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 <[email protected]>
   7  *
   8  * Some code borrowed from https://github.com/xairy/kasan-prototype by
   9  *        Andrey Konovalov <[email protected]>
  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 "kasan.h"
  37 #include "../slab.h"
  38
  39 /* Shadow layout customization. */
  40 #define SHADOW_BYTES_PER_BLOCK 1
  41 #define SHADOW_BLOCKS_PER_ROW 16
  42 #define SHADOW_BYTES_PER_ROW (SHADOW_BLOCKS_PER_ROW * SHADOW_BYTES_PER_BLOCK)
  43 #define SHADOW_ROWS_AROUND_ADDR 2
  44
  45 static unsigned long kasan_flags;
  46
  47 #define KASAN_BIT_REPORTED      0
  48 #define KASAN_BIT_MULTI_SHOT    1
  49
  50 bool kasan_save_enable_multi_shot(void)
  51 {
  52         return test_and_set_bit(KASAN_BIT_MULTI_SHOT, &kasan_flags);
  53 }
  54 EXPORT_SYMBOL_GPL(kasan_save_enable_multi_shot);
  55
  56 void kasan_restore_multi_shot(bool enabled)
  57 {
  58         if (!enabled)
  59                 clear_bit(KASAN_BIT_MULTI_SHOT, &kasan_flags);
  60 }
  61 EXPORT_SYMBOL_GPL(kasan_restore_multi_shot);
  62
  63 static int __init kasan_set_multi_shot(char *str)
  64 {
  65         set_bit(KASAN_BIT_MULTI_SHOT, &kasan_flags);
  66         return 1;
  67 }
  68 __setup("kasan_multi_shot", kasan_set_multi_shot);
  69
  70 static void print_error_description(struct kasan_access_info *info)
  71 {
  72         pr_err("BUG: KASAN: %s in %pS\n",
  73                 get_bug_type(info), (void *)info->ip);
  74         pr_err("%s of size %zu at addr %px by task %s/%d\n",
  75                 info->is_write ? "Write" : "Read", info->access_size,
  76                 info->access_addr, current->comm, task_pid_nr(current));
  77 }
  78
  79 static DEFINE_SPINLOCK(report_lock);
  80
  81 static void start_report(unsigned long *flags)
  82 {
  83         /*
  84          * Make sure we don't end up in loop.
  85          */
  86         kasan_disable_current();
  87         spin_lock_irqsave(&report_lock, *flags);
  88         pr_err("==================================================================\n");
  89 }
  90
  91 static void end_report(unsigned long *flags)
  92 {
  93         pr_err("==================================================================\n");
  94         add_taint(TAINT_BAD_PAGE, LOCKDEP_NOW_UNRELIABLE);
  95         spin_unlock_irqrestore(&report_lock, *flags);
  96         if (panic_on_warn) {
  97                 /*
  98                  * This thread may hit another WARN() in the panic path.
  99                  * Resetting this prevents additional WARN() from panicking the
 100                  * system on this thread.  Other threads are blocked by the
 101                  * panic_mutex in panic().
 102                  */
 103                 panic_on_warn = 0;
 104                 panic("panic_on_warn set ...\n");
 105         }
 106         kasan_enable_current();
 107 }
 108
 109 static void print_stack(depot_stack_handle_t stack)
 110 {
 111         unsigned long *entries;
 112         unsigned int nr_entries;
 113
 114         nr_entries = stack_depot_fetch(stack, &entries);
 115         stack_trace_print(entries, nr_entries, 0);
 116 }
 117
 118 static void print_track(struct kasan_track *track, const char *prefix)
 119 {
 120         pr_err("%s by task %u:\n", prefix, track->pid);
 121         if (track->stack) {
 122                 print_stack(track->stack);
 123         } else {
 124                 pr_err("(stack is not available)\n");
 125         }
 126 }
 127
 128 struct page *kasan_addr_to_page(const void *addr)
 129 {
 130         if ((addr >= (void *)PAGE_OFFSET) &&
 131                         (addr < high_memory))
 132                 return virt_to_head_page(addr);
 133         return NULL;
 134 }
 135
 136 static void describe_object_addr(struct kmem_cache *cache, void *object,
 137                                 const void *addr)
 138 {
 139         unsigned long access_addr = (unsigned long)addr;
 140         unsigned long object_addr = (unsigned long)object;
 141         const char *rel_type;
 142         int rel_bytes;
 143
 144         pr_err("The buggy address belongs to the object at %px\n"
 145                " which belongs to the cache %s of size %d\n",
 146                 object, cache->name, cache->object_size);
 147
 148         if (!addr)
 149                 return;
 150
 151         if (access_addr < object_addr) {
 152                 rel_type = "to the left";
 153                 rel_bytes = object_addr - access_addr;
 154         } else if (access_addr >= object_addr + cache->object_size) {
 155                 rel_type = "to the right";
 156                 rel_bytes = access_addr - (object_addr + cache->object_size);
 157         } else {
 158                 rel_type = "inside";
 159                 rel_bytes = access_addr - object_addr;
 160         }
 161
 162         pr_err("The buggy address is located %d bytes %s of\n"
 163                " %d-byte region [%px, %px)\n",
 164                 rel_bytes, rel_type, cache->object_size, (void *)object_addr,
 165                 (void *)(object_addr + cache->object_size));
 166 }
 167
 168 static void describe_object(struct kmem_cache *cache, void *object,
 169                                 const void *addr, u8 tag)
 170 {
 171         struct kasan_alloc_meta *alloc_info = get_alloc_info(cache, object);
 172
 173         if (cache->flags & SLAB_KASAN) {
 174                 struct kasan_track *free_track;
 175
 176                 print_track(&alloc_info->alloc_track, "Allocated");
 177                 pr_err("\n");
 178                 free_track = kasan_get_free_track(cache, object, tag);
 179                 if (free_track) {
 180                         print_track(free_track, "Freed");
 181                         pr_err("\n");
 182                 }
 183
 184 #ifdef CONFIG_KASAN_GENERIC
 185                 if (alloc_info->aux_stack[0]) {
 186                         pr_err("Last call_rcu():\n");
 187                         print_stack(alloc_info->aux_stack[0]);
 188                         pr_err("\n");
 189                 }
 190                 if (alloc_info->aux_stack[1]) {
 191                         pr_err("Second to last call_rcu():\n");
 192                         print_stack(alloc_info->aux_stack[1]);
 193                         pr_err("\n");
 194                 }
 195 #endif
 196         }
 197
 198         describe_object_addr(cache, object, addr);
 199 }
 200
 201 static inline bool kernel_or_module_addr(const void *addr)
 202 {
 203         if (addr >= (void *)_stext && addr < (void *)_end)
 204                 return true;
 205         if (is_module_address((unsigned long)addr))
 206                 return true;
 207         return false;
 208 }
 209
 210 static inline bool init_task_stack_addr(const void *addr)
 211 {
 212         return addr >= (void *)&init_thread_union.stack &&
 213                 (addr <= (void *)&init_thread_union.stack +
 214                         sizeof(init_thread_union.stack));
 215 }
 216
 217 static bool __must_check tokenize_frame_descr(const char **frame_descr,
 218                                               char *token, size_t max_tok_len,
 219                                               unsigned long *value)
 220 {
 221         const char *sep = strchr(*frame_descr, ' ');
 222
 223         if (sep == NULL)
 224                 sep = *frame_descr + strlen(*frame_descr);
 225
 226         if (token != NULL) {
 227                 const size_t tok_len = sep - *frame_descr;
 228
 229                 if (tok_len + 1 > max_tok_len) {
 230                         pr_err("KASAN internal error: frame description too long: %s\n",
 231                                *frame_descr);
 232                         return false;
 233                 }
 234
 235                 /* Copy token (+ 1 byte for '\0'). */
 236                 strlcpy(token, *frame_descr, tok_len + 1);
 237         }
 238
 239         /* Advance frame_descr past separator. */
 240         *frame_descr = sep + 1;
 241
 242         if (value != NULL && kstrtoul(token, 10, value)) {
 243                 pr_err("KASAN internal error: not a valid number: %s\n", token);
 244                 return false;
 245         }
 246
 247         return true;
 248 }
 249
 250 static void print_decoded_frame_descr(const char *frame_descr)
 251 {
 252         /*
 253          * We need to parse the following string:
 254          *    "n alloc_1 alloc_2 ... alloc_n"
 255          * where alloc_i looks like
 256          *    "offset size len name"
 257          * or "offset size len name:line".
 258          */
 259
 260         char token[64];
 261         unsigned long num_objects;
 262
 263         if (!tokenize_frame_descr(&frame_descr, token, sizeof(token),
 264                                   &num_objects))
 265                 return;
 266
 267         pr_err("\n");
 268         pr_err("this frame has %lu %s:\n", num_objects,
 269                num_objects == 1 ? "object" : "objects");
 270
 271         while (num_objects--) {
 272                 unsigned long offset;
 273                 unsigned long size;
 274
 275                 /* access offset */
 276                 if (!tokenize_frame_descr(&frame_descr, token, sizeof(token),
 277                                           &offset))
 278                         return;
 279                 /* access size */
 280                 if (!tokenize_frame_descr(&frame_descr, token, sizeof(token),
 281                                           &size))
 282                         return;
 283                 /* name length (unused) */
 284                 if (!tokenize_frame_descr(&frame_descr, NULL, 0, NULL))
 285                         return;
 286                 /* object name */
 287                 if (!tokenize_frame_descr(&frame_descr, token, sizeof(token),
 288                                           NULL))
 289                         return;
 290
 291                 /* Strip line number; without filename it's not very helpful. */
 292                 strreplace(token, ':', '\0');
 293
 294                 /* Finally, print object information. */
 295                 pr_err(" [%lu, %lu) '%s'", offset, offset + size, token);
 296         }
 297 }
 298
 299 static bool __must_check get_address_stack_frame_info(const void *addr,
 300                                                       unsigned long *offset,
 301                                                       const char **frame_descr,
 302                                                       const void **frame_pc)
 303 {
 304         unsigned long aligned_addr;
 305         unsigned long mem_ptr;
 306         const u8 *shadow_bottom;
 307         const u8 *shadow_ptr;
 308         const unsigned long *frame;
 309
 310         BUILD_BUG_ON(IS_ENABLED(CONFIG_STACK_GROWSUP));
 311
 312         /*
 313          * NOTE: We currently only support printing frame information for
 314          * accesses to the task's own stack.
 315          */
 316         if (!object_is_on_stack(addr))
 317                 return false;
 318
 319         aligned_addr = round_down((unsigned long)addr, sizeof(long));
 320         mem_ptr = round_down(aligned_addr, KASAN_SHADOW_SCALE_SIZE);
 321         shadow_ptr = kasan_mem_to_shadow((void *)aligned_addr);
 322         shadow_bottom = kasan_mem_to_shadow(end_of_stack(current));
 323
 324         while (shadow_ptr >= shadow_bottom && *shadow_ptr != KASAN_STACK_LEFT) {
 325                 shadow_ptr--;
 326                 mem_ptr -= KASAN_SHADOW_SCALE_SIZE;
 327         }
 328
 329         while (shadow_ptr >= shadow_bottom && *shadow_ptr == KASAN_STACK_LEFT) {
 330                 shadow_ptr--;
 331                 mem_ptr -= KASAN_SHADOW_SCALE_SIZE;
 332         }
 333
 334         if (shadow_ptr < shadow_bottom)
 335                 return false;
 336
 337         frame = (const unsigned long *)(mem_ptr + KASAN_SHADOW_SCALE_SIZE);
 338         if (frame[0] != KASAN_CURRENT_STACK_FRAME_MAGIC) {
 339                 pr_err("KASAN internal error: frame info validation failed; invalid marker: %lu\n",
 340                        frame[0]);
 341                 return false;
 342         }
 343
 344         *offset = (unsigned long)addr - (unsigned long)frame;
 345         *frame_descr = (const char *)frame[1];
 346         *frame_pc = (void *)frame[2];
 347
 348         return true;
 349 }
 350
 351 static void print_address_stack_frame(const void *addr)
 352 {
 353         unsigned long offset;
 354         const char *frame_descr;
 355         const void *frame_pc;
 356
 357         if (IS_ENABLED(CONFIG_KASAN_SW_TAGS))
 358                 return;
 359
 360         if (!get_address_stack_frame_info(addr, &offset, &frame_descr,
 361                                           &frame_pc))
 362                 return;
 363
 364         /*
 365          * get_address_stack_frame_info only returns true if the given addr is
 366          * on the current task's stack.
 367          */
 368         pr_err("\n");
 369         pr_err("addr %px is located in stack of task %s/%d at offset %lu in frame:\n",
 370                addr, current->comm, task_pid_nr(current), offset);
 371         pr_err(" %pS\n", frame_pc);
 372
 373         if (!frame_descr)
 374                 return;
 375
 376         print_decoded_frame_descr(frame_descr);
 377 }
 378
 379 static void print_address_description(void *addr, u8 tag)
 380 {
 381         struct page *page = kasan_addr_to_page(addr);
 382
 383         dump_stack();
 384         pr_err("\n");
 385
 386         if (page && PageSlab(page)) {
 387                 struct kmem_cache *cache = page->slab_cache;
 388                 void *object = nearest_obj(cache, page, addr);
 389
 390                 describe_object(cache, object, addr, tag);
 391         }
 392
 393         if (kernel_or_module_addr(addr) && !init_task_stack_addr(addr)) {
 394                 pr_err("The buggy address belongs to the variable:\n");
 395                 pr_err(" %pS\n", addr);
 396         }
 397
 398         if (page) {
 399                 pr_err("The buggy address belongs to the page:\n");
 400                 dump_page(page, "kasan: bad access detected");
 401         }
 402
 403         print_address_stack_frame(addr);
 404 }
 405
 406 static bool row_is_guilty(const void *row, const void *guilty)
 407 {
 408         return (row <= guilty) && (guilty < row + SHADOW_BYTES_PER_ROW);
 409 }
 410
 411 static int shadow_pointer_offset(const void *row, const void *shadow)
 412 {
 413         /* The length of ">ff00ff00ff00ff00: " is
 414          *    3 + (BITS_PER_LONG/8)*2 chars.
 415          */
 416         return 3 + (BITS_PER_LONG/8)*2 + (shadow - row)*2 +
 417                 (shadow - row) / SHADOW_BYTES_PER_BLOCK + 1;
 418 }
 419
 420 static void print_shadow_for_address(const void *addr)
 421 {
 422         int i;
 423         const void *shadow = kasan_mem_to_shadow(addr);
 424         const void *shadow_row;
 425
 426         shadow_row = (void *)round_down((unsigned long)shadow,
 427                                         SHADOW_BYTES_PER_ROW)
 428                 - SHADOW_ROWS_AROUND_ADDR * SHADOW_BYTES_PER_ROW;
 429
 430         pr_err("Memory state around the buggy address:\n");
 431
 432         for (i = -SHADOW_ROWS_AROUND_ADDR; i <= SHADOW_ROWS_AROUND_ADDR; i++) {
 433                 const void *kaddr = kasan_shadow_to_mem(shadow_row);
 434                 char buffer[4 + (BITS_PER_LONG/8)*2];
 435                 char shadow_buf[SHADOW_BYTES_PER_ROW];
 436
 437                 snprintf(buffer, sizeof(buffer),
 438                         (i == 0) ? ">%px: " : " %px: ", kaddr);
 439                 /*
 440                  * We should not pass a shadow pointer to generic
 441                  * function, because generic functions may try to
 442                  * access kasan mapping for the passed address.
 443                  */
 444                 memcpy(shadow_buf, shadow_row, SHADOW_BYTES_PER_ROW);
 445                 print_hex_dump(KERN_ERR, buffer,
 446                         DUMP_PREFIX_NONE, SHADOW_BYTES_PER_ROW, 1,
 447                         shadow_buf, SHADOW_BYTES_PER_ROW, 0);
 448
 449                 if (row_is_guilty(shadow_row, shadow))
 450                         pr_err("%*c\n",
 451                                 shadow_pointer_offset(shadow_row, shadow),
 452                                 '^');
 453
 454                 shadow_row += SHADOW_BYTES_PER_ROW;
 455         }
 456 }
 457
 458 static bool report_enabled(void)
 459 {
 460         if (current->kasan_depth)
 461                 return false;
 462         if (test_bit(KASAN_BIT_MULTI_SHOT, &kasan_flags))
 463                 return true;
 464         return !test_and_set_bit(KASAN_BIT_REPORTED, &kasan_flags);
 465 }
 466
 467 void kasan_report_invalid_free(void *object, unsigned long ip)
 468 {
 469         unsigned long flags;
 470         u8 tag = get_tag(object);
 471
 472         object = reset_tag(object);
 473         start_report(&flags);
 474         pr_err("BUG: KASAN: double-free or invalid-free in %pS\n", (void *)ip);
 475         print_tags(tag, object);
 476         pr_err("\n");
 477         print_address_description(object, tag);
 478         pr_err("\n");
 479         print_shadow_for_address(object);
 480         end_report(&flags);
 481 }
 482
 483 static void __kasan_report(unsigned long addr, size_t size, bool is_write,
 484                                 unsigned long ip)
 485 {
 486         struct kasan_access_info info;
 487         void *tagged_addr;
 488         void *untagged_addr;
 489         unsigned long flags;
 490
 491         disable_trace_on_warning();
 492
 493         tagged_addr = (void *)addr;
 494         untagged_addr = reset_tag(tagged_addr);
 495
 496         info.access_addr = tagged_addr;
 497         if (addr_has_shadow(untagged_addr))
 498                 info.first_bad_addr = find_first_bad_addr(tagged_addr, size);
 499         else
 500                 info.first_bad_addr = untagged_addr;
 501         info.access_size = size;
 502         info.is_write = is_write;
 503         info.ip = ip;
 504
 505         start_report(&flags);
 506
 507         print_error_description(&info);
 508         if (addr_has_shadow(untagged_addr))
 509                 print_tags(get_tag(tagged_addr), info.first_bad_addr);
 510         pr_err("\n");
 511
 512         if (addr_has_shadow(untagged_addr)) {
 513                 print_address_description(untagged_addr, get_tag(tagged_addr));
 514                 pr_err("\n");
 515                 print_shadow_for_address(info.first_bad_addr);
 516         } else {
 517                 dump_stack();
 518         }
 519
 520         end_report(&flags);
 521 }
 522
 523 bool kasan_report(unsigned long addr, size_t size, bool is_write,
 524                         unsigned long ip)
 525 {
 526         unsigned long flags = user_access_save();
 527         bool ret = false;
 528
 529         if (likely(report_enabled())) {
 530                 __kasan_report(addr, size, is_write, ip);
 531                 ret = true;
 532         }
 533
 534         user_access_restore(flags);
 535
 536         return ret;
 537 }
 538
 539 #ifdef CONFIG_KASAN_INLINE
 540 /*
 541  * With CONFIG_KASAN_INLINE, accesses to bogus pointers (outside the high
 542  * canonical half of the address space) cause out-of-bounds shadow memory reads
 543  * before the actual access. For addresses in the low canonical half of the
 544  * address space, as well as most non-canonical addresses, that out-of-bounds
 545  * shadow memory access lands in the non-canonical part of the address space.
 546  * Help the user figure out what the original bogus pointer was.
 547  */
 548 void kasan_non_canonical_hook(unsigned long addr)
 549 {
 550         unsigned long orig_addr;
 551         const char *bug_type;
 552
 553         if (addr < KASAN_SHADOW_OFFSET)
 554                 return;
 555
 556         orig_addr = (addr - KASAN_SHADOW_OFFSET) << KASAN_SHADOW_SCALE_SHIFT;
 557         /*
 558          * For faults near the shadow address for NULL, we can be fairly certain
 559          * that this is a KASAN shadow memory access.
 560          * For faults that correspond to shadow for low canonical addresses, we
 561          * can still be pretty sure - that shadow region is a fairly narrow
 562          * chunk of the non-canonical address space.
 563          * But faults that look like shadow for non-canonical addresses are a
 564          * really large chunk of the address space. In that case, we still
 565          * print the decoded address, but make it clear that this is not
 566          * necessarily what's actually going on.
 567          */
 568         if (orig_addr < PAGE_SIZE)
 569                 bug_type = "null-ptr-deref";
 570         else if (orig_addr < TASK_SIZE)
 571                 bug_type = "probably user-memory-access";
 572         else
 573                 bug_type = "maybe wild-memory-access";
 574         pr_alert("KASAN: %s in range [0x%016lx-0x%016lx]\n", bug_type,
 575                  orig_addr, orig_addr + KASAN_SHADOW_MASK);
 576 }
 577 #endif