[PATCH] kprobe: sync issue's on ftraced-kprobe.

[Levi Yun <ppbuk5246@gmail.com>]

In kprobe_ftrace_handler, it accesses get kporbe without kprobe_mutex
held.

This makes some of synchronizing issue when we use kprobe API in
kernel-module.

Below is what i experienced:

CPU 0									CPU 1
<...>									<In module code>
kprobe_ftrace_handler
    get_kprobe
        __this_cpu_write
									unregister_kprobe
									unload_module
						<			kprobe memory gone>
	p->pre_handler <access invalid memory>
	page_fault
		kprobe_fault_handler
			(In here, kprobe memory gone,
			 double page fault is happening inifinie).

Signed-off-by: Levi Yun <ppbuk5246@gmail.com>
---
 arch/x86/kernel/kprobes/ftrace.c | 3 +++
 include/linux/kprobes.h          | 2 ++
 kernel/kprobes.c                 | 2 +-
 3 files changed, 6 insertions(+), 1 deletion(-)

diff --git a/arch/x86/kernel/kprobes/ftrace.c b/arch/x86/kernel/kprobes/ftrace.c
index dd2ec14adb77..76147ff6ed88 100644
--- a/arch/x86/kernel/kprobes/ftrace.c
+++ b/arch/x86/kernel/kprobes/ftrace.c
@@ -25,6 +25,7 @@ void kprobe_ftrace_handler(unsigned long ip, unsigned long parent_ip,
 	if (bit < 0)
 		return;
 
+	mutex_lock(&kprobe_mutex);
 	p = get_kprobe((kprobe_opcode_t *)ip);
 	if (unlikely(!p) || kprobe_disabled(p))
 		goto out;
@@ -57,7 +58,9 @@ void kprobe_ftrace_handler(unsigned long ip, unsigned long parent_ip,
 		 */
 		__this_cpu_write(current_kprobe, NULL);
 	}
+
 out:
+	mutex_unlock(&kprobe_mutex);
 	ftrace_test_recursion_unlock(bit);
 }
 NOKPROBE_SYMBOL(kprobe_ftrace_handler);
diff --git a/include/linux/kprobes.h b/include/linux/kprobes.h
index 157168769fc2..4a18147ff6d6 100644
--- a/include/linux/kprobes.h
+++ b/include/linux/kprobes.h
@@ -191,6 +191,8 @@ struct kprobe_blacklist_entry {
 DECLARE_PER_CPU(struct kprobe *, current_kprobe);
 DECLARE_PER_CPU(struct kprobe_ctlblk, kprobe_ctlblk);
 
+extern struct mutex kprobe_mutex;
+
 extern void kprobe_busy_begin(void);
 extern void kprobe_busy_end(void);
 
diff --git a/kernel/kprobes.c b/kernel/kprobes.c
index dd58c0be9ce2..b65f055b6fa2 100644
--- a/kernel/kprobes.c
+++ b/kernel/kprobes.c
@@ -64,7 +64,7 @@ static struct hlist_head kprobe_table[KPROBE_TABLE_SIZE];
 static bool kprobes_all_disarmed;
 
 /* This protects 'kprobe_table' and 'optimizing_list' */
-static DEFINE_MUTEX(kprobe_mutex);
+DEFINE_MUTEX(kprobe_mutex);
 static DEFINE_PER_CPU(struct kprobe *, kprobe_instance);
 
 kprobe_opcode_t * __weak kprobe_lookup_name(const char *name,
-- 
2.35.1