Re: [PATCH v10 06/22] kasan, arm64: adjust shadow size for tag-based mode

[Andrey Konovalov]

On Wed, Nov 7, 2018 at 5:54 PM, Mark Rutland <mark.rutland@xxxxxxx> wrote:

[...]

>> --- 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)

Seems that we need the same for KBUILD_CPPFLAGS and KBUILD_AFLAGS.


>> 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.

Will do in v11, thanks!