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/* SPDX-License-Identifier: GPL-2.0 */
/*
* arch/arm/include/asm/kasan_def.h
*
* Copyright (c) 2018 Huawei Technologies Co., Ltd.
*
* Author: Abbott Liu <[email protected]>
*/
#ifndef __ASM_KASAN_DEF_H
#define __ASM_KASAN_DEF_H
#ifdef CONFIG_KASAN
/*
* Define KASAN_SHADOW_OFFSET,KASAN_SHADOW_START and KASAN_SHADOW_END for
* the Arm kernel address sanitizer. We are "stealing" lowmem (the 4GB
* addressable by a 32bit architecture) out of the virtual address
* space to use as shadow memory for KASan as follows:
*
* +----+ 0xffffffff
* | | \
* | | |-> Static kernel image (vmlinux) BSS and page table
* | |/
* +----+ PAGE_OFFSET
* | | \
* | | |-> Loadable kernel modules virtual address space area
* | |/
* +----+ MODULES_VADDR = KASAN_SHADOW_END
* | | \
* | | |-> The shadow area of kernel virtual address.
* | |/
* +----+-> TASK_SIZE (start of kernel space) = KASAN_SHADOW_START the
* | |\ shadow address of MODULES_VADDR
* | | |
* | | |
* | | |-> The user space area in lowmem. The kernel address
* | | | sanitizer do not use this space, nor does it map it.
* | | |
* | | |
* | | |
* | | |
* | |/
* ------ 0
*
* 1) KASAN_SHADOW_START
* This value begins with the MODULE_VADDR's shadow address. It is the
* start of kernel virtual space. Since we have modules to load, we need
* to cover also that area with shadow memory so we can find memory
* bugs in modules.
*
* 2) KASAN_SHADOW_END
* This value is the 0x100000000's shadow address: the mapping that would
* be after the end of the kernel memory at 0xffffffff. It is the end of
* kernel address sanitizer shadow area. It is also the start of the
* module area.
*
* 3) KASAN_SHADOW_OFFSET:
* This value is used to map an address to the corresponding shadow
* address by the following formula:
*
* shadow_addr = (address >> 3) + KASAN_SHADOW_OFFSET;
*
* As you would expect, >> 3 is equal to dividing by 8, meaning each
* byte in the shadow memory covers 8 bytes of kernel memory, so one
* bit shadow memory per byte of kernel memory is used.
*
* The KASAN_SHADOW_OFFSET is provided in a Kconfig option depending
* on the VMSPLIT layout of the system: the kernel and userspace can
* split up lowmem in different ways according to needs, so we calculate
* the shadow offset depending on this.
*/
#define KASAN_SHADOW_SCALE_SHIFT 3
#define KASAN_SHADOW_OFFSET _AC(CONFIG_KASAN_SHADOW_OFFSET, UL)
#define KASAN_SHADOW_END ((UL(1) << (32 - KASAN_SHADOW_SCALE_SHIFT)) \
+ KASAN_SHADOW_OFFSET)
#define KASAN_SHADOW_START ((KASAN_SHADOW_END >> 3) + KASAN_SHADOW_OFFSET)
#endif
#endif
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