blob: 0e987c9ca052d5421acdece1896b82f636e4a1db [file] [log] [blame]
// SPDX-License-Identifier: GPL-2.0
* This file contains core tag-based KASAN code.
* Copyright (c) 2018 Google, Inc.
* Author: Andrey Konovalov <>
* This program is free software; you can redistribute it and/or modify
* it under the terms of the GNU General Public License version 2 as
* published by the Free Software Foundation.
#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
#include <linux/export.h>
#include <linux/interrupt.h>
#include <linux/init.h>
#include <linux/kasan.h>
#include <linux/kernel.h>
#include <linux/kmemleak.h>
#include <linux/linkage.h>
#include <linux/memblock.h>
#include <linux/memory.h>
#include <linux/mm.h>
#include <linux/module.h>
#include <linux/printk.h>
#include <linux/random.h>
#include <linux/sched.h>
#include <linux/sched/task_stack.h>
#include <linux/slab.h>
#include <linux/stacktrace.h>
#include <linux/string.h>
#include <linux/types.h>
#include <linux/vmalloc.h>
#include <linux/bug.h>
#include "kasan.h"
#include "../slab.h"
static DEFINE_PER_CPU(u32, prng_state);
void kasan_init_tags(void)
int cpu;
per_cpu(prng_state, cpu) = (u32)get_cycles();
* If a preemption happens between this_cpu_read and this_cpu_write, the only
* side effect is that we'll give a few allocated in different contexts objects
* the same tag. Since tag-based KASAN is meant to be used a probabilistic
* bug-detection debug feature, this doesn't have significant negative impact.
* Ideally the tags use strong randomness to prevent any attempts to predict
* them during explicit exploit attempts. But strong randomness is expensive,
* and we did an intentional trade-off to use a PRNG. This non-atomic RMW
* sequence has in fact positive effect, since interrupts that randomly skew
* PRNG at unpredictable points do only good.
u8 random_tag(void)
u32 state = this_cpu_read(prng_state);
state = 1664525 * state + 1013904223;
this_cpu_write(prng_state, state);
return (u8)(state % (KASAN_TAG_MAX + 1));
void *kasan_reset_tag(const void *addr)
return reset_tag(addr);
bool check_memory_region(unsigned long addr, size_t size, bool write,
unsigned long ret_ip)
u8 tag;
u8 *shadow_first, *shadow_last, *shadow;
void *untagged_addr;
if (unlikely(size == 0))
return true;
tag = get_tag((const void *)addr);
* Ignore accesses for pointers tagged with 0xff (native kernel
* pointer tag) to suppress false positives caused by kmap.
* Some kernel code was written to account for archs that don't keep
* high memory mapped all the time, but rather map and unmap particular
* pages when needed. Instead of storing a pointer to the kernel memory,
* this code saves the address of the page structure and offset within
* that page for later use. Those pages are then mapped and unmapped
* with kmap/kunmap when necessary and virt_to_page is used to get the
* virtual address of the page. For arm64 (that keeps the high memory
* mapped all the time), kmap is turned into a page_address call.
* The issue is that with use of the page_address + virt_to_page
* sequence the top byte value of the original pointer gets lost (gets
* set to KASAN_TAG_KERNEL (0xFF)).
if (tag == KASAN_TAG_KERNEL)
return true;
untagged_addr = reset_tag((const void *)addr);
if (unlikely(untagged_addr <
kasan_shadow_to_mem((void *)KASAN_SHADOW_START))) {
kasan_report(addr, size, write, ret_ip);
return false;
shadow_first = kasan_mem_to_shadow(untagged_addr);
shadow_last = kasan_mem_to_shadow(untagged_addr + size - 1);
for (shadow = shadow_first; shadow <= shadow_last; shadow++) {
if (*shadow != tag) {
kasan_report(addr, size, write, ret_ip);
return false;
return true;
void __hwasan_load##size##_noabort(unsigned long addr) \
{ \
check_memory_region(addr, size, false, _RET_IP_); \
} \
EXPORT_SYMBOL(__hwasan_load##size##_noabort); \
void __hwasan_store##size##_noabort(unsigned long addr) \
{ \
check_memory_region(addr, size, true, _RET_IP_); \
} \
void __hwasan_loadN_noabort(unsigned long addr, unsigned long size)
check_memory_region(addr, size, false, _RET_IP_);
void __hwasan_storeN_noabort(unsigned long addr, unsigned long size)
check_memory_region(addr, size, true, _RET_IP_);
void __hwasan_tag_memory(unsigned long addr, u8 tag, unsigned long size)
kasan_poison_shadow((void *)addr, size, tag);