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Re: [Qemu-devel] [PATCH 0/7] Provide support for the software TPM emulat

From: Stefan Berger
Subject: Re: [Qemu-devel] [PATCH 0/7] Provide support for the software TPM emulator
Date: Wed, 5 Apr 2017 11:04:07 -0400
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:45.0) Gecko/20100101 Thunderbird/45.4.0

On 04/05/2017 03:09 AM, Amarnath Valluri wrote:

On 03.04.2017 20:07, Daniel P. Berrange wrote:
On Fri, Mar 31, 2017 at 04:10:09PM +0300, Amarnath Valluri wrote:
Briefly, Theses set of patches introduces:
  - new TPM backend driver to support software TPM emulators(swtpm(1)).
- and few supported fixes/enhancements/cleanup to existing tpm backend code.

The similar idea was initiated earliar(2) by Stefan Berger(CCed) with slightly different approach, using CUSE. As swtpm has excellent support for unix domain sockets, hence this implementation uses unix domain sockets to communicate with

When Qemu is configured with 'emulator' tpm backend, it spawns 'swtpm' and
communicates its via Unix domain sockets.
I'm not convinced that having QEMU spawning swtpm itself is a desirable
approach, as it means QEMU needs to have all the privileges that swtpm
will need, so that swtpm can inherit them. At the very least I think we
need to have a way to disable this spawning, so it can connect to a
pre-existing swtpm process that's been spawned ahead of time. This will
let us have stricter privilege separation.
Both spawning inside qemu and connecting to already running swtpm has its own pros, Hence we can make this spawning as backend configuration detail, So it looks like this:

-tpmdev emulator,id=id,tpmstatedir=dir[,spawn=[on|off],data-path=path,ctrl-path=path,logfile=path,loglevel=number]
  Options details:
tpmstatedir - Directory path, which swtpm should use for storing TPM state
     *spawn      - should spawn new process, defaults to 'off'
     *path         - swtpm binary path to spawn, ignored if spawn is off
     *data-path - Socket path to use/connect for data messages
*ctrl-path - Socket path to use/connect for out-of-band control messages

FD passing would work?

     *logfile       - File path to use for swtpm logs
*loglevel - log level number, defaults to 5 (ignored if no logfile provided)

- If spawn is off, data-path and ctrl-path must be provided to qemu, where to connect already running swtpm - If spawn if on, both data-path and ctrl-path are optional. If not provided, qemu uses socket pairs to communicates with swptm, as it is doing now.

Hope this satisfies all usecases, if everyone here happy with this i can submit the new patch with these changes.

- Amarnath

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