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Wed, 21 Oct 2026 19:05:10 +0000 (GMT) Received: from li-43857255-d5e6-4659-90f1-fc5cee4750ad.ibm.com (unknown [9.77.162.217]) by smtpav03.dal12v.mail.ibm.com (Postfix) with ESMTP; Wed, 21 Oct 2026 19:05:10 +0000 (GMT) Message-ID: <8d8833fac61558a94af415143530884349584a2f.camel@linux.ibm.com> Subject: Re: [PATCH RFC 00/20] attestation: Add a common subsystem and TDX support From: Mimi Zohar To: Jason Gunthorpe Cc: Jiri Pirko , 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 In-Reply-To: <20261021143529.GP3008132@nvidia.com> References: <20261017203407.GM13920@nvidia.com> <20261017231007.GP13920@nvidia.com> <20261019225658.GS13920@nvidia.com> <103486a4a29ecc7b72940dd051c00ae59266bd05.camel@linux.ibm.com> <20261021143529.GP3008132@nvidia.com> Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable Date: Wed, 21 Oct 2026 15:05:09 -0400 X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Post: List-Help: List-Subscribe: List-Unsubscribe: List-Owner: Precedence: list MIME-Version: 1.0 User-Agent: Evolution 3.58.3 (3.58.3-2.fc43) X-TM-AS-GCONF: 00 X-Proofpoint-Reinject: loops=2 maxloops=12 X-Proofpoint-GUID: ydaOzlwPIUk9SIhOIcCkK3SVXfS2DDcg X-Proofpoint-ORIG-GUID: GzBYn879Oa5NzXnY4sgOMq8X1dbUx1fB X-Proofpoint-Spam-Info: AW1haW4tMjYxMDIxMDA3NCBTYWx0ZWRfXwyVoKuAud310 A3MMgRuO3P9BfDlryZr7ihLhpK+1PPfP0xO1xgsoY0qD3mT++OvGba+8UA0zkcoD+iWg/elNtcH Z8gPzXT/JWDMgUcPZBCKi26sOkrkUsY= X-Proofpoint-Spam-Details-Enc: AW1haW4tMjYxMDIxMDA3NCBTYWx0ZWRfX1hmDKI4a0lIN oCbznsJRgcS0JN6foELRHP6ISHyPt+L/UW64K16gcO4VrYiohYmtKf0oW63pkMniBR5FA572QN5 ieNRoOqQ5C+MUuzixWaCYc9xzLcGBWUGx03ndwS3NTq8ewrjFeaaF25ZgavBj0gzJcdgbUGxSh1 z/ImEgbAtQpFnbxfpY5IGBnzAOUVBhPlq7kbzT4jo+YS8enEUnhx0XveFs7pUFwmfqtIhy7rfMr /eNM5pZnlbLbm0Swwddnnl31pEYsNFSv3Bp6+k2s2ORgrk1ke5QlzwIRPi80LBWPLiKzQs+u8rS SF8vdtLnNGB//AB0FOdXciN8gmxl2uGcWMN78g8nK/9aLNTmGVGxuGAPsMu90zKkHsZHcndSc2b gg2i2oceWWm/HafsY/e03vEgK0dQEZfnGympFncPnRryoEodcVL2DFBslRUkKJieyf7rN1+dJEg a9Wr0QwuxTURorMH4dw== X-Authority-Analysis: v=2.4 cv=Gb2CDgXL c=1 sm=1 tr=0 ts=6ad90ceb cx=c_pps a=3Bg1Hr4SwmMryq2xdFQyZA==:117 a=3Bg1Hr4SwmMryq2xdFQyZA==:17 a=IkcTkHD0fZMA:10 a=660iZSQnnn4A:10 a=VkNPw1HP01LnGYTKEx00:22 a=RnoormkPH1_aCDwRdu11:22 a=uAbxVGIbfxUO_5tXvNgY:22 a=yVQDdmlqToHGFoNqkO4A:9 a=QEXdDO2ut3YA:10 X-Proofpoint-Virus-Version: vendor=baseguard engine=ICAP:2.0.293,Aquarius:18.0.1176,Hydra:6.1.138,FMLib:17.12.100.49 definitions=2026-10-21_05,2026-10-21_02,2025-10-01_01 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 suspectscore=0 adultscore=0 malwarescore=0 spamscore=0 phishscore=0 clxscore=1015 bulkscore=0 impostorscore=0 lowpriorityscore=0 priorityscore=1501 classifier=typeunknown authscore=0 authtc= authcc= route=outbound adjust=0 reason=mlx scancount=1 engine=8.22.0-2610190000 definitions=main-2610210074 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 u= API > > > > 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. > > >=20 > > > Okay, dropping the log from this set. > >=20 > > 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 multiplex= ing the > > extension path), not by combining distinct measurement lists. >=20 > I'm not sure what you mean? >=20 > 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. >=20 > Multiplexing extension alone isn't enough. We need some scheme to > reconstruct interleaved logs too. >=20 > 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. >=20 > 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. >=20 > Maybe we can build a multiplexed scheme on the spare? I don't know. To avoid interleaving the logs, AI had suggested multiplexing or virtualiza= tion of the RTMRs. Whether is has any merit, I'll leave to you. Here's the ver= y short AI explanation: "Instead of allowing external drivers or subsystems to execute a direct, ra= w extend command to a specific hardware register index, the new attestation subsystem should act as a Hypervisor for Registers." >=20 > 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. >=20 > 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