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

[Jarkko Sakkinen]

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