Re: [PATCH v11 2/6] x86/entry: Add STACKLEAK erasing the kernel stack at the end of syscalls

[Laura Abbott]

On 04/16/2018 11:29 AM, Kees Cook wrote:
> On Fri, Apr 6, 2018 at 7:22 AM, Alexander Popov <alex.popov@xxxxxxxxx> wrote:
> > 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.
>
> Thanks for sending this again! And thanks for the updated reasoning
> for why this remains a valuable addition:
>
> https://lkml.kernel.org/r/1523024546-6150-1-git-send-email-alex.popov@xxxxxxxxx
>
> I, too, remain convinced this is a good protection to have, even as we
> slowly remove VLAs and try to improve the compiler's initialization of
> stack variables.
>
> Dave, Ingo, Linus: how does this look? With the assembly rewritten
> into C, the entry changes are very small:
>
> >   arch/x86/entry/entry_32.S        |  7 ++++++
> >   arch/x86/entry/entry_64.S        |  3 +++
> >   arch/x86/entry/entry_64_compat.S |  5 ++++
> >   arch/x86/entry/erase.c           | 54 ++++++++++++++++++++++++++++++++++++++++
>
> I'd really like to get people's Ack/Review. :)
>
> Laura, can this C version work for arm64 as well?
>
> Thanks,
>
> -Kees

I did a quick port and it seems to work on a minimal system
(passes LKDTM tests). I'll clean it up and do a few more
tests to send out and see about give this series another
review.

Thanks,
Laura