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

From: Pavel Machek <pavel@ucw.cz>
To: Thomas Garnier <thgarnie@google.com>
Cc: Kate Stewart <kstewart@linuxfoundation.org>,
	Nicolas Pitre <nicolas.pitre@linaro.org>,
	the arch/x86 maintainers <x86@kernel.org>,
	Sergey Senozhatsky <sergey.senozhatsky.work@gmail.com>,
	Petr Mladek <pmladek@suse.com>, Len Brown <len.brown@intel.com>,
	Peter Zijlstra <peterz@infradead.org>, Yonghong Song <yhs@fb.com>,
	Christopher Li <sparse@chrisli.org>,
	Dave Hansen <dave.hansen@linux.intel.com>,
	Dominik Brodowski <linux@dominikbrodowski.net>,
	LKML <linux-kernel@vger.kernel.org>,
	Masahiro Yamada <yamada.masahiro@socionext.com>,
	Jan Beulich <JBeulich@suse.com>,
	"H . Peter Anvin" <hpa@zytor.com>,
	Kernel Hardening <kernel-hardening@lists.openwall.com>,
	Christoph Lameter <cl@linux.com>,
	Alok Kataria <akataria@vmware.com>,
	Linux Doc Mailing List <linux-doc@vger.kernel.org>,
	linux-arch <linux-arch@vger.kernel.org>,
	Jonathan Corbet <corbet@lwn.net>, Herbert Xu <herbert@gondor.>
Subject: Re: [PATCH v3 09/27] x86/acpi: Adapt assembly for PIE support
Date: Fri, 25 May 2018 11:14:47 +0200	[thread overview]
Message-ID: <20180525091447.GC9666__39068.3532962159$1527239600$gmane$org@amd> (raw)
In-Reply-To: <CAJcbSZFJ84+VC5xDQZGHctupdqwmMBgqzLzFRqCTBpi5t-2Gvw@mail.gmail.com>

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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,
							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

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