Andrea Arcangeli | 86039bd | 2015-09-04 15:46:31 -0700 | [diff] [blame] | 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 | |
| 30 | enum userfaultfd_state { |
| 31 | UFFD_STATE_WAIT_API, |
| 32 | UFFD_STATE_RUNNING, |
| 33 | }; |
| 34 | |
| 35 | struct userfaultfd_ctx { |
| 36 | /* pseudo fd refcounting */ |
| 37 | atomic_t refcount; |
| 38 | /* waitqueue head for the userfaultfd page faults */ |
| 39 | wait_queue_head_t fault_wqh; |
| 40 | /* waitqueue head for the pseudo fd to wakeup poll/read */ |
| 41 | wait_queue_head_t fd_wqh; |
| 42 | /* userfaultfd syscall flags */ |
| 43 | unsigned int flags; |
| 44 | /* state machine */ |
| 45 | enum userfaultfd_state state; |
| 46 | /* released */ |
| 47 | bool released; |
| 48 | /* mm with one ore more vmas attached to this userfaultfd_ctx */ |
| 49 | struct mm_struct *mm; |
| 50 | }; |
| 51 | |
| 52 | struct userfaultfd_wait_queue { |
Andrea Arcangeli | a9b85f9 | 2015-09-04 15:46:37 -0700 | [diff] [blame^] | 53 | struct uffd_msg msg; |
Andrea Arcangeli | 86039bd | 2015-09-04 15:46:31 -0700 | [diff] [blame] | 54 | wait_queue_t wq; |
| 55 | bool pending; |
| 56 | struct userfaultfd_ctx *ctx; |
| 57 | }; |
| 58 | |
| 59 | struct userfaultfd_wake_range { |
| 60 | unsigned long start; |
| 61 | unsigned long len; |
| 62 | }; |
| 63 | |
| 64 | static int userfaultfd_wake_function(wait_queue_t *wq, unsigned mode, |
| 65 | int wake_flags, void *key) |
| 66 | { |
| 67 | struct userfaultfd_wake_range *range = key; |
| 68 | int ret; |
| 69 | struct userfaultfd_wait_queue *uwq; |
| 70 | unsigned long start, len; |
| 71 | |
| 72 | uwq = container_of(wq, struct userfaultfd_wait_queue, wq); |
| 73 | ret = 0; |
| 74 | /* don't wake the pending ones to avoid reads to block */ |
| 75 | if (uwq->pending && !ACCESS_ONCE(uwq->ctx->released)) |
| 76 | goto out; |
| 77 | /* len == 0 means wake all */ |
| 78 | start = range->start; |
| 79 | len = range->len; |
Andrea Arcangeli | a9b85f9 | 2015-09-04 15:46:37 -0700 | [diff] [blame^] | 80 | if (len && (start > uwq->msg.arg.pagefault.address || |
| 81 | start + len <= uwq->msg.arg.pagefault.address)) |
Andrea Arcangeli | 86039bd | 2015-09-04 15:46:31 -0700 | [diff] [blame] | 82 | goto out; |
| 83 | ret = wake_up_state(wq->private, mode); |
| 84 | if (ret) |
| 85 | /* |
| 86 | * Wake only once, autoremove behavior. |
| 87 | * |
| 88 | * After the effect of list_del_init is visible to the |
| 89 | * other CPUs, the waitqueue may disappear from under |
| 90 | * us, see the !list_empty_careful() in |
| 91 | * handle_userfault(). try_to_wake_up() has an |
| 92 | * implicit smp_mb__before_spinlock, and the |
| 93 | * wq->private is read before calling the extern |
| 94 | * function "wake_up_state" (which in turns calls |
| 95 | * try_to_wake_up). While the spin_lock;spin_unlock; |
| 96 | * wouldn't be enough, the smp_mb__before_spinlock is |
| 97 | * enough to avoid an explicit smp_mb() here. |
| 98 | */ |
| 99 | list_del_init(&wq->task_list); |
| 100 | out: |
| 101 | return ret; |
| 102 | } |
| 103 | |
| 104 | /** |
| 105 | * userfaultfd_ctx_get - Acquires a reference to the internal userfaultfd |
| 106 | * context. |
| 107 | * @ctx: [in] Pointer to the userfaultfd context. |
| 108 | * |
| 109 | * Returns: In case of success, returns not zero. |
| 110 | */ |
| 111 | static void userfaultfd_ctx_get(struct userfaultfd_ctx *ctx) |
| 112 | { |
| 113 | if (!atomic_inc_not_zero(&ctx->refcount)) |
| 114 | BUG(); |
| 115 | } |
| 116 | |
| 117 | /** |
| 118 | * userfaultfd_ctx_put - Releases a reference to the internal userfaultfd |
| 119 | * context. |
| 120 | * @ctx: [in] Pointer to userfaultfd context. |
| 121 | * |
| 122 | * The userfaultfd context reference must have been previously acquired either |
| 123 | * with userfaultfd_ctx_get() or userfaultfd_ctx_fdget(). |
| 124 | */ |
| 125 | static void userfaultfd_ctx_put(struct userfaultfd_ctx *ctx) |
| 126 | { |
| 127 | if (atomic_dec_and_test(&ctx->refcount)) { |
| 128 | VM_BUG_ON(spin_is_locked(&ctx->fault_pending_wqh.lock)); |
| 129 | VM_BUG_ON(waitqueue_active(&ctx->fault_pending_wqh)); |
| 130 | VM_BUG_ON(spin_is_locked(&ctx->fault_wqh.lock)); |
| 131 | VM_BUG_ON(waitqueue_active(&ctx->fault_wqh)); |
| 132 | VM_BUG_ON(spin_is_locked(&ctx->fd_wqh.lock)); |
| 133 | VM_BUG_ON(waitqueue_active(&ctx->fd_wqh)); |
| 134 | mmput(ctx->mm); |
| 135 | kfree(ctx); |
| 136 | } |
| 137 | } |
| 138 | |
Andrea Arcangeli | a9b85f9 | 2015-09-04 15:46:37 -0700 | [diff] [blame^] | 139 | static inline void msg_init(struct uffd_msg *msg) |
Andrea Arcangeli | 86039bd | 2015-09-04 15:46:31 -0700 | [diff] [blame] | 140 | { |
Andrea Arcangeli | a9b85f9 | 2015-09-04 15:46:37 -0700 | [diff] [blame^] | 141 | BUILD_BUG_ON(sizeof(struct uffd_msg) != 32); |
| 142 | /* |
| 143 | * Must use memset to zero out the paddings or kernel data is |
| 144 | * leaked to userland. |
| 145 | */ |
| 146 | memset(msg, 0, sizeof(struct uffd_msg)); |
| 147 | } |
| 148 | |
| 149 | static inline struct uffd_msg userfault_msg(unsigned long address, |
| 150 | unsigned int flags, |
| 151 | unsigned long reason) |
| 152 | { |
| 153 | struct uffd_msg msg; |
| 154 | msg_init(&msg); |
| 155 | msg.event = UFFD_EVENT_PAGEFAULT; |
| 156 | msg.arg.pagefault.address = address; |
Andrea Arcangeli | 86039bd | 2015-09-04 15:46:31 -0700 | [diff] [blame] | 157 | if (flags & FAULT_FLAG_WRITE) |
| 158 | /* |
Andrea Arcangeli | a9b85f9 | 2015-09-04 15:46:37 -0700 | [diff] [blame^] | 159 | * If UFFD_FEATURE_PAGEFAULT_FLAG_WRITE was set in the |
| 160 | * uffdio_api.features and UFFD_PAGEFAULT_FLAG_WRITE |
| 161 | * was not set in a UFFD_EVENT_PAGEFAULT, it means it |
| 162 | * was a read fault, otherwise if set it means it's |
| 163 | * a write fault. |
Andrea Arcangeli | 86039bd | 2015-09-04 15:46:31 -0700 | [diff] [blame] | 164 | */ |
Andrea Arcangeli | a9b85f9 | 2015-09-04 15:46:37 -0700 | [diff] [blame^] | 165 | msg.arg.pagefault.flags |= UFFD_PAGEFAULT_FLAG_WRITE; |
Andrea Arcangeli | 86039bd | 2015-09-04 15:46:31 -0700 | [diff] [blame] | 166 | if (reason & VM_UFFD_WP) |
| 167 | /* |
Andrea Arcangeli | a9b85f9 | 2015-09-04 15:46:37 -0700 | [diff] [blame^] | 168 | * If UFFD_FEATURE_PAGEFAULT_FLAG_WP was set in the |
| 169 | * uffdio_api.features and UFFD_PAGEFAULT_FLAG_WP was |
| 170 | * not set in a UFFD_EVENT_PAGEFAULT, it means it was |
| 171 | * a missing fault, otherwise if set it means it's a |
| 172 | * write protect fault. |
Andrea Arcangeli | 86039bd | 2015-09-04 15:46:31 -0700 | [diff] [blame] | 173 | */ |
Andrea Arcangeli | a9b85f9 | 2015-09-04 15:46:37 -0700 | [diff] [blame^] | 174 | msg.arg.pagefault.flags |= UFFD_PAGEFAULT_FLAG_WP; |
| 175 | return msg; |
Andrea Arcangeli | 86039bd | 2015-09-04 15:46:31 -0700 | [diff] [blame] | 176 | } |
| 177 | |
| 178 | /* |
| 179 | * The locking rules involved in returning VM_FAULT_RETRY depending on |
| 180 | * FAULT_FLAG_ALLOW_RETRY, FAULT_FLAG_RETRY_NOWAIT and |
| 181 | * FAULT_FLAG_KILLABLE are not straightforward. The "Caution" |
| 182 | * recommendation in __lock_page_or_retry is not an understatement. |
| 183 | * |
| 184 | * If FAULT_FLAG_ALLOW_RETRY is set, the mmap_sem must be released |
| 185 | * before returning VM_FAULT_RETRY only if FAULT_FLAG_RETRY_NOWAIT is |
| 186 | * not set. |
| 187 | * |
| 188 | * If FAULT_FLAG_ALLOW_RETRY is set but FAULT_FLAG_KILLABLE is not |
| 189 | * set, VM_FAULT_RETRY can still be returned if and only if there are |
| 190 | * fatal_signal_pending()s, and the mmap_sem must be released before |
| 191 | * returning it. |
| 192 | */ |
| 193 | int handle_userfault(struct vm_area_struct *vma, unsigned long address, |
| 194 | unsigned int flags, unsigned long reason) |
| 195 | { |
| 196 | struct mm_struct *mm = vma->vm_mm; |
| 197 | struct userfaultfd_ctx *ctx; |
| 198 | struct userfaultfd_wait_queue uwq; |
| 199 | |
| 200 | BUG_ON(!rwsem_is_locked(&mm->mmap_sem)); |
| 201 | |
| 202 | ctx = vma->vm_userfaultfd_ctx.ctx; |
| 203 | if (!ctx) |
| 204 | return VM_FAULT_SIGBUS; |
| 205 | |
| 206 | BUG_ON(ctx->mm != mm); |
| 207 | |
| 208 | VM_BUG_ON(reason & ~(VM_UFFD_MISSING|VM_UFFD_WP)); |
| 209 | VM_BUG_ON(!(reason & VM_UFFD_MISSING) ^ !!(reason & VM_UFFD_WP)); |
| 210 | |
| 211 | /* |
| 212 | * If it's already released don't get it. This avoids to loop |
| 213 | * in __get_user_pages if userfaultfd_release waits on the |
| 214 | * caller of handle_userfault to release the mmap_sem. |
| 215 | */ |
| 216 | if (unlikely(ACCESS_ONCE(ctx->released))) |
| 217 | return VM_FAULT_SIGBUS; |
| 218 | |
| 219 | /* |
| 220 | * Check that we can return VM_FAULT_RETRY. |
| 221 | * |
| 222 | * NOTE: it should become possible to return VM_FAULT_RETRY |
| 223 | * even if FAULT_FLAG_TRIED is set without leading to gup() |
| 224 | * -EBUSY failures, if the userfaultfd is to be extended for |
| 225 | * VM_UFFD_WP tracking and we intend to arm the userfault |
| 226 | * without first stopping userland access to the memory. For |
| 227 | * VM_UFFD_MISSING userfaults this is enough for now. |
| 228 | */ |
| 229 | if (unlikely(!(flags & FAULT_FLAG_ALLOW_RETRY))) { |
| 230 | /* |
| 231 | * Validate the invariant that nowait must allow retry |
| 232 | * to be sure not to return SIGBUS erroneously on |
| 233 | * nowait invocations. |
| 234 | */ |
| 235 | BUG_ON(flags & FAULT_FLAG_RETRY_NOWAIT); |
| 236 | #ifdef CONFIG_DEBUG_VM |
| 237 | if (printk_ratelimit()) { |
| 238 | printk(KERN_WARNING |
| 239 | "FAULT_FLAG_ALLOW_RETRY missing %x\n", flags); |
| 240 | dump_stack(); |
| 241 | } |
| 242 | #endif |
| 243 | return VM_FAULT_SIGBUS; |
| 244 | } |
| 245 | |
| 246 | /* |
| 247 | * Handle nowait, not much to do other than tell it to retry |
| 248 | * and wait. |
| 249 | */ |
| 250 | if (flags & FAULT_FLAG_RETRY_NOWAIT) |
| 251 | return VM_FAULT_RETRY; |
| 252 | |
| 253 | /* take the reference before dropping the mmap_sem */ |
| 254 | userfaultfd_ctx_get(ctx); |
| 255 | |
| 256 | /* be gentle and immediately relinquish the mmap_sem */ |
| 257 | up_read(&mm->mmap_sem); |
| 258 | |
| 259 | init_waitqueue_func_entry(&uwq.wq, userfaultfd_wake_function); |
| 260 | uwq.wq.private = current; |
Andrea Arcangeli | a9b85f9 | 2015-09-04 15:46:37 -0700 | [diff] [blame^] | 261 | uwq.msg = userfault_msg(address, flags, reason); |
Andrea Arcangeli | 86039bd | 2015-09-04 15:46:31 -0700 | [diff] [blame] | 262 | uwq.pending = true; |
| 263 | uwq.ctx = ctx; |
| 264 | |
| 265 | spin_lock(&ctx->fault_wqh.lock); |
| 266 | /* |
| 267 | * After the __add_wait_queue the uwq is visible to userland |
| 268 | * through poll/read(). |
| 269 | */ |
| 270 | __add_wait_queue(&ctx->fault_wqh, &uwq.wq); |
| 271 | for (;;) { |
| 272 | set_current_state(TASK_KILLABLE); |
| 273 | if (!uwq.pending || ACCESS_ONCE(ctx->released) || |
| 274 | fatal_signal_pending(current)) |
| 275 | break; |
| 276 | spin_unlock(&ctx->fault_wqh.lock); |
| 277 | |
| 278 | wake_up_poll(&ctx->fd_wqh, POLLIN); |
| 279 | schedule(); |
| 280 | |
| 281 | spin_lock(&ctx->fault_wqh.lock); |
| 282 | } |
| 283 | __remove_wait_queue(&ctx->fault_wqh, &uwq.wq); |
| 284 | __set_current_state(TASK_RUNNING); |
| 285 | spin_unlock(&ctx->fault_wqh.lock); |
| 286 | |
| 287 | /* |
| 288 | * ctx may go away after this if the userfault pseudo fd is |
| 289 | * already released. |
| 290 | */ |
| 291 | userfaultfd_ctx_put(ctx); |
| 292 | |
| 293 | return VM_FAULT_RETRY; |
| 294 | } |
| 295 | |
| 296 | static int userfaultfd_release(struct inode *inode, struct file *file) |
| 297 | { |
| 298 | struct userfaultfd_ctx *ctx = file->private_data; |
| 299 | struct mm_struct *mm = ctx->mm; |
| 300 | struct vm_area_struct *vma, *prev; |
| 301 | /* len == 0 means wake all */ |
| 302 | struct userfaultfd_wake_range range = { .len = 0, }; |
| 303 | unsigned long new_flags; |
| 304 | |
| 305 | ACCESS_ONCE(ctx->released) = true; |
| 306 | |
| 307 | /* |
| 308 | * Flush page faults out of all CPUs. NOTE: all page faults |
| 309 | * must be retried without returning VM_FAULT_SIGBUS if |
| 310 | * userfaultfd_ctx_get() succeeds but vma->vma_userfault_ctx |
| 311 | * changes while handle_userfault released the mmap_sem. So |
| 312 | * it's critical that released is set to true (above), before |
| 313 | * taking the mmap_sem for writing. |
| 314 | */ |
| 315 | down_write(&mm->mmap_sem); |
| 316 | prev = NULL; |
| 317 | for (vma = mm->mmap; vma; vma = vma->vm_next) { |
| 318 | cond_resched(); |
| 319 | BUG_ON(!!vma->vm_userfaultfd_ctx.ctx ^ |
| 320 | !!(vma->vm_flags & (VM_UFFD_MISSING | VM_UFFD_WP))); |
| 321 | if (vma->vm_userfaultfd_ctx.ctx != ctx) { |
| 322 | prev = vma; |
| 323 | continue; |
| 324 | } |
| 325 | new_flags = vma->vm_flags & ~(VM_UFFD_MISSING | VM_UFFD_WP); |
| 326 | prev = vma_merge(mm, prev, vma->vm_start, vma->vm_end, |
| 327 | new_flags, vma->anon_vma, |
| 328 | vma->vm_file, vma->vm_pgoff, |
| 329 | vma_policy(vma), |
| 330 | NULL_VM_UFFD_CTX); |
| 331 | if (prev) |
| 332 | vma = prev; |
| 333 | else |
| 334 | prev = vma; |
| 335 | vma->vm_flags = new_flags; |
| 336 | vma->vm_userfaultfd_ctx = NULL_VM_UFFD_CTX; |
| 337 | } |
| 338 | up_write(&mm->mmap_sem); |
| 339 | |
| 340 | /* |
| 341 | * After no new page faults can wait on this fault_wqh, flush |
| 342 | * the last page faults that may have been already waiting on |
| 343 | * the fault_wqh. |
| 344 | */ |
| 345 | spin_lock(&ctx->fault_wqh.lock); |
| 346 | __wake_up_locked_key(&ctx->fault_wqh, TASK_NORMAL, 0, &range); |
| 347 | spin_unlock(&ctx->fault_wqh.lock); |
| 348 | |
| 349 | wake_up_poll(&ctx->fd_wqh, POLLHUP); |
| 350 | userfaultfd_ctx_put(ctx); |
| 351 | return 0; |
| 352 | } |
| 353 | |
| 354 | /* fault_wqh.lock must be hold by the caller */ |
| 355 | static inline unsigned int find_userfault(struct userfaultfd_ctx *ctx, |
| 356 | struct userfaultfd_wait_queue **uwq) |
| 357 | { |
| 358 | wait_queue_t *wq; |
| 359 | struct userfaultfd_wait_queue *_uwq; |
| 360 | unsigned int ret = 0; |
| 361 | |
| 362 | VM_BUG_ON(!spin_is_locked(&ctx->fault_wqh.lock)); |
| 363 | |
| 364 | list_for_each_entry(wq, &ctx->fault_wqh.task_list, task_list) { |
| 365 | _uwq = container_of(wq, struct userfaultfd_wait_queue, wq); |
| 366 | if (_uwq->pending) { |
| 367 | ret = POLLIN; |
| 368 | if (!uwq) |
| 369 | /* |
| 370 | * If there's at least a pending and |
| 371 | * we don't care which one it is, |
| 372 | * break immediately and leverage the |
| 373 | * efficiency of the LIFO walk. |
| 374 | */ |
| 375 | break; |
| 376 | /* |
| 377 | * If we need to find which one was pending we |
| 378 | * keep walking until we find the first not |
| 379 | * pending one, so we read() them in FIFO order. |
| 380 | */ |
| 381 | *uwq = _uwq; |
| 382 | } else |
| 383 | /* |
| 384 | * break the loop at the first not pending |
| 385 | * one, there cannot be pending userfaults |
| 386 | * after the first not pending one, because |
| 387 | * all new pending ones are inserted at the |
| 388 | * head and we walk it in LIFO. |
| 389 | */ |
| 390 | break; |
| 391 | } |
| 392 | |
| 393 | return ret; |
| 394 | } |
| 395 | |
| 396 | static unsigned int userfaultfd_poll(struct file *file, poll_table *wait) |
| 397 | { |
| 398 | struct userfaultfd_ctx *ctx = file->private_data; |
| 399 | unsigned int ret; |
| 400 | |
| 401 | poll_wait(file, &ctx->fd_wqh, wait); |
| 402 | |
| 403 | switch (ctx->state) { |
| 404 | case UFFD_STATE_WAIT_API: |
| 405 | return POLLERR; |
| 406 | case UFFD_STATE_RUNNING: |
| 407 | spin_lock(&ctx->fault_wqh.lock); |
| 408 | ret = find_userfault(ctx, NULL); |
| 409 | spin_unlock(&ctx->fault_wqh.lock); |
| 410 | return ret; |
| 411 | default: |
| 412 | BUG(); |
| 413 | } |
| 414 | } |
| 415 | |
| 416 | static ssize_t userfaultfd_ctx_read(struct userfaultfd_ctx *ctx, int no_wait, |
Andrea Arcangeli | a9b85f9 | 2015-09-04 15:46:37 -0700 | [diff] [blame^] | 417 | struct uffd_msg *msg) |
Andrea Arcangeli | 86039bd | 2015-09-04 15:46:31 -0700 | [diff] [blame] | 418 | { |
| 419 | ssize_t ret; |
| 420 | DECLARE_WAITQUEUE(wait, current); |
| 421 | struct userfaultfd_wait_queue *uwq = NULL; |
| 422 | |
| 423 | /* always take the fd_wqh lock before the fault_wqh lock */ |
| 424 | spin_lock(&ctx->fd_wqh.lock); |
| 425 | __add_wait_queue(&ctx->fd_wqh, &wait); |
| 426 | for (;;) { |
| 427 | set_current_state(TASK_INTERRUPTIBLE); |
| 428 | spin_lock(&ctx->fault_wqh.lock); |
| 429 | if (find_userfault(ctx, &uwq)) { |
| 430 | /* |
| 431 | * The fault_wqh.lock prevents the uwq to |
| 432 | * disappear from under us. |
| 433 | */ |
| 434 | uwq->pending = false; |
Andrea Arcangeli | a9b85f9 | 2015-09-04 15:46:37 -0700 | [diff] [blame^] | 435 | /* careful to always initialize msg if ret == 0 */ |
| 436 | *msg = uwq->msg; |
Andrea Arcangeli | 86039bd | 2015-09-04 15:46:31 -0700 | [diff] [blame] | 437 | spin_unlock(&ctx->fault_wqh.lock); |
| 438 | ret = 0; |
| 439 | break; |
| 440 | } |
| 441 | spin_unlock(&ctx->fault_wqh.lock); |
| 442 | if (signal_pending(current)) { |
| 443 | ret = -ERESTARTSYS; |
| 444 | break; |
| 445 | } |
| 446 | if (no_wait) { |
| 447 | ret = -EAGAIN; |
| 448 | break; |
| 449 | } |
| 450 | spin_unlock(&ctx->fd_wqh.lock); |
| 451 | schedule(); |
| 452 | spin_lock(&ctx->fd_wqh.lock); |
| 453 | } |
| 454 | __remove_wait_queue(&ctx->fd_wqh, &wait); |
| 455 | __set_current_state(TASK_RUNNING); |
| 456 | spin_unlock(&ctx->fd_wqh.lock); |
| 457 | |
| 458 | return ret; |
| 459 | } |
| 460 | |
| 461 | static ssize_t userfaultfd_read(struct file *file, char __user *buf, |
| 462 | size_t count, loff_t *ppos) |
| 463 | { |
| 464 | struct userfaultfd_ctx *ctx = file->private_data; |
| 465 | ssize_t _ret, ret = 0; |
Andrea Arcangeli | a9b85f9 | 2015-09-04 15:46:37 -0700 | [diff] [blame^] | 466 | struct uffd_msg msg; |
Andrea Arcangeli | 86039bd | 2015-09-04 15:46:31 -0700 | [diff] [blame] | 467 | int no_wait = file->f_flags & O_NONBLOCK; |
| 468 | |
| 469 | if (ctx->state == UFFD_STATE_WAIT_API) |
| 470 | return -EINVAL; |
| 471 | BUG_ON(ctx->state != UFFD_STATE_RUNNING); |
| 472 | |
| 473 | for (;;) { |
Andrea Arcangeli | a9b85f9 | 2015-09-04 15:46:37 -0700 | [diff] [blame^] | 474 | if (count < sizeof(msg)) |
Andrea Arcangeli | 86039bd | 2015-09-04 15:46:31 -0700 | [diff] [blame] | 475 | return ret ? ret : -EINVAL; |
Andrea Arcangeli | a9b85f9 | 2015-09-04 15:46:37 -0700 | [diff] [blame^] | 476 | _ret = userfaultfd_ctx_read(ctx, no_wait, &msg); |
Andrea Arcangeli | 86039bd | 2015-09-04 15:46:31 -0700 | [diff] [blame] | 477 | if (_ret < 0) |
| 478 | return ret ? ret : _ret; |
Andrea Arcangeli | a9b85f9 | 2015-09-04 15:46:37 -0700 | [diff] [blame^] | 479 | if (copy_to_user((__u64 __user *) buf, &msg, sizeof(msg))) |
Andrea Arcangeli | 86039bd | 2015-09-04 15:46:31 -0700 | [diff] [blame] | 480 | return ret ? ret : -EFAULT; |
Andrea Arcangeli | a9b85f9 | 2015-09-04 15:46:37 -0700 | [diff] [blame^] | 481 | ret += sizeof(msg); |
| 482 | buf += sizeof(msg); |
| 483 | count -= sizeof(msg); |
Andrea Arcangeli | 86039bd | 2015-09-04 15:46:31 -0700 | [diff] [blame] | 484 | /* |
| 485 | * Allow to read more than one fault at time but only |
| 486 | * block if waiting for the very first one. |
| 487 | */ |
| 488 | no_wait = O_NONBLOCK; |
| 489 | } |
| 490 | } |
| 491 | |
| 492 | static void __wake_userfault(struct userfaultfd_ctx *ctx, |
| 493 | struct userfaultfd_wake_range *range) |
| 494 | { |
| 495 | unsigned long start, end; |
| 496 | |
| 497 | start = range->start; |
| 498 | end = range->start + range->len; |
| 499 | |
| 500 | spin_lock(&ctx->fault_wqh.lock); |
| 501 | /* wake all in the range and autoremove */ |
| 502 | __wake_up_locked_key(&ctx->fault_wqh, TASK_NORMAL, 0, range); |
| 503 | spin_unlock(&ctx->fault_wqh.lock); |
| 504 | } |
| 505 | |
| 506 | static __always_inline void wake_userfault(struct userfaultfd_ctx *ctx, |
| 507 | struct userfaultfd_wake_range *range) |
| 508 | { |
| 509 | /* |
| 510 | * To be sure waitqueue_active() is not reordered by the CPU |
| 511 | * before the pagetable update, use an explicit SMP memory |
| 512 | * barrier here. PT lock release or up_read(mmap_sem) still |
| 513 | * have release semantics that can allow the |
| 514 | * waitqueue_active() to be reordered before the pte update. |
| 515 | */ |
| 516 | smp_mb(); |
| 517 | |
| 518 | /* |
| 519 | * Use waitqueue_active because it's very frequent to |
| 520 | * change the address space atomically even if there are no |
| 521 | * userfaults yet. So we take the spinlock only when we're |
| 522 | * sure we've userfaults to wake. |
| 523 | */ |
| 524 | if (waitqueue_active(&ctx->fault_wqh)) |
| 525 | __wake_userfault(ctx, range); |
| 526 | } |
| 527 | |
| 528 | static __always_inline int validate_range(struct mm_struct *mm, |
| 529 | __u64 start, __u64 len) |
| 530 | { |
| 531 | __u64 task_size = mm->task_size; |
| 532 | |
| 533 | if (start & ~PAGE_MASK) |
| 534 | return -EINVAL; |
| 535 | if (len & ~PAGE_MASK) |
| 536 | return -EINVAL; |
| 537 | if (!len) |
| 538 | return -EINVAL; |
| 539 | if (start < mmap_min_addr) |
| 540 | return -EINVAL; |
| 541 | if (start >= task_size) |
| 542 | return -EINVAL; |
| 543 | if (len > task_size - start) |
| 544 | return -EINVAL; |
| 545 | return 0; |
| 546 | } |
| 547 | |
| 548 | static int userfaultfd_register(struct userfaultfd_ctx *ctx, |
| 549 | unsigned long arg) |
| 550 | { |
| 551 | struct mm_struct *mm = ctx->mm; |
| 552 | struct vm_area_struct *vma, *prev, *cur; |
| 553 | int ret; |
| 554 | struct uffdio_register uffdio_register; |
| 555 | struct uffdio_register __user *user_uffdio_register; |
| 556 | unsigned long vm_flags, new_flags; |
| 557 | bool found; |
| 558 | unsigned long start, end, vma_end; |
| 559 | |
| 560 | user_uffdio_register = (struct uffdio_register __user *) arg; |
| 561 | |
| 562 | ret = -EFAULT; |
| 563 | if (copy_from_user(&uffdio_register, user_uffdio_register, |
| 564 | sizeof(uffdio_register)-sizeof(__u64))) |
| 565 | goto out; |
| 566 | |
| 567 | ret = -EINVAL; |
| 568 | if (!uffdio_register.mode) |
| 569 | goto out; |
| 570 | if (uffdio_register.mode & ~(UFFDIO_REGISTER_MODE_MISSING| |
| 571 | UFFDIO_REGISTER_MODE_WP)) |
| 572 | goto out; |
| 573 | vm_flags = 0; |
| 574 | if (uffdio_register.mode & UFFDIO_REGISTER_MODE_MISSING) |
| 575 | vm_flags |= VM_UFFD_MISSING; |
| 576 | if (uffdio_register.mode & UFFDIO_REGISTER_MODE_WP) { |
| 577 | vm_flags |= VM_UFFD_WP; |
| 578 | /* |
| 579 | * FIXME: remove the below error constraint by |
| 580 | * implementing the wprotect tracking mode. |
| 581 | */ |
| 582 | ret = -EINVAL; |
| 583 | goto out; |
| 584 | } |
| 585 | |
| 586 | ret = validate_range(mm, uffdio_register.range.start, |
| 587 | uffdio_register.range.len); |
| 588 | if (ret) |
| 589 | goto out; |
| 590 | |
| 591 | start = uffdio_register.range.start; |
| 592 | end = start + uffdio_register.range.len; |
| 593 | |
| 594 | down_write(&mm->mmap_sem); |
| 595 | vma = find_vma_prev(mm, start, &prev); |
| 596 | |
| 597 | ret = -ENOMEM; |
| 598 | if (!vma) |
| 599 | goto out_unlock; |
| 600 | |
| 601 | /* check that there's at least one vma in the range */ |
| 602 | ret = -EINVAL; |
| 603 | if (vma->vm_start >= end) |
| 604 | goto out_unlock; |
| 605 | |
| 606 | /* |
| 607 | * Search for not compatible vmas. |
| 608 | * |
| 609 | * FIXME: this shall be relaxed later so that it doesn't fail |
| 610 | * on tmpfs backed vmas (in addition to the current allowance |
| 611 | * on anonymous vmas). |
| 612 | */ |
| 613 | found = false; |
| 614 | for (cur = vma; cur && cur->vm_start < end; cur = cur->vm_next) { |
| 615 | cond_resched(); |
| 616 | |
| 617 | BUG_ON(!!cur->vm_userfaultfd_ctx.ctx ^ |
| 618 | !!(cur->vm_flags & (VM_UFFD_MISSING | VM_UFFD_WP))); |
| 619 | |
| 620 | /* check not compatible vmas */ |
| 621 | ret = -EINVAL; |
| 622 | if (cur->vm_ops) |
| 623 | goto out_unlock; |
| 624 | |
| 625 | /* |
| 626 | * Check that this vma isn't already owned by a |
| 627 | * different userfaultfd. We can't allow more than one |
| 628 | * userfaultfd to own a single vma simultaneously or we |
| 629 | * wouldn't know which one to deliver the userfaults to. |
| 630 | */ |
| 631 | ret = -EBUSY; |
| 632 | if (cur->vm_userfaultfd_ctx.ctx && |
| 633 | cur->vm_userfaultfd_ctx.ctx != ctx) |
| 634 | goto out_unlock; |
| 635 | |
| 636 | found = true; |
| 637 | } |
| 638 | BUG_ON(!found); |
| 639 | |
| 640 | if (vma->vm_start < start) |
| 641 | prev = vma; |
| 642 | |
| 643 | ret = 0; |
| 644 | do { |
| 645 | cond_resched(); |
| 646 | |
| 647 | BUG_ON(vma->vm_ops); |
| 648 | BUG_ON(vma->vm_userfaultfd_ctx.ctx && |
| 649 | vma->vm_userfaultfd_ctx.ctx != ctx); |
| 650 | |
| 651 | /* |
| 652 | * Nothing to do: this vma is already registered into this |
| 653 | * userfaultfd and with the right tracking mode too. |
| 654 | */ |
| 655 | if (vma->vm_userfaultfd_ctx.ctx == ctx && |
| 656 | (vma->vm_flags & vm_flags) == vm_flags) |
| 657 | goto skip; |
| 658 | |
| 659 | if (vma->vm_start > start) |
| 660 | start = vma->vm_start; |
| 661 | vma_end = min(end, vma->vm_end); |
| 662 | |
| 663 | new_flags = (vma->vm_flags & ~vm_flags) | vm_flags; |
| 664 | prev = vma_merge(mm, prev, start, vma_end, new_flags, |
| 665 | vma->anon_vma, vma->vm_file, vma->vm_pgoff, |
| 666 | vma_policy(vma), |
| 667 | ((struct vm_userfaultfd_ctx){ ctx })); |
| 668 | if (prev) { |
| 669 | vma = prev; |
| 670 | goto next; |
| 671 | } |
| 672 | if (vma->vm_start < start) { |
| 673 | ret = split_vma(mm, vma, start, 1); |
| 674 | if (ret) |
| 675 | break; |
| 676 | } |
| 677 | if (vma->vm_end > end) { |
| 678 | ret = split_vma(mm, vma, end, 0); |
| 679 | if (ret) |
| 680 | break; |
| 681 | } |
| 682 | next: |
| 683 | /* |
| 684 | * In the vma_merge() successful mprotect-like case 8: |
| 685 | * the next vma was merged into the current one and |
| 686 | * the current one has not been updated yet. |
| 687 | */ |
| 688 | vma->vm_flags = new_flags; |
| 689 | vma->vm_userfaultfd_ctx.ctx = ctx; |
| 690 | |
| 691 | skip: |
| 692 | prev = vma; |
| 693 | start = vma->vm_end; |
| 694 | vma = vma->vm_next; |
| 695 | } while (vma && vma->vm_start < end); |
| 696 | out_unlock: |
| 697 | up_write(&mm->mmap_sem); |
| 698 | if (!ret) { |
| 699 | /* |
| 700 | * Now that we scanned all vmas we can already tell |
| 701 | * userland which ioctls methods are guaranteed to |
| 702 | * succeed on this range. |
| 703 | */ |
| 704 | if (put_user(UFFD_API_RANGE_IOCTLS, |
| 705 | &user_uffdio_register->ioctls)) |
| 706 | ret = -EFAULT; |
| 707 | } |
| 708 | out: |
| 709 | return ret; |
| 710 | } |
| 711 | |
| 712 | static int userfaultfd_unregister(struct userfaultfd_ctx *ctx, |
| 713 | unsigned long arg) |
| 714 | { |
| 715 | struct mm_struct *mm = ctx->mm; |
| 716 | struct vm_area_struct *vma, *prev, *cur; |
| 717 | int ret; |
| 718 | struct uffdio_range uffdio_unregister; |
| 719 | unsigned long new_flags; |
| 720 | bool found; |
| 721 | unsigned long start, end, vma_end; |
| 722 | const void __user *buf = (void __user *)arg; |
| 723 | |
| 724 | ret = -EFAULT; |
| 725 | if (copy_from_user(&uffdio_unregister, buf, sizeof(uffdio_unregister))) |
| 726 | goto out; |
| 727 | |
| 728 | ret = validate_range(mm, uffdio_unregister.start, |
| 729 | uffdio_unregister.len); |
| 730 | if (ret) |
| 731 | goto out; |
| 732 | |
| 733 | start = uffdio_unregister.start; |
| 734 | end = start + uffdio_unregister.len; |
| 735 | |
| 736 | down_write(&mm->mmap_sem); |
| 737 | vma = find_vma_prev(mm, start, &prev); |
| 738 | |
| 739 | ret = -ENOMEM; |
| 740 | if (!vma) |
| 741 | goto out_unlock; |
| 742 | |
| 743 | /* check that there's at least one vma in the range */ |
| 744 | ret = -EINVAL; |
| 745 | if (vma->vm_start >= end) |
| 746 | goto out_unlock; |
| 747 | |
| 748 | /* |
| 749 | * Search for not compatible vmas. |
| 750 | * |
| 751 | * FIXME: this shall be relaxed later so that it doesn't fail |
| 752 | * on tmpfs backed vmas (in addition to the current allowance |
| 753 | * on anonymous vmas). |
| 754 | */ |
| 755 | found = false; |
| 756 | ret = -EINVAL; |
| 757 | for (cur = vma; cur && cur->vm_start < end; cur = cur->vm_next) { |
| 758 | cond_resched(); |
| 759 | |
| 760 | BUG_ON(!!cur->vm_userfaultfd_ctx.ctx ^ |
| 761 | !!(cur->vm_flags & (VM_UFFD_MISSING | VM_UFFD_WP))); |
| 762 | |
| 763 | /* |
| 764 | * Check not compatible vmas, not strictly required |
| 765 | * here as not compatible vmas cannot have an |
| 766 | * userfaultfd_ctx registered on them, but this |
| 767 | * provides for more strict behavior to notice |
| 768 | * unregistration errors. |
| 769 | */ |
| 770 | if (cur->vm_ops) |
| 771 | goto out_unlock; |
| 772 | |
| 773 | found = true; |
| 774 | } |
| 775 | BUG_ON(!found); |
| 776 | |
| 777 | if (vma->vm_start < start) |
| 778 | prev = vma; |
| 779 | |
| 780 | ret = 0; |
| 781 | do { |
| 782 | cond_resched(); |
| 783 | |
| 784 | BUG_ON(vma->vm_ops); |
| 785 | |
| 786 | /* |
| 787 | * Nothing to do: this vma is already registered into this |
| 788 | * userfaultfd and with the right tracking mode too. |
| 789 | */ |
| 790 | if (!vma->vm_userfaultfd_ctx.ctx) |
| 791 | goto skip; |
| 792 | |
| 793 | if (vma->vm_start > start) |
| 794 | start = vma->vm_start; |
| 795 | vma_end = min(end, vma->vm_end); |
| 796 | |
| 797 | new_flags = vma->vm_flags & ~(VM_UFFD_MISSING | VM_UFFD_WP); |
| 798 | prev = vma_merge(mm, prev, start, vma_end, new_flags, |
| 799 | vma->anon_vma, vma->vm_file, vma->vm_pgoff, |
| 800 | vma_policy(vma), |
| 801 | NULL_VM_UFFD_CTX); |
| 802 | if (prev) { |
| 803 | vma = prev; |
| 804 | goto next; |
| 805 | } |
| 806 | if (vma->vm_start < start) { |
| 807 | ret = split_vma(mm, vma, start, 1); |
| 808 | if (ret) |
| 809 | break; |
| 810 | } |
| 811 | if (vma->vm_end > end) { |
| 812 | ret = split_vma(mm, vma, end, 0); |
| 813 | if (ret) |
| 814 | break; |
| 815 | } |
| 816 | next: |
| 817 | /* |
| 818 | * In the vma_merge() successful mprotect-like case 8: |
| 819 | * the next vma was merged into the current one and |
| 820 | * the current one has not been updated yet. |
| 821 | */ |
| 822 | vma->vm_flags = new_flags; |
| 823 | vma->vm_userfaultfd_ctx = NULL_VM_UFFD_CTX; |
| 824 | |
| 825 | skip: |
| 826 | prev = vma; |
| 827 | start = vma->vm_end; |
| 828 | vma = vma->vm_next; |
| 829 | } while (vma && vma->vm_start < end); |
| 830 | out_unlock: |
| 831 | up_write(&mm->mmap_sem); |
| 832 | out: |
| 833 | return ret; |
| 834 | } |
| 835 | |
| 836 | /* |
| 837 | * This is mostly needed to re-wakeup those userfaults that were still |
| 838 | * pending when userland wake them up the first time. We don't wake |
| 839 | * the pending one to avoid blocking reads to block, or non blocking |
| 840 | * read to return -EAGAIN, if used with POLLIN, to avoid userland |
| 841 | * doubts on why POLLIN wasn't reliable. |
| 842 | */ |
| 843 | static int userfaultfd_wake(struct userfaultfd_ctx *ctx, |
| 844 | unsigned long arg) |
| 845 | { |
| 846 | int ret; |
| 847 | struct uffdio_range uffdio_wake; |
| 848 | struct userfaultfd_wake_range range; |
| 849 | const void __user *buf = (void __user *)arg; |
| 850 | |
| 851 | ret = -EFAULT; |
| 852 | if (copy_from_user(&uffdio_wake, buf, sizeof(uffdio_wake))) |
| 853 | goto out; |
| 854 | |
| 855 | ret = validate_range(ctx->mm, uffdio_wake.start, uffdio_wake.len); |
| 856 | if (ret) |
| 857 | goto out; |
| 858 | |
| 859 | range.start = uffdio_wake.start; |
| 860 | range.len = uffdio_wake.len; |
| 861 | |
| 862 | /* |
| 863 | * len == 0 means wake all and we don't want to wake all here, |
| 864 | * so check it again to be sure. |
| 865 | */ |
| 866 | VM_BUG_ON(!range.len); |
| 867 | |
| 868 | wake_userfault(ctx, &range); |
| 869 | ret = 0; |
| 870 | |
| 871 | out: |
| 872 | return ret; |
| 873 | } |
| 874 | |
| 875 | /* |
| 876 | * userland asks for a certain API version and we return which bits |
| 877 | * and ioctl commands are implemented in this kernel for such API |
| 878 | * version or -EINVAL if unknown. |
| 879 | */ |
| 880 | static int userfaultfd_api(struct userfaultfd_ctx *ctx, |
| 881 | unsigned long arg) |
| 882 | { |
| 883 | struct uffdio_api uffdio_api; |
| 884 | void __user *buf = (void __user *)arg; |
| 885 | int ret; |
| 886 | |
| 887 | ret = -EINVAL; |
| 888 | if (ctx->state != UFFD_STATE_WAIT_API) |
| 889 | goto out; |
| 890 | ret = -EFAULT; |
Andrea Arcangeli | a9b85f9 | 2015-09-04 15:46:37 -0700 | [diff] [blame^] | 891 | if (copy_from_user(&uffdio_api, buf, sizeof(uffdio_api))) |
Andrea Arcangeli | 86039bd | 2015-09-04 15:46:31 -0700 | [diff] [blame] | 892 | goto out; |
Andrea Arcangeli | a9b85f9 | 2015-09-04 15:46:37 -0700 | [diff] [blame^] | 893 | if (uffdio_api.api != UFFD_API || uffdio_api.features) { |
Andrea Arcangeli | 86039bd | 2015-09-04 15:46:31 -0700 | [diff] [blame] | 894 | memset(&uffdio_api, 0, sizeof(uffdio_api)); |
| 895 | if (copy_to_user(buf, &uffdio_api, sizeof(uffdio_api))) |
| 896 | goto out; |
| 897 | ret = -EINVAL; |
| 898 | goto out; |
| 899 | } |
Pavel Emelyanov | 3f602d2 | 2015-09-04 15:46:34 -0700 | [diff] [blame] | 900 | uffdio_api.features = UFFD_API_FEATURES; |
Andrea Arcangeli | 86039bd | 2015-09-04 15:46:31 -0700 | [diff] [blame] | 901 | uffdio_api.ioctls = UFFD_API_IOCTLS; |
| 902 | ret = -EFAULT; |
| 903 | if (copy_to_user(buf, &uffdio_api, sizeof(uffdio_api))) |
| 904 | goto out; |
| 905 | ctx->state = UFFD_STATE_RUNNING; |
| 906 | ret = 0; |
| 907 | out: |
| 908 | return ret; |
| 909 | } |
| 910 | |
| 911 | static long userfaultfd_ioctl(struct file *file, unsigned cmd, |
| 912 | unsigned long arg) |
| 913 | { |
| 914 | int ret = -EINVAL; |
| 915 | struct userfaultfd_ctx *ctx = file->private_data; |
| 916 | |
| 917 | switch(cmd) { |
| 918 | case UFFDIO_API: |
| 919 | ret = userfaultfd_api(ctx, arg); |
| 920 | break; |
| 921 | case UFFDIO_REGISTER: |
| 922 | ret = userfaultfd_register(ctx, arg); |
| 923 | break; |
| 924 | case UFFDIO_UNREGISTER: |
| 925 | ret = userfaultfd_unregister(ctx, arg); |
| 926 | break; |
| 927 | case UFFDIO_WAKE: |
| 928 | ret = userfaultfd_wake(ctx, arg); |
| 929 | break; |
| 930 | } |
| 931 | return ret; |
| 932 | } |
| 933 | |
| 934 | #ifdef CONFIG_PROC_FS |
| 935 | static void userfaultfd_show_fdinfo(struct seq_file *m, struct file *f) |
| 936 | { |
| 937 | struct userfaultfd_ctx *ctx = f->private_data; |
| 938 | wait_queue_t *wq; |
| 939 | struct userfaultfd_wait_queue *uwq; |
| 940 | unsigned long pending = 0, total = 0; |
| 941 | |
| 942 | spin_lock(&ctx->fault_wqh.lock); |
| 943 | list_for_each_entry(wq, &ctx->fault_wqh.task_list, task_list) { |
| 944 | uwq = container_of(wq, struct userfaultfd_wait_queue, wq); |
| 945 | if (uwq->pending) |
| 946 | pending++; |
| 947 | total++; |
| 948 | } |
| 949 | spin_unlock(&ctx->fault_wqh.lock); |
| 950 | |
| 951 | /* |
| 952 | * If more protocols will be added, there will be all shown |
| 953 | * separated by a space. Like this: |
| 954 | * protocols: aa:... bb:... |
| 955 | */ |
| 956 | seq_printf(m, "pending:\t%lu\ntotal:\t%lu\nAPI:\t%Lx:%x:%Lx\n", |
Pavel Emelyanov | 3f602d2 | 2015-09-04 15:46:34 -0700 | [diff] [blame] | 957 | pending, total, UFFD_API, UFFD_API_FEATURES, |
Andrea Arcangeli | 86039bd | 2015-09-04 15:46:31 -0700 | [diff] [blame] | 958 | UFFD_API_IOCTLS|UFFD_API_RANGE_IOCTLS); |
| 959 | } |
| 960 | #endif |
| 961 | |
| 962 | static const struct file_operations userfaultfd_fops = { |
| 963 | #ifdef CONFIG_PROC_FS |
| 964 | .show_fdinfo = userfaultfd_show_fdinfo, |
| 965 | #endif |
| 966 | .release = userfaultfd_release, |
| 967 | .poll = userfaultfd_poll, |
| 968 | .read = userfaultfd_read, |
| 969 | .unlocked_ioctl = userfaultfd_ioctl, |
| 970 | .compat_ioctl = userfaultfd_ioctl, |
| 971 | .llseek = noop_llseek, |
| 972 | }; |
| 973 | |
| 974 | /** |
| 975 | * userfaultfd_file_create - Creates an userfaultfd file pointer. |
| 976 | * @flags: Flags for the userfaultfd file. |
| 977 | * |
| 978 | * This function creates an userfaultfd file pointer, w/out installing |
| 979 | * it into the fd table. This is useful when the userfaultfd file is |
| 980 | * used during the initialization of data structures that require |
| 981 | * extra setup after the userfaultfd creation. So the userfaultfd |
| 982 | * creation is split into the file pointer creation phase, and the |
| 983 | * file descriptor installation phase. In this way races with |
| 984 | * userspace closing the newly installed file descriptor can be |
| 985 | * avoided. Returns an userfaultfd file pointer, or a proper error |
| 986 | * pointer. |
| 987 | */ |
| 988 | static struct file *userfaultfd_file_create(int flags) |
| 989 | { |
| 990 | struct file *file; |
| 991 | struct userfaultfd_ctx *ctx; |
| 992 | |
| 993 | BUG_ON(!current->mm); |
| 994 | |
| 995 | /* Check the UFFD_* constants for consistency. */ |
| 996 | BUILD_BUG_ON(UFFD_CLOEXEC != O_CLOEXEC); |
| 997 | BUILD_BUG_ON(UFFD_NONBLOCK != O_NONBLOCK); |
| 998 | |
| 999 | file = ERR_PTR(-EINVAL); |
| 1000 | if (flags & ~UFFD_SHARED_FCNTL_FLAGS) |
| 1001 | goto out; |
| 1002 | |
| 1003 | file = ERR_PTR(-ENOMEM); |
| 1004 | ctx = kmalloc(sizeof(*ctx), GFP_KERNEL); |
| 1005 | if (!ctx) |
| 1006 | goto out; |
| 1007 | |
| 1008 | atomic_set(&ctx->refcount, 1); |
| 1009 | init_waitqueue_head(&ctx->fault_wqh); |
| 1010 | init_waitqueue_head(&ctx->fd_wqh); |
| 1011 | ctx->flags = flags; |
| 1012 | ctx->state = UFFD_STATE_WAIT_API; |
| 1013 | ctx->released = false; |
| 1014 | ctx->mm = current->mm; |
| 1015 | /* prevent the mm struct to be freed */ |
| 1016 | atomic_inc(&ctx->mm->mm_users); |
| 1017 | |
| 1018 | file = anon_inode_getfile("[userfaultfd]", &userfaultfd_fops, ctx, |
| 1019 | O_RDWR | (flags & UFFD_SHARED_FCNTL_FLAGS)); |
| 1020 | if (IS_ERR(file)) |
| 1021 | kfree(ctx); |
| 1022 | out: |
| 1023 | return file; |
| 1024 | } |
| 1025 | |
| 1026 | SYSCALL_DEFINE1(userfaultfd, int, flags) |
| 1027 | { |
| 1028 | int fd, error; |
| 1029 | struct file *file; |
| 1030 | |
| 1031 | error = get_unused_fd_flags(flags & UFFD_SHARED_FCNTL_FLAGS); |
| 1032 | if (error < 0) |
| 1033 | return error; |
| 1034 | fd = error; |
| 1035 | |
| 1036 | file = userfaultfd_file_create(flags); |
| 1037 | if (IS_ERR(file)) { |
| 1038 | error = PTR_ERR(file); |
| 1039 | goto err_put_unused_fd; |
| 1040 | } |
| 1041 | fd_install(fd, file); |
| 1042 | |
| 1043 | return fd; |
| 1044 | |
| 1045 | err_put_unused_fd: |
| 1046 | put_unused_fd(fd); |
| 1047 | |
| 1048 | return error; |
| 1049 | } |