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From:   "Jason A. Donenfeld" <Jason@zx2c4.com>
Date:   Fri, 22 Apr 2022 15:42:46 +0200
Message-ID: <CAHmME9rmeQAD2DwG=APTmDxuVxFDH=6GXoKpgPrU9rc9oXrmxQ@mail.gmail.com>
Subject: Re: [PATCH v1] random: block in /dev/urandom
To:     Guenter Roeck <linux@roeck-us.net>
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>
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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
your various tests and does all the toolchain things right, so I can
just point it at that tree and iterate?

Jason