bpf: Return -ENOTSUPP if callbacks are not allowed in non-JITed programs

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]# ./test_verifier | grep FAIL
  #107/p inline simple bpf_loop call FAIL
  #108/p don't inline bpf_loop call, flags non-zero FAIL
  #109/p don't inline bpf_loop call, callback non-constant FAIL
  #110/p bpf_loop_inline and a dead func FAIL
  #111/p bpf_loop_inline stack locations for loop vars FAIL
  #112/p inline bpf_loop call in a big program FAIL
  Summary: 505 PASSED, 266 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 return -ENOTSUPP instead of -EINVAL for pseudo
calls in fixup_call_args().

With this patch:

  [root@linux bpf]# echo 0 > /proc/sys/net/core/bpf_jit_enable
  [root@linux bpf]# ./test_verifier | grep FAIL
  Summary: 505 PASSED, 272 SKIPPED, 0 FAILED

Signed-off-by: Tiezhu Yang <[email protected]>

Author: seehearfeel

kernel/bpf/verifier.c

@@ -19067,7 +19067,7 @@ static int fixup_call_args(struct bpf_verifier_env *env)
 			 * have to be rejected, since interpreter doesn't support them yet.
 			 */
 			verbose(env, "callbacks are not allowed in non-JITed programs\n");
-			return -EINVAL;
+			return -ENOTSUPP;
 		}
 
 		if (!bpf_pseudo_call(insn))