Re: [Qemu-devel] [PATCH v4 0/4] Extend TPM support with a QEMU-external TPM

[Michael S. Tsirkin]

On Tue, Jun 23, 2015 at 08:07:16AM -0400, Stefan Berger wrote:
> "Michael S. Tsirkin" <address@hidden> wrote on 06/23/2015 01:26:13 AM:
> 
> > From: "Michael S. Tsirkin" <address@hidden>
> > To: Stefan Berger <address@hidden>
> > Cc: address@hidden, address@hidden, Stefan Berger/Watson/address@hidden
> > Date: 06/23/2015 01:26 AM
> > Subject: Re: [PATCH v4 0/4] Extend TPM support with a QEMU-external TPM
> >
> > On Mon, Jun 08, 2015 at 07:17:33AM -0400, Stefan Berger wrote:
> > > The following series of patches extends TPM support with an
> > > external TPM that offers a Linux CUSE (character device in userspace)
> > > interface. This TPM lets each VM access its own private vTPM.
> > > The CUSE TPM supports suspend/resume and migration. Much
> > > out-of-band functionality necessary to control the CUSE TPM is
> > > implemented using ioctls.
> >
> > I was hoping this can get a wider discussion, but apparently no one
> > noticed this.
> >
> > This needs some thought: how do we decide which ioctls we support?
> 
> The ioctls the patches are currently using support all necessary aspects for
> controlling that
> external TPM following interaction with the TPM TIS emulation (tpm_tis.c) and
> virtual machine migration. [Excluding support for DRTM]
> 
> There's an ioctl that returns a bitfield of supported features. The patches 
> use
> the ioctl
> to determine whether enough features are supported to for example support
> migration.
> A supported feature then means supporting its corresponding ioctl and
> associated data structure.
> 
> > It's easier with kernel since we know distros ship it, but
> > will they do so with this tpm? We do want to reuse system components
> 
> I haven't packaged the swtpm for Fedora (for example) yet. I wanted to delay
> the tagging of version 0.1
> of swtpm until the code that's using it is in QEMU.
> 

Yes, and it's a bit of a chicken and egg problem.
Aren't there other uses besides QEMU?

> > but we don't want random parts of QEMU delegated to a random
> > out of tree module.
> 
> It's hopefully not that random. There's nothing comparable out there. Just
> having the TPM passthrough
> isn't useful. Usefulness comes with the CUSE TPM driver and external CUSE TPM,
> since this provides a
> private and fully functional TPM to each QEMU VM.
> 
> >
> > Couldn't you re-use in-kernel interfaces for the CUSE module?
> 
> The CUSE TPM uses the ioctl's for out-of-band control. The out-of-band control
> happens on a different
> level than what is out there in the kernel right now, since we are 
> implementing
> a layer that is
> typically implemented in hardware. Otherwise I am not sure what re-use of
> in-kernel interfaces you
> are referring to.
> 

I don't really know :( I was just trying to help. If you could reuse
an existing interface that is already supported by some system,
it would be easier.

> > Then existing pass-through in QEMU would more or less just work with it -
> > merely open a different chardev.
> 
> Having implemented 10+ ioctls for out-of-band control shows a necessity for
> out-of-band control.
> It is not enough to support a read()/write() interface where we can send TPM
> request through.
> 
>    Stefan

It was just a thought. I was looking for an interface that's useful
outside VM.

> >
> >
> > > Stefan Berger (4):
> > >   Provide support for the CUSE TPM
> > >   Introduce condition to notify waiters of completed command
> > >   Introduce condition in TPM backend for notification
> > >   Add support for VM suspend/resume for TPM TIS
> > >
> > >  hmp.c                        |   6 +
> > >  hw/tpm/tpm_int.h             |   4 +
> > >  hw/tpm/tpm_ioctl.h           | 209 ++++++++++++++++++++++
> > >  hw/tpm/tpm_passthrough.c     | 409 ++++++++++++++++++++++++++++++
> > +++++++++++--
> > >  hw/tpm/tpm_tis.c             | 151 +++++++++++++++-
> > >  hw/tpm/tpm_tis.h             |   2 +
> > >  hw/tpm/tpm_util.c            | 223 +++++++++++++++++++++++
> > >  hw/tpm/tpm_util.h            |   7 +
> > >  include/sysemu/tpm_backend.h |  12 ++
> > >  qapi-schema.json             |  18 +-
> > >  qemu-options.hx              |  21 ++-
> > >  qmp-commands.hx              |   2 +-
> > >  tpm.c                        |  11 +-
> > >  13 files changed, 1056 insertions(+), 19 deletions(-)
> > >  create mode 100644 hw/tpm/tpm_ioctl.h
> > >
> > > --
> > > 1.9.3
> >