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

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Message-ID: <4DDC4107.5060006@zytor.com>
Date:	Tue, 24 May 2011 16:36:39 -0700
From:	"H. Peter Anvin" <hpa@...or.com>
To:	Dan Rosenberg <drosenberg@...curity.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 05/24/2011 04:34 PM, Dan Rosenberg wrote:
> 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.
> 

I think those patches came after the discussion were already over.  I'll
try to look for it.

	-hpa
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