linux/mm/kasan/report.c
Marco Elver 452c03fdbe kasan: add support for kasan.fault=panic_on_write
KASAN's boot time kernel parameter 'kasan.fault=' currently supports
'report' and 'panic', which results in either only reporting bugs or also
panicking on reports.

However, some users may wish to have more control over when KASAN reports
result in a kernel panic: in particular, KASAN reported invalid _writes_
are of special interest, because they have greater potential to corrupt
random kernel memory or be more easily exploited.

To panic on invalid writes only, introduce 'kasan.fault=panic_on_write',
which allows users to choose to continue running on invalid reads, but
panic only on invalid writes.

Link: https://lkml.kernel.org/r/20230614095158.1133673-1-elver@google.com
Signed-off-by: Marco Elver <elver@google.com>
Reviewed-by: Alexander Potapenko <glider@google.com>
Cc: Aleksandr Nogikh <nogikh@google.com>
Cc: Andrey Konovalov <andreyknvl@gmail.com>
Cc: Andrey Ryabinin <ryabinin.a.a@gmail.com>
Cc: Dmitry Vyukov <dvyukov@google.com>
Cc: Jonathan Corbet <corbet@lwn.net>
Cc: Taras Madan <tarasmadan@google.com>
Cc: Vincenzo Frascino <vincenzo.frascino@arm.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
2023-06-19 16:19:33 -07:00

663 lines
17 KiB
C

// SPDX-License-Identifier: GPL-2.0
/*
* This file contains common KASAN error reporting code.
*
* Copyright (c) 2014 Samsung Electronics Co., Ltd.
* Author: Andrey Ryabinin <ryabinin.a.a@gmail.com>
*
* Some code borrowed from https://github.com/xairy/kasan-prototype by
* Andrey Konovalov <andreyknvl@gmail.com>
*/
#include <kunit/test.h>
#include <linux/bitops.h>
#include <linux/ftrace.h>
#include <linux/init.h>
#include <linux/kernel.h>
#include <linux/lockdep.h>
#include <linux/mm.h>
#include <linux/printk.h>
#include <linux/sched.h>
#include <linux/slab.h>
#include <linux/stackdepot.h>
#include <linux/stacktrace.h>
#include <linux/string.h>
#include <linux/types.h>
#include <linux/kasan.h>
#include <linux/module.h>
#include <linux/sched/task_stack.h>
#include <linux/uaccess.h>
#include <trace/events/error_report.h>
#include <asm/sections.h>
#include "kasan.h"
#include "../slab.h"
static unsigned long kasan_flags;
#define KASAN_BIT_REPORTED 0
#define KASAN_BIT_MULTI_SHOT 1
enum kasan_arg_fault {
KASAN_ARG_FAULT_DEFAULT,
KASAN_ARG_FAULT_REPORT,
KASAN_ARG_FAULT_PANIC,
KASAN_ARG_FAULT_PANIC_ON_WRITE,
};
static enum kasan_arg_fault kasan_arg_fault __ro_after_init = KASAN_ARG_FAULT_DEFAULT;
/* kasan.fault=report/panic */
static int __init early_kasan_fault(char *arg)
{
if (!arg)
return -EINVAL;
if (!strcmp(arg, "report"))
kasan_arg_fault = KASAN_ARG_FAULT_REPORT;
else if (!strcmp(arg, "panic"))
kasan_arg_fault = KASAN_ARG_FAULT_PANIC;
else if (!strcmp(arg, "panic_on_write"))
kasan_arg_fault = KASAN_ARG_FAULT_PANIC_ON_WRITE;
else
return -EINVAL;
return 0;
}
early_param("kasan.fault", early_kasan_fault);
static int __init kasan_set_multi_shot(char *str)
{
set_bit(KASAN_BIT_MULTI_SHOT, &kasan_flags);
return 1;
}
__setup("kasan_multi_shot", kasan_set_multi_shot);
/*
* This function is used to check whether KASAN reports are suppressed for
* software KASAN modes via kasan_disable/enable_current() critical sections.
*
* This is done to avoid:
* 1. False-positive reports when accessing slab metadata,
* 2. Deadlocking when poisoned memory is accessed by the reporting code.
*
* Hardware Tag-Based KASAN instead relies on:
* For #1: Resetting tags via kasan_reset_tag().
* For #2: Suppression of tag checks via CPU, see report_suppress_start/end().
*/
static bool report_suppressed_sw(void)
{
#if defined(CONFIG_KASAN_GENERIC) || defined(CONFIG_KASAN_SW_TAGS)
if (current->kasan_depth)
return true;
#endif
return false;
}
static void report_suppress_start(void)
{
#ifdef CONFIG_KASAN_HW_TAGS
/*
* Disable preemption for the duration of printing a KASAN report, as
* hw_suppress_tag_checks_start() disables checks on the current CPU.
*/
preempt_disable();
hw_suppress_tag_checks_start();
#else
kasan_disable_current();
#endif
}
static void report_suppress_stop(void)
{
#ifdef CONFIG_KASAN_HW_TAGS
hw_suppress_tag_checks_stop();
preempt_enable();
#else
kasan_enable_current();
#endif
}
/*
* Used to avoid reporting more than one KASAN bug unless kasan_multi_shot
* is enabled. Note that KASAN tests effectively enable kasan_multi_shot
* for their duration.
*/
static bool report_enabled(void)
{
if (test_bit(KASAN_BIT_MULTI_SHOT, &kasan_flags))
return true;
return !test_and_set_bit(KASAN_BIT_REPORTED, &kasan_flags);
}
#if IS_ENABLED(CONFIG_KASAN_KUNIT_TEST) || IS_ENABLED(CONFIG_KASAN_MODULE_TEST)
bool kasan_save_enable_multi_shot(void)
{
return test_and_set_bit(KASAN_BIT_MULTI_SHOT, &kasan_flags);
}
EXPORT_SYMBOL_GPL(kasan_save_enable_multi_shot);
void kasan_restore_multi_shot(bool enabled)
{
if (!enabled)
clear_bit(KASAN_BIT_MULTI_SHOT, &kasan_flags);
}
EXPORT_SYMBOL_GPL(kasan_restore_multi_shot);
#endif
#if IS_ENABLED(CONFIG_KASAN_KUNIT_TEST)
/*
* Whether the KASAN KUnit test suite is currently being executed.
* Updated in kasan_test.c.
*/
static bool kasan_kunit_executing;
void kasan_kunit_test_suite_start(void)
{
WRITE_ONCE(kasan_kunit_executing, true);
}
EXPORT_SYMBOL_GPL(kasan_kunit_test_suite_start);
void kasan_kunit_test_suite_end(void)
{
WRITE_ONCE(kasan_kunit_executing, false);
}
EXPORT_SYMBOL_GPL(kasan_kunit_test_suite_end);
static bool kasan_kunit_test_suite_executing(void)
{
return READ_ONCE(kasan_kunit_executing);
}
#else /* CONFIG_KASAN_KUNIT_TEST */
static inline bool kasan_kunit_test_suite_executing(void) { return false; }
#endif /* CONFIG_KASAN_KUNIT_TEST */
#if IS_ENABLED(CONFIG_KUNIT)
static void fail_non_kasan_kunit_test(void)
{
struct kunit *test;
if (kasan_kunit_test_suite_executing())
return;
test = current->kunit_test;
if (test)
kunit_set_failure(test);
}
#else /* CONFIG_KUNIT */
static inline void fail_non_kasan_kunit_test(void) { }
#endif /* CONFIG_KUNIT */
static DEFINE_SPINLOCK(report_lock);
static void start_report(unsigned long *flags, bool sync)
{
fail_non_kasan_kunit_test();
/* Respect the /proc/sys/kernel/traceoff_on_warning interface. */
disable_trace_on_warning();
/* Do not allow LOCKDEP mangling KASAN reports. */
lockdep_off();
/* Make sure we don't end up in loop. */
report_suppress_start();
spin_lock_irqsave(&report_lock, *flags);
pr_err("==================================================================\n");
}
static void end_report(unsigned long *flags, const void *addr, bool is_write)
{
if (addr)
trace_error_report_end(ERROR_DETECTOR_KASAN,
(unsigned long)addr);
pr_err("==================================================================\n");
spin_unlock_irqrestore(&report_lock, *flags);
if (!test_bit(KASAN_BIT_MULTI_SHOT, &kasan_flags))
check_panic_on_warn("KASAN");
switch (kasan_arg_fault) {
case KASAN_ARG_FAULT_DEFAULT:
case KASAN_ARG_FAULT_REPORT:
break;
case KASAN_ARG_FAULT_PANIC:
panic("kasan.fault=panic set ...\n");
break;
case KASAN_ARG_FAULT_PANIC_ON_WRITE:
if (is_write)
panic("kasan.fault=panic_on_write set ...\n");
break;
}
add_taint(TAINT_BAD_PAGE, LOCKDEP_NOW_UNRELIABLE);
lockdep_on();
report_suppress_stop();
}
static void print_error_description(struct kasan_report_info *info)
{
pr_err("BUG: KASAN: %s in %pS\n", info->bug_type, (void *)info->ip);
if (info->type != KASAN_REPORT_ACCESS) {
pr_err("Free of addr %px by task %s/%d\n",
info->access_addr, current->comm, task_pid_nr(current));
return;
}
if (info->access_size)
pr_err("%s of size %zu at addr %px by task %s/%d\n",
info->is_write ? "Write" : "Read", info->access_size,
info->access_addr, current->comm, task_pid_nr(current));
else
pr_err("%s at addr %px by task %s/%d\n",
info->is_write ? "Write" : "Read",
info->access_addr, current->comm, task_pid_nr(current));
}
static void print_track(struct kasan_track *track, const char *prefix)
{
pr_err("%s by task %u:\n", prefix, track->pid);
if (track->stack)
stack_depot_print(track->stack);
else
pr_err("(stack is not available)\n");
}
static inline struct page *addr_to_page(const void *addr)
{
if (virt_addr_valid(addr))
return virt_to_head_page(addr);
return NULL;
}
static void describe_object_addr(const void *addr, struct kasan_report_info *info)
{
unsigned long access_addr = (unsigned long)addr;
unsigned long object_addr = (unsigned long)info->object;
const char *rel_type, *region_state = "";
int rel_bytes;
pr_err("The buggy address belongs to the object at %px\n"
" which belongs to the cache %s of size %d\n",
info->object, info->cache->name, info->cache->object_size);
if (access_addr < object_addr) {
rel_type = "to the left";
rel_bytes = object_addr - access_addr;
} else if (access_addr >= object_addr + info->alloc_size) {
rel_type = "to the right";
rel_bytes = access_addr - (object_addr + info->alloc_size);
} else {
rel_type = "inside";
rel_bytes = access_addr - object_addr;
}
/*
* Tag-Based modes use the stack ring to infer the bug type, but the
* memory region state description is generated based on the metadata.
* Thus, defining the region state as below can contradict the metadata.
* Fixing this requires further improvements, so only infer the state
* for the Generic mode.
*/
if (IS_ENABLED(CONFIG_KASAN_GENERIC)) {
if (strcmp(info->bug_type, "slab-out-of-bounds") == 0)
region_state = "allocated ";
else if (strcmp(info->bug_type, "slab-use-after-free") == 0)
region_state = "freed ";
}
pr_err("The buggy address is located %d bytes %s of\n"
" %s%zu-byte region [%px, %px)\n",
rel_bytes, rel_type, region_state, info->alloc_size,
(void *)object_addr, (void *)(object_addr + info->alloc_size));
}
static void describe_object_stacks(struct kasan_report_info *info)
{
if (info->alloc_track.stack) {
print_track(&info->alloc_track, "Allocated");
pr_err("\n");
}
if (info->free_track.stack) {
print_track(&info->free_track, "Freed");
pr_err("\n");
}
kasan_print_aux_stacks(info->cache, info->object);
}
static void describe_object(const void *addr, struct kasan_report_info *info)
{
if (kasan_stack_collection_enabled())
describe_object_stacks(info);
describe_object_addr(addr, info);
}
static inline bool kernel_or_module_addr(const void *addr)
{
if (is_kernel((unsigned long)addr))
return true;
if (is_module_address((unsigned long)addr))
return true;
return false;
}
static inline bool init_task_stack_addr(const void *addr)
{
return addr >= (void *)&init_thread_union.stack &&
(addr <= (void *)&init_thread_union.stack +
sizeof(init_thread_union.stack));
}
static void print_address_description(void *addr, u8 tag,
struct kasan_report_info *info)
{
struct page *page = addr_to_page(addr);
dump_stack_lvl(KERN_ERR);
pr_err("\n");
if (info->cache && info->object) {
describe_object(addr, info);
pr_err("\n");
}
if (kernel_or_module_addr(addr) && !init_task_stack_addr(addr)) {
pr_err("The buggy address belongs to the variable:\n");
pr_err(" %pS\n", addr);
pr_err("\n");
}
if (object_is_on_stack(addr)) {
/*
* Currently, KASAN supports printing frame information only
* for accesses to the task's own stack.
*/
kasan_print_address_stack_frame(addr);
pr_err("\n");
}
if (is_vmalloc_addr(addr)) {
struct vm_struct *va = find_vm_area(addr);
if (va) {
pr_err("The buggy address belongs to the virtual mapping at\n"
" [%px, %px) created by:\n"
" %pS\n",
va->addr, va->addr + va->size, va->caller);
pr_err("\n");
page = vmalloc_to_page(addr);
}
}
if (page) {
pr_err("The buggy address belongs to the physical page:\n");
dump_page(page, "kasan: bad access detected");
pr_err("\n");
}
}
static bool meta_row_is_guilty(const void *row, const void *addr)
{
return (row <= addr) && (addr < row + META_MEM_BYTES_PER_ROW);
}
static int meta_pointer_offset(const void *row, const void *addr)
{
/*
* Memory state around the buggy address:
* ff00ff00ff00ff00: 00 00 00 05 fe fe fe fe fe fe fe fe fe fe fe fe
* ...
*
* The length of ">ff00ff00ff00ff00: " is
* 3 + (BITS_PER_LONG / 8) * 2 chars.
* The length of each granule metadata is 2 bytes
* plus 1 byte for space.
*/
return 3 + (BITS_PER_LONG / 8) * 2 +
(addr - row) / KASAN_GRANULE_SIZE * 3 + 1;
}
static void print_memory_metadata(const void *addr)
{
int i;
void *row;
row = (void *)round_down((unsigned long)addr, META_MEM_BYTES_PER_ROW)
- META_ROWS_AROUND_ADDR * META_MEM_BYTES_PER_ROW;
pr_err("Memory state around the buggy address:\n");
for (i = -META_ROWS_AROUND_ADDR; i <= META_ROWS_AROUND_ADDR; i++) {
char buffer[4 + (BITS_PER_LONG / 8) * 2];
char metadata[META_BYTES_PER_ROW];
snprintf(buffer, sizeof(buffer),
(i == 0) ? ">%px: " : " %px: ", row);
/*
* We should not pass a shadow pointer to generic
* function, because generic functions may try to
* access kasan mapping for the passed address.
*/
kasan_metadata_fetch_row(&metadata[0], row);
print_hex_dump(KERN_ERR, buffer,
DUMP_PREFIX_NONE, META_BYTES_PER_ROW, 1,
metadata, META_BYTES_PER_ROW, 0);
if (meta_row_is_guilty(row, addr))
pr_err("%*c\n", meta_pointer_offset(row, addr), '^');
row += META_MEM_BYTES_PER_ROW;
}
}
static void print_report(struct kasan_report_info *info)
{
void *addr = kasan_reset_tag((void *)info->access_addr);
u8 tag = get_tag((void *)info->access_addr);
print_error_description(info);
if (addr_has_metadata(addr))
kasan_print_tags(tag, info->first_bad_addr);
pr_err("\n");
if (addr_has_metadata(addr)) {
print_address_description(addr, tag, info);
print_memory_metadata(info->first_bad_addr);
} else {
dump_stack_lvl(KERN_ERR);
}
}
static void complete_report_info(struct kasan_report_info *info)
{
void *addr = kasan_reset_tag((void *)info->access_addr);
struct slab *slab;
if (info->type == KASAN_REPORT_ACCESS)
info->first_bad_addr = kasan_find_first_bad_addr(
(void *)info->access_addr, info->access_size);
else
info->first_bad_addr = addr;
slab = kasan_addr_to_slab(addr);
if (slab) {
info->cache = slab->slab_cache;
info->object = nearest_obj(info->cache, slab, addr);
/* Try to determine allocation size based on the metadata. */
info->alloc_size = kasan_get_alloc_size(info->object, info->cache);
/* Fallback to the object size if failed. */
if (!info->alloc_size)
info->alloc_size = info->cache->object_size;
} else
info->cache = info->object = NULL;
switch (info->type) {
case KASAN_REPORT_INVALID_FREE:
info->bug_type = "invalid-free";
break;
case KASAN_REPORT_DOUBLE_FREE:
info->bug_type = "double-free";
break;
default:
/* bug_type filled in by kasan_complete_mode_report_info. */
break;
}
/* Fill in mode-specific report info fields. */
kasan_complete_mode_report_info(info);
}
void kasan_report_invalid_free(void *ptr, unsigned long ip, enum kasan_report_type type)
{
unsigned long flags;
struct kasan_report_info info;
/*
* Do not check report_suppressed_sw(), as an invalid-free cannot be
* caused by accessing poisoned memory and thus should not be suppressed
* by kasan_disable/enable_current() critical sections.
*
* Note that for Hardware Tag-Based KASAN, kasan_report_invalid_free()
* is triggered by explicit tag checks and not by the ones performed by
* the CPU. Thus, reporting invalid-free is not suppressed as well.
*/
if (unlikely(!report_enabled()))
return;
start_report(&flags, true);
memset(&info, 0, sizeof(info));
info.type = type;
info.access_addr = ptr;
info.access_size = 0;
info.is_write = false;
info.ip = ip;
complete_report_info(&info);
print_report(&info);
/*
* Invalid free is considered a "write" since the allocator's metadata
* updates involves writes.
*/
end_report(&flags, ptr, true);
}
/*
* kasan_report() is the only reporting function that uses
* user_access_save/restore(): kasan_report_invalid_free() cannot be called
* from a UACCESS region, and kasan_report_async() is not used on x86.
*/
bool kasan_report(const void *addr, size_t size, bool is_write,
unsigned long ip)
{
bool ret = true;
unsigned long ua_flags = user_access_save();
unsigned long irq_flags;
struct kasan_report_info info;
if (unlikely(report_suppressed_sw()) || unlikely(!report_enabled())) {
ret = false;
goto out;
}
start_report(&irq_flags, true);
memset(&info, 0, sizeof(info));
info.type = KASAN_REPORT_ACCESS;
info.access_addr = addr;
info.access_size = size;
info.is_write = is_write;
info.ip = ip;
complete_report_info(&info);
print_report(&info);
end_report(&irq_flags, (void *)addr, is_write);
out:
user_access_restore(ua_flags);
return ret;
}
#ifdef CONFIG_KASAN_HW_TAGS
void kasan_report_async(void)
{
unsigned long flags;
/*
* Do not check report_suppressed_sw(), as
* kasan_disable/enable_current() critical sections do not affect
* Hardware Tag-Based KASAN.
*/
if (unlikely(!report_enabled()))
return;
start_report(&flags, false);
pr_err("BUG: KASAN: invalid-access\n");
pr_err("Asynchronous fault: no details available\n");
pr_err("\n");
dump_stack_lvl(KERN_ERR);
/*
* Conservatively set is_write=true, because no details are available.
* In this mode, kasan.fault=panic_on_write is like kasan.fault=panic.
*/
end_report(&flags, NULL, true);
}
#endif /* CONFIG_KASAN_HW_TAGS */
#ifdef CONFIG_KASAN_INLINE
/*
* With CONFIG_KASAN_INLINE, accesses to bogus pointers (outside the high
* canonical half of the address space) cause out-of-bounds shadow memory reads
* before the actual access. For addresses in the low canonical half of the
* address space, as well as most non-canonical addresses, that out-of-bounds
* shadow memory access lands in the non-canonical part of the address space.
* Help the user figure out what the original bogus pointer was.
*/
void kasan_non_canonical_hook(unsigned long addr)
{
unsigned long orig_addr;
const char *bug_type;
if (addr < KASAN_SHADOW_OFFSET)
return;
orig_addr = (addr - KASAN_SHADOW_OFFSET) << KASAN_SHADOW_SCALE_SHIFT;
/*
* For faults near the shadow address for NULL, we can be fairly certain
* that this is a KASAN shadow memory access.
* For faults that correspond to shadow for low canonical addresses, we
* can still be pretty sure - that shadow region is a fairly narrow
* chunk of the non-canonical address space.
* But faults that look like shadow for non-canonical addresses are a
* really large chunk of the address space. In that case, we still
* print the decoded address, but make it clear that this is not
* necessarily what's actually going on.
*/
if (orig_addr < PAGE_SIZE)
bug_type = "null-ptr-deref";
else if (orig_addr < TASK_SIZE)
bug_type = "probably user-memory-access";
else
bug_type = "maybe wild-memory-access";
pr_alert("KASAN: %s in range [0x%016lx-0x%016lx]\n", bug_type,
orig_addr, orig_addr + KASAN_GRANULE_SIZE - 1);
}
#endif