1 /* 2 * fs/userfaultfd.c 3 * 4 * Copyright (C) 2007 Davide Libenzi <davidel@xmailserver.org> 5 * Copyright (C) 2008-2009 Red Hat, Inc. 6 * Copyright (C) 2015 Red Hat, Inc. 7 * 8 * This work is licensed under the terms of the GNU GPL, version 2. See 9 * the COPYING file in the top-level directory. 10 * 11 * Some part derived from fs/eventfd.c (anon inode setup) and 12 * mm/ksm.c (mm hashing). 13 */ 14 15 #include <linux/list.h> 16 #include <linux/hashtable.h> 17 #include <linux/sched/signal.h> 18 #include <linux/sched/mm.h> 19 #include <linux/mm.h> 20 #include <linux/poll.h> 21 #include <linux/slab.h> 22 #include <linux/seq_file.h> 23 #include <linux/file.h> 24 #include <linux/bug.h> 25 #include <linux/anon_inodes.h> 26 #include <linux/syscalls.h> 27 #include <linux/userfaultfd_k.h> 28 #include <linux/mempolicy.h> 29 #include <linux/ioctl.h> 30 #include <linux/security.h> 31 #include <linux/hugetlb.h> 32 33 static struct kmem_cache *userfaultfd_ctx_cachep __read_mostly; 34 35 enum userfaultfd_state { 36 UFFD_STATE_WAIT_API, 37 UFFD_STATE_RUNNING, 38 }; 39 40 /* 41 * Start with fault_pending_wqh and fault_wqh so they're more likely 42 * to be in the same cacheline. 43 */ 44 struct userfaultfd_ctx { 45 /* waitqueue head for the pending (i.e. not read) userfaults */ 46 wait_queue_head_t fault_pending_wqh; 47 /* waitqueue head for the userfaults */ 48 wait_queue_head_t fault_wqh; 49 /* waitqueue head for the pseudo fd to wakeup poll/read */ 50 wait_queue_head_t fd_wqh; 51 /* waitqueue head for events */ 52 wait_queue_head_t event_wqh; 53 /* a refile sequence protected by fault_pending_wqh lock */ 54 struct seqcount refile_seq; 55 /* pseudo fd refcounting */ 56 atomic_t refcount; 57 /* userfaultfd syscall flags */ 58 unsigned int flags; 59 /* features requested from the userspace */ 60 unsigned int features; 61 /* state machine */ 62 enum userfaultfd_state state; 63 /* released */ 64 bool released; 65 /* mm with one ore more vmas attached to this userfaultfd_ctx */ 66 struct mm_struct *mm; 67 }; 68 69 struct userfaultfd_fork_ctx { 70 struct userfaultfd_ctx *orig; 71 struct userfaultfd_ctx *new; 72 struct list_head list; 73 }; 74 75 struct userfaultfd_unmap_ctx { 76 struct userfaultfd_ctx *ctx; 77 unsigned long start; 78 unsigned long end; 79 struct list_head list; 80 }; 81 82 struct userfaultfd_wait_queue { 83 struct uffd_msg msg; 84 wait_queue_t wq; 85 struct userfaultfd_ctx *ctx; 86 bool waken; 87 }; 88 89 struct userfaultfd_wake_range { 90 unsigned long start; 91 unsigned long len; 92 }; 93 94 static int userfaultfd_wake_function(wait_queue_t *wq, unsigned mode, 95 int wake_flags, void *key) 96 { 97 struct userfaultfd_wake_range *range = key; 98 int ret; 99 struct userfaultfd_wait_queue *uwq; 100 unsigned long start, len; 101 102 uwq = container_of(wq, struct userfaultfd_wait_queue, wq); 103 ret = 0; 104 /* len == 0 means wake all */ 105 start = range->start; 106 len = range->len; 107 if (len && (start > uwq->msg.arg.pagefault.address || 108 start + len <= uwq->msg.arg.pagefault.address)) 109 goto out; 110 WRITE_ONCE(uwq->waken, true); 111 /* 112 * The implicit smp_mb__before_spinlock in try_to_wake_up() 113 * renders uwq->waken visible to other CPUs before the task is 114 * waken. 115 */ 116 ret = wake_up_state(wq->private, mode); 117 if (ret) 118 /* 119 * Wake only once, autoremove behavior. 120 * 121 * After the effect of list_del_init is visible to the 122 * other CPUs, the waitqueue may disappear from under 123 * us, see the !list_empty_careful() in 124 * handle_userfault(). try_to_wake_up() has an 125 * implicit smp_mb__before_spinlock, and the 126 * wq->private is read before calling the extern 127 * function "wake_up_state" (which in turns calls 128 * try_to_wake_up). While the spin_lock;spin_unlock; 129 * wouldn't be enough, the smp_mb__before_spinlock is 130 * enough to avoid an explicit smp_mb() here. 131 */ 132 list_del_init(&wq->task_list); 133 out: 134 return ret; 135 } 136 137 /** 138 * userfaultfd_ctx_get - Acquires a reference to the internal userfaultfd 139 * context. 140 * @ctx: [in] Pointer to the userfaultfd context. 141 */ 142 static void userfaultfd_ctx_get(struct userfaultfd_ctx *ctx) 143 { 144 if (!atomic_inc_not_zero(&ctx->refcount)) 145 BUG(); 146 } 147 148 /** 149 * userfaultfd_ctx_put - Releases a reference to the internal userfaultfd 150 * context. 151 * @ctx: [in] Pointer to userfaultfd context. 152 * 153 * The userfaultfd context reference must have been previously acquired either 154 * with userfaultfd_ctx_get() or userfaultfd_ctx_fdget(). 155 */ 156 static void userfaultfd_ctx_put(struct userfaultfd_ctx *ctx) 157 { 158 if (atomic_dec_and_test(&ctx->refcount)) { 159 VM_BUG_ON(spin_is_locked(&ctx->fault_pending_wqh.lock)); 160 VM_BUG_ON(waitqueue_active(&ctx->fault_pending_wqh)); 161 VM_BUG_ON(spin_is_locked(&ctx->fault_wqh.lock)); 162 VM_BUG_ON(waitqueue_active(&ctx->fault_wqh)); 163 VM_BUG_ON(spin_is_locked(&ctx->event_wqh.lock)); 164 VM_BUG_ON(waitqueue_active(&ctx->event_wqh)); 165 VM_BUG_ON(spin_is_locked(&ctx->fd_wqh.lock)); 166 VM_BUG_ON(waitqueue_active(&ctx->fd_wqh)); 167 mmdrop(ctx->mm); 168 kmem_cache_free(userfaultfd_ctx_cachep, ctx); 169 } 170 } 171 172 static inline void msg_init(struct uffd_msg *msg) 173 { 174 BUILD_BUG_ON(sizeof(struct uffd_msg) != 32); 175 /* 176 * Must use memset to zero out the paddings or kernel data is 177 * leaked to userland. 178 */ 179 memset(msg, 0, sizeof(struct uffd_msg)); 180 } 181 182 static inline struct uffd_msg userfault_msg(unsigned long address, 183 unsigned int flags, 184 unsigned long reason) 185 { 186 struct uffd_msg msg; 187 msg_init(&msg); 188 msg.event = UFFD_EVENT_PAGEFAULT; 189 msg.arg.pagefault.address = address; 190 if (flags & FAULT_FLAG_WRITE) 191 /* 192 * If UFFD_FEATURE_PAGEFAULT_FLAG_WP was set in the 193 * uffdio_api.features and UFFD_PAGEFAULT_FLAG_WRITE 194 * was not set in a UFFD_EVENT_PAGEFAULT, it means it 195 * was a read fault, otherwise if set it means it's 196 * a write fault. 197 */ 198 msg.arg.pagefault.flags |= UFFD_PAGEFAULT_FLAG_WRITE; 199 if (reason & VM_UFFD_WP) 200 /* 201 * If UFFD_FEATURE_PAGEFAULT_FLAG_WP was set in the 202 * uffdio_api.features and UFFD_PAGEFAULT_FLAG_WP was 203 * not set in a UFFD_EVENT_PAGEFAULT, it means it was 204 * a missing fault, otherwise if set it means it's a 205 * write protect fault. 206 */ 207 msg.arg.pagefault.flags |= UFFD_PAGEFAULT_FLAG_WP; 208 return msg; 209 } 210 211 #ifdef CONFIG_HUGETLB_PAGE 212 /* 213 * Same functionality as userfaultfd_must_wait below with modifications for 214 * hugepmd ranges. 215 */ 216 static inline bool userfaultfd_huge_must_wait(struct userfaultfd_ctx *ctx, 217 unsigned long address, 218 unsigned long flags, 219 unsigned long reason) 220 { 221 struct mm_struct *mm = ctx->mm; 222 pte_t *pte; 223 bool ret = true; 224 225 VM_BUG_ON(!rwsem_is_locked(&mm->mmap_sem)); 226 227 pte = huge_pte_offset(mm, address); 228 if (!pte) 229 goto out; 230 231 ret = false; 232 233 /* 234 * Lockless access: we're in a wait_event so it's ok if it 235 * changes under us. 236 */ 237 if (huge_pte_none(*pte)) 238 ret = true; 239 if (!huge_pte_write(*pte) && (reason & VM_UFFD_WP)) 240 ret = true; 241 out: 242 return ret; 243 } 244 #else 245 static inline bool userfaultfd_huge_must_wait(struct userfaultfd_ctx *ctx, 246 unsigned long address, 247 unsigned long flags, 248 unsigned long reason) 249 { 250 return false; /* should never get here */ 251 } 252 #endif /* CONFIG_HUGETLB_PAGE */ 253 254 /* 255 * Verify the pagetables are still not ok after having reigstered into 256 * the fault_pending_wqh to avoid userland having to UFFDIO_WAKE any 257 * userfault that has already been resolved, if userfaultfd_read and 258 * UFFDIO_COPY|ZEROPAGE are being run simultaneously on two different 259 * threads. 260 */ 261 static inline bool userfaultfd_must_wait(struct userfaultfd_ctx *ctx, 262 unsigned long address, 263 unsigned long flags, 264 unsigned long reason) 265 { 266 struct mm_struct *mm = ctx->mm; 267 pgd_t *pgd; 268 p4d_t *p4d; 269 pud_t *pud; 270 pmd_t *pmd, _pmd; 271 pte_t *pte; 272 bool ret = true; 273 274 VM_BUG_ON(!rwsem_is_locked(&mm->mmap_sem)); 275 276 pgd = pgd_offset(mm, address); 277 if (!pgd_present(*pgd)) 278 goto out; 279 p4d = p4d_offset(pgd, address); 280 if (!p4d_present(*p4d)) 281 goto out; 282 pud = pud_offset(p4d, address); 283 if (!pud_present(*pud)) 284 goto out; 285 pmd = pmd_offset(pud, address); 286 /* 287 * READ_ONCE must function as a barrier with narrower scope 288 * and it must be equivalent to: 289 * _pmd = *pmd; barrier(); 290 * 291 * This is to deal with the instability (as in 292 * pmd_trans_unstable) of the pmd. 293 */ 294 _pmd = READ_ONCE(*pmd); 295 if (!pmd_present(_pmd)) 296 goto out; 297 298 ret = false; 299 if (pmd_trans_huge(_pmd)) 300 goto out; 301 302 /* 303 * the pmd is stable (as in !pmd_trans_unstable) so we can re-read it 304 * and use the standard pte_offset_map() instead of parsing _pmd. 305 */ 306 pte = pte_offset_map(pmd, address); 307 /* 308 * Lockless access: we're in a wait_event so it's ok if it 309 * changes under us. 310 */ 311 if (pte_none(*pte)) 312 ret = true; 313 pte_unmap(pte); 314 315 out: 316 return ret; 317 } 318 319 /* 320 * The locking rules involved in returning VM_FAULT_RETRY depending on 321 * FAULT_FLAG_ALLOW_RETRY, FAULT_FLAG_RETRY_NOWAIT and 322 * FAULT_FLAG_KILLABLE are not straightforward. The "Caution" 323 * recommendation in __lock_page_or_retry is not an understatement. 324 * 325 * If FAULT_FLAG_ALLOW_RETRY is set, the mmap_sem must be released 326 * before returning VM_FAULT_RETRY only if FAULT_FLAG_RETRY_NOWAIT is 327 * not set. 328 * 329 * If FAULT_FLAG_ALLOW_RETRY is set but FAULT_FLAG_KILLABLE is not 330 * set, VM_FAULT_RETRY can still be returned if and only if there are 331 * fatal_signal_pending()s, and the mmap_sem must be released before 332 * returning it. 333 */ 334 int handle_userfault(struct vm_fault *vmf, unsigned long reason) 335 { 336 struct mm_struct *mm = vmf->vma->vm_mm; 337 struct userfaultfd_ctx *ctx; 338 struct userfaultfd_wait_queue uwq; 339 int ret; 340 bool must_wait, return_to_userland; 341 long blocking_state; 342 343 BUG_ON(!rwsem_is_locked(&mm->mmap_sem)); 344 345 ret = VM_FAULT_SIGBUS; 346 ctx = vmf->vma->vm_userfaultfd_ctx.ctx; 347 if (!ctx) 348 goto out; 349 350 BUG_ON(ctx->mm != mm); 351 352 VM_BUG_ON(reason & ~(VM_UFFD_MISSING|VM_UFFD_WP)); 353 VM_BUG_ON(!(reason & VM_UFFD_MISSING) ^ !!(reason & VM_UFFD_WP)); 354 355 /* 356 * If it's already released don't get it. This avoids to loop 357 * in __get_user_pages if userfaultfd_release waits on the 358 * caller of handle_userfault to release the mmap_sem. 359 */ 360 if (unlikely(ACCESS_ONCE(ctx->released))) 361 goto out; 362 363 /* 364 * We don't do userfault handling for the final child pid update. 365 */ 366 if (current->flags & PF_EXITING) 367 goto out; 368 369 /* 370 * Check that we can return VM_FAULT_RETRY. 371 * 372 * NOTE: it should become possible to return VM_FAULT_RETRY 373 * even if FAULT_FLAG_TRIED is set without leading to gup() 374 * -EBUSY failures, if the userfaultfd is to be extended for 375 * VM_UFFD_WP tracking and we intend to arm the userfault 376 * without first stopping userland access to the memory. For 377 * VM_UFFD_MISSING userfaults this is enough for now. 378 */ 379 if (unlikely(!(vmf->flags & FAULT_FLAG_ALLOW_RETRY))) { 380 /* 381 * Validate the invariant that nowait must allow retry 382 * to be sure not to return SIGBUS erroneously on 383 * nowait invocations. 384 */ 385 BUG_ON(vmf->flags & FAULT_FLAG_RETRY_NOWAIT); 386 #ifdef CONFIG_DEBUG_VM 387 if (printk_ratelimit()) { 388 printk(KERN_WARNING 389 "FAULT_FLAG_ALLOW_RETRY missing %x\n", 390 vmf->flags); 391 dump_stack(); 392 } 393 #endif 394 goto out; 395 } 396 397 /* 398 * Handle nowait, not much to do other than tell it to retry 399 * and wait. 400 */ 401 ret = VM_FAULT_RETRY; 402 if (vmf->flags & FAULT_FLAG_RETRY_NOWAIT) 403 goto out; 404 405 /* take the reference before dropping the mmap_sem */ 406 userfaultfd_ctx_get(ctx); 407 408 init_waitqueue_func_entry(&uwq.wq, userfaultfd_wake_function); 409 uwq.wq.private = current; 410 uwq.msg = userfault_msg(vmf->address, vmf->flags, reason); 411 uwq.ctx = ctx; 412 uwq.waken = false; 413 414 return_to_userland = 415 (vmf->flags & (FAULT_FLAG_USER|FAULT_FLAG_KILLABLE)) == 416 (FAULT_FLAG_USER|FAULT_FLAG_KILLABLE); 417 blocking_state = return_to_userland ? TASK_INTERRUPTIBLE : 418 TASK_KILLABLE; 419 420 spin_lock(&ctx->fault_pending_wqh.lock); 421 /* 422 * After the __add_wait_queue the uwq is visible to userland 423 * through poll/read(). 424 */ 425 __add_wait_queue(&ctx->fault_pending_wqh, &uwq.wq); 426 /* 427 * The smp_mb() after __set_current_state prevents the reads 428 * following the spin_unlock to happen before the list_add in 429 * __add_wait_queue. 430 */ 431 set_current_state(blocking_state); 432 spin_unlock(&ctx->fault_pending_wqh.lock); 433 434 if (!is_vm_hugetlb_page(vmf->vma)) 435 must_wait = userfaultfd_must_wait(ctx, vmf->address, vmf->flags, 436 reason); 437 else 438 must_wait = userfaultfd_huge_must_wait(ctx, vmf->address, 439 vmf->flags, reason); 440 up_read(&mm->mmap_sem); 441 442 if (likely(must_wait && !ACCESS_ONCE(ctx->released) && 443 (return_to_userland ? !signal_pending(current) : 444 !fatal_signal_pending(current)))) { 445 wake_up_poll(&ctx->fd_wqh, POLLIN); 446 schedule(); 447 ret |= VM_FAULT_MAJOR; 448 449 /* 450 * False wakeups can orginate even from rwsem before 451 * up_read() however userfaults will wait either for a 452 * targeted wakeup on the specific uwq waitqueue from 453 * wake_userfault() or for signals or for uffd 454 * release. 455 */ 456 while (!READ_ONCE(uwq.waken)) { 457 /* 458 * This needs the full smp_store_mb() 459 * guarantee as the state write must be 460 * visible to other CPUs before reading 461 * uwq.waken from other CPUs. 462 */ 463 set_current_state(blocking_state); 464 if (READ_ONCE(uwq.waken) || 465 READ_ONCE(ctx->released) || 466 (return_to_userland ? signal_pending(current) : 467 fatal_signal_pending(current))) 468 break; 469 schedule(); 470 } 471 } 472 473 __set_current_state(TASK_RUNNING); 474 475 if (return_to_userland) { 476 if (signal_pending(current) && 477 !fatal_signal_pending(current)) { 478 /* 479 * If we got a SIGSTOP or SIGCONT and this is 480 * a normal userland page fault, just let 481 * userland return so the signal will be 482 * handled and gdb debugging works. The page 483 * fault code immediately after we return from 484 * this function is going to release the 485 * mmap_sem and it's not depending on it 486 * (unlike gup would if we were not to return 487 * VM_FAULT_RETRY). 488 * 489 * If a fatal signal is pending we still take 490 * the streamlined VM_FAULT_RETRY failure path 491 * and there's no need to retake the mmap_sem 492 * in such case. 493 */ 494 down_read(&mm->mmap_sem); 495 ret = VM_FAULT_NOPAGE; 496 } 497 } 498 499 /* 500 * Here we race with the list_del; list_add in 501 * userfaultfd_ctx_read(), however because we don't ever run 502 * list_del_init() to refile across the two lists, the prev 503 * and next pointers will never point to self. list_add also 504 * would never let any of the two pointers to point to 505 * self. So list_empty_careful won't risk to see both pointers 506 * pointing to self at any time during the list refile. The 507 * only case where list_del_init() is called is the full 508 * removal in the wake function and there we don't re-list_add 509 * and it's fine not to block on the spinlock. The uwq on this 510 * kernel stack can be released after the list_del_init. 511 */ 512 if (!list_empty_careful(&uwq.wq.task_list)) { 513 spin_lock(&ctx->fault_pending_wqh.lock); 514 /* 515 * No need of list_del_init(), the uwq on the stack 516 * will be freed shortly anyway. 517 */ 518 list_del(&uwq.wq.task_list); 519 spin_unlock(&ctx->fault_pending_wqh.lock); 520 } 521 522 /* 523 * ctx may go away after this if the userfault pseudo fd is 524 * already released. 525 */ 526 userfaultfd_ctx_put(ctx); 527 528 out: 529 return ret; 530 } 531 532 static void userfaultfd_event_wait_completion(struct userfaultfd_ctx *ctx, 533 struct userfaultfd_wait_queue *ewq) 534 { 535 if (WARN_ON_ONCE(current->flags & PF_EXITING)) 536 goto out; 537 538 ewq->ctx = ctx; 539 init_waitqueue_entry(&ewq->wq, current); 540 541 spin_lock(&ctx->event_wqh.lock); 542 /* 543 * After the __add_wait_queue the uwq is visible to userland 544 * through poll/read(). 545 */ 546 __add_wait_queue(&ctx->event_wqh, &ewq->wq); 547 for (;;) { 548 set_current_state(TASK_KILLABLE); 549 if (ewq->msg.event == 0) 550 break; 551 if (ACCESS_ONCE(ctx->released) || 552 fatal_signal_pending(current)) { 553 __remove_wait_queue(&ctx->event_wqh, &ewq->wq); 554 if (ewq->msg.event == UFFD_EVENT_FORK) { 555 struct userfaultfd_ctx *new; 556 557 new = (struct userfaultfd_ctx *) 558 (unsigned long) 559 ewq->msg.arg.reserved.reserved1; 560 561 userfaultfd_ctx_put(new); 562 } 563 break; 564 } 565 566 spin_unlock(&ctx->event_wqh.lock); 567 568 wake_up_poll(&ctx->fd_wqh, POLLIN); 569 schedule(); 570 571 spin_lock(&ctx->event_wqh.lock); 572 } 573 __set_current_state(TASK_RUNNING); 574 spin_unlock(&ctx->event_wqh.lock); 575 576 /* 577 * ctx may go away after this if the userfault pseudo fd is 578 * already released. 579 */ 580 out: 581 userfaultfd_ctx_put(ctx); 582 } 583 584 static void userfaultfd_event_complete(struct userfaultfd_ctx *ctx, 585 struct userfaultfd_wait_queue *ewq) 586 { 587 ewq->msg.event = 0; 588 wake_up_locked(&ctx->event_wqh); 589 __remove_wait_queue(&ctx->event_wqh, &ewq->wq); 590 } 591 592 int dup_userfaultfd(struct vm_area_struct *vma, struct list_head *fcs) 593 { 594 struct userfaultfd_ctx *ctx = NULL, *octx; 595 struct userfaultfd_fork_ctx *fctx; 596 597 octx = vma->vm_userfaultfd_ctx.ctx; 598 if (!octx || !(octx->features & UFFD_FEATURE_EVENT_FORK)) { 599 vma->vm_userfaultfd_ctx = NULL_VM_UFFD_CTX; 600 vma->vm_flags &= ~(VM_UFFD_WP | VM_UFFD_MISSING); 601 return 0; 602 } 603 604 list_for_each_entry(fctx, fcs, list) 605 if (fctx->orig == octx) { 606 ctx = fctx->new; 607 break; 608 } 609 610 if (!ctx) { 611 fctx = kmalloc(sizeof(*fctx), GFP_KERNEL); 612 if (!fctx) 613 return -ENOMEM; 614 615 ctx = kmem_cache_alloc(userfaultfd_ctx_cachep, GFP_KERNEL); 616 if (!ctx) { 617 kfree(fctx); 618 return -ENOMEM; 619 } 620 621 atomic_set(&ctx->refcount, 1); 622 ctx->flags = octx->flags; 623 ctx->state = UFFD_STATE_RUNNING; 624 ctx->features = octx->features; 625 ctx->released = false; 626 ctx->mm = vma->vm_mm; 627 atomic_inc(&ctx->mm->mm_count); 628 629 userfaultfd_ctx_get(octx); 630 fctx->orig = octx; 631 fctx->new = ctx; 632 list_add_tail(&fctx->list, fcs); 633 } 634 635 vma->vm_userfaultfd_ctx.ctx = ctx; 636 return 0; 637 } 638 639 static void dup_fctx(struct userfaultfd_fork_ctx *fctx) 640 { 641 struct userfaultfd_ctx *ctx = fctx->orig; 642 struct userfaultfd_wait_queue ewq; 643 644 msg_init(&ewq.msg); 645 646 ewq.msg.event = UFFD_EVENT_FORK; 647 ewq.msg.arg.reserved.reserved1 = (unsigned long)fctx->new; 648 649 userfaultfd_event_wait_completion(ctx, &ewq); 650 } 651 652 void dup_userfaultfd_complete(struct list_head *fcs) 653 { 654 struct userfaultfd_fork_ctx *fctx, *n; 655 656 list_for_each_entry_safe(fctx, n, fcs, list) { 657 dup_fctx(fctx); 658 list_del(&fctx->list); 659 kfree(fctx); 660 } 661 } 662 663 void mremap_userfaultfd_prep(struct vm_area_struct *vma, 664 struct vm_userfaultfd_ctx *vm_ctx) 665 { 666 struct userfaultfd_ctx *ctx; 667 668 ctx = vma->vm_userfaultfd_ctx.ctx; 669 if (ctx && (ctx->features & UFFD_FEATURE_EVENT_REMAP)) { 670 vm_ctx->ctx = ctx; 671 userfaultfd_ctx_get(ctx); 672 } 673 } 674 675 void mremap_userfaultfd_complete(struct vm_userfaultfd_ctx *vm_ctx, 676 unsigned long from, unsigned long to, 677 unsigned long len) 678 { 679 struct userfaultfd_ctx *ctx = vm_ctx->ctx; 680 struct userfaultfd_wait_queue ewq; 681 682 if (!ctx) 683 return; 684 685 if (to & ~PAGE_MASK) { 686 userfaultfd_ctx_put(ctx); 687 return; 688 } 689 690 msg_init(&ewq.msg); 691 692 ewq.msg.event = UFFD_EVENT_REMAP; 693 ewq.msg.arg.remap.from = from; 694 ewq.msg.arg.remap.to = to; 695 ewq.msg.arg.remap.len = len; 696 697 userfaultfd_event_wait_completion(ctx, &ewq); 698 } 699 700 bool userfaultfd_remove(struct vm_area_struct *vma, 701 unsigned long start, unsigned long end) 702 { 703 struct mm_struct *mm = vma->vm_mm; 704 struct userfaultfd_ctx *ctx; 705 struct userfaultfd_wait_queue ewq; 706 707 ctx = vma->vm_userfaultfd_ctx.ctx; 708 if (!ctx || !(ctx->features & UFFD_FEATURE_EVENT_REMOVE)) 709 return true; 710 711 userfaultfd_ctx_get(ctx); 712 up_read(&mm->mmap_sem); 713 714 msg_init(&ewq.msg); 715 716 ewq.msg.event = UFFD_EVENT_REMOVE; 717 ewq.msg.arg.remove.start = start; 718 ewq.msg.arg.remove.end = end; 719 720 userfaultfd_event_wait_completion(ctx, &ewq); 721 722 return false; 723 } 724 725 static bool has_unmap_ctx(struct userfaultfd_ctx *ctx, struct list_head *unmaps, 726 unsigned long start, unsigned long end) 727 { 728 struct userfaultfd_unmap_ctx *unmap_ctx; 729 730 list_for_each_entry(unmap_ctx, unmaps, list) 731 if (unmap_ctx->ctx == ctx && unmap_ctx->start == start && 732 unmap_ctx->end == end) 733 return true; 734 735 return false; 736 } 737 738 int userfaultfd_unmap_prep(struct vm_area_struct *vma, 739 unsigned long start, unsigned long end, 740 struct list_head *unmaps) 741 { 742 for ( ; vma && vma->vm_start < end; vma = vma->vm_next) { 743 struct userfaultfd_unmap_ctx *unmap_ctx; 744 struct userfaultfd_ctx *ctx = vma->vm_userfaultfd_ctx.ctx; 745 746 if (!ctx || !(ctx->features & UFFD_FEATURE_EVENT_UNMAP) || 747 has_unmap_ctx(ctx, unmaps, start, end)) 748 continue; 749 750 unmap_ctx = kzalloc(sizeof(*unmap_ctx), GFP_KERNEL); 751 if (!unmap_ctx) 752 return -ENOMEM; 753 754 userfaultfd_ctx_get(ctx); 755 unmap_ctx->ctx = ctx; 756 unmap_ctx->start = start; 757 unmap_ctx->end = end; 758 list_add_tail(&unmap_ctx->list, unmaps); 759 } 760 761 return 0; 762 } 763 764 void userfaultfd_unmap_complete(struct mm_struct *mm, struct list_head *uf) 765 { 766 struct userfaultfd_unmap_ctx *ctx, *n; 767 struct userfaultfd_wait_queue ewq; 768 769 list_for_each_entry_safe(ctx, n, uf, list) { 770 msg_init(&ewq.msg); 771 772 ewq.msg.event = UFFD_EVENT_UNMAP; 773 ewq.msg.arg.remove.start = ctx->start; 774 ewq.msg.arg.remove.end = ctx->end; 775 776 userfaultfd_event_wait_completion(ctx->ctx, &ewq); 777 778 list_del(&ctx->list); 779 kfree(ctx); 780 } 781 } 782 783 static int userfaultfd_release(struct inode *inode, struct file *file) 784 { 785 struct userfaultfd_ctx *ctx = file->private_data; 786 struct mm_struct *mm = ctx->mm; 787 struct vm_area_struct *vma, *prev; 788 /* len == 0 means wake all */ 789 struct userfaultfd_wake_range range = { .len = 0, }; 790 unsigned long new_flags; 791 792 ACCESS_ONCE(ctx->released) = true; 793 794 if (!mmget_not_zero(mm)) 795 goto wakeup; 796 797 /* 798 * Flush page faults out of all CPUs. NOTE: all page faults 799 * must be retried without returning VM_FAULT_SIGBUS if 800 * userfaultfd_ctx_get() succeeds but vma->vma_userfault_ctx 801 * changes while handle_userfault released the mmap_sem. So 802 * it's critical that released is set to true (above), before 803 * taking the mmap_sem for writing. 804 */ 805 down_write(&mm->mmap_sem); 806 prev = NULL; 807 for (vma = mm->mmap; vma; vma = vma->vm_next) { 808 cond_resched(); 809 BUG_ON(!!vma->vm_userfaultfd_ctx.ctx ^ 810 !!(vma->vm_flags & (VM_UFFD_MISSING | VM_UFFD_WP))); 811 if (vma->vm_userfaultfd_ctx.ctx != ctx) { 812 prev = vma; 813 continue; 814 } 815 new_flags = vma->vm_flags & ~(VM_UFFD_MISSING | VM_UFFD_WP); 816 prev = vma_merge(mm, prev, vma->vm_start, vma->vm_end, 817 new_flags, vma->anon_vma, 818 vma->vm_file, vma->vm_pgoff, 819 vma_policy(vma), 820 NULL_VM_UFFD_CTX); 821 if (prev) 822 vma = prev; 823 else 824 prev = vma; 825 vma->vm_flags = new_flags; 826 vma->vm_userfaultfd_ctx = NULL_VM_UFFD_CTX; 827 } 828 up_write(&mm->mmap_sem); 829 mmput(mm); 830 wakeup: 831 /* 832 * After no new page faults can wait on this fault_*wqh, flush 833 * the last page faults that may have been already waiting on 834 * the fault_*wqh. 835 */ 836 spin_lock(&ctx->fault_pending_wqh.lock); 837 __wake_up_locked_key(&ctx->fault_pending_wqh, TASK_NORMAL, &range); 838 __wake_up_locked_key(&ctx->fault_wqh, TASK_NORMAL, &range); 839 spin_unlock(&ctx->fault_pending_wqh.lock); 840 841 wake_up_poll(&ctx->fd_wqh, POLLHUP); 842 userfaultfd_ctx_put(ctx); 843 return 0; 844 } 845 846 /* fault_pending_wqh.lock must be hold by the caller */ 847 static inline struct userfaultfd_wait_queue *find_userfault_in( 848 wait_queue_head_t *wqh) 849 { 850 wait_queue_t *wq; 851 struct userfaultfd_wait_queue *uwq; 852 853 VM_BUG_ON(!spin_is_locked(&wqh->lock)); 854 855 uwq = NULL; 856 if (!waitqueue_active(wqh)) 857 goto out; 858 /* walk in reverse to provide FIFO behavior to read userfaults */ 859 wq = list_last_entry(&wqh->task_list, typeof(*wq), task_list); 860 uwq = container_of(wq, struct userfaultfd_wait_queue, wq); 861 out: 862 return uwq; 863 } 864 865 static inline struct userfaultfd_wait_queue *find_userfault( 866 struct userfaultfd_ctx *ctx) 867 { 868 return find_userfault_in(&ctx->fault_pending_wqh); 869 } 870 871 static inline struct userfaultfd_wait_queue *find_userfault_evt( 872 struct userfaultfd_ctx *ctx) 873 { 874 return find_userfault_in(&ctx->event_wqh); 875 } 876 877 static unsigned int userfaultfd_poll(struct file *file, poll_table *wait) 878 { 879 struct userfaultfd_ctx *ctx = file->private_data; 880 unsigned int ret; 881 882 poll_wait(file, &ctx->fd_wqh, wait); 883 884 switch (ctx->state) { 885 case UFFD_STATE_WAIT_API: 886 return POLLERR; 887 case UFFD_STATE_RUNNING: 888 /* 889 * poll() never guarantees that read won't block. 890 * userfaults can be waken before they're read(). 891 */ 892 if (unlikely(!(file->f_flags & O_NONBLOCK))) 893 return POLLERR; 894 /* 895 * lockless access to see if there are pending faults 896 * __pollwait last action is the add_wait_queue but 897 * the spin_unlock would allow the waitqueue_active to 898 * pass above the actual list_add inside 899 * add_wait_queue critical section. So use a full 900 * memory barrier to serialize the list_add write of 901 * add_wait_queue() with the waitqueue_active read 902 * below. 903 */ 904 ret = 0; 905 smp_mb(); 906 if (waitqueue_active(&ctx->fault_pending_wqh)) 907 ret = POLLIN; 908 else if (waitqueue_active(&ctx->event_wqh)) 909 ret = POLLIN; 910 911 return ret; 912 default: 913 WARN_ON_ONCE(1); 914 return POLLERR; 915 } 916 } 917 918 static const struct file_operations userfaultfd_fops; 919 920 static int resolve_userfault_fork(struct userfaultfd_ctx *ctx, 921 struct userfaultfd_ctx *new, 922 struct uffd_msg *msg) 923 { 924 int fd; 925 struct file *file; 926 unsigned int flags = new->flags & UFFD_SHARED_FCNTL_FLAGS; 927 928 fd = get_unused_fd_flags(flags); 929 if (fd < 0) 930 return fd; 931 932 file = anon_inode_getfile("[userfaultfd]", &userfaultfd_fops, new, 933 O_RDWR | flags); 934 if (IS_ERR(file)) { 935 put_unused_fd(fd); 936 return PTR_ERR(file); 937 } 938 939 fd_install(fd, file); 940 msg->arg.reserved.reserved1 = 0; 941 msg->arg.fork.ufd = fd; 942 943 return 0; 944 } 945 946 static ssize_t userfaultfd_ctx_read(struct userfaultfd_ctx *ctx, int no_wait, 947 struct uffd_msg *msg) 948 { 949 ssize_t ret; 950 DECLARE_WAITQUEUE(wait, current); 951 struct userfaultfd_wait_queue *uwq; 952 /* 953 * Handling fork event requires sleeping operations, so 954 * we drop the event_wqh lock, then do these ops, then 955 * lock it back and wake up the waiter. While the lock is 956 * dropped the ewq may go away so we keep track of it 957 * carefully. 958 */ 959 LIST_HEAD(fork_event); 960 struct userfaultfd_ctx *fork_nctx = NULL; 961 962 /* always take the fd_wqh lock before the fault_pending_wqh lock */ 963 spin_lock(&ctx->fd_wqh.lock); 964 __add_wait_queue(&ctx->fd_wqh, &wait); 965 for (;;) { 966 set_current_state(TASK_INTERRUPTIBLE); 967 spin_lock(&ctx->fault_pending_wqh.lock); 968 uwq = find_userfault(ctx); 969 if (uwq) { 970 /* 971 * Use a seqcount to repeat the lockless check 972 * in wake_userfault() to avoid missing 973 * wakeups because during the refile both 974 * waitqueue could become empty if this is the 975 * only userfault. 976 */ 977 write_seqcount_begin(&ctx->refile_seq); 978 979 /* 980 * The fault_pending_wqh.lock prevents the uwq 981 * to disappear from under us. 982 * 983 * Refile this userfault from 984 * fault_pending_wqh to fault_wqh, it's not 985 * pending anymore after we read it. 986 * 987 * Use list_del() by hand (as 988 * userfaultfd_wake_function also uses 989 * list_del_init() by hand) to be sure nobody 990 * changes __remove_wait_queue() to use 991 * list_del_init() in turn breaking the 992 * !list_empty_careful() check in 993 * handle_userfault(). The uwq->wq.task_list 994 * must never be empty at any time during the 995 * refile, or the waitqueue could disappear 996 * from under us. The "wait_queue_head_t" 997 * parameter of __remove_wait_queue() is unused 998 * anyway. 999 */ 1000 list_del(&uwq->wq.task_list); 1001 __add_wait_queue(&ctx->fault_wqh, &uwq->wq); 1002 1003 write_seqcount_end(&ctx->refile_seq); 1004 1005 /* careful to always initialize msg if ret == 0 */ 1006 *msg = uwq->msg; 1007 spin_unlock(&ctx->fault_pending_wqh.lock); 1008 ret = 0; 1009 break; 1010 } 1011 spin_unlock(&ctx->fault_pending_wqh.lock); 1012 1013 spin_lock(&ctx->event_wqh.lock); 1014 uwq = find_userfault_evt(ctx); 1015 if (uwq) { 1016 *msg = uwq->msg; 1017 1018 if (uwq->msg.event == UFFD_EVENT_FORK) { 1019 fork_nctx = (struct userfaultfd_ctx *) 1020 (unsigned long) 1021 uwq->msg.arg.reserved.reserved1; 1022 list_move(&uwq->wq.task_list, &fork_event); 1023 spin_unlock(&ctx->event_wqh.lock); 1024 ret = 0; 1025 break; 1026 } 1027 1028 userfaultfd_event_complete(ctx, uwq); 1029 spin_unlock(&ctx->event_wqh.lock); 1030 ret = 0; 1031 break; 1032 } 1033 spin_unlock(&ctx->event_wqh.lock); 1034 1035 if (signal_pending(current)) { 1036 ret = -ERESTARTSYS; 1037 break; 1038 } 1039 if (no_wait) { 1040 ret = -EAGAIN; 1041 break; 1042 } 1043 spin_unlock(&ctx->fd_wqh.lock); 1044 schedule(); 1045 spin_lock(&ctx->fd_wqh.lock); 1046 } 1047 __remove_wait_queue(&ctx->fd_wqh, &wait); 1048 __set_current_state(TASK_RUNNING); 1049 spin_unlock(&ctx->fd_wqh.lock); 1050 1051 if (!ret && msg->event == UFFD_EVENT_FORK) { 1052 ret = resolve_userfault_fork(ctx, fork_nctx, msg); 1053 1054 if (!ret) { 1055 spin_lock(&ctx->event_wqh.lock); 1056 if (!list_empty(&fork_event)) { 1057 uwq = list_first_entry(&fork_event, 1058 typeof(*uwq), 1059 wq.task_list); 1060 list_del(&uwq->wq.task_list); 1061 __add_wait_queue(&ctx->event_wqh, &uwq->wq); 1062 userfaultfd_event_complete(ctx, uwq); 1063 } 1064 spin_unlock(&ctx->event_wqh.lock); 1065 } 1066 } 1067 1068 return ret; 1069 } 1070 1071 static ssize_t userfaultfd_read(struct file *file, char __user *buf, 1072 size_t count, loff_t *ppos) 1073 { 1074 struct userfaultfd_ctx *ctx = file->private_data; 1075 ssize_t _ret, ret = 0; 1076 struct uffd_msg msg; 1077 int no_wait = file->f_flags & O_NONBLOCK; 1078 1079 if (ctx->state == UFFD_STATE_WAIT_API) 1080 return -EINVAL; 1081 1082 for (;;) { 1083 if (count < sizeof(msg)) 1084 return ret ? ret : -EINVAL; 1085 _ret = userfaultfd_ctx_read(ctx, no_wait, &msg); 1086 if (_ret < 0) 1087 return ret ? ret : _ret; 1088 if (copy_to_user((__u64 __user *) buf, &msg, sizeof(msg))) 1089 return ret ? ret : -EFAULT; 1090 ret += sizeof(msg); 1091 buf += sizeof(msg); 1092 count -= sizeof(msg); 1093 /* 1094 * Allow to read more than one fault at time but only 1095 * block if waiting for the very first one. 1096 */ 1097 no_wait = O_NONBLOCK; 1098 } 1099 } 1100 1101 static void __wake_userfault(struct userfaultfd_ctx *ctx, 1102 struct userfaultfd_wake_range *range) 1103 { 1104 unsigned long start, end; 1105 1106 start = range->start; 1107 end = range->start + range->len; 1108 1109 spin_lock(&ctx->fault_pending_wqh.lock); 1110 /* wake all in the range and autoremove */ 1111 if (waitqueue_active(&ctx->fault_pending_wqh)) 1112 __wake_up_locked_key(&ctx->fault_pending_wqh, TASK_NORMAL, 1113 range); 1114 if (waitqueue_active(&ctx->fault_wqh)) 1115 __wake_up_locked_key(&ctx->fault_wqh, TASK_NORMAL, range); 1116 spin_unlock(&ctx->fault_pending_wqh.lock); 1117 } 1118 1119 static __always_inline void wake_userfault(struct userfaultfd_ctx *ctx, 1120 struct userfaultfd_wake_range *range) 1121 { 1122 unsigned seq; 1123 bool need_wakeup; 1124 1125 /* 1126 * To be sure waitqueue_active() is not reordered by the CPU 1127 * before the pagetable update, use an explicit SMP memory 1128 * barrier here. PT lock release or up_read(mmap_sem) still 1129 * have release semantics that can allow the 1130 * waitqueue_active() to be reordered before the pte update. 1131 */ 1132 smp_mb(); 1133 1134 /* 1135 * Use waitqueue_active because it's very frequent to 1136 * change the address space atomically even if there are no 1137 * userfaults yet. So we take the spinlock only when we're 1138 * sure we've userfaults to wake. 1139 */ 1140 do { 1141 seq = read_seqcount_begin(&ctx->refile_seq); 1142 need_wakeup = waitqueue_active(&ctx->fault_pending_wqh) || 1143 waitqueue_active(&ctx->fault_wqh); 1144 cond_resched(); 1145 } while (read_seqcount_retry(&ctx->refile_seq, seq)); 1146 if (need_wakeup) 1147 __wake_userfault(ctx, range); 1148 } 1149 1150 static __always_inline int validate_range(struct mm_struct *mm, 1151 __u64 start, __u64 len) 1152 { 1153 __u64 task_size = mm->task_size; 1154 1155 if (start & ~PAGE_MASK) 1156 return -EINVAL; 1157 if (len & ~PAGE_MASK) 1158 return -EINVAL; 1159 if (!len) 1160 return -EINVAL; 1161 if (start < mmap_min_addr) 1162 return -EINVAL; 1163 if (start >= task_size) 1164 return -EINVAL; 1165 if (len > task_size - start) 1166 return -EINVAL; 1167 return 0; 1168 } 1169 1170 static inline bool vma_can_userfault(struct vm_area_struct *vma) 1171 { 1172 return vma_is_anonymous(vma) || is_vm_hugetlb_page(vma) || 1173 vma_is_shmem(vma); 1174 } 1175 1176 static int userfaultfd_register(struct userfaultfd_ctx *ctx, 1177 unsigned long arg) 1178 { 1179 struct mm_struct *mm = ctx->mm; 1180 struct vm_area_struct *vma, *prev, *cur; 1181 int ret; 1182 struct uffdio_register uffdio_register; 1183 struct uffdio_register __user *user_uffdio_register; 1184 unsigned long vm_flags, new_flags; 1185 bool found; 1186 bool non_anon_pages; 1187 unsigned long start, end, vma_end; 1188 1189 user_uffdio_register = (struct uffdio_register __user *) arg; 1190 1191 ret = -EFAULT; 1192 if (copy_from_user(&uffdio_register, user_uffdio_register, 1193 sizeof(uffdio_register)-sizeof(__u64))) 1194 goto out; 1195 1196 ret = -EINVAL; 1197 if (!uffdio_register.mode) 1198 goto out; 1199 if (uffdio_register.mode & ~(UFFDIO_REGISTER_MODE_MISSING| 1200 UFFDIO_REGISTER_MODE_WP)) 1201 goto out; 1202 vm_flags = 0; 1203 if (uffdio_register.mode & UFFDIO_REGISTER_MODE_MISSING) 1204 vm_flags |= VM_UFFD_MISSING; 1205 if (uffdio_register.mode & UFFDIO_REGISTER_MODE_WP) { 1206 vm_flags |= VM_UFFD_WP; 1207 /* 1208 * FIXME: remove the below error constraint by 1209 * implementing the wprotect tracking mode. 1210 */ 1211 ret = -EINVAL; 1212 goto out; 1213 } 1214 1215 ret = validate_range(mm, uffdio_register.range.start, 1216 uffdio_register.range.len); 1217 if (ret) 1218 goto out; 1219 1220 start = uffdio_register.range.start; 1221 end = start + uffdio_register.range.len; 1222 1223 ret = -ENOMEM; 1224 if (!mmget_not_zero(mm)) 1225 goto out; 1226 1227 down_write(&mm->mmap_sem); 1228 vma = find_vma_prev(mm, start, &prev); 1229 if (!vma) 1230 goto out_unlock; 1231 1232 /* check that there's at least one vma in the range */ 1233 ret = -EINVAL; 1234 if (vma->vm_start >= end) 1235 goto out_unlock; 1236 1237 /* 1238 * If the first vma contains huge pages, make sure start address 1239 * is aligned to huge page size. 1240 */ 1241 if (is_vm_hugetlb_page(vma)) { 1242 unsigned long vma_hpagesize = vma_kernel_pagesize(vma); 1243 1244 if (start & (vma_hpagesize - 1)) 1245 goto out_unlock; 1246 } 1247 1248 /* 1249 * Search for not compatible vmas. 1250 */ 1251 found = false; 1252 non_anon_pages = false; 1253 for (cur = vma; cur && cur->vm_start < end; cur = cur->vm_next) { 1254 cond_resched(); 1255 1256 BUG_ON(!!cur->vm_userfaultfd_ctx.ctx ^ 1257 !!(cur->vm_flags & (VM_UFFD_MISSING | VM_UFFD_WP))); 1258 1259 /* check not compatible vmas */ 1260 ret = -EINVAL; 1261 if (!vma_can_userfault(cur)) 1262 goto out_unlock; 1263 /* 1264 * If this vma contains ending address, and huge pages 1265 * check alignment. 1266 */ 1267 if (is_vm_hugetlb_page(cur) && end <= cur->vm_end && 1268 end > cur->vm_start) { 1269 unsigned long vma_hpagesize = vma_kernel_pagesize(cur); 1270 1271 ret = -EINVAL; 1272 1273 if (end & (vma_hpagesize - 1)) 1274 goto out_unlock; 1275 } 1276 1277 /* 1278 * Check that this vma isn't already owned by a 1279 * different userfaultfd. We can't allow more than one 1280 * userfaultfd to own a single vma simultaneously or we 1281 * wouldn't know which one to deliver the userfaults to. 1282 */ 1283 ret = -EBUSY; 1284 if (cur->vm_userfaultfd_ctx.ctx && 1285 cur->vm_userfaultfd_ctx.ctx != ctx) 1286 goto out_unlock; 1287 1288 /* 1289 * Note vmas containing huge pages 1290 */ 1291 if (is_vm_hugetlb_page(cur) || vma_is_shmem(cur)) 1292 non_anon_pages = true; 1293 1294 found = true; 1295 } 1296 BUG_ON(!found); 1297 1298 if (vma->vm_start < start) 1299 prev = vma; 1300 1301 ret = 0; 1302 do { 1303 cond_resched(); 1304 1305 BUG_ON(!vma_can_userfault(vma)); 1306 BUG_ON(vma->vm_userfaultfd_ctx.ctx && 1307 vma->vm_userfaultfd_ctx.ctx != ctx); 1308 1309 /* 1310 * Nothing to do: this vma is already registered into this 1311 * userfaultfd and with the right tracking mode too. 1312 */ 1313 if (vma->vm_userfaultfd_ctx.ctx == ctx && 1314 (vma->vm_flags & vm_flags) == vm_flags) 1315 goto skip; 1316 1317 if (vma->vm_start > start) 1318 start = vma->vm_start; 1319 vma_end = min(end, vma->vm_end); 1320 1321 new_flags = (vma->vm_flags & ~vm_flags) | vm_flags; 1322 prev = vma_merge(mm, prev, start, vma_end, new_flags, 1323 vma->anon_vma, vma->vm_file, vma->vm_pgoff, 1324 vma_policy(vma), 1325 ((struct vm_userfaultfd_ctx){ ctx })); 1326 if (prev) { 1327 vma = prev; 1328 goto next; 1329 } 1330 if (vma->vm_start < start) { 1331 ret = split_vma(mm, vma, start, 1); 1332 if (ret) 1333 break; 1334 } 1335 if (vma->vm_end > end) { 1336 ret = split_vma(mm, vma, end, 0); 1337 if (ret) 1338 break; 1339 } 1340 next: 1341 /* 1342 * In the vma_merge() successful mprotect-like case 8: 1343 * the next vma was merged into the current one and 1344 * the current one has not been updated yet. 1345 */ 1346 vma->vm_flags = new_flags; 1347 vma->vm_userfaultfd_ctx.ctx = ctx; 1348 1349 skip: 1350 prev = vma; 1351 start = vma->vm_end; 1352 vma = vma->vm_next; 1353 } while (vma && vma->vm_start < end); 1354 out_unlock: 1355 up_write(&mm->mmap_sem); 1356 mmput(mm); 1357 if (!ret) { 1358 /* 1359 * Now that we scanned all vmas we can already tell 1360 * userland which ioctls methods are guaranteed to 1361 * succeed on this range. 1362 */ 1363 if (put_user(non_anon_pages ? UFFD_API_RANGE_IOCTLS_BASIC : 1364 UFFD_API_RANGE_IOCTLS, 1365 &user_uffdio_register->ioctls)) 1366 ret = -EFAULT; 1367 } 1368 out: 1369 return ret; 1370 } 1371 1372 static int userfaultfd_unregister(struct userfaultfd_ctx *ctx, 1373 unsigned long arg) 1374 { 1375 struct mm_struct *mm = ctx->mm; 1376 struct vm_area_struct *vma, *prev, *cur; 1377 int ret; 1378 struct uffdio_range uffdio_unregister; 1379 unsigned long new_flags; 1380 bool found; 1381 unsigned long start, end, vma_end; 1382 const void __user *buf = (void __user *)arg; 1383 1384 ret = -EFAULT; 1385 if (copy_from_user(&uffdio_unregister, buf, sizeof(uffdio_unregister))) 1386 goto out; 1387 1388 ret = validate_range(mm, uffdio_unregister.start, 1389 uffdio_unregister.len); 1390 if (ret) 1391 goto out; 1392 1393 start = uffdio_unregister.start; 1394 end = start + uffdio_unregister.len; 1395 1396 ret = -ENOMEM; 1397 if (!mmget_not_zero(mm)) 1398 goto out; 1399 1400 down_write(&mm->mmap_sem); 1401 vma = find_vma_prev(mm, start, &prev); 1402 if (!vma) 1403 goto out_unlock; 1404 1405 /* check that there's at least one vma in the range */ 1406 ret = -EINVAL; 1407 if (vma->vm_start >= end) 1408 goto out_unlock; 1409 1410 /* 1411 * If the first vma contains huge pages, make sure start address 1412 * is aligned to huge page size. 1413 */ 1414 if (is_vm_hugetlb_page(vma)) { 1415 unsigned long vma_hpagesize = vma_kernel_pagesize(vma); 1416 1417 if (start & (vma_hpagesize - 1)) 1418 goto out_unlock; 1419 } 1420 1421 /* 1422 * Search for not compatible vmas. 1423 */ 1424 found = false; 1425 ret = -EINVAL; 1426 for (cur = vma; cur && cur->vm_start < end; cur = cur->vm_next) { 1427 cond_resched(); 1428 1429 BUG_ON(!!cur->vm_userfaultfd_ctx.ctx ^ 1430 !!(cur->vm_flags & (VM_UFFD_MISSING | VM_UFFD_WP))); 1431 1432 /* 1433 * Check not compatible vmas, not strictly required 1434 * here as not compatible vmas cannot have an 1435 * userfaultfd_ctx registered on them, but this 1436 * provides for more strict behavior to notice 1437 * unregistration errors. 1438 */ 1439 if (!vma_can_userfault(cur)) 1440 goto out_unlock; 1441 1442 found = true; 1443 } 1444 BUG_ON(!found); 1445 1446 if (vma->vm_start < start) 1447 prev = vma; 1448 1449 ret = 0; 1450 do { 1451 cond_resched(); 1452 1453 BUG_ON(!vma_can_userfault(vma)); 1454 1455 /* 1456 * Nothing to do: this vma is already registered into this 1457 * userfaultfd and with the right tracking mode too. 1458 */ 1459 if (!vma->vm_userfaultfd_ctx.ctx) 1460 goto skip; 1461 1462 if (vma->vm_start > start) 1463 start = vma->vm_start; 1464 vma_end = min(end, vma->vm_end); 1465 1466 if (userfaultfd_missing(vma)) { 1467 /* 1468 * Wake any concurrent pending userfault while 1469 * we unregister, so they will not hang 1470 * permanently and it avoids userland to call 1471 * UFFDIO_WAKE explicitly. 1472 */ 1473 struct userfaultfd_wake_range range; 1474 range.start = start; 1475 range.len = vma_end - start; 1476 wake_userfault(vma->vm_userfaultfd_ctx.ctx, &range); 1477 } 1478 1479 new_flags = vma->vm_flags & ~(VM_UFFD_MISSING | VM_UFFD_WP); 1480 prev = vma_merge(mm, prev, start, vma_end, new_flags, 1481 vma->anon_vma, vma->vm_file, vma->vm_pgoff, 1482 vma_policy(vma), 1483 NULL_VM_UFFD_CTX); 1484 if (prev) { 1485 vma = prev; 1486 goto next; 1487 } 1488 if (vma->vm_start < start) { 1489 ret = split_vma(mm, vma, start, 1); 1490 if (ret) 1491 break; 1492 } 1493 if (vma->vm_end > end) { 1494 ret = split_vma(mm, vma, end, 0); 1495 if (ret) 1496 break; 1497 } 1498 next: 1499 /* 1500 * In the vma_merge() successful mprotect-like case 8: 1501 * the next vma was merged into the current one and 1502 * the current one has not been updated yet. 1503 */ 1504 vma->vm_flags = new_flags; 1505 vma->vm_userfaultfd_ctx = NULL_VM_UFFD_CTX; 1506 1507 skip: 1508 prev = vma; 1509 start = vma->vm_end; 1510 vma = vma->vm_next; 1511 } while (vma && vma->vm_start < end); 1512 out_unlock: 1513 up_write(&mm->mmap_sem); 1514 mmput(mm); 1515 out: 1516 return ret; 1517 } 1518 1519 /* 1520 * userfaultfd_wake may be used in combination with the 1521 * UFFDIO_*_MODE_DONTWAKE to wakeup userfaults in batches. 1522 */ 1523 static int userfaultfd_wake(struct userfaultfd_ctx *ctx, 1524 unsigned long arg) 1525 { 1526 int ret; 1527 struct uffdio_range uffdio_wake; 1528 struct userfaultfd_wake_range range; 1529 const void __user *buf = (void __user *)arg; 1530 1531 ret = -EFAULT; 1532 if (copy_from_user(&uffdio_wake, buf, sizeof(uffdio_wake))) 1533 goto out; 1534 1535 ret = validate_range(ctx->mm, uffdio_wake.start, uffdio_wake.len); 1536 if (ret) 1537 goto out; 1538 1539 range.start = uffdio_wake.start; 1540 range.len = uffdio_wake.len; 1541 1542 /* 1543 * len == 0 means wake all and we don't want to wake all here, 1544 * so check it again to be sure. 1545 */ 1546 VM_BUG_ON(!range.len); 1547 1548 wake_userfault(ctx, &range); 1549 ret = 0; 1550 1551 out: 1552 return ret; 1553 } 1554 1555 static int userfaultfd_copy(struct userfaultfd_ctx *ctx, 1556 unsigned long arg) 1557 { 1558 __s64 ret; 1559 struct uffdio_copy uffdio_copy; 1560 struct uffdio_copy __user *user_uffdio_copy; 1561 struct userfaultfd_wake_range range; 1562 1563 user_uffdio_copy = (struct uffdio_copy __user *) arg; 1564 1565 ret = -EFAULT; 1566 if (copy_from_user(&uffdio_copy, user_uffdio_copy, 1567 /* don't copy "copy" last field */ 1568 sizeof(uffdio_copy)-sizeof(__s64))) 1569 goto out; 1570 1571 ret = validate_range(ctx->mm, uffdio_copy.dst, uffdio_copy.len); 1572 if (ret) 1573 goto out; 1574 /* 1575 * double check for wraparound just in case. copy_from_user() 1576 * will later check uffdio_copy.src + uffdio_copy.len to fit 1577 * in the userland range. 1578 */ 1579 ret = -EINVAL; 1580 if (uffdio_copy.src + uffdio_copy.len <= uffdio_copy.src) 1581 goto out; 1582 if (uffdio_copy.mode & ~UFFDIO_COPY_MODE_DONTWAKE) 1583 goto out; 1584 if (mmget_not_zero(ctx->mm)) { 1585 ret = mcopy_atomic(ctx->mm, uffdio_copy.dst, uffdio_copy.src, 1586 uffdio_copy.len); 1587 mmput(ctx->mm); 1588 } else { 1589 return -ENOSPC; 1590 } 1591 if (unlikely(put_user(ret, &user_uffdio_copy->copy))) 1592 return -EFAULT; 1593 if (ret < 0) 1594 goto out; 1595 BUG_ON(!ret); 1596 /* len == 0 would wake all */ 1597 range.len = ret; 1598 if (!(uffdio_copy.mode & UFFDIO_COPY_MODE_DONTWAKE)) { 1599 range.start = uffdio_copy.dst; 1600 wake_userfault(ctx, &range); 1601 } 1602 ret = range.len == uffdio_copy.len ? 0 : -EAGAIN; 1603 out: 1604 return ret; 1605 } 1606 1607 static int userfaultfd_zeropage(struct userfaultfd_ctx *ctx, 1608 unsigned long arg) 1609 { 1610 __s64 ret; 1611 struct uffdio_zeropage uffdio_zeropage; 1612 struct uffdio_zeropage __user *user_uffdio_zeropage; 1613 struct userfaultfd_wake_range range; 1614 1615 user_uffdio_zeropage = (struct uffdio_zeropage __user *) arg; 1616 1617 ret = -EFAULT; 1618 if (copy_from_user(&uffdio_zeropage, user_uffdio_zeropage, 1619 /* don't copy "zeropage" last field */ 1620 sizeof(uffdio_zeropage)-sizeof(__s64))) 1621 goto out; 1622 1623 ret = validate_range(ctx->mm, uffdio_zeropage.range.start, 1624 uffdio_zeropage.range.len); 1625 if (ret) 1626 goto out; 1627 ret = -EINVAL; 1628 if (uffdio_zeropage.mode & ~UFFDIO_ZEROPAGE_MODE_DONTWAKE) 1629 goto out; 1630 1631 if (mmget_not_zero(ctx->mm)) { 1632 ret = mfill_zeropage(ctx->mm, uffdio_zeropage.range.start, 1633 uffdio_zeropage.range.len); 1634 mmput(ctx->mm); 1635 } 1636 if (unlikely(put_user(ret, &user_uffdio_zeropage->zeropage))) 1637 return -EFAULT; 1638 if (ret < 0) 1639 goto out; 1640 /* len == 0 would wake all */ 1641 BUG_ON(!ret); 1642 range.len = ret; 1643 if (!(uffdio_zeropage.mode & UFFDIO_ZEROPAGE_MODE_DONTWAKE)) { 1644 range.start = uffdio_zeropage.range.start; 1645 wake_userfault(ctx, &range); 1646 } 1647 ret = range.len == uffdio_zeropage.range.len ? 0 : -EAGAIN; 1648 out: 1649 return ret; 1650 } 1651 1652 static inline unsigned int uffd_ctx_features(__u64 user_features) 1653 { 1654 /* 1655 * For the current set of features the bits just coincide 1656 */ 1657 return (unsigned int)user_features; 1658 } 1659 1660 /* 1661 * userland asks for a certain API version and we return which bits 1662 * and ioctl commands are implemented in this kernel for such API 1663 * version or -EINVAL if unknown. 1664 */ 1665 static int userfaultfd_api(struct userfaultfd_ctx *ctx, 1666 unsigned long arg) 1667 { 1668 struct uffdio_api uffdio_api; 1669 void __user *buf = (void __user *)arg; 1670 int ret; 1671 __u64 features; 1672 1673 ret = -EINVAL; 1674 if (ctx->state != UFFD_STATE_WAIT_API) 1675 goto out; 1676 ret = -EFAULT; 1677 if (copy_from_user(&uffdio_api, buf, sizeof(uffdio_api))) 1678 goto out; 1679 features = uffdio_api.features; 1680 if (uffdio_api.api != UFFD_API || (features & ~UFFD_API_FEATURES)) { 1681 memset(&uffdio_api, 0, sizeof(uffdio_api)); 1682 if (copy_to_user(buf, &uffdio_api, sizeof(uffdio_api))) 1683 goto out; 1684 ret = -EINVAL; 1685 goto out; 1686 } 1687 /* report all available features and ioctls to userland */ 1688 uffdio_api.features = UFFD_API_FEATURES; 1689 uffdio_api.ioctls = UFFD_API_IOCTLS; 1690 ret = -EFAULT; 1691 if (copy_to_user(buf, &uffdio_api, sizeof(uffdio_api))) 1692 goto out; 1693 ctx->state = UFFD_STATE_RUNNING; 1694 /* only enable the requested features for this uffd context */ 1695 ctx->features = uffd_ctx_features(features); 1696 ret = 0; 1697 out: 1698 return ret; 1699 } 1700 1701 static long userfaultfd_ioctl(struct file *file, unsigned cmd, 1702 unsigned long arg) 1703 { 1704 int ret = -EINVAL; 1705 struct userfaultfd_ctx *ctx = file->private_data; 1706 1707 if (cmd != UFFDIO_API && ctx->state == UFFD_STATE_WAIT_API) 1708 return -EINVAL; 1709 1710 switch(cmd) { 1711 case UFFDIO_API: 1712 ret = userfaultfd_api(ctx, arg); 1713 break; 1714 case UFFDIO_REGISTER: 1715 ret = userfaultfd_register(ctx, arg); 1716 break; 1717 case UFFDIO_UNREGISTER: 1718 ret = userfaultfd_unregister(ctx, arg); 1719 break; 1720 case UFFDIO_WAKE: 1721 ret = userfaultfd_wake(ctx, arg); 1722 break; 1723 case UFFDIO_COPY: 1724 ret = userfaultfd_copy(ctx, arg); 1725 break; 1726 case UFFDIO_ZEROPAGE: 1727 ret = userfaultfd_zeropage(ctx, arg); 1728 break; 1729 } 1730 return ret; 1731 } 1732 1733 #ifdef CONFIG_PROC_FS 1734 static void userfaultfd_show_fdinfo(struct seq_file *m, struct file *f) 1735 { 1736 struct userfaultfd_ctx *ctx = f->private_data; 1737 wait_queue_t *wq; 1738 struct userfaultfd_wait_queue *uwq; 1739 unsigned long pending = 0, total = 0; 1740 1741 spin_lock(&ctx->fault_pending_wqh.lock); 1742 list_for_each_entry(wq, &ctx->fault_pending_wqh.task_list, task_list) { 1743 uwq = container_of(wq, struct userfaultfd_wait_queue, wq); 1744 pending++; 1745 total++; 1746 } 1747 list_for_each_entry(wq, &ctx->fault_wqh.task_list, task_list) { 1748 uwq = container_of(wq, struct userfaultfd_wait_queue, wq); 1749 total++; 1750 } 1751 spin_unlock(&ctx->fault_pending_wqh.lock); 1752 1753 /* 1754 * If more protocols will be added, there will be all shown 1755 * separated by a space. Like this: 1756 * protocols: aa:... bb:... 1757 */ 1758 seq_printf(m, "pending:\t%lu\ntotal:\t%lu\nAPI:\t%Lx:%x:%Lx\n", 1759 pending, total, UFFD_API, UFFD_API_FEATURES, 1760 UFFD_API_IOCTLS|UFFD_API_RANGE_IOCTLS); 1761 } 1762 #endif 1763 1764 static const struct file_operations userfaultfd_fops = { 1765 #ifdef CONFIG_PROC_FS 1766 .show_fdinfo = userfaultfd_show_fdinfo, 1767 #endif 1768 .release = userfaultfd_release, 1769 .poll = userfaultfd_poll, 1770 .read = userfaultfd_read, 1771 .unlocked_ioctl = userfaultfd_ioctl, 1772 .compat_ioctl = userfaultfd_ioctl, 1773 .llseek = noop_llseek, 1774 }; 1775 1776 static void init_once_userfaultfd_ctx(void *mem) 1777 { 1778 struct userfaultfd_ctx *ctx = (struct userfaultfd_ctx *) mem; 1779 1780 init_waitqueue_head(&ctx->fault_pending_wqh); 1781 init_waitqueue_head(&ctx->fault_wqh); 1782 init_waitqueue_head(&ctx->event_wqh); 1783 init_waitqueue_head(&ctx->fd_wqh); 1784 seqcount_init(&ctx->refile_seq); 1785 } 1786 1787 /** 1788 * userfaultfd_file_create - Creates a userfaultfd file pointer. 1789 * @flags: Flags for the userfaultfd file. 1790 * 1791 * This function creates a userfaultfd file pointer, w/out installing 1792 * it into the fd table. This is useful when the userfaultfd file is 1793 * used during the initialization of data structures that require 1794 * extra setup after the userfaultfd creation. So the userfaultfd 1795 * creation is split into the file pointer creation phase, and the 1796 * file descriptor installation phase. In this way races with 1797 * userspace closing the newly installed file descriptor can be 1798 * avoided. Returns a userfaultfd file pointer, or a proper error 1799 * pointer. 1800 */ 1801 static struct file *userfaultfd_file_create(int flags) 1802 { 1803 struct file *file; 1804 struct userfaultfd_ctx *ctx; 1805 1806 BUG_ON(!current->mm); 1807 1808 /* Check the UFFD_* constants for consistency. */ 1809 BUILD_BUG_ON(UFFD_CLOEXEC != O_CLOEXEC); 1810 BUILD_BUG_ON(UFFD_NONBLOCK != O_NONBLOCK); 1811 1812 file = ERR_PTR(-EINVAL); 1813 if (flags & ~UFFD_SHARED_FCNTL_FLAGS) 1814 goto out; 1815 1816 file = ERR_PTR(-ENOMEM); 1817 ctx = kmem_cache_alloc(userfaultfd_ctx_cachep, GFP_KERNEL); 1818 if (!ctx) 1819 goto out; 1820 1821 atomic_set(&ctx->refcount, 1); 1822 ctx->flags = flags; 1823 ctx->features = 0; 1824 ctx->state = UFFD_STATE_WAIT_API; 1825 ctx->released = false; 1826 ctx->mm = current->mm; 1827 /* prevent the mm struct to be freed */ 1828 mmgrab(ctx->mm); 1829 1830 file = anon_inode_getfile("[userfaultfd]", &userfaultfd_fops, ctx, 1831 O_RDWR | (flags & UFFD_SHARED_FCNTL_FLAGS)); 1832 if (IS_ERR(file)) { 1833 mmdrop(ctx->mm); 1834 kmem_cache_free(userfaultfd_ctx_cachep, ctx); 1835 } 1836 out: 1837 return file; 1838 } 1839 1840 SYSCALL_DEFINE1(userfaultfd, int, flags) 1841 { 1842 int fd, error; 1843 struct file *file; 1844 1845 error = get_unused_fd_flags(flags & UFFD_SHARED_FCNTL_FLAGS); 1846 if (error < 0) 1847 return error; 1848 fd = error; 1849 1850 file = userfaultfd_file_create(flags); 1851 if (IS_ERR(file)) { 1852 error = PTR_ERR(file); 1853 goto err_put_unused_fd; 1854 } 1855 fd_install(fd, file); 1856 1857 return fd; 1858 1859 err_put_unused_fd: 1860 put_unused_fd(fd); 1861 1862 return error; 1863 } 1864 1865 static int __init userfaultfd_init(void) 1866 { 1867 userfaultfd_ctx_cachep = kmem_cache_create("userfaultfd_ctx_cache", 1868 sizeof(struct userfaultfd_ctx), 1869 0, 1870 SLAB_HWCACHE_ALIGN|SLAB_PANIC, 1871 init_once_userfaultfd_ctx); 1872 return 0; 1873 } 1874 __initcall(userfaultfd_init); 1875