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

Tejun Heo
2009-02-10T15:39:56Z

Brian Gerst wrote:
> 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?

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

--
tejun