linux-kernel - Re: [PATCH v6 0/5] /dev/random

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Message-ID: <20160821031439.GA392@gondor.apana.org.au>
Date:   Sun, 21 Aug 2016 11:14:39 +0800
From:   Herbert Xu <herbert@...dor.apana.org.au>
To:     "H. Peter Anvin" <hpa@...ux.intel.com>
Cc:     Theodore Ts'o <tytso@....edu>, Pavel Machek <pavel@....cz>,
        Stephan Mueller <smueller@...onox.de>, sandyinchina@...il.com,
        Jason Cooper <cryptography@...edaemon.net>,
        John Denker <jsd@...n.com>, Joe Perches <joe@...ches.com>,
        George Spelvin <linux@...izon.com>,
        linux-crypto@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v6 0/5] /dev/random - a new approach

On Fri, Aug 19, 2016 at 10:20:18AM -0700, H. Peter Anvin wrote:
> On 08/18/16 22:56, Herbert Xu wrote:
> > On Thu, Aug 18, 2016 at 10:49:47PM -0400, Theodore Ts'o wrote:
> >>
> >> That really depends on the system.  We can't assume that people are
> >> using systems with a 100Hz clock interrupt.  More often than not
> >> people are using tickless kernels these days.  That's actually the
> >> problem with changing /dev/urandom to block until things are
> >> initialized.
> > 
> > Couldn't we disable tickless until urandom has been seeded? In fact
> > perhaps we should accelerate the timer interrupt rate until it has
> > been seeded?
> > 
> 
> The biggest problem there is that the timer interrupt adds *no* entropy
> unless there is a source of asynchronicity in the system.  On PCs,
> traditionally the timer has been run from a completely different crystal
> (14.31818 MHz) than the CPU, which is the ideal situation, but if they
> are run off the same crystal and run in lockstep, there is very little
> if anything there.  On some systems, the timer may even *be* the only
> source of time, and the entropy truly is zero.

Sure, but that's orthorgonal to what Ted was talking about above.

Thanks,
-- 
Email: Herbert Xu <herbert@...dor.apana.org.au>
Home Page: http://gondor.apana.org.au/~herbert/
PGP Key: http://gondor.apana.org.au/~herbert/pubkey.txt