Re: kaslr: better rng

[Taylor R Campbell <campbell+netbsd-tech-kern%mumble.net@localhost>]

> Date: Mon, 6 Nov 2017 19:04:44 +0100
> From: Maxime Villard <max%m00nbsd.net@localhost>
> 
> Well, we could indeed extend /var/db/entropy-file. However, I would really
> prefer the random area to be generated from a previous run of the system, and
> not from the bootloader taking a seed in the file. Unless there is a
> combination of both?

The entropy file is supposed to be rewritten each time it's read, and
on shutdown, or something like that.

> Note that such a PRNG would also have to be implemented in the prekern and
> in the kernel, and we would need three independent seeds.

keccak.o appears to be 3000 bytes long, and can be quickly adapted to
squeeze three seeds out after absorbing one with the magic of modern
cryptography.