Re: [PATCH v9 01/11] KEYS: trusted: Use get_random-fallback for TPM

Mimi Zohar
2026-03-19T14:33:28Z

On Wed, 2026-03-18 at 10:36 -0700, Chris Fenner wrote:
> Apologies if my long message derailed this discussion. I meant to
> support Mimi's concern here and project a future vision where
> TCG_TPM2_HMAC doesn't conflict with other features.
>
> More concisely, I think that:
>
> > tpm2_get_random() is costly when TCG_TPM2_HMAC is enabled
>
> is not a compelling argument for removing TPM as an RNG source,
> because TCG_TPM2_HMAC is known to have poor performance already
> anyway.

Agreed. Thanks, Chris! FYI, we raised concerns about IMA performance with the
TPM HMAC and encrypted feature while it was being developed. James had some
ideas, at the time, as to how to resolve the performance issue for IMA. Yet it
was upstreamed without those changes and with CONFIG_TCG_TPM2_HMAC enabled by
default on x86 systems.

Jarkko has queued this patch in the "queue" branch, without indicating whether
it will eventually be upstreamed or not.

Mimi