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From: "Theodore Y. Ts'o" <tytso@mit.edu>
To: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Thomas Gleixner <tglx@linutronix.de>,
	"Ahmed S. Darwish" <darwish.07@gmail.com>,
	LKML <linux-kernel@vger.kernel.org>,
	Nicholas Mc Guire <hofrat@opentech.at>,
	the arch/x86 maintainers <x86@kernel.org>,
	Andy Lutomirski <luto@kernel.org>,
	Kees Cook <keescook@chromium.org>
Subject: Re: x86/random: Speculation to the rescue
Date: Mon, 30 Sep 2019 09:16:39 -0400
Message-ID: <20190930131639.GF4994@mit.edu> (raw)
In-Reply-To: <20190930033706.GD4994@mit.edu>

On Sun, Sep 29, 2019 at 11:37:06PM -0400, Theodore Y. Ts'o wrote:
> I'm OK with this as a starting point.  If a jitter entropy system
> allow us to get pass this logjam, let's do it.  At least for the x86
> architecture, it will be security through obscurity.  And if the
> alternative is potentially failing where the adversary can attack the
> CRNG, it's my preference.  It's certainly better than nothing.

Upon rereading this, this came out wrong.  What I was trying to say is
in the very worst case, it will be security through obscurity, and if
the alternative "don't block, because blocking is always worse than an
guessable value being returned through getrandom(0)", it's better than
nothing.

Which is to say, I'm still worried that people with deep access to the
implementation details of a CPU might be able to reverse engineer what
a jitter entropy scheme produces.  This is why I'd be curious to see
the results when someone tries to attack a jitter scheme on a fully
open, simple architecture such as RISC-V.

						- Ted

  reply index

Thread overview: 37+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-09-28 22:24 Thomas Gleixner
2019-09-28 23:53 ` Linus Torvalds
2019-09-29  7:40   ` Thomas Gleixner
2019-09-29  8:05   ` Alexander E. Patrakov
2019-09-30  1:16   ` Linus Torvalds
2019-09-30  2:59     ` Linus Torvalds
2019-09-30  6:10       ` Borislav Petkov
2019-09-30 16:06         ` Linus Torvalds
2019-10-01 13:51           ` Borislav Petkov
2019-10-01 17:14             ` Linus Torvalds
2019-10-01 17:50               ` [PATCH] char/random: Add a newline at the end of the file Borislav Petkov
2019-09-30 18:05         ` x86/random: Speculation to the rescue Kees Cook
2019-09-30  3:37     ` Theodore Y. Ts'o
2019-09-30 13:16       ` Theodore Y. Ts'o [this message]
2019-09-30 16:15         ` Linus Torvalds
2019-09-30 16:32           ` Peter Zijlstra
2019-09-30 17:03             ` Linus Torvalds
2019-10-01 10:28           ` David Laight
2019-10-15 21:50             ` Thomas Gleixner
2019-10-01 16:15   ` Ahmed S. Darwish
2019-10-01 16:37     ` Kees Cook
2019-10-01 17:18       ` Ahmed S. Darwish
2019-10-01 17:25     ` Linus Torvalds
2019-10-06 12:07       ` Pavel Machek
2019-10-02 12:01     ` Theodore Y. Ts'o
2019-10-06 11:41   ` Pavel Machek
2019-10-06 17:26     ` Linus Torvalds
2019-10-06 17:35       ` Pavel Machek
2019-10-06 18:06         ` Linus Torvalds
2019-10-06 18:21           ` Pavel Machek
2019-10-06 18:26             ` Linus Torvalds
2019-10-07 11:47             ` Theodore Y. Ts'o
2019-10-07 22:18               ` Pavel Machek
2019-10-08 11:33                 ` David Laight
2019-10-09  8:02                   ` Pavel Machek
2019-10-09  9:37                     ` David Laight
2019-10-01  2:14 hgntkwis

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