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