[PATCH bpf-next v4 3/4] selftests/bpf: Add a test case to confirm a tailcall infinite loop issue has been prevented

[Leon Hwang <leon.hwang@linux.dev>]

cd tools/testing/selftests/bpf; ./test_progs -t tailcalls
335/26  tailcalls/tailcall_bpf2bpf_freplace:OK
335     tailcalls:OK
Summary: 1/26 PASSED, 0 SKIPPED, 0 FAILED

Signed-off-by: Leon Hwang <leon.hwang@linux.dev>
---
 .../selftests/bpf/prog_tests/tailcalls.c      | 99 ++++++++++++++++++-
 .../testing/selftests/bpf/progs/tc_bpf2bpf.c  | 24 ++++-
 2 files changed, 119 insertions(+), 4 deletions(-)

diff --git a/tools/testing/selftests/bpf/prog_tests/tailcalls.c b/tools/testing/selftests/bpf/prog_tests/tailcalls.c
index 21c5a37846ade..fa3f3bb11b098 100644
--- a/tools/testing/selftests/bpf/prog_tests/tailcalls.c
+++ b/tools/testing/selftests/bpf/prog_tests/tailcalls.c
@@ -1525,7 +1525,8 @@ static void test_tailcall_freplace(void)
 
 	prog_fd = bpf_program__fd(tc_skel->progs.entry_tc);
 	freplace_prog = freplace_skel->progs.entry_freplace;
-	err = bpf_program__set_attach_target(freplace_prog, prog_fd, "subprog");
+	err = bpf_program__set_attach_target(freplace_prog, prog_fd,
+					     "subprog_tailcall_tc");
 	if (!ASSERT_OK(err, "set_attach_target"))
 		goto out;
 
@@ -1534,7 +1535,7 @@ static void test_tailcall_freplace(void)
 		goto out;
 
 	freplace_link = bpf_program__attach_freplace(freplace_prog, prog_fd,
-						     "subprog");
+						     "subprog_tailcall_tc");
 	if (!ASSERT_OK_PTR(freplace_link, "attach_freplace"))
 		goto out;
 
@@ -1556,6 +1557,98 @@ static void test_tailcall_freplace(void)
 	tailcall_freplace__destroy(freplace_skel);
 }
 
+/* test_tailcall_bpf2bpf_freplace checks the failure that fails to attach a tail
+ * callee prog with freplace prog or fails to update an extended prog to
+ * prog_array map.
+ */
+static void test_tailcall_bpf2bpf_freplace(void)
+{
+	struct tailcall_freplace *freplace_skel = NULL;
+	struct bpf_link *freplace_link = NULL;
+	struct tc_bpf2bpf *tc_skel = NULL;
+	char buff[128] = {};
+	int prog_fd, map_fd;
+	int err, key;
+
+	LIBBPF_OPTS(bpf_test_run_opts, topts,
+		    .data_in = buff,
+		    .data_size_in = sizeof(buff),
+		    .repeat = 1,
+	);
+
+	tc_skel = tc_bpf2bpf__open_and_load();
+	if (!ASSERT_OK_PTR(tc_skel, "tc_bpf2bpf__open_and_load"))
+		goto out;
+
+	prog_fd = bpf_program__fd(tc_skel->progs.entry_tc);
+	freplace_skel = tailcall_freplace__open();
+	if (!ASSERT_OK_PTR(freplace_skel, "tailcall_freplace__open"))
+		goto out;
+
+	err = bpf_program__set_attach_target(freplace_skel->progs.entry_freplace,
+					     prog_fd, "subprog_tc");
+	if (!ASSERT_OK(err, "set_attach_target"))
+		goto out;
+
+	err = tailcall_freplace__load(freplace_skel);
+	if (!ASSERT_OK(err, "tailcall_freplace__load"))
+		goto out;
+
+	/* OK to attach then detach freplace prog. */
+
+	freplace_link = bpf_program__attach_freplace(freplace_skel->progs.entry_freplace,
+						     prog_fd, "subprog_tc");
+	if (!ASSERT_OK_PTR(freplace_link, "attach_freplace"))
+		goto out;
+
+	err = bpf_link__destroy(freplace_link);
+	if (!ASSERT_OK(err, "destroy link"))
+		goto out;
+
+	/* OK to update prog_array map then delete element from the map. */
+
+	key = 0;
+	map_fd = bpf_map__fd(freplace_skel->maps.jmp_table);
+	err = bpf_map_update_elem(map_fd, &key, &prog_fd, BPF_ANY);
+	if (!ASSERT_OK(err, "update jmp_table"))
+		goto out;
+
+	err = bpf_map_delete_elem(map_fd, &key);
+	if (!ASSERT_OK(err, "delete_elem from jmp_table"))
+		goto out;
+
+	/* Fail to attach a tail callee prog with freplace prog. */
+
+	err = bpf_map_update_elem(map_fd, &key, &prog_fd, BPF_ANY);
+	if (!ASSERT_OK(err, "update jmp_table"))
+		goto out;
+
+	freplace_link = bpf_program__attach_freplace(freplace_skel->progs.entry_freplace,
+						     prog_fd, "subprog_tc");
+	if (!ASSERT_ERR_PTR(freplace_link, "attach_freplace failure"))
+		goto out;
+
+	err = bpf_map_delete_elem(map_fd, &key);
+	if (!ASSERT_OK(err, "delete_elem from jmp_table"))
+		goto out;
+
+	/* Fail to update an extended prog to prog_array map. */
+
+	freplace_link = bpf_program__attach_freplace(freplace_skel->progs.entry_freplace,
+						     prog_fd, "subprog_tc");
+	if (!ASSERT_OK_PTR(freplace_link, "attach_freplace"))
+		goto out;
+
+	err = bpf_map_update_elem(map_fd, &key, &prog_fd, BPF_ANY);
+	if (!ASSERT_ERR(err, "update jmp_table failure"))
+		goto out;
+
+out:
+	bpf_link__destroy(freplace_link);
+	tailcall_freplace__destroy(freplace_skel);
+	tc_bpf2bpf__destroy(tc_skel);
+}
+
 void test_tailcalls(void)
 {
 	if (test__start_subtest("tailcall_1"))
@@ -1606,4 +1699,6 @@ void test_tailcalls(void)
 	test_tailcall_bpf2bpf_hierarchy_3();
 	if (test__start_subtest("tailcall_freplace"))
 		test_tailcall_freplace();
+	if (test__start_subtest("tailcall_bpf2bpf_freplace"))
+		test_tailcall_bpf2bpf_freplace();
 }
diff --git a/tools/testing/selftests/bpf/progs/tc_bpf2bpf.c b/tools/testing/selftests/bpf/progs/tc_bpf2bpf.c
index 8a0632c37839a..34f3c780194e4 100644
--- a/tools/testing/selftests/bpf/progs/tc_bpf2bpf.c
+++ b/tools/testing/selftests/bpf/progs/tc_bpf2bpf.c
@@ -4,11 +4,30 @@
 #include <bpf/bpf_helpers.h>
 #include "bpf_misc.h"
 
+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");
+
+__noinline
+int subprog_tailcall_tc(struct __sk_buff *skb)
+{
+	int ret = 1;
+
+	bpf_tail_call_static(skb, &jmp_table, 0);
+	__sink(skb);
+	__sink(ret);
+	return ret;
+}
+
 __noinline
-int subprog(struct __sk_buff *skb)
+int subprog_tc(struct __sk_buff *skb)
 {
 	int ret = 1;
 
+	__sink(skb);
 	__sink(ret);
 	return ret;
 }
@@ -16,7 +35,8 @@ int subprog(struct __sk_buff *skb)
 SEC("tc")
 int entry_tc(struct __sk_buff *skb)
 {
-	return subprog(skb);
+	subprog_tc(skb);
+	return subprog_tailcall_tc(skb);
 }
 
 char __license[] SEC("license") = "GPL";
-- 
2.44.0