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                 /*
  97                  * This thread may hit another WARN() in the panic path.
  98                  * Resetting this prevents additional WARN() from panicking the
  99                  * system on this thread.  Other threads are blocked by the
 100                  * panic_mutex in panic().
 101                  */
 102                 panic_on_warn = 0;
 103                 panic("panic_on_warn set ...\n");
 104         }
 105         kasan_enable_current();
 106 }
 107
 108 static void print_track(struct kasan_track *track, const char *prefix)
 109 {
 110         pr_err("%s by task %u:\n", prefix, track->pid);
 111         if (track->stack) {
 112                 unsigned long *entries;
 113                 unsigned int nr_entries;
 114
 115                 nr_entries = stack_depot_fetch(track->stack, &entries);
 116                 stack_trace_print(entries, nr_entries, 0);
 117         } else {
 118                 pr_err("(stack is not available)\n");
 119         }
 120 }
 121
 122 struct page *kasan_addr_to_page(const void *addr)
 123 {
 124         if ((addr >= (void *)PAGE_OFFSET) &&
 125                         (addr < high_memory))
 126                 return virt_to_head_page(addr);
 127         return NULL;
 128 }
 129
 130 static void describe_object_addr(struct kmem_cache *cache, void *object,
 131                                 const void *addr)
 132 {
 133         unsigned long access_addr = (unsigned long)addr;
 134         unsigned long object_addr = (unsigned long)object;
 135         const char *rel_type;
 136         int rel_bytes;
 137
 138         pr_err("The buggy address belongs to the object at %px\n"
 139                " which belongs to the cache %s of size %d\n",
 140                 object, cache->name, cache->object_size);
 141
 142         if (!addr)
 143                 return;
 144
 145         if (access_addr < object_addr) {
 146                 rel_type = "to the left";
 147                 rel_bytes = object_addr - access_addr;
 148         } else if (access_addr >= object_addr + cache->object_size) {
 149                 rel_type = "to the right";
 150                 rel_bytes = access_addr - (object_addr + cache->object_size);
 151         } else {
 152                 rel_type = "inside";
 153                 rel_bytes = access_addr - object_addr;
 154         }
 155
 156         pr_err("The buggy address is located %d bytes %s of\n"
 157                " %d-byte region [%px, %px)\n",
 158                 rel_bytes, rel_type, cache->object_size, (void *)object_addr,
 159                 (void *)(object_addr + cache->object_size));
 160 }
 161
 162 static struct kasan_track *kasan_get_free_track(struct kmem_cache *cache,
 163                 void *object, u8 tag)
 164 {
 165         struct kasan_alloc_meta *alloc_meta;
 166         int i = 0;
 167
 168         alloc_meta = get_alloc_info(cache, object);
 169
 170 #ifdef CONFIG_KASAN_SW_TAGS_IDENTIFY
 171         for (i = 0; i < KASAN_NR_FREE_STACKS; i++) {
 172                 if (alloc_meta->free_pointer_tag[i] == tag)
 173                         break;
 174         }
 175         if (i == KASAN_NR_FREE_STACKS)
 176                 i = alloc_meta->free_track_idx;
 177 #endif
 178
 179         return &alloc_meta->free_track[i];
 180 }
 181
 182 static void describe_object(struct kmem_cache *cache, void *object,
 183                                 const void *addr, u8 tag)
 184 {
 185         struct kasan_alloc_meta *alloc_info = get_alloc_info(cache, object);
 186
 187         if (cache->flags & SLAB_KASAN) {
 188                 struct kasan_track *free_track;
 189
 190                 print_track(&alloc_info->alloc_track, "Allocated");
 191                 pr_err("\n");
 192                 free_track = kasan_get_free_track(cache, object, tag);
 193                 print_track(free_track, "Freed");
 194                 pr_err("\n");
 195         }
 196
 197         describe_object_addr(cache, object, addr);
 198 }
 199
 200 static inline bool kernel_or_module_addr(const void *addr)
 201 {
 202         if (addr >= (void *)_stext && addr < (void *)_end)
 203                 return true;
 204         if (is_module_address((unsigned long)addr))
 205                 return true;
 206         return false;
 207 }
 208
 209 static inline bool init_task_stack_addr(const void *addr)
 210 {
 211         return addr >= (void *)&init_thread_union.stack &&
 212                 (addr <= (void *)&init_thread_union.stack +
 213                         sizeof(init_thread_union.stack));
 214 }
 215
 216 static bool __must_check tokenize_frame_descr(const char **frame_descr,
 217                                               char *token, size_t max_tok_len,
 218                                               unsigned long *value)
 219 {
 220         const char *sep = strchr(*frame_descr, ' ');
 221
 222         if (sep == NULL)
 223                 sep = *frame_descr + strlen(*frame_descr);
 224
 225         if (token != NULL) {
 226                 const size_t tok_len = sep - *frame_descr;
 227
 228                 if (tok_len + 1 > max_tok_len) {
 229                         pr_err("KASAN internal error: frame description too long: %s\n",
 230                                *frame_descr);
 231                         return false;
 232                 }
 233
 234                 /* Copy token (+ 1 byte for '\0'). */
 235                 strlcpy(token, *frame_descr, tok_len + 1);
 236         }
 237
 238         /* Advance frame_descr past separator. */
 239         *frame_descr = sep + 1;
 240
 241         if (value != NULL && kstrtoul(token, 10, value)) {
 242                 pr_err("KASAN internal error: not a valid number: %s\n", token);
 243                 return false;
 244         }
 245
 246         return true;
 247 }
 248
 249 static void print_decoded_frame_descr(const char *frame_descr)
 250 {
 251         /*
 252          * We need to parse the following string:
 253          *    "n alloc_1 alloc_2 ... alloc_n"
 254          * where alloc_i looks like
 255          *    "offset size len name"
 256          * or "offset size len name:line".
 257          */
 258
 259         char token[64];
 260         unsigned long num_objects;
 261
 262         if (!tokenize_frame_descr(&frame_descr, token, sizeof(token),
 263                                   &num_objects))
 264                 return;
 265
 266         pr_err("\n");
 267         pr_err("this frame has %lu %s:\n", num_objects,
 268                num_objects == 1 ? "object" : "objects");
 269
 270         while (num_objects--) {
 271                 unsigned long offset;
 272                 unsigned long size;
 273
 274                 /* access offset */
 275                 if (!tokenize_frame_descr(&frame_descr, token, sizeof(token),
 276                                           &offset))
 277                         return;
 278                 /* access size */
 279                 if (!tokenize_frame_descr(&frame_descr, token, sizeof(token),
 280                                           &size))
 281                         return;
 282                 /* name length (unused) */
 283                 if (!tokenize_frame_descr(&frame_descr, NULL, 0, NULL))
 284                         return;
 285                 /* object name */
 286                 if (!tokenize_frame_descr(&frame_descr, token, sizeof(token),
 287                                           NULL))
 288                         return;
 289
 290                 /* Strip line number; without filename it's not very helpful. */
 291                 strreplace(token, ':', '\0');
 292
 293                 /* Finally, print object information. */
 294                 pr_err(" [%lu, %lu) '%s'", offset, offset + size, token);
 295         }
 296 }
 297
 298 static bool __must_check get_address_stack_frame_info(const void *addr,
 299                                                       unsigned long *offset,
 300                                                       const char **frame_descr,
 301                                                       const void **frame_pc)
 302 {
 303         unsigned long aligned_addr;
 304         unsigned long mem_ptr;
 305         const u8 *shadow_bottom;
 306         const u8 *shadow_ptr;
 307         const unsigned long *frame;
 308
 309         BUILD_BUG_ON(IS_ENABLED(CONFIG_STACK_GROWSUP));
 310
 311         /*
 312          * NOTE: We currently only support printing frame information for
 313          * accesses to the task's own stack.
 314          */
 315         if (!object_is_on_stack(addr))
 316                 return false;
 317
 318         aligned_addr = round_down((unsigned long)addr, sizeof(long));
 319         mem_ptr = round_down(aligned_addr, KASAN_SHADOW_SCALE_SIZE);
 320         shadow_ptr = kasan_mem_to_shadow((void *)aligned_addr);
 321         shadow_bottom = kasan_mem_to_shadow(end_of_stack(current));
 322
 323         while (shadow_ptr >= shadow_bottom && *shadow_ptr != KASAN_STACK_LEFT) {
 324                 shadow_ptr--;
 325                 mem_ptr -= KASAN_SHADOW_SCALE_SIZE;
 326         }
 327
 328         while (shadow_ptr >= shadow_bottom && *shadow_ptr == KASAN_STACK_LEFT) {
 329                 shadow_ptr--;
 330                 mem_ptr -= KASAN_SHADOW_SCALE_SIZE;
 331         }
 332
 333         if (shadow_ptr < shadow_bottom)
 334                 return false;
 335
 336         frame = (const unsigned long *)(mem_ptr + KASAN_SHADOW_SCALE_SIZE);
 337         if (frame[0] != KASAN_CURRENT_STACK_FRAME_MAGIC) {
 338                 pr_err("KASAN internal error: frame info validation failed; invalid marker: %lu\n",
 339                        frame[0]);
 340                 return false;
 341         }
 342
 343         *offset = (unsigned long)addr - (unsigned long)frame;
 344         *frame_descr = (const char *)frame[1];
 345         *frame_pc = (void *)frame[2];
 346
 347         return true;
 348 }
 349
 350 static void print_address_stack_frame(const void *addr)
 351 {
 352         unsigned long offset;
 353         const char *frame_descr;
 354         const void *frame_pc;
 355
 356         if (IS_ENABLED(CONFIG_KASAN_SW_TAGS))
 357                 return;
 358
 359         if (!get_address_stack_frame_info(addr, &offset, &frame_descr,
 360                                           &frame_pc))
 361                 return;
 362
 363         /*
 364          * get_address_stack_frame_info only returns true if the given addr is
 365          * on the current task's stack.
 366          */
 367         pr_err("\n");
 368         pr_err("addr %px is located in stack of task %s/%d at offset %lu in frame:\n",
 369                addr, current->comm, task_pid_nr(current), offset);
 370         pr_err(" %pS\n", frame_pc);
 371
 372         if (!frame_descr)
 373                 return;
 374
 375         print_decoded_frame_descr(frame_descr);
 376 }
 377
 378 static void print_address_description(void *addr, u8 tag)
 379 {
 380         struct page *page = kasan_addr_to_page(addr);
 381
 382         dump_stack();
 383         pr_err("\n");
 384
 385         if (page && PageSlab(page)) {
 386                 struct kmem_cache *cache = page->slab_cache;
 387                 void *object = nearest_obj(cache, page, addr);
 388
 389                 describe_object(cache, object, addr, tag);
 390         }
 391
 392         if (kernel_or_module_addr(addr) && !init_task_stack_addr(addr)) {
 393                 pr_err("The buggy address belongs to the variable:\n");
 394                 pr_err(" %pS\n", addr);
 395         }
 396
 397         if (page) {
 398                 pr_err("The buggy address belongs to the page:\n");
 399                 dump_page(page, "kasan: bad access detected");
 400         }
 401
 402         print_address_stack_frame(addr);
 403 }
 404
 405 static bool row_is_guilty(const void *row, const void *guilty)
 406 {
 407         return (row <= guilty) && (guilty < row + SHADOW_BYTES_PER_ROW);
 408 }
 409
 410 static int shadow_pointer_offset(const void *row, const void *shadow)
 411 {
 412         /* The length of ">ff00ff00ff00ff00: " is
 413          *    3 + (BITS_PER_LONG/8)*2 chars.
 414          */
 415         return 3 + (BITS_PER_LONG/8)*2 + (shadow - row)*2 +
 416                 (shadow - row) / SHADOW_BYTES_PER_BLOCK + 1;
 417 }
 418
 419 static void print_shadow_for_address(const void *addr)
 420 {
 421         int i;
 422         const void *shadow = kasan_mem_to_shadow(addr);
 423         const void *shadow_row;
 424
 425         shadow_row = (void *)round_down((unsigned long)shadow,
 426                                         SHADOW_BYTES_PER_ROW)
 427                 - SHADOW_ROWS_AROUND_ADDR * SHADOW_BYTES_PER_ROW;
 428
 429         pr_err("Memory state around the buggy address:\n");
 430
 431         for (i = -SHADOW_ROWS_AROUND_ADDR; i <= SHADOW_ROWS_AROUND_ADDR; i++) {
 432                 const void *kaddr = kasan_shadow_to_mem(shadow_row);
 433                 char buffer[4 + (BITS_PER_LONG/8)*2];
 434                 char shadow_buf[SHADOW_BYTES_PER_ROW];
 435
 436                 snprintf(buffer, sizeof(buffer),
 437                         (i == 0) ? ">%px: " : " %px: ", kaddr);
 438                 /*
 439                  * We should not pass a shadow pointer to generic
 440                  * function, because generic functions may try to
 441                  * access kasan mapping for the passed address.
 442                  */
 443                 memcpy(shadow_buf, shadow_row, SHADOW_BYTES_PER_ROW);
 444                 print_hex_dump(KERN_ERR, buffer,
 445                         DUMP_PREFIX_NONE, SHADOW_BYTES_PER_ROW, 1,
 446                         shadow_buf, SHADOW_BYTES_PER_ROW, 0);
 447
 448                 if (row_is_guilty(shadow_row, shadow))
 449                         pr_err("%*c\n",
 450                                 shadow_pointer_offset(shadow_row, shadow),
 451                                 '^');
 452
 453                 shadow_row += SHADOW_BYTES_PER_ROW;
 454         }
 455 }
 456
 457 bool report_enabled(void)
 458 {
 459         if (current->kasan_depth)
 460                 return false;
 461         if (test_bit(KASAN_BIT_MULTI_SHOT, &kasan_flags))
 462                 return true;
 463         return !test_and_set_bit(KASAN_BIT_REPORTED, &kasan_flags);
 464 }
 465
 466 void kasan_report_invalid_free(void *object, unsigned long ip)
 467 {
 468         unsigned long flags;
 469         u8 tag = get_tag(object);
 470
 471         object = reset_tag(object);
 472         start_report(&flags);
 473         pr_err("BUG: KASAN: double-free or invalid-free in %pS\n", (void *)ip);
 474         print_tags(tag, object);
 475         pr_err("\n");
 476         print_address_description(object, tag);
 477         pr_err("\n");
 478         print_shadow_for_address(object);
 479         end_report(&flags);
 480 }
 481
 482 void __kasan_report(unsigned long addr, size_t size, bool is_write, unsigned long ip)
 483 {
 484         struct kasan_access_info info;
 485         void *tagged_addr;
 486         void *untagged_addr;
 487         unsigned long flags;
 488
 489         disable_trace_on_warning();
 490
 491         tagged_addr = (void *)addr;
 492         untagged_addr = reset_tag(tagged_addr);
 493
 494         info.access_addr = tagged_addr;
 495         if (addr_has_shadow(untagged_addr))
 496                 info.first_bad_addr = find_first_bad_addr(tagged_addr, size);
 497         else
 498                 info.first_bad_addr = untagged_addr;
 499         info.access_size = size;
 500         info.is_write = is_write;
 501         info.ip = ip;
 502
 503         start_report(&flags);
 504
 505         print_error_description(&info);
 506         if (addr_has_shadow(untagged_addr))
 507                 print_tags(get_tag(tagged_addr), info.first_bad_addr);
 508         pr_err("\n");
 509
 510         if (addr_has_shadow(untagged_addr)) {
 511                 print_address_description(untagged_addr, get_tag(tagged_addr));
 512                 pr_err("\n");
 513                 print_shadow_for_address(info.first_bad_addr);
 514         } else {
 515                 dump_stack();
 516         }
 517
 518         end_report(&flags);
 519 }
 520
 521 #ifdef CONFIG_KASAN_INLINE
 522 /*
 523  * With CONFIG_KASAN_INLINE, accesses to bogus pointers (outside the high
 524  * canonical half of the address space) cause out-of-bounds shadow memory reads
 525  * before the actual access. For addresses in the low canonical half of the
 526  * address space, as well as most non-canonical addresses, that out-of-bounds
 527  * shadow memory access lands in the non-canonical part of the address space.
 528  * Help the user figure out what the original bogus pointer was.
 529  */
 530 void kasan_non_canonical_hook(unsigned long addr)
 531 {
 532         unsigned long orig_addr;
 533         const char *bug_type;
 534
 535         if (addr < KASAN_SHADOW_OFFSET)
 536                 return;
 537
 538         orig_addr = (addr - KASAN_SHADOW_OFFSET) << KASAN_SHADOW_SCALE_SHIFT;
 539         /*
 540          * For faults near the shadow address for NULL, we can be fairly certain
 541          * that this is a KASAN shadow memory access.
 542          * For faults that correspond to shadow for low canonical addresses, we
 543          * can still be pretty sure - that shadow region is a fairly narrow
 544          * chunk of the non-canonical address space.
 545          * But faults that look like shadow for non-canonical addresses are a
 546          * really large chunk of the address space. In that case, we still
 547          * print the decoded address, but make it clear that this is not
 548          * necessarily what's actually going on.
 549          */
 550         if (orig_addr < PAGE_SIZE)
 551                 bug_type = "null-ptr-deref";
 552         else if (orig_addr < TASK_SIZE)
 553                 bug_type = "probably user-memory-access";
 554         else
 555                 bug_type = "maybe wild-memory-access";
 556         pr_alert("KASAN: %s in range [0x%016lx-0x%016lx]\n", bug_type,
 557                  orig_addr, orig_addr + KASAN_SHADOW_MASK);
 558 }
 559 #endif