selftests/bpf: Add test to access union argument in tracing program

Adding verifier test for accessing union argument in tracing programs.

The test program loads 1st argument of bpf_fentry_test11 function
which is union and checks that verifier allows that.

cd tools/testing/selftests/bpf
./test_progs -t verifier_btf_ctx
501/7   verifier_btf_ctx_access/btf_ctx_access union arg accept:OK
501     verifier_btf_ctx_access:OK
Summary: 1/7 PASSED, 0 SKIPPED, 0 FAILED

Signed-off-by: Leon Hwang <[email protected]>

Author: Asphaltt

net/bpf/test_run.c

@@ -574,6 +574,16 @@ noinline int bpf_fentry_test10(const void *a)
 	return (long)a;
 }
 
+typedef union {
+	void *arg0;
+	int *arg1;
+} union_test_t;
+
+noinline int bpf_fentry_test11(union_test_t t)
+{
+	return (int)(long)t.arg0;
+}
+
 noinline void bpf_fentry_test_sinfo(struct skb_shared_info *sinfo)
 {
 }
@@ -688,6 +698,7 @@ int bpf_prog_test_run_tracing(struct bpf_prog *prog,
 	struct bpf_fentry_test_t arg = {};
 	u16 side_effect = 0, ret = 0;
 	int b = 2, err = -EFAULT;
+	union_test_t utt = {};
 	u32 retval = 0;
 
 	if (kattr->test.flags || kattr->test.cpu || kattr->test.batch_size)
@@ -705,7 +716,8 @@ int bpf_prog_test_run_tracing(struct bpf_prog *prog,
 		    bpf_fentry_test7((struct bpf_fentry_test_t *)0) != 0 ||
 		    bpf_fentry_test8(&arg) != 0 ||
 		    bpf_fentry_test9(&retval) != 0 ||
-		    bpf_fentry_test10((void *)0) != 0)
+		    bpf_fentry_test10((void *)0) != 0 ||
+		    bpf_fentry_test11(utt) != 0)
 			goto out;
 		break;
 	case BPF_MODIFY_RETURN:

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

@@ -77,4 +77,16 @@ __naked void ctx_access_const_void_pointer_accept(void)
 "	::: __clobber_all);
 }
 
+SEC("fentry/bpf_fentry_test11")
+__description("btf_ctx_access union arg accept")
+__success __retval(0)
+__naked void ctx_access_union_arg_accept(void)
+{
+	asm volatile ("					\
+	r2 = *(u64 *)(r1 + 0);		/* load 1st argument value (union) */\
+	r0 = 0;						\
+	exit;						\
+"	::: __clobber_all);
+}
+
 char _license[] SEC("license") = "GPL";