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 void print_track(struct kasan_track *track)
 120 {
 121         pr_err("PID = %u\n", track->pid);
 122         if (track->stack) {
 123                 struct stack_trace trace;
 124
 125                 depot_fetch_stack(track->stack, &trace);
 126                 print_stack_trace(&trace, 0);
 127         } else {
 128                 pr_err("(stack is not available)\n");
 129         }
 130 }
 131
 132 static void kasan_object_err(struct kmem_cache *cache, struct page *page,
 133                                 void *object, char *unused_reason)
 134 {
 135         struct kasan_alloc_meta *alloc_info = get_alloc_info(cache, object);
 136
 137         dump_stack();
 138         pr_err("Object at %p, in cache %s size: %d\n", object, cache->name,
 139                 cache->object_size);
 140
 141         if (!(cache->flags & SLAB_KASAN))
 142                 return;
 143
 144         pr_err("Allocated:\n");
 145         print_track(&alloc_info->alloc_track);
 146         pr_err("Freed:\n");
 147         print_track(&alloc_info->free_track);
 148 }
 149
 150 static void print_address_description(struct kasan_access_info *info)
 151 {
 152         const void *addr = info->access_addr;
 153
 154         if ((addr >= (void *)PAGE_OFFSET) &&
 155                 (addr < high_memory)) {
 156                 struct page *page = virt_to_head_page(addr);
 157
 158                 if (PageSlab(page)) {
 159                         void *object;
 160                         struct kmem_cache *cache = page->slab_cache;
 161                         object = nearest_obj(cache, page,
 162                                                 (void *)info->access_addr);
 163                         kasan_object_err(cache, page, object,
 164                                         "kasan: bad access detected");
 165                         return;
 166                 }
 167                 dump_page(page, "kasan: bad access detected");
 168         }
 169
 170         if (kernel_or_module_addr(addr)) {
 171                 if (!init_task_stack_addr(addr))
 172                         pr_err("Address belongs to variable %pS\n", addr);
 173         }
 174         dump_stack();
 175 }
 176
 177 static bool row_is_guilty(const void *row, const void *guilty)
 178 {
 179         return (row <= guilty) && (guilty < row + SHADOW_BYTES_PER_ROW);
 180 }
 181
 182 static int shadow_pointer_offset(const void *row, const void *shadow)
 183 {
 184         /* The length of ">ff00ff00ff00ff00: " is
 185          *    3 + (BITS_PER_LONG/8)*2 chars.
 186          */
 187         return 3 + (BITS_PER_LONG/8)*2 + (shadow - row)*2 +
 188                 (shadow - row) / SHADOW_BYTES_PER_BLOCK + 1;
 189 }
 190
 191 static void print_shadow_for_address(const void *addr)
 192 {
 193         int i;
 194         const void *shadow = kasan_mem_to_shadow(addr);
 195         const void *shadow_row;
 196
 197         shadow_row = (void *)round_down((unsigned long)shadow,
 198                                         SHADOW_BYTES_PER_ROW)
 199                 - SHADOW_ROWS_AROUND_ADDR * SHADOW_BYTES_PER_ROW;
 200
 201         pr_err("Memory state around the buggy address:\n");
 202
 203         for (i = -SHADOW_ROWS_AROUND_ADDR; i <= SHADOW_ROWS_AROUND_ADDR; i++) {
 204                 const void *kaddr = kasan_shadow_to_mem(shadow_row);
 205                 char buffer[4 + (BITS_PER_LONG/8)*2];
 206                 char shadow_buf[SHADOW_BYTES_PER_ROW];
 207
 208                 snprintf(buffer, sizeof(buffer),
 209                         (i == 0) ? ">%p: " : " %p: ", kaddr);
 210                 /*
 211                  * We should not pass a shadow pointer to generic
 212                  * function, because generic functions may try to
 213                  * access kasan mapping for the passed address.
 214                  */
 215                 memcpy(shadow_buf, shadow_row, SHADOW_BYTES_PER_ROW);
 216                 print_hex_dump(KERN_ERR, buffer,
 217                         DUMP_PREFIX_NONE, SHADOW_BYTES_PER_ROW, 1,
 218                         shadow_buf, SHADOW_BYTES_PER_ROW, 0);
 219
 220                 if (row_is_guilty(shadow_row, shadow))
 221                         pr_err("%*c\n",
 222                                 shadow_pointer_offset(shadow_row, shadow),
 223                                 '^');
 224
 225                 shadow_row += SHADOW_BYTES_PER_ROW;
 226         }
 227 }
 228
 229 static DEFINE_SPINLOCK(report_lock);
 230
 231 static void kasan_report_error(struct kasan_access_info *info)
 232 {
 233         unsigned long flags;
 234         const char *bug_type;
 235
 236         /*
 237          * Make sure we don't end up in loop.
 238          */
 239         kasan_disable_current();
 240         spin_lock_irqsave(&report_lock, flags);
 241         pr_err("==================================================================\n");
 242         if (info->access_addr <
 243                         kasan_shadow_to_mem((void *)KASAN_SHADOW_START)) {
 244                 if ((unsigned long)info->access_addr < PAGE_SIZE)
 245                         bug_type = "null-ptr-deref";
 246                 else if ((unsigned long)info->access_addr < TASK_SIZE)
 247                         bug_type = "user-memory-access";
 248                 else
 249                         bug_type = "wild-memory-access";
 250                 pr_err("BUG: KASAN: %s on address %p\n",
 251                         bug_type, info->access_addr);
 252                 pr_err("%s of size %zu by task %s/%d\n",
 253                         info->is_write ? "Write" : "Read",
 254                         info->access_size, current->comm,
 255                         task_pid_nr(current));
 256                 dump_stack();
 257         } else {
 258                 print_error_description(info);
 259                 print_address_description(info);
 260                 print_shadow_for_address(info->first_bad_addr);
 261         }
 262         pr_err("==================================================================\n");
 263         add_taint(TAINT_BAD_PAGE, LOCKDEP_NOW_UNRELIABLE);
 264         spin_unlock_irqrestore(&report_lock, flags);
 265         kasan_enable_current();
 266 }
 267
 268 void kasan_report(unsigned long addr, size_t size,
 269                 bool is_write, unsigned long ip)
 270 {
 271         struct kasan_access_info info;
 272
 273         if (likely(!kasan_report_enabled()))
 274                 return;
 275
 276         info.access_addr = (void *)addr;
 277         info.access_size = size;
 278         info.is_write = is_write;
 279         info.ip = ip;
 280
 281         kasan_report_error(&info);
 282 }
 283
 284
 285 #define DEFINE_ASAN_REPORT_LOAD(size)                     \
 286 void __asan_report_load##size##_noabort(unsigned long addr) \
 287 {                                                         \
 288         kasan_report(addr, size, false, _RET_IP_);        \
 289 }                                                         \
 290 EXPORT_SYMBOL(__asan_report_load##size##_noabort)
 291
 292 #define DEFINE_ASAN_REPORT_STORE(size)                     \
 293 void __asan_report_store##size##_noabort(unsigned long addr) \
 294 {                                                          \
 295         kasan_report(addr, size, true, _RET_IP_);          \
 296 }                                                          \
 297 EXPORT_SYMBOL(__asan_report_store##size##_noabort)
 298
 299 DEFINE_ASAN_REPORT_LOAD(1);
 300 DEFINE_ASAN_REPORT_LOAD(2);
 301 DEFINE_ASAN_REPORT_LOAD(4);
 302 DEFINE_ASAN_REPORT_LOAD(8);
 303 DEFINE_ASAN_REPORT_LOAD(16);
 304 DEFINE_ASAN_REPORT_STORE(1);
 305 DEFINE_ASAN_REPORT_STORE(2);
 306 DEFINE_ASAN_REPORT_STORE(4);
 307 DEFINE_ASAN_REPORT_STORE(8);
 308 DEFINE_ASAN_REPORT_STORE(16);
 309
 310 void __asan_report_load_n_noabort(unsigned long addr, size_t size)
 311 {
 312         kasan_report(addr, size, false, _RET_IP_);
 313 }
 314 EXPORT_SYMBOL(__asan_report_load_n_noabort);
 315
 316 void __asan_report_store_n_noabort(unsigned long addr, size_t size)
 317 {
 318         kasan_report(addr, size, true, _RET_IP_);
 319 }
 320 EXPORT_SYMBOL(__asan_report_store_n_noabort);