selftests/bpf: Add test case for different expected_attach_type

Add a small test case which adds two programs - one calling the other
through a tailcall - and check that BPF rejects them in case of different
expected_attach_type values:

# ./vmtest.sh -- ./test_progs -t xdp_devmap
[...]
#641/1 xdp_devmap_attach/DEVMAP with programs in entries:OK
#641/2 xdp_devmap_attach/DEVMAP with frags programs in entries:OK
#641/3 xdp_devmap_attach/Verifier check of DEVMAP programs:OK
#641/4 xdp_devmap_attach/DEVMAP with programs in entries on veth:OK
#641 xdp_devmap_attach:OK
Summary: 2/4 PASSED, 0 SKIPPED, 0 FAILED

Signed-off-by: Daniel Borkmann <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Alexei Starovoitov <[e-mail]>

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

···
 #include <test_progs.h>
 
 #include "test_xdp_devmap_helpers.skel.h"
+#include "test_xdp_devmap_tailcall.skel.h"
 #include "test_xdp_with_devmap_frags_helpers.skel.h"
 #include "test_xdp_with_devmap_helpers.skel.h"
 
···
 		    "Load of XDP program accessing egress ifindex without attach type")) {
 		test_xdp_devmap_helpers__destroy(skel);
 	}
+}
+
+static void test_xdp_devmap_tailcall(enum bpf_attach_type prog_dev,
+				     enum bpf_attach_type prog_tail,
+				     bool expect_reject)
+{
+	struct test_xdp_devmap_tailcall *skel;
+	int err;
+
+	skel = test_xdp_devmap_tailcall__open();
+	if (!ASSERT_OK_PTR(skel, "test_xdp_devmap_tailcall__open"))
+		return;
+
+	bpf_program__set_expected_attach_type(skel->progs.xdp_devmap, prog_dev);
+	bpf_program__set_expected_attach_type(skel->progs.xdp_entry, prog_tail);
+
+	err = test_xdp_devmap_tailcall__load(skel);
+	if (expect_reject)
+		ASSERT_ERR(err, "test_xdp_devmap_tailcall__load");
+	else
+		ASSERT_OK(err, "test_xdp_devmap_tailcall__load");
+
+	test_xdp_devmap_tailcall__destroy(skel);
 }
 
 static void test_xdp_with_devmap_frags_helpers(void)
···
 	if (test__start_subtest("DEVMAP with frags programs in entries"))
 		test_xdp_with_devmap_frags_helpers();
 
-	if (test__start_subtest("Verifier check of DEVMAP programs"))
+	if (test__start_subtest("Verifier check of DEVMAP programs")) {
 		test_neg_xdp_devmap_helpers();
+		test_xdp_devmap_tailcall(BPF_XDP_DEVMAP, BPF_XDP_DEVMAP, false);
+		test_xdp_devmap_tailcall(0, 0, true);
+		test_xdp_devmap_tailcall(BPF_XDP_DEVMAP, 0, true);
+		test_xdp_devmap_tailcall(0, BPF_XDP_DEVMAP, true);
+	}
 
 	if (test__start_subtest("DEVMAP with programs in entries on veth"))
 		test_xdp_with_devmap_helpers_veth();

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

···
+// SPDX-License-Identifier: GPL-2.0
+
+#include "vmlinux.h"
+#include <bpf/bpf_helpers.h>
+#include <bpf/bpf_tracing.h>
+
+SEC("xdp")
+int xdp_devmap(struct xdp_md *ctx)
+{
+	return ctx->egress_ifindex;
+}
+
+struct {
+	__uint(type, BPF_MAP_TYPE_PROG_ARRAY);
+	__uint(max_entries, 1);
+	__uint(key_size, sizeof(__u32));
+	__array(values, int (void *));
+} xdp_map SEC(".maps") = {
+	.values = {
+		[0] = (void *)&xdp_devmap,
+	},
+};
+
+SEC("xdp")
+int xdp_entry(struct xdp_md *ctx)
+{
+	bpf_tail_call(ctx, &xdp_map, 0);
+	return 0;
+}