linux-kernel - Re: [PATCH v2 6/7] tpm: expose spaces via a device link /dev/tpms<n>

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Date:   Fri, 24 Feb 2017 08:02:08 -0500
From:   James Bottomley <James.Bottomley@...senPartnership.com>
To:     Jarkko Sakkinen <jarkko.sakkinen@...ux.intel.com>,
        tpmdd-devel@...ts.sourceforge.net
Cc:     linux-security-module@...r.kernel.org, dhowells@...hat.com,
        Peter Huewe <peterhuewe@....de>,
        Marcel Selhorst <tpmdd@...horst.net>,
        Jason Gunthorpe <jgunthorpe@...idianresearch.com>,
        open list <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2 6/7] tpm: expose spaces via a device link /dev/tpms<n>

On Thu, 2017-02-23 at 11:09 +0200, Jarkko Sakkinen wrote:
> On Thu, Feb 16, 2017 at 09:25:19PM +0200, Jarkko Sakkinen wrote:
> > From: James Bottomley <James.Bottomley@...senPartnership.com>
> > 
> > Currently the tpm spaces are not exposed to userspace.  Make this
> > exposure via a separate device, which can now be opened multiple 
> > times because each read/write transaction goes separately via the
> > space.
> > 
> > Concurrency is protected by the chip->tpm_mutex for each read/write
> > transaction separately.  The TPM is cleared of all transient 
> > objects by the time the mutex is dropped, so there should be no
> > interference between the kernel and userspace.
> > Signed-off-by: James Bottomley <
> > 
> > James.Bottomley@...senPartnershp.com>

> Reviewed-by: Jarkko Sakkinen <jarkko.sakkine@...ux.intel.com>
> Tested-by: Jarkko Sakkinen <jarkko.sakkine@...ux.intel.com>

Thanks!

> Nitpicking but I've been thinking about naming. What about calling 
> the device as tpmrc0 as in resource context. I think that would be a
> better name than TPM space.

Well the original name was tpmrm<n> for TPM with Resource Manager.  You
wanted it to be tpms<n> for TPM with Spaces.

I'm not entirely sold on the Resource Context name ... I think Resource Manager (because it's what the TCG calls it) or Spaces (because it's what all the code comments call it) are better.  Resource Context sounds like what TPM2_SaveContext() creates for you rather than the interface.

>  You do not mix it up with namespaces and/or virtualization. With
> resource in front it cannot be easily mixed up with TPM contexts
> either.

I'm a containers person.  What this set of patches does is precisely OS
level virtualization in my book, so I don't think you need to pretend
it is't; and OS level virtualization is what a namespace does.  The
only difference between this and the other kernel namespaces is that
you get a new namespace automatically when you open the device and you
can't enter an existing namespace.

I think therefore that tpmns<n> for TPM Namespace would be very
appropriate.

> This does not require any effort from your side. I could do the
> renaming.
>
> PS. Could you go through my commits and test and review them at some
> point so we would have the whole patch set peer tested?

Already reviewed, just doing a test build (I'm travelling, so it
actually has to be on my physical laptop).

James