From: Pavel Machek <pavel@ucw.cz>
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>,
Theodore Ts'o <tytso@mit.edu>,
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: Sun, 6 Oct 2019 20:21:03 +0200 [thread overview]
Message-ID: <20191006182103.GA2394@amd> (raw)
In-Reply-To: <CAHk-=whgfz2+OgBTVrHLoHK57emYb4gN6TtJ_s-607U=jBQ+ig@mail.gmail.com>
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On Sun 2019-10-06 11:06:38, Linus Torvalds wrote:
> On Sun, Oct 6, 2019 at 10:35 AM Pavel Machek <pavel@ucw.cz> wrote:
> >
> > It will not: boot is now halted because systemd wants some
> > entropy. Everything is idle and very little interrupts are
> > happening. We have spinning rust, but it is idle, and thus not
> > generating any interrupts.
>
> Yes, but we have that problem now solved.
>
> Except on embedded platforms that have garbage CPU's without even a
> cycle counter.
>
> But those won't have spinning rust anyway.
>
> Yes, bad SSD's and MMC disks (that they do have) will generate timing
> noise too, but in the absense of a cycle counter, that noise won't be
> much use.
Even without cycle counter... if we _know_ we are trying to generate
entropy and have MMC available, we don't care about power and
performance.
So we can just...
issue read request on MMC
while (!interrupt_done)
i++
...and then use i++ as poor man's version of cycle counter.
[We would not want to do that in normal operation, for obvious
reasons, just when userland is blocked and waiting for entropy.]
Hmm?
Best regards,
Pavel
--
(english) http://www.livejournal.com/~pavelmachek
(cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html
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next prev parent reply other threads:[~2019-10-06 18:21 UTC|newest]
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
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 [this message]
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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