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[81.97.203.96]) by smtp.gmail.com with ESMTPSA id a10-20020a056000050a00b002d78a96cf5fsm6368842wrf.70.2023.03.22.03.34.03 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 22 Mar 2023 03:34:04 -0700 (PDT) Date: Wed, 22 Mar 2023 10:34:01 +0000 From: "Dr. David Alan Gilbert" To: Alexander Graf Cc: =?iso-8859-1?Q?J=F6rg_R=F6del?= , amd-sev-snp@lists.suse.com, linux-coco@lists.linux.dev, kvm@vger.kernel.org Subject: Re: [ANNOUNCEMENT] COCONUT Secure VM Service Module for SEV-SNP Message-ID: References: <444b0d8d-3a8c-8e6d-1df3-35f57046e58e@amazon.com> MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-1 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <444b0d8d-3a8c-8e6d-1df3-35f57046e58e@amazon.com> User-Agent: Mutt/2.2.9 (2022-11-12) Precedence: bulk List-ID: X-Mailing-List: kvm@vger.kernel.org * Alexander Graf (graf@amazon.com) wrote: > Hi Jörg, > > On 22.03.23 10:19, Jörg Rödel wrote: > > > On Tue, Mar 21, 2023 at 07:53:58PM +0000, Dr. David Alan Gilbert wrote: > > > OK; the other thing that needs to get nailed down for the vTPM's is the > > > relationship between the vTPM attestation and the SEV attestation. > > > i.e. how to prove that the vTPM you're dealing with is from an SNP host. > > > (Azure have a hack of putting an SNP attestation report into the vTPM > > > NVRAM; see > > > https://github.com/Azure/confidential-computing-cvm-guest-attestation/blob/main/cvm-guest-attestation.md > > > ) > > When using the SVSM TPM protocol it should be proven already that the > > vTPM is part of the SNP trusted base, no? The TPM communication is > > implicitly encrypted by the VMs memory key and the SEV attestation > > report proves that the correct vTPM is executing. > > > What you want to achieve eventually is to take a report from the vTPM and > submit only that to an external authorization entity that looks at it and > says "Yup, you ran in SEV-SNP, I trust your TCB, I trust your TPM > implementation, I also trust your PCR values" and based on that provides > access to whatever resource you want to access. > > To do that, you need to link SEV-SNP and TPM measurements/reports together. > And the easiest way to do that is by providing the SEV-SNP report as part of > the TPM: You can then use the hash of the SEV-SNP report as signing key for > example. Yeh; I think the SVSM TPM protocol has some proof of that as well; the SVSM spec lists 'SVSM_ATTEST_SINGLE_SERVICE Manifest Data' that contains 'TPMT_PUBLIC structure of the endorsement key'. So I *think* that's saying that the SEV attestation report contains something from the EK of the vTPM. > I think the key here is that you need to propagate that link to an external > party, not (only) to the VM. Yeh. Dave > > > Alex > > > > > > Amazon Development Center Germany GmbH > Krausenstr. 38 > 10117 Berlin > Geschaeftsfuehrung: Christian Schlaeger, Jonathan Weiss > Eingetragen am Amtsgericht Charlottenburg unter HRB 149173 B > Sitz: Berlin > Ust-ID: DE 289 237 879 > > -- Dr. David Alan Gilbert / dgilbert@redhat.com / Manchester, UK