linux-kernel - Re: [tpmdd-devel] [PATCH RFC 0/4] RFC: in-kernel resource manager

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Date:   Wed, 4 Jan 2017 12:24:23 -0700
From:   Jason Gunthorpe <jgunthorpe@...idianresearch.com>
To:     James Bottomley <James.Bottomley@...senPartnership.com>
Cc:     linux-security-module@...r.kernel.org,
        tpmdd-devel@...ts.sourceforge.net,
        Andy Lutomirski <luto@...nel.org>,
        open list <linux-kernel@...r.kernel.org>
Subject: Re: [tpmdd-devel] [PATCH RFC 0/4] RFC: in-kernel resource manager

On Wed, Jan 04, 2017 at 10:57:51AM -0800, James Bottomley wrote:

> > You are doing all this work to get the user space side in shape, I'd
> > like to see matching kernel support. To me that means out-of-the-box
> > a user can just use your plugins, the plugins will access /dev/tmps
> > and everything will work fine for RSA key storage.
> 
> Actually, not necessarily; you're not considering the setup issue:
> right at the moment users get delivered TPMs mostly in the cleared

I have no problem with users being instructed to do 'sudo
tpm2-provision' or having that happen via GUI using the usual
privilege escalation techniques.

> state (thankfully they no longer have to clear via bios).  So the first
> thing a new user has to do is set all the authorizations and create an
> SRK equivalent primary object at 0x81000001.  I think in the interests
> of best practice we want to make that as easy as possible; saying they
> have to do this as root and use a different device is problematic.

The device names should never be exposed to the user. The user should
specify a chip number (default to 0) and the tools should select the
correct available device to do what the user is asking.

First try /dev/tpms and elevate filter, then try /dev/tpmX, then fail.

> You can say they don't have to use a different device because the
> filter can be lifted for root, but then how do I lock down root apps
> for this untrusted root setup secure boot has going on?

Presumably the same way you lock down /dev/tpm0 today?

selinux I guess?

> I suppose we could use TPMA_PERMANENT for this. The first three bits
> indicate whether the authorizations are set, so if they're all clear,
> we can assume an unowned TPM and lift the filter?  A sort of trust on
> first use model.

I feel tpm provisioning is something that should only be done by the
system owner, and that means root in unix parlance.

I don't want random end-users provisioning the TPM in my server, for
instance.

Jason