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Bug#736126: Please install haveged on physical machines

Hi Holger,

On Thu, May 24, 2018 at 09:06:27AM +0000, Holger Levsen wrote:
> > > Do we have a reasonablish way of telling whether a system is “real”
> > > hardware or a virtual machine, and choose whether to install haveged or not
> > > accordingly?
> why only install it on physical machines? IME haveged is useful on real
> *and* virtual machines.

Regardless of the platform, haveged will put data into random(4) and use
the appropriate ioctl to increase the entropy counter, which is useful in
that it prevents random(4) from “running out” of entropy. [0]

On virtual machines, however, the data that the HAVEGE algorithm produces
is not necessarily unpredictable [1]; hence, we shouldn't install haveged
on those environments.

Moreover, on virtual machines, the host virtualization system should provide
entropy to its guests, for instance through virtio-rng (which can be picked
up with rngd).

TL;DR: On VMs, haveged might be unsafe, depending on the virtualization
       environment's configuration, and we (d-i/tasksel) do not have enough
       information available to make that call.



[0]: Gods, this is painful to write. There is no reason for random(4) to
     ever “run out” of entropy once initialized, but for some
     misconceptions about cryptography; however, this is the implemented
     behaviour and we kinda have to live with it for now.

[1]: https://tls.mbed.org/tech-updates/security-advisories/polarssl-security-advisory-2011-02
     is an example of the same algorithm failing on VMs.

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