Received-SPF: pass (google.com: domain of linux-crypto-owner@vger.kernel.org designates 23.128.96.18 as permitted sender) client-ip=23.128.96.18;
From:   Alexander Dahl <ada@thorsis.com>
To:     linux-crypto@vger.kernel.org
Cc:     Stephan =?ISO-8859-1?Q?M=FCller?= <smueller@chronox.de>
Subject: jitterentropy_rng on armv5 embedded target
Date:   Fri, 08 May 2020 13:40:08 +0200
Message-ID: <2567555.LKkejuagh6@ada>
Content-Transfer-Encoding: quoted-printable
Content-Type: text/plain; charset="iso-8859-1"
Sender: linux-crypto-owner@vger.kernel.org
Precedence: bulk

Hello,

after upgrading OpenSSL to 1.1.1g on an armv5 based embedded target I had a=
=20
deeper look into entropy generation for that device and stumbled over the i=
n=20
kernel 'jitterentropy_rng' module.

As far as I understood it's supposed to do the same as the well known=20
'haveged' or the userspace daemon 'jitterentropy-rngd' by Stephan M=FCller =
[1],=20
right? (Although those daemons would solve my problem, I currently try to=20
avoid them, because memory on my platform is very restricted and every=20
additional running userspace process costs at least around 1 MB.)

If so, then how is it supposed to be set up? I built it for 4.9.x LTS, but=
=20
after loading it with 'modprobe' I see nothing in the kernel log and there'=
s=20
no significant change in /proc/sys/kernel/random/entropy_avail (stays well=
=20
below 100 most of the time). Isn't that module supposed to gather entropy f=
rom=20
cpu timing jitter?

Puzzled
Alex

[1] https://www.chronox.de/jent.html