summaryrefslogtreecommitdiff
path: root/mm/kasan/report.c
blob: 5ef9f24f566b438a3a8de742fbf20dc0ccca8e75 (plain)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
417
418
419
420
421
422
423
424
425
426
427
428
429
430
431
432
433
434
435
436
437
438
439
440
441
442
443
444
445
446
447
448
449
450
451
452
453
454
455
456
457
458
459
460
461
462
463
464
465
466
467
468
469
470
471
472
473
474
475
476
477
478
479
480
481
482
483
484
485
486
487
488
489
490
491
492
493
494
495
496
497
498
499
500
501
502
503
504
505
506
507
508
509
510
511
512
513
514
515
516
517
518
519
520
521
522
523
524
525
526
527
528
529
530
531
532
533
534
535
536
537
538
539
540
541
542
543
544
545
546
547
548
549
550
551
552
553
554
// SPDX-License-Identifier: GPL-2.0
/*
 * This file contains common generic and tag-based KASAN error reporting code.
 *
 * Copyright (c) 2014 Samsung Electronics Co., Ltd.
 * Author: Andrey Ryabinin <ryabinin.a.a@gmail.com>
 *
 * Some code borrowed from https://github.com/xairy/kasan-prototype by
 *        Andrey Konovalov <andreyknvl@gmail.com>
 *
 * This program is free software; you can redistribute it and/or modify
 * it under the terms of the GNU General Public License version 2 as
 * published by the Free Software Foundation.
 *
 */

#include <linux/bitops.h>
#include <linux/ftrace.h>
#include <linux/init.h>
#include <linux/kernel.h>
#include <linux/mm.h>
#include <linux/printk.h>
#include <linux/sched.h>
#include <linux/slab.h>
#include <linux/stackdepot.h>
#include <linux/stacktrace.h>
#include <linux/string.h>
#include <linux/types.h>
#include <linux/kasan.h>
#include <linux/module.h>
#include <linux/sched/task_stack.h>

#include <asm/sections.h>

#include "kasan.h"
#include "../slab.h"

/* Shadow layout customization. */
#define SHADOW_BYTES_PER_BLOCK 1
#define SHADOW_BLOCKS_PER_ROW 16
#define SHADOW_BYTES_PER_ROW (SHADOW_BLOCKS_PER_ROW * SHADOW_BYTES_PER_BLOCK)
#define SHADOW_ROWS_AROUND_ADDR 2

static unsigned long kasan_flags;

#define KASAN_BIT_REPORTED	0
#define KASAN_BIT_MULTI_SHOT	1

bool kasan_save_enable_multi_shot(void)
{
	return test_and_set_bit(KASAN_BIT_MULTI_SHOT, &kasan_flags);
}
EXPORT_SYMBOL_GPL(kasan_save_enable_multi_shot);

void kasan_restore_multi_shot(bool enabled)
{
	if (!enabled)
		clear_bit(KASAN_BIT_MULTI_SHOT, &kasan_flags);
}
EXPORT_SYMBOL_GPL(kasan_restore_multi_shot);

static int __init kasan_set_multi_shot(char *str)
{
	set_bit(KASAN_BIT_MULTI_SHOT, &kasan_flags);
	return 1;
}
__setup("kasan_multi_shot", kasan_set_multi_shot);

static void print_error_description(struct kasan_access_info *info)
{
	pr_err("BUG: KASAN: %s in %pS\n",
		get_bug_type(info), (void *)info->ip);
	pr_err("%s of size %zu at addr %px by task %s/%d\n",
		info->is_write ? "Write" : "Read", info->access_size,
		info->access_addr, current->comm, task_pid_nr(current));
}

static DEFINE_SPINLOCK(report_lock);

static void start_report(unsigned long *flags)
{
	/*
	 * Make sure we don't end up in loop.
	 */
	kasan_disable_current();
	spin_lock_irqsave(&report_lock, *flags);
	pr_err("==================================================================\n");
}

static void end_report(unsigned long *flags)
{
	pr_err("==================================================================\n");
	add_taint(TAINT_BAD_PAGE, LOCKDEP_NOW_UNRELIABLE);
	spin_unlock_irqrestore(&report_lock, *flags);
	if (panic_on_warn)
		panic("panic_on_warn set ...\n");
	kasan_enable_current();
}

static void print_track(struct kasan_track *track, const char *prefix)
{
	pr_err("%s by task %u:\n", prefix, track->pid);
	if (track->stack) {
		unsigned long *entries;
		unsigned int nr_entries;

		nr_entries = stack_depot_fetch(track->stack, &entries);
		stack_trace_print(entries, nr_entries, 0);
	} else {
		pr_err("(stack is not available)\n");
	}
}

struct page *kasan_addr_to_page(const void *addr)
{
	if ((addr >= (void *)PAGE_OFFSET) &&
			(addr < high_memory))
		return virt_to_head_page(addr);
	return NULL;
}

static void describe_object_addr(struct kmem_cache *cache, void *object,
				const void *addr)
{
	unsigned long access_addr = (unsigned long)addr;
	unsigned long object_addr = (unsigned long)object;
	const char *rel_type;
	int rel_bytes;

	pr_err("The buggy address belongs to the object at %px\n"
	       " which belongs to the cache %s of size %d\n",
		object, cache->name, cache->object_size);

	if (!addr)
		return;

	if (access_addr < object_addr) {
		rel_type = "to the left";
		rel_bytes = object_addr - access_addr;
	} else if (access_addr >= object_addr + cache->object_size) {
		rel_type = "to the right";
		rel_bytes = access_addr - (object_addr + cache->object_size);
	} else {
		rel_type = "inside";
		rel_bytes = access_addr - object_addr;
	}

	pr_err("The buggy address is located %d bytes %s of\n"
	       " %d-byte region [%px, %px)\n",
		rel_bytes, rel_type, cache->object_size, (void *)object_addr,
		(void *)(object_addr + cache->object_size));
}

static struct kasan_track *kasan_get_free_track(struct kmem_cache *cache,
		void *object, u8 tag)
{
	struct kasan_alloc_meta *alloc_meta;
	int i = 0;

	alloc_meta = get_alloc_info(cache, object);

#ifdef CONFIG_KASAN_SW_TAGS_IDENTIFY
	for (i = 0; i < KASAN_NR_FREE_STACKS; i++) {
		if (alloc_meta->free_pointer_tag[i] == tag)
			break;
	}
	if (i == KASAN_NR_FREE_STACKS)
		i = alloc_meta->free_track_idx;
#endif

	return &alloc_meta->free_track[i];
}

static void describe_object(struct kmem_cache *cache, void *object,
				const void *addr, u8 tag)
{
	struct kasan_alloc_meta *alloc_info = get_alloc_info(cache, object);

	if (cache->flags & SLAB_KASAN) {
		struct kasan_track *free_track;

		print_track(&alloc_info->alloc_track, "Allocated");
		pr_err("\n");
		free_track = kasan_get_free_track(cache, object, tag);
		print_track(free_track, "Freed");
		pr_err("\n");
	}

	describe_object_addr(cache, object, addr);
}

static inline bool kernel_or_module_addr(const void *addr)
{
	if (addr >= (void *)_stext && addr < (void *)_end)
		return true;
	if (is_module_address((unsigned long)addr))
		return true;
	return false;
}

static inline bool init_task_stack_addr(const void *addr)
{
	return addr >= (void *)&init_thread_union.stack &&
		(addr <= (void *)&init_thread_union.stack +
			sizeof(init_thread_union.stack));
}

static bool __must_check tokenize_frame_descr(const char **frame_descr,
					      char *token, size_t max_tok_len,
					      unsigned long *value)
{
	const char *sep = strchr(*frame_descr, ' ');

	if (sep == NULL)
		sep = *frame_descr + strlen(*frame_descr);

	if (token != NULL) {
		const size_t tok_len = sep - *frame_descr;

		if (tok_len + 1 > max_tok_len) {
			pr_err("KASAN internal error: frame description too long: %s\n",
			       *frame_descr);
			return false;
		}

		/* Copy token (+ 1 byte for '\0'). */
		strlcpy(token, *frame_descr, tok_len + 1);
	}

	/* Advance frame_descr past separator. */
	*frame_descr = sep + 1;

	if (value != NULL && kstrtoul(token, 10, value)) {
		pr_err("KASAN internal error: not a valid number: %s\n", token);
		return false;
	}

	return true;
}

static void print_decoded_frame_descr(const char *frame_descr)
{
	/*
	 * We need to parse the following string:
	 *    "n alloc_1 alloc_2 ... alloc_n"
	 * where alloc_i looks like
	 *    "offset size len name"
	 * or "offset size len name:line".
	 */

	char token[64];
	unsigned long num_objects;

	if (!tokenize_frame_descr(&frame_descr, token, sizeof(token),
				  &num_objects))
		return;

	pr_err("\n");
	pr_err("this frame has %lu %s:\n", num_objects,
	       num_objects == 1 ? "object" : "objects");

	while (num_objects--) {
		unsigned long offset;
		unsigned long size;

		/* access offset */
		if (!tokenize_frame_descr(&frame_descr, token, sizeof(token),
					  &offset))
			return;
		/* access size */
		if (!tokenize_frame_descr(&frame_descr, token, sizeof(token),
					  &size))
			return;
		/* name length (unused) */
		if (!tokenize_frame_descr(&frame_descr, NULL, 0, NULL))
			return;
		/* object name */
		if (!tokenize_frame_descr(&frame_descr, token, sizeof(token),
					  NULL))
			return;

		/* Strip line number; without filename it's not very helpful. */
		strreplace(token, ':', '\0');

		/* Finally, print object information. */
		pr_err(" [%lu, %lu) '%s'", offset, offset + size, token);
	}
}

static bool __must_check get_address_stack_frame_info(const void *addr,
						      unsigned long *offset,
						      const char **frame_descr,
						      const void **frame_pc)
{
	unsigned long aligned_addr;
	unsigned long mem_ptr;
	const u8 *shadow_bottom;
	const u8 *shadow_ptr;
	const unsigned long *frame;

	BUILD_BUG_ON(IS_ENABLED(CONFIG_STACK_GROWSUP));

	/*
	 * NOTE: We currently only support printing frame information for
	 * accesses to the task's own stack.
	 */
	if (!object_is_on_stack(addr))
		return false;

	aligned_addr = round_down((unsigned long)addr, sizeof(long));
	mem_ptr = round_down(aligned_addr, KASAN_SHADOW_SCALE_SIZE);
	shadow_ptr = kasan_mem_to_shadow((void *)aligned_addr);
	shadow_bottom = kasan_mem_to_shadow(end_of_stack(current));

	while (shadow_ptr >= shadow_bottom && *shadow_ptr != KASAN_STACK_LEFT) {
		shadow_ptr--;
		mem_ptr -= KASAN_SHADOW_SCALE_SIZE;
	}

	while (shadow_ptr >= shadow_bottom && *shadow_ptr == KASAN_STACK_LEFT) {
		shadow_ptr--;
		mem_ptr -= KASAN_SHADOW_SCALE_SIZE;
	}

	if (shadow_ptr < shadow_bottom)
		return false;

	frame = (const unsigned long *)(mem_ptr + KASAN_SHADOW_SCALE_SIZE);
	if (frame[0] != KASAN_CURRENT_STACK_FRAME_MAGIC) {
		pr_err("KASAN internal error: frame info validation failed; invalid marker: %lu\n",
		       frame[0]);
		return false;
	}

	*offset = (unsigned long)addr - (unsigned long)frame;
	*frame_descr = (const char *)frame[1];
	*frame_pc = (void *)frame[2];

	return true;
}

static void print_address_stack_frame(const void *addr)
{
	unsigned long offset;
	const char *frame_descr;
	const void *frame_pc;

	if (IS_ENABLED(CONFIG_KASAN_SW_TAGS))
		return;

	if (!get_address_stack_frame_info(addr, &offset, &frame_descr,
					  &frame_pc))
		return;

	/*
	 * get_address_stack_frame_info only returns true if the given addr is
	 * on the current task's stack.
	 */
	pr_err("\n");
	pr_err("addr %px is located in stack of task %s/%d at offset %lu in frame:\n",
	       addr, current->comm, task_pid_nr(current), offset);
	pr_err(" %pS\n", frame_pc);

	if (!frame_descr)
		return;

	print_decoded_frame_descr(frame_descr);
}

static void print_address_description(void *addr, u8 tag)
{
	struct page *page = kasan_addr_to_page(addr);

	dump_stack();
	pr_err("\n");

	if (page && PageSlab(page)) {
		struct kmem_cache *cache = page->slab_cache;
		void *object = nearest_obj(cache, page,	addr);

		describe_object(cache, object, addr, tag);
	}

	if (kernel_or_module_addr(addr) && !init_task_stack_addr(addr)) {
		pr_err("The buggy address belongs to the variable:\n");
		pr_err(" %pS\n", addr);
	}

	if (page) {
		pr_err("The buggy address belongs to the page:\n");
		dump_page(page, "kasan: bad access detected");
	}

	print_address_stack_frame(addr);
}

static bool row_is_guilty(const void *row, const void *guilty)
{
	return (row <= guilty) && (guilty < row + SHADOW_BYTES_PER_ROW);
}

static int shadow_pointer_offset(const void *row, const void *shadow)
{
	/* The length of ">ff00ff00ff00ff00: " is
	 *    3 + (BITS_PER_LONG/8)*2 chars.
	 */
	return 3 + (BITS_PER_LONG/8)*2 + (shadow - row)*2 +
		(shadow - row) / SHADOW_BYTES_PER_BLOCK + 1;
}

static void print_shadow_for_address(const void *addr)
{
	int i;
	const void *shadow = kasan_mem_to_shadow(addr);
	const void *shadow_row;

	shadow_row = (void *)round_down((unsigned long)shadow,
					SHADOW_BYTES_PER_ROW)
		- SHADOW_ROWS_AROUND_ADDR * SHADOW_BYTES_PER_ROW;

	pr_err("Memory state around the buggy address:\n");

	for (i = -SHADOW_ROWS_AROUND_ADDR; i <= SHADOW_ROWS_AROUND_ADDR; i++) {
		const void *kaddr = kasan_shadow_to_mem(shadow_row);
		char buffer[4 + (BITS_PER_LONG/8)*2];
		char shadow_buf[SHADOW_BYTES_PER_ROW];

		snprintf(buffer, sizeof(buffer),
			(i == 0) ? ">%px: " : " %px: ", kaddr);
		/*
		 * We should not pass a shadow pointer to generic
		 * function, because generic functions may try to
		 * access kasan mapping for the passed address.
		 */
		memcpy(shadow_buf, shadow_row, SHADOW_BYTES_PER_ROW);
		print_hex_dump(KERN_ERR, buffer,
			DUMP_PREFIX_NONE, SHADOW_BYTES_PER_ROW, 1,
			shadow_buf, SHADOW_BYTES_PER_ROW, 0);

		if (row_is_guilty(shadow_row, shadow))
			pr_err("%*c\n",
				shadow_pointer_offset(shadow_row, shadow),
				'^');

		shadow_row += SHADOW_BYTES_PER_ROW;
	}
}

static bool report_enabled(void)
{
	if (current->kasan_depth)
		return false;
	if (test_bit(KASAN_BIT_MULTI_SHOT, &kasan_flags))
		return true;
	return !test_and_set_bit(KASAN_BIT_REPORTED, &kasan_flags);
}

void kasan_report_invalid_free(void *object, unsigned long ip)
{
	unsigned long flags;
	u8 tag = get_tag(object);

	object = reset_tag(object);
	start_report(&flags);
	pr_err("BUG: KASAN: double-free or invalid-free in %pS\n", (void *)ip);
	print_tags(tag, object);
	pr_err("\n");
	print_address_description(object, tag);
	pr_err("\n");
	print_shadow_for_address(object);
	end_report(&flags);
}

void __kasan_report(unsigned long addr, size_t size, bool is_write, unsigned long ip)
{
	struct kasan_access_info info;
	void *tagged_addr;
	void *untagged_addr;
	unsigned long flags;

	if (likely(!report_enabled()))
		return;

	disable_trace_on_warning();

	tagged_addr = (void *)addr;
	untagged_addr = reset_tag(tagged_addr);

	info.access_addr = tagged_addr;
	if (addr_has_shadow(untagged_addr))
		info.first_bad_addr = find_first_bad_addr(tagged_addr, size);
	else
		info.first_bad_addr = untagged_addr;
	info.access_size = size;
	info.is_write = is_write;
	info.ip = ip;

	start_report(&flags);

	print_error_description(&info);
	if (addr_has_shadow(untagged_addr))
		print_tags(get_tag(tagged_addr), info.first_bad_addr);
	pr_err("\n");

	if (addr_has_shadow(untagged_addr)) {
		print_address_description(untagged_addr, get_tag(tagged_addr));
		pr_err("\n");
		print_shadow_for_address(info.first_bad_addr);
	} else {
		dump_stack();
	}

	end_report(&flags);
}

#ifdef CONFIG_KASAN_INLINE
/*
 * With CONFIG_KASAN_INLINE, accesses to bogus pointers (outside the high
 * canonical half of the address space) cause out-of-bounds shadow memory reads
 * before the actual access. For addresses in the low canonical half of the
 * address space, as well as most non-canonical addresses, that out-of-bounds
 * shadow memory access lands in the non-canonical part of the address space.
 * Help the user figure out what the original bogus pointer was.
 */
void kasan_non_canonical_hook(unsigned long addr)
{
	unsigned long orig_addr;
	const char *bug_type;

	if (addr < KASAN_SHADOW_OFFSET)
		return;

	orig_addr = (addr - KASAN_SHADOW_OFFSET) << KASAN_SHADOW_SCALE_SHIFT;
	/*
	 * For faults near the shadow address for NULL, we can be fairly certain
	 * that this is a KASAN shadow memory access.
	 * For faults that correspond to shadow for low canonical addresses, we
	 * can still be pretty sure - that shadow region is a fairly narrow
	 * chunk of the non-canonical address space.
	 * But faults that look like shadow for non-canonical addresses are a
	 * really large chunk of the address space. In that case, we still
	 * print the decoded address, but make it clear that this is not
	 * necessarily what's actually going on.
	 */
	if (orig_addr < PAGE_SIZE)
		bug_type = "null-ptr-deref";
	else if (orig_addr < TASK_SIZE)
		bug_type = "probably user-memory-access";
	else
		bug_type = "maybe wild-memory-access";
	pr_alert("KASAN: %s in range [0x%016lx-0x%016lx]\n", bug_type,
		 orig_addr, orig_addr + KASAN_SHADOW_MASK);
}
#endif