linux-kernel - Re: [PATCH] random: mix in architectural randomness in extract

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Message-ID: <20120728023938.GA3766@thunk.org>
Date:	Fri, 27 Jul 2012 22:39:38 -0400
From:	Theodore Ts'o <tytso@....edu>
To:	"H. Peter Anvin" <hpa@...or.com>
Cc:	linux-kernel@...r.kernel.org,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Ingo Molnar <mingo@...nel.org>, w@....edu, ewust@...ch.edu,
	zakir@...ch.edu, greg@...ah.com, mpm@...enic.com,
	nadiah@...ucsd.edu, jhalderm@...ch.edu, tglx@...utronix.de,
	davem@...emloft.net, stable@...r.kernel.org,
	DJ Johnston <dj.johnston@...el.com>,
	"H. Peter Anvin" <hpa@...ux.intel.com>
Subject: Re: [PATCH] random: mix in architectural randomness in extract_buf()

Ok, I'll add this patch to the random tree.  I've modified the commit
message a bit since the speed advertisement of RDRAND is rather
pointless --- processes aren't generating session keys or long term
keys at a high rate, and programs can't count on /dev/random being
super fast and having unlimited entropy, since for most platforms and
even most x86 CPU's deployed in service today, this isn't true --- and
making your userspace program depond upon /dev/random in such a way
that it only works on Ivy Bridge CPU's might be good for Intel from a
vendor lock-in perspective, but it's really bad, non-portable
programming style.

Also, in the future arch_get_random_long() will almost certainly be
hooked up for other architectures, so putting an extended
advertisement for RDRAND really isn't appropriate.

					- Ted

commit d2e7c96af1e54b507ae2a6a7dd2baf588417a7e5
Author: H. Peter Anvin <hpa@...ux.intel.com>
Date:   Fri Jul 27 22:26:08 2012 -0400

    random: mix in architectural randomness in extract_buf()

    Mix in any architectural randomness in extract_buf() instead of
    xfer_secondary_buf().  This allows us to mix in more architectural
    randomness, and it also makes xfer_secondary_buf() faster, moving a
    tiny bit of additional CPU overhead to process which is extracting the
    randomness.

    [ Commit description modified by tytso to remove an extended
      advertisement for the RDRAND instruction. ]

    Signed-off-by: H. Peter Anvin <hpa@...ux.intel.com>
    Acked-by: Ingo Molnar <mingo@...nel.org>
    Cc: DJ Johnston <dj.johnston@...el.com>
    Signed-off-by: Theodore Ts'o <tytso@....edu>
    Cc: stable@...r.kernel.org
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