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

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Date:	Fri, 27 May 2011 19:46:44 +0200
From:	Ingo Molnar <mingo@...e.hu>
To:	Linus Torvalds <torvalds@...ux-foundation.org>
Cc:	Dan Rosenberg <drosenberg@...curity.com>,
	"Rafael J. Wysocki" <rjw@...k.pl>, Tony Luck <tony.luck@...il.com>,
	linux-kernel@...r.kernel.org, davej@...hat.com,
	kees.cook@...onical.com, davem@...emloft.net, eranian@...gle.com,
	adobriyan@...il.com, penberg@...nel.org, hpa@...or.com,
	Arjan van de Ven <arjan@...radead.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Valdis.Kletnieks@...edu, pageexec@...email.hu
Subject: Re: [RFC][PATCH] Randomize kernel base address on boot


* Linus Torvalds <torvalds@...ux-foundation.org> wrote:

> On Fri, May 27, 2011 at 10:16 AM, Ingo Molnar <mingo@...e.hu> wrote:
> >
> > Well, 'fixing the info leaks' will obfuscate previously useful files
> > such as /proc/kallsyms ...
> 
> Guys, stop with the crazy already.
> 
> YOU HAVE TO DO THAT FOR THE LINK-TIME-OBFUSCATION TOO!
>
> > That's one of the advantages of randomization: it allows us to 
> > expose RIPs without them being an instant information leak.
> 
> Except you clearly aren't thinking that through AT ALL.
> 
> The obfuscation of things like /proc/kallsyms is *exactly*the*same* 
> whether you do the randomization at boot-time or install-time.

Well, but two mails ago you said:

> And load-time randomization has all these nasty problems with 
> memory maps etc, because we obviously have to shift the whole 
> kernel around by some fixed offset. But if there was some way to 
> just re-link the distro kernel easily, then it could be done by the 
> kernel install scripts, and it could potentially do more than just 
> "shift up load address by some random number".

If i understood you correctly you suggest randomizing the image by 
shifting the symbols in it around. The boot loader would still load 
an 'image' where it always loads it - just that image itself is 
randomized internally somewhat, right?

( because that's the only way we can avoid the problems with e820 
  memory maps which you referred to, if don't actually change the 
  load address. )

Have i understood you correctly?

Thanks,

	Ingo
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