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vm: clear references on context unload

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Remove argument and local references from the reference counter when
returning from function.
This commit is contained in:
Evgenii Stratonikov 2020-07-22 11:11:28 +03:00
parent aec9111961
commit c0d7b9d234
3 changed files with 62 additions and 1 deletions
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7
pkg/vm/slot.go
View file

@ -45,3 +45,10 @@ func (s *Slot) Get(i int) stackitem.Item {
// Size returns slot size.
func (s *Slot) Size() int { return len(s.storage) }
// Clear removes all slot variables from reference counter.
func (s *Slot) Clear() {
for _, item := range s.storage {
s.refs.Remove(item)
}
}

16
pkg/vm/vm.go
View file

@ -1262,9 +1262,10 @@ func (v *VM) execute(ctx *Context, op opcode.Opcode, parameter []byte) (err erro
}
case opcode.RET:
v.istack.Pop()
oldCtx := v.istack.Pop().Value().(*Context)
oldEstack := v.estack
v.unloadContext(oldCtx)
if v.istack.Len() == 0 {
v.state = haltState
break
@ -1372,6 +1373,19 @@ func (v *VM) execute(ctx *Context, op opcode.Opcode, parameter []byte) (err erro
return
}
func (v *VM) unloadContext(ctx *Context) {
if ctx.local != nil {
ctx.local.Clear()
}
if ctx.arguments != nil {
ctx.arguments.Clear()
}
currCtx := v.Context()
if ctx.static != nil && currCtx != nil && ctx.static != currCtx.static {
ctx.static.Clear()
}
}
// getJumpCondition performs opcode specific comparison of a and b
func getJumpCondition(op opcode.Opcode, a, b *big.Int) bool {
cmp := a.Cmp(b)

40
pkg/vm/vm_test.go
View file

@ -1142,6 +1142,46 @@ func getTestFuncForVM(prog []byte, result interface{}, args ...interface{}) func
return getCustomTestFuncForVM(prog, f, args...)
}
func makeRETProgram(t *testing.T, argCount, localCount int) []byte {
require.True(t, argCount+localCount <= 255)
fProg := []opcode.Opcode{opcode.INITSLOT, opcode.Opcode(localCount), opcode.Opcode(argCount)}
for i := 0; i < localCount; i++ {
fProg = append(fProg, opcode.PUSH8, opcode.STLOC, opcode.Opcode(i))
}
fProg = append(fProg, opcode.RET)
offset := uint32(len(fProg) + 5)
param := make([]byte, 4)
binary.LittleEndian.PutUint32(param, offset)
ops := []opcode.Opcode{
opcode.INITSSLOT, 0x01,
opcode.PUSHA, 11, 0, 0, 0,
opcode.STSFLD0,
opcode.JMPL, opcode.Opcode(param[0]), opcode.Opcode(param[1]), opcode.Opcode(param[2]), opcode.Opcode(param[3]),
}
ops = append(ops, fProg...)
// execute func multiple times to ensure total reference count is less than max
callCount := MaxStackSize/(argCount+localCount) + 1
args := make([]opcode.Opcode, argCount)
for i := range args {
args[i] = opcode.PUSH7
}
for i := 0; i < callCount; i++ {
ops = append(ops, args...)
ops = append(ops, opcode.LDSFLD0, opcode.CALLA)
}
return makeProgram(ops...)
}
func TestRETReferenceClear(t *testing.T) {
// 42 is a canary
t.Run("Argument", getTestFuncForVM(makeRETProgram(t, 100, 0), 42, 42))
t.Run("Local", getTestFuncForVM(makeRETProgram(t, 0, 100), 42, 42))
}
func TestNOTEQUALByteArray(t *testing.T) {
prog := makeProgram(opcode.NOTEQUAL)
t.Run("True", getTestFuncForVM(prog, true, []byte{1, 2}, []byte{0, 1, 2}))