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

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Date:   Tue, 22 Mar 2022 11:09:58 -0600
From:   "Jason A. Donenfeld" <Jason@...c4.com>
To:     Guenter Roeck <linux@...ck-us.net>
Cc:     linux-kernel@...r.kernel.org, linux-crypto@...r.kernel.org,
        linux-arch@...r.kernel.org, Dinh Nguyen <dinguyen@...nel.org>,
        Nick Hu <nickhu@...estech.com>,
        Max Filippov <jcmvbkbc@...il.com>,
        Palmer Dabbelt <palmer@...belt.com>,
        "David S . Miller" <davem@...emloft.net>,
        Yoshinori Sato <ysato@...rs.sourceforge.jp>,
        Michal Simek <monstr@...str.eu>,
        Borislav Petkov <bp@...en8.de>, Guo Ren <guoren@...nel.org>,
        Geert Uytterhoeven <geert@...ux-m68k.org>,
        Joshua Kinard <kumba@...too.org>,
        David Laight <David.Laight@...lab.com>,
        Dominik Brodowski <linux@...inikbrodowski.net>,
        Eric Biggers <ebiggers@...gle.com>,
        Ard Biesheuvel <ardb@...nel.org>,
        Arnd Bergmann <arnd@...db.de>,
        Thomas Gleixner <tglx@...utronix.de>,
        Andy Lutomirski <luto@...nel.org>,
        Kees Cook <keescook@...omium.org>,
        Lennart Poettering <mzxreary@...inter.de>,
        Konstantin Ryabitsev <konstantin@...uxfoundation.org>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Theodore Ts'o <tytso@....edu>
Subject: Re: [PATCH v1] random: block in /dev/urandom

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.

Jason