linux-kernel - Re: [PATCH] x86/power/64: Do not refer to __PAGE

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Date:	Fri, 5 Aug 2016 08:21:31 -0700
From:	Thomas Garnier <thgarnie@...gle.com>
To:	"Rafael J. Wysocki" <rjw@...ysocki.net>
Cc:	Pavel Machek <pavel@...x.de>,
	"the arch/x86 maintainers" <x86@...nel.org>,
	Linux PM list <linux-pm@...r.kernel.org>,
	"Rafael J. Wysocki" <rafael@...nel.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...hat.com>,
	"H . Peter Anvin" <hpa@...or.com>,
	Kees Cook <keescook@...omium.org>,
	Yinghai Lu <yinghai@...nel.org>,
	LKML <linux-kernel@...r.kernel.org>,
	kernel-hardening@...ts.openwall.com
Subject: Re: [PATCH] x86/power/64: Do not refer to __PAGE_OFFSET from assembly code

On Fri, Aug 5, 2016 at 7:44 AM, Rafael J. Wysocki <rjw@...ysocki.net> wrote:
> On Friday, August 05, 2016 12:37:13 PM Pavel Machek wrote:
>> On Wed 2016-08-03 01:19:26, Rafael J. Wysocki wrote:
>> > From: Rafael J. Wysocki <rafael.j.wysocki@...el.com>
>> >
>> > When CONFIG_RANDOMIZE_MEMORY is set on x86-64, __PAGE_OFFSET becomes
>> > a variable and using it as a symbol in the image memory restoration
>> > assembly code under core_restore_code is not correct any more.
>>
>> On a related note... we should really have page_offset variable in
>> such case, and use that -- having __FOO_BAR not being a constant is
>> ugly/confusing/dangerous.
>>
>> > To avoid that problem, modify set_up_temporary_mappings() to compute
>> > the physical address of the temporary page tables and store it in
>> > temp_level4_pgt, so that the value of that variable is ready to be
>> > written into CR3.  Then, the assembly code doesn't have to worry
>> > about converting that value into a physical address and things work
>> > regardless of whether or not CONFIG_RANDOMIZE_MEMORY is set.
>> >
>> > Reported-and-tested-by: Thomas Garnier <thgarnie@...gle.com>
>> > Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@...el.com>
>>
>> Acked-by: Pavel Machek <pavel@....cz>
>>
>> Is similar patch needed for i386?
>
> Yes, it is, in general, for i386 hibernation to work with ASLR.
>
> But it doesn't work with it for other reasons ATM, AFAICS.
>
> Unfortunately, I won't really have the time to take care of this any time
> soon.
>

KASLR memory randomization is only available for x64 right now. I plan
on porting to 32bit eventually and will test/adapt hibernation as part
of it.

> Thanks,
> Rafael
>