linux-kernel - Re: [PATCH 3/3] tpm: ibmvtpm: Add support for TPM 2

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Date:   Thu, 13 Feb 2020 15:50:26 -0400
From:   Jason Gunthorpe <jgg@...pe.ca>
To:     Stefan Berger <stefanb@...ux.ibm.com>
Cc:     Nayna <nayna@...ux.vnet.ibm.com>,
        Stefan Berger <stefanb@...ux.vnet.ibm.com>,
        linux-integrity@...r.kernel.org, aik@...abs.ru,
        david@...son.dropbear.id.au, linux-kernel@...r.kernel.org,
        gcwilson@...ux.ibm.com
Subject: Re: [PATCH 3/3] tpm: ibmvtpm: Add support for TPM 2

On Thu, Feb 13, 2020 at 02:45:49PM -0500, Stefan Berger wrote:
> > Any driver that knows the TPM must be started prior to Linux
> > booting should not use the flag.  vtpm drivers in general would seem
> > to be the case where we can make this statement.
> 
> Wouldn't this statement apply to all systems, including embedded ones? 
> Basically all firmwares should implement the CRTM and do the TPM
> initialization.

It is not mandatory that systems with TPMs start it in the
firmware. That is only required if the TPM PCR feature is going to be
used. A TPM can quite happily be used for key storage without FW
support.

Arguably this is sort of done wrong. eg if the platform has provided
TPM information through uEFI or something then we shouldn't try to
auto start the system TPM. At least for TPM1 detecting a non-started
TPM was harmless, so nobody really cared. I wonder if TPM2 is much
different..

But certainly auto startup should *not* be required to have a working
TPM driver, that is just fundamentally wrong.

Jason