linux-kernel - Re: [PATCH v8 5/5] x86/tdx: Add Quote generation support

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Date:   Thu, 21 Jul 2022 10:19:30 -0700
From:   Dave Hansen <dave.hansen@...el.com>
To:     Sathyanarayanan Kuppuswamy 
        <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
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>,
        Kai Huang <kai.huang@...el.com>,
        Wander Lairson Costa <wander@...hat.com>,
        Isaku Yamahata <isaku.yamahata@...il.com>,
        marcelo.cerri@...onical.com, tim.gardner@...onical.com,
        khalid.elmously@...onical.com, philip.cox@...onical.com,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v8 5/5] x86/tdx: Add Quote generation support

On 7/21/22 10:16, Sathyanarayanan Kuppuswamy wrote:
>> What is this "additional data"?  Is that "REPORTDATA" from the TDX
>> module spec?
>>
>> 	"Additional REPORTDATA, a 64-byte value, is provided by the
>> 	guest TD to be included in the TDG.MR.REPORT."
> 
> It is not the REPORTDATA. REPORTDATA is already included in the TDREPORT during
> REPORT generation process (using TDG.MR.REPORT).
> 
> Spec does not clearly define the details about the additional data. I think it is
> related to certificates.
> 
> Isaku, do you have more details about it?
> 
> Current ABI allows attestation service and agent to decide the quote size. So
> we can't make assumptions on what that size will be.
> 
> Following is copied from TDX Module specification, sec titled "Measurement
> and Attestation"
> 
> An Intel SGX Quoting Enclave, written specifically to support quoting Intel TDX TDs,
> uses a new ENCLU instruction leaf, EVERIFYREPORT2, to help check the integrity of the
> TDG.MR.REPORT. If it passes, the Quoting Enclave can use a certified quote signing key
> to sign a quote containing the guest TD’s measurements and the additional data being
> quoted.

<sigh> We're off in the weeds again.

How many bytes does the TDX module read from and write to the guest
physical address space?  What are the absolute limits?  What is the
minimum and the maximum that the kernel needs to handle?