linux-kernel - Re: [PATCH V4 1/3] platform/x86/intel/sdsi: Add ioctl SPDM transport

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Date: Sat, 8 Jun 2024 14:46:58 +0200
From: Lukas Wunner <lukas@...ner.de>
To: "David E. Box" <david.e.box@...ux.intel.com>
Cc: linux-doc@...r.kernel.org, ilpo.jarvinen@...ux.intel.com,
	hdegoede@...hat.com, linux-kernel@...r.kernel.org,
	platform-driver-x86@...r.kernel.org
Subject: Re: [PATCH V4 1/3] platform/x86/intel/sdsi: Add ioctl SPDM transport

On Fri, Jun 07, 2024 at 08:42:45PM -0700, David E. Box wrote:
> Intel On Demand adds attestation and firmware measurement retrieval
> services through use of the protocols defined the Security Protocols and
> Data Measurement (SPDM) specification. SPDM messages exchanges are used to
> authenticate On Demand hardware and to retrieve signed measurements of the
> NVRAM state used to track feature provisioning and the NVRAM state used for
> metering services. These allow software to verify the authenticity of the
> On Demand hardware as well as the integrity of the reported silicon
> configuration.
> 
> Add an ioctl interface for sending SPDM messages through the On Demand
> mailbox. Provides commands to get a list of SPDM enabled devices, get the
> message size limits for SPDM Requesters and Responders, and perform an SPDM
> message exchange.

I've amended the in-kernel SPDM implementation to expose signatures
received from the device in sysfs, together with all ancillary data
necessary to re-verify signatures from user space (transcript, hash
algorithm, etc).  It is also possible to set the next requester nonce
from user space if the kernel is mistrusted to always use a fresh nonce.

See the two top-most commits on this branch:

https://github.com/l1k/linux/commits/doe

I intend to submit these patches by end of June.  There are two things
still missing before I can resubmit:  Exposure of certificate chains in
sysfs (currently a WIP) and expiration of older signatures (to limit the
amount of memory consumed for their storage).  After submission, I intend
to forward-port your measurement patch in Q3.

I recall S3M folks rejected use of the in-kernel SPDM implementation for
SDSi because it previously didn't allow for re-verification of signatures
by user space.  Perhaps with the added functionality they'll reconsider?

Thanks,

Lukas