[PATCH v4 4/4] locking/lockdep: Add kasan_check_byte() check in lock_acquire()

[Waiman Long <longman@redhat.com>]

KASAN instrumentation of lockdep has been disabled as we don't need
KASAN to check the validity of lockdep internal data structures and
incur unnecessary performance overhead. However, the lockdep_map pointer
passed in externally may not be valid (e.g. use-after-free) and we run
the risk of using garbage data resulting in false lockdep reports. Add
kasan_check_byte() call in lock_acquire() for non kernel core data
object to catch invalid lockdep_map and abort lockdep processing if
input data isn't valid.

Suggested-by: Marco Elver <elver@google.com>
Signed-off-by: Waiman Long <longman@redhat.com>
---
 kernel/locking/lock_events_list.h |  1 +
 kernel/locking/lockdep.c          | 14 ++++++++++++++
 2 files changed, 15 insertions(+)

diff --git a/kernel/locking/lock_events_list.h b/kernel/locking/lock_events_list.h
index 9ef9850aeebe..bed59b2195c7 100644
--- a/kernel/locking/lock_events_list.h
+++ b/kernel/locking/lock_events_list.h
@@ -95,3 +95,4 @@ LOCK_EVENT(rtmutex_deadlock)	/* # of rt_mutex_handle_deadlock()'s	*/
 LOCK_EVENT(lockdep_acquire)
 LOCK_EVENT(lockdep_lock)
 LOCK_EVENT(lockdep_nocheck)
+LOCK_EVENT(lockdep_kasan_fail)
diff --git a/kernel/locking/lockdep.c b/kernel/locking/lockdep.c
index 8436f017c74d..98dd0455d4be 100644
--- a/kernel/locking/lockdep.c
+++ b/kernel/locking/lockdep.c
@@ -57,6 +57,7 @@
 #include <linux/lockdep.h>
 #include <linux/context_tracking.h>
 #include <linux/console.h>
+#include <linux/kasan.h>
 
 #include <asm/sections.h>
 
@@ -5830,6 +5831,19 @@ void lock_acquire(struct lockdep_map *lock, unsigned int subclass,
 	if (!debug_locks)
 		return;
 
+	/*
+	 * As KASAN instrumentation is disabled and lock_acquire() is usually
+	 * the first lockdep call when a task tries to acquire a lock, add
+	 * kasan_check_byte() here to check for use-after-free of non kernel
+	 * core lockdep_map data to avoid referencing garbage data.
+	 */
+	if (unlikely(IS_ENABLED(CONFIG_KASAN) &&
+		     !is_kernel_core_data((unsigned long)lock) &&
+		     !kasan_check_byte(lock))) {
+		lockevent_inc(lockdep_kasan_fail);
+		return;
+	}
+
 	if (unlikely(!lockdep_enabled())) {
 		/* XXX allow trylock from NMI ?!? */
 		if (lockdep_nmi() && !trylock) {
-- 
2.48.1