Re: [PATCH v9 08/24] mm: Protect VMA modifications using VMA sequence count

[Laurent Dufour]

On 27/03/2018 23:57, David Rientjes wrote:
> On Tue, 13 Mar 2018, Laurent Dufour wrote:
> 
>> diff --git a/mm/mmap.c b/mm/mmap.c
>> index 5898255d0aeb..d6533cb85213 100644
>> --- a/mm/mmap.c
>> +++ b/mm/mmap.c
>> @@ -847,17 +847,18 @@ int __vma_adjust(struct vm_area_struct *vma, unsigned long start,
>>  	}
>>  
>>  	if (start != vma->vm_start) {
>> -		vma->vm_start = start;
>> +		WRITE_ONCE(vma->vm_start, start);
>>  		start_changed = true;
>>  	}
>>  	if (end != vma->vm_end) {
>> -		vma->vm_end = end;
>> +		WRITE_ONCE(vma->vm_end, end);
>>  		end_changed = true;
>>  	}
>> -	vma->vm_pgoff = pgoff;
>> +	WRITE_ONCE(vma->vm_pgoff, pgoff);
>>  	if (adjust_next) {
>> -		next->vm_start += adjust_next << PAGE_SHIFT;
>> -		next->vm_pgoff += adjust_next;
>> +		WRITE_ONCE(next->vm_start,
>> +			   next->vm_start + (adjust_next << PAGE_SHIFT));
>> +		WRITE_ONCE(next->vm_pgoff, next->vm_pgoff + adjust_next);
>>  	}
>>  
>>  	if (root) {
>> @@ -1781,6 +1782,7 @@ unsigned long mmap_region(struct file *file, unsigned long addr,
>>  out:
>>  	perf_event_mmap(vma);
>>  
>> +	vm_write_begin(vma);
>>  	vm_stat_account(mm, vm_flags, len >> PAGE_SHIFT);
>>  	if (vm_flags & VM_LOCKED) {
>>  		if (!((vm_flags & VM_SPECIAL) || is_vm_hugetlb_page(vma) ||
>> @@ -1803,6 +1805,7 @@ unsigned long mmap_region(struct file *file, unsigned long addr,
>>  	vma->vm_flags |= VM_SOFTDIRTY;
>>  
>>  	vma_set_page_prot(vma);
>> +	vm_write_end(vma);
>>  
>>  	return addr;
>>  
> 
> Shouldn't this also protect vma->vm_flags?

Nice catch !
I just found that too while reviewing the entire patch to answer your previous
email.

> 
> diff --git a/mm/mmap.c b/mm/mmap.c
> --- a/mm/mmap.c
> +++ b/mm/mmap.c
> @@ -1796,7 +1796,8 @@ unsigned long mmap_region(struct file *file, unsigned long addr,
>  					vma == get_gate_vma(current->mm)))
>  			mm->locked_vm += (len >> PAGE_SHIFT);
>  		else
> -			vma->vm_flags &= VM_LOCKED_CLEAR_MASK;
> +			WRITE_ONCE(vma->vm_flags,
> +				   vma->vm_flags & VM_LOCKED_CLEAR_MASK);
>  	}
> 
>  	if (file)
> @@ -1809,7 +1810,7 @@ unsigned long mmap_region(struct file *file, unsigned long addr,
>  	 * then new mapped in-place (which must be aimed as
>  	 * a completely new data area).
>  	 */
> -	vma->vm_flags |= VM_SOFTDIRTY;
> +	WRITE_ONCE(vma->vm_flags, vma->vm_flags | VM_SOFTDIRTY);
> 
>  	vma_set_page_prot(vma);
>  	vm_write_end(vma);
>