[PATCH bpf-next v2 3/3] selftests/bpf: Accept extra arguments if they are not used.

[Kui-Feng Lee <thinker.li@gmail.com>]

A struct_ops program can have more arguments than what the corresponding
function pointer in the kernel has if the program doesn't access the
arguments. For example, a struct_ops operator may have 2 arguments, but
your program may defined with 3 or more arguments. It is acceptable as long
as the program doesn't use these arguments.

Signed-off-by: Kui-Feng Lee <thinker.li@gmail.com>
---
 .../bpf/prog_tests/test_struct_ops_module.c   | 56 +++++++++++++++++++
 .../bpf/progs/struct_ops_extra_arg.c          | 49 ++++++++++++++++
 2 files changed, 105 insertions(+)
 create mode 100644 tools/testing/selftests/bpf/progs/struct_ops_extra_arg.c

diff --git a/tools/testing/selftests/bpf/prog_tests/test_struct_ops_module.c b/tools/testing/selftests/bpf/prog_tests/test_struct_ops_module.c
index 098776d00ab4..a146bf079a60 100644
--- a/tools/testing/selftests/bpf/prog_tests/test_struct_ops_module.c
+++ b/tools/testing/selftests/bpf/prog_tests/test_struct_ops_module.c
@@ -4,6 +4,7 @@
 #include <time.h>
 
 #include "struct_ops_module.skel.h"
+#include "struct_ops_extra_arg.skel.h"
 
 static void check_map_info(struct bpf_map_info *info)
 {
@@ -138,11 +139,66 @@ static void test_struct_ops_not_zeroed(void)
 	struct_ops_module__destroy(skel);
 }
 
+/* Handle BPF programs with additional arguments that don't appear in the
+ * function pointer prototype in the kernel.
+ */
+static void test_struct_ops_extra_arg(void)
+{
+	struct struct_ops_extra_arg *skel;
+	int err;
+
+	/* test_extra_arg() has an extra argument, so testmod_1 should fail
+	 * to load.
+	 *
+	 * Since extra_arg is used in test_extra_arg(), it should be
+	 * rejected by the verifier.
+	 */
+	skel = struct_ops_extra_arg__open();
+	if (!ASSERT_OK_PTR(skel, "struct_ops_extra_arg_open_extra_arg"))
+		return;
+
+	err = struct_ops_extra_arg__load(skel);
+	ASSERT_ERR(err, "struct_ops_extra_arg_load_extra_arg");
+
+	struct_ops_extra_arg__destroy(skel);
+
+	/* Switch to test_2() */
+	skel = struct_ops_extra_arg__open();
+	if (!ASSERT_OK_PTR(skel, "struct_ops_extra_arg_open"))
+		return;
+
+	skel->struct_ops.testmod_1->test_2 = skel->progs.test_2;
+
+	err = struct_ops_extra_arg__load(skel);
+	ASSERT_OK(err, "struct_ops_extra_arg_load");
+
+	struct_ops_extra_arg__destroy(skel);
+
+	/* Switch to test_extra_arg_unused()
+	 *
+	 * Since extra_arg is never used, it should be accepted by the
+	 * verifier. The verifier would accept a program with extra
+	 * arguments as long as they are not used.
+	 */
+	skel = struct_ops_extra_arg__open();
+	if (!ASSERT_OK_PTR(skel, "struct_ops_extra_arg_open_unused"))
+		return;
+
+	skel->struct_ops.testmod_1->test_2 = skel->progs.test_extra_arg_unused;
+
+	err = struct_ops_extra_arg__load(skel);
+	ASSERT_OK(err, "struct_ops_extra_arg_load_unused");
+
+	struct_ops_extra_arg__destroy(skel);
+}
+
 void serial_test_struct_ops_module(void)
 {
 	if (test__start_subtest("test_struct_ops_load"))
 		test_struct_ops_load();
 	if (test__start_subtest("test_struct_ops_not_zeroed"))
 		test_struct_ops_not_zeroed();
+	if (test__start_subtest("test_struct_ops_extra_arg"))
+		test_struct_ops_extra_arg();
 }
 
diff --git a/tools/testing/selftests/bpf/progs/struct_ops_extra_arg.c b/tools/testing/selftests/bpf/progs/struct_ops_extra_arg.c
new file mode 100644
index 000000000000..4b73b279ad22
--- /dev/null
+++ b/tools/testing/selftests/bpf/progs/struct_ops_extra_arg.c
@@ -0,0 +1,49 @@
+// SPDX-License-Identifier: GPL-2.0
+/* Copyright (c) 2024 Meta Platforms, Inc. and affiliates. */
+#include <vmlinux.h>
+#include <bpf/bpf_helpers.h>
+#include <bpf/bpf_tracing.h>
+#include "../bpf_testmod/bpf_testmod.h"
+
+char _license[] SEC("license") = "GPL";
+
+int test_1_result = 0;
+int test_2_result = 0;
+
+SEC("struct_ops/test_1")
+int BPF_PROG(test_1)
+{
+	test_1_result = 0xdeadbeef;
+	return 0;
+}
+
+SEC("?struct_ops/test_2")
+void BPF_PROG(test_2, int a, int b)
+{
+	test_2_result = a + b;
+}
+
+SEC("?struct_ops/test_extra_arg")
+void BPF_PROG(test_extra_arg, int a, int b, int extra_arg)
+{
+	/* Accessing extra_arg will cause a verifier error since it
+	 * accesses the context data beyond the size of the context.
+	 */
+	test_2_result = a + b + extra_arg + 3;
+}
+
+SEC("?struct_ops/test_extra_arg_unused")
+void BPF_PROG(test_extra_arg_unused, int a, int b, int extra_arg)
+{
+	/* The extra_arg is not used, so it should not cause a verifier
+	 * error.
+	 */
+	test_2_result = a + b + 3;
+}
+
+SEC(".struct_ops.link")
+struct bpf_testmod_ops testmod_1 = {
+	.test_1 = (void *)test_1,
+	.test_2 = (void *)test_extra_arg,
+	.data = 0x1,
+};
-- 
2.34.1