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

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Date:	Tue, 10 Feb 2009 10:25:06 -0500
From:	Brian Gerst <brgerst@...il.com>
To:	Tejun Heo <tj@...nel.org>
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

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?

--
Brian Gerst
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