NDK集成OLLVM模块流程记录

一

集成流程

具体的编译NDK的LLVM的流程可参考文章：编译NDK特定的LLVM版本的流程记录https://bbs.kanxue.com/thread-277727.htm

获取 ollvm 混淆部分代码：https://github.com/isrc-cas/flounder

1.复制混淆部分 pass 到 llvm12 中：

flounder/llvm/include/llvm/Transforms/Obfuscation  -> toolchain/llvm-project/llvm/include/llvm/Transforms/Obfuscation

flounder/llvm/lib/Transforms/Obfuscation -> toolchain/llvm-project/llvm/lib/Transforms/Obfuscation

2.添加下面这行到 llvm-project\llvm\lib\Transforms\CMakeLists.txt 的第13行：

add_subdirectory(Obfuscation)

3.添加下面这行到 llvm-project\llvm\lib\Transforms\IPO\CMakeLists.txt 的 73 行：

Obfuscation

4.在llvm-project\llvm\lib\Transforms\IPO\PassManagerBuilder.cpp导入头文件：

#include "llvm/Transforms/Obfuscation/BogusControlFlow.h"
#include "llvm/Transforms/Obfuscation/Flattening.h"
#include "llvm/Transforms/Obfuscation/Split.h"
#include "llvm/Transforms/Obfuscation/Substitution.h"
#include "llvm/Transforms/Obfuscation/CryptoUtils.h"
#include "llvm/Transforms/Obfuscation/StringObfuscation.h"

在同一个文件的第 93 行：

// Flags for obfuscation
static cl::opt<std::string> Seed("seed", cl::init(""), cl::desc("seed for the random"));
static cl::opt<std::string> AesSeed("aesSeed", cl::init(""), cl::desc("seed for the AES-CTR PRNG"));
static cl::opt<bool> StringObf("sobf", cl::init(false), cl::desc("Enable the string obfuscation"));  
static cl::opt<bool> Flattening("fla", cl::init(false), cl::desc("Enable the flattening pass"));
static cl::opt<bool> BogusControlFlow("bcf", cl::init(false), cl::desc("Enable bogus control flow"));
static cl::opt<bool> Substitution("sub", cl::init(false), cl::desc("Enable instruction substitutions"));
static cl::opt<bool> Split("split", cl::init(false), cl::desc("Enable basic block splitting"));
// Flags for obfuscation

在同一个文件的第 569 行：

//obfuscation related pass
MPM.add(createSplitBasicBlockPass(Split));
MPM.add(createBogusPass(BogusControlFlow));
MPM.add(createFlatteningPass(Flattening));
MPM.add(createStringObfuscationPass(StringObf));
MPM.add(createSubstitutionPass(Substitution));

5.在llvm-project\llvm\lib\Transforms\Obfuscation\StringObfuscation.cpp文件：

在第 15 行加入：

#include "llvm/IR/Instructions.h"

在同一个文件的第 174 处（共三处地方）：

LoadInst *ptr_19 = new LoadInst(gvar->getType()->getArrayElementType(),
                                gvar, "", false, label_for_body);
ptr_19->setAlignment(Align(8));
...
LoadInst* int8_20 = new LoadInst(ptr_arrayidx->getType()->getArrayElementType(), ptr_arrayidx, "", false, label_for_body);
int8_20->setAlignment(Align(1));
...
void_21->setAlignment(Align(1));

6.在llvm-project\llvm\lib\Transforms\Obfuscation\Substitution.cpp文件的第 215 行：

// Implementation of a = -(-b + (-c))
void Substitution::addDoubleNeg(BinaryOperator *bo) {
  BinaryOperator *op, *op2 = NULL;
  UnaryOperator *op3, *op4;
  if (bo->getOpcode() == Instruction::Add) {
    op = BinaryOperator::CreateNeg(bo->getOperand(0), "", bo);
    op2 = BinaryOperator::CreateNeg(bo->getOperand(1), "", bo);
    op = BinaryOperator::Create(Instruction::Add, op, op2, "", bo);
    op = BinaryOperator::CreateNeg(op, "", bo);
    bo->replaceAllUsesWith(op);
    // Check signed wrap
    //op->setHasNoSignedWrap(bo->hasNoSignedWrap());
    //op->setHasNoUnsignedWrap(bo->hasNoUnsignedWrap());
  } else {
    op3 = UnaryOperator::CreateFNeg(bo->getOperand(0), "", bo);
    op4 = UnaryOperator::CreateFNeg(bo->getOperand(1), "", bo);
    op = BinaryOperator::Create(Instruction::FAdd, op3, op4, "", bo);
    op3 = UnaryOperator::CreateFNeg(op, "", bo);
    bo->replaceAllUsesWith(op3);
  }  
}

在第 319 行（原 299 行）修改 Substitution::subNeg 函数：

// Implementation of a = b + (-c)
void Substitution::subNeg(BinaryOperator *bo) {
  BinaryOperator *op = NULL;  
  if (bo->getOpcode() == Instruction::Sub) {
    op = BinaryOperator::CreateNeg(bo->getOperand(1), "", bo);
    op = BinaryOperator::Create(Instruction::Add, bo->getOperand(0), op, "", bo);
    // Check signed wrap
    //op->setHasNoSignedWrap(bo->hasNoSignedWrap());
    //op->setHasNoUnsignedWrap(bo->hasNoUnsignedWrap());
  } else {
    auto op1 = UnaryOperator::CreateFNeg(bo->getOperand(1), "", bo);
    op = BinaryOperator::Create(Instruction::FAdd, bo->getOperand(0), op1, "", bo);
  }
  bo->replaceAllUsesWith(op);
}

7.在文件llvm-project\llvm\lib\Transforms\Obfuscation\BogusControlFlow.cpp文件 380 添加：

UnaryOperator *op2;

在同一个文件的 422 行：

case 1: op2 = UnaryOperator::CreateFNeg(i->getOperand(0),*var,&*i);

在同一个文件的 573 行：

opX = new LoadInst (x->getType()->getElementType(), (Value *)x, "", (*i));
opY = new LoadInst (x->getType()->getElementType(), (Value *)y, "", (*i));

在文件 llvm-project\llvm\include\llvm\InitializePasses.h 的第 453 行添加：

void initializeFlatteningPass(PassRegistry&);

在文件 llvm-project\llvm\lib\Transforms\Obfuscation\Flattening.cpp 的 17 行添加：

#include "llvm/InitializePasses.h"

在相同文件的 123 修改：

load = new LoadInst(switchVar->getType()->getElementType(), switchVar, "switchVar", loopEntry);

在相同文件的 239 修改：

二

混淆效果

Android.mk的参数配置(全局)：

LOCAL_CFLAGS += -mllvm -bcf -mllvm -bcf_loop=4 -mllvm -bcf_prob=100 -mllvm -sub -mllvm -sub_loop=2 -mllvm -fla -mllvm -sobf -mllvm -split

指定函数(局部)：

int binaryInsertionSort() __attribute((__annotate__(("bcf"))));

CMakeLists.txt的参数配置(全局)：

set(CMAKE_C_FLAGS_RELEASE "${CMAKE_C_FLAGS_RELEASE} -mllvm -sub -mllvm -sobf -mllvm -fla ")
set(CMAKE_CXX_FLAGS_RELEASE "${CMAKE_CXX_FLAGS_RELEASE} -mllvm -sub -mllvm -sobf -mllvm -fla")

set(CMAKE_C_FLAGS_DEBUG "${CMAKE_C_FLAGS_DEBUG} -mllvm -sub -mllvm -sobf -mllvm -fla" )
set(CMAKE_CXX_FLAGS_DEBUG "${CMAKE_CXX_FLAGS_DEBUG} -mllvm -sub -mllvm -sobf -mllvm -fla" )

指定函数混淆（局部）：

__attribute((__annotate__("bcf")))
__attribute((__annotate__("fla")))
__attribute((__annotate__("sub")))
__attribute((__annotate__("split")))
__attribute((__annotate__("sobf")))
void binaryInsertionSort(int arr[], int n) {}

混淆效果：

三

总结

这里只是参考网上的帖子对 ollvm 整个源码下载，到编译集成到特定的 NDK 版本的过程做一个学习记录，但具体每个 pass 的性能、具体的防护效果、以及可能存在的问题在这里是暂还没深入考究，这个系列待后续继续待补充完善。

参考资料

https://github.com/0x3f97/ollvm-12.x

https://github.com/yangyiyu08/ollvm-project

https://android.googlesource.com/toolchain/llvm-project

看雪ID：blx2024

https://bbs.kanxue.com/user-home-928718.htm

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