summaryrefslogtreecommitdiff
path: root/mm/kasan/report.c
blob: 6e3cb118d20ed53eb3ad39b07a579be13fa7cd3b (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
555
556
557
558
559
560
561
562
563
564
565
566
567
568
569
570
571
572
573
574
575
576
577
578
579
580
581
582
583
584
585
586
587
588
589
590
591
592
593
594
595
596
597
598
599
600
601
602
603
604
605
606
607
608
609
610
611
612
613
614
615
616
617
618
619
620
621
622
623
624
625
626
627
628
629
630
631
632
633
634
635
636
637
638
639
640
641
642
643
644
645
646
647
648
649
650
651
652
653
654
655
656
657
658
659
660
661
662
// SPDX-License-Identifier: GPL-2.0
/*
 * This file contains common 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>
 */

#include <kunit/test.h>
#include <linux/bitops.h>
#include <linux/ftrace.h>
#include <linux/init.h>
#include <linux/kernel.h>
#include <linux/lockdep.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 <linux/uaccess.h>
#include <trace/events/error_report.h>

#include <asm/sections.h>

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

static unsigned long kasan_flags;

#define KASAN_BIT_REPORTED	0
#define KASAN_BIT_MULTI_SHOT	1

enum kasan_arg_fault {
	KASAN_ARG_FAULT_DEFAULT,
	KASAN_ARG_FAULT_REPORT,
	KASAN_ARG_FAULT_PANIC,
	KASAN_ARG_FAULT_PANIC_ON_WRITE,
};

static enum kasan_arg_fault kasan_arg_fault __ro_after_init = KASAN_ARG_FAULT_DEFAULT;

/* kasan.fault=report/panic */
static int __init early_kasan_fault(char *arg)
{
	if (!arg)
		return -EINVAL;

	if (!strcmp(arg, "report"))
		kasan_arg_fault = KASAN_ARG_FAULT_REPORT;
	else if (!strcmp(arg, "panic"))
		kasan_arg_fault = KASAN_ARG_FAULT_PANIC;
	else if (!strcmp(arg, "panic_on_write"))
		kasan_arg_fault = KASAN_ARG_FAULT_PANIC_ON_WRITE;
	else
		return -EINVAL;

	return 0;
}
early_param("kasan.fault", early_kasan_fault);

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);

/*
 * This function is used to check whether KASAN reports are suppressed for
 * software KASAN modes via kasan_disable/enable_current() critical sections.
 *
 * This is done to avoid:
 * 1. False-positive reports when accessing slab metadata,
 * 2. Deadlocking when poisoned memory is accessed by the reporting code.
 *
 * Hardware Tag-Based KASAN instead relies on:
 * For #1: Resetting tags via kasan_reset_tag().
 * For #2: Suppression of tag checks via CPU, see report_suppress_start/end().
 */
static bool report_suppressed_sw(void)
{
#if defined(CONFIG_KASAN_GENERIC) || defined(CONFIG_KASAN_SW_TAGS)
	if (current->kasan_depth)
		return true;
#endif
	return false;
}

static void report_suppress_start(void)
{
#ifdef CONFIG_KASAN_HW_TAGS
	/*
	 * Disable preemption for the duration of printing a KASAN report, as
	 * hw_suppress_tag_checks_start() disables checks on the current CPU.
	 */
	preempt_disable();
	hw_suppress_tag_checks_start();
#else
	kasan_disable_current();
#endif
}

static void report_suppress_stop(void)
{
#ifdef CONFIG_KASAN_HW_TAGS
	hw_suppress_tag_checks_stop();
	preempt_enable();
#else
	kasan_enable_current();
#endif
}

/*
 * Used to avoid reporting more than one KASAN bug unless kasan_multi_shot
 * is enabled. Note that KASAN tests effectively enable kasan_multi_shot
 * for their duration.
 */
static bool report_enabled(void)
{
	if (test_bit(KASAN_BIT_MULTI_SHOT, &kasan_flags))
		return true;
	return !test_and_set_bit(KASAN_BIT_REPORTED, &kasan_flags);
}

#if IS_ENABLED(CONFIG_KASAN_KUNIT_TEST) || IS_ENABLED(CONFIG_KASAN_MODULE_TEST)

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);

#endif

#if IS_ENABLED(CONFIG_KASAN_KUNIT_TEST)

/*
 * Whether the KASAN KUnit test suite is currently being executed.
 * Updated in kasan_test.c.
 */
static bool kasan_kunit_executing;

void kasan_kunit_test_suite_start(void)
{
	WRITE_ONCE(kasan_kunit_executing, true);
}
EXPORT_SYMBOL_GPL(kasan_kunit_test_suite_start);

void kasan_kunit_test_suite_end(void)
{
	WRITE_ONCE(kasan_kunit_executing, false);
}
EXPORT_SYMBOL_GPL(kasan_kunit_test_suite_end);

static bool kasan_kunit_test_suite_executing(void)
{
	return READ_ONCE(kasan_kunit_executing);
}

#else /* CONFIG_KASAN_KUNIT_TEST */

static inline bool kasan_kunit_test_suite_executing(void) { return false; }

#endif /* CONFIG_KASAN_KUNIT_TEST */

#if IS_ENABLED(CONFIG_KUNIT)

static void fail_non_kasan_kunit_test(void)
{
	struct kunit *test;

	if (kasan_kunit_test_suite_executing())
		return;

	test = current->kunit_test;
	if (test)
		kunit_set_failure(test);
}

#else /* CONFIG_KUNIT */

static inline void fail_non_kasan_kunit_test(void) { }

#endif /* CONFIG_KUNIT */

static DEFINE_SPINLOCK(report_lock);

static void start_report(unsigned long *flags, bool sync)
{
	fail_non_kasan_kunit_test();
	/* Respect the /proc/sys/kernel/traceoff_on_warning interface. */
	disable_trace_on_warning();
	/* Do not allow LOCKDEP mangling KASAN reports. */
	lockdep_off();
	/* Make sure we don't end up in loop. */
	report_suppress_start();
	spin_lock_irqsave(&report_lock, *flags);
	pr_err("==================================================================\n");
}

static void end_report(unsigned long *flags, const void *addr, bool is_write)
{
	if (addr)
		trace_error_report_end(ERROR_DETECTOR_KASAN,
				       (unsigned long)addr);
	pr_err("==================================================================\n");
	spin_unlock_irqrestore(&report_lock, *flags);
	if (!test_bit(KASAN_BIT_MULTI_SHOT, &kasan_flags))
		check_panic_on_warn("KASAN");
	switch (kasan_arg_fault) {
	case KASAN_ARG_FAULT_DEFAULT:
	case KASAN_ARG_FAULT_REPORT:
		break;
	case KASAN_ARG_FAULT_PANIC:
		panic("kasan.fault=panic set ...\n");
		break;
	case KASAN_ARG_FAULT_PANIC_ON_WRITE:
		if (is_write)
			panic("kasan.fault=panic_on_write set ...\n");
		break;
	}
	add_taint(TAINT_BAD_PAGE, LOCKDEP_NOW_UNRELIABLE);
	lockdep_on();
	report_suppress_stop();
}

static void print_error_description(struct kasan_report_info *info)
{
	pr_err("BUG: KASAN: %s in %pS\n", info->bug_type, (void *)info->ip);

	if (info->type != KASAN_REPORT_ACCESS) {
		pr_err("Free of addr %px by task %s/%d\n",
			info->access_addr, current->comm, task_pid_nr(current));
		return;
	}

	if (info->access_size)
		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));
	else
		pr_err("%s at addr %px by task %s/%d\n",
			info->is_write ? "Write" : "Read",
			info->access_addr, current->comm, task_pid_nr(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)
		stack_depot_print(track->stack);
	else
		pr_err("(stack is not available)\n");
}

static inline struct page *addr_to_page(const void *addr)
{
	if (virt_addr_valid(addr))
		return virt_to_head_page(addr);
	return NULL;
}

static void describe_object_addr(const void *addr, struct kasan_report_info *info)
{
	unsigned long access_addr = (unsigned long)addr;
	unsigned long object_addr = (unsigned long)info->object;
	const char *rel_type, *region_state = "";
	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",
		info->object, info->cache->name, info->cache->object_size);

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

	/*
	 * Tag-Based modes use the stack ring to infer the bug type, but the
	 * memory region state description is generated based on the metadata.
	 * Thus, defining the region state as below can contradict the metadata.
	 * Fixing this requires further improvements, so only infer the state
	 * for the Generic mode.
	 */
	if (IS_ENABLED(CONFIG_KASAN_GENERIC)) {
		if (strcmp(info->bug_type, "slab-out-of-bounds") == 0)
			region_state = "allocated ";
		else if (strcmp(info->bug_type, "slab-use-after-free") == 0)
			region_state = "freed ";
	}

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

static void describe_object_stacks(struct kasan_report_info *info)
{
	if (info->alloc_track.stack) {
		print_track(&info->alloc_track, "Allocated");
		pr_err("\n");
	}

	if (info->free_track.stack) {
		print_track(&info->free_track, "Freed");
		pr_err("\n");
	}

	kasan_print_aux_stacks(info->cache, info->object);
}

static void describe_object(const void *addr, struct kasan_report_info *info)
{
	if (kasan_stack_collection_enabled())
		describe_object_stacks(info);
	describe_object_addr(addr, info);
}

static inline bool kernel_or_module_addr(const void *addr)
{
	if (is_kernel((unsigned long)addr))
		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 void print_address_description(void *addr, u8 tag,
				      struct kasan_report_info *info)
{
	struct page *page = addr_to_page(addr);

	dump_stack_lvl(KERN_ERR);
	pr_err("\n");

	if (info->cache && info->object) {
		describe_object(addr, info);
		pr_err("\n");
	}

	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);
		pr_err("\n");
	}

	if (object_is_on_stack(addr)) {
		/*
		 * Currently, KASAN supports printing frame information only
		 * for accesses to the task's own stack.
		 */
		kasan_print_address_stack_frame(addr);
		pr_err("\n");
	}

	if (is_vmalloc_addr(addr)) {
		struct vm_struct *va = find_vm_area(addr);

		if (va) {
			pr_err("The buggy address belongs to the virtual mapping at\n"
			       " [%px, %px) created by:\n"
			       " %pS\n",
			       va->addr, va->addr + va->size, va->caller);
			pr_err("\n");

			page = vmalloc_to_page(addr);
		}
	}

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

static bool meta_row_is_guilty(const void *row, const void *addr)
{
	return (row <= addr) && (addr < row + META_MEM_BYTES_PER_ROW);
}

static int meta_pointer_offset(const void *row, const void *addr)
{
	/*
	 * Memory state around the buggy address:
	 *  ff00ff00ff00ff00: 00 00 00 05 fe fe fe fe fe fe fe fe fe fe fe fe
	 *  ...
	 *
	 * The length of ">ff00ff00ff00ff00: " is
	 *    3 + (BITS_PER_LONG / 8) * 2 chars.
	 * The length of each granule metadata is 2 bytes
	 *    plus 1 byte for space.
	 */
	return 3 + (BITS_PER_LONG / 8) * 2 +
		(addr - row) / KASAN_GRANULE_SIZE * 3 + 1;
}

static void print_memory_metadata(const void *addr)
{
	int i;
	void *row;

	row = (void *)round_down((unsigned long)addr, META_MEM_BYTES_PER_ROW)
			- META_ROWS_AROUND_ADDR * META_MEM_BYTES_PER_ROW;

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

	for (i = -META_ROWS_AROUND_ADDR; i <= META_ROWS_AROUND_ADDR; i++) {
		char buffer[4 + (BITS_PER_LONG / 8) * 2];
		char metadata[META_BYTES_PER_ROW];

		snprintf(buffer, sizeof(buffer),
				(i == 0) ? ">%px: " : " %px: ", row);

		/*
		 * We should not pass a shadow pointer to generic
		 * function, because generic functions may try to
		 * access kasan mapping for the passed address.
		 */
		kasan_metadata_fetch_row(&metadata[0], row);

		print_hex_dump(KERN_ERR, buffer,
			DUMP_PREFIX_NONE, META_BYTES_PER_ROW, 1,
			metadata, META_BYTES_PER_ROW, 0);

		if (meta_row_is_guilty(row, addr))
			pr_err("%*c\n", meta_pointer_offset(row, addr), '^');

		row += META_MEM_BYTES_PER_ROW;
	}
}

static void print_report(struct kasan_report_info *info)
{
	void *addr = kasan_reset_tag((void *)info->access_addr);
	u8 tag = get_tag((void *)info->access_addr);

	print_error_description(info);
	if (addr_has_metadata(addr))
		kasan_print_tags(tag, info->first_bad_addr);
	pr_err("\n");

	if (addr_has_metadata(addr)) {
		print_address_description(addr, tag, info);
		print_memory_metadata(info->first_bad_addr);
	} else {
		dump_stack_lvl(KERN_ERR);
	}
}

static void complete_report_info(struct kasan_report_info *info)
{
	void *addr = kasan_reset_tag((void *)info->access_addr);
	struct slab *slab;

	if (info->type == KASAN_REPORT_ACCESS)
		info->first_bad_addr = kasan_find_first_bad_addr(
					(void *)info->access_addr, info->access_size);
	else
		info->first_bad_addr = addr;

	slab = kasan_addr_to_slab(addr);
	if (slab) {
		info->cache = slab->slab_cache;
		info->object = nearest_obj(info->cache, slab, addr);

		/* Try to determine allocation size based on the metadata. */
		info->alloc_size = kasan_get_alloc_size(info->object, info->cache);
		/* Fallback to the object size if failed. */
		if (!info->alloc_size)
			info->alloc_size = info->cache->object_size;
	} else
		info->cache = info->object = NULL;

	switch (info->type) {
	case KASAN_REPORT_INVALID_FREE:
		info->bug_type = "invalid-free";
		break;
	case KASAN_REPORT_DOUBLE_FREE:
		info->bug_type = "double-free";
		break;
	default:
		/* bug_type filled in by kasan_complete_mode_report_info. */
		break;
	}

	/* Fill in mode-specific report info fields. */
	kasan_complete_mode_report_info(info);
}

void kasan_report_invalid_free(void *ptr, unsigned long ip, enum kasan_report_type type)
{
	unsigned long flags;
	struct kasan_report_info info;

	/*
	 * Do not check report_suppressed_sw(), as an invalid-free cannot be
	 * caused by accessing poisoned memory and thus should not be suppressed
	 * by kasan_disable/enable_current() critical sections.
	 *
	 * Note that for Hardware Tag-Based KASAN, kasan_report_invalid_free()
	 * is triggered by explicit tag checks and not by the ones performed by
	 * the CPU. Thus, reporting invalid-free is not suppressed as well.
	 */
	if (unlikely(!report_enabled()))
		return;

	start_report(&flags, true);

	memset(&info, 0, sizeof(info));
	info.type = type;
	info.access_addr = ptr;
	info.access_size = 0;
	info.is_write = false;
	info.ip = ip;

	complete_report_info(&info);

	print_report(&info);

	/*
	 * Invalid free is considered a "write" since the allocator's metadata
	 * updates involves writes.
	 */
	end_report(&flags, ptr, true);
}

/*
 * kasan_report() is the only reporting function that uses
 * user_access_save/restore(): kasan_report_invalid_free() cannot be called
 * from a UACCESS region, and kasan_report_async() is not used on x86.
 */
bool kasan_report(const void *addr, size_t size, bool is_write,
			unsigned long ip)
{
	bool ret = true;
	unsigned long ua_flags = user_access_save();
	unsigned long irq_flags;
	struct kasan_report_info info;

	if (unlikely(report_suppressed_sw()) || unlikely(!report_enabled())) {
		ret = false;
		goto out;
	}

	start_report(&irq_flags, true);

	memset(&info, 0, sizeof(info));
	info.type = KASAN_REPORT_ACCESS;
	info.access_addr = addr;
	info.access_size = size;
	info.is_write = is_write;
	info.ip = ip;

	complete_report_info(&info);

	print_report(&info);

	end_report(&irq_flags, (void *)addr, is_write);

out:
	user_access_restore(ua_flags);

	return ret;
}

#ifdef CONFIG_KASAN_HW_TAGS
void kasan_report_async(void)
{
	unsigned long flags;

	/*
	 * Do not check report_suppressed_sw(), as
	 * kasan_disable/enable_current() critical sections do not affect
	 * Hardware Tag-Based KASAN.
	 */
	if (unlikely(!report_enabled()))
		return;

	start_report(&flags, false);
	pr_err("BUG: KASAN: invalid-access\n");
	pr_err("Asynchronous fault: no details available\n");
	pr_err("\n");
	dump_stack_lvl(KERN_ERR);
	/*
	 * Conservatively set is_write=true, because no details are available.
	 * In this mode, kasan.fault=panic_on_write is like kasan.fault=panic.
	 */
	end_report(&flags, NULL, true);
}
#endif /* CONFIG_KASAN_HW_TAGS */

#if defined(CONFIG_KASAN_GENERIC) || defined(CONFIG_KASAN_SW_TAGS)
/*
 * 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_GRANULE_SIZE - 1);
}
#endif