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From:   "Jason A. Donenfeld" <Jason@zx2c4.com>
Date:   Thu, 20 Jan 2022 16:03:41 +0100
Message-ID: <CAHmME9pxJFBv-ZZ3bPMJdmxUO4oeY-wS4BtW34w1ncbeeU=MeA@mail.gmail.com>
Subject: Re: [PATCH v2] random: avoid superfluous call to RDRAND in CRNG extraction
To:     "Theodore Ts'o" <tytso@mit.edu>
Cc:     LKML <linux-kernel@vger.kernel.org>
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On Tue, Jan 4, 2022 at 6:55 AM Theodore Ts'o <tytso@mit.edu> wrote:
> If we want to worry about what happens if we could actually manage to
> call _extract_crng() more than 2**64 times before the reseed interval
> is up --- which *is* one of the benefits of:
>
>    if (arch_get_random_long(^v))
>         crng->state[14] ^= v;
>
> I could see doing perhaps this instead:
>
>     if (crng->state[12] == 0) {
>         crng->state[13]++;
>         if (crng->state[13] == 0) {
>             crng->state[14]++;
>             if (crng->state[14] == 0) {
>                 crng->state[15]++;
>             }
>         }
>    }

While probably overkill, I've got a patch that does this while also
labeling these constants. I'll send that as a reply to this message.

Jason