bpf: selftest: Ensure the return value of the bpf_per_cpu_ptr() must be checked

This patch tests all pointers returned by bpf_per_cpu_ptr() must be
tested for NULL first before it can be accessed.

This patch adds a subtest "null_check", so it moves the ".data..percpu"
existence check to the very beginning and before doing any subtest.

Signed-off-by: Martin KaFai Lau <kafai@fb.com>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Link: https://lore.kernel.org/bpf/20201019194225.1051596-1-kafai@fb.com

1 files changed, 31 insertions, 0 deletions

diff --git a/tools/testing/selftests/bpf/progs/test_ksyms_btf_null_check.c b/tools/testing/selftests/bpf/progs/test_ksyms_btf_null_check.c
new file mode 100644
index 000000000000..8bc8f7c637bc
--- /dev/null
+++ b/tools/testing/selftests/bpf/progs/test_ksyms_btf_null_check.c
@@ -0,0 +1,31 @@
+// SPDX-License-Identifier: GPL-2.0
+/* Copyright (c) 2020 Facebook */
+
+#include "vmlinux.h"
+
+#include <bpf/bpf_helpers.h>
+
+extern const struct rq runqueues __ksym; /* struct type global var. */
+extern const int bpf_prog_active __ksym; /* int type global var. */
+
+SEC("raw_tp/sys_enter")
+int handler(const void *ctx)
+{
+	struct rq *rq;
+	int *active;
+	__u32 cpu;
+
+	cpu = bpf_get_smp_processor_id();
+	rq = (struct rq *)bpf_per_cpu_ptr(&runqueues, cpu);
+	active = (int *)bpf_per_cpu_ptr(&bpf_prog_active, cpu);
+	if (active) {
+		/* READ_ONCE */
+		*(volatile int *)active;
+		/* !rq has not been tested, so verifier should reject. */
+		*(volatile int *)(&rq->cpu);
+	}
+
+	return 0;
+}
+
+char _license[] SEC("license") = "GPL";