linux-kernel - Re: [PATCH] random: silence compiler warnings and fix race

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Date:   Tue, 20 Jun 2017 05:36:42 -0400
From:   Theodore Ts'o <tytso@....edu>
To:     "Jason A. Donenfeld" <Jason@...c4.com>
Cc:     noloader@...il.com, tglx@...akpoint.cc,
        David Miller <davem@...emloft.net>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Eric Biggers <ebiggers3@...il.com>,
        LKML <linux-kernel@...r.kernel.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        kernel-hardening@...ts.openwall.com,
        Linux Crypto Mailing List <linux-crypto@...r.kernel.org>,
        Michael Ellerman <mpe@...erman.id.au>
Subject: Re: [PATCH] random: silence compiler warnings and fix race

On Tue, Jun 20, 2017 at 10:53:35AM +0200, Jason A. Donenfeld wrote:
> > Suppressing all messages for all configurations cast a wider net than
> > necessary. Configurations that could potentially be detected and fixed
> > likely will go unnoticed. If the problem is not brought to light, then
> > it won't be fixed.
> 
> I more or less agree with you that we should just turn this on for all
> users and they'll just have to live with the spam and report odd
> entries, and overtime we'll fix all the violations.

Fix all the problems *how*?  If you are on an old system which doesn't
a hardware random number generator, and which doesn't have a high
resolution cycle counter, and may not have a lot of entropy easily
harvestable from the environment, there may not be a lot you can do.
Sure, you can pretend that the cache (which by the way is usually
determinstic) is ***so*** complicated that no one can figure it out,
and essentially pretend that you have entropy when you probably don't;
that just simply becomes a different way of handwaving and suppressing
the warning messages.

> But I think there's another camp that would mutiny in the face of this
> kind of hubris.

Blocking the boot for hours and hours until we have enough entropy to
initialize the CRNG is ***not*** an acceptable way of making the
warning messages go away.  Do that and the users **will** mutiny.

It's this sort of attitude which is why Linus has in the past said
that security people are sometimes insane....

						- Ted