linux-kernel - Re: [PATCH 1/5] tpm: add functions to set and unset the tpm chips reset state

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Date:   Thu, 14 Apr 2022 15:13:20 +0300
From:   Jarkko Sakkinen <jarkko@...nel.org>
To:     Jason Gunthorpe <jgg@...pe.ca>
Cc:     Lukas Wunner <lukas@...ner.de>,
        Lino Sanfilippo <LinoSanfilippo@....de>, peterhuewe@....de,
        devicetree@...r.kernel.org, linux-integrity@...r.kernel.org,
        linux-kernel@...r.kernel.org, stefanb@...ux.ibm.com,
        p.rosenberger@...bus.com
Subject: Re: [PATCH 1/5] tpm: add functions to set and unset the tpm chips
 reset state

On Mon, Apr 11, 2022 at 08:47:41AM -0300, Jason Gunthorpe wrote:
> On Sun, Apr 10, 2022 at 07:11:23PM +0200, Lukas Wunner wrote:
> > On Thu, Apr 07, 2022 at 11:25:26AM -0300, Jason Gunthorpe wrote:
> > > On Thu, Apr 07, 2022 at 01:18:45PM +0200, Lino Sanfilippo wrote:
> > > > Currently it is not possible to set the tpm chips reset state from within
> > > > the driver. This is problematic if the chip is still in reset after the
> > > > system comes up. This may e.g. happen if the reset line is pulled into
> > > > reset state by a pin configuration in the device tree.
> > > 
> > > This kind of system is badly misdesigned.
> > > 
> > > TPM PCRs fundementally cannot work if the TPM reset line is under
> > > software control.
> > 
> > Not every system which incorporates a TPM wants to use or is even capable
> > of measuring software state of any kind or perform secure boot.
> > 
> > Those systems may merely want to use the TPM to store key material.
> 
> Then maybe the TPM driver should make it clear somehow that the PCRs
> don't work in these systems.
> 
> It is really dangerous to add capabilities like this that should
> never, ever be used in sanely designed systems.
> 
> Jason

I agree. That niche should do the bad things with oot patches.

BR, Jarkko