I was investigating an apparent bug in the trusted keys implementation where periodically the key operation barfs and returns an error to userspace. It turns out this error is because the TPM returns TPM_RC_RETRY to an operation. The TPM spec is a bit unclear why the TPM would return TPM_RC_RETRY, but it is clear that it may happen on a lot of operations. I checked with the microsoft reference implementation: https://github.com/Microsoft/ms-tpm-20-ref/ Which implies it's only set if the lockout check is invoked by the command and the previous TPM shutdown wasn't orderly. It does seem to me that I've only seen it involving objects with DA implications, which explains why it's seen in trusted keys. If I read the UEFI TPM API, it does automatic retries. This is the note: The firmware SHALL not return TPM2_RC_RETRY prior to the completion of the call to ExitBootServices(). Implementer’s Note: the implementation of this function should check the return value in the TPM response and, if it is TPM2_RC_RETRY, resend the command. The implementation may abort if a sufficient number of retries has been done. I really think if UEFI does it, we should do it too (and it will fix my trusted key bug). What does everyone else think? If it's agreed, I'll code up the patch. James
