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; 598 struct page *pages; 599 int i; 600 601 if (!arch_kfence_init_pool()) 602 return (unsigned long)__kfence_pool; 603 604 addr = (unsigned long)__kfence_pool; 605 pages = virt_to_page(__kfence_pool); 606 607 /* 608 * Set up object pages: they must have PG_slab set, to avoid freeing 609 * these as real pages. 610 * 611 * We also want to avoid inserting kfence_free() in the kfree() 612 * fast-path in SLUB, and therefore need to ensure kfree() correctly 613 * enters __slab_free() slow-path. 614 */ 615 for (i = 0; i < KFENCE_POOL_SIZE / PAGE_SIZE; i++) { 616 struct slab *slab = page_slab(nth_page(pages, i)); 617 618 if (!i || (i % 2)) 619 continue; 620 621 __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 = page_slab(nth_page(pages, i)); 669 670 if (!i || (i % 2)) 671 continue; 672 #ifdef CONFIG_MEMCG 673 slab->obj_exts = 0; 674 #endif 675 __folio_clear_slab(slab_folio(slab)); 676 } 677 678 return addr; 679 } 680 681 static bool __init kfence_init_pool_early(void) 682 { 683 unsigned long addr; 684 685 if (!__kfence_pool) 686 return false; 687 688 addr = kfence_init_pool(); 689 690 if (!addr) { 691 /* 692 * The pool is live and will never be deallocated from this point on. 693 * Ignore the pool object from the kmemleak phys object tree, as it would 694 * otherwise overlap with allocations returned by kfence_alloc(), which 695 * are registered with kmemleak through the slab post-alloc hook. 696 */ 697 kmemleak_ignore_phys(__pa(__kfence_pool)); 698 return true; 699 } 700 701 /* 702 * Only release unprotected pages, and do not try to go back and change 703 * page attributes due to risk of failing to do so as well. If changing 704 * page attributes for some pages fails, it is very likely that it also 705 * fails for the first page, and therefore expect addr==__kfence_pool in 706 * most failure cases. 707 */ 708 memblock_free_late(__pa(addr), KFENCE_POOL_SIZE - (addr - (unsigned long)__kfence_pool)); 709 __kfence_pool = NULL; 710 711 memblock_free_late(__pa(kfence_metadata_init), KFENCE_METADATA_SIZE); 712 kfence_metadata_init = NULL; 713 714 return false; 715 } 716 717 /* === DebugFS Interface ==================================================== */ 718 719 static int stats_show(struct seq_file *seq, void *v) 720 { 721 int i; 722 723 seq_printf(seq, "enabled: %i\n", READ_ONCE(kfence_enabled)); 724 for (i = 0; i < KFENCE_COUNTER_COUNT; i++) 725 seq_printf(seq, "%s: %ld\n", counter_names[i], atomic_long_read(&counters[i])); 726 727 return 0; 728 } 729 DEFINE_SHOW_ATTRIBUTE(stats); 730 731 /* 732 * debugfs seq_file operations for /sys/kernel/debug/kfence/objects. 733 * start_object() and next_object() return the object index + 1, because NULL is used 734 * to stop iteration. 735 */ 736 static void *start_object(struct seq_file *seq, loff_t *pos) 737 { 738 if (*pos < CONFIG_KFENCE_NUM_OBJECTS) 739 return (void *)((long)*pos + 1); 740 return NULL; 741 } 742 743 static void stop_object(struct seq_file *seq, void *v) 744 { 745 } 746 747 static void *next_object(struct seq_file *seq, void *v, loff_t *pos) 748 { 749 ++*pos; 750 if (*pos < CONFIG_KFENCE_NUM_OBJECTS) 751 return (void *)((long)*pos + 1); 752 return NULL; 753 } 754 755 static int show_object(struct seq_file *seq, void *v) 756 { 757 struct kfence_metadata *meta = &kfence_metadata[(long)v - 1]; 758 unsigned long flags; 759 760 raw_spin_lock_irqsave(&meta->lock, flags); 761 kfence_print_object(seq, meta); 762 raw_spin_unlock_irqrestore(&meta->lock, flags); 763 seq_puts(seq, "---------------------------------\n"); 764 765 return 0; 766 } 767 768 static const struct seq_operations objects_sops = { 769 .start = start_object, 770 .next = next_object, 771 .stop = stop_object, 772 .show = show_object, 773 }; 774 DEFINE_SEQ_ATTRIBUTE(objects); 775 776 static int kfence_debugfs_init(void) 777 { 778 struct dentry *kfence_dir; 779 780 if (!READ_ONCE(kfence_enabled)) 781 return 0; 782 783 kfence_dir = debugfs_create_dir("kfence", NULL); 784 debugfs_create_file("stats", 0444, kfence_dir, NULL, &stats_fops); 785 debugfs_create_file("objects", 0400, kfence_dir, NULL, &objects_fops); 786 return 0; 787 } 788 789 late_initcall(kfence_debugfs_init); 790 791 /* === Panic Notifier ====================================================== */ 792 793 static void kfence_check_all_canary(void) 794 { 795 int i; 796 797 for (i = 0; i < CONFIG_KFENCE_NUM_OBJECTS; i++) { 798 struct kfence_metadata *meta = &kfence_metadata[i]; 799 800 if (kfence_obj_allocated(meta)) 801 check_canary(meta); 802 } 803 } 804 805 static int kfence_check_canary_callback(struct notifier_block *nb, 806 unsigned long reason, void *arg) 807 { 808 kfence_check_all_canary(); 809 return NOTIFY_OK; 810 } 811 812 static struct notifier_block kfence_check_canary_notifier = { 813 .notifier_call = kfence_check_canary_callback, 814 }; 815 816 /* === Allocation Gate Timer ================================================ */ 817 818 static struct delayed_work kfence_timer; 819 820 #ifdef CONFIG_KFENCE_STATIC_KEYS 821 /* Wait queue to wake up allocation-gate timer task. */ 822 static DECLARE_WAIT_QUEUE_HEAD(allocation_wait); 823 824 static void wake_up_kfence_timer(struct irq_work *work) 825 { 826 wake_up(&allocation_wait); 827 } 828 static DEFINE_IRQ_WORK(wake_up_kfence_timer_work, wake_up_kfence_timer); 829 #endif 830 831 /* 832 * Set up delayed work, which will enable and disable the static key. We need to 833 * use a work queue (rather than a simple timer), since enabling and disabling a 834 * static key cannot be done from an interrupt. 835 * 836 * Note: Toggling a static branch currently causes IPIs, and here we'll end up 837 * with a total of 2 IPIs to all CPUs. If this ends up a problem in future (with 838 * more aggressive sampling intervals), we could get away with a variant that 839 * avoids IPIs, at the cost of not immediately capturing allocations if the 840 * instructions remain cached. 841 */ 842 static void toggle_allocation_gate(struct work_struct *work) 843 { 844 if (!READ_ONCE(kfence_enabled)) 845 return; 846 847 atomic_set(&kfence_allocation_gate, -kfence_burst); 848 #ifdef CONFIG_KFENCE_STATIC_KEYS 849 /* Enable static key, and await allocation to happen. */ 850 static_branch_enable(&kfence_allocation_key); 851 852 wait_event_idle(allocation_wait, atomic_read(&kfence_allocation_gate) > 0); 853 854 /* Disable static key and reset timer. */ 855 static_branch_disable(&kfence_allocation_key); 856 #endif 857 queue_delayed_work(system_unbound_wq, &kfence_timer, 858 msecs_to_jiffies(kfence_sample_interval)); 859 } 860 861 /* === Public interface ===================================================== */ 862 863 void __init kfence_alloc_pool_and_metadata(void) 864 { 865 if (!kfence_sample_interval) 866 return; 867 868 /* 869 * If the pool has already been initialized by arch, there is no need to 870 * re-allocate the memory pool. 871 */ 872 if (!__kfence_pool) 873 __kfence_pool = memblock_alloc(KFENCE_POOL_SIZE, PAGE_SIZE); 874 875 if (!__kfence_pool) { 876 pr_err("failed to allocate pool\n"); 877 return; 878 } 879 880 /* The memory allocated by memblock has been zeroed out. */ 881 kfence_metadata_init = memblock_alloc(KFENCE_METADATA_SIZE, PAGE_SIZE); 882 if (!kfence_metadata_init) { 883 pr_err("failed to allocate metadata\n"); 884 memblock_free(__kfence_pool, KFENCE_POOL_SIZE); 885 __kfence_pool = NULL; 886 } 887 } 888 889 static void kfence_init_enable(void) 890 { 891 if (!IS_ENABLED(CONFIG_KFENCE_STATIC_KEYS)) 892 static_branch_enable(&kfence_allocation_key); 893 894 if (kfence_deferrable) 895 INIT_DEFERRABLE_WORK(&kfence_timer, toggle_allocation_gate); 896 else 897 INIT_DELAYED_WORK(&kfence_timer, toggle_allocation_gate); 898 899 if (kfence_check_on_panic) 900 atomic_notifier_chain_register(&panic_notifier_list, &kfence_check_canary_notifier); 901 902 WRITE_ONCE(kfence_enabled, true); 903 queue_delayed_work(system_unbound_wq, &kfence_timer, 0); 904 905 pr_info("initialized - using %lu bytes for %d objects at 0x%p-0x%p\n", KFENCE_POOL_SIZE, 906 CONFIG_KFENCE_NUM_OBJECTS, (void *)__kfence_pool, 907 (void *)(__kfence_pool + KFENCE_POOL_SIZE)); 908 } 909 910 void __init kfence_init(void) 911 { 912 stack_hash_seed = get_random_u32(); 913 914 /* Setting kfence_sample_interval to 0 on boot disables KFENCE. */ 915 if (!kfence_sample_interval) 916 return; 917 918 if (!kfence_init_pool_early()) { 919 pr_err("%s failed\n", __func__); 920 return; 921 } 922 923 kfence_init_enable(); 924 } 925 926 static int kfence_init_late(void) 927 { 928 const unsigned long nr_pages_pool = KFENCE_POOL_SIZE / PAGE_SIZE; 929 const unsigned long nr_pages_meta = KFENCE_METADATA_SIZE / PAGE_SIZE; 930 unsigned long addr = (unsigned long)__kfence_pool; 931 unsigned long free_size = KFENCE_POOL_SIZE; 932 int err = -ENOMEM; 933 934 #ifdef CONFIG_CONTIG_ALLOC 935 struct page *pages; 936 937 pages = alloc_contig_pages(nr_pages_pool, GFP_KERNEL, first_online_node, 938 NULL); 939 if (!pages) 940 return -ENOMEM; 941 942 __kfence_pool = page_to_virt(pages); 943 pages = alloc_contig_pages(nr_pages_meta, GFP_KERNEL, first_online_node, 944 NULL); 945 if (pages) 946 kfence_metadata_init = page_to_virt(pages); 947 #else 948 if (nr_pages_pool > MAX_ORDER_NR_PAGES || 949 nr_pages_meta > MAX_ORDER_NR_PAGES) { 950 pr_warn("KFENCE_NUM_OBJECTS too large for buddy allocator\n"); 951 return -EINVAL; 952 } 953 954 __kfence_pool = alloc_pages_exact(KFENCE_POOL_SIZE, GFP_KERNEL); 955 if (!__kfence_pool) 956 return -ENOMEM; 957 958 kfence_metadata_init = alloc_pages_exact(KFENCE_METADATA_SIZE, GFP_KERNEL); 959 #endif 960 961 if (!kfence_metadata_init) 962 goto free_pool; 963 964 memzero_explicit(kfence_metadata_init, KFENCE_METADATA_SIZE); 965 addr = kfence_init_pool(); 966 if (!addr) { 967 kfence_init_enable(); 968 kfence_debugfs_init(); 969 return 0; 970 } 971 972 pr_err("%s failed\n", __func__); 973 free_size = KFENCE_POOL_SIZE - (addr - (unsigned long)__kfence_pool); 974 err = -EBUSY; 975 976 #ifdef CONFIG_CONTIG_ALLOC 977 free_contig_range(page_to_pfn(virt_to_page((void *)kfence_metadata_init)), 978 nr_pages_meta); 979 free_pool: 980 free_contig_range(page_to_pfn(virt_to_page((void *)addr)), 981 free_size / PAGE_SIZE); 982 #else 983 free_pages_exact((void *)kfence_metadata_init, KFENCE_METADATA_SIZE); 984 free_pool: 985 free_pages_exact((void *)addr, free_size); 986 #endif 987 988 kfence_metadata_init = NULL; 989 __kfence_pool = NULL; 990 return err; 991 } 992 993 static int kfence_enable_late(void) 994 { 995 if (!__kfence_pool) 996 return kfence_init_late(); 997 998 WRITE_ONCE(kfence_enabled, true); 999 queue_delayed_work(system_unbound_wq, &kfence_timer, 0); 1000 pr_info("re-enabled\n"); 1001 return 0; 1002 } 1003 1004 void kfence_shutdown_cache(struct kmem_cache *s) 1005 { 1006 unsigned long flags; 1007 struct kfence_metadata *meta; 1008 int i; 1009 1010 /* Pairs with release in kfence_init_pool(). */ 1011 if (!smp_load_acquire(&kfence_metadata)) 1012 return; 1013 1014 for (i = 0; i < CONFIG_KFENCE_NUM_OBJECTS; i++) { 1015 bool in_use; 1016 1017 meta = &kfence_metadata[i]; 1018 1019 /* 1020 * If we observe some inconsistent cache and state pair where we 1021 * should have returned false here, cache destruction is racing 1022 * with either kmem_cache_alloc() or kmem_cache_free(). Taking 1023 * the lock will not help, as different critical section 1024 * serialization will have the same outcome. 1025 */ 1026 if (READ_ONCE(meta->cache) != s || !kfence_obj_allocated(meta)) 1027 continue; 1028 1029 raw_spin_lock_irqsave(&meta->lock, flags); 1030 in_use = meta->cache == s && kfence_obj_allocated(meta); 1031 raw_spin_unlock_irqrestore(&meta->lock, flags); 1032 1033 if (in_use) { 1034 /* 1035 * This cache still has allocations, and we should not 1036 * release them back into the freelist so they can still 1037 * safely be used and retain the kernel's default 1038 * behaviour of keeping the allocations alive (leak the 1039 * cache); however, they effectively become "zombie 1040 * allocations" as the KFENCE objects are the only ones 1041 * still in use and the owning cache is being destroyed. 1042 * 1043 * We mark them freed, so that any subsequent use shows 1044 * more useful error messages that will include stack 1045 * traces of the user of the object, the original 1046 * allocation, and caller to shutdown_cache(). 1047 */ 1048 kfence_guarded_free((void *)meta->addr, meta, /*zombie=*/true); 1049 } 1050 } 1051 1052 for (i = 0; i < CONFIG_KFENCE_NUM_OBJECTS; i++) { 1053 meta = &kfence_metadata[i]; 1054 1055 /* See above. */ 1056 if (READ_ONCE(meta->cache) != s || READ_ONCE(meta->state) != KFENCE_OBJECT_FREED) 1057 continue; 1058 1059 raw_spin_lock_irqsave(&meta->lock, flags); 1060 if (meta->cache == s && meta->state == KFENCE_OBJECT_FREED) 1061 meta->cache = NULL; 1062 raw_spin_unlock_irqrestore(&meta->lock, flags); 1063 } 1064 } 1065 1066 void *__kfence_alloc(struct kmem_cache *s, size_t size, gfp_t flags) 1067 { 1068 unsigned long stack_entries[KFENCE_STACK_DEPTH]; 1069 size_t num_stack_entries; 1070 u32 alloc_stack_hash; 1071 int allocation_gate; 1072 1073 /* 1074 * Perform size check before switching kfence_allocation_gate, so that 1075 * we don't disable KFENCE without making an allocation. 1076 */ 1077 if (size > PAGE_SIZE) { 1078 atomic_long_inc(&counters[KFENCE_COUNTER_SKIP_INCOMPAT]); 1079 return NULL; 1080 } 1081 1082 /* 1083 * Skip allocations from non-default zones, including DMA. We cannot 1084 * guarantee that pages in the KFENCE pool will have the requested 1085 * properties (e.g. reside in DMAable memory). 1086 */ 1087 if ((flags & GFP_ZONEMASK) || 1088 ((flags & __GFP_THISNODE) && num_online_nodes() > 1) || 1089 (s->flags & (SLAB_CACHE_DMA | SLAB_CACHE_DMA32))) { 1090 atomic_long_inc(&counters[KFENCE_COUNTER_SKIP_INCOMPAT]); 1091 return NULL; 1092 } 1093 1094 /* 1095 * Skip allocations for this slab, if KFENCE has been disabled for 1096 * this slab. 1097 */ 1098 if (s->flags & SLAB_SKIP_KFENCE) 1099 return NULL; 1100 1101 allocation_gate = atomic_inc_return(&kfence_allocation_gate); 1102 if (allocation_gate > 1) 1103 return NULL; 1104 #ifdef CONFIG_KFENCE_STATIC_KEYS 1105 /* 1106 * waitqueue_active() is fully ordered after the update of 1107 * kfence_allocation_gate per atomic_inc_return(). 1108 */ 1109 if (allocation_gate == 1 && waitqueue_active(&allocation_wait)) { 1110 /* 1111 * Calling wake_up() here may deadlock when allocations happen 1112 * from within timer code. Use an irq_work to defer it. 1113 */ 1114 irq_work_queue(&wake_up_kfence_timer_work); 1115 } 1116 #endif 1117 1118 if (!READ_ONCE(kfence_enabled)) 1119 return NULL; 1120 1121 num_stack_entries = stack_trace_save(stack_entries, KFENCE_STACK_DEPTH, 0); 1122 1123 /* 1124 * Do expensive check for coverage of allocation in slow-path after 1125 * allocation_gate has already become non-zero, even though it might 1126 * mean not making any allocation within a given sample interval. 1127 * 1128 * This ensures reasonable allocation coverage when the pool is almost 1129 * full, including avoiding long-lived allocations of the same source 1130 * filling up the pool (e.g. pagecache allocations). 1131 */ 1132 alloc_stack_hash = get_alloc_stack_hash(stack_entries, num_stack_entries); 1133 if (should_skip_covered() && alloc_covered_contains(alloc_stack_hash)) { 1134 atomic_long_inc(&counters[KFENCE_COUNTER_SKIP_COVERED]); 1135 return NULL; 1136 } 1137 1138 return kfence_guarded_alloc(s, size, flags, stack_entries, num_stack_entries, 1139 alloc_stack_hash); 1140 } 1141 1142 size_t kfence_ksize(const void *addr) 1143 { 1144 const struct kfence_metadata *meta = addr_to_metadata((unsigned long)addr); 1145 1146 /* 1147 * Read locklessly -- if there is a race with __kfence_alloc(), this is 1148 * either a use-after-free or invalid access. 1149 */ 1150 return meta ? meta->size : 0; 1151 } 1152 1153 void *kfence_object_start(const void *addr) 1154 { 1155 const struct kfence_metadata *meta = addr_to_metadata((unsigned long)addr); 1156 1157 /* 1158 * Read locklessly -- if there is a race with __kfence_alloc(), this is 1159 * either a use-after-free or invalid access. 1160 */ 1161 return meta ? (void *)meta->addr : NULL; 1162 } 1163 1164 void __kfence_free(void *addr) 1165 { 1166 struct kfence_metadata *meta = addr_to_metadata((unsigned long)addr); 1167 1168 #ifdef CONFIG_MEMCG 1169 KFENCE_WARN_ON(meta->obj_exts.objcg); 1170 #endif 1171 /* 1172 * If the objects of the cache are SLAB_TYPESAFE_BY_RCU, defer freeing 1173 * the object, as the object page may be recycled for other-typed 1174 * objects once it has been freed. meta->cache may be NULL if the cache 1175 * was destroyed. 1176 * Save the stack trace here so that reports show where the user freed 1177 * the object. 1178 */ 1179 if (unlikely(meta->cache && (meta->cache->flags & SLAB_TYPESAFE_BY_RCU))) { 1180 unsigned long flags; 1181 1182 raw_spin_lock_irqsave(&meta->lock, flags); 1183 metadata_update_state(meta, KFENCE_OBJECT_RCU_FREEING, NULL, 0); 1184 raw_spin_unlock_irqrestore(&meta->lock, flags); 1185 call_rcu(&meta->rcu_head, rcu_guarded_free); 1186 } else { 1187 kfence_guarded_free(addr, meta, false); 1188 } 1189 } 1190 1191 bool kfence_handle_page_fault(unsigned long addr, bool is_write, struct pt_regs *regs) 1192 { 1193 const int page_index = (addr - (unsigned long)__kfence_pool) / PAGE_SIZE; 1194 struct kfence_metadata *to_report = NULL; 1195 enum kfence_error_type error_type; 1196 unsigned long flags; 1197 1198 if (!is_kfence_address((void *)addr)) 1199 return false; 1200 1201 if (!READ_ONCE(kfence_enabled)) /* If disabled at runtime ... */ 1202 return kfence_unprotect(addr); /* ... unprotect and proceed. */ 1203 1204 atomic_long_inc(&counters[KFENCE_COUNTER_BUGS]); 1205 1206 if (page_index % 2) { 1207 /* This is a redzone, report a buffer overflow. */ 1208 struct kfence_metadata *meta; 1209 int distance = 0; 1210 1211 meta = addr_to_metadata(addr - PAGE_SIZE); 1212 if (meta && kfence_obj_allocated(meta)) { 1213 to_report = meta; 1214 /* Data race ok; distance calculation approximate. */ 1215 distance = addr - data_race(meta->addr + meta->size); 1216 } 1217 1218 meta = addr_to_metadata(addr + PAGE_SIZE); 1219 if (meta && kfence_obj_allocated(meta)) { 1220 /* Data race ok; distance calculation approximate. */ 1221 if (!to_report || distance > data_race(meta->addr) - addr) 1222 to_report = meta; 1223 } 1224 1225 if (!to_report) 1226 goto out; 1227 1228 raw_spin_lock_irqsave(&to_report->lock, flags); 1229 to_report->unprotected_page = addr; 1230 error_type = KFENCE_ERROR_OOB; 1231 1232 /* 1233 * If the object was freed before we took the look we can still 1234 * report this as an OOB -- the report will simply show the 1235 * stacktrace of the free as well. 1236 */ 1237 } else { 1238 to_report = addr_to_metadata(addr); 1239 if (!to_report) 1240 goto out; 1241 1242 raw_spin_lock_irqsave(&to_report->lock, flags); 1243 error_type = KFENCE_ERROR_UAF; 1244 /* 1245 * We may race with __kfence_alloc(), and it is possible that a 1246 * freed object may be reallocated. We simply report this as a 1247 * use-after-free, with the stack trace showing the place where 1248 * the object was re-allocated. 1249 */ 1250 } 1251 1252 out: 1253 if (to_report) { 1254 kfence_report_error(addr, is_write, regs, to_report, error_type); 1255 raw_spin_unlock_irqrestore(&to_report->lock, flags); 1256 } else { 1257 /* This may be a UAF or OOB access, but we can't be sure. */ 1258 kfence_report_error(addr, is_write, regs, NULL, KFENCE_ERROR_INVALID); 1259 } 1260 1261 return kfence_unprotect(addr); /* Unprotect and let access proceed. */ 1262 } 1263