linux-kernel - Re: [PATCH RFC 4/4] tpm: add the infrastructure for TPM space for TPM 2.0

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Date:   Wed, 4 Jan 2017 14:45:13 +0200
From:   Jarkko Sakkinen <jarkko.sakkinen@...ux.intel.com>
To:     Jason Gunthorpe <jgunthorpe@...idianresearch.com>
Cc:     tpmdd-devel@...ts.sourceforge.net,
        linux-security-module@...r.kernel.org,
        Peter Huewe <peterhuewe@....de>,
        Marcel Selhorst <tpmdd@...horst.net>,
        open list <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH RFC 4/4] tpm: add the infrastructure for TPM space for
 TPM 2.0

On Tue, Jan 03, 2017 at 12:16:34PM -0700, Jason Gunthorpe wrote:
> On Tue, Jan 03, 2017 at 02:37:30AM +0200, Jarkko Sakkinen wrote:
> > On Mon, Jan 02, 2017 at 02:09:53PM -0700, Jason Gunthorpe wrote:
> > > On Mon, Jan 02, 2017 at 03:22:10PM +0200, Jarkko Sakkinen wrote:
> > > > Added a ioctl for creating a TPM space. The space is isolated from the
> > > > other users of the TPM. Only a process holding the file with the handle
> > > > can access the objects and only objects that are created through that
> > > > file handle can be accessed.
> > > 
> > > I don't understand this comment. /dev/tpmX is forced to be
> > > single-process-open, so how can there ever be more than 1 FD for it?
> > > 
> > > Since the space is tied to that single fd these patches just create a
> > > way for the single user-space process to auto-cleanup if it crashes?
> > > 
> > > Is that the entire intent of this design? I guess it is OK as a
> > > stepping point..
> > 
> > is_open is cleared in tpm_ioc_new_space.
> 
> There is also a bug with the uncondtional clear of is_open in
> tpm_release - this cannot happen if the ioctl is done - but I think
> this approach of using an ioctl is not a good idea.
> 
> I have pondered using an open flag in the past - what about using
> something like O_EXCL to indicate that the fd is to be used in
> resource sharing mode? Not sure if that would be considered abuse of
> the open flags or not.

I've now leaned toward James' idea of having a separate /dev/tpms0.

> Jason

/Jarkko