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

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Date:	Mon, 12 Jan 2009 15:05:51 -0800
From:	Mike Waychison <mikew@...gle.com>
To:	Andrew Morton <akpm@...ux-foundation.org>
CC:	Ying Han <yinghan@...gle.com>, linux-mm@...ck.org,
	linux-kernel@...r.kernel.org, rohitseth@...gle.com
Subject: Re: [PATCH]Fix: 32bit binary has 64bit address of stack vma

Andrew Morton wrote:
> On Mon, 5 Jan 2009 15:39:07 -0800
> Ying Han <yinghan@...gle.com> wrote:
> 
>> From: Ying Han <yinghan@...gle.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@...gle.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@...gle.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]
> 
> 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.
> 

The problem is that the offset was stored without taking into account 
the shift.

> Signed-off-by: Ying Han <yinghan@...gle.com>
> Cc: Mike Waychison <mikew@...gle.com>
> Cc: Hugh Dickins <hugh@...itas.com>
> Signed-off-by: Andrew Morton <akpm@...ux-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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