[PATCH v4 09/14] mm/mprotect: Break COW PTE before changing protection

Chih-En Lin
2023-02-07T03:54:27Z

If the PTE table is COW-ed, break it before changing the protection.

Signed-off-by: Chih-En Lin <shiyn.lin@gmail.com>
---
mm/mprotect.c | 9 +++++++++
1 file changed, 9 insertions(+)

diff --git a/mm/mprotect.c b/mm/mprotect.c
index 61cf60015a8b..8b18cd0e5c5e 100644
--- a/mm/mprotect.c
+++ b/mm/mprotect.c
@@ -103,6 +103,9 @@ static unsigned long change_pte_range(struct mmu_gather *tlb,
if (pmd_trans_unstable(pmd))
return 0;

+ if (break_cow_pte(vma, pmd, addr))
+ return 0;
+
/*
* The pmd points to a regular pte so the pmd can't change
* from under us even if the mmap_lock is only hold for
@@ -314,6 +317,12 @@ static inline int pmd_none_or_clear_bad_unless_trans_huge(pmd_t *pmd)
return 1;
if (pmd_trans_huge(pmdval))
return 0;
+ /*
+ * If the entry point to COW-ed PTE, it's write protection bit
+ * will cause pmd_bad().
+ */
+ if (!pmd_write(pmdval))
+ return 0;
if (unlikely(pmd_bad(pmdval))) {
pmd_clear_bad(pmd);
return 1;
--
2.34.1