Re: [PATCH 00/12] PCI device authentication

[Lukas Wunner <lukas@wunner.de>]

On Fri, Oct 06, 2023 at 09:06:13AM -0700, Dan Williams wrote:
> Lukas Wunner wrote:
> > The root of trust is initially an in-kernel key ring of certificates.
> > We can discuss linking the system key ring into it, thereby allowing
> > EFI to pass trusted certificates to the kernel for CMA.  Alternatively,
> > a bundle of trusted certificates could be loaded from the initrd.
> > I envision that we'll add TPMs or remote attestation services such as
> > https://keylime.dev/ to create an ecosystem of various trust sources.
> 
> Linux also has an interest in accommodating opt-in to using platform
> managed keys, so the design requires that key management and session
> ownership is a system owner policy choice.

You're pointing out a gap in the specification:

There's an existing mechanism to negotiate which PCI features are
handled natively by the OS and which by platform firmware and that's
the _OSC Control Field (PCI Firmware Spec r3.3 table 4-5 and 4-6).

There are currently 10 features whose ownership is negotiated with _OSC,
examples are Hotplug control and DPC configuration control.

I propose adding an 11th bit to negotiate ownership of the CMA-SPDM
session.

Once that's added to the PCI Firmware Spec, amending the implementation
to honor it is trivial:  Just check for platform ownership at the top
of pci_cma_init() and return.

Thanks,

Lukas