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/hashtable.h> 16#include <linux/sched.h> 17#include <linux/mm.h> 18#include <linux/poll.h> 19#include <linux/slab.h> 20#include <linux/seq_file.h> 21#include <linux/file.h> 22#include <linux/bug.h> 23#include <linux/anon_inodes.h> 24#include <linux/syscalls.h> 25#include <linux/userfaultfd_k.h> 26#include <linux/mempolicy.h> 27#include <linux/ioctl.h> 28#include <linux/security.h> 29 30static struct kmem_cache *userfaultfd_ctx_cachep __read_mostly; 31 32enum userfaultfd_state { 33 UFFD_STATE_WAIT_API, 34 UFFD_STATE_RUNNING, 35}; 36 37/* 38 * Start with fault_pending_wqh and fault_wqh so they're more likely 39 * to be in the same cacheline. 40 */ 41struct userfaultfd_ctx { 42 /* waitqueue head for the pending (i.e. not read) userfaults */ 43 wait_queue_head_t fault_pending_wqh; 44 /* waitqueue head for the userfaults */ 45 wait_queue_head_t fault_wqh; 46 /* waitqueue head for the pseudo fd to wakeup poll/read */ 47 wait_queue_head_t fd_wqh; 48 /* a refile sequence protected by fault_pending_wqh lock */ 49 struct seqcount refile_seq; 50 /* pseudo fd refcounting */ 51 atomic_t refcount; 52 /* userfaultfd syscall flags */ 53 unsigned int flags; 54 /* state machine */ 55 enum userfaultfd_state state; 56 /* released */ 57 bool released; 58 /* mm with one ore more vmas attached to this userfaultfd_ctx */ 59 struct mm_struct *mm; 60}; 61 62struct userfaultfd_wait_queue { 63 struct uffd_msg msg; 64 wait_queue_t wq; 65 struct userfaultfd_ctx *ctx; 66}; 67 68struct userfaultfd_wake_range { 69 unsigned long start; 70 unsigned long len; 71}; 72 73static int userfaultfd_wake_function(wait_queue_t *wq, unsigned mode, 74 int wake_flags, void *key) 75{ 76 struct userfaultfd_wake_range *range = key; 77 int ret; 78 struct userfaultfd_wait_queue *uwq; 79 unsigned long start, len; 80 81 uwq = container_of(wq, struct userfaultfd_wait_queue, wq); 82 ret = 0; 83 /* len == 0 means wake all */ 84 start = range->start; 85 len = range->len; 86 if (len && (start > uwq->msg.arg.pagefault.address || 87 start + len <= uwq->msg.arg.pagefault.address)) 88 goto out; 89 ret = wake_up_state(wq->private, mode); 90 if (ret) 91 /* 92 * Wake only once, autoremove behavior. 93 * 94 * After the effect of list_del_init is visible to the 95 * other CPUs, the waitqueue may disappear from under 96 * us, see the !list_empty_careful() in 97 * handle_userfault(). try_to_wake_up() has an 98 * implicit smp_mb__before_spinlock, and the 99 * wq->private is read before calling the extern 100 * function "wake_up_state" (which in turns calls 101 * try_to_wake_up). While the spin_lock;spin_unlock; 102 * wouldn't be enough, the smp_mb__before_spinlock is 103 * enough to avoid an explicit smp_mb() here. 104 */ 105 list_del_init(&wq->task_list); 106out: 107 return ret; 108} 109 110/** 111 * userfaultfd_ctx_get - Acquires a reference to the internal userfaultfd 112 * context. 113 * @ctx: [in] Pointer to the userfaultfd context. 114 * 115 * Returns: In case of success, returns not zero. 116 */ 117static void userfaultfd_ctx_get(struct userfaultfd_ctx *ctx) 118{ 119 if (!atomic_inc_not_zero(&ctx->refcount)) 120 BUG(); 121} 122 123/** 124 * userfaultfd_ctx_put - Releases a reference to the internal userfaultfd 125 * context. 126 * @ctx: [in] Pointer to userfaultfd context. 127 * 128 * The userfaultfd context reference must have been previously acquired either 129 * with userfaultfd_ctx_get() or userfaultfd_ctx_fdget(). 130 */ 131static void userfaultfd_ctx_put(struct userfaultfd_ctx *ctx) 132{ 133 if (atomic_dec_and_test(&ctx->refcount)) { 134 VM_BUG_ON(spin_is_locked(&ctx->fault_pending_wqh.lock)); 135 VM_BUG_ON(waitqueue_active(&ctx->fault_pending_wqh)); 136 VM_BUG_ON(spin_is_locked(&ctx->fault_wqh.lock)); 137 VM_BUG_ON(waitqueue_active(&ctx->fault_wqh)); 138 VM_BUG_ON(spin_is_locked(&ctx->fd_wqh.lock)); 139 VM_BUG_ON(waitqueue_active(&ctx->fd_wqh)); 140 mmput(ctx->mm); 141 kmem_cache_free(userfaultfd_ctx_cachep, ctx); 142 } 143} 144 145static inline void msg_init(struct uffd_msg *msg) 146{ 147 BUILD_BUG_ON(sizeof(struct uffd_msg) != 32); 148 /* 149 * Must use memset to zero out the paddings or kernel data is 150 * leaked to userland. 151 */ 152 memset(msg, 0, sizeof(struct uffd_msg)); 153} 154 155static inline struct uffd_msg userfault_msg(unsigned long address, 156 unsigned int flags, 157 unsigned long reason) 158{ 159 struct uffd_msg msg; 160 msg_init(&msg); 161 msg.event = UFFD_EVENT_PAGEFAULT; 162 msg.arg.pagefault.address = address; 163 if (flags & FAULT_FLAG_WRITE) 164 /* 165 * If UFFD_FEATURE_PAGEFAULT_FLAG_WRITE was set in the 166 * uffdio_api.features and UFFD_PAGEFAULT_FLAG_WRITE 167 * was not set in a UFFD_EVENT_PAGEFAULT, it means it 168 * was a read fault, otherwise if set it means it's 169 * a write fault. 170 */ 171 msg.arg.pagefault.flags |= UFFD_PAGEFAULT_FLAG_WRITE; 172 if (reason & VM_UFFD_WP) 173 /* 174 * If UFFD_FEATURE_PAGEFAULT_FLAG_WP was set in the 175 * uffdio_api.features and UFFD_PAGEFAULT_FLAG_WP was 176 * not set in a UFFD_EVENT_PAGEFAULT, it means it was 177 * a missing fault, otherwise if set it means it's a 178 * write protect fault. 179 */ 180 msg.arg.pagefault.flags |= UFFD_PAGEFAULT_FLAG_WP; 181 return msg; 182} 183 184/* 185 * Verify the pagetables are still not ok after having reigstered into 186 * the fault_pending_wqh to avoid userland having to UFFDIO_WAKE any 187 * userfault that has already been resolved, if userfaultfd_read and 188 * UFFDIO_COPY|ZEROPAGE are being run simultaneously on two different 189 * threads. 190 */ 191static inline bool userfaultfd_must_wait(struct userfaultfd_ctx *ctx, 192 unsigned long address, 193 unsigned long flags, 194 unsigned long reason) 195{ 196 struct mm_struct *mm = ctx->mm; 197 pgd_t *pgd; 198 pud_t *pud; 199 pmd_t *pmd, _pmd; 200 pte_t *pte; 201 bool ret = true; 202 203 VM_BUG_ON(!rwsem_is_locked(&mm->mmap_sem)); 204 205 pgd = pgd_offset(mm, address); 206 if (!pgd_present(*pgd)) 207 goto out; 208 pud = pud_offset(pgd, address); 209 if (!pud_present(*pud)) 210 goto out; 211 pmd = pmd_offset(pud, address); 212 /* 213 * READ_ONCE must function as a barrier with narrower scope 214 * and it must be equivalent to: 215 * _pmd = *pmd; barrier(); 216 * 217 * This is to deal with the instability (as in 218 * pmd_trans_unstable) of the pmd. 219 */ 220 _pmd = READ_ONCE(*pmd); 221 if (!pmd_present(_pmd)) 222 goto out; 223 224 ret = false; 225 if (pmd_trans_huge(_pmd)) 226 goto out; 227 228 /* 229 * the pmd is stable (as in !pmd_trans_unstable) so we can re-read it 230 * and use the standard pte_offset_map() instead of parsing _pmd. 231 */ 232 pte = pte_offset_map(pmd, address); 233 /* 234 * Lockless access: we're in a wait_event so it's ok if it 235 * changes under us. 236 */ 237 if (pte_none(*pte)) 238 ret = true; 239 pte_unmap(pte); 240 241out: 242 return ret; 243} 244 245/* 246 * The locking rules involved in returning VM_FAULT_RETRY depending on 247 * FAULT_FLAG_ALLOW_RETRY, FAULT_FLAG_RETRY_NOWAIT and 248 * FAULT_FLAG_KILLABLE are not straightforward. The "Caution" 249 * recommendation in __lock_page_or_retry is not an understatement. 250 * 251 * If FAULT_FLAG_ALLOW_RETRY is set, the mmap_sem must be released 252 * before returning VM_FAULT_RETRY only if FAULT_FLAG_RETRY_NOWAIT is 253 * not set. 254 * 255 * If FAULT_FLAG_ALLOW_RETRY is set but FAULT_FLAG_KILLABLE is not 256 * set, VM_FAULT_RETRY can still be returned if and only if there are 257 * fatal_signal_pending()s, and the mmap_sem must be released before 258 * returning it. 259 */ 260int handle_userfault(struct vm_area_struct *vma, unsigned long address, 261 unsigned int flags, unsigned long reason) 262{ 263 struct mm_struct *mm = vma->vm_mm; 264 struct userfaultfd_ctx *ctx; 265 struct userfaultfd_wait_queue uwq; 266 int ret; 267 bool must_wait, return_to_userland; 268 269 BUG_ON(!rwsem_is_locked(&mm->mmap_sem)); 270 271 ret = VM_FAULT_SIGBUS; 272 ctx = vma->vm_userfaultfd_ctx.ctx; 273 if (!ctx) 274 goto out; 275 276 BUG_ON(ctx->mm != mm); 277 278 VM_BUG_ON(reason & ~(VM_UFFD_MISSING|VM_UFFD_WP)); 279 VM_BUG_ON(!(reason & VM_UFFD_MISSING) ^ !!(reason & VM_UFFD_WP)); 280 281 /* 282 * If it's already released don't get it. This avoids to loop 283 * in __get_user_pages if userfaultfd_release waits on the 284 * caller of handle_userfault to release the mmap_sem. 285 */ 286 if (unlikely(ACCESS_ONCE(ctx->released))) 287 goto out; 288 289 /* 290 * We don't do userfault handling for the final child pid update. 291 */ 292 if (current->flags & PF_EXITING) 293 goto out; 294 295 /* 296 * Check that we can return VM_FAULT_RETRY. 297 * 298 * NOTE: it should become possible to return VM_FAULT_RETRY 299 * even if FAULT_FLAG_TRIED is set without leading to gup() 300 * -EBUSY failures, if the userfaultfd is to be extended for 301 * VM_UFFD_WP tracking and we intend to arm the userfault 302 * without first stopping userland access to the memory. For 303 * VM_UFFD_MISSING userfaults this is enough for now. 304 */ 305 if (unlikely(!(flags & FAULT_FLAG_ALLOW_RETRY))) { 306 /* 307 * Validate the invariant that nowait must allow retry 308 * to be sure not to return SIGBUS erroneously on 309 * nowait invocations. 310 */ 311 BUG_ON(flags & FAULT_FLAG_RETRY_NOWAIT); 312#ifdef CONFIG_DEBUG_VM 313 if (printk_ratelimit()) { 314 printk(KERN_WARNING 315 "FAULT_FLAG_ALLOW_RETRY missing %x\n", flags); 316 dump_stack(); 317 } 318#endif 319 goto out; 320 } 321 322 /* 323 * Handle nowait, not much to do other than tell it to retry 324 * and wait. 325 */ 326 ret = VM_FAULT_RETRY; 327 if (flags & FAULT_FLAG_RETRY_NOWAIT) 328 goto out; 329 330 /* take the reference before dropping the mmap_sem */ 331 userfaultfd_ctx_get(ctx); 332 333 init_waitqueue_func_entry(&uwq.wq, userfaultfd_wake_function); 334 uwq.wq.private = current; 335 uwq.msg = userfault_msg(address, flags, reason); 336 uwq.ctx = ctx; 337 338 return_to_userland = (flags & (FAULT_FLAG_USER|FAULT_FLAG_KILLABLE)) == 339 (FAULT_FLAG_USER|FAULT_FLAG_KILLABLE); 340 341 spin_lock(&ctx->fault_pending_wqh.lock); 342 /* 343 * After the __add_wait_queue the uwq is visible to userland 344 * through poll/read(). 345 */ 346 __add_wait_queue(&ctx->fault_pending_wqh, &uwq.wq); 347 /* 348 * The smp_mb() after __set_current_state prevents the reads 349 * following the spin_unlock to happen before the list_add in 350 * __add_wait_queue. 351 */ 352 set_current_state(return_to_userland ? TASK_INTERRUPTIBLE : 353 TASK_KILLABLE); 354 spin_unlock(&ctx->fault_pending_wqh.lock); 355 356 must_wait = userfaultfd_must_wait(ctx, address, flags, reason); 357 up_read(&mm->mmap_sem); 358 359 if (likely(must_wait && !ACCESS_ONCE(ctx->released) && 360 (return_to_userland ? !signal_pending(current) : 361 !fatal_signal_pending(current)))) { 362 wake_up_poll(&ctx->fd_wqh, POLLIN); 363 schedule(); 364 ret |= VM_FAULT_MAJOR; 365 } 366 367 __set_current_state(TASK_RUNNING); 368 369 if (return_to_userland) { 370 if (signal_pending(current) && 371 !fatal_signal_pending(current)) { 372 /* 373 * If we got a SIGSTOP or SIGCONT and this is 374 * a normal userland page fault, just let 375 * userland return so the signal will be 376 * handled and gdb debugging works. The page 377 * fault code immediately after we return from 378 * this function is going to release the 379 * mmap_sem and it's not depending on it 380 * (unlike gup would if we were not to return 381 * VM_FAULT_RETRY). 382 * 383 * If a fatal signal is pending we still take 384 * the streamlined VM_FAULT_RETRY failure path 385 * and there's no need to retake the mmap_sem 386 * in such case. 387 */ 388 down_read(&mm->mmap_sem); 389 ret = 0; 390 } 391 } 392 393 /* 394 * Here we race with the list_del; list_add in 395 * userfaultfd_ctx_read(), however because we don't ever run 396 * list_del_init() to refile across the two lists, the prev 397 * and next pointers will never point to self. list_add also 398 * would never let any of the two pointers to point to 399 * self. So list_empty_careful won't risk to see both pointers 400 * pointing to self at any time during the list refile. The 401 * only case where list_del_init() is called is the full 402 * removal in the wake function and there we don't re-list_add 403 * and it's fine not to block on the spinlock. The uwq on this 404 * kernel stack can be released after the list_del_init. 405 */ 406 if (!list_empty_careful(&uwq.wq.task_list)) { 407 spin_lock(&ctx->fault_pending_wqh.lock); 408 /* 409 * No need of list_del_init(), the uwq on the stack 410 * will be freed shortly anyway. 411 */ 412 list_del(&uwq.wq.task_list); 413 spin_unlock(&ctx->fault_pending_wqh.lock); 414 } 415 416 /* 417 * ctx may go away after this if the userfault pseudo fd is 418 * already released. 419 */ 420 userfaultfd_ctx_put(ctx); 421 422out: 423 return ret; 424} 425 426static int userfaultfd_release(struct inode *inode, struct file *file) 427{ 428 struct userfaultfd_ctx *ctx = file->private_data; 429 struct mm_struct *mm = ctx->mm; 430 struct vm_area_struct *vma, *prev; 431 /* len == 0 means wake all */ 432 struct userfaultfd_wake_range range = { .len = 0, }; 433 unsigned long new_flags; 434 435 ACCESS_ONCE(ctx->released) = true; 436 437 /* 438 * Flush page faults out of all CPUs. NOTE: all page faults 439 * must be retried without returning VM_FAULT_SIGBUS if 440 * userfaultfd_ctx_get() succeeds but vma->vma_userfault_ctx 441 * changes while handle_userfault released the mmap_sem. So 442 * it's critical that released is set to true (above), before 443 * taking the mmap_sem for writing. 444 */ 445 down_write(&mm->mmap_sem); 446 prev = NULL; 447 for (vma = mm->mmap; vma; vma = vma->vm_next) { 448 cond_resched(); 449 BUG_ON(!!vma->vm_userfaultfd_ctx.ctx ^ 450 !!(vma->vm_flags & (VM_UFFD_MISSING | VM_UFFD_WP))); 451 if (vma->vm_userfaultfd_ctx.ctx != ctx) { 452 prev = vma; 453 continue; 454 } 455 new_flags = vma->vm_flags & ~(VM_UFFD_MISSING | VM_UFFD_WP); 456 prev = vma_merge(mm, prev, vma->vm_start, vma->vm_end, 457 new_flags, vma->anon_vma, 458 vma->vm_file, vma->vm_pgoff, 459 vma_policy(vma), 460 NULL_VM_UFFD_CTX); 461 if (prev) 462 vma = prev; 463 else 464 prev = vma; 465 vma->vm_flags = new_flags; 466 vma->vm_userfaultfd_ctx = NULL_VM_UFFD_CTX; 467 } 468 up_write(&mm->mmap_sem); 469 470 /* 471 * After no new page faults can wait on this fault_*wqh, flush 472 * the last page faults that may have been already waiting on 473 * the fault_*wqh. 474 */ 475 spin_lock(&ctx->fault_pending_wqh.lock); 476 __wake_up_locked_key(&ctx->fault_pending_wqh, TASK_NORMAL, &range); 477 __wake_up_locked_key(&ctx->fault_wqh, TASK_NORMAL, &range); 478 spin_unlock(&ctx->fault_pending_wqh.lock); 479 480 wake_up_poll(&ctx->fd_wqh, POLLHUP); 481 userfaultfd_ctx_put(ctx); 482 return 0; 483} 484 485/* fault_pending_wqh.lock must be hold by the caller */ 486static inline struct userfaultfd_wait_queue *find_userfault( 487 struct userfaultfd_ctx *ctx) 488{ 489 wait_queue_t *wq; 490 struct userfaultfd_wait_queue *uwq; 491 492 VM_BUG_ON(!spin_is_locked(&ctx->fault_pending_wqh.lock)); 493 494 uwq = NULL; 495 if (!waitqueue_active(&ctx->fault_pending_wqh)) 496 goto out; 497 /* walk in reverse to provide FIFO behavior to read userfaults */ 498 wq = list_last_entry(&ctx->fault_pending_wqh.task_list, 499 typeof(*wq), task_list); 500 uwq = container_of(wq, struct userfaultfd_wait_queue, wq); 501out: 502 return uwq; 503} 504 505static unsigned int userfaultfd_poll(struct file *file, poll_table *wait) 506{ 507 struct userfaultfd_ctx *ctx = file->private_data; 508 unsigned int ret; 509 510 poll_wait(file, &ctx->fd_wqh, wait); 511 512 switch (ctx->state) { 513 case UFFD_STATE_WAIT_API: 514 return POLLERR; 515 case UFFD_STATE_RUNNING: 516 /* 517 * poll() never guarantees that read won't block. 518 * userfaults can be waken before they're read(). 519 */ 520 if (unlikely(!(file->f_flags & O_NONBLOCK))) 521 return POLLERR; 522 /* 523 * lockless access to see if there are pending faults 524 * __pollwait last action is the add_wait_queue but 525 * the spin_unlock would allow the waitqueue_active to 526 * pass above the actual list_add inside 527 * add_wait_queue critical section. So use a full 528 * memory barrier to serialize the list_add write of 529 * add_wait_queue() with the waitqueue_active read 530 * below. 531 */ 532 ret = 0; 533 smp_mb(); 534 if (waitqueue_active(&ctx->fault_pending_wqh)) 535 ret = POLLIN; 536 return ret; 537 default: 538 BUG(); 539 } 540} 541 542static ssize_t userfaultfd_ctx_read(struct userfaultfd_ctx *ctx, int no_wait, 543 struct uffd_msg *msg) 544{ 545 ssize_t ret; 546 DECLARE_WAITQUEUE(wait, current); 547 struct userfaultfd_wait_queue *uwq; 548 549 /* always take the fd_wqh lock before the fault_pending_wqh lock */ 550 spin_lock(&ctx->fd_wqh.lock); 551 __add_wait_queue(&ctx->fd_wqh, &wait); 552 for (;;) { 553 set_current_state(TASK_INTERRUPTIBLE); 554 spin_lock(&ctx->fault_pending_wqh.lock); 555 uwq = find_userfault(ctx); 556 if (uwq) { 557 /* 558 * Use a seqcount to repeat the lockless check 559 * in wake_userfault() to avoid missing 560 * wakeups because during the refile both 561 * waitqueue could become empty if this is the 562 * only userfault. 563 */ 564 write_seqcount_begin(&ctx->refile_seq); 565 566 /* 567 * The fault_pending_wqh.lock prevents the uwq 568 * to disappear from under us. 569 * 570 * Refile this userfault from 571 * fault_pending_wqh to fault_wqh, it's not 572 * pending anymore after we read it. 573 * 574 * Use list_del() by hand (as 575 * userfaultfd_wake_function also uses 576 * list_del_init() by hand) to be sure nobody 577 * changes __remove_wait_queue() to use 578 * list_del_init() in turn breaking the 579 * !list_empty_careful() check in 580 * handle_userfault(). The uwq->wq.task_list 581 * must never be empty at any time during the 582 * refile, or the waitqueue could disappear 583 * from under us. The "wait_queue_head_t" 584 * parameter of __remove_wait_queue() is unused 585 * anyway. 586 */ 587 list_del(&uwq->wq.task_list); 588 __add_wait_queue(&ctx->fault_wqh, &uwq->wq); 589 590 write_seqcount_end(&ctx->refile_seq); 591 592 /* careful to always initialize msg if ret == 0 */ 593 *msg = uwq->msg; 594 spin_unlock(&ctx->fault_pending_wqh.lock); 595 ret = 0; 596 break; 597 } 598 spin_unlock(&ctx->fault_pending_wqh.lock); 599 if (signal_pending(current)) { 600 ret = -ERESTARTSYS; 601 break; 602 } 603 if (no_wait) { 604 ret = -EAGAIN; 605 break; 606 } 607 spin_unlock(&ctx->fd_wqh.lock); 608 schedule(); 609 spin_lock(&ctx->fd_wqh.lock); 610 } 611 __remove_wait_queue(&ctx->fd_wqh, &wait); 612 __set_current_state(TASK_RUNNING); 613 spin_unlock(&ctx->fd_wqh.lock); 614 615 return ret; 616} 617 618static ssize_t userfaultfd_read(struct file *file, char __user *buf, 619 size_t count, loff_t *ppos) 620{ 621 struct userfaultfd_ctx *ctx = file->private_data; 622 ssize_t _ret, ret = 0; 623 struct uffd_msg msg; 624 int no_wait = file->f_flags & O_NONBLOCK; 625 626 if (ctx->state == UFFD_STATE_WAIT_API) 627 return -EINVAL; 628 629 for (;;) { 630 if (count < sizeof(msg)) 631 return ret ? ret : -EINVAL; 632 _ret = userfaultfd_ctx_read(ctx, no_wait, &msg); 633 if (_ret < 0) 634 return ret ? ret : _ret; 635 if (copy_to_user((__u64 __user *) buf, &msg, sizeof(msg))) 636 return ret ? ret : -EFAULT; 637 ret += sizeof(msg); 638 buf += sizeof(msg); 639 count -= sizeof(msg); 640 /* 641 * Allow to read more than one fault at time but only 642 * block if waiting for the very first one. 643 */ 644 no_wait = O_NONBLOCK; 645 } 646} 647 648static void __wake_userfault(struct userfaultfd_ctx *ctx, 649 struct userfaultfd_wake_range *range) 650{ 651 unsigned long start, end; 652 653 start = range->start; 654 end = range->start + range->len; 655 656 spin_lock(&ctx->fault_pending_wqh.lock); 657 /* wake all in the range and autoremove */ 658 if (waitqueue_active(&ctx->fault_pending_wqh)) 659 __wake_up_locked_key(&ctx->fault_pending_wqh, TASK_NORMAL, 660 range); 661 if (waitqueue_active(&ctx->fault_wqh)) 662 __wake_up_locked_key(&ctx->fault_wqh, TASK_NORMAL, range); 663 spin_unlock(&ctx->fault_pending_wqh.lock); 664} 665 666static __always_inline void wake_userfault(struct userfaultfd_ctx *ctx, 667 struct userfaultfd_wake_range *range) 668{ 669 unsigned seq; 670 bool need_wakeup; 671 672 /* 673 * To be sure waitqueue_active() is not reordered by the CPU 674 * before the pagetable update, use an explicit SMP memory 675 * barrier here. PT lock release or up_read(mmap_sem) still 676 * have release semantics that can allow the 677 * waitqueue_active() to be reordered before the pte update. 678 */ 679 smp_mb(); 680 681 /* 682 * Use waitqueue_active because it's very frequent to 683 * change the address space atomically even if there are no 684 * userfaults yet. So we take the spinlock only when we're 685 * sure we've userfaults to wake. 686 */ 687 do { 688 seq = read_seqcount_begin(&ctx->refile_seq); 689 need_wakeup = waitqueue_active(&ctx->fault_pending_wqh) || 690 waitqueue_active(&ctx->fault_wqh); 691 cond_resched(); 692 } while (read_seqcount_retry(&ctx->refile_seq, seq)); 693 if (need_wakeup) 694 __wake_userfault(ctx, range); 695} 696 697static __always_inline int validate_range(struct mm_struct *mm, 698 __u64 start, __u64 len) 699{ 700 __u64 task_size = mm->task_size; 701 702 if (start & ~PAGE_MASK) 703 return -EINVAL; 704 if (len & ~PAGE_MASK) 705 return -EINVAL; 706 if (!len) 707 return -EINVAL; 708 if (start < mmap_min_addr) 709 return -EINVAL; 710 if (start >= task_size) 711 return -EINVAL; 712 if (len > task_size - start) 713 return -EINVAL; 714 return 0; 715} 716 717static int userfaultfd_register(struct userfaultfd_ctx *ctx, 718 unsigned long arg) 719{ 720 struct mm_struct *mm = ctx->mm; 721 struct vm_area_struct *vma, *prev, *cur; 722 int ret; 723 struct uffdio_register uffdio_register; 724 struct uffdio_register __user *user_uffdio_register; 725 unsigned long vm_flags, new_flags; 726 bool found; 727 unsigned long start, end, vma_end; 728 729 user_uffdio_register = (struct uffdio_register __user *) arg; 730 731 ret = -EFAULT; 732 if (copy_from_user(&uffdio_register, user_uffdio_register, 733 sizeof(uffdio_register)-sizeof(__u64))) 734 goto out; 735 736 ret = -EINVAL; 737 if (!uffdio_register.mode) 738 goto out; 739 if (uffdio_register.mode & ~(UFFDIO_REGISTER_MODE_MISSING| 740 UFFDIO_REGISTER_MODE_WP)) 741 goto out; 742 vm_flags = 0; 743 if (uffdio_register.mode & UFFDIO_REGISTER_MODE_MISSING) 744 vm_flags |= VM_UFFD_MISSING; 745 if (uffdio_register.mode & UFFDIO_REGISTER_MODE_WP) { 746 vm_flags |= VM_UFFD_WP; 747 /* 748 * FIXME: remove the below error constraint by 749 * implementing the wprotect tracking mode. 750 */ 751 ret = -EINVAL; 752 goto out; 753 } 754 755 ret = validate_range(mm, uffdio_register.range.start, 756 uffdio_register.range.len); 757 if (ret) 758 goto out; 759 760 start = uffdio_register.range.start; 761 end = start + uffdio_register.range.len; 762 763 down_write(&mm->mmap_sem); 764 vma = find_vma_prev(mm, start, &prev); 765 766 ret = -ENOMEM; 767 if (!vma) 768 goto out_unlock; 769 770 /* check that there's at least one vma in the range */ 771 ret = -EINVAL; 772 if (vma->vm_start >= end) 773 goto out_unlock; 774 775 /* 776 * Search for not compatible vmas. 777 * 778 * FIXME: this shall be relaxed later so that it doesn't fail 779 * on tmpfs backed vmas (in addition to the current allowance 780 * on anonymous vmas). 781 */ 782 found = false; 783 for (cur = vma; cur && cur->vm_start < end; cur = cur->vm_next) { 784 cond_resched(); 785 786 BUG_ON(!!cur->vm_userfaultfd_ctx.ctx ^ 787 !!(cur->vm_flags & (VM_UFFD_MISSING | VM_UFFD_WP))); 788 789 /* check not compatible vmas */ 790 ret = -EINVAL; 791 if (cur->vm_ops) 792 goto out_unlock; 793 794 /* 795 * Check that this vma isn't already owned by a 796 * different userfaultfd. We can't allow more than one 797 * userfaultfd to own a single vma simultaneously or we 798 * wouldn't know which one to deliver the userfaults to. 799 */ 800 ret = -EBUSY; 801 if (cur->vm_userfaultfd_ctx.ctx && 802 cur->vm_userfaultfd_ctx.ctx != ctx) 803 goto out_unlock; 804 805 found = true; 806 } 807 BUG_ON(!found); 808 809 if (vma->vm_start < start) 810 prev = vma; 811 812 ret = 0; 813 do { 814 cond_resched(); 815 816 BUG_ON(vma->vm_ops); 817 BUG_ON(vma->vm_userfaultfd_ctx.ctx && 818 vma->vm_userfaultfd_ctx.ctx != ctx); 819 820 /* 821 * Nothing to do: this vma is already registered into this 822 * userfaultfd and with the right tracking mode too. 823 */ 824 if (vma->vm_userfaultfd_ctx.ctx == ctx && 825 (vma->vm_flags & vm_flags) == vm_flags) 826 goto skip; 827 828 if (vma->vm_start > start) 829 start = vma->vm_start; 830 vma_end = min(end, vma->vm_end); 831 832 new_flags = (vma->vm_flags & ~vm_flags) | vm_flags; 833 prev = vma_merge(mm, prev, start, vma_end, new_flags, 834 vma->anon_vma, vma->vm_file, vma->vm_pgoff, 835 vma_policy(vma), 836 ((struct vm_userfaultfd_ctx){ ctx })); 837 if (prev) { 838 vma = prev; 839 goto next; 840 } 841 if (vma->vm_start < start) { 842 ret = split_vma(mm, vma, start, 1); 843 if (ret) 844 break; 845 } 846 if (vma->vm_end > end) { 847 ret = split_vma(mm, vma, end, 0); 848 if (ret) 849 break; 850 } 851 next: 852 /* 853 * In the vma_merge() successful mprotect-like case 8: 854 * the next vma was merged into the current one and 855 * the current one has not been updated yet. 856 */ 857 vma->vm_flags = new_flags; 858 vma->vm_userfaultfd_ctx.ctx = ctx; 859 860 skip: 861 prev = vma; 862 start = vma->vm_end; 863 vma = vma->vm_next; 864 } while (vma && vma->vm_start < end); 865out_unlock: 866 up_write(&mm->mmap_sem); 867 if (!ret) { 868 /* 869 * Now that we scanned all vmas we can already tell 870 * userland which ioctls methods are guaranteed to 871 * succeed on this range. 872 */ 873 if (put_user(UFFD_API_RANGE_IOCTLS, 874 &user_uffdio_register->ioctls)) 875 ret = -EFAULT; 876 } 877out: 878 return ret; 879} 880 881static int userfaultfd_unregister(struct userfaultfd_ctx *ctx, 882 unsigned long arg) 883{ 884 struct mm_struct *mm = ctx->mm; 885 struct vm_area_struct *vma, *prev, *cur; 886 int ret; 887 struct uffdio_range uffdio_unregister; 888 unsigned long new_flags; 889 bool found; 890 unsigned long start, end, vma_end; 891 const void __user *buf = (void __user *)arg; 892 893 ret = -EFAULT; 894 if (copy_from_user(&uffdio_unregister, buf, sizeof(uffdio_unregister))) 895 goto out; 896 897 ret = validate_range(mm, uffdio_unregister.start, 898 uffdio_unregister.len); 899 if (ret) 900 goto out; 901 902 start = uffdio_unregister.start; 903 end = start + uffdio_unregister.len; 904 905 down_write(&mm->mmap_sem); 906 vma = find_vma_prev(mm, start, &prev); 907 908 ret = -ENOMEM; 909 if (!vma) 910 goto out_unlock; 911 912 /* check that there's at least one vma in the range */ 913 ret = -EINVAL; 914 if (vma->vm_start >= end) 915 goto out_unlock; 916 917 /* 918 * Search for not compatible vmas. 919 * 920 * FIXME: this shall be relaxed later so that it doesn't fail 921 * on tmpfs backed vmas (in addition to the current allowance 922 * on anonymous vmas). 923 */ 924 found = false; 925 ret = -EINVAL; 926 for (cur = vma; cur && cur->vm_start < end; cur = cur->vm_next) { 927 cond_resched(); 928 929 BUG_ON(!!cur->vm_userfaultfd_ctx.ctx ^ 930 !!(cur->vm_flags & (VM_UFFD_MISSING | VM_UFFD_WP))); 931 932 /* 933 * Check not compatible vmas, not strictly required 934 * here as not compatible vmas cannot have an 935 * userfaultfd_ctx registered on them, but this 936 * provides for more strict behavior to notice 937 * unregistration errors. 938 */ 939 if (cur->vm_ops) 940 goto out_unlock; 941 942 found = true; 943 } 944 BUG_ON(!found); 945 946 if (vma->vm_start < start) 947 prev = vma; 948 949 ret = 0; 950 do { 951 cond_resched(); 952 953 BUG_ON(vma->vm_ops); 954 955 /* 956 * Nothing to do: this vma is already registered into this 957 * userfaultfd and with the right tracking mode too. 958 */ 959 if (!vma->vm_userfaultfd_ctx.ctx) 960 goto skip; 961 962 if (vma->vm_start > start) 963 start = vma->vm_start; 964 vma_end = min(end, vma->vm_end); 965 966 new_flags = vma->vm_flags & ~(VM_UFFD_MISSING | VM_UFFD_WP); 967 prev = vma_merge(mm, prev, start, vma_end, new_flags, 968 vma->anon_vma, vma->vm_file, vma->vm_pgoff, 969 vma_policy(vma), 970 NULL_VM_UFFD_CTX); 971 if (prev) { 972 vma = prev; 973 goto next; 974 } 975 if (vma->vm_start < start) { 976 ret = split_vma(mm, vma, start, 1); 977 if (ret) 978 break; 979 } 980 if (vma->vm_end > end) { 981 ret = split_vma(mm, vma, end, 0); 982 if (ret) 983 break; 984 } 985 next: 986 /* 987 * In the vma_merge() successful mprotect-like case 8: 988 * the next vma was merged into the current one and 989 * the current one has not been updated yet. 990 */ 991 vma->vm_flags = new_flags; 992 vma->vm_userfaultfd_ctx = NULL_VM_UFFD_CTX; 993 994 skip: 995 prev = vma; 996 start = vma->vm_end; 997 vma = vma->vm_next; 998 } while (vma && vma->vm_start < end); 999out_unlock: 1000 up_write(&mm->mmap_sem); 1001out: 1002 return ret; 1003} 1004 1005/* 1006 * userfaultfd_wake may be used in combination with the 1007 * UFFDIO_*_MODE_DONTWAKE to wakeup userfaults in batches. 1008 */ 1009static int userfaultfd_wake(struct userfaultfd_ctx *ctx, 1010 unsigned long arg) 1011{ 1012 int ret; 1013 struct uffdio_range uffdio_wake; 1014 struct userfaultfd_wake_range range; 1015 const void __user *buf = (void __user *)arg; 1016 1017 ret = -EFAULT; 1018 if (copy_from_user(&uffdio_wake, buf, sizeof(uffdio_wake))) 1019 goto out; 1020 1021 ret = validate_range(ctx->mm, uffdio_wake.start, uffdio_wake.len); 1022 if (ret) 1023 goto out; 1024 1025 range.start = uffdio_wake.start; 1026 range.len = uffdio_wake.len; 1027 1028 /* 1029 * len == 0 means wake all and we don't want to wake all here, 1030 * so check it again to be sure. 1031 */ 1032 VM_BUG_ON(!range.len); 1033 1034 wake_userfault(ctx, &range); 1035 ret = 0; 1036 1037out: 1038 return ret; 1039} 1040 1041static int userfaultfd_copy(struct userfaultfd_ctx *ctx, 1042 unsigned long arg) 1043{ 1044 __s64 ret; 1045 struct uffdio_copy uffdio_copy; 1046 struct uffdio_copy __user *user_uffdio_copy; 1047 struct userfaultfd_wake_range range; 1048 1049 user_uffdio_copy = (struct uffdio_copy __user *) arg; 1050 1051 ret = -EFAULT; 1052 if (copy_from_user(&uffdio_copy, user_uffdio_copy, 1053 /* don't copy "copy" last field */ 1054 sizeof(uffdio_copy)-sizeof(__s64))) 1055 goto out; 1056 1057 ret = validate_range(ctx->mm, uffdio_copy.dst, uffdio_copy.len); 1058 if (ret) 1059 goto out; 1060 /* 1061 * double check for wraparound just in case. copy_from_user() 1062 * will later check uffdio_copy.src + uffdio_copy.len to fit 1063 * in the userland range. 1064 */ 1065 ret = -EINVAL; 1066 if (uffdio_copy.src + uffdio_copy.len <= uffdio_copy.src) 1067 goto out; 1068 if (uffdio_copy.mode & ~UFFDIO_COPY_MODE_DONTWAKE) 1069 goto out; 1070 1071 ret = mcopy_atomic(ctx->mm, uffdio_copy.dst, uffdio_copy.src, 1072 uffdio_copy.len); 1073 if (unlikely(put_user(ret, &user_uffdio_copy->copy))) 1074 return -EFAULT; 1075 if (ret < 0) 1076 goto out; 1077 BUG_ON(!ret); 1078 /* len == 0 would wake all */ 1079 range.len = ret; 1080 if (!(uffdio_copy.mode & UFFDIO_COPY_MODE_DONTWAKE)) { 1081 range.start = uffdio_copy.dst; 1082 wake_userfault(ctx, &range); 1083 } 1084 ret = range.len == uffdio_copy.len ? 0 : -EAGAIN; 1085out: 1086 return ret; 1087} 1088 1089static int userfaultfd_zeropage(struct userfaultfd_ctx *ctx, 1090 unsigned long arg) 1091{ 1092 __s64 ret; 1093 struct uffdio_zeropage uffdio_zeropage; 1094 struct uffdio_zeropage __user *user_uffdio_zeropage; 1095 struct userfaultfd_wake_range range; 1096 1097 user_uffdio_zeropage = (struct uffdio_zeropage __user *) arg; 1098 1099 ret = -EFAULT; 1100 if (copy_from_user(&uffdio_zeropage, user_uffdio_zeropage, 1101 /* don't copy "zeropage" last field */ 1102 sizeof(uffdio_zeropage)-sizeof(__s64))) 1103 goto out; 1104 1105 ret = validate_range(ctx->mm, uffdio_zeropage.range.start, 1106 uffdio_zeropage.range.len); 1107 if (ret) 1108 goto out; 1109 ret = -EINVAL; 1110 if (uffdio_zeropage.mode & ~UFFDIO_ZEROPAGE_MODE_DONTWAKE) 1111 goto out; 1112 1113 ret = mfill_zeropage(ctx->mm, uffdio_zeropage.range.start, 1114 uffdio_zeropage.range.len); 1115 if (unlikely(put_user(ret, &user_uffdio_zeropage->zeropage))) 1116 return -EFAULT; 1117 if (ret < 0) 1118 goto out; 1119 /* len == 0 would wake all */ 1120 BUG_ON(!ret); 1121 range.len = ret; 1122 if (!(uffdio_zeropage.mode & UFFDIO_ZEROPAGE_MODE_DONTWAKE)) { 1123 range.start = uffdio_zeropage.range.start; 1124 wake_userfault(ctx, &range); 1125 } 1126 ret = range.len == uffdio_zeropage.range.len ? 0 : -EAGAIN; 1127out: 1128 return ret; 1129} 1130 1131/* 1132 * userland asks for a certain API version and we return which bits 1133 * and ioctl commands are implemented in this kernel for such API 1134 * version or -EINVAL if unknown. 1135 */ 1136static int userfaultfd_api(struct userfaultfd_ctx *ctx, 1137 unsigned long arg) 1138{ 1139 struct uffdio_api uffdio_api; 1140 void __user *buf = (void __user *)arg; 1141 int ret; 1142 1143 ret = -EINVAL; 1144 if (ctx->state != UFFD_STATE_WAIT_API) 1145 goto out; 1146 ret = -EFAULT; 1147 if (copy_from_user(&uffdio_api, buf, sizeof(uffdio_api))) 1148 goto out; 1149 if (uffdio_api.api != UFFD_API || uffdio_api.features) { 1150 memset(&uffdio_api, 0, sizeof(uffdio_api)); 1151 if (copy_to_user(buf, &uffdio_api, sizeof(uffdio_api))) 1152 goto out; 1153 ret = -EINVAL; 1154 goto out; 1155 } 1156 uffdio_api.features = UFFD_API_FEATURES; 1157 uffdio_api.ioctls = UFFD_API_IOCTLS; 1158 ret = -EFAULT; 1159 if (copy_to_user(buf, &uffdio_api, sizeof(uffdio_api))) 1160 goto out; 1161 ctx->state = UFFD_STATE_RUNNING; 1162 ret = 0; 1163out: 1164 return ret; 1165} 1166 1167static long userfaultfd_ioctl(struct file *file, unsigned cmd, 1168 unsigned long arg) 1169{ 1170 int ret = -EINVAL; 1171 struct userfaultfd_ctx *ctx = file->private_data; 1172 1173 if (cmd != UFFDIO_API && ctx->state == UFFD_STATE_WAIT_API) 1174 return -EINVAL; 1175 1176 switch(cmd) { 1177 case UFFDIO_API: 1178 ret = userfaultfd_api(ctx, arg); 1179 break; 1180 case UFFDIO_REGISTER: 1181 ret = userfaultfd_register(ctx, arg); 1182 break; 1183 case UFFDIO_UNREGISTER: 1184 ret = userfaultfd_unregister(ctx, arg); 1185 break; 1186 case UFFDIO_WAKE: 1187 ret = userfaultfd_wake(ctx, arg); 1188 break; 1189 case UFFDIO_COPY: 1190 ret = userfaultfd_copy(ctx, arg); 1191 break; 1192 case UFFDIO_ZEROPAGE: 1193 ret = userfaultfd_zeropage(ctx, arg); 1194 break; 1195 } 1196 return ret; 1197} 1198 1199#ifdef CONFIG_PROC_FS 1200static void userfaultfd_show_fdinfo(struct seq_file *m, struct file *f) 1201{ 1202 struct userfaultfd_ctx *ctx = f->private_data; 1203 wait_queue_t *wq; 1204 struct userfaultfd_wait_queue *uwq; 1205 unsigned long pending = 0, total = 0; 1206 1207 spin_lock(&ctx->fault_pending_wqh.lock); 1208 list_for_each_entry(wq, &ctx->fault_pending_wqh.task_list, task_list) { 1209 uwq = container_of(wq, struct userfaultfd_wait_queue, wq); 1210 pending++; 1211 total++; 1212 } 1213 list_for_each_entry(wq, &ctx->fault_wqh.task_list, task_list) { 1214 uwq = container_of(wq, struct userfaultfd_wait_queue, wq); 1215 total++; 1216 } 1217 spin_unlock(&ctx->fault_pending_wqh.lock); 1218 1219 /* 1220 * If more protocols will be added, there will be all shown 1221 * separated by a space. Like this: 1222 * protocols: aa:... bb:... 1223 */ 1224 seq_printf(m, "pending:\t%lu\ntotal:\t%lu\nAPI:\t%Lx:%x:%Lx\n", 1225 pending, total, UFFD_API, UFFD_API_FEATURES, 1226 UFFD_API_IOCTLS|UFFD_API_RANGE_IOCTLS); 1227} 1228#endif 1229 1230static const struct file_operations userfaultfd_fops = { 1231#ifdef CONFIG_PROC_FS 1232 .show_fdinfo = userfaultfd_show_fdinfo, 1233#endif 1234 .release = userfaultfd_release, 1235 .poll = userfaultfd_poll, 1236 .read = userfaultfd_read, 1237 .unlocked_ioctl = userfaultfd_ioctl, 1238 .compat_ioctl = userfaultfd_ioctl, 1239 .llseek = noop_llseek, 1240}; 1241 1242static void init_once_userfaultfd_ctx(void *mem) 1243{ 1244 struct userfaultfd_ctx *ctx = (struct userfaultfd_ctx *) mem; 1245 1246 init_waitqueue_head(&ctx->fault_pending_wqh); 1247 init_waitqueue_head(&ctx->fault_wqh); 1248 init_waitqueue_head(&ctx->fd_wqh); 1249 seqcount_init(&ctx->refile_seq); 1250} 1251 1252/** 1253 * userfaultfd_file_create - Creates an userfaultfd file pointer. 1254 * @flags: Flags for the userfaultfd file. 1255 * 1256 * This function creates an userfaultfd file pointer, w/out installing 1257 * it into the fd table. This is useful when the userfaultfd file is 1258 * used during the initialization of data structures that require 1259 * extra setup after the userfaultfd creation. So the userfaultfd 1260 * creation is split into the file pointer creation phase, and the 1261 * file descriptor installation phase. In this way races with 1262 * userspace closing the newly installed file descriptor can be 1263 * avoided. Returns an userfaultfd file pointer, or a proper error 1264 * pointer. 1265 */ 1266static struct file *userfaultfd_file_create(int flags) 1267{ 1268 struct file *file; 1269 struct userfaultfd_ctx *ctx; 1270 1271 BUG_ON(!current->mm); 1272 1273 /* Check the UFFD_* constants for consistency. */ 1274 BUILD_BUG_ON(UFFD_CLOEXEC != O_CLOEXEC); 1275 BUILD_BUG_ON(UFFD_NONBLOCK != O_NONBLOCK); 1276 1277 file = ERR_PTR(-EINVAL); 1278 if (flags & ~UFFD_SHARED_FCNTL_FLAGS) 1279 goto out; 1280 1281 file = ERR_PTR(-ENOMEM); 1282 ctx = kmem_cache_alloc(userfaultfd_ctx_cachep, GFP_KERNEL); 1283 if (!ctx) 1284 goto out; 1285 1286 atomic_set(&ctx->refcount, 1); 1287 ctx->flags = flags; 1288 ctx->state = UFFD_STATE_WAIT_API; 1289 ctx->released = false; 1290 ctx->mm = current->mm; 1291 /* prevent the mm struct to be freed */ 1292 atomic_inc(&ctx->mm->mm_users); 1293 1294 file = anon_inode_getfile("[userfaultfd]", &userfaultfd_fops, ctx, 1295 O_RDWR | (flags & UFFD_SHARED_FCNTL_FLAGS)); 1296 if (IS_ERR(file)) { 1297 mmput(ctx->mm); 1298 kmem_cache_free(userfaultfd_ctx_cachep, ctx); 1299 } 1300out: 1301 return file; 1302} 1303 1304SYSCALL_DEFINE1(userfaultfd, int, flags) 1305{ 1306 int fd, error; 1307 struct file *file; 1308 1309 error = get_unused_fd_flags(flags & UFFD_SHARED_FCNTL_FLAGS); 1310 if (error < 0) 1311 return error; 1312 fd = error; 1313 1314 file = userfaultfd_file_create(flags); 1315 if (IS_ERR(file)) { 1316 error = PTR_ERR(file); 1317 goto err_put_unused_fd; 1318 } 1319 fd_install(fd, file); 1320 1321 return fd; 1322 1323err_put_unused_fd: 1324 put_unused_fd(fd); 1325 1326 return error; 1327} 1328 1329static int __init userfaultfd_init(void) 1330{ 1331 userfaultfd_ctx_cachep = kmem_cache_create("userfaultfd_ctx_cache", 1332 sizeof(struct userfaultfd_ctx), 1333 0, 1334 SLAB_HWCACHE_ALIGN|SLAB_PANIC, 1335 init_once_userfaultfd_ctx); 1336 return 0; 1337} 1338__initcall(userfaultfd_init); 1339