Re: [PATCH v2 4/9] random: ensure early RDSEED goes through mixer on init

From: Dominik Brodowski <linux@dominikbrodowski.net>
To: "Jason A. Donenfeld" <Jason@zx2c4.com>
Cc: linux-crypto@vger.kernel.org, linux-kernel@vger.kernel.org,
	tytso@mit.edu, ebiggers@kernel.org,
	Eric Biggers <ebiggers@google.com>
Subject: Re: [PATCH v2 4/9] random: ensure early RDSEED goes through mixer on init
Date: Wed, 9 Feb 2022 09:23:09 +0100	[thread overview]
Message-ID: <YgN57QP5xH9ebrH/@owl.dominikbrodowski.net> (raw)
In-Reply-To: <20220209011919.493762-5-Jason@zx2c4.com>

Am Wed, Feb 09, 2022 at 02:19:14AM +0100 schrieb Jason A. Donenfeld:
> Continuing the reasoning of "random: use RDSEED instead of RDRAND in
> entropy extraction" from this series, at init time we also don't want to
> be xoring RDSEED directly into the crng. Instead it's safer to put it
> into our entropy collector and then re-extract it, so that it goes
> through a hash function with preimage resistance.

Any reason why you re-order

> +	mix_pool_bytes(utsname(), sizeof(*(utsname())));
>  	mix_pool_bytes(&now, sizeof(now));

? It shouldn't matter, but it's an additional change I see no rationale for.

Also, AFAICS, we now only call rdseed 8 times (to mix into the input pool
directly and to update the primary pool indirectly) instead of 8 times (for
the input pool) and 12 times (for initializing the primary pool). That's
still 64 bytes, and we use that to seed 48 bytes, we're still on the safe
side. So feel free to add my

	Reviewed-by: Dominik Brodowski <linux@dominikbrodowski.net>

Thanks,
	Dominik