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/kernel.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
  28 #include <asm/sections.h>
  29
  30 #include "kasan.h"
  31 #include "../slab.h"
  32
  33 /* Shadow layout customization. */
  34 #define SHADOW_BYTES_PER_BLOCK 1
  35 #define SHADOW_BLOCKS_PER_ROW 16
  36 #define SHADOW_BYTES_PER_ROW (SHADOW_BLOCKS_PER_ROW * SHADOW_BYTES_PER_BLOCK)
  37 #define SHADOW_ROWS_AROUND_ADDR 2
  38
  39 static const void *find_first_bad_addr(const void *addr, size_t size)
  40 {
  41         u8 shadow_val = *(u8 *)kasan_mem_to_shadow(addr);
  42         const void *first_bad_addr = addr;
  43
  44         while (!shadow_val && first_bad_addr < addr + size) {
  45                 first_bad_addr += KASAN_SHADOW_SCALE_SIZE;
  46                 shadow_val = *(u8 *)kasan_mem_to_shadow(first_bad_addr);
  47         }
  48         return first_bad_addr;
  49 }
  50
  51 static void print_error_description(struct kasan_access_info *info)
  52 {
  53         const char *bug_type = "unknown-crash";
  54         u8 *shadow_addr;
  55
  56         info->first_bad_addr = find_first_bad_addr(info->access_addr,
  57                                                 info->access_size);
  58
  59         shadow_addr = (u8 *)kasan_mem_to_shadow(info->first_bad_addr);
  60
  61         /*
  62          * If shadow byte value is in [0, KASAN_SHADOW_SCALE_SIZE) we can look
  63          * at the next shadow byte to determine the type of the bad access.
  64          */
  65         if (*shadow_addr > 0 && *shadow_addr <= KASAN_SHADOW_SCALE_SIZE - 1)
  66                 shadow_addr++;
  67
  68         switch (*shadow_addr) {
  69         case 0 ... KASAN_SHADOW_SCALE_SIZE - 1:
  70                 /*
  71                  * In theory it's still possible to see these shadow values
  72                  * due to a data race in the kernel code.
  73                  */
  74                 bug_type = "out-of-bounds";
  75                 break;
  76         case KASAN_PAGE_REDZONE:
  77         case KASAN_KMALLOC_REDZONE:
  78                 bug_type = "slab-out-of-bounds";
  79                 break;
  80         case KASAN_GLOBAL_REDZONE:
  81                 bug_type = "global-out-of-bounds";
  82                 break;
  83         case KASAN_STACK_LEFT:
  84         case KASAN_STACK_MID:
  85         case KASAN_STACK_RIGHT:
  86         case KASAN_STACK_PARTIAL:
  87                 bug_type = "stack-out-of-bounds";
  88                 break;
  89         case KASAN_FREE_PAGE:
  90         case KASAN_KMALLOC_FREE:
  91                 bug_type = "use-after-free";
  92                 break;
  93         }
  94
  95         pr_err("BUG: KASAN: %s in %pS at addr %p\n",
  96                 bug_type, (void *)info->ip,
  97                 info->access_addr);
  98         pr_err("%s of size %zu by task %s/%d\n",
  99                 info->is_write ? "Write" : "Read",
 100                 info->access_size, current->comm, task_pid_nr(current));
 101 }
 102
 103 static inline bool kernel_or_module_addr(const void *addr)
 104 {
 105         if (addr >= (void *)_stext && addr < (void *)_end)
 106                 return true;
 107         if (is_module_address((unsigned long)addr))
 108                 return true;
 109         return false;
 110 }
 111
 112 static inline bool init_task_stack_addr(const void *addr)
 113 {
 114         return addr >= (void *)&init_thread_union.stack &&
 115                 (addr <= (void *)&init_thread_union.stack +
 116                         sizeof(init_thread_union.stack));
 117 }
 118
 119 static DEFINE_SPINLOCK(report_lock);
 120
 121 static void kasan_start_report(unsigned long *flags)
 122 {
 123         /*
 124          * Make sure we don't end up in loop.
 125          */
 126         kasan_disable_current();
 127         spin_lock_irqsave(&report_lock, *flags);
 128         pr_err("==================================================================\n");
 129 }
 130
 131 static void kasan_end_report(unsigned long *flags)
 132 {
 133         pr_err("==================================================================\n");
 134         add_taint(TAINT_BAD_PAGE, LOCKDEP_NOW_UNRELIABLE);
 135         spin_unlock_irqrestore(&report_lock, *flags);
 136         kasan_enable_current();
 137 }
 138
 139 static void print_track(struct kasan_track *track)
 140 {
 141         pr_err("PID = %u\n", track->pid);
 142         if (track->stack) {
 143                 struct stack_trace trace;
 144
 145                 depot_fetch_stack(track->stack, &trace);
 146                 print_stack_trace(&trace, 0);
 147         } else {
 148                 pr_err("(stack is not available)\n");
 149         }
 150 }
 151
 152 static void kasan_object_err(struct kmem_cache *cache, void *object)
 153 {
 154         struct kasan_alloc_meta *alloc_info = get_alloc_info(cache, object);
 155
 156         dump_stack();
 157         pr_err("Object at %p, in cache %s size: %d\n", object, cache->name,
 158                 cache->object_size);
 159
 160         if (!(cache->flags & SLAB_KASAN))
 161                 return;
 162
 163         pr_err("Allocated:\n");
 164         print_track(&alloc_info->alloc_track);
 165         pr_err("Freed:\n");
 166         print_track(&alloc_info->free_track);
 167 }
 168
 169 void kasan_report_double_free(struct kmem_cache *cache, void *object,
 170                         s8 shadow)
 171 {
 172         unsigned long flags;
 173
 174         kasan_start_report(&flags);
 175         pr_err("BUG: Double free or freeing an invalid pointer\n");
 176         pr_err("Unexpected shadow byte: 0x%hhX\n", shadow);
 177         kasan_object_err(cache, object);
 178         kasan_end_report(&flags);
 179 }
 180
 181 static void print_address_description(struct kasan_access_info *info)
 182 {
 183         const void *addr = info->access_addr;
 184
 185         if ((addr >= (void *)PAGE_OFFSET) &&
 186                 (addr < high_memory)) {
 187                 struct page *page = virt_to_head_page(addr);
 188
 189                 if (PageSlab(page)) {
 190                         void *object;
 191                         struct kmem_cache *cache = page->slab_cache;
 192                         object = nearest_obj(cache, page,
 193                                                 (void *)info->access_addr);
 194                         kasan_object_err(cache, object);
 195                         return;
 196                 }
 197                 dump_page(page, "kasan: bad access detected");
 198         }
 199
 200         if (kernel_or_module_addr(addr)) {
 201                 if (!init_task_stack_addr(addr))
 202                         pr_err("Address belongs to variable %pS\n", addr);
 203         }
 204         dump_stack();
 205 }
 206
 207 static bool row_is_guilty(const void *row, const void *guilty)
 208 {
 209         return (row <= guilty) && (guilty < row + SHADOW_BYTES_PER_ROW);
 210 }
 211
 212 static int shadow_pointer_offset(const void *row, const void *shadow)
 213 {
 214         /* The length of ">ff00ff00ff00ff00: " is
 215          *    3 + (BITS_PER_LONG/8)*2 chars.
 216          */
 217         return 3 + (BITS_PER_LONG/8)*2 + (shadow - row)*2 +
 218                 (shadow - row) / SHADOW_BYTES_PER_BLOCK + 1;
 219 }
 220
 221 static void print_shadow_for_address(const void *addr)
 222 {
 223         int i;
 224         const void *shadow = kasan_mem_to_shadow(addr);
 225         const void *shadow_row;
 226
 227         shadow_row = (void *)round_down((unsigned long)shadow,
 228                                         SHADOW_BYTES_PER_ROW)
 229                 - SHADOW_ROWS_AROUND_ADDR * SHADOW_BYTES_PER_ROW;
 230
 231         pr_err("Memory state around the buggy address:\n");
 232
 233         for (i = -SHADOW_ROWS_AROUND_ADDR; i <= SHADOW_ROWS_AROUND_ADDR; i++) {
 234                 const void *kaddr = kasan_shadow_to_mem(shadow_row);
 235                 char buffer[4 + (BITS_PER_LONG/8)*2];
 236                 char shadow_buf[SHADOW_BYTES_PER_ROW];
 237
 238                 snprintf(buffer, sizeof(buffer),
 239                         (i == 0) ? ">%p: " : " %p: ", kaddr);
 240                 /*
 241                  * We should not pass a shadow pointer to generic
 242                  * function, because generic functions may try to
 243                  * access kasan mapping for the passed address.
 244                  */
 245                 memcpy(shadow_buf, shadow_row, SHADOW_BYTES_PER_ROW);
 246                 print_hex_dump(KERN_ERR, buffer,
 247                         DUMP_PREFIX_NONE, SHADOW_BYTES_PER_ROW, 1,
 248                         shadow_buf, SHADOW_BYTES_PER_ROW, 0);
 249
 250                 if (row_is_guilty(shadow_row, shadow))
 251                         pr_err("%*c\n",
 252                                 shadow_pointer_offset(shadow_row, shadow),
 253                                 '^');
 254
 255                 shadow_row += SHADOW_BYTES_PER_ROW;
 256         }
 257 }
 258
 259 static void kasan_report_error(struct kasan_access_info *info)
 260 {
 261         unsigned long flags;
 262         const char *bug_type;
 263
 264         kasan_start_report(&flags);
 265
 266         if (info->access_addr <
 267                         kasan_shadow_to_mem((void *)KASAN_SHADOW_START)) {
 268                 if ((unsigned long)info->access_addr < PAGE_SIZE)
 269                         bug_type = "null-ptr-deref";
 270                 else if ((unsigned long)info->access_addr < TASK_SIZE)
 271                         bug_type = "user-memory-access";
 272                 else
 273                         bug_type = "wild-memory-access";
 274                 pr_err("BUG: KASAN: %s on address %p\n",
 275                         bug_type, info->access_addr);
 276                 pr_err("%s of size %zu by task %s/%d\n",
 277                         info->is_write ? "Write" : "Read",
 278                         info->access_size, current->comm,
 279                         task_pid_nr(current));
 280                 dump_stack();
 281         } else {
 282                 print_error_description(info);
 283                 print_address_description(info);
 284                 print_shadow_for_address(info->first_bad_addr);
 285         }
 286
 287         kasan_end_report(&flags);
 288 }
 289
 290 void kasan_report(unsigned long addr, size_t size,
 291                 bool is_write, unsigned long ip)
 292 {
 293         struct kasan_access_info info;
 294
 295         if (likely(!kasan_report_enabled()))
 296                 return;
 297
 298         info.access_addr = (void *)addr;
 299         info.access_size = size;
 300         info.is_write = is_write;
 301         info.ip = ip;
 302
 303         kasan_report_error(&info);
 304 }
 305
 306
 307 #define DEFINE_ASAN_REPORT_LOAD(size)                     \
 308 void __asan_report_load##size##_noabort(unsigned long addr) \
 309 {                                                         \
 310         kasan_report(addr, size, false, _RET_IP_);        \
 311 }                                                         \
 312 EXPORT_SYMBOL(__asan_report_load##size##_noabort)
 313
 314 #define DEFINE_ASAN_REPORT_STORE(size)                     \
 315 void __asan_report_store##size##_noabort(unsigned long addr) \
 316 {                                                          \
 317         kasan_report(addr, size, true, _RET_IP_);          \
 318 }                                                          \
 319 EXPORT_SYMBOL(__asan_report_store##size##_noabort)
 320
 321 DEFINE_ASAN_REPORT_LOAD(1);
 322 DEFINE_ASAN_REPORT_LOAD(2);
 323 DEFINE_ASAN_REPORT_LOAD(4);
 324 DEFINE_ASAN_REPORT_LOAD(8);
 325 DEFINE_ASAN_REPORT_LOAD(16);
 326 DEFINE_ASAN_REPORT_STORE(1);
 327 DEFINE_ASAN_REPORT_STORE(2);
 328 DEFINE_ASAN_REPORT_STORE(4);
 329 DEFINE_ASAN_REPORT_STORE(8);
 330 DEFINE_ASAN_REPORT_STORE(16);
 331
 332 void __asan_report_load_n_noabort(unsigned long addr, size_t size)
 333 {
 334         kasan_report(addr, size, false, _RET_IP_);
 335 }
 336 EXPORT_SYMBOL(__asan_report_load_n_noabort);
 337
 338 void __asan_report_store_n_noabort(unsigned long addr, size_t size)
 339 {
 340         kasan_report(addr, size, true, _RET_IP_);
 341 }
 342 EXPORT_SYMBOL(__asan_report_store_n_noabort);