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Message-ID: <20170620093642.3ri6dct5qkf7vhuc@thunk.org>
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
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