Agreed, the feature needs some work in order to provide meaningful security value, and disabling it by default facilitates that work.
Reviewed-By: Chris Fenner <[email protected]> On Thu, Sep 18, 2025 at 12:12 PM Jarkko Sakkinen <[email protected]> wrote: > > On Thu, Sep 18, 2025 at 07:56:53PM +0100, Jonathan McDowell wrote: > > On Mon, Aug 25, 2025 at 11:32:23PM +0300, Jarkko Sakkinen wrote: > > > After reading all the feedback, right now disabling the TPM2_TCG_HMAC > > > is the right call. > > > > > > Other views discussed: > > > > > > A. Having a kernel command-line parameter or refining the feature > > > otherwise. This goes to the area of improvements. E.g., one > > > example is my own idea where the null key specific code would be > > > replaced with a persistent handle parameter (which can be > > > *unambigously* defined as part of attestation process when > > > done correctly). > > > > > > B. Removing the code. I don't buy this because that is same as saying > > > that HMAC encryption cannot work at all (if really nitpicking) in > > > any form. Also I disagree on the view that the feature could not > > > be refined to something more reasoable. > > > > > > Also, both A and B are worst options in terms of backporting. > > > > > > Thus, this is the best possible choice. > > > > I think this is reasonable; it's adding runtime overhead and not adding > > enough benefit to be the default upstream. > > Yes, I think this is a balanced change. I agree what you say and at the > same time this gives more space to refine it something usable. Right now > it is much harder to tackle those issue, as it is part of the default > config. By looking at things from this angle, the change is also > benefical for the feature itself (in the long run). > > > Reviewed-By: Jonathan McDowell <[email protected]> > > Thank you! I appreciate this and will append this to the commit. > > BR, Jarkko
