On Mon, Oct 27, 2025 at 04:09:35PM -0400, James Bottomley wrote: > On Mon, 2025-10-27 at 21:38 +0200, Jarkko Sakkinen wrote: > > On Mon, Oct 20, 2025 at 01:53:30PM +0200, Roberto Sassu wrote: > [...] > > > Hi Jonathan > > > > > > do I understand it correctly, that a process might open the TPM > > > with O_EXCL, and this will prevent IMA from extending a PCR until > > > that process closes the file descriptor? > > > > > > If yes, this might be a concern, and I think an additional API to > > > prevent such behavior would be needed (for example when IMA is > > > active, i.e. there is a measurement policy loaded). > > > > Also this would be a problem with hwrng. > > > > This probably needs to be refined somehow. I don't have a solution at > > hand but "invariant" is that in-kernel caller should override user > > space exclusion, even when O_EXCL is used. > > Also, are we sure we need O_EXCL in the first place? A well > functioning TPM is supposed to be able to cope with field upgrade while > it receives other commands. When it's in this state, it's supposed to > return TPM_RC_UPGRADE to inappropriate commands, so if we made sure we > can correctly handle that in the kernel, that might be enough to get > all this to work correctly without needing an exclusive open. > > Of course, Field Upgrade is likely to be the least well tested of any > TPM capability, so there's a good chance at least one TPM out there > isn't going to behave as the standard says it should. > > Regards, > > James
I get that depending on configuration someone really would want to have guaranteed exclusive access to the device. Since it is opt-in via O_EXCL, I don't have anything in principle againts adding it. The patch set needs rework but feature itself is totally fine. BR, Jarkko
