selftests/bpf: Test if shadow types work correctly.

Change the values of fields, including scalar types and function pointers,
and check if the struct_ops map works as expected.

The test changes the field "test_2" of "testmod_1" from the pointer to
test_2() to pointer to test_3() and the field "data" to 13. The function
test_2() and test_3() both compute a new value for "test_2_result", but in
different way. By checking the value of "test_2_result", it ensures the
struct_ops map works as expected with changes through shadow types.

Signed-off-by: Kui-Feng Lee <thinker.li@gmail.com>
Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Link: https://lore.kernel.org/bpf/20240229064523.2091270-6-thinker.li@gmail.com

2 files changed, 18 insertions, 1 deletions

diff --git a/tools/testing/selftests/bpf/bpf_testmod/bpf_testmod.c b/tools/testing/selftests/bpf/bpf_testmod/bpf_testmod.c
index 66787e99ba1b..098ddd067224 100644
--- a/tools/testing/selftests/bpf/bpf_testmod/bpf_testmod.c
+++ b/tools/testing/selftests/bpf/bpf_testmod/bpf_testmod.c
@@ -539,6 +539,15 @@ static int bpf_testmod_ops_init_member(const struct btf_type *t,
 				       const struct btf_member *member,
 				       void *kdata, const void *udata)
 {
+	if (member->offset == offsetof(struct bpf_testmod_ops, data) * 8) {
+		/* For data fields, this function has to copy it and return
+		 * 1 to indicate that the data has been handled by the
+		 * struct_ops type, or the verifier will reject the map if
+		 * the value of the data field is not zero.
+		 */
+		((struct bpf_testmod_ops *)kdata)->data = ((struct bpf_testmod_ops *)udata)->data;
+		return 1;
+	}
 	return 0;
 }
 
@@ -559,7 +568,7 @@ static int bpf_dummy_reg(void *kdata)
 	 * initialized, so we need to check for NULL.
 	 */
 	if (ops->test_2)
-		ops->test_2(4, 3);
+		ops->test_2(4, ops->data);
 
 	return 0;
 }
diff --git a/tools/testing/selftests/bpf/bpf_testmod/bpf_testmod.h b/tools/testing/selftests/bpf/bpf_testmod/bpf_testmod.h
index c3b0cf788f9f..971458acfac3 100644
--- a/tools/testing/selftests/bpf/bpf_testmod/bpf_testmod.h
+++ b/tools/testing/selftests/bpf/bpf_testmod/bpf_testmod.h
@@ -35,6 +35,14 @@ struct bpf_testmod_ops {
 	void (*test_2)(int a, int b);
 	/* Used to test nullable arguments. */
 	int (*test_maybe_null)(int dummy, struct task_struct *task);
+
+	/* The following fields are used to test shadow copies. */
+	char onebyte;
+	struct {
+		int a;
+		int b;
+	} unsupported;
+	int data;
 };
 
 #endif /* _BPF_TESTMOD_H */