Re: [PATCH RFC 17/20] attestation: Add CTLV operation handling

[Jiri Pirko]

Fri, Nov 06, 2026 at 03:36:50PM +0100, yeoreum.yun@xxxxxxx wrote:
>> Fri, Nov 06, 2026 at 09:57:25AM +0100, yeoreum.yun@xxxxxxx 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@xxxxxxx wrote:
>> >> >On Thu, Nov 05, 2026 at 01:32:49PM +0100, Jiri Pirko wrote:
>> >> >> Wed, Nov 04, 2026 at 08:46:22PM +0100, jgg@xxxxxxxx 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.



>
>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.


>
>What is the relation-ship between mr-selecation and getting the TPM's
>EK certificate getting from NV storage?
>
>-- 
>Sincerely,
>Yeoreum Yun