selftests/bpf: Skip callback tests if jit is disabled in test_verifier

If CONFIG_BPF_JIT_ALWAYS_ON is not set and bpf_jit_enable is 0, there
exist 6 failed tests.

  [root@linux bpf]# echo 0 > /proc/sys/net/core/bpf_jit_enable
  [root@linux bpf]# echo 0 > /proc/sys/kernel/unprivileged_bpf_disabled
  [root@linux bpf]# ./test_verifier | grep FAIL
  torvalds#106/p inline simple bpf_loop call FAIL
  torvalds#107/p don't inline bpf_loop call, flags non-zero FAIL
  torvalds#108/p don't inline bpf_loop call, callback non-constant FAIL
  torvalds#109/p bpf_loop_inline and a dead func FAIL
  torvalds#110/p bpf_loop_inline stack locations for loop vars FAIL
  torvalds#111/p inline bpf_loop call in a big program FAIL
  Summary: 768 PASSED, 15 SKIPPED, 6 FAILED

The test log shows that callbacks are not allowed in non-JITed programs,
interpreter doesn't support them yet, thus these tests should be skipped
if jit is disabled, just handle this case in do_test_single().

With this patch:

  [root@linux bpf]# echo 0 > /proc/sys/net/core/bpf_jit_enable
  [root@linux bpf]# echo 0 > /proc/sys/kernel/unprivileged_bpf_disabled
  [root@linux bpf]# ./test_verifier | grep FAIL
  Summary: 768 PASSED, 21 SKIPPED, 0 FAILED

Signed-off-by: Tiezhu Yang <yangtiezhu@loongson.cn>
Acked-by: Hou Tao <houtao1@huawei.com>
Acked-by: Song Liu <song@kernel.org>

tools/testing/selftests/bpf/test_verifier.c

@@ -74,6 +74,7 @@
 		    1ULL << CAP_BPF)
 #define UNPRIV_SYSCTL "kernel/unprivileged_bpf_disabled"
 static bool unpriv_disabled = false;
+static bool jit_disabled;
 static int skips;
 static bool verbose = false;
 static int verif_log_level = 0;
@@ -1622,6 +1623,16 @@ static void do_test_single(struct bpf_test *test, bool unpriv,
 	alignment_prevented_execution = 0;
 
 	if (expected_ret == ACCEPT || expected_ret == VERBOSE_ACCEPT) {
+		if (fd_prog < 0 && saved_errno == EINVAL && jit_disabled) {
+			for (i = 0; i < prog_len; i++, prog++) {
+				if (!insn_is_pseudo_func(prog))
+					continue;
+				printf("SKIP (callbacks are not allowed in non-JITed programs)\n");
+				skips++;
+				goto close_fds;
+			}
+		}
+
 		if (fd_prog < 0) {
 			printf("FAIL\nFailed to load prog '%s'!\n",
 			       strerror(saved_errno));
@@ -1844,6 +1855,8 @@ int main(int argc, char **argv)
 		return EXIT_FAILURE;
 	}
 
+	jit_disabled = !is_jit_enabled();
+
 	/* Use libbpf 1.0 API mode */
 	libbpf_set_strict_mode(LIBBPF_STRICT_ALL);