xref: /linux/mm/kasan/report.c (revision 79790b6818e96c58fe2bffee1b418c16e64e7b80)
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 <linux/bitops.h>
14 #include <linux/ftrace.h>
15 #include <linux/init.h>
16 #include <linux/kernel.h>
17 #include <linux/lockdep.h>
18 #include <linux/mm.h>
19 #include <linux/printk.h>
20 #include <linux/sched.h>
21 #include <linux/slab.h>
22 #include <linux/stackdepot.h>
23 #include <linux/stacktrace.h>
24 #include <linux/string.h>
25 #include <linux/types.h>
26 #include <linux/vmalloc.h>
27 #include <linux/kasan.h>
28 #include <linux/module.h>
29 #include <linux/sched/task_stack.h>
30 #include <linux/uaccess.h>
31 #include <trace/events/error_report.h>
32 
33 #include <asm/sections.h>
34 
35 #include "kasan.h"
36 #include "../slab.h"
37 
38 static unsigned long kasan_flags;
39 
40 #define KASAN_BIT_REPORTED	0
41 #define KASAN_BIT_MULTI_SHOT	1
42 
43 enum kasan_arg_fault {
44 	KASAN_ARG_FAULT_DEFAULT,
45 	KASAN_ARG_FAULT_REPORT,
46 	KASAN_ARG_FAULT_PANIC,
47 	KASAN_ARG_FAULT_PANIC_ON_WRITE,
48 };
49 
50 static enum kasan_arg_fault kasan_arg_fault __ro_after_init = KASAN_ARG_FAULT_DEFAULT;
51 
52 /* kasan.fault=report/panic */
early_kasan_fault(char * arg)53 static int __init early_kasan_fault(char *arg)
54 {
55 	if (!arg)
56 		return -EINVAL;
57 
58 	if (!strcmp(arg, "report"))
59 		kasan_arg_fault = KASAN_ARG_FAULT_REPORT;
60 	else if (!strcmp(arg, "panic"))
61 		kasan_arg_fault = KASAN_ARG_FAULT_PANIC;
62 	else if (!strcmp(arg, "panic_on_write"))
63 		kasan_arg_fault = KASAN_ARG_FAULT_PANIC_ON_WRITE;
64 	else
65 		return -EINVAL;
66 
67 	return 0;
68 }
69 early_param("kasan.fault", early_kasan_fault);
70 
kasan_set_multi_shot(char * str)71 static int __init kasan_set_multi_shot(char *str)
72 {
73 	set_bit(KASAN_BIT_MULTI_SHOT, &kasan_flags);
74 	return 1;
75 }
76 __setup("kasan_multi_shot", kasan_set_multi_shot);
77 
78 /*
79  * This function is used to check whether KASAN reports are suppressed for
80  * software KASAN modes via kasan_disable/enable_current() critical sections.
81  *
82  * This is done to avoid:
83  * 1. False-positive reports when accessing slab metadata,
84  * 2. Deadlocking when poisoned memory is accessed by the reporting code.
85  *
86  * Hardware Tag-Based KASAN instead relies on:
87  * For #1: Resetting tags via kasan_reset_tag().
88  * For #2: Suppression of tag checks via CPU, see report_suppress_start/end().
89  */
report_suppressed_sw(void)90 static bool report_suppressed_sw(void)
91 {
92 #if defined(CONFIG_KASAN_GENERIC) || defined(CONFIG_KASAN_SW_TAGS)
93 	if (current->kasan_depth)
94 		return true;
95 #endif
96 	return false;
97 }
98 
report_suppress_start(void)99 static void report_suppress_start(void)
100 {
101 #ifdef CONFIG_KASAN_HW_TAGS
102 	/*
103 	 * Disable preemption for the duration of printing a KASAN report, as
104 	 * hw_suppress_tag_checks_start() disables checks on the current CPU.
105 	 */
106 	preempt_disable();
107 	hw_suppress_tag_checks_start();
108 #else
109 	kasan_disable_current();
110 #endif
111 }
112 
report_suppress_stop(void)113 static void report_suppress_stop(void)
114 {
115 #ifdef CONFIG_KASAN_HW_TAGS
116 	hw_suppress_tag_checks_stop();
117 	preempt_enable();
118 #else
119 	kasan_enable_current();
120 #endif
121 }
122 
123 /*
124  * Used to avoid reporting more than one KASAN bug unless kasan_multi_shot
125  * is enabled. Note that KASAN tests effectively enable kasan_multi_shot
126  * for their duration.
127  */
report_enabled(void)128 static bool report_enabled(void)
129 {
130 	if (test_bit(KASAN_BIT_MULTI_SHOT, &kasan_flags))
131 		return true;
132 	return !test_and_set_bit(KASAN_BIT_REPORTED, &kasan_flags);
133 }
134 
135 #if IS_ENABLED(CONFIG_KASAN_KUNIT_TEST) || IS_ENABLED(CONFIG_KASAN_MODULE_TEST)
136 
kasan_save_enable_multi_shot(void)137 bool kasan_save_enable_multi_shot(void)
138 {
139 	return test_and_set_bit(KASAN_BIT_MULTI_SHOT, &kasan_flags);
140 }
141 EXPORT_SYMBOL_GPL(kasan_save_enable_multi_shot);
142 
kasan_restore_multi_shot(bool enabled)143 void kasan_restore_multi_shot(bool enabled)
144 {
145 	if (!enabled)
146 		clear_bit(KASAN_BIT_MULTI_SHOT, &kasan_flags);
147 }
148 EXPORT_SYMBOL_GPL(kasan_restore_multi_shot);
149 
150 #endif
151 
152 #if IS_ENABLED(CONFIG_KASAN_KUNIT_TEST)
153 
154 /*
155  * Whether the KASAN KUnit test suite is currently being executed.
156  * Updated in kasan_test.c.
157  */
158 static bool kasan_kunit_executing;
159 
kasan_kunit_test_suite_start(void)160 void kasan_kunit_test_suite_start(void)
161 {
162 	WRITE_ONCE(kasan_kunit_executing, true);
163 }
164 EXPORT_SYMBOL_GPL(kasan_kunit_test_suite_start);
165 
kasan_kunit_test_suite_end(void)166 void kasan_kunit_test_suite_end(void)
167 {
168 	WRITE_ONCE(kasan_kunit_executing, false);
169 }
170 EXPORT_SYMBOL_GPL(kasan_kunit_test_suite_end);
171 
kasan_kunit_test_suite_executing(void)172 static bool kasan_kunit_test_suite_executing(void)
173 {
174 	return READ_ONCE(kasan_kunit_executing);
175 }
176 
177 #else /* CONFIG_KASAN_KUNIT_TEST */
178 
kasan_kunit_test_suite_executing(void)179 static inline bool kasan_kunit_test_suite_executing(void) { return false; }
180 
181 #endif /* CONFIG_KASAN_KUNIT_TEST */
182 
183 #if IS_ENABLED(CONFIG_KUNIT)
184 
fail_non_kasan_kunit_test(void)185 static void fail_non_kasan_kunit_test(void)
186 {
187 	struct kunit *test;
188 
189 	if (kasan_kunit_test_suite_executing())
190 		return;
191 
192 	test = current->kunit_test;
193 	if (test)
194 		kunit_set_failure(test);
195 }
196 
197 #else /* CONFIG_KUNIT */
198 
fail_non_kasan_kunit_test(void)199 static inline void fail_non_kasan_kunit_test(void) { }
200 
201 #endif /* CONFIG_KUNIT */
202 
203 static DEFINE_SPINLOCK(report_lock);
204 
start_report(unsigned long * flags,bool sync)205 static void start_report(unsigned long *flags, bool sync)
206 {
207 	fail_non_kasan_kunit_test();
208 	/* Respect the /proc/sys/kernel/traceoff_on_warning interface. */
209 	disable_trace_on_warning();
210 	/* Do not allow LOCKDEP mangling KASAN reports. */
211 	lockdep_off();
212 	/* Make sure we don't end up in loop. */
213 	report_suppress_start();
214 	spin_lock_irqsave(&report_lock, *flags);
215 	pr_err("==================================================================\n");
216 }
217 
end_report(unsigned long * flags,const void * addr,bool is_write)218 static void end_report(unsigned long *flags, const void *addr, bool is_write)
219 {
220 	if (addr)
221 		trace_error_report_end(ERROR_DETECTOR_KASAN,
222 				       (unsigned long)addr);
223 	pr_err("==================================================================\n");
224 	spin_unlock_irqrestore(&report_lock, *flags);
225 	if (!test_bit(KASAN_BIT_MULTI_SHOT, &kasan_flags))
226 		check_panic_on_warn("KASAN");
227 	switch (kasan_arg_fault) {
228 	case KASAN_ARG_FAULT_DEFAULT:
229 	case KASAN_ARG_FAULT_REPORT:
230 		break;
231 	case KASAN_ARG_FAULT_PANIC:
232 		panic("kasan.fault=panic set ...\n");
233 		break;
234 	case KASAN_ARG_FAULT_PANIC_ON_WRITE:
235 		if (is_write)
236 			panic("kasan.fault=panic_on_write set ...\n");
237 		break;
238 	}
239 	add_taint(TAINT_BAD_PAGE, LOCKDEP_NOW_UNRELIABLE);
240 	lockdep_on();
241 	report_suppress_stop();
242 }
243 
print_error_description(struct kasan_report_info * info)244 static void print_error_description(struct kasan_report_info *info)
245 {
246 	pr_err("BUG: KASAN: %s in %pS\n", info->bug_type, (void *)info->ip);
247 
248 	if (info->type != KASAN_REPORT_ACCESS) {
249 		pr_err("Free of addr %px by task %s/%d\n",
250 			info->access_addr, current->comm, task_pid_nr(current));
251 		return;
252 	}
253 
254 	if (info->access_size)
255 		pr_err("%s of size %zu at addr %px by task %s/%d\n",
256 			info->is_write ? "Write" : "Read", info->access_size,
257 			info->access_addr, current->comm, task_pid_nr(current));
258 	else
259 		pr_err("%s at addr %px by task %s/%d\n",
260 			info->is_write ? "Write" : "Read",
261 			info->access_addr, current->comm, task_pid_nr(current));
262 }
263 
print_track(struct kasan_track * track,const char * prefix)264 static void print_track(struct kasan_track *track, const char *prefix)
265 {
266 #ifdef CONFIG_KASAN_EXTRA_INFO
267 	u64 ts_nsec = track->timestamp;
268 	unsigned long rem_usec;
269 
270 	ts_nsec <<= 9;
271 	rem_usec = do_div(ts_nsec, NSEC_PER_SEC) / 1000;
272 
273 	pr_err("%s by task %u on cpu %d at %lu.%06lus:\n",
274 			prefix, track->pid, track->cpu,
275 			(unsigned long)ts_nsec, rem_usec);
276 #else
277 	pr_err("%s by task %u:\n", prefix, track->pid);
278 #endif /* CONFIG_KASAN_EXTRA_INFO */
279 	if (track->stack)
280 		stack_depot_print(track->stack);
281 	else
282 		pr_err("(stack is not available)\n");
283 }
284 
addr_to_page(const void * addr)285 static inline struct page *addr_to_page(const void *addr)
286 {
287 	if (virt_addr_valid(addr))
288 		return virt_to_head_page(addr);
289 	return NULL;
290 }
291 
describe_object_addr(const void * addr,struct kasan_report_info * info)292 static void describe_object_addr(const void *addr, struct kasan_report_info *info)
293 {
294 	unsigned long access_addr = (unsigned long)addr;
295 	unsigned long object_addr = (unsigned long)info->object;
296 	const char *rel_type, *region_state = "";
297 	int rel_bytes;
298 
299 	pr_err("The buggy address belongs to the object at %px\n"
300 	       " which belongs to the cache %s of size %d\n",
301 		info->object, info->cache->name, info->cache->object_size);
302 
303 	if (access_addr < object_addr) {
304 		rel_type = "to the left";
305 		rel_bytes = object_addr - access_addr;
306 	} else if (access_addr >= object_addr + info->alloc_size) {
307 		rel_type = "to the right";
308 		rel_bytes = access_addr - (object_addr + info->alloc_size);
309 	} else {
310 		rel_type = "inside";
311 		rel_bytes = access_addr - object_addr;
312 	}
313 
314 	/*
315 	 * Tag-Based modes use the stack ring to infer the bug type, but the
316 	 * memory region state description is generated based on the metadata.
317 	 * Thus, defining the region state as below can contradict the metadata.
318 	 * Fixing this requires further improvements, so only infer the state
319 	 * for the Generic mode.
320 	 */
321 	if (IS_ENABLED(CONFIG_KASAN_GENERIC)) {
322 		if (strcmp(info->bug_type, "slab-out-of-bounds") == 0)
323 			region_state = "allocated ";
324 		else if (strcmp(info->bug_type, "slab-use-after-free") == 0)
325 			region_state = "freed ";
326 	}
327 
328 	pr_err("The buggy address is located %d bytes %s of\n"
329 	       " %s%zu-byte region [%px, %px)\n",
330 	       rel_bytes, rel_type, region_state, info->alloc_size,
331 	       (void *)object_addr, (void *)(object_addr + info->alloc_size));
332 }
333 
describe_object_stacks(struct kasan_report_info * info)334 static void describe_object_stacks(struct kasan_report_info *info)
335 {
336 	if (info->alloc_track.stack) {
337 		print_track(&info->alloc_track, "Allocated");
338 		pr_err("\n");
339 	}
340 
341 	if (info->free_track.stack) {
342 		print_track(&info->free_track, "Freed");
343 		pr_err("\n");
344 	}
345 
346 	kasan_print_aux_stacks(info->cache, info->object);
347 }
348 
describe_object(const void * addr,struct kasan_report_info * info)349 static void describe_object(const void *addr, struct kasan_report_info *info)
350 {
351 	if (kasan_stack_collection_enabled())
352 		describe_object_stacks(info);
353 	describe_object_addr(addr, info);
354 }
355 
kernel_or_module_addr(const void * addr)356 static inline bool kernel_or_module_addr(const void *addr)
357 {
358 	if (is_kernel((unsigned long)addr))
359 		return true;
360 	if (is_module_address((unsigned long)addr))
361 		return true;
362 	return false;
363 }
364 
init_task_stack_addr(const void * addr)365 static inline bool init_task_stack_addr(const void *addr)
366 {
367 	return addr >= (void *)&init_thread_union.stack &&
368 		(addr <= (void *)&init_thread_union.stack +
369 			sizeof(init_thread_union.stack));
370 }
371 
print_address_description(void * addr,u8 tag,struct kasan_report_info * info)372 static void print_address_description(void *addr, u8 tag,
373 				      struct kasan_report_info *info)
374 {
375 	struct page *page = addr_to_page(addr);
376 
377 	dump_stack_lvl(KERN_ERR);
378 	pr_err("\n");
379 
380 	if (info->cache && info->object) {
381 		describe_object(addr, info);
382 		pr_err("\n");
383 	}
384 
385 	if (kernel_or_module_addr(addr) && !init_task_stack_addr(addr)) {
386 		pr_err("The buggy address belongs to the variable:\n");
387 		pr_err(" %pS\n", addr);
388 		pr_err("\n");
389 	}
390 
391 	if (object_is_on_stack(addr)) {
392 		/*
393 		 * Currently, KASAN supports printing frame information only
394 		 * for accesses to the task's own stack.
395 		 */
396 		kasan_print_address_stack_frame(addr);
397 		pr_err("\n");
398 	}
399 
400 	if (is_vmalloc_addr(addr)) {
401 		struct vm_struct *va = find_vm_area(addr);
402 
403 		if (va) {
404 			pr_err("The buggy address belongs to the virtual mapping at\n"
405 			       " [%px, %px) created by:\n"
406 			       " %pS\n",
407 			       va->addr, va->addr + va->size, va->caller);
408 			pr_err("\n");
409 
410 			page = vmalloc_to_page(addr);
411 		}
412 	}
413 
414 	if (page) {
415 		pr_err("The buggy address belongs to the physical page:\n");
416 		dump_page(page, "kasan: bad access detected");
417 		pr_err("\n");
418 	}
419 }
420 
meta_row_is_guilty(const void * row,const void * addr)421 static bool meta_row_is_guilty(const void *row, const void *addr)
422 {
423 	return (row <= addr) && (addr < row + META_MEM_BYTES_PER_ROW);
424 }
425 
meta_pointer_offset(const void * row,const void * addr)426 static int meta_pointer_offset(const void *row, const void *addr)
427 {
428 	/*
429 	 * Memory state around the buggy address:
430 	 *  ff00ff00ff00ff00: 00 00 00 05 fe fe fe fe fe fe fe fe fe fe fe fe
431 	 *  ...
432 	 *
433 	 * The length of ">ff00ff00ff00ff00: " is
434 	 *    3 + (BITS_PER_LONG / 8) * 2 chars.
435 	 * The length of each granule metadata is 2 bytes
436 	 *    plus 1 byte for space.
437 	 */
438 	return 3 + (BITS_PER_LONG / 8) * 2 +
439 		(addr - row) / KASAN_GRANULE_SIZE * 3 + 1;
440 }
441 
print_memory_metadata(const void * addr)442 static void print_memory_metadata(const void *addr)
443 {
444 	int i;
445 	void *row;
446 
447 	row = (void *)round_down((unsigned long)addr, META_MEM_BYTES_PER_ROW)
448 			- META_ROWS_AROUND_ADDR * META_MEM_BYTES_PER_ROW;
449 
450 	pr_err("Memory state around the buggy address:\n");
451 
452 	for (i = -META_ROWS_AROUND_ADDR; i <= META_ROWS_AROUND_ADDR; i++) {
453 		char buffer[4 + (BITS_PER_LONG / 8) * 2];
454 		char metadata[META_BYTES_PER_ROW];
455 
456 		snprintf(buffer, sizeof(buffer),
457 				(i == 0) ? ">%px: " : " %px: ", row);
458 
459 		/*
460 		 * We should not pass a shadow pointer to generic
461 		 * function, because generic functions may try to
462 		 * access kasan mapping for the passed address.
463 		 */
464 		kasan_metadata_fetch_row(&metadata[0], row);
465 
466 		print_hex_dump(KERN_ERR, buffer,
467 			DUMP_PREFIX_NONE, META_BYTES_PER_ROW, 1,
468 			metadata, META_BYTES_PER_ROW, 0);
469 
470 		if (meta_row_is_guilty(row, addr))
471 			pr_err("%*c\n", meta_pointer_offset(row, addr), '^');
472 
473 		row += META_MEM_BYTES_PER_ROW;
474 	}
475 }
476 
print_report(struct kasan_report_info * info)477 static void print_report(struct kasan_report_info *info)
478 {
479 	void *addr = kasan_reset_tag((void *)info->access_addr);
480 	u8 tag = get_tag((void *)info->access_addr);
481 
482 	print_error_description(info);
483 	if (addr_has_metadata(addr))
484 		kasan_print_tags(tag, info->first_bad_addr);
485 	pr_err("\n");
486 
487 	if (addr_has_metadata(addr)) {
488 		print_address_description(addr, tag, info);
489 		print_memory_metadata(info->first_bad_addr);
490 	} else {
491 		dump_stack_lvl(KERN_ERR);
492 	}
493 }
494 
complete_report_info(struct kasan_report_info * info)495 static void complete_report_info(struct kasan_report_info *info)
496 {
497 	void *addr = kasan_reset_tag((void *)info->access_addr);
498 	struct slab *slab;
499 
500 	if (info->type == KASAN_REPORT_ACCESS)
501 		info->first_bad_addr = kasan_find_first_bad_addr(
502 					(void *)info->access_addr, info->access_size);
503 	else
504 		info->first_bad_addr = addr;
505 
506 	slab = kasan_addr_to_slab(addr);
507 	if (slab) {
508 		info->cache = slab->slab_cache;
509 		info->object = nearest_obj(info->cache, slab, addr);
510 
511 		/* Try to determine allocation size based on the metadata. */
512 		info->alloc_size = kasan_get_alloc_size(info->object, info->cache);
513 		/* Fallback to the object size if failed. */
514 		if (!info->alloc_size)
515 			info->alloc_size = info->cache->object_size;
516 	} else
517 		info->cache = info->object = NULL;
518 
519 	switch (info->type) {
520 	case KASAN_REPORT_INVALID_FREE:
521 		info->bug_type = "invalid-free";
522 		break;
523 	case KASAN_REPORT_DOUBLE_FREE:
524 		info->bug_type = "double-free";
525 		break;
526 	default:
527 		/* bug_type filled in by kasan_complete_mode_report_info. */
528 		break;
529 	}
530 
531 	/* Fill in mode-specific report info fields. */
532 	kasan_complete_mode_report_info(info);
533 }
534 
kasan_report_invalid_free(void * ptr,unsigned long ip,enum kasan_report_type type)535 void kasan_report_invalid_free(void *ptr, unsigned long ip, enum kasan_report_type type)
536 {
537 	unsigned long flags;
538 	struct kasan_report_info info;
539 
540 	/*
541 	 * Do not check report_suppressed_sw(), as an invalid-free cannot be
542 	 * caused by accessing poisoned memory and thus should not be suppressed
543 	 * by kasan_disable/enable_current() critical sections.
544 	 *
545 	 * Note that for Hardware Tag-Based KASAN, kasan_report_invalid_free()
546 	 * is triggered by explicit tag checks and not by the ones performed by
547 	 * the CPU. Thus, reporting invalid-free is not suppressed as well.
548 	 */
549 	if (unlikely(!report_enabled()))
550 		return;
551 
552 	start_report(&flags, true);
553 
554 	__memset(&info, 0, sizeof(info));
555 	info.type = type;
556 	info.access_addr = ptr;
557 	info.access_size = 0;
558 	info.is_write = false;
559 	info.ip = ip;
560 
561 	complete_report_info(&info);
562 
563 	print_report(&info);
564 
565 	/*
566 	 * Invalid free is considered a "write" since the allocator's metadata
567 	 * updates involves writes.
568 	 */
569 	end_report(&flags, ptr, true);
570 }
571 
572 /*
573  * kasan_report() is the only reporting function that uses
574  * user_access_save/restore(): kasan_report_invalid_free() cannot be called
575  * from a UACCESS region, and kasan_report_async() is not used on x86.
576  */
kasan_report(const void * addr,size_t size,bool is_write,unsigned long ip)577 bool kasan_report(const void *addr, size_t size, bool is_write,
578 			unsigned long ip)
579 {
580 	bool ret = true;
581 	unsigned long ua_flags = user_access_save();
582 	unsigned long irq_flags;
583 	struct kasan_report_info info;
584 
585 	if (unlikely(report_suppressed_sw()) || unlikely(!report_enabled())) {
586 		ret = false;
587 		goto out;
588 	}
589 
590 	start_report(&irq_flags, true);
591 
592 	__memset(&info, 0, sizeof(info));
593 	info.type = KASAN_REPORT_ACCESS;
594 	info.access_addr = addr;
595 	info.access_size = size;
596 	info.is_write = is_write;
597 	info.ip = ip;
598 
599 	complete_report_info(&info);
600 
601 	print_report(&info);
602 
603 	end_report(&irq_flags, (void *)addr, is_write);
604 
605 out:
606 	user_access_restore(ua_flags);
607 
608 	return ret;
609 }
610 
611 #ifdef CONFIG_KASAN_HW_TAGS
kasan_report_async(void)612 void kasan_report_async(void)
613 {
614 	unsigned long flags;
615 
616 	/*
617 	 * Do not check report_suppressed_sw(), as
618 	 * kasan_disable/enable_current() critical sections do not affect
619 	 * Hardware Tag-Based KASAN.
620 	 */
621 	if (unlikely(!report_enabled()))
622 		return;
623 
624 	start_report(&flags, false);
625 	pr_err("BUG: KASAN: invalid-access\n");
626 	pr_err("Asynchronous fault: no details available\n");
627 	pr_err("\n");
628 	dump_stack_lvl(KERN_ERR);
629 	/*
630 	 * Conservatively set is_write=true, because no details are available.
631 	 * In this mode, kasan.fault=panic_on_write is like kasan.fault=panic.
632 	 */
633 	end_report(&flags, NULL, true);
634 }
635 #endif /* CONFIG_KASAN_HW_TAGS */
636 
637 #if defined(CONFIG_KASAN_GENERIC) || defined(CONFIG_KASAN_SW_TAGS)
638 /*
639  * With compiler-based KASAN modes, accesses to bogus pointers (outside of the
640  * mapped kernel address space regions) cause faults when KASAN tries to check
641  * the shadow memory before the actual memory access. This results in cryptic
642  * GPF reports, which are hard for users to interpret. This hook helps users to
643  * figure out what the original bogus pointer was.
644  */
kasan_non_canonical_hook(unsigned long addr)645 void kasan_non_canonical_hook(unsigned long addr)
646 {
647 	unsigned long orig_addr;
648 	const char *bug_type;
649 
650 	/*
651 	 * All addresses that came as a result of the memory-to-shadow mapping
652 	 * (even for bogus pointers) must be >= KASAN_SHADOW_OFFSET.
653 	 */
654 	if (addr < KASAN_SHADOW_OFFSET)
655 		return;
656 
657 	orig_addr = (unsigned long)kasan_shadow_to_mem((void *)addr);
658 
659 	/*
660 	 * For faults near the shadow address for NULL, we can be fairly certain
661 	 * that this is a KASAN shadow memory access.
662 	 * For faults that correspond to the shadow for low or high canonical
663 	 * addresses, we can still be pretty sure: these shadow regions are a
664 	 * fairly narrow chunk of the address space.
665 	 * But the shadow for non-canonical addresses is a really large chunk
666 	 * of the address space. For this case, we still print the decoded
667 	 * address, but make it clear that this is not necessarily what's
668 	 * actually going on.
669 	 */
670 	if (orig_addr < PAGE_SIZE)
671 		bug_type = "null-ptr-deref";
672 	else if (orig_addr < TASK_SIZE)
673 		bug_type = "probably user-memory-access";
674 	else if (addr_in_shadow((void *)addr))
675 		bug_type = "probably wild-memory-access";
676 	else
677 		bug_type = "maybe wild-memory-access";
678 	pr_alert("KASAN: %s in range [0x%016lx-0x%016lx]\n", bug_type,
679 		 orig_addr, orig_addr + KASAN_GRANULE_SIZE - 1);
680 }
681 #endif
682