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 (panic_on_warn && !test_bit(KASAN_BIT_MULTI_SHOT, &kasan_flags)) {
  99                 /*
 100                  * This thread may hit another WARN() in the panic path.
 101                  * Resetting this prevents additional WARN() from panicking the
 102                  * system on this thread.  Other threads are blocked by the
 103                  * panic_mutex in panic().
 104                  */
 105                 panic_on_warn = 0;
 106                 panic("panic_on_warn set ...\n");
 107         }
 108         kasan_enable_current();
 109 }
 110
 111 static void print_stack(depot_stack_handle_t stack)
 112 {
 113         unsigned long *entries;
 114         unsigned int nr_entries;
 115
 116         nr_entries = stack_depot_fetch(stack, &entries);
 117         stack_trace_print(entries, nr_entries, 0);
 118 }
 119
 120 static void print_track(struct kasan_track *track, const char *prefix)
 121 {
 122         pr_err("%s by task %u:\n", prefix, track->pid);
 123         if (track->stack) {
 124                 print_stack(track->stack);
 125         } else {
 126                 pr_err("(stack is not available)\n");
 127         }
 128 }
 129
 130 struct page *kasan_addr_to_page(const void *addr)
 131 {
 132         if ((addr >= (void *)PAGE_OFFSET) &&
 133                         (addr < high_memory))
 134                 return virt_to_head_page(addr);
 135         return NULL;
 136 }
 137
 138 static void describe_object_addr(struct kmem_cache *cache, void *object,
 139                                 const void *addr)
 140 {
 141         unsigned long access_addr = (unsigned long)addr;
 142         unsigned long object_addr = (unsigned long)object;
 143         const char *rel_type;
 144         int rel_bytes;
 145
 146         pr_err("The buggy address belongs to the object at %px\n"
 147                " which belongs to the cache %s of size %d\n",
 148                 object, cache->name, cache->object_size);
 149
 150         if (!addr)
 151                 return;
 152
 153         if (access_addr < object_addr) {
 154                 rel_type = "to the left";
 155                 rel_bytes = object_addr - access_addr;
 156         } else if (access_addr >= object_addr + cache->object_size) {
 157                 rel_type = "to the right";
 158                 rel_bytes = access_addr - (object_addr + cache->object_size);
 159         } else {
 160                 rel_type = "inside";
 161                 rel_bytes = access_addr - object_addr;
 162         }
 163
 164         pr_err("The buggy address is located %d bytes %s of\n"
 165                " %d-byte region [%px, %px)\n",
 166                 rel_bytes, rel_type, cache->object_size, (void *)object_addr,
 167                 (void *)(object_addr + cache->object_size));
 168 }
 169
 170 static void describe_object(struct kmem_cache *cache, void *object,
 171                                 const void *addr, u8 tag)
 172 {
 173         struct kasan_alloc_meta *alloc_info = get_alloc_info(cache, object);
 174
 175         if (cache->flags & SLAB_KASAN) {
 176                 struct kasan_track *free_track;
 177
 178                 print_track(&alloc_info->alloc_track, "Allocated");
 179                 pr_err("\n");
 180                 free_track = kasan_get_free_track(cache, object, tag);
 181                 if (free_track) {
 182                         print_track(free_track, "Freed");
 183                         pr_err("\n");
 184                 }
 185
 186 #ifdef CONFIG_KASAN_GENERIC
 187                 if (alloc_info->aux_stack[0]) {
 188                         pr_err("Last potentially related work creation:\n");
 189                         print_stack(alloc_info->aux_stack[0]);
 190                         pr_err("\n");
 191                 }
 192                 if (alloc_info->aux_stack[1]) {
 193                         pr_err("Second to last potentially related work creation:\n");
 194                         print_stack(alloc_info->aux_stack[1]);
 195                         pr_err("\n");
 196                 }
 197 #endif
 198         }
 199
 200         describe_object_addr(cache, object, addr);
 201 }
 202
 203 static inline bool kernel_or_module_addr(const void *addr)
 204 {
 205         if (addr >= (void *)_stext && addr < (void *)_end)
 206                 return true;
 207         if (is_module_address((unsigned long)addr))
 208                 return true;
 209         return false;
 210 }
 211
 212 static inline bool init_task_stack_addr(const void *addr)
 213 {
 214         return addr >= (void *)&init_thread_union.stack &&
 215                 (addr <= (void *)&init_thread_union.stack +
 216                         sizeof(init_thread_union.stack));
 217 }
 218
 219 static bool __must_check tokenize_frame_descr(const char **frame_descr,
 220                                               char *token, size_t max_tok_len,
 221                                               unsigned long *value)
 222 {
 223         const char *sep = strchr(*frame_descr, ' ');
 224
 225         if (sep == NULL)
 226                 sep = *frame_descr + strlen(*frame_descr);
 227
 228         if (token != NULL) {
 229                 const size_t tok_len = sep - *frame_descr;
 230
 231                 if (tok_len + 1 > max_tok_len) {
 232                         pr_err("KASAN internal error: frame description too long: %s\n",
 233                                *frame_descr);
 234                         return false;
 235                 }
 236
 237                 /* Copy token (+ 1 byte for '\0'). */
 238                 strlcpy(token, *frame_descr, tok_len + 1);
 239         }
 240
 241         /* Advance frame_descr past separator. */
 242         *frame_descr = sep + 1;
 243
 244         if (value != NULL && kstrtoul(token, 10, value)) {
 245                 pr_err("KASAN internal error: not a valid number: %s\n", token);
 246                 return false;
 247         }
 248
 249         return true;
 250 }
 251
 252 static void print_decoded_frame_descr(const char *frame_descr)
 253 {
 254         /*
 255          * We need to parse the following string:
 256          *    "n alloc_1 alloc_2 ... alloc_n"
 257          * where alloc_i looks like
 258          *    "offset size len name"
 259          * or "offset size len name:line".
 260          */
 261
 262         char token[64];
 263         unsigned long num_objects;
 264
 265         if (!tokenize_frame_descr(&frame_descr, token, sizeof(token),
 266                                   &num_objects))
 267                 return;
 268
 269         pr_err("\n");
 270         pr_err("this frame has %lu %s:\n", num_objects,
 271                num_objects == 1 ? "object" : "objects");
 272
 273         while (num_objects--) {
 274                 unsigned long offset;
 275                 unsigned long size;
 276
 277                 /* access offset */
 278                 if (!tokenize_frame_descr(&frame_descr, token, sizeof(token),
 279                                           &offset))
 280                         return;
 281                 /* access size */
 282                 if (!tokenize_frame_descr(&frame_descr, token, sizeof(token),
 283                                           &size))
 284                         return;
 285                 /* name length (unused) */
 286                 if (!tokenize_frame_descr(&frame_descr, NULL, 0, NULL))
 287                         return;
 288                 /* object name */
 289                 if (!tokenize_frame_descr(&frame_descr, token, sizeof(token),
 290                                           NULL))
 291                         return;
 292
 293                 /* Strip line number; without filename it's not very helpful. */
 294                 strreplace(token, ':', '\0');
 295
 296                 /* Finally, print object information. */
 297                 pr_err(" [%lu, %lu) '%s'", offset, offset + size, token);
 298         }
 299 }
 300
 301 static bool __must_check get_address_stack_frame_info(const void *addr,
 302                                                       unsigned long *offset,
 303                                                       const char **frame_descr,
 304                                                       const void **frame_pc)
 305 {
 306         unsigned long aligned_addr;
 307         unsigned long mem_ptr;
 308         const u8 *shadow_bottom;
 309         const u8 *shadow_ptr;
 310         const unsigned long *frame;
 311
 312         BUILD_BUG_ON(IS_ENABLED(CONFIG_STACK_GROWSUP));
 313
 314         /*
 315          * NOTE: We currently only support printing frame information for
 316          * accesses to the task's own stack.
 317          */
 318         if (!object_is_on_stack(addr))
 319                 return false;
 320
 321         aligned_addr = round_down((unsigned long)addr, sizeof(long));
 322         mem_ptr = round_down(aligned_addr, KASAN_SHADOW_SCALE_SIZE);
 323         shadow_ptr = kasan_mem_to_shadow((void *)aligned_addr);
 324         shadow_bottom = kasan_mem_to_shadow(end_of_stack(current));
 325
 326         while (shadow_ptr >= shadow_bottom && *shadow_ptr != KASAN_STACK_LEFT) {
 327                 shadow_ptr--;
 328                 mem_ptr -= KASAN_SHADOW_SCALE_SIZE;
 329         }
 330
 331         while (shadow_ptr >= shadow_bottom && *shadow_ptr == KASAN_STACK_LEFT) {
 332                 shadow_ptr--;
 333                 mem_ptr -= KASAN_SHADOW_SCALE_SIZE;
 334         }
 335
 336         if (shadow_ptr < shadow_bottom)
 337                 return false;
 338
 339         frame = (const unsigned long *)(mem_ptr + KASAN_SHADOW_SCALE_SIZE);
 340         if (frame[0] != KASAN_CURRENT_STACK_FRAME_MAGIC) {
 341                 pr_err("KASAN internal error: frame info validation failed; invalid marker: %lu\n",
 342                        frame[0]);
 343                 return false;
 344         }
 345
 346         *offset = (unsigned long)addr - (unsigned long)frame;
 347         *frame_descr = (const char *)frame[1];
 348         *frame_pc = (void *)frame[2];
 349
 350         return true;
 351 }
 352
 353 static void print_address_stack_frame(const void *addr)
 354 {
 355         unsigned long offset;
 356         const char *frame_descr;
 357         const void *frame_pc;
 358
 359         if (IS_ENABLED(CONFIG_KASAN_SW_TAGS))
 360                 return;
 361
 362         if (!get_address_stack_frame_info(addr, &offset, &frame_descr,
 363                                           &frame_pc))
 364                 return;
 365
 366         /*
 367          * get_address_stack_frame_info only returns true if the given addr is
 368          * on the current task's stack.
 369          */
 370         pr_err("\n");
 371         pr_err("addr %px is located in stack of task %s/%d at offset %lu in frame:\n",
 372                addr, current->comm, task_pid_nr(current), offset);
 373         pr_err(" %pS\n", frame_pc);
 374
 375         if (!frame_descr)
 376                 return;
 377
 378         print_decoded_frame_descr(frame_descr);
 379 }
 380
 381 static void print_address_description(void *addr, u8 tag)
 382 {
 383         struct page *page = kasan_addr_to_page(addr);
 384
 385         dump_stack();
 386         pr_err("\n");
 387
 388         if (page && PageSlab(page)) {
 389                 struct kmem_cache *cache = page->slab_cache;
 390                 void *object = nearest_obj(cache, page, addr);
 391
 392                 describe_object(cache, object, addr, tag);
 393         }
 394
 395         if (kernel_or_module_addr(addr) && !init_task_stack_addr(addr)) {
 396                 pr_err("The buggy address belongs to the variable:\n");
 397                 pr_err(" %pS\n", addr);
 398         }
 399
 400         if (page) {
 401                 pr_err("The buggy address belongs to the page:\n");
 402                 dump_page(page, "kasan: bad access detected");
 403         }
 404
 405         print_address_stack_frame(addr);
 406 }
 407
 408 static bool row_is_guilty(const void *row, const void *guilty)
 409 {
 410         return (row <= guilty) && (guilty < row + SHADOW_BYTES_PER_ROW);
 411 }
 412
 413 static int shadow_pointer_offset(const void *row, const void *shadow)
 414 {
 415         /* The length of ">ff00ff00ff00ff00: " is
 416          *    3 + (BITS_PER_LONG/8)*2 chars.
 417          */
 418         return 3 + (BITS_PER_LONG/8)*2 + (shadow - row)*2 +
 419                 (shadow - row) / SHADOW_BYTES_PER_BLOCK + 1;
 420 }
 421
 422 static void print_shadow_for_address(const void *addr)
 423 {
 424         int i;
 425         const void *shadow = kasan_mem_to_shadow(addr);
 426         const void *shadow_row;
 427
 428         shadow_row = (void *)round_down((unsigned long)shadow,
 429                                         SHADOW_BYTES_PER_ROW)
 430                 - SHADOW_ROWS_AROUND_ADDR * SHADOW_BYTES_PER_ROW;
 431
 432         pr_err("Memory state around the buggy address:\n");
 433
 434         for (i = -SHADOW_ROWS_AROUND_ADDR; i <= SHADOW_ROWS_AROUND_ADDR; i++) {
 435                 const void *kaddr = kasan_shadow_to_mem(shadow_row);
 436                 char buffer[4 + (BITS_PER_LONG/8)*2];
 437                 char shadow_buf[SHADOW_BYTES_PER_ROW];
 438
 439                 snprintf(buffer, sizeof(buffer),
 440                         (i == 0) ? ">%px: " : " %px: ", kaddr);
 441                 /*
 442                  * We should not pass a shadow pointer to generic
 443                  * function, because generic functions may try to
 444                  * access kasan mapping for the passed address.
 445                  */
 446                 memcpy(shadow_buf, shadow_row, SHADOW_BYTES_PER_ROW);
 447                 print_hex_dump(KERN_ERR, buffer,
 448                         DUMP_PREFIX_NONE, SHADOW_BYTES_PER_ROW, 1,
 449                         shadow_buf, SHADOW_BYTES_PER_ROW, 0);
 450
 451                 if (row_is_guilty(shadow_row, shadow))
 452                         pr_err("%*c\n",
 453                                 shadow_pointer_offset(shadow_row, shadow),
 454                                 '^');
 455
 456                 shadow_row += SHADOW_BYTES_PER_ROW;
 457         }
 458 }
 459
 460 static bool report_enabled(void)
 461 {
 462         if (current->kasan_depth)
 463                 return false;
 464         if (test_bit(KASAN_BIT_MULTI_SHOT, &kasan_flags))
 465                 return true;
 466         return !test_and_set_bit(KASAN_BIT_REPORTED, &kasan_flags);
 467 }
 468
 469 #if IS_ENABLED(CONFIG_KUNIT)
 470 static void kasan_update_kunit_status(struct kunit *cur_test)
 471 {
 472         struct kunit_resource *resource;
 473         struct kunit_kasan_expectation *kasan_data;
 474
 475         resource = kunit_find_named_resource(cur_test, "kasan_data");
 476
 477         if (!resource) {
 478                 kunit_set_failure(cur_test);
 479                 return;
 480         }
 481
 482         kasan_data = (struct kunit_kasan_expectation *)resource->data;
 483         kasan_data->report_found = true;
 484         kunit_put_resource(resource);
 485 }
 486 #endif /* IS_ENABLED(CONFIG_KUNIT) */
 487
 488 void kasan_report_invalid_free(void *object, unsigned long ip)
 489 {
 490         unsigned long flags;
 491         u8 tag = get_tag(object);
 492
 493         object = reset_tag(object);
 494
 495 #if IS_ENABLED(CONFIG_KUNIT)
 496         if (current->kunit_test)
 497                 kasan_update_kunit_status(current->kunit_test);
 498 #endif /* IS_ENABLED(CONFIG_KUNIT) */
 499
 500         start_report(&flags);
 501         pr_err("BUG: KASAN: double-free or invalid-free in %pS\n", (void *)ip);
 502         print_tags(tag, object);
 503         pr_err("\n");
 504         print_address_description(object, tag);
 505         pr_err("\n");
 506         print_shadow_for_address(object);
 507         end_report(&flags);
 508 }
 509
 510 static void __kasan_report(unsigned long addr, size_t size, bool is_write,
 511                                 unsigned long ip)
 512 {
 513         struct kasan_access_info info;
 514         void *tagged_addr;
 515         void *untagged_addr;
 516         unsigned long flags;
 517
 518 #if IS_ENABLED(CONFIG_KUNIT)
 519         if (current->kunit_test)
 520                 kasan_update_kunit_status(current->kunit_test);
 521 #endif /* IS_ENABLED(CONFIG_KUNIT) */
 522
 523         disable_trace_on_warning();
 524
 525         tagged_addr = (void *)addr;
 526         untagged_addr = reset_tag(tagged_addr);
 527
 528         info.access_addr = tagged_addr;
 529         if (addr_has_shadow(untagged_addr))
 530                 info.first_bad_addr = find_first_bad_addr(tagged_addr, size);
 531         else
 532                 info.first_bad_addr = untagged_addr;
 533         info.access_size = size;
 534         info.is_write = is_write;
 535         info.ip = ip;
 536
 537         start_report(&flags);
 538
 539         print_error_description(&info);
 540         if (addr_has_shadow(untagged_addr))
 541                 print_tags(get_tag(tagged_addr), info.first_bad_addr);
 542         pr_err("\n");
 543
 544         if (addr_has_shadow(untagged_addr)) {
 545                 print_address_description(untagged_addr, get_tag(tagged_addr));
 546                 pr_err("\n");
 547                 print_shadow_for_address(info.first_bad_addr);
 548         } else {
 549                 dump_stack();
 550         }
 551
 552         end_report(&flags);
 553 }
 554
 555 bool kasan_report(unsigned long addr, size_t size, bool is_write,
 556                         unsigned long ip)
 557 {
 558         unsigned long flags = user_access_save();
 559         bool ret = false;
 560
 561         if (likely(report_enabled())) {
 562                 __kasan_report(addr, size, is_write, ip);
 563                 ret = true;
 564         }
 565
 566         user_access_restore(flags);
 567
 568         return ret;
 569 }
 570
 571 #ifdef CONFIG_KASAN_INLINE
 572 /*
 573  * With CONFIG_KASAN_INLINE, accesses to bogus pointers (outside the high
 574  * canonical half of the address space) cause out-of-bounds shadow memory reads
 575  * before the actual access. For addresses in the low canonical half of the
 576  * address space, as well as most non-canonical addresses, that out-of-bounds
 577  * shadow memory access lands in the non-canonical part of the address space.
 578  * Help the user figure out what the original bogus pointer was.
 579  */
 580 void kasan_non_canonical_hook(unsigned long addr)
 581 {
 582         unsigned long orig_addr;
 583         const char *bug_type;
 584
 585         if (addr < KASAN_SHADOW_OFFSET)
 586                 return;
 587
 588         orig_addr = (addr - KASAN_SHADOW_OFFSET) << KASAN_SHADOW_SCALE_SHIFT;
 589         /*
 590          * For faults near the shadow address for NULL, we can be fairly certain
 591          * that this is a KASAN shadow memory access.
 592          * For faults that correspond to shadow for low canonical addresses, we
 593          * can still be pretty sure - that shadow region is a fairly narrow
 594          * chunk of the non-canonical address space.
 595          * But faults that look like shadow for non-canonical addresses are a
 596          * really large chunk of the address space. In that case, we still
 597          * print the decoded address, but make it clear that this is not
 598          * necessarily what's actually going on.
 599          */
 600         if (orig_addr < PAGE_SIZE)
 601                 bug_type = "null-ptr-deref";
 602         else if (orig_addr < TASK_SIZE)
 603                 bug_type = "probably user-memory-access";
 604         else
 605                 bug_type = "maybe wild-memory-access";
 606         pr_alert("KASAN: %s in range [0x%016lx-0x%016lx]\n", bug_type,
 607                  orig_addr, orig_addr + KASAN_SHADOW_MASK);
 608 }
 609 #endif