODE_WP))
1477                         ioctls_out &= ~((__u64)1 << _UFFDIO_WRITEPROTECT);
1478
1479                 /* CONTINUE ioctl is only supported for MINOR ranges. */
1480                 if (!(uffdio_register.mode & UFFDIO_REGISTER_MODE_MINOR))
1481                         ioctls_out &= ~((__u64)1 << _UFFDIO_CONTINUE);
1482
1483                 /*
1484                  * Now that we scanned all vmas we can already tell
1485                  * userland which ioctls methods are guaranteed to
1486                  * succeed on this range.
1487                  */
1488                 if (put_user(ioctls_out, &user_uffdio_register->ioctls))
1489                         ret = -EFAULT;
1490         }
1491 out:
1492         return ret;
1493 }
1494
1495 static int userfaultfd_unregister(struct userfaultfd_ctx *ctx,
1496                                   unsigned long arg)
1497 {
1498         struct mm_struct *mm = ctx->mm;
1499         struct vm_area_struct *vma, *prev, *cur;
1500         int ret;
1501         struct uffdio_range uffdio_unregister;
1502         unsigned long new_flags;
1503         bool found;
1504         unsigned long start, end, vma_end;
1505         const void __user *buf = (void __user *)arg;
1506
1507         ret = -EFAULT;
1508         if (copy_from_user(&uffdio_unregister, buf, sizeof(uffdio_unregister)))
1509                 goto out;
1510
1511         ret = validate_range(mm, uffdio_unregister.start,
1512                              uffdio_unregister.len);
1513         if (ret)
1514                 goto out;
1515
1516         start = uffdio_unregister.start;
1517         end = start + uffdio_unregister.len;
1518
1519         ret = -ENOMEM;
1520         if (!mmget_not_zero(mm))
1521                 goto out;
1522
1523         mmap_write_lock(mm);
1524         vma = find_vma_prev(mm, start, &prev);
1525         if (!vma)
1526                 goto out_unlock;
1527
1528         /* check that there's at least one vma in the range */
1529         ret = -EINVAL;
1530         if (vma->vm_start >= end)
1531                 goto out_unlock;
1532
1533         /*
1534          * If the first vma contains huge pages, make sure start address
1535          * is aligned to huge page size.
1536          */
1537         if (is_vm_hugetlb_page(vma)) {
1538                 unsigned long vma_hpagesize = vma_kernel_pagesize(vma);
1539
1540                 if (start & (vma_hpagesize - 1))
1541                         goto out_unlock;
1542         }
1543
1544         /*
1545          * Search for not compatible vmas.
1546          */
1547         found = false;
1548         ret = -EINVAL;
1549         for (cur = vma; cur && cur->vm_start < end; cur = cur->vm_next) {
1550                 cond_resched();
1551
1552                 BUG_ON(!!cur->vm_userfaultfd_ctx.ctx ^
1553                        !!(cur->vm_flags & __VM_UFFD_FLAGS));
1554
1555                 /*
1556                  * Check not compatible vmas, not strictly required
1557                  * here as not compatible vmas cannot have an
1558                  * userfaultfd_ctx registered on them, but this
1559                  * provides for more strict behavior to notice
1560                  * unregistration errors.
1561                  */
1562                 if (!vma_can_userfault(cur, cur->vm_flags))
1563                         goto out_unlock;
1564
1565                 found = true;
1566         }
1567         BUG_ON(!found);
1568
1569         if (vma->vm_start < start)
1570                 prev = vma;
1571
1572         ret = 0;
1573         do {
1574                 cond_resched();
1575
1576                 BUG_ON(!vma_can_userfault(vma, vma->vm_flags));
1577
1578                 /*
1579                  * Nothing to do: this vma is already registered into this
1580                  * userfaultfd and with the right tracking mode too.
1581                  */
1582                 if (!vma->vm_userfaultfd_ctx.ctx)
1583                         goto skip;
1584
1585                 WARN_ON(!(vma->vm_flags & VM_MAYWRITE));
1586
1587                 if (vma->vm_start > start)
1588                         start = vma->vm_start;
1589                 vma_end = min(end, vma->vm_end);
1590
1591                 if (userfaultfd_missing(vma)) {
1592                         /*
1593                          * Wake any concurrent pending userfault while
1594                          * we unregister, so they will not hang
1595                          * permanently and it avoids userland to call
1596                          * UFFDIO_WAKE explicitly.
1597                          */
1598                         struct userfaultfd_wake_range range;
1599                         range.start = start;
1600                         range.len = vma_end - start;
1601                         wake_userfault(vma->vm_userfaultfd_ctx.ctx, &range);
1602                 }
1603
1604                 new_flags = vma->vm_flags & ~__VM_UFFD_FLAGS;
1605                 prev = vma_merge(mm, prev, start, vma_end, new_flags,
1606                                  vma->anon_vma, vma->vm_file, vma->vm_pgoff,
1607                                  vma_policy(vma),
1608                                  NULL_VM_UFFD_CTX, anon_vma_name(vma));
1609                 if (prev) {
1610                         vma = prev;
1611                         goto next;
1612                 }
1613                 if (vma->vm_start < start) {
1614                         ret = split_vma(mm, vma, start, 1);
1615                         if (ret)
1616                                 break;
1617                 }
1618                 if (vma->vm_end > end) {
1619                         ret = split_vma(mm, vma, end, 0);
1620                         if (ret)
1621                                 break;
1622                 }
1623         next:
1624                 /*
1625                  * In the vma_merge() successful mprotect-like case 8:
1626                  * the next vma was merged into the current one and
1627                  * the current one has not been updated yet.
1628                  */
1629                 vma->vm_flags = new_flags;
1630                 vma->vm_userfaultfd_ctx = NULL_VM_UFFD_CTX;
1631
1632         skip:
1633                 prev = vma;
1634                 start = vma->vm_end;
1635                 vma = vma->vm_next;
1636         } while (vma && vma->vm_start < end);
1637 out_unlock:
1638         mmap_write_unlock(mm);
1639         mmput(mm);
1640 out:
1641         return ret;
1642 }
1643
1644 /*
1645  * userfaultfd_wake may be used in combination with the
1646  * UFFDIO_*_MODE_DONTWAKE to wakeup userfaults in batches.
1647  */
1648 static int userfaultfd_wake(struct userfaultfd_ctx *ctx,
1649                             unsigned long arg)
1650 {
1651         int ret;
1652         struct uffdio_range uffdio_wake;
1653         struct userfaultfd_wake_range range;
1654         const void __user *buf = (void __user *)arg;
1655
1656         ret = -EFAULT;
1657         if (copy_from_user(&uffdio_wake, buf, sizeof(uffdio_wake)))
1658                 goto out;
1659
1660         ret = validate_range(ctx->mm, uffdio_wake.start, uffdio_wake.len);
1661         if (ret)
1662                 goto out;
1663
1664         range.start = uffdio_wake.start;
1665         range.len = uffdio_wake.len;
1666
1667         /*
1668          * len == 0 means wake all and we don't want to wake all here,
1669          * so check it again to be sure.
1670          */
1671         VM_BUG_ON(!range.len);
1672
1673         wake_userfault(ctx, &range);
1674         ret = 0;
1675
1676 out:
1677         return ret;
1678 }
1679
1680 static int userfaultfd_copy(struct userfaultfd_ctx *ctx,
1681                             unsigned long arg)
1682 {
1683         __s64 ret;
1684         struct uffdio_copy uffdio_copy;
1685         struct uffdio_copy __user *user_uffdio_copy;
1686         struct userfaultfd_wake_range range;
1687
1688         user_uffdio_copy = (struct uffdio_copy __user *) arg;
1689
1690         ret = -EAGAIN;
1691         if (atomic_read(&ctx->mmap_changing))
1692                 goto out;
1693
1694         ret = -EFAULT;
1695         if (copy_from_user(&uffdio_copy, user_uffdio_copy,
1696                            /* don't copy "copy" last field */
1697                            sizeof(uffdio_copy)-sizeof(__s64)))
1698                 goto out;
1699
1700         ret = validate_range(ctx->mm, uffdio_copy.dst, uffdio_copy.len);
1701         if (ret)
1702                 goto out;
1703         /*
1704          * double check for wraparound just in case. copy_from_user()
1705          * will later check uffdio_copy.src + uffdio_copy.len to fit
1706          * in the userland range.
1707          */
1708         ret = -EINVAL;
1709         if (uffdio_copy.src + uffdio_copy.len <= uffdio_copy.src)
1710                 goto out;
1711         if (uffdio_copy.mode & ~(UFFDIO_COPY_MODE_DONTWAKE|UFFDIO_COPY_MODE_WP))
1712                 goto out;
1713         if (mmget_not_zero(ctx->mm)) {
1714                 ret = mcopy_atomic(ctx->mm, uffdio_copy.dst, uffdio_copy.src,
1715                                    uffdio_copy.len, &ctx->mmap_changing,
1716                                    uffdio_copy.mode);
1717                 mmput(ctx->mm);
1718         } else {
1719                 return -ESRCH;
1720         }
1721         if (unlikely(put_user(ret, &user_uffdio_copy->copy)))
1722                 return -EFAULT;
1723         if (ret < 0)
1724                 goto out;
1725         BUG_ON(!ret);
1726         /* len == 0 would wake all */
1727         range.len = ret;
1728         if (!(uffdio_copy.mode & UFFDIO_COPY_MODE_DONTWAKE)) {
1729                 range.start = uffdio_copy.dst;
1730                 wake_userfault(ctx, &range);
1731         }
1732         ret = range.len == uffdio_copy.len ? 0 : -EAGAIN;
1733 out:
1734         return ret;
1735 }
1736
1737 static int userfaultfd_zeropage(struct userfaultfd_ctx *ctx,
1738                                 unsigned long arg)
1739 {
1740         __s64 ret;
1741         struct uffdio_zeropage uffdio_zeropage;
1742         struct uffdio_zeropage __user *user_uffdio_zeropage;
1743         struct userfaultfd_wake_range range;
1744
1745         user_uffdio_zeropage = (struct uffdio_zeropage __user *) arg;
1746
1747         ret = -EAGAIN;
1748         if (atomic_read(&ctx->mmap_changing))
1749                 goto out;
1750
1751         ret = -EFAULT;
1752         if (copy_from_user(&uffdio_zeropage, user_uffdio_zeropage,
1753                            /* don't copy "zeropage" last field */
1754                            sizeof(uffdio_zeropage)-sizeof(__s64)))
1755                 goto out;
1756
1757         ret = validate_range(ctx->mm, uffdio_zeropage.range.start,
1758                              uffdio_zeropage.range.len);
1759         if (ret)
1760                 goto out;
1761         ret = -EINVAL;
1762         if (uffdio_zeropage.mode & ~UFFDIO_ZEROPAGE_MODE_DONTWAKE)
1763                 goto out;
1764
1765         if (mmget_not_zero(ctx->mm)) {
1766                 ret = mfill_zeropage(ctx->mm, uffdio_zeropage.range.start,
1767                                      uffdio_zeropage.range.len,
1768                                      &ctx->mmap_changing);
1769                 mmput(ctx->mm);
1770         } else {
1771                 return -ESRCH;
1772         }
1773         if (unlikely(put_user(ret, &user_uffdio_zeropage->zeropage)))
1774                 return -EFAULT;
1775         if (ret < 0)
1776                 goto out;
1777         /* len == 0 would wake all */
1778         BUG_ON(!ret);
1779         range.len = ret;
1780         if (!(uffdio_zeropage.mode & UFFDIO_ZEROPAGE_MODE_DONTWAKE)) {
1781                 range.start = uffdio_zeropage.range.start;
1782                 wake_userfault(ctx, &range);
1783         }
1784         ret = range.len == uffdio_zeropage.range.len ? 0 : -EAGAIN;
1785 out:
1786         return ret;
1787 }
1788
1789 static int userfaultfd_writeprotect(struct userfaultfd_ctx *ctx,
1790                                     unsigned long arg)
1791 {
1792         int ret;
1793         struct uffdio_writeprotect uffdio_wp;
1794         struct uffdio_writeprotect __user *user_uffdio_wp;
1795         struct userfaultfd_wake_range range;
1796         bool mode_wp, mode_dontwake;
1797
1798         if (atomic_read(&ctx->mmap_changing))
1799                 return -EAGAIN;
1800
1801         user_uffdio_wp = (struct uffdio_writeprotect __user *) arg;
1802
1803         if (copy_from_user(&uffdio_wp, user_uffdio_wp,
1804                            sizeof(struct uffdio_writeprotect)))
1805                 return -EFAULT;
1806
1807         ret = validate_range(ctx->mm, uffdio_wp.range.start,
1808                              uffdio_wp.range.len);
1809         if (ret)
1810                 return ret;
1811
1812         if (uffdio_wp.mode & ~(UFFDIO_WRITEPROTECT_MODE_DONTWAKE |
1813                                UFFDIO_WRITEPROTECT_MODE_WP))
1814                 return -EINVAL;
1815
1816         mode_wp = uffdio_wp.mode & UFFDIO_WRITEPROTECT_MODE_WP;
1817         mode_dontwake = uffdio_wp.mode & UFFDIO_WRITEPROTECT_MODE_DONTWAKE;
1818
1819         if (mode_wp && mode_dontwake)
1820                 return -EINVAL;
1821
1822         if (mmget_not_zero(ctx->mm)) {
1823                 ret = mwriteprotect_range(ctx->mm, uffdio_wp.range.start,
1824                                           uffdio_wp.range.len, mode_wp,
1825                                           &ctx->mmap_changing);
1826                 mmput(ctx->mm);
1827         } else {
1828                 return -ESRCH;
1829         }
1830
1831         if (ret)
1832                 return ret;
1833
1834         if (!mode_wp && !mode_dontwake) {
1835                 range.start = uffdio_wp.range.start;
1836                 range.len = uffdio_wp.range.len;
1837                 wake_userfault(ctx, &range);
1838         }
1839         return ret;
1840 }
1841
1842 static int userfaultfd_continue(struct userfaultfd_ctx *ctx, unsigned long arg)
1843 {
1844         __s64 ret;
1845         struct uffdio_continue uffdio_continue;
1846         struct uffdio_continue __user *user_uffdio_continue;
1847         struct userfaultfd_wake_range range;
1848
1849         user_uffdio_continue = (struct uffdio_continue __user *)arg;
1850
1851         ret = -EAGAIN;
1852         if (atomic_read(&ctx->mmap_changing))
1853                 goto out;
1854
1855         ret = -EFAULT;
1856         if (copy_from_user(&uffdio_continue, user_uffdio_continue,
1857                            /* don't copy the output fields */
1858                            sizeof(uffdio_continue) - (sizeof(__s64))))
1859                 goto out;
1860
1861         ret = validate_range(ctx->mm, uffdio_continue.range.start,
1862                              uffdio_continue.range.len);
1863         if (ret)
1864                 goto out;
1865
1866         ret = -EINVAL;
1867         /* double check for wraparound just in case. */
1868         if (uffdio_continue.range.start + uffdio_continue.range.len <=
1869             uffdio_continue.range.start) {
1870                 goto out;
1871         }
1872         if (uffdio_continue.mode & ~UFFDIO_CONTINUE_MODE_DONTWAKE)
1873                 goto out;
1874
1875         if (mmget_not_zero(ctx->mm)) {
1876                 ret = mcopy_continue(ctx->mm, uffdio_continue.range.start,
1877                                      uffdio_continue.range.len,
1878                                      &ctx->mmap_changing);
1879                 mmput(ctx->mm);
1880         } else {
1881                 return -ESRCH;
1882         }
1883
1884         if (unlikely(put_user(ret, &user_uffdio_continue->mapped)))
1885                 return -EFAULT;
1886         if (ret < 0)
1887                 goto out;
1888
1889         /* len == 0 would wake all */
1890         BUG_ON(!ret);
1891         range.len = ret;
1892         if (!(uffdio_continue.mode & UFFDIO_CONTINUE_MODE_DONTWAKE)) {
1893                 range.start = uffdio_continue.range.start;
1894                 wake_userfault(ctx, &range);
1895         }
1896         ret = range.len == uffdio_continue.range.len ? 0 : -EAGAIN;
1897
1898 out:
1899         return ret;
1900 }
1901
1902 static inline unsigned int uffd_ctx_features(__u64 user_features)
1903 {
1904         /*
1905          * For the current set of features the bits just coincide. Set
1906          * UFFD_FEATURE_INITIALIZED to mark the features as enabled.
1907          */
1908         return (unsigned int)user_features | UFFD_FEATURE_INITIALIZED;
1909 }
1910
1911 /*
1912  * userland asks for a certain API version and we return which bits
1913  * and ioctl commands are implemented in this kernel for such API
1914  * version or -EINVAL if unknown.
1915  */
1916 static int userfaultfd_api(struct userfaultfd_ctx *ctx,
1917                            unsigned long arg)
1918 {
1919         struct uffdio_api uffdio_api;
1920         void __user *buf = (void __user *)arg;
1921         unsigned int ctx_features;
1922         int ret;
1923         __u64 features;
1924
1925         ret = -EFAULT;
1926         if (copy_from_user(&uffdio_api, buf, sizeof(uffdio_api)))
1927                 goto out;
1928         /* Ignore unsupported features (userspace built against newer kernel) */
1929         features = uffdio_api.features & UFFD_API_FEATURES;
1930         ret = -EPERM;
1931         if ((features & UFFD_FEATURE_EVENT_FORK) && !capable(CAP_SYS_PTRACE))
1932                 goto err_out;
1933         /* report all available features and ioctls to userland */
1934         uffdio_api.features = UFFD_API_FEATURES;
1935 #ifndef CONFIG_HAVE_ARCH_USERFAULTFD_MINOR
1936         uffdio_api.features &=
1937                 ~(UFFD_FEATURE_MINOR_HUGETLBFS | UFFD_FEATURE_MINOR_SHMEM);
1938 #endif
1939 #ifndef CONFIG_HAVE_ARCH_USERFAULTFD_WP
1940         uffdio_api.features &= ~UFFD_FEATURE_PAGEFAULT_FLAG_WP;
1941 #endif
1942 #ifndef CONFIG_PTE_MARKER_UFFD_WP
1943         uffdio_api.features &= ~UFFD_FEATURE_WP_HUGETLBFS_SHMEM;
1944 #endif
1945         uffdio_api.ioctls = UFFD_API_IOCTLS;
1946         ret = -EFAULT;
1947         if (copy_to_user(buf, &uffdio_api, sizeof(uffdio_api)))
1948                 goto out;
1949
1950         /* only enable the requested features for this uffd context */
1951         ctx_features = uffd_ctx_features(features);
1952         ret = -EINVAL;
1953         if (cmpxchg(&ctx->features, 0, ctx_features) != 0)
1954                 goto err_out;
1955
1956         ret = 0;
1957 out:
1958         return ret;
1959 err_out:
1960         memset(&uffdio_api, 0, sizeof(uffdio_api));
1961         if (copy_to_user(buf, &uffdio_api, sizeof(uffdio_api)))
1962                 ret = -EFAULT;
1963         goto out;
1964 }
1965
1966 static long userfaultfd_ioctl(struct file *file, unsigned cmd,
1967                               unsigned long arg)
1968 {
1969         int ret = -EINVAL;
1970         struct userfaultfd_ctx *ctx = file->private_data;
1971
1972         if (cmd != UFFDIO_API && !userfaultfd_is_initialized(ctx))
1973                 return -EINVAL;
1974
1975         switch(cmd) {
1976         case UFFDIO_API:
1977                 ret = userfaultfd_api(ctx, arg);
1978                 break;
1979         case UFFDIO_REGISTER:
1980                 ret = userfaultfd_register(ctx, arg);
1981                 break;
1982         case UFFDIO_UNREGISTER:
1983                 ret = userfaultfd_unregister(ctx, arg);
1984                 break;
1985         case UFFDIO_WAKE:
1986                 ret = userfaultfd_wake(ctx, arg);
1987                 break;
1988         case UFFDIO_COPY:
1989                 ret = userfaultfd_copy(ctx, arg);
1990                 break;
1991         case UFFDIO_ZEROPAGE:
1992                 ret = userfaultfd_zeropage(ctx, arg);
1993                 break;
1994         case UFFDIO_WRITEPROTECT:
1995                 ret = userfaultfd_writeprotect(ctx, arg);
1996                 break;
1997         case UFFDIO_CONTINUE:
1998                 ret = userfaultfd_continue(ctx, arg);
1999                 break;
2000         }
2001         return ret;
2002 }
2003
2004 #ifdef CONFIG_PROC_FS
2005 static void userfaultfd_show_fdinfo(struct seq_file *m, struct file *f)
2006 {
2007         struct userfaultfd_ctx *ctx = f->private_data;
2008         wait_queue_entry_t *wq;
2009         unsigned long pending = 0, total = 0;
2010
2011         spin_lock_irq(&ctx->fault_pending_wqh.lock);
2012         list_for_each_entry(wq, &ctx->fault_pending_wqh.head, entry) {
2013                 pending++;
2014                 total++;
2015         }
2016         list_for_each_entry(wq, &ctx->fault_wqh.head, entry) {
2017                 total++;
2018         }
2019         spin_unlock_irq(&ctx->fault_pending_wqh.lock);
2020
2021         /*
2022          * If more protocols will be added, there will be all shown
2023          * separated by a space. Like this:
2024          *      protocols: aa:... bb:...
2025          */
2026         seq_printf(m, "pending:\t%lu\ntotal:\t%lu\nAPI:\t%Lx:%x:%Lx\n",
2027                    pending, total, UFFD_API, ctx->features,
2028                    UFFD_API_IOCTLS|UFFD_API_RANGE_IOCTLS);
2029 }
2030 #endif
2031
2032 static const struct file_operations userfaultfd_fops = {
2033 #ifdef CONFIG_PROC_FS
2034         .show_fdinfo    = userfaultfd_show_fdinfo,
2035 #endif
2036         .release        = userfaultfd_release,
2037         .poll           = userfaultfd_poll,
2038         .read           = userfaultfd_read,
2039         .unlocked_ioctl = userfaultfd_ioctl,
2040         .compat_ioctl   = compat_ptr_ioctl,
2041         .llseek         = noop_llseek,
2042 };
2043
2044 static void init_once_userfaultfd_ctx(void *mem)
2045 {
2046         struct userfaultfd_ctx *ctx = (struct userfaultfd_ctx *) mem;
2047
2048         init_waitqueue_head(&ctx->fault_pending_wqh);
2049         init_waitqueue_head(&ctx->fault_wqh);
2050         init_waitqueue_head(&ctx->event_wqh);
2051         init_waitqueue_head(&ctx->fd_wqh);
2052         seqcount_spinlock_init(&ctx->refile_seq, &ctx->fault_pending_wqh.lock);
2053 }
2054
2055 SYSCALL_DEFINE1(userfaultfd, int, flags)
2056 {
2057         struct userfaultfd_ctx *ctx;
2058         int fd;
2059
2060         if (!sysctl_unprivileged_userfaultfd &&
2061             (flags & UFFD_USER_MODE_ONLY) == 0 &&
2062             !capable(CAP_SYS_PTRACE)) {
2063                 printk_once(KERN_WARNING "uffd: Set unprivileged_userfaultfd "
2064                         "sysctl knob to 1 if kernel faults must be handled "
2065                         "without obtaining CAP_SYS_PTRACE capability\n");
2066                 return -EPERM;
2067         }
2068
2069         BUG_ON(!current->mm);
2070
2071         /* Check the UFFD_* constants for consistency.  */
2072         BUILD_BUG_ON(UFFD_USER_MODE_ONLY & UFFD_SHARED_FCNTL_FLAGS);
2073         BUILD_BUG_ON(UFFD_CLOEXEC != O_CLOEXEC);
2074         BUILD_BUG_ON(UFFD_NONBLOCK != O_NONBLOCK);
2075
2076         if (flags & ~(UFFD_SHARED_FCNTL_FLAGS | UFFD_USER_MODE_ONLY))
2077                 return -EINVAL;
2078
2079         ctx = kmem_cache_alloc(userfaultfd_ctx_cachep, GFP_KERNEL);
2080         if (!ctx)
2081                 return -ENOMEM;
2082
2083         refcount_set(&ctx->refcount, 1);
2084         ctx->flags = flags;
2085         ctx->features = 0;
2086         ctx->released = false;
2087         atomic_set(&ctx->mmap_changing, 0);
2088         ctx->mm = current->mm;
2089         /* prevent the mm struct to be freed */
2090         mmgrab(ctx->mm);
2091
2092         fd = anon_inode_getfd_secure("[userfaultfd]", &userfaultfd_fops, ctx,
2093                         O_RDWR | (flags & UFFD_SHARED_FCNTL_FLAGS), NULL);
2094         if (fd < 0) {
2095                 mmdrop(ctx->mm);
2096                 kmem_cache_free(userfaultfd_ctx_cachep, ctx);
2097         }
2098         return fd;
2099 }
2100
2101 static int __init userfaultfd_init(void)
2102 {
2103         userfaultfd_ctx_cachep = kmem_cache_create("userfaultfd_ctx_cache",
2104                                                 sizeof(struct userfaultfd_ctx),
2105                                                 0,
2106                                                 SLAB_HWCACHE_ALIGN|SLAB_PANIC,
2107                                                 init_once_userfaultfd_ctx);
2108         return 0;
2109 }
2110 __initcall(userfaultfd_init);