Re: [PATCH v3 2/3] virt: tdx-guest: Add Quote generation support

["Huang, Kai" <kai.huang@intel.com>]

On Sun, 2023-05-14 at 00:23 -0700, Kuppuswamy Sathyanarayanan wrote:
> In TDX guest, the attestation process is used to verify the TDX guest
> trustworthiness to other entities before provisioning secrets to the
> guest. The First step in the attestation process is TDREPORT
> generation, which involves getting the guest measurement data in the
> format of TDREPORT, which is further used to validate the authenticity
> of the TDX guest. TDREPORT by design is integrity-protected and can
> only be verified on the local machine.
> 
> To support remote verification of the TDREPORT (in a SGX-based
> attestation), the TDREPORT needs to be sent to the SGX Quoting Enclave
> (QE) to convert it to a remote verifiable Quote. SGX QE by design can
> only run outside of the TDX guest (i.e. in a host process or in a
> normal VM) and guest can use communication channels like vsock or
> TCP/IP to send the TDREPORT to the QE. But for security concerns, the
> TDX guest may not support these communication channels. To handle such
> cases, TDX defines a GetQuote hypercall which can be used by the guest
> to request the host VMM to communicate with the SGX QE. More details
> about GetQuote hypercall can be found in TDX Guest-Host Communication
> Interface (GHCI) for Intel TDX 1.0, section titled
> "TDG.VP.VMCALL<GetQuote>".
> 
> Add support for TDX_CMD_GET_QUOTE IOCTL to allow an attestation agent
> to submit GetQuote requests from the user space using GetQuote
> hypercall.
> 
> Since GetQuote is an asynchronous request hypercall, VMM will use the
> callback interrupt vector configured by the SetupEventNotifyInterrupt
> hypercall to notify the guest about Quote generation completion or
> failure. So register an IRQ handler for it.
> 
> GetQuote TDVMCALL requires TD guest pass a 4K aligned shared buffer
> with TDREPORT data as input, which is further used by the VMM to copy
> the TD Quote result after successful Quote generation. To create the
> shared buffer, allocate a large enough memory and mark it shared using
> set_memory_decrypted() in tdx_guest_init(). This buffer will be re-used
> for GetQuote requests in TDX_CMD_GET_QUOTE IOCTL handler.
> 
> Although this method reserves a fixed chunk of memory for GetQuote
> requests, such one-time allocation is preferable to the alternative
> choice of repeatedly allocating/freeing the shared buffer in the
> TDX_CMD_GET_QUOTE IOCTL handler, which will damage the direct map
> (because the sharing/unsharing process modifies the direct map). This
> allocation model is similar to that used by the AMD SEV guest driver.
> 
> Since the Quote generation process is not time-critical or frequently
> used, the current version does not support parallel GetQuote requests.
> 
> Reviewed-by: Tony Luck <tony.luck@intel.com>
> Reviewed-by: Andi Kleen <ak@linux.intel.com>
> Reviewed-by: Mika Westerberg <mika.westerberg@linux.intel.com>
> Reviewed-by: Erdem Aktas <erdemaktas@google.com>
> Acked-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
> Signed-off-by: Kuppuswamy Sathyanarayanan <sathyanarayanan.kuppuswamy@linux.intel.com>
> 

Acked-by: Kai Huang <kai.huang@intel.com>