linux-kernel - Re: [PATCH 1/2] x86/random: Retry on RDSEED failure

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Date: Tue, 13 Feb 2024 18:13:41 -0500
From: "Theodore Ts'o" <tytso@....edu>
To: Dan Williams <dan.j.williams@...el.com>
Cc: "Reshetova, Elena" <elena.reshetova@...el.com>,
        "Jason A. Donenfeld" <Jason@...c4.com>,
        "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
        "H. Peter Anvin" <hpa@...or.com>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Thomas Gleixner <tglx@...utronix.de>, Ingo Molnar <mingo@...hat.com>,
        Borislav Petkov <bp@...en8.de>, "x86@...nel.org" <x86@...nel.org>,
        Kuppuswamy Sathyanarayanan <sathyanarayanan.kuppuswamy@...ux.intel.com>,
        "Nakajima, Jun" <jun.nakajima@...el.com>,
        Tom Lendacky <thomas.lendacky@....com>,
        "Kalra, Ashish" <ashish.kalra@....com>,
        Sean Christopherson <seanjc@...gle.com>,
        "linux-coco@...ts.linux.dev" <linux-coco@...ts.linux.dev>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 1/2] x86/random: Retry on RDSEED failure

On Mon, Feb 12, 2024 at 11:28:31PM -0800, Dan Williams wrote:
> Sure there is, that is what, for example, PCI TDISP (TEE Device
> Interface Security Protocol) is about. Set aside the difficulty of doing
> the PCI TDISP flow early in boot, and validating the device certficate
> and measurements based on golden values without talking to a remote
> verifier etc..., but if such a device has been accepted and its driver
> calls hwrng_register() it should be added as an entropy source.

How real is TDISP?  What hardware exists today and how much of this
support is ready to land in the kernel?  Looking at the news articles,
it appears to me like bleeding edge technology, and what an unkind
person might call "vaporware"?  Is that an unfair characterization?

There have plenty of things that have squirted out of standards
bodies, like for example, "objected base storage", which has turned
out to be a complete commercial failure and was never actually
deployed in any real numbers, other than sample hardare being provided
to academic researchers.  How can we be sure that PCI TDISP won't end
up going down that route?

In any case, if we are going to go down this path, we will need to
have some kind of policy engine hwrng_register() reject
non-authenticated hardware if Confidential Compute is enabled (and
possibly in other cases).

				- Ted