xref: /linux/mm/kasan/report.c (revision 2942242dde896ea8544f321617c86f941899c544)

// 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 <kunit/visibility.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/vmalloc.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)

VISIBLE_IF_KUNIT bool kasan_save_enable_multi_shot(void)
{
	return test_and_set_bit(KASAN_BIT_MULTI_SHOT, &kasan_flags);
}
EXPORT_SYMBOL_IF_KUNIT(kasan_save_enable_multi_shot);

VISIBLE_IF_KUNIT void kasan_restore_multi_shot(bool enabled)
{
	if (!enabled)
		clear_bit(KASAN_BIT_MULTI_SHOT, &kasan_flags);
}
EXPORT_SYMBOL_IF_KUNIT(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;

VISIBLE_IF_KUNIT void kasan_kunit_test_suite_start(void)
{
	WRITE_ONCE(kasan_kunit_executing, true);
}
EXPORT_SYMBOL_IF_KUNIT(kasan_kunit_test_suite_start);

VISIBLE_IF_KUNIT void kasan_kunit_test_suite_end(void)
{
	WRITE_ONCE(kasan_kunit_executing, false);
}
EXPORT_SYMBOL_IF_KUNIT(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_RAW_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();
	raw_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");
	raw_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)
{
#ifdef CONFIG_KASAN_EXTRA_INFO
	u64 ts_nsec = track->timestamp;
	unsigned long rem_usec;

	ts_nsec <<= 9;
	rem_usec = do_div(ts_nsec, NSEC_PER_SEC) / 1000;

	pr_err("%s by task %u on cpu %d at %lu.%06lus:\n",
			prefix, track->pid, track->cpu,
			(unsigned long)ts_nsec, rem_usec);
#else
	pr_err("%s by task %u:\n", prefix, track->pid);
#endif /* CONFIG_KASAN_EXTRA_INFO */
	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)) {
		pr_err("The buggy address belongs to a");
		if (!vmalloc_dump_obj(addr))
			pr_cont(" vmalloc virtual mapping\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 */

#if defined(CONFIG_KASAN_GENERIC) || defined(CONFIG_KASAN_SW_TAGS)
/*
 * With compiler-based KASAN modes, accesses to bogus pointers (outside of the
 * mapped kernel address space regions) cause faults when KASAN tries to check
 * the shadow memory before the actual memory access. This results in cryptic
 * GPF reports, which are hard for users to interpret. This hook helps users to
 * figure out what the original bogus pointer was.
 */
void kasan_non_canonical_hook(unsigned long addr)
{
	unsigned long orig_addr;
	const char *bug_type;

	/*
	 * All addresses that came as a result of the memory-to-shadow mapping
	 * (even for bogus pointers) must be >= KASAN_SHADOW_OFFSET.
	 */
	if (addr < KASAN_SHADOW_OFFSET)
		return;

	orig_addr = (unsigned long)kasan_shadow_to_mem((void *)addr);

	/*
	 * 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 the shadow for low or high canonical
	 * addresses, we can still be pretty sure: these shadow regions are a
	 * fairly narrow chunk of the address space.
	 * But the shadow for non-canonical addresses is a really large chunk
	 * of the address space. For this 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 if (addr_in_shadow((void *)addr))
		bug_type = "probably wild-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