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Sat, 07 Nov 2026 09:25:59 -0800 (PST) Received: from localhost ([140.209.217.211]) by smtp.gmail.com with ESMTPSA id a640c23a62f3a-c4d3569edc9sm165153366b.50.2026.11.07.09.25.58 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Sat, 07 Nov 2026 09:25:58 -0800 (PST) Date: Sat, 7 Nov 2026 18:25:54 +0100 From: Jiri Pirko To: Yeoreum Yun Cc: Jason Gunthorpe , 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, drdeeglaze@gmail.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, aneesh.kumar@kernel.org Subject: Re: [PATCH RFC 17/20] attestation: Add CTLV operation handling Message-ID: References: <20261104194622.GC3889730@ziepe.ca> 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: Fri, Nov 06, 2026 at 05:19:59PM +0100, yeoreum.yun@arm.com wrote: >On Fri, Nov 06, 2026 at 05:03:32PM +0100, Jiri Pirko wrote: >> Fri, Nov 06, 2026 at 03:36:50PM +0100, yeoreum.yun@arm.com wrote: >> >> Fri, Nov 06, 2026 at 09:57:25AM +0100, yeoreum.yun@arm.com wrote: >> >> >On Fri, Nov 06, 2026 at 09:27:42AM +0100, Jiri Pirko wrote: >> >> >> Thu, Nov 05, 2026 at 02:52:19PM +0100, yeoreum.yun@arm.com wrote: >> >> >> >On Thu, Nov 05, 2026 at 01:32:49PM +0100, Jiri Pirko wrote: >> >> >> >> Wed, Nov 04, 2026 at 08:46:22PM +0100, jgg@ziepe.ca wrote: >> >> >> >> >On Wed, Nov 04, 2026 at 07:11:44PM +0000, Yeoreum Yun wrote: >> >> >> >> >> [..snip..] >> >> >> >> >> >> >> >> >> >> > +static int attestation_evidence_request_decode(struct attestation *att, struct ctlv_op_ctx *ctx, >> >> >> >> >> > + const struct ctlv_cursor *request, >> >> >> >> >> > + struct attestation_evidence_request *decoded, >> >> >> >> >> > + struct attestation_evidence_object_request **objects) >> >> >> >> >> > +{ >> >> >> >> >> > + const struct attestation_evidence_caps *caps = att->provider->evidence_caps; >> >> >> >> >> > + u32 challenge_length; >> >> >> >> >> > + >> >> >> >> >> > + decoded->challenge = >> >> >> >> >> > + ctlv_attestation_evidence_get_evidence_challenge_get(request, &challenge_length); >> >> >> >> >> > + decoded->challenge_length = challenge_length; >> >> >> >> >> > + if (challenge_length < caps->min_challenge_length || >> >> >> >> >> > + challenge_length > caps->max_challenge_length) >> >> >> >> >> >> >> >> >> >> Hmm, I'm not sure whether this check is required for >> >> >> >> >> ATTESTATION_EVIDENCE_BLOB_EVENT_LOG blob type. >> >> >> >> >> >> >> >> >> >> for example, if the provider provides two evidence: >> >> >> >> >> - ATTESTATION_EVIDENCE_BLOB_PRIMARY (might attestation token) >> >> >> >> >> - ATTESTATION_EVIDENCE_BLOB_EVENT_LOG >> >> >> >> >> >> >> >> >> >> might challenge is reuiqred for generating the token >> >> >> >> >> and this would be marked at min/max_challenge_size in evidence_cap. >> >> >> >> >> >> >> >> >> >> However, in case of eventlog, it wouldn't require challenge. >> >> >> >> >> for example, TPM event log or CCEL event log. >> >> >> >> > >> >> >> >> >Right >> >> >> >> > >> >> >> >> >> Do we need some field on attestation_evidence_supported_object whether >> >> >> >> >> it requires challenge or not and applies this sanity check per the object? >> >> >> >> >> >> >> >> >> >> Otherwise, to get eventlog, it would need to send *dummy* challenge >> >> >> >> >> always. >> >> >> >> > >> >> >> >> >I wonder if we should have two interfaces here for signed and unsigned >> >> >> >> >evidence? It would be clearer for userspace then when it needs to >> >> >> >> >provide a challenge or not. >> >> >> >> >> >> >> >> Isn't the challenge field provided/not-provided enough? >> >> >> >> >> >> >> >> Currently on the introspection side, device-get op would provide >> >> >> >> challenge-lengths array: >> >> >> >> >> >> >> >> evidence?: >> >> >> >> challenge-lengths[8]: >> >> >> >> length?: uint(..4096) >> >> >> >> min-length?: uint(..4096) >> >> >> >> max-length?: uint(..4096) >> >> >> >> objects[16]: >> >> >> >> blob-class: evidence-blob-class >> >> >> >> max-length: uint >> >> >> >> blob-instance?: uint(..u32-max) >> >> >> >> >> >> >> >> I think it would make sense to have challenge-lengths array per object: >> >> >> >> >> >> >> >> objects[16]: >> >> >> >> blob-class: evidence-blob-class >> >> >> >> max-length: uint >> >> >> >> blob-instance?: uint(..u32-max) >> >> >> >> challenge-lengths[8]: >> >> >> >> length?: uint(..4096) >> >> >> >> min-length?: uint(..4096) >> >> >> >> max-length?: uint(..4096) >> >> >> >> >> >> >> >> Then the unsigned object would just simply have challenge-lengths empty? >> >> >> > >> >> >> >This looks good to me. :) >> >> >> >> >> >> The challenge is one of several open points that all depend on what an >> >> >> evidence object is: Rick's TDREPORT, legacy versus DICE Quotes, >> >> >> "primary", "raw" and the format strings. Here is my proposal to settle >> >> >> these together: >> >> >> >> >> >> The model: >> >> >> >> >> >> 1. device-get lists each object with an id, a class (signed, event-log, >> >> >> cert-chain or auxiliary), the formats it may come in, its max-length >> >> >> and, for signed objects only, challenge-lengths. >> >> >> 2. evidence-get names objects by id, as MR ops name MRs, each with its >> >> >> output blob. It carries a challenge exactly when it names a signed >> >> >> object, and the challenge has to fit each of them. >> >> >> 3. The reply gives each object's format, length and, where the TCB >> >> >> vouches for it, the TCB's digest. The output is always {label, data}. >> >> >> 4. A signed object is made by the call, over the challenge, and never >> >> >> reused. The rest are read as they stand. >> >> >> >> >> >> This settles following issues discussed during this patchset review: >> >> >> >> >> >> 1. One op, not two. Per-object challenge-lengths tell userspace when to >> >> >> pass a challenge, and one call returns the signed object with the log >> >> >> and certificates needed to check it. >> >> >> 2. TDX's TDREPORT goes: it is MAC'd for the platform, not signed. >> >> >> /dev/tdx_guest keeps TDX_CMD_GET_REPORT0. >> >> >> 3. TDX's Quote object lists the legacy and the DICE format. The provider >> >> >> labels what the host returned and fails on a Quote it cannot label. >> >> >> 4. "primary" becomes "signed", manifest joins auxiliary, spdm-vca, >> >> >> spdm-measurements and tdisp-report become formats, and signature >> >> >> goes, as a signed object carries its own. >> >> >> 5. "raw" goes with the representation attr. The TCB digest is a reply >> >> >> field, so a blob always holds the object's own bytes. >> >> >> >> >> >> Formats become an enum each provider family defines, instead of free >> >> >> strings. I'm still unsure if format should be entirely provider-specific >> >> >> and defined as "extension", or it should be somehow mixture of common >> >> >> and provider-specific. Looks there is not really much common >> >> >> anyway, so I lean towards provider-specific only. So far I have: >> >> > >> >> >Overall, This is plausible for me with some small question. >> >> > >> >> >> >> >> >> ====== ============ ========== ========= =========================== >> >> >> Family Format Class Challenge Bytes >> >> >> ====== ============ ========== ========= =========================== >> >> >[...] >> >> >> tpm ek-cert cert-chain none EK certificate from NV >> >> > >> >> >Just a thought, but how are we planning to retrieve >> >> >the NV index for EK certificate? >> >> > >> >> >As far as I know, TPM NV storage doesn't support labeling. >> >> > >> >> >Should I assume that the NV index would be specified as part of the >> >> >challenge to retrieve the certificate from TPM NV storage? >> >> >> >> evidence-get allows to accept mr-selection as part of the request >> >> alongside the challenge. >> > >> >Sorry. Could you explain a little bit detail for this?. >> >AFAIU, this is to get the EK certificate from TPM non-volatile storage. >> >But, I don't know why *EK* certificate get would be relevant for >> >*mr selection*. AFAIK, the TPM_Quote will be used AK not a EK. >> >> You are right, my mistake. I misunderstood the question. >> >> mr-selection selects PCRs for Quote, or an extend-NV measurement >> register for NV Certify. >> >> An NV-resident EK certificate is retrieved using NV_Read. I think >> blob-instance is a good fit. For TPM certificate objects, it could >> identify the certificate's NV index. > >Ah. I missed the TCG_EK_Credential_Profile specification which defines >the NV index value for EK certificate: > >2.2.1.4 Low Range > The Low Range is at NV Indices 0x01c00002 - 0x01c0000c. > 0x01c00002 RSA 2048 EK Certificate > 0x01c00003 RSA 2048 EK Nonce > 0x01c00004 RSA 2048 EK Template > 0x01c0000a ECC NIST P256 EK Certificate > 0x01c0000b ECC NIST P256 EK Nonce > 0x01c0000c ECC NIST P256 EK Template > >But, do we need some argument to get which EK certificate to get? >(RSA or ECC NIST P256)? Why blob-instance 0-10 is not good enough here? > >Otherwise, Is this interface going to print all EK certificate >regardless of alg? > >> >Also, AFAIK, mr_selection is meaningful when the evidence_accept is >> >supported. >> >> These are independent. mr-selection chooses the measurements included >> in evidence. EVIDENCE_ACCEPT authorizes a subsequent native transition. >> The TPM provider can quote selected PCRs without supporting acceptance. > >Acked. > >-- >Sincerely, >Yeoreum Yun