Add assert_invalid tests and harden against malicious binary. (#30)

2021-10-15 10:00:47 +09:00
parent 2e34bad267
commit 69dbb2f8fb
15 changed files with 1051 additions and 524 deletions
--- a/.github/workflows/commit.yaml
+++ b/.github/workflows/commit.yaml
@@ -47,11 +47,4 @@ jobs:
            ~/go/pkg/mod
          key: ${{ runner.os }}-go-${{ hashFiles('**/go.sum') }}

-      - name: Install TinyGo
-        run: |
-          wget https://github.com/tinygo-org/tinygo/releases/download/v0.20.0/tinygo_0.20.0_amd64.deb
-          sudo dpkg -i tinygo_0.20.0_amd64.deb
-
-      - run: make build.examples
-
      - run: make test
--- a/README.md
+++ b/README.md
@@ -1,6 +1,6 @@
 # Gasm

-A minimal implementation of Wasm Virtual machine purely written in Go. The VM passes all the [Wasm Spec test suites](https://github.com/WebAssembly/spec/tree/master/test/core) and is fully compatible Wasm v1.0 Specification.
+A minimal implementation of Wasm Virtual Machine purely written in Go. The VM passes all the [Wasm Spec test suites](https://github.com/WebAssembly/spec/tree/wg-1.0/test/core) and is fully compatible with the WebAssembly v1.0 Specification.

 The VM can be embedded in your Go program without any dependency like cgo, and enables Gophers to write Wasm host environments easily.

--- a/wasm/const_expr.go
+++ b/wasm/const_expr.go
@@ -15,52 +15,58 @@ type ConstantExpression struct {
 	Data    []byte
 }

-func (s *Store) executeConstExpression(target *ModuleInstance, expr *ConstantExpression) (v interface{}, err error) {
+func (s *Store) executeConstExpression(target *ModuleInstance, expr *ConstantExpression) (v interface{}, valueType ValueType, err error) {
 	r := bytes.NewBuffer(expr.Data)
 	switch expr.OptCode {
 	case OptCodeI32Const:
 		v, _, err = leb128.DecodeInt32(r)
 		if err != nil {
-			return nil, fmt.Errorf("read uint32: %w", err)
+			return nil, 0, fmt.Errorf("read uint32: %w", err)
 		}
+		return v, ValueTypeI32, nil
 	case OptCodeI64Const:
 		v, _, err = leb128.DecodeInt32(r)
 		if err != nil {
-			return nil, fmt.Errorf("read uint64: %w", err)
+			return nil, 0, fmt.Errorf("read uint64: %w", err)
 		}
+		return v, ValueTypeI64, nil
 	case OptCodeF32Const:
 		v, err = readFloat32(r)
 		if err != nil {
-			return nil, fmt.Errorf("read f34: %w", err)
+			return nil, 0, fmt.Errorf("read f34: %w", err)
 		}
+		return v, ValueTypeF32, nil
 	case OptCodeF64Const:
 		v, err = readFloat64(r)
 		if err != nil {
-			return nil, fmt.Errorf("read f64: %w", err)
+			return nil, 0, fmt.Errorf("read f64: %w", err)
 		}
+		return v, ValueTypeF64, nil
 	case OptCodeGlobalGet:
 		id, _, err := leb128.DecodeUint32(r)
 		if err != nil {
-			return nil, fmt.Errorf("read index of global: %w", err)
+			return nil, 0, fmt.Errorf("read index of global: %w", err)
 		}
 		if uint32(len(target.GlobalsAddrs)) <= id {
-			return nil, fmt.Errorf("global index out of range")
+			return nil, 0, fmt.Errorf("global index out of range")
 		}
 		g := s.Globals[target.GlobalsAddrs[id]]
 		switch g.Type.ValType {
 		case ValueTypeI32:
 			v = int32(g.Val)
+			return v, ValueTypeI32, nil
 		case ValueTypeI64:
 			v = int64(g.Val)
+			return v, ValueTypeI64, nil
 		case ValueTypeF32:
 			v = math.Float32frombits(uint32(g.Val))
+			return v, ValueTypeF32, nil
 		case ValueTypeF64:
 			v = math.Float64frombits(uint64(g.Val))
+			return v, ValueTypeF64, nil
 		}
-	default:
-		return nil, fmt.Errorf("invalid opt code: %#x", expr.OptCode)
 	}
-	return v, nil
+	return nil, 0, fmt.Errorf("invalid opt code: %#x", expr.OptCode)
 }

 func readConstantExpression(r io.Reader) (*ConstantExpression, error) {
--- a/wasm/optcode.go
+++ b/wasm/optcode.go
@@ -56,12 +56,13 @@ const (
 	OptCodeMemorySize OptCode = 0x3f
 	OptCodeMemoryGrow OptCode = 0x40

-	// numeric instruction
+	// const instructions.
 	OptCodeI32Const OptCode = 0x41
 	OptCodeI64Const OptCode = 0x42
 	OptCodeF32Const OptCode = 0x43
 	OptCodeF64Const OptCode = 0x44

+	// numeric instructions.
 	OptCodeI32eqz OptCode = 0x45
 	OptCodeI32eq  OptCode = 0x46
 	OptCodeI32ne  OptCode = 0x47
--- a/wasm/section.go
+++ b/wasm/section.go
@@ -70,7 +70,7 @@ func (m *Module) readSections(r *Reader) error {
 			err = errors.New("invalid section id")
 		}

-		if sectionContentStart+int(ss) != r.read {
+		if err == nil && sectionContentStart+int(ss) != r.read {
 			err = fmt.Errorf("invalid section length: expected to be %d but got %d", ss, r.read-sectionContentStart)
 		}

@@ -149,7 +149,7 @@ func (m *Module) readSectionFunctions(r *Reader) error {
 	for i := range m.FunctionSection {
 		m.FunctionSection[i], _, err = leb128.DecodeUint32(r)
 		if err != nil {
-			return fmt.Errorf("get typeidx: %v", err)
+			return fmt.Errorf("get type index: %v", err)
 		}
 	}
 	return nil
@@ -215,7 +215,9 @@ func (m *Module) readSectionExports(r *Reader) error {
 		if err != nil {
 			return fmt.Errorf("read export: %v", err)
 		}
-
+		if _, ok := m.ExportSection[expDesc.Name]; ok {
+			return fmt.Errorf("duplicate export name: %s", expDesc.Name)
+		}
 		m.ExportSection[expDesc.Name] = expDesc
 	}
 	return nil
@@ -257,7 +259,7 @@ func (m *Module) readSectionCodes(r *Reader) error {
 	for i := range m.CodeSection {
 		m.CodeSection[i], err = readCodeSegment(r)
 		if err != nil {
-			return fmt.Errorf("read code segment: %v", err)
+			return fmt.Errorf("read %d-th code segment: %v", i, err)
 		}
 	}
 	return nil
--- a/wasm/segment.go
+++ b/wasm/segment.go
@@ -3,12 +3,18 @@ package wasm
 import (
 	"fmt"
 	"io"
-	"io/ioutil"
 	"math"

 	"github.com/mathetake/gasm/wasm/leb128"
 )

+const (
+	ImportKindFunction = 0x00
+	ImportKindTable    = 0x01
+	ImportKindMemory   = 0x02
+	ImportKindGlobal   = 0x03
+)
+
 type ImportDesc struct {
 	Kind byte

@@ -25,41 +31,40 @@ func readImportDesc(r io.Reader) (*ImportDesc, error) {
 	}

 	switch b[0] {
-	case 0x00:
+	case ImportKindFunction:
 		tID, _, err := leb128.DecodeUint32(r)
 		if err != nil {
 			return nil, fmt.Errorf("read typeindex: %v", err)
 		}
 		return &ImportDesc{
-			Kind:         0x00,
+			Kind:         ImportKindFunction,
 			TypeIndexPtr: &tID,
 		}, nil
-	case 0x01:
+	case ImportKindTable:
 		tt, err := readTableType(r)
 		if err != nil {
 			return nil, fmt.Errorf("read table type: %v", err)
 		}
 		return &ImportDesc{
-			Kind:         0x01,
+			Kind:         ImportKindTable,
 			TableTypePtr: tt,
 		}, nil
-	case 0x02:
+	case ImportKindMemory:
 		mt, err := readMemoryType(r)
 		if err != nil {
 			return nil, fmt.Errorf("read table type: %v", err)
 		}
 		return &ImportDesc{
-			Kind:       0x02,
+			Kind:       ImportKindMemory,
 			MemTypePtr: mt,
 		}, nil
-	case 0x03:
+	case ImportKindGlobal:
 		gt, err := readGlobalType(r)
 		if err != nil {
 			return nil, fmt.Errorf("read global type: %v", err)
 		}
-
 		return &ImportDesc{
-			Kind:          0x03,
+			Kind:          ImportKindGlobal,
 			GlobalTypePtr: gt,
 		}, nil
 	default:
@@ -206,8 +211,9 @@ func readElementSegment(r io.Reader) (*ElementSegment, error) {
 }

 type CodeSegment struct {
-	NumLocals uint32
-	Body      []byte
+	NumLocals  uint32
+	LocalTypes []ValueType
+	Body       []byte
 }

 func readCodeSegment(r io.Reader) (*CodeSegment, error) {
@@ -221,29 +227,46 @@ func readCodeSegment(r io.Reader) (*CodeSegment, error) {
 	// parse locals
 	ls, _, err := leb128.DecodeUint32(r)
 	if err != nil {
-		return nil, fmt.Errorf("get the size locals: %w", err)
+		return nil, fmt.Errorf("get the size locals: %v", err)
 	}

-	var numLocals uint64
+	var nums []uint64
+	var types []ValueType
+	var sum uint64
 	b := make([]byte, 1)
 	for i := uint32(0); i < ls; i++ {
 		n, _, err := leb128.DecodeUint32(r)
 		if err != nil {
-			return nil, fmt.Errorf("read n of locals: %w", err)
+			return nil, fmt.Errorf("read n of locals: %v", err)
 		}
-		numLocals += uint64(n)
+		sum += uint64(n)
+		nums = append(nums, uint64(n))

-		if _, err := io.ReadFull(r, b); err != nil {
-			return nil, fmt.Errorf("read type of local")
+		_, err = io.ReadFull(r, b)
+		if err != nil {
+			return nil, fmt.Errorf("read type of local: %v", err)
+		}
+		switch vt := ValueType(b[0]); vt {
+		case ValueTypeI32, ValueTypeF32, ValueTypeI64, ValueTypeF64:
+			types = append(types, vt)
+		default:
+			return nil, fmt.Errorf("invalid local type: 0x%x", vt)
 		}
 	}

-	if numLocals > math.MaxUint32 {
-		return nil, fmt.Errorf("too many locals: %d", numLocals)
+	if sum > math.MaxUint32 {
+		return nil, fmt.Errorf("too many locals: %d", sum)
 	}

-	// extract body
-	body, err := ioutil.ReadAll(r)
+	var localTypes []ValueType
+	for i, num := range nums {
+		t := types[i]
+		for j := uint64(0); j < num; j++ {
+			localTypes = append(localTypes, t)
+		}
+	}
+
+	body, err := io.ReadAll(r)
 	if err != nil {
 		return nil, fmt.Errorf("read body: %w", err)
 	}
@@ -253,8 +276,9 @@ func readCodeSegment(r io.Reader) (*CodeSegment, error) {
 	}

 	return &CodeSegment{
-		Body:      body[:len(body)-1],
-		NumLocals: uint32(numLocals),
+		Body:       body,
+		NumLocals:  uint32(sum),
+		LocalTypes: localTypes,
 	}, nil
 }

--- a/wasm/segment_test.go
+++ b/wasm/segment_test.go
@@ -1,231 +0,0 @@
-package wasm
-
-import (
-	"bytes"
-	"errors"
-	"strconv"
-	"testing"
-
-	"github.com/stretchr/testify/assert"
-	"github.com/stretchr/testify/require"
-)
-
-func TestReadImportDesc(t *testing.T) {
-	t.Run("ng", func(t *testing.T) {
-		buf := []byte{0x04}
-		_, err := readImportDesc(bytes.NewBuffer(buf))
-		require.True(t, errors.Is(err, ErrInvalidByte))
-		t.Log(err)
-	})
-
-	for i, c := range []struct {
-		bytes []byte
-		exp   *ImportDesc
-	}{
-		{
-			bytes: []byte{0x00, 0x0a},
-			exp: &ImportDesc{
-				Kind:         0,
-				TypeIndexPtr: uint32Ptr(10),
-			},
-		},
-		{
-			bytes: []byte{0x01, 0x70, 0x0, 0x0a},
-			exp: &ImportDesc{
-				Kind: 1,
-				TableTypePtr: &TableType{
-					ElemType: 0x70,
-					Limit:    &LimitsType{Min: 10},
-				},
-			},
-		},
-		{
-			bytes: []byte{0x02, 0x0, 0x0a},
-			exp: &ImportDesc{
-				Kind:       2,
-				MemTypePtr: &MemoryType{Min: 10},
-			},
-		},
-		{
-			bytes: []byte{0x03, 0x7e, 0x01},
-			exp: &ImportDesc{
-				Kind:          3,
-				GlobalTypePtr: &GlobalType{ValType: ValueTypeI64, Mutable: true},
-			},
-		},
-	} {
-		t.Run(strconv.Itoa(i), func(t *testing.T) {
-			actual, err := readImportDesc(bytes.NewBuffer(c.bytes))
-			require.NoError(t, err)
-			assert.Equal(t, c.exp, actual)
-		})
-
-	}
-}
-
-func TestReadImportSegment(t *testing.T) {
-	exp := &ImportSegment{
-		Module: "abc",
-		Name:   "ABC",
-		Desc:   &ImportDesc{Kind: 0, TypeIndexPtr: uint32Ptr(10)},
-	}
-
-	buf := []byte{byte(len(exp.Module))}
-	buf = append(buf, exp.Module...)
-	buf = append(buf, byte(len(exp.Name)))
-	buf = append(buf, exp.Name...)
-	buf = append(buf, 0x00, 0x0a)
-
-	actual, err := readImportSegment(bytes.NewBuffer(buf))
-	require.NoError(t, err)
-	assert.Equal(t, exp, actual)
-}
-
-func TestReadGlobalSegment(t *testing.T) {
-	exp := &GlobalSegment{
-		Type: &GlobalType{ValType: ValueTypeI64, Mutable: false},
-		Init: &ConstantExpression{
-			OptCode: OptCodeI64Const,
-			Data:    []byte{0x01},
-		},
-	}
-
-	buf := []byte{0x7e, 0x00, 0x42, 0x01, 0x0b}
-	actual, err := readGlobalSegment(bytes.NewBuffer(buf))
-	require.NoError(t, err)
-	assert.Equal(t, exp, actual)
-}
-
-func TestReadExportDesc(t *testing.T) {
-	t.Run("ng", func(t *testing.T) {
-		buf := []byte{0x04}
-		_, err := readExportDesc(bytes.NewBuffer(buf))
-		require.True(t, errors.Is(err, ErrInvalidByte))
-		t.Log(err)
-	})
-
-	for i, c := range []struct {
-		bytes []byte
-		exp   *ExportDesc
-	}{
-		{
-			bytes: []byte{0x00, 0x0a},
-			exp:   &ExportDesc{Kind: 0, Index: 10},
-		},
-		{
-			bytes: []byte{0x01, 0x05},
-			exp:   &ExportDesc{Kind: 1, Index: 5},
-		},
-		{
-			bytes: []byte{0x02, 0x01},
-			exp:   &ExportDesc{Kind: 2, Index: 1},
-		},
-		{
-			bytes: []byte{0x03, 0x0b},
-			exp:   &ExportDesc{Kind: 3, Index: 11},
-		},
-	} {
-		t.Run(strconv.Itoa(i), func(t *testing.T) {
-			actual, err := readExportDesc(bytes.NewBuffer(c.bytes))
-			require.NoError(t, err)
-			assert.Equal(t, c.exp, actual)
-		})
-
-	}
-}
-
-func TestReadExportSegment(t *testing.T) {
-	exp := &ExportSegment{
-		Name: "ABC",
-		Desc: &ExportDesc{Kind: 0, Index: 10},
-	}
-
-	buf := []byte{byte(len(exp.Name))}
-	buf = append(buf, exp.Name...)
-	buf = append(buf, 0x00, 0x0a)
-
-	actual, err := readExportSegment(bytes.NewBuffer(buf))
-	require.NoError(t, err)
-	assert.Equal(t, exp, actual)
-}
-
-func TestReadElementSegment(t *testing.T) {
-	for i, c := range []struct {
-		bytes []byte
-		exp   *ElementSegment
-	}{
-		{
-			bytes: []byte{0xa, 0x41, 0x1, 0x0b, 0x02, 0x05, 0x07},
-			exp: &ElementSegment{
-				TableIndex: 10,
-				OffsetExpr: &ConstantExpression{
-					OptCode: OptCodeI32Const,
-					Data:    []byte{0x01},
-				},
-				Init: []uint32{5, 7},
-			},
-		},
-		{
-			bytes: []byte{0x3, 0x41, 0x04, 0x0b, 0x01, 0x0a},
-			exp: &ElementSegment{
-				TableIndex: 3,
-				OffsetExpr: &ConstantExpression{
-					OptCode: OptCodeI32Const,
-					Data:    []byte{0x04},
-				},
-				Init: []uint32{10},
-			},
-		},
-	} {
-		t.Run(strconv.Itoa(i), func(t *testing.T) {
-			actual, err := readElementSegment(bytes.NewBuffer(c.bytes))
-			require.NoError(t, err)
-			assert.Equal(t, c.exp, actual)
-		})
-	}
-}
-
-func TestReadCodeSegment(t *testing.T) {
-	buf := []byte{0x9, 0x1, 0x1, 0x1, 0x1, 0x1, 0x12, 0x3, 0x01, 0x0b}
-	exp := &CodeSegment{
-		NumLocals: 0x01,
-		Body:      []byte{0x1, 0x1, 0x12, 0x3, 0x01},
-	}
-	actual, err := readCodeSegment(bytes.NewBuffer(buf))
-	require.NoError(t, err)
-	assert.Equal(t, exp, actual)
-}
-
-func TestDataSegment(t *testing.T) {
-	for i, c := range []struct {
-		bytes []byte
-		exp   *DataSegment
-	}{
-		{
-			bytes: []byte{0x0, 0x41, 0x1, 0x0b, 0x02, 0x05, 0x07},
-			exp: &DataSegment{
-				OffsetExpression: &ConstantExpression{
-					OptCode: OptCodeI32Const,
-					Data:    []byte{0x01},
-				},
-				Init: []byte{5, 7},
-			},
-		},
-		{
-			bytes: []byte{0x0, 0x41, 0x04, 0x0b, 0x01, 0x0a},
-			exp: &DataSegment{
-				OffsetExpression: &ConstantExpression{
-					OptCode: OptCodeI32Const,
-					Data:    []byte{0x04},
-				},
-				Init: []byte{0x0a},
-			},
-		},
-	} {
-		t.Run(strconv.Itoa(i), func(t *testing.T) {
-			actual, err := readDataSegment(bytes.NewBuffer(c.bytes))
-			require.NoError(t, err)
-			assert.Equal(t, c.exp, actual)
-		})
-	}
-}
--- a/wasm/spectests/spec_test.go
+++ b/wasm/spectests/spec_test.go
@@ -202,8 +202,8 @@ func TestSpecification(t *testing.T) {

 		var base testbase
 		require.NoError(t, json.Unmarshal(raw, &base))
-
 		wastName := filepath.Base(base.SourceFile)
+
 		t.Run(wastName, func(t *testing.T) {
 			vm, err := wasm.NewVM()
 			require.NoError(t, err)
@@ -317,7 +317,17 @@ func TestSpecification(t *testing.T) {
 							t.Fatalf("unsupported action type type: %v", c)
 						}
 					case "assert_invalid":
-						// TODO:
+						if c.ModuleType == "text" {
+							// We don't support direct loading of wast yet.
+							t.Skip()
+						}
+						buf, err := os.ReadFile(filepath.Join(caseDir, c.Filename))
+						require.NoError(t, err, msg)
+						mod, err := wasm.DecodeModule(buf)
+						if err == nil {
+							err = vm.InstantiateModule(mod, "")
+						}
+						require.Error(t, err, msg)
 					case "assert_exhaustion":
 						// TODO:
 					case "assert_unlinkable":
--- a/wasm/store.go
+++ b/wasm/store.go
--- a/wasm/type.go
+++ b/wasm/type.go
@@ -39,6 +39,8 @@ func readFunctionType(r io.Reader) (*FunctionType, error) {
 	s, _, err = leb128.DecodeUint32(r)
 	if err != nil {
 		return nil, fmt.Errorf("get the size of output value types: %w", err)
+	} else if s > 1 {
+		return nil, fmt.Errorf("multi value results not supported")
 	}

 	op, err := readValueTypes(r, s)
@@ -116,7 +118,21 @@ func readTableType(r io.Reader) (*TableType, error) {
 type MemoryType = LimitsType

 func readMemoryType(r io.Reader) (*MemoryType, error) {
-	return readLimitsType(r)
+	ret, err := readLimitsType(r)
+	if err != nil {
+		return nil, err
+	}
+	if ret.Min > uint32(PageSize) {
+		return nil, fmt.Errorf("memory min must be at most 65536 pages (4GiB)")
+	}
+	if ret.Max != nil {
+		if *ret.Max < ret.Min {
+			return nil, fmt.Errorf("memory size minimum must not be greater than maximum")
+		} else if *ret.Max > uint32(PageSize) {
+			return nil, fmt.Errorf("memory max must be at most 65536 pages (4GiB)")
+		}
+	}
+	return ret, nil
 }

 type GlobalType struct {
--- a/wasm/type_test.go
+++ b/wasm/type_test.go
@@ -1,155 +0,0 @@
-package wasm
-
-import (
-	"bytes"
-	"errors"
-	"strconv"
-	"testing"
-
-	"github.com/stretchr/testify/assert"
-	"github.com/stretchr/testify/require"
-)
-
-func TestReadFunctionType(t *testing.T) {
-	t.Run("ng", func(t *testing.T) {
-		buf := []byte{0x00}
-		_, err := readFunctionType(bytes.NewBuffer(buf))
-		assert.True(t, errors.Is(err, ErrInvalidByte))
-		t.Log(err)
-	})
-
-	for i, c := range []struct {
-		bytes []byte
-		exp   *FunctionType
-	}{
-		{
-			bytes: []byte{0x60, 0x0, 0x0},
-			exp: &FunctionType{
-				InputTypes:  []ValueType{},
-				ReturnTypes: []ValueType{},
-			},
-		},
-		{
-			bytes: []byte{0x60, 0x2, 0x7f, 0x7e, 0x0},
-			exp: &FunctionType{
-				InputTypes:  []ValueType{ValueTypeI32, ValueTypeI64},
-				ReturnTypes: []ValueType{},
-			},
-		},
-		{
-			bytes: []byte{0x60, 0x1, 0x7e, 0x2, 0x7f, 0x7e},
-			exp: &FunctionType{
-				InputTypes:  []ValueType{ValueTypeI64},
-				ReturnTypes: []ValueType{ValueTypeI32, ValueTypeI64},
-			},
-		},
-		{
-			bytes: []byte{0x60, 0x0, 0x2, 0x7f, 0x7e},
-			exp: &FunctionType{
-				InputTypes:  []ValueType{},
-				ReturnTypes: []ValueType{ValueTypeI32, ValueTypeI64},
-			},
-		},
-	} {
-		t.Run(strconv.Itoa(i), func(t *testing.T) {
-			actual, err := readFunctionType(bytes.NewBuffer(c.bytes))
-			require.NoError(t, err)
-			assert.Equal(t, c.exp, actual)
-		})
-	}
-}
-
-func TestReadLimitsType(t *testing.T) {
-	for i, c := range []struct {
-		bytes []byte
-		exp   *LimitsType
-	}{
-		{bytes: []byte{0x00, 0xa}, exp: &LimitsType{Min: 10}},
-		{bytes: []byte{0x01, 0xa, 0xa}, exp: &LimitsType{Min: 10, Max: uint32Ptr(10)}},
-	} {
-		t.Run(strconv.Itoa(i), func(t *testing.T) {
-			actual, err := readLimitsType(bytes.NewBuffer(c.bytes))
-			require.NoError(t, err)
-			assert.Equal(t, c.exp, actual)
-		})
-	}
-}
-
-func uint32Ptr(in uint32) *uint32 {
-	return &in
-}
-
-func TestReadTableType(t *testing.T) {
-	t.Run("ng", func(t *testing.T) {
-		buf := []byte{0x00}
-		_, err := readTableType(bytes.NewBuffer(buf))
-		require.True(t, errors.Is(err, ErrInvalidByte))
-		t.Log(err)
-	})
-
-	for i, c := range []struct {
-		bytes []byte
-		exp   *TableType
-	}{
-		{
-			bytes: []byte{0x70, 0x00, 0xa},
-			exp: &TableType{
-				ElemType: 0x70,
-				Limit:    &LimitsType{Min: 10},
-			},
-		},
-		{
-			bytes: []byte{0x70, 0x01, 0x01, 0xa},
-			exp: &TableType{
-				ElemType: 0x70,
-				Limit:    &LimitsType{Min: 1, Max: uint32Ptr(10)},
-			},
-		},
-	} {
-		c := c
-		t.Run(strconv.Itoa(i), func(t *testing.T) {
-			actual, err := readTableType(bytes.NewBuffer(c.bytes))
-			require.NoError(t, err)
-			assert.Equal(t, c.exp, actual)
-		})
-	}
-}
-
-func TestReadMemoryType(t *testing.T) {
-	for i, c := range []struct {
-		bytes []byte
-		exp   *MemoryType
-	}{
-		{bytes: []byte{0x00, 0xa}, exp: &MemoryType{Min: 10}},
-		{bytes: []byte{0x01, 0xa, 0xa}, exp: &MemoryType{Min: 10, Max: uint32Ptr(10)}},
-	} {
-		t.Run(strconv.Itoa(i), func(t *testing.T) {
-			actual, err := readMemoryType(bytes.NewBuffer(c.bytes))
-			require.NoError(t, err)
-			assert.Equal(t, c.exp, actual)
-		})
-	}
-}
-
-func TestReadGlobalType(t *testing.T) {
-	t.Run("ng", func(t *testing.T) {
-		buf := []byte{0x7e, 0x3}
-		_, err := readGlobalType(bytes.NewBuffer(buf))
-		require.True(t, errors.Is(err, ErrInvalidByte))
-		t.Log(err)
-	})
-
-	for i, c := range []struct {
-		bytes []byte
-		exp   *GlobalType
-	}{
-		{bytes: []byte{0x7e, 0x00}, exp: &GlobalType{ValType: ValueTypeI64, Mutable: false}},
-		{bytes: []byte{0x7e, 0x01}, exp: &GlobalType{ValType: ValueTypeI64, Mutable: true}},
-	} {
-		t.Run(strconv.Itoa(i), func(t *testing.T) {
-			actual, err := readGlobalType(bytes.NewBuffer(c.bytes))
-			require.NoError(t, err)
-			assert.Equal(t, c.exp, actual)
-		})
-	}
-}
--- a/wasm/value.go
+++ b/wasm/value.go
@@ -3,6 +3,7 @@ package wasm
 import (
 	"fmt"
 	"io"
+	"unicode/utf8"

 	"github.com/mathetake/gasm/wasm/leb128"
 )
@@ -46,6 +47,10 @@ func readNameValue(r io.Reader) (string, error) {
 		return "", fmt.Errorf("read bytes of name: %v", err)
 	}

+	if !utf8.Valid(buf) {
+		return "", fmt.Errorf("name must be valid as utf8")
+	}
+
 	return string(buf), nil
 }

--- a/wasm/vm.go
+++ b/wasm/vm.go
@@ -61,7 +61,7 @@ func (vm *VirtualMachine) ExecExportedFunction(moduleName, funcName string, args

 	exp, ok := m.Exports[funcName]
 	if !ok {
-		return nil, nil, fmt.Errorf("exported func of name '%s' not found in '%s'", funcName, moduleName)
+		return nil, nil, fmt.Errorf("exported function '%s' not found in '%s'", funcName, moduleName)
 	}

 	if exp.Kind != ExportKindFunction {
--- a/wasm/vm_func.go
+++ b/wasm/vm_func.go
@@ -15,7 +15,8 @@ type (
 	}
 	NativeFunction struct {
 		Signature      *FunctionType
-		NumLocal       uint32
+		NumLocals      uint32
+		LocalTypes     []ValueType
 		Body           []byte
 		Blocks         map[uint64]*NativeFunctionBlock
 		ModuleInstance *ModuleInstance
@@ -24,6 +25,8 @@ type (
 		StartAt, ElseAt, EndAt uint64
 		BlockType              *FunctionType
 		BlockTypeBytes         uint64
+		IsLoop                 bool // TODO: might not be necessary
+		IsIf                   bool // TODO: might not be necessary
 	}
 )

@@ -83,7 +86,7 @@ func (h *HostFunction) Call(vm *VirtualMachine) {

 func (n *NativeFunction) Call(vm *VirtualMachine) {
 	al := len(n.Signature.InputTypes)
-	locals := make([]uint64, n.NumLocal+uint32(al))
+	locals := make([]uint64, n.NumLocals+uint32(al))
 	for i := 0; i < al; i++ {
 		locals[al-1-i] = vm.OperandStack.Pop()
 	}
--- a/wasm/vm_global.go
+++ b/wasm/vm_global.go
@@ -12,7 +12,6 @@ func setGlobal(vm *VirtualMachine) {
 	vm.ActiveContext.PC++
 	index := vm.FetchUint32()
 	addr := vm.ActiveContext.Function.ModuleInstance.GlobalsAddrs[index]
-	// TODO: Check mutatability.
 	vm.Store.Globals[addr].Val = vm.OperandStack.Pop()
 	vm.ActiveContext.PC++
 }