attester: tdx: make libtdx-attest optional #905
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TDX Guest driver support is problematic: configfs-tsm currently does not allow to request bare TD reports. It's always a signed TD quote that needs exits to QGS for signing. However, for the initdata checks, we only need the TD report. Linux still supports the /dev/tdx_guest ioctl() for getting the report. Since the early days, we have used libtdx-attest wrappers for the ioctls(). However, getting the C libraries and headers installed in various places has turned out to be problematic. Furthermore, it isn't even necessary for uses cases like kbs-client (where only the configfs-tsm GetQuote is needed). Move the get_report() method to use raw ioctls() using iocuddle. This follows the sev crate implementation and which turns out to be very simple to adopt here too. Signed-off-by: Mikko Ylinen <mikko.ylinen@intel.com>
For the use-cases needed by CoCo and supported by upstream Linux, we don't need libtdx-attest so make the dependency a build-time opt-in feature. Signed-off-by: Mikko Ylinen <mikko.ylinen@intel.com>
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For configurations where the out-of-tree RTMR extend ioctl() is available and/or the libtdx-attest supported way to get the TD quote is needed, add a customized tdx-attester feature that supports this. Signed-off-by: Mikko Ylinen <mikko.ylinen@intel.com>
Signed-off-by: Mikko Ylinen <mikko.ylinen@intel.com>
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mkulke
approved these changes
Feb 14, 2025
fitzthum
approved these changes
Feb 14, 2025
| @@ -76,6 +76,7 @@ all-attesters = [ | |||
| "cca-attester", | |||
| ] | |||
| tdx-attester = ["kbs_protocol?/tdx-attester", "attester/tdx-attester"] | |||
| tdx-attester-oot = ["kbs_protocol?/tdx-attester-oot", "attester/tdx-attester", "attester/tdx-attest-dcap-ioctls"] | |||
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Can we add a comment about what this is. Is oot the best name for the feature? This is referring to a non-upstream kernel? Maybe we should just call it -libtdx or something.
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TDX Guest driver support is problematic: configfs-tsm currently
does not allow to request bare TD reports. It's always a signed
TD quote that needs exits to QGS for signing. However, for the
initdata checks, we only need the TD report.
Linux still supports the /dev/tdx_guest ioctl() for getting the
report. Since the early days, we have used libtdx-attest wrappers
for the ioctls(). However, getting the C libraries and headers
installed in various places has turned out to be problematic.
Furthermore, it isn't even necessary for uses cases like
kbs-client (where only the configfs-tsm GetQuote is needed).