From:   Boris Krasnovskiy <Boris.Krasnovskiy@lairdconnect.com>
To:     "Jason A. Donenfeld" <Jason@zx2c4.com>,
        Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        Linux Crypto Mailing List <linux-crypto@vger.kernel.org>
CC:     Simo Sorce <simo@redhat.com>, Jeffrey Walton <noloader@gmail.com>,
        Stephan Mueller <smueller@chronox.de>, Tso Ted <tytso@mit.edu>,
        Willy Tarreau <w@1wt.eu>, Nicolai Stange <nstange@suse.de>,
        LKML <linux-kernel@vger.kernel.org>,
        Arnd Bergmann <arnd@arndb.de>,
        "Eric W. Biederman" <ebiederm@xmission.com>,
        "Alexander E. Patrakov" <patrakov@gmail.com>,
        "Ahmed S. Darwish" <darwish.07@gmail.com>,
        Matthew Garrett <mjg59@srcf.ucam.org>,
        Vito Caputo <vcaputo@pengaru.com>,
        Andreas Dilger <adilger.kernel@dilger.ca>,
        Jan Kara <jack@suse.cz>, Ray Strode <rstrode@redhat.com>,
        William Jon McCann <mccann@jhu.edu>,
        zhangjs <zachary@baishancloud.com>,
        Andy Lutomirski <luto@kernel.org>,
        Florian Weimer <fweimer@redhat.com>,
        Lennart Poettering <mzxreary@0pointer.de>,
        Peter Matthias <matthias.peter@bsi.bund.de>,
        Eric Biggers <ebiggers@kernel.org>,
        Marcelo Henrique Cerri <marcelo.cerri@canonical.com>,
        Neil Horman <nhorman@redhat.com>,
        Randy Dunlap <rdunlap@infradead.org>,
        Julia Lawall <julia.lawall@inria.fr>,
        Dan Carpenter <dan.carpenter@oracle.com>,
        Andy Lavr <andy.lavr@gmail.com>,
        Petr Tesarik <ptesarik@suse.cz>,
        John Haxby <john.haxby@oracle.com>,
        Alexander Lobakin <alobakin@mailbox.org>,
        Jirka Hladky <jhladky@redhat.com>
Subject: Re: [PATCH v43 01/15] Linux Random Number Generator
Thread-Topic: [PATCH v43 01/15] Linux Random Number Generator
Thread-Index: AQHX5sz0mOv14rnNIkKw7OyLfJ1msawd4ZyAgAAJbXc=
Date:   Wed, 1 Dec 2021 17:55:32 +0000
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Hi Jason, Greg,

a lot of the issues LRNG address are related to RNG and FIPS on embedded/Io=
T devices.

The problem we have is that /dev/random as it stands today in many cases do=
es not generate enough entropy to support cryptography on embedded/IoT devi=
ces. Embedded devices in most cases have limited interrupt and IO activity,=
 they do have in many cases aggressive power management where device is up =
and running few seconds at a time and fallbacks into suspend mode, this is =
done to preserve power (battery and otherwise), and now such operation even=
 the legal mandate in EU (we are going green).

What options do we have here:

Use hardware random number if CPU supports it. Yes, some people do not trus=
t it, but it's better than nothing. /dev/random currently does not allow to=
 mix in Hardware RNG unless quality parameter is set, and none of the kerne=
l Hardware RNG have it set out of the box.

Not all CPUs have hardware RNG to use or have non-compliant Hardware RNG (w=
hich is after 90C was adopted most of the older ones, 90C requires runtime =
test on raw entropy which is not exposed outside of the IC), what to do now=
? This is one of the areas where Jitter RNG comes in. It has fast entropy c=
ollection, meets FIPS requirements and could be run on any CPU, provided it=
 has High Resolution Timer, does not require storing seed on the file syste=
m that is prohibited by FIPS. There is no option as of today to mix in or f=
lood Jitter entropy into /dev/random inside kernel.

I am aware that there are userspace daemons that take entropy from Hardware=
 RNG or Jitter and feed into /dev/random, but is it really the best approac=
h?
Now let get into FIPS on such systems.

I hoped I explained earlier why existing /dev/random is unusable.
If userspace solution to /dev/random is used, one has to demonstrate that e=
ntropy fed by userspace daemon floods /dev/random to the point where other =
sources of entropy statistically does not matter. That increases cost of FI=
PS certification by about 30% last time we checked.

This is why it would help a lot if one can choose from kernel configuration=
 which RNG is appropriate for the system at hand, and this exactly what LRN=
G does.

Thank you,
Boris
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