jump label: Fix deadlock b/w jump_label_mutex vs. text_mutex

register_kprobe() downs the 'text_mutex' and then calls
jump_label_text_reserved(), which downs the 'jump_label_mutex'.
However, the jump label code takes those mutexes in the reverse
order.

Fix by requiring the caller of jump_label_text_reserved() to do
the jump label locking via the newly added: jump_label_lock(),
jump_label_unlock(). Currently, kprobes is the only user
of jump_label_text_reserved().

Reported-by: Ingo Molnar <mingo@elte.hu>
Acked-by: Masami Hiramatsu <masami.hiramatsu.pt@hitachi.com>
Signed-off-by: Jason Baron <jbaron@redhat.com>
LKML-Reference: <759032c48d5e30c27f0bba003d09bffa8e9f28bb.1285965957.git.jbaron@redhat.com>
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>

3 files changed, 32 insertions, 12 deletions

diff --git a/include/linux/jump_label.h b/include/linux/jump_label.h
index b67cb180e6e9..1947a1212678 100644
--- a/include/linux/jump_label.h
+++ b/include/linux/jump_label.h
@@ -18,6 +18,8 @@ struct module;
 extern struct jump_entry __start___jump_table[];
 extern struct jump_entry __stop___jump_table[];
 
+extern void jump_label_lock(void);
+extern void jump_label_unlock(void);
 extern void arch_jump_label_transform(struct jump_entry *entry,
                                  enum jump_label_type type);
 extern void arch_jump_label_text_poke_early(jump_label_t addr);
@@ -59,6 +61,9 @@ static inline int jump_label_text_reserved(void *start, void *end)
         return 0;
 }
 
+static inline void jump_label_lock(void) {}
+static inline void jump_label_unlock(void) {}
+
 #endif
 
 #define COND_STMT(key, stmt)                                    \
diff --git a/kernel/jump_label.c b/kernel/jump_label.c
index be9e105345eb..12cce78e9568 100644
--- a/kernel/jump_label.c
+++ b/kernel/jump_label.c
@@ -39,6 +39,16 @@ struct jump_label_module_entry {
         struct module *mod;
 };
 
+void jump_label_lock(void)
+{
+        mutex_lock(&jump_label_mutex);
+}
+
+void jump_label_unlock(void)
+{
+        mutex_unlock(&jump_label_mutex);
+}
+
 static int jump_label_cmp(const void *a, const void *b)
 {
         const struct jump_entry *jea = a;
@@ -152,7 +162,7 @@ void jump_label_update(unsigned long key, enum jump_label_type type)
         struct jump_label_module_entry *e_module;
         int count;
 
-        mutex_lock(&jump_label_mutex);
+        jump_label_lock();
         entry = get_jump_label_entry((jump_label_t)key);
         if (entry) {
                 count = entry->nr_entries;
@@ -175,7 +185,7 @@ void jump_label_update(unsigned long key, enum jump_label_type type)
                         }
                 }
         }
-        mutex_unlock(&jump_label_mutex);
+        jump_label_unlock();
 }
 
 static int addr_conflict(struct jump_entry *entry, void *start, void *end)
@@ -232,6 +242,7 @@ out:
  * overlaps with any of the jump label patch addresses. Code
  * that wants to modify kernel text should first verify that
  * it does not overlap with any of the jump label addresses.
+ * Caller must hold jump_label_mutex.
  *
  * returns 1 if there is an overlap, 0 otherwise
  */
@@ -242,7 +253,6 @@ int jump_label_text_reserved(void *start, void *end)
         struct jump_entry *iter_stop = __start___jump_table;
         int conflict = 0;
 
-        mutex_lock(&jump_label_mutex);
         iter = iter_start;
         while (iter < iter_stop) {
                 if (addr_conflict(iter, start, end)) {
@@ -257,7 +267,6 @@ int jump_label_text_reserved(void *start, void *end)
         conflict = module_conflict(start, end);
 #endif
 out:
-        mutex_unlock(&jump_label_mutex);
         return conflict;
 }
 
@@ -268,7 +277,7 @@ static __init int init_jump_label(void)
         struct jump_entry *iter_stop = __stop___jump_table;
         struct jump_entry *iter;
 
-        mutex_lock(&jump_label_mutex);
+        jump_label_lock();
         ret = build_jump_label_hashtable(__start___jump_table,
                                          __stop___jump_table);
         iter = iter_start;
@@ -276,7 +285,7 @@ static __init int init_jump_label(void)
                 arch_jump_label_text_poke_early(iter->code);
                 iter++;
         }
-        mutex_unlock(&jump_label_mutex);
+        jump_label_unlock();
         return ret;
 }
 early_initcall(init_jump_label);
@@ -409,21 +418,21 @@ jump_label_module_notify(struct notifier_block *self, unsigned long val,
 
         switch (val) {
         case MODULE_STATE_COMING:
-                mutex_lock(&jump_label_mutex);
+                jump_label_lock();
                 ret = add_jump_label_module(mod);
                 if (ret)
                         remove_jump_label_module(mod);
-                mutex_unlock(&jump_label_mutex);
+                jump_label_unlock();
                 break;
         case MODULE_STATE_GOING:
-                mutex_lock(&jump_label_mutex);
+                jump_label_lock();
                 remove_jump_label_module(mod);
-                mutex_unlock(&jump_label_mutex);
+                jump_label_unlock();
                 break;
         case MODULE_STATE_LIVE:
-                mutex_lock(&jump_label_mutex);
+                jump_label_lock();
                 remove_jump_label_module_init(mod);
-                mutex_unlock(&jump_label_mutex);
+                jump_label_unlock();
                 break;
         }
         return ret;
diff --git a/kernel/kprobes.c b/kernel/kprobes.c
index 99865c33a60d..9437e14f36bd 100644
--- a/kernel/kprobes.c
+++ b/kernel/kprobes.c
@@ -1146,13 +1146,16 @@ int __kprobes register_kprobe(struct kprobe *p)
                 return ret;
 
         preempt_disable();
+        jump_label_lock();
         if (!kernel_text_address((unsigned long) p->addr) ||
             in_kprobes_functions((unsigned long) p->addr) ||
             ftrace_text_reserved(p->addr, p->addr) ||
             jump_label_text_reserved(p->addr, p->addr)) {
                 preempt_enable();
+                jump_label_unlock();
                 return -EINVAL;
         }
+        jump_label_unlock();
 
         /* User can pass only KPROBE_FLAG_DISABLED to register_kprobe */
         p->flags &= KPROBE_FLAG_DISABLED;
@@ -1187,6 +1190,8 @@ int __kprobes register_kprobe(struct kprobe *p)
         INIT_LIST_HEAD(&p->list);
         mutex_lock(&kprobe_mutex);
 
+        jump_label_lock(); /* needed to call jump_label_text_reserved() */
+
         get_online_cpus();      /* For avoiding text_mutex deadlock. */
         mutex_lock(&text_mutex);
 
@@ -1214,6 +1219,7 @@ int __kprobes register_kprobe(struct kprobe *p)
 out:
         mutex_unlock(&text_mutex);
         put_online_cpus();
+        jump_label_unlock();
         mutex_unlock(&kprobe_mutex);
 
         if (probed_mod)