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Thu, 22 Oct 2026 03:54:36 -0700 (PDT) Received: from localhost ([140.209.217.211]) by smtp.gmail.com with ESMTPSA id ffacd0b85a97d-48e2583522esm11890881f8f.35.2026.10.22.03.54.35 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 22 Oct 2026 03:54:35 -0700 (PDT) Date: Thu, 22 Oct 2026 12:54:30 +0200 From: Jiri Pirko To: Mimi Zohar Cc: Jason Gunthorpe , Dionna Glaze , Jarkko Sakkinen , linux-coco@lists.linux.dev, linux-kernel@vger.kernel.org, linux-api@vger.kernel.org, x86@kernel.org, kvm@vger.kernel.org, linux-doc@vger.kernel.org, david.quigley@intel.com, lukas@wunner.de, ksinyuk@kernel.org, rodrigo.vivi@intel.com, cedric.xing@intel.com, sameo@meta.com, James.Bottomley@hansenpartnership.com, aik@amd.com, jpiotrowski@nvidia.com, qinkun@google.com, pgonda@google.com, jic23@kernel.org, alistair.francis@wdc.com, ankita@nvidia.com, suzuki.poulose@arm.com, kas@kernel.org, rick.p.edgecombe@intel.com, elena.reshetova@intel.com, dave.hansen@linux.intel.com, sathyanarayanan.kuppuswamy@linux.intel.com, peter.fang@intel.com, roberto.sassu@huawei.com Subject: Re: [PATCH RFC 00/20] attestation: Add a common subsystem and TDX support Message-ID: References: <20261017231007.GP13920@nvidia.com> <20261019225658.GS13920@nvidia.com> <103486a4a29ecc7b72940dd051c00ae59266bd05.camel@linux.ibm.com> <20261021143529.GP3008132@nvidia.com> <8d8833fac61558a94af415143530884349584a2f.camel@linux.ibm.com> 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 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <8d8833fac61558a94af415143530884349584a2f.camel@linux.ibm.com> Wed, Oct 21, 2026 at 09:05:09PM +0200, zohar@linux.ibm.com wrote: >On Wed, 2026-10-21 at 11:35 -0300, Jason Gunthorpe wrote: >> On Wed, Oct 21, 2026 at 10:12:34AM -0400, Mimi Zohar wrote: >> > > > I think for now we should not include a new dynamic log here, the uAPI >> > > > around this Jiri drafted can remain a future step. I don't want to >> > > > open complicated discussions about new functionality at this >> > > > stage. The whole CTLV idea in general is a big enough thing to bite >> > > > off for this series. >> > > >> > > Okay, dropping the log from this set. >> > >> > Thank you. Please keep in mind going forward, that the scarce hardware register >> > limitation (like the 4 TDX RTMRs) should be resolved (e.g. by multiplexing the >> > extension path), not by combining distinct measurement lists. >> >> I'm not sure what you mean? >> >> Since the HW doesn't support sealing the only *technical* requirement >> is the verifier can reproduce the measurement register hash. So long >> as we can get there we can do whatever. >> >> Multiplexing extension alone isn't enough. We need some scheme to >> reconstruct interleaved logs too. >> >> For example we could add an atomic sequence number for each >> extend. Every log sharing a register can report the sequence >> number. The verifier would have to globally sort all logs to confirm >> the hash. >> >> Hopefully we don't have to tackle this problem. I hope that 4 >> registers is enough for Linux. One for IMA, one for systemd, one for >> user? Plus a spare! > >Agreed, I hope you don't have to tackle it either. > >> >> Maybe we can build a multiplexed scheme on the spare? I don't know. > >To avoid interleaving the logs, AI had suggested multiplexing or virtualization >of the RTMRs. Whether is has any merit, I'll leave to you. Here's the very >short AI explanation: > >"Instead of allowing external drivers or subsystems to execute a direct, raw >extend command to a specific hardware register index, the new attestation >subsystem should act as a Hypervisor for Registers." Isn't the hypervisor what we are doing now? I mean multiple extension originators share the same register and eventually the same log. Or do you suggest to go even further having a "generic_registerX" exposed for every hw implementation allowing the user to have full abstraction? The "generic_registerX" would be always alias to something hw specific, like RTMR2 for example of TDX. > >> >> But we almost certainly need to have logs sequentially created in time >> occupying the same register. Ie IMA may take over the register from >> UEFI logging. Here we'd want to report the start/end hash values of >> the logs back to userspace so the verifier can stitch the order back >> together. >> >> It would also be nice to think about a way to restrict the registers >> to help avoid multi-user conflicts from misconfiguration. > >That would definitely be a plus. > >Mimi