1// SPDX-License-Identifier: GPL-2.0
2/*
3 * This file contains core generic KASAN code.
4 *
5 * Copyright (c) 2014 Samsung Electronics Co., Ltd.
6 * Author: Andrey Ryabinin <ryabinin.a.a@gmail.com>
7 *
8 * Some code borrowed from https://github.com/xairy/kasan-prototype by
9 * Andrey Konovalov <andreyknvl@gmail.com>
10 */
11
12#include <linux/export.h>
13#include <linux/interrupt.h>
14#include <linux/init.h>
15#include <linux/kasan.h>
16#include <linux/kernel.h>
17#include <linux/kfence.h>
18#include <linux/kmemleak.h>
19#include <linux/linkage.h>
20#include <linux/memblock.h>
21#include <linux/memory.h>
22#include <linux/mm.h>
23#include <linux/module.h>
24#include <linux/printk.h>
25#include <linux/sched.h>
26#include <linux/sched/task_stack.h>
27#include <linux/slab.h>
28#include <linux/spinlock.h>
29#include <linux/stackdepot.h>
30#include <linux/stacktrace.h>
31#include <linux/string.h>
32#include <linux/types.h>
33#include <linux/vmalloc.h>
34#include <linux/bug.h>
35
36#include "kasan.h"
37#include "../slab.h"
38
39/*
40 * Initialize Generic KASAN and enable runtime checks.
41 * This should be called from arch kasan_init() once shadow memory is ready.
42 */
43void __init kasan_init_generic(void)
44{
45 kasan_enable();
46
47 pr_info("KernelAddressSanitizer initialized (generic)\n");
48}
49
50/*
51 * All functions below always inlined so compiler could
52 * perform better optimizations in each of __asan_loadX/__assn_storeX
53 * depending on memory access size X.
54 */
55
56static __always_inline bool memory_is_poisoned_1(const void *addr)
57{
58 s8 shadow_value = *(s8 *)kasan_mem_to_shadow(addr);
59
60 if (unlikely(shadow_value)) {
61 s8 last_accessible_byte = (unsigned long)addr & KASAN_GRANULE_MASK;
62 return unlikely(last_accessible_byte >= shadow_value);
63 }
64
65 return false;
66}
67
68static __always_inline bool memory_is_poisoned_2_4_8(const void *addr,
69 unsigned long size)
70{
71 u8 *shadow_addr = (u8 *)kasan_mem_to_shadow(addr);
72
73 /*
74 * Access crosses 8(shadow size)-byte boundary. Such access maps
75 * into 2 shadow bytes, so we need to check them both.
76 */
77 if (unlikely((((unsigned long)addr + size - 1) & KASAN_GRANULE_MASK) < size - 1))
78 return *shadow_addr || memory_is_poisoned_1(addr: addr + size - 1);
79
80 return memory_is_poisoned_1(addr: addr + size - 1);
81}
82
83static __always_inline bool memory_is_poisoned_16(const void *addr)
84{
85 u16 *shadow_addr = (u16 *)kasan_mem_to_shadow(addr);
86
87 /* Unaligned 16-bytes access maps into 3 shadow bytes. */
88 if (unlikely(!IS_ALIGNED((unsigned long)addr, KASAN_GRANULE_SIZE)))
89 return *shadow_addr || memory_is_poisoned_1(addr: addr + 15);
90
91 return *shadow_addr;
92}
93
94static __always_inline unsigned long bytes_is_nonzero(const u8 *start,
95 size_t size)
96{
97 while (size) {
98 if (unlikely(*start))
99 return (unsigned long)start;
100 start++;
101 size--;
102 }
103
104 return 0;
105}
106
107static __always_inline unsigned long memory_is_nonzero(const void *start,
108 const void *end)
109{
110 unsigned int words;
111 unsigned long ret;
112 unsigned int prefix = (unsigned long)start % 8;
113
114 if (end - start <= 16)
115 return bytes_is_nonzero(start, size: end - start);
116
117 if (prefix) {
118 prefix = 8 - prefix;
119 ret = bytes_is_nonzero(start, size: prefix);
120 if (unlikely(ret))
121 return ret;
122 start += prefix;
123 }
124
125 words = (end - start) / 8;
126 while (words) {
127 if (unlikely(*(u64 *)start))
128 return bytes_is_nonzero(start, size: 8);
129 start += 8;
130 words--;
131 }
132
133 return bytes_is_nonzero(start, size: (end - start) % 8);
134}
135
136static __always_inline bool memory_is_poisoned_n(const void *addr, size_t size)
137{
138 unsigned long ret;
139
140 ret = memory_is_nonzero(start: kasan_mem_to_shadow(addr),
141 end: kasan_mem_to_shadow(addr: addr + size - 1) + 1);
142
143 if (unlikely(ret)) {
144 const void *last_byte = addr + size - 1;
145 s8 *last_shadow = (s8 *)kasan_mem_to_shadow(addr: last_byte);
146 s8 last_accessible_byte = (unsigned long)last_byte & KASAN_GRANULE_MASK;
147
148 if (unlikely(ret != (unsigned long)last_shadow ||
149 last_accessible_byte >= *last_shadow))
150 return true;
151 }
152 return false;
153}
154
155static __always_inline bool memory_is_poisoned(const void *addr, size_t size)
156{
157 if (__builtin_constant_p(size)) {
158 switch (size) {
159 case 1:
160 return memory_is_poisoned_1(addr);
161 case 2:
162 case 4:
163 case 8:
164 return memory_is_poisoned_2_4_8(addr, size);
165 case 16:
166 return memory_is_poisoned_16(addr);
167 default:
168 BUILD_BUG();
169 }
170 }
171
172 return memory_is_poisoned_n(addr, size);
173}
174
175static __always_inline bool check_region_inline(const void *addr,
176 size_t size, bool write,
177 unsigned long ret_ip)
178{
179 if (!kasan_enabled())
180 return true;
181
182 if (unlikely(size == 0))
183 return true;
184
185 if (unlikely(addr + size < addr))
186 return !kasan_report(addr, size, is_write: write, ip: ret_ip);
187
188 if (unlikely(!addr_has_metadata(addr)))
189 return !kasan_report(addr, size, is_write: write, ip: ret_ip);
190
191 if (likely(!memory_is_poisoned(addr, size)))
192 return true;
193
194 return !kasan_report(addr, size, is_write: write, ip: ret_ip);
195}
196
197bool kasan_check_range(const void *addr, size_t size, bool write,
198 unsigned long ret_ip)
199{
200 return check_region_inline(addr, size, write, ret_ip);
201}
202
203bool kasan_byte_accessible(const void *addr)
204{
205 s8 shadow_byte;
206
207 if (!kasan_enabled())
208 return true;
209
210 shadow_byte = READ_ONCE(*(s8 *)kasan_mem_to_shadow(addr));
211
212 return shadow_byte >= 0 && shadow_byte < KASAN_GRANULE_SIZE;
213}
214
215void kasan_cache_shrink(struct kmem_cache *cache)
216{
217 kasan_quarantine_remove_cache(cache);
218}
219
220void kasan_cache_shutdown(struct kmem_cache *cache)
221{
222 if (!__kmem_cache_empty(cache))
223 kasan_quarantine_remove_cache(cache);
224}
225
226static void register_global(struct kasan_global *global)
227{
228 size_t aligned_size = round_up(global->size, KASAN_GRANULE_SIZE);
229
230 kasan_unpoison(addr: global->beg, size: global->size, init: false);
231
232 kasan_poison(addr: global->beg + aligned_size,
233 size: global->size_with_redzone - aligned_size,
234 KASAN_GLOBAL_REDZONE, init: false);
235}
236
237void __asan_register_globals(void *ptr, ssize_t size)
238{
239 int i;
240 struct kasan_global *globals = ptr;
241
242 for (i = 0; i < size; i++)
243 register_global(global: &globals[i]);
244}
245EXPORT_SYMBOL(__asan_register_globals);
246
247void __asan_unregister_globals(void *ptr, ssize_t size)
248{
249}
250EXPORT_SYMBOL(__asan_unregister_globals);
251
252#define DEFINE_ASAN_LOAD_STORE(size) \
253 void __asan_load##size(void *addr) \
254 { \
255 check_region_inline(addr, size, false, _RET_IP_); \
256 } \
257 EXPORT_SYMBOL(__asan_load##size); \
258 __alias(__asan_load##size) \
259 void __asan_load##size##_noabort(void *); \
260 EXPORT_SYMBOL(__asan_load##size##_noabort); \
261 void __asan_store##size(void *addr) \
262 { \
263 check_region_inline(addr, size, true, _RET_IP_); \
264 } \
265 EXPORT_SYMBOL(__asan_store##size); \
266 __alias(__asan_store##size) \
267 void __asan_store##size##_noabort(void *); \
268 EXPORT_SYMBOL(__asan_store##size##_noabort)
269
270DEFINE_ASAN_LOAD_STORE(1);
271DEFINE_ASAN_LOAD_STORE(2);
272DEFINE_ASAN_LOAD_STORE(4);
273DEFINE_ASAN_LOAD_STORE(8);
274DEFINE_ASAN_LOAD_STORE(16);
275
276void __asan_loadN(void *addr, ssize_t size)
277{
278 kasan_check_range(addr, size, write: false, _RET_IP_);
279}
280EXPORT_SYMBOL(__asan_loadN);
281
282__alias(__asan_loadN)
283void __asan_loadN_noabort(void *, ssize_t);
284EXPORT_SYMBOL(__asan_loadN_noabort);
285
286void __asan_storeN(void *addr, ssize_t size)
287{
288 kasan_check_range(addr, size, write: true, _RET_IP_);
289}
290EXPORT_SYMBOL(__asan_storeN);
291
292__alias(__asan_storeN)
293void __asan_storeN_noabort(void *, ssize_t);
294EXPORT_SYMBOL(__asan_storeN_noabort);
295
296/* to shut up compiler complaints */
297void __asan_handle_no_return(void) {}
298EXPORT_SYMBOL(__asan_handle_no_return);
299
300/* Emitted by compiler to poison alloca()ed objects. */
301void __asan_alloca_poison(void *addr, ssize_t size)
302{
303 size_t rounded_up_size = round_up(size, KASAN_GRANULE_SIZE);
304 size_t padding_size = round_up(size, KASAN_ALLOCA_REDZONE_SIZE) -
305 rounded_up_size;
306 size_t rounded_down_size = round_down(size, KASAN_GRANULE_SIZE);
307
308 const void *left_redzone = (const void *)(addr -
309 KASAN_ALLOCA_REDZONE_SIZE);
310 const void *right_redzone = (const void *)(addr + rounded_up_size);
311
312 WARN_ON(!IS_ALIGNED((unsigned long)addr, KASAN_ALLOCA_REDZONE_SIZE));
313
314 kasan_unpoison(addr: (const void *)(addr + rounded_down_size),
315 size: size - rounded_down_size, init: false);
316 kasan_poison(addr: left_redzone, KASAN_ALLOCA_REDZONE_SIZE,
317 KASAN_ALLOCA_LEFT, init: false);
318 kasan_poison(addr: right_redzone, size: padding_size + KASAN_ALLOCA_REDZONE_SIZE,
319 KASAN_ALLOCA_RIGHT, init: false);
320}
321EXPORT_SYMBOL(__asan_alloca_poison);
322
323/* Emitted by compiler to unpoison alloca()ed areas when the stack unwinds. */
324void __asan_allocas_unpoison(void *stack_top, ssize_t stack_bottom)
325{
326 if (unlikely(!stack_top || stack_top > (void *)stack_bottom))
327 return;
328
329 kasan_unpoison(addr: stack_top, size: (void *)stack_bottom - stack_top, init: false);
330}
331EXPORT_SYMBOL(__asan_allocas_unpoison);
332
333/* Emitted by the compiler to [un]poison local variables. */
334#define DEFINE_ASAN_SET_SHADOW(byte) \
335 void __asan_set_shadow_##byte(const void *addr, ssize_t size) \
336 { \
337 __memset((void *)addr, 0x##byte, size); \
338 } \
339 EXPORT_SYMBOL(__asan_set_shadow_##byte)
340
341DEFINE_ASAN_SET_SHADOW(00);
342DEFINE_ASAN_SET_SHADOW(f1);
343DEFINE_ASAN_SET_SHADOW(f2);
344DEFINE_ASAN_SET_SHADOW(f3);
345DEFINE_ASAN_SET_SHADOW(f5);
346DEFINE_ASAN_SET_SHADOW(f8);
347
348/*
349 * Adaptive redzone policy taken from the userspace AddressSanitizer runtime.
350 * For larger allocations larger redzones are used.
351 */
352static inline unsigned int optimal_redzone(unsigned int object_size)
353{
354 return
355 object_size <= 64 - 16 ? 16 :
356 object_size <= 128 - 32 ? 32 :
357 object_size <= 512 - 64 ? 64 :
358 object_size <= 4096 - 128 ? 128 :
359 object_size <= (1 << 14) - 256 ? 256 :
360 object_size <= (1 << 15) - 512 ? 512 :
361 object_size <= (1 << 16) - 1024 ? 1024 : 2048;
362}
363
364void kasan_cache_create(struct kmem_cache *cache, unsigned int *size,
365 slab_flags_t *flags)
366{
367 unsigned int ok_size;
368 unsigned int optimal_size;
369 unsigned int rem_free_meta_size;
370 unsigned int orig_alloc_meta_offset;
371
372 if (!kasan_requires_meta())
373 return;
374
375 /*
376 * SLAB_KASAN is used to mark caches that are sanitized by KASAN and
377 * that thus have per-object metadata. Currently, this flag is used in
378 * slab_ksize() to account for per-object metadata when calculating the
379 * size of the accessible memory within the object. Additionally, we use
380 * SLAB_NO_MERGE to prevent merging of caches with per-object metadata.
381 */
382 *flags |= SLAB_KASAN | SLAB_NO_MERGE;
383
384 ok_size = *size;
385
386 /* Add alloc meta into the redzone. */
387 cache->kasan_info.alloc_meta_offset = *size;
388 *size += sizeof(struct kasan_alloc_meta);
389
390 /* If alloc meta doesn't fit, don't add it. */
391 if (*size > KMALLOC_MAX_SIZE) {
392 cache->kasan_info.alloc_meta_offset = 0;
393 *size = ok_size;
394 /* Continue, since free meta might still fit. */
395 }
396
397 ok_size = *size;
398 orig_alloc_meta_offset = cache->kasan_info.alloc_meta_offset;
399
400 /*
401 * Store free meta in the redzone when it's not possible to store
402 * it in the object. This is the case when:
403 * 1. Object is SLAB_TYPESAFE_BY_RCU, which means that it can
404 * be touched after it was freed, or
405 * 2. Object has a constructor, which means it's expected to
406 * retain its content until the next allocation, or
407 * 3. It is from a kmalloc cache which enables the debug option
408 * to store original size.
409 */
410 if ((cache->flags & SLAB_TYPESAFE_BY_RCU) || cache->ctor ||
411 slub_debug_orig_size(s: cache)) {
412 cache->kasan_info.free_meta_offset = *size;
413 *size += sizeof(struct kasan_free_meta);
414 goto free_meta_added;
415 }
416
417 /*
418 * Otherwise, if the object is large enough to contain free meta,
419 * store it within the object.
420 */
421 if (sizeof(struct kasan_free_meta) <= cache->object_size) {
422 /* cache->kasan_info.free_meta_offset = 0 is implied. */
423 goto free_meta_added;
424 }
425
426 /*
427 * For smaller objects, store the beginning of free meta within the
428 * object and the end in the redzone. And thus shift the location of
429 * alloc meta to free up space for free meta.
430 * This is only possible when slub_debug is disabled, as otherwise
431 * the end of free meta will overlap with slub_debug metadata.
432 */
433 if (!__slub_debug_enabled()) {
434 rem_free_meta_size = sizeof(struct kasan_free_meta) -
435 cache->object_size;
436 *size += rem_free_meta_size;
437 if (cache->kasan_info.alloc_meta_offset != 0)
438 cache->kasan_info.alloc_meta_offset += rem_free_meta_size;
439 goto free_meta_added;
440 }
441
442 /*
443 * If the object is small and slub_debug is enabled, store free meta
444 * in the redzone after alloc meta.
445 */
446 cache->kasan_info.free_meta_offset = *size;
447 *size += sizeof(struct kasan_free_meta);
448
449free_meta_added:
450 /* If free meta doesn't fit, don't add it. */
451 if (*size > KMALLOC_MAX_SIZE) {
452 cache->kasan_info.free_meta_offset = KASAN_NO_FREE_META;
453 cache->kasan_info.alloc_meta_offset = orig_alloc_meta_offset;
454 *size = ok_size;
455 }
456
457 /* Calculate size with optimal redzone. */
458 optimal_size = cache->object_size + optimal_redzone(object_size: cache->object_size);
459 /* Limit it with KMALLOC_MAX_SIZE. */
460 if (optimal_size > KMALLOC_MAX_SIZE)
461 optimal_size = KMALLOC_MAX_SIZE;
462 /* Use optimal size if the size with added metas is not large enough. */
463 if (*size < optimal_size)
464 *size = optimal_size;
465}
466
467struct kasan_alloc_meta *kasan_get_alloc_meta(struct kmem_cache *cache,
468 const void *object)
469{
470 if (!cache->kasan_info.alloc_meta_offset)
471 return NULL;
472 return (void *)object + cache->kasan_info.alloc_meta_offset;
473}
474
475struct kasan_free_meta *kasan_get_free_meta(struct kmem_cache *cache,
476 const void *object)
477{
478 BUILD_BUG_ON(sizeof(struct kasan_free_meta) > 32);
479 if (cache->kasan_info.free_meta_offset == KASAN_NO_FREE_META)
480 return NULL;
481 return (void *)object + cache->kasan_info.free_meta_offset;
482}
483
484void kasan_init_object_meta(struct kmem_cache *cache, const void *object)
485{
486 struct kasan_alloc_meta *alloc_meta;
487
488 alloc_meta = kasan_get_alloc_meta(cache, object);
489 if (alloc_meta) {
490 /* Zero out alloc meta to mark it as invalid. */
491 __memset(s: alloc_meta, c: 0, n: sizeof(*alloc_meta));
492 }
493
494 /*
495 * Explicitly marking free meta as invalid is not required: the shadow
496 * value for the first 8 bytes of a newly allocated object is not
497 * KASAN_SLAB_FREE_META.
498 */
499}
500
501static void release_alloc_meta(struct kasan_alloc_meta *meta)
502{
503 /* Zero out alloc meta to mark it as invalid. */
504 __memset(s: meta, c: 0, n: sizeof(*meta));
505}
506
507static void release_free_meta(const void *object, struct kasan_free_meta *meta)
508{
509 /* Check if free meta is valid. */
510 if (*(u8 *)kasan_mem_to_shadow(addr: object) != KASAN_SLAB_FREE_META)
511 return;
512
513 /* Mark free meta as invalid. */
514 *(u8 *)kasan_mem_to_shadow(addr: object) = KASAN_SLAB_FREE;
515}
516
517size_t kasan_metadata_size(struct kmem_cache *cache, bool in_object)
518{
519 struct kasan_cache *info = &cache->kasan_info;
520
521 if (!kasan_requires_meta())
522 return 0;
523
524 if (in_object)
525 return (info->free_meta_offset ?
526 0 : sizeof(struct kasan_free_meta));
527 else
528 return (info->alloc_meta_offset ?
529 sizeof(struct kasan_alloc_meta) : 0) +
530 ((info->free_meta_offset &&
531 info->free_meta_offset != KASAN_NO_FREE_META) ?
532 sizeof(struct kasan_free_meta) : 0);
533}
534
535/*
536 * This function avoids dynamic memory allocations and thus can be called from
537 * contexts that do not allow allocating memory.
538 */
539void kasan_record_aux_stack(void *addr)
540{
541 struct slab *slab = kasan_addr_to_slab(addr);
542 struct kmem_cache *cache;
543 struct kasan_alloc_meta *alloc_meta;
544 void *object;
545
546 if (is_kfence_address(addr) || !slab)
547 return;
548
549 cache = slab->slab_cache;
550 object = nearest_obj(cache, slab, x: addr);
551 alloc_meta = kasan_get_alloc_meta(cache, object);
552 if (!alloc_meta)
553 return;
554
555 alloc_meta->aux_stack[1] = alloc_meta->aux_stack[0];
556 alloc_meta->aux_stack[0] = kasan_save_stack(flags: 0, depot_flags: 0);
557}
558
559void kasan_save_alloc_info(struct kmem_cache *cache, void *object, gfp_t flags)
560{
561 struct kasan_alloc_meta *alloc_meta;
562
563 alloc_meta = kasan_get_alloc_meta(cache, object);
564 if (!alloc_meta)
565 return;
566
567 /* Invalidate previous stack traces (might exist for krealloc or mempool). */
568 release_alloc_meta(meta: alloc_meta);
569
570 kasan_save_track(track: &alloc_meta->alloc_track, flags);
571}
572
573void kasan_save_free_info(struct kmem_cache *cache, void *object)
574{
575 struct kasan_free_meta *free_meta;
576
577 free_meta = kasan_get_free_meta(cache, object);
578 if (!free_meta)
579 return;
580
581 /* Invalidate previous stack trace (might exist for mempool). */
582 release_free_meta(object, meta: free_meta);
583
584 kasan_save_track(track: &free_meta->free_track, flags: 0);
585
586 /* Mark free meta as valid. */
587 *(u8 *)kasan_mem_to_shadow(addr: object) = KASAN_SLAB_FREE_META;
588}
589

source code of linux/mm/kasan/generic.c