mm/kasan/report.c

   1 // SPDX-License-Identifier: GPL-2.0
   2 /*
   3  * This file contains common generic and tag-based KASAN error reporting code.
   4  *
   5  * Copyright (c) 2014 Samsung Electronics Co., Ltd.
   6  * Author: Andrey Ryabinin <ryabinin.a.a@gmail.com>
   7  *
   8  * Some code borrowed from https://github.com/xairy/kasan-prototype by
   9  *        Andrey Konovalov <andreyknvl@gmail.com>
  10  *
  11  * This program is free software; you can redistribute it and/or modify
  12  * it under the terms of the GNU General Public License version 2 as
  13  * published by the Free Software Foundation.
  14  *
  15  */
  16
  17 #include <linux/bitops.h>
  18 #include <linux/ftrace.h>
  19 #include <linux/init.h>
  20 #include <linux/kernel.h>
  21 #include <linux/mm.h>
  22 #include <linux/printk.h>
  23 #include <linux/sched.h>
  24 #include <linux/slab.h>
  25 #include <linux/stackdepot.h>
  26 #include <linux/stacktrace.h>
  27 #include <linux/string.h>
  28 #include <linux/types.h>
  29 #include <linux/kasan.h>
  30 #include <linux/module.h>
  31 #include <linux/sched/task_stack.h>
  32
  33 #include <asm/sections.h>
  34
  35 #include "kasan.h"
  36 #include "../slab.h"
  37
  38 /* Shadow layout customization. */
  39 #define SHADOW_BYTES_PER_BLOCK 1
  40 #define SHADOW_BLOCKS_PER_ROW 16
  41 #define SHADOW_BYTES_PER_ROW (SHADOW_BLOCKS_PER_ROW * SHADOW_BYTES_PER_BLOCK)
  42 #define SHADOW_ROWS_AROUND_ADDR 2
  43
  44 static unsigned long kasan_flags;
  45
  46 #define KASAN_BIT_REPORTED      0
  47 #define KASAN_BIT_MULTI_SHOT    1
  48
  49 bool kasan_save_enable_multi_shot(void)
  50 {
  51         return test_and_set_bit(KASAN_BIT_MULTI_SHOT, &kasan_flags);
  52 }
  53 EXPORT_SYMBOL_GPL(kasan_save_enable_multi_shot);
  54
  55 void kasan_restore_multi_shot(bool enabled)
  56 {
  57         if (!enabled)
  58                 clear_bit(KASAN_BIT_MULTI_SHOT, &kasan_flags);
  59 }
  60 EXPORT_SYMBOL_GPL(kasan_restore_multi_shot);
  61
  62 static int __init kasan_set_multi_shot(char *str)
  63 {
  64         set_bit(KASAN_BIT_MULTI_SHOT, &kasan_flags);
  65         return 1;
  66 }
  67 __setup("kasan_multi_shot", kasan_set_multi_shot);
  68
  69 static void print_error_description(struct kasan_access_info *info)
  70 {
  71         pr_err("BUG: KASAN: %s in %pS\n",
  72                 get_bug_type(info), (void *)info->ip);
  73         pr_err("%s of size %zu at addr %px by task %s/%d\n",
  74                 info->is_write ? "Write" : "Read", info->access_size,
  75                 info->access_addr, current->comm, task_pid_nr(current));
  76 }
  77
  78 static DEFINE_SPINLOCK(report_lock);
  79
  80 static void start_report(unsigned long *flags)
  81 {
  82         /*
  83          * Make sure we don't end up in loop.
  84          */
  85         kasan_disable_current();
  86         spin_lock_irqsave(&report_lock, *flags);
  87         pr_err("==================================================================\n");
  88 }
  89
  90 static void end_report(unsigned long *flags)
  91 {
  92         pr_err("==================================================================\n");
  93         add_taint(TAINT_BAD_PAGE, LOCKDEP_NOW_UNRELIABLE);
  94         spin_unlock_irqrestore(&report_lock, *flags);
  95         if (panic_on_warn)
  96                 panic("panic_on_warn set ...\n");
  97         kasan_enable_current();
  98 }
  99
 100 static void print_track(struct kasan_track *track, const char *prefix)
 101 {
 102         pr_err("%s by task %u:\n", prefix, track->pid);
 103         if (track->stack) {
 104                 unsigned long *entries;
 105                 unsigned int nr_entries;
 106
 107                 nr_entries = stack_depot_fetch(track->stack, &entries);
 108                 stack_trace_print(entries, nr_entries, 0);
 109         } else {
 110                 pr_err("(stack is not available)\n");
 111         }
 112 }
 113
 114 struct page *kasan_addr_to_page(const void *addr)
 115 {
 116         if ((addr >= (void *)PAGE_OFFSET) &&
 117                         (addr < high_memory))
 118                 return virt_to_head_page(addr);
 119         return NULL;
 120 }
 121
 122 static void describe_object_addr(struct kmem_cache *cache, void *object,
 123                                 const void *addr)
 124 {
 125         unsigned long access_addr = (unsigned long)addr;
 126         unsigned long object_addr = (unsigned long)object;
 127         const char *rel_type;
 128         int rel_bytes;
 129
 130         pr_err("The buggy address belongs to the object at %px\n"
 131                " which belongs to the cache %s of size %d\n",
 132                 object, cache->name, cache->object_size);
 133
 134         if (!addr)
 135                 return;
 136
 137         if (access_addr < object_addr) {
 138                 rel_type = "to the left";
 139                 rel_bytes = object_addr - access_addr;
 140         } else if (access_addr >= object_addr + cache->object_size) {
 141                 rel_type = "to the right";
 142                 rel_bytes = access_addr - (object_addr + cache->object_size);
 143         } else {
 144                 rel_type = "inside";
 145                 rel_bytes = access_addr - object_addr;
 146         }
 147
 148         pr_err("The buggy address is located %d bytes %s of\n"
 149                " %d-byte region [%px, %px)\n",
 150                 rel_bytes, rel_type, cache->object_size, (void *)object_addr,
 151                 (void *)(object_addr + cache->object_size));
 152 }
 153
 154 static struct kasan_track *kasan_get_free_track(struct kmem_cache *cache,
 155                 void *object, u8 tag)
 156 {
 157         struct kasan_alloc_meta *alloc_meta;
 158         int i = 0;
 159
 160         alloc_meta = get_alloc_info(cache, object);
 161
 162 #ifdef CONFIG_KASAN_SW_TAGS_IDENTIFY
 163         for (i = 0; i < KASAN_NR_FREE_STACKS; i++) {
 164                 if (alloc_meta->free_pointer_tag[i] == tag)
 165                         break;
 166         }
 167         if (i == KASAN_NR_FREE_STACKS)
 168                 i = alloc_meta->free_track_idx;
 169 #endif
 170
 171         return &alloc_meta->free_track[i];
 172 }
 173
 174 static void describe_object(struct kmem_cache *cache, void *object,
 175                                 const void *addr, u8 tag)
 176 {
 177         struct kasan_alloc_meta *alloc_info = get_alloc_info(cache, object);
 178
 179         if (cache->flags & SLAB_KASAN) {
 180                 struct kasan_track *free_track;
 181
 182                 print_track(&alloc_info->alloc_track, "Allocated");
 183                 pr_err("\n");
 184                 free_track = kasan_get_free_track(cache, object, tag);
 185                 print_track(free_track, "Freed");
 186                 pr_err("\n");
 187         }
 188
 189         describe_object_addr(cache, object, addr);
 190 }
 191
 192 static inline bool kernel_or_module_addr(const void *addr)
 193 {
 194         if (addr >= (void *)_stext && addr < (void *)_end)
 195                 return true;
 196         if (is_module_address((unsigned long)addr))
 197                 return true;
 198         return false;
 199 }
 200
 201 static inline bool init_task_stack_addr(const void *addr)
 202 {
 203         return addr >= (void *)&init_thread_union.stack &&
 204                 (addr <= (void *)&init_thread_union.stack +
 205                         sizeof(init_thread_union.stack));
 206 }
 207
 208 static bool __must_check tokenize_frame_descr(const char **frame_descr,
 209                                               char *token, size_t max_tok_len,
 210                                               unsigned long *value)
 211 {
 212         const char *sep = strchr(*frame_descr, ' ');
 213
 214         if (sep == NULL)
 215                 sep = *frame_descr + strlen(*frame_descr);
 216
 217         if (token != NULL) {
 218                 const size_t tok_len = sep - *frame_descr;
 219
 220                 if (tok_len + 1 > max_tok_len) {
 221                         pr_err("KASAN internal error: frame description too long: %s\n",
 222                                *frame_descr);
 223                         return false;
 224                 }
 225
 226                 /* Copy token (+ 1 byte for '\0'). */
 227                 strlcpy(token, *frame_descr, tok_len + 1);
 228         }
 229
 230         /* Advance frame_descr past separator. */
 231         *frame_descr = sep + 1;
 232
 233         if (value != NULL && kstrtoul(token, 10, value)) {
 234                 pr_err("KASAN internal error: not a valid number: %s\n", token);
 235                 return false;
 236         }
 237
 238         return true;
 239 }
 240
 241 static void print_decoded_frame_descr(const char *frame_descr)
 242 {
 243         /*
 244          * We need to parse the following string:
 245          *    "n alloc_1 alloc_2 ... alloc_n"
 246          * where alloc_i looks like
 247          *    "offset size len name"
 248          * or "offset size len name:line".
 249          */
 250
 251         char token[64];
 252         unsigned long num_objects;
 253
 254         if (!tokenize_frame_descr(&frame_descr, token, sizeof(token),
 255                                   &num_objects))
 256                 return;
 257
 258         pr_err("\n");
 259         pr_err("this frame has %lu %s:\n", num_objects,
 260                num_objects == 1 ? "object" : "objects");
 261
 262         while (num_objects--) {
 263                 unsigned long offset;
 264                 unsigned long size;
 265
 266                 /* access offset */
 267                 if (!tokenize_frame_descr(&frame_descr, token, sizeof(token),
 268                                           &offset))
 269                         return;
 270                 /* access size */
 271                 if (!tokenize_frame_descr(&frame_descr, token, sizeof(token),
 272                                           &size))
 273                         return;
 274                 /* name length (unused) */
 275                 if (!tokenize_frame_descr(&frame_descr, NULL, 0, NULL))
 276                         return;
 277                 /* object name */
 278                 if (!tokenize_frame_descr(&frame_descr, token, sizeof(token),
 279                                           NULL))
 280                         return;
 281
 282                 /* Strip line number; without filename it's not very helpful. */
 283                 strreplace(token, ':', '\0');
 284
 285                 /* Finally, print object information. */
 286                 pr_err(" [%lu, %lu) '%s'", offset, offset + size, token);
 287         }
 288 }
 289
 290 static bool __must_check get_address_stack_frame_info(const void *addr,
 291                                                       unsigned long *offset,
 292                                                       const char **frame_descr,
 293                                                       const void **frame_pc)
 294 {
 295         unsigned long aligned_addr;
 296         unsigned long mem_ptr;
 297         const u8 *shadow_bottom;
 298         const u8 *shadow_ptr;
 299         const unsigned long *frame;
 300
 301         BUILD_BUG_ON(IS_ENABLED(CONFIG_STACK_GROWSUP));
 302
 303         /*
 304          * NOTE: We currently only support printing frame information for
 305          * accesses to the task's own stack.
 306          */
 307         if (!object_is_on_stack(addr))
 308                 return false;
 309
 310         aligned_addr = round_down((unsigned long)addr, sizeof(long));
 311         mem_ptr = round_down(aligned_addr, KASAN_SHADOW_SCALE_SIZE);
 312         shadow_ptr = kasan_mem_to_shadow((void *)aligned_addr);
 313         shadow_bottom = kasan_mem_to_shadow(end_of_stack(current));
 314
 315         while (shadow_ptr >= shadow_bottom && *shadow_ptr != KASAN_STACK_LEFT) {
 316                 shadow_ptr--;
 317                 mem_ptr -= KASAN_SHADOW_SCALE_SIZE;
 318         }
 319
 320         while (shadow_ptr >= shadow_bottom && *shadow_ptr == KASAN_STACK_LEFT) {
 321                 shadow_ptr--;
 322                 mem_ptr -= KASAN_SHADOW_SCALE_SIZE;
 323         }
 324
 325         if (shadow_ptr < shadow_bottom)
 326                 return false;
 327
 328         frame = (const unsigned long *)(mem_ptr + KASAN_SHADOW_SCALE_SIZE);
 329         if (frame[0] != KASAN_CURRENT_STACK_FRAME_MAGIC) {
 330                 pr_err("KASAN internal error: frame info validation failed; invalid marker: %lu\n",
 331                        frame[0]);
 332                 return false;
 333         }
 334
 335         *offset = (unsigned long)addr - (unsigned long)frame;
 336         *frame_descr = (const char *)frame[1];
 337         *frame_pc = (void *)frame[2];
 338
 339         return true;
 340 }
 341
 342 static void print_address_stack_frame(const void *addr)
 343 {
 344         unsigned long offset;
 345         const char *frame_descr;
 346         const void *frame_pc;
 347
 348         if (IS_ENABLED(CONFIG_KASAN_SW_TAGS))
 349                 return;
 350
 351         if (!get_address_stack_frame_info(addr, &offset, &frame_descr,
 352                                           &frame_pc))
 353                 return;
 354
 355         /*
 356          * get_address_stack_frame_info only returns true if the given addr is
 357          * on the current task's stack.
 358          */
 359         pr_err("\n");
 360         pr_err("addr %px is located in stack of task %s/%d at offset %lu in frame:\n",
 361                addr, current->comm, task_pid_nr(current), offset);
 362         pr_err(" %pS\n", frame_pc);
 363
 364         if (!frame_descr)
 365                 return;
 366
 367         print_decoded_frame_descr(frame_descr);
 368 }
 369
 370 static void print_address_description(void *addr, u8 tag)
 371 {
 372         struct page *page = kasan_addr_to_page(addr);
 373
 374         dump_stack();
 375         pr_err("\n");
 376
 377         if (page && PageSlab(page)) {
 378                 struct kmem_cache *cache = page->slab_cache;
 379                 void *object = nearest_obj(cache, page, addr);
 380
 381                 describe_object(cache, object, addr, tag);
 382         }
 383
 384         if (kernel_or_module_addr(addr) && !init_task_stack_addr(addr)) {
 385                 pr_err("The buggy address belongs to the variable:\n");
 386                 pr_err(" %pS\n", addr);
 387         }
 388
 389         if (page) {
 390                 pr_err("The buggy address belongs to the page:\n");
 391                 dump_page(page, "kasan: bad access detected");
 392         }
 393
 394         print_address_stack_frame(addr);
 395 }
 396
 397 static bool row_is_guilty(const void *row, const void *guilty)
 398 {
 399         return (row <= guilty) && (guilty < row + SHADOW_BYTES_PER_ROW);
 400 }
 401
 402 static int shadow_pointer_offset(const void *row, const void *shadow)
 403 {
 404         /* The length of ">ff00ff00ff00ff00: " is
 405          *    3 + (BITS_PER_LONG/8)*2 chars.
 406          */
 407         return 3 + (BITS_PER_LONG/8)*2 + (shadow - row)*2 +
 408                 (shadow - row) / SHADOW_BYTES_PER_BLOCK + 1;
 409 }
 410
 411 static void print_shadow_for_address(const void *addr)
 412 {
 413         int i;
 414         const void *shadow = kasan_mem_to_shadow(addr);
 415         const void *shadow_row;
 416
 417         shadow_row = (void *)round_down((unsigned long)shadow,
 418                                         SHADOW_BYTES_PER_ROW)
 419                 - SHADOW_ROWS_AROUND_ADDR * SHADOW_BYTES_PER_ROW;
 420
 421         pr_err("Memory state around the buggy address:\n");
 422
 423         for (i = -SHADOW_ROWS_AROUND_ADDR; i <= SHADOW_ROWS_AROUND_ADDR; i++) {
 424                 const void *kaddr = kasan_shadow_to_mem(shadow_row);
 425                 char buffer[4 + (BITS_PER_LONG/8)*2];
 426                 char shadow_buf[SHADOW_BYTES_PER_ROW];
 427
 428                 snprintf(buffer, sizeof(buffer),
 429                         (i == 0) ? ">%px: " : " %px: ", kaddr);
 430                 /*
 431                  * We should not pass a shadow pointer to generic
 432                  * function, because generic functions may try to
 433                  * access kasan mapping for the passed address.
 434                  */
 435                 memcpy(shadow_buf, shadow_row, SHADOW_BYTES_PER_ROW);
 436                 print_hex_dump(KERN_ERR, buffer,
 437                         DUMP_PREFIX_NONE, SHADOW_BYTES_PER_ROW, 1,
 438                         shadow_buf, SHADOW_BYTES_PER_ROW, 0);
 439
 440                 if (row_is_guilty(shadow_row, shadow))
 441                         pr_err("%*c\n",
 442                                 shadow_pointer_offset(shadow_row, shadow),
 443                                 '^');
 444
 445                 shadow_row += SHADOW_BYTES_PER_ROW;
 446         }
 447 }
 448
 449 static bool report_enabled(void)
 450 {
 451         if (current->kasan_depth)
 452                 return false;
 453         if (test_bit(KASAN_BIT_MULTI_SHOT, &kasan_flags))
 454                 return true;
 455         return !test_and_set_bit(KASAN_BIT_REPORTED, &kasan_flags);
 456 }
 457
 458 void kasan_report_invalid_free(void *object, unsigned long ip)
 459 {
 460         unsigned long flags;
 461         u8 tag = get_tag(object);
 462
 463         object = reset_tag(object);
 464         start_report(&flags);
 465         pr_err("BUG: KASAN: double-free or invalid-free in %pS\n", (void *)ip);
 466         print_tags(tag, object);
 467         pr_err("\n");
 468         print_address_description(object, tag);
 469         pr_err("\n");
 470         print_shadow_for_address(object);
 471         end_report(&flags);
 472 }
 473
 474 void __kasan_report(unsigned long addr, size_t size, bool is_write, unsigned long ip)
 475 {
 476         struct kasan_access_info info;
 477         void *tagged_addr;
 478         void *untagged_addr;
 479         unsigned long flags;
 480
 481         if (likely(!report_enabled()))
 482                 return;
 483
 484         disable_trace_on_warning();
 485
 486         tagged_addr = (void *)addr;
 487         untagged_addr = reset_tag(tagged_addr);
 488
 489         info.access_addr = tagged_addr;
 490         if (addr_has_shadow(untagged_addr))
 491                 info.first_bad_addr = find_first_bad_addr(tagged_addr, size);
 492         else
 493                 info.first_bad_addr = untagged_addr;
 494         info.access_size = size;
 495         info.is_write = is_write;
 496         info.ip = ip;
 497
 498         start_report(&flags);
 499
 500         print_error_description(&info);
 501         if (addr_has_shadow(untagged_addr))
 502                 print_tags(get_tag(tagged_addr), info.first_bad_addr);
 503         pr_err("\n");
 504
 505         if (addr_has_shadow(untagged_addr)) {
 506                 print_address_description(untagged_addr, get_tag(tagged_addr));
 507                 pr_err("\n");
 508                 print_shadow_for_address(info.first_bad_addr);
 509         } else {
 510                 dump_stack();
 511         }
 512
 513         end_report(&flags);
 514 }
 515
 516 #ifdef CONFIG_KASAN_INLINE
 517 /*
 518  * With CONFIG_KASAN_INLINE, accesses to bogus pointers (outside the high
 519  * canonical half of the address space) cause out-of-bounds shadow memory reads
 520  * before the actual access. For addresses in the low canonical half of the
 521  * address space, as well as most non-canonical addresses, that out-of-bounds
 522  * shadow memory access lands in the non-canonical part of the address space.
 523  * Help the user figure out what the original bogus pointer was.
 524  */
 525 void kasan_non_canonical_hook(unsigned long addr)
 526 {
 527         unsigned long orig_addr;
 528         const char *bug_type;
 529
 530         if (addr < KASAN_SHADOW_OFFSET)
 531                 return;
 532
 533         orig_addr = (addr - KASAN_SHADOW_OFFSET) << KASAN_SHADOW_SCALE_SHIFT;
 534         /*
 535          * For faults near the shadow address for NULL, we can be fairly certain
 536          * that this is a KASAN shadow memory access.
 537          * For faults that correspond to shadow for low canonical addresses, we
 538          * can still be pretty sure - that shadow region is a fairly narrow
 539          * chunk of the non-canonical address space.
 540          * But faults that look like shadow for non-canonical addresses are a
 541          * really large chunk of the address space. In that case, we still
 542          * print the decoded address, but make it clear that this is not
 543          * necessarily what's actually going on.
 544          */
 545         if (orig_addr < PAGE_SIZE)
 546                 bug_type = "null-ptr-deref";
 547         else if (orig_addr < TASK_SIZE)
 548                 bug_type = "probably user-memory-access";
 549         else
 550                 bug_type = "maybe wild-memory-access";
 551         pr_alert("KASAN: %s in range [0x%016lx-0x%016lx]\n", bug_type,
 552                  orig_addr, orig_addr + KASAN_SHADOW_MASK);
 553 }
 554 #endif