When protection of wired read-only mapping is changed to read-write,

install new shadow object behind the map entry and copy the pages
from the underlying objects to it. This makes the mprotect(2) call to
actually perform the requested operation instead of silently do nothing
and return success, that causes SIGSEGV on later write access to the
mapping.

Reuse vm_fault_copy_entry() to do the copying, modifying it to behave
correctly when src_entry == dst_entry.

Reviewed by:	alc
MFC after:	3 weeks

1 files changed, 10 insertions, 4 deletions

diff --git a/sys/vm/vm_map.c b/sys/vm/vm_map.c
index 1166712..06ae63e 100644
--- a/sys/vm/vm_map.c
+++ b/sys/vm/vm_map.c
@@ -1805,10 +1805,10 @@ int
 vm_map_protect(vm_map_t map, vm_offset_t start, vm_offset_t end,
 	       vm_prot_t new_prot, boolean_t set_max)
 {
-	vm_map_entry_t current;
-	vm_map_entry_t entry;
+	vm_map_entry_t current, entry;
 	vm_object_t obj;
 	struct uidinfo *uip;
+	vm_prot_t old_prot;
 
 	vm_map_lock(map);
 
@@ -1897,9 +1897,8 @@ vm_map_protect(vm_map_t map, vm_offset_t start, vm_offset_t end,
 	 */
 	current = entry;
 	while ((current != &map->header) && (current->start < end)) {
-		vm_prot_t old_prot;
-
 		old_prot = current->protection;
+
 		if (set_max)
 			current->protection =
 			    (current->max_protection = new_prot) &
@@ -1907,6 +1906,13 @@ vm_map_protect(vm_map_t map, vm_offset_t start, vm_offset_t end,
 		else
 			current->protection = new_prot;
 
+		if ((current->eflags & (MAP_ENTRY_COW | MAP_ENTRY_USER_WIRED))
+		     == (MAP_ENTRY_COW | MAP_ENTRY_USER_WIRED) &&
+		    (current->protection & VM_PROT_WRITE) != 0 &&
+		    (old_prot & VM_PROT_WRITE) == 0) {
+			vm_fault_copy_entry(map, map, current, current, NULL);
+		}
+
 		/*
 		 * Update physical map if necessary. Worry about copy-on-write
 		 * here.