linux-kernel - Re: [PATCH 6/6] arm64: switch to relative exception tables

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Date:	Mon, 04 Jan 2016 10:13:46 -0800
From:	"H. Peter Anvin" <hpa@...or.com>
To:	Will Deacon <will.deacon@....com>,
	Ard Biesheuvel <ard.biesheuvel@...aro.org>
CC:	linux-alpha@...r.kernel.org, linux-kernel@...r.kernel.org,
	linux-arm-kernel@...ts.infradead.org, linux-ia64@...r.kernel.org,
	linux-s390@...r.kernel.org, x86@...nel.org, mingo@...hat.com,
	heiko.carstens@...ibm.com, schwidefsky@...ibm.com,
	mattst88@...il.com, ink@...assic.park.msu.ru, rth@...ddle.net,
	tony.luck@...el.com, fenghua.yu@...el.com, catalin.marinas@....com,
	arnd@...db.de, akpm@...ux-foundation.org, mark.rutland@....com,
	marc.zyngier@....com
Subject: Re: [PATCH 6/6] arm64: switch to relative exception tables

On 01/04/2016 06:46 AM, Will Deacon wrote:
> On Sun, Jan 03, 2016 at 05:05:57PM +0100, Ard Biesheuvel wrote:
>> Instead of using absolute addresses for both the exception location
>> and the fixup, use offsets relative to the exception table entry values.
>> Not only does this cut the size of the exception table in half, it is
>> also a prerequisite for KASLR, since absolute exception table entries
>> are subject to dynamic relocation, which is incompatible with the sorting
>> of the exception table that occurs at build time.
>>
>> Cc: Catalin Marinas <catalin.marinas@....com>
>> Cc: Will Deacon <will.deacon@....com>
>> Signed-off-by: Ard Biesheuvel <ard.biesheuvel@...aro.org>
>> ---
>>
>> Note that this patch supersedes the version I sent as part of the series that
>> implements KASLR for arm64: http://thread.gmane.org/gmane.linux.kernel/2116531
>>
>>  arch/arm64/include/asm/assembler.h   |  2 +-
>>  arch/arm64/include/asm/futex.h       |  4 ++--
>>  arch/arm64/include/asm/uaccess.h     | 18 ++++++++++--------
>>  arch/arm64/kernel/armv8_deprecated.c |  4 ++--
>>  arch/arm64/mm/extable.c              |  2 +-
>>  scripts/sortextable.c                |  2 +-
>>  6 files changed, 17 insertions(+), 15 deletions(-)
> 
> This looks good to me, so for the arm64 part (i.e. this patch):
> 
>   Acked-by: Will Deacon <will.deacon@....com>

May I humbly ask why the [Finnish] you don't use the equivalent of the
x86 _ASM_EXTABLE() macro?  In fact, why don't we make that one generic, too?

	-hpa


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