linux-kernel - Re: x86/random: Speculation to the rescue

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Message-ID: <201909301054.4E4F12B6D7@keescook>
Date:   Mon, 30 Sep 2019 11:05:20 -0700
From:   Kees Cook <keescook@...omium.org>
To:     Borislav Petkov <bp@...en8.de>
Cc:     Linus Torvalds <torvalds@...ux-foundation.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        "Ahmed S. Darwish" <darwish.07@...il.com>,
        LKML <linux-kernel@...r.kernel.org>,
        Theodore Ts'o <tytso@....edu>,
        Nicholas Mc Guire <hofrat@...ntech.at>,
        the arch/x86 maintainers <x86@...nel.org>,
        Andy Lutomirski <luto@...nel.org>
Subject: Re: x86/random: Speculation to the rescue

On Mon, Sep 30, 2019 at 08:10:15AM +0200, Borislav Petkov wrote:
> On Sun, Sep 29, 2019 at 07:59:19PM -0700, Linus Torvalds wrote:
> > All my smoke testing looked fine - I disabled trusting the CPU, I
> > increased the required entropy a lot, and to actually trigger the
> > lockup issue without the broken user space, I made /dev/urandom do
> > that "wait for entropy" thing too.
> 
> Hohum, seems to get rid of the longish delay during boot on my test
> boxes here:

Yes; for me too. This makes a huge difference in my ARM emulation
environments (where I wasn't using virtio-rng-device). Those VMs were
very boot entropy starved -- I was waiting minutes for sshd to start.

I doubt running something like dieharder on urandom would actually show
any deficiencies, but I've started a test up anyway. I'll yell in a few
hours if it actually has something bad to say. :)

-- 
Kees Cook