[02/13] mm/hugetlb: fix cow where page writtable in child

Commit Message

Andrew Morton May 15, 2021, 12:27 a.m. UTC

From: Peter Xu <[e-mail]>
Subject: mm/hugetlb: fix cow where page writtable in child

When rework early cow of pinned hugetlb pages, we moved huge_ptep_get()
upper but overlooked a side effect that the huge_ptep_get() will fetch the
pte after wr-protection.  After moving it upwards, we need explicit
wr-protect of child pte or we will keep the write bit set in the child
process, which could cause data corrution where the child can write to the
original page directly.

This issue can also be exposed by "memfd_test hugetlbfs" kselftest.

Link: https://lkml.kernel.org/r/[e-mail]
Fixes: 4eae4efa2c299 ("hugetlb: do early cow when page pinned on src mm")
Signed-off-by: Peter Xu <[e-mail]>
Reviewed-by: Mike Kravetz <[e-mail]>
Cc: Hugh Dickins <[e-mail]>
Cc: Joel Fernandes (Google) <[e-mail]>
Cc: <[e-mail]>
Signed-off-by: Andrew Morton <[e-mail]>
---

 mm/hugetlb.c |    1 +
 1 file changed, 1 insertion(+)

Patch

--- a/mm/hugetlb.c~mm-hugetlb-fix-cow-where-page-writtable-in-child
+++ a/mm/hugetlb.c
@@ -4056,6 +4056,7 @@  again:
 				 * See Documentation/vm/mmu_notifier.rst
 				 */
 				huge_ptep_set_wrprotect(src, addr, src_pte);
+				entry = huge_pte_wrprotect(entry);
 			}
 
 			page_dup_rmap(ptepage, true);