From: Mike Kravetz <mike.kravetz@xxxxxxxxxx> commit 73bdf65ea74857d7fb2ec3067a3cec0e261b1462 upstream. migrate_pages/mempolicy semantics state that CAP_SYS_NICE is required to move pages shared with another process to a different node. page_mapcount > 1 is being used to determine if a hugetlb page is shared. However, a hugetlb page will have a mapcount of 1 if mapped by multiple processes via a shared PMD. As a result, hugetlb pages shared by multiple processes and mapped with a shared PMD can be moved by a process without CAP_SYS_NICE. To fix, check for a shared PMD if mapcount is 1. If a shared PMD is found consider the page shared. Link: https://lkml.kernel.org/r/20230126222721.222195-3-mike.kravetz@xxxxxxxxxx Fixes: e2d8cf405525 ("migrate: add hugepage migration code to migrate_pages()") Signed-off-by: Mike Kravetz <mike.kravetz@xxxxxxxxxx> Acked-by: Peter Xu <peterx@xxxxxxxxxx> Acked-by: David Hildenbrand <david@xxxxxxxxxx> Cc: James Houghton <jthoughton@xxxxxxxxxx> Cc: Matthew Wilcox <willy@xxxxxxxxxxxxx> Cc: Michal Hocko <mhocko@xxxxxxxx> Cc: Muchun Song <songmuchun@xxxxxxxxxxxxx> Cc: Naoya Horiguchi <naoya.horiguchi@xxxxxxxxx> Cc: Vishal Moola (Oracle) <vishal.moola@xxxxxxxxx> Cc: Yang Shi <shy828301@xxxxxxxxx> Cc: <stable@xxxxxxxxxxxxxxx> Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx> --- mm/mempolicy.c | 3 ++- 1 file changed, 2 insertions(+), 1 deletion(-) --- a/mm/mempolicy.c +++ b/mm/mempolicy.c @@ -574,7 +574,8 @@ static int queue_pages_hugetlb(pte_t *pt goto unlock; /* With MPOL_MF_MOVE, we migrate only unshared hugepage. */ if (flags & (MPOL_MF_MOVE_ALL) || - (flags & MPOL_MF_MOVE && page_mapcount(page) == 1)) + (flags & MPOL_MF_MOVE && page_mapcount(page) == 1 && + !hugetlb_pmd_shared(pte))) isolate_huge_page(page, qp->pagelist); unlock: spin_unlock(ptl);
