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Date:   Sat, 7 Oct 2023 12:04:33 +0200
From:   Lukas Wunner <lukas@wunner.de>
To:     Dan Williams <dan.j.williams@intel.com>
Cc:     Bjorn Helgaas <helgaas@kernel.org>,
        David Howells <dhowells@redhat.com>,
        David Woodhouse <dwmw2@infradead.org>,
        Herbert Xu <herbert@gondor.apana.org.au>,
        "David S. Miller" <davem@davemloft.net>,
        Alex Williamson <alex.williamson@redhat.com>,
        linux-pci@vger.kernel.org, linux-cxl@vger.kernel.org,
        linux-coco@lists.linux.dev, keyrings@vger.kernel.org,
        linux-crypto@vger.kernel.org, kvm@vger.kernel.org,
        Jonathan Cameron <Jonathan.Cameron@huawei.com>,
        linuxarm@huawei.com, David Box <david.e.box@intel.com>,
        Dave Jiang <dave.jiang@intel.com>,
        "Li, Ming" <ming4.li@intel.com>, Zhi Wang <zhi.a.wang@intel.com>,
        Alistair Francis <alistair.francis@wdc.com>,
        Wilfred Mallawa <wilfred.mallawa@wdc.com>,
        Alexey Kardashevskiy <aik@amd.com>,
        Tom Lendacky <thomas.lendacky@amd.com>,
        Sean Christopherson <seanjc@google.com>,
        Alexander Graf <graf@amazon.com>
Subject: Re: [PATCH 00/12] PCI device authentication
Message-ID: <20231007100433.GA7596@wunner.de>
References: <cover.1695921656.git.lukas@wunner.de>
 <652030759e42d_ae7e72946@dwillia2-xfh.jf.intel.com.notmuch>
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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