1 // SPDX-License-Identifier: GPL-2.0 2 /* 3 * KFENCE guarded object allocator and fault handling. 4 * 5 * Copyright (C) 2020, Google LLC. 6 */ 7 8 #define pr_fmt(fmt) "kfence: " fmt 9 10 #include <linux/atomic.h> 11 #include <linux/bug.h> 12 #include <linux/debugfs.h> 13 #include <linux/hash.h> 14 #include <linux/irq_work.h> 15 #include <linux/jhash.h> 16 #include <linux/kcsan-checks.h> 17 #include <linux/kfence.h> 18 #include <linux/kmemleak.h> 19 #include <linux/list.h> 20 #include <linux/lockdep.h> 21 #include <linux/log2.h> 22 #include <linux/memblock.h> 23 #include <linux/moduleparam.h> 24 #include <linux/nodemask.h> 25 #include <linux/notifier.h> 26 #include <linux/panic_notifier.h> 27 #include <linux/random.h> 28 #include <linux/rcupdate.h> 29 #include <linux/sched/clock.h> 30 #include <linux/seq_file.h> 31 #include <linux/slab.h> 32 #include <linux/spinlock.h> 33 #include <linux/string.h> 34 35 #include <asm/kfence.h> 36 37 #include "kfence.h" 38 39 /* Disables KFENCE on the first warning assuming an irrecoverable error. */ 40 #define KFENCE_WARN_ON(cond) \ 41 ({ \ 42 const bool __cond = WARN_ON(cond); \ 43 if (unlikely(__cond)) { \ 44 WRITE_ONCE(kfence_enabled, false); \ 45 disabled_by_warn = true; \ 46 } \ 47 __cond; \ 48 }) 49 50 /* === Data ================================================================= */ 51 52 static bool kfence_enabled __read_mostly; 53 static bool disabled_by_warn __read_mostly; 54 55 unsigned long kfence_sample_interval __read_mostly = CONFIG_KFENCE_SAMPLE_INTERVAL; 56 EXPORT_SYMBOL_GPL(kfence_sample_interval); /* Export for test modules. */ 57 58 #ifdef MODULE_PARAM_PREFIX 59 #undef MODULE_PARAM_PREFIX 60 #endif 61 #define MODULE_PARAM_PREFIX "kfence." 62 63 static int kfence_enable_late(void); 64 static int param_set_sample_interval(const char *val, const struct kernel_param *kp) 65 { 66 unsigned long num; 67 int ret = kstrtoul(val, 0, &num); 68 69 if (ret < 0) 70 return ret; 71 72 /* Using 0 to indicate KFENCE is disabled. */ 73 if (!num && READ_ONCE(kfence_enabled)) { 74 pr_info("disabled\n"); 75 WRITE_ONCE(kfence_enabled, false); 76 } 77 78 *((unsigned long *)kp->arg) = num; 79 80 if (num && !READ_ONCE(kfence_enabled) && system_state != SYSTEM_BOOTING) 81 return disabled_by_warn ? -EINVAL : kfence_enable_late(); 82 return 0; 83 } 84 85 static int param_get_sample_interval(char *buffer, const struct kernel_param *kp) 86 { 87 if (!READ_ONCE(kfence_enabled)) 88 return sprintf(buffer, "0\n"); 89 90 return param_get_ulong(buffer, kp); 91 } 92 93 static const struct kernel_param_ops sample_interval_param_ops = { 94 .set = param_set_sample_interval, 95 .get = param_get_sample_interval, 96 }; 97 module_param_cb(sample_interval, &sample_interval_param_ops, &kfence_sample_interval, 0600); 98 99 /* Pool usage% threshold when currently covered allocations are skipped. */ 100 static unsigned long kfence_skip_covered_thresh __read_mostly = 75; 101 module_param_named(skip_covered_thresh, kfence_skip_covered_thresh, ulong, 0644); 102 103 /* Allocation burst count: number of excess KFENCE allocations per sample. */ 104 static unsigned int kfence_burst __read_mostly; 105 module_param_named(burst, kfence_burst, uint, 0644); 106 107 /* If true, use a deferrable timer. */ 108 static bool kfence_deferrable __read_mostly = IS_ENABLED(CONFIG_KFENCE_DEFERRABLE); 109 module_param_named(deferrable, kfence_deferrable, bool, 0444); 110 111 /* If true, check all canary bytes on panic. */ 112 static bool kfence_check_on_panic __read_mostly; 113 module_param_named(check_on_panic, kfence_check_on_panic, bool, 0444); 114 115 /* The pool of pages used for guard pages and objects. */ 116 char *__kfence_pool __read_mostly; 117 EXPORT_SYMBOL(__kfence_pool); /* Export for test modules. */ 118 119 /* 120 * Per-object metadata, with one-to-one mapping of object metadata to 121 * backing pages (in __kfence_pool). 122 */ 123 static_assert(CONFIG_KFENCE_NUM_OBJECTS > 0); 124 struct kfence_metadata *kfence_metadata __read_mostly; 125 126 /* 127 * If kfence_metadata is not NULL, it may be accessed by kfence_shutdown_cache(). 128 * So introduce kfence_metadata_init to initialize metadata, and then make 129 * kfence_metadata visible after initialization is successful. This prevents 130 * potential UAF or access to uninitialized metadata. 131 */ 132 static struct kfence_metadata *kfence_metadata_init __read_mostly; 133 134 /* Freelist with available objects. */ 135 static struct list_head kfence_freelist = LIST_HEAD_INIT(kfence_freelist); 136 static DEFINE_RAW_SPINLOCK(kfence_freelist_lock); /* Lock protecting freelist. */ 137 138 /* 139 * The static key to set up a KFENCE allocation; or if static keys are not used 140 * to gate allocations, to avoid a load and compare if KFENCE is disabled. 141 */ 142 DEFINE_STATIC_KEY_FALSE(kfence_allocation_key); 143 144 /* Gates the allocation, ensuring only one succeeds in a given period. */ 145 atomic_t kfence_allocation_gate = ATOMIC_INIT(1); 146 147 /* 148 * A Counting Bloom filter of allocation coverage: limits currently covered 149 * allocations of the same source filling up the pool. 150 * 151 * Assuming a range of 15%-85% unique allocations in the pool at any point in 152 * time, the below parameters provide a probablity of 0.02-0.33 for false 153 * positive hits respectively: 154 * 155 * P(alloc_traces) = (1 - e^(-HNUM * (alloc_traces / SIZE)) ^ HNUM 156 */ 157 #define ALLOC_COVERED_HNUM 2 158 #define ALLOC_COVERED_ORDER (const_ilog2(CONFIG_KFENCE_NUM_OBJECTS) + 2) 159 #define ALLOC_COVERED_SIZE (1 << ALLOC_COVERED_ORDER) 160 #define ALLOC_COVERED_HNEXT(h) hash_32(h, ALLOC_COVERED_ORDER) 161 #define ALLOC_COVERED_MASK (ALLOC_COVERED_SIZE - 1) 162 static atomic_t alloc_covered[ALLOC_COVERED_SIZE]; 163 164 /* Stack depth used to determine uniqueness of an allocation. */ 165 #define UNIQUE_ALLOC_STACK_DEPTH ((size_t)8) 166 167 /* 168 * Randomness for stack hashes, making the same collisions across reboots and 169 * different machines less likely. 170 */ 171 static u32 stack_hash_seed __ro_after_init; 172 173 /* Statistics counters for debugfs. */ 174 enum kfence_counter_id { 175 KFENCE_COUNTER_ALLOCATED, 176 KFENCE_COUNTER_ALLOCS, 177 KFENCE_COUNTER_FREES, 178 KFENCE_COUNTER_ZOMBIES, 179 KFENCE_COUNTER_BUGS, 180 KFENCE_COUNTER_SKIP_INCOMPAT, 181 KFENCE_COUNTER_SKIP_CAPACITY, 182 KFENCE_COUNTER_SKIP_COVERED, 183 KFENCE_COUNTER_COUNT, 184 }; 185 static atomic_long_t counters[KFENCE_COUNTER_COUNT]; 186 static const char *const counter_names[] = { 187 [KFENCE_COUNTER_ALLOCATED] = "currently allocated", 188 [KFENCE_COUNTER_ALLOCS] = "total allocations", 189 [KFENCE_COUNTER_FREES] = "total frees", 190 [KFENCE_COUNTER_ZOMBIES] = "zombie allocations", 191 [KFENCE_COUNTER_BUGS] = "total bugs", 192 [KFENCE_COUNTER_SKIP_INCOMPAT] = "skipped allocations (incompatible)", 193 [KFENCE_COUNTER_SKIP_CAPACITY] = "skipped allocations (capacity)", 194 [KFENCE_COUNTER_SKIP_COVERED] = "skipped allocations (covered)", 195 }; 196 static_assert(ARRAY_SIZE(counter_names) == KFENCE_COUNTER_COUNT); 197 198 /* === Internals ============================================================ */ 199 200 static inline bool should_skip_covered(void) 201 { 202 unsigned long thresh = (CONFIG_KFENCE_NUM_OBJECTS * kfence_skip_covered_thresh) / 100; 203 204 return atomic_long_read(&counters[KFENCE_COUNTER_ALLOCATED]) > thresh; 205 } 206 207 static u32 get_alloc_stack_hash(unsigned long *stack_entries, size_t num_entries) 208 { 209 num_entries = min(num_entries, UNIQUE_ALLOC_STACK_DEPTH); 210 num_entries = filter_irq_stacks(stack_entries, num_entries); 211 return jhash(stack_entries, num_entries * sizeof(stack_entries[0]), stack_hash_seed); 212 } 213 214 /* 215 * Adds (or subtracts) count @val for allocation stack trace hash 216 * @alloc_stack_hash from Counting Bloom filter. 217 */ 218 static void alloc_covered_add(u32 alloc_stack_hash, int val) 219 { 220 int i; 221 222 for (i = 0; i < ALLOC_COVERED_HNUM; i++) { 223 atomic_add(val, &alloc_covered[alloc_stack_hash & ALLOC_COVERED_MASK]); 224 alloc_stack_hash = ALLOC_COVERED_HNEXT(alloc_stack_hash); 225 } 226 } 227 228 /* 229 * Returns true if the allocation stack trace hash @alloc_stack_hash is 230 * currently contained (non-zero count) in Counting Bloom filter. 231 */ 232 static bool alloc_covered_contains(u32 alloc_stack_hash) 233 { 234 int i; 235 236 for (i = 0; i < ALLOC_COVERED_HNUM; i++) { 237 if (!atomic_read(&alloc_covered[alloc_stack_hash & ALLOC_COVERED_MASK])) 238 return false; 239 alloc_stack_hash = ALLOC_COVERED_HNEXT(alloc_stack_hash); 240 } 241 242 return true; 243 } 244 245 static bool kfence_protect(unsigned long addr) 246 { 247 return !KFENCE_WARN_ON(!kfence_protect_page(ALIGN_DOWN(addr, PAGE_SIZE), true)); 248 } 249 250 static bool kfence_unprotect(unsigned long addr) 251 { 252 return !KFENCE_WARN_ON(!kfence_protect_page(ALIGN_DOWN(addr, PAGE_SIZE), false)); 253 } 254 255 static inline unsigned long metadata_to_pageaddr(const struct kfence_metadata *meta) 256 { 257 unsigned long offset = (meta - kfence_metadata + 1) * PAGE_SIZE * 2; 258 unsigned long pageaddr = (unsigned long)&__kfence_pool[offset]; 259 260 /* The checks do not affect performance; only called from slow-paths. */ 261 262 /* Only call with a pointer into kfence_metadata. */ 263 if (KFENCE_WARN_ON(meta < kfence_metadata || 264 meta >= kfence_metadata + CONFIG_KFENCE_NUM_OBJECTS)) 265 return 0; 266 267 /* 268 * This metadata object only ever maps to 1 page; verify that the stored 269 * address is in the expected range. 270 */ 271 if (KFENCE_WARN_ON(ALIGN_DOWN(meta->addr, PAGE_SIZE) != pageaddr)) 272 return 0; 273 274 return pageaddr; 275 } 276 277 static inline bool kfence_obj_allocated(const struct kfence_metadata *meta) 278 { 279 enum kfence_object_state state = READ_ONCE(meta->state); 280 281 return state == KFENCE_OBJECT_ALLOCATED || state == KFENCE_OBJECT_RCU_FREEING; 282 } 283 284 /* 285 * Update the object's metadata state, including updating the alloc/free stacks 286 * depending on the state transition. 287 */ 288 static noinline void 289 metadata_update_state(struct kfence_metadata *meta, enum kfence_object_state next, 290 unsigned long *stack_entries, size_t num_stack_entries) 291 { 292 struct kfence_track *track = 293 next == KFENCE_OBJECT_ALLOCATED ? &meta->alloc_track : &meta->free_track; 294 295 lockdep_assert_held(&meta->lock); 296 297 /* Stack has been saved when calling rcu, skip. */ 298 if (READ_ONCE(meta->state) == KFENCE_OBJECT_RCU_FREEING) 299 goto out; 300 301 if (stack_entries) { 302 memcpy(track->stack_entries, stack_entries, 303 num_stack_entries * sizeof(stack_entries[0])); 304 } else { 305 /* 306 * Skip over 1 (this) functions; noinline ensures we do not 307 * accidentally skip over the caller by never inlining. 308 */ 309 num_stack_entries = stack_trace_save(track->stack_entries, KFENCE_STACK_DEPTH, 1); 310 } 311 track->num_stack_entries = num_stack_entries; 312 track->pid = task_pid_nr(current); 313 track->cpu = raw_smp_processor_id(); 314 track->ts_nsec = local_clock(); /* Same source as printk timestamps. */ 315 316 out: 317 /* 318 * Pairs with READ_ONCE() in 319 * kfence_shutdown_cache(), 320 * kfence_handle_page_fault(). 321 */ 322 WRITE_ONCE(meta->state, next); 323 } 324 325 #ifdef CONFIG_KMSAN 326 #define check_canary_attributes noinline __no_kmsan_checks 327 #else 328 #define check_canary_attributes inline 329 #endif 330 331 /* Check canary byte at @addr. */ 332 static check_canary_attributes bool check_canary_byte(u8 *addr) 333 { 334 struct kfence_metadata *meta; 335 unsigned long flags; 336 337 if (likely(*addr == KFENCE_CANARY_PATTERN_U8(addr))) 338 return true; 339 340 atomic_long_inc(&counters[KFENCE_COUNTER_BUGS]); 341 342 meta = addr_to_metadata((unsigned long)addr); 343 raw_spin_lock_irqsave(&meta->lock, flags); 344 kfence_report_error((unsigned long)addr, false, NULL, meta, KFENCE_ERROR_CORRUPTION); 345 raw_spin_unlock_irqrestore(&meta->lock, flags); 346 347 return false; 348 } 349 350 static inline void set_canary(const struct kfence_metadata *meta) 351 { 352 const unsigned long pageaddr = ALIGN_DOWN(meta->addr, PAGE_SIZE); 353 unsigned long addr = pageaddr; 354 355 /* 356 * The canary may be written to part of the object memory, but it does 357 * not affect it. The user should initialize the object before using it. 358 */ 359 for (; addr < meta->addr; addr += sizeof(u64)) 360 *((u64 *)addr) = KFENCE_CANARY_PATTERN_U64; 361 362 addr = ALIGN_DOWN(meta->addr + meta->size, sizeof(u64)); 363 for (; addr - pageaddr < PAGE_SIZE; addr += sizeof(u64)) 364 *((u64 *)addr) = KFENCE_CANARY_PATTERN_U64; 365 } 366 367 static check_canary_attributes void 368 check_canary(const struct kfence_metadata *meta) 369 { 370 const unsigned long pageaddr = ALIGN_DOWN(meta->addr, PAGE_SIZE); 371 unsigned long addr = pageaddr; 372 373 /* 374 * We'll iterate over each canary byte per-side until a corrupted byte 375 * is found. However, we'll still iterate over the canary bytes to the 376 * right of the object even if there was an error in the canary bytes to 377 * the left of the object. Specifically, if check_canary_byte() 378 * generates an error, showing both sides might give more clues as to 379 * what the error is about when displaying which bytes were corrupted. 380 */ 381 382 /* Apply to left of object. */ 383 for (; meta->addr - addr >= sizeof(u64); addr += sizeof(u64)) { 384 if (unlikely(*((u64 *)addr) != KFENCE_CANARY_PATTERN_U64)) 385 break; 386 } 387 388 /* 389 * If the canary is corrupted in a certain 64 bytes, or the canary 390 * memory cannot be completely covered by multiple consecutive 64 bytes, 391 * it needs to be checked one by one. 392 */ 393 for (; addr < meta->addr; addr++) { 394 if (unlikely(!check_canary_byte((u8 *)addr))) 395 break; 396 } 397 398 /* Apply to right of object. */ 399 for (addr = meta->addr + meta->size; addr % sizeof(u64) != 0; addr++) { 400 if (unlikely(!check_canary_byte((u8 *)addr))) 401 return; 402 } 403 for (; addr - pageaddr < PAGE_SIZE; addr += sizeof(u64)) { 404 if (unlikely(*((u64 *)addr) != KFENCE_CANARY_PATTERN_U64)) { 405 406 for (; addr - pageaddr < PAGE_SIZE; addr++) { 407 if (!check_canary_byte((u8 *)addr)) 408 return; 409 } 410 } 411 } 412 } 413 414 static void *kfence_guarded_alloc(struct kmem_cache *cache, size_t size, gfp_t gfp, 415 unsigned long *stack_entries, size_t num_stack_entries, 416 u32 alloc_stack_hash) 417 { 418 struct kfence_metadata *meta = NULL; 419 unsigned long flags; 420 struct slab *slab; 421 void *addr; 422 const bool random_right_allocate = get_random_u32_below(2); 423 const bool random_fault = CONFIG_KFENCE_STRESS_TEST_FAULTS && 424 !get_random_u32_below(CONFIG_KFENCE_STRESS_TEST_FAULTS); 425 426 /* Try to obtain a free object. */ 427 raw_spin_lock_irqsave(&kfence_freelist_lock, flags); 428 if (!list_empty(&kfence_freelist)) { 429 meta = list_entry(kfence_freelist.next, struct kfence_metadata, list); 430 list_del_init(&meta->list); 431 } 432 raw_spin_unlock_irqrestore(&kfence_freelist_lock, flags); 433 if (!meta) { 434 atomic_long_inc(&counters[KFENCE_COUNTER_SKIP_CAPACITY]); 435 return NULL; 436 } 437 438 if (unlikely(!raw_spin_trylock_irqsave(&meta->lock, flags))) { 439 /* 440 * This is extremely unlikely -- we are reporting on a 441 * use-after-free, which locked meta->lock, and the reporting 442 * code via printk calls kmalloc() which ends up in 443 * kfence_alloc() and tries to grab the same object that we're 444 * reporting on. While it has never been observed, lockdep does 445 * report that there is a possibility of deadlock. Fix it by 446 * using trylock and bailing out gracefully. 447 */ 448 raw_spin_lock_irqsave(&kfence_freelist_lock, flags); 449 /* Put the object back on the freelist. */ 450 list_add_tail(&meta->list, &kfence_freelist); 451 raw_spin_unlock_irqrestore(&kfence_freelist_lock, flags); 452 453 return NULL; 454 } 455 456 meta->addr = metadata_to_pageaddr(meta); 457 /* Unprotect if we're reusing this page. */ 458 if (meta->state == KFENCE_OBJECT_FREED) 459 kfence_unprotect(meta->addr); 460 461 /* 462 * Note: for allocations made before RNG initialization, will always 463 * return zero. We still benefit from enabling KFENCE as early as 464 * possible, even when the RNG is not yet available, as this will allow 465 * KFENCE to detect bugs due to earlier allocations. The only downside 466 * is that the out-of-bounds accesses detected are deterministic for 467 * such allocations. 468 */ 469 if (random_right_allocate) { 470 /* Allocate on the "right" side, re-calculate address. */ 471 meta->addr += PAGE_SIZE - size; 472 meta->addr = ALIGN_DOWN(meta->addr, cache->align); 473 } 474 475 addr = (void *)meta->addr; 476 477 /* Update remaining metadata. */ 478 metadata_update_state(meta, KFENCE_OBJECT_ALLOCATED, stack_entries, num_stack_entries); 479 /* Pairs with READ_ONCE() in kfence_shutdown_cache(). */ 480 WRITE_ONCE(meta->cache, cache); 481 meta->size = size; 482 meta->alloc_stack_hash = alloc_stack_hash; 483 raw_spin_unlock_irqrestore(&meta->lock, flags); 484 485 alloc_covered_add(alloc_stack_hash, 1); 486 487 /* Set required slab fields. */ 488 slab = virt_to_slab((void *)meta->addr); 489 slab->slab_cache = cache; 490 slab->objects = 1; 491 492 /* Memory initialization. */ 493 set_canary(meta); 494 495 /* 496 * We check slab_want_init_on_alloc() ourselves, rather than letting 497 * SL*B do the initialization, as otherwise we might overwrite KFENCE's 498 * redzone. 499 */ 500 if (unlikely(slab_want_init_on_alloc(gfp, cache))) 501 memzero_explicit(addr, size); 502 if (cache->ctor) 503 cache->ctor(addr); 504 505 if (random_fault) 506 kfence_protect(meta->addr); /* Random "faults" by protecting the object. */ 507 508 atomic_long_inc(&counters[KFENCE_COUNTER_ALLOCATED]); 509 atomic_long_inc(&counters[KFENCE_COUNTER_ALLOCS]); 510 511 return addr; 512 } 513 514 static void kfence_guarded_free(void *addr, struct kfence_metadata *meta, bool zombie) 515 { 516 struct kcsan_scoped_access assert_page_exclusive; 517 unsigned long flags; 518 bool init; 519 520 raw_spin_lock_irqsave(&meta->lock, flags); 521 522 if (!kfence_obj_allocated(meta) || meta->addr != (unsigned long)addr) { 523 /* Invalid or double-free, bail out. */ 524 atomic_long_inc(&counters[KFENCE_COUNTER_BUGS]); 525 kfence_report_error((unsigned long)addr, false, NULL, meta, 526 KFENCE_ERROR_INVALID_FREE); 527 raw_spin_unlock_irqrestore(&meta->lock, flags); 528 return; 529 } 530 531 /* Detect racy use-after-free, or incorrect reallocation of this page by KFENCE. */ 532 kcsan_begin_scoped_access((void *)ALIGN_DOWN((unsigned long)addr, PAGE_SIZE), PAGE_SIZE, 533 KCSAN_ACCESS_SCOPED | KCSAN_ACCESS_WRITE | KCSAN_ACCESS_ASSERT, 534 &assert_page_exclusive); 535 536 if (CONFIG_KFENCE_STRESS_TEST_FAULTS) 537 kfence_unprotect((unsigned long)addr); /* To check canary bytes. */ 538 539 /* Restore page protection if there was an OOB access. */ 540 if (meta->unprotected_page) { 541 memzero_explicit((void *)ALIGN_DOWN(meta->unprotected_page, PAGE_SIZE), PAGE_SIZE); 542 kfence_protect(meta->unprotected_page); 543 meta->unprotected_page = 0; 544 } 545 546 /* Mark the object as freed. */ 547 metadata_update_state(meta, KFENCE_OBJECT_FREED, NULL, 0); 548 init = slab_want_init_on_free(meta->cache); 549 raw_spin_unlock_irqrestore(&meta->lock, flags); 550 551 alloc_covered_add(meta->alloc_stack_hash, -1); 552 553 /* Check canary bytes for memory corruption. */ 554 check_canary(meta); 555 556 /* 557 * Clear memory if init-on-free is set. While we protect the page, the 558 * data is still there, and after a use-after-free is detected, we 559 * unprotect the page, so the data is still accessible. 560 */ 561 if (!zombie && unlikely(init)) 562 memzero_explicit(addr, meta->size); 563 564 /* Protect to detect use-after-frees. */ 565 kfence_protect((unsigned long)addr); 566 567 kcsan_end_scoped_access(&assert_page_exclusive); 568 if (!zombie) { 569 /* Add it to the tail of the freelist for reuse. */ 570 raw_spin_lock_irqsave(&kfence_freelist_lock, flags); 571 KFENCE_WARN_ON(!list_empty(&meta->list)); 572 list_add_tail(&meta->list, &kfence_freelist); 573 raw_spin_unlock_irqrestore(&kfence_freelist_lock, flags); 574 575 atomic_long_dec(&counters[KFENCE_COUNTER_ALLOCATED]); 576 atomic_long_inc(&counters[KFENCE_COUNTER_FREES]); 577 } else { 578 /* See kfence_shutdown_cache(). */ 579 atomic_long_inc(&counters[KFENCE_COUNTER_ZOMBIES]); 580 } 581 } 582 583 static void rcu_guarded_free(struct rcu_head *h) 584 { 585 struct kfence_metadata *meta = container_of(h, struct kfence_metadata, rcu_head); 586 587 kfence_guarded_free((void *)meta->addr, meta, false); 588 } 589 590 /* 591 * Initialization of the KFENCE pool after its allocation. 592 * Returns 0 on success; otherwise returns the address up to 593 * which partial initialization succeeded. 594 */ 595 static unsigned long kfence_init_pool(void) 596 { 597 unsigned long addr, start_pfn; 598 int i; 599 600 if (!arch_kfence_init_pool()) 601 return (unsigned long)__kfence_pool; 602 603 addr = (unsigned long)__kfence_pool; 604 start_pfn = PHYS_PFN(virt_to_phys(__kfence_pool)); 605 606 /* 607 * Set up object pages: they must have PGTY_slab set to avoid freeing 608 * them as real pages. 609 * 610 * We also want to avoid inserting kfence_free() in the kfree() 611 * fast-path in SLUB, and therefore need to ensure kfree() correctly 612 * enters __slab_free() slow-path. 613 */ 614 for (i = 0; i < KFENCE_POOL_SIZE / PAGE_SIZE; i++) { 615 struct slab *slab; 616 617 if (!i || (i % 2)) 618 continue; 619 620 slab = page_slab(pfn_to_page(start_pfn + i)); 621 __folio_set_slab(slab_folio(slab)); 622 #ifdef CONFIG_MEMCG 623 slab->obj_exts = (unsigned long)&kfence_metadata_init[i / 2 - 1].obj_exts | 624 MEMCG_DATA_OBJEXTS; 625 #endif 626 } 627 628 /* 629 * Protect the first 2 pages. The first page is mostly unnecessary, and 630 * merely serves as an extended guard page. However, adding one 631 * additional page in the beginning gives us an even number of pages, 632 * which simplifies the mapping of address to metadata index. 633 */ 634 for (i = 0; i < 2; i++) { 635 if (unlikely(!kfence_protect(addr))) 636 return addr; 637 638 addr += PAGE_SIZE; 639 } 640 641 for (i = 0; i < CONFIG_KFENCE_NUM_OBJECTS; i++) { 642 struct kfence_metadata *meta = &kfence_metadata_init[i]; 643 644 /* Initialize metadata. */ 645 INIT_LIST_HEAD(&meta->list); 646 raw_spin_lock_init(&meta->lock); 647 meta->state = KFENCE_OBJECT_UNUSED; 648 meta->addr = addr; /* Initialize for validation in metadata_to_pageaddr(). */ 649 list_add_tail(&meta->list, &kfence_freelist); 650 651 /* Protect the right redzone. */ 652 if (unlikely(!kfence_protect(addr + PAGE_SIZE))) 653 goto reset_slab; 654 655 addr += 2 * PAGE_SIZE; 656 } 657 658 /* 659 * Make kfence_metadata visible only when initialization is successful. 660 * Otherwise, if the initialization fails and kfence_metadata is freed, 661 * it may cause UAF in kfence_shutdown_cache(). 662 */ 663 smp_store_release(&kfence_metadata, kfence_metadata_init); 664 return 0; 665 666 reset_slab: 667 for (i = 0; i < KFENCE_POOL_SIZE / PAGE_SIZE; i++) { 668 struct slab *slab; 669 670 if (!i || (i % 2)) 671 continue; 672 673 slab = page_slab(pfn_to_page(start_pfn + i)); 674 #ifdef CONFIG_MEMCG 675 slab->obj_exts = 0; 676 #endif 677 __folio_clear_slab(slab_folio(slab)); 678 } 679 680 return addr; 681 } 682 683 static bool __init kfence_init_pool_early(void) 684 { 685 unsigned long addr; 686 687 if (!__kfence_pool) 688 return false; 689 690 addr = kfence_init_pool(); 691 692 if (!addr) { 693 /* 694 * The pool is live and will never be deallocated from this point on. 695 * Ignore the pool object from the kmemleak phys object tree, as it would 696 * otherwise overlap with allocations returned by kfence_alloc(), which 697 * are registered with kmemleak through the slab post-alloc hook. 698 */ 699 kmemleak_ignore_phys(__pa(__kfence_pool)); 700 return true; 701 } 702 703 /* 704 * Only release unprotected pages, and do not try to go back and change 705 * page attributes due to risk of failing to do so as well. If changing 706 * page attributes for some pages fails, it is very likely that it also 707 * fails for the first page, and therefore expect addr==__kfence_pool in 708 * most failure cases. 709 */ 710 memblock_free_late(__pa(addr), KFENCE_POOL_SIZE - (addr - (unsigned long)__kfence_pool)); 711 __kfence_pool = NULL; 712 713 memblock_free_late(__pa(kfence_metadata_init), KFENCE_METADATA_SIZE); 714 kfence_metadata_init = NULL; 715 716 return false; 717 } 718 719 /* === DebugFS Interface ==================================================== */ 720 721 static int stats_show(struct seq_file *seq, void *v) 722 { 723 int i; 724 725 seq_printf(seq, "enabled: %i\n", READ_ONCE(kfence_enabled)); 726 for (i = 0; i < KFENCE_COUNTER_COUNT; i++) 727 seq_printf(seq, "%s: %ld\n", counter_names[i], atomic_long_read(&counters[i])); 728 729 return 0; 730 } 731 DEFINE_SHOW_ATTRIBUTE(stats); 732 733 /* 734 * debugfs seq_file operations for /sys/kernel/debug/kfence/objects. 735 * start_object() and next_object() return the object index + 1, because NULL is used 736 * to stop iteration. 737 */ 738 static void *start_object(struct seq_file *seq, loff_t *pos) 739 { 740 if (*pos < CONFIG_KFENCE_NUM_OBJECTS) 741 return (void *)((long)*pos + 1); 742 return NULL; 743 } 744 745 static void stop_object(struct seq_file *seq, void *v) 746 { 747 } 748 749 static void *next_object(struct seq_file *seq, void *v, loff_t *pos) 750 { 751 ++*pos; 752 if (*pos < CONFIG_KFENCE_NUM_OBJECTS) 753 return (void *)((long)*pos + 1); 754 return NULL; 755 } 756 757 static int show_object(struct seq_file *seq, void *v) 758 { 759 struct kfence_metadata *meta = &kfence_metadata[(long)v - 1]; 760 unsigned long flags; 761 762 raw_spin_lock_irqsave(&meta->lock, flags); 763 kfence_print_object(seq, meta); 764 raw_spin_unlock_irqrestore(&meta->lock, flags); 765 seq_puts(seq, "---------------------------------\n"); 766 767 return 0; 768 } 769 770 static const struct seq_operations objects_sops = { 771 .start = start_object, 772 .next = next_object, 773 .stop = stop_object, 774 .show = show_object, 775 }; 776 DEFINE_SEQ_ATTRIBUTE(objects); 777 778 static int kfence_debugfs_init(void) 779 { 780 struct dentry *kfence_dir; 781 782 if (!READ_ONCE(kfence_enabled)) 783 return 0; 784 785 kfence_dir = debugfs_create_dir("kfence", NULL); 786 debugfs_create_file("stats", 0444, kfence_dir, NULL, &stats_fops); 787 debugfs_create_file("objects", 0400, kfence_dir, NULL, &objects_fops); 788 return 0; 789 } 790 791 late_initcall(kfence_debugfs_init); 792 793 /* === Panic Notifier ====================================================== */ 794 795 static void kfence_check_all_canary(void) 796 { 797 int i; 798 799 for (i = 0; i < CONFIG_KFENCE_NUM_OBJECTS; i++) { 800 struct kfence_metadata *meta = &kfence_metadata[i]; 801 802 if (kfence_obj_allocated(meta)) 803 check_canary(meta); 804 } 805 } 806 807 static int kfence_check_canary_callback(struct notifier_block *nb, 808 unsigned long reason, void *arg) 809 { 810 kfence_check_all_canary(); 811 return NOTIFY_OK; 812 } 813 814 static struct notifier_block kfence_check_canary_notifier = { 815 .notifier_call = kfence_check_canary_callback, 816 }; 817 818 /* === Allocation Gate Timer ================================================ */ 819 820 static struct delayed_work kfence_timer; 821 822 #ifdef CONFIG_KFENCE_STATIC_KEYS 823 /* Wait queue to wake up allocation-gate timer task. */ 824 static DECLARE_WAIT_QUEUE_HEAD(allocation_wait); 825 826 static void wake_up_kfence_timer(struct irq_work *work) 827 { 828 wake_up(&allocation_wait); 829 } 830 static DEFINE_IRQ_WORK(wake_up_kfence_timer_work, wake_up_kfence_timer); 831 #endif 832 833 /* 834 * Set up delayed work, which will enable and disable the static key. We need to 835 * use a work queue (rather than a simple timer), since enabling and disabling a 836 * static key cannot be done from an interrupt. 837 * 838 * Note: Toggling a static branch currently causes IPIs, and here we'll end up 839 * with a total of 2 IPIs to all CPUs. If this ends up a problem in future (with 840 * more aggressive sampling intervals), we could get away with a variant that 841 * avoids IPIs, at the cost of not immediately capturing allocations if the 842 * instructions remain cached. 843 */ 844 static void toggle_allocation_gate(struct work_struct *work) 845 { 846 if (!READ_ONCE(kfence_enabled)) 847 return; 848 849 atomic_set(&kfence_allocation_gate, -kfence_burst); 850 #ifdef CONFIG_KFENCE_STATIC_KEYS 851 /* Enable static key, and await allocation to happen. */ 852 static_branch_enable(&kfence_allocation_key); 853 854 wait_event_idle(allocation_wait, atomic_read(&kfence_allocation_gate) > 0); 855 856 /* Disable static key and reset timer. */ 857 static_branch_disable(&kfence_allocation_key); 858 #endif 859 queue_delayed_work(system_unbound_wq, &kfence_timer, 860 msecs_to_jiffies(kfence_sample_interval)); 861 } 862 863 /* === Public interface ===================================================== */ 864 865 void __init kfence_alloc_pool_and_metadata(void) 866 { 867 if (!kfence_sample_interval) 868 return; 869 870 /* 871 * If the pool has already been initialized by arch, there is no need to 872 * re-allocate the memory pool. 873 */ 874 if (!__kfence_pool) 875 __kfence_pool = memblock_alloc(KFENCE_POOL_SIZE, PAGE_SIZE); 876 877 if (!__kfence_pool) { 878 pr_err("failed to allocate pool\n"); 879 return; 880 } 881 882 /* The memory allocated by memblock has been zeroed out. */ 883 kfence_metadata_init = memblock_alloc(KFENCE_METADATA_SIZE, PAGE_SIZE); 884 if (!kfence_metadata_init) { 885 pr_err("failed to allocate metadata\n"); 886 memblock_free(__kfence_pool, KFENCE_POOL_SIZE); 887 __kfence_pool = NULL; 888 } 889 } 890 891 static void kfence_init_enable(void) 892 { 893 if (!IS_ENABLED(CONFIG_KFENCE_STATIC_KEYS)) 894 static_branch_enable(&kfence_allocation_key); 895 896 if (kfence_deferrable) 897 INIT_DEFERRABLE_WORK(&kfence_timer, toggle_allocation_gate); 898 else 899 INIT_DELAYED_WORK(&kfence_timer, toggle_allocation_gate); 900 901 if (kfence_check_on_panic) 902 atomic_notifier_chain_register(&panic_notifier_list, &kfence_check_canary_notifier); 903 904 WRITE_ONCE(kfence_enabled, true); 905 queue_delayed_work(system_unbound_wq, &kfence_timer, 0); 906 907 pr_info("initialized - using %lu bytes for %d objects at 0x%p-0x%p\n", KFENCE_POOL_SIZE, 908 CONFIG_KFENCE_NUM_OBJECTS, (void *)__kfence_pool, 909 (void *)(__kfence_pool + KFENCE_POOL_SIZE)); 910 } 911 912 void __init kfence_init(void) 913 { 914 stack_hash_seed = get_random_u32(); 915 916 /* Setting kfence_sample_interval to 0 on boot disables KFENCE. */ 917 if (!kfence_sample_interval) 918 return; 919 920 if (!kfence_init_pool_early()) { 921 pr_err("%s failed\n", __func__); 922 return; 923 } 924 925 kfence_init_enable(); 926 } 927 928 static int kfence_init_late(void) 929 { 930 const unsigned long nr_pages_pool = KFENCE_POOL_SIZE / PAGE_SIZE; 931 const unsigned long nr_pages_meta = KFENCE_METADATA_SIZE / PAGE_SIZE; 932 unsigned long addr = (unsigned long)__kfence_pool; 933 unsigned long free_size = KFENCE_POOL_SIZE; 934 int err = -ENOMEM; 935 936 #ifdef CONFIG_CONTIG_ALLOC 937 struct page *pages; 938 939 pages = alloc_contig_pages(nr_pages_pool, GFP_KERNEL, first_online_node, 940 NULL); 941 if (!pages) 942 return -ENOMEM; 943 944 __kfence_pool = page_to_virt(pages); 945 pages = alloc_contig_pages(nr_pages_meta, GFP_KERNEL, first_online_node, 946 NULL); 947 if (pages) 948 kfence_metadata_init = page_to_virt(pages); 949 #else 950 if (nr_pages_pool > MAX_ORDER_NR_PAGES || 951 nr_pages_meta > MAX_ORDER_NR_PAGES) { 952 pr_warn("KFENCE_NUM_OBJECTS too large for buddy allocator\n"); 953 return -EINVAL; 954 } 955 956 __kfence_pool = alloc_pages_exact(KFENCE_POOL_SIZE, GFP_KERNEL); 957 if (!__kfence_pool) 958 return -ENOMEM; 959 960 kfence_metadata_init = alloc_pages_exact(KFENCE_METADATA_SIZE, GFP_KERNEL); 961 #endif 962 963 if (!kfence_metadata_init) 964 goto free_pool; 965 966 memzero_explicit(kfence_metadata_init, KFENCE_METADATA_SIZE); 967 addr = kfence_init_pool(); 968 if (!addr) { 969 kfence_init_enable(); 970 kfence_debugfs_init(); 971 return 0; 972 } 973 974 pr_err("%s failed\n", __func__); 975 free_size = KFENCE_POOL_SIZE - (addr - (unsigned long)__kfence_pool); 976 err = -EBUSY; 977 978 #ifdef CONFIG_CONTIG_ALLOC 979 free_contig_range(page_to_pfn(virt_to_page((void *)kfence_metadata_init)), 980 nr_pages_meta); 981 free_pool: 982 free_contig_range(page_to_pfn(virt_to_page((void *)addr)), 983 free_size / PAGE_SIZE); 984 #else 985 free_pages_exact((void *)kfence_metadata_init, KFENCE_METADATA_SIZE); 986 free_pool: 987 free_pages_exact((void *)addr, free_size); 988 #endif 989 990 kfence_metadata_init = NULL; 991 __kfence_pool = NULL; 992 return err; 993 } 994 995 static int kfence_enable_late(void) 996 { 997 if (!__kfence_pool) 998 return kfence_init_late(); 999 1000 WRITE_ONCE(kfence_enabled, true); 1001 queue_delayed_work(system_unbound_wq, &kfence_timer, 0); 1002 pr_info("re-enabled\n"); 1003 return 0; 1004 } 1005 1006 void kfence_shutdown_cache(struct kmem_cache *s) 1007 { 1008 unsigned long flags; 1009 struct kfence_metadata *meta; 1010 int i; 1011 1012 /* Pairs with release in kfence_init_pool(). */ 1013 if (!smp_load_acquire(&kfence_metadata)) 1014 return; 1015 1016 for (i = 0; i < CONFIG_KFENCE_NUM_OBJECTS; i++) { 1017 bool in_use; 1018 1019 meta = &kfence_metadata[i]; 1020 1021 /* 1022 * If we observe some inconsistent cache and state pair where we 1023 * should have returned false here, cache destruction is racing 1024 * with either kmem_cache_alloc() or kmem_cache_free(). Taking 1025 * the lock will not help, as different critical section 1026 * serialization will have the same outcome. 1027 */ 1028 if (READ_ONCE(meta->cache) != s || !kfence_obj_allocated(meta)) 1029 continue; 1030 1031 raw_spin_lock_irqsave(&meta->lock, flags); 1032 in_use = meta->cache == s && kfence_obj_allocated(meta); 1033 raw_spin_unlock_irqrestore(&meta->lock, flags); 1034 1035 if (in_use) { 1036 /* 1037 * This cache still has allocations, and we should not 1038 * release them back into the freelist so they can still 1039 * safely be used and retain the kernel's default 1040 * behaviour of keeping the allocations alive (leak the 1041 * cache); however, they effectively become "zombie 1042 * allocations" as the KFENCE objects are the only ones 1043 * still in use and the owning cache is being destroyed. 1044 * 1045 * We mark them freed, so that any subsequent use shows 1046 * more useful error messages that will include stack 1047 * traces of the user of the object, the original 1048 * allocation, and caller to shutdown_cache(). 1049 */ 1050 kfence_guarded_free((void *)meta->addr, meta, /*zombie=*/true); 1051 } 1052 } 1053 1054 for (i = 0; i < CONFIG_KFENCE_NUM_OBJECTS; i++) { 1055 meta = &kfence_metadata[i]; 1056 1057 /* See above. */ 1058 if (READ_ONCE(meta->cache) != s || READ_ONCE(meta->state) != KFENCE_OBJECT_FREED) 1059 continue; 1060 1061 raw_spin_lock_irqsave(&meta->lock, flags); 1062 if (meta->cache == s && meta->state == KFENCE_OBJECT_FREED) 1063 meta->cache = NULL; 1064 raw_spin_unlock_irqrestore(&meta->lock, flags); 1065 } 1066 } 1067 1068 void *__kfence_alloc(struct kmem_cache *s, size_t size, gfp_t flags) 1069 { 1070 unsigned long stack_entries[KFENCE_STACK_DEPTH]; 1071 size_t num_stack_entries; 1072 u32 alloc_stack_hash; 1073 int allocation_gate; 1074 1075 /* 1076 * Perform size check before switching kfence_allocation_gate, so that 1077 * we don't disable KFENCE without making an allocation. 1078 */ 1079 if (size > PAGE_SIZE) { 1080 atomic_long_inc(&counters[KFENCE_COUNTER_SKIP_INCOMPAT]); 1081 return NULL; 1082 } 1083 1084 /* 1085 * Skip allocations from non-default zones, including DMA. We cannot 1086 * guarantee that pages in the KFENCE pool will have the requested 1087 * properties (e.g. reside in DMAable memory). 1088 */ 1089 if ((flags & GFP_ZONEMASK) || 1090 ((flags & __GFP_THISNODE) && num_online_nodes() > 1) || 1091 (s->flags & (SLAB_CACHE_DMA | SLAB_CACHE_DMA32))) { 1092 atomic_long_inc(&counters[KFENCE_COUNTER_SKIP_INCOMPAT]); 1093 return NULL; 1094 } 1095 1096 /* 1097 * Skip allocations for this slab, if KFENCE has been disabled for 1098 * this slab. 1099 */ 1100 if (s->flags & SLAB_SKIP_KFENCE) 1101 return NULL; 1102 1103 allocation_gate = atomic_inc_return(&kfence_allocation_gate); 1104 if (allocation_gate > 1) 1105 return NULL; 1106 #ifdef CONFIG_KFENCE_STATIC_KEYS 1107 /* 1108 * waitqueue_active() is fully ordered after the update of 1109 * kfence_allocation_gate per atomic_inc_return(). 1110 */ 1111 if (allocation_gate == 1 && waitqueue_active(&allocation_wait)) { 1112 /* 1113 * Calling wake_up() here may deadlock when allocations happen 1114 * from within timer code. Use an irq_work to defer it. 1115 */ 1116 irq_work_queue(&wake_up_kfence_timer_work); 1117 } 1118 #endif 1119 1120 if (!READ_ONCE(kfence_enabled)) 1121 return NULL; 1122 1123 num_stack_entries = stack_trace_save(stack_entries, KFENCE_STACK_DEPTH, 0); 1124 1125 /* 1126 * Do expensive check for coverage of allocation in slow-path after 1127 * allocation_gate has already become non-zero, even though it might 1128 * mean not making any allocation within a given sample interval. 1129 * 1130 * This ensures reasonable allocation coverage when the pool is almost 1131 * full, including avoiding long-lived allocations of the same source 1132 * filling up the pool (e.g. pagecache allocations). 1133 */ 1134 alloc_stack_hash = get_alloc_stack_hash(stack_entries, num_stack_entries); 1135 if (should_skip_covered() && alloc_covered_contains(alloc_stack_hash)) { 1136 atomic_long_inc(&counters[KFENCE_COUNTER_SKIP_COVERED]); 1137 return NULL; 1138 } 1139 1140 return kfence_guarded_alloc(s, size, flags, stack_entries, num_stack_entries, 1141 alloc_stack_hash); 1142 } 1143 1144 size_t kfence_ksize(const void *addr) 1145 { 1146 const struct kfence_metadata *meta = addr_to_metadata((unsigned long)addr); 1147 1148 /* 1149 * Read locklessly -- if there is a race with __kfence_alloc(), this is 1150 * either a use-after-free or invalid access. 1151 */ 1152 return meta ? meta->size : 0; 1153 } 1154 1155 void *kfence_object_start(const void *addr) 1156 { 1157 const struct kfence_metadata *meta = addr_to_metadata((unsigned long)addr); 1158 1159 /* 1160 * Read locklessly -- if there is a race with __kfence_alloc(), this is 1161 * either a use-after-free or invalid access. 1162 */ 1163 return meta ? (void *)meta->addr : NULL; 1164 } 1165 1166 void __kfence_free(void *addr) 1167 { 1168 struct kfence_metadata *meta = addr_to_metadata((unsigned long)addr); 1169 1170 #ifdef CONFIG_MEMCG 1171 KFENCE_WARN_ON(meta->obj_exts.objcg); 1172 #endif 1173 /* 1174 * If the objects of the cache are SLAB_TYPESAFE_BY_RCU, defer freeing 1175 * the object, as the object page may be recycled for other-typed 1176 * objects once it has been freed. meta->cache may be NULL if the cache 1177 * was destroyed. 1178 * Save the stack trace here so that reports show where the user freed 1179 * the object. 1180 */ 1181 if (unlikely(meta->cache && (meta->cache->flags & SLAB_TYPESAFE_BY_RCU))) { 1182 unsigned long flags; 1183 1184 raw_spin_lock_irqsave(&meta->lock, flags); 1185 metadata_update_state(meta, KFENCE_OBJECT_RCU_FREEING, NULL, 0); 1186 raw_spin_unlock_irqrestore(&meta->lock, flags); 1187 call_rcu(&meta->rcu_head, rcu_guarded_free); 1188 } else { 1189 kfence_guarded_free(addr, meta, false); 1190 } 1191 } 1192 1193 bool kfence_handle_page_fault(unsigned long addr, bool is_write, struct pt_regs *regs) 1194 { 1195 const int page_index = (addr - (unsigned long)__kfence_pool) / PAGE_SIZE; 1196 struct kfence_metadata *to_report = NULL; 1197 enum kfence_error_type error_type; 1198 unsigned long flags; 1199 1200 if (!is_kfence_address((void *)addr)) 1201 return false; 1202 1203 if (!READ_ONCE(kfence_enabled)) /* If disabled at runtime ... */ 1204 return kfence_unprotect(addr); /* ... unprotect and proceed. */ 1205 1206 atomic_long_inc(&counters[KFENCE_COUNTER_BUGS]); 1207 1208 if (page_index % 2) { 1209 /* This is a redzone, report a buffer overflow. */ 1210 struct kfence_metadata *meta; 1211 int distance = 0; 1212 1213 meta = addr_to_metadata(addr - PAGE_SIZE); 1214 if (meta && kfence_obj_allocated(meta)) { 1215 to_report = meta; 1216 /* Data race ok; distance calculation approximate. */ 1217 distance = addr - data_race(meta->addr + meta->size); 1218 } 1219 1220 meta = addr_to_metadata(addr + PAGE_SIZE); 1221 if (meta && kfence_obj_allocated(meta)) { 1222 /* Data race ok; distance calculation approximate. */ 1223 if (!to_report || distance > data_race(meta->addr) - addr) 1224 to_report = meta; 1225 } 1226 1227 if (!to_report) 1228 goto out; 1229 1230 raw_spin_lock_irqsave(&to_report->lock, flags); 1231 to_report->unprotected_page = addr; 1232 error_type = KFENCE_ERROR_OOB; 1233 1234 /* 1235 * If the object was freed before we took the look we can still 1236 * report this as an OOB -- the report will simply show the 1237 * stacktrace of the free as well. 1238 */ 1239 } else { 1240 to_report = addr_to_metadata(addr); 1241 if (!to_report) 1242 goto out; 1243 1244 raw_spin_lock_irqsave(&to_report->lock, flags); 1245 error_type = KFENCE_ERROR_UAF; 1246 /* 1247 * We may race with __kfence_alloc(), and it is possible that a 1248 * freed object may be reallocated. We simply report this as a 1249 * use-after-free, with the stack trace showing the place where 1250 * the object was re-allocated. 1251 */ 1252 } 1253 1254 out: 1255 if (to_report) { 1256 kfence_report_error(addr, is_write, regs, to_report, error_type); 1257 raw_spin_unlock_irqrestore(&to_report->lock, flags); 1258 } else { 1259 /* This may be a UAF or OOB access, but we can't be sure. */ 1260 kfence_report_error(addr, is_write, regs, NULL, KFENCE_ERROR_INVALID); 1261 } 1262 1263 return kfence_unprotect(addr); /* Unprotect and let access proceed. */ 1264 } 1265