Re: [RFC PATCH v1 02/11] attestation: Filter evidence objects per instance

Wed, Oct 28, 2026 at 04:26:09PM +0100, aneesh.kumar@kernel.org wrote:

Allow an attestation instance to expose only the evidence objects its
device supports. Add an optional evidence_object_supported() callback
and use it both when building DEVICE_GET capabilities and when checking
EVIDENCE_GET requests.

The following PCI/TSM patch uses one attestation implementation for
devices that support different evidence objects. Its list includes
certificate slots 0-7, SPDM VCA, measurements, and a TDISP interface
report. Each device must expose only the objects it supports, for
example:

 Instance                  Supported evidence objects
 ------------------------  ------------------------------------------
 Host link using slot zero Certificate slot 0
 CCA guest device          Certificate slot 0, VCA, measurements,
                           TDISP interface report
 Host PF0 after discovery  Certificate slots reported populated by SPDM

PCI/TSM checks the TSM driver's evidence_types bitmap or, after SPDM
discovery on a host PF0, the populated-slot bitmap. The preceding patch
controls whether EVIDENCE_GET is enabled; this patch controls which
objects that operation can retrieve.

For SPDM slots, I think it would make sense to distinguish supported
slot addresses from discovered population. DEVICE_GET describes fixed
object tuples, formats and limits; SPDM_GET reports the populated
slots and their certificate digests. An empty supported slot
returns -ENOENT.

Fixed differences between backend instances can be selected before
publication. Please do not make the capability set follow a
populated-slot bitmap that can change during the instance lifetime.

[..]