bpf: mark a NULL kfunc argument precisegrafted

check_kfunc_arg() allows bpf_register_is_null() for nullable arguments
w/o marking the underlying scalar register precise. Hence a checkpoint
created on such a path would prune against arbitrary scalar value.

Fixes: 3bda08b63670 ("bpf: Allow NULL buffers in bpf_dynptr_slice(_rw)")
Signed-off-by: Eduard Zingerman <eddyz87@gmail.com>
Link: https://lore.kernel.org/r/20260904-register-is-null-precise-fixes-v1-5-0f5a360ff15d@gmail.com
Signed-off-by: Alexei Starovoitov <ast@kernel.org>

1 files changed, 71 insertions, 0 deletions

diff --git a/tools/perf/util/rwsem.c b/tools/perf/util/rwsem.c
new file mode 100644
index 000000000..9d2683239
--- /dev/null
+++ b/tools/perf/util/rwsem.c
@@ -0,0 +1,71 @@
+// SPDX-License-Identifier: GPL-2.0
+#include "util.h"
+#include "rwsem.h"
+
+#if RWS_ERRORCHECK
+#include "mutex.h"
+#endif
+
+int init_rwsem(struct rw_semaphore *sem)
+{
+#if RWS_ERRORCHECK
+	mutex_init(&sem->mtx);
+	return 0;
+#else
+	return pthread_rwlock_init(&sem->lock, NULL);
+#endif
+}
+
+int exit_rwsem(struct rw_semaphore *sem)
+{
+#if RWS_ERRORCHECK
+	mutex_destroy(&sem->mtx);
+	return 0;
+#else
+	return pthread_rwlock_destroy(&sem->lock);
+#endif
+}
+
+int down_read(struct rw_semaphore *sem)
+	NO_THREAD_SAFETY_ANALYSIS
+{
+#if RWS_ERRORCHECK
+	mutex_lock(&sem->mtx);
+	return 0;
+#else
+	return perf_singlethreaded ? 0 : pthread_rwlock_rdlock(&sem->lock);
+#endif
+}
+
+int up_read(struct rw_semaphore *sem)
+	NO_THREAD_SAFETY_ANALYSIS
+{
+#if RWS_ERRORCHECK
+	mutex_unlock(&sem->mtx);
+	return 0;
+#else
+	return perf_singlethreaded ? 0 : pthread_rwlock_unlock(&sem->lock);
+#endif
+}
+
+int down_write(struct rw_semaphore *sem)
+	NO_THREAD_SAFETY_ANALYSIS
+{
+#if RWS_ERRORCHECK
+	mutex_lock(&sem->mtx);
+	return 0;
+#else
+	return perf_singlethreaded ? 0 : pthread_rwlock_wrlock(&sem->lock);
+#endif
+}
+
+int up_write(struct rw_semaphore *sem)
+	NO_THREAD_SAFETY_ANALYSIS
+{
+#if RWS_ERRORCHECK
+	mutex_unlock(&sem->mtx);
+	return 0;
+#else
+	return perf_singlethreaded ? 0 : pthread_rwlock_unlock(&sem->lock);
+#endif
+}