linux-kernel - Re: [PATCH] drivers/net: remove network drivers' last few uses of IRQF_SAMPLE

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Message-ID: <483C3A5A.6020207@hp.com>
Date:	Tue, 27 May 2008 09:44:10 -0700
From:	Rick Jones <rick.jones2@...com>
To:	Bill Fink <billfink@...dspring.com>
CC:	Alejandro Riveira Fernández <ariveira@...il.com>,
	Theodore Tso <tytso@....EDU>, Glen Turner <gdt@....id.au>,
	Chris Peterson <cpeterso@...terso.com>,
	Alan Cox <alan@...rguk.ukuu.org.uk>,
	Lennart Sorensen <lsorense@...lub.uwaterloo.ca>,
	Jeff Garzik <jeff@...zik.org>,
	"Kok, Auke" <auke-jan.h.kok@...el.com>,
	"Brandeburg, Jesse" <jesse.brandeburg@...el.com>,
	netdev@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] drivers/net: remove network drivers' last few uses of
 IRQF_SAMPLE_RANDOM

> For systems with high resolution timers, even if an attacker has total
> knowledge/control of the network, it doesn't seem realistically possible
> for them to determine the low order bits of the nanosecond timer of
> disk and network I/O system calls, if those were used as a source of
> entropy. 

Around the same time I was working on getting the performance figures 
for the RNG in the Infineon TPM in the system I had, I tried, however 
briefly, to concoct a test using netperf and pulling the ITC on an 
Itanium processor to generate some randomness.  I'm not at all sure I 
was doing things correctly - I was pulling the bottom one to 4 bits of 
the ITC after each call to recv() of a TCP_RR test - but when I tried to 
feed the resulting trickle of data through diehard (which I may have 
been running poorly) it was giving nothing but a p value of 0.000000 
which while I don't grok the p-value itself, I understand that 
consistent value of 0.000000 is bad :(

So, I may have had a bad test case.  If someone has some suggestions for 
  a better test of the low-order-bits-of-the-interval-timer hypothesis 
I'd love to hear about them.

rick jones
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