[PATCH 1/3] tpm: Disable TCG_TPM2_HMAC by default

[Jarkko Sakkinen]

On Thu May 23, 2024 at 10:59 AM EEST, Vitor Soares wrote:
> On Wed, 2024-05-22 at 19:11 +0300, Jarkko Sakkinen wrote:
> > On Wed May 22, 2024 at 5:58 PM EEST, Vitor Soares wrote:
> > > I did run with ftrace, but need some more time to go through it.
> > > 
> > > Here the step I did:
> > > kernel config:
> > >   CONFIG_FUNCTION_TRACER
> > >   CONFIG_FUNCTION_GRAPH_TRACER
> > > 
> > > ftrace:
> > >   # set filters
> > >   echo tpm* > set_ftrace_filter
> > > 
> > >   # set tracer
> > >   echo function_graph > current_tracer
> > > 
> > >   # take the sample
> > >   echo 1 > tracing_on; time modprobe tpm_tis_spi; echo 0 > tracing_on
> > > 
> > > regards,
> > > Vitor Soares
> > 
> > I'm now compiling distro kernel (OpenSUSE) for NUC7 with v6.10 contents.
> > 
> > After I have that setup, I'll develop a perf test either with perf or
> > bpftrace. I'll come back with the possible CONFIG_* that should be in
> > place in your kernel. Might take up until next week as I have some
> > conference stuff to prepare but I try to have stuff ready early next
> > week.
> > 
> > No need to rush with this as long as possible patches go to rc2 or rc3.
> > Let's do a proper analysis instead.
> > 
> > In the meantime you could check if you get perf and/or bpftrace to 
> > your image that use to boot up your device. Preferably both but
> > please inform about this.
> > 
>
> I already have perf running, for the bpftrace I might not be able to help.

The interesting function to look at with/without hmac is probably
tpm2_get_random().

I attached a patch that removes hmac shenigans out of tpm2_get_random()
for the sake of proper comparative testing.

BR, Jarkko