linux-kernel - Re: [PATCH v4 70/75] x86/head/64: Don't call verify

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Message-ID: <20200720152955.GA620@8bytes.org>
Date:   Mon, 20 Jul 2020 17:29:55 +0200
From:   Joerg Roedel <joro@...tes.org>
To:     Kees Cook <keescook@...omium.org>
Cc:     Joerg Roedel <jroedel@...e.de>, 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>,
        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>,
        Sean Christopherson <sean.j.christopherson@...el.com>,
        Martin Radev <martin.b.radev@...il.com>,
        linux-kernel@...r.kernel.org, kvm@...r.kernel.org,
        virtualization@...ts.linux-foundation.org
Subject: Re: [PATCH v4 70/75] x86/head/64: Don't call verify_cpu() on
 starting APs

On Wed, Jul 15, 2020 at 12:49:23PM -0700, Kees Cook wrote:
> Aaah. I see. Thanks for the details there. So ... can you add a bunch
> more comments about why/when the new entry path is being used? I really
> don't want to accidentally discover some unrelated refactoring down
> the road (in months, years, unrelated to SEV, etc) starts to also skip
> verify_cpu() on Intel systems. There had been a lot of BIOSes that set
> this MSR to disable NX, and I don't want to repeat that pain: Linux must
> never start an Intel CPU with that MSR set. :P

Understood :)

I added a comment above the label explaining why it is only used for
SEV-ES guests and pointing out the importance of running verify_cpu() on
all other systems, especially if they are Intel based.

Regards,

	Joerg