x86, kaslr: Add a circular multiply for better bit diffusion

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If we don't have RDRAND (in which case nothing else *should* matter),
most sources have a highly biased entropy distribution.  Use a
circular multiply to diffuse the entropic bits.  A circular multiply
is a good operation for this: it is cheap on standard hardware and
because it is symmetric (unlike an ordinary multiply) it doesn't
introduce its own bias.

Cc: Kees Cook <keescook@chromium.org>
Signed-off-by: H. Peter Anvin <hpa@zytor.com>
Link: http://lkml.kernel.org/r/20131111222839.GA28616@www.outflux.net

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H. Peter Anvin 2013-11-11 22:45:20 -08:00

parent a653f3563c

commit e8236c4d93

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arch/x86/boot/compressed/aslr.c

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