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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 <liuwenliang@huawei.com>
+ */
+
+#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