bpf: Add dummy BPF STRUCT_OPS for test purpose

Currently the test of BPF STRUCT_OPS depends on the specific bpf
implementation of tcp_congestion_ops, but it can not cover all
basic functionalities (e.g, return value handling), so introduce
a dummy BPF STRUCT_OPS for test purpose.

Loading a bpf_dummy_ops implementation from userspace is prohibited,
and its only purpose is to run BPF_PROG_TYPE_STRUCT_OPS program
through bpf(BPF_PROG_TEST_RUN). Now programs for test_1() & test_2()
are supported. The following three cases are exercised in
bpf_dummy_struct_ops_test_run():

(1) test and check the value returned from state arg in test_1(state)
The content of state is copied from userspace pointer and copied back
after calling test_1(state). The user pointer is saved in an u64 array
and the array address is passed through ctx_in.

(2) test and check the return value of test_1(NULL)
Just simulate the case in which an invalid input argument is passed in.

(3) test multiple arguments passing in test_2(state, ...)
5 arguments are passed through ctx_in in form of u64 array. The first
element of array is userspace pointer of state and others 4 arguments
follow.

Signed-off-by: Hou Tao <houtao1@huawei.com>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Acked-by: Martin KaFai Lau <kafai@fb.com>
Link: https://lore.kernel.org/bpf/20211025064025.2567443-4-houtao1@huawei.com

1 files changed, 16 insertions, 0 deletions

diff --git a/include/linux/bpf.h b/include/linux/bpf.h
index 67f71e7def56..c098089c1b54 100644
--- a/include/linux/bpf.h
+++ b/include/linux/bpf.h
@@ -1018,6 +1018,22 @@ static inline void bpf_module_put(const void *data, struct module *owner)
 	else
 		module_put(owner);
 }
+
+#ifdef CONFIG_NET
+/* Define it here to avoid the use of forward declaration */
+struct bpf_dummy_ops_state {
+	int val;
+};
+
+struct bpf_dummy_ops {
+	int (*test_1)(struct bpf_dummy_ops_state *cb);
+	int (*test_2)(struct bpf_dummy_ops_state *cb, int a1, unsigned short a2,
+		      char a3, unsigned long a4);
+};
+
+int bpf_struct_ops_test_run(struct bpf_prog *prog, const union bpf_attr *kattr,
+			    union bpf_attr __user *uattr);
+#endif
 #else
 static inline const struct bpf_struct_ops *bpf_struct_ops_find(u32 type_id)
 {