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