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 <kunit/test.h>
  13 #include <linux/bitops.h>
  14 #include <linux/ftrace.h>
  15 #include <linux/init.h>
  16 #include <linux/kernel.h>
  17 #include <linux/lockdep.h>
  18 #include <linux/mm.h>
  19 #include <linux/printk.h>
  20 #include <linux/sched.h>
  21 #include <linux/slab.h>
  22 #include <linux/stackdepot.h>
  23 #include <linux/stacktrace.h>
  24 #include <linux/string.h>
  25 #include <linux/types.h>
  26 #include <linux/kasan.h>
  27 #include <linux/module.h>
  28 #include <linux/sched/task_stack.h>
  29 #include <linux/uaccess.h>
  30 #include <trace/events/error_report.h>
  31
  32 #include <asm/sections.h>
  33
  34 #include "kasan.h"
  35 #include "../slab.h"
  36
  37 static unsigned long kasan_flags;
  38
  39 #define KASAN_BIT_REPORTED      0
  40 #define KASAN_BIT_MULTI_SHOT    1
  41
  42 enum kasan_arg_fault {
  43         KASAN_ARG_FAULT_DEFAULT,
  44         KASAN_ARG_FAULT_REPORT,
  45         KASAN_ARG_FAULT_PANIC,
  46 };
  47
  48 static enum kasan_arg_fault kasan_arg_fault __ro_after_init = KASAN_ARG_FAULT_DEFAULT;
  49
  50 /* kasan.fault=report/panic */
  51 static int __init early_kasan_fault(char *arg)
  52 {
  53         if (!arg)
  54                 return -EINVAL;
  55
  56         if (!strcmp(arg, "report"))
  57                 kasan_arg_fault = KASAN_ARG_FAULT_REPORT;
  58         else if (!strcmp(arg, "panic"))
  59                 kasan_arg_fault = KASAN_ARG_FAULT_PANIC;
  60         else
  61                 return -EINVAL;
  62
  63         return 0;
  64 }
  65 early_param("kasan.fault", early_kasan_fault);
  66
  67 static int __init kasan_set_multi_shot(char *str)
  68 {
  69         set_bit(KASAN_BIT_MULTI_SHOT, &kasan_flags);
  70         return 1;
  71 }
  72 __setup("kasan_multi_shot", kasan_set_multi_shot);
  73
  74 /*
  75  * This function is used to check whether KASAN reports are suppressed for
  76  * software KASAN modes via kasan_disable/enable_current() critical sections.
  77  *
  78  * This is done to avoid:
  79  * 1. False-positive reports when accessing slab metadata,
  80  * 2. Deadlocking when poisoned memory is accessed by the reporting code.
  81  *
  82  * Hardware Tag-Based KASAN instead relies on:
  83  * For #1: Resetting tags via kasan_reset_tag().
  84  * For #2: Suppression of tag checks via CPU, see report_suppress_start/end().
  85  */
  86 static bool report_suppressed_sw(void)
  87 {
  88 #if defined(CONFIG_KASAN_GENERIC) || defined(CONFIG_KASAN_SW_TAGS)
  89         if (current->kasan_depth)
  90                 return true;
  91 #endif
  92         return false;
  93 }
  94
  95 static void report_suppress_start(void)
  96 {
  97 #ifdef CONFIG_KASAN_HW_TAGS
  98         /*
  99          * Disable preemption for the duration of printing a KASAN report, as
 100          * hw_suppress_tag_checks_start() disables checks on the current CPU.
 101          */
 102         preempt_disable();
 103         hw_suppress_tag_checks_start();
 104 #else
 105         kasan_disable_current();
 106 #endif
 107 }
 108
 109 static void report_suppress_stop(void)
 110 {
 111 #ifdef CONFIG_KASAN_HW_TAGS
 112         hw_suppress_tag_checks_stop();
 113         preempt_enable();
 114 #else
 115         kasan_enable_current();
 116 #endif
 117 }
 118
 119 /*
 120  * Used to avoid reporting more than one KASAN bug unless kasan_multi_shot
 121  * is enabled. Note that KASAN tests effectively enable kasan_multi_shot
 122  * for their duration.
 123  */
 124 static bool report_enabled(void)
 125 {
 126         if (test_bit(KASAN_BIT_MULTI_SHOT, &kasan_flags))
 127                 return true;
 128         return !test_and_set_bit(KASAN_BIT_REPORTED, &kasan_flags);
 129 }
 130
 131 #if IS_ENABLED(CONFIG_KASAN_KUNIT_TEST) || IS_ENABLED(CONFIG_KASAN_MODULE_TEST)
 132
 133 bool kasan_save_enable_multi_shot(void)
 134 {
 135         return test_and_set_bit(KASAN_BIT_MULTI_SHOT, &kasan_flags);
 136 }
 137 EXPORT_SYMBOL_GPL(kasan_save_enable_multi_shot);
 138
 139 void kasan_restore_multi_shot(bool enabled)
 140 {
 141         if (!enabled)
 142                 clear_bit(KASAN_BIT_MULTI_SHOT, &kasan_flags);
 143 }
 144 EXPORT_SYMBOL_GPL(kasan_restore_multi_shot);
 145
 146 #endif
 147
 148 #if IS_ENABLED(CONFIG_KASAN_KUNIT_TEST)
 149
 150 /*
 151  * Whether the KASAN KUnit test suite is currently being executed.
 152  * Updated in kasan_test.c.
 153  */
 154 static bool kasan_kunit_executing;
 155
 156 void kasan_kunit_test_suite_start(void)
 157 {
 158         WRITE_ONCE(kasan_kunit_executing, true);
 159 }
 160 EXPORT_SYMBOL_GPL(kasan_kunit_test_suite_start);
 161
 162 void kasan_kunit_test_suite_end(void)
 163 {
 164         WRITE_ONCE(kasan_kunit_executing, false);
 165 }
 166 EXPORT_SYMBOL_GPL(kasan_kunit_test_suite_end);
 167
 168 static bool kasan_kunit_test_suite_executing(void)
 169 {
 170         return READ_ONCE(kasan_kunit_executing);
 171 }
 172
 173 #else /* CONFIG_KASAN_KUNIT_TEST */
 174
 175 static inline bool kasan_kunit_test_suite_executing(void) { return false; }
 176
 177 #endif /* CONFIG_KASAN_KUNIT_TEST */
 178
 179 #if IS_ENABLED(CONFIG_KUNIT)
 180
 181 static void fail_non_kasan_kunit_test(void)
 182 {
 183         struct kunit *test;
 184
 185         if (kasan_kunit_test_suite_executing())
 186                 return;
 187
 188         test = current->kunit_test;
 189         if (test)
 190                 kunit_set_failure(test);
 191 }
 192
 193 #else /* CONFIG_KUNIT */
 194
 195 static inline void fail_non_kasan_kunit_test(void) { }
 196
 197 #endif /* CONFIG_KUNIT */
 198
 199 static DEFINE_SPINLOCK(report_lock);
 200
 201 static void start_report(unsigned long *flags, bool sync)
 202 {
 203         fail_non_kasan_kunit_test();
 204         /* Respect the /proc/sys/kernel/traceoff_on_warning interface. */
 205         disable_trace_on_warning();
 206         /* Do not allow LOCKDEP mangling KASAN reports. */
 207         lockdep_off();
 208         /* Make sure we don't end up in loop. */
 209         report_suppress_start();
 210         spin_lock_irqsave(&report_lock, *flags);
 211         pr_err("==================================================================\n");
 212 }
 213
 214 static void end_report(unsigned long *flags, void *addr)
 215 {
 216         if (addr)
 217                 trace_error_report_end(ERROR_DETECTOR_KASAN,
 218                                        (unsigned long)addr);
 219         pr_err("==================================================================\n");
 220         spin_unlock_irqrestore(&report_lock, *flags);
 221         if (!test_bit(KASAN_BIT_MULTI_SHOT, &kasan_flags))
 222                 check_panic_on_warn("KASAN");
 223         if (kasan_arg_fault == KASAN_ARG_FAULT_PANIC)
 224                 panic("kasan.fault=panic set ...\n");
 225         add_taint(TAINT_BAD_PAGE, LOCKDEP_NOW_UNRELIABLE);
 226         lockdep_on();
 227         report_suppress_stop();
 228 }
 229
 230 static void print_error_description(struct kasan_report_info *info)
 231 {
 232         pr_err("BUG: KASAN: %s in %pS\n", info->bug_type, (void *)info->ip);
 233
 234         if (info->type != KASAN_REPORT_ACCESS) {
 235                 pr_err("Free of addr %px by task %s/%d\n",
 236                         info->access_addr, current->comm, task_pid_nr(current));
 237                 return;
 238         }
 239
 240         if (info->access_size)
 241                 pr_err("%s of size %zu at addr %px by task %s/%d\n",
 242                         info->is_write ? "Write" : "Read", info->access_size,
 243                         info->access_addr, current->comm, task_pid_nr(current));
 244         else
 245                 pr_err("%s at addr %px by task %s/%d\n",
 246                         info->is_write ? "Write" : "Read",
 247                         info->access_addr, current->comm, task_pid_nr(current));
 248 }
 249
 250 static void print_track(struct kasan_track *track, const char *prefix)
 251 {
 252         pr_err("%s by task %u:\n", prefix, track->pid);
 253         if (track->stack)
 254                 stack_depot_print(track->stack);
 255         else
 256                 pr_err("(stack is not available)\n");
 257 }
 258
 259 static inline struct page *addr_to_page(const void *addr)
 260 {
 261         if (virt_addr_valid(addr))
 262                 return virt_to_head_page(addr);
 263         return NULL;
 264 }
 265
 266 static void describe_object_addr(const void *addr, struct kasan_report_info *info)
 267 {
 268         unsigned long access_addr = (unsigned long)addr;
 269         unsigned long object_addr = (unsigned long)info->object;
 270         const char *rel_type, *region_state = "";
 271         int rel_bytes;
 272
 273         pr_err("The buggy address belongs to the object at %px\n"
 274                " which belongs to the cache %s of size %d\n",
 275                 info->object, info->cache->name, info->cache->object_size);
 276
 277         if (access_addr < object_addr) {
 278                 rel_type = "to the left";
 279                 rel_bytes = object_addr - access_addr;
 280         } else if (access_addr >= object_addr + info->alloc_size) {
 281                 rel_type = "to the right";
 282                 rel_bytes = access_addr - (object_addr + info->alloc_size);
 283         } else {
 284                 rel_type = "inside";
 285                 rel_bytes = access_addr - object_addr;
 286         }
 287
 288         /*
 289          * Tag-Based modes use the stack ring to infer the bug type, but the
 290          * memory region state description is generated based on the metadata.
 291          * Thus, defining the region state as below can contradict the metadata.
 292          * Fixing this requires further improvements, so only infer the state
 293          * for the Generic mode.
 294          */
 295         if (IS_ENABLED(CONFIG_KASAN_GENERIC)) {
 296                 if (strcmp(info->bug_type, "slab-out-of-bounds") == 0)
 297                         region_state = "allocated ";
 298                 else if (strcmp(info->bug_type, "slab-use-after-free") == 0)
 299                         region_state = "freed ";
 300         }
 301
 302         pr_err("The buggy address is located %d bytes %s of\n"
 303                " %s%zu-byte region [%px, %px)\n",
 304                rel_bytes, rel_type, region_state, info->alloc_size,
 305                (void *)object_addr, (void *)(object_addr + info->alloc_size));
 306 }
 307
 308 static void describe_object_stacks(struct kasan_report_info *info)
 309 {
 310         if (info->alloc_track.stack) {
 311                 print_track(&info->alloc_track, "Allocated");
 312                 pr_err("\n");
 313         }
 314
 315         if (info->free_track.stack) {
 316                 print_track(&info->free_track, "Freed");
 317                 pr_err("\n");
 318         }
 319
 320         kasan_print_aux_stacks(info->cache, info->object);
 321 }
 322
 323 static void describe_object(const void *addr, struct kasan_report_info *info)
 324 {
 325         if (kasan_stack_collection_enabled())
 326                 describe_object_stacks(info);
 327         describe_object_addr(addr, info);
 328 }
 329
 330 static inline bool kernel_or_module_addr(const void *addr)
 331 {
 332         if (is_kernel((unsigned long)addr))
 333                 return true;
 334         if (is_module_address((unsigned long)addr))
 335                 return true;
 336         return false;
 337 }
 338
 339 static inline bool init_task_stack_addr(const void *addr)
 340 {
 341         return addr >= (void *)&init_thread_union.stack &&
 342                 (addr <= (void *)&init_thread_union.stack +
 343                         sizeof(init_thread_union.stack));
 344 }
 345
 346 static void print_address_description(void *addr, u8 tag,
 347                                       struct kasan_report_info *info)
 348 {
 349         struct page *page = addr_to_page(addr);
 350
 351         dump_stack_lvl(KERN_ERR);
 352         pr_err("\n");
 353
 354         if (info->cache && info->object) {
 355                 describe_object(addr, info);
 356                 pr_err("\n");
 357         }
 358
 359         if (kernel_or_module_addr(addr) && !init_task_stack_addr(addr)) {
 360                 pr_err("The buggy address belongs to the variable:\n");
 361                 pr_err(" %pS\n", addr);
 362                 pr_err("\n");
 363         }
 364
 365         if (object_is_on_stack(addr)) {
 366                 /*
 367                  * Currently, KASAN supports printing frame information only
 368                  * for accesses to the task's own stack.
 369                  */
 370                 kasan_print_address_stack_frame(addr);
 371                 pr_err("\n");
 372         }
 373
 374         if (is_vmalloc_addr(addr)) {
 375                 struct vm_struct *va = find_vm_area(addr);
 376
 377                 if (va) {
 378                         pr_err("The buggy address belongs to the virtual mapping at\n"
 379                                " [%px, %px) created by:\n"
 380                                " %pS\n",
 381                                va->addr, va->addr + va->size, va->caller);
 382                         pr_err("\n");
 383
 384                         page = vmalloc_to_page(addr);
 385                 }
 386         }
 387
 388         if (page) {
 389                 pr_err("The buggy address belongs to the physical page:\n");
 390                 dump_page(page, "kasan: bad access detected");
 391                 pr_err("\n");
 392         }
 393 }
 394
 395 static bool meta_row_is_guilty(const void *row, const void *addr)
 396 {
 397         return (row <= addr) && (addr < row + META_MEM_BYTES_PER_ROW);
 398 }
 399
 400 static int meta_pointer_offset(const void *row, const void *addr)
 401 {
 402         /*
 403          * Memory state around the buggy address:
 404          *  ff00ff00ff00ff00: 00 00 00 05 fe fe fe fe fe fe fe fe fe fe fe fe
 405          *  ...
 406          *
 407          * The length of ">ff00ff00ff00ff00: " is
 408          *    3 + (BITS_PER_LONG / 8) * 2 chars.
 409          * The length of each granule metadata is 2 bytes
 410          *    plus 1 byte for space.
 411          */
 412         return 3 + (BITS_PER_LONG / 8) * 2 +
 413                 (addr - row) / KASAN_GRANULE_SIZE * 3 + 1;
 414 }
 415
 416 static void print_memory_metadata(const void *addr)
 417 {
 418         int i;
 419         void *row;
 420
 421         row = (void *)round_down((unsigned long)addr, META_MEM_BYTES_PER_ROW)
 422                         - META_ROWS_AROUND_ADDR * META_MEM_BYTES_PER_ROW;
 423
 424         pr_err("Memory state around the buggy address:\n");
 425
 426         for (i = -META_ROWS_AROUND_ADDR; i <= META_ROWS_AROUND_ADDR; i++) {
 427                 char buffer[4 + (BITS_PER_LONG / 8) * 2];
 428                 char metadata[META_BYTES_PER_ROW];
 429
 430                 snprintf(buffer, sizeof(buffer),
 431                                 (i == 0) ? ">%px: " : " %px: ", row);
 432
 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                 kasan_metadata_fetch_row(&metadata[0], row);
 439
 440                 print_hex_dump(KERN_ERR, buffer,
 441                         DUMP_PREFIX_NONE, META_BYTES_PER_ROW, 1,
 442                         metadata, META_BYTES_PER_ROW, 0);
 443
 444                 if (meta_row_is_guilty(row, addr))
 445                         pr_err("%*c\n", meta_pointer_offset(row, addr), '^');
 446
 447                 row += META_MEM_BYTES_PER_ROW;
 448         }
 449 }
 450
 451 static void print_report(struct kasan_report_info *info)
 452 {
 453         void *addr = kasan_reset_tag(info->access_addr);
 454         u8 tag = get_tag(info->access_addr);
 455
 456         print_error_description(info);
 457         if (addr_has_metadata(addr))
 458                 kasan_print_tags(tag, info->first_bad_addr);
 459         pr_err("\n");
 460
 461         if (addr_has_metadata(addr)) {
 462                 print_address_description(addr, tag, info);
 463                 print_memory_metadata(info->first_bad_addr);
 464         } else {
 465                 dump_stack_lvl(KERN_ERR);
 466         }
 467 }
 468
 469 static void complete_report_info(struct kasan_report_info *info)
 470 {
 471         void *addr = kasan_reset_tag(info->access_addr);
 472         struct slab *slab;
 473
 474         if (info->type == KASAN_REPORT_ACCESS)
 475                 info->first_bad_addr = kasan_find_first_bad_addr(
 476                                         info->access_addr, info->access_size);
 477         else
 478                 info->first_bad_addr = addr;
 479
 480         slab = kasan_addr_to_slab(addr);
 481         if (slab) {
 482                 info->cache = slab->slab_cache;
 483                 info->object = nearest_obj(info->cache, slab, addr);
 484
 485                 /* Try to determine allocation size based on the metadata. */
 486                 info->alloc_size = kasan_get_alloc_size(info->object, info->cache);
 487                 /* Fallback to the object size if failed. */
 488                 if (!info->alloc_size)
 489                         info->alloc_size = info->cache->object_size;
 490         } else
 491                 info->cache = info->object = NULL;
 492
 493         switch (info->type) {
 494         case KASAN_REPORT_INVALID_FREE:
 495                 info->bug_type = "invalid-free";
 496                 break;
 497         case KASAN_REPORT_DOUBLE_FREE:
 498                 info->bug_type = "double-free";
 499                 break;
 500         default:
 501                 /* bug_type filled in by kasan_complete_mode_report_info. */
 502                 break;
 503         }
 504
 505         /* Fill in mode-specific report info fields. */
 506         kasan_complete_mode_report_info(info);
 507 }
 508
 509 void kasan_report_invalid_free(void *ptr, unsigned long ip, enum kasan_report_type type)
 510 {
 511         unsigned long flags;
 512         struct kasan_report_info info;
 513
 514         /*
 515          * Do not check report_suppressed_sw(), as an invalid-free cannot be
 516          * caused by accessing poisoned memory and thus should not be suppressed
 517          * by kasan_disable/enable_current() critical sections.
 518          *
 519          * Note that for Hardware Tag-Based KASAN, kasan_report_invalid_free()
 520          * is triggered by explicit tag checks and not by the ones performed by
 521          * the CPU. Thus, reporting invalid-free is not suppressed as well.
 522          */
 523         if (unlikely(!report_enabled()))
 524                 return;
 525
 526         start_report(&flags, true);
 527
 528         memset(&info, 0, sizeof(info));
 529         info.type = type;
 530         info.access_addr = ptr;
 531         info.access_size = 0;
 532         info.is_write = false;
 533         info.ip = ip;
 534
 535         complete_report_info(&info);
 536
 537         print_report(&info);
 538
 539         end_report(&flags, ptr);
 540 }
 541
 542 /*
 543  * kasan_report() is the only reporting function that uses
 544  * user_access_save/restore(): kasan_report_invalid_free() cannot be called
 545  * from a UACCESS region, and kasan_report_async() is not used on x86.
 546  */
 547 bool kasan_report(unsigned long addr, size_t size, bool is_write,
 548                         unsigned long ip)
 549 {
 550         bool ret = true;
 551         void *ptr = (void *)addr;
 552         unsigned long ua_flags = user_access_save();
 553         unsigned long irq_flags;
 554         struct kasan_report_info info;
 555
 556         if (unlikely(report_suppressed_sw()) || unlikely(!report_enabled())) {
 557                 ret = false;
 558                 goto out;
 559         }
 560
 561         start_report(&irq_flags, true);
 562
 563         memset(&info, 0, sizeof(info));
 564         info.type = KASAN_REPORT_ACCESS;
 565         info.access_addr = ptr;
 566         info.access_size = size;
 567         info.is_write = is_write;
 568         info.ip = ip;
 569
 570         complete_report_info(&info);
 571
 572         print_report(&info);
 573
 574         end_report(&irq_flags, ptr);
 575
 576 out:
 577         user_access_restore(ua_flags);
 578
 579         return ret;
 580 }
 581
 582 #ifdef CONFIG_KASAN_HW_TAGS
 583 void kasan_report_async(void)
 584 {
 585         unsigned long flags;
 586
 587         /*
 588          * Do not check report_suppressed_sw(), as
 589          * kasan_disable/enable_current() critical sections do not affect
 590          * Hardware Tag-Based KASAN.
 591          */
 592         if (unlikely(!report_enabled()))
 593                 return;
 594
 595         start_report(&flags, false);
 596         pr_err("BUG: KASAN: invalid-access\n");
 597         pr_err("Asynchronous fault: no details available\n");
 598         pr_err("\n");
 599         dump_stack_lvl(KERN_ERR);
 600         end_report(&flags, NULL);
 601 }
 602 #endif /* CONFIG_KASAN_HW_TAGS */
 603
 604 #ifdef CONFIG_KASAN_INLINE
 605 /*
 606  * With CONFIG_KASAN_INLINE, accesses to bogus pointers (outside the high
 607  * canonical half of the address space) cause out-of-bounds shadow memory reads
 608  * before the actual access. For addresses in the low canonical half of the
 609  * address space, as well as most non-canonical addresses, that out-of-bounds
 610  * shadow memory access lands in the non-canonical part of the address space.
 611  * Help the user figure out what the original bogus pointer was.
 612  */
 613 void kasan_non_canonical_hook(unsigned long addr)
 614 {
 615         unsigned long orig_addr;
 616         const char *bug_type;
 617
 618         if (addr < KASAN_SHADOW_OFFSET)
 619                 return;
 620
 621         orig_addr = (addr - KASAN_SHADOW_OFFSET) << KASAN_SHADOW_SCALE_SHIFT;
 622         /*
 623          * For faults near the shadow address for NULL, we can be fairly certain
 624          * that this is a KASAN shadow memory access.
 625          * For faults that correspond to shadow for low canonical addresses, we
 626          * can still be pretty sure - that shadow region is a fairly narrow
 627          * chunk of the non-canonical address space.
 628          * But faults that look like shadow for non-canonical addresses are a
 629          * really large chunk of the address space. In that case, we still
 630          * print the decoded address, but make it clear that this is not
 631          * necessarily what's actually going on.
 632          */
 633         if (orig_addr < PAGE_SIZE)
 634                 bug_type = "null-ptr-deref";
 635         else if (orig_addr < TASK_SIZE)
 636                 bug_type = "probably user-memory-access";
 637         else
 638                 bug_type = "maybe wild-memory-access";
 639         pr_alert("KASAN: %s in range [0x%016lx-0x%016lx]\n", bug_type,
 640                  orig_addr, orig_addr + KASAN_GRANULE_SIZE - 1);
 641 }
 642 #endif