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 <linux/bitops.h>
13 #include <linux/ftrace.h>
14 #include <linux/init.h>
15 #include <linux/kernel.h>
16 #include <linux/lockdep.h>
17 #include <linux/mm.h>
18 #include <linux/printk.h>
19 #include <linux/sched.h>
20 #include <linux/slab.h>
21 #include <linux/stackdepot.h>
22 #include <linux/stacktrace.h>
23 #include <linux/string.h>
24 #include <linux/types.h>
25 #include <linux/kasan.h>
26 #include <linux/module.h>
27 #include <linux/sched/task_stack.h>
28 #include <linux/uaccess.h>
29 #include <trace/events/error_report.h>
30 
31 #include <asm/sections.h>
32 
33 #include <kunit/test.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 };
48 
49 static enum kasan_arg_fault kasan_arg_fault __ro_after_init = KASAN_ARG_FAULT_DEFAULT;
50 
51 /* kasan.fault=report/panic */
early_kasan_fault(char * arg)52 static int __init early_kasan_fault(char *arg)
53 {
54 	if (!arg)
55 		return -EINVAL;
56 
57 	if (!strcmp(arg, "report"))
58 		kasan_arg_fault = KASAN_ARG_FAULT_REPORT;
59 	else if (!strcmp(arg, "panic"))
60 		kasan_arg_fault = KASAN_ARG_FAULT_PANIC;
61 	else
62 		return -EINVAL;
63 
64 	return 0;
65 }
66 early_param("kasan.fault", early_kasan_fault);
67 
kasan_set_multi_shot(char * str)68 static int __init kasan_set_multi_shot(char *str)
69 {
70 	set_bit(KASAN_BIT_MULTI_SHOT, &kasan_flags);
71 	return 1;
72 }
73 __setup("kasan_multi_shot", kasan_set_multi_shot);
74 
75 /*
76  * Used to suppress reports within kasan_disable/enable_current() critical
77  * sections, which are used for marking accesses to slab metadata.
78  */
report_suppressed(void)79 static bool report_suppressed(void)
80 {
81 #if defined(CONFIG_KASAN_GENERIC) || defined(CONFIG_KASAN_SW_TAGS)
82 	if (current->kasan_depth)
83 		return true;
84 #endif
85 	return false;
86 }
87 
88 /*
89  * Used to avoid reporting more than one KASAN bug unless kasan_multi_shot
90  * is enabled. Note that KASAN tests effectively enable kasan_multi_shot
91  * for their duration.
92  */
report_enabled(void)93 static bool report_enabled(void)
94 {
95 	if (test_bit(KASAN_BIT_MULTI_SHOT, &kasan_flags))
96 		return true;
97 	return !test_and_set_bit(KASAN_BIT_REPORTED, &kasan_flags);
98 }
99 
100 #if IS_ENABLED(CONFIG_KASAN_KUNIT_TEST) || IS_ENABLED(CONFIG_KASAN_MODULE_TEST)
101 
kasan_save_enable_multi_shot(void)102 bool kasan_save_enable_multi_shot(void)
103 {
104 	return test_and_set_bit(KASAN_BIT_MULTI_SHOT, &kasan_flags);
105 }
106 EXPORT_SYMBOL_GPL(kasan_save_enable_multi_shot);
107 
kasan_restore_multi_shot(bool enabled)108 void kasan_restore_multi_shot(bool enabled)
109 {
110 	if (!enabled)
111 		clear_bit(KASAN_BIT_MULTI_SHOT, &kasan_flags);
112 }
113 EXPORT_SYMBOL_GPL(kasan_restore_multi_shot);
114 
115 #endif
116 
117 #if IS_ENABLED(CONFIG_KASAN_KUNIT_TEST)
update_kunit_status(bool sync)118 static void update_kunit_status(bool sync)
119 {
120 	struct kunit *test;
121 	struct kunit_resource *resource;
122 	struct kunit_kasan_status *status;
123 
124 	test = current->kunit_test;
125 	if (!test)
126 		return;
127 
128 	resource = kunit_find_named_resource(test, "kasan_status");
129 	if (!resource) {
130 		kunit_set_failure(test);
131 		return;
132 	}
133 
134 	status = (struct kunit_kasan_status *)resource->data;
135 	WRITE_ONCE(status->report_found, true);
136 	WRITE_ONCE(status->sync_fault, sync);
137 
138 	kunit_put_resource(resource);
139 }
140 #else
update_kunit_status(bool sync)141 static void update_kunit_status(bool sync) { }
142 #endif
143 
144 static DEFINE_SPINLOCK(report_lock);
145 
start_report(unsigned long * flags,bool sync)146 static void start_report(unsigned long *flags, bool sync)
147 {
148 	/* Respect the /proc/sys/kernel/traceoff_on_warning interface. */
149 	disable_trace_on_warning();
150 	/* Update status of the currently running KASAN test. */
151 	update_kunit_status(sync);
152 	/* Do not allow LOCKDEP mangling KASAN reports. */
153 	lockdep_off();
154 	/* Make sure we don't end up in loop. */
155 	kasan_disable_current();
156 	spin_lock_irqsave(&report_lock, *flags);
157 	pr_err("==================================================================\n");
158 }
159 
end_report(unsigned long * flags,void * addr)160 static void end_report(unsigned long *flags, void *addr)
161 {
162 	if (addr)
163 		trace_error_report_end(ERROR_DETECTOR_KASAN,
164 				       (unsigned long)addr);
165 	pr_err("==================================================================\n");
166 	spin_unlock_irqrestore(&report_lock, *flags);
167 	if (panic_on_warn && !test_bit(KASAN_BIT_MULTI_SHOT, &kasan_flags))
168 		panic("panic_on_warn set ...\n");
169 	if (kasan_arg_fault == KASAN_ARG_FAULT_PANIC)
170 		panic("kasan.fault=panic set ...\n");
171 	add_taint(TAINT_BAD_PAGE, LOCKDEP_NOW_UNRELIABLE);
172 	lockdep_on();
173 	kasan_enable_current();
174 }
175 
print_error_description(struct kasan_report_info * info)176 static void print_error_description(struct kasan_report_info *info)
177 {
178 	if (info->type == KASAN_REPORT_INVALID_FREE) {
179 		pr_err("BUG: KASAN: double-free or invalid-free in %pS\n",
180 		       (void *)info->ip);
181 		return;
182 	}
183 
184 	pr_err("BUG: KASAN: %s in %pS\n",
185 		kasan_get_bug_type(info), (void *)info->ip);
186 	if (info->access_size)
187 		pr_err("%s of size %zu at addr %px by task %s/%d\n",
188 			info->is_write ? "Write" : "Read", info->access_size,
189 			info->access_addr, current->comm, task_pid_nr(current));
190 	else
191 		pr_err("%s at addr %px by task %s/%d\n",
192 			info->is_write ? "Write" : "Read",
193 			info->access_addr, current->comm, task_pid_nr(current));
194 }
195 
print_track(struct kasan_track * track,const char * prefix)196 static void print_track(struct kasan_track *track, const char *prefix)
197 {
198 	pr_err("%s by task %u:\n", prefix, track->pid);
199 	if (track->stack) {
200 		stack_depot_print(track->stack);
201 	} else {
202 		pr_err("(stack is not available)\n");
203 	}
204 }
205 
kasan_addr_to_page(const void * addr)206 struct page *kasan_addr_to_page(const void *addr)
207 {
208 	if ((addr >= (void *)PAGE_OFFSET) &&
209 			(addr < high_memory))
210 		return virt_to_head_page(addr);
211 	return NULL;
212 }
213 
kasan_addr_to_slab(const void * addr)214 struct slab *kasan_addr_to_slab(const void *addr)
215 {
216 	if ((addr >= (void *)PAGE_OFFSET) &&
217 			(addr < high_memory))
218 		return virt_to_slab(addr);
219 	return NULL;
220 }
221 
describe_object_addr(struct kmem_cache * cache,void * object,const void * addr)222 static void describe_object_addr(struct kmem_cache *cache, void *object,
223 				const void *addr)
224 {
225 	unsigned long access_addr = (unsigned long)addr;
226 	unsigned long object_addr = (unsigned long)object;
227 	const char *rel_type;
228 	int rel_bytes;
229 
230 	pr_err("The buggy address belongs to the object at %px\n"
231 	       " which belongs to the cache %s of size %d\n",
232 		object, cache->name, cache->object_size);
233 
234 	if (access_addr < object_addr) {
235 		rel_type = "to the left";
236 		rel_bytes = object_addr - access_addr;
237 	} else if (access_addr >= object_addr + cache->object_size) {
238 		rel_type = "to the right";
239 		rel_bytes = access_addr - (object_addr + cache->object_size);
240 	} else {
241 		rel_type = "inside";
242 		rel_bytes = access_addr - object_addr;
243 	}
244 
245 	pr_err("The buggy address is located %d bytes %s of\n"
246 	       " %d-byte region [%px, %px)\n",
247 		rel_bytes, rel_type, cache->object_size, (void *)object_addr,
248 		(void *)(object_addr + cache->object_size));
249 }
250 
describe_object_stacks(struct kmem_cache * cache,void * object,const void * addr,u8 tag)251 static void describe_object_stacks(struct kmem_cache *cache, void *object,
252 					const void *addr, u8 tag)
253 {
254 	struct kasan_alloc_meta *alloc_meta;
255 	struct kasan_track *free_track;
256 
257 	alloc_meta = kasan_get_alloc_meta(cache, object);
258 	if (alloc_meta) {
259 		print_track(&alloc_meta->alloc_track, "Allocated");
260 		pr_err("\n");
261 	}
262 
263 	free_track = kasan_get_free_track(cache, object, tag);
264 	if (free_track) {
265 		print_track(free_track, "Freed");
266 		pr_err("\n");
267 	}
268 
269 #ifdef CONFIG_KASAN_GENERIC
270 	if (!alloc_meta)
271 		return;
272 	if (alloc_meta->aux_stack[0]) {
273 		pr_err("Last potentially related work creation:\n");
274 		stack_depot_print(alloc_meta->aux_stack[0]);
275 		pr_err("\n");
276 	}
277 	if (alloc_meta->aux_stack[1]) {
278 		pr_err("Second to last potentially related work creation:\n");
279 		stack_depot_print(alloc_meta->aux_stack[1]);
280 		pr_err("\n");
281 	}
282 #endif
283 }
284 
describe_object(struct kmem_cache * cache,void * object,const void * addr,u8 tag)285 static void describe_object(struct kmem_cache *cache, void *object,
286 				const void *addr, u8 tag)
287 {
288 	if (kasan_stack_collection_enabled())
289 		describe_object_stacks(cache, object, addr, tag);
290 	describe_object_addr(cache, object, addr);
291 }
292 
kernel_or_module_addr(const void * addr)293 static inline bool kernel_or_module_addr(const void *addr)
294 {
295 	if (is_kernel((unsigned long)addr))
296 		return true;
297 	if (is_module_address((unsigned long)addr))
298 		return true;
299 	return false;
300 }
301 
init_task_stack_addr(const void * addr)302 static inline bool init_task_stack_addr(const void *addr)
303 {
304 	return addr >= (void *)&init_thread_union.stack &&
305 		(addr <= (void *)&init_thread_union.stack +
306 			sizeof(init_thread_union.stack));
307 }
308 
print_address_description(void * addr,u8 tag)309 static void print_address_description(void *addr, u8 tag)
310 {
311 	struct page *page = kasan_addr_to_page(addr);
312 
313 	dump_stack_lvl(KERN_ERR);
314 	pr_err("\n");
315 
316 	if (page && PageSlab(page)) {
317 		struct slab *slab = page_slab(page);
318 		struct kmem_cache *cache = slab->slab_cache;
319 		void *object = nearest_obj(cache, slab,	addr);
320 
321 		describe_object(cache, object, addr, tag);
322 		pr_err("\n");
323 	}
324 
325 	if (kernel_or_module_addr(addr) && !init_task_stack_addr(addr)) {
326 		pr_err("The buggy address belongs to the variable:\n");
327 		pr_err(" %pS\n", addr);
328 		pr_err("\n");
329 	}
330 
331 	if (object_is_on_stack(addr)) {
332 		/*
333 		 * Currently, KASAN supports printing frame information only
334 		 * for accesses to the task's own stack.
335 		 */
336 		kasan_print_address_stack_frame(addr);
337 		pr_err("\n");
338 	}
339 
340 	if (is_vmalloc_addr(addr)) {
341 		struct vm_struct *va = find_vm_area(addr);
342 
343 		if (va) {
344 			pr_err("The buggy address belongs to the virtual mapping at\n"
345 			       " [%px, %px) created by:\n"
346 			       " %pS\n",
347 			       va->addr, va->addr + va->size, va->caller);
348 			pr_err("\n");
349 
350 			page = vmalloc_to_page(addr);
351 		}
352 	}
353 
354 	if (page) {
355 		pr_err("The buggy address belongs to the physical page:\n");
356 		dump_page(page, "kasan: bad access detected");
357 		pr_err("\n");
358 	}
359 }
360 
meta_row_is_guilty(const void * row,const void * addr)361 static bool meta_row_is_guilty(const void *row, const void *addr)
362 {
363 	return (row <= addr) && (addr < row + META_MEM_BYTES_PER_ROW);
364 }
365 
meta_pointer_offset(const void * row,const void * addr)366 static int meta_pointer_offset(const void *row, const void *addr)
367 {
368 	/*
369 	 * Memory state around the buggy address:
370 	 *  ff00ff00ff00ff00: 00 00 00 05 fe fe fe fe fe fe fe fe fe fe fe fe
371 	 *  ...
372 	 *
373 	 * The length of ">ff00ff00ff00ff00: " is
374 	 *    3 + (BITS_PER_LONG / 8) * 2 chars.
375 	 * The length of each granule metadata is 2 bytes
376 	 *    plus 1 byte for space.
377 	 */
378 	return 3 + (BITS_PER_LONG / 8) * 2 +
379 		(addr - row) / KASAN_GRANULE_SIZE * 3 + 1;
380 }
381 
print_memory_metadata(const void * addr)382 static void print_memory_metadata(const void *addr)
383 {
384 	int i;
385 	void *row;
386 
387 	row = (void *)round_down((unsigned long)addr, META_MEM_BYTES_PER_ROW)
388 			- META_ROWS_AROUND_ADDR * META_MEM_BYTES_PER_ROW;
389 
390 	pr_err("Memory state around the buggy address:\n");
391 
392 	for (i = -META_ROWS_AROUND_ADDR; i <= META_ROWS_AROUND_ADDR; i++) {
393 		char buffer[4 + (BITS_PER_LONG / 8) * 2];
394 		char metadata[META_BYTES_PER_ROW];
395 
396 		snprintf(buffer, sizeof(buffer),
397 				(i == 0) ? ">%px: " : " %px: ", row);
398 
399 		/*
400 		 * We should not pass a shadow pointer to generic
401 		 * function, because generic functions may try to
402 		 * access kasan mapping for the passed address.
403 		 */
404 		kasan_metadata_fetch_row(&metadata[0], row);
405 
406 		print_hex_dump(KERN_ERR, buffer,
407 			DUMP_PREFIX_NONE, META_BYTES_PER_ROW, 1,
408 			metadata, META_BYTES_PER_ROW, 0);
409 
410 		if (meta_row_is_guilty(row, addr))
411 			pr_err("%*c\n", meta_pointer_offset(row, addr), '^');
412 
413 		row += META_MEM_BYTES_PER_ROW;
414 	}
415 }
416 
print_report(struct kasan_report_info * info)417 static void print_report(struct kasan_report_info *info)
418 {
419 	void *tagged_addr = info->access_addr;
420 	void *untagged_addr = kasan_reset_tag(tagged_addr);
421 	u8 tag = get_tag(tagged_addr);
422 
423 	print_error_description(info);
424 	if (addr_has_metadata(untagged_addr))
425 		kasan_print_tags(tag, info->first_bad_addr);
426 	pr_err("\n");
427 
428 	if (addr_has_metadata(untagged_addr)) {
429 		print_address_description(untagged_addr, tag);
430 		print_memory_metadata(info->first_bad_addr);
431 	} else {
432 		dump_stack_lvl(KERN_ERR);
433 	}
434 }
435 
kasan_report_invalid_free(void * ptr,unsigned long ip)436 void kasan_report_invalid_free(void *ptr, unsigned long ip)
437 {
438 	unsigned long flags;
439 	struct kasan_report_info info;
440 
441 	/*
442 	 * Do not check report_suppressed(), as an invalid-free cannot be
443 	 * caused by accessing slab metadata and thus should not be
444 	 * suppressed by kasan_disable/enable_current() critical sections.
445 	 */
446 	if (unlikely(!report_enabled()))
447 		return;
448 
449 	start_report(&flags, true);
450 
451 	info.type = KASAN_REPORT_INVALID_FREE;
452 	info.access_addr = ptr;
453 	info.first_bad_addr = kasan_reset_tag(ptr);
454 	info.access_size = 0;
455 	info.is_write = false;
456 	info.ip = ip;
457 
458 	print_report(&info);
459 
460 	end_report(&flags, ptr);
461 }
462 
463 /*
464  * kasan_report() is the only reporting function that uses
465  * user_access_save/restore(): kasan_report_invalid_free() cannot be called
466  * from a UACCESS region, and kasan_report_async() is not used on x86.
467  */
kasan_report(unsigned long addr,size_t size,bool is_write,unsigned long ip)468 bool kasan_report(unsigned long addr, size_t size, bool is_write,
469 			unsigned long ip)
470 {
471 	bool ret = true;
472 	void *ptr = (void *)addr;
473 	unsigned long ua_flags = user_access_save();
474 	unsigned long irq_flags;
475 	struct kasan_report_info info;
476 
477 	if (unlikely(report_suppressed()) || unlikely(!report_enabled())) {
478 		ret = false;
479 		goto out;
480 	}
481 
482 	start_report(&irq_flags, true);
483 
484 	info.type = KASAN_REPORT_ACCESS;
485 	info.access_addr = ptr;
486 	info.first_bad_addr = kasan_find_first_bad_addr(ptr, size);
487 	info.access_size = size;
488 	info.is_write = is_write;
489 	info.ip = ip;
490 
491 	print_report(&info);
492 
493 	end_report(&irq_flags, ptr);
494 
495 out:
496 	user_access_restore(ua_flags);
497 
498 	return ret;
499 }
500 
501 #ifdef CONFIG_KASAN_HW_TAGS
kasan_report_async(void)502 void kasan_report_async(void)
503 {
504 	unsigned long flags;
505 
506 	/*
507 	 * Do not check report_suppressed(), as kasan_disable/enable_current()
508 	 * critical sections do not affect Hardware Tag-Based KASAN.
509 	 */
510 	if (unlikely(!report_enabled()))
511 		return;
512 
513 	start_report(&flags, false);
514 	pr_err("BUG: KASAN: invalid-access\n");
515 	pr_err("Asynchronous fault: no details available\n");
516 	pr_err("\n");
517 	dump_stack_lvl(KERN_ERR);
518 	end_report(&flags, NULL);
519 }
520 #endif /* CONFIG_KASAN_HW_TAGS */
521 
522 #ifdef CONFIG_KASAN_INLINE
523 /*
524  * With CONFIG_KASAN_INLINE, accesses to bogus pointers (outside the high
525  * canonical half of the address space) cause out-of-bounds shadow memory reads
526  * before the actual access. For addresses in the low canonical half of the
527  * address space, as well as most non-canonical addresses, that out-of-bounds
528  * shadow memory access lands in the non-canonical part of the address space.
529  * Help the user figure out what the original bogus pointer was.
530  */
kasan_non_canonical_hook(unsigned long addr)531 void kasan_non_canonical_hook(unsigned long addr)
532 {
533 	unsigned long orig_addr;
534 	const char *bug_type;
535 
536 	if (addr < KASAN_SHADOW_OFFSET)
537 		return;
538 
539 	orig_addr = (addr - KASAN_SHADOW_OFFSET) << KASAN_SHADOW_SCALE_SHIFT;
540 	/*
541 	 * For faults near the shadow address for NULL, we can be fairly certain
542 	 * that this is a KASAN shadow memory access.
543 	 * For faults that correspond to shadow for low canonical addresses, we
544 	 * can still be pretty sure - that shadow region is a fairly narrow
545 	 * chunk of the non-canonical address space.
546 	 * But faults that look like shadow for non-canonical addresses are a
547 	 * really large chunk of the address space. In that case, we still
548 	 * print the decoded address, but make it clear that this is not
549 	 * necessarily what's actually going on.
550 	 */
551 	if (orig_addr < PAGE_SIZE)
552 		bug_type = "null-ptr-deref";
553 	else if (orig_addr < TASK_SIZE)
554 		bug_type = "probably user-memory-access";
555 	else
556 		bug_type = "maybe wild-memory-access";
557 	pr_alert("KASAN: %s in range [0x%016lx-0x%016lx]\n", bug_type,
558 		 orig_addr, orig_addr + KASAN_GRANULE_SIZE - 1);
559 }
560 #endif
561