linux-kernel - Re: [PATCH v2] random: use SipHash as interrupt entropy accumulator

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Date:   Sat, 12 Mar 2022 17:24:40 -0700
From:   "Jason A. Donenfeld" <Jason@...c4.com>
To:     Eric Biggers <ebiggers@...nel.org>
Cc:     LKML <linux-kernel@...r.kernel.org>,
        Linux Crypto Mailing List <linux-crypto@...r.kernel.org>,
        "Theodore Ts'o" <tytso@....edu>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Jean-Philippe Aumasson <jeanphilippe.aumasson@...il.com>
Subject: Re: [PATCH v2] random: use SipHash as interrupt entropy accumulator

On Sat, Mar 12, 2022 at 5:23 PM Eric Biggers <ebiggers@...nel.org> wrote:
> That isn't mentioned in Documentation/security/siphash.rst at all.  It actually
> makes it pretty clear that hsiphash() is "HalfSipHash".

Send a documentation patch and I'll queue it up.

>
> > > So on 64-bit platforms it now throws away half of the pool.
> > >
> > > It should use 'u8 pool[sizeof(fast_pool->pool)]' to avoid hardcoding a size.
> >
> > Actually the commit message notes that we intentionally dump half of
> > it on 64bit. This is intentional.
> >
>
> It doesn't explain *why* it does that.  Also, the code is much more important
> than the commit message, and there's no explanation in the code at all; it just
> looks like a bug.

Yea. I'll augment that and send a v+1.

Jason