Re: [PATCH v6 0/5] /dev/random - a new approach

Am Dienstag, 16. August 2016, 15:28:45 CEST schrieb H. Peter Anvin:

Hi Peter,

quoted

There are two motivations for that:

- the current /dev/random is compliant to NTG.1 from AIS 20/31 which
requires (in brief words) that entropy comes from auditible noise
sources. Currently in my LRNG only RDRAND is a fast noise source which is
not auditible (and it is designed to cause a VM exit making it even
harder to assess it). To make the LRNG to comply with NTG.1, RDRAND can
provide entropy but must not become the sole entropy provider which is
the case now with that change.

- the current /dev/random implementation follows the same concept with the
exception of 3.15 and 3.16 where RDRAND was not rate-limited. In later
versions, this was changed.

I'm not saying it should be *sole*.  I am questioning the value in
limiting it, as it seems to me that it could only ever produce a worse
result.

It is not about the limiting of the data. It is all about the entropy estimate 
for those noise sources and how they affect the entropy estimator behind /dev/
random. If that fast noise source injects large amount of data but does not 
increase the entropy estimator, it is of no concern.

Ciao
Stephan