linux-kernel - Re: [PATCH v3 4/4] platform/x86: intel_tdx_attest: Add TDX Guest attestation interface driver

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Date:   Tue, 19 Apr 2022 07:13:11 -0700
From:   Dave Hansen <dave.hansen@...el.com>
To:     Kai Huang <kai.huang@...el.com>,
        Kuppuswamy Sathyanarayanan 
        <sathyanarayanan.kuppuswamy@...ux.intel.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        Dave Hansen <dave.hansen@...ux.intel.com>, x86@...nel.org,
        Hans de Goede <hdegoede@...hat.com>,
        Mark Gross <mgross@...ux.intel.com>
Cc:     "H . Peter Anvin" <hpa@...or.com>,
        "Kirill A . Shutemov" <kirill.shutemov@...ux.intel.com>,
        Tony Luck <tony.luck@...el.com>,
        Andi Kleen <ak@...ux.intel.com>, linux-kernel@...r.kernel.org,
        platform-driver-x86@...r.kernel.org
Subject: Re: [PATCH v3 4/4] platform/x86: intel_tdx_attest: Add TDX Guest
 attestation interface driver

On 4/19/22 00:47, Kai Huang wrote:
>>>From security's perspective, attestation is an essential part of TDX.  That
> being said, w/o attestation support in TD guest, I guess nobody will seriously
> use TD guest.

Are you saying you can't think of a single threat model where there's a
benefit to running a TDX guest without attestation?  Will TDX only be
used in environments where secrets are provisioned to guests on the
basis of attestation?

>>>From this perspective, I am not sure what's the value of having a dedicated
> INTEL_TDX_ATTESTATION Kconfig.  The attestation support code should be turned on
> unconditionally when CONFIG_INTEL_TDX_GUEST is on.  The code can also be just
> under arch/x86/coco/tdx/ I guess?

How much code are we talking about?  What's the difference in the size
of the binaries with this compiled in?