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

[Jarkko Sakkinen]

On Tue, Jan 03, 2017 at 08:14:55AM -0800, James Bottomley wrote:
> On Tue, 2017-01-03 at 15:41 +0200, Jarkko Sakkinen wrote:
> > 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?
> 
> Agreed.  As I've already said, the space and interface code is working
> well for me in production on my laptop.
> 
> > Just thinking how to split up the non-RFC patch set. This was also 
> > what Jason suggested if I understood his remark correctly.
> 
> SUre ... let's get agreement on how we move forward first.  How the
> patch is activated by the user has to be sorted out as well before it
> can go in, but it doesn't have to be the first thing we do.  I'm happy
> to continue playing with the interfaces to see what works and what
> doesn't.  My main current feedback is that I think separate devices
> works way better than an ioctl becuase the separate devices approach
> allows differing system policies for who accesses the RM backed TPM vs
> who accesses the raw one.

I think I see your point. I would rather name the device as tpms0 but
otherwise I think we could do it in the way you suggest...

> James

/Jarkko