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    SubjectRe: [RFC/PATCH 0/3] Add devicetree scanning for randomness
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    On Mon, 17 Feb 2014 17:13:07 +0100, Arnd Bergmann <arnd@arndb.de> wrote:
    > On Monday 17 February 2014 15:54:19 Grant Likely wrote:
    > > On Wed, 12 Feb 2014 11:20:00 -0700, Jason Gunthorpe <jgunthorpe@obsidianresearch.com> 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.
    >
    > Arnd

    Yes, I think that is a good solution.

    g.



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