bpf: Allow union argument in trampoline based programs

arch/x86/net/bpf_jit_comp.c

@@ -3164,7 +3164,7 @@ static int __arch_prepare_bpf_trampoline(struct bpf_tramp_image *im, void *rw_im
 
 	/* extra registers for struct arguments */
 	for (i = 0; i < m->nr_args; i++) {
-		if (m->arg_flags[i] & BTF_FMODEL_STRUCT_ARG)
+		if (m->arg_flags[i] & (BTF_FMODEL_STRUCT_ARG | BTF_FMODEL_UNION_ARG))
 			nr_regs += (m->arg_size[i] + 7) / 8 - 1;
 	}
 

include/linux/bpf.h

@@ -1119,6 +1119,9 @@ struct bpf_prog_offload {
 /* The argument is signed. */
 #define BTF_FMODEL_SIGNED_ARG		BIT(1)
 
+/* The argument is a union. */
+#define BTF_FMODEL_UNION_ARG		BIT(2)
+
 struct btf_func_model {
 	u8 ret_size;
 	u8 ret_flags;

include/linux/btf.h

@@ -404,6 +404,11 @@ static inline bool btf_type_is_struct(const struct btf_type *t)
 	return kind == BTF_KIND_STRUCT || kind == BTF_KIND_UNION;
 }
 
+static inline bool __btf_type_is_union(const struct btf_type *t)
+{
+	return BTF_INFO_KIND(t->info) == BTF_KIND_UNION;
+}
+
 static inline bool __btf_type_is_struct(const struct btf_type *t)
 {
 	return BTF_INFO_KIND(t->info) == BTF_KIND_STRUCT;

kernel/bpf/btf.c

@@ -6762,7 +6762,7 @@ bool btf_ctx_access(int off, int size, enum bpf_access_type type,
 	/* skip modifiers */
 	while (btf_type_is_modifier(t))
 		t = btf_type_by_id(btf, t->type);
-	if (btf_type_is_small_int(t) || btf_is_any_enum(t) || __btf_type_is_struct(t))
+	if (btf_type_is_small_int(t) || btf_is_any_enum(t) || btf_type_is_struct(t))
 		/* accessing a scalar */
 		return true;
 	if (!btf_type_is_ptr(t)) {
@@ -7334,7 +7334,7 @@ static int __get_type_size(struct btf *btf, u32 btf_id,
 	if (btf_type_is_ptr(t))
 		/* kernel size of pointer. Not BPF's size of pointer*/
 		return sizeof(void *);
-	if (btf_type_is_int(t) || btf_is_any_enum(t) || __btf_type_is_struct(t))
+	if (btf_type_is_int(t) || btf_is_any_enum(t) || btf_type_is_struct(t))
 		return t->size;
 	return -EINVAL;
 }
@@ -7347,6 +7347,8 @@ static u8 __get_type_fmodel_flags(const struct btf_type *t)
 		flags |= BTF_FMODEL_STRUCT_ARG;
 	if (btf_type_is_signed_int(t))
 		flags |= BTF_FMODEL_SIGNED_ARG;
+	if (__btf_type_is_union(t))
+		flags |= BTF_FMODEL_UNION_ARG;
 
 	return flags;
 }
@@ -7384,7 +7386,7 @@ int btf_distill_func_proto(struct bpf_verifier_log *log,
 		return -EINVAL;
 	}
 	ret = __get_type_size(btf, func->type, &t);
-	if (ret < 0 || __btf_type_is_struct(t)) {
+	if (ret < 0 || btf_type_is_struct(t)) {
 		bpf_log(log,
 			"The function %s return type %s is unsupported.\n",
 			tname, btf_type_str(t));

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

@@ -112,10 +112,39 @@ static void test_struct_many_args(void)
 	tracing_struct_many_args__destroy(skel);
 }
 
+static void test_union_args(void)
+{
+	struct tracing_struct *skel;
+	int err;
+
+	skel = tracing_struct__open_and_load();
+	if (!ASSERT_OK_PTR(skel, "tracing_struct__open_and_load"))
+		return;
+
+	err = tracing_struct__attach(skel);
+	if (!ASSERT_OK(err, "tracing_struct__attach"))
+		goto out;
+
+	ASSERT_OK(trigger_module_test_read(256), "trigger_read");
+
+	ASSERT_EQ(skel->bss->ut1_a_a, 1, "ut1:a.arg.a");
+	ASSERT_EQ(skel->bss->ut1_b, 4, "ut1:b");
+	ASSERT_EQ(skel->bss->ut1_c, 5, "ut1:c");
+
+	ASSERT_EQ(skel->bss->ut2_a, 6, "ut2:a");
+	ASSERT_EQ(skel->bss->ut2_b_a, 2, "ut2:b.arg.a");
+	ASSERT_EQ(skel->bss->ut2_b_b, 3, "ut2:b.arg.b");
+
+out:
+	tracing_struct__destroy(skel);
+}
+
 void test_tracing_struct(void)
 {
 	if (test__start_subtest("struct_args"))
 		test_struct_args();
 	if (test__start_subtest("struct_many_args"))
 		test_struct_many_args();
+	if (test__start_subtest("union_args"))
+		test_union_args();
 }

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

@@ -18,6 +18,18 @@ struct bpf_testmod_struct_arg_3 {
 	int b[];
 };
 
+union bpf_testmod_union_arg_1 {
+	char a;
+	short b;
+	struct bpf_testmod_struct_arg_1 arg;
+};
+
+union bpf_testmod_union_arg_2 {
+	int a;
+	long b;
+	struct bpf_testmod_struct_arg_2 arg;
+};
+
 long t1_a_a, t1_a_b, t1_b, t1_c, t1_ret, t1_nregs;
 __u64 t1_reg0, t1_reg1, t1_reg2, t1_reg3;
 long t2_a, t2_b_a, t2_b_b, t2_c, t2_ret;
@@ -26,6 +38,9 @@ long t4_a_a, t4_b, t4_c, t4_d, t4_e_a, t4_e_b, t4_ret;
 long t5_ret;
 int t6;
 
+long ut1_a_a, ut1_b, ut1_c;
+long ut2_a, ut2_b_a, ut2_b_b;
+
 SEC("fentry/bpf_testmod_test_struct_arg_1")
 int BPF_PROG2(test_struct_arg_1, struct bpf_testmod_struct_arg_2, a, int, b, int, c)
 {
@@ -130,4 +145,22 @@ int BPF_PROG2(test_struct_arg_11, struct bpf_testmod_struct_arg_3 *, a)
 	return 0;
 }
 
+SEC("fexit/bpf_testmod_test_union_arg_1")
+int BPF_PROG2(test_union_arg_1, union bpf_testmod_union_arg_1, a, int, b, int, c)
+{
+	ut1_a_a = a.arg.a;
+	ut1_b = b;
+	ut1_c = c;
+	return 0;
+}
+
+SEC("fexit/bpf_testmod_test_union_arg_2")
+int BPF_PROG2(test_union_arg_2, int, a, union bpf_testmod_union_arg_2, b)
+{
+	ut2_a = a;
+	ut2_b_a = b.arg.a;
+	ut2_b_b = b.arg.b;
+	return 0;
+}
+
 char _license[] SEC("license") = "GPL";

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

@@ -62,6 +62,18 @@ struct bpf_testmod_struct_arg_5 {
 	long d;
 };
 
+union bpf_testmod_union_arg_1 {
+	char a;
+	short b;
+	struct bpf_testmod_struct_arg_1 arg;
+};
+
+union bpf_testmod_union_arg_2 {
+	int a;
+	long b;
+	struct bpf_testmod_struct_arg_2 arg;
+};
+
 __bpf_hook_start();
 
 noinline int
@@ -128,6 +140,20 @@ bpf_testmod_test_struct_arg_9(u64 a, void *b, short c, int d, void *e, char f,
 	return bpf_testmod_test_struct_arg_result;
 }
 
+noinline int
+bpf_testmod_test_union_arg_1(union bpf_testmod_union_arg_1 a, int b, int c)
+{
+	bpf_testmod_test_struct_arg_result = a.arg.a + b + c;
+	return bpf_testmod_test_struct_arg_result;
+}
+
+noinline int
+bpf_testmod_test_union_arg_2(int a, union bpf_testmod_union_arg_2 b)
+{
+	bpf_testmod_test_struct_arg_result = a + b.arg.a + b.arg.b;
+	return bpf_testmod_test_struct_arg_result;
+}
+
 noinline int
 bpf_testmod_test_arg_ptr_to_struct(struct bpf_testmod_struct_arg_1 *a) {
 	bpf_testmod_test_struct_arg_result = a->a;
@@ -398,6 +424,8 @@ bpf_testmod_test_read(struct file *file, struct kobject *kobj,
 	struct bpf_testmod_struct_arg_3 *struct_arg3;
 	struct bpf_testmod_struct_arg_4 struct_arg4 = {21, 22};
 	struct bpf_testmod_struct_arg_5 struct_arg5 = {23, 24, 25, 26};
+	union bpf_testmod_union_arg_1 union_arg1 = { .arg = {1} };
+	union bpf_testmod_union_arg_2 union_arg2 = { .arg = {2, 3} };
 	int i = 1;
 
 	while (bpf_testmod_return_ptr(i))
@@ -415,6 +443,9 @@ bpf_testmod_test_read(struct file *file, struct kobject *kobj,
 	(void)bpf_testmod_test_struct_arg_9(16, (void *)17, 18, 19, (void *)20,
 					    21, 22, struct_arg5, 27);
 
+	(void)bpf_testmod_test_union_arg_1(union_arg1, 4, 5);
+	(void)bpf_testmod_test_union_arg_2(6, union_arg2);
+
 	(void)bpf_testmod_test_arg_ptr_to_struct(&struct_arg1_2);
 
 	(void)trace_bpf_testmod_test_raw_tp_null_tp(NULL);