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

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Date:	Tue, 31 May 2011 19:51:22 +0100
From:	Matthew Garrett <mjg@...hat.com>
To:	"H. Peter Anvin" <hpa@...or.com>
Cc:	Dan Rosenberg <drosenberg@...curity.com>,
	Tony Luck <tony.luck@...il.com>, linux-kernel@...r.kernel.org,
	kees.cook@...onical.com, davej@...hat.com,
	torvalds@...ux-foundation.org, adobriyan@...il.com,
	eranian@...gle.com, penberg@...nel.org, davem@...emloft.net,
	Arjan van de Ven <arjan@...radead.org>,
	Valdis.Kletnieks@...edu, Andrew Morton <akpm@...ux-foundation.org>,
	pageexec@...email.hu, Ingo Molnar <mingo@...e.hu>,
	Vivek Goyal <vgoyal@...hat.com>
Subject: Re: [RFC][PATCH] Randomize kernel base address on boot

On Tue, May 31, 2011 at 11:40:13AM -0700, H. Peter Anvin wrote:
> On 05/31/2011 09:52 AM, Matthew Garrett wrote:
> > The BIOS E820 map, or the kernel representation? In either case, this 
> > isn't going to work well with EFI. There are regions that will be marked 
> > as available in the E820 map that we *mustn't* touch until we've entered 
> > EFI virtual mode.
> > 
> > (This is, clearly, insane).
> > 
> 
> I believe we could (should!) mark them reserved, not available, in the
> E820 map and free them later.

That was my original approach, but it requires that the bootloader be 
modified and it turns out that it's a lot harder to hand reserved 
regions back to the OS than it is to just reserve it in-kernel. The 
complete inflexibility of e820 is massively unhelpful here. It's just 
not possible to represent all of the EFI memory map data in it.

-- 
Matthew Garrett | mjg59@...f.ucam.org
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