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Subject: Re: [PATCH RFC v4 1/1] random: WARN on large getrandom() waits and
 introduce getrandom2()
To:     Linus Torvalds <torvalds@linux-foundation.org>,
        Andy Lutomirski <luto@kernel.org>
Cc:     "Ahmed S. Darwish" <darwish.07@gmail.com>,
        Lennart Poettering <mzxreary@0pointer.de>,
        "Theodore Y. Ts'o" <tytso@mit.edu>,
        "Eric W. Biederman" <ebiederm@xmission.com>,
        Michael Kerrisk <mtk.manpages@gmail.com>,
        Willy Tarreau <w@1wt.eu>,
        Matthew Garrett <mjg59@srcf.ucam.org>,
        lkml <linux-kernel@vger.kernel.org>,
        Ext4 Developers List <linux-ext4@vger.kernel.org>,
        Linux API <linux-api@vger.kernel.org>,
        linux-man <linux-man@vger.kernel.org>
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From:   "Alexander E. Patrakov" <patrakov@gmail.com>
Message-ID: <ff3504ba-c21b-6560-6b87-e8c5b964b1a4@gmail.com>
Date:   Sat, 21 Sep 2019 01:11:57 +0500
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21.09.2019 00:51, Linus Torvalds =D0=BF=D0=B8=D1=88=D0=B5=D1=82:

> And we'll also have to make getrandom(0) be really _timely_. Security
> people would likely rather wait for minutes before they are happy with
> it. But because it's a boot constraint as things are now, it will not
> just be jitter-entropy, it will be _accelerated_ jitter-entropy in 15
> seconds or whatever, and since it can't use up all of CPU time, it's
> realistically more like "15 second timeout, but less of actual CPU
> time for jitter".

I don't think that "accelerated jitter" makes sense. The jitterentropy=20
hwrng that I sent earlier fills the entropy buffer in less than 2=20
seconds, even with quality=3D4, so there is no need to accelerate it even=
=20
more.

> That said, if we can all convince everybody (hah!) that jitter entropy
> in the kernel would be sufficient, then we can make the whole point
> entirely moot, and just say "we'll just change crng_wait() to do
> jitter entropy instead and be done with it. Then any getrandom() user
> will just basically wait for a (very limited) time and the system will
> be happy.
>=20
> If that is the case we wouldn't need new flags at all. But I don't
> think you can make everybody agree to that, which is why I suspect
> we'll need the new flag, and I'll just take the heat for saying "0 is
> now off limits, because it does this thing that a lot of people
> dislike".

I 100% agree with that.

--=20
Alexander E. Patrakov


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