linux-kernel - Re: [PATCH] tpm: Start the tpm2 before running a self test.

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Message-ID: <20240715173905.GA81987@francesco-nb>
Date: Mon, 15 Jul 2024 19:39:05 +0200
From: Francesco Dolcini <francesco@...cini.it>
To: Jarkko Sakkinen <jarkko@...nel.org>
Cc: Hermin Anggawijaya <hermin.anggawijaya@...iedtelesis.co.nz>,
	peterhuewe@....de, jgg@...pe.ca, linux-integrity@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] tpm: Start the tpm2 before running a self test.

Hello Jarkko and all,
resurrecting this old thread for a question ...

On Fri, Nov 24, 2023 at 03:42:29AM +0200, Jarkko Sakkinen wrote:
> On Wed Nov 22, 2023 at 8:55 AM EET, Hermin Anggawijaya wrote:
> > Before sending a command to attempt the self test, the TPM
> > may need to be started, otherwise the self test returns
> > TPM2_RC_INITIALIZE value causing a log as follows:
> > "tpm tpm0: A TPM error (256) occurred attempting the self test".
> >
> > Signed-off-by: Hermin Anggawijaya <hermin.anggawijaya@...iedtelesis.co.nz>
> 
> Firmware does TPM power on.

Do you have any explanation on why this is required? Any kind of pointer
to documentation is welcome.

What I am looking for is to understand what are the major limitations if
the firmware is not doing it.

I understand that you cannot use any functionality that requires the TPM
to be enabled at boot, for example "Measured Boot". Is there anything
else that is prevented if the firmware is not enabling it?

Thanks,
Francesco