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

[David Rientjes]

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);