Hi Andrey, On Tue, Nov 06, 2018 at 06:30:21PM +0100, Andrey Konovalov wrote: > 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. > > Reviewed-by: Andrey Ryabinin <aryabinin@xxxxxxxxxxxxx> > Reviewed-by: Dmitry Vyukov <dvyukov@xxxxxxxxxx> > Signed-off-by: Andrey Konovalov <andreyknvl@xxxxxxxxxx> > --- > 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 6cb9fc7e9382..9887492381d9 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 $(CONFIG_KASAN_SW_TAGS), 4, 3) We could make this something like: ifeq ($(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) > 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 ... and remove the constant entirely here, avoiding duplication. Maybe factor that into a Makefile.kasan if things are going to get much more complicated. Thanks, Mark. > #define KASAN_SHADOW_SIZE (UL(1) << (VA_BITS - KASAN_SHADOW_SCALE_SHIFT)) > #define KASAN_THREAD_SHIFT 1 > #else > -- > 2.19.1.930.g4563a0d9d0-goog >
