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 <andreyknvl@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         case KASAN_ALLOCA_LEFT:
 106         case KASAN_ALLOCA_RIGHT:
 107                 bug_type = "alloca-out-of-bounds";
 108                 break;
 109         }
 110
 111         return bug_type;
 112 }
 113
 114 static const char *get_wild_bug_type(struct kasan_access_info *info)
 115 {
 116         const char *bug_type = "unknown-crash";
 117
 118         if ((unsigned long)info->access_addr < PAGE_SIZE)
 119                 bug_type = "null-ptr-deref";
 120         else if ((unsigned long)info->access_addr < TASK_SIZE)
 121                 bug_type = "user-memory-access";
 122         else
 123                 bug_type = "wild-memory-access";
 124
 125         return bug_type;
 126 }
 127
 128 static const char *get_bug_type(struct kasan_access_info *info)
 129 {
 130         if (addr_has_shadow(info))
 131                 return get_shadow_bug_type(info);
 132         return get_wild_bug_type(info);
 133 }
 134
 135 static void print_error_description(struct kasan_access_info *info)
 136 {
 137         const char *bug_type = get_bug_type(info);
 138
 139         pr_err("BUG: KASAN: %s in %pS\n",
 140                 bug_type, (void *)info->ip);
 141         pr_err("%s of size %zu at addr %px by task %s/%d\n",
 142                 info->is_write ? "Write" : "Read", info->access_size,
 143                 info->access_addr, current->comm, task_pid_nr(current));
 144 }
 145
 146 static inline bool kernel_or_module_addr(const void *addr)
 147 {
 148         if (addr >= (void *)_stext && addr < (void *)_end)
 149                 return true;
 150         if (is_module_address((unsigned long)addr))
 151                 return true;
 152         return false;
 153 }
 154
 155 static inline bool init_task_stack_addr(const void *addr)
 156 {
 157         return addr >= (void *)&init_thread_union.stack &&
 158                 (addr <= (void *)&init_thread_union.stack +
 159                         sizeof(init_thread_union.stack));
 160 }
 161
 162 static DEFINE_SPINLOCK(report_lock);
 163
 164 static void kasan_start_report(unsigned long *flags)
 165 {
 166         /*
 167          * Make sure we don't end up in loop.
 168          */
 169         kasan_disable_current();
 170         spin_lock_irqsave(&report_lock, *flags);
 171         pr_err("==================================================================\n");
 172 }
 173
 174 static void kasan_end_report(unsigned long *flags)
 175 {
 176         pr_err("==================================================================\n");
 177         add_taint(TAINT_BAD_PAGE, LOCKDEP_NOW_UNRELIABLE);
 178         spin_unlock_irqrestore(&report_lock, *flags);
 179         check_panic_on_warn("KASAN");
 180         kasan_enable_current();
 181 }
 182
 183 static void print_track(struct kasan_track *track, const char *prefix)
 184 {
 185         pr_err("%s by task %u:\n", prefix, track->pid);
 186         if (track->stack) {
 187                 struct stack_trace trace;
 188
 189                 depot_fetch_stack(track->stack, &trace);
 190                 print_stack_trace(&trace, 0);
 191         } else {
 192                 pr_err("(stack is not available)\n");
 193         }
 194 }
 195
 196 static struct page *addr_to_page(const void *addr)
 197 {
 198         if ((addr >= (void *)PAGE_OFFSET) &&
 199                         (addr < high_memory))
 200                 return virt_to_head_page(addr);
 201         return NULL;
 202 }
 203
 204 static void describe_object_addr(struct kmem_cache *cache, void *object,
 205                                 const void *addr)
 206 {
 207         unsigned long access_addr = (unsigned long)addr;
 208         unsigned long object_addr = (unsigned long)object;
 209         const char *rel_type;
 210         int rel_bytes;
 211
 212         pr_err("The buggy address belongs to the object at %px\n"
 213                " which belongs to the cache %s of size %d\n",
 214                 object, cache->name, cache->object_size);
 215
 216         if (!addr)
 217                 return;
 218
 219         if (access_addr < object_addr) {
 220                 rel_type = "to the left";
 221                 rel_bytes = object_addr - access_addr;
 222         } else if (access_addr >= object_addr + cache->object_size) {
 223                 rel_type = "to the right";
 224                 rel_bytes = access_addr - (object_addr + cache->object_size);
 225         } else {
 226                 rel_type = "inside";
 227                 rel_bytes = access_addr - object_addr;
 228         }
 229
 230         pr_err("The buggy address is located %d bytes %s of\n"
 231                " %d-byte region [%px, %px)\n",
 232                 rel_bytes, rel_type, cache->object_size, (void *)object_addr,
 233                 (void *)(object_addr + cache->object_size));
 234 }
 235
 236 static void describe_object(struct kmem_cache *cache, void *object,
 237                                 const void *addr)
 238 {
 239         struct kasan_alloc_meta *alloc_info = get_alloc_info(cache, object);
 240
 241         if (cache->flags & SLAB_KASAN) {
 242                 print_track(&alloc_info->alloc_track, "Allocated");
 243                 pr_err("\n");
 244                 print_track(&alloc_info->free_track, "Freed");
 245                 pr_err("\n");
 246         }
 247
 248         describe_object_addr(cache, object, addr);
 249 }
 250
 251 static void print_address_description(void *addr)
 252 {
 253         struct page *page = addr_to_page(addr);
 254
 255         dump_stack();
 256         pr_err("\n");
 257
 258         if (page && PageSlab(page)) {
 259                 struct kmem_cache *cache = page->slab_cache;
 260                 void *object = nearest_obj(cache, page, addr);
 261
 262                 describe_object(cache, object, addr);
 263         }
 264
 265         if (kernel_or_module_addr(addr) && !init_task_stack_addr(addr)) {
 266                 pr_err("The buggy address belongs to the variable:\n");
 267                 pr_err(" %pS\n", addr);
 268         }
 269
 270         if (page) {
 271                 pr_err("The buggy address belongs to the page:\n");
 272                 dump_page(page, "kasan: bad access detected");
 273         }
 274 }
 275
 276 static bool row_is_guilty(const void *row, const void *guilty)
 277 {
 278         return (row <= guilty) && (guilty < row + SHADOW_BYTES_PER_ROW);
 279 }
 280
 281 static int shadow_pointer_offset(const void *row, const void *shadow)
 282 {
 283         /* The length of ">ff00ff00ff00ff00: " is
 284          *    3 + (BITS_PER_LONG/8)*2 chars.
 285          */
 286         return 3 + (BITS_PER_LONG/8)*2 + (shadow - row)*2 +
 287                 (shadow - row) / SHADOW_BYTES_PER_BLOCK + 1;
 288 }
 289
 290 static void print_shadow_for_address(const void *addr)
 291 {
 292         int i;
 293         const void *shadow = kasan_mem_to_shadow(addr);
 294         const void *shadow_row;
 295
 296         shadow_row = (void *)round_down((unsigned long)shadow,
 297                                         SHADOW_BYTES_PER_ROW)
 298                 - SHADOW_ROWS_AROUND_ADDR * SHADOW_BYTES_PER_ROW;
 299
 300         pr_err("Memory state around the buggy address:\n");
 301
 302         for (i = -SHADOW_ROWS_AROUND_ADDR; i <= SHADOW_ROWS_AROUND_ADDR; i++) {
 303                 const void *kaddr = kasan_shadow_to_mem(shadow_row);
 304                 char buffer[4 + (BITS_PER_LONG/8)*2];
 305                 char shadow_buf[SHADOW_BYTES_PER_ROW];
 306
 307                 snprintf(buffer, sizeof(buffer),
 308                         (i == 0) ? ">%px: " : " %px: ", kaddr);
 309                 /*
 310                  * We should not pass a shadow pointer to generic
 311                  * function, because generic functions may try to
 312                  * access kasan mapping for the passed address.
 313                  */
 314                 memcpy(shadow_buf, shadow_row, SHADOW_BYTES_PER_ROW);
 315                 print_hex_dump(KERN_ERR, buffer,
 316                         DUMP_PREFIX_NONE, SHADOW_BYTES_PER_ROW, 1,
 317                         shadow_buf, SHADOW_BYTES_PER_ROW, 0);
 318
 319                 if (row_is_guilty(shadow_row, shadow))
 320                         pr_err("%*c\n",
 321                                 shadow_pointer_offset(shadow_row, shadow),
 322                                 '^');
 323
 324                 shadow_row += SHADOW_BYTES_PER_ROW;
 325         }
 326 }
 327
 328 void kasan_report_invalid_free(void *object, unsigned long ip)
 329 {
 330         unsigned long flags;
 331
 332         kasan_start_report(&flags);
 333         pr_err("BUG: KASAN: double-free or invalid-free in %pS\n", (void *)ip);
 334         pr_err("\n");
 335         print_address_description(object);
 336         pr_err("\n");
 337         print_shadow_for_address(object);
 338         kasan_end_report(&flags);
 339 }
 340
 341 static void kasan_report_error(struct kasan_access_info *info)
 342 {
 343         unsigned long flags;
 344
 345         kasan_start_report(&flags);
 346
 347         print_error_description(info);
 348         pr_err("\n");
 349
 350         if (!addr_has_shadow(info)) {
 351                 dump_stack();
 352         } else {
 353                 print_address_description((void *)info->access_addr);
 354                 pr_err("\n");
 355                 print_shadow_for_address(info->first_bad_addr);
 356         }
 357
 358         kasan_end_report(&flags);
 359 }
 360
 361 static unsigned long kasan_flags;
 362
 363 #define KASAN_BIT_REPORTED      0
 364 #define KASAN_BIT_MULTI_SHOT    1
 365
 366 bool kasan_save_enable_multi_shot(void)
 367 {
 368         return test_and_set_bit(KASAN_BIT_MULTI_SHOT, &kasan_flags);
 369 }
 370 EXPORT_SYMBOL_GPL(kasan_save_enable_multi_shot);
 371
 372 void kasan_restore_multi_shot(bool enabled)
 373 {
 374         if (!enabled)
 375                 clear_bit(KASAN_BIT_MULTI_SHOT, &kasan_flags);
 376 }
 377 EXPORT_SYMBOL_GPL(kasan_restore_multi_shot);
 378
 379 static int __init kasan_set_multi_shot(char *str)
 380 {
 381         set_bit(KASAN_BIT_MULTI_SHOT, &kasan_flags);
 382         return 1;
 383 }
 384 __setup("kasan_multi_shot", kasan_set_multi_shot);
 385
 386 static inline bool kasan_report_enabled(void)
 387 {
 388         if (current->kasan_depth)
 389                 return false;
 390         if (test_bit(KASAN_BIT_MULTI_SHOT, &kasan_flags))
 391                 return true;
 392         return !test_and_set_bit(KASAN_BIT_REPORTED, &kasan_flags);
 393 }
 394
 395 void kasan_report(unsigned long addr, size_t size,
 396                 bool is_write, unsigned long ip)
 397 {
 398         struct kasan_access_info info;
 399
 400         if (likely(!kasan_report_enabled()))
 401                 return;
 402
 403         disable_trace_on_warning();
 404
 405         info.access_addr = (void *)addr;
 406         info.first_bad_addr = (void *)addr;
 407         info.access_size = size;
 408         info.is_write = is_write;
 409         info.ip = ip;
 410
 411         kasan_report_error(&info);
 412 }
 413
 414
 415 #define DEFINE_ASAN_REPORT_LOAD(size)                     \
 416 void __asan_report_load##size##_noabort(unsigned long addr) \
 417 {                                                         \
 418         kasan_report(addr, size, false, _RET_IP_);        \
 419 }                                                         \
 420 EXPORT_SYMBOL(__asan_report_load##size##_noabort)
 421
 422 #define DEFINE_ASAN_REPORT_STORE(size)                     \
 423 void __asan_report_store##size##_noabort(unsigned long addr) \
 424 {                                                          \
 425         kasan_report(addr, size, true, _RET_IP_);          \
 426 }                                                          \
 427 EXPORT_SYMBOL(__asan_report_store##size##_noabort)
 428
 429 DEFINE_ASAN_REPORT_LOAD(1);
 430 DEFINE_ASAN_REPORT_LOAD(2);
 431 DEFINE_ASAN_REPORT_LOAD(4);
 432 DEFINE_ASAN_REPORT_LOAD(8);
 433 DEFINE_ASAN_REPORT_LOAD(16);
 434 DEFINE_ASAN_REPORT_STORE(1);
 435 DEFINE_ASAN_REPORT_STORE(2);
 436 DEFINE_ASAN_REPORT_STORE(4);
 437 DEFINE_ASAN_REPORT_STORE(8);
 438 DEFINE_ASAN_REPORT_STORE(16);
 439
 440 void __asan_report_load_n_noabort(unsigned long addr, size_t size)
 441 {
 442         kasan_report(addr, size, false, _RET_IP_);
 443 }
 444 EXPORT_SYMBOL(__asan_report_load_n_noabort);
 445
 446 void __asan_report_store_n_noabort(unsigned long addr, size_t size)
 447 {
 448         kasan_report(addr, size, true, _RET_IP_);
 449 }
 450 EXPORT_SYMBOL(__asan_report_store_n_noabort);