Re: [PATCH v1] random: block in /dev/urandom

From: Guenter Roeck <linux@roeck-us.net>
To: "Jason A. Donenfeld" <Jason@zx2c4.com>
Cc: LKML <linux-kernel@vger.kernel.org>,
	Linux Crypto Mailing List <linux-crypto@vger.kernel.org>,
	linux-arch <linux-arch@vger.kernel.org>,
	Dinh Nguyen <dinguyen@kernel.org>, Nick Hu <nickhu@andestech.com>,
	Max Filippov <jcmvbkbc@gmail.com>,
	Palmer Dabbelt <palmer@dabbelt.com>,
	"David S . Miller" <davem@davemloft.net>,
	Yoshinori Sato <ysato@users.sourceforge.jp>,
	Michal Simek <monstr@monstr.eu>, Borislav Petkov <bp@alien8.de>,
	Guo Ren <guoren@kernel.org>,
	Geert Uytterhoeven <geert@linux-m68k.org>,
	Joshua Kinard <kumba@gentoo.org>,
	David Laight <David.Laight@aculab.com>,
	Dominik Brodowski <linux@dominikbrodowski.net>,
	Eric Biggers <ebiggers@google.com>,
	Ard Biesheuvel <ardb@kernel.org>, Arnd Bergmann <arnd@arndb.de>,
	Thomas Gleixner <tglx@linutronix.de>,
	Andy Lutomirski <luto@kernel.org>,
	Kees Cook <keescook@chromium.org>,
	Lennart Poettering <mzxreary@0pointer.de>,
	Konstantin Ryabitsev <konstantin@linuxfoundation.org>,
	Linus Torvalds <torvalds@linux-foundation.org>,
	Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
	Theodore Ts'o <tytso@mit.edu>
Subject: Re: [PATCH v1] random: block in /dev/urandom
Date: Fri, 22 Apr 2022 16:46:44 -0700	[thread overview]
Message-ID: <20220422234644.GB3442771@roeck-us.net> (raw)
In-Reply-To: <CAHmME9rmeQAD2DwG=APTmDxuVxFDH=6GXoKpgPrU9rc9oXrmxQ@mail.gmail.com>

On Fri, Apr 22, 2022 at 03:42:46PM +0200, Jason A. Donenfeld wrote:
> Hey Guenter,
> 
> On Tue, Mar 22, 2022 at 6:56 PM Guenter Roeck <linux@roeck-us.net> wrote:
> >
> > On 3/22/22 10:09, Jason A. Donenfeld wrote:
> > > Hey Guenter,
> > >
> > > On Tue, Mar 22, 2022 at 08:58:20AM -0700, Guenter Roeck wrote:
> > >> On Thu, Feb 17, 2022 at 05:28:48PM +0100, Jason A. Donenfeld wrote:
> > >>> This topic has come up countless times, and usually doesn't go anywhere.
> > >>> This time I thought I'd bring it up with a slightly narrower focus,
> > >>> updated for some developments over the last three years: we finally can
> > >>> make /dev/urandom always secure, in light of the fact that our RNG is
> > >>> now always seeded.
> > >>>
> > >>
> > >> [ ... ]
> > >>
> > >> This patch (or a later version of it) made it into mainline and causes a
> > >> large number of qemu boot test failures for various architectures (arm,
> > >> m68k, microblaze, sparc32, xtensa are the ones I observed). Common
> > >> denominator is that boot hangs at "Saving random seed:". A sample bisect
> > >> log is attached. Reverting this patch fixes the problem.
> > >
> > > As Linus said, it was worth a try, but I guess it just didn't work. For
> > > my own curiosity, though, do you have a link to those QEMU VMs you could
> > > share? I'd sort of like to poke around, and if we do ever reattempt this
> > > sometime down the road, it seems like understanding everything about why
> > > the previous time failed might be a good idea.
> > >
> >
> > Everything - including the various root file systems - is at
> > git@github.com:groeck/linux-build-test.git. Look into rootfs/ for the
> > various boot tests. I'll be happy to provide some qemu command lines
> > if needed.
> 
> I've been playing with a few things, and I'm wondering how close I am
> to making this problem go away. I just made this branch:
> https://git.kernel.org/pub/scm/linux/kernel/git/crng/random.git/log/?h=jd/for-guenter
> 
> Any interest in setting your tests on that and seeing if it still
> breaks? Or, perhaps better, do you have a single script that runs all

I applied your branch to my 'testing' branch. It will build tonight.
We should have results by tomorrow morning.

> your various tests and does all the toolchain things right, so I can
> just point it at that tree and iterate?
> 

Sorry, my system isn't that fancy. I don't mind running tests like this one,
though.

Guenter