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

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Date:	Mon, 11 Nov 2013 20:58:53 +0100
From:	Ingo Molnar <mingo@...nel.org>
To:	"H. Peter Anvin" <hpa@...or.com>
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


* H. Peter Anvin <hpa@...or.com> wrote:

> On 11/11/2013 11:37 AM, Kees Cook wrote:
> > On Mon, Nov 11, 2013 at 11:27 AM, H. Peter Anvin <hpa@...or.com> wrote:
> >> On 11/11/2013 10:20 AM, Ingo Molnar wrote:
> >>>
> >>> Why aren't the 3 sources of entropy XOR-ed together?
> >>
> >> Note we don't want to poke i8254 if we have any other sources, as the
> >> i8254 may not be present on newer systems and in some other cases not
> >> safe to touch.  We can XOR in the TSC with RDRAND although it seems a
> >> bit odd.
> > 
> > I await the final decision! :)
> > 
> 
> 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.

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

Thanks,

	Ingo
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