bpf: Move BPF_STX reserved field check into BPF_STX verifier code

I can't find a reason why this code is in resolve_pseudo_ldimm64;
since I'll be modifying it in a subsequent commit, tidy it up.
Signed-off-by: Brendan Jackman <jackmanb@google.com>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Acked-by: Yonghong Song <yhs@fb.com>
Acked-by: John Fastabend <john.fastabend@gmail.com>
Link: https://lore.kernel.org/bpf/20210114181751.768687-6-jackmanb@google.com

kernel/bpf/verifier.c

@@ -9528,6 +9528,12 @@ static int do_check(struct bpf_verifier_env *env)
 		} else if (class == BPF_STX) {
 			enum bpf_reg_type *prev_dst_type, dst_reg_type;
 
+			if (((BPF_MODE(insn->code) != BPF_MEM &&
+			      BPF_MODE(insn->code) != BPF_ATOMIC) || insn->imm != 0)) {
+				verbose(env, "BPF_STX uses reserved fields\n");
+				return -EINVAL;
+			}
+
 			if (BPF_MODE(insn->code) == BPF_ATOMIC) {
 				err = check_atomic(env, env->insn_idx, insn);
 				if (err)
@@ -10012,13 +10018,6 @@ static int resolve_pseudo_ldimm64(struct bpf_verifier_env *env)
 			return -EINVAL;
 		}
 
-		if (BPF_CLASS(insn->code) == BPF_STX &&
-		    ((BPF_MODE(insn->code) != BPF_MEM &&
-		      BPF_MODE(insn->code) != BPF_ATOMIC) || insn->imm != 0)) {
-			verbose(env, "BPF_STX uses reserved fields\n");
-			return -EINVAL;
-		}
-
 		if (insn[0].code == (BPF_LD | BPF_IMM | BPF_DW)) {
 			struct bpf_insn_aux_data *aux;
 			struct bpf_map *map;