bpf: verifier: Fix return value of fixup_call_args

Run bloom_filter_map selftests (./test_progs -t bloom_filter_map) on a
Loongarch platform, an error message "JIT doesn't support bpf-to-bpf calls"
is got in user space, together with an unexpected errno EINVAL (22), not
ENOTSUPP (524):

 libbpf: prog 'inner_map': BPF program load failed: Invalid argument
 libbpf: prog 'inner_map': -- BEGIN PROG LOAD LOG --
 JIT doesn't support bpf-to-bpf calls
 callbacks are not allowed in non-JITed programs
 processed 37 insns (limit 1000000) max_states_per_insn 1 total_states
 -- END PROG LOAD LOG --
 libbpf: prog 'inner_map': failed to load: -22
 libbpf: failed to load object 'bloom_filter_map'
 libbpf: failed to load BPF skeleton 'bloom_filter_map': -22
 setup_progs:FAIL:bloom_filter_map__open_and_load unexpected error: -22
 #16      bloom_filter_map:FAIL

Although the return value of jit_subprogs() does be set as "ENOTSUPP":

	verbose(env, "JIT doesn't support bpf-to-bpf calls\n");
	err = -ENOTSUPP;
	goto out_free;

But afterwards in fixup_call_args(), the return value of jit_subprogs()
is ignored, and overwritten as "-EINVAL":

	verbose(env, "callbacks are not allowed in non-JITed programs\n");
	return -EINVAL;

This patch fixes this by changing return values of fixup_call_args() from
"-EINVAL" to "err ?: -EINVAL". With this change, errno 524 is got in user
space now:

 libbpf: prog 'inner_map': BPF program load failed: unknown error (-524)
 libbpf: prog 'inner_map': -- BEGIN PROG LOAD LOG --
 JIT doesn't support bpf-to-bpf calls
 processed 37 insns (limit 1000000) max_states_per_insn 1 total_states
 -- END PROG LOAD LOG --
 libbpf: prog 'inner_map': failed to load: -524
 libbpf: failed to load object 'bloom_filter_map'
 libbpf: failed to load BPF skeleton 'bloom_filter_map': -524
 setup_progs:FAIL:bloom_filter_map__open_and_load unexpected error: -524

Signed-off-by: Geliang Tang <tanggeliang@kylinos.cn>

Author: Geliang Tang

kernel/bpf/verifier.c

@@ -19717,22 +19717,22 @@ static int fixup_call_args(struct bpf_verifier_env *env)
 #ifndef CONFIG_BPF_JIT_ALWAYS_ON
 	if (has_kfunc_call) {
 		verbose(env, "calling kernel functions are not allowed in non-JITed programs\n");
-		return -EINVAL;
+		return err ?: -EINVAL;
 	}
 	if (env->subprog_cnt > 1 && env->prog->aux->tail_call_reachable) {
 		/* When JIT fails the progs with bpf2bpf calls and tail_calls
 		 * have to be rejected, since interpreter doesn't support them yet.
 		 */
 		verbose(env, "tail_calls are not allowed in non-JITed programs with bpf-to-bpf calls\n");
-		return -EINVAL;
+		return err ?: -EINVAL;
 	}
 	for (i = 0; i < prog->len; i++, insn++) {
 		if (bpf_pseudo_func(insn)) {
 			/* When JIT fails the progs with callback calls
 			 * 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 err ?: -EINVAL;
 		}
 
 		if (!bpf_pseudo_call(insn))