rcu_assign_pointer needs to use ACCESS_ONCE to make the assignment to
the destination pointer volatile, to protect against compilers too
clever for their own good.
In addition, since rcu_assign_pointer force-casts the source pointer to
add the __rcu address space (overriding any existing address space), add
an explicit check that the source pointer has the __kernel address space
to start with.
This new check produces warnings like this, when attempting to assign
from a __user pointer:
test.c:25:9: warning: incorrect type in argument 2 (different address spaces)
test.c:25:9: expected struct foo *<noident>
test.c:25:9: got struct foo [noderef] <asn:1>*badsrc
Signed-off-by: Josh Triplett <j...@joshtriplett.org>
---
include/linux/rcupdate.h | 12 +++++++++++-
1 file changed, 11 insertions(+), 1 deletion(-)
diff --git a/include/linux/rcupdate.h b/include/linux/rcupdate.h
index 4b14bdc..3f62def 100644
--- a/include/linux/rcupdate.h
+++ b/include/linux/rcupdate.h
@@ -510,8 +510,17 @@ static inline void rcu_preempt_sleep_check(void)
#ifdef __CHECKER__
#define rcu_dereference_sparse(p, space) \
((void)(((typeof(*p) space *)p) == p))
+/* The dummy first argument in __rcu_assign_pointer_typecheck makes the
+ * typechecked pointer the second argument, matching rcu_assign_pointer itself;
+ * this avoids confusion about argument numbers in warning messages. */
+#define __rcu_assign_pointer_check_kernel(v) \
+ do { \
+ extern void __rcu_assign_pointer_typecheck(int, typeof(*(v))
__kernel *); \
+ __rcu_assign_pointer_typecheck(0, v); \
+ } while (0)
#else /* #ifdef __CHECKER__ */
#define rcu_dereference_sparse(p, space)
+#define __rcu_assign_pointer_check_kernel(v) do { } while (0)
#endif /* #else #ifdef __CHECKER__ */
#define __rcu_access_pointer(p, space) \
@@ -555,7 +564,8 @@ static inline void rcu_preempt_sleep_check(void)
#define __rcu_assign_pointer(p, v, space) \
do { \
smp_wmb(); \
- (p) = (typeof(*v) __force space *)(v); \
+ __rcu_assign_pointer_check_kernel(v); \
+ ACCESS_ONCE(p) = (typeof(*(v)) __force space *)(v); \
} while (0)
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