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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: Tue, 4 Apr 2017 08:08:47 -0400
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:45.0) Gecko/20100101 Thunderbird/45.4.0

On 04/03/2017 01:07 PM, 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.
I had implemented it like that. For this I have a libvirt driver that starts swtpm, sets up cgroups for swtpm (e.g., CPU consumption limits), and drops unnecessary Linux capabilities...


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