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Date:      Tue, 24 Feb 2015 10:25:07 -0800
From:      John-Mark Gurney <jmg@funkthat.com>
To:        Alfred Perlstein <alfred@freebsd.org>
Cc:        Konstantin Belousov <kostikbel@gmail.com>, Harrison Grundy <harrison.grundy@astrodoggroup.com>, freebsd-arch@freebsd.org
Subject:   Re: locks and kernel randomness...
Message-ID:  <20150224182507.GI46794@funkthat.com>
In-Reply-To: <54ECBD4B.6000007@freebsd.org>
References:  <20150224012026.GY46794@funkthat.com> <20150224015721.GT74514@kib.kiev.ua> <54EBDC1C.3060007@astrodoggroup.com> <20150224024250.GV74514@kib.kiev.ua> <DD06E2EA-68D6-43D7-AA17-FB230750E55A@bsdimp.com> <20150224174053.GG46794@funkthat.com> <54ECBD4B.6000007@freebsd.org>

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Alfred Perlstein wrote this message on Tue, Feb 24, 2015 at 13:04 -0500:
> On 2/24/15 12:40 PM, John-Mark Gurney wrote:
> > Warner Losh wrote this message on Tue, Feb 24, 2015 at 07:56 -0700:
> >> Then again, if you want to change random(), provide a weak_random() that???s
> >> the traditional non-crypto thing that???s fast and lockless. That would make it easy
> >> to audit in our tree. The scheduler doesn???t need cryptographic randomness, it
> >> just needs to make different choices sometimes to ensure its notion of fairness.
> >
> > I do not support having a weak_random...  If the consumer is sure
> > enough that you don't need a secure random, then they can pick an LCG
> > and implement it themselves and deal (or not) w/ the locking issues...
> >
> > It appears that the scheduler had an LCG but for some reason the authors
> > didn't feel like using it here..
> 
> The way I read this argument is that no low quality sources of 
> randomness shall be allowed.

No, I'm saying that the person who needs the predictable randomness
needs to do extra work to get it...  If they care that much about
performance/predictability/etc, then a little extra work won't hurt
them..  And if they don't know what an LCG is, then they aren't
qualified to make the decision that a weaker RNG is correct for their
situation..

> So we should get rid of rand(3)?  When do we deprecate that?

No, we should replace it w/ proper randomness like OpenBSD has...
I'm willing to go that far and I think FreeBSD should...  OpenBSD has
done a lot of leg work in tracking down ports that correctly use
rand(3), and letting them keep their deterministic randomness, while
the remaining get real random..

> Your argument doesn't hold water.

Sorry, you're argument sounds like it's from the 90's when we didn't
know any better on how to make secure systems...  Will you promise to
audit all new uses of randomness in the system to make sure that they
are using the correct, secure API?

Considering that it's been recommended that people NOT use
read_random(9) for 14 years, yet people continue to use it in new code,
demonstrates that people do not know what they are doing (wrt
randomness), and the only way to make sure they do the correct, secure
thing is to only provide the secure API...

-- 
  John-Mark Gurney				Voice: +1 415 225 5579

     "All that I will do, has been done, All that I have, has not."



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