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
  12 #include <linux/bitops.h>
  13 #include <linux/ftrace.h>
  14 #include <linux/init.h>
  15 #include <linux/kernel.h>
  16 #include <linux/mm.h>
  17 #include <linux/printk.h>
  18 #include <linux/sched.h>
  19 #include <linux/slab.h>
  20 #include <linux/stackdepot.h>
  21 #include <linux/stacktrace.h>
  22 #include <linux/string.h>
  23 #include <linux/types.h>
  24 #include <linux/kasan.h>
  25 #include <linux/module.h>
  26 #include <linux/sched/task_stack.h>
  27 #include <linux/uaccess.h>
  28
  29 #include <asm/sections.h>
  30
  31 #include <kunit/test.h>
  32
  33 #include "kasan.h"
  34 #include "../slab.h"
  35
  36 /* Shadow layout customization. */
  37 #define SHADOW_BYTES_PER_BLOCK 1
  38 #define SHADOW_BLOCKS_PER_ROW 16
  39 #define SHADOW_BYTES_PER_ROW (SHADOW_BLOCKS_PER_ROW * SHADOW_BYTES_PER_BLOCK)
  40 #define SHADOW_ROWS_AROUND_ADDR 2
  41
  42 static unsigned long kasan_flags;
  43
  44 #define KASAN_BIT_REPORTED      0
  45 #define KASAN_BIT_MULTI_SHOT    1
  46
  47 bool kasan_save_enable_multi_shot(void)
  48 {
  49         return test_and_set_bit(KASAN_BIT_MULTI_SHOT, &kasan_flags);
  50 }
  51 EXPORT_SYMBOL_GPL(kasan_save_enable_multi_shot);
  52
  53 void kasan_restore_multi_shot(bool enabled)
  54 {
  55         if (!enabled)
  56                 clear_bit(KASAN_BIT_MULTI_SHOT, &kasan_flags);
  57 }
  58 EXPORT_SYMBOL_GPL(kasan_restore_multi_shot);
  59
  60 static int __init kasan_set_multi_shot(char *str)
  61 {
  62         set_bit(KASAN_BIT_MULTI_SHOT, &kasan_flags);
  63         return 1;
  64 }
  65 __setup("kasan_multi_shot", kasan_set_multi_shot);
  66
  67 static void print_error_description(struct kasan_access_info *info)
  68 {
  69         pr_err("BUG: KASAN: %s in %pS\n",
  70                 get_bug_type(info), (void *)info->ip);
  71         pr_err("%s of size %zu at addr %px by task %s/%d\n",
  72                 info->is_write ? "Write" : "Read", info->access_size,
  73                 info->access_addr, current->comm, task_pid_nr(current));
  74 }
  75
  76 static DEFINE_SPINLOCK(report_lock);
  77
  78 static void start_report(unsigned long *flags)
  79 {
  80         /*
  81          * Make sure we don't end up in loop.
  82          */
  83         kasan_disable_current();
  84         spin_lock_irqsave(&report_lock, *flags);
  85         pr_err("==================================================================\n");
  86 }
  87
  88 static void end_report(unsigned long *flags)
  89 {
  90         pr_err("==================================================================\n");
  91         add_taint(TAINT_BAD_PAGE, LOCKDEP_NOW_UNRELIABLE);
  92         spin_unlock_irqrestore(&report_lock, *flags);
  93         if (panic_on_warn && !test_bit(KASAN_BIT_MULTI_SHOT, &kasan_flags)) {
  94                 /*
  95                  * This thread may hit another WARN() in the panic path.
  96                  * Resetting this prevents additional WARN() from panicking the
  97                  * system on this thread.  Other threads are blocked by the
  98                  * panic_mutex in panic().
  99                  */
 100                 panic_on_warn = 0;
 101                 panic("panic_on_warn set ...\n");
 102         }
 103         kasan_enable_current();
 104 }
 105
 106 static void print_stack(depot_stack_handle_t stack)
 107 {
 108         unsigned long *entries;
 109         unsigned int nr_entries;
 110
 111         nr_entries = stack_depot_fetch(stack, &entries);
 112         stack_trace_print(entries, nr_entries, 0);
 113 }
 114
 115 static void print_track(struct kasan_track *track, const char *prefix)
 116 {
 117         pr_err("%s by task %u:\n", prefix, track->pid);
 118         if (track->stack) {
 119                 print_stack(track->stack);
 120         } else {
 121                 pr_err("(stack is not available)\n");
 122         }
 123 }
 124
 125 struct page *kasan_addr_to_page(const void *addr)
 126 {
 127         if ((addr >= (void *)PAGE_OFFSET) &&
 128                         (addr < high_memory))
 129                 return virt_to_head_page(addr);
 130         return NULL;
 131 }
 132
 133 static void describe_object_addr(struct kmem_cache *cache, void *object,
 134                                 const void *addr)
 135 {
 136         unsigned long access_addr = (unsigned long)addr;
 137         unsigned long object_addr = (unsigned long)object;
 138         const char *rel_type;
 139         int rel_bytes;
 140
 141         pr_err("The buggy address belongs to the object at %px\n"
 142                " which belongs to the cache %s of size %d\n",
 143                 object, cache->name, cache->object_size);
 144
 145         if (!addr)
 146                 return;
 147
 148         if (access_addr < object_addr) {
 149                 rel_type = "to the left";
 150                 rel_bytes = object_addr - access_addr;
 151         } else if (access_addr >= object_addr + cache->object_size) {
 152                 rel_type = "to the right";
 153                 rel_bytes = access_addr - (object_addr + cache->object_size);
 154         } else {
 155                 rel_type = "inside";
 156                 rel_bytes = access_addr - object_addr;
 157         }
 158
 159         pr_err("The buggy address is located %d bytes %s of\n"
 160                " %d-byte region [%px, %px)\n",
 161                 rel_bytes, rel_type, cache->object_size, (void *)object_addr,
 162                 (void *)(object_addr + cache->object_size));
 163 }
 164
 165 static void describe_object(struct kmem_cache *cache, void *object,
 166                                 const void *addr, u8 tag)
 167 {
 168         struct kasan_alloc_meta *alloc_info = get_alloc_info(cache, object);
 169
 170         if (cache->flags & SLAB_KASAN) {
 171                 struct kasan_track *free_track;
 172
 173                 print_track(&alloc_info->alloc_track, "Allocated");
 174                 pr_err("\n");
 175                 free_track = kasan_get_free_track(cache, object, tag);
 176                 if (free_track) {
 177                         print_track(free_track, "Freed");
 178                         pr_err("\n");
 179                 }
 180
 181 #ifdef CONFIG_KASAN_GENERIC
 182                 if (alloc_info->aux_stack[0]) {
 183                         pr_err("Last potentially related work creation:\n");
 184                         print_stack(alloc_info->aux_stack[0]);
 185                         pr_err("\n");
 186                 }
 187                 if (alloc_info->aux_stack[1]) {
 188                         pr_err("Second to last potentially related work creation:\n");
 189                         print_stack(alloc_info->aux_stack[1]);
 190                         pr_err("\n");
 191                 }
 192 #endif
 193         }
 194
 195         describe_object_addr(cache, object, addr);
 196 }
 197
 198 static inline bool kernel_or_module_addr(const void *addr)
 199 {
 200         if (addr >= (void *)_stext && addr < (void *)_end)
 201                 return true;
 202         if (is_module_address((unsigned long)addr))
 203                 return true;
 204         return false;
 205 }
 206
 207 static inline bool init_task_stack_addr(const void *addr)
 208 {
 209         return addr >= (void *)&init_thread_union.stack &&
 210                 (addr <= (void *)&init_thread_union.stack +
 211                         sizeof(init_thread_union.stack));
 212 }
 213
 214 static bool __must_check tokenize_frame_descr(const char **frame_descr,
 215                                               char *token, size_t max_tok_len,
 216                                               unsigned long *value)
 217 {
 218         const char *sep = strchr(*frame_descr, ' ');
 219
 220         if (sep == NULL)
 221                 sep = *frame_descr + strlen(*frame_descr);
 222
 223         if (token != NULL) {
 224                 const size_t tok_len = sep - *frame_descr;
 225
 226                 if (tok_len + 1 > max_tok_len) {
 227                         pr_err("KASAN internal error: frame description too long: %s\n",
 228                                *frame_descr);
 229                         return false;
 230                 }
 231
 232                 /* Copy token (+ 1 byte for '\0'). */
 233                 strlcpy(token, *frame_descr, tok_len + 1);
 234         }
 235
 236         /* Advance frame_descr past separator. */
 237         *frame_descr = sep + 1;
 238
 239         if (value != NULL && kstrtoul(token, 10, value)) {
 240                 pr_err("KASAN internal error: not a valid number: %s\n", token);
 241                 return false;
 242         }
 243
 244         return true;
 245 }
 246
 247 static void print_decoded_frame_descr(const char *frame_descr)
 248 {
 249         /*
 250          * We need to parse the following string:
 251          *    "n alloc_1 alloc_2 ... alloc_n"
 252          * where alloc_i looks like
 253          *    "offset size len name"
 254          * or "offset size len name:line".
 255          */
 256
 257         char token[64];
 258         unsigned long num_objects;
 259
 260         if (!tokenize_frame_descr(&frame_descr, token, sizeof(token),
 261                                   &num_objects))
 262                 return;
 263
 264         pr_err("\n");
 265         pr_err("this frame has %lu %s:\n", num_objects,
 266                num_objects == 1 ? "object" : "objects");
 267
 268         while (num_objects--) {
 269                 unsigned long offset;
 270                 unsigned long size;
 271
 272                 /* access offset */
 273                 if (!tokenize_frame_descr(&frame_descr, token, sizeof(token),
 274                                           &offset))
 275                         return;
 276                 /* access size */
 277                 if (!tokenize_frame_descr(&frame_descr, token, sizeof(token),
 278                                           &size))
 279                         return;
 280                 /* name length (unused) */
 281                 if (!tokenize_frame_descr(&frame_descr, NULL, 0, NULL))
 282                         return;
 283                 /* object name */
 284                 if (!tokenize_frame_descr(&frame_descr, token, sizeof(token),
 285                                           NULL))
 286                         return;
 287
 288                 /* Strip line number; without filename it's not very helpful. */
 289                 strreplace(token, ':', '\0');
 290
 291                 /* Finally, print object information. */
 292                 pr_err(" [%lu, %lu) '%s'", offset, offset + size, token);
 293         }
 294 }
 295
 296 static bool __must_check get_address_stack_frame_info(const void *addr,
 297                                                       unsigned long *offset,
 298                                                       const char **frame_descr,
 299                                                       const void **frame_pc)
 300 {
 301         unsigned long aligned_addr;
 302         unsigned long mem_ptr;
 303         const u8 *shadow_bottom;
 304         const u8 *shadow_ptr;
 305         const unsigned long *frame;
 306
 307         BUILD_BUG_ON(IS_ENABLED(CONFIG_STACK_GROWSUP));
 308
 309         /*
 310          * NOTE: We currently only support printing frame information for
 311          * accesses to the task's own stack.
 312          */
 313         if (!object_is_on_stack(addr))
 314                 return false;
 315
 316         aligned_addr = round_down((unsigned long)addr, sizeof(long));
 317         mem_ptr = round_down(aligned_addr, KASAN_GRANULE_SIZE);
 318         shadow_ptr = kasan_mem_to_shadow((void *)aligned_addr);
 319         shadow_bottom = kasan_mem_to_shadow(end_of_stack(current));
 320
 321         while (shadow_ptr >= shadow_bottom && *shadow_ptr != KASAN_STACK_LEFT) {
 322                 shadow_ptr--;
 323                 mem_ptr -= KASAN_GRANULE_SIZE;
 324         }
 325
 326         while (shadow_ptr >= shadow_bottom && *shadow_ptr == KASAN_STACK_LEFT) {
 327                 shadow_ptr--;
 328                 mem_ptr -= KASAN_GRANULE_SIZE;
 329         }
 330
 331         if (shadow_ptr < shadow_bottom)
 332                 return false;
 333
 334         frame = (const unsigned long *)(mem_ptr + KASAN_GRANULE_SIZE);
 335         if (frame[0] != KASAN_CURRENT_STACK_FRAME_MAGIC) {
 336                 pr_err("KASAN internal error: frame info validation failed; invalid marker: %lu\n",
 337                        frame[0]);
 338                 return false;
 339         }
 340
 341         *offset = (unsigned long)addr - (unsigned long)frame;
 342         *frame_descr = (const char *)frame[1];
 343         *frame_pc = (void *)frame[2];
 344
 345         return true;
 346 }
 347
 348 static void print_address_stack_frame(const void *addr)
 349 {
 350         unsigned long offset;
 351         const char *frame_descr;
 352         const void *frame_pc;
 353
 354         if (IS_ENABLED(CONFIG_KASAN_SW_TAGS))
 355                 return;
 356
 357         if (!get_address_stack_frame_info(addr, &offset, &frame_descr,
 358                                           &frame_pc))
 359                 return;
 360
 361         /*
 362          * get_address_stack_frame_info only returns true if the given addr is
 363          * on the current task's stack.
 364          */
 365         pr_err("\n");
 366         pr_err("addr %px is located in stack of task %s/%d at offset %lu in frame:\n",
 367                addr, current->comm, task_pid_nr(current), offset);
 368         pr_err(" %pS\n", frame_pc);
 369
 370         if (!frame_descr)
 371                 return;
 372
 373         print_decoded_frame_descr(frame_descr);
 374 }
 375
 376 static void print_address_description(void *addr, u8 tag)
 377 {
 378         struct page *page = kasan_addr_to_page(addr);
 379
 380         dump_stack();
 381         pr_err("\n");
 382
 383         if (page && PageSlab(page)) {
 384                 struct kmem_cache *cache = page->slab_cache;
 385                 void *object = nearest_obj(cache, page, addr);
 386
 387                 describe_object(cache, object, addr, tag);
 388         }
 389
 390         if (kernel_or_module_addr(addr) && !init_task_stack_addr(addr)) {
 391                 pr_err("The buggy address belongs to the variable:\n");
 392                 pr_err(" %pS\n", addr);
 393         }
 394
 395         if (page) {
 396                 pr_err("The buggy address belongs to the page:\n");
 397                 dump_page(page, "kasan: bad access detected");
 398         }
 399
 400         print_address_stack_frame(addr);
 401 }
 402
 403 static bool row_is_guilty(const void *row, const void *guilty)
 404 {
 405         return (row <= guilty) && (guilty < row + SHADOW_BYTES_PER_ROW);
 406 }
 407
 408 static int shadow_pointer_offset(const void *row, const void *shadow)
 409 {
 410         /* The length of ">ff00ff00ff00ff00: " is
 411          *    3 + (BITS_PER_LONG/8)*2 chars.
 412          */
 413         return 3 + (BITS_PER_LONG/8)*2 + (shadow - row)*2 +
 414                 (shadow - row) / SHADOW_BYTES_PER_BLOCK + 1;
 415 }
 416
 417 static void print_shadow_for_address(const void *addr)
 418 {
 419         int i;
 420         const void *shadow = kasan_mem_to_shadow(addr);
 421         const void *shadow_row;
 422
 423         shadow_row = (void *)round_down((unsigned long)shadow,
 424                                         SHADOW_BYTES_PER_ROW)
 425                 - SHADOW_ROWS_AROUND_ADDR * SHADOW_BYTES_PER_ROW;
 426
 427         pr_err("Memory state around the buggy address:\n");
 428
 429         for (i = -SHADOW_ROWS_AROUND_ADDR; i <= SHADOW_ROWS_AROUND_ADDR; i++) {
 430                 const void *kaddr = kasan_shadow_to_mem(shadow_row);
 431                 char buffer[4 + (BITS_PER_LONG/8)*2];
 432                 char shadow_buf[SHADOW_BYTES_PER_ROW];
 433
 434                 snprintf(buffer, sizeof(buffer),
 435                         (i == 0) ? ">%px: " : " %px: ", kaddr);
 436                 /*
 437                  * We should not pass a shadow pointer to generic
 438                  * function, because generic functions may try to
 439                  * access kasan mapping for the passed address.
 440                  */
 441                 memcpy(shadow_buf, shadow_row, SHADOW_BYTES_PER_ROW);
 442                 print_hex_dump(KERN_ERR, buffer,
 443                         DUMP_PREFIX_NONE, SHADOW_BYTES_PER_ROW, 1,
 444                         shadow_buf, SHADOW_BYTES_PER_ROW, 0);
 445
 446                 if (row_is_guilty(shadow_row, shadow))
 447                         pr_err("%*c\n",
 448                                 shadow_pointer_offset(shadow_row, shadow),
 449                                 '^');
 450
 451                 shadow_row += SHADOW_BYTES_PER_ROW;
 452         }
 453 }
 454
 455 static bool report_enabled(void)
 456 {
 457         if (current->kasan_depth)
 458                 return false;
 459         if (test_bit(KASAN_BIT_MULTI_SHOT, &kasan_flags))
 460                 return true;
 461         return !test_and_set_bit(KASAN_BIT_REPORTED, &kasan_flags);
 462 }
 463
 464 #if IS_ENABLED(CONFIG_KUNIT)
 465 static void kasan_update_kunit_status(struct kunit *cur_test)
 466 {
 467         struct kunit_resource *resource;
 468         struct kunit_kasan_expectation *kasan_data;
 469
 470         resource = kunit_find_named_resource(cur_test, "kasan_data");
 471
 472         if (!resource) {
 473                 kunit_set_failure(cur_test);
 474                 return;
 475         }
 476
 477         kasan_data = (struct kunit_kasan_expectation *)resource->data;
 478         kasan_data->report_found = true;
 479         kunit_put_resource(resource);
 480 }
 481 #endif /* IS_ENABLED(CONFIG_KUNIT) */
 482
 483 void kasan_report_invalid_free(void *object, unsigned long ip)
 484 {
 485         unsigned long flags;
 486         u8 tag = get_tag(object);
 487
 488         object = reset_tag(object);
 489
 490 #if IS_ENABLED(CONFIG_KUNIT)
 491         if (current->kunit_test)
 492                 kasan_update_kunit_status(current->kunit_test);
 493 #endif /* IS_ENABLED(CONFIG_KUNIT) */
 494
 495         start_report(&flags);
 496         pr_err("BUG: KASAN: double-free or invalid-free in %pS\n", (void *)ip);
 497         print_tags(tag, object);
 498         pr_err("\n");
 499         print_address_description(object, tag);
 500         pr_err("\n");
 501         print_shadow_for_address(object);
 502         end_report(&flags);
 503 }
 504
 505 static void __kasan_report(unsigned long addr, size_t size, bool is_write,
 506                                 unsigned long ip)
 507 {
 508         struct kasan_access_info info;
 509         void *tagged_addr;
 510         void *untagged_addr;
 511         unsigned long flags;
 512
 513 #if IS_ENABLED(CONFIG_KUNIT)
 514         if (current->kunit_test)
 515                 kasan_update_kunit_status(current->kunit_test);
 516 #endif /* IS_ENABLED(CONFIG_KUNIT) */
 517
 518         disable_trace_on_warning();
 519
 520         tagged_addr = (void *)addr;
 521         untagged_addr = reset_tag(tagged_addr);
 522
 523         info.access_addr = tagged_addr;
 524         if (addr_has_shadow(untagged_addr))
 525                 info.first_bad_addr = find_first_bad_addr(tagged_addr, size);
 526         else
 527                 info.first_bad_addr = untagged_addr;
 528         info.access_size = size;
 529         info.is_write = is_write;
 530         info.ip = ip;
 531
 532         start_report(&flags);
 533
 534         print_error_description(&info);
 535         if (addr_has_shadow(untagged_addr))
 536                 print_tags(get_tag(tagged_addr), info.first_bad_addr);
 537         pr_err("\n");
 538
 539         if (addr_has_shadow(untagged_addr)) {
 540                 print_address_description(untagged_addr, get_tag(tagged_addr));
 541                 pr_err("\n");
 542                 print_shadow_for_address(info.first_bad_addr);
 543         } else {
 544                 dump_stack();
 545         }
 546
 547         end_report(&flags);
 548 }
 549
 550 bool kasan_report(unsigned long addr, size_t size, bool is_write,
 551                         unsigned long ip)
 552 {
 553         unsigned long flags = user_access_save();
 554         bool ret = false;
 555
 556         if (likely(report_enabled())) {
 557                 __kasan_report(addr, size, is_write, ip);
 558                 ret = true;
 559         }
 560
 561         user_access_restore(flags);
 562
 563         return ret;
 564 }
 565
 566 #ifdef CONFIG_KASAN_INLINE
 567 /*
 568  * With CONFIG_KASAN_INLINE, accesses to bogus pointers (outside the high
 569  * canonical half of the address space) cause out-of-bounds shadow memory reads
 570  * before the actual access. For addresses in the low canonical half of the
 571  * address space, as well as most non-canonical addresses, that out-of-bounds
 572  * shadow memory access lands in the non-canonical part of the address space.
 573  * Help the user figure out what the original bogus pointer was.
 574  */
 575 void kasan_non_canonical_hook(unsigned long addr)
 576 {
 577         unsigned long orig_addr;
 578         const char *bug_type;
 579
 580         if (addr < KASAN_SHADOW_OFFSET)
 581                 return;
 582
 583         orig_addr = (addr - KASAN_SHADOW_OFFSET) << KASAN_SHADOW_SCALE_SHIFT;
 584         /*
 585          * For faults near the shadow address for NULL, we can be fairly certain
 586          * that this is a KASAN shadow memory access.
 587          * For faults that correspond to shadow for low canonical addresses, we
 588          * can still be pretty sure - that shadow region is a fairly narrow
 589          * chunk of the non-canonical address space.
 590          * But faults that look like shadow for non-canonical addresses are a
 591          * really large chunk of the address space. In that case, we still
 592          * print the decoded address, but make it clear that this is not
 593          * necessarily what's actually going on.
 594          */
 595         if (orig_addr < PAGE_SIZE)
 596                 bug_type = "null-ptr-deref";
 597         else if (orig_addr < TASK_SIZE)
 598                 bug_type = "probably user-memory-access";
 599         else
 600                 bug_type = "maybe wild-memory-access";
 601         pr_alert("KASAN: %s in range [0x%016lx-0x%016lx]\n", bug_type,
 602                  orig_addr, orig_addr + KASAN_GRANULE_SIZE - 1);
 603 }
 604 #endif