// SPDX-License-Identifier: GPL-2.0
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/*
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* This file contains core tag-based KASAN code.
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*
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* Copyright (c) 2018 Google, Inc.
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* Author: Andrey Konovalov <andreyknvl@google.com>
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*
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* This program is free software; you can redistribute it and/or modify
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* it under the terms of the GNU General Public License version 2 as
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* published by the Free Software Foundation.
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*
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*/
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#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
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#define DISABLE_BRANCH_PROFILING
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#include <linux/export.h>
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#include <linux/interrupt.h>
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#include <linux/init.h>
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#include <linux/kasan.h>
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#include <linux/kernel.h>
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#include <linux/kmemleak.h>
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#include <linux/linkage.h>
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#include <linux/memblock.h>
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#include <linux/memory.h>
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#include <linux/mm.h>
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#include <linux/module.h>
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#include <linux/printk.h>
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#include <linux/random.h>
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#include <linux/sched.h>
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#include <linux/sched/task_stack.h>
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#include <linux/slab.h>
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#include <linux/stacktrace.h>
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#include <linux/string.h>
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#include <linux/types.h>
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#include <linux/vmalloc.h>
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#include <linux/bug.h>
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#include "kasan.h"
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#include "../slab.h"
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static DEFINE_PER_CPU(u32, prng_state);
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void kasan_init_tags(void)
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{
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int cpu;
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for_each_possible_cpu(cpu)
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per_cpu(prng_state, cpu) = (u32)get_cycles();
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}
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/*
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* If a preemption happens between this_cpu_read and this_cpu_write, the only
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* side effect is that we'll give a few allocated in different contexts objects
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* the same tag. Since tag-based KASAN is meant to be used a probabilistic
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* bug-detection debug feature, this doesn't have significant negative impact.
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*
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* Ideally the tags use strong randomness to prevent any attempts to predict
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* them during explicit exploit attempts. But strong randomness is expensive,
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* and we did an intentional trade-off to use a PRNG. This non-atomic RMW
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* sequence has in fact positive effect, since interrupts that randomly skew
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* PRNG at unpredictable points do only good.
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*/
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u8 random_tag(void)
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{
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u32 state = this_cpu_read(prng_state);
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state = 1664525 * state + 1013904223;
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this_cpu_write(prng_state, state);
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return (u8)(state % (KASAN_TAG_MAX + 1));
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}
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void *kasan_reset_tag(const void *addr)
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{
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return reset_tag(addr);
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}
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void check_memory_region(unsigned long addr, size_t size, bool write,
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unsigned long ret_ip)
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{
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u8 tag;
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u8 *shadow_first, *shadow_last, *shadow;
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void *untagged_addr;
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if (unlikely(size == 0))
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return;
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tag = get_tag((const void *)addr);
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/*
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* Ignore accesses for pointers tagged with 0xff (native kernel
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* pointer tag) to suppress false positives caused by kmap.
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*
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* Some kernel code was written to account for archs that don't keep
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* high memory mapped all the time, but rather map and unmap particular
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* pages when needed. Instead of storing a pointer to the kernel memory,
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* this code saves the address of the page structure and offset within
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* that page for later use. Those pages are then mapped and unmapped
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* with kmap/kunmap when necessary and virt_to_page is used to get the
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* virtual address of the page. For arm64 (that keeps the high memory
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* mapped all the time), kmap is turned into a page_address call.
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* The issue is that with use of the page_address + virt_to_page
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* sequence the top byte value of the original pointer gets lost (gets
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* set to KASAN_TAG_KERNEL (0xFF)).
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*/
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if (tag == KASAN_TAG_KERNEL)
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return;
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untagged_addr = reset_tag((const void *)addr);
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if (unlikely(untagged_addr <
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kasan_shadow_to_mem((void *)KASAN_SHADOW_START))) {
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kasan_report(addr, size, write, ret_ip);
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return;
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}
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shadow_first = kasan_mem_to_shadow(untagged_addr);
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shadow_last = kasan_mem_to_shadow(untagged_addr + size - 1);
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for (shadow = shadow_first; shadow <= shadow_last; shadow++) {
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if (*shadow != tag) {
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kasan_report(addr, size, write, ret_ip);
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return;
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}
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}
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}
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#define DEFINE_HWASAN_LOAD_STORE(size) \
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void __hwasan_load##size##_noabort(unsigned long addr) \
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{ \
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check_memory_region(addr, size, false, _RET_IP_); \
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} \
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EXPORT_SYMBOL(__hwasan_load##size##_noabort); \
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void __hwasan_store##size##_noabort(unsigned long addr) \
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{ \
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check_memory_region(addr, size, true, _RET_IP_); \
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} \
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EXPORT_SYMBOL(__hwasan_store##size##_noabort)
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DEFINE_HWASAN_LOAD_STORE(1);
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DEFINE_HWASAN_LOAD_STORE(2);
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DEFINE_HWASAN_LOAD_STORE(4);
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DEFINE_HWASAN_LOAD_STORE(8);
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DEFINE_HWASAN_LOAD_STORE(16);
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void __hwasan_loadN_noabort(unsigned long addr, unsigned long size)
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{
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check_memory_region(addr, size, false, _RET_IP_);
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}
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EXPORT_SYMBOL(__hwasan_loadN_noabort);
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void __hwasan_storeN_noabort(unsigned long addr, unsigned long size)
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{
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check_memory_region(addr, size, true, _RET_IP_);
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}
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EXPORT_SYMBOL(__hwasan_storeN_noabort);
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void __hwasan_tag_memory(unsigned long addr, u8 tag, unsigned long size)
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{
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kasan_poison_shadow((void *)addr, size, tag);
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}
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EXPORT_SYMBOL(__hwasan_tag_memory);
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