Re: [PATCH]Fix: 32bit binary has 64bit address of stack vma

[Ying Han <yinghan@google.com>]

Thanks Andrew.

On Mon, Jan 12, 2009 at 2:59 PM, Andrew Morton
<akpm@linux-foundation.org> wrote:
> On Mon, 5 Jan 2009 15:39:07 -0800
> Ying Han <yinghan@google.com> wrote:
>
>> From: Ying Han <yinghan@google.com>
>>
>> Fix 32bit binary get 64bit stack vma offset.
>>
>> 32bit binary running on 64bit system, the /proc/pid/maps shows for the
>> vma represents stack get a 64bit adress:
>> ff96c000-ff981000 rwxp 7ffffffea000 00:00 0 [stack]
>>
>> Signed-off-by:        Ying Han <yinghan@google.com>
>>
>> fs/exec.c                     |    5 +-
>>
>> diff --git a/fs/exec.c b/fs/exec.c
>> index 4e834f1..8c3eff4 100644
>> --- a/fs/exec.c
>> +++ b/fs/exec.c
>> @@ -517,6 +517,7 @@ static int shift_arg_pages(struct vm_area_struct *vma, uns
>>       unsigned long length = old_end - old_start;
>>       unsigned long new_start = old_start - shift;
>>       unsigned long new_end = old_end - shift;
>> +     unsigned long new_pgoff = new_start >> PAGE_SHIFT;
>>       struct mmu_gather *tlb;
>>
>>       BUG_ON(new_start > new_end);
>> @@ -531,7 +532,7 @@ static int shift_arg_pages(struct vm_area_struct *vma, uns
>>       /*
>>        * cover the whole range: [new_start, old_end)
>>        */
>> -     vma_adjust(vma, new_start, old_end, vma->vm_pgoff, NULL);
>> +     vma_adjust(vma, new_start, old_end, new_pgoff, NULL);
>>
>>       /*
>>        * move the page tables downwards, on failure we rely on
>> @@ -564,7 +565,7 @@ static int shift_arg_pages(struct vm_area_struct *vma, uns
>>       /*
>>        * shrink the vma to just the new range.
>>        */
>> -     vma_adjust(vma, new_start, new_end, vma->vm_pgoff, NULL);
>> +     vma_adjust(vma, new_start, new_end, new_pgoff, NULL);
>>
>>       return 0;
>
> I rewrote the chagnelog as below.  Please confirm that it makes sense?
>
>
> Subject: fs/exec.c: fix value of vma->vm_pgoff for the stack VMA of 32-bit processes
> From: Ying Han <yinghan@google.com>
>
> With a 32 bit binary running on a 64 bit system, the /proc/pid/maps for
> the [stack] VMA displays a 64-bit address:
>
> ff96c000-ff981000 rwxp 7ffffffea000 00:00 0 [stack]
looks good.
>
> This is because vma->vm_pgoff for that VMA is incorrectly being stored in
> units of offset-in-bytes.  It should be stored in units of offset-in-pages.
that is not the problem. the real problem here is that the
vma->vm_pgoff is initialized as 64bit address. When
it is doing the shift_arg_pages, it supposed to be readjust to 32bit.
It did for newstart and newend, but still
used the old vma->start(64bit) for vma->pgoff. Here i make the change
to get the newpgoff based on the newstart.
> Signed-off-by: Ying Han <yinghan@google.com>
> Cc: Mike Waychison <mikew@google.com>
> Cc: Hugh Dickins <hugh@veritas.com>
> Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
> ---
>
>  fs/exec.c |    5 +++--
>  1 file changed, 3 insertions(+), 2 deletions(-)
>
> diff -puN fs/exec.c~fs-execc-fix-value-of-vma-vm_pgoff-for-the-stack-vma-of-32-bit-processes fs/exec.c
> --- a/fs/exec.c~fs-execc-fix-value-of-vma-vm_pgoff-for-the-stack-vma-of-32-bit-processes
> +++ a/fs/exec.c
> @@ -509,6 +509,7 @@ static int shift_arg_pages(struct vm_are
>        unsigned long length = old_end - old_start;
>        unsigned long new_start = old_start - shift;
>        unsigned long new_end = old_end - shift;
> +       unsigned long new_pgoff = new_start >> PAGE_SHIFT;
>        struct mmu_gather *tlb;
>
>        BUG_ON(new_start > new_end);
> @@ -523,7 +524,7 @@ static int shift_arg_pages(struct vm_are
>        /*
>         * cover the whole range: [new_start, old_end)
>         */
> -       vma_adjust(vma, new_start, old_end, vma->vm_pgoff, NULL);
> +       vma_adjust(vma, new_start, old_end, new_pgoff, NULL);
>
>        /*
>         * move the page tables downwards, on failure we rely on
> @@ -556,7 +557,7 @@ static int shift_arg_pages(struct vm_are
>        /*
>         * shrink the vma to just the new range.
>         */
> -       vma_adjust(vma, new_start, new_end, vma->vm_pgoff, NULL);
> +       vma_adjust(vma, new_start, new_end, new_pgoff, NULL);
>
>        return 0;
>  }
> _
>
>

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