[PATCH v1 bpf-next 06/18] selftests/bpf: Test fmod_ret BTF decl tags and attach permission

[Anton Protopopov <a.s.protopopov@gmail.com>]

Check that resolve_btfids tags the fmod_ret targets of vmlinux and of
bpf_testmod with "bpf_fmodret", that only bpf_fentry_test1 has the
"bpf_fmodret_sleepable" tag, and that a function which is not a target
has none.

Load minimal fmod_ret programs to check that the kernel builds its
target set from the tags: a target loads, a function which is not a
target does not, and sleepable programs load only for the sleepable
target.

Signed-off-by: Anton Protopopov <a.s.protopopov@gmail.com>
---
 .../selftests/bpf/prog_tests/fmodret_tags.c   | 155 ++++++++++++++++++
 1 file changed, 155 insertions(+)
 create mode 100644 tools/testing/selftests/bpf/prog_tests/fmodret_tags.c

diff --git a/tools/testing/selftests/bpf/prog_tests/fmodret_tags.c b/tools/testing/selftests/bpf/prog_tests/fmodret_tags.c
new file mode 100644
index 000000000000..62efe11af826
--- /dev/null
+++ b/tools/testing/selftests/bpf/prog_tests/fmodret_tags.c
@@ -0,0 +1,155 @@
+// SPDX-License-Identifier: GPL-2.0
+
+#include <test_progs.h>
+#include <linux/filter.h>
+#include <bpf/btf.h>
+
+#define TAG_FMODRET		"bpf_fmodret"
+#define TAG_FMODRET_SLEEPABLE	"bpf_fmodret_sleepable"
+
+static bool func_has_tag(const struct btf *btf, const char *func, const char *tag)
+{
+	int func_id, id, nr_types;
+
+	func_id = btf__find_by_name_kind(btf, func, BTF_KIND_FUNC);
+	if (func_id < 0)
+		return false;
+
+	nr_types = btf__type_cnt(btf);
+	for (id = 1; id < nr_types; id++) {
+		const struct btf_type *t = btf__type_by_id(btf, id);
+
+		if (!btf_is_decl_tag(t) || t->type != func_id ||
+		    btf_decl_tag(t)->component_idx != -1)
+			continue;
+		if (!strcmp(btf__name_by_offset(btf, t->name_off), tag))
+			return true;
+	}
+
+	return false;
+}
+
+static void test_vmlinux_tags(void)
+{
+	struct btf *btf;
+
+	btf = btf__load_vmlinux_btf();
+	if (!ASSERT_OK_PTR(btf, "btf__load_vmlinux_btf"))
+		return;
+
+	ASSERT_TRUE(func_has_tag(btf, "bpf_modify_return_test", TAG_FMODRET), "modify_return_test");
+	ASSERT_TRUE(func_has_tag(btf, "bpf_modify_return_test2", TAG_FMODRET),
+		    "modify_return_test2");
+	ASSERT_TRUE(func_has_tag(btf, "bpf_modify_return_test_tp", TAG_FMODRET),
+		    "modify_return_test_tp");
+	ASSERT_TRUE(func_has_tag(btf, "bpf_fentry_test1", TAG_FMODRET), "fentry_test1");
+	ASSERT_TRUE(func_has_tag(btf, "update_socket_protocol", TAG_FMODRET),
+		    "update_socket_protocol");
+
+	/* Only bpf_fentry_test1 is a sleepable target */
+	ASSERT_TRUE(func_has_tag(btf, "bpf_fentry_test1", TAG_FMODRET_SLEEPABLE),
+		    "fentry_test1_sleepable");
+	ASSERT_FALSE(func_has_tag(btf, "bpf_modify_return_test", TAG_FMODRET_SLEEPABLE),
+		     "modify_return_test_sleepable");
+	ASSERT_FALSE(func_has_tag(btf, "bpf_modify_return_test2", TAG_FMODRET_SLEEPABLE),
+		     "modify_return_test2_sleepable");
+	ASSERT_FALSE(func_has_tag(btf, "bpf_modify_return_test_tp", TAG_FMODRET_SLEEPABLE),
+		     "modify_return_test_tp_sleepable");
+	ASSERT_FALSE(func_has_tag(btf, "update_socket_protocol", TAG_FMODRET_SLEEPABLE),
+		     "update_socket_protocol_sleepable");
+
+	/* A function which is not a target has no tag */
+	ASSERT_GT(btf__find_by_name_kind(btf, "bpf_fentry_test2", BTF_KIND_FUNC), 0,
+		  "fentry_test2_exists");
+	ASSERT_FALSE(func_has_tag(btf, "bpf_fentry_test2", TAG_FMODRET), "fentry_test2");
+	ASSERT_FALSE(func_has_tag(btf, "bpf_fentry_test2", TAG_FMODRET_SLEEPABLE),
+		     "fentry_test2_sleepable");
+
+	btf__free(btf);
+}
+
+static void test_module_tags(void)
+{
+	struct btf *vmlinux_btf, *module_btf;
+
+	if (!env.has_testmod) {
+		test__skip();
+		return;
+	}
+
+	vmlinux_btf = btf__load_vmlinux_btf();
+	if (!ASSERT_OK_PTR(vmlinux_btf, "btf__load_vmlinux_btf"))
+		return;
+	module_btf = btf__load_module_btf("bpf_testmod", vmlinux_btf);
+	if (!module_btf && errno == ENOENT) {
+		printf("%s:SKIP:bpf_testmod has no BTF\n", __func__);
+		test__skip();
+		goto out;
+	}
+	if (!ASSERT_OK_PTR(module_btf, "btf__load_module_btf"))
+		goto out;
+
+	ASSERT_TRUE(func_has_tag(module_btf, "bpf_testmod_trampoline_count_test", TAG_FMODRET),
+		    "trampoline_count_test");
+	ASSERT_FALSE(func_has_tag(module_btf, "bpf_testmod_trampoline_count_test",
+				  TAG_FMODRET_SLEEPABLE), "trampoline_count_test_sleepable");
+	ASSERT_FALSE(func_has_tag(module_btf, "bpf_testmod_fentry_test1", TAG_FMODRET),
+		     "testmod_fentry_test1");
+
+	btf__free(module_btf);
+out:
+	btf__free(vmlinux_btf);
+}
+
+/* Load a minimal fmod_ret program which attaches to function BTF_ID */
+static int load_fmod_ret(int btf_id, __u32 prog_flags)
+{
+	struct bpf_insn insns[] = {
+		BPF_MOV64_IMM(BPF_REG_0, 0),
+		BPF_EXIT_INSN(),
+	};
+	LIBBPF_OPTS(bpf_prog_load_opts, opts,
+		.expected_attach_type = BPF_MODIFY_RETURN,
+		.prog_flags = prog_flags,
+		.attach_btf_id = btf_id,
+	);
+
+	return bpf_prog_load(BPF_PROG_TYPE_TRACING, NULL, "GPL", insns, ARRAY_SIZE(insns), &opts);
+}
+
+static void check_load(const char *func, __u32 prog_flags, bool allowed, const char *name)
+{
+	int btf_id, fd;
+
+	btf_id = libbpf_find_vmlinux_btf_id(func, BPF_MODIFY_RETURN);
+	if (!ASSERT_GT(btf_id, 0, func))
+		return;
+	fd = load_fmod_ret(btf_id, prog_flags);
+	if (allowed)
+		ASSERT_GE(fd, 0, name);
+	else
+		ASSERT_LT(fd, 0, name);
+	if (fd >= 0)
+		close(fd);
+}
+
+static void test_attach_permission(void)
+{
+	check_load("bpf_modify_return_test", 0, true, "target");
+	check_load("bpf_fentry_test1", 0, true, "sleepable_target");
+	check_load("bpf_fentry_test2", 0, false, "not_a_target");
+
+	check_load("bpf_fentry_test1", BPF_F_SLEEPABLE, true, "sleepable_prog_sleepable_target");
+	check_load("bpf_modify_return_test", BPF_F_SLEEPABLE, false,
+		   "sleepable_prog_nonsleepable_target");
+}
+
+void test_fmodret_tags(void)
+{
+	if (test__start_subtest("vmlinux"))
+		test_vmlinux_tags();
+	if (test__start_subtest("module"))
+		test_module_tags();
+	if (test__start_subtest("attach_permission"))
+		test_attach_permission();
+}
-- 
2.43.0