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

[David Rientjes <rientjes@xxxxxxxxxx>]

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?

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);