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    SubjectRe: [PATCH v9 1/6] x86/tdx: Add TDX Guest attestation interface driver
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    On 8/18/22 07:18, Borislav Petkov wrote:
    >> + /*
    >> + * Generate TDREPORT using "TDG.MR.REPORT" TDCALL.
    >> + *
    >> + * Get the TDREPORT using REPORTDATA as input. Refer to
    >> + * section 22.3.3 TDG.MR.REPORT leaf in the TDX Module 1.0
    >> + * Specification for detailed information.
    >> + */
    >> + ret = __tdx_module_call(TDX_GET_REPORT, virt_to_phys(tdreport),
    >> + virt_to_phys(reportdata), req.subtype,
    > That subtype you're not checking either.

    I'll chime in here a bit since you're touching on something that bugged
    me too. This whole mechanism is because of two TDX shortcuts. (calling
    them shortcuts is generous, but I digress...)

    1. TDX guest attestation relies on SGX. TDX does not have its own
    attestation mechanism.
    2. TDX guests can not run SGX enclaves. Only TDX hosts can.

    As a result, any TDX guest that wants to do the attestation dance has to
    talk to the host, who them talks to the SGX enclave. There's actually a
    nice diagram of it in here (Figure 5.8):

    > https://www.intel.com/content/dam/develop/external/us/en/documents/tdx-whitepaper-v4.pdf

    This "talking" can be done via any old communication mechanism. Shared
    memory, virtio, morse code, whatever. TDX_GET_REPORT just happens to be
    yet another communication mechanism dedicated *only* to these
    attestation reports.

    So, this is not a *STRICTLY* required ABI. Guests _can_ use other
    mechanisms to talk to an SGX attestation (quoting) enclave. Second,
    this ABI *is* TDX-specific because no other hardware architectures have
    made the same design "choices".

    That's why this was jettisoned for v10. It might reappear later, though.

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