linux-kernel - Re: [RFC][PATCH] Randomize kernel base address on boot

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Message-ID: <1306280089.1921.18.camel@dan>
Date:	Tue, 24 May 2011 19:34:49 -0400
From:	Dan Rosenberg <drosenberg@...curity.com>
To:	"H. Peter Anvin" <hpa@...or.com>
Cc:	Tony Luck <tony.luck@...il.com>, linux-kernel@...r.kernel.org,
	davej@...hat.com, kees.cook@...onical.com, davem@...emloft.net,
	eranian@...gle.com, torvalds@...ux-foundation.org,
	adobriyan@...il.com, penberg@...nel.org,
	Arjan van de Ven <arjan@...radead.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Valdis.Kletnieks@...edu, Ingo Molnar <mingo@...e.hu>,
	pageexec@...email.hu
Subject: Re: [RFC][PATCH] Randomize kernel base address on boot

On Tue, 2011-05-24 at 16:07 -0700, H. Peter Anvin wrote:
> On 05/24/2011 04:04 PM, Dan Rosenberg wrote:
> > 
> >> 2. Not introduce a performance regression (we avoid locating in the
> >>    bottom 16 MiB for performance reasons, except on very small systems);
> > 
> > I altered the boot code so that it uses CONFIG_PHYSICAL_START, which
> > defaults to 16 MiB, as a lower bound on location.  So nothing will ever
> > get loaded below there, and I still can take advantage of higher
> > alignment granularity.  Are there other problems I'm not anticipating?
> > 
> 
> Please look at the discussion as to what led us to do things this way.
> 

Would you be able to point me to said discussion?  The only thing I can
find is this:

http://marc.info/?l=linux-kernel&m=124173552516435&w=2

This set PHYSICAL_START at 16 MB and alignment at 2/4 MB.  Then, three
days later, this was committed:

http://git.kernel.org/?p=linux/kernel/git/torvalds/linux-2.6.git;a=commit;h=ceefccc93932b920a8ec6f35f596db05202a12fe

This sets the alignment to 16 MB, with the only justification being that
relocatable kernels also need to start above 16 MB.

Thanks,
Dan

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