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Message-ID: <20181107165438.34kb5ufoe5ve2f6i@lakrids.cambridge.arm.com>
Date: Wed, 7 Nov 2018 16:54:38 +0000
From: Mark Rutland <mark.rutland@....com>
To: Andrey Konovalov <andreyknvl@...gle.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, linux-doc@...r.kernel.org,
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Vishwath Mohan <vishwath@...gle.com>
Subject: Re: [PATCH v10 06/22] kasan, arm64: adjust shadow size for tag-based
mode
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@...tuozzo.com>
> Reviewed-by: Dmitry Vyukov <dvyukov@...gle.com>
> Signed-off-by: Andrey Konovalov <andreyknvl@...gle.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 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
>
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