[PATCH 20/20] context_tracking: Use arch_atomic_read() in __ct_state for KASAN

Frederic Weisbecker
2022-06-28T13:19:45Z

From: "Paul E. McKenney" <paulmck@kernel.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.

Reported-by: kernel test robot <lkp@intel.com>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
Cc: Frederic Weisbecker <frederic@kernel.org>
Cc: Marco Elver <elver@google.com>
Reviewed-by: Marco Elver <elver@google.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 e20a74bc0597..4a4d56f77180 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

--
2.25.1