linux-kernel - [PATCH v2 1/1] context_tracking: Use arch_atomic_read() in __ct

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Message-Id: <20220622225102.2112026-2-joel@joelfernandes.org>
Date:   Wed, 22 Jun 2022 22:50:54 +0000
From:   "Joel Fernandes (Google)" <joel@...lfernandes.org>
To:     rcu@...r.kernel.org
Cc:     linux-kernel@...r.kernel.org, rushikesh.s.kadam@...el.com,
        urezki@...il.com, neeraj.iitr10@...il.com, frederic@...nel.org,
        paulmck@...nel.org, rostedt@...dmis.org, vineeth@...byteword.org,
        Marco Elver <elver@...gle.com>
Subject: [PATCH v2 1/1] context_tracking: Use arch_atomic_read() in __ct_state for KASAN

From: "Paul E. McKenney" <paulmck@...nel.org>

Context tracking's __ct_state() function can be invoked from noinstr state
where RCU is not watching.  This means that its use of atomic_read()
causes KASAN to invoke the non-noinstr __kasan_check_read() function
from the noinstr function __ct_state().  This is problematic because
someone tracing the __kasan_check_read() function could get a nasty
surprise because of RCU not watching.

This commit therefore replaces the __ct_state() function's use of
atomic_read() with arch_atomic_read(), which KASAN does not attempt to
add instrumention to.

Signed-off-by: Paul E. McKenney <paulmck@...nel.org>
Cc: Frederic Weisbecker <frederic@...nel.org>
Cc: Marco Elver <elver@...gle.com>
Reviewed-by: Marco Elver <elver@...gle.com>
---
 include/linux/context_tracking_state.h | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/include/linux/context_tracking_state.h b/include/linux/context_tracking_state.h
index 0aecc07fb4f5..81c51e5f0314 100644
--- a/include/linux/context_tracking_state.h
+++ b/include/linux/context_tracking_state.h
@@ -49,7 +49,7 @@ DECLARE_PER_CPU(struct context_tracking, context_tracking);

 static __always_inline int __ct_state(void)
 {
-	return atomic_read(this_cpu_ptr(&context_tracking.state)) & CT_STATE_MASK;
+	return arch_atomic_read(this_cpu_ptr(&context_tracking.state)) & CT_STATE_MASK;
 }
 #endif

-- 
2.37.0.rc0.104.g0611611a94-goog