root/fs/userfaultfd.c

DEFINITIONS

1. userfaultfd_wake_function
2. userfaultfd_ctx_get
3. userfaultfd_ctx_put
4. msg_init
5. userfault_msg
6. userfaultfd_huge_must_wait
7. userfaultfd_huge_must_wait
8. userfaultfd_must_wait
9. handle_userfault
10. userfaultfd_event_wait_completion
11. userfaultfd_event_complete
12. dup_userfaultfd
13. dup_fctx
14. dup_userfaultfd_complete
15. mremap_userfaultfd_prep
16. mremap_userfaultfd_complete
17. userfaultfd_remove
18. has_unmap_ctx
19. userfaultfd_unmap_prep
20. userfaultfd_unmap_complete
21. userfaultfd_release
22. find_userfault_in
23. find_userfault
24. find_userfault_evt
25. userfaultfd_poll
26. resolve_userfault_fork
27. userfaultfd_ctx_read
28. userfaultfd_read
29. __wake_userfault
30. wake_userfault
31. validate_range
32. vma_can_userfault
33. userfaultfd_register
34. userfaultfd_unregister
35. userfaultfd_wake
36. userfaultfd_copy
37. userfaultfd_zeropage
38. uffd_ctx_features
39. userfaultfd_api
40. userfaultfd_ioctl
41. userfaultfd_show_fdinfo
42. init_once_userfaultfd_ctx
43. SYSCALL_DEFINE1
44. userfaultfd_init

   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         *start = untagged_addr(*start);
1280 
1281         if (*start & ~PAGE_MASK)
1282                 return -EINVAL;
1283         if (len & ~PAGE_MASK)
1284                 return -EINVAL;
1285         if (!len)
1286                 return -EINVAL;
1287         if (*start < mmap_min_addr)
1288                 return -EINVAL;
1289         if (*start >= task_size)
1290                 return -EINVAL;
1291         if (len > task_size - *start)
1292                 return -EINVAL;
1293         return 0;
1294 }
1295 
1296 static inline bool vma_can_userfault(struct vm_area_struct *vma)
1297 {
1298         return vma_is_anonymous(vma) || is_vm_hugetlb_page(vma) ||
1299                 vma_is_shmem(vma);
1300 }
1301 
1302 static int userfaultfd_register(struct userfaultfd_ctx *ctx,
1303                                 unsigned long arg)
1304 {
1305         struct mm_struct *mm = ctx->mm;
1306         struct vm_area_struct *vma, *prev, *cur;
1307         int ret;
1308         struct uffdio_register uffdio_register;
1309         struct uffdio_register __user *user_uffdio_register;
1310         unsigned long vm_flags, new_flags;
1311         bool found;
1312         bool basic_ioctls;
1313         unsigned long start, end, vma_end;
1314 
1315         user_uffdio_register = (struct uffdio_register __user *) arg;
1316 
1317         ret = -EFAULT;
1318         if (copy_from_user(&uffdio_register, user_uffdio_register,
1319                            sizeof(uffdio_register)-sizeof(__u64)))
1320                 goto out;
1321 
1322         ret = -EINVAL;
1323         if (!uffdio_register.mode)
1324                 goto out;
1325         if (uffdio_register.mode & ~(UFFDIO_REGISTER_MODE_MISSING|
1326                                      UFFDIO_REGISTER_MODE_WP))
1327                 goto out;
1328         vm_flags = 0;
1329         if (uffdio_register.mode & UFFDIO_REGISTER_MODE_MISSING)
1330                 vm_flags |= VM_UFFD_MISSING;
1331         if (uffdio_register.mode & UFFDIO_REGISTER_MODE_WP) {
1332                 vm_flags |= VM_UFFD_WP;
1333                 /*
1334                  * FIXME: remove the below error constraint by
1335                  * implementing the wprotect tracking mode.
1336                  */
1337                 ret = -EINVAL;
1338                 goto out;
1339         }
1340 
1341         ret = validate_range(mm, &uffdio_register.range.start,
1342                              uffdio_register.range.len);
1343         if (ret)
1344                 goto out;
1345 
1346         start = uffdio_register.range.start;
1347         end = start + uffdio_register.range.len;
1348 
1349         ret = -ENOMEM;
1350         if (!mmget_not_zero(mm))
1351                 goto out;
1352 
1353         down_write(&mm->mmap_sem);
1354         if (!mmget_still_valid(mm))
1355                 goto out_unlock;
1356         vma = find_vma_prev(mm, start, &prev);
1357         if (!vma)
1358                 goto out_unlock;
1359 
1360         /* check that there's at least one vma in the range */
1361         ret = -EINVAL;
1362         if (vma->vm_start >= end)
1363                 goto out_unlock;
1364 
1365         /*
1366          * If the first vma contains huge pages, make sure start address
1367          * is aligned to huge page size.
1368          */
1369         if (is_vm_hugetlb_page(vma)) {
1370                 unsigned long vma_hpagesize = vma_kernel_pagesize(vma);
1371 
1372                 if (start & (vma_hpagesize - 1))
1373                         goto out_unlock;
1374         }
1375 
1376         /*
1377          * Search for not compatible vmas.
1378          */
1379         found = false;
1380         basic_ioctls = false;
1381         for (cur = vma; cur && cur->vm_start < end; cur = cur->vm_next) {
1382                 cond_resched();
1383 
1384                 BUG_ON(!!cur->vm_userfaultfd_ctx.ctx ^
1385                        !!(cur->vm_flags & (VM_UFFD_MISSING | VM_UFFD_WP)));
1386 
1387                 /* check not compatible vmas */
1388                 ret = -EINVAL;
1389                 if (!vma_can_userfault(cur))
1390                         goto out_unlock;
1391 
1392                 /*
1393                  * UFFDIO_COPY will fill file holes even without
1394                  * PROT_WRITE. This check enforces that if this is a
1395                  * MAP_SHARED, the process has write permission to the backing
1396                  * file. If VM_MAYWRITE is set it also enforces that on a
1397                  * MAP_SHARED vma: there is no F_WRITE_SEAL and no further
1398                  * F_WRITE_SEAL can be taken until the vma is destroyed.
1399                  */
1400                 ret = -EPERM;
1401                 if (unlikely(!(cur->vm_flags & VM_MAYWRITE)))
1402                         goto out_unlock;
1403 
1404                 /*
1405                  * If this vma contains ending address, and huge pages
1406                  * check alignment.
1407                  */
1408                 if (is_vm_hugetlb_page(cur) && end <= cur->vm_end &&
1409                     end > cur->vm_start) {
1410                         unsigned long vma_hpagesize = vma_kernel_pagesize(cur);
1411 
1412                         ret = -EINVAL;
1413 
1414                         if (end & (vma_hpagesize - 1))
1415                                 goto out_unlock;
1416                 }
1417 
1418                 /*
1419                  * Check that this vma isn't already owned by a
1420                  * different userfaultfd. We can't allow more than one
1421                  * userfaultfd to own a single vma simultaneously or we
1422                  * wouldn't know which one to deliver the userfaults to.
1423                  */
1424                 ret = -EBUSY;
1425                 if (cur->vm_userfaultfd_ctx.ctx &&
1426                     cur->vm_userfaultfd_ctx.ctx != ctx)
1427                         goto out_unlock;
1428 
1429                 /*
1430                  * Note vmas containing huge pages
1431                  */
1432                 if (is_vm_hugetlb_page(cur))
1433                         basic_ioctls = true;
1434 
1435                 found = true;
1436         }
1437         BUG_ON(!found);
1438 
1439         if (vma->vm_start < start)
1440                 prev = vma;
1441 
1442         ret = 0;
1443         do {
1444                 cond_resched();
1445 
1446                 BUG_ON(!vma_can_userfault(vma));
1447                 BUG_ON(vma->vm_userfaultfd_ctx.ctx &&
1448                        vma->vm_userfaultfd_ctx.ctx != ctx);
1449                 WARN_ON(!(vma->vm_flags & VM_MAYWRITE));
1450 
1451                 /*
1452                  * Nothing to do: this vma is already registered into this
1453                  * userfaultfd and with the right tracking mode too.
1454                  */
1455                 if (vma->vm_userfaultfd_ctx.ctx == ctx &&
1456                     (vma->vm_flags & vm_flags) == vm_flags)
1457                         goto skip;
1458 
1459                 if (vma->vm_start > start)
1460                         start = vma->vm_start;
1461                 vma_end = min(end, vma->vm_end);
1462 
1463                 new_flags = (vma->vm_flags & ~vm_flags) | vm_flags;
1464                 prev = vma_merge(mm, prev, start, vma_end, new_flags,
1465                                  vma->anon_vma, vma->vm_file, vma->vm_pgoff,
1466                                  vma_policy(vma),
1467                                  ((struct vm_userfaultfd_ctx){ ctx }));
1468                 if (prev) {
1469                         vma = prev;
1470                         goto next;
1471                 }
1472                 if (vma->vm_start < start) {
1473                         ret = split_vma(mm, vma, start, 1);
1474                         if (ret)
1475                                 break;
1476                 }
1477                 if (vma->vm_end > end) {
1478                         ret = split_vma(mm, vma, end, 0);
1479                         if (ret)
1480                                 break;
1481                 }
1482         next:
1483                 /*
1484                  * In the vma_merge() successful mprotect-like case 8:
1485                  * the next vma was merged into the current one and
1486                  * the current one has not been updated yet.
1487                  */
1488                 vma->vm_flags = new_flags;
1489                 vma->vm_userfaultfd_ctx.ctx = ctx;
1490 
1491         skip:
1492                 prev = vma;
1493                 start = vma->vm_end;
1494                 vma = vma->vm_next;
1495         } while (vma && vma->vm_start < end);
1496 out_unlock:
1497         up_write(&mm->mmap_sem);
1498         mmput(mm);
1499         if (!ret) {
1500                 /*
1501                  * Now that we scanned all vmas we can already tell
1502                  * userland which ioctls methods are guaranteed to
1503                  * succeed on this range.
1504                  */
1505                 if (put_user(basic_ioctls ? UFFD_API_RANGE_IOCTLS_BASIC :
1506                              UFFD_API_RANGE_IOCTLS,
1507                              &user_uffdio_register->ioctls))
1508                         ret = -EFAULT;
1509         }
1510 out:
1511         return ret;
1512 }
1513 
1514 static int userfaultfd_unregister(struct userfaultfd_ctx *ctx,
1515                                   unsigned long arg)
1516 {
1517         struct mm_struct *mm = ctx->mm;
1518         struct vm_area_struct *vma, *prev, *cur;
1519         int ret;
1520         struct uffdio_range uffdio_unregister;
1521         unsigned long new_flags;
1522         bool found;
1523         unsigned long start, end, vma_end;
1524         const void __user *buf = (void __user *)arg;
1525 
1526         ret = -EFAULT;
1527         if (copy_from_user(&uffdio_unregister, buf, sizeof(uffdio_unregister)))
1528                 goto out;
1529 
1530         ret = validate_range(mm, &uffdio_unregister.start,
1531                              uffdio_unregister.len);
1532         if (ret)
1533                 goto out;
1534 
1535         start = uffdio_unregister.start;
1536         end = start + uffdio_unregister.len;
1537 
1538         ret = -ENOMEM;
1539         if (!mmget_not_zero(mm))
1540                 goto out;
1541 
1542         down_write(&mm->mmap_sem);
1543         if (!mmget_still_valid(mm))
1544                 goto out_unlock;
1545         vma = find_vma_prev(mm, start, &prev);
1546         if (!vma)
1547                 goto out_unlock;
1548 
1549         /* check that there's at least one vma in the range */
1550         ret = -EINVAL;
1551         if (vma->vm_start >= end)
1552                 goto out_unlock;
1553 
1554         /*
1555          * If the first vma contains huge pages, make sure start address
1556          * is aligned to huge page size.
1557          */
1558         if (is_vm_hugetlb_page(vma)) {
1559                 unsigned long vma_hpagesize = vma_kernel_pagesize(vma);
1560 
1561                 if (start & (vma_hpagesize - 1))
1562                         goto out_unlock;
1563         }
1564 
1565         /*
1566          * Search for not compatible vmas.
1567          */
1568         found = false;
1569         ret = -EINVAL;
1570         for (cur = vma; cur && cur->vm_start < end; cur = cur->vm_next) {
1571                 cond_resched();
1572 
1573                 BUG_ON(!!cur->vm_userfaultfd_ctx.ctx ^
1574                        !!(cur->vm_flags & (VM_UFFD_MISSING | VM_UFFD_WP)));
1575 
1576                 /*
1577                  * Check not compatible vmas, not strictly required
1578                  * here as not compatible vmas cannot have an
1579                  * userfaultfd_ctx registered on them, but this
1580                  * provides for more strict behavior to notice
1581                  * unregistration errors.
1582                  */
1583                 if (!vma_can_userfault(cur))
1584                         goto out_unlock;
1585 
1586                 found = true;
1587         }
1588         BUG_ON(!found);
1589 
1590         if (vma->vm_start < start)
1591                 prev = vma;
1592 
1593         ret = 0;
1594         do {
1595                 cond_resched();
1596 
1597                 BUG_ON(!vma_can_userfault(vma));
1598 
1599                 /*
1600                  * Nothing to do: this vma is already registered into this
1601                  * userfaultfd and with the right tracking mode too.
1602                  */
1603                 if (!vma->vm_userfaultfd_ctx.ctx)
1604                         goto skip;
1605 
1606                 WARN_ON(!(vma->vm_flags & VM_MAYWRITE));
1607 
1608                 if (vma->vm_start > start)
1609                         start = vma->vm_start;
1610                 vma_end = min(end, vma->vm_end);
1611 
1612                 if (userfaultfd_missing(vma)) {
1613                         /*
1614                          * Wake any concurrent pending userfault while
1615                          * we unregister, so they will not hang
1616                          * permanently and it avoids userland to call
1617                          * UFFDIO_WAKE explicitly.
1618                          */
1619                         struct userfaultfd_wake_range range;
1620                         range.start = start;
1621                         range.len = vma_end - start;
1622                         wake_userfault(vma->vm_userfaultfd_ctx.ctx, &range);
1623                 }
1624 
1625                 new_flags = vma->vm_flags & ~(VM_UFFD_MISSING | VM_UFFD_WP);
1626                 prev = vma_merge(mm, prev, start, vma_end, new_flags,
1627                                  vma->anon_vma, vma->vm_file, vma->vm_pgoff,
1628                                  vma_policy(vma),
1629                                  NULL_VM_UFFD_CTX);
1630                 if (prev) {
1631                         vma = prev;
1632                         goto next;
1633                 }
1634                 if (vma->vm_start < start) {
1635                         ret = split_vma(mm, vma, start, 1);
1636                         if (ret)
1637                                 break;
1638                 }
1639                 if (vma->vm_end > end) {
1640                         ret = split_vma(mm, vma, end, 0);
1641                         if (ret)
1642                                 break;
1643                 }
1644         next:
1645                 /*
1646                  * In the vma_merge() successful mprotect-like case 8:
1647                  * the next vma was merged into the current one and
1648                  * the current one has not been updated yet.
1649                  */
1650                 vma->vm_flags = new_flags;
1651                 vma->vm_userfaultfd_ctx = NULL_VM_UFFD_CTX;
1652 
1653         skip:
1654                 prev = vma;
1655                 start = vma->vm_end;
1656                 vma = vma->vm_next;
1657         } while (vma && vma->vm_start < end);
1658 out_unlock:
1659         up_write(&mm->mmap_sem);
1660         mmput(mm);
1661 out:
1662         return ret;
1663 }
1664 
1665 /*
1666  * userfaultfd_wake may be used in combination with the
1667  * UFFDIO_*_MODE_DONTWAKE to wakeup userfaults in batches.
1668  */
1669 static int userfaultfd_wake(struct userfaultfd_ctx *ctx,
1670                             unsigned long arg)
1671 {
1672         int ret;
1673         struct uffdio_range uffdio_wake;
1674         struct userfaultfd_wake_range range;
1675         const void __user *buf = (void __user *)arg;
1676 
1677         ret = -EFAULT;
1678         if (copy_from_user(&uffdio_wake, buf, sizeof(uffdio_wake)))
1679                 goto out;
1680 
1681         ret = validate_range(ctx->mm, &uffdio_wake.start, uffdio_wake.len);
1682         if (ret)
1683                 goto out;
1684 
1685         range.start = uffdio_wake.start;
1686         range.len = uffdio_wake.len;
1687 
1688         /*
1689          * len == 0 means wake all and we don't want to wake all here,
1690          * so check it again to be sure.
1691          */
1692         VM_BUG_ON(!range.len);
1693 
1694         wake_userfault(ctx, &range);
1695         ret = 0;
1696 
1697 out:
1698         return ret;
1699 }
1700 
1701 static int userfaultfd_copy(struct userfaultfd_ctx *ctx,
1702                             unsigned long arg)
1703 {
1704         __s64 ret;
1705         struct uffdio_copy uffdio_copy;
1706         struct uffdio_copy __user *user_uffdio_copy;
1707         struct userfaultfd_wake_range range;
1708 
1709         user_uffdio_copy = (struct uffdio_copy __user *) arg;
1710 
1711         ret = -EAGAIN;
1712         if (READ_ONCE(ctx->mmap_changing))
1713                 goto out;
1714 
1715         ret = -EFAULT;
1716         if (copy_from_user(&uffdio_copy, user_uffdio_copy,
1717                            /* don't copy "copy" last field */
1718                            sizeof(uffdio_copy)-sizeof(__s64)))
1719                 goto out;
1720 
1721         ret = validate_range(ctx->mm, &uffdio_copy.dst, uffdio_copy.len);
1722         if (ret)
1723                 goto out;
1724         /*
1725          * double check for wraparound just in case. copy_from_user()
1726          * will later check uffdio_copy.src + uffdio_copy.len to fit
1727          * in the userland range.
1728          */
1729         ret = -EINVAL;
1730         if (uffdio_copy.src + uffdio_copy.len <= uffdio_copy.src)
1731                 goto out;
1732         if (uffdio_copy.mode & ~UFFDIO_COPY_MODE_DONTWAKE)
1733                 goto out;
1734         if (mmget_not_zero(ctx->mm)) {
1735                 ret = mcopy_atomic(ctx->mm, uffdio_copy.dst, uffdio_copy.src,
1736                                    uffdio_copy.len, &ctx->mmap_changing);
1737                 mmput(ctx->mm);
1738         } else {
1739                 return -ESRCH;
1740         }
1741         if (unlikely(put_user(ret, &user_uffdio_copy->copy)))
1742                 return -EFAULT;
1743         if (ret < 0)
1744                 goto out;
1745         BUG_ON(!ret);
1746         /* len == 0 would wake all */
1747         range.len = ret;
1748         if (!(uffdio_copy.mode & UFFDIO_COPY_MODE_DONTWAKE)) {
1749                 range.start = uffdio_copy.dst;
1750                 wake_userfault(ctx, &range);
1751         }
1752         ret = range.len == uffdio_copy.len ? 0 : -EAGAIN;
1753 out:
1754         return ret;
1755 }
1756 
1757 static int userfaultfd_zeropage(struct userfaultfd_ctx *ctx,
1758                                 unsigned long arg)
1759 {
1760         __s64 ret;
1761         struct uffdio_zeropage uffdio_zeropage;
1762         struct uffdio_zeropage __user *user_uffdio_zeropage;
1763         struct userfaultfd_wake_range range;
1764 
1765         user_uffdio_zeropage = (struct uffdio_zeropage __user *) arg;
1766 
1767         ret = -EAGAIN;
1768         if (READ_ONCE(ctx->mmap_changing))
1769                 goto out;
1770 
1771         ret = -EFAULT;
1772         if (copy_from_user(&uffdio_zeropage, user_uffdio_zeropage,
1773                            /* don't copy "zeropage" last field */
1774                            sizeof(uffdio_zeropage)-sizeof(__s64)))
1775                 goto out;
1776 
1777         ret = validate_range(ctx->mm, &uffdio_zeropage.range.start,
1778                              uffdio_zeropage.range.len);
1779         if (ret)
1780                 goto out;
1781         ret = -EINVAL;
1782         if (uffdio_zeropage.mode & ~UFFDIO_ZEROPAGE_MODE_DONTWAKE)
1783                 goto out;
1784 
1785         if (mmget_not_zero(ctx->mm)) {
1786                 ret = mfill_zeropage(ctx->mm, uffdio_zeropage.range.start,
1787                                      uffdio_zeropage.range.len,
1788                                      &ctx->mmap_changing);
1789                 mmput(ctx->mm);
1790         } else {
1791                 return -ESRCH;
1792         }
1793         if (unlikely(put_user(ret, &user_uffdio_zeropage->zeropage)))
1794                 return -EFAULT;
1795         if (ret < 0)
1796                 goto out;
1797         /* len == 0 would wake all */
1798         BUG_ON(!ret);
1799         range.len = ret;
1800         if (!(uffdio_zeropage.mode & UFFDIO_ZEROPAGE_MODE_DONTWAKE)) {
1801                 range.start = uffdio_zeropage.range.start;
1802                 wake_userfault(ctx, &range);
1803         }
1804         ret = range.len == uffdio_zeropage.range.len ? 0 : -EAGAIN;
1805 out:
1806         return ret;
1807 }
1808 
1809 static inline unsigned int uffd_ctx_features(__u64 user_features)
1810 {
1811         /*
1812          * For the current set of features the bits just coincide
1813          */
1814         return (unsigned int)user_features;
1815 }
1816 
1817 /*
1818  * userland asks for a certain API version and we return which bits
1819  * and ioctl commands are implemented in this kernel for such API
1820  * version or -EINVAL if unknown.
1821  */
1822 static int userfaultfd_api(struct userfaultfd_ctx *ctx,
1823                            unsigned long arg)
1824 {
1825         struct uffdio_api uffdio_api;
1826         void __user *buf = (void __user *)arg;
1827         int ret;
1828         __u64 features;
1829 
1830         ret = -EINVAL;
1831         if (ctx->state != UFFD_STATE_WAIT_API)
1832                 goto out;
1833         ret = -EFAULT;
1834         if (copy_from_user(&uffdio_api, buf, sizeof(uffdio_api)))
1835                 goto out;
1836         features = uffdio_api.features;
1837         ret = -EINVAL;
1838         if (uffdio_api.api != UFFD_API || (features & ~UFFD_API_FEATURES))
1839                 goto err_out;
1840         ret = -EPERM;
1841         if ((features & UFFD_FEATURE_EVENT_FORK) && !capable(CAP_SYS_PTRACE))
1842                 goto err_out;
1843         /* report all available features and ioctls to userland */
1844         uffdio_api.features = UFFD_API_FEATURES;
1845         uffdio_api.ioctls = UFFD_API_IOCTLS;
1846         ret = -EFAULT;
1847         if (copy_to_user(buf, &uffdio_api, sizeof(uffdio_api)))
1848                 goto out;
1849         ctx->state = UFFD_STATE_RUNNING;
1850         /* only enable the requested features for this uffd context */
1851         ctx->features = uffd_ctx_features(features);
1852         ret = 0;
1853 out:
1854         return ret;
1855 err_out:
1856         memset(&uffdio_api, 0, sizeof(uffdio_api));
1857         if (copy_to_user(buf, &uffdio_api, sizeof(uffdio_api)))
1858                 ret = -EFAULT;
1859         goto out;
1860 }
1861 
1862 static long userfaultfd_ioctl(struct file *file, unsigned cmd,
1863                               unsigned long arg)
1864 {
1865         int ret = -EINVAL;
1866         struct userfaultfd_ctx *ctx = file->private_data;
1867 
1868         if (cmd != UFFDIO_API && ctx->state == UFFD_STATE_WAIT_API)
1869                 return -EINVAL;
1870 
1871         switch(cmd) {
1872         case UFFDIO_API:
1873                 ret = userfaultfd_api(ctx, arg);
1874                 break;
1875         case UFFDIO_REGISTER:
1876                 ret = userfaultfd_register(ctx, arg);
1877                 break;
1878         case UFFDIO_UNREGISTER:
1879                 ret = userfaultfd_unregister(ctx, arg);
1880                 break;
1881         case UFFDIO_WAKE:
1882                 ret = userfaultfd_wake(ctx, arg);
1883                 break;
1884         case UFFDIO_COPY:
1885                 ret = userfaultfd_copy(ctx, arg);
1886                 break;
1887         case UFFDIO_ZEROPAGE:
1888                 ret = userfaultfd_zeropage(ctx, arg);
1889                 break;
1890         }
1891         return ret;
1892 }
1893 
1894 #ifdef CONFIG_PROC_FS
1895 static void userfaultfd_show_fdinfo(struct seq_file *m, struct file *f)
1896 {
1897         struct userfaultfd_ctx *ctx = f->private_data;
1898         wait_queue_entry_t *wq;
1899         unsigned long pending = 0, total = 0;
1900 
1901         spin_lock_irq(&ctx->fault_pending_wqh.lock);
1902         list_for_each_entry(wq, &ctx->fault_pending_wqh.head, entry) {
1903                 pending++;
1904                 total++;
1905         }
1906         list_for_each_entry(wq, &ctx->fault_wqh.head, entry) {
1907                 total++;
1908         }
1909         spin_unlock_irq(&ctx->fault_pending_wqh.lock);
1910 
1911         /*
1912          * If more protocols will be added, there will be all shown
1913          * separated by a space. Like this:
1914          *      protocols: aa:... bb:...
1915          */
1916         seq_printf(m, "pending:\t%lu\ntotal:\t%lu\nAPI:\t%Lx:%x:%Lx\n",
1917                    pending, total, UFFD_API, ctx->features,
1918                    UFFD_API_IOCTLS|UFFD_API_RANGE_IOCTLS);
1919 }
1920 #endif
1921 
1922 static const struct file_operations userfaultfd_fops = {
1923 #ifdef CONFIG_PROC_FS
1924         .show_fdinfo    = userfaultfd_show_fdinfo,
1925 #endif
1926         .release        = userfaultfd_release,
1927         .poll           = userfaultfd_poll,
1928         .read           = userfaultfd_read,
1929         .unlocked_ioctl = userfaultfd_ioctl,
1930         .compat_ioctl   = userfaultfd_ioctl,
1931         .llseek         = noop_llseek,
1932 };
1933 
1934 static void init_once_userfaultfd_ctx(void *mem)
1935 {
1936         struct userfaultfd_ctx *ctx = (struct userfaultfd_ctx *) mem;
1937 
1938         init_waitqueue_head(&ctx->fault_pending_wqh);
1939         init_waitqueue_head(&ctx->fault_wqh);
1940         init_waitqueue_head(&ctx->event_wqh);
1941         init_waitqueue_head(&ctx->fd_wqh);
1942         seqcount_init(&ctx->refile_seq);
1943 }
1944 
1945 SYSCALL_DEFINE1(userfaultfd, int, flags)
1946 {
1947         struct userfaultfd_ctx *ctx;
1948         int fd;
1949 
1950         if (!sysctl_unprivileged_userfaultfd && !capable(CAP_SYS_PTRACE))
1951                 return -EPERM;
1952 
1953         BUG_ON(!current->mm);
1954 
1955         /* Check the UFFD_* constants for consistency.  */
1956         BUILD_BUG_ON(UFFD_CLOEXEC != O_CLOEXEC);
1957         BUILD_BUG_ON(UFFD_NONBLOCK != O_NONBLOCK);
1958 
1959         if (flags & ~UFFD_SHARED_FCNTL_FLAGS)
1960                 return -EINVAL;
1961 
1962         ctx = kmem_cache_alloc(userfaultfd_ctx_cachep, GFP_KERNEL);
1963         if (!ctx)
1964                 return -ENOMEM;
1965 
1966         refcount_set(&ctx->refcount, 1);
1967         ctx->flags = flags;
1968         ctx->features = 0;
1969         ctx->state = UFFD_STATE_WAIT_API;
1970         ctx->released = false;
1971         ctx->mmap_changing = false;
1972         ctx->mm = current->mm;
1973         /* prevent the mm struct to be freed */
1974         mmgrab(ctx->mm);
1975 
1976         fd = anon_inode_getfd("[userfaultfd]", &userfaultfd_fops, ctx,
1977                               O_RDWR | (flags & UFFD_SHARED_FCNTL_FLAGS));
1978         if (fd < 0) {
1979                 mmdrop(ctx->mm);
1980                 kmem_cache_free(userfaultfd_ctx_cachep, ctx);
1981         }
1982         return fd;
1983 }
1984 
1985 static int __init userfaultfd_init(void)
1986 {
1987         userfaultfd_ctx_cachep = kmem_cache_create("userfaultfd_ctx_cache",
1988                                                 sizeof(struct userfaultfd_ctx),
1989                                                 0,
1990                                                 SLAB_HWCACHE_ALIGN|SLAB_PANIC,
1991                                                 init_once_userfaultfd_ctx);
1992         return 0;
1993 }
1994 __initcall(userfaultfd_init);