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TDX guest driver exposes IOCTL interfaces to service TDX guest user-specific requests. Currently, it is only used to allow the user to get the TDREPORT to support TDX attestation. Details about the TDX attestation process are documented in Documentation/x86/tdx.rst, and the IOCTL details are documented in Documentation/virt/coco/tdx-guest.rst. Operations like getting TDREPORT involves sending a blob of data as input and getting another blob of data as output. It was considered to use a sysfs interface for this, but it doesn't fit well into the standard sysfs model for configuring values. It would be possible to do read/write on files, but it would need multiple file descriptors, which would be somewhat messy. IOCTLs seem to be the best fitting and simplest model for this use case. The AMD sev-guest driver also uses the IOCTL interface to support attestation. [Bagas Sanjaya: Ack is for documentation portion] Signed-off-by: Kuppuswamy Sathyanarayanan <sathyanarayanan.kuppuswamy@linux.intel.com> Signed-off-by: Dave Hansen <dave.hansen@linux.intel.com> Reviewed-by: Bagas Sanjaya <bagasdotme@gmail.com> Reviewed-by: Tony Luck <tony.luck@intel.com> Reviewed-by: Mika Westerberg <mika.westerberg@linux.intel.com> Acked-by: Kai Huang <kai.huang@intel.com> Acked-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com> Acked-by: Wander Lairson Costa <wander@redhat.com> Link: https://lore.kernel.org/all/20221116223820.819090-3-sathyanarayanan.kuppuswamy%40linux.intel.com
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.. SPDX-License-Identifier: GPL-2.0
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===================================================================
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TDX Guest API Documentation
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===================================================================
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1. General description
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======================
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The TDX guest driver exposes IOCTL interfaces via the /dev/tdx-guest misc
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device to allow userspace to get certain TDX guest-specific details.
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2. API description
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==================
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In this section, for each supported IOCTL, the following information is
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provided along with a generic description.
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:Input parameters: Parameters passed to the IOCTL and related details.
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:Output: Details about output data and return value (with details about
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the non common error values).
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2.1 TDX_CMD_GET_REPORT0
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-----------------------
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:Input parameters: struct tdx_report_req
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:Output: Upon successful execution, TDREPORT data is copied to
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tdx_report_req.tdreport and return 0. Return -EINVAL for invalid
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operands, -EIO on TDCALL failure or standard error number on other
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common failures.
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The TDX_CMD_GET_REPORT0 IOCTL can be used by the attestation software to get
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the TDREPORT0 (a.k.a. TDREPORT subtype 0) from the TDX module using
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TDCALL[TDG.MR.REPORT].
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A subtype index is added at the end of this IOCTL CMD to uniquely identify the
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subtype-specific TDREPORT request. Although the subtype option is mentioned in
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the TDX Module v1.0 specification, section titled "TDG.MR.REPORT", it is not
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currently used, and it expects this value to be 0. So to keep the IOCTL
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implementation simple, the subtype option was not included as part of the input
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ABI. However, in the future, if the TDX Module supports more than one subtype,
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a new IOCTL CMD will be created to handle it. To keep the IOCTL naming
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consistent, a subtype index is added as part of the IOCTL CMD.
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Reference
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---------
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TDX reference material is collected here:
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https://www.intel.com/content/www/us/en/developer/articles/technical/intel-trust-domain-extensions.html
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The driver is based on TDX module specification v1.0 and TDX GHCI specification v1.0.
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