Re: [PATCH] x86/power/64: Do not refer to __PAGE_OFFSET from assembly code

[Rafael J. Wysocki]

On Friday, August 05, 2016 08:21:31 AM Thomas Garnier wrote:
> On Fri, Aug 5, 2016 at 7:44 AM, Rafael J. Wysocki <rjw@xxxxxxxxxxxxx> 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@xxxxxxxxx>
> >> >
> >> > 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@xxxxxxxxxx>
> >> > Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@xxxxxxxxx>
> >>
> >> Acked-by: Pavel Machek <pavel@xxxxxx>
> >>
> >> 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.

Great to hear that, but you need to be aware that the i386 hibernate code has
not been touched for a long time and it makes some heavy assumptions that
are not made on x86-64.

Please keep me and Pavel in the loop, though.

Thanks,
Rafael