Messages in this thread | | | Date | Thu, 18 Aug 2022 09:25:57 -0700 | Subject | Re: [PATCH v9 1/6] x86/tdx: Add TDX Guest attestation interface driver | From | Dave Hansen <> |
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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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