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

From: Jarkko Sakkinen
Date: Tue Jan 03 2017 - 08:42:45 EST


On Mon, Jan 02, 2017 at 09:26:58PM -0800, James Bottomley wrote:
> On Mon, 2017-01-02 at 13:40 -0800, James Bottomley wrote:
> > On Mon, 2017-01-02 at 21:33 +0200, Jarkko Sakkinen wrote:
> > > On Mon, Jan 02, 2017 at 08:36:20AM -0800, James Bottomley wrote:
> > > > On Mon, 2017-01-02 at 15:22 +0200, Jarkko Sakkinen wrote:
> > > > > This patch set adds support for TPM spaces that provide a
> > > > > context for isolating and swapping transient objects. This
> > > > > patch set does not yet include support for isolating policy and
> > > > > HMAC sessions but it is trivial to add once the basic approach
> > > > > is settled (and that's why I created an RFC patch set).
> > > >
> > > > The approach looks fine to me. The only basic query I have is
> > > > about the default: shouldn't it be with resource manager on
> > > > rather than off? I can't really think of a use case that wants
> > > > the RM off (even if you're running your own, having another
> > > > doesn't hurt anything, and it's still required to share with in
> > > > -kernel uses).
> > >
> > > This is a valid question and here's a longish explanation.
> > >
> > > In TPM2_GetCapability and maybe couple of other commands you can
> > > get handles in the response body. I do not want to have special
> > > cases in the kernel for response bodies because there is no a
> > > generic way to do the substitution. What's worse, new commands in
> > > the standard future revisions could have such commands requiring
> > > special cases. In addition, vendor specific commans could have
> > > handles in the response bodies.
> >
> > OK, in general I buy this ... what you're effectively saying is that
> > we need a non-RM interface for certain management type commands.
> >
> > However, let me expand a bit on why I'm fretting about the non-RM use
> > case. Right at the moment, we have a single TPM device which you use
> > for access to the kernel TPM. The current tss2 just makes direct use
> > of this, meaning it has to have 0666 permissions. This means that
> > any local user can simply DoS the TPM by running us out of transient
> > resources if they don't activate the RM. If they get a connection
> > always via the RM, this isn't a worry. Perhaps the best way of
> > fixing this is to expose two separate device nodes: one raw to the
> > TPM which we could keep at 0600 and one with an always RM connection
> > which we can set to 0666. That would mean that access to the non-RM
> > connection is either root only or governed by a system set ACL.
>
> OK, so I put a patch together that does this (see below). It all works
> nicely (with a udev script that sets the resource manager device to
> 0666):

This is not yet a comment about this suggestion but I guess one thing
is clear: the stuff in tpm2-space.c and tpm-interface.c changes are the
thing that we can mostly agree on and the area of argumentation is the
user space interface to it?

Just thinking how to split up the non-RFC patch set. This was also what
Jason suggested if I understood his remark correctly.

/Jarkko