#ifdef CONFIG_HAVE_ARCH_USERFAULTFD_WP
static inline int pte_uffd_wp(pte_t pte)
{
- return pte_flags(pte) & _PAGE_UFFD_WP;
+ bool wp = pte_flags(pte) & _PAGE_UFFD_WP;
+
+#ifdef CONFIG_DEBUG_VM
+ /*
+ * Having write bit for wr-protect-marked present ptes is fatal,
+ * because it means the uffd-wp bit will be ignored and write will
+ * just go through.
+ *
+ * Use any chance of pgtable walking to verify this (e.g., when
+ * page swapped out or being migrated for all purposes). It means
+ * something is already wrong. Tell the admin even before the
+ * process crashes. We also nail it with wrong pgtable setup.
+ */
+ WARN_ON_ONCE(wp && pte_write(pte));
+#endif
+
+ return wp;
}
static inline pte_t pte_mkuffd_wp(pte_t pte)