report.c

  1// SPDX-License-Identifier: GPL-2.0
  2/*
  3 * This file contains common KASAN error reporting 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 <kunit/test.h>
 13#include <kunit/visibility.h>
 14#include <linux/bitops.h>
 15#include <linux/ftrace.h>
 16#include <linux/init.h>
 17#include <linux/kernel.h>
 18#include <linux/lockdep.h>
 19#include <linux/mm.h>
 20#include <linux/printk.h>
 21#include <linux/sched.h>
 22#include <linux/slab.h>
 23#include <linux/stackdepot.h>
 24#include <linux/stacktrace.h>
 25#include <linux/string.h>
 26#include <linux/types.h>
 27#include <linux/vmalloc.h>
 28#include <linux/kasan.h>
 29#include <linux/module.h>
 30#include <linux/sched/task_stack.h>
 31#include <linux/uaccess.h>
 32#include <trace/events/error_report.h>
 33
 34#include <asm/sections.h>
 35
 36#include "kasan.h"
 37#include "../slab.h"
 38
 39static unsigned long kasan_flags;
 40
 41#define KASAN_BIT_REPORTED	0
 42#define KASAN_BIT_MULTI_SHOT	1
 43
 44enum kasan_arg_fault {
 45	KASAN_ARG_FAULT_DEFAULT,
 46	KASAN_ARG_FAULT_REPORT,
 47	KASAN_ARG_FAULT_PANIC,
 48	KASAN_ARG_FAULT_PANIC_ON_WRITE,
 49};
 50
 51static enum kasan_arg_fault kasan_arg_fault __ro_after_init = KASAN_ARG_FAULT_DEFAULT;
 52
 53/* kasan.fault=report/panic */
 54static int __init early_kasan_fault(char *arg)
 55{
 56	if (!arg)
 57		return -EINVAL;
 58
 59	if (!strcmp(arg, "report"))
 60		kasan_arg_fault = KASAN_ARG_FAULT_REPORT;
 61	else if (!strcmp(arg, "panic"))
 62		kasan_arg_fault = KASAN_ARG_FAULT_PANIC;
 63	else if (!strcmp(arg, "panic_on_write"))
 64		kasan_arg_fault = KASAN_ARG_FAULT_PANIC_ON_WRITE;
 65	else
 66		return -EINVAL;
 67
 68	return 0;
 69}
 70early_param("kasan.fault", early_kasan_fault);
 71
 72static int __init kasan_set_multi_shot(char *str)
 73{
 74	set_bit(KASAN_BIT_MULTI_SHOT, &kasan_flags);
 75	return 1;
 76}
 77__setup("kasan_multi_shot", kasan_set_multi_shot);
 78
 79/*
 80 * This function is used to check whether KASAN reports are suppressed for
 81 * software KASAN modes via kasan_disable/enable_current() critical sections.
 82 *
 83 * This is done to avoid:
 84 * 1. False-positive reports when accessing slab metadata,
 85 * 2. Deadlocking when poisoned memory is accessed by the reporting code.
 86 *
 87 * Hardware Tag-Based KASAN instead relies on:
 88 * For #1: Resetting tags via kasan_reset_tag().
 89 * For #2: Suppression of tag checks via CPU, see report_suppress_start/end().
 90 */
 91static bool report_suppressed_sw(void)
 92{
 93#if defined(CONFIG_KASAN_GENERIC) || defined(CONFIG_KASAN_SW_TAGS)
 94	if (current->kasan_depth)
 95		return true;
 96#endif
 97	return false;
 98}
 99
100static void report_suppress_start(void)
101{
102#ifdef CONFIG_KASAN_HW_TAGS
103	/*
104	 * Disable preemption for the duration of printing a KASAN report, as
105	 * hw_suppress_tag_checks_start() disables checks on the current CPU.
106	 */
107	preempt_disable();
108	hw_suppress_tag_checks_start();
109#else
110	kasan_disable_current();
111#endif
112}
113
114static void report_suppress_stop(void)
115{
116#ifdef CONFIG_KASAN_HW_TAGS
117	hw_suppress_tag_checks_stop();
118	preempt_enable();
119#else
120	kasan_enable_current();
121#endif
122}
123
124/*
125 * Used to avoid reporting more than one KASAN bug unless kasan_multi_shot
126 * is enabled. Note that KASAN tests effectively enable kasan_multi_shot
127 * for their duration.
128 */
129static bool report_enabled(void)
130{
131	if (test_bit(KASAN_BIT_MULTI_SHOT, &kasan_flags))
132		return true;
133	return !test_and_set_bit(KASAN_BIT_REPORTED, &kasan_flags);
134}
135
136#if IS_ENABLED(CONFIG_KASAN_KUNIT_TEST)
137
138VISIBLE_IF_KUNIT bool kasan_save_enable_multi_shot(void)
139{
140	return test_and_set_bit(KASAN_BIT_MULTI_SHOT, &kasan_flags);
141}
142EXPORT_SYMBOL_IF_KUNIT(kasan_save_enable_multi_shot);
143
144VISIBLE_IF_KUNIT void kasan_restore_multi_shot(bool enabled)
145{
146	if (!enabled)
147		clear_bit(KASAN_BIT_MULTI_SHOT, &kasan_flags);
148}
149EXPORT_SYMBOL_IF_KUNIT(kasan_restore_multi_shot);
150
151#endif
152
153#if IS_ENABLED(CONFIG_KASAN_KUNIT_TEST)
154
155/*
156 * Whether the KASAN KUnit test suite is currently being executed.
157 * Updated in kasan_test.c.
158 */
159static bool kasan_kunit_executing;
160
161VISIBLE_IF_KUNIT void kasan_kunit_test_suite_start(void)
162{
163	WRITE_ONCE(kasan_kunit_executing, true);
164}
165EXPORT_SYMBOL_IF_KUNIT(kasan_kunit_test_suite_start);
166
167VISIBLE_IF_KUNIT void kasan_kunit_test_suite_end(void)
168{
169	WRITE_ONCE(kasan_kunit_executing, false);
170}
171EXPORT_SYMBOL_IF_KUNIT(kasan_kunit_test_suite_end);
172
173static bool kasan_kunit_test_suite_executing(void)
174{
175	return READ_ONCE(kasan_kunit_executing);
176}
177
178#else /* CONFIG_KASAN_KUNIT_TEST */
179
180static inline bool kasan_kunit_test_suite_executing(void) { return false; }
181
182#endif /* CONFIG_KASAN_KUNIT_TEST */
183
184#if IS_ENABLED(CONFIG_KUNIT)
185
186static void fail_non_kasan_kunit_test(void)
187{
188	struct kunit *test;
189
190	if (kasan_kunit_test_suite_executing())
191		return;
192
193	test = current->kunit_test;
194	if (test)
195		kunit_set_failure(test);
196}
197
198#else /* CONFIG_KUNIT */
199
200static inline void fail_non_kasan_kunit_test(void) { }
201
202#endif /* CONFIG_KUNIT */
203
204static DEFINE_RAW_SPINLOCK(report_lock);
205
206static void start_report(unsigned long *flags, bool sync)
207{
208	fail_non_kasan_kunit_test();
209	/* Respect the /proc/sys/kernel/traceoff_on_warning interface. */
210	disable_trace_on_warning();
211	/* Do not allow LOCKDEP mangling KASAN reports. */
212	lockdep_off();
213	/* Make sure we don't end up in loop. */
214	report_suppress_start();
215	raw_spin_lock_irqsave(&report_lock, *flags);
216	pr_err("==================================================================\n");
217}
218
219static void end_report(unsigned long *flags, const void *addr, bool is_write)
220{
221	if (addr)
222		trace_error_report_end(ERROR_DETECTOR_KASAN,
223				       (unsigned long)addr);
224	pr_err("==================================================================\n");
225	raw_spin_unlock_irqrestore(&report_lock, *flags);
226	if (!test_bit(KASAN_BIT_MULTI_SHOT, &kasan_flags))
227		check_panic_on_warn("KASAN");
228	switch (kasan_arg_fault) {
229	case KASAN_ARG_FAULT_DEFAULT:
230	case KASAN_ARG_FAULT_REPORT:
231		break;
232	case KASAN_ARG_FAULT_PANIC:
233		panic("kasan.fault=panic set ...\n");
234		break;
235	case KASAN_ARG_FAULT_PANIC_ON_WRITE:
236		if (is_write)
237			panic("kasan.fault=panic_on_write set ...\n");
238		break;
239	}
240	add_taint(TAINT_BAD_PAGE, LOCKDEP_NOW_UNRELIABLE);
241	lockdep_on();
242	report_suppress_stop();
243}
244
245static void print_error_description(struct kasan_report_info *info)
246{
247	pr_err("BUG: KASAN: %s in %pS\n", info->bug_type, (void *)info->ip);
248
249	if (info->type != KASAN_REPORT_ACCESS) {
250		pr_err("Free of addr %px by task %s/%d\n",
251			info->access_addr, current->comm, task_pid_nr(current));
252		return;
253	}
254
255	if (info->access_size)
256		pr_err("%s of size %zu at addr %px by task %s/%d\n",
257			info->is_write ? "Write" : "Read", info->access_size,
258			info->access_addr, current->comm, task_pid_nr(current));
259	else
260		pr_err("%s at addr %px by task %s/%d\n",
261			info->is_write ? "Write" : "Read",
262			info->access_addr, current->comm, task_pid_nr(current));
263}
264
265static void print_track(struct kasan_track *track, const char *prefix)
266{
267#ifdef CONFIG_KASAN_EXTRA_INFO
268	u64 ts_nsec = track->timestamp;
269	unsigned long rem_usec;
270
271	ts_nsec <<= 9;
272	rem_usec = do_div(ts_nsec, NSEC_PER_SEC) / 1000;
273
274	pr_err("%s by task %u on cpu %d at %lu.%06lus:\n",
275			prefix, track->pid, track->cpu,
276			(unsigned long)ts_nsec, rem_usec);
277#else
278	pr_err("%s by task %u:\n", prefix, track->pid);
279#endif /* CONFIG_KASAN_EXTRA_INFO */
280	if (track->stack)
281		stack_depot_print(track->stack);
282	else
283		pr_err("(stack is not available)\n");
284}
285
286static inline struct page *addr_to_page(const void *addr)
287{
288	if (virt_addr_valid(addr))
289		return virt_to_head_page(addr);
290	return NULL;
291}
292
293static void describe_object_addr(const void *addr, struct kasan_report_info *info)
294{
295	unsigned long access_addr = (unsigned long)addr;
296	unsigned long object_addr = (unsigned long)info->object;
297	const char *rel_type, *region_state = "";
298	int rel_bytes;
299
300	pr_err("The buggy address belongs to the object at %px\n"
301	       " which belongs to the cache %s of size %d\n",
302		info->object, info->cache->name, info->cache->object_size);
303
304	if (access_addr < object_addr) {
305		rel_type = "to the left";
306		rel_bytes = object_addr - access_addr;
307	} else if (access_addr >= object_addr + info->alloc_size) {
308		rel_type = "to the right";
309		rel_bytes = access_addr - (object_addr + info->alloc_size);
310	} else {
311		rel_type = "inside";
312		rel_bytes = access_addr - object_addr;
313	}
314
315	/*
316	 * Tag-Based modes use the stack ring to infer the bug type, but the
317	 * memory region state description is generated based on the metadata.
318	 * Thus, defining the region state as below can contradict the metadata.
319	 * Fixing this requires further improvements, so only infer the state
320	 * for the Generic mode.
321	 */
322	if (IS_ENABLED(CONFIG_KASAN_GENERIC)) {
323		if (strcmp(info->bug_type, "slab-out-of-bounds") == 0)
324			region_state = "allocated ";
325		else if (strcmp(info->bug_type, "slab-use-after-free") == 0)
326			region_state = "freed ";
327	}
328
329	pr_err("The buggy address is located %d bytes %s of\n"
330	       " %s%zu-byte region [%px, %px)\n",
331	       rel_bytes, rel_type, region_state, info->alloc_size,
332	       (void *)object_addr, (void *)(object_addr + info->alloc_size));
333}
334
335static void describe_object_stacks(struct kasan_report_info *info)
336{
337	if (info->alloc_track.stack) {
338		print_track(&info->alloc_track, "Allocated");
339		pr_err("\n");
340	}
341
342	if (info->free_track.stack) {
343		print_track(&info->free_track, "Freed");
344		pr_err("\n");
345	}
346
347	kasan_print_aux_stacks(info->cache, info->object);
348}
349
350static void describe_object(const void *addr, struct kasan_report_info *info)
351{
352	if (kasan_stack_collection_enabled())
353		describe_object_stacks(info);
354	describe_object_addr(addr, info);
355}
356
357static inline bool kernel_or_module_addr(const void *addr)
358{
359	if (is_kernel((unsigned long)addr))
360		return true;
361	if (is_module_address((unsigned long)addr))
362		return true;
363	return false;
364}
365
366static inline bool init_task_stack_addr(const void *addr)
367{
368	return addr >= (void *)&init_thread_union.stack &&
369		(addr <= (void *)&init_thread_union.stack +
370			sizeof(init_thread_union.stack));
371}
372
373static void print_address_description(void *addr, u8 tag,
374				      struct kasan_report_info *info)
375{
376	struct page *page = addr_to_page(addr);
377
378	dump_stack_lvl(KERN_ERR);
379	pr_err("\n");
380
381	if (info->cache && info->object) {
382		describe_object(addr, info);
383		pr_err("\n");
384	}
385
386	if (kernel_or_module_addr(addr) && !init_task_stack_addr(addr)) {
387		pr_err("The buggy address belongs to the variable:\n");
388		pr_err(" %pS\n", addr);
389		pr_err("\n");
390	}
391
392	if (object_is_on_stack(addr)) {
393		/*
394		 * Currently, KASAN supports printing frame information only
395		 * for accesses to the task's own stack.
396		 */
397		kasan_print_address_stack_frame(addr);
398		pr_err("\n");
399	}
400
401	if (is_vmalloc_addr(addr)) {
402		pr_err("The buggy address belongs to a");
403		if (!vmalloc_dump_obj(addr))
404			pr_cont(" vmalloc virtual mapping\n");
405		page = vmalloc_to_page(addr);
406	}
407
408	if (page) {
409		pr_err("The buggy address belongs to the physical page:\n");
410		dump_page(page, "kasan: bad access detected");
411		pr_err("\n");
412	}
413}
414
415static bool meta_row_is_guilty(const void *row, const void *addr)
416{
417	return (row <= addr) && (addr < row + META_MEM_BYTES_PER_ROW);
418}
419
420static int meta_pointer_offset(const void *row, const void *addr)
421{
422	/*
423	 * Memory state around the buggy address:
424	 *  ff00ff00ff00ff00: 00 00 00 05 fe fe fe fe fe fe fe fe fe fe fe fe
425	 *  ...
426	 *
427	 * The length of ">ff00ff00ff00ff00: " is
428	 *    3 + (BITS_PER_LONG / 8) * 2 chars.
429	 * The length of each granule metadata is 2 bytes
430	 *    plus 1 byte for space.
431	 */
432	return 3 + (BITS_PER_LONG / 8) * 2 +
433		(addr - row) / KASAN_GRANULE_SIZE * 3 + 1;
434}
435
436static void print_memory_metadata(const void *addr)
437{
438	int i;
439	void *row;
440
441	row = (void *)round_down((unsigned long)addr, META_MEM_BYTES_PER_ROW)
442			- META_ROWS_AROUND_ADDR * META_MEM_BYTES_PER_ROW;
443
444	pr_err("Memory state around the buggy address:\n");
445
446	for (i = -META_ROWS_AROUND_ADDR; i <= META_ROWS_AROUND_ADDR; i++) {
447		char buffer[4 + (BITS_PER_LONG / 8) * 2];
448		char metadata[META_BYTES_PER_ROW];
449
450		snprintf(buffer, sizeof(buffer),
451				(i == 0) ? ">%px: " : " %px: ", row);
452
453		/*
454		 * We should not pass a shadow pointer to generic
455		 * function, because generic functions may try to
456		 * access kasan mapping for the passed address.
457		 */
458		kasan_metadata_fetch_row(&metadata[0], row);
459
460		print_hex_dump(KERN_ERR, buffer,
461			DUMP_PREFIX_NONE, META_BYTES_PER_ROW, 1,
462			metadata, META_BYTES_PER_ROW, 0);
463
464		if (meta_row_is_guilty(row, addr))
465			pr_err("%*c\n", meta_pointer_offset(row, addr), '^');
466
467		row += META_MEM_BYTES_PER_ROW;
468	}
469}
470
471static void print_report(struct kasan_report_info *info)
472{
473	void *addr = kasan_reset_tag((void *)info->access_addr);
474	u8 tag = get_tag((void *)info->access_addr);
475
476	print_error_description(info);
477	if (addr_has_metadata(addr))
478		kasan_print_tags(tag, info->first_bad_addr);
479	pr_err("\n");
480
481	if (addr_has_metadata(addr)) {
482		print_address_description(addr, tag, info);
483		print_memory_metadata(info->first_bad_addr);
484	} else {
485		dump_stack_lvl(KERN_ERR);
486	}
487}
488
489static void complete_report_info(struct kasan_report_info *info)
490{
491	void *addr = kasan_reset_tag((void *)info->access_addr);
492	struct slab *slab;
493
494	if (info->type == KASAN_REPORT_ACCESS)
495		info->first_bad_addr = kasan_find_first_bad_addr(
496					(void *)info->access_addr, info->access_size);
497	else
498		info->first_bad_addr = addr;
499
500	slab = kasan_addr_to_slab(addr);
501	if (slab) {
502		info->cache = slab->slab_cache;
503		info->object = nearest_obj(info->cache, slab, addr);
504
505		/* Try to determine allocation size based on the metadata. */
506		info->alloc_size = kasan_get_alloc_size(info->object, info->cache);
507		/* Fallback to the object size if failed. */
508		if (!info->alloc_size)
509			info->alloc_size = info->cache->object_size;
510	} else
511		info->cache = info->object = NULL;
512
513	switch (info->type) {
514	case KASAN_REPORT_INVALID_FREE:
515		info->bug_type = "invalid-free";
516		break;
517	case KASAN_REPORT_DOUBLE_FREE:
518		info->bug_type = "double-free";
519		break;
520	default:
521		/* bug_type filled in by kasan_complete_mode_report_info. */
522		break;
523	}
524
525	/* Fill in mode-specific report info fields. */
526	kasan_complete_mode_report_info(info);
527}
528
529void kasan_report_invalid_free(void *ptr, unsigned long ip, enum kasan_report_type type)
530{
531	unsigned long flags;
532	struct kasan_report_info info;
533
534	/*
535	 * Do not check report_suppressed_sw(), as an invalid-free cannot be
536	 * caused by accessing poisoned memory and thus should not be suppressed
537	 * by kasan_disable/enable_current() critical sections.
538	 *
539	 * Note that for Hardware Tag-Based KASAN, kasan_report_invalid_free()
540	 * is triggered by explicit tag checks and not by the ones performed by
541	 * the CPU. Thus, reporting invalid-free is not suppressed as well.
542	 */
543	if (unlikely(!report_enabled()))
544		return;
545
546	start_report(&flags, true);
547
548	__memset(&info, 0, sizeof(info));
549	info.type = type;
550	info.access_addr = ptr;
551	info.access_size = 0;
552	info.is_write = false;
553	info.ip = ip;
554
555	complete_report_info(&info);
556
557	print_report(&info);
558
559	/*
560	 * Invalid free is considered a "write" since the allocator's metadata
561	 * updates involves writes.
562	 */
563	end_report(&flags, ptr, true);
564}
565
566/*
567 * kasan_report() is the only reporting function that uses
568 * user_access_save/restore(): kasan_report_invalid_free() cannot be called
569 * from a UACCESS region, and kasan_report_async() is not used on x86.
570 */
571bool kasan_report(const void *addr, size_t size, bool is_write,
572			unsigned long ip)
573{
574	bool ret = true;
575	unsigned long ua_flags = user_access_save();
576	unsigned long irq_flags;
577	struct kasan_report_info info;
578
579	if (unlikely(report_suppressed_sw()) || unlikely(!report_enabled())) {
580		ret = false;
581		goto out;
582	}
583
584	start_report(&irq_flags, true);
585
586	__memset(&info, 0, sizeof(info));
587	info.type = KASAN_REPORT_ACCESS;
588	info.access_addr = addr;
589	info.access_size = size;
590	info.is_write = is_write;
591	info.ip = ip;
592
593	complete_report_info(&info);
594
595	print_report(&info);
596
597	end_report(&irq_flags, (void *)addr, is_write);
598
599out:
600	user_access_restore(ua_flags);
601
602	return ret;
603}
604
605#ifdef CONFIG_KASAN_HW_TAGS
606void kasan_report_async(void)
607{
608	unsigned long flags;
609
610	/*
611	 * Do not check report_suppressed_sw(), as
612	 * kasan_disable/enable_current() critical sections do not affect
613	 * Hardware Tag-Based KASAN.
614	 */
615	if (unlikely(!report_enabled()))
616		return;
617
618	start_report(&flags, false);
619	pr_err("BUG: KASAN: invalid-access\n");
620	pr_err("Asynchronous fault: no details available\n");
621	pr_err("\n");
622	dump_stack_lvl(KERN_ERR);
623	/*
624	 * Conservatively set is_write=true, because no details are available.
625	 * In this mode, kasan.fault=panic_on_write is like kasan.fault=panic.
626	 */
627	end_report(&flags, NULL, true);
628}
629#endif /* CONFIG_KASAN_HW_TAGS */
630
631#if defined(CONFIG_KASAN_GENERIC) || defined(CONFIG_KASAN_SW_TAGS)
632/*
633 * With compiler-based KASAN modes, accesses to bogus pointers (outside of the
634 * mapped kernel address space regions) cause faults when KASAN tries to check
635 * the shadow memory before the actual memory access. This results in cryptic
636 * GPF reports, which are hard for users to interpret. This hook helps users to
637 * figure out what the original bogus pointer was.
638 */
639void kasan_non_canonical_hook(unsigned long addr)
640{
641	unsigned long orig_addr;
642	const char *bug_type;
643
644	/*
645	 * All addresses that came as a result of the memory-to-shadow mapping
646	 * (even for bogus pointers) must be >= KASAN_SHADOW_OFFSET.
647	 */
648	if (addr < KASAN_SHADOW_OFFSET)
649		return;
650
651	orig_addr = (unsigned long)kasan_shadow_to_mem((void *)addr);
652
653	/*
654	 * For faults near the shadow address for NULL, we can be fairly certain
655	 * that this is a KASAN shadow memory access.
656	 * For faults that correspond to the shadow for low or high canonical
657	 * addresses, we can still be pretty sure: these shadow regions are a
658	 * fairly narrow chunk of the address space.
659	 * But the shadow for non-canonical addresses is a really large chunk
660	 * of the address space. For this case, we still print the decoded
661	 * address, but make it clear that this is not necessarily what's
662	 * actually going on.
663	 */
664	if (orig_addr < PAGE_SIZE)
665		bug_type = "null-ptr-deref";
666	else if (orig_addr < TASK_SIZE)
667		bug_type = "probably user-memory-access";
668	else if (addr_in_shadow((void *)addr))
669		bug_type = "probably wild-memory-access";
670	else
671		bug_type = "maybe wild-memory-access";
672	pr_alert("KASAN: %s in range [0x%016lx-0x%016lx]\n", bug_type,
673		 orig_addr, orig_addr + KASAN_GRANULE_SIZE - 1);
674}
675#endif