mm/kasan/report.c

   1 // SPDX-License-Identifier: GPL-2.0
   2 /*
   3  * This file contains common 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/lockdep.h>
  17 #include <linux/mm.h>
  18 #include <linux/printk.h>
  19 #include <linux/sched.h>
  20 #include <linux/slab.h>
  21 #include <linux/stackdepot.h>
  22 #include <linux/stacktrace.h>
  23 #include <linux/string.h>
  24 #include <linux/types.h>
  25 #include <linux/kasan.h>
  26 #include <linux/module.h>
  27 #include <linux/sched/task_stack.h>
  28 #include <linux/uaccess.h>
  29 #include <trace/events/error_report.h>
  30
  31 #include <asm/sections.h>
  32
  33 #include <kunit/test.h>
  34
  35 #include "kasan.h"
  36 #include "../slab.h"
  37
  38 static unsigned long kasan_flags;
  39
  40 #define KASAN_BIT_REPORTED      0
  41 #define KASAN_BIT_MULTI_SHOT    1
  42
  43 enum kasan_arg_fault {
  44         KASAN_ARG_FAULT_DEFAULT,
  45         KASAN_ARG_FAULT_REPORT,
  46         KASAN_ARG_FAULT_PANIC,
  47 };
  48
  49 static enum kasan_arg_fault kasan_arg_fault __ro_after_init = KASAN_ARG_FAULT_DEFAULT;
  50
  51 /* kasan.fault=report/panic */
  52 static int __init early_kasan_fault(char *arg)
  53 {
  54         if (!arg)
  55                 return -EINVAL;
  56
  57         if (!strcmp(arg, "report"))
  58                 kasan_arg_fault = KASAN_ARG_FAULT_REPORT;
  59         else if (!strcmp(arg, "panic"))
  60                 kasan_arg_fault = KASAN_ARG_FAULT_PANIC;
  61         else
  62                 return -EINVAL;
  63
  64         return 0;
  65 }
  66 early_param("kasan.fault", early_kasan_fault);
  67
  68 static int __init kasan_set_multi_shot(char *str)
  69 {
  70         set_bit(KASAN_BIT_MULTI_SHOT, &kasan_flags);
  71         return 1;
  72 }
  73 __setup("kasan_multi_shot", kasan_set_multi_shot);
  74
  75 /*
  76  * Used to suppress reports within kasan_disable/enable_current() critical
  77  * sections, which are used for marking accesses to slab metadata.
  78  */
  79 static bool report_suppressed(void)
  80 {
  81 #if defined(CONFIG_KASAN_GENERIC) || defined(CONFIG_KASAN_SW_TAGS)
  82         if (current->kasan_depth)
  83                 return true;
  84 #endif
  85         return false;
  86 }
  87
  88 /*
  89  * Used to avoid reporting more than one KASAN bug unless kasan_multi_shot
  90  * is enabled. Note that KASAN tests effectively enable kasan_multi_shot
  91  * for their duration.
  92  */
  93 static bool report_enabled(void)
  94 {
  95         if (test_bit(KASAN_BIT_MULTI_SHOT, &kasan_flags))
  96                 return true;
  97         return !test_and_set_bit(KASAN_BIT_REPORTED, &kasan_flags);
  98 }
  99
 100 #if IS_ENABLED(CONFIG_KASAN_KUNIT_TEST) || IS_ENABLED(CONFIG_KASAN_MODULE_TEST)
 101
 102 bool kasan_save_enable_multi_shot(void)
 103 {
 104         return test_and_set_bit(KASAN_BIT_MULTI_SHOT, &kasan_flags);
 105 }
 106 EXPORT_SYMBOL_GPL(kasan_save_enable_multi_shot);
 107
 108 void kasan_restore_multi_shot(bool enabled)
 109 {
 110         if (!enabled)
 111                 clear_bit(KASAN_BIT_MULTI_SHOT, &kasan_flags);
 112 }
 113 EXPORT_SYMBOL_GPL(kasan_restore_multi_shot);
 114
 115 #endif
 116
 117 #if IS_ENABLED(CONFIG_KASAN_KUNIT_TEST)
 118 static void update_kunit_status(bool sync)
 119 {
 120         struct kunit *test;
 121         struct kunit_resource *resource;
 122         struct kunit_kasan_status *status;
 123
 124         test = current->kunit_test;
 125         if (!test)
 126                 return;
 127
 128         resource = kunit_find_named_resource(test, "kasan_status");
 129         if (!resource) {
 130                 kunit_set_failure(test);
 131                 return;
 132         }
 133
 134         status = (struct kunit_kasan_status *)resource->data;
 135         WRITE_ONCE(status->report_found, true);
 136         WRITE_ONCE(status->sync_fault, sync);
 137
 138         kunit_put_resource(resource);
 139 }
 140 #else
 141 static void update_kunit_status(bool sync) { }
 142 #endif
 143
 144 static DEFINE_SPINLOCK(report_lock);
 145
 146 static void start_report(unsigned long *flags, bool sync)
 147 {
 148         /* Respect the /proc/sys/kernel/traceoff_on_warning interface. */
 149         disable_trace_on_warning();
 150         /* Update status of the currently running KASAN test. */
 151         update_kunit_status(sync);
 152         /* Do not allow LOCKDEP mangling KASAN reports. */
 153         lockdep_off();
 154         /* Make sure we don't end up in loop. */
 155         kasan_disable_current();
 156         spin_lock_irqsave(&report_lock, *flags);
 157         pr_err("==================================================================\n");
 158 }
 159
 160 static void end_report(unsigned long *flags, void *addr)
 161 {
 162         if (addr)
 163                 trace_error_report_end(ERROR_DETECTOR_KASAN,
 164                                        (unsigned long)addr);
 165         pr_err("==================================================================\n");
 166         spin_unlock_irqrestore(&report_lock, *flags);
 167         if (panic_on_warn && !test_bit(KASAN_BIT_MULTI_SHOT, &kasan_flags))
 168                 panic("panic_on_warn set ...\n");
 169         if (kasan_arg_fault == KASAN_ARG_FAULT_PANIC)
 170                 panic("kasan.fault=panic set ...\n");
 171         add_taint(TAINT_BAD_PAGE, LOCKDEP_NOW_UNRELIABLE);
 172         lockdep_on();
 173         kasan_enable_current();
 174 }
 175
 176 static void print_error_description(struct kasan_report_info *info)
 177 {
 178         if (info->type == KASAN_REPORT_INVALID_FREE) {
 179                 pr_err("BUG: KASAN: double-free or invalid-free in %pS\n",
 180                        (void *)info->ip);
 181                 return;
 182         }
 183
 184         pr_err("BUG: KASAN: %s in %pS\n",
 185                 kasan_get_bug_type(info), (void *)info->ip);
 186         if (info->access_size)
 187                 pr_err("%s of size %zu at addr %px by task %s/%d\n",
 188                         info->is_write ? "Write" : "Read", info->access_size,
 189                         info->access_addr, current->comm, task_pid_nr(current));
 190         else
 191                 pr_err("%s at addr %px by task %s/%d\n",
 192                         info->is_write ? "Write" : "Read",
 193                         info->access_addr, current->comm, task_pid_nr(current));
 194 }
 195
 196 static void print_track(struct kasan_track *track, const char *prefix)
 197 {
 198         pr_err("%s by task %u:\n", prefix, track->pid);
 199         if (track->stack) {
 200                 stack_depot_print(track->stack);
 201         } else {
 202                 pr_err("(stack is not available)\n");
 203         }
 204 }
 205
 206 struct page *kasan_addr_to_page(const void *addr)
 207 {
 208         if ((addr >= (void *)PAGE_OFFSET) &&
 209                         (addr < high_memory))
 210                 return virt_to_head_page(addr);
 211         return NULL;
 212 }
 213
 214 struct slab *kasan_addr_to_slab(const void *addr)
 215 {
 216         if ((addr >= (void *)PAGE_OFFSET) &&
 217                         (addr < high_memory))
 218                 return virt_to_slab(addr);
 219         return NULL;
 220 }
 221
 222 static void describe_object_addr(struct kmem_cache *cache, void *object,
 223                                 const void *addr)
 224 {
 225         unsigned long access_addr = (unsigned long)addr;
 226         unsigned long object_addr = (unsigned long)object;
 227         const char *rel_type;
 228         int rel_bytes;
 229
 230         pr_err("The buggy address belongs to the object at %px\n"
 231                " which belongs to the cache %s of size %d\n",
 232                 object, cache->name, cache->object_size);
 233
 234         if (access_addr < object_addr) {
 235                 rel_type = "to the left";
 236                 rel_bytes = object_addr - access_addr;
 237         } else if (access_addr >= object_addr + cache->object_size) {
 238                 rel_type = "to the right";
 239                 rel_bytes = access_addr - (object_addr + cache->object_size);
 240         } else {
 241                 rel_type = "inside";
 242                 rel_bytes = access_addr - object_addr;
 243         }
 244
 245         pr_err("The buggy address is located %d bytes %s of\n"
 246                " %d-byte region [%px, %px)\n",
 247                 rel_bytes, rel_type, cache->object_size, (void *)object_addr,
 248                 (void *)(object_addr + cache->object_size));
 249 }
 250
 251 static void describe_object_stacks(struct kmem_cache *cache, void *object,
 252                                         const void *addr, u8 tag)
 253 {
 254         struct kasan_alloc_meta *alloc_meta;
 255         struct kasan_track *free_track;
 256
 257         alloc_meta = kasan_get_alloc_meta(cache, object);
 258         if (alloc_meta) {
 259                 print_track(&alloc_meta->alloc_track, "Allocated");
 260                 pr_err("\n");
 261         }
 262
 263         free_track = kasan_get_free_track(cache, object, tag);
 264         if (free_track) {
 265                 print_track(free_track, "Freed");
 266                 pr_err("\n");
 267         }
 268
 269 #ifdef CONFIG_KASAN_GENERIC
 270         if (!alloc_meta)
 271                 return;
 272         if (alloc_meta->aux_stack[0]) {
 273                 pr_err("Last potentially related work creation:\n");
 274                 stack_depot_print(alloc_meta->aux_stack[0]);
 275                 pr_err("\n");
 276         }
 277         if (alloc_meta->aux_stack[1]) {
 278                 pr_err("Second to last potentially related work creation:\n");
 279                 stack_depot_print(alloc_meta->aux_stack[1]);
 280                 pr_err("\n");
 281         }
 282 #endif
 283 }
 284
 285 static void describe_object(struct kmem_cache *cache, void *object,
 286                                 const void *addr, u8 tag)
 287 {
 288         if (kasan_stack_collection_enabled())
 289                 describe_object_stacks(cache, object, addr, tag);
 290         describe_object_addr(cache, object, addr);
 291 }
 292
 293 static inline bool kernel_or_module_addr(const void *addr)
 294 {
 295         if (is_kernel((unsigned long)addr))
 296                 return true;
 297         if (is_module_address((unsigned long)addr))
 298                 return true;
 299         return false;
 300 }
 301
 302 static inline bool init_task_stack_addr(const void *addr)
 303 {
 304         return addr >= (void *)&init_thread_union.stack &&
 305                 (addr <= (void *)&init_thread_union.stack +
 306                         sizeof(init_thread_union.stack));
 307 }
 308
 309 static void print_address_description(void *addr, u8 tag)
 310 {
 311         struct page *page = kasan_addr_to_page(addr);
 312
 313         dump_stack_lvl(KERN_ERR);
 314         pr_err("\n");
 315
 316         if (page && PageSlab(page)) {
 317                 struct slab *slab = page_slab(page);
 318                 struct kmem_cache *cache = slab->slab_cache;
 319                 void *object = nearest_obj(cache, slab, addr);
 320
 321                 describe_object(cache, object, addr, tag);
 322                 pr_err("\n");
 323         }
 324
 325         if (kernel_or_module_addr(addr) && !init_task_stack_addr(addr)) {
 326                 pr_err("The buggy address belongs to the variable:\n");
 327                 pr_err(" %pS\n", addr);
 328                 pr_err("\n");
 329         }
 330
 331         if (object_is_on_stack(addr)) {
 332                 /*
 333                  * Currently, KASAN supports printing frame information only
 334                  * for accesses to the task's own stack.
 335                  */
 336                 kasan_print_address_stack_frame(addr);
 337                 pr_err("\n");
 338         }
 339
 340         if (is_vmalloc_addr(addr)) {
 341                 struct vm_struct *va = find_vm_area(addr);
 342
 343                 if (va) {
 344                         pr_err("The buggy address belongs to the virtual mapping at\n"
 345                                " [%px, %px) created by:\n"
 346                                " %pS\n",
 347                                va->addr, va->addr + va->size, va->caller);
 348                         pr_err("\n");
 349
 350                         page = vmalloc_to_page(addr);
 351                 }
 352         }
 353
 354         if (page) {
 355                 pr_err("The buggy address belongs to the physical page:\n");
 356                 dump_page(page, "kasan: bad access detected");
 357                 pr_err("\n");
 358         }
 359 }
 360
 361 static bool meta_row_is_guilty(const void *row, const void *addr)
 362 {
 363         return (row <= addr) && (addr < row + META_MEM_BYTES_PER_ROW);
 364 }
 365
 366 static int meta_pointer_offset(const void *row, const void *addr)
 367 {
 368         /*
 369          * Memory state around the buggy address:
 370          *  ff00ff00ff00ff00: 00 00 00 05 fe fe fe fe fe fe fe fe fe fe fe fe
 371          *  ...
 372          *
 373          * The length of ">ff00ff00ff00ff00: " is
 374          *    3 + (BITS_PER_LONG / 8) * 2 chars.
 375          * The length of each granule metadata is 2 bytes
 376          *    plus 1 byte for space.
 377          */
 378         return 3 + (BITS_PER_LONG / 8) * 2 +
 379                 (addr - row) / KASAN_GRANULE_SIZE * 3 + 1;
 380 }
 381
 382 static void print_memory_metadata(const void *addr)
 383 {
 384         int i;
 385         void *row;
 386
 387         row = (void *)round_down((unsigned long)addr, META_MEM_BYTES_PER_ROW)
 388                         - META_ROWS_AROUND_ADDR * META_MEM_BYTES_PER_ROW;
 389
 390         pr_err("Memory state around the buggy address:\n");
 391
 392         for (i = -META_ROWS_AROUND_ADDR; i <= META_ROWS_AROUND_ADDR; i++) {
 393                 char buffer[4 + (BITS_PER_LONG / 8) * 2];
 394                 char metadata[META_BYTES_PER_ROW];
 395
 396                 snprintf(buffer, sizeof(buffer),
 397                                 (i == 0) ? ">%px: " : " %px: ", row);
 398
 399                 /*
 400                  * We should not pass a shadow pointer to generic
 401                  * function, because generic functions may try to
 402                  * access kasan mapping for the passed address.
 403                  */
 404                 kasan_metadata_fetch_row(&metadata[0], row);
 405
 406                 print_hex_dump(KERN_ERR, buffer,
 407                         DUMP_PREFIX_NONE, META_BYTES_PER_ROW, 1,
 408                         metadata, META_BYTES_PER_ROW, 0);
 409
 410                 if (meta_row_is_guilty(row, addr))
 411                         pr_err("%*c\n", meta_pointer_offset(row, addr), '^');
 412
 413                 row += META_MEM_BYTES_PER_ROW;
 414         }
 415 }
 416
 417 static void print_report(struct kasan_report_info *info)
 418 {
 419         void *tagged_addr = info->access_addr;
 420         void *untagged_addr = kasan_reset_tag(tagged_addr);
 421         u8 tag = get_tag(tagged_addr);
 422
 423         print_error_description(info);
 424         if (addr_has_metadata(untagged_addr))
 425                 kasan_print_tags(tag, info->first_bad_addr);
 426         pr_err("\n");
 427
 428         if (addr_has_metadata(untagged_addr)) {
 429                 print_address_description(untagged_addr, tag);
 430                 print_memory_metadata(info->first_bad_addr);
 431         } else {
 432                 dump_stack_lvl(KERN_ERR);
 433         }
 434 }
 435
 436 void kasan_report_invalid_free(void *ptr, unsigned long ip)
 437 {
 438         unsigned long flags;
 439         struct kasan_report_info info;
 440
 441         /*
 442          * Do not check report_suppressed(), as an invalid-free cannot be
 443          * caused by accessing slab metadata and thus should not be
 444          * suppressed by kasan_disable/enable_current() critical sections.
 445          */
 446         if (unlikely(!report_enabled()))
 447                 return;
 448
 449         start_report(&flags, true);
 450
 451         info.type = KASAN_REPORT_INVALID_FREE;
 452         info.access_addr = ptr;
 453         info.first_bad_addr = kasan_reset_tag(ptr);
 454         info.access_size = 0;
 455         info.is_write = false;
 456         info.ip = ip;
 457
 458         print_report(&info);
 459
 460         end_report(&flags, ptr);
 461 }
 462
 463 /*
 464  * kasan_report() is the only reporting function that uses
 465  * user_access_save/restore(): kasan_report_invalid_free() cannot be called
 466  * from a UACCESS region, and kasan_report_async() is not used on x86.
 467  */
 468 bool kasan_report(unsigned long addr, size_t size, bool is_write,
 469                         unsigned long ip)
 470 {
 471         bool ret = true;
 472         void *ptr = (void *)addr;
 473         unsigned long ua_flags = user_access_save();
 474         unsigned long irq_flags;
 475         struct kasan_report_info info;
 476
 477         if (unlikely(report_suppressed()) || unlikely(!report_enabled())) {
 478                 ret = false;
 479                 goto out;
 480         }
 481
 482         start_report(&irq_flags, true);
 483
 484         info.type = KASAN_REPORT_ACCESS;
 485         info.access_addr = ptr;
 486         info.first_bad_addr = kasan_find_first_bad_addr(ptr, size);
 487         info.access_size = size;
 488         info.is_write = is_write;
 489         info.ip = ip;
 490
 491         print_report(&info);
 492
 493         end_report(&irq_flags, ptr);
 494
 495 out:
 496         user_access_restore(ua_flags);
 497
 498         return ret;
 499 }
 500
 501 #ifdef CONFIG_KASAN_HW_TAGS
 502 void kasan_report_async(void)
 503 {
 504         unsigned long flags;
 505
 506         /*
 507          * Do not check report_suppressed(), as kasan_disable/enable_current()
 508          * critical sections do not affect Hardware Tag-Based KASAN.
 509          */
 510         if (unlikely(!report_enabled()))
 511                 return;
 512
 513         start_report(&flags, false);
 514         pr_err("BUG: KASAN: invalid-access\n");
 515         pr_err("Asynchronous fault: no details available\n");
 516         pr_err("\n");
 517         dump_stack_lvl(KERN_ERR);
 518         end_report(&flags, NULL);
 519 }
 520 #endif /* CONFIG_KASAN_HW_TAGS */
 521
 522 #ifdef CONFIG_KASAN_INLINE
 523 /*
 524  * With CONFIG_KASAN_INLINE, accesses to bogus pointers (outside the high
 525  * canonical half of the address space) cause out-of-bounds shadow memory reads
 526  * before the actual access. For addresses in the low canonical half of the
 527  * address space, as well as most non-canonical addresses, that out-of-bounds
 528  * shadow memory access lands in the non-canonical part of the address space.
 529  * Help the user figure out what the original bogus pointer was.
 530  */
 531 void kasan_non_canonical_hook(unsigned long addr)
 532 {
 533         unsigned long orig_addr;
 534         const char *bug_type;
 535
 536         if (addr < KASAN_SHADOW_OFFSET)
 537                 return;
 538
 539         orig_addr = (addr - KASAN_SHADOW_OFFSET) << KASAN_SHADOW_SCALE_SHIFT;
 540         /*
 541          * For faults near the shadow address for NULL, we can be fairly certain
 542          * that this is a KASAN shadow memory access.
 543          * For faults that correspond to shadow for low canonical addresses, we
 544          * can still be pretty sure - that shadow region is a fairly narrow
 545          * chunk of the non-canonical address space.
 546          * But faults that look like shadow for non-canonical addresses are a
 547          * really large chunk of the address space. In that case, we still
 548          * print the decoded address, but make it clear that this is not
 549          * necessarily what's actually going on.
 550          */
 551         if (orig_addr < PAGE_SIZE)
 552                 bug_type = "null-ptr-deref";
 553         else if (orig_addr < TASK_SIZE)
 554                 bug_type = "probably user-memory-access";
 555         else
 556                 bug_type = "maybe wild-memory-access";
 557         pr_alert("KASAN: %s in range [0x%016lx-0x%016lx]\n", bug_type,
 558                  orig_addr, orig_addr + KASAN_GRANULE_SIZE - 1);
 559 }
 560 #endif