jump label: Fix module __init section race

Jump label uses is_module_text_address() to ensure that the module
__init sections are valid before updating them. However, between the
check for a valid module __init section and the subsequent jump
label update, the module's __init section could be freed out from under
us.

We fix this potential race by adding a notifier callback to the
MODULE_STATE_LIVE state. This notifier is called *after* the __init
section has been run but before it is going to be freed. In the
callback, the jump label code zeros the key value for any __init jump
code within the module, and we add a check for a non-zero key value when
we update jump labels. In this way we require no additional data
structures.

Thanks to Mathieu Desnoyers for pointing out this race condition.

Reported-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Cc: Masami Hiramatsu <masami.hiramatsu.pt@hitachi.com>
Signed-off-by: Jason Baron <jbaron@redhat.com>
LKML-Reference: <c6f037b7598777668025ceedd9294212fd95fa34.1285965957.git.jbaron@redhat.com>

[ Renamed remove_module_init() to remove_jump_label_module_init()
  as suggested by Masami Hiramatsu. ]

Signed-off-by: Steven Rostedt <rostedt@goodmis.org>

diff --git a/kernel/jump_label.c b/kernel/jump_label.c
index 7be868b..be9e105 100644 (file)
--- a/kernel/jump_label.c
+++ b/kernel/jump_label.c
@@ -168,7 +168,8 @@ void jump_label_update(unsigned long key, enum jump_label_type type)
                        count = e_module->nr_entries;
                        iter = e_module->table;
                        while (count--) {
-                               if (kernel_text_address(iter->code))
+                               if (iter->key &&
+                                               kernel_text_address(iter->code))
                                        arch_jump_label_transform(iter, type);
                                iter++;
                        }
@@ -366,6 +367,39 @@ static void remove_jump_label_module(struct module *mod)
        }
 }
 
+static void remove_jump_label_module_init(struct module *mod)
+{
+       struct hlist_head *head;
+       struct hlist_node *node, *node_next, *module_node, *module_node_next;
+       struct jump_label_entry *e;
+       struct jump_label_module_entry *e_module;
+       struct jump_entry *iter;
+       int i, count;
+
+       /* if the module doesn't have jump label entries, just return */
+       if (!mod->num_jump_entries)
+               return;
+
+       for (i = 0; i < JUMP_LABEL_TABLE_SIZE; i++) {
+               head = &jump_label_table[i];
+               hlist_for_each_entry_safe(e, node, node_next, head, hlist) {
+                       hlist_for_each_entry_safe(e_module, module_node,
+                                                 module_node_next,
+                                                 &(e->modules), hlist) {
+                               if (e_module->mod != mod)
+                                       continue;
+                               count = e_module->nr_entries;
+                               iter = e_module->table;
+                               while (count--) {
+                                       if (within_module_init(iter->code, mod))
+                                               iter->key = 0;
+                                       iter++;
+                               }
+                       }
+               }
+       }
+}
+
 static int
 jump_label_module_notify(struct notifier_block *self, unsigned long val,
                         void *data)
@@ -386,6 +420,11 @@ jump_label_module_notify(struct notifier_block *self, unsigned long val,
                remove_jump_label_module(mod);
                mutex_unlock(&jump_label_mutex);
                break;
+       case MODULE_STATE_LIVE:
+               mutex_lock(&jump_label_mutex);
+               remove_jump_label_module_init(mod);
+               mutex_unlock(&jump_label_mutex);
+               break;
        }
        return ret;
 }