linux-kernel - Re: [tip:x86/kaslr] x86, kaslr: Provide randomness functions

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Message-ID: <52813842.40709@zytor.com>
Date:	Mon, 11 Nov 2013 12:04:18 -0800
From:	"H. Peter Anvin" <hpa@...or.com>
To:	Ingo Molnar <mingo@...nel.org>
CC:	Kees Cook <keescook@...omium.org>,
	LKML <linux-kernel@...r.kernel.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	"H. Peter Anvin" <hpa@...ux.intel.com>,
	"linux-tip-commits@...r.kernel.org" 
	<linux-tip-commits@...r.kernel.org>
Subject: Re: [tip:x86/kaslr] x86, kaslr: Provide randomness functions

On 11/11/2013 11:58 AM, Ingo Molnar wrote:
>>
>> Use the i8254 if and only if nothing else is available, it isn't safe to
>> touch on some newer systems.
> 
> I concur - the i8254 is probably also a low entry source, given that this 
> all runs early bootup.
> 

Well, it is a 16-bit 1.19318 MHz counter so at least on older systems it
is likely to provide at least a modicum on entropy.  On systems with a
TSC it is likely to be redundant with the TSC.

> In any case there's no excuse for not mixing RDRAND and RDTSC entropy.

	-hpa


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