Re: kaslr: better rng

[Maxime Villard <max%m00nbsd.net@localhost>]

Le 06/11/2017 à 18:28, Thor Lancelot Simon a écrit :
> On Mon, Nov 06, 2017 at 07:30:35AM +0100, Maxime Villard wrote:
> > I'm in a point where I need to have a better rng before continuing - and an
> > rng that can be used in the bootloader, in the prekern and in the kernel
> > (early).
> >
> > I would like to use a system similar to the /var/db/entropy-file implementation.
> > That is to say, when running the system generates /var/db/random-file, which
> > would contain at least 256bytes of random data. When booting the bootloader
> > reads this file, can use some of its bytes to get random values. It then gives
> > the file to the prekern which will use some other parts of it. The prekern
> > finally gives the file to the kernel which can use the rest.
>
> What is the reason for using only part of the file, in any application?

I meant to say that the components don't take random values from the same
area in the file, for them not to use the same random numbers twice.

For example, if the bootloader consumes the first four uint64_t of the file,
the prekern will virtually do an "lseek(4*sizeof(uint64_t))" and use the rest
of the file as a random pool. Same for the kernel, which will lseek over the
area consumed by the prekern.