Re: [Qemu-devel] [PATCH 0/4] tpm: Provide a software vTPM

[Corey Bryant]

On 11/19/2013 02:50 PM, Anthony Liguori wrote:
> On Wed, Nov 6, 2013 at 6:38 AM, Corey Bryant <address@hidden> wrote:
> > This patch series provides support for a software Trusted Platform
> > Module (otherwise known as a vTPM).  This support is provided via a
> > new backend that works with the existing QEMU tpm-tis front end.
>
> We do device emulation within QEMU.  This is fundamentally what QEMU does.
>
> Why should we link against an external library instead of providing
> TPM emulation within QEMU itself?  What makes TPM so special here?

Because 70k+ LOC *definitely* doesn't have a chance of getting into 
QEMU, so it makes more sense to link against a library.

> I know the answer to these questions of course.  There isn't a good
> reason but there exists vTPM as an external tool for historical
> reasons.  I don't think that's a good justification for doing this.
> libtpms has had no review by anyone and does not have a community
> around it.  Once we link against it, we are responsible for resolving

The source is now more readily available on github and while the 
community is small, there is a community.  Besides, QEMU uses other 
libraries that have very small communities doesn't it?

> any security issue around it and fixing any bug within it.

Is this really true?  Is QEMU responsible for fixing every bug in glibc?

--
Regards,
Corey Bryant

> That's essentially asking us to merge 70k+ LOCS without any review or
> validation ahead of time.  That's an unreasonable request.
>
> Regards,
>
> Anthony Liguori
>
> > With this patch series, multiple guests can run with their own vTPM.
> > In comparison, the existing passthrough vTPM does not allow this
> > because the host TPM cannot be shared.
> >
> > Note: There is seabios code that is not yet upstream that is
> > required to run with this support.  It provides support such as
> > initialization, ACPI table updates, and menu updates.  If anyone
> > would like to run with that support, let me know and I can send you
> > a bios.bin.
> >
> > Following is a sample command line:
> >
> > qemu-img create -f qcow2 /home/qemu/images/nvram.qcow2 500K
> >
> > qemu-system-x86_64 ... \
> > -drive file=/home/qemu/images/nvram.qcow2,if=none,id=nvram0-0-0,format=qcow2 \
> > -device tpm-tis,tpmdev=tpm-tpm0,id=tpm0 \
> > -tpmdev libtpms,id=tpm-tpm0,nvram=nvram0-0-0
> >
> > Corey Bryant (4):
> >    tpm: Add TPM NVRAM implementation
> >    tpm: Share tpm_write_fatal_error_response
> >    tpm: QMP/HMP support for libtpms TPM backend
> >    tpm: Provide libtpms software TPM backend
> >
> >   configure                    |   24 ++
> >   hmp.c                        |    5 +
> >   hw/tpm/Makefile.objs         |    2 +
> >   hw/tpm/tpm_libtpms.c         |  885 ++++++++++++++++++++++++++++++++++++++++++
> >   hw/tpm/tpm_nvram.c           |  340 ++++++++++++++++
> >   hw/tpm/tpm_nvram.h           |   25 ++
> >   hw/tpm/tpm_passthrough.c     |   14 -
> >   hw/tpm/tpm_tis.h             |    1 +
> >   include/sysemu/tpm_backend.h |    3 +
> >   qapi-schema.json             |   18 +-
> >   qemu-options.hx              |   31 ++-
> >   tpm.c                        |   28 ++-
> >   12 files changed, 1357 insertions(+), 19 deletions(-)
> >   create mode 100644 hw/tpm/tpm_libtpms.c
> >   create mode 100644 hw/tpm/tpm_nvram.c
> >   create mode 100644 hw/tpm/tpm_nvram.h