/*
Copyright (C) 2011-2012 de4dot@gmail.com
This file is part of de4dot.
de4dot is free software: you can redistribute it and/or modify
it under the terms of the GNU General Public License as published by
the Free Software Foundation, either version 3 of the License, or
(at your option) any later version.
de4dot is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
GNU General Public License for more details.
You should have received a copy of the GNU General Public License
along with de4dot. If not, see .
*/
using System;
using System.Collections.Generic;
using dnlib.DotNet;
using dnlib.DotNet.Emit;
namespace de4dot.blocks.cflow {
class SwitchCflowDeobfuscator : BlockDeobfuscator {
InstructionEmulator instructionEmulator = new InstructionEmulator();
protected override bool deobfuscate(Block switchBlock) {
if (switchBlock.LastInstr.OpCode.Code != Code.Switch)
return false;
if (isSwitchTopOfStack(switchBlock) && deobfuscateTos(switchBlock))
return true;
if (isLdlocBranch(switchBlock, true) && deobfuscateLdloc(switchBlock))
return true;
if (isStLdlocBranch(switchBlock, true) && deobfuscateStLdloc(switchBlock))
return true;
if (isSwitchType1(switchBlock) && deobfuscateType1(switchBlock))
return true;
if (isSwitchType2(switchBlock) && deobfuscateType2(switchBlock))
return true;
if (switchBlock.FirstInstr.isLdloc() && fixSwitchBranch(switchBlock))
return true;
return false;
}
static bool isSwitchTopOfStack(Block switchBlock) {
return switchBlock.Instructions.Count == 1;
}
static bool isLdlocBranch(Block switchBlock, bool isSwitch) {
int numInstrs = 1 + (isSwitch ? 1 : 0);
return switchBlock.Instructions.Count == numInstrs && switchBlock.Instructions[0].isLdloc();
}
static bool isSwitchType1(Block switchBlock) {
return switchBlock.FirstInstr.isLdloc();
}
bool isSwitchType2(Block switchBlock) {
Local local = null;
foreach (var instr in switchBlock.Instructions) {
if (!instr.isLdloc())
continue;
local = Instr.getLocalVar(blocks.Locals, instr);
break;
}
if (local == null)
return false;
foreach (var source in switchBlock.Sources) {
var instrs = source.Instructions;
for (int i = 1; i < instrs.Count; i++) {
var ldci4 = instrs[i - 1];
if (!ldci4.isLdcI4())
continue;
var stloc = instrs[i];
if (!stloc.isStloc())
continue;
if (Instr.getLocalVar(blocks.Locals, stloc) != local)
continue;
return true;
}
}
return false;
}
bool isStLdlocBranch(Block switchBlock, bool isSwitch) {
int numInstrs = 2 + (isSwitch ? 1 : 0);
return switchBlock.Instructions.Count == numInstrs &&
switchBlock.Instructions[0].isStloc() &&
switchBlock.Instructions[1].isLdloc() &&
Instr.getLocalVar(blocks.Locals, switchBlock.Instructions[0]) == Instr.getLocalVar(blocks.Locals, switchBlock.Instructions[1]);
}
bool deobfuscateTos(Block switchBlock) {
bool changed = false;
if (switchBlock.Targets == null)
return changed;
var targets = new List(switchBlock.Targets);
changed |= deobfuscateTos(targets, switchBlock.FallThrough, switchBlock);
return changed;
}
bool deobfuscateLdloc(Block switchBlock) {
bool changed = false;
var switchVariable = Instr.getLocalVar(blocks.Locals, switchBlock.Instructions[0]);
if (switchVariable == null)
return changed;
if (switchBlock.Targets == null)
return changed;
var targets = new List(switchBlock.Targets);
changed |= deobfuscateLdloc(targets, switchBlock.FallThrough, switchBlock, switchVariable);
return changed;
}
bool deobfuscateStLdloc(Block switchBlock) {
bool changed = false;
var switchVariable = Instr.getLocalVar(blocks.Locals, switchBlock.Instructions[0]);
if (switchVariable == null)
return changed;
if (switchBlock.Targets == null)
return changed;
var targets = new List(switchBlock.Targets);
changed |= deobfuscateStLdloc(targets, switchBlock.FallThrough, switchBlock);
return changed;
}
// Switch deobfuscation when block uses stloc N, ldloc N to load switch constant
// blk1:
// ldc.i4 X
// br swblk
// swblk:
// stloc N
// ldloc N
// switch (......)
bool deobfuscateStLdloc(IList switchTargets, Block switchFallThrough, Block block) {
bool changed = false;
foreach (var source in new List(block.Sources)) {
if (!isBranchBlock(source))
continue;
instructionEmulator.init(blocks);
instructionEmulator.emulate(source.Instructions);
var target = getSwitchTarget(switchTargets, switchFallThrough, instructionEmulator.pop());
if (target == null)
continue;
source.replaceLastNonBranchWithBranch(0, target);
source.add(new Instr(OpCodes.Pop.ToInstruction()));
changed = true;
}
return changed;
}
// Switch deobfuscation when block uses ldloc N to load switch constant
// blk1:
// ldc.i4 X
// stloc N
// br swblk / bcc swblk
// swblk:
// ldloc N
// switch (......)
bool deobfuscateLdloc(IList switchTargets, Block switchFallThrough, Block block, Local switchVariable) {
bool changed = false;
foreach (var source in new List(block.Sources)) {
if (isBranchBlock(source)) {
instructionEmulator.init(blocks);
instructionEmulator.emulate(source.Instructions);
var target = getSwitchTarget(switchTargets, switchFallThrough, instructionEmulator.getLocal(switchVariable));
if (target == null)
continue;
source.replaceLastNonBranchWithBranch(0, target);
changed = true;
}
else if (isBccBlock(source)) {
instructionEmulator.init(blocks);
instructionEmulator.emulate(source.Instructions);
var target = getSwitchTarget(switchTargets, switchFallThrough, instructionEmulator.getLocal(switchVariable));
if (target == null)
continue;
if (source.Targets[0] == block) {
source.setNewTarget(0, target);
changed = true;
}
if (source.FallThrough == block) {
source.setNewFallThrough(target);
changed = true;
}
}
}
return changed;
}
// Switch deobfuscation when block has switch contant on TOS:
// blk1:
// ldc.i4 X
// br swblk
// swblk:
// switch (......)
bool deobfuscateTos(IList switchTargets, Block switchFallThrough, Block block) {
bool changed = false;
foreach (var source in new List(block.Sources)) {
if (!isBranchBlock(source))
continue;
instructionEmulator.init(blocks);
instructionEmulator.emulate(source.Instructions);
var target = getSwitchTarget(switchTargets, switchFallThrough, instructionEmulator.pop());
if (target == null) {
changed |= deobfuscateTos_Ldloc(switchTargets, switchFallThrough, source);
}
else {
source.replaceLastNonBranchWithBranch(0, target);
source.add(new Instr(OpCodes.Pop.ToInstruction()));
changed = true;
}
}
return changed;
}
// ldloc N
// br swblk
// or
// stloc N
// ldloc N
// br swblk
bool deobfuscateTos_Ldloc(IList switchTargets, Block switchFallThrough, Block block) {
if (isLdlocBranch(block, false)) {
var switchVariable = Instr.getLocalVar(blocks.Locals, block.Instructions[0]);
if (switchVariable == null)
return false;
return deobfuscateLdloc(switchTargets, switchFallThrough, block, switchVariable);
}
else if (isStLdlocBranch(block, false))
return deobfuscateStLdloc(switchTargets, switchFallThrough, block);
return false;
}
static bool isBranchBlock(Block block) {
if (block.Targets != null)
return false;
if (block.FallThrough == null)
return false;
switch (block.LastInstr.OpCode.Code) {
case Code.Switch:
case Code.Leave:
case Code.Leave_S:
return false;
default:
return true;
}
}
static bool isBccBlock(Block block) {
if (block.Targets == null || block.Targets.Count != 1)
return false;
if (block.FallThrough == null)
return false;
switch (block.LastInstr.OpCode.Code) {
case Code.Beq:
case Code.Beq_S:
case Code.Bge:
case Code.Bge_S:
case Code.Bge_Un:
case Code.Bge_Un_S:
case Code.Bgt:
case Code.Bgt_S:
case Code.Bgt_Un:
case Code.Bgt_Un_S:
case Code.Ble:
case Code.Ble_S:
case Code.Ble_Un:
case Code.Ble_Un_S:
case Code.Blt:
case Code.Blt_S:
case Code.Blt_Un:
case Code.Blt_Un_S:
case Code.Bne_Un:
case Code.Bne_Un_S:
case Code.Brfalse:
case Code.Brfalse_S:
case Code.Brtrue:
case Code.Brtrue_S:
return true;
default:
return false;
}
}
bool deobfuscateType1(Block switchBlock) {
Block target;
if (!emulateGetTarget(switchBlock, out target) || target != null)
return false;
bool changed = false;
foreach (var source in new List(switchBlock.Sources)) {
if (!source.canAppend(switchBlock))
continue;
if (!willHaveKnownTarget(switchBlock, source))
continue;
source.append(switchBlock);
changed = true;
}
return changed;
}
bool deobfuscateType2(Block switchBlock) {
bool changed = false;
var bccSources = new List();
foreach (var source in new List(switchBlock.Sources)) {
if (source.LastInstr.isConditionalBranch()) {
bccSources.Add(source);
continue;
}
if (!source.canAppend(switchBlock))
continue;
if (!willHaveKnownTarget(switchBlock, source))
continue;
source.append(switchBlock);
changed = true;
}
foreach (var bccSource in bccSources) {
if (!willHaveKnownTarget(switchBlock, bccSource))
continue;
var consts = getBccLocalConstants(bccSource);
if (consts.Count == 0)
continue;
var newFallThrough = createBlock(consts, bccSource.FallThrough);
var newTarget = createBlock(consts, bccSource.Targets[0]);
var oldFallThrough = bccSource.FallThrough;
var oldTarget = bccSource.Targets[0];
bccSource.setNewFallThrough(newFallThrough);
bccSource.setNewTarget(0, newTarget);
newFallThrough.setNewFallThrough(oldFallThrough);
newTarget.setNewFallThrough(oldTarget);
changed = true;
}
return changed;
}
static Block createBlock(Dictionary consts, Block fallThrough) {
var block = new Block();
foreach (var kv in consts) {
block.Instructions.Add(new Instr(Instruction.CreateLdcI4(kv.Value)));
block.Instructions.Add(new Instr(OpCodes.Stloc.ToInstruction(kv.Key)));
}
fallThrough.Parent.add(block);
return block;
}
Dictionary getBccLocalConstants(Block block) {
var dict = new Dictionary();
var instrs = block.Instructions;
for (int i = 0; i < instrs.Count; i++) {
var instr = instrs[i];
if (instr.isStloc()) {
var local = Instr.getLocalVar(blocks.Locals, instr);
if (local == null)
continue;
var ldci4 = i == 0 ? null : instrs[i - 1];
if (ldci4 == null || !ldci4.isLdcI4())
dict.Remove(local);
else
dict[local] = ldci4.getLdcI4Value();
}
else if (instr.isLdloc()) {
var local = Instr.getLocalVar(blocks.Locals, instr);
if (local != null)
dict.Remove(local);
}
else if (instr.OpCode.Code == Code.Ldloca || instr.OpCode.Code == Code.Ldloca_S) {
var local = instr.Operand as Local;
if (local != null)
dict.Remove(local);
}
}
return dict;
}
bool emulateGetTarget(Block switchBlock, out Block target) {
instructionEmulator.init(blocks);
try {
instructionEmulator.emulate(switchBlock.Instructions, 0, switchBlock.Instructions.Count - 1);
}
catch (NullReferenceException) {
// Here if eg. invalid metadata token in a call instruction (operand is null)
target = null;
return false;
}
target = getTarget(switchBlock);
return true;
}
bool willHaveKnownTarget(Block switchBlock, Block source) {
instructionEmulator.init(blocks);
try {
instructionEmulator.emulate(source.Instructions);
instructionEmulator.emulate(switchBlock.Instructions, 0, switchBlock.Instructions.Count - 1);
}
catch (NullReferenceException) {
// Here if eg. invalid metadata token in a call instruction (operand is null)
return false;
}
return getTarget(switchBlock) != null;
}
Block getTarget(Block switchBlock) {
var val1 = instructionEmulator.pop();
if (!val1.isInt32())
return null;
return CflowUtils.getSwitchTarget(switchBlock.Targets, switchBlock.FallThrough, (Int32Value)val1);
}
static Block getSwitchTarget(IList targets, Block fallThrough, Value value) {
if (!value.isInt32())
return null;
return CflowUtils.getSwitchTarget(targets, fallThrough, (Int32Value)value);
}
static bool fixSwitchBranch(Block switchBlock) {
// Code:
// blk1:
// ldc.i4 XXX
// br common
// blk2:
// ldc.i4 YYY
// br common
// common:
// stloc X
// br swblk
// swblk:
// ldloc X
// switch
// Inline common into blk1 and blk2.
bool changed = false;
foreach (var commonSource in new List(switchBlock.Sources)) {
if (commonSource.Instructions.Count != 1)
continue;
if (!commonSource.FirstInstr.isStloc())
continue;
foreach (var blk in new List(commonSource.Sources)) {
if (blk.canAppend(commonSource)) {
blk.append(commonSource);
changed = true;
}
}
}
return changed;
}
}
}