linux-kernel - Re: Large post detailing recent Linux RNG improvements

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Date:   Thu, 24 Mar 2022 14:51:45 +0800
From:   Sandy Harris <sandyinchina@...il.com>
To:     "Jason A. Donenfeld" <Jason@...c4.com>
Cc:     LKML <linux-kernel@...r.kernel.org>,
        Kernel Hardening <kernel-hardening@...ts.openwall.com>,
        "Theodore Ts'o" <tytso@....edu>
Subject: Re: Large post detailing recent Linux RNG improvements

Jason A. Donenfeld <Jason@...c4.com> wrote:

> Thought I should mention here that I've written up the various RNG
> things I've been working on for 5.17 & 5.18 here:
> https://www.zx2c4.com/projects/linux-rng-5.17-5.18/ .
>
> Feel free to discuss on list here if you'd like, or if you see
> something you don't like, I'll happily review patches!

Your code includes:

enum {
    POOL_BITS = BLAKE2S_HASH_SIZE * 8,
    POOL_MIN_BITS = POOL_BITS /* No point in settling for less. */
};

static struct {
    struct blake2s_state hash;
    spinlock_t lock;
    unsigned int entropy_count;
} input_pool = {
    .hash.h = { BLAKE2S_IV0 ^ (0x01010000 | BLAKE2S_HASH_SIZE),
            BLAKE2S_IV1, BLAKE2S_IV2, BLAKE2S_IV3, BLAKE2S_IV4,
            BLAKE2S_IV5, BLAKE2S_IV6, BLAKE2S_IV7 },
    .hash.outlen = BLAKE2S_HASH_SIZE,
    .lock = __SPIN_LOCK_UNLOCKED(input_pool.lock),
};

As far as I can tell, you have eliminated the 4K-bit input pool
that this driver has always used & are just using the hash
context as the input pool. To me, this looks like an error.

A side effect of that is losing the latent-entropy attribute
on input_pool[] so we no longer get initialisation from
the plugin. Another error.