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-rw-r--r--include/linux/pgtable.h28
1 files changed, 28 insertions, 0 deletions
diff --git a/include/linux/pgtable.h b/include/linux/pgtable.h
index 3cdc16cfd867..014ee8f0fbaa 100644
--- a/include/linux/pgtable.h
+++ b/include/linux/pgtable.h
@@ -1689,4 +1689,32 @@ typedef unsigned int pgtbl_mod_mask;
#define MAX_PTRS_PER_P4D PTRS_PER_P4D
#endif
+/* description of effects of mapping type and prot in current implementation.
+ * this is due to the limited x86 page protection hardware. The expected
+ * behavior is in parens:
+ *
+ * map_type prot
+ * PROT_NONE PROT_READ PROT_WRITE PROT_EXEC
+ * MAP_SHARED r: (no) no r: (yes) yes r: (no) yes r: (no) yes
+ * w: (no) no w: (no) no w: (yes) yes w: (no) no
+ * x: (no) no x: (no) yes x: (no) yes x: (yes) yes
+ *
+ * MAP_PRIVATE r: (no) no r: (yes) yes r: (no) yes r: (no) yes
+ * w: (no) no w: (no) no w: (copy) copy w: (no) no
+ * x: (no) no x: (no) yes x: (no) yes x: (yes) yes
+ *
+ * On arm64, PROT_EXEC has the following behaviour for both MAP_SHARED and
+ * MAP_PRIVATE (with Enhanced PAN supported):
+ * r: (no) no
+ * w: (no) no
+ * x: (yes) yes
+ */
+#define DECLARE_VM_GET_PAGE_PROT \
+pgprot_t vm_get_page_prot(unsigned long vm_flags) \
+{ \
+ return protection_map[vm_flags & \
+ (VM_READ | VM_WRITE | VM_EXEC | VM_SHARED)]; \
+} \
+EXPORT_SYMBOL(vm_get_page_prot);
+
#endif /* _LINUX_PGTABLE_H */