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

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Date:   Mon, 12 Nov 2018 18:50:57 +0100
From:   Andrey Konovalov <andreyknvl@...gle.com>
To:     Mark Rutland <mark.rutland@....com>
Cc:     Andrey Ryabinin <aryabinin@...tuozzo.com>,
        Alexander Potapenko <glider@...gle.com>,
        Dmitry Vyukov <dvyukov@...gle.com>,
        Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will.deacon@....com>,
        Christoph Lameter <cl@...ux.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Nick Desaulniers <ndesaulniers@...gle.com>,
        Marc Zyngier <marc.zyngier@....com>,
        Dave Martin <dave.martin@....com>,
        Ard Biesheuvel <ard.biesheuvel@...aro.org>,
        "Eric W . Biederman" <ebiederm@...ssion.com>,
        Ingo Molnar <mingo@...nel.org>,
        Paul Lawrence <paullawrence@...gle.com>,
        Geert Uytterhoeven <geert@...ux-m68k.org>,
        Arnd Bergmann <arnd@...db.de>,
        "Kirill A . Shutemov" <kirill.shutemov@...ux.intel.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Kate Stewart <kstewart@...uxfoundation.org>,
        Mike Rapoport <rppt@...ux.vnet.ibm.com>,
        kasan-dev@...glegroups.com,
        "open list:DOCUMENTATION" <linux-doc@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Linux ARM <linux-arm-kernel@...ts.infradead.org>,
        linux-sparse@...r.kernel.org,
        Linux Memory Management List <linux-mm@...ck.org>,
        Linux Kbuild mailing list <linux-kbuild@...r.kernel.org>,
        Kostya Serebryany <kcc@...gle.com>,
        Evgeniy Stepanov <eugenis@...gle.com>,
        Lee Smith <Lee.Smith@....com>,
        Ramana Radhakrishnan <Ramana.Radhakrishnan@....com>,
        Jacob Bramley <Jacob.Bramley@....com>,
        Ruben Ayrapetyan <Ruben.Ayrapetyan@....com>,
        Jann Horn <jannh@...gle.com>,
        Mark Brand <markbrand@...gle.com>,
        Chintan Pandya <cpandya@...eaurora.org>,
        Vishwath Mohan <vishwath@...gle.com>
Subject: Re: [PATCH v10 06/22] kasan, arm64: adjust shadow size for tag-based mode

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