core/vm: update subroutines acc to eip: disallow walk-into

core/vm/errors.go

@@ -23,6 +23,9 @@ import (
 
 // List evm execution errors
 var (
+	// ErrInvalidSubroutineEntry means that a BEGINSUB was reached via iteration,
+	// as opposed to from a JUMPSUB instruction
+	ErrInvalidSubroutineEntry   = errors.New("invalid subroutine entry")
 	ErrOutOfGas                 = errors.New("out of gas")
 	ErrCodeStoreOutOfGas        = errors.New("contract creation code storage out of gas")
 	ErrDepth                    = errors.New("max call depth exceeded")

core/vm/instructions.go

@@ -665,7 +665,7 @@ func opJumpdest(pc *uint64, interpreter *EVMInterpreter, callContext *callCtx) (
 }
 
 func opBeginSub(pc *uint64, interpreter *EVMInterpreter, callContext *callCtx) ([]byte, error) {
-	return nil, nil
+	return nil, ErrInvalidSubroutineEntry
 }
 
 func opJumpSub(pc *uint64, interpreter *EVMInterpreter, callContext *callCtx) ([]byte, error) {
@@ -681,7 +681,7 @@ func opJumpSub(pc *uint64, interpreter *EVMInterpreter, callContext *callCtx) ([
 		return nil, ErrInvalidJump
 	}
 	callContext.rstack.push(*pc)
-	*pc = posU64
+	*pc = posU64+1
 	interpreter.intPool.put(pos)
 	return nil, nil
 }

core/vm/runtime/runtime_test.go

@@ -538,7 +538,7 @@ func TestEipExampleCases(t *testing.T) {
 		prettyPrint("This should fail at first opcode, due to shallow `return_stack`", code)
 
 	}
-	{ // First eip testcase
+	{
 		code := []byte{
 			byte(vm.PUSH1), 5, // Jump past the subroutine
 			byte(vm.JUMP),
@@ -553,4 +553,13 @@ func TestEipExampleCases(t *testing.T) {
 			"and not exit with error", code)
 	}
 
+	{
+		code := []byte{
+			byte(vm.BEGINSUB),
+			byte(vm.RETURNSUB),
+			byte(vm.STOP),
+		}
+		prettyPrint("In this example, the code 'walks' into a subroutine, which is not "+
+			"allowed, and causes an error", code)
+	}
 }