On Wed, Feb 12, 2014 at 08:12:23PM +0100, Arnd Bergmann wrote: > On Wednesday 12 February 2014 13:45:21 Jason Cooper wrote: > > On Wed, Feb 12, 2014 at 07:17:41PM +0100, Arnd Bergmann wrote: > > > On Wednesday 12 February 2014 12:45:54 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. > > > > > > I like the idea, but wouldn't it be easier to pass actual random data > > > using DT, rather than the address/size? > > > > I thought about that at first, but that requires either that the > > bootloader be upgraded to insert the data, or that userspace is > > modifying the dtb at least twice per boot. > > > > I chose address/size to facilitate modifying existing/fielded devices. > > The user could modify the dtb once, and modify the bootloader > > environment to load X amount to Y address. As a fallback, it could be > > expressed on the commandline for non-DT bootloaders. > > Ah, so you are interested in boot loaders that can be scripted to do > what you had in mind but cannot be scripted to add or modify a DT > property. I hadn't considered that, but you are probably right that > this is at least 90% of the systems you'd find in the wild today. Yes, exactly. > Thinking this a bit further, I wonder if (at least upstream) u-boot > has a way to modify DT properties in a scripted way that would allow > the direct property. It sounds like a generally useful feature not > just for randomness, so if that doesn't already work, maybe someone > can implement it. In the simplest case, you'd only need to find the > address of an existing property in the dtb and load a file to > that location. Like fdtget from dtc? The thing is, this address would only need to be setup once per board. Hypothetically, debian's flash-kernel could set the address in the dtb, then set it in the u-boot environment. From then on, only the normal initscript writing to random-seed would be needed. thx, Jason. -- 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
