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charset="UTF-8" Content-Transfer-Encoding: quoted-printable User-Agent: Evolution 3.56.2 X-Mailing-List: linux-coco@lists.linux.dev List-Id: List-Post: List-Help: List-Subscribe: List-Unsubscribe: List-Owner: Precedence: list MIME-Version: 1.0 On Wed, 2026-10-21 at 11:35 -0300, Jason Gunthorpe wrote: > Maybe we can build a multiplexed scheme on the spare? I don't know. Direct sharing of PCRs is certainly possible, but not in all circumstances. To share a log, each logging entity must record entries in such a way that the relying party can disentangle them with absolute certainty. The problem with the latter is that both the TCG and the IMA log format have unmeasured (or advisory) log entries. You can fool a relying party trying to disentangle a combined log simply by converting the advisory entry of one logging entity to being the advisory entry of another and bingo, it disappears from the other log. There are certainly ways around the problem by doing indirect sharing (where the real PCR logs measured capsule entries for each virtual PCR including the virtual PCR entry) but there are no standards for attesting, or quoting, such a log. Even if you look at our gold standard for virtual PCRs: vTPMs, their quotes are only reliable if you trust the entity provisioning and running the vTPM. The closest we come to having an autonomously attested vTPM is the SVSM-vTPM in SEV- SNP which can give an attestation of the ephemeral EK tied to the launch measurement of the enclave. Regards, James