linux-kernel - Re: [PATCH v1 2/2] x86/power/64: Fix __PAGE

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Date:	Tue, 2 Aug 2016 23:08:03 +0200
From:	"Rafael J. Wysocki" <rafael@...nel.org>
To:	Thomas Garnier <thgarnie@...gle.com>
Cc:	"Rafael J. Wysocki" <rafael@...nel.org>,
	"Rafael J. Wysocki" <rjw@...ysocki.net>,
	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>, Pavel Machek <pavel@....cz>,
	"the arch/x86 maintainers" <x86@...nel.org>,
	LKML <linux-kernel@...r.kernel.org>,
	Linux PM list <linux-pm@...r.kernel.org>,
	kernel-hardening@...ts.openwall.com
Subject: Re: [PATCH v1 2/2] x86/power/64: Fix __PAGE_OFFSET usage on restore

On Tue, Aug 2, 2016 at 10:59 PM, Thomas Garnier <thgarnie@...gle.com> wrote:
> On Tue, Aug 2, 2016 at 1:47 PM, Rafael J. Wysocki <rafael@...nel.org> wrote:
>> On Tue, Aug 2, 2016 at 4:34 PM, Thomas Garnier <thgarnie@...gle.com> wrote:
>>> On Mon, Aug 1, 2016 at 5:38 PM, Rafael J. Wysocki <rjw@...ysocki.net> wrote:
>>>> On Monday, August 01, 2016 10:08:00 AM Thomas Garnier wrote:
>>>>> When KASLR memory randomization is used, __PAGE_OFFSET is a global
>>>>> variable changed during boot. The assembly code was using the variable
>>>>> as an immediate value to calculate the cr3 physical address. The
>>>>> physical address was incorrect resulting to a GP fault.
>>>>>
>>>>> Signed-off-by: Thomas Garnier <thgarnie@...gle.com>
>>>>> ---
>>>>>  arch/x86/power/hibernate_asm_64.S | 12 +++++++++++-
>>>>>  1 file changed, 11 insertions(+), 1 deletion(-)
>>>>>
>>>>> diff --git a/arch/x86/power/hibernate_asm_64.S b/arch/x86/power/hibernate_asm_64.S
>>>>> index 8eee0e9..8db4905 100644
>>>>> --- a/arch/x86/power/hibernate_asm_64.S
>>>>> +++ b/arch/x86/power/hibernate_asm_64.S
>>>>> @@ -23,6 +23,16 @@
>>>>>  #include <asm/processor-flags.h>
>>>>>  #include <asm/frame.h>
>>>>>
>>>>> +/*
>>>>> + * A global variable holds the page_offset when KASLR memory randomization
>>>>> + * is enabled.
>>>>> + */
>>>>> +#ifdef CONFIG_RANDOMIZE_MEMORY
>>>>> +#define __PAGE_OFFSET_REF __PAGE_OFFSET
>>>>> +#else
>>>>> +#define __PAGE_OFFSET_REF $__PAGE_OFFSET
>>>>> +#endif
>>>>> +
>>>>>  ENTRY(swsusp_arch_suspend)
>>>>>       movq    $saved_context, %rax
>>>>>       movq    %rsp, pt_regs_sp(%rax)
>>>>> @@ -72,7 +82,7 @@ ENTRY(restore_image)
>>>>>       /* code below has been relocated to a safe page */
>>>>>  ENTRY(core_restore_code)
>>>>>       /* switch to temporary page tables */
>>>>> -     movq    $__PAGE_OFFSET, %rcx
>>>>> +     movq    __PAGE_OFFSET_REF, %rcx
>>>>>       subq    %rcx, %rax
>>>>>       movq    %rax, %cr3
>>>>>       /* flush TLB */
>>>>>
>>>>
>>>> I'm not particularly liking the #ifdefs and they won't be really
>>>> necessary if the subtraction is carried out by the C code IMO.
>>>>
>>>> What about the patch below instead?
>>>>
>>>
>>> Yes, I think that's a good idea. I will test it and send PATCH v2.
>>
>> No need to send this patch again.  Please just let me know if it works
>> for you. :-)
>>
>
> It worked well when I tested it and I agree that's a better approach.

OK, thanks!

Let me add a changelog to it then.