[kernel-hardening] Re: [PATCH RFC v6 1/6] x86/entry: Add STACKLEAK erasing the kernel stack at the end of syscalls

[Alexander Popov <alex.popov@linux.com>]

Hello Peter,

On 08.12.2017 14:44, Peter Zijlstra wrote:
> On Wed, Dec 06, 2017 at 02:33:42AM +0300, Alexander Popov wrote:
>> The STACKLEAK feature erases the kernel stack before returning from
>> syscalls. That reduces the information which kernel stack leak bugs can
>> reveal and blocks some uninitialized stack variable attacks. Moreover,
>> STACKLEAK provides runtime checks for kernel stack overflow detection.
>>
>> This commit introduces the architecture-specific code filling the used
>> part of the kernel stack with a poison value before returning to the
>> userspace. Full STACKLEAK feature also contains the gcc plugin which
>> comes in a separate commit.
> 
> Have you looked at the entry rework in this series:
> 
>   https://lkml.kernel.org/r/20171204140706.296109558@linutronix.de

Thanks for the link. I briefly looked through WIP.x86/pti branch. Should I
rebase STACKLEAK patch series onto it?

Although I don't fully understand some of the commits, I can suppose that
STACKLEAK stack erasing must be modified because of this trampoline stack
introduction:
https://git.kernel.org/pub/scm/linux/kernel/git/tip/tip.git/commit/?h=WIP.x86/pti&id=813b4125a835f2eb9aa6fb08dac0bc8eeadd69a1

Am I right? Are there other changes which I should consider?

May I also ask for your feedback on this version of the STACKLEAK patch series?
Thanks!

Best regards,
Alexander