Re: [PATCH v1 2/2] x86/power/64: Fix __PAGE_OFFSET usage on restore

[Thomas Garnier]

On Mon, Aug 1, 2016 at 5:38 PM, Rafael J. Wysocki <rjw@xxxxxxxxxxxxx> 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@xxxxxxxxxx>
>> ---
>>  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.

Thanks for the quick feedback.

> ---
>  arch/x86/power/hibernate_64.c     |   18 +++++++++---------
>  arch/x86/power/hibernate_asm_64.S |    2 --
>  2 files changed, 9 insertions(+), 11 deletions(-)
>
> Index: linux-pm/arch/x86/power/hibernate_asm_64.S
> ===================================================================
> --- linux-pm.orig/arch/x86/power/hibernate_asm_64.S
> +++ linux-pm/arch/x86/power/hibernate_asm_64.S
> @@ -72,8 +72,6 @@ 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
> -       subq    %rcx, %rax
>         movq    %rax, %cr3
>         /* flush TLB */
>         movq    %rbx, %rcx
> Index: linux-pm/arch/x86/power/hibernate_64.c
> ===================================================================
> --- linux-pm.orig/arch/x86/power/hibernate_64.c
> +++ linux-pm/arch/x86/power/hibernate_64.c
> @@ -37,11 +37,11 @@ unsigned long jump_address_phys;
>   */
>  unsigned long restore_cr3 __visible;
>
> -pgd_t *temp_level4_pgt __visible;
> +unsigned long temp_level4_pgt __visible;
>
>  unsigned long relocated_restore_code __visible;
>
> -static int set_up_temporary_text_mapping(void)
> +static int set_up_temporary_text_mapping(pgd_t *pgd)
>  {
>         pmd_t *pmd;
>         pud_t *pud;
> @@ -71,7 +71,7 @@ static int set_up_temporary_text_mapping
>                 __pmd((jump_address_phys & PMD_MASK) | __PAGE_KERNEL_LARGE_EXEC));
>         set_pud(pud + pud_index(restore_jump_address),
>                 __pud(__pa(pmd) | _KERNPG_TABLE));
> -       set_pgd(temp_level4_pgt + pgd_index(restore_jump_address),
> +       set_pgd(pgd + pgd_index(restore_jump_address),
>                 __pgd(__pa(pud) | _KERNPG_TABLE));
>
>         return 0;
> @@ -90,15 +90,16 @@ static int set_up_temporary_mappings(voi
>                 .kernel_mapping = true,
>         };
>         unsigned long mstart, mend;
> +       pgd_t *pgd;
>         int result;
>         int i;
>
> -       temp_level4_pgt = (pgd_t *)get_safe_page(GFP_ATOMIC);
> -       if (!temp_level4_pgt)
> +       pgd = (pgd_t *)get_safe_page(GFP_ATOMIC);
> +       if (!pgd)
>                 return -ENOMEM;
>
>         /* Prepare a temporary mapping for the kernel text */
> -       result = set_up_temporary_text_mapping();
> +       result = set_up_temporary_text_mapping(pgd);
>         if (result)
>                 return result;
>
> @@ -107,13 +108,12 @@ static int set_up_temporary_mappings(voi
>                 mstart = pfn_mapped[i].start << PAGE_SHIFT;
>                 mend   = pfn_mapped[i].end << PAGE_SHIFT;
>
> -               result = kernel_ident_mapping_init(&info, temp_level4_pgt,
> -                                                  mstart, mend);
> -
> +               result = kernel_ident_mapping_init(&info, pgd, mstart, mend);
>                 if (result)
>                         return result;
>         }
>
> +       temp_level4_pgt = (unsigned long)pgd - __PAGE_OFFSET;
>         return 0;
>  }
>
>