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

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Message-ID: <CAGXu5jJTSqtOMBNeOGEXfj_1iWGbE7p_YooeHT9wc4WRDjcGyQ@mail.gmail.com>
Date:	Fri, 13 Jun 2014 10:32:56 -0700
From:	Kees Cook <keescook@...omium.org>
To:	Pavel Machek <pavel@....cz>
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, 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?

-Kees

-- 
Kees Cook
Chrome OS Security
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