linux-kernel - Re: [PATCH 11/11] x86: implement x86

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Message-ID: <49919FA2.9050309@kernel.org>
Date:	Wed, 11 Feb 2009 00:39:14 +0900
From:	Tejun Heo <tj@...nel.org>
To:	Brian Gerst <brgerst@...il.com>
CC:	hpa@...or.com, jeremy@...p.org, tglx@...utronix.de, mingo@...e.hu,
	linux-kernel@...r.kernel.org, x86@...nel.org, rusty@...tcorp.com.au
Subject: Re: [PATCH 11/11] x86: implement x86_32 stack protector

Brian Gerst wrote:
> On Mon, Feb 9, 2009 at 8:39 AM, Tejun Heo <tj@...nel.org> wrote:
>> Impact: stack protector for x86_32
>>
>> Implement stack protector for x86_32.  GDT entry 28 is used for it.
>> It's set to point to stack_canary-20 and have the length of 24 bytes.
>> CONFIG_CC_STACKPROTECTOR turns off CONFIG_X86_32_LAZY_GS and sets %gs
>> to the stack canary segment on entry.  As %gs is otherwise unused by
>> the kernel, the canary can be anywhere.  It's defined as a percpu
>> variable.
>>
>> x86_32 exception handlers take register frame on stack directly as
>> struct pt_regs.  With -fstack-protector turned on, gcc copies the
>> whole structure after the stack canary and (of course) doesn't copy
>> back on return thus losing all changed.  For now, -fno-stack-protector
>> is added to all files which contain those functions.  We definitely
>> need something better.
>>
>> Signed-off-by: Tejun Heo <tj@...nel.org>
> 
> Am I missing something, or does this patch not actually implement the
> offset of the start of the segment by 20 from the stack_canary
> variable?

Yeah, it seems I forgot to subtract 20 from the address.  Will prep a
patch.  Thanks for spotting it.

-- 
tejun
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