selftests/bpf: Add test for lsm tail call

Add test for lsm tail call to ensure tail call can only be used between
bpf lsm progs attached to the same hook.

Signed-off-by: Xu Kuohai <xukuohai@huawei.com>
Link: https://lore.kernel.org/r/20240719110059.797546-9-xukuohai@huaweicloud.com
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Signed-off-by: Andrii Nakryiko <andrii@kernel.org>

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

@@ -12,6 +12,7 @@
 #include <stdlib.h>
 
 #include "lsm.skel.h"
+#include "lsm_tailcall.skel.h"
 
 char *CMD_ARGS[] = {"true", NULL};
 
@@ -95,7 +96,7 @@ static int test_lsm(struct lsm *skel)
 	return 0;
 }
 
-void test_test_lsm(void)
+static void test_lsm_basic(void)
 {
 	struct lsm *skel = NULL;
 	int err;
@@ -114,3 +115,46 @@ void test_test_lsm(void)
 close_prog:
 	lsm__destroy(skel);
 }
+
+static void test_lsm_tailcall(void)
+{
+	struct lsm_tailcall *skel = NULL;
+	int map_fd, prog_fd;
+	int err, key;
+
+	skel = lsm_tailcall__open_and_load();
+	if (!ASSERT_OK_PTR(skel, "lsm_tailcall__skel_load"))
+		goto close_prog;
+
+	map_fd = bpf_map__fd(skel->maps.jmp_table);
+	if (CHECK_FAIL(map_fd < 0))
+		goto close_prog;
+
+	prog_fd = bpf_program__fd(skel->progs.lsm_file_permission_prog);
+	if (CHECK_FAIL(prog_fd < 0))
+		goto close_prog;
+
+	key = 0;
+	err = bpf_map_update_elem(map_fd, &key, &prog_fd, BPF_ANY);
+	if (CHECK_FAIL(!err))
+		goto close_prog;
+
+	prog_fd = bpf_program__fd(skel->progs.lsm_file_alloc_security_prog);
+	if (CHECK_FAIL(prog_fd < 0))
+		goto close_prog;
+
+	err = bpf_map_update_elem(map_fd, &key, &prog_fd, BPF_ANY);
+	if (CHECK_FAIL(err))
+		goto close_prog;
+
+close_prog:
+	lsm_tailcall__destroy(skel);
+}
+
+void test_test_lsm(void)
+{
+	if (test__start_subtest("lsm_basic"))
+		test_lsm_basic();
+	if (test__start_subtest("lsm_tailcall"))
+		test_lsm_tailcall();
+}

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

@@ -0,0 +1,34 @@
+// SPDX-License-Identifier: GPL-2.0
+/* Copyright (c) 2024 Huawei Technologies Co., Ltd */
+
+#include "vmlinux.h"
+#include <errno.h>
+#include <bpf/bpf_helpers.h>
+
+char _license[] SEC("license") = "GPL";
+
+struct {
+	__uint(type, BPF_MAP_TYPE_PROG_ARRAY);
+	__uint(max_entries, 1);
+	__uint(key_size, sizeof(__u32));
+	__uint(value_size, sizeof(__u32));
+} jmp_table SEC(".maps");
+
+SEC("lsm/file_permission")
+int lsm_file_permission_prog(void *ctx)
+{
+	return 0;
+}
+
+SEC("lsm/file_alloc_security")
+int lsm_file_alloc_security_prog(void *ctx)
+{
+	return 0;
+}
+
+SEC("lsm/file_alloc_security")
+int lsm_file_alloc_security_entry(void *ctx)
+{
+	bpf_tail_call_static(ctx, &jmp_table, 0);
+	return 0;
+}