linux-kernel - [RFD] Direct support for the x86 RDRAND instruction

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Date:	Fri, 29 Jul 2011 13:37:45 -0700
From:	"H. Peter Anvin" <hpa@...ux.intel.com>
To:	Linus Torvalds <torvalds@...ux-foundation.org>,
	"H. Peter Anvin" <hpa@...or.com>, Ingo Molnar <mingo@...e.hu>,
	Thomas Gleixner <tglx@...utronix.de>,
	Fenghua Yu <fenghua.yu@...el.com>,
	Matt Mackall <mpm@...enic.com>,
	Herbert Xu <herbert@...dor.apana.org.au>,
	Theodore Ts'o <tytso@....edu>, Jeff Garzik <jgarzik@...ox.com>,
	linux-kernel@...r.kernel.org
Cc:	"H. Peter Anvin" <hpa@...ux.intel.com>
Subject: [RFD] Direct support for the x86 RDRAND instruction

From: "H. Peter Anvin" <hpa@...ux.intel.com>

This is a proposed patchset to enable the new x86 RDRAND instruction,
labelled "Bull Mountain Technology" by Intel.  It is a different beast
than any other hardware random number generator that I have personally
encountered: it is not just a random number source, but contains a
high bandwidth random number generator, an AES cryptographic whitener,
and integrity monitoring all in hardware.

For technical documentation see:

http://software.intel.com/en-us/articles/download-the-latest-bull-mountain-software-implementation-guide/

This proposed patchset enables RDRAND bypass for current users of the
nonblocking random pool (that is, for /dev/urandom and its equvalent
in-kernel users) but not for the blocking pool (/dev/random).  This is
because RDRAND, although reseeded way more frequently than what is
practical to do in software, is technically a nonblocking source that
can behave as a PRNG.  It can be used as a source for randomness for
/dev/random, but that is not addressed by this patchset.
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