On Mon, Feb 17, 2014 at 05:13:07PM +0100, Arnd Bergmann wrote: > On Monday 17 February 2014 15:54:19 Grant Likely wrote: > > On Wed, 12 Feb 2014 11:20:00 -0700, Jason Gunthorpe <jgunthorpe@xxxxxxxxxxxxxxxxxxxx> wrote: > > > On Wed, Feb 12, 2014 at 12:45:54PM -0500, Jason Cooper wrote: > > > > > > > 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. > > > > > > Sure is a neat idea, but I think in general it would probably be smart > > > to include the entire FDT blob in the early random pool, that way you > > > get MACs and other machine unique data too. > > > > I applied a patch that did exactly that (109b623629), and then reverted > > it (b920ecc82) shortly thereafter because add_device_randomness() is > > a rather slow function and FDTs can get large. I'd like to see someone > > do a reasonable analysis on the cost of using an FDT for randomness > > before I reapply a patch doing something similar. An awful lot of the > > FDT data is not very random, but there are certainly portions of it that > > are appropriate for the random pool. > > Could we use a faster hash function that scans the entire device tree and > then just feed the output of that into add_device_randomness? We probably > can't expect that there is a lot of entropy in the DT blob, so the > result wouldn't be all that different in terms of quality of the random > seed. I think it would be easier to identify the few attributes that differ from board to board (mac address, serial number, etc), and differ from boot to boot (random-seed, timestamp) and just extract and feed those in. We already have the fdt parsing code in the decompressor... 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
