From mboxrd@z Thu Jan 1 00:00:00 1970 From: Olof Johansson Subject: Re: [RFC/PATCH 0/3] Add devicetree scanning for randomness Date: Wed, 12 Feb 2014 10:13:59 -0800 Message-ID: References: <1392168805-14200-1-git-send-email-lauraa@codeaurora.org> <201402121251.06280.arnd@arndb.de> <20140212174554.GM27395@titan.lakedaemon.net> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1 Return-path: In-Reply-To: <20140212174554.GM27395-u4khhh1J0LxI1Ri9qeTfzeTW4wlIGRCZ@public.gmane.org> Sender: devicetree-owner-u79uwXL29TY76Z2rM5mHXA@public.gmane.org To: Jason Cooper Cc: Arnd Bergmann , Kees Cook , Laura Abbott , Grant Likely , Rob Herring , "linux-kernel-u79uwXL29TY76Z2rM5mHXA@public.gmane.org" , "devicetree-u79uwXL29TY76Z2rM5mHXA@public.gmane.org" , "linux-arm-kernel-IAPFreCvJWM7uuMidbF8XUB+6BGkLq7r@public.gmane.org" , Kumar Gala List-Id: devicetree@vger.kernel.org On Wed, Feb 12, 2014 at 9:45 AM, Jason Cooper wrote: > I brought this up at last weeks devicetree irc meeting. My goal is to > provide early randomness for kaslr on ARM. Currently, my idea is modify > the init script to save an additional random seed from /dev/urandom to > /boot/random-seed. > > The bootloader would then load this file into ram, and pass the > address/size to the kernel either via dt, or commandline. kaslr (run in > the decompressor) would consume some of this randomness, and then > random.c would consume the rest in a non-crediting initialization. > > While not ideal, it works in absence of an HRNG, and is no worse than > the current situation of storing the seed in /var/lib/misc/random-seed. > It also doesn't require modification of the bootloaders. Just an > updated kernel, and update the bootloader environment to load the > seed. Hmm. There are some drawbacks with this -- it assumes you can "just update the bootloader environment" which in general isn't easy to do. Also, you can't assume that /boot is writable or exists on all embedded systems. In general, taking both runtime and system-dependend data and using that to see entropy is a good idea. For example, device trees that contain serial numbers and mac addresses for the individual system. I think x86 feeds the DMI table in for similar purposes. If that can be amended on some systems with a runtime seed (from /boot), that's good but we can't rely on it. -Olof -- To unsubscribe from this list: send the line "unsubscribe devicetree" in the body of a message to majordomo-u79uwXL29TY76Z2rM5mHXA@public.gmane.org More majordomo info at http://vger.kernel.org/majordomo-info.html