On Fri, Aug 15, 2025 at 08:45:06AM -0700, Chris Fenner wrote: > I have a Linux machine with a standard off-the-shelf Infineon SLB9670 > TPM. Without the session salting, each PCR extension takes just 4-5 > ms. With session salting, it takes: > * 30ms to load the null key from its context blob > * 108ms to start the auth session and extend the PCR inside it > * 1ms to flush the null key > > for an overhead of about 2880%. Depending on the configuration of the > kernel/IMA and how many PCR measurements it's making, this could add > up to a good chunk of time and explain reports like [3] where people > are noting that turning this feature on adds minutes to or triples the > boot time.
I'll with shoot another proposal. Let's delete null primary creation code and add a parameter 'tpm.integrity_handle', which will refers to persistent primary handle: 1. It simplifies the code considerably. 2. It makes whole a lot more sense especially given that there's ambiguity with the key. This comes from earlier off-list discussion where you made this argument, and I'll buy that. I.e. even if we could certify null primary we cannot certify it is "unambiguousness". 3. Update tpm-security documentation accordingly. I think this might be "the long-term fix" that could be done right noW. BR, Jarkko
