On Wed, Feb 12, 2014 at 9:45 AM, Jason Cooper <jason@xxxxxxxxxxxxxx> 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@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
