Re: [RFC PATCH] tpm: Allow the TPM2 pcr_extend HMAC capability to be disabled on boot

["Jarkko Sakkinen" <jarkko@kernel.org>]

On Thu Nov 7, 2024 at 1:22 AM EET, Jarkko Sakkinen wrote:
> > I'm a bit confused here.  It's TPM2_PCR_Extend we have the trouble with
> > (as Mimi says in her email that you quoted) not TPM2_GetRandom.
> >
> > The random number generator reseed occurs in a kernel thread that fires
> > about once a minute, so it doesn't show up in really any of the boot
> > timings.  Plus even with sessions added, what there now isn't a
> > significant overhead even to the running kernel given it's asynchronous
> > and called infrequently.
>
> Ah, right then we need the boot flag, and my earlier comments to the
> parameter apply. I've never used IMA so I don't actually even know in
> detail how it is using TPM.
>
> Now that I did some seek I mixed this up with the report:
>
> https://chaos.social/@gromit/113345582873908273
>
> Anyway concerning this issue and patch, my earlier comments still apply.

Makes me wonder tho why do we then export tpm_get_random() in the first
place? HWRNG does not needed that export, and the code does not have any
of the mentioned features.

BR, Jarkko