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>

1 files changed, 40 insertions, 1 deletions

diff --git a/kernel/jump_label.c b/kernel/jump_label.c
index 7be868bf25c6..be9e105345eb 100644
--- 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;
 }