linux-kernel - Re: [PATCH v6 08/42] x86/sev-es: initialize sev

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Date:   Wed, 27 Oct 2021 13:17:11 +0200
From:   Borislav Petkov <bp@...en8.de>
To:     Michael Roth <michael.roth@....com>
Cc:     Brijesh Singh <brijesh.singh@....com>, x86@...nel.org,
        linux-kernel@...r.kernel.org, kvm@...r.kernel.org,
        linux-efi@...r.kernel.org, platform-driver-x86@...r.kernel.org,
        linux-coco@...ts.linux.dev, linux-mm@...ck.org,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Joerg Roedel <jroedel@...e.de>,
        Tom Lendacky <thomas.lendacky@....com>,
        "H. Peter Anvin" <hpa@...or.com>, Ard Biesheuvel <ardb@...nel.org>,
        Paolo Bonzini <pbonzini@...hat.com>,
        Sean Christopherson <seanjc@...gle.com>,
        Vitaly Kuznetsov <vkuznets@...hat.com>,
        Jim Mattson <jmattson@...gle.com>,
        Andy Lutomirski <luto@...nel.org>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Sergio Lopez <slp@...hat.com>, Peter Gonda <pgonda@...gle.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Srinivas Pandruvada <srinivas.pandruvada@...ux.intel.com>,
        David Rientjes <rientjes@...gle.com>,
        Dov Murik <dovmurik@...ux.ibm.com>,
        Tobin Feldman-Fitzthum <tobin@....com>,
        Vlastimil Babka <vbabka@...e.cz>,
        "Kirill A . Shutemov" <kirill@...temov.name>,
        Andi Kleen <ak@...ux.intel.com>,
        "Dr . David Alan Gilbert" <dgilbert@...hat.com>,
        tony.luck@...el.com, marcorr@...gle.com,
        sathyanarayanan.kuppuswamy@...ux.intel.com
Subject: Re: [PATCH v6 08/42] x86/sev-es: initialize sev_status/features
 within #VC handler

On Mon, Oct 25, 2021 at 11:35:18AM -0500, Michael Roth wrote:
> As counter-intuitive as it sounds, it actually doesn't buy us if the CPUID
> table is part of the PSP attestation report, since:

Thanks for taking the time to explain in detail - I think I know now
what's going on, and David explained some additional stuff to me
yesterday.

So, to cut to the chase:

 - yeah, ok, I guess guest owner attestation is what should happen.

 - as to the boot detection, I think you should do in sme_enable(), in
pseudo:

	bool snp_guest_detected;

        if (CPUID page address) {
                read SEV_STATUS;

                snp_guest_detected = SEV_STATUS & MSR_AMD64_SEV_SNP_ENABLED;
        }

        /* old SME/SEV detection path */
        read 0x8000_001F_EAX and look at bits SME and SEV, yadda yadda.

        if (snp_guest_detected && (!SME || !SEV))
                /*
		 * HV is lying to me, do something there, dunno what. I guess we can
		 * continue booting unencrypted so that the guest owner knows that
		 * detection has failed and maybe the HV didn't want us to force SNP.
		 * This way, attestation will fail and the user will know why.
		 * Or something like that.
		 */


        /* normal feature detection continues. */

How does that sound?

-- 
Regards/Gruss,
    Boris.

https://people.kernel.org/tglx/notes-about-netiquette