bpf: refactor fixup_bpf_calls()

reduce indent and make it iterate over instructions similar to
convert_ctx_accesses(). Also convert hard BUG_ON into soft verifier error.
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Acked-by: Daniel Borkmann <daniel@iogearbox.net>
Signed-off-by: David S. Miller <davem@davemloft.net>

kernel/bpf/verifier.c

@@ -3233,29 +3233,21 @@ static int convert_ctx_accesses(struct bpf_verifier_env *env)
 	return 0;
 }
 
-/* fixup insn->imm field of bpf_call instructions:
- * if (insn->imm == BPF_FUNC_map_lookup_elem)
- *      insn->imm = bpf_map_lookup_elem - __bpf_call_base;
- * else if (insn->imm == BPF_FUNC_map_update_elem)
- *      insn->imm = bpf_map_update_elem - __bpf_call_base;
- * else ...
+/* fixup insn->imm field of bpf_call instructions
  *
  * this function is called after eBPF program passed verification
  */
-static void fixup_bpf_calls(struct bpf_prog *prog)
+static int fixup_bpf_calls(struct bpf_verifier_env *env)
 {
+	struct bpf_prog *prog = env->prog;
+	struct bpf_insn *insn = prog->insnsi;
 	const struct bpf_func_proto *fn;
+	const int insn_cnt = prog->len;
 	int i;
 
-	for (i = 0; i < prog->len; i++) {
-		struct bpf_insn *insn = &prog->insnsi[i];
-
-		if (insn->code == (BPF_JMP | BPF_CALL)) {
-			/* we reach here when program has bpf_call instructions
-			 * and it passed bpf_check(), means that
-			 * ops->get_func_proto must have been supplied, check it
-			 */
-			BUG_ON(!prog->aux->ops->get_func_proto);
+	for (i = 0; i < insn_cnt; i++, insn++) {
+		if (insn->code != (BPF_JMP | BPF_CALL))
+			continue;
 
 		if (insn->imm == BPF_FUNC_get_route_realm)
 			prog->dst_needed = 1;
@@ -3264,12 +3256,10 @@ static void fixup_bpf_calls(struct bpf_prog *prog)
 		if (insn->imm == BPF_FUNC_xdp_adjust_head)
 			prog->xdp_adjust_head = 1;
 		if (insn->imm == BPF_FUNC_tail_call) {
-				/* mark bpf_tail_call as different opcode
-				 * to avoid conditional branch in
-				 * interpeter for every normal call
-				 * and to prevent accidental JITing by
-				 * JIT compiler that doesn't support
-				 * bpf_tail_call yet
+			/* mark bpf_tail_call as different opcode to avoid
+			 * conditional branch in the interpeter for every normal
+			 * call and to prevent accidental JITing by JIT compiler
+			 * that doesn't support bpf_tail_call yet
 			 */
 			insn->imm = 0;
 			insn->code |= BPF_X;
@@ -3280,12 +3270,16 @@ static void fixup_bpf_calls(struct bpf_prog *prog)
 		/* all functions that have prototype and verifier allowed
 		 * programs to call them, must be real in-kernel functions
 		 */
-			BUG_ON(!fn->func);
-			insn->imm = fn->func - __bpf_call_base;
+		if (!fn->func) {
+			verbose("kernel subsystem misconfigured func %s#%d\n",
+				func_id_name(insn->imm), insn->imm);
+			return -EFAULT;
 		}
+		insn->imm = fn->func - __bpf_call_base;
 	}
-}
 
+	return 0;
+}
 
 static void free_states(struct bpf_verifier_env *env)
 {
@@ -3383,7 +3377,7 @@ int bpf_check(struct bpf_prog **prog, union bpf_attr *attr)
 		ret = convert_ctx_accesses(env);
 
 	if (ret == 0)
-		fixup_bpf_calls(env->prog);
+		ret = fixup_bpf_calls(env);
 
 	if (log_level && log_len >= log_size - 1) {
 		BUG_ON(log_len >= log_size);