From: Borislav Petkov <bp@alien8.de>
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: Tue, 1 Oct 2019 15:51:08 +0200 [thread overview]
Message-ID: <20191001135108.GD5390@zn.tnic> (raw)
In-Reply-To: <CAHk-=wjfLfnOyGkHM+ZRn6bc6JD6CU3Ewix3cJDqCqjbMO5PNA@mail.gmail.com>
On Mon, Sep 30, 2019 at 09:06:36AM -0700, Linus Torvalds wrote:
> Obviously, that can be a problem if you then need sshd in order to get
> into a headless box, so my patch fixes things for you too, but at
> least your box doesn't show the problem that Ahmed had, and the boot
> completing presumably means that you got more entropy from other disk
> IO being done by the rest of the boot.
Right, another observation I did was that when it would wait for
entropy, if I press random keys, it would get done faster because
apparently it would collect entropy from the key presses too.
> If you want to test my hacky "do /dev/urandom too", it was this one-liner:
>
> --- a/drivers/char/random.c
> +++ b/drivers/char/random.c
> @@ -2027,6 +2027,7 @@ urandom_read(struct file *file, char __user
> *buf, size_t nbytes, loff_t *ppos)
> static int maxwarn = 10;
> int ret;
>
> + if (!crng_ready()) try_to_generate_entropy();
> if (!crng_ready() && maxwarn > 0) {
> maxwarn--;
> if (__ratelimit(&urandom_warning))
>
> and that should get rid of the warnings.
So when I add this by hand and do git diff, it adds a second hunk:
---
diff --git a/drivers/char/random.c b/drivers/char/random.c
index c2f7de9dc543..93bad17bef98 100644
--- a/drivers/char/random.c
+++ b/drivers/char/random.c
@@ -2027,6 +2027,7 @@ urandom_read(struct file *file, char __user *buf, size_t nbytes, loff_t *ppos)
static int maxwarn = 10;
int ret;
+ if (!crng_ready()) try_to_generate_entropy();
if (!crng_ready() && maxwarn > 0) {
maxwarn--;
if (__ratelimit(&urandom_warning))
@@ -2520,4 +2521,4 @@ void add_bootloader_randomness(const void *buf, unsigned int size)
else
add_device_randomness(buf, size);
}
-EXPORT_SYMBOL_GPL(add_bootloader_randomness);
\ No newline at end of file
+EXPORT_SYMBOL_GPL(add_bootloader_randomness);
---
and I kinda get what it is trying to tell me but this is new. And when I
do
$ xxd drivers/char/random.c
..
000125e0: 646f 6d6e 6573 7329 3b0a domness);.
there's a 0xa at the end so what's git really trying to tell me?
Anyway, that does get rid of the warns too.
> Doing something like the above to /dev/urandom is likely the right
> thing to do eventually, but I didn't want to mix up "we can perhaps
> improve the urandom situation too" with the basic "let's fix the boot
> problem". The urandom behavior change would be a separate thing.
So make it a separate patch and let's hammer on it during the next weeks
and see what happens?
> Also, talking about "future changes". Right now
> "try_to_generate_entropy()" is actually uninterruptible once it gets
> started. I think we should add a test for signal_pending() too, but it
Wouldn't that even increase its entropy, which would be a good thing?
> should generally complete really fairly quickly so I left it without
> one just to see if anybody even notices.
Right.
Thx.
--
Regards/Gruss,
Boris.
https://people.kernel.org/tglx/notes-about-netiquette
next prev parent reply other threads:[~2019-10-01 13:51 UTC|newest]
Thread overview: 37+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-09-28 22:24 x86/random: Speculation to the rescue 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 [this message]
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
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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