linux-kernel - Re: [tpmdd-devel] [PATCH 09/13] tpm: Pull everything related to sysfs into tpm-sysfs.c

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Message-ID: <20130923204232.GB16345@obsidianresearch.com>
Date:	Mon, 23 Sep 2013 14:42:32 -0600
From:	Jason Gunthorpe <jgunthorpe@...idianresearch.com>
To:	Daniel De Graaf <dgdegra@...ho.nsa.gov>
Cc:	tpmdd-devel@...ts.sourceforge.net,
	Leonidas Da Silva Barbosa <leosilva@...ux.vnet.ibm.com>,
	linux-kernel@...r.kernel.org, Rajiv Andrade <mail@...jiv.net>,
	Sirrix AG <tpmdd@...rix.com>
Subject: Re: [tpmdd-devel] [PATCH 09/13] tpm: Pull everything related to
 sysfs into tpm-sysfs.c

On Mon, Sep 23, 2013 at 04:20:51PM -0400, Daniel De Graaf wrote:

> That's fine; it wasn't really advertised in the description, and was
> mostly added in order to demonstrate the locality security label binding
> in Xen's vtpm-stubdom.

Ok, lets take it out for now then? I'll send a patch.

> >It looks like this driver was introduced in the 3.12 merge window, we
> >could drop the attribute, and try to merge a core supported locality
> >API in 3.13? What do you think?
> >
> >But, if you say it is needed, it is easy enough to adjust this patch
> >series.

> If it's replaced with an alternative, I don't think the sysfs attribute
> will need to remain.  I am not aware of any clients that currently use
> this attribute.  The sysfs attribute could remain as the common interface
> for changing locality, unless you think an ioctl on /dev/tpm0 or
> something else would be preferable (the attribute was just the simplest
> way to implement locality switching at the time).

Off the very top of my head:

I suspect that a good API would be a sysfs attribute
'default_locality' and an IOCTL to change localities.  The
default_locality would only take effect when the /dev/tpmX is opened,
so fiddling with sysfs doesn't break active users.

The struct ops I've added would have a function to change localities,
some of the generic TPM functions should be revised to have a locality
argument.

Some thought is needed to determine what locality in-kernel users
should be using. I suspect userspace and kernel space should not be
forced to the same locality.

Should user space be restricted to a subset of localities?

What use models do you see with the security label binding mechanism
you have on the hypervisor side?

Jason
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