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From: Catalin Marinas <catalin.marinas@arm.com>
To: Steve Capper <steve.capper@arm.com>
Cc: crecklin@redhat.com, ard.biesheuvel@linaro.org, maz@kernel.org,
	bhsharma@redhat.com, will@kernel.org,
	linux-arm-kernel@lists.infradead.org
Subject: Re: [PATCH V5 03/12] arm64: kasan: Switch to using KASAN_SHADOW_OFFSET
Date: Wed, 7 Aug 2019 17:12:39 +0100	[thread overview]
Message-ID: <20190807161239.GB1766@arrakis.emea.arm.com> (raw)
In-Reply-To: <20190807155524.5112-4-steve.capper@arm.com>

On Wed, Aug 07, 2019 at 04:55:15PM +0100, Steve Capper wrote:
> KASAN_SHADOW_OFFSET is a constant that is supplied to gcc as a command
> line argument and affects the codegen of the inline address sanetiser.
> 
> Essentially, for an example memory access:
>     *ptr1 = val;
> The compiler will insert logic similar to the below:
>     shadowValue = *(ptr1 >> KASAN_SHADOW_SCALE_SHIFT + KASAN_SHADOW_OFFSET)
>     if (somethingWrong(shadowValue))
>         flagAnError();
> 
> This code sequence is inserted into many places, thus
> KASAN_SHADOW_OFFSET is essentially baked into many places in the kernel
> text.
> 
> If we want to run a single kernel binary with multiple address spaces,
> then we need to do this with KASAN_SHADOW_OFFSET fixed.
> 
> Thankfully, due to the way the KASAN_SHADOW_OFFSET is used to provide
> shadow addresses we know that the end of the shadow region is constant
> w.r.t. VA space size:
>     KASAN_SHADOW_END = ~0 >> KASAN_SHADOW_SCALE_SHIFT + KASAN_SHADOW_OFFSET
> 
> This means that if we increase the size of the VA space, the start of
> the KASAN region expands into lower addresses whilst the end of the
> KASAN region is fixed.
> 
> Currently the arm64 code computes KASAN_SHADOW_OFFSET at build time via
> build scripts with the VA size used as a parameter. (There are build
> time checks in the C code too to ensure that expected values are being
> derived). It is sufficient, and indeed is a simplification, to remove
> the build scripts (and build time checks) entirely and instead provide
> KASAN_SHADOW_OFFSET values.
> 
> This patch removes the logic to compute the KASAN_SHADOW_OFFSET in the
> arm64 Makefile, and instead we adopt the approach used by x86 to supply
> offset values in kConfig. To help debug/develop future VA space changes,
> the Makefile logic has been preserved in a script file in the arm64
> Documentation folder.
> 
> Signed-off-by: Steve Capper <steve.capper@arm.com>

Reviewed-by: Catalin Marinas <catalin.marinas@arm.com>

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  reply	other threads:[~2019-08-07 16:12 UTC|newest]

Thread overview: 38+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-08-07 15:55 [PATCH V5 00/12] 52-bit kernel + user VAs Steve Capper
2019-08-07 15:55 ` [PATCH V5 01/12] arm64: mm: Remove bit-masking optimisations for PAGE_OFFSET and VMEMMAP_START Steve Capper
2019-08-07 15:55 ` [PATCH V5 02/12] arm64: mm: Flip kernel VA space Steve Capper
2019-08-07 16:12   ` Catalin Marinas
2019-08-07 15:55 ` [PATCH V5 03/12] arm64: kasan: Switch to using KASAN_SHADOW_OFFSET Steve Capper
2019-08-07 16:12   ` Catalin Marinas [this message]
2019-08-14 15:20   ` [PATCH] arm64: fix CONFIG_KASAN_SW_TAGS && CONFIG_KASAN_INLINE (was: Re: [PATCH V5 03/12] arm64: kasan: Switch to using) KASAN_SHADOW_OFFSET Mark Rutland
2019-08-14 15:57     ` Will Deacon
2019-08-14 16:03       ` Mark Rutland
2019-08-14 17:53         ` Steve Capper
2019-08-15 12:09         ` Will Deacon
2019-08-15 12:21           ` [PATCH] arm64: fix CONFIG_KASAN_SW_TAGS && CONFIG_KASAN_INLINE Andrey Ryabinin
2019-08-15 12:22             ` Will Deacon
2019-08-20  6:02           ` [PATCH] arm64: fix CONFIG_KASAN_SW_TAGS && CONFIG_KASAN_INLINE (was: Re: [PATCH V5 03/12] arm64: kasan: Switch to using) KASAN_SHADOW_OFFSET Bhupesh Sharma
2019-08-14 16:07     ` Steve Capper
2019-08-14 16:14       ` Steve Capper
2019-08-07 15:55 ` [PATCH V5 04/12] arm64: dump: De-constify VA_START and KASAN_SHADOW_START Steve Capper
2019-08-07 15:55 ` [PATCH V5 05/12] arm64: mm: Introduce VA_BITS_MIN Steve Capper
2019-08-07 16:14   ` Catalin Marinas
2019-08-07 15:55 ` [PATCH V5 06/12] arm64: mm: Introduce vabits_actual Steve Capper
2019-08-07 16:16   ` Catalin Marinas
2019-08-07 15:55 ` [PATCH V5 07/12] arm64: mm: Logic to make offset_ttbr1 conditional Steve Capper
2019-08-07 15:55 ` [PATCH V5 08/12] arm64: mm: Separate out vmemmap Steve Capper
2019-08-07 15:55 ` [PATCH V5 09/12] arm64: mm: Modify calculation of VMEMMAP_SIZE Steve Capper
2019-08-07 15:55 ` [PATCH V5 10/12] arm64: mm: Introduce 52-bit Kernel VAs Steve Capper
2019-08-07 15:55 ` [PATCH V5 11/12] arm64: mm: Remove vabits_user Steve Capper
2019-08-07 16:17   ` Catalin Marinas
2019-08-07 15:55 ` [PATCH V5 12/12] docs: arm64: Add layout and 52-bit info to memory document Steve Capper
2019-08-09 16:47 ` [PATCH V5 00/12] 52-bit kernel + user VAs Will Deacon
2019-08-13 11:23   ` Steve Capper
2019-08-13 11:59     ` Will Deacon
2019-08-13 12:43   ` Geert Uytterhoeven
2019-08-13 13:10     ` Will Deacon
2019-08-13 13:36       ` Geert Uytterhoeven
2019-08-14  8:04         ` Bhupesh Sharma
2019-08-14  8:21           ` Will Deacon
2019-08-14 11:59             ` Bhupesh Sharma
2019-08-14 12:24               ` Will Deacon

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