selftests/bpf: Bad_struct_ops test

When loading struct_ops programs kernel requires BTF id of the
struct_ops type and member index for attachment point inside that
type. This makes impossible to use same BPF program in several
struct_ops maps that have different struct_ops type.
Check if libbpf rejects such BPF objects files.

Signed-off-by: Eduard Zingerman <eddyz87@gmail.com>
Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Acked-by: Andrii Nakryiko <andrii@kernel.org>
Link: https://lore.kernel.org/bpf/20240306104529.6453-7-eddyz87@gmail.com

Author: eddyz87

tools/testing/selftests/bpf/bpf_testmod/bpf_testmod.c

@@ -611,6 +611,29 @@ struct bpf_struct_ops bpf_bpf_testmod_ops = {
 	.owner = THIS_MODULE,
 };
 
+static int bpf_dummy_reg2(void *kdata)
+{
+	struct bpf_testmod_ops2 *ops = kdata;
+
+	ops->test_1();
+	return 0;
+}
+
+static struct bpf_testmod_ops2 __bpf_testmod_ops2 = {
+	.test_1 = bpf_testmod_test_1,
+};
+
+struct bpf_struct_ops bpf_testmod_ops2 = {
+	.verifier_ops = &bpf_testmod_verifier_ops,
+	.init = bpf_testmod_ops_init,
+	.init_member = bpf_testmod_ops_init_member,
+	.reg = bpf_dummy_reg2,
+	.unreg = bpf_dummy_unreg,
+	.cfi_stubs = &__bpf_testmod_ops2,
+	.name = "bpf_testmod_ops2",
+	.owner = THIS_MODULE,
+};
+
 extern int bpf_fentry_test1(int a);
 
 static int bpf_testmod_init(void)
@@ -622,6 +645,7 @@ static int bpf_testmod_init(void)
 	ret = ret ?: register_btf_kfunc_id_set(BPF_PROG_TYPE_TRACING, &bpf_testmod_kfunc_set);
 	ret = ret ?: register_btf_kfunc_id_set(BPF_PROG_TYPE_SYSCALL, &bpf_testmod_kfunc_set);
 	ret = ret ?: register_bpf_struct_ops(&bpf_bpf_testmod_ops, bpf_testmod_ops);
+	ret = ret ?: register_bpf_struct_ops(&bpf_testmod_ops2, bpf_testmod_ops2);
 	if (ret < 0)
 		return ret;
 	if (bpf_fentry_test1(0) < 0)

tools/testing/selftests/bpf/bpf_testmod/bpf_testmod.h

@@ -89,4 +89,8 @@ struct bpf_testmod_ops {
 	int (*tramp_40)(int value);
 };
 
+struct bpf_testmod_ops2 {
+	int (*test_1)(void);
+};
+
 #endif /* _BPF_TESTMOD_H */

tools/testing/selftests/bpf/prog_tests/bad_struct_ops.c

@@ -0,0 +1,35 @@
+// SPDX-License-Identifier: GPL-2.0
+
+#include <test_progs.h>
+#include "bad_struct_ops.skel.h"
+
+static void invalid_prog_reuse(void)
+{
+	struct bad_struct_ops *skel;
+	char *log = NULL;
+	int err;
+
+	skel = bad_struct_ops__open();
+	if (!ASSERT_OK_PTR(skel, "bad_struct_ops__open"))
+		return;
+
+	if (start_libbpf_log_capture())
+		goto cleanup;
+
+	err = bad_struct_ops__load(skel);
+	log = stop_libbpf_log_capture();
+	ASSERT_ERR(err, "bad_struct_ops__load should fail");
+	ASSERT_HAS_SUBSTR(log,
+		"struct_ops init_kern testmod_2 func ptr test_1: invalid reuse of prog test_1",
+		"expected init_kern message");
+
+cleanup:
+	free(log);
+	bad_struct_ops__destroy(skel);
+}
+
+void test_bad_struct_ops(void)
+{
+	if (test__start_subtest("invalid_prog_reuse"))
+		invalid_prog_reuse();
+}

tools/testing/selftests/bpf/progs/bad_struct_ops.c

@@ -0,0 +1,25 @@
+// SPDX-License-Identifier: GPL-2.0
+
+#include <vmlinux.h>
+#include <bpf/bpf_helpers.h>
+#include <bpf/bpf_tracing.h>
+#include "../bpf_testmod/bpf_testmod.h"
+
+char _license[] SEC("license") = "GPL";
+
+SEC("struct_ops/test_1")
+int BPF_PROG(test_1) { return 0; }
+
+SEC("struct_ops/test_2")
+int BPF_PROG(test_2) { return 0; }
+
+SEC(".struct_ops.link")
+struct bpf_testmod_ops testmod_1 = {
+	.test_1 = (void *)test_1,
+	.test_2 = (void *)test_2
+};
+
+SEC(".struct_ops.link")
+struct bpf_testmod_ops2 testmod_2 = {
+	.test_1 = (void *)test_1
+};