[BUG] kmsan: instrumentation recursion problems

[Changbin Du]

Hey, folks,
I found two instrumentation recursion issues on mainline kernel.

1. recur on preempt count.
__msan_metadata_ptr_for_load_4() -> kmsan_virt_addr_valid() -> preempt_disable() -> __msan_metadata_ptr_for_load_4()

2. recur in lockdep and rcu
__msan_metadata_ptr_for_load_4() -> kmsan_virt_addr_valid() -> pfn_valid() -> rcu_read_lock_sched() -> lock_acquire() -> rcu_is_watching() -> __msan_metadata_ptr_for_load_8()


Here is an unofficial fix, I don't know if it will generate false reports.

$ git show
commit 7f0120b621c1cbb667822b0f7eb89f3c25868509 (HEAD -> master)
Author: Changbin Du <changbin.du@xxxxxxxxxx>
Date:   Fri Mar 8 20:21:48 2024 +0800

    kmsan: fix instrumentation recursions

    Signed-off-by: Changbin Du <changbin.du@xxxxxxxxxx>

diff --git a/kernel/locking/Makefile b/kernel/locking/Makefile
index 0db4093d17b8..ea925731fa40 100644
--- a/kernel/locking/Makefile
+++ b/kernel/locking/Makefile
@@ -7,6 +7,7 @@ obj-y += mutex.o semaphore.o rwsem.o percpu-rwsem.o

 # Avoid recursion lockdep -> sanitizer -> ... -> lockdep.
 KCSAN_SANITIZE_lockdep.o := n
+KMSAN_SANITIZE_lockdep.o := n

 ifdef CONFIG_FUNCTION_TRACER
 CFLAGS_REMOVE_lockdep.o = $(CC_FLAGS_FTRACE)
diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c
index b2bccfd37c38..8935cc866e2d 100644
--- a/kernel/rcu/tree.c
+++ b/kernel/rcu/tree.c
@@ -692,7 +692,7 @@ static void rcu_disable_urgency_upon_qs(struct rcu_data *rdp)
  * Make notrace because it can be called by the internal functions of
  * ftrace, and making this notrace removes unnecessary recursion calls.
  */
-notrace bool rcu_is_watching(void)
+notrace __no_sanitize_memory bool rcu_is_watching(void)
 {
        bool ret;

diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index 9116bcc90346..33aa4df8fd82 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -5848,7 +5848,7 @@ static inline void preempt_latency_start(int val)
        }
 }

-void preempt_count_add(int val)
+void __no_sanitize_memory preempt_count_add(int val)
 {
 #ifdef CONFIG_DEBUG_PREEMPT
        /*
@@ -5880,7 +5880,7 @@ static inline void preempt_latency_stop(int val)
                trace_preempt_on(CALLER_ADDR0, get_lock_parent_ip());
 }

-void preempt_count_sub(int val)
+void __no_sanitize_memory preempt_count_sub(int val)
 {
 #ifdef CONFIG_DEBUG_PREEMPT


-- 
Cheers,
Changbin Du