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);