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

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Date:   Tue, 22 Mar 2022 22:25:24 +0000
From:   David Laight <David.Laight@...LAB.COM>
To:     'Guenter Roeck' <linux@...ck-us.net>,
        Mark Brown <broonie@...nel.org>
CC:     "Jason A. Donenfeld" <Jason@...c4.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-crypto@...r.kernel.org" <linux-crypto@...r.kernel.org>,
        "linux-arch@...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>,
        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

From: Guenter Roeck
> Sent: 22 March 2022 21:54
> 
> On 3/22/22 11:24, Mark Brown wrote:
> > On Tue, Mar 22, 2022 at 08:58:20AM -0700, Guenter Roeck wrote:
> >
> >> 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.
> >
> > Just as a datapoint for debugging at least qemu/arm is getting coverage
> > in CI systems (KernelCI is covering a bunch of different emulated
> > machines and LKFT has at least one configuration as well, clang's tests
> > have some wider architecture coverage as well I think) and they don't
> > seem to be seeing any problems - there's some other variable in there.
> >
> > For example current basic boot tests for KernelCI are at:
> >
> >     https://linux.kernelci.org/test/job/mainline/branch/master/kernel/v5.17-1442-
> gb47d5a4f6b8d/plan/baseline/
> >
> > for mainline and -next has:
> >
> >     https://linux.kernelci.org/test/job/next/branch/master/kernel/next-20220322/plan/baseline/
> >
> > These are with a buildroot based rootfs that has a "Saving random seed: "
> > step in the boot process FWIW.
> 
> I use buildroot 2021.02.3. I have not changed the buildroot code, and it
> still seems to be the same in 2022.02. I don't see the problem with all
> boot tests, only with the architectures mentioned above, and not with all
> qemu machines on the affected platforms. For arm, mostly older machines
> are affected (versatile, realview, pxa configurations, collie, integratorcp,
> sx1, mps2-an385, vexpress-a9, cubieboard). I didn't check, but maybe
> kernelci doesn't test those machines ?

I was trying to fix the buildroot save/restore random seed of a system
of mine.
I thought I'd fixed it - needed to use a persistent filesystem.
But I can't get rid of the 'uninitialised random read' messages.
(Which I expected to go away after writing the seed.)
But a quick look at the kernel code didn't seem to credit the
write into the correct logic.
I didn't check whether the data actually got used though.

	David

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