selftests/bpf: Add test to access const void pointer argument in tracing program

Adding verifier test for accessing const void pointer argument in
tracing programs.

The test program loads 1st argument of bpf_fentry_test10 function
which is const void pointer and checks that verifier allows that.

Signed-off-by: KaFai Wan <[email protected]>
Signed-off-by: Andrii Nakryiko <[email protected]>
Acked-by: Jiri Olsa <[email protected]>
Link: https://lore.kernel.org/bpf/[email protected]

Author: mannkafai

net/bpf/test_run.c

@@ -569,6 +569,11 @@ __bpf_kfunc u32 bpf_fentry_test9(u32 *a)
 	return *a;
 }
 
+int noinline bpf_fentry_test10(const void *a)
+{
+	return (long)a;
+}
+
 void noinline bpf_fentry_test_sinfo(struct skb_shared_info *sinfo)
 {
 }
@@ -699,7 +704,8 @@ int bpf_prog_test_run_tracing(struct bpf_prog *prog,
 		    bpf_fentry_test6(16, (void *)17, 18, 19, (void *)20, 21) != 111 ||
 		    bpf_fentry_test7((struct bpf_fentry_test_t *)0) != 0 ||
 		    bpf_fentry_test8(&arg) != 0 ||
-		    bpf_fentry_test9(&retval) != 0)
+		    bpf_fentry_test9(&retval) != 0 ||
+		    bpf_fentry_test10((void *)0) != 0)
 			goto out;
 		break;
 	case BPF_MODIFY_RETURN:

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

@@ -65,4 +65,16 @@ __naked void ctx_access_u32_pointer_reject_8(void)
 "	::: __clobber_all);
 }
 
+SEC("fentry/bpf_fentry_test10")
+__description("btf_ctx_access const void pointer accept")
+__success __retval(0)
+__naked void ctx_access_const_void_pointer_accept(void)
+{
+	asm volatile ("					\
+	r2 = *(u64 *)(r1 + 0);		/* load 1st argument value (const void pointer) */\
+	r0 = 0;						\
+	exit;						\
+"	::: __clobber_all);
+}
+
 char _license[] SEC("license") = "GPL";