Re: [PATCH 11/11] x86: implement x86_32 stack protector

Brian Gerst
2009-02-10T15:25:24Z

On Mon, Feb 9, 2009 at 8:39 AM, Tejun Heo <tj@kernel.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@kernel.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