Re: TPM 2.0 Linux sysfs interface

[Mimi Zohar <zohar@linux.ibm.com>]

On Mon, 2019-08-26 at 22:05 -0300, Jason Gunthorpe wrote:
> The sysfs is not done, fundamentally, because the sysfs structure of
> the existing TPM1 stuff is grandfathered in, and doing anything like
> it for TPM2 is a complete NAK for not following the normal sysfs
> interface design rules, particularly of one value per file. This is a
> big part of why it was dropped for TPM2.

The original TPM 2.0 support was missing a lot of TPM 1.2
functionality, including exporting the TPM event log.  So it wasn't
clear that leaving out the sysfs support was intentional or simply a
question of someone needing to implement it.

> 
> So exposing PCRs and things through sysfs is not going to happen.
> 
> If you had some very narrowly defined things like version, then
> *maybe* but I think a well defined use case is needed for why this
> needs to be sysfs and can't be done in C as Jarkko explained.

Piotr's request for a sysfs file to differentiate between TPM 1.2 and
TPM 2.0 is a reasonable request and probably could be implemented on
TPM registration.

If exposing the PCRs through sysfs is not acceptable, then perhaps
suggest an alternative.

Mimi
> 
> A good reason would be something like needing to trigger a systemd
> unit from udev.
> 
> Jason