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_RDONLY | (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                 /* Reset ptes for the whole vma range if wr-protected */
1605                 if (userfaultfd_wp(vma))
1606                         uffd_wp_range(mm, vma, start, vma_end - start, false);
1607
1608                 new_flags = vma->vm_flags & ~__VM_UFFD_FLAGS;
1609                 prev = vma_merge(mm, prev, start, vma_end, new_flags,
1610                                  vma->anon_vma, vma->vm_file, vma->vm_pgoff,
1611                                  vma_policy(vma),
1612                                  NULL_VM_UFFD_CTX, anon_vma_name(vma));
1613                 if (prev) {
1614                         vma = prev;
1615                         goto next;
1616                 }
1617                 if (vma->vm_start < start) {
1618                         ret = split_vma(mm, vma, start, 1);
1619                         if (ret)
1620                                 break;
1621                 }
1622                 if (vma->vm_end > end) {
1623                         ret = split_vma(mm, vma, end, 0);
1624                         if (ret)
1625                                 break;
1626                 }
1627         next:
1628                 /*
1629                  * In the vma_merge() successful mprotect-like case 8:
1630                  * the next vma was merged into the current one and
1631                  * the current one has not been updated yet.
1632                  */
1633                 vma->vm_flags = new_flags;
1634                 vma->vm_userfaultfd_ctx = NULL_VM_UFFD_CTX;
1635
1636         skip:
1637                 prev = vma;
1638                 start = vma->vm_end;
1639                 vma = vma->vm_next;
1640         } while (vma && vma->vm_start < end);
1641 out_unlock:
1642         mmap_write_unlock(mm);
1643         mmput(mm);
1644 out:
1645         return ret;
1646 }
1647
1648 /*
1649  * userfaultfd_wake may be used in combination with the
1650  * UFFDIO_*_MODE_DONTWAKE to wakeup userfaults in batches.
1651  */
1652 static int userfaultfd_wake(struct userfaultfd_ctx *ctx,
1653                             unsigned long arg)
1654 {
1655         int ret;
1656         struct uffdio_range uffdio_wake;
1657         struct userfaultfd_wake_range range;
1658         const void __user *buf = (void __user *)arg;
1659
1660         ret = -EFAULT;
1661         if (copy_from_user(&uffdio_wake, buf, sizeof(uffdio_wake)))
1662                 goto out;
1663
1664         ret = validate_range(ctx->mm, uffdio_wake.start, uffdio_wake.len);
1665         if (ret)
1666                 goto out;
1667
1668         range.start = uffdio_wake.start;
1669         range.len = uffdio_wake.len;
1670
1671         /*
1672          * len == 0 means wake all and we don't want to wake all here,
1673          * so check it again to be sure.
1674          */
1675         VM_BUG_ON(!range.len);
1676
1677         wake_userfault(ctx, &range);
1678         ret = 0;
1679
1680 out:
1681         return ret;
1682 }
1683
1684 static int userfaultfd_copy(struct userfaultfd_ctx *ctx,
1685                             unsigned long arg)
1686 {
1687         __s64 ret;
1688         struct uffdio_copy uffdio_copy;
1689         struct uffdio_copy __user *user_uffdio_copy;
1690         struct userfaultfd_wake_range range;
1691
1692         user_uffdio_copy = (struct uffdio_copy __user *) arg;
1693
1694         ret = -EAGAIN;
1695         if (atomic_read(&ctx->mmap_changing))
1696                 goto out;
1697
1698         ret = -EFAULT;
1699         if (copy_from_user(&uffdio_copy, user_uffdio_copy,
1700                            /* don't copy "copy" last field */
1701                            sizeof(uffdio_copy)-sizeof(__s64)))
1702                 goto out;
1703
1704         ret = validate_range(ctx->mm, uffdio_copy.dst, uffdio_copy.len);
1705         if (ret)
1706                 goto out;
1707         /*
1708          * double check for wraparound just in case. copy_from_user()
1709          * will later check uffdio_copy.src + uffdio_copy.len to fit
1710          * in the userland range.
1711          */
1712         ret = -EINVAL;
1713         if (uffdio_copy.src + uffdio_copy.len <= uffdio_copy.src)
1714                 goto out;
1715         if (uffdio_copy.mode & ~(UFFDIO_COPY_MODE_DONTWAKE|UFFDIO_COPY_MODE_WP))
1716                 goto out;
1717         if (mmget_not_zero(ctx->mm)) {
1718                 ret = mcopy_atomic(ctx->mm, uffdio_copy.dst, uffdio_copy.src,
1719                                    uffdio_copy.len, &ctx->mmap_changing,
1720                                    uffdio_copy.mode);
1721                 mmput(ctx->mm);
1722         } else {
1723                 return -ESRCH;
1724         }
1725         if (unlikely(put_user(ret, &user_uffdio_copy->copy)))
1726                 return -EFAULT;
1727         if (ret < 0)
1728                 goto out;
1729         BUG_ON(!ret);
1730         /* len == 0 would wake all */
1731         range.len = ret;
1732         if (!(uffdio_copy.mode & UFFDIO_COPY_MODE_DONTWAKE)) {
1733                 range.start = uffdio_copy.dst;
1734                 wake_userfault(ctx, &range);
1735         }
1736         ret = range.len == uffdio_copy.len ? 0 : -EAGAIN;
1737 out:
1738         return ret;
1739 }
1740
1741 static int userfaultfd_zeropage(struct userfaultfd_ctx *ctx,
1742                                 unsigned long arg)
1743 {
1744         __s64 ret;
1745         struct uffdio_zeropage uffdio_zeropage;
1746         struct uffdio_zeropage __user *user_uffdio_zeropage;
1747         struct userfaultfd_wake_range range;
1748
1749         user_uffdio_zeropage = (struct uffdio_zeropage __user *) arg;
1750
1751         ret = -EAGAIN;
1752         if (atomic_read(&ctx->mmap_changing))
1753                 goto out;
1754
1755         ret = -EFAULT;
1756         if (copy_from_user(&uffdio_zeropage, user_uffdio_zeropage,
1757                            /* don't copy "zeropage" last field */
1758                            sizeof(uffdio_zeropage)-sizeof(__s64)))
1759                 goto out;
1760
1761         ret = validate_range(ctx->mm, uffdio_zeropage.range.start,
1762                              uffdio_zeropage.range.len);
1763         if (ret)
1764                 goto out;
1765         ret = -EINVAL;
1766         if (uffdio_zeropage.mode & ~UFFDIO_ZEROPAGE_MODE_DONTWAKE)
1767                 goto out;
1768
1769         if (mmget_not_zero(ctx->mm)) {
1770                 ret = mfill_zeropage(ctx->mm, uffdio_zeropage.range.start,
1771                                      uffdio_zeropage.range.len,
1772                                      &ctx->mmap_changing);
1773                 mmput(ctx->mm);
1774         } else {
1775                 return -ESRCH;
1776         }
1777         if (unlikely(put_user(ret, &user_uffdio_zeropage->zeropage)))
1778                 return -EFAULT;
1779         if (ret < 0)
1780                 goto out;
1781         /* len == 0 would wake all */
1782         BUG_ON(!ret);
1783         range.len = ret;
1784         if (!(uffdio_zeropage.mode & UFFDIO_ZEROPAGE_MODE_DONTWAKE)) {
1785                 range.start = uffdio_zeropage.range.start;
1786                 wake_userfault(ctx, &range);
1787         }
1788         ret = range.len == uffdio_zeropage.range.len ? 0 : -EAGAIN;
1789 out:
1790         return ret;
1791 }
1792
1793 static int userfaultfd_writeprotect(struct userfaultfd_ctx *ctx,
1794                                     unsigned long arg)
1795 {
1796         int ret;
1797         struct uffdio_writeprotect uffdio_wp;
1798         struct uffdio_writeprotect __user *user_uffdio_wp;
1799         struct userfaultfd_wake_range range;
1800         bool mode_wp, mode_dontwake;
1801
1802         if (atomic_read(&ctx->mmap_changing))
1803                 return -EAGAIN;
1804
1805         user_uffdio_wp = (struct uffdio_writeprotect __user *) arg;
1806
1807         if (copy_from_user(&uffdio_wp, user_uffdio_wp,
1808                            sizeof(struct uffdio_writeprotect)))
1809                 return -EFAULT;
1810
1811         ret = validate_range(ctx->mm, uffdio_wp.range.start,
1812                              uffdio_wp.range.len);
1813         if (ret)
1814                 return ret;
1815
1816         if (uffdio_wp.mode & ~(UFFDIO_WRITEPROTECT_MODE_DONTWAKE |
1817                                UFFDIO_WRITEPROTECT_MODE_WP))
1818                 return -EINVAL;
1819
1820         mode_wp = uffdio_wp.mode & UFFDIO_WRITEPROTECT_MODE_WP;
1821         mode_dontwake = uffdio_wp.mode & UFFDIO_WRITEPROTECT_MODE_DONTWAKE;
1822
1823         if (mode_wp && mode_dontwake)
1824                 return -EINVAL;
1825
1826         if (mmget_not_zero(ctx->mm)) {
1827                 ret = mwriteprotect_range(ctx->mm, uffdio_wp.range.start,
1828                                           uffdio_wp.range.len, mode_wp,
1829                                           &ctx->mmap_changing);
1830                 mmput(ctx->mm);
1831         } else {
1832                 return -ESRCH;
1833         }
1834
1835         if (ret)
1836                 return ret;
1837
1838         if (!mode_wp && !mode_dontwake) {
1839                 range.start = uffdio_wp.range.start;
1840                 range.len = uffdio_wp.range.len;
1841                 wake_userfault(ctx, &range);
1842         }
1843         return ret;
1844 }
1845
1846 static int userfaultfd_continue(struct userfaultfd_ctx *ctx, unsigned long arg)
1847 {
1848         __s64 ret;
1849         struct uffdio_continue uffdio_continue;
1850         struct uffdio_continue __user *user_uffdio_continue;
1851         struct userfaultfd_wake_range range;
1852
1853         user_uffdio_continue = (struct uffdio_continue __user *)arg;
1854
1855         ret = -EAGAIN;
1856         if (atomic_read(&ctx->mmap_changing))
1857                 goto out;
1858
1859         ret = -EFAULT;
1860         if (copy_from_user(&uffdio_continue, user_uffdio_continue,
1861                            /* don't copy the output fields */
1862                            sizeof(uffdio_continue) - (sizeof(__s64))))
1863                 goto out;
1864
1865         ret = validate_range(ctx->mm, uffdio_continue.range.start,
1866                              uffdio_continue.range.len);
1867         if (ret)
1868                 goto out;
1869
1870         ret = -EINVAL;
1871         /* double check for wraparound just in case. */
1872         if (uffdio_continue.range.start + uffdio_continue.range.len <=
1873             uffdio_continue.range.start) {
1874                 goto out;
1875         }
1876         if (uffdio_continue.mode & ~UFFDIO_CONTINUE_MODE_DONTWAKE)
1877                 goto out;
1878
1879         if (mmget_not_zero(ctx->mm)) {
1880                 ret = mcopy_continue(ctx->mm, uffdio_continue.range.start,
1881                                      uffdio_continue.range.len,
1882                                      &ctx->mmap_changing);
1883                 mmput(ctx->mm);
1884         } else {
1885                 return -ESRCH;
1886         }
1887
1888         if (unlikely(put_user(ret, &user_uffdio_continue->mapped)))
1889                 return -EFAULT;
1890         if (ret < 0)
1891                 goto out;
1892
1893         /* len == 0 would wake all */
1894         BUG_ON(!ret);
1895         range.len = ret;
1896         if (!(uffdio_continue.mode & UFFDIO_CONTINUE_MODE_DONTWAKE)) {
1897                 range.start = uffdio_continue.range.start;
1898                 wake_userfault(ctx, &range);
1899         }
1900         ret = range.len == uffdio_continue.range.len ? 0 : -EAGAIN;
1901
1902 out:
1903         return ret;
1904 }
1905
1906 static inline unsigned int uffd_ctx_features(__u64 user_features)
1907 {
1908         /*
1909          * For the current set of features the bits just coincide. Set
1910          * UFFD_FEATURE_INITIALIZED to mark the features as enabled.
1911          */
1912         return (unsigned int)user_features | UFFD_FEATURE_INITIALIZED;
1913 }
1914
1915 /*
1916  * userland asks for a certain API version and we return which bits
1917  * and ioctl commands are implemented in this kernel for such API
1918  * version or -EINVAL if unknown.
1919  */
1920 static int userfaultfd_api(struct userfaultfd_ctx *ctx,
1921                            unsigned long arg)
1922 {
1923         struct uffdio_api uffdio_api;
1924         void __user *buf = (void __user *)arg;
1925         unsigned int ctx_features;
1926         int ret;
1927         __u64 features;
1928
1929         ret = -EFAULT;
1930         if (copy_from_user(&uffdio_api, buf, sizeof(uffdio_api)))
1931                 goto out;
1932         /* Ignore unsupported features (userspace built against newer kernel) */
1933         features = uffdio_api.features & UFFD_API_FEATURES;
1934         ret = -EPERM;
1935         if ((features & UFFD_FEATURE_EVENT_FORK) && !capable(CAP_SYS_PTRACE))
1936                 goto err_out;
1937         /* report all available features and ioctls to userland */
1938         uffdio_api.features = UFFD_API_FEATURES;
1939 #ifndef CONFIG_HAVE_ARCH_USERFAULTFD_MINOR
1940         uffdio_api.features &=
1941                 ~(UFFD_FEATURE_MINOR_HUGETLBFS | UFFD_FEATURE_MINOR_SHMEM);
1942 #endif
1943 #ifndef CONFIG_HAVE_ARCH_USERFAULTFD_WP
1944         uffdio_api.features &= ~UFFD_FEATURE_PAGEFAULT_FLAG_WP;
1945 #endif
1946 #ifndef CONFIG_PTE_MARKER_UFFD_WP
1947         uffdio_api.features &= ~UFFD_FEATURE_WP_HUGETLBFS_SHMEM;
1948 #endif
1949         uffdio_api.ioctls = UFFD_API_IOCTLS;
1950         ret = -EFAULT;
1951         if (copy_to_user(buf, &uffdio_api, sizeof(uffdio_api)))
1952                 goto out;
1953
1954         /* only enable the requested features for this uffd context */
1955         ctx_features = uffd_ctx_features(features);
1956         ret = -EINVAL;
1957         if (cmpxchg(&ctx->features, 0, ctx_features) != 0)
1958                 goto err_out;
1959
1960         ret = 0;
1961 out:
1962         return ret;
1963 err_out:
1964         memset(&uffdio_api, 0, sizeof(uffdio_api));
1965         if (copy_to_user(buf, &uffdio_api, sizeof(uffdio_api)))
1966                 ret = -EFAULT;
1967         goto out;
1968 }
1969
1970 static long userfaultfd_ioctl(struct file *file, unsigned cmd,
1971                               unsigned long arg)
1972 {
1973         int ret = -EINVAL;
1974         struct userfaultfd_ctx *ctx = file->private_data;
1975
1976         if (cmd != UFFDIO_API && !userfaultfd_is_initialized(ctx))
1977                 return -EINVAL;
1978
1979         switch(cmd) {
1980         case UFFDIO_API:
1981                 ret = userfaultfd_api(ctx, arg);
1982                 break;
1983         case UFFDIO_REGISTER:
1984                 ret = userfaultfd_register(ctx, arg);
1985                 break;
1986         case UFFDIO_UNREGISTER:
1987                 ret = userfaultfd_unregister(ctx, arg);
1988                 break;
1989         case UFFDIO_WAKE:
1990                 ret = userfaultfd_wake(ctx, arg);
1991                 break;
1992         case UFFDIO_COPY:
1993                 ret = userfaultfd_copy(ctx, arg);
1994                 break;
1995         case UFFDIO_ZEROPAGE:
1996                 ret = userfaultfd_zeropage(ctx, arg);
1997                 break;
1998         case UFFDIO_WRITEPROTECT:
1999                 ret = userfaultfd_writeprotect(ctx, arg);
2000                 break;
2001         case UFFDIO_CONTINUE:
2002                 ret = userfaultfd_continue(ctx, arg);
2003                 break;
2004         }
2005         return ret;
2006 }
2007
2008 #ifdef CONFIG_PROC_FS
2009 static void userfaultfd_show_fdinfo(struct seq_file *m, struct file *f)
2010 {
2011         struct userfaultfd_ctx *ctx = f->private_data;
2012         wait_queue_entry_t *wq;
2013         unsigned long pending = 0, total = 0;
2014
2015         spin_lock_irq(&ctx->fault_pending_wqh.lock);
2016         list_for_each_entry(wq, &ctx->fault_pending_wqh.head, entry) {
2017                 pending++;
2018                 total++;
2019         }
2020         list_for_each_entry(wq, &ctx->fault_wqh.head, entry) {
2021                 total++;
2022         }
2023         spin_unlock_irq(&ctx->fault_pending_wqh.lock);
2024
2025         /*
2026          * If more protocols will be added, there will be all shown
2027          * separated by a space. Like this:
2028          *      protocols: aa:... bb:...
2029          */
2030         seq_printf(m, "pending:\t%lu\ntotal:\t%lu\nAPI:\t%Lx:%x:%Lx\n",
2031                    pending, total, UFFD_API, ctx->features,
2032                    UFFD_API_IOCTLS|UFFD_API_RANGE_IOCTLS);
2033 }
2034 #endif
2035
2036 static const struct file_operations userfaultfd_fops = {
2037 #ifdef CONFIG_PROC_FS
2038         .show_fdinfo    = userfaultfd_show_fdinfo,
2039 #endif
2040         .release        = userfaultfd_release,
2041         .poll           = userfaultfd_poll,
2042         .read           = userfaultfd_read,
2043         .unlocked_ioctl = userfaultfd_ioctl,
2044         .compat_ioctl   = compat_ptr_ioctl,
2045         .llseek         = noop_llseek,
2046 };
2047
2048 static void init_once_userfaultfd_ctx(void *mem)
2049 {
2050         struct userfaultfd_ctx *ctx = (struct userfaultfd_ctx *) mem;
2051
2052         init_waitqueue_head(&ctx->fault_pending_wqh);
2053         init_waitqueue_head(&ctx->fault_wqh);
2054         init_waitqueue_head(&ctx->event_wqh);
2055         init_waitqueue_head(&ctx->fd_wqh);
2056         seqcount_spinlock_init(&ctx->refile_seq, &ctx->fault_pending_wqh.lock);
2057 }
2058
2059 SYSCALL_DEFINE1(userfaultfd, int, flags)
2060 {
2061         struct userfaultfd_ctx *ctx;
2062         int fd;
2063
2064         if (!sysctl_unprivileged_userfaultfd &&
2065             (flags & UFFD_USER_MODE_ONLY) == 0 &&
2066             !capable(CAP_SYS_PTRACE)) {
2067                 printk_once(KERN_WARNING "uffd: Set unprivileged_userfaultfd "
2068                         "sysctl knob to 1 if kernel faults must be handled "
2069                         "without obtaining CAP_SYS_PTRACE capability\n");
2070                 return -EPERM;
2071         }
2072
2073         BUG_ON(!current->mm);
2074
2075         /* Check the UFFD_* constants for consistency.  */
2076         BUILD_BUG_ON(UFFD_USER_MODE_ONLY & UFFD_SHARED_FCNTL_FLAGS);
2077         BUILD_BUG_ON(UFFD_CLOEXEC != O_CLOEXEC);
2078         BUILD_BUG_ON(UFFD_NONBLOCK != O_NONBLOCK);
2079
2080         if (flags & ~(UFFD_SHARED_FCNTL_FLAGS | UFFD_USER_MODE_ONLY))
2081                 return -EINVAL;
2082
2083         ctx = kmem_cache_alloc(userfaultfd_ctx_cachep, GFP_KERNEL);
2084         if (!ctx)
2085                 return -ENOMEM;
2086
2087         refcount_set(&ctx->refcount, 1);
2088         ctx->flags = flags;
2089         ctx->features = 0;
2090         ctx->released = false;
2091         atomic_set(&ctx->mmap_changing, 0);
2092         ctx->mm = current->mm;
2093         /* prevent the mm struct to be freed */
2094         mmgrab(ctx->mm);
2095
2096         fd = anon_inode_getfd_secure("[userfaultfd]", &userfaultfd_fops, ctx,
2097                         O_RDONLY | (flags & UFFD_SHARED_FCNTL_FLAGS), NULL);
2098         if (fd < 0) {
2099                 mmdrop(ctx->mm);
2100                 kmem_cache_free(userfaultfd_ctx_cachep, ctx);
2101         }
2102         return fd;
2103 }
2104
2105 static int __init userfaultfd_init(void)
2106 {
2107         userfaultfd_ctx_cachep = kmem_cache_create("userfaultfd_ctx_cache",
2108                                                 sizeof(struct userfaultfd_ctx),
2109                                                 0,
2110                                                 SLAB_HWCACHE_ALIGN|SLAB_PANIC,
2111                                                 init_once_userfaultfd_ctx);
2112         return 0;
2113 }
2114 __initcall(userfaultfd_init);