Re: [Qemu-devel] [RFC] Virtio RNG: Consider changing the default entropy source to /dev/urandom?

[Richard Henderson]

On 5/7/19 8:22 AM, Daniel P. Berrangé wrote:
> On Tue, May 07, 2019 at 11:59:05AM +0200, Nikos Mavrogiannopoulos wrote:
>> In terms of RHEL what is preferred is (1) use a crypto lib, and (2) if
>> that's not possible use getrandom(). That is summarized in this
>> article:
>>
>> https://www.redhat.com/en/blog/understanding-red-hat-enterprise-linux-random-number-generator-interface
> 
> For QEMU this would mean re-writing the code to use qcrypto_random_bytes
> instead. This internal API is backed by a crypto lib if available,
> falling back to /dev/urandom or /dev/random on UNIX, or CryptGenRandom
> on Windows. We could add getrandom() support there too.

At least this last step is done:

  https://patchwork.ozlabs.org/patch/1056828/


> The main question is whether to implement a new backends/rng-builtin.c
> or modify backends/rng-random.c so that it has a NULL filename by
> default, which would be taken as meaning use the qcrypto_random_bytes
> API.  The latter benefits that all existing VMs which don't have a
> filename set would get the new behaviour. The latter has downside
> that it is not discoverable from mgmt apps, so they won't know if
> they can rely on it or not.
> 
> Thus I'd probably tend towards a new backend for discoverability.

What does it mean to rely on the filename, really?

We could special case "/dev/urandom" as qcrypto_random_bytes, which would end
up using getrandom(2) or /dev/urandom via the crypto lib anyway.

We could even special case "/dev/random" as getrandom(2) w/GRND_RANDOM, if we
cared to bypass the crypto lib.

Only oddballs like "/dev/myhwrng" truly need to go through the filesystem
interface in order to preserve behaviour, I would think.


r~