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 */
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
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 */
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
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
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 */
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
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
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
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
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
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
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
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
199 static inline void fail_non_kasan_kunit_test(void) { }
200
201 #endif /* CONFIG_KUNIT */
202
203 static DEFINE_SPINLOCK(report_lock);
204
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
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
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
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
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
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
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
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
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
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
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
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
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
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
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
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
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 */
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
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 */
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
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