arch/arm/include/asm/kasan_def.h

   1 /* SPDX-License-Identifier: GPL-2.0 */
   2 /*
   3  *  arch/arm/include/asm/kasan_def.h
   4  *
   5  *  Copyright (c) 2018 Huawei Technologies Co., Ltd.
   6  *
   7  *  Author: Abbott Liu <liuwenliang@huawei.com>
   8  */
   9
  10 #ifndef __ASM_KASAN_DEF_H
  11 #define __ASM_KASAN_DEF_H
  12
  13 #ifdef CONFIG_KASAN
  14
  15 /*
  16  * Define KASAN_SHADOW_OFFSET,KASAN_SHADOW_START and KASAN_SHADOW_END for
  17  * the Arm kernel address sanitizer. We are "stealing" lowmem (the 4GB
  18  * addressable by a 32bit architecture) out of the virtual address
  19  * space to use as shadow memory for KASan as follows:
  20  *
  21  * +----+ 0xffffffff
  22  * |    |                                                       \
  23  * |    | |-> Static kernel image (vmlinux) BSS and page table
  24  * |    |/
  25  * +----+ PAGE_OFFSET
  26  * |    |                                                       \
  27  * |    | |->  Loadable kernel modules virtual address space area
  28  * |    |/
  29  * +----+ MODULES_VADDR = KASAN_SHADOW_END
  30  * |    |                                               \
  31  * |    | |-> The shadow area of kernel virtual address.
  32  * |    |/
  33  * +----+->  TASK_SIZE (start of kernel space) = KASAN_SHADOW_START the
  34  * |    |\   shadow address of MODULES_VADDR
  35  * |    | |
  36  * |    | |
  37  * |    | |-> The user space area in lowmem. The kernel address
  38  * |    | |   sanitizer do not use this space, nor does it map it.
  39  * |    | |
  40  * |    | |
  41  * |    | |
  42  * |    | |
  43  * |    |/
  44  * ------ 0
  45  *
  46  * 1) KASAN_SHADOW_START
  47  *   This value begins with the MODULE_VADDR's shadow address. It is the
  48  *   start of kernel virtual space. Since we have modules to load, we need
  49  *   to cover also that area with shadow memory so we can find memory
  50  *   bugs in modules.
  51  *
  52  * 2) KASAN_SHADOW_END
  53  *   This value is the 0x100000000's shadow address: the mapping that would
  54  *   be after the end of the kernel memory at 0xffffffff. It is the end of
  55  *   kernel address sanitizer shadow area. It is also the start of the
  56  *   module area.
  57  *
  58  * 3) KASAN_SHADOW_OFFSET:
  59  *   This value is used to map an address to the corresponding shadow
  60  *   address by the following formula:
  61  *
  62  *      shadow_addr = (address >> 3) + KASAN_SHADOW_OFFSET;
  63  *
  64  *  As you would expect, >> 3 is equal to dividing by 8, meaning each
  65  *  byte in the shadow memory covers 8 bytes of kernel memory, so one
  66  *  bit shadow memory per byte of kernel memory is used.
  67  *
  68  *  The KASAN_SHADOW_OFFSET is provided in a Kconfig option depending
  69  *  on the VMSPLIT layout of the system: the kernel and userspace can
  70  *  split up lowmem in different ways according to needs, so we calculate
  71  *  the shadow offset depending on this.
  72  */
  73
  74 #define KASAN_SHADOW_SCALE_SHIFT        3
  75 #define KASAN_SHADOW_OFFSET     _AC(CONFIG_KASAN_SHADOW_OFFSET, UL)
  76 #define KASAN_SHADOW_END        ((UL(1) << (32 - KASAN_SHADOW_SCALE_SHIFT)) \
  77                                  + KASAN_SHADOW_OFFSET)
  78 #define KASAN_SHADOW_START      ((KASAN_SHADOW_END >> 3) + KASAN_SHADOW_OFFSET)
  79
  80 #endif
  81 #endif