kasan, arm64: adjust shadow size for tag-based mode

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.

Link: http://lkml.kernel.org/r/308b6bd49f756bb5e533be93c6f085ba99b30339.1544099024.git.andreyknvl@google.com
Signed-off-by: Andrey Konovalov <andreyknvl@google.com>
Reviewed-by: Andrey Ryabinin <aryabinin@virtuozzo.com>
Reviewed-by: Dmitry Vyukov <dvyukov@google.com>
Acked-by: Will Deacon <will.deacon@arm.com>
Cc: Christoph Lameter <cl@linux.com>
Cc: Mark Rutland <mark.rutland@arm.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

Author: xairy

arch/arm64/Makefile

@@ -101,10 +101,19 @@ else
 TEXT_OFFSET := 0x00080000
 endif
 
+ifeq ($(CONFIG_KASAN_SW_TAGS), y)
+KASAN_SHADOW_SCALE_SHIFT := 4
+else
+KASAN_SHADOW_SCALE_SHIFT := 3
+endif
+
+KBUILD_CFLAGS += -DKASAN_SHADOW_SCALE_SHIFT=$(KASAN_SHADOW_SCALE_SHIFT)
+KBUILD_CPPFLAGS += -DKASAN_SHADOW_SCALE_SHIFT=$(KASAN_SHADOW_SCALE_SHIFT)
+KBUILD_AFLAGS += -DKASAN_SHADOW_SCALE_SHIFT=$(KASAN_SHADOW_SCALE_SHIFT)
+
 # 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_OFFSET := $(shell printf "0x%08x00000000\n" $$(( \
 	(0xffffffff & (-1 << ($(CONFIG_ARM64_VA_BITS) - 32))) \
 	+ (1 << ($(CONFIG_ARM64_VA_BITS) - 32 - $(KASAN_SHADOW_SCALE_SHIFT))) \

arch/arm64/include/asm/memory.h

@@ -74,13 +74,11 @@
 #endif
 
 /*
- * 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, and then double it again if KASAN_EXTRA is
- * on.
+ * 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
-#define KASAN_SHADOW_SCALE_SHIFT 3
 #define KASAN_SHADOW_SIZE	(UL(1) << (VA_BITS - KASAN_SHADOW_SCALE_SHIFT))
 #ifdef CONFIG_KASAN_EXTRA
 #define KASAN_THREAD_SHIFT	2