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

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Date:	Tue, 2 Aug 2016 13:59:01 -0700
From:	Thomas Garnier <thgarnie@...gle.com>
To:	"Rafael J. Wysocki" <rafael@...nel.org>
Cc:	"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 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.

> Thanks,
> Rafael