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 #include <linux/uaccess.h>
  33
  34 #include <asm/sections.h>
  35
  36 #include <kunit/test.h>
  37
  38 #include "kasan.h"
  39 #include "../slab.h"
  40
  41 /* Shadow layout customization. */
  42 #define SHADOW_BYTES_PER_BLOCK 1
  43 #define SHADOW_BLOCKS_PER_ROW 16
  44 #define SHADOW_BYTES_PER_ROW (SHADOW_BLOCKS_PER_ROW * SHADOW_BYTES_PER_BLOCK)
  45 #define SHADOW_ROWS_AROUND_ADDR 2
  46
  47 static unsigned long kasan_flags;
  48
  49 #define KASAN_BIT_REPORTED      0
  50 #define KASAN_BIT_MULTI_SHOT    1
  51
  52 bool kasan_save_enable_multi_shot(void)
  53 {
  54         return test_and_set_bit(KASAN_BIT_MULTI_SHOT, &kasan_flags);
  55 }
  56 EXPORT_SYMBOL_GPL(kasan_save_enable_multi_shot);
  57
  58 void kasan_restore_multi_shot(bool enabled)
  59 {
  60         if (!enabled)
  61                 clear_bit(KASAN_BIT_MULTI_SHOT, &kasan_flags);
  62 }
  63 EXPORT_SYMBOL_GPL(kasan_restore_multi_shot);
  64
  65 static int __init kasan_set_multi_shot(char *str)
  66 {
  67         set_bit(KASAN_BIT_MULTI_SHOT, &kasan_flags);
  68         return 1;
  69 }
  70 __setup("kasan_multi_shot", kasan_set_multi_shot);
  71
  72 static void print_error_description(struct kasan_access_info *info)
  73 {
  74         pr_err("BUG: KASAN: %s in %pS\n",
  75                 get_bug_type(info), (void *)info->ip);
  76         pr_err("%s of size %zu at addr %px by task %s/%d\n",
  77                 info->is_write ? "Write" : "Read", info->access_size,
  78                 info->access_addr, current->comm, task_pid_nr(current));
  79 }
  80
  81 static DEFINE_SPINLOCK(report_lock);
  82
  83 static void start_report(unsigned long *flags)
  84 {
  85         /*
  86          * Make sure we don't end up in loop.
  87          */
  88         kasan_disable_current();
  89         spin_lock_irqsave(&report_lock, *flags);
  90         pr_err("==================================================================\n");
  91 }
  92
  93 static void end_report(unsigned long *flags)
  94 {
  95         pr_err("==================================================================\n");
  96         add_taint(TAINT_BAD_PAGE, LOCKDEP_NOW_UNRELIABLE);
  97         spin_unlock_irqrestore(&report_lock, *flags);
  98         if (!test_bit(KASAN_BIT_MULTI_SHOT, &kasan_flags))
  99                 check_panic_on_warn("KASAN");
 100         kasan_enable_current();
 101 }
 102
 103 static void print_stack(depot_stack_handle_t stack)
 104 {
 105         unsigned long *entries;
 106         unsigned int nr_entries;
 107
 108         nr_entries = stack_depot_fetch(stack, &entries);
 109         stack_trace_print(entries, nr_entries, 0);
 110 }
 111
 112 static void print_track(struct kasan_track *track, const char *prefix)
 113 {
 114         pr_err("%s by task %u:\n", prefix, track->pid);
 115         if (track->stack) {
 116                 print_stack(track->stack);
 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 void describe_object(struct kmem_cache *cache, void *object,
 163                                 const void *addr, u8 tag)
 164 {
 165         struct kasan_alloc_meta *alloc_info = get_alloc_info(cache, object);
 166
 167         if (cache->flags & SLAB_KASAN) {
 168                 struct kasan_track *free_track;
 169
 170                 print_track(&alloc_info->alloc_track, "Allocated");
 171                 pr_err("\n");
 172                 free_track = kasan_get_free_track(cache, object, tag);
 173                 if (free_track) {
 174                         print_track(free_track, "Freed");
 175                         pr_err("\n");
 176                 }
 177
 178 #ifdef CONFIG_KASAN_GENERIC
 179                 if (alloc_info->aux_stack[0]) {
 180                         pr_err("Last call_rcu():\n");
 181                         print_stack(alloc_info->aux_stack[0]);
 182                         pr_err("\n");
 183                 }
 184                 if (alloc_info->aux_stack[1]) {
 185                         pr_err("Second to last call_rcu():\n");
 186                         print_stack(alloc_info->aux_stack[1]);
 187                         pr_err("\n");
 188                 }
 189 #endif
 190         }
 191
 192         describe_object_addr(cache, object, addr);
 193 }
 194
 195 static inline bool kernel_or_module_addr(const void *addr)
 196 {
 197         if (addr >= (void *)_stext && addr < (void *)_end)
 198                 return true;
 199         if (is_module_address((unsigned long)addr))
 200                 return true;
 201         return false;
 202 }
 203
 204 static inline bool init_task_stack_addr(const void *addr)
 205 {
 206         return addr >= (void *)&init_thread_union.stack &&
 207                 (addr <= (void *)&init_thread_union.stack +
 208                         sizeof(init_thread_union.stack));
 209 }
 210
 211 static bool __must_check tokenize_frame_descr(const char **frame_descr,
 212                                               char *token, size_t max_tok_len,
 213                                               unsigned long *value)
 214 {
 215         const char *sep = strchr(*frame_descr, ' ');
 216
 217         if (sep == NULL)
 218                 sep = *frame_descr + strlen(*frame_descr);
 219
 220         if (token != NULL) {
 221                 const size_t tok_len = sep - *frame_descr;
 222
 223                 if (tok_len + 1 > max_tok_len) {
 224                         pr_err("KASAN internal error: frame description too long: %s\n",
 225                                *frame_descr);
 226                         return false;
 227                 }
 228
 229                 /* Copy token (+ 1 byte for '\0'). */
 230                 strlcpy(token, *frame_descr, tok_len + 1);
 231         }
 232
 233         /* Advance frame_descr past separator. */
 234         *frame_descr = sep + 1;
 235
 236         if (value != NULL && kstrtoul(token, 10, value)) {
 237                 pr_err("KASAN internal error: not a valid number: %s\n", token);
 238                 return false;
 239         }
 240
 241         return true;
 242 }
 243
 244 static void print_decoded_frame_descr(const char *frame_descr)
 245 {
 246         /*
 247          * We need to parse the following string:
 248          *    "n alloc_1 alloc_2 ... alloc_n"
 249          * where alloc_i looks like
 250          *    "offset size len name"
 251          * or "offset size len name:line".
 252          */
 253
 254         char token[64];
 255         unsigned long num_objects;
 256
 257         if (!tokenize_frame_descr(&frame_descr, token, sizeof(token),
 258                                   &num_objects))
 259                 return;
 260
 261         pr_err("\n");
 262         pr_err("this frame has %lu %s:\n", num_objects,
 263                num_objects == 1 ? "object" : "objects");
 264
 265         while (num_objects--) {
 266                 unsigned long offset;
 267                 unsigned long size;
 268
 269                 /* access offset */
 270                 if (!tokenize_frame_descr(&frame_descr, token, sizeof(token),
 271                                           &offset))
 272                         return;
 273                 /* access size */
 274                 if (!tokenize_frame_descr(&frame_descr, token, sizeof(token),
 275                                           &size))
 276                         return;
 277                 /* name length (unused) */
 278                 if (!tokenize_frame_descr(&frame_descr, NULL, 0, NULL))
 279                         return;
 280                 /* object name */
 281                 if (!tokenize_frame_descr(&frame_descr, token, sizeof(token),
 282                                           NULL))
 283                         return;
 284
 285                 /* Strip line number; without filename it's not very helpful. */
 286                 strreplace(token, ':', '\0');
 287
 288                 /* Finally, print object information. */
 289                 pr_err(" [%lu, %lu) '%s'", offset, offset + size, token);
 290         }
 291 }
 292
 293 static bool __must_check get_address_stack_frame_info(const void *addr,
 294                                                       unsigned long *offset,
 295                                                       const char **frame_descr,
 296                                                       const void **frame_pc)
 297 {
 298         unsigned long aligned_addr;
 299         unsigned long mem_ptr;
 300         const u8 *shadow_bottom;
 301         const u8 *shadow_ptr;
 302         const unsigned long *frame;
 303
 304         BUILD_BUG_ON(IS_ENABLED(CONFIG_STACK_GROWSUP));
 305
 306         /*
 307          * NOTE: We currently only support printing frame information for
 308          * accesses to the task's own stack.
 309          */
 310         if (!object_is_on_stack(addr))
 311                 return false;
 312
 313         aligned_addr = round_down((unsigned long)addr, sizeof(long));
 314         mem_ptr = round_down(aligned_addr, KASAN_SHADOW_SCALE_SIZE);
 315         shadow_ptr = kasan_mem_to_shadow((void *)aligned_addr);
 316         shadow_bottom = kasan_mem_to_shadow(end_of_stack(current));
 317
 318         while (shadow_ptr >= shadow_bottom && *shadow_ptr != KASAN_STACK_LEFT) {
 319                 shadow_ptr--;
 320                 mem_ptr -= KASAN_SHADOW_SCALE_SIZE;
 321         }
 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         if (shadow_ptr < shadow_bottom)
 329                 return false;
 330
 331         frame = (const unsigned long *)(mem_ptr + KASAN_SHADOW_SCALE_SIZE);
 332         if (frame[0] != KASAN_CURRENT_STACK_FRAME_MAGIC) {
 333                 pr_err("KASAN internal error: frame info validation failed; invalid marker: %lu\n",
 334                        frame[0]);
 335                 return false;
 336         }
 337
 338         *offset = (unsigned long)addr - (unsigned long)frame;
 339         *frame_descr = (const char *)frame[1];
 340         *frame_pc = (void *)frame[2];
 341
 342         return true;
 343 }
 344
 345 static void print_address_stack_frame(const void *addr)
 346 {
 347         unsigned long offset;
 348         const char *frame_descr;
 349         const void *frame_pc;
 350
 351         if (IS_ENABLED(CONFIG_KASAN_SW_TAGS))
 352                 return;
 353
 354         if (!get_address_stack_frame_info(addr, &offset, &frame_descr,
 355                                           &frame_pc))
 356                 return;
 357
 358         /*
 359          * get_address_stack_frame_info only returns true if the given addr is
 360          * on the current task's stack.
 361          */
 362         pr_err("\n");
 363         pr_err("addr %px is located in stack of task %s/%d at offset %lu in frame:\n",
 364                addr, current->comm, task_pid_nr(current), offset);
 365         pr_err(" %pS\n", frame_pc);
 366
 367         if (!frame_descr)
 368                 return;
 369
 370         print_decoded_frame_descr(frame_descr);
 371 }
 372
 373 static void print_address_description(void *addr, u8 tag)
 374 {
 375         struct page *page = kasan_addr_to_page(addr);
 376
 377         dump_stack();
 378         pr_err("\n");
 379
 380         if (page && PageSlab(page)) {
 381                 struct kmem_cache *cache = page->slab_cache;
 382                 void *object = nearest_obj(cache, page, addr);
 383
 384                 describe_object(cache, object, addr, tag);
 385         }
 386
 387         if (kernel_or_module_addr(addr) && !init_task_stack_addr(addr)) {
 388                 pr_err("The buggy address belongs to the variable:\n");
 389                 pr_err(" %pS\n", addr);
 390         }
 391
 392         if (page) {
 393                 pr_err("The buggy address belongs to the page:\n");
 394                 dump_page(page, "kasan: bad access detected");
 395         }
 396
 397         print_address_stack_frame(addr);
 398 }
 399
 400 static bool row_is_guilty(const void *row, const void *guilty)
 401 {
 402         return (row <= guilty) && (guilty < row + SHADOW_BYTES_PER_ROW);
 403 }
 404
 405 static int shadow_pointer_offset(const void *row, const void *shadow)
 406 {
 407         /* The length of ">ff00ff00ff00ff00: " is
 408          *    3 + (BITS_PER_LONG/8)*2 chars.
 409          */
 410         return 3 + (BITS_PER_LONG/8)*2 + (shadow - row)*2 +
 411                 (shadow - row) / SHADOW_BYTES_PER_BLOCK + 1;
 412 }
 413
 414 static void print_shadow_for_address(const void *addr)
 415 {
 416         int i;
 417         const void *shadow = kasan_mem_to_shadow(addr);
 418         const void *shadow_row;
 419
 420         shadow_row = (void *)round_down((unsigned long)shadow,
 421                                         SHADOW_BYTES_PER_ROW)
 422                 - SHADOW_ROWS_AROUND_ADDR * SHADOW_BYTES_PER_ROW;
 423
 424         pr_err("Memory state around the buggy address:\n");
 425
 426         for (i = -SHADOW_ROWS_AROUND_ADDR; i <= SHADOW_ROWS_AROUND_ADDR; i++) {
 427                 const void *kaddr = kasan_shadow_to_mem(shadow_row);
 428                 char buffer[4 + (BITS_PER_LONG/8)*2];
 429                 char shadow_buf[SHADOW_BYTES_PER_ROW];
 430
 431                 snprintf(buffer, sizeof(buffer),
 432                         (i == 0) ? ">%px: " : " %px: ", kaddr);
 433                 /*
 434                  * We should not pass a shadow pointer to generic
 435                  * function, because generic functions may try to
 436                  * access kasan mapping for the passed address.
 437                  */
 438                 memcpy(shadow_buf, shadow_row, SHADOW_BYTES_PER_ROW);
 439                 print_hex_dump(KERN_ERR, buffer,
 440                         DUMP_PREFIX_NONE, SHADOW_BYTES_PER_ROW, 1,
 441                         shadow_buf, SHADOW_BYTES_PER_ROW, 0);
 442
 443                 if (row_is_guilty(shadow_row, shadow))
 444                         pr_err("%*c\n",
 445                                 shadow_pointer_offset(shadow_row, shadow),
 446                                 '^');
 447
 448                 shadow_row += SHADOW_BYTES_PER_ROW;
 449         }
 450 }
 451
 452 static bool report_enabled(void)
 453 {
 454         if (current->kasan_depth)
 455                 return false;
 456         if (test_bit(KASAN_BIT_MULTI_SHOT, &kasan_flags))
 457                 return true;
 458         return !test_and_set_bit(KASAN_BIT_REPORTED, &kasan_flags);
 459 }
 460
 461 #if IS_ENABLED(CONFIG_KUNIT)
 462 static void kasan_update_kunit_status(struct kunit *cur_test)
 463 {
 464         struct kunit_resource *resource;
 465         struct kunit_kasan_expectation *kasan_data;
 466
 467         resource = kunit_find_named_resource(cur_test, "kasan_data");
 468
 469         if (!resource) {
 470                 kunit_set_failure(cur_test);
 471                 return;
 472         }
 473
 474         kasan_data = (struct kunit_kasan_expectation *)resource->data;
 475         kasan_data->report_found = true;
 476         kunit_put_resource(resource);
 477 }
 478 #endif /* IS_ENABLED(CONFIG_KUNIT) */
 479
 480 void kasan_report_invalid_free(void *object, unsigned long ip)
 481 {
 482         unsigned long flags;
 483         u8 tag = get_tag(object);
 484
 485         object = reset_tag(object);
 486
 487 #if IS_ENABLED(CONFIG_KUNIT)
 488         if (current->kunit_test)
 489                 kasan_update_kunit_status(current->kunit_test);
 490 #endif /* IS_ENABLED(CONFIG_KUNIT) */
 491
 492         start_report(&flags);
 493         pr_err("BUG: KASAN: double-free or invalid-free in %pS\n", (void *)ip);
 494         print_tags(tag, object);
 495         pr_err("\n");
 496         print_address_description(object, tag);
 497         pr_err("\n");
 498         print_shadow_for_address(object);
 499         end_report(&flags);
 500 }
 501
 502 static void __kasan_report(unsigned long addr, size_t size, bool is_write,
 503                                 unsigned long ip)
 504 {
 505         struct kasan_access_info info;
 506         void *tagged_addr;
 507         void *untagged_addr;
 508         unsigned long flags;
 509
 510 #if IS_ENABLED(CONFIG_KUNIT)
 511         if (current->kunit_test)
 512                 kasan_update_kunit_status(current->kunit_test);
 513 #endif /* IS_ENABLED(CONFIG_KUNIT) */
 514
 515         disable_trace_on_warning();
 516
 517         tagged_addr = (void *)addr;
 518         untagged_addr = reset_tag(tagged_addr);
 519
 520         info.access_addr = tagged_addr;
 521         if (addr_has_shadow(untagged_addr))
 522                 info.first_bad_addr = find_first_bad_addr(tagged_addr, size);
 523         else
 524                 info.first_bad_addr = untagged_addr;
 525         info.access_size = size;
 526         info.is_write = is_write;
 527         info.ip = ip;
 528
 529         start_report(&flags);
 530
 531         print_error_description(&info);
 532         if (addr_has_shadow(untagged_addr))
 533                 print_tags(get_tag(tagged_addr), info.first_bad_addr);
 534         pr_err("\n");
 535
 536         if (addr_has_shadow(untagged_addr)) {
 537                 print_address_description(untagged_addr, get_tag(tagged_addr));
 538                 pr_err("\n");
 539                 print_shadow_for_address(info.first_bad_addr);
 540         } else {
 541                 dump_stack();
 542         }
 543
 544         end_report(&flags);
 545 }
 546
 547 bool kasan_report(unsigned long addr, size_t size, bool is_write,
 548                         unsigned long ip)
 549 {
 550         unsigned long flags = user_access_save();
 551         bool ret = false;
 552
 553         if (likely(report_enabled())) {
 554                 __kasan_report(addr, size, is_write, ip);
 555                 ret = true;
 556         }
 557
 558         user_access_restore(flags);
 559
 560         return ret;
 561 }
 562
 563 /*
 564  * With CONFIG_KASAN, accesses to bogus pointers (outside the high
 565  * canonical half of the address space) cause out-of-bounds shadow memory reads
 566  * before the actual access. For addresses in the low canonical half of the
 567  * address space, as well as most non-canonical addresses, that out-of-bounds
 568  * shadow memory access lands in the non-canonical part of the address space.
 569  * Help the user figure out what the original bogus pointer was.
 570  */
 571 void kasan_non_canonical_hook(unsigned long addr)
 572 {
 573         unsigned long orig_addr;
 574         const char *bug_type;
 575
 576         if (addr < KASAN_SHADOW_OFFSET)
 577                 return;
 578
 579         orig_addr = (addr - KASAN_SHADOW_OFFSET) << KASAN_SHADOW_SCALE_SHIFT;
 580         /*
 581          * For faults near the shadow address for NULL, we can be fairly certain
 582          * that this is a KASAN shadow memory access.
 583          * For faults that correspond to shadow for low canonical addresses, we
 584          * can still be pretty sure - that shadow region is a fairly narrow
 585          * chunk of the non-canonical address space.
 586          * But faults that look like shadow for non-canonical addresses are a
 587          * really large chunk of the address space. In that case, we still
 588          * print the decoded address, but make it clear that this is not
 589          * necessarily what's actually going on.
 590          */
 591         if (orig_addr < PAGE_SIZE)
 592                 bug_type = "null-ptr-deref";
 593         else if (orig_addr < TASK_SIZE)
 594                 bug_type = "probably user-memory-access";
 595         else
 596                 bug_type = "maybe wild-memory-access";
 597         pr_alert("KASAN: %s in range [0x%016lx-0x%016lx]\n", bug_type,
 598                  orig_addr, orig_addr + KASAN_SHADOW_MASK);
 599 }