kasan: avoid -Wmaybe-uninitialized warning
[sfrench/cifs-2.6.git] / mm / kasan / report.c
1 /*
2  * This file contains error reporting code.
3  *
4  * Copyright (c) 2014 Samsung Electronics Co., Ltd.
5  * Author: Andrey Ryabinin <ryabinin.a.a@gmail.com>
6  *
7  * Some code borrowed from https://github.com/xairy/kasan-prototype by
8  *        Andrey Konovalov <adech.fo@gmail.com>
9  *
10  * This program is free software; you can redistribute it and/or modify
11  * it under the terms of the GNU General Public License version 2 as
12  * published by the Free Software Foundation.
13  *
14  */
15
16 #include <linux/bitops.h>
17 #include <linux/ftrace.h>
18 #include <linux/init.h>
19 #include <linux/kernel.h>
20 #include <linux/mm.h>
21 #include <linux/printk.h>
22 #include <linux/sched.h>
23 #include <linux/slab.h>
24 #include <linux/stackdepot.h>
25 #include <linux/stacktrace.h>
26 #include <linux/string.h>
27 #include <linux/types.h>
28 #include <linux/kasan.h>
29 #include <linux/module.h>
30
31 #include <asm/sections.h>
32
33 #include "kasan.h"
34 #include "../slab.h"
35
36 /* Shadow layout customization. */
37 #define SHADOW_BYTES_PER_BLOCK 1
38 #define SHADOW_BLOCKS_PER_ROW 16
39 #define SHADOW_BYTES_PER_ROW (SHADOW_BLOCKS_PER_ROW * SHADOW_BYTES_PER_BLOCK)
40 #define SHADOW_ROWS_AROUND_ADDR 2
41
42 static const void *find_first_bad_addr(const void *addr, size_t size)
43 {
44         u8 shadow_val = *(u8 *)kasan_mem_to_shadow(addr);
45         const void *first_bad_addr = addr;
46
47         while (!shadow_val && first_bad_addr < addr + size) {
48                 first_bad_addr += KASAN_SHADOW_SCALE_SIZE;
49                 shadow_val = *(u8 *)kasan_mem_to_shadow(first_bad_addr);
50         }
51         return first_bad_addr;
52 }
53
54 static bool addr_has_shadow(struct kasan_access_info *info)
55 {
56         return (info->access_addr >=
57                 kasan_shadow_to_mem((void *)KASAN_SHADOW_START));
58 }
59
60 static const char *get_shadow_bug_type(struct kasan_access_info *info)
61 {
62         const char *bug_type = "unknown-crash";
63         u8 *shadow_addr;
64
65         info->first_bad_addr = find_first_bad_addr(info->access_addr,
66                                                 info->access_size);
67
68         shadow_addr = (u8 *)kasan_mem_to_shadow(info->first_bad_addr);
69
70         /*
71          * If shadow byte value is in [0, KASAN_SHADOW_SCALE_SIZE) we can look
72          * at the next shadow byte to determine the type of the bad access.
73          */
74         if (*shadow_addr > 0 && *shadow_addr <= KASAN_SHADOW_SCALE_SIZE - 1)
75                 shadow_addr++;
76
77         switch (*shadow_addr) {
78         case 0 ... KASAN_SHADOW_SCALE_SIZE - 1:
79                 /*
80                  * In theory it's still possible to see these shadow values
81                  * due to a data race in the kernel code.
82                  */
83                 bug_type = "out-of-bounds";
84                 break;
85         case KASAN_PAGE_REDZONE:
86         case KASAN_KMALLOC_REDZONE:
87                 bug_type = "slab-out-of-bounds";
88                 break;
89         case KASAN_GLOBAL_REDZONE:
90                 bug_type = "global-out-of-bounds";
91                 break;
92         case KASAN_STACK_LEFT:
93         case KASAN_STACK_MID:
94         case KASAN_STACK_RIGHT:
95         case KASAN_STACK_PARTIAL:
96                 bug_type = "stack-out-of-bounds";
97                 break;
98         case KASAN_FREE_PAGE:
99         case KASAN_KMALLOC_FREE:
100                 bug_type = "use-after-free";
101                 break;
102         case KASAN_USE_AFTER_SCOPE:
103                 bug_type = "use-after-scope";
104                 break;
105         }
106
107         return bug_type;
108 }
109
110 static const char *get_wild_bug_type(struct kasan_access_info *info)
111 {
112         const char *bug_type = "unknown-crash";
113
114         if ((unsigned long)info->access_addr < PAGE_SIZE)
115                 bug_type = "null-ptr-deref";
116         else if ((unsigned long)info->access_addr < TASK_SIZE)
117                 bug_type = "user-memory-access";
118         else
119                 bug_type = "wild-memory-access";
120
121         return bug_type;
122 }
123
124 static const char *get_bug_type(struct kasan_access_info *info)
125 {
126         if (addr_has_shadow(info))
127                 return get_shadow_bug_type(info);
128         return get_wild_bug_type(info);
129 }
130
131 static void print_error_description(struct kasan_access_info *info)
132 {
133         const char *bug_type = get_bug_type(info);
134
135         pr_err("BUG: KASAN: %s in %pS\n",
136                 bug_type, (void *)info->ip);
137         pr_err("%s of size %zu at addr %p by task %s/%d\n",
138                 info->is_write ? "Write" : "Read", info->access_size,
139                 info->access_addr, current->comm, task_pid_nr(current));
140 }
141
142 static inline bool kernel_or_module_addr(const void *addr)
143 {
144         if (addr >= (void *)_stext && addr < (void *)_end)
145                 return true;
146         if (is_module_address((unsigned long)addr))
147                 return true;
148         return false;
149 }
150
151 static inline bool init_task_stack_addr(const void *addr)
152 {
153         return addr >= (void *)&init_thread_union.stack &&
154                 (addr <= (void *)&init_thread_union.stack +
155                         sizeof(init_thread_union.stack));
156 }
157
158 static DEFINE_SPINLOCK(report_lock);
159
160 static void kasan_start_report(unsigned long *flags)
161 {
162         /*
163          * Make sure we don't end up in loop.
164          */
165         kasan_disable_current();
166         spin_lock_irqsave(&report_lock, *flags);
167         pr_err("==================================================================\n");
168 }
169
170 static void kasan_end_report(unsigned long *flags)
171 {
172         pr_err("==================================================================\n");
173         add_taint(TAINT_BAD_PAGE, LOCKDEP_NOW_UNRELIABLE);
174         spin_unlock_irqrestore(&report_lock, *flags);
175         if (panic_on_warn)
176                 panic("panic_on_warn set ...\n");
177         kasan_enable_current();
178 }
179
180 static void print_track(struct kasan_track *track, const char *prefix)
181 {
182         pr_err("%s by task %u:\n", prefix, track->pid);
183         if (track->stack) {
184                 struct stack_trace trace;
185
186                 depot_fetch_stack(track->stack, &trace);
187                 print_stack_trace(&trace, 0);
188         } else {
189                 pr_err("(stack is not available)\n");
190         }
191 }
192
193 static struct page *addr_to_page(const void *addr)
194 {
195         if ((addr >= (void *)PAGE_OFFSET) &&
196                         (addr < high_memory))
197                 return virt_to_head_page(addr);
198         return NULL;
199 }
200
201 static void describe_object_addr(struct kmem_cache *cache, void *object,
202                                 const void *addr)
203 {
204         unsigned long access_addr = (unsigned long)addr;
205         unsigned long object_addr = (unsigned long)object;
206         const char *rel_type;
207         int rel_bytes;
208
209         pr_err("The buggy address belongs to the object at %p\n"
210                " which belongs to the cache %s of size %d\n",
211                 object, cache->name, cache->object_size);
212
213         if (!addr)
214                 return;
215
216         if (access_addr < object_addr) {
217                 rel_type = "to the left";
218                 rel_bytes = object_addr - access_addr;
219         } else if (access_addr >= object_addr + cache->object_size) {
220                 rel_type = "to the right";
221                 rel_bytes = access_addr - (object_addr + cache->object_size);
222         } else {
223                 rel_type = "inside";
224                 rel_bytes = access_addr - object_addr;
225         }
226
227         pr_err("The buggy address is located %d bytes %s of\n"
228                " %d-byte region [%p, %p)\n",
229                 rel_bytes, rel_type, cache->object_size, (void *)object_addr,
230                 (void *)(object_addr + cache->object_size));
231 }
232
233 static void describe_object(struct kmem_cache *cache, void *object,
234                                 const void *addr)
235 {
236         struct kasan_alloc_meta *alloc_info = get_alloc_info(cache, object);
237
238         if (cache->flags & SLAB_KASAN) {
239                 print_track(&alloc_info->alloc_track, "Allocated");
240                 pr_err("\n");
241                 print_track(&alloc_info->free_track, "Freed");
242                 pr_err("\n");
243         }
244
245         describe_object_addr(cache, object, addr);
246 }
247
248 static void print_address_description(void *addr)
249 {
250         struct page *page = addr_to_page(addr);
251
252         dump_stack();
253         pr_err("\n");
254
255         if (page && PageSlab(page)) {
256                 struct kmem_cache *cache = page->slab_cache;
257                 void *object = nearest_obj(cache, page, addr);
258
259                 describe_object(cache, object, addr);
260         }
261
262         if (kernel_or_module_addr(addr) && !init_task_stack_addr(addr)) {
263                 pr_err("The buggy address belongs to the variable:\n");
264                 pr_err(" %pS\n", addr);
265         }
266
267         if (page) {
268                 pr_err("The buggy address belongs to the page:\n");
269                 dump_page(page, "kasan: bad access detected");
270         }
271 }
272
273 static bool row_is_guilty(const void *row, const void *guilty)
274 {
275         return (row <= guilty) && (guilty < row + SHADOW_BYTES_PER_ROW);
276 }
277
278 static int shadow_pointer_offset(const void *row, const void *shadow)
279 {
280         /* The length of ">ff00ff00ff00ff00: " is
281          *    3 + (BITS_PER_LONG/8)*2 chars.
282          */
283         return 3 + (BITS_PER_LONG/8)*2 + (shadow - row)*2 +
284                 (shadow - row) / SHADOW_BYTES_PER_BLOCK + 1;
285 }
286
287 static void print_shadow_for_address(const void *addr)
288 {
289         int i;
290         const void *shadow = kasan_mem_to_shadow(addr);
291         const void *shadow_row;
292
293         shadow_row = (void *)round_down((unsigned long)shadow,
294                                         SHADOW_BYTES_PER_ROW)
295                 - SHADOW_ROWS_AROUND_ADDR * SHADOW_BYTES_PER_ROW;
296
297         pr_err("Memory state around the buggy address:\n");
298
299         for (i = -SHADOW_ROWS_AROUND_ADDR; i <= SHADOW_ROWS_AROUND_ADDR; i++) {
300                 const void *kaddr = kasan_shadow_to_mem(shadow_row);
301                 char buffer[4 + (BITS_PER_LONG/8)*2];
302                 char shadow_buf[SHADOW_BYTES_PER_ROW];
303
304                 snprintf(buffer, sizeof(buffer),
305                         (i == 0) ? ">%p: " : " %p: ", kaddr);
306                 /*
307                  * We should not pass a shadow pointer to generic
308                  * function, because generic functions may try to
309                  * access kasan mapping for the passed address.
310                  */
311                 memcpy(shadow_buf, shadow_row, SHADOW_BYTES_PER_ROW);
312                 print_hex_dump(KERN_ERR, buffer,
313                         DUMP_PREFIX_NONE, SHADOW_BYTES_PER_ROW, 1,
314                         shadow_buf, SHADOW_BYTES_PER_ROW, 0);
315
316                 if (row_is_guilty(shadow_row, shadow))
317                         pr_err("%*c\n",
318                                 shadow_pointer_offset(shadow_row, shadow),
319                                 '^');
320
321                 shadow_row += SHADOW_BYTES_PER_ROW;
322         }
323 }
324
325 void kasan_report_double_free(struct kmem_cache *cache, void *object,
326                                 void *ip)
327 {
328         unsigned long flags;
329
330         kasan_start_report(&flags);
331         pr_err("BUG: KASAN: double-free or invalid-free in %pS\n", ip);
332         pr_err("\n");
333         print_address_description(object);
334         pr_err("\n");
335         print_shadow_for_address(object);
336         kasan_end_report(&flags);
337 }
338
339 static void kasan_report_error(struct kasan_access_info *info)
340 {
341         unsigned long flags;
342
343         kasan_start_report(&flags);
344
345         print_error_description(info);
346         pr_err("\n");
347
348         if (!addr_has_shadow(info)) {
349                 dump_stack();
350         } else {
351                 print_address_description((void *)info->access_addr);
352                 pr_err("\n");
353                 print_shadow_for_address(info->first_bad_addr);
354         }
355
356         kasan_end_report(&flags);
357 }
358
359 static unsigned long kasan_flags;
360
361 #define KASAN_BIT_REPORTED      0
362 #define KASAN_BIT_MULTI_SHOT    1
363
364 bool kasan_save_enable_multi_shot(void)
365 {
366         return test_and_set_bit(KASAN_BIT_MULTI_SHOT, &kasan_flags);
367 }
368 EXPORT_SYMBOL_GPL(kasan_save_enable_multi_shot);
369
370 void kasan_restore_multi_shot(bool enabled)
371 {
372         if (!enabled)
373                 clear_bit(KASAN_BIT_MULTI_SHOT, &kasan_flags);
374 }
375 EXPORT_SYMBOL_GPL(kasan_restore_multi_shot);
376
377 static int __init kasan_set_multi_shot(char *str)
378 {
379         set_bit(KASAN_BIT_MULTI_SHOT, &kasan_flags);
380         return 1;
381 }
382 __setup("kasan_multi_shot", kasan_set_multi_shot);
383
384 static inline bool kasan_report_enabled(void)
385 {
386         if (current->kasan_depth)
387                 return false;
388         if (test_bit(KASAN_BIT_MULTI_SHOT, &kasan_flags))
389                 return true;
390         return !test_and_set_bit(KASAN_BIT_REPORTED, &kasan_flags);
391 }
392
393 void kasan_report(unsigned long addr, size_t size,
394                 bool is_write, unsigned long ip)
395 {
396         struct kasan_access_info info;
397
398         if (likely(!kasan_report_enabled()))
399                 return;
400
401         disable_trace_on_warning();
402
403         info.access_addr = (void *)addr;
404         info.first_bad_addr = (void *)addr;
405         info.access_size = size;
406         info.is_write = is_write;
407         info.ip = ip;
408
409         kasan_report_error(&info);
410 }
411
412
413 #define DEFINE_ASAN_REPORT_LOAD(size)                     \
414 void __asan_report_load##size##_noabort(unsigned long addr) \
415 {                                                         \
416         kasan_report(addr, size, false, _RET_IP_);        \
417 }                                                         \
418 EXPORT_SYMBOL(__asan_report_load##size##_noabort)
419
420 #define DEFINE_ASAN_REPORT_STORE(size)                     \
421 void __asan_report_store##size##_noabort(unsigned long addr) \
422 {                                                          \
423         kasan_report(addr, size, true, _RET_IP_);          \
424 }                                                          \
425 EXPORT_SYMBOL(__asan_report_store##size##_noabort)
426
427 DEFINE_ASAN_REPORT_LOAD(1);
428 DEFINE_ASAN_REPORT_LOAD(2);
429 DEFINE_ASAN_REPORT_LOAD(4);
430 DEFINE_ASAN_REPORT_LOAD(8);
431 DEFINE_ASAN_REPORT_LOAD(16);
432 DEFINE_ASAN_REPORT_STORE(1);
433 DEFINE_ASAN_REPORT_STORE(2);
434 DEFINE_ASAN_REPORT_STORE(4);
435 DEFINE_ASAN_REPORT_STORE(8);
436 DEFINE_ASAN_REPORT_STORE(16);
437
438 void __asan_report_load_n_noabort(unsigned long addr, size_t size)
439 {
440         kasan_report(addr, size, false, _RET_IP_);
441 }
442 EXPORT_SYMBOL(__asan_report_load_n_noabort);
443
444 void __asan_report_store_n_noabort(unsigned long addr, size_t size)
445 {
446         kasan_report(addr, size, true, _RET_IP_);
447 }
448 EXPORT_SYMBOL(__asan_report_store_n_noabort);