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

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Date:   Fri, 24 Feb 2017 16:23:27 -0700
From:   Jason Gunthorpe <jgunthorpe@...idianresearch.com>
To:     James Bottomley <James.Bottomley@...senPartnership.com>
Cc:     open list <linux-kernel@...r.kernel.org>, dhowells@...hat.com,
        linux-security-module@...r.kernel.org,
        tpmdd-devel@...ts.sourceforge.net
Subject: Re: [tpmdd-devel] [PATCH v2 6/7] tpm: expose spaces via a device
 link /dev/tpms<n>

On Fri, Feb 24, 2017 at 06:01:00PM -0500, James Bottomley wrote:

> Well, as a glib answer, I'd say the TPM is a device, so the thing which
> restricts device access to containers is the device cgroup ... that's
> what we should be plugging into.  I'd have to look, but I suspect the
> device cgroup basically operates on device node appearance, so it
> should "just work"(tm).  I can explore when I'm back home.

Seems reasonable..

It just seems confusing to call something a namespace that isn't also
a CLONE_NEW* option..

FWIW more background on the topic:

Stefan was concerned about information leakage via sysfs of TPM data,
eg that a container could still touch the host's TPM. I wonder if
device cgroup could be extended to block access to the sysfs
directories containing a disallowed 'dev' ?

I was also wondering about kernel use from within the container -
all kernel consumers are locked to physical tpm0.. But maybe the
kernel can consult the right device cgroup to find an allowed TPM?

Jason