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1// SPDX-License-Identifier: GPL-2.02/*3 * KFENCE guarded object allocator and fault handling.4 *5 * Copyright (C) 2020, Google LLC.6 */7 8#define pr_fmt(fmt) "kfence: " fmt9 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/notifier.h>25#include <linux/panic_notifier.h>26#include <linux/random.h>27#include <linux/rcupdate.h>28#include <linux/sched/clock.h>29#include <linux/seq_file.h>30#include <linux/slab.h>31#include <linux/spinlock.h>32#include <linux/string.h>33 34#include <asm/kfence.h>35 36#include "kfence.h"37 38/* Disables KFENCE on the first warning assuming an irrecoverable error. */39#define KFENCE_WARN_ON(cond) \40 ({ \41 const bool __cond = WARN_ON(cond); \42 if (unlikely(__cond)) { \43 WRITE_ONCE(kfence_enabled, false); \44 disabled_by_warn = true; \45 } \46 __cond; \47 })48 49/* === Data ================================================================= */50 51static bool kfence_enabled __read_mostly;52static bool disabled_by_warn __read_mostly;53 54unsigned long kfence_sample_interval __read_mostly = CONFIG_KFENCE_SAMPLE_INTERVAL;55EXPORT_SYMBOL_GPL(kfence_sample_interval); /* Export for test modules. */56 57#ifdef MODULE_PARAM_PREFIX58#undef MODULE_PARAM_PREFIX59#endif60#define MODULE_PARAM_PREFIX "kfence."61 62static int kfence_enable_late(void);63static int param_set_sample_interval(const char *val, const struct kernel_param *kp)64{65 unsigned long num;66 int ret = kstrtoul(val, 0, &num);67 68 if (ret < 0)69 return ret;70 71 /* Using 0 to indicate KFENCE is disabled. */72 if (!num && READ_ONCE(kfence_enabled)) {73 pr_info("disabled\n");74 WRITE_ONCE(kfence_enabled, false);75 }76 77 *((unsigned long *)kp->arg) = num;78 79 if (num && !READ_ONCE(kfence_enabled) && system_state != SYSTEM_BOOTING)80 return disabled_by_warn ? -EINVAL : kfence_enable_late();81 return 0;82}83 84static int param_get_sample_interval(char *buffer, const struct kernel_param *kp)85{86 if (!READ_ONCE(kfence_enabled))87 return sprintf(buffer, "0\n");88 89 return param_get_ulong(buffer, kp);90}91 92static const struct kernel_param_ops sample_interval_param_ops = {93 .set = param_set_sample_interval,94 .get = param_get_sample_interval,95};96module_param_cb(sample_interval, &sample_interval_param_ops, &kfence_sample_interval, 0600);97 98/* Pool usage% threshold when currently covered allocations are skipped. */99static unsigned long kfence_skip_covered_thresh __read_mostly = 75;100module_param_named(skip_covered_thresh, kfence_skip_covered_thresh, ulong, 0644);101 102/* Allocation burst count: number of excess KFENCE allocations per sample. */103static unsigned int kfence_burst __read_mostly;104module_param_named(burst, kfence_burst, uint, 0644);105 106/* If true, use a deferrable timer. */107static bool kfence_deferrable __read_mostly = IS_ENABLED(CONFIG_KFENCE_DEFERRABLE);108module_param_named(deferrable, kfence_deferrable, bool, 0444);109 110/* If true, check all canary bytes on panic. */111static bool kfence_check_on_panic __read_mostly;112module_param_named(check_on_panic, kfence_check_on_panic, bool, 0444);113 114/* The pool of pages used for guard pages and objects. */115char *__kfence_pool __read_mostly;116EXPORT_SYMBOL(__kfence_pool); /* Export for test modules. */117 118/*119 * Per-object metadata, with one-to-one mapping of object metadata to120 * backing pages (in __kfence_pool).121 */122static_assert(CONFIG_KFENCE_NUM_OBJECTS > 0);123struct kfence_metadata *kfence_metadata __read_mostly;124 125/*126 * If kfence_metadata is not NULL, it may be accessed by kfence_shutdown_cache().127 * So introduce kfence_metadata_init to initialize metadata, and then make128 * kfence_metadata visible after initialization is successful. This prevents129 * potential UAF or access to uninitialized metadata.130 */131static struct kfence_metadata *kfence_metadata_init __read_mostly;132 133/* Freelist with available objects. */134static struct list_head kfence_freelist = LIST_HEAD_INIT(kfence_freelist);135static DEFINE_RAW_SPINLOCK(kfence_freelist_lock); /* Lock protecting freelist. */136 137/*138 * The static key to set up a KFENCE allocation; or if static keys are not used139 * to gate allocations, to avoid a load and compare if KFENCE is disabled.140 */141DEFINE_STATIC_KEY_FALSE(kfence_allocation_key);142 143/* Gates the allocation, ensuring only one succeeds in a given period. */144atomic_t kfence_allocation_gate = ATOMIC_INIT(1);145 146/*147 * A Counting Bloom filter of allocation coverage: limits currently covered148 * allocations of the same source filling up the pool.149 *150 * Assuming a range of 15%-85% unique allocations in the pool at any point in151 * time, the below parameters provide a probablity of 0.02-0.33 for false152 * positive hits respectively:153 *154 * P(alloc_traces) = (1 - e^(-HNUM * (alloc_traces / SIZE)) ^ HNUM155 */156#define ALLOC_COVERED_HNUM 2157#define ALLOC_COVERED_ORDER (const_ilog2(CONFIG_KFENCE_NUM_OBJECTS) + 2)158#define ALLOC_COVERED_SIZE (1 << ALLOC_COVERED_ORDER)159#define ALLOC_COVERED_HNEXT(h) hash_32(h, ALLOC_COVERED_ORDER)160#define ALLOC_COVERED_MASK (ALLOC_COVERED_SIZE - 1)161static atomic_t alloc_covered[ALLOC_COVERED_SIZE];162 163/* Stack depth used to determine uniqueness of an allocation. */164#define UNIQUE_ALLOC_STACK_DEPTH ((size_t)8)165 166/*167 * Randomness for stack hashes, making the same collisions across reboots and168 * different machines less likely.169 */170static u32 stack_hash_seed __ro_after_init;171 172/* Statistics counters for debugfs. */173enum kfence_counter_id {174 KFENCE_COUNTER_ALLOCATED,175 KFENCE_COUNTER_ALLOCS,176 KFENCE_COUNTER_FREES,177 KFENCE_COUNTER_ZOMBIES,178 KFENCE_COUNTER_BUGS,179 KFENCE_COUNTER_SKIP_INCOMPAT,180 KFENCE_COUNTER_SKIP_CAPACITY,181 KFENCE_COUNTER_SKIP_COVERED,182 KFENCE_COUNTER_COUNT,183};184static atomic_long_t counters[KFENCE_COUNTER_COUNT];185static const char *const counter_names[] = {186 [KFENCE_COUNTER_ALLOCATED] = "currently allocated",187 [KFENCE_COUNTER_ALLOCS] = "total allocations",188 [KFENCE_COUNTER_FREES] = "total frees",189 [KFENCE_COUNTER_ZOMBIES] = "zombie allocations",190 [KFENCE_COUNTER_BUGS] = "total bugs",191 [KFENCE_COUNTER_SKIP_INCOMPAT] = "skipped allocations (incompatible)",192 [KFENCE_COUNTER_SKIP_CAPACITY] = "skipped allocations (capacity)",193 [KFENCE_COUNTER_SKIP_COVERED] = "skipped allocations (covered)",194};195static_assert(ARRAY_SIZE(counter_names) == KFENCE_COUNTER_COUNT);196 197/* === Internals ============================================================ */198 199static inline bool should_skip_covered(void)200{201 unsigned long thresh = (CONFIG_KFENCE_NUM_OBJECTS * kfence_skip_covered_thresh) / 100;202 203 return atomic_long_read(&counters[KFENCE_COUNTER_ALLOCATED]) > thresh;204}205 206static u32 get_alloc_stack_hash(unsigned long *stack_entries, size_t num_entries)207{208 num_entries = min(num_entries, UNIQUE_ALLOC_STACK_DEPTH);209 num_entries = filter_irq_stacks(stack_entries, num_entries);210 return jhash(stack_entries, num_entries * sizeof(stack_entries[0]), stack_hash_seed);211}212 213/*214 * Adds (or subtracts) count @val for allocation stack trace hash215 * @alloc_stack_hash from Counting Bloom filter.216 */217static void alloc_covered_add(u32 alloc_stack_hash, int val)218{219 int i;220 221 for (i = 0; i < ALLOC_COVERED_HNUM; i++) {222 atomic_add(val, &alloc_covered[alloc_stack_hash & ALLOC_COVERED_MASK]);223 alloc_stack_hash = ALLOC_COVERED_HNEXT(alloc_stack_hash);224 }225}226 227/*228 * Returns true if the allocation stack trace hash @alloc_stack_hash is229 * currently contained (non-zero count) in Counting Bloom filter.230 */231static bool alloc_covered_contains(u32 alloc_stack_hash)232{233 int i;234 235 for (i = 0; i < ALLOC_COVERED_HNUM; i++) {236 if (!atomic_read(&alloc_covered[alloc_stack_hash & ALLOC_COVERED_MASK]))237 return false;238 alloc_stack_hash = ALLOC_COVERED_HNEXT(alloc_stack_hash);239 }240 241 return true;242}243 244static bool kfence_protect(unsigned long addr)245{246 return !KFENCE_WARN_ON(!kfence_protect_page(ALIGN_DOWN(addr, PAGE_SIZE), true));247}248 249static bool kfence_unprotect(unsigned long addr)250{251 return !KFENCE_WARN_ON(!kfence_protect_page(ALIGN_DOWN(addr, PAGE_SIZE), false));252}253 254static inline unsigned long metadata_to_pageaddr(const struct kfence_metadata *meta)255{256 unsigned long offset = (meta - kfence_metadata + 1) * PAGE_SIZE * 2;257 unsigned long pageaddr = (unsigned long)&__kfence_pool[offset];258 259 /* The checks do not affect performance; only called from slow-paths. */260 261 /* Only call with a pointer into kfence_metadata. */262 if (KFENCE_WARN_ON(meta < kfence_metadata ||263 meta >= kfence_metadata + CONFIG_KFENCE_NUM_OBJECTS))264 return 0;265 266 /*267 * This metadata object only ever maps to 1 page; verify that the stored268 * address is in the expected range.269 */270 if (KFENCE_WARN_ON(ALIGN_DOWN(meta->addr, PAGE_SIZE) != pageaddr))271 return 0;272 273 return pageaddr;274}275 276static inline bool kfence_obj_allocated(const struct kfence_metadata *meta)277{278 enum kfence_object_state state = READ_ONCE(meta->state);279 280 return state == KFENCE_OBJECT_ALLOCATED || state == KFENCE_OBJECT_RCU_FREEING;281}282 283/*284 * Update the object's metadata state, including updating the alloc/free stacks285 * depending on the state transition.286 */287static noinline void288metadata_update_state(struct kfence_metadata *meta, enum kfence_object_state next,289 unsigned long *stack_entries, size_t num_stack_entries)290{291 struct kfence_track *track =292 next == KFENCE_OBJECT_ALLOCATED ? &meta->alloc_track : &meta->free_track;293 294 lockdep_assert_held(&meta->lock);295 296 /* Stack has been saved when calling rcu, skip. */297 if (READ_ONCE(meta->state) == KFENCE_OBJECT_RCU_FREEING)298 goto out;299 300 if (stack_entries) {301 memcpy(track->stack_entries, stack_entries,302 num_stack_entries * sizeof(stack_entries[0]));303 } else {304 /*305 * Skip over 1 (this) functions; noinline ensures we do not306 * accidentally skip over the caller by never inlining.307 */308 num_stack_entries = stack_trace_save(track->stack_entries, KFENCE_STACK_DEPTH, 1);309 }310 track->num_stack_entries = num_stack_entries;311 track->pid = task_pid_nr(current);312 track->cpu = raw_smp_processor_id();313 track->ts_nsec = local_clock(); /* Same source as printk timestamps. */314 315out:316 /*317 * Pairs with READ_ONCE() in318 * kfence_shutdown_cache(),319 * kfence_handle_page_fault().320 */321 WRITE_ONCE(meta->state, next);322}323 324#ifdef CONFIG_KMSAN325#define check_canary_attributes noinline __no_kmsan_checks326#else327#define check_canary_attributes inline328#endif329 330/* Check canary byte at @addr. */331static check_canary_attributes bool check_canary_byte(u8 *addr)332{333 struct kfence_metadata *meta;334 unsigned long flags;335 336 if (likely(*addr == KFENCE_CANARY_PATTERN_U8(addr)))337 return true;338 339 atomic_long_inc(&counters[KFENCE_COUNTER_BUGS]);340 341 meta = addr_to_metadata((unsigned long)addr);342 raw_spin_lock_irqsave(&meta->lock, flags);343 kfence_report_error((unsigned long)addr, false, NULL, meta, KFENCE_ERROR_CORRUPTION);344 raw_spin_unlock_irqrestore(&meta->lock, flags);345 346 return false;347}348 349static inline void set_canary(const struct kfence_metadata *meta)350{351 const unsigned long pageaddr = ALIGN_DOWN(meta->addr, PAGE_SIZE);352 unsigned long addr = pageaddr;353 354 /*355 * The canary may be written to part of the object memory, but it does356 * not affect it. The user should initialize the object before using it.357 */358 for (; addr < meta->addr; addr += sizeof(u64))359 *((u64 *)addr) = KFENCE_CANARY_PATTERN_U64;360 361 addr = ALIGN_DOWN(meta->addr + meta->size, sizeof(u64));362 for (; addr - pageaddr < PAGE_SIZE; addr += sizeof(u64))363 *((u64 *)addr) = KFENCE_CANARY_PATTERN_U64;364}365 366static check_canary_attributes void367check_canary(const struct kfence_metadata *meta)368{369 const unsigned long pageaddr = ALIGN_DOWN(meta->addr, PAGE_SIZE);370 unsigned long addr = pageaddr;371 372 /*373 * We'll iterate over each canary byte per-side until a corrupted byte374 * is found. However, we'll still iterate over the canary bytes to the375 * right of the object even if there was an error in the canary bytes to376 * the left of the object. Specifically, if check_canary_byte()377 * generates an error, showing both sides might give more clues as to378 * what the error is about when displaying which bytes were corrupted.379 */380 381 /* Apply to left of object. */382 for (; meta->addr - addr >= sizeof(u64); addr += sizeof(u64)) {383 if (unlikely(*((u64 *)addr) != KFENCE_CANARY_PATTERN_U64))384 break;385 }386 387 /*388 * If the canary is corrupted in a certain 64 bytes, or the canary389 * memory cannot be completely covered by multiple consecutive 64 bytes,390 * it needs to be checked one by one.391 */392 for (; addr < meta->addr; addr++) {393 if (unlikely(!check_canary_byte((u8 *)addr)))394 break;395 }396 397 /* Apply to right of object. */398 for (addr = meta->addr + meta->size; addr % sizeof(u64) != 0; addr++) {399 if (unlikely(!check_canary_byte((u8 *)addr)))400 return;401 }402 for (; addr - pageaddr < PAGE_SIZE; addr += sizeof(u64)) {403 if (unlikely(*((u64 *)addr) != KFENCE_CANARY_PATTERN_U64)) {404 405 for (; addr - pageaddr < PAGE_SIZE; addr++) {406 if (!check_canary_byte((u8 *)addr))407 return;408 }409 }410 }411}412 413static void *kfence_guarded_alloc(struct kmem_cache *cache, size_t size, gfp_t gfp,414 unsigned long *stack_entries, size_t num_stack_entries,415 u32 alloc_stack_hash)416{417 struct kfence_metadata *meta = NULL;418 unsigned long flags;419 struct slab *slab;420 void *addr;421 const bool random_right_allocate = get_random_u32_below(2);422 const bool random_fault = CONFIG_KFENCE_STRESS_TEST_FAULTS &&423 !get_random_u32_below(CONFIG_KFENCE_STRESS_TEST_FAULTS);424 425 /* Try to obtain a free object. */426 raw_spin_lock_irqsave(&kfence_freelist_lock, flags);427 if (!list_empty(&kfence_freelist)) {428 meta = list_entry(kfence_freelist.next, struct kfence_metadata, list);429 list_del_init(&meta->list);430 }431 raw_spin_unlock_irqrestore(&kfence_freelist_lock, flags);432 if (!meta) {433 atomic_long_inc(&counters[KFENCE_COUNTER_SKIP_CAPACITY]);434 return NULL;435 }436 437 if (unlikely(!raw_spin_trylock_irqsave(&meta->lock, flags))) {438 /*439 * This is extremely unlikely -- we are reporting on a440 * use-after-free, which locked meta->lock, and the reporting441 * code via printk calls kmalloc() which ends up in442 * kfence_alloc() and tries to grab the same object that we're443 * reporting on. While it has never been observed, lockdep does444 * report that there is a possibility of deadlock. Fix it by445 * using trylock and bailing out gracefully.446 */447 raw_spin_lock_irqsave(&kfence_freelist_lock, flags);448 /* Put the object back on the freelist. */449 list_add_tail(&meta->list, &kfence_freelist);450 raw_spin_unlock_irqrestore(&kfence_freelist_lock, flags);451 452 return NULL;453 }454 455 meta->addr = metadata_to_pageaddr(meta);456 /* Unprotect if we're reusing this page. */457 if (meta->state == KFENCE_OBJECT_FREED)458 kfence_unprotect(meta->addr);459 460 /*461 * Note: for allocations made before RNG initialization, will always462 * return zero. We still benefit from enabling KFENCE as early as463 * possible, even when the RNG is not yet available, as this will allow464 * KFENCE to detect bugs due to earlier allocations. The only downside465 * is that the out-of-bounds accesses detected are deterministic for466 * such allocations.467 */468 if (random_right_allocate) {469 /* Allocate on the "right" side, re-calculate address. */470 meta->addr += PAGE_SIZE - size;471 meta->addr = ALIGN_DOWN(meta->addr, cache->align);472 }473 474 addr = (void *)meta->addr;475 476 /* Update remaining metadata. */477 metadata_update_state(meta, KFENCE_OBJECT_ALLOCATED, stack_entries, num_stack_entries);478 /* Pairs with READ_ONCE() in kfence_shutdown_cache(). */479 WRITE_ONCE(meta->cache, cache);480 meta->size = size;481 meta->alloc_stack_hash = alloc_stack_hash;482 raw_spin_unlock_irqrestore(&meta->lock, flags);483 484 alloc_covered_add(alloc_stack_hash, 1);485 486 /* Set required slab fields. */487 slab = virt_to_slab((void *)meta->addr);488 slab->slab_cache = cache;489 slab->objects = 1;490 491 /* Memory initialization. */492 set_canary(meta);493 494 /*495 * We check slab_want_init_on_alloc() ourselves, rather than letting496 * SL*B do the initialization, as otherwise we might overwrite KFENCE's497 * redzone.498 */499 if (unlikely(slab_want_init_on_alloc(gfp, cache)))500 memzero_explicit(addr, size);501 if (cache->ctor)502 cache->ctor(addr);503 504 if (random_fault)505 kfence_protect(meta->addr); /* Random "faults" by protecting the object. */506 507 atomic_long_inc(&counters[KFENCE_COUNTER_ALLOCATED]);508 atomic_long_inc(&counters[KFENCE_COUNTER_ALLOCS]);509 510 return addr;511}512 513static void kfence_guarded_free(void *addr, struct kfence_metadata *meta, bool zombie)514{515 struct kcsan_scoped_access assert_page_exclusive;516 unsigned long flags;517 bool init;518 519 raw_spin_lock_irqsave(&meta->lock, flags);520 521 if (!kfence_obj_allocated(meta) || meta->addr != (unsigned long)addr) {522 /* Invalid or double-free, bail out. */523 atomic_long_inc(&counters[KFENCE_COUNTER_BUGS]);524 kfence_report_error((unsigned long)addr, false, NULL, meta,525 KFENCE_ERROR_INVALID_FREE);526 raw_spin_unlock_irqrestore(&meta->lock, flags);527 return;528 }529 530 /* Detect racy use-after-free, or incorrect reallocation of this page by KFENCE. */531 kcsan_begin_scoped_access((void *)ALIGN_DOWN((unsigned long)addr, PAGE_SIZE), PAGE_SIZE,532 KCSAN_ACCESS_SCOPED | KCSAN_ACCESS_WRITE | KCSAN_ACCESS_ASSERT,533 &assert_page_exclusive);534 535 if (CONFIG_KFENCE_STRESS_TEST_FAULTS)536 kfence_unprotect((unsigned long)addr); /* To check canary bytes. */537 538 /* Restore page protection if there was an OOB access. */539 if (meta->unprotected_page) {540 memzero_explicit((void *)ALIGN_DOWN(meta->unprotected_page, PAGE_SIZE), PAGE_SIZE);541 kfence_protect(meta->unprotected_page);542 meta->unprotected_page = 0;543 }544 545 /* Mark the object as freed. */546 metadata_update_state(meta, KFENCE_OBJECT_FREED, NULL, 0);547 init = slab_want_init_on_free(meta->cache);548 raw_spin_unlock_irqrestore(&meta->lock, flags);549 550 alloc_covered_add(meta->alloc_stack_hash, -1);551 552 /* Check canary bytes for memory corruption. */553 check_canary(meta);554 555 /*556 * Clear memory if init-on-free is set. While we protect the page, the557 * data is still there, and after a use-after-free is detected, we558 * unprotect the page, so the data is still accessible.559 */560 if (!zombie && unlikely(init))561 memzero_explicit(addr, meta->size);562 563 /* Protect to detect use-after-frees. */564 kfence_protect((unsigned long)addr);565 566 kcsan_end_scoped_access(&assert_page_exclusive);567 if (!zombie) {568 /* Add it to the tail of the freelist for reuse. */569 raw_spin_lock_irqsave(&kfence_freelist_lock, flags);570 KFENCE_WARN_ON(!list_empty(&meta->list));571 list_add_tail(&meta->list, &kfence_freelist);572 raw_spin_unlock_irqrestore(&kfence_freelist_lock, flags);573 574 atomic_long_dec(&counters[KFENCE_COUNTER_ALLOCATED]);575 atomic_long_inc(&counters[KFENCE_COUNTER_FREES]);576 } else {577 /* See kfence_shutdown_cache(). */578 atomic_long_inc(&counters[KFENCE_COUNTER_ZOMBIES]);579 }580}581 582static void rcu_guarded_free(struct rcu_head *h)583{584 struct kfence_metadata *meta = container_of(h, struct kfence_metadata, rcu_head);585 586 kfence_guarded_free((void *)meta->addr, meta, false);587}588 589/*590 * Initialization of the KFENCE pool after its allocation.591 * Returns 0 on success; otherwise returns the address up to592 * which partial initialization succeeded.593 */594static unsigned long kfence_init_pool(void)595{596 unsigned long addr;597 struct page *pages;598 int i;599 600 if (!arch_kfence_init_pool())601 return (unsigned long)__kfence_pool;602 603 addr = (unsigned long)__kfence_pool;604 pages = virt_to_page(__kfence_pool);605 606 /*607 * Set up object pages: they must have PG_slab set, to avoid freeing608 * these 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() correctly612 * enters __slab_free() slow-path.613 */614 for (i = 0; i < KFENCE_POOL_SIZE / PAGE_SIZE; i++) {615 struct slab *slab = page_slab(nth_page(pages, i));616 617 if (!i || (i % 2))618 continue;619 620 __folio_set_slab(slab_folio(slab));621#ifdef CONFIG_MEMCG622 slab->obj_exts = (unsigned long)&kfence_metadata_init[i / 2 - 1].obj_exts |623 MEMCG_DATA_OBJEXTS;624#endif625 }626 627 /*628 * Protect the first 2 pages. The first page is mostly unnecessary, and629 * merely serves as an extended guard page. However, adding one630 * additional page in the beginning gives us an even number of pages,631 * which simplifies the mapping of address to metadata index.632 */633 for (i = 0; i < 2; i++) {634 if (unlikely(!kfence_protect(addr)))635 return addr;636 637 addr += PAGE_SIZE;638 }639 640 for (i = 0; i < CONFIG_KFENCE_NUM_OBJECTS; i++) {641 struct kfence_metadata *meta = &kfence_metadata_init[i];642 643 /* Initialize metadata. */644 INIT_LIST_HEAD(&meta->list);645 raw_spin_lock_init(&meta->lock);646 meta->state = KFENCE_OBJECT_UNUSED;647 meta->addr = addr; /* Initialize for validation in metadata_to_pageaddr(). */648 list_add_tail(&meta->list, &kfence_freelist);649 650 /* Protect the right redzone. */651 if (unlikely(!kfence_protect(addr + PAGE_SIZE)))652 goto reset_slab;653 654 addr += 2 * PAGE_SIZE;655 }656 657 /*658 * Make kfence_metadata visible only when initialization is successful.659 * Otherwise, if the initialization fails and kfence_metadata is freed,660 * it may cause UAF in kfence_shutdown_cache().661 */662 smp_store_release(&kfence_metadata, kfence_metadata_init);663 return 0;664 665reset_slab:666 for (i = 0; i < KFENCE_POOL_SIZE / PAGE_SIZE; i++) {667 struct slab *slab = page_slab(nth_page(pages, i));668 669 if (!i || (i % 2))670 continue;671#ifdef CONFIG_MEMCG672 slab->obj_exts = 0;673#endif674 __folio_clear_slab(slab_folio(slab));675 }676 677 return addr;678}679 680static bool __init kfence_init_pool_early(void)681{682 unsigned long addr;683 684 if (!__kfence_pool)685 return false;686 687 addr = kfence_init_pool();688 689 if (!addr) {690 /*691 * The pool is live and will never be deallocated from this point on.692 * Ignore the pool object from the kmemleak phys object tree, as it would693 * otherwise overlap with allocations returned by kfence_alloc(), which694 * are registered with kmemleak through the slab post-alloc hook.695 */696 kmemleak_ignore_phys(__pa(__kfence_pool));697 return true;698 }699 700 /*701 * Only release unprotected pages, and do not try to go back and change702 * page attributes due to risk of failing to do so as well. If changing703 * page attributes for some pages fails, it is very likely that it also704 * fails for the first page, and therefore expect addr==__kfence_pool in705 * most failure cases.706 */707 memblock_free_late(__pa(addr), KFENCE_POOL_SIZE - (addr - (unsigned long)__kfence_pool));708 __kfence_pool = NULL;709 710 memblock_free_late(__pa(kfence_metadata_init), KFENCE_METADATA_SIZE);711 kfence_metadata_init = NULL;712 713 return false;714}715 716/* === DebugFS Interface ==================================================== */717 718static int stats_show(struct seq_file *seq, void *v)719{720 int i;721 722 seq_printf(seq, "enabled: %i\n", READ_ONCE(kfence_enabled));723 for (i = 0; i < KFENCE_COUNTER_COUNT; i++)724 seq_printf(seq, "%s: %ld\n", counter_names[i], atomic_long_read(&counters[i]));725 726 return 0;727}728DEFINE_SHOW_ATTRIBUTE(stats);729 730/*731 * debugfs seq_file operations for /sys/kernel/debug/kfence/objects.732 * start_object() and next_object() return the object index + 1, because NULL is used733 * to stop iteration.734 */735static void *start_object(struct seq_file *seq, loff_t *pos)736{737 if (*pos < CONFIG_KFENCE_NUM_OBJECTS)738 return (void *)((long)*pos + 1);739 return NULL;740}741 742static void stop_object(struct seq_file *seq, void *v)743{744}745 746static void *next_object(struct seq_file *seq, void *v, loff_t *pos)747{748 ++*pos;749 if (*pos < CONFIG_KFENCE_NUM_OBJECTS)750 return (void *)((long)*pos + 1);751 return NULL;752}753 754static int show_object(struct seq_file *seq, void *v)755{756 struct kfence_metadata *meta = &kfence_metadata[(long)v - 1];757 unsigned long flags;758 759 raw_spin_lock_irqsave(&meta->lock, flags);760 kfence_print_object(seq, meta);761 raw_spin_unlock_irqrestore(&meta->lock, flags);762 seq_puts(seq, "---------------------------------\n");763 764 return 0;765}766 767static const struct seq_operations objects_sops = {768 .start = start_object,769 .next = next_object,770 .stop = stop_object,771 .show = show_object,772};773DEFINE_SEQ_ATTRIBUTE(objects);774 775static int kfence_debugfs_init(void)776{777 struct dentry *kfence_dir;778 779 if (!READ_ONCE(kfence_enabled))780 return 0;781 782 kfence_dir = debugfs_create_dir("kfence", NULL);783 debugfs_create_file("stats", 0444, kfence_dir, NULL, &stats_fops);784 debugfs_create_file("objects", 0400, kfence_dir, NULL, &objects_fops);785 return 0;786}787 788late_initcall(kfence_debugfs_init);789 790/* === Panic Notifier ====================================================== */791 792static void kfence_check_all_canary(void)793{794 int i;795 796 for (i = 0; i < CONFIG_KFENCE_NUM_OBJECTS; i++) {797 struct kfence_metadata *meta = &kfence_metadata[i];798 799 if (kfence_obj_allocated(meta))800 check_canary(meta);801 }802}803 804static int kfence_check_canary_callback(struct notifier_block *nb,805 unsigned long reason, void *arg)806{807 kfence_check_all_canary();808 return NOTIFY_OK;809}810 811static struct notifier_block kfence_check_canary_notifier = {812 .notifier_call = kfence_check_canary_callback,813};814 815/* === Allocation Gate Timer ================================================ */816 817static struct delayed_work kfence_timer;818 819#ifdef CONFIG_KFENCE_STATIC_KEYS820/* Wait queue to wake up allocation-gate timer task. */821static DECLARE_WAIT_QUEUE_HEAD(allocation_wait);822 823static void wake_up_kfence_timer(struct irq_work *work)824{825 wake_up(&allocation_wait);826}827static DEFINE_IRQ_WORK(wake_up_kfence_timer_work, wake_up_kfence_timer);828#endif829 830/*831 * Set up delayed work, which will enable and disable the static key. We need to832 * use a work queue (rather than a simple timer), since enabling and disabling a833 * static key cannot be done from an interrupt.834 *835 * Note: Toggling a static branch currently causes IPIs, and here we'll end up836 * with a total of 2 IPIs to all CPUs. If this ends up a problem in future (with837 * more aggressive sampling intervals), we could get away with a variant that838 * avoids IPIs, at the cost of not immediately capturing allocations if the839 * instructions remain cached.840 */841static void toggle_allocation_gate(struct work_struct *work)842{843 if (!READ_ONCE(kfence_enabled))844 return;845 846 atomic_set(&kfence_allocation_gate, -kfence_burst);847#ifdef CONFIG_KFENCE_STATIC_KEYS848 /* Enable static key, and await allocation to happen. */849 static_branch_enable(&kfence_allocation_key);850 851 wait_event_idle(allocation_wait, atomic_read(&kfence_allocation_gate) > 0);852 853 /* Disable static key and reset timer. */854 static_branch_disable(&kfence_allocation_key);855#endif856 queue_delayed_work(system_unbound_wq, &kfence_timer,857 msecs_to_jiffies(kfence_sample_interval));858}859 860/* === Public interface ===================================================== */861 862void __init kfence_alloc_pool_and_metadata(void)863{864 if (!kfence_sample_interval)865 return;866 867 /*868 * If the pool has already been initialized by arch, there is no need to869 * re-allocate the memory pool.870 */871 if (!__kfence_pool)872 __kfence_pool = memblock_alloc(KFENCE_POOL_SIZE, PAGE_SIZE);873 874 if (!__kfence_pool) {875 pr_err("failed to allocate pool\n");876 return;877 }878 879 /* The memory allocated by memblock has been zeroed out. */880 kfence_metadata_init = memblock_alloc(KFENCE_METADATA_SIZE, PAGE_SIZE);881 if (!kfence_metadata_init) {882 pr_err("failed to allocate metadata\n");883 memblock_free(__kfence_pool, KFENCE_POOL_SIZE);884 __kfence_pool = NULL;885 }886}887 888static void kfence_init_enable(void)889{890 if (!IS_ENABLED(CONFIG_KFENCE_STATIC_KEYS))891 static_branch_enable(&kfence_allocation_key);892 893 if (kfence_deferrable)894 INIT_DEFERRABLE_WORK(&kfence_timer, toggle_allocation_gate);895 else896 INIT_DELAYED_WORK(&kfence_timer, toggle_allocation_gate);897 898 if (kfence_check_on_panic)899 atomic_notifier_chain_register(&panic_notifier_list, &kfence_check_canary_notifier);900 901 WRITE_ONCE(kfence_enabled, true);902 queue_delayed_work(system_unbound_wq, &kfence_timer, 0);903 904 pr_info("initialized - using %lu bytes for %d objects at 0x%p-0x%p\n", KFENCE_POOL_SIZE,905 CONFIG_KFENCE_NUM_OBJECTS, (void *)__kfence_pool,906 (void *)(__kfence_pool + KFENCE_POOL_SIZE));907}908 909void __init kfence_init(void)910{911 stack_hash_seed = get_random_u32();912 913 /* Setting kfence_sample_interval to 0 on boot disables KFENCE. */914 if (!kfence_sample_interval)915 return;916 917 if (!kfence_init_pool_early()) {918 pr_err("%s failed\n", __func__);919 return;920 }921 922 kfence_init_enable();923}924 925static int kfence_init_late(void)926{927 const unsigned long nr_pages_pool = KFENCE_POOL_SIZE / PAGE_SIZE;928 const unsigned long nr_pages_meta = KFENCE_METADATA_SIZE / PAGE_SIZE;929 unsigned long addr = (unsigned long)__kfence_pool;930 unsigned long free_size = KFENCE_POOL_SIZE;931 int err = -ENOMEM;932 933#ifdef CONFIG_CONTIG_ALLOC934 struct page *pages;935 936 pages = alloc_contig_pages(nr_pages_pool, GFP_KERNEL, first_online_node,937 NULL);938 if (!pages)939 return -ENOMEM;940 941 __kfence_pool = page_to_virt(pages);942 pages = alloc_contig_pages(nr_pages_meta, GFP_KERNEL, first_online_node,943 NULL);944 if (pages)945 kfence_metadata_init = page_to_virt(pages);946#else947 if (nr_pages_pool > MAX_ORDER_NR_PAGES ||948 nr_pages_meta > MAX_ORDER_NR_PAGES) {949 pr_warn("KFENCE_NUM_OBJECTS too large for buddy allocator\n");950 return -EINVAL;951 }952 953 __kfence_pool = alloc_pages_exact(KFENCE_POOL_SIZE, GFP_KERNEL);954 if (!__kfence_pool)955 return -ENOMEM;956 957 kfence_metadata_init = alloc_pages_exact(KFENCE_METADATA_SIZE, GFP_KERNEL);958#endif959 960 if (!kfence_metadata_init)961 goto free_pool;962 963 memzero_explicit(kfence_metadata_init, KFENCE_METADATA_SIZE);964 addr = kfence_init_pool();965 if (!addr) {966 kfence_init_enable();967 kfence_debugfs_init();968 return 0;969 }970 971 pr_err("%s failed\n", __func__);972 free_size = KFENCE_POOL_SIZE - (addr - (unsigned long)__kfence_pool);973 err = -EBUSY;974 975#ifdef CONFIG_CONTIG_ALLOC976 free_contig_range(page_to_pfn(virt_to_page((void *)kfence_metadata_init)),977 nr_pages_meta);978free_pool:979 free_contig_range(page_to_pfn(virt_to_page((void *)addr)),980 free_size / PAGE_SIZE);981#else982 free_pages_exact((void *)kfence_metadata_init, KFENCE_METADATA_SIZE);983free_pool:984 free_pages_exact((void *)addr, free_size);985#endif986 987 kfence_metadata_init = NULL;988 __kfence_pool = NULL;989 return err;990}991 992static int kfence_enable_late(void)993{994 if (!__kfence_pool)995 return kfence_init_late();996 997 WRITE_ONCE(kfence_enabled, true);998 queue_delayed_work(system_unbound_wq, &kfence_timer, 0);999 pr_info("re-enabled\n");1000 return 0;1001}1002 1003void kfence_shutdown_cache(struct kmem_cache *s)1004{1005 unsigned long flags;1006 struct kfence_metadata *meta;1007 int i;1008 1009 /* Pairs with release in kfence_init_pool(). */1010 if (!smp_load_acquire(&kfence_metadata))1011 return;1012 1013 for (i = 0; i < CONFIG_KFENCE_NUM_OBJECTS; i++) {1014 bool in_use;1015 1016 meta = &kfence_metadata[i];1017 1018 /*1019 * If we observe some inconsistent cache and state pair where we1020 * should have returned false here, cache destruction is racing1021 * with either kmem_cache_alloc() or kmem_cache_free(). Taking1022 * the lock will not help, as different critical section1023 * serialization will have the same outcome.1024 */1025 if (READ_ONCE(meta->cache) != s || !kfence_obj_allocated(meta))1026 continue;1027 1028 raw_spin_lock_irqsave(&meta->lock, flags);1029 in_use = meta->cache == s && kfence_obj_allocated(meta);1030 raw_spin_unlock_irqrestore(&meta->lock, flags);1031 1032 if (in_use) {1033 /*1034 * This cache still has allocations, and we should not1035 * release them back into the freelist so they can still1036 * safely be used and retain the kernel's default1037 * behaviour of keeping the allocations alive (leak the1038 * cache); however, they effectively become "zombie1039 * allocations" as the KFENCE objects are the only ones1040 * still in use and the owning cache is being destroyed.1041 *1042 * We mark them freed, so that any subsequent use shows1043 * more useful error messages that will include stack1044 * traces of the user of the object, the original1045 * allocation, and caller to shutdown_cache().1046 */1047 kfence_guarded_free((void *)meta->addr, meta, /*zombie=*/true);1048 }1049 }1050 1051 for (i = 0; i < CONFIG_KFENCE_NUM_OBJECTS; i++) {1052 meta = &kfence_metadata[i];1053 1054 /* See above. */1055 if (READ_ONCE(meta->cache) != s || READ_ONCE(meta->state) != KFENCE_OBJECT_FREED)1056 continue;1057 1058 raw_spin_lock_irqsave(&meta->lock, flags);1059 if (meta->cache == s && meta->state == KFENCE_OBJECT_FREED)1060 meta->cache = NULL;1061 raw_spin_unlock_irqrestore(&meta->lock, flags);1062 }1063}1064 1065void *__kfence_alloc(struct kmem_cache *s, size_t size, gfp_t flags)1066{1067 unsigned long stack_entries[KFENCE_STACK_DEPTH];1068 size_t num_stack_entries;1069 u32 alloc_stack_hash;1070 int allocation_gate;1071 1072 /*1073 * Perform size check before switching kfence_allocation_gate, so that1074 * we don't disable KFENCE without making an allocation.1075 */1076 if (size > PAGE_SIZE) {1077 atomic_long_inc(&counters[KFENCE_COUNTER_SKIP_INCOMPAT]);1078 return NULL;1079 }1080 1081 /*1082 * Skip allocations from non-default zones, including DMA. We cannot1083 * guarantee that pages in the KFENCE pool will have the requested1084 * properties (e.g. reside in DMAable memory).1085 */1086 if ((flags & GFP_ZONEMASK) ||1087 (s->flags & (SLAB_CACHE_DMA | SLAB_CACHE_DMA32))) {1088 atomic_long_inc(&counters[KFENCE_COUNTER_SKIP_INCOMPAT]);1089 return NULL;1090 }1091 1092 /*1093 * Skip allocations for this slab, if KFENCE has been disabled for1094 * this slab.1095 */1096 if (s->flags & SLAB_SKIP_KFENCE)1097 return NULL;1098 1099 allocation_gate = atomic_inc_return(&kfence_allocation_gate);1100 if (allocation_gate > 1)1101 return NULL;1102#ifdef CONFIG_KFENCE_STATIC_KEYS1103 /*1104 * waitqueue_active() is fully ordered after the update of1105 * kfence_allocation_gate per atomic_inc_return().1106 */1107 if (allocation_gate == 1 && waitqueue_active(&allocation_wait)) {1108 /*1109 * Calling wake_up() here may deadlock when allocations happen1110 * from within timer code. Use an irq_work to defer it.1111 */1112 irq_work_queue(&wake_up_kfence_timer_work);1113 }1114#endif1115 1116 if (!READ_ONCE(kfence_enabled))1117 return NULL;1118 1119 num_stack_entries = stack_trace_save(stack_entries, KFENCE_STACK_DEPTH, 0);1120 1121 /*1122 * Do expensive check for coverage of allocation in slow-path after1123 * allocation_gate has already become non-zero, even though it might1124 * mean not making any allocation within a given sample interval.1125 *1126 * This ensures reasonable allocation coverage when the pool is almost1127 * full, including avoiding long-lived allocations of the same source1128 * filling up the pool (e.g. pagecache allocations).1129 */1130 alloc_stack_hash = get_alloc_stack_hash(stack_entries, num_stack_entries);1131 if (should_skip_covered() && alloc_covered_contains(alloc_stack_hash)) {1132 atomic_long_inc(&counters[KFENCE_COUNTER_SKIP_COVERED]);1133 return NULL;1134 }1135 1136 return kfence_guarded_alloc(s, size, flags, stack_entries, num_stack_entries,1137 alloc_stack_hash);1138}1139 1140size_t kfence_ksize(const void *addr)1141{1142 const struct kfence_metadata *meta = addr_to_metadata((unsigned long)addr);1143 1144 /*1145 * Read locklessly -- if there is a race with __kfence_alloc(), this is1146 * either a use-after-free or invalid access.1147 */1148 return meta ? meta->size : 0;1149}1150 1151void *kfence_object_start(const void *addr)1152{1153 const struct kfence_metadata *meta = addr_to_metadata((unsigned long)addr);1154 1155 /*1156 * Read locklessly -- if there is a race with __kfence_alloc(), this is1157 * either a use-after-free or invalid access.1158 */1159 return meta ? (void *)meta->addr : NULL;1160}1161 1162void __kfence_free(void *addr)1163{1164 struct kfence_metadata *meta = addr_to_metadata((unsigned long)addr);1165 1166#ifdef CONFIG_MEMCG1167 KFENCE_WARN_ON(meta->obj_exts.objcg);1168#endif1169 /*1170 * If the objects of the cache are SLAB_TYPESAFE_BY_RCU, defer freeing1171 * the object, as the object page may be recycled for other-typed1172 * objects once it has been freed. meta->cache may be NULL if the cache1173 * was destroyed.1174 * Save the stack trace here so that reports show where the user freed1175 * the object.1176 */1177 if (unlikely(meta->cache && (meta->cache->flags & SLAB_TYPESAFE_BY_RCU))) {1178 unsigned long flags;1179 1180 raw_spin_lock_irqsave(&meta->lock, flags);1181 metadata_update_state(meta, KFENCE_OBJECT_RCU_FREEING, NULL, 0);1182 raw_spin_unlock_irqrestore(&meta->lock, flags);1183 call_rcu(&meta->rcu_head, rcu_guarded_free);1184 } else {1185 kfence_guarded_free(addr, meta, false);1186 }1187}1188 1189bool kfence_handle_page_fault(unsigned long addr, bool is_write, struct pt_regs *regs)1190{1191 const int page_index = (addr - (unsigned long)__kfence_pool) / PAGE_SIZE;1192 struct kfence_metadata *to_report = NULL;1193 enum kfence_error_type error_type;1194 unsigned long flags;1195 1196 if (!is_kfence_address((void *)addr))1197 return false;1198 1199 if (!READ_ONCE(kfence_enabled)) /* If disabled at runtime ... */1200 return kfence_unprotect(addr); /* ... unprotect and proceed. */1201 1202 atomic_long_inc(&counters[KFENCE_COUNTER_BUGS]);1203 1204 if (page_index % 2) {1205 /* This is a redzone, report a buffer overflow. */1206 struct kfence_metadata *meta;1207 int distance = 0;1208 1209 meta = addr_to_metadata(addr - PAGE_SIZE);1210 if (meta && kfence_obj_allocated(meta)) {1211 to_report = meta;1212 /* Data race ok; distance calculation approximate. */1213 distance = addr - data_race(meta->addr + meta->size);1214 }1215 1216 meta = addr_to_metadata(addr + PAGE_SIZE);1217 if (meta && kfence_obj_allocated(meta)) {1218 /* Data race ok; distance calculation approximate. */1219 if (!to_report || distance > data_race(meta->addr) - addr)1220 to_report = meta;1221 }1222 1223 if (!to_report)1224 goto out;1225 1226 raw_spin_lock_irqsave(&to_report->lock, flags);1227 to_report->unprotected_page = addr;1228 error_type = KFENCE_ERROR_OOB;1229 1230 /*1231 * If the object was freed before we took the look we can still1232 * report this as an OOB -- the report will simply show the1233 * stacktrace of the free as well.1234 */1235 } else {1236 to_report = addr_to_metadata(addr);1237 if (!to_report)1238 goto out;1239 1240 raw_spin_lock_irqsave(&to_report->lock, flags);1241 error_type = KFENCE_ERROR_UAF;1242 /*1243 * We may race with __kfence_alloc(), and it is possible that a1244 * freed object may be reallocated. We simply report this as a1245 * use-after-free, with the stack trace showing the place where1246 * the object was re-allocated.1247 */1248 }1249 1250out:1251 if (to_report) {1252 kfence_report_error(addr, is_write, regs, to_report, error_type);1253 raw_spin_unlock_irqrestore(&to_report->lock, flags);1254 } else {1255 /* This may be a UAF or OOB access, but we can't be sure. */1256 kfence_report_error(addr, is_write, regs, NULL, KFENCE_ERROR_INVALID);1257 }1258 1259 return kfence_unprotect(addr); /* Unprotect and let access proceed. */1260}1261