Re: [PATCH v1 1/2] random-bits: Factor out entropy generating function

[Adhemerval Zanella <adhemerval.zanella@linaro.org>]

On 01/04/2022 15:01, Cristian Rodríguez wrote:
> On Thu, Mar 31, 2022 at 8:05 PM Noah Goldstein <goldstein.w.n@gmail.com> wrote:
> 
>> AFAIK our goal is entropy more so than security. For example
>> if this is used to generate jiffies to stagger threads its not a security
>> issue in any sense, it's just not ideal for performance.
> 
> In any case this should be more than fast enough for the other use
> cases of random_bits() .. maybe one new random_bits_fast() function
> foe edge cases where even this is too slow?

I think we are bike-shedding in the same issue OpenBSD guys stumbled 
and which they have solved 10 years ago [1].  Essentially, we need to 
come  up with a internal PRNG interface that can be used internally and
externally, instead of reinventing cleaver ways to use the timer as 
entropy source.

The issue is not really the cypher used, ideally it could be replace if
we find out that it does not fit.  The main issue is to glue together 
all the requirements to have a concise internal interface, taking in
consideration the glibc constrains to work with multiple kernel version
and environments (where we can't assume we have access to a source or
reliable entropy like getrandom syscall).

My plan to rehearse Florian arc4random proposal to have some simpler
to where we might improve upon (a simpler fork detection for kernels
without MADV_WIPEONFORK that just issue a atfork handle, maybe using
ChaCha20 as virtually all other systems do, no per-thread state).

[1] https://www.youtube.com/watch?v=gp_90-3R0pE