mm: arm64: fix the out-of-bounds issue in contpte_clear_young_dirty_ptes

We are passing a huge nr to __clear_young_dirty_ptes() right now.  While
we should pass the number of pages, we are actually passing CONT_PTE_SIZE.
This is causing lots of crashes of MADV_FREE, panic oops could vary
everytime.

Link: https://lkml.kernel.org/r/[email protected]
Fixes: 89e8685 ("mm/arm64: override clear_young_dirty_ptes() batch helper")
Signed-off-by: Barry Song <[email protected]>
Reviewed-by: Baolin Wang <[email protected]>
Acked-by: Lance Yang <[email protected]>
Acked-by: David Hildenbrand <[email protected]>
Acked-by: Chris Li <[email protected]>
Cc: Barry Song <[email protected]>
Cc: Ryan Roberts <[email protected]>
Cc: Jeff Xie <[email protected]>
Cc: Kefeng Wang <[email protected]>
Cc: Michal Hocko <[email protected]>
Cc: Minchan Kim <[email protected]>
Cc: Muchun Song <[email protected]>
Cc: Peter Xu <[email protected]>
Cc: Yang Shi <[email protected]>
Cc: Yin Fengwei <[email protected]>
Cc: Zach O'Keefe <[email protected]>
Cc: Catalin Marinas <[email protected]>
Cc: Will Deacon <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>

Author: Barry Song

arch/arm64/mm/contpte.c

@@ -376,7 +376,7 @@ void contpte_clear_young_dirty_ptes(struct vm_area_struct *vma,
 	 * clearing access/dirty for the whole block.
 	 */
 	unsigned long start = addr;
-	unsigned long end = start + nr;
+	unsigned long end = start + nr * PAGE_SIZE;
 
 	if (pte_cont(__ptep_get(ptep + nr - 1)))
 		end = ALIGN(end, CONT_PTE_SIZE);
@@ -386,7 +386,7 @@ void contpte_clear_young_dirty_ptes(struct vm_area_struct *vma,
 		ptep = contpte_align_down(ptep);
 	}
 
-	__clear_young_dirty_ptes(vma, start, ptep, end - start, flags);
+	__clear_young_dirty_ptes(vma, start, ptep, (end - start) / PAGE_SIZE, flags);
 }
 EXPORT_SYMBOL_GPL(contpte_clear_young_dirty_ptes);