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/kasan-enabled.h> 17 #include <linux/kcsan-checks.h> 18 #include <linux/kfence.h> 19 #include <linux/kmemleak.h> 20 #include <linux/list.h> 21 #include <linux/lockdep.h> 22 #include <linux/log2.h> 23 #include <linux/memblock.h> 24 #include <linux/moduleparam.h> 25 #include <linux/nodemask.h> 26 #include <linux/notifier.h> 27 #include <linux/panic_notifier.h> 28 #include <linux/random.h> 29 #include <linux/rcupdate.h> 30 #include <linux/reboot.h> 31 #include <linux/sched/clock.h> 32 #include <linux/seq_file.h> 33 #include <linux/slab.h> 34 #include <linux/spinlock.h> 35 #include <linux/string.h> 36 37 #include <asm/kfence.h> 38 39 #include "kfence.h" 40 41 /* Disables KFENCE on the first warning assuming an irrecoverable error. */ 42 #define KFENCE_WARN_ON(cond) \ 43 ({ \ 44 const bool __cond = WARN_ON(cond); \ 45 if (unlikely(__cond)) { \ 46 WRITE_ONCE(kfence_enabled, false); \ 47 disabled_by_warn = true; \ 48 } \ 49 __cond; \ 50 }) 51 52 /* === Data ================================================================= */ 53 54 bool kfence_enabled __read_mostly; 55 static bool disabled_by_warn __read_mostly; 56 57 unsigned long kfence_sample_interval __read_mostly = CONFIG_KFENCE_SAMPLE_INTERVAL; 58 EXPORT_SYMBOL_GPL(kfence_sample_interval); /* Export for test modules. */ 59 60 #ifdef MODULE_PARAM_PREFIX 61 #undef MODULE_PARAM_PREFIX 62 #endif 63 #define MODULE_PARAM_PREFIX "kfence." 64 65 static int kfence_enable_late(void); 66 static int param_set_sample_interval(const char *val, const struct kernel_param *kp) 67 { 68 unsigned long num; 69 int ret = kstrtoul(val, 0, &num); 70 71 if (ret < 0) 72 return ret; 73 74 /* Using 0 to indicate KFENCE is disabled. */ 75 if (!num && READ_ONCE(kfence_enabled)) { 76 pr_info("disabled\n"); 77 WRITE_ONCE(kfence_enabled, false); 78 } 79 80 *((unsigned long *)kp->arg) = num; 81 82 if (num && !READ_ONCE(kfence_enabled) && system_state != SYSTEM_BOOTING) 83 return disabled_by_warn ? -EINVAL : kfence_enable_late(); 84 return 0; 85 } 86 87 static int param_get_sample_interval(char *buffer, const struct kernel_param *kp) 88 { 89 if (!READ_ONCE(kfence_enabled)) 90 return sprintf(buffer, "0\n"); 91 92 return param_get_ulong(buffer, kp); 93 } 94 95 static const struct kernel_param_ops sample_interval_param_ops = { 96 .set = param_set_sample_interval, 97 .get = param_get_sample_interval, 98 }; 99 module_param_cb(sample_interval, &sample_interval_param_ops, &kfence_sample_interval, 0600); 100 101 /* Pool usage% threshold when currently covered allocations are skipped. */ 102 static unsigned long kfence_skip_covered_thresh __read_mostly = 75; 103 module_param_named(skip_covered_thresh, kfence_skip_covered_thresh, ulong, 0644); 104 105 /* Allocation burst count: number of excess KFENCE allocations per sample. */ 106 static unsigned int kfence_burst __read_mostly; 107 module_param_named(burst, kfence_burst, uint, 0644); 108 109 /* If true, use a deferrable timer. */ 110 static bool kfence_deferrable __read_mostly = IS_ENABLED(CONFIG_KFENCE_DEFERRABLE); 111 module_param_named(deferrable, kfence_deferrable, bool, 0444); 112 113 /* If true, check all canary bytes on panic. */ 114 static bool kfence_check_on_panic __read_mostly; 115 module_param_named(check_on_panic, kfence_check_on_panic, bool, 0444); 116 117 /* The pool of pages used for guard pages and objects. */ 118 char *__kfence_pool __read_mostly; 119 EXPORT_SYMBOL(__kfence_pool); /* Export for test modules. */ 120 121 /* 122 * Per-object metadata, with one-to-one mapping of object metadata to 123 * backing pages (in __kfence_pool). 124 */ 125 static_assert(CONFIG_KFENCE_NUM_OBJECTS > 0); 126 struct kfence_metadata *kfence_metadata __read_mostly; 127 128 /* 129 * If kfence_metadata is not NULL, it may be accessed by kfence_shutdown_cache(). 130 * So introduce kfence_metadata_init to initialize metadata, and then make 131 * kfence_metadata visible after initialization is successful. This prevents 132 * potential UAF or access to uninitialized metadata. 133 */ 134 static struct kfence_metadata *kfence_metadata_init __read_mostly; 135 136 /* Freelist with available objects. */ 137 DEFINE_RAW_SPINLOCK(kfence_freelist_lock); /* Lock protecting freelist. */ 138 static struct list_head kfence_freelist __guarded_by(&kfence_freelist_lock) = LIST_HEAD_INIT(kfence_freelist); 139 140 /* 141 * The static key to set up a KFENCE allocation; or if static keys are not used 142 * to gate allocations, to avoid a load and compare if KFENCE is disabled. 143 */ 144 DEFINE_STATIC_KEY_FALSE(kfence_allocation_key); 145 146 /* Gates the allocation, ensuring only one succeeds in a given period. */ 147 atomic_t kfence_allocation_gate = ATOMIC_INIT(1); 148 149 /* 150 * A Counting Bloom filter of allocation coverage: limits currently covered 151 * allocations of the same source filling up the pool. 152 * 153 * Assuming a range of 15%-85% unique allocations in the pool at any point in 154 * time, the below parameters provide a probablity of 0.02-0.33 for false 155 * positive hits respectively: 156 * 157 * P(alloc_traces) = (1 - e^(-HNUM * (alloc_traces / SIZE)) ^ HNUM 158 */ 159 #define ALLOC_COVERED_HNUM 2 160 #define ALLOC_COVERED_ORDER (const_ilog2(CONFIG_KFENCE_NUM_OBJECTS) + 2) 161 #define ALLOC_COVERED_SIZE (1 << ALLOC_COVERED_ORDER) 162 #define ALLOC_COVERED_HNEXT(h) hash_32(h, ALLOC_COVERED_ORDER) 163 #define ALLOC_COVERED_MASK (ALLOC_COVERED_SIZE - 1) 164 static atomic_t alloc_covered[ALLOC_COVERED_SIZE]; 165 166 /* Stack depth used to determine uniqueness of an allocation. */ 167 #define UNIQUE_ALLOC_STACK_DEPTH ((size_t)8) 168 169 /* 170 * Randomness for stack hashes, making the same collisions across reboots and 171 * different machines less likely. 172 */ 173 static u32 stack_hash_seed __ro_after_init; 174 175 /* Statistics counters for debugfs. */ 176 enum kfence_counter_id { 177 KFENCE_COUNTER_ALLOCATED, 178 KFENCE_COUNTER_ALLOCS, 179 KFENCE_COUNTER_FREES, 180 KFENCE_COUNTER_ZOMBIES, 181 KFENCE_COUNTER_BUGS, 182 KFENCE_COUNTER_SKIP_INCOMPAT, 183 KFENCE_COUNTER_SKIP_CAPACITY, 184 KFENCE_COUNTER_SKIP_COVERED, 185 KFENCE_COUNTER_COUNT, 186 }; 187 static atomic_long_t counters[KFENCE_COUNTER_COUNT]; 188 static const char *const counter_names[] = { 189 [KFENCE_COUNTER_ALLOCATED] = "currently allocated", 190 [KFENCE_COUNTER_ALLOCS] = "total allocations", 191 [KFENCE_COUNTER_FREES] = "total frees", 192 [KFENCE_COUNTER_ZOMBIES] = "zombie allocations", 193 [KFENCE_COUNTER_BUGS] = "total bugs", 194 [KFENCE_COUNTER_SKIP_INCOMPAT] = "skipped allocations (incompatible)", 195 [KFENCE_COUNTER_SKIP_CAPACITY] = "skipped allocations (capacity)", 196 [KFENCE_COUNTER_SKIP_COVERED] = "skipped allocations (covered)", 197 }; 198 static_assert(ARRAY_SIZE(counter_names) == KFENCE_COUNTER_COUNT); 199 200 /* === Internals ============================================================ */ 201 202 static inline bool should_skip_covered(void) 203 { 204 unsigned long thresh = (CONFIG_KFENCE_NUM_OBJECTS * kfence_skip_covered_thresh) / 100; 205 206 return atomic_long_read(&counters[KFENCE_COUNTER_ALLOCATED]) > thresh; 207 } 208 209 static u32 get_alloc_stack_hash(unsigned long *stack_entries, size_t num_entries) 210 { 211 num_entries = min(num_entries, UNIQUE_ALLOC_STACK_DEPTH); 212 num_entries = filter_irq_stacks(stack_entries, num_entries); 213 return jhash(stack_entries, num_entries * sizeof(stack_entries[0]), stack_hash_seed); 214 } 215 216 /* 217 * Adds (or subtracts) count @val for allocation stack trace hash 218 * @alloc_stack_hash from Counting Bloom filter. 219 */ 220 static void alloc_covered_add(u32 alloc_stack_hash, int val) 221 { 222 int i; 223 224 for (i = 0; i < ALLOC_COVERED_HNUM; i++) { 225 atomic_add(val, &alloc_covered[alloc_stack_hash & ALLOC_COVERED_MASK]); 226 alloc_stack_hash = ALLOC_COVERED_HNEXT(alloc_stack_hash); 227 } 228 } 229 230 /* 231 * Returns true if the allocation stack trace hash @alloc_stack_hash is 232 * currently contained (non-zero count) in Counting Bloom filter. 233 */ 234 static bool alloc_covered_contains(u32 alloc_stack_hash) 235 { 236 int i; 237 238 for (i = 0; i < ALLOC_COVERED_HNUM; i++) { 239 if (!atomic_read(&alloc_covered[alloc_stack_hash & ALLOC_COVERED_MASK])) 240 return false; 241 alloc_stack_hash = ALLOC_COVERED_HNEXT(alloc_stack_hash); 242 } 243 244 return true; 245 } 246 247 static bool kfence_protect(unsigned long addr) 248 { 249 return !KFENCE_WARN_ON(!kfence_protect_page(ALIGN_DOWN(addr, PAGE_SIZE), true)); 250 } 251 252 static bool kfence_unprotect(unsigned long addr) 253 { 254 return !KFENCE_WARN_ON(!kfence_protect_page(ALIGN_DOWN(addr, PAGE_SIZE), false)); 255 } 256 257 static inline unsigned long metadata_to_pageaddr(const struct kfence_metadata *meta) 258 __must_hold(&meta->lock) 259 { 260 unsigned long offset = (meta - kfence_metadata + 1) * PAGE_SIZE * 2; 261 unsigned long pageaddr = (unsigned long)&__kfence_pool[offset]; 262 263 /* The checks do not affect performance; only called from slow-paths. */ 264 265 /* Only call with a pointer into kfence_metadata. */ 266 if (KFENCE_WARN_ON(meta < kfence_metadata || 267 meta >= kfence_metadata + CONFIG_KFENCE_NUM_OBJECTS)) 268 return 0; 269 270 /* 271 * This metadata object only ever maps to 1 page; verify that the stored 272 * address is in the expected range. 273 */ 274 if (KFENCE_WARN_ON(ALIGN_DOWN(meta->addr, PAGE_SIZE) != pageaddr)) 275 return 0; 276 277 return pageaddr; 278 } 279 280 static inline bool kfence_obj_allocated(const struct kfence_metadata *meta) 281 { 282 enum kfence_object_state state = READ_ONCE(meta->state); 283 284 return state == KFENCE_OBJECT_ALLOCATED || state == KFENCE_OBJECT_RCU_FREEING; 285 } 286 287 /* 288 * Update the object's metadata state, including updating the alloc/free stacks 289 * depending on the state transition. 290 */ 291 static noinline void 292 metadata_update_state(struct kfence_metadata *meta, enum kfence_object_state next, 293 unsigned long *stack_entries, size_t num_stack_entries) 294 __must_hold(&meta->lock) 295 { 296 struct kfence_track *track = 297 next == KFENCE_OBJECT_ALLOCATED ? &meta->alloc_track : &meta->free_track; 298 299 lockdep_assert_held(&meta->lock); 300 301 /* Stack has been saved when calling rcu, skip. */ 302 if (READ_ONCE(meta->state) == KFENCE_OBJECT_RCU_FREEING) 303 goto out; 304 305 if (stack_entries) { 306 memcpy(track->stack_entries, stack_entries, 307 num_stack_entries * sizeof(stack_entries[0])); 308 } else { 309 /* 310 * Skip over 1 (this) functions; noinline ensures we do not 311 * accidentally skip over the caller by never inlining. 312 */ 313 num_stack_entries = stack_trace_save(track->stack_entries, KFENCE_STACK_DEPTH, 1); 314 } 315 track->num_stack_entries = num_stack_entries; 316 track->pid = task_pid_nr(current); 317 track->cpu = raw_smp_processor_id(); 318 track->ts_nsec = local_clock(); /* Same source as printk timestamps. */ 319 320 out: 321 /* 322 * Pairs with READ_ONCE() in 323 * kfence_shutdown_cache(), 324 * kfence_handle_page_fault(). 325 */ 326 WRITE_ONCE(meta->state, next); 327 } 328 329 #ifdef CONFIG_KMSAN 330 #define check_canary_attributes noinline __no_kmsan_checks 331 #else 332 #define check_canary_attributes inline 333 #endif 334 335 /* Check canary byte at @addr. */ 336 static check_canary_attributes bool check_canary_byte(u8 *addr) 337 { 338 struct kfence_metadata *meta; 339 enum kfence_fault fault; 340 unsigned long flags; 341 342 if (likely(*addr == KFENCE_CANARY_PATTERN_U8(addr))) 343 return true; 344 345 atomic_long_inc(&counters[KFENCE_COUNTER_BUGS]); 346 347 meta = addr_to_metadata((unsigned long)addr); 348 raw_spin_lock_irqsave(&meta->lock, flags); 349 fault = kfence_report_error((unsigned long)addr, false, NULL, meta, KFENCE_ERROR_CORRUPTION); 350 raw_spin_unlock_irqrestore(&meta->lock, flags); 351 kfence_handle_fault(fault); 352 353 return false; 354 } 355 356 static inline void set_canary(const struct kfence_metadata *meta) 357 { 358 const unsigned long pageaddr = ALIGN_DOWN(meta->addr, PAGE_SIZE); 359 unsigned long addr = pageaddr; 360 361 /* 362 * The canary may be written to part of the object memory, but it does 363 * not affect it. The user should initialize the object before using it. 364 */ 365 for (; addr < meta->addr; addr += sizeof(u64)) 366 *((u64 *)addr) = KFENCE_CANARY_PATTERN_U64; 367 368 addr = ALIGN_DOWN(meta->addr + meta->size, sizeof(u64)); 369 for (; addr - pageaddr < PAGE_SIZE; addr += sizeof(u64)) 370 *((u64 *)addr) = KFENCE_CANARY_PATTERN_U64; 371 } 372 373 static check_canary_attributes void 374 check_canary(const struct kfence_metadata *meta) 375 { 376 const unsigned long pageaddr = ALIGN_DOWN(meta->addr, PAGE_SIZE); 377 unsigned long addr = pageaddr; 378 379 /* 380 * We'll iterate over each canary byte per-side until a corrupted byte 381 * is found. However, we'll still iterate over the canary bytes to the 382 * right of the object even if there was an error in the canary bytes to 383 * the left of the object. Specifically, if check_canary_byte() 384 * generates an error, showing both sides might give more clues as to 385 * what the error is about when displaying which bytes were corrupted. 386 */ 387 388 /* Apply to left of object. */ 389 for (; meta->addr - addr >= sizeof(u64); addr += sizeof(u64)) { 390 if (unlikely(*((u64 *)addr) != KFENCE_CANARY_PATTERN_U64)) 391 break; 392 } 393 394 /* 395 * If the canary is corrupted in a certain 64 bytes, or the canary 396 * memory cannot be completely covered by multiple consecutive 64 bytes, 397 * it needs to be checked one by one. 398 */ 399 for (; addr < meta->addr; addr++) { 400 if (unlikely(!check_canary_byte((u8 *)addr))) 401 break; 402 } 403 404 /* Apply to right of object. */ 405 for (addr = meta->addr + meta->size; addr % sizeof(u64) != 0; addr++) { 406 if (unlikely(!check_canary_byte((u8 *)addr))) 407 return; 408 } 409 for (; addr - pageaddr < PAGE_SIZE; addr += sizeof(u64)) { 410 if (unlikely(*((u64 *)addr) != KFENCE_CANARY_PATTERN_U64)) { 411 412 for (; addr - pageaddr < PAGE_SIZE; addr++) { 413 if (!check_canary_byte((u8 *)addr)) 414 return; 415 } 416 } 417 } 418 } 419 420 static void *kfence_guarded_alloc(struct kmem_cache *cache, size_t size, gfp_t gfp, 421 unsigned long *stack_entries, size_t num_stack_entries, 422 u32 alloc_stack_hash) 423 { 424 struct kfence_metadata *meta = NULL; 425 unsigned long flags; 426 struct slab *slab; 427 void *addr; 428 const bool random_right_allocate = get_random_u32_below(2); 429 const bool random_fault = CONFIG_KFENCE_STRESS_TEST_FAULTS && 430 !get_random_u32_below(CONFIG_KFENCE_STRESS_TEST_FAULTS); 431 432 /* Try to obtain a free object. */ 433 raw_spin_lock_irqsave(&kfence_freelist_lock, flags); 434 if (!list_empty(&kfence_freelist)) { 435 meta = list_entry(kfence_freelist.next, struct kfence_metadata, list); 436 list_del_init(&meta->list); 437 } 438 raw_spin_unlock_irqrestore(&kfence_freelist_lock, flags); 439 if (!meta) { 440 atomic_long_inc(&counters[KFENCE_COUNTER_SKIP_CAPACITY]); 441 return NULL; 442 } 443 444 if (unlikely(!raw_spin_trylock_irqsave(&meta->lock, flags))) { 445 /* 446 * This is extremely unlikely -- we are reporting on a 447 * use-after-free, which locked meta->lock, and the reporting 448 * code via printk calls kmalloc() which ends up in 449 * kfence_alloc() and tries to grab the same object that we're 450 * reporting on. While it has never been observed, lockdep does 451 * report that there is a possibility of deadlock. Fix it by 452 * using trylock and bailing out gracefully. 453 */ 454 raw_spin_lock_irqsave(&kfence_freelist_lock, flags); 455 /* Put the object back on the freelist. */ 456 list_add_tail(&meta->list, &kfence_freelist); 457 raw_spin_unlock_irqrestore(&kfence_freelist_lock, flags); 458 459 return NULL; 460 } 461 462 meta->addr = metadata_to_pageaddr(meta); 463 /* Unprotect if we're reusing this page. */ 464 if (meta->state == KFENCE_OBJECT_FREED) 465 kfence_unprotect(meta->addr); 466 467 /* 468 * Note: for allocations made before RNG initialization, will always 469 * return zero. We still benefit from enabling KFENCE as early as 470 * possible, even when the RNG is not yet available, as this will allow 471 * KFENCE to detect bugs due to earlier allocations. The only downside 472 * is that the out-of-bounds accesses detected are deterministic for 473 * such allocations. 474 */ 475 if (random_right_allocate) { 476 /* Allocate on the "right" side, re-calculate address. */ 477 meta->addr += PAGE_SIZE - size; 478 meta->addr = ALIGN_DOWN(meta->addr, cache->align); 479 } 480 481 addr = (void *)meta->addr; 482 483 /* Update remaining metadata. */ 484 metadata_update_state(meta, KFENCE_OBJECT_ALLOCATED, stack_entries, num_stack_entries); 485 /* Pairs with READ_ONCE() in kfence_shutdown_cache(). */ 486 WRITE_ONCE(meta->cache, cache); 487 meta->size = size; 488 meta->alloc_stack_hash = alloc_stack_hash; 489 raw_spin_unlock_irqrestore(&meta->lock, flags); 490 491 alloc_covered_add(alloc_stack_hash, 1); 492 493 /* Set required slab fields. */ 494 slab = virt_to_slab(addr); 495 slab->slab_cache = cache; 496 slab->objects = 1; 497 498 /* Memory initialization. */ 499 set_canary(meta); 500 501 /* 502 * We check slab_want_init_on_alloc() ourselves, rather than letting 503 * SL*B do the initialization, as otherwise we might overwrite KFENCE's 504 * redzone. 505 */ 506 if (unlikely(slab_want_init_on_alloc(gfp, cache))) 507 memzero_explicit(addr, size); 508 if (cache->ctor) 509 cache->ctor(addr); 510 511 if (random_fault) 512 kfence_protect(meta->addr); /* Random "faults" by protecting the object. */ 513 514 atomic_long_inc(&counters[KFENCE_COUNTER_ALLOCATED]); 515 atomic_long_inc(&counters[KFENCE_COUNTER_ALLOCS]); 516 517 return addr; 518 } 519 520 static void kfence_guarded_free(void *addr, struct kfence_metadata *meta, bool zombie) 521 { 522 struct kcsan_scoped_access assert_page_exclusive; 523 u32 alloc_stack_hash; 524 unsigned long flags; 525 bool init; 526 527 raw_spin_lock_irqsave(&meta->lock, flags); 528 529 if (!kfence_obj_allocated(meta) || meta->addr != (unsigned long)addr) { 530 enum kfence_fault fault; 531 532 /* Invalid or double-free, bail out. */ 533 atomic_long_inc(&counters[KFENCE_COUNTER_BUGS]); 534 fault = kfence_report_error((unsigned long)addr, false, NULL, meta, 535 KFENCE_ERROR_INVALID_FREE); 536 raw_spin_unlock_irqrestore(&meta->lock, flags); 537 kfence_handle_fault(fault); 538 return; 539 } 540 541 /* Detect racy use-after-free, or incorrect reallocation of this page by KFENCE. */ 542 kcsan_begin_scoped_access((void *)ALIGN_DOWN((unsigned long)addr, PAGE_SIZE), PAGE_SIZE, 543 KCSAN_ACCESS_SCOPED | KCSAN_ACCESS_WRITE | KCSAN_ACCESS_ASSERT, 544 &assert_page_exclusive); 545 546 if (CONFIG_KFENCE_STRESS_TEST_FAULTS) 547 kfence_unprotect((unsigned long)addr); /* To check canary bytes. */ 548 549 /* Restore page protection if there was an OOB access. */ 550 if (meta->unprotected_page) { 551 memzero_explicit((void *)ALIGN_DOWN(meta->unprotected_page, PAGE_SIZE), PAGE_SIZE); 552 kfence_protect(meta->unprotected_page); 553 meta->unprotected_page = 0; 554 } 555 556 /* Mark the object as freed. */ 557 metadata_update_state(meta, KFENCE_OBJECT_FREED, NULL, 0); 558 init = slab_want_init_on_free(meta->cache); 559 alloc_stack_hash = meta->alloc_stack_hash; 560 raw_spin_unlock_irqrestore(&meta->lock, flags); 561 562 alloc_covered_add(alloc_stack_hash, -1); 563 564 /* Check canary bytes for memory corruption. */ 565 check_canary(meta); 566 567 /* 568 * Clear memory if init-on-free is set. While we protect the page, the 569 * data is still there, and after a use-after-free is detected, we 570 * unprotect the page, so the data is still accessible. 571 */ 572 if (!zombie && unlikely(init)) 573 memzero_explicit(addr, meta->size); 574 575 /* Protect to detect use-after-frees. */ 576 kfence_protect((unsigned long)addr); 577 578 kcsan_end_scoped_access(&assert_page_exclusive); 579 if (!zombie) { 580 /* Add it to the tail of the freelist for reuse. */ 581 raw_spin_lock_irqsave(&kfence_freelist_lock, flags); 582 KFENCE_WARN_ON(!list_empty(&meta->list)); 583 list_add_tail(&meta->list, &kfence_freelist); 584 raw_spin_unlock_irqrestore(&kfence_freelist_lock, flags); 585 586 atomic_long_dec(&counters[KFENCE_COUNTER_ALLOCATED]); 587 atomic_long_inc(&counters[KFENCE_COUNTER_FREES]); 588 } else { 589 /* See kfence_shutdown_cache(). */ 590 atomic_long_inc(&counters[KFENCE_COUNTER_ZOMBIES]); 591 } 592 } 593 594 static void rcu_guarded_free(struct rcu_head *h) 595 { 596 struct kfence_metadata *meta = container_of(h, struct kfence_metadata, rcu_head); 597 598 kfence_guarded_free((void *)meta->addr, meta, false); 599 } 600 601 /* 602 * Initialization of the KFENCE pool after its allocation. 603 * Returns 0 on success; otherwise returns the address up to 604 * which partial initialization succeeded. 605 */ 606 static unsigned long kfence_init_pool(void) 607 __context_unsafe(/* constructor */) 608 { 609 unsigned long addr, start_pfn; 610 int i, rand; 611 612 if (!arch_kfence_init_pool()) 613 return (unsigned long)__kfence_pool; 614 615 addr = (unsigned long)__kfence_pool; 616 start_pfn = PHYS_PFN(virt_to_phys(__kfence_pool)); 617 618 /* 619 * Set up object pages: they must have PGTY_slab set to avoid freeing 620 * them as real pages. 621 * 622 * We also want to avoid inserting kfence_free() in the kfree() 623 * fast-path in SLUB, and therefore need to ensure kfree() correctly 624 * enters __slab_free() slow-path. 625 */ 626 for (i = 0; i < KFENCE_POOL_SIZE / PAGE_SIZE; i++) { 627 struct page *page; 628 629 if (!i || (i % 2)) 630 continue; 631 632 page = pfn_to_page(start_pfn + i); 633 __SetPageSlab(page); 634 #ifdef CONFIG_MEMCG 635 struct slab *slab = page_slab(page); 636 slab->obj_exts = (unsigned long)&kfence_metadata_init[i / 2 - 1].obj_exts | 637 MEMCG_DATA_OBJEXTS; 638 #endif 639 } 640 641 /* 642 * Protect the first 2 pages. The first page is mostly unnecessary, and 643 * merely serves as an extended guard page. However, adding one 644 * additional page in the beginning gives us an even number of pages, 645 * which simplifies the mapping of address to metadata index. 646 */ 647 for (i = 0; i < 2; i++) { 648 if (unlikely(!kfence_protect(addr))) 649 return addr; 650 651 addr += PAGE_SIZE; 652 } 653 654 for (i = 0; i < CONFIG_KFENCE_NUM_OBJECTS; i++) { 655 struct kfence_metadata *meta = &kfence_metadata_init[i]; 656 657 /* Initialize metadata. */ 658 INIT_LIST_HEAD(&meta->list); 659 raw_spin_lock_init(&meta->lock); 660 meta->state = KFENCE_OBJECT_UNUSED; 661 /* Use addr to randomize the freelist. */ 662 meta->addr = i; 663 664 /* Protect the right redzone. */ 665 if (unlikely(!kfence_protect(addr + 2 * i * PAGE_SIZE + PAGE_SIZE))) 666 goto reset_slab; 667 } 668 669 for (i = CONFIG_KFENCE_NUM_OBJECTS; i > 0; i--) { 670 rand = get_random_u32_below(i); 671 swap(kfence_metadata_init[i - 1].addr, kfence_metadata_init[rand].addr); 672 } 673 674 for (i = 0; i < CONFIG_KFENCE_NUM_OBJECTS; i++) { 675 struct kfence_metadata *meta_1 = &kfence_metadata_init[i]; 676 struct kfence_metadata *meta_2 = &kfence_metadata_init[meta_1->addr]; 677 678 list_add_tail(&meta_2->list, &kfence_freelist); 679 } 680 for (i = 0; i < CONFIG_KFENCE_NUM_OBJECTS; i++) { 681 kfence_metadata_init[i].addr = addr; 682 addr += 2 * PAGE_SIZE; 683 } 684 685 /* 686 * Make kfence_metadata visible only when initialization is successful. 687 * Otherwise, if the initialization fails and kfence_metadata is freed, 688 * it may cause UAF in kfence_shutdown_cache(). 689 */ 690 smp_store_release(&kfence_metadata, kfence_metadata_init); 691 return 0; 692 693 reset_slab: 694 addr += 2 * i * PAGE_SIZE; 695 for (i = 0; i < KFENCE_POOL_SIZE / PAGE_SIZE; i++) { 696 struct page *page; 697 698 if (!i || (i % 2)) 699 continue; 700 701 page = pfn_to_page(start_pfn + i); 702 #ifdef CONFIG_MEMCG 703 struct slab *slab = page_slab(page); 704 slab->obj_exts = 0; 705 #endif 706 __ClearPageSlab(page); 707 } 708 709 return addr; 710 } 711 712 static bool __init kfence_init_pool_early(void) 713 { 714 unsigned long addr; 715 716 if (!__kfence_pool) 717 return false; 718 719 addr = kfence_init_pool(); 720 721 if (!addr) { 722 /* 723 * The pool is live and will never be deallocated from this point on. 724 * Ignore the pool object from the kmemleak phys object tree, as it would 725 * otherwise overlap with allocations returned by kfence_alloc(), which 726 * are registered with kmemleak through the slab post-alloc hook. 727 */ 728 kmemleak_ignore_phys(__pa(__kfence_pool)); 729 return true; 730 } 731 732 /* 733 * Only release unprotected pages, and do not try to go back and change 734 * page attributes due to risk of failing to do so as well. If changing 735 * page attributes for some pages fails, it is very likely that it also 736 * fails for the first page, and therefore expect addr==__kfence_pool in 737 * most failure cases. 738 */ 739 memblock_free((void *)addr, KFENCE_POOL_SIZE - (addr - (unsigned long)__kfence_pool)); 740 __kfence_pool = NULL; 741 742 memblock_free(kfence_metadata_init, KFENCE_METADATA_SIZE); 743 kfence_metadata_init = NULL; 744 745 return false; 746 } 747 748 /* === DebugFS Interface ==================================================== */ 749 750 static int stats_show(struct seq_file *seq, void *v) 751 { 752 int i; 753 754 seq_printf(seq, "enabled: %i\n", READ_ONCE(kfence_enabled)); 755 for (i = 0; i < KFENCE_COUNTER_COUNT; i++) 756 seq_printf(seq, "%s: %ld\n", counter_names[i], atomic_long_read(&counters[i])); 757 758 return 0; 759 } 760 DEFINE_SHOW_ATTRIBUTE(stats); 761 762 /* 763 * debugfs seq_file operations for /sys/kernel/debug/kfence/objects. 764 * start_object() and next_object() return the object index + 1, because NULL is used 765 * to stop iteration. 766 */ 767 static void *start_object(struct seq_file *seq, loff_t *pos) 768 { 769 if (*pos < CONFIG_KFENCE_NUM_OBJECTS) 770 return (void *)((long)*pos + 1); 771 return NULL; 772 } 773 774 static void stop_object(struct seq_file *seq, void *v) 775 { 776 } 777 778 static void *next_object(struct seq_file *seq, void *v, loff_t *pos) 779 { 780 ++*pos; 781 if (*pos < CONFIG_KFENCE_NUM_OBJECTS) 782 return (void *)((long)*pos + 1); 783 return NULL; 784 } 785 786 static int show_object(struct seq_file *seq, void *v) 787 { 788 struct kfence_metadata *meta = &kfence_metadata[(long)v - 1]; 789 unsigned long flags; 790 791 raw_spin_lock_irqsave(&meta->lock, flags); 792 kfence_print_object(seq, meta); 793 raw_spin_unlock_irqrestore(&meta->lock, flags); 794 seq_puts(seq, "---------------------------------\n"); 795 796 return 0; 797 } 798 799 static const struct seq_operations objects_sops = { 800 .start = start_object, 801 .next = next_object, 802 .stop = stop_object, 803 .show = show_object, 804 }; 805 DEFINE_SEQ_ATTRIBUTE(objects); 806 807 static int kfence_debugfs_init(void) 808 { 809 struct dentry *kfence_dir; 810 811 if (!READ_ONCE(kfence_enabled)) 812 return 0; 813 814 kfence_dir = debugfs_create_dir("kfence", NULL); 815 debugfs_create_file("stats", 0444, kfence_dir, NULL, &stats_fops); 816 debugfs_create_file("objects", 0400, kfence_dir, NULL, &objects_fops); 817 return 0; 818 } 819 820 late_initcall(kfence_debugfs_init); 821 822 /* === Panic Notifier ====================================================== */ 823 824 static void kfence_check_all_canary(void) 825 { 826 int i; 827 828 for (i = 0; i < CONFIG_KFENCE_NUM_OBJECTS; i++) { 829 struct kfence_metadata *meta = &kfence_metadata[i]; 830 831 if (kfence_obj_allocated(meta)) 832 check_canary(meta); 833 } 834 } 835 836 static int kfence_check_canary_callback(struct notifier_block *nb, 837 unsigned long reason, void *arg) 838 { 839 if (READ_ONCE(kfence_enabled)) 840 kfence_check_all_canary(); 841 return NOTIFY_OK; 842 } 843 844 static struct notifier_block kfence_check_canary_notifier = { 845 .notifier_call = kfence_check_canary_callback, 846 }; 847 848 /* === Allocation Gate Timer ================================================ */ 849 850 static struct delayed_work kfence_timer; 851 852 #ifdef CONFIG_KFENCE_STATIC_KEYS 853 /* Wait queue to wake up allocation-gate timer task. */ 854 static DECLARE_WAIT_QUEUE_HEAD(allocation_wait); 855 856 static int kfence_reboot_callback(struct notifier_block *nb, 857 unsigned long action, void *data) 858 { 859 /* 860 * Disable kfence to avoid static keys IPI synchronization during 861 * late shutdown/kexec 862 */ 863 WRITE_ONCE(kfence_enabled, false); 864 /* Cancel any pending timer work */ 865 cancel_delayed_work(&kfence_timer); 866 /* 867 * Wake up any blocked toggle_allocation_gate() so it can complete 868 * early while the system is still able to handle IPIs. 869 */ 870 wake_up(&allocation_wait); 871 872 return NOTIFY_OK; 873 } 874 875 static struct notifier_block kfence_reboot_notifier = { 876 .notifier_call = kfence_reboot_callback, 877 .priority = INT_MAX, /* Run early to stop timers ASAP */ 878 }; 879 880 static void wake_up_kfence_timer(struct irq_work *work) 881 { 882 wake_up(&allocation_wait); 883 } 884 static DEFINE_IRQ_WORK(wake_up_kfence_timer_work, wake_up_kfence_timer); 885 #endif 886 887 /* 888 * Set up delayed work, which will enable and disable the static key. We need to 889 * use a work queue (rather than a simple timer), since enabling and disabling a 890 * static key cannot be done from an interrupt. 891 * 892 * Note: Toggling a static branch currently causes IPIs, and here we'll end up 893 * with a total of 2 IPIs to all CPUs. If this ends up a problem in future (with 894 * more aggressive sampling intervals), we could get away with a variant that 895 * avoids IPIs, at the cost of not immediately capturing allocations if the 896 * instructions remain cached. 897 */ 898 static void toggle_allocation_gate(struct work_struct *work) 899 { 900 if (!READ_ONCE(kfence_enabled)) 901 return; 902 903 atomic_set(&kfence_allocation_gate, -kfence_burst); 904 #ifdef CONFIG_KFENCE_STATIC_KEYS 905 /* Enable static key, and await allocation to happen. */ 906 static_branch_enable(&kfence_allocation_key); 907 908 wait_event_idle(allocation_wait, 909 atomic_read(&kfence_allocation_gate) > 0 || 910 !READ_ONCE(kfence_enabled)); 911 912 /* Disable static key and reset timer. */ 913 static_branch_disable(&kfence_allocation_key); 914 #endif 915 queue_delayed_work(system_dfl_wq, &kfence_timer, 916 msecs_to_jiffies(kfence_sample_interval)); 917 } 918 919 /* === Public interface ===================================================== */ 920 921 void __init kfence_alloc_pool_and_metadata(void) 922 { 923 if (!kfence_sample_interval) 924 return; 925 926 /* 927 * If KASAN hardware tags are enabled, disable KFENCE, because it 928 * does not support MTE yet. 929 */ 930 if (kasan_hw_tags_enabled()) { 931 pr_info("disabled as KASAN HW tags are enabled\n"); 932 if (__kfence_pool) { 933 memblock_free(__kfence_pool, KFENCE_POOL_SIZE); 934 __kfence_pool = NULL; 935 } 936 kfence_sample_interval = 0; 937 return; 938 } 939 940 /* 941 * If the pool has already been initialized by arch, there is no need to 942 * re-allocate the memory pool. 943 */ 944 if (!__kfence_pool) 945 __kfence_pool = memblock_alloc(KFENCE_POOL_SIZE, PAGE_SIZE); 946 947 if (!__kfence_pool) { 948 pr_err("failed to allocate pool\n"); 949 return; 950 } 951 952 /* The memory allocated by memblock has been zeroed out. */ 953 kfence_metadata_init = memblock_alloc(KFENCE_METADATA_SIZE, PAGE_SIZE); 954 if (!kfence_metadata_init) { 955 pr_err("failed to allocate metadata\n"); 956 memblock_free(__kfence_pool, KFENCE_POOL_SIZE); 957 __kfence_pool = NULL; 958 } 959 } 960 961 static void kfence_init_enable(void) 962 { 963 if (!IS_ENABLED(CONFIG_KFENCE_STATIC_KEYS)) 964 static_branch_enable(&kfence_allocation_key); 965 966 if (kfence_deferrable) 967 INIT_DEFERRABLE_WORK(&kfence_timer, toggle_allocation_gate); 968 else 969 INIT_DELAYED_WORK(&kfence_timer, toggle_allocation_gate); 970 971 if (kfence_check_on_panic) 972 atomic_notifier_chain_register(&panic_notifier_list, &kfence_check_canary_notifier); 973 974 #ifdef CONFIG_KFENCE_STATIC_KEYS 975 register_reboot_notifier(&kfence_reboot_notifier); 976 #endif 977 978 WRITE_ONCE(kfence_enabled, true); 979 queue_delayed_work(system_dfl_wq, &kfence_timer, 0); 980 981 pr_info("initialized - using %lu bytes for %d objects at 0x%p-0x%p\n", KFENCE_POOL_SIZE, 982 CONFIG_KFENCE_NUM_OBJECTS, (void *)__kfence_pool, 983 (void *)(__kfence_pool + KFENCE_POOL_SIZE)); 984 } 985 986 void __init kfence_init(void) 987 { 988 stack_hash_seed = get_random_u32(); 989 990 /* Setting kfence_sample_interval to 0 on boot disables KFENCE. */ 991 if (!kfence_sample_interval) 992 return; 993 994 if (!kfence_init_pool_early()) { 995 pr_err("%s failed\n", __func__); 996 return; 997 } 998 999 kfence_init_enable(); 1000 } 1001 1002 static int kfence_init_late(void) 1003 { 1004 const unsigned long nr_pages_pool = KFENCE_POOL_SIZE / PAGE_SIZE; 1005 const unsigned long nr_pages_meta = KFENCE_METADATA_SIZE / PAGE_SIZE; 1006 unsigned long addr = (unsigned long)__kfence_pool; 1007 unsigned long free_size = KFENCE_POOL_SIZE; 1008 int err = -ENOMEM; 1009 1010 #ifdef CONFIG_CONTIG_ALLOC 1011 struct page *pages; 1012 1013 pages = alloc_contig_pages(nr_pages_pool, GFP_KERNEL | __GFP_SKIP_KASAN, 1014 first_online_node, NULL); 1015 if (!pages) 1016 return -ENOMEM; 1017 1018 __kfence_pool = page_to_virt(pages); 1019 pages = alloc_contig_pages(nr_pages_meta, GFP_KERNEL | __GFP_SKIP_KASAN, 1020 first_online_node, NULL); 1021 if (pages) 1022 kfence_metadata_init = page_to_virt(pages); 1023 #else 1024 if (nr_pages_pool > MAX_ORDER_NR_PAGES || 1025 nr_pages_meta > MAX_ORDER_NR_PAGES) { 1026 pr_warn("KFENCE_NUM_OBJECTS too large for buddy allocator\n"); 1027 return -EINVAL; 1028 } 1029 1030 __kfence_pool = alloc_pages_exact(KFENCE_POOL_SIZE, 1031 GFP_KERNEL | __GFP_SKIP_KASAN); 1032 if (!__kfence_pool) 1033 return -ENOMEM; 1034 1035 kfence_metadata_init = alloc_pages_exact(KFENCE_METADATA_SIZE, 1036 GFP_KERNEL | __GFP_SKIP_KASAN); 1037 #endif 1038 1039 if (!kfence_metadata_init) 1040 goto free_pool; 1041 1042 memzero_explicit(kfence_metadata_init, KFENCE_METADATA_SIZE); 1043 addr = kfence_init_pool(); 1044 if (!addr) { 1045 kfence_init_enable(); 1046 kfence_debugfs_init(); 1047 return 0; 1048 } 1049 1050 pr_err("%s failed\n", __func__); 1051 free_size = KFENCE_POOL_SIZE - (addr - (unsigned long)__kfence_pool); 1052 err = -EBUSY; 1053 1054 #ifdef CONFIG_CONTIG_ALLOC 1055 free_contig_range(page_to_pfn(virt_to_page((void *)kfence_metadata_init)), 1056 nr_pages_meta); 1057 free_pool: 1058 free_contig_range(page_to_pfn(virt_to_page((void *)addr)), 1059 free_size / PAGE_SIZE); 1060 #else 1061 free_pages_exact((void *)kfence_metadata_init, KFENCE_METADATA_SIZE); 1062 free_pool: 1063 free_pages_exact((void *)addr, free_size); 1064 #endif 1065 1066 kfence_metadata_init = NULL; 1067 __kfence_pool = NULL; 1068 return err; 1069 } 1070 1071 static int kfence_enable_late(void) 1072 { 1073 if (!__kfence_pool) 1074 return kfence_init_late(); 1075 1076 WRITE_ONCE(kfence_enabled, true); 1077 queue_delayed_work(system_dfl_wq, &kfence_timer, 0); 1078 pr_info("re-enabled\n"); 1079 return 0; 1080 } 1081 1082 void kfence_shutdown_cache(struct kmem_cache *s) 1083 { 1084 unsigned long flags; 1085 struct kfence_metadata *meta; 1086 int i; 1087 1088 /* Pairs with release in kfence_init_pool(). */ 1089 if (!smp_load_acquire(&kfence_metadata)) 1090 return; 1091 1092 for (i = 0; i < CONFIG_KFENCE_NUM_OBJECTS; i++) { 1093 bool in_use; 1094 1095 meta = &kfence_metadata[i]; 1096 1097 /* 1098 * If we observe some inconsistent cache and state pair where we 1099 * should have returned false here, cache destruction is racing 1100 * with either kmem_cache_alloc() or kmem_cache_free(). Taking 1101 * the lock will not help, as different critical section 1102 * serialization will have the same outcome. 1103 */ 1104 if (READ_ONCE(meta->cache) != s || !kfence_obj_allocated(meta)) 1105 continue; 1106 1107 raw_spin_lock_irqsave(&meta->lock, flags); 1108 in_use = meta->cache == s && kfence_obj_allocated(meta); 1109 raw_spin_unlock_irqrestore(&meta->lock, flags); 1110 1111 if (in_use) { 1112 /* 1113 * This cache still has allocations, and we should not 1114 * release them back into the freelist so they can still 1115 * safely be used and retain the kernel's default 1116 * behaviour of keeping the allocations alive (leak the 1117 * cache); however, they effectively become "zombie 1118 * allocations" as the KFENCE objects are the only ones 1119 * still in use and the owning cache is being destroyed. 1120 * 1121 * We mark them freed, so that any subsequent use shows 1122 * more useful error messages that will include stack 1123 * traces of the user of the object, the original 1124 * allocation, and caller to shutdown_cache(). 1125 */ 1126 kfence_guarded_free((void *)meta->addr, meta, /*zombie=*/true); 1127 } 1128 } 1129 1130 for (i = 0; i < CONFIG_KFENCE_NUM_OBJECTS; i++) { 1131 meta = &kfence_metadata[i]; 1132 1133 /* See above. */ 1134 if (READ_ONCE(meta->cache) != s || READ_ONCE(meta->state) != KFENCE_OBJECT_FREED) 1135 continue; 1136 1137 raw_spin_lock_irqsave(&meta->lock, flags); 1138 if (meta->cache == s && meta->state == KFENCE_OBJECT_FREED) 1139 meta->cache = NULL; 1140 raw_spin_unlock_irqrestore(&meta->lock, flags); 1141 } 1142 } 1143 1144 void *__kfence_alloc(struct kmem_cache *s, size_t size, gfp_t flags) 1145 { 1146 unsigned long stack_entries[KFENCE_STACK_DEPTH]; 1147 size_t num_stack_entries; 1148 u32 alloc_stack_hash; 1149 int allocation_gate; 1150 1151 /* 1152 * Perform size check before switching kfence_allocation_gate, so that 1153 * we don't disable KFENCE without making an allocation. 1154 */ 1155 if (size > PAGE_SIZE) { 1156 atomic_long_inc(&counters[KFENCE_COUNTER_SKIP_INCOMPAT]); 1157 return NULL; 1158 } 1159 1160 /* 1161 * Skip allocations from non-default zones, including DMA. We cannot 1162 * guarantee that pages in the KFENCE pool will have the requested 1163 * properties (e.g. reside in DMAable memory). 1164 */ 1165 if ((flags & GFP_ZONEMASK) || 1166 ((flags & __GFP_THISNODE) && num_online_nodes() > 1) || 1167 (s->flags & (SLAB_CACHE_DMA | SLAB_CACHE_DMA32))) { 1168 atomic_long_inc(&counters[KFENCE_COUNTER_SKIP_INCOMPAT]); 1169 return NULL; 1170 } 1171 1172 /* 1173 * Skip allocations for this slab, if KFENCE has been disabled for 1174 * this slab. 1175 */ 1176 if (s->flags & SLAB_SKIP_KFENCE) 1177 return NULL; 1178 1179 allocation_gate = atomic_inc_return(&kfence_allocation_gate); 1180 if (allocation_gate > 1) 1181 return NULL; 1182 #ifdef CONFIG_KFENCE_STATIC_KEYS 1183 /* 1184 * waitqueue_active() is fully ordered after the update of 1185 * kfence_allocation_gate per atomic_inc_return(). 1186 */ 1187 if (allocation_gate == 1 && waitqueue_active(&allocation_wait)) { 1188 /* 1189 * Calling wake_up() here may deadlock when allocations happen 1190 * from within timer code. Use an irq_work to defer it. 1191 */ 1192 irq_work_queue(&wake_up_kfence_timer_work); 1193 } 1194 #endif 1195 1196 if (!READ_ONCE(kfence_enabled)) 1197 return NULL; 1198 1199 num_stack_entries = stack_trace_save(stack_entries, KFENCE_STACK_DEPTH, 0); 1200 1201 /* 1202 * Do expensive check for coverage of allocation in slow-path after 1203 * allocation_gate has already become non-zero, even though it might 1204 * mean not making any allocation within a given sample interval. 1205 * 1206 * This ensures reasonable allocation coverage when the pool is almost 1207 * full, including avoiding long-lived allocations of the same source 1208 * filling up the pool (e.g. pagecache allocations). 1209 */ 1210 alloc_stack_hash = get_alloc_stack_hash(stack_entries, num_stack_entries); 1211 if (should_skip_covered() && alloc_covered_contains(alloc_stack_hash)) { 1212 atomic_long_inc(&counters[KFENCE_COUNTER_SKIP_COVERED]); 1213 return NULL; 1214 } 1215 1216 return kfence_guarded_alloc(s, size, flags, stack_entries, num_stack_entries, 1217 alloc_stack_hash); 1218 } 1219 1220 size_t kfence_ksize(const void *addr) 1221 { 1222 const struct kfence_metadata *meta = addr_to_metadata((unsigned long)addr); 1223 1224 /* 1225 * Read locklessly -- if there is a race with __kfence_alloc(), this is 1226 * either a use-after-free or invalid access. 1227 */ 1228 return meta ? meta->size : 0; 1229 } 1230 1231 void *kfence_object_start(const void *addr) 1232 { 1233 const struct kfence_metadata *meta = addr_to_metadata((unsigned long)addr); 1234 1235 /* 1236 * Read locklessly -- if there is a race with __kfence_alloc(), this is 1237 * either a use-after-free or invalid access. 1238 */ 1239 return meta ? (void *)meta->addr : NULL; 1240 } 1241 1242 void __kfence_free(void *addr) 1243 { 1244 struct kfence_metadata *meta = addr_to_metadata((unsigned long)addr); 1245 1246 #ifdef CONFIG_MEMCG 1247 KFENCE_WARN_ON(meta->obj_exts.objcg); 1248 #endif 1249 /* 1250 * If the objects of the cache are SLAB_TYPESAFE_BY_RCU, defer freeing 1251 * the object, as the object page may be recycled for other-typed 1252 * objects once it has been freed. meta->cache may be NULL if the cache 1253 * was destroyed. 1254 * Save the stack trace here so that reports show where the user freed 1255 * the object. 1256 */ 1257 if (unlikely(meta->cache && (meta->cache->flags & SLAB_TYPESAFE_BY_RCU))) { 1258 unsigned long flags; 1259 1260 raw_spin_lock_irqsave(&meta->lock, flags); 1261 metadata_update_state(meta, KFENCE_OBJECT_RCU_FREEING, NULL, 0); 1262 raw_spin_unlock_irqrestore(&meta->lock, flags); 1263 call_rcu(&meta->rcu_head, rcu_guarded_free); 1264 } else { 1265 kfence_guarded_free(addr, meta, false); 1266 } 1267 } 1268 1269 bool kfence_handle_page_fault(unsigned long addr, bool is_write, struct pt_regs *regs) 1270 { 1271 const int page_index = (addr - (unsigned long)__kfence_pool) / PAGE_SIZE; 1272 struct kfence_metadata *to_report = NULL; 1273 unsigned long unprotected_page = 0; 1274 enum kfence_error_type error_type; 1275 enum kfence_fault fault; 1276 unsigned long flags; 1277 1278 if (!is_kfence_address((void *)addr)) 1279 return false; 1280 1281 if (!READ_ONCE(kfence_enabled)) /* If disabled at runtime ... */ 1282 return kfence_unprotect(addr); /* ... unprotect and proceed. */ 1283 1284 atomic_long_inc(&counters[KFENCE_COUNTER_BUGS]); 1285 1286 if (page_index % 2) { 1287 /* This is a redzone, report a buffer overflow. */ 1288 struct kfence_metadata *meta; 1289 int distance = 0; 1290 1291 meta = addr_to_metadata(addr - PAGE_SIZE); 1292 if (meta && kfence_obj_allocated(meta)) { 1293 to_report = meta; 1294 /* Data race ok; distance calculation approximate. */ 1295 distance = addr - data_race(meta->addr + meta->size); 1296 } 1297 1298 meta = addr_to_metadata(addr + PAGE_SIZE); 1299 if (meta && kfence_obj_allocated(meta)) { 1300 /* Data race ok; distance calculation approximate. */ 1301 if (!to_report || distance > data_race(meta->addr) - addr) 1302 to_report = meta; 1303 } 1304 1305 if (!to_report) 1306 goto out; 1307 1308 error_type = KFENCE_ERROR_OOB; 1309 unprotected_page = addr; 1310 1311 /* 1312 * If the object was freed before we took the look we can still 1313 * report this as an OOB -- the report will simply show the 1314 * stacktrace of the free as well. 1315 */ 1316 } else { 1317 to_report = addr_to_metadata(addr); 1318 if (!to_report) 1319 goto out; 1320 1321 error_type = KFENCE_ERROR_UAF; 1322 /* 1323 * We may race with __kfence_alloc(), and it is possible that a 1324 * freed object may be reallocated. We simply report this as a 1325 * use-after-free, with the stack trace showing the place where 1326 * the object was re-allocated. 1327 */ 1328 } 1329 1330 out: 1331 if (to_report) { 1332 raw_spin_lock_irqsave(&to_report->lock, flags); 1333 to_report->unprotected_page = unprotected_page; 1334 fault = kfence_report_error(addr, is_write, regs, to_report, error_type); 1335 raw_spin_unlock_irqrestore(&to_report->lock, flags); 1336 } else { 1337 /* This may be a UAF or OOB access, but we can't be sure. */ 1338 fault = kfence_report_error(addr, is_write, regs, NULL, KFENCE_ERROR_INVALID); 1339 } 1340 1341 kfence_handle_fault(fault); 1342 1343 return kfence_unprotect(addr); /* Unprotect and let access proceed. */ 1344 } 1345