linux-kernel - Re: Fwd: [Bug 150021] New: kernel panic: "kernel tried to execute NX-protected page" when resuming from hibernate to disk

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Message-ID: <2437449.FpDj7DlX4Y@vostro.rjw.lan>
Date:	Tue, 26 Jul 2016 22:24:11 +0200
From:	"Rafael J. Wysocki" <rjw@...ysocki.net>
To:	Borislav Petkov <bp@...e.de>
Cc:	Ingo Molnar <mingo@...nel.org>,
	Josh Poimboeuf <jpoimboe@...hat.com>,
	Pavel Machek <pavel@....cz>,
	Linux PM list <linux-pm@...r.kernel.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Thomas Gleixner <tglx@...utronix.de>, shuzzle@...lbox.org,
	Thomas Garnier <thgarnie@...gle.com>,
	Kees Cook <keescook@...omium.org>
Subject: Re: Fwd: [Bug 150021] New: kernel panic: "kernel tried to execute NX-protected page" when resuming from hibernate to disk

On Tuesday, July 26, 2016 04:04:42 PM Borislav Petkov wrote:
> On Tue, Jul 26, 2016 at 01:32:28PM +0200, Rafael J. Wysocki wrote:
> > Hi,
> > 
> > The following commit:
> > 
> > commit 13523309495cdbd57a0d344c0d5d574987af007f
> > Author: Josh Poimboeuf <jpoimboe@...hat.com>
> > Date:   Thu Jan 21 16:49:21 2016 -0600
> > 
> >     x86/asm/acpi: Create a stack frame in do_suspend_lowlevel()
> >     
> >     do_suspend_lowlevel() is a callable non-leaf function which doesn't
> >     honor CONFIG_FRAME_POINTER, which can result in bad stack traces.
> >     
> >     Create a stack frame for it when CONFIG_FRAME_POINTER is enabled.
> > 
> > is reported to cause a resume-from-hibernation regression due to an attempt
> > to execute an NX page (we've seen quite a bit of that recently).
> > 
> > I'm asking the reporter to try 4.7, but if the problem is still there, we'll
> > need to revert the above I'm afraid.
> 
> So I can't resume properly from disk too, on the Intel laptop this time. Top
> commit is from tip/master:
> 
> commit 516f48acf59722429acd323b3d283f74f02891fe (refs/remotes/tip/master)
> Merge: a4823bbffc96 dd9506954539
> Author: Ingo Molnar <mingo@...nel.org>
> Date:   Mon Jul 25 08:39:43 2016 +0200
> 
>     Merge branch 'linus'
> 
> 
> So I thought it might be Josh's patch above and reverted it. No joy.
> 
> Then I remembered that I enabled CONFIG_RANDOMIZE_MEMORY for the
> microcode loader breakage which we've been debugging. Turned that off
> and machine resumes fine again.

Well, I wasn't aware of *another* flavor of ASLR in the works.  And there
was no hope it would not break hibernation if you asked me.

> It looks like
> 
>   0483e1fa6e09 ("x86/mm: Implement ASLR for kernel memory regions")
> 
> broke a bunch of things. Off the top of my head, we probably should make
> suspend to disk and CONFIG_RANDOMIZE_MEMORY mutually exclusive, like it
> was the case with ASLR previously, AFAIR.

Please no.

First off, it should be perfectly possible to make hibernation work along
with this new variant of ASLR.  Second, quite obviously, the author of these
ASLR changes had not done sufficient research to estimate the possible
impact of them.

Honestly, I don't think it is a good idea to introduce random Kconfig options
for working around cases in which the author of some changes cannot be bothered
with doing things right.  Even if that is security.

So IMO, either we should fix the problem, or that whole new ASLR stuff should
be reverted.

I think I know how to fix it, but I won't be able to get to that before the
next week.  I guess it can wait till then, though.

Thanks,
Rafael