Re: [PATCH v2 5/9] random: do not xor RDRAND when writing into /dev/random

Dominik Brodowski
2022-02-09T12:08:27Z

Am Wed, Feb 09, 2022 at 02:19:15AM +0100 schrieb Jason A. Donenfeld:
> Continuing the reasoning of "random: ensure early RDSEED goes through
> mixer on init", we don't want RDRAND interacting with anything without
> going through the mixer function, as a backdoored CPU could presumably
> cancel out data during an xor, which it'd have a harder time doing when
> being forced through a cryptographic hash function. There's actually no
> need at all to be calling RDRAND in write_pool(), because before we
> extract from the pool, we always do so with 32 bytes of RDSEED hashed in
> at that stage. Xoring at this stage is needless and introduces a minor
> liability.

Looks good generally, just one unrelated change slipped in:

> bytes = min(count, sizeof(buf));
> - if (copy_from_user(&buf, p, bytes))
> + if (copy_from_user(buf, p, bytes))
> return -EFAULT;

Otherwise:

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

Thanks,
Dominik