On Fri, Mar 16, 2018 at 11:36:28AM +0100, Javier Martinez Canillas wrote: > [adding Philip Tricca to the cc list] > > Hello James, > > On 03/15/2018 07:02 PM, James Bottomley wrote: > > 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. > > > > That's a very good question. I don't know the answer but maybe Philip does > since he said that would ask the TCG TSS WG members for their thoughts on > this [0]. > > We had the same issue in the tpm2-software project, and at the end Philip > added a macro that retries sending commands on TPM_RC_RETRY responses [1]. > > If the kernel handles this, then such a macro won't be needed anymore for > user-space programs and will simplify things. So I'm in favour to handle > at the driver level but I'm not sure if is the correct thing to do or not. Can we get input from TCG how to fix this properly and request to update their specs accordingly? /Jarkko
