linux-kernel - Re: [PATCH v3 40/75] x86/sev-es: Compile early handler code into kernel image

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Message-ID: <20200611100519.GB32093@8bytes.org>
Date:   Thu, 11 Jun 2020 12:05:19 +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>,
        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 40/75] x86/sev-es: Compile early handler code into
 kernel image

On Thu, Jun 04, 2020 at 05:19:53PM +0200, Borislav Petkov wrote:
> On Thu, Jun 04, 2020 at 01:54:13PM +0200, Joerg Roedel wrote:
> > It is not only the trace-point, this would also eliminate exception
> > handling in case the MSR access triggers a #GP. The "Unhandled MSR
> > read/write" messages would turn into a "General Protection Fault"
> > message.
> 
> But the early ones can trigger a #GP too. And there we can't handle
> those #GPs.
> 
> Why would the late ones need exception handling all of a sudden? And
> for the GHCB MSR, of all MSRs which the SEV-ES guest has used so far to
> bootstrap?!

For example when there is a bug in the code which triggers an SEV-ES-only
code-path at runtime on bare-metal or in a non-SEV-ES VM. When the MSR
is accessed accidentially in that code-path the exception handling will
be helpful.


	Joerg