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

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Date:	Wed, 01 Jun 2011 08:44:48 -0700
From:	"H. Peter Anvin" <hpa@...or.com>
To:	Ingo Molnar <mingo@...e.hu>
CC:	Dan Rosenberg <drosenberg@...curity.com>,
	Matthew Garrett <mjg@...hat.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, Vivek Goyal <vgoyal@...hat.com>
Subject: Re: [RFC][PATCH] Randomize kernel base address on boot

On 05/31/2011 11:18 PM, Ingo Molnar wrote:
>>
>> Older boot loaders did not know how big the kernel image was, 
>> therefore had no way to avoid memory space collision.  That is 
>> fixed in boot protocol 2.10.
> 
> But i loaded really large kernel images way back 10 years ago on 
> various systems and never had any problems until the default 
> allyesconfig hit a ~40 MB kernel image size limit ;-)
> 
> (which limit was in the kernel, not in the bootloader)

But it would have depended on the target hardware!  That's the problem.

> 
> So yes, a large kernel image "can" be an issue with old bootloaders 
> in some situations on weird machines but we don't really "break" them 
> via randomization, they were broken and fragile in some situations to 
> begin with.
> 

Well, yes; and I don't think the randomization. is a signifiant problem.

> It's fixed in any distro that cares and which would use our (not even 
> released) kernel that might one day have randomization.
> 
> Is that a fair summary of the bootloader situation?

No, because I don't think Grub is fixed in any of its flavors.

	-hpa

-- 
H. Peter Anvin, Intel Open Source Technology Center
I work for Intel.  I don't speak on their behalf.

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