linux-kernel - Re: [PATCH 0/2] make kASLR vs hibernation boot-time selectable

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Date:	Fri, 13 Jun 2014 22:26:34 +0200
From:	Pavel Machek <pavel@....cz>
To:	Kees Cook <keescook@...omium.org>
Cc:	"H. Peter Anvin" <hpa@...or.com>,
	LKML <linux-kernel@...r.kernel.org>,
	Randy Dunlap <rdunlap@...radead.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...hat.com>,
	"x86@...nel.org" <x86@...nel.org>,
	"Rafael J. Wysocki" <rjw@...ysocki.net>,
	Len Brown <len.brown@...el.com>,
	Wei Yongjun <yongjun_wei@...ndmicro.com.cn>,
	"linux-doc@...r.kernel.org" <linux-doc@...r.kernel.org>,
	linux-pm@...r.kernel.org
Subject: Re: [PATCH 0/2] make kASLR vs hibernation boot-time selectable

On Fri 2014-06-13 10:32:56, Kees Cook wrote:
> On Fri, Jun 13, 2014 at 3:51 AM, Pavel Machek <pavel@....cz> wrote:
> > Hi!
> >
> >
> >> >>> Any way we can make them work together instead?
> >> >>
> >> >> I'm sure there is, but I don't know the solution. :)
> >> >>
> >> >> At the very least this gets us one step closer (we can build them together).
> >> >>
> >> >
> >> > But it is really invasive.
> >>
> >> Well, I don't agree there. I actually would like to be able to turn
> >> off hibernation support on distro kernels regardless of kASLR, so I
> >> think this is really killing two birds with one stone.
> >>
> >> > I have to admit to being somewhat fuzzy on what the core problem with
> >> > hibernation and kASLR is... in both cases there is a set of pages that
> >> > need to be installed, some of which will overlap the loader kernel.
> >> > What am I missing?
> >>
> >> I don't know how resume works, but I have assumed that the newly
> >> loaded kernel stays in memory and pulls in the vmalloc, kmalloc,
> >> modules, and userspace memory maps from disk. Since these things can
> >> easily contain references to kernel text, if the newly loaded kernel
> >> has moved with regard to the hibernated image, everything breaks.
> >> IIUC, this is similar why you can't rebuild your kernel and resume
> >> from a different version.
> >
> > x86-64 can resume from different kernel that did the suspend. kASLR
> > should not be too different from that. (You just include kernel text
> > in the hibernation image. It is small enough to do that.)
> 
> Oooh, that's very exciting! How does that work (what happens to the
> kernel that booted first, etc)? I assume physical memory layout can't
> change between hibernation and resume? Or, where should I be reading
> code that does this?

I'm not sure what you mean by "physical memory layout can't
change". You may not remove RAM between suspend/resume, no.

It is Rafael's design, actually, you can see it in
arch/x86/power/hibernate_asm_64.S .

32bit version does have that ability, IIRC.

									Pavel
-- 
(english) http://www.livejournal.com/~pavelmachek
(cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html
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