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