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

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Date:	Fri, 27 May 2011 10:57:44 -0700
From:	Linus Torvalds <torvalds@...ux-foundation.org>
To:	Ingo Molnar <mingo@...e.hu>
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

On Fri, May 27, 2011 at 10:46 AM, Ingo Molnar <mingo@...e.hu> wrote:
>
> 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?

You snipped the other part of my email you responded to:

  For chrissake - you're doing the same thing. The only question is
  "when" (and the fact that if you do it at install-time, you can do a
  fancier job of it)

ie the fact that if you do it at install-time, you have the option of
being much more fancy about it.

So sure, the install time option *can* do more. It doesn't *have* to do more.

But being able to do a better job of randomization is *better*. Ok? It
doesn't mean you have to, but you have more options to do things if
you want to.

IOW, there is absolutely zero difference between doing it at
install-time or run-time, but the install-time one is (a) likely
easier and (b) certainly more flexible. But both of them do the exact
same thing, and require the exact same support in things like
/proc/kallsyms.

Of course, if we end up doing something really fancy (which the
install-time option allows), that obviously does mean that the
remapping by %pK thing for kallsyms needs to be much smarter too.

But at %pK time, you can *afford* to do that kind of things. At
boot-time, before you're even loaded and have a hard time even parsing
the e820 maps? Yeah, you're not going to do anything smart there, I
can tell you.

                   Linus
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