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

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Message-ID: <CAK8P3a0Fzryo8Wi2exbQz=qXKGOGU6yxP0FGowa-fJkr0aGJFg@mail.gmail.com>
Date:   Wed, 23 Mar 2022 17:41:01 +0100
From:   Arnd Bergmann <arnd@...db.de>
To:     Mark Brown <broonie@...nel.org>
Cc:     Arnd Bergmann <arnd@...db.de>, Guenter Roeck <linux@...ck-us.net>,
        "Jason A. Donenfeld" <Jason@...c4.com>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        "open list:HARDWARE RANDOM NUMBER GENERATOR CORE" 
        <linux-crypto@...r.kernel.org>,
        linux-arch <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>,
        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

On Wed, Mar 23, 2022 at 5:18 PM Mark Brown <broonie@...nel.org> wrote:
>
> On Wed, Mar 23, 2022 at 04:53:13PM +0100, Arnd Bergmann wrote:
> > On Wed, Mar 23, 2022 at 3:23 PM Guenter Roeck <linux@...ck-us.net> wrote:
>
> > > I don't think it is entirely academic. versatile-pb fails for me;
> > > if it doesn't fail at KernelCI, I'd like to understand why - not to
> > > fix it in my test environment, but to make sure that I _don't_ fix it.
> > > After all, it _is_ a regression. Even if that regression is triggered
> > > by bad (for a given definition of "bad") userspace code, it is still
> > > a regression.
>
> > Maybe kernelci has a virtio-rng device assigned to the machine
> > and you don't? That would clearly avoid the issue here.
>
> No, nothing I can see in the boot log:
>
> https://storage.kernelci.org/next/master/next-20220323/arm/versatile_defconfig/gcc-10/lab-baylibre/baseline-qemu_arm-versatilepb.html
>
> and I'd be surprised if virtio devices made it through with a specific
> platform emulation.

In general they do: virtio devices appear as regular PCI devices
and get probed from there, as long as the drivers are available.

It looks like the PCI driver does not get initialized here though,
presumably because it's not enabled in versatile_defconfig.
It used to also not be enabled in multi_v5_defconfig, but I have
merged a patch from Anders that enables it in 5.18 for the
multi_v5_defconfig.

> However it looks like for that test the init
> scripts didn't do anything with the random seed (possibly due to running
> from ramdisk?) so we'd not have hit the condition.

Right.

     Arnd