[0/2] prandom: add crypto warnings and switch to new PRNG

Message

Markus Theil Feb. 14, 2025, 8:18 a.m. UTC

This series builds on top of the series:
	"prandom: remove next_pseudo_random32."

With the current cryptographically safe PRNG in drivers/char/random.c
fast enough for most purposes, make annoyingly clear, that no one should
use the prandom PRNG for cryptographic purposes without known about
this.

While looking at the prandom/random32 code, I informed myself about
PRNGs and saw that currently fast PRNGs with better statistical
properties than LFSR113, which is currently used, are available.

Recent alternatives to consider are in my opinion:
* PCG: https://www.pcg-random.org
* Xoshiro: https://prng.di.unimi.it

While both seem to have good statistical properties, I recommend
to chose Xoshiro256++ here, because it seems to be even faster than
RNGs from the PCG series.

Furthermore, the authors of Xoshiro provide a small RNG named SplitMix64
for generating high quality seeds for the Xoshiro RNG. By using this in
the default way, no further seed checks or state warmup are necessary.
This simplifies the PRNG code IMHO.

Markus Theil (2):
  prandom: add usage comments for cryptography
  prandom/random32: switch to Xoshiro256++

 include/linux/prandom.h |  30 +---
 lib/random32.c          | 351 ++++++++++++++++++++--------------------
 2 files changed, 180 insertions(+), 201 deletions(-)