Re: [PATCH v3 09/27] x86/acpi: Adapt assembly for PIE support

Thomas Garnier
2018-05-25T17:00:04Z

On Fri, May 25, 2018 at 2:14 AM Pavel Machek <pavel@ucw.cz> wrote:

> On Thu 2018-05-24 09:35:42, Thomas Garnier wrote:
> > On Thu, May 24, 2018 at 4:03 AM Pavel Machek <pavel@ucw.cz> wrote:
> >
> > > On Wed 2018-05-23 12:54:03, Thomas Garnier wrote:
> > > > Change the assembly code to use only relative references of symbols
for
> > the
> > > > kernel to be PIE compatible.
> > > >
> > > > Position Independent Executable (PIE) support will allow to
extended the
> > > > KASLR randomization range below the -2G memory limit.
> >
> > > What testing did this get?
> >
> > Tested boot, hibernation and performance on qemu and dedicated machine.

> Well, this is suspend, not hibernation code.

> So "sudo pm-suspend" or "echo mem > /sys/power/state" would be good
> way to test this.

Thanks, it worked. I added this to the testsuite I use for KASLR.

> Thanks,
> Pavel

> > > > diff --git a/arch/x86/kernel/acpi/wakeup_64.S
> > b/arch/x86/kernel/acpi/wakeup_64.S
> > > > index 50b8ed0317a3..472659c0f811 100644
> > > > --- a/arch/x86/kernel/acpi/wakeup_64.S
> > > > +++ b/arch/x86/kernel/acpi/wakeup_64.S
> > > > @@ -14,7 +14,7 @@
> > > > * Hooray, we are in Long 64-bit mode (but still running in
low
> > memory)
> > > > */
> > > > ENTRY(wakeup_long64)
> > > > - movq saved_magic, %rax
> > > > + movq saved_magic(%rip), %rax
> > > > movq $0x123456789abcdef0, %rdx
> > > > cmpq %rdx, %rax
> > > > jne bogus_64_magic
> >
> > > Because, as comment says, this is rather tricky code.
> >
> > I agree, I think maintainers feedback is very important for this
patchset.

> --
> (english) http://www.livejournal.com/~pavelmachek
> (cesky, pictures)
http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html

--
Thomas