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Message-ID: <20200603152108.GD23071@8bytes.org>
Date: Wed, 3 Jun 2020 17:21:08 +0200
From: Joerg Roedel <joro@...tes.org>
To: Borislav Petkov <bp@...en8.de>
Cc: x86@...nel.org, hpa@...or.com, Andy Lutomirski <luto@...nel.org>,
Dave Hansen <dave.hansen@...ux.intel.com>,
Peter Zijlstra <peterz@...radead.org>,
Thomas Hellstrom <thellstrom@...are.com>,
Jiri Slaby <jslaby@...e.cz>,
Dan Williams <dan.j.williams@...el.com>,
Tom Lendacky <thomas.lendacky@....com>,
Juergen Gross <jgross@...e.com>,
Kees Cook <keescook@...omium.org>,
David Rientjes <rientjes@...gle.com>,
Cfir Cohen <cfir@...gle.com>,
Erdem Aktas <erdemaktas@...gle.com>,
Masami Hiramatsu <mhiramat@...nel.org>,
Mike Stunes <mstunes@...are.com>,
Joerg Roedel <jroedel@...e.de>, linux-kernel@...r.kernel.org,
kvm@...r.kernel.org, virtualization@...ts.linux-foundation.org
Subject: Re: [PATCH v3 35/75] x86/head/64: Build k/head64.c with
-fno-stack-protector
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@...e.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
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