linux-kernel - Re: [PATCH v43 01/15] Linux Random Number Generator

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Date:   Mon, 10 Jan 2022 09:29:04 -0500
From:   "Theodore Ts'o" <tytso@....edu>
To:     "Jason A. Donenfeld" <Jason@...c4.com>
Cc:     Marcelo Henrique Cerri <marcelo.cerri@...onical.com>,
        Simo Sorce <simo@...hat.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Jeffrey Walton <noloader@...il.com>,
        Stephan Mueller <smueller@...onox.de>,
        Linux Crypto Mailing List <linux-crypto@...r.kernel.org>,
        Willy Tarreau <w@....eu>, Nicolai Stange <nstange@...e.de>,
        LKML <linux-kernel@...r.kernel.org>,
        Arnd Bergmann <arnd@...db.de>,
        "Eric W. Biederman" <ebiederm@...ssion.com>,
        "Alexander E. Patrakov" <patrakov@...il.com>,
        "Ahmed S. Darwish" <darwish.07@...il.com>,
        Matthew Garrett <mjg59@...f.ucam.org>,
        Vito Caputo <vcaputo@...garu.com>,
        Andreas Dilger <adilger.kernel@...ger.ca>,
        Jan Kara <jack@...e.cz>, Ray Strode <rstrode@...hat.com>,
        William Jon McCann <mccann@....edu>,
        zhangjs <zachary@...shancloud.com>,
        Andy Lutomirski <luto@...nel.org>,
        Florian Weimer <fweimer@...hat.com>,
        Lennart Poettering <mzxreary@...inter.de>,
        Peter Matthias <matthias.peter@....bund.de>,
        Eric Biggers <ebiggers@...nel.org>,
        Neil Horman <nhorman@...hat.com>,
        Randy Dunlap <rdunlap@...radead.org>,
        Julia Lawall <julia.lawall@...ia.fr>,
        Dan Carpenter <dan.carpenter@...cle.com>,
        Andy Lavr <andy.lavr@...il.com>,
        Petr Tesarik <ptesarik@...e.cz>,
        John Haxby <john.haxby@...cle.com>,
        Alexander Lobakin <alobakin@...lbox.org>,
        Jirka Hladky <jhladky@...hat.com>
Subject: Re: [PATCH v43 01/15] Linux Random Number Generator

On Mon, Jan 10, 2022 at 03:11:46PM +0100, Jason A. Donenfeld wrote:
> On Mon, Jan 10, 2022 at 2:24 PM Marcelo Henrique Cerri
> <marcelo.cerri@...onical.com> wrote:
> > Hoping that might help with the discussion and to explain why I do
> > consider those solutions a "hack", that's the patch we've been using
> > so far to achieve SP 800-90B compliance:
> >
> > https://kernel.ubuntu.com/~mhcerri/0001-UBUNTU-SAUCE-random-Use-Crypto-API-DRBG-for-urandom-.patch
> 
> Thanks for sending this in response to my request for it in our private thread.
> 
> Just to confirm, this little patch here gives you FIPS certification?

There might be some FIPS certification labs that might be willing to
be taken in by the jitterentropy story, but when I've had private
communications from people who are familiar with the Intel
microarchitecture saying that jitterentropy is mostly "security by
obscurity", I'd be strongly opposed to replacing the current scheme
with something which is purely jitteretropy.

Perhaps an build-time option where one of the seeds into the CRNG is
"jitterentropy", but we keep everything else.  That way, jitterentropy
can still be TSA-style "security theatre", but we're not utterly
dependant on the "the CPU microarchitecture is SOOOOOOO complicated,
it *must* be unpredictable".

						- Ted