Re: [PATCH v3 35/75] x86/head/64: Build k/head64.c with -fno-stack-protector

Joerg Roedel
2020-06-03T15:21:13Z

On Tue, May 19, 2020 at 11:15:26AM +0200, Borislav Petkov wrote:
> On Tue, Apr 28, 2020 at 05:16:45PM +0200, Joerg Roedel wrote:
> > From: Joerg Roedel <jroedel@suse.de>
> >
> > The code inserted by the stack protector does not work in the early
> > boot environment because it uses the GS segment, at least with memory
> > encryption enabled.
>
> Can you elaborate on why is that a problem?
>
> The stack cookie is not generated that early yet so it should be
> comparing %gs:40 to 0.

Yes, and when GS_BASE is 0 it will dereference NULL pointer, which
generates a page-fault before the kernel is able to handle it.

Joerg