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Subject[PATCH v8 05/20] kasan, arm64: adjust shadow size for tag-based mode
Date
Tag-based KASAN uses 1 shadow byte for 16 bytes of kernel memory, so it
requires 1/16th of the kernel virtual address space for the shadow memory.

This commit sets KASAN_SHADOW_SCALE_SHIFT to 4 when the tag-based KASAN
mode is enabled.

Signed-off-by: Andrey Konovalov <andreyknvl@google.com>
---
arch/arm64/Makefile | 2 +-
arch/arm64/include/asm/memory.h | 13 +++++++++----
2 files changed, 10 insertions(+), 5 deletions(-)

diff --git a/arch/arm64/Makefile b/arch/arm64/Makefile
index 106039d25e2f..11f4750d8d41 100644
--- a/arch/arm64/Makefile
+++ b/arch/arm64/Makefile
@@ -94,7 +94,7 @@ endif
# KASAN_SHADOW_OFFSET = VA_START + (1 << (VA_BITS - KASAN_SHADOW_SCALE_SHIFT))
# - (1 << (64 - KASAN_SHADOW_SCALE_SHIFT))
# in 32-bit arithmetic
-KASAN_SHADOW_SCALE_SHIFT := 3
+KASAN_SHADOW_SCALE_SHIFT := $(if $(CONFIG_KASAN_SW_TAGS), 4, 3)
KASAN_SHADOW_OFFSET := $(shell printf "0x%08x00000000\n" $$(( \
(0xffffffff & (-1 << ($(CONFIG_ARM64_VA_BITS) - 32))) \
+ (1 << ($(CONFIG_ARM64_VA_BITS) - 32 - $(KASAN_SHADOW_SCALE_SHIFT))) \
diff --git a/arch/arm64/include/asm/memory.h b/arch/arm64/include/asm/memory.h
index b96442960aea..0f1e024a951f 100644
--- a/arch/arm64/include/asm/memory.h
+++ b/arch/arm64/include/asm/memory.h
@@ -74,12 +74,17 @@
#define KERNEL_END _end

/*
- * KASAN requires 1/8th of the kernel virtual address space for the shadow
- * region. KASAN can bloat the stack significantly, so double the (minimum)
- * stack size when KASAN is in use.
+ * Generic and tag-based KASAN require 1/8th and 1/16th of the kernel virtual
+ * address space for the shadow region respectively. They can bloat the stack
+ * significantly, so double the (minimum) stack size when they are in use.
*/
-#ifdef CONFIG_KASAN
+#ifdef CONFIG_KASAN_GENERIC
#define KASAN_SHADOW_SCALE_SHIFT 3
+#endif
+#ifdef CONFIG_KASAN_SW_TAGS
+#define KASAN_SHADOW_SCALE_SHIFT 4
+#endif
+#ifdef CONFIG_KASAN
#define KASAN_SHADOW_SIZE (UL(1) << (VA_BITS - KASAN_SHADOW_SCALE_SHIFT))
#define KASAN_THREAD_SHIFT 1
#else
--
2.19.0.397.gdd90340f6a-goog
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