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riscv: Improve kasan definitions 

There is no functional change here, only improvement in code readability
by adding comments to explain where the kasan constants come from and by
replacing hardcoded numerical constant by the corresponding define.

Note that the comments come from arm64.

Signed-off-by: Alexandre Ghiti <alex@ghiti.fr>
Signed-off-by: Palmer Dabbelt <palmerdabbelt@google.com>
This commit is contained in:
Alexandre Ghiti 2021-02-08 14:30:14 -05:00 committed by Palmer Dabbelt
parent 0f02de4481
commit 7899ed260c
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GPG Key ID: 2E1319F35FBB1889
1 changed files with 19 additions and 3 deletions
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22
arch/riscv/include/asm/kasan.h
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@ -8,12 +8,28 @@
#ifdef CONFIG_KASAN
/*
* The following comment was copied from arm64:
* KASAN_SHADOW_START: beginning of the kernel virtual addresses.
* KASAN_SHADOW_END: KASAN_SHADOW_START + 1/N of kernel virtual addresses,
* where N = (1 << KASAN_SHADOW_SCALE_SHIFT).
*
* KASAN_SHADOW_OFFSET:
* This value is used to map an address to the corresponding shadow
* address by the following formula:
* shadow_addr = (address >> KASAN_SHADOW_SCALE_SHIFT) + KASAN_SHADOW_OFFSET
*
* (1 << (64 - KASAN_SHADOW_SCALE_SHIFT)) shadow addresses that lie in range
* [KASAN_SHADOW_OFFSET, KASAN_SHADOW_END) cover all 64-bits of virtual
* addresses. So KASAN_SHADOW_OFFSET should satisfy the following equation:
* KASAN_SHADOW_OFFSET = KASAN_SHADOW_END -
* (1ULL << (64 - KASAN_SHADOW_SCALE_SHIFT))
*/
#define KASAN_SHADOW_SCALE_SHIFT 3
#define KASAN_SHADOW_SIZE (UL(1) << (38 - KASAN_SHADOW_SCALE_SHIFT))
#define KASAN_SHADOW_START KERN_VIRT_START /* 2^64 - 2^38 */
#define KASAN_SHADOW_SIZE (UL(1) << ((CONFIG_VA_BITS - 1) - KASAN_SHADOW_SCALE_SHIFT))
#define KASAN_SHADOW_START KERN_VIRT_START
#define KASAN_SHADOW_END (KASAN_SHADOW_START + KASAN_SHADOW_SIZE)
#define KASAN_SHADOW_OFFSET (KASAN_SHADOW_END - (1ULL << \
(64 - KASAN_SHADOW_SCALE_SHIFT)))