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

[Jarkko Sakkinen <jarkko.sakkinen@linux.intel.com>]

On Mon, Jan 02, 2017 at 01:40:48PM -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.

Not only that.

Doing virtualization for commands like GetCapability is just a better
fit for doing in the user space. You could have a thin translation layer
in your TSS library for example to handle these specific messages.

> 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.

I'm not sure about this. Why you couldn't have a very thin daemon that
prepares the file descriptor and sends it through UDS socket to a
client.  The non-RFC version will also have whitelisting ioctl for
further restricting the file descriptor to only specific TPM commands.

This is also architecture I preseted in my LSS presentation and I think
it makes sense especially when I add the whitelisting to the pack.

> James

I'm more dilated to keep things way they are now. I'll stick to that at
least with the first non-RFC version and hopefully get the tpm2-space.c
part reviewed as I split that stuff to a separate commit.

/Jarkko