linux-kernel - Re: PROBLEM: Resume form hibernate broken by setting NX on gap

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Date:	Sat, 11 Jun 2016 22:48:08 -0600
From:	Logan Gunthorpe <logang@...tatee.com>
To:	"Rafael J. Wysocki" <rjw@...ysocki.net>
Cc:	Kees Cook <keescook@...omium.org>,
	"Rafael J. Wysocki" <rafael@...nel.org>,
	Stephen Smalley <sds@...ho.nsa.gov>,
	Ingo Molnar <mingo@...nel.org>, Ingo Molnar <mingo@...hat.com>,
	the arch/x86 maintainers <x86@...nel.org>,
	"linux-pm@...r.kernel.org" <linux-pm@...r.kernel.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Andy Lutomirski <luto@...nel.org>,
	Borislav Petkov <bp@...en8.de>,
	Denys Vlasenko <dvlasenk@...hat.com>,
	Brian Gerst <brgerst@...il.com>
Subject: Re: PROBLEM: Resume form hibernate broken by setting NX on gap

Hey,

On 11/06/16 07:05 PM, Rafael J. Wysocki wrote:
>> 1) Commit ab76f7b4ab only extends the NX bit between __ex_table and
>> rodata; which, by my understanding, shouldn't be used by anything. And
>> __ex_table and rodata are fixed by the kernel's binary so both symbols
>> should be the same in both the image kernel and the boot kernel given
>> that both are running from the same binary.
>
> Well, what if the kernel is relocated?

Ah, I'm sure I don't fully grasp the implications of that but I would 
assume that if the image kernel were located somewhere else it would 
still be far away from the boot kernel's ex_table/rodata boundary.

>> 2) When ab76f7b4ab is reverted, hibernation seems to work 100%. Though,
>> when it's in place, it only works some of the time. Given that commit is
>> only extending the NX region a bit, if there is some random mismatch,
>> why does it never reach rodata? In other words, why is rodata a magic
>> line that seems to work all the time -- why doesn't this random mismatch
>> ever extend into the rodata region? rodata isn't _that_ far away from
>> the end of ex_table.
>
> That's a very good question. :-)

Yeah, I guess if we knew the answer we'd understand what was going on 
and have a fix.


> Can you please check if the patch below makes any difference?

I'm afraid it's no different. The kernel still freezes on resume. 
Though, no warnings with this one.

Thanks,

Logan