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0ce20dd8 AP |
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> | |
08f6b106 | 13 | #include <linux/hash.h> |
407f1d8c | 14 | #include <linux/irq_work.h> |
08f6b106 | 15 | #include <linux/jhash.h> |
0ce20dd8 AP |
16 | #include <linux/kcsan-checks.h> |
17 | #include <linux/kfence.h> | |
95511580 | 18 | #include <linux/kmemleak.h> |
0ce20dd8 AP |
19 | #include <linux/list.h> |
20 | #include <linux/lockdep.h> | |
08f6b106 | 21 | #include <linux/log2.h> |
0ce20dd8 AP |
22 | #include <linux/memblock.h> |
23 | #include <linux/moduleparam.h> | |
24 | #include <linux/random.h> | |
25 | #include <linux/rcupdate.h> | |
4bbf04aa | 26 | #include <linux/sched/clock.h> |
37c9284f | 27 | #include <linux/sched/sysctl.h> |
0ce20dd8 AP |
28 | #include <linux/seq_file.h> |
29 | #include <linux/slab.h> | |
30 | #include <linux/spinlock.h> | |
31 | #include <linux/string.h> | |
32 | ||
33 | #include <asm/kfence.h> | |
34 | ||
35 | #include "kfence.h" | |
36 | ||
37 | /* Disables KFENCE on the first warning assuming an irrecoverable error. */ | |
38 | #define KFENCE_WARN_ON(cond) \ | |
39 | ({ \ | |
40 | const bool __cond = WARN_ON(cond); \ | |
41 | if (unlikely(__cond)) \ | |
42 | WRITE_ONCE(kfence_enabled, false); \ | |
43 | __cond; \ | |
44 | }) | |
45 | ||
46 | /* === Data ================================================================= */ | |
47 | ||
48 | static bool kfence_enabled __read_mostly; | |
49 | ||
50 | static unsigned long kfence_sample_interval __read_mostly = CONFIG_KFENCE_SAMPLE_INTERVAL; | |
51 | ||
52 | #ifdef MODULE_PARAM_PREFIX | |
53 | #undef MODULE_PARAM_PREFIX | |
54 | #endif | |
55 | #define MODULE_PARAM_PREFIX "kfence." | |
56 | ||
57 | static int param_set_sample_interval(const char *val, const struct kernel_param *kp) | |
58 | { | |
59 | unsigned long num; | |
60 | int ret = kstrtoul(val, 0, &num); | |
61 | ||
62 | if (ret < 0) | |
63 | return ret; | |
64 | ||
65 | if (!num) /* Using 0 to indicate KFENCE is disabled. */ | |
66 | WRITE_ONCE(kfence_enabled, false); | |
67 | else if (!READ_ONCE(kfence_enabled) && system_state != SYSTEM_BOOTING) | |
68 | return -EINVAL; /* Cannot (re-)enable KFENCE on-the-fly. */ | |
69 | ||
70 | *((unsigned long *)kp->arg) = num; | |
71 | return 0; | |
72 | } | |
73 | ||
74 | static int param_get_sample_interval(char *buffer, const struct kernel_param *kp) | |
75 | { | |
76 | if (!READ_ONCE(kfence_enabled)) | |
77 | return sprintf(buffer, "0\n"); | |
78 | ||
79 | return param_get_ulong(buffer, kp); | |
80 | } | |
81 | ||
82 | static const struct kernel_param_ops sample_interval_param_ops = { | |
83 | .set = param_set_sample_interval, | |
84 | .get = param_get_sample_interval, | |
85 | }; | |
86 | module_param_cb(sample_interval, &sample_interval_param_ops, &kfence_sample_interval, 0600); | |
87 | ||
08f6b106 ME |
88 | /* Pool usage% threshold when currently covered allocations are skipped. */ |
89 | static unsigned long kfence_skip_covered_thresh __read_mostly = 75; | |
90 | module_param_named(skip_covered_thresh, kfence_skip_covered_thresh, ulong, 0644); | |
91 | ||
0ce20dd8 AP |
92 | /* The pool of pages used for guard pages and objects. */ |
93 | char *__kfence_pool __ro_after_init; | |
94 | EXPORT_SYMBOL(__kfence_pool); /* Export for test modules. */ | |
95 | ||
96 | /* | |
97 | * Per-object metadata, with one-to-one mapping of object metadata to | |
98 | * backing pages (in __kfence_pool). | |
99 | */ | |
100 | static_assert(CONFIG_KFENCE_NUM_OBJECTS > 0); | |
101 | struct kfence_metadata kfence_metadata[CONFIG_KFENCE_NUM_OBJECTS]; | |
102 | ||
103 | /* Freelist with available objects. */ | |
104 | static struct list_head kfence_freelist = LIST_HEAD_INIT(kfence_freelist); | |
105 | static DEFINE_RAW_SPINLOCK(kfence_freelist_lock); /* Lock protecting freelist. */ | |
106 | ||
07e8481d ME |
107 | /* |
108 | * The static key to set up a KFENCE allocation; or if static keys are not used | |
109 | * to gate allocations, to avoid a load and compare if KFENCE is disabled. | |
110 | */ | |
0ce20dd8 | 111 | DEFINE_STATIC_KEY_FALSE(kfence_allocation_key); |
0ce20dd8 AP |
112 | |
113 | /* Gates the allocation, ensuring only one succeeds in a given period. */ | |
114 | atomic_t kfence_allocation_gate = ATOMIC_INIT(1); | |
115 | ||
08f6b106 ME |
116 | /* |
117 | * A Counting Bloom filter of allocation coverage: limits currently covered | |
118 | * allocations of the same source filling up the pool. | |
119 | * | |
120 | * Assuming a range of 15%-85% unique allocations in the pool at any point in | |
121 | * time, the below parameters provide a probablity of 0.02-0.33 for false | |
122 | * positive hits respectively: | |
123 | * | |
124 | * P(alloc_traces) = (1 - e^(-HNUM * (alloc_traces / SIZE)) ^ HNUM | |
125 | */ | |
126 | #define ALLOC_COVERED_HNUM 2 | |
127 | #define ALLOC_COVERED_ORDER (const_ilog2(CONFIG_KFENCE_NUM_OBJECTS) + 2) | |
128 | #define ALLOC_COVERED_SIZE (1 << ALLOC_COVERED_ORDER) | |
129 | #define ALLOC_COVERED_HNEXT(h) hash_32(h, ALLOC_COVERED_ORDER) | |
130 | #define ALLOC_COVERED_MASK (ALLOC_COVERED_SIZE - 1) | |
131 | static atomic_t alloc_covered[ALLOC_COVERED_SIZE]; | |
132 | ||
133 | /* Stack depth used to determine uniqueness of an allocation. */ | |
134 | #define UNIQUE_ALLOC_STACK_DEPTH ((size_t)8) | |
135 | ||
136 | /* | |
137 | * Randomness for stack hashes, making the same collisions across reboots and | |
138 | * different machines less likely. | |
139 | */ | |
140 | static u32 stack_hash_seed __ro_after_init; | |
141 | ||
0ce20dd8 AP |
142 | /* Statistics counters for debugfs. */ |
143 | enum kfence_counter_id { | |
144 | KFENCE_COUNTER_ALLOCATED, | |
145 | KFENCE_COUNTER_ALLOCS, | |
146 | KFENCE_COUNTER_FREES, | |
147 | KFENCE_COUNTER_ZOMBIES, | |
148 | KFENCE_COUNTER_BUGS, | |
9a19aeb5 ME |
149 | KFENCE_COUNTER_SKIP_INCOMPAT, |
150 | KFENCE_COUNTER_SKIP_CAPACITY, | |
08f6b106 | 151 | KFENCE_COUNTER_SKIP_COVERED, |
0ce20dd8 AP |
152 | KFENCE_COUNTER_COUNT, |
153 | }; | |
154 | static atomic_long_t counters[KFENCE_COUNTER_COUNT]; | |
155 | static const char *const counter_names[] = { | |
156 | [KFENCE_COUNTER_ALLOCATED] = "currently allocated", | |
157 | [KFENCE_COUNTER_ALLOCS] = "total allocations", | |
158 | [KFENCE_COUNTER_FREES] = "total frees", | |
159 | [KFENCE_COUNTER_ZOMBIES] = "zombie allocations", | |
160 | [KFENCE_COUNTER_BUGS] = "total bugs", | |
9a19aeb5 ME |
161 | [KFENCE_COUNTER_SKIP_INCOMPAT] = "skipped allocations (incompatible)", |
162 | [KFENCE_COUNTER_SKIP_CAPACITY] = "skipped allocations (capacity)", | |
08f6b106 | 163 | [KFENCE_COUNTER_SKIP_COVERED] = "skipped allocations (covered)", |
0ce20dd8 AP |
164 | }; |
165 | static_assert(ARRAY_SIZE(counter_names) == KFENCE_COUNTER_COUNT); | |
166 | ||
167 | /* === Internals ============================================================ */ | |
168 | ||
08f6b106 ME |
169 | static inline bool should_skip_covered(void) |
170 | { | |
171 | unsigned long thresh = (CONFIG_KFENCE_NUM_OBJECTS * kfence_skip_covered_thresh) / 100; | |
172 | ||
173 | return atomic_long_read(&counters[KFENCE_COUNTER_ALLOCATED]) > thresh; | |
174 | } | |
175 | ||
176 | static u32 get_alloc_stack_hash(unsigned long *stack_entries, size_t num_entries) | |
177 | { | |
178 | num_entries = min(num_entries, UNIQUE_ALLOC_STACK_DEPTH); | |
179 | num_entries = filter_irq_stacks(stack_entries, num_entries); | |
180 | return jhash(stack_entries, num_entries * sizeof(stack_entries[0]), stack_hash_seed); | |
181 | } | |
182 | ||
183 | /* | |
184 | * Adds (or subtracts) count @val for allocation stack trace hash | |
185 | * @alloc_stack_hash from Counting Bloom filter. | |
186 | */ | |
187 | static void alloc_covered_add(u32 alloc_stack_hash, int val) | |
188 | { | |
189 | int i; | |
190 | ||
191 | for (i = 0; i < ALLOC_COVERED_HNUM; i++) { | |
192 | atomic_add(val, &alloc_covered[alloc_stack_hash & ALLOC_COVERED_MASK]); | |
193 | alloc_stack_hash = ALLOC_COVERED_HNEXT(alloc_stack_hash); | |
194 | } | |
195 | } | |
196 | ||
197 | /* | |
198 | * Returns true if the allocation stack trace hash @alloc_stack_hash is | |
199 | * currently contained (non-zero count) in Counting Bloom filter. | |
200 | */ | |
201 | static bool alloc_covered_contains(u32 alloc_stack_hash) | |
202 | { | |
203 | int i; | |
204 | ||
205 | for (i = 0; i < ALLOC_COVERED_HNUM; i++) { | |
206 | if (!atomic_read(&alloc_covered[alloc_stack_hash & ALLOC_COVERED_MASK])) | |
207 | return false; | |
208 | alloc_stack_hash = ALLOC_COVERED_HNEXT(alloc_stack_hash); | |
209 | } | |
210 | ||
211 | return true; | |
212 | } | |
213 | ||
0ce20dd8 AP |
214 | static bool kfence_protect(unsigned long addr) |
215 | { | |
216 | return !KFENCE_WARN_ON(!kfence_protect_page(ALIGN_DOWN(addr, PAGE_SIZE), true)); | |
217 | } | |
218 | ||
219 | static bool kfence_unprotect(unsigned long addr) | |
220 | { | |
221 | return !KFENCE_WARN_ON(!kfence_protect_page(ALIGN_DOWN(addr, PAGE_SIZE), false)); | |
222 | } | |
223 | ||
224 | static inline struct kfence_metadata *addr_to_metadata(unsigned long addr) | |
225 | { | |
226 | long index; | |
227 | ||
228 | /* The checks do not affect performance; only called from slow-paths. */ | |
229 | ||
230 | if (!is_kfence_address((void *)addr)) | |
231 | return NULL; | |
232 | ||
233 | /* | |
234 | * May be an invalid index if called with an address at the edge of | |
235 | * __kfence_pool, in which case we would report an "invalid access" | |
236 | * error. | |
237 | */ | |
238 | index = (addr - (unsigned long)__kfence_pool) / (PAGE_SIZE * 2) - 1; | |
239 | if (index < 0 || index >= CONFIG_KFENCE_NUM_OBJECTS) | |
240 | return NULL; | |
241 | ||
242 | return &kfence_metadata[index]; | |
243 | } | |
244 | ||
245 | static inline unsigned long metadata_to_pageaddr(const struct kfence_metadata *meta) | |
246 | { | |
247 | unsigned long offset = (meta - kfence_metadata + 1) * PAGE_SIZE * 2; | |
248 | unsigned long pageaddr = (unsigned long)&__kfence_pool[offset]; | |
249 | ||
250 | /* The checks do not affect performance; only called from slow-paths. */ | |
251 | ||
252 | /* Only call with a pointer into kfence_metadata. */ | |
253 | if (KFENCE_WARN_ON(meta < kfence_metadata || | |
254 | meta >= kfence_metadata + CONFIG_KFENCE_NUM_OBJECTS)) | |
255 | return 0; | |
256 | ||
257 | /* | |
258 | * This metadata object only ever maps to 1 page; verify that the stored | |
259 | * address is in the expected range. | |
260 | */ | |
261 | if (KFENCE_WARN_ON(ALIGN_DOWN(meta->addr, PAGE_SIZE) != pageaddr)) | |
262 | return 0; | |
263 | ||
264 | return pageaddr; | |
265 | } | |
266 | ||
267 | /* | |
268 | * Update the object's metadata state, including updating the alloc/free stacks | |
269 | * depending on the state transition. | |
270 | */ | |
a9ab52bb ME |
271 | static noinline void |
272 | metadata_update_state(struct kfence_metadata *meta, enum kfence_object_state next, | |
273 | unsigned long *stack_entries, size_t num_stack_entries) | |
0ce20dd8 AP |
274 | { |
275 | struct kfence_track *track = | |
276 | next == KFENCE_OBJECT_FREED ? &meta->free_track : &meta->alloc_track; | |
277 | ||
278 | lockdep_assert_held(&meta->lock); | |
279 | ||
a9ab52bb ME |
280 | if (stack_entries) { |
281 | memcpy(track->stack_entries, stack_entries, | |
282 | num_stack_entries * sizeof(stack_entries[0])); | |
283 | } else { | |
284 | /* | |
285 | * Skip over 1 (this) functions; noinline ensures we do not | |
286 | * accidentally skip over the caller by never inlining. | |
287 | */ | |
288 | num_stack_entries = stack_trace_save(track->stack_entries, KFENCE_STACK_DEPTH, 1); | |
289 | } | |
290 | track->num_stack_entries = num_stack_entries; | |
0ce20dd8 | 291 | track->pid = task_pid_nr(current); |
4bbf04aa ME |
292 | track->cpu = raw_smp_processor_id(); |
293 | track->ts_nsec = local_clock(); /* Same source as printk timestamps. */ | |
0ce20dd8 AP |
294 | |
295 | /* | |
296 | * Pairs with READ_ONCE() in | |
297 | * kfence_shutdown_cache(), | |
298 | * kfence_handle_page_fault(). | |
299 | */ | |
300 | WRITE_ONCE(meta->state, next); | |
301 | } | |
302 | ||
303 | /* Write canary byte to @addr. */ | |
304 | static inline bool set_canary_byte(u8 *addr) | |
305 | { | |
306 | *addr = KFENCE_CANARY_PATTERN(addr); | |
307 | return true; | |
308 | } | |
309 | ||
310 | /* Check canary byte at @addr. */ | |
311 | static inline bool check_canary_byte(u8 *addr) | |
312 | { | |
49332956 ME |
313 | struct kfence_metadata *meta; |
314 | unsigned long flags; | |
315 | ||
0ce20dd8 AP |
316 | if (likely(*addr == KFENCE_CANARY_PATTERN(addr))) |
317 | return true; | |
318 | ||
319 | atomic_long_inc(&counters[KFENCE_COUNTER_BUGS]); | |
49332956 ME |
320 | |
321 | meta = addr_to_metadata((unsigned long)addr); | |
322 | raw_spin_lock_irqsave(&meta->lock, flags); | |
323 | kfence_report_error((unsigned long)addr, false, NULL, meta, KFENCE_ERROR_CORRUPTION); | |
324 | raw_spin_unlock_irqrestore(&meta->lock, flags); | |
325 | ||
0ce20dd8 AP |
326 | return false; |
327 | } | |
328 | ||
329 | /* __always_inline this to ensure we won't do an indirect call to fn. */ | |
330 | static __always_inline void for_each_canary(const struct kfence_metadata *meta, bool (*fn)(u8 *)) | |
331 | { | |
332 | const unsigned long pageaddr = ALIGN_DOWN(meta->addr, PAGE_SIZE); | |
333 | unsigned long addr; | |
334 | ||
0ce20dd8 AP |
335 | /* |
336 | * We'll iterate over each canary byte per-side until fn() returns | |
337 | * false. However, we'll still iterate over the canary bytes to the | |
338 | * right of the object even if there was an error in the canary bytes to | |
339 | * the left of the object. Specifically, if check_canary_byte() | |
340 | * generates an error, showing both sides might give more clues as to | |
341 | * what the error is about when displaying which bytes were corrupted. | |
342 | */ | |
343 | ||
344 | /* Apply to left of object. */ | |
345 | for (addr = pageaddr; addr < meta->addr; addr++) { | |
346 | if (!fn((u8 *)addr)) | |
347 | break; | |
348 | } | |
349 | ||
350 | /* Apply to right of object. */ | |
351 | for (addr = meta->addr + meta->size; addr < pageaddr + PAGE_SIZE; addr++) { | |
352 | if (!fn((u8 *)addr)) | |
353 | break; | |
354 | } | |
355 | } | |
356 | ||
a9ab52bb | 357 | static void *kfence_guarded_alloc(struct kmem_cache *cache, size_t size, gfp_t gfp, |
08f6b106 ME |
358 | unsigned long *stack_entries, size_t num_stack_entries, |
359 | u32 alloc_stack_hash) | |
0ce20dd8 AP |
360 | { |
361 | struct kfence_metadata *meta = NULL; | |
362 | unsigned long flags; | |
8dae0cfe | 363 | struct slab *slab; |
0ce20dd8 AP |
364 | void *addr; |
365 | ||
366 | /* Try to obtain a free object. */ | |
367 | raw_spin_lock_irqsave(&kfence_freelist_lock, flags); | |
368 | if (!list_empty(&kfence_freelist)) { | |
369 | meta = list_entry(kfence_freelist.next, struct kfence_metadata, list); | |
370 | list_del_init(&meta->list); | |
371 | } | |
372 | raw_spin_unlock_irqrestore(&kfence_freelist_lock, flags); | |
9a19aeb5 ME |
373 | if (!meta) { |
374 | atomic_long_inc(&counters[KFENCE_COUNTER_SKIP_CAPACITY]); | |
0ce20dd8 | 375 | return NULL; |
9a19aeb5 | 376 | } |
0ce20dd8 AP |
377 | |
378 | if (unlikely(!raw_spin_trylock_irqsave(&meta->lock, flags))) { | |
379 | /* | |
380 | * This is extremely unlikely -- we are reporting on a | |
381 | * use-after-free, which locked meta->lock, and the reporting | |
382 | * code via printk calls kmalloc() which ends up in | |
383 | * kfence_alloc() and tries to grab the same object that we're | |
384 | * reporting on. While it has never been observed, lockdep does | |
385 | * report that there is a possibility of deadlock. Fix it by | |
386 | * using trylock and bailing out gracefully. | |
387 | */ | |
388 | raw_spin_lock_irqsave(&kfence_freelist_lock, flags); | |
389 | /* Put the object back on the freelist. */ | |
390 | list_add_tail(&meta->list, &kfence_freelist); | |
391 | raw_spin_unlock_irqrestore(&kfence_freelist_lock, flags); | |
392 | ||
393 | return NULL; | |
394 | } | |
395 | ||
396 | meta->addr = metadata_to_pageaddr(meta); | |
397 | /* Unprotect if we're reusing this page. */ | |
398 | if (meta->state == KFENCE_OBJECT_FREED) | |
399 | kfence_unprotect(meta->addr); | |
400 | ||
401 | /* | |
402 | * Note: for allocations made before RNG initialization, will always | |
403 | * return zero. We still benefit from enabling KFENCE as early as | |
404 | * possible, even when the RNG is not yet available, as this will allow | |
405 | * KFENCE to detect bugs due to earlier allocations. The only downside | |
406 | * is that the out-of-bounds accesses detected are deterministic for | |
407 | * such allocations. | |
408 | */ | |
409 | if (prandom_u32_max(2)) { | |
410 | /* Allocate on the "right" side, re-calculate address. */ | |
411 | meta->addr += PAGE_SIZE - size; | |
412 | meta->addr = ALIGN_DOWN(meta->addr, cache->align); | |
413 | } | |
414 | ||
415 | addr = (void *)meta->addr; | |
416 | ||
417 | /* Update remaining metadata. */ | |
a9ab52bb | 418 | metadata_update_state(meta, KFENCE_OBJECT_ALLOCATED, stack_entries, num_stack_entries); |
0ce20dd8 AP |
419 | /* Pairs with READ_ONCE() in kfence_shutdown_cache(). */ |
420 | WRITE_ONCE(meta->cache, cache); | |
421 | meta->size = size; | |
08f6b106 | 422 | meta->alloc_stack_hash = alloc_stack_hash; |
49332956 | 423 | raw_spin_unlock_irqrestore(&meta->lock, flags); |
08f6b106 | 424 | |
49332956 | 425 | alloc_covered_add(alloc_stack_hash, 1); |
0ce20dd8 | 426 | |
8dae0cfe VB |
427 | /* Set required slab fields. */ |
428 | slab = virt_to_slab((void *)meta->addr); | |
429 | slab->slab_cache = cache; | |
b89fb5ef | 430 | if (IS_ENABLED(CONFIG_SLUB)) |
8dae0cfe | 431 | slab->objects = 1; |
d3fb45f3 | 432 | if (IS_ENABLED(CONFIG_SLAB)) |
8dae0cfe | 433 | slab->s_mem = addr; |
0ce20dd8 | 434 | |
0ce20dd8 | 435 | /* Memory initialization. */ |
49332956 | 436 | for_each_canary(meta, set_canary_byte); |
0ce20dd8 AP |
437 | |
438 | /* | |
439 | * We check slab_want_init_on_alloc() ourselves, rather than letting | |
440 | * SL*B do the initialization, as otherwise we might overwrite KFENCE's | |
441 | * redzone. | |
442 | */ | |
443 | if (unlikely(slab_want_init_on_alloc(gfp, cache))) | |
444 | memzero_explicit(addr, size); | |
445 | if (cache->ctor) | |
446 | cache->ctor(addr); | |
447 | ||
448 | if (CONFIG_KFENCE_STRESS_TEST_FAULTS && !prandom_u32_max(CONFIG_KFENCE_STRESS_TEST_FAULTS)) | |
449 | kfence_protect(meta->addr); /* Random "faults" by protecting the object. */ | |
450 | ||
451 | atomic_long_inc(&counters[KFENCE_COUNTER_ALLOCATED]); | |
452 | atomic_long_inc(&counters[KFENCE_COUNTER_ALLOCS]); | |
453 | ||
454 | return addr; | |
455 | } | |
456 | ||
457 | static void kfence_guarded_free(void *addr, struct kfence_metadata *meta, bool zombie) | |
458 | { | |
459 | struct kcsan_scoped_access assert_page_exclusive; | |
460 | unsigned long flags; | |
49332956 | 461 | bool init; |
0ce20dd8 AP |
462 | |
463 | raw_spin_lock_irqsave(&meta->lock, flags); | |
464 | ||
465 | if (meta->state != KFENCE_OBJECT_ALLOCATED || meta->addr != (unsigned long)addr) { | |
466 | /* Invalid or double-free, bail out. */ | |
467 | atomic_long_inc(&counters[KFENCE_COUNTER_BUGS]); | |
bc8fbc5f ME |
468 | kfence_report_error((unsigned long)addr, false, NULL, meta, |
469 | KFENCE_ERROR_INVALID_FREE); | |
0ce20dd8 AP |
470 | raw_spin_unlock_irqrestore(&meta->lock, flags); |
471 | return; | |
472 | } | |
473 | ||
474 | /* Detect racy use-after-free, or incorrect reallocation of this page by KFENCE. */ | |
475 | kcsan_begin_scoped_access((void *)ALIGN_DOWN((unsigned long)addr, PAGE_SIZE), PAGE_SIZE, | |
476 | KCSAN_ACCESS_SCOPED | KCSAN_ACCESS_WRITE | KCSAN_ACCESS_ASSERT, | |
477 | &assert_page_exclusive); | |
478 | ||
479 | if (CONFIG_KFENCE_STRESS_TEST_FAULTS) | |
480 | kfence_unprotect((unsigned long)addr); /* To check canary bytes. */ | |
481 | ||
482 | /* Restore page protection if there was an OOB access. */ | |
483 | if (meta->unprotected_page) { | |
94868a1e | 484 | memzero_explicit((void *)ALIGN_DOWN(meta->unprotected_page, PAGE_SIZE), PAGE_SIZE); |
0ce20dd8 AP |
485 | kfence_protect(meta->unprotected_page); |
486 | meta->unprotected_page = 0; | |
487 | } | |
488 | ||
49332956 ME |
489 | /* Mark the object as freed. */ |
490 | metadata_update_state(meta, KFENCE_OBJECT_FREED, NULL, 0); | |
491 | init = slab_want_init_on_free(meta->cache); | |
492 | raw_spin_unlock_irqrestore(&meta->lock, flags); | |
493 | ||
494 | alloc_covered_add(meta->alloc_stack_hash, -1); | |
495 | ||
0ce20dd8 AP |
496 | /* Check canary bytes for memory corruption. */ |
497 | for_each_canary(meta, check_canary_byte); | |
498 | ||
499 | /* | |
500 | * Clear memory if init-on-free is set. While we protect the page, the | |
501 | * data is still there, and after a use-after-free is detected, we | |
502 | * unprotect the page, so the data is still accessible. | |
503 | */ | |
49332956 | 504 | if (!zombie && unlikely(init)) |
0ce20dd8 AP |
505 | memzero_explicit(addr, meta->size); |
506 | ||
0ce20dd8 AP |
507 | /* Protect to detect use-after-frees. */ |
508 | kfence_protect((unsigned long)addr); | |
509 | ||
510 | kcsan_end_scoped_access(&assert_page_exclusive); | |
511 | if (!zombie) { | |
512 | /* Add it to the tail of the freelist for reuse. */ | |
513 | raw_spin_lock_irqsave(&kfence_freelist_lock, flags); | |
514 | KFENCE_WARN_ON(!list_empty(&meta->list)); | |
515 | list_add_tail(&meta->list, &kfence_freelist); | |
516 | raw_spin_unlock_irqrestore(&kfence_freelist_lock, flags); | |
517 | ||
518 | atomic_long_dec(&counters[KFENCE_COUNTER_ALLOCATED]); | |
519 | atomic_long_inc(&counters[KFENCE_COUNTER_FREES]); | |
520 | } else { | |
521 | /* See kfence_shutdown_cache(). */ | |
522 | atomic_long_inc(&counters[KFENCE_COUNTER_ZOMBIES]); | |
523 | } | |
524 | } | |
525 | ||
526 | static void rcu_guarded_free(struct rcu_head *h) | |
527 | { | |
528 | struct kfence_metadata *meta = container_of(h, struct kfence_metadata, rcu_head); | |
529 | ||
530 | kfence_guarded_free((void *)meta->addr, meta, false); | |
531 | } | |
532 | ||
533 | static bool __init kfence_init_pool(void) | |
534 | { | |
535 | unsigned long addr = (unsigned long)__kfence_pool; | |
536 | struct page *pages; | |
537 | int i; | |
538 | ||
539 | if (!__kfence_pool) | |
540 | return false; | |
541 | ||
542 | if (!arch_kfence_init_pool()) | |
543 | goto err; | |
544 | ||
545 | pages = virt_to_page(addr); | |
546 | ||
547 | /* | |
548 | * Set up object pages: they must have PG_slab set, to avoid freeing | |
549 | * these as real pages. | |
550 | * | |
551 | * We also want to avoid inserting kfence_free() in the kfree() | |
552 | * fast-path in SLUB, and therefore need to ensure kfree() correctly | |
553 | * enters __slab_free() slow-path. | |
554 | */ | |
555 | for (i = 0; i < KFENCE_POOL_SIZE / PAGE_SIZE; i++) { | |
556 | if (!i || (i % 2)) | |
557 | continue; | |
558 | ||
559 | /* Verify we do not have a compound head page. */ | |
560 | if (WARN_ON(compound_head(&pages[i]) != &pages[i])) | |
561 | goto err; | |
562 | ||
563 | __SetPageSlab(&pages[i]); | |
564 | } | |
565 | ||
566 | /* | |
567 | * Protect the first 2 pages. The first page is mostly unnecessary, and | |
568 | * merely serves as an extended guard page. However, adding one | |
569 | * additional page in the beginning gives us an even number of pages, | |
570 | * which simplifies the mapping of address to metadata index. | |
571 | */ | |
572 | for (i = 0; i < 2; i++) { | |
573 | if (unlikely(!kfence_protect(addr))) | |
574 | goto err; | |
575 | ||
576 | addr += PAGE_SIZE; | |
577 | } | |
578 | ||
579 | for (i = 0; i < CONFIG_KFENCE_NUM_OBJECTS; i++) { | |
580 | struct kfence_metadata *meta = &kfence_metadata[i]; | |
581 | ||
582 | /* Initialize metadata. */ | |
583 | INIT_LIST_HEAD(&meta->list); | |
584 | raw_spin_lock_init(&meta->lock); | |
585 | meta->state = KFENCE_OBJECT_UNUSED; | |
586 | meta->addr = addr; /* Initialize for validation in metadata_to_pageaddr(). */ | |
587 | list_add_tail(&meta->list, &kfence_freelist); | |
588 | ||
589 | /* Protect the right redzone. */ | |
590 | if (unlikely(!kfence_protect(addr + PAGE_SIZE))) | |
591 | goto err; | |
592 | ||
593 | addr += 2 * PAGE_SIZE; | |
594 | } | |
595 | ||
95511580 ME |
596 | /* |
597 | * The pool is live and will never be deallocated from this point on. | |
598 | * Remove the pool object from the kmemleak object tree, as it would | |
599 | * otherwise overlap with allocations returned by kfence_alloc(), which | |
600 | * are registered with kmemleak through the slab post-alloc hook. | |
601 | */ | |
602 | kmemleak_free(__kfence_pool); | |
603 | ||
0ce20dd8 AP |
604 | return true; |
605 | ||
606 | err: | |
607 | /* | |
608 | * Only release unprotected pages, and do not try to go back and change | |
609 | * page attributes due to risk of failing to do so as well. If changing | |
610 | * page attributes for some pages fails, it is very likely that it also | |
611 | * fails for the first page, and therefore expect addr==__kfence_pool in | |
612 | * most failure cases. | |
613 | */ | |
614 | memblock_free_late(__pa(addr), KFENCE_POOL_SIZE - (addr - (unsigned long)__kfence_pool)); | |
615 | __kfence_pool = NULL; | |
616 | return false; | |
617 | } | |
618 | ||
619 | /* === DebugFS Interface ==================================================== */ | |
620 | ||
621 | static int stats_show(struct seq_file *seq, void *v) | |
622 | { | |
623 | int i; | |
624 | ||
625 | seq_printf(seq, "enabled: %i\n", READ_ONCE(kfence_enabled)); | |
626 | for (i = 0; i < KFENCE_COUNTER_COUNT; i++) | |
627 | seq_printf(seq, "%s: %ld\n", counter_names[i], atomic_long_read(&counters[i])); | |
628 | ||
629 | return 0; | |
630 | } | |
631 | DEFINE_SHOW_ATTRIBUTE(stats); | |
632 | ||
633 | /* | |
634 | * debugfs seq_file operations for /sys/kernel/debug/kfence/objects. | |
635 | * start_object() and next_object() return the object index + 1, because NULL is used | |
636 | * to stop iteration. | |
637 | */ | |
638 | static void *start_object(struct seq_file *seq, loff_t *pos) | |
639 | { | |
640 | if (*pos < CONFIG_KFENCE_NUM_OBJECTS) | |
641 | return (void *)((long)*pos + 1); | |
642 | return NULL; | |
643 | } | |
644 | ||
645 | static void stop_object(struct seq_file *seq, void *v) | |
646 | { | |
647 | } | |
648 | ||
649 | static void *next_object(struct seq_file *seq, void *v, loff_t *pos) | |
650 | { | |
651 | ++*pos; | |
652 | if (*pos < CONFIG_KFENCE_NUM_OBJECTS) | |
653 | return (void *)((long)*pos + 1); | |
654 | return NULL; | |
655 | } | |
656 | ||
657 | static int show_object(struct seq_file *seq, void *v) | |
658 | { | |
659 | struct kfence_metadata *meta = &kfence_metadata[(long)v - 1]; | |
660 | unsigned long flags; | |
661 | ||
662 | raw_spin_lock_irqsave(&meta->lock, flags); | |
663 | kfence_print_object(seq, meta); | |
664 | raw_spin_unlock_irqrestore(&meta->lock, flags); | |
665 | seq_puts(seq, "---------------------------------\n"); | |
666 | ||
667 | return 0; | |
668 | } | |
669 | ||
670 | static const struct seq_operations object_seqops = { | |
671 | .start = start_object, | |
672 | .next = next_object, | |
673 | .stop = stop_object, | |
674 | .show = show_object, | |
675 | }; | |
676 | ||
677 | static int open_objects(struct inode *inode, struct file *file) | |
678 | { | |
679 | return seq_open(file, &object_seqops); | |
680 | } | |
681 | ||
682 | static const struct file_operations objects_fops = { | |
683 | .open = open_objects, | |
684 | .read = seq_read, | |
685 | .llseek = seq_lseek, | |
686 | }; | |
687 | ||
688 | static int __init kfence_debugfs_init(void) | |
689 | { | |
690 | struct dentry *kfence_dir = debugfs_create_dir("kfence", NULL); | |
691 | ||
692 | debugfs_create_file("stats", 0444, kfence_dir, NULL, &stats_fops); | |
693 | debugfs_create_file("objects", 0400, kfence_dir, NULL, &objects_fops); | |
694 | return 0; | |
695 | } | |
696 | ||
697 | late_initcall(kfence_debugfs_init); | |
698 | ||
699 | /* === Allocation Gate Timer ================================================ */ | |
700 | ||
407f1d8c ME |
701 | #ifdef CONFIG_KFENCE_STATIC_KEYS |
702 | /* Wait queue to wake up allocation-gate timer task. */ | |
703 | static DECLARE_WAIT_QUEUE_HEAD(allocation_wait); | |
704 | ||
705 | static void wake_up_kfence_timer(struct irq_work *work) | |
706 | { | |
707 | wake_up(&allocation_wait); | |
708 | } | |
709 | static DEFINE_IRQ_WORK(wake_up_kfence_timer_work, wake_up_kfence_timer); | |
710 | #endif | |
711 | ||
0ce20dd8 AP |
712 | /* |
713 | * Set up delayed work, which will enable and disable the static key. We need to | |
714 | * use a work queue (rather than a simple timer), since enabling and disabling a | |
715 | * static key cannot be done from an interrupt. | |
716 | * | |
717 | * Note: Toggling a static branch currently causes IPIs, and here we'll end up | |
718 | * with a total of 2 IPIs to all CPUs. If this ends up a problem in future (with | |
719 | * more aggressive sampling intervals), we could get away with a variant that | |
720 | * avoids IPIs, at the cost of not immediately capturing allocations if the | |
721 | * instructions remain cached. | |
722 | */ | |
723 | static struct delayed_work kfence_timer; | |
724 | static void toggle_allocation_gate(struct work_struct *work) | |
725 | { | |
726 | if (!READ_ONCE(kfence_enabled)) | |
727 | return; | |
728 | ||
0ce20dd8 AP |
729 | atomic_set(&kfence_allocation_gate, 0); |
730 | #ifdef CONFIG_KFENCE_STATIC_KEYS | |
407f1d8c | 731 | /* Enable static key, and await allocation to happen. */ |
0ce20dd8 | 732 | static_branch_enable(&kfence_allocation_key); |
407f1d8c | 733 | |
37c9284f ME |
734 | if (sysctl_hung_task_timeout_secs) { |
735 | /* | |
736 | * During low activity with no allocations we might wait a | |
737 | * while; let's avoid the hung task warning. | |
738 | */ | |
8fd0e995 ME |
739 | wait_event_idle_timeout(allocation_wait, atomic_read(&kfence_allocation_gate), |
740 | sysctl_hung_task_timeout_secs * HZ / 2); | |
37c9284f | 741 | } else { |
8fd0e995 | 742 | wait_event_idle(allocation_wait, atomic_read(&kfence_allocation_gate)); |
37c9284f | 743 | } |
407f1d8c | 744 | |
0ce20dd8 AP |
745 | /* Disable static key and reset timer. */ |
746 | static_branch_disable(&kfence_allocation_key); | |
747 | #endif | |
ff06e45d | 748 | queue_delayed_work(system_unbound_wq, &kfence_timer, |
36f0b35d | 749 | msecs_to_jiffies(kfence_sample_interval)); |
0ce20dd8 AP |
750 | } |
751 | static DECLARE_DELAYED_WORK(kfence_timer, toggle_allocation_gate); | |
752 | ||
753 | /* === Public interface ===================================================== */ | |
754 | ||
755 | void __init kfence_alloc_pool(void) | |
756 | { | |
757 | if (!kfence_sample_interval) | |
758 | return; | |
759 | ||
760 | __kfence_pool = memblock_alloc(KFENCE_POOL_SIZE, PAGE_SIZE); | |
761 | ||
762 | if (!__kfence_pool) | |
763 | pr_err("failed to allocate pool\n"); | |
764 | } | |
765 | ||
766 | void __init kfence_init(void) | |
767 | { | |
768 | /* Setting kfence_sample_interval to 0 on boot disables KFENCE. */ | |
769 | if (!kfence_sample_interval) | |
770 | return; | |
771 | ||
08f6b106 | 772 | stack_hash_seed = (u32)random_get_entropy(); |
0ce20dd8 AP |
773 | if (!kfence_init_pool()) { |
774 | pr_err("%s failed\n", __func__); | |
775 | return; | |
776 | } | |
777 | ||
07e8481d ME |
778 | if (!IS_ENABLED(CONFIG_KFENCE_STATIC_KEYS)) |
779 | static_branch_enable(&kfence_allocation_key); | |
0ce20dd8 | 780 | WRITE_ONCE(kfence_enabled, true); |
ff06e45d | 781 | queue_delayed_work(system_unbound_wq, &kfence_timer, 0); |
35beccf0 ME |
782 | pr_info("initialized - using %lu bytes for %d objects at 0x%p-0x%p\n", KFENCE_POOL_SIZE, |
783 | CONFIG_KFENCE_NUM_OBJECTS, (void *)__kfence_pool, | |
784 | (void *)(__kfence_pool + KFENCE_POOL_SIZE)); | |
0ce20dd8 AP |
785 | } |
786 | ||
787 | void kfence_shutdown_cache(struct kmem_cache *s) | |
788 | { | |
789 | unsigned long flags; | |
790 | struct kfence_metadata *meta; | |
791 | int i; | |
792 | ||
793 | for (i = 0; i < CONFIG_KFENCE_NUM_OBJECTS; i++) { | |
794 | bool in_use; | |
795 | ||
796 | meta = &kfence_metadata[i]; | |
797 | ||
798 | /* | |
799 | * If we observe some inconsistent cache and state pair where we | |
800 | * should have returned false here, cache destruction is racing | |
801 | * with either kmem_cache_alloc() or kmem_cache_free(). Taking | |
802 | * the lock will not help, as different critical section | |
803 | * serialization will have the same outcome. | |
804 | */ | |
805 | if (READ_ONCE(meta->cache) != s || | |
806 | READ_ONCE(meta->state) != KFENCE_OBJECT_ALLOCATED) | |
807 | continue; | |
808 | ||
809 | raw_spin_lock_irqsave(&meta->lock, flags); | |
810 | in_use = meta->cache == s && meta->state == KFENCE_OBJECT_ALLOCATED; | |
811 | raw_spin_unlock_irqrestore(&meta->lock, flags); | |
812 | ||
813 | if (in_use) { | |
814 | /* | |
815 | * This cache still has allocations, and we should not | |
816 | * release them back into the freelist so they can still | |
817 | * safely be used and retain the kernel's default | |
818 | * behaviour of keeping the allocations alive (leak the | |
819 | * cache); however, they effectively become "zombie | |
820 | * allocations" as the KFENCE objects are the only ones | |
821 | * still in use and the owning cache is being destroyed. | |
822 | * | |
823 | * We mark them freed, so that any subsequent use shows | |
824 | * more useful error messages that will include stack | |
825 | * traces of the user of the object, the original | |
826 | * allocation, and caller to shutdown_cache(). | |
827 | */ | |
828 | kfence_guarded_free((void *)meta->addr, meta, /*zombie=*/true); | |
829 | } | |
830 | } | |
831 | ||
832 | for (i = 0; i < CONFIG_KFENCE_NUM_OBJECTS; i++) { | |
833 | meta = &kfence_metadata[i]; | |
834 | ||
835 | /* See above. */ | |
836 | if (READ_ONCE(meta->cache) != s || READ_ONCE(meta->state) != KFENCE_OBJECT_FREED) | |
837 | continue; | |
838 | ||
839 | raw_spin_lock_irqsave(&meta->lock, flags); | |
840 | if (meta->cache == s && meta->state == KFENCE_OBJECT_FREED) | |
841 | meta->cache = NULL; | |
842 | raw_spin_unlock_irqrestore(&meta->lock, flags); | |
843 | } | |
844 | } | |
845 | ||
846 | void *__kfence_alloc(struct kmem_cache *s, size_t size, gfp_t flags) | |
847 | { | |
a9ab52bb ME |
848 | unsigned long stack_entries[KFENCE_STACK_DEPTH]; |
849 | size_t num_stack_entries; | |
08f6b106 | 850 | u32 alloc_stack_hash; |
a9ab52bb | 851 | |
235a85cb AP |
852 | /* |
853 | * Perform size check before switching kfence_allocation_gate, so that | |
854 | * we don't disable KFENCE without making an allocation. | |
855 | */ | |
9a19aeb5 ME |
856 | if (size > PAGE_SIZE) { |
857 | atomic_long_inc(&counters[KFENCE_COUNTER_SKIP_INCOMPAT]); | |
235a85cb | 858 | return NULL; |
9a19aeb5 | 859 | } |
235a85cb | 860 | |
236e9f15 AP |
861 | /* |
862 | * Skip allocations from non-default zones, including DMA. We cannot | |
863 | * guarantee that pages in the KFENCE pool will have the requested | |
864 | * properties (e.g. reside in DMAable memory). | |
865 | */ | |
866 | if ((flags & GFP_ZONEMASK) || | |
9a19aeb5 ME |
867 | (s->flags & (SLAB_CACHE_DMA | SLAB_CACHE_DMA32))) { |
868 | atomic_long_inc(&counters[KFENCE_COUNTER_SKIP_INCOMPAT]); | |
236e9f15 | 869 | return NULL; |
9a19aeb5 | 870 | } |
236e9f15 | 871 | |
07e8481d | 872 | if (atomic_inc_return(&kfence_allocation_gate) > 1) |
0ce20dd8 | 873 | return NULL; |
407f1d8c ME |
874 | #ifdef CONFIG_KFENCE_STATIC_KEYS |
875 | /* | |
876 | * waitqueue_active() is fully ordered after the update of | |
877 | * kfence_allocation_gate per atomic_inc_return(). | |
878 | */ | |
879 | if (waitqueue_active(&allocation_wait)) { | |
880 | /* | |
881 | * Calling wake_up() here may deadlock when allocations happen | |
882 | * from within timer code. Use an irq_work to defer it. | |
883 | */ | |
884 | irq_work_queue(&wake_up_kfence_timer_work); | |
885 | } | |
886 | #endif | |
0ce20dd8 AP |
887 | |
888 | if (!READ_ONCE(kfence_enabled)) | |
889 | return NULL; | |
890 | ||
a9ab52bb ME |
891 | num_stack_entries = stack_trace_save(stack_entries, KFENCE_STACK_DEPTH, 0); |
892 | ||
08f6b106 ME |
893 | /* |
894 | * Do expensive check for coverage of allocation in slow-path after | |
895 | * allocation_gate has already become non-zero, even though it might | |
896 | * mean not making any allocation within a given sample interval. | |
897 | * | |
898 | * This ensures reasonable allocation coverage when the pool is almost | |
899 | * full, including avoiding long-lived allocations of the same source | |
900 | * filling up the pool (e.g. pagecache allocations). | |
901 | */ | |
902 | alloc_stack_hash = get_alloc_stack_hash(stack_entries, num_stack_entries); | |
903 | if (should_skip_covered() && alloc_covered_contains(alloc_stack_hash)) { | |
904 | atomic_long_inc(&counters[KFENCE_COUNTER_SKIP_COVERED]); | |
905 | return NULL; | |
906 | } | |
907 | ||
908 | return kfence_guarded_alloc(s, size, flags, stack_entries, num_stack_entries, | |
909 | alloc_stack_hash); | |
0ce20dd8 AP |
910 | } |
911 | ||
912 | size_t kfence_ksize(const void *addr) | |
913 | { | |
914 | const struct kfence_metadata *meta = addr_to_metadata((unsigned long)addr); | |
915 | ||
916 | /* | |
917 | * Read locklessly -- if there is a race with __kfence_alloc(), this is | |
918 | * either a use-after-free or invalid access. | |
919 | */ | |
920 | return meta ? meta->size : 0; | |
921 | } | |
922 | ||
923 | void *kfence_object_start(const void *addr) | |
924 | { | |
925 | const struct kfence_metadata *meta = addr_to_metadata((unsigned long)addr); | |
926 | ||
927 | /* | |
928 | * Read locklessly -- if there is a race with __kfence_alloc(), this is | |
929 | * either a use-after-free or invalid access. | |
930 | */ | |
931 | return meta ? (void *)meta->addr : NULL; | |
932 | } | |
933 | ||
934 | void __kfence_free(void *addr) | |
935 | { | |
936 | struct kfence_metadata *meta = addr_to_metadata((unsigned long)addr); | |
937 | ||
938 | /* | |
939 | * If the objects of the cache are SLAB_TYPESAFE_BY_RCU, defer freeing | |
940 | * the object, as the object page may be recycled for other-typed | |
941 | * objects once it has been freed. meta->cache may be NULL if the cache | |
942 | * was destroyed. | |
943 | */ | |
944 | if (unlikely(meta->cache && (meta->cache->flags & SLAB_TYPESAFE_BY_RCU))) | |
945 | call_rcu(&meta->rcu_head, rcu_guarded_free); | |
946 | else | |
947 | kfence_guarded_free(addr, meta, false); | |
948 | } | |
949 | ||
bc8fbc5f | 950 | bool kfence_handle_page_fault(unsigned long addr, bool is_write, struct pt_regs *regs) |
0ce20dd8 AP |
951 | { |
952 | const int page_index = (addr - (unsigned long)__kfence_pool) / PAGE_SIZE; | |
953 | struct kfence_metadata *to_report = NULL; | |
954 | enum kfence_error_type error_type; | |
955 | unsigned long flags; | |
956 | ||
957 | if (!is_kfence_address((void *)addr)) | |
958 | return false; | |
959 | ||
960 | if (!READ_ONCE(kfence_enabled)) /* If disabled at runtime ... */ | |
961 | return kfence_unprotect(addr); /* ... unprotect and proceed. */ | |
962 | ||
963 | atomic_long_inc(&counters[KFENCE_COUNTER_BUGS]); | |
964 | ||
965 | if (page_index % 2) { | |
966 | /* This is a redzone, report a buffer overflow. */ | |
967 | struct kfence_metadata *meta; | |
968 | int distance = 0; | |
969 | ||
970 | meta = addr_to_metadata(addr - PAGE_SIZE); | |
971 | if (meta && READ_ONCE(meta->state) == KFENCE_OBJECT_ALLOCATED) { | |
972 | to_report = meta; | |
973 | /* Data race ok; distance calculation approximate. */ | |
974 | distance = addr - data_race(meta->addr + meta->size); | |
975 | } | |
976 | ||
977 | meta = addr_to_metadata(addr + PAGE_SIZE); | |
978 | if (meta && READ_ONCE(meta->state) == KFENCE_OBJECT_ALLOCATED) { | |
979 | /* Data race ok; distance calculation approximate. */ | |
980 | if (!to_report || distance > data_race(meta->addr) - addr) | |
981 | to_report = meta; | |
982 | } | |
983 | ||
984 | if (!to_report) | |
985 | goto out; | |
986 | ||
987 | raw_spin_lock_irqsave(&to_report->lock, flags); | |
988 | to_report->unprotected_page = addr; | |
989 | error_type = KFENCE_ERROR_OOB; | |
990 | ||
991 | /* | |
992 | * If the object was freed before we took the look we can still | |
993 | * report this as an OOB -- the report will simply show the | |
994 | * stacktrace of the free as well. | |
995 | */ | |
996 | } else { | |
997 | to_report = addr_to_metadata(addr); | |
998 | if (!to_report) | |
999 | goto out; | |
1000 | ||
1001 | raw_spin_lock_irqsave(&to_report->lock, flags); | |
1002 | error_type = KFENCE_ERROR_UAF; | |
1003 | /* | |
1004 | * We may race with __kfence_alloc(), and it is possible that a | |
1005 | * freed object may be reallocated. We simply report this as a | |
1006 | * use-after-free, with the stack trace showing the place where | |
1007 | * the object was re-allocated. | |
1008 | */ | |
1009 | } | |
1010 | ||
1011 | out: | |
1012 | if (to_report) { | |
bc8fbc5f | 1013 | kfence_report_error(addr, is_write, regs, to_report, error_type); |
0ce20dd8 AP |
1014 | raw_spin_unlock_irqrestore(&to_report->lock, flags); |
1015 | } else { | |
1016 | /* This may be a UAF or OOB access, but we can't be sure. */ | |
bc8fbc5f | 1017 | kfence_report_error(addr, is_write, regs, NULL, KFENCE_ERROR_INVALID); |
0ce20dd8 AP |
1018 | } |
1019 | ||
1020 | return kfence_unprotect(addr); /* Unprotect and let access proceed. */ | |
1021 | } |