实战还原 V8 bytenode 保护 JS（V8 字节码分析记录）
V8 字节码分析，简单写写在前辈们的基础上，又遇到些什么问题（绝对不是我水不出很长的文章的问题）
（如有错漏，敬请指正，因为是在弄完后过了很久才写的）
我的blog：blog.dorimu.cn
0x00 前言
拿到一个需要逆向分析的 JS start.js。
目标环境：
- Node.js：
16.14.0 - 对应 V8：
9.4.146.24-node.20（flag hashed0ab240）
核心代码如下：
javascript
const vm = require('vm');
const v8 = require('v8');
const zlib = require('zlib');
const fs = require('fs');
const path = require('path');
const Module = require('module');
v8.setFlagsFromString('--no-lazy');
v8.setFlagsFromString('--no-flush-bytecode');
global.generateScript=function(cachedData, filename) {
cachedData = zlib.brotliDecompressSync(cachedData);
fixBytecode(cachedData);
const length = readSourceHash(cachedData);
let dummyCode = '';
if (length > 1) {
dummyCode = '"' + '\u200b'.repeat(length - 2) + '"';
}
const script = new vm.Script(dummyCode, {
cachedData,
filename
});
if (script.cachedDataRejected) {
throw new Error('');
}
return script;
}
global.compileCode = function(javascriptCode, compress) {
const script = new vm.Script(javascriptCode, {
produceCachedData: true
});
let bytecodeBuffer = (script.createCachedData && script.createCachedData.call) ?
script.createCachedData() :
script.cachedData;
if (compress) bytecodeBuffer = zlib.brotliCompressSync(bytecodeBuffer);
return bytecodeBuffer;
};
global.fixBytecode = function(bytecodeBuffer) {
const dummyBytecode = compileCode('');
dummyBytecode.subarray(12, 16).copy(bytecodeBuffer, 12);
};
global.readSourceHash = function(bytecodeBuffer) {
return bytecodeBuffer.subarray(8, 12).reduce((sum, number, power) => sum += number * Math.pow(256, power), 0);
};
try {
Module._extensions['.jsc'] = function(fileModule, filename) {
const data = fs.readFileSync(filename, 'utf8')
const bytecodeBuffer = Buffer.from(data, 'base64');
const script = generateScript(bytecodeBuffer, filename);
function require(id) {
return fileModule.require(id);
}
require.resolve = function(request, options) {
return Module._resolveFilename(request, fileModule, false, options);
};
if (process.main) {
require.main = process.main;
}
require.extensions = Module._extensions;
require.cache = Module._cache;
const compiledWrapper = script.runInThisContext({
filename: filename,
lineOffset: 0,
columnOffset: 0,
displayErrors: true
});
const dirname = path.dirname(filename);
const args = [
fileModule.exports, require, fileModule, filename, dirname, process, global
];
return compiledWrapper.apply(fileModule.exports, args);
};
} catch (ex) {
console.error('xrequire:' + ex.message);
}
require("${codeScript}")经过搜索资料发现：
这就是V8 cachedData / bytenode 方案。
0x01 第一次尝试：View8
定位到 bytecode 后，我先上了 View8：
https://github.com/suleram/View8
然后配套 9.4.146.24.exe 去跑反编译。
发现问题：
- 输出一点代码后自动崩溃退出。
- View8 因 d8 崩溃只导出 23 个外围函数，关键的函数基本丢失。
当时第一反应是项目太久没维护，又去github找别的项目。
0x02 第二次尝试：jsc2js
又看了 jsc2js：
https://github.com/xqy2006/jsc2js
这个仓库新一些，也有 patch + CI 体系。
把 patch 套到 v8 9.4.146.24，结果仍然和第一轮差不多。
这时候基本就炸毛了（先躺一会）：
字节码本来就不太好 hook，现成工具又不稳定。
于是查阅相关资料：
- https://www.aynakeya.com/articles/ctf/a-quick-guide-to-disassemble-v8-bytecode/
- https://rce.moe/2025/01/07/v8-bytecode-decompiler/
V8 bytecode 就是 V8 自己序列化的一段内部数据。
想稳定拿结果，必须回到 V8 源码层改输出逻辑。
不同 V8 版本在字节码层差异很大，尤其是 opcode、参数语义、寄存器布局。
0x03 第三次尝试：拉 V8 仓库
bat
@echo off
set PATH=E:\Dev\SDKs\depot_tools;%PATH%
set DEPOT_TOOLS_WIN_TOOLCHAIN=0
mkdir v8_941
cd v8_941
echo solutions = [{ > .gclient
echo "name": "v8", >> .gclient
echo "url": "https://chromium.googlesource.com/v8/v8.git@9.4.146.24", >> .gclient
echo "deps_file": "DEPS", >> .gclient
echo "managed": False, >> .gclient
echo "custom_deps": {}, >> .gclient
echo }] >> .gclient
git clone --depth=1 --branch 9.4.146.24 https://chromium.googlesource.com/v8/v8.git v8
gclient sync -D --no-history0x04 patch + 编译参数
先patch，再单独构建 d8：
bat
cd /d <dir>\v8_941\v8
python ..\..\apply_patches_v8_94.py .
gn gen out/release
ninja -C out/release d8构建参数：
gn
dcheck_always_on = false
is_clang = false
is_component_build = false
is_debug = false
target_cpu = "x64"
use_custom_libcxx = false
v8_monolithic = true
v8_use_external_startup_data = false
v8_static_library = true
v8_enable_disassembler = true
v8_enable_object_print = true
treat_warnings_as_errors = false
v8_enable_pointer_compression = false
v8_enable_31bit_smis_on_64bit_arch = false
v8_enable_lite_mode = false
v8_enable_i18n_support = true
v8_enable_webassembly = true0x05 改动阶段
真男人就要硬刚v8，部分diff我就不贴出来了，把问题和思路贴一下，欸嘿~
0x06 问题一：cachedData 反序列化被拒绝
CodeSerializer::Deserialize 默认会严检 magic/version/flags/hash/checksum/source hash。
如果任何一项没通过，它会直接 reject 掉这份缓存，返回空对象。
src/snapshot/code-serializer.cc：
diff
@@ SerializedCodeData::SanityCheck
- SanityCheckResult result = SanityCheckWithoutSource();
- if (result != CHECK_SUCCESS) return result;
- ...
- return CHECK_SUCCESS;
+ return SerializedCodeData::SanityCheckResult::CHECK_SUCCESS;
@@ SerializedCodeData::SanityCheckWithoutSource
- if (this->size_ < kHeaderSize) return INVALID_HEADER;
- uint32_t magic_number = GetMagicNumber();
- if (magic_number != kMagicNumber) return MAGIC_NUMBER_MISMATCH;
- ...
- if (Checksum(ChecksummedContent()) != c) return CHECKSUM_MISMATCH;
- return CHECK_SUCCESS;
+ return SerializedCodeData::SanityCheckResult::CHECK_SUCCESS;src/snapshot/deserializer.cc：
diff
@@ Deserializer<IsolateT>::Deserializer
- CHECK_EQ(magic_number_, SerializedData::kMagicNumber);
+ /*
+ CHECK_EQ(magic_number_, SerializedData::kMagicNumber);
+ */
@@ ReadSingleBytecodeData
+ std::fprintf(stderr, "[FATAL] Unknown serializer bytecode: 0x%02x\n", data);0x07 问题二：反汇编/打印阶段栈溢出
这里就是之前view8打印不出来的主要问题：
BytecodeArray::Disassemble- 打常量池
- 命中
SharedFunctionInfo SharedFunctionInfoPrint- 再次
Disassemble - 深度叠加，最终栈爆
- 改动：TLS guard + SEH
src/diagnostics/objects-printer.cc：
diff
+thread_local int g_in_bytecode_disasm = 0;
...
+ ++g_in_bytecode_disasm;
+ hbc->Disassemble(*(c->os));
+ --g_in_bytecode_disasm;
@@ SharedFunctionInfoPrint
- PrintSourceCode(os);
+ // PrintSourceCode(os);
+ int exc = SehWrapCall(DoBcDisasm, &ctx);
+ if (exc != 0) { os << "<BytecodeArray Disassemble CRASHED ...>"; }src/objects/objects.cc：
diff
+extern thread_local int g_in_bytecode_disasm;
+void SafePrintSharedFunctionInfo(...);
+void SafePrintFixedArray(...);
...
case SHARED_FUNCTION_INFO_TYPE:
+ if (g_in_bytecode_disasm > 0) { break; }
+ SafePrintSharedFunctionInfo(shared, os);
case FIXED_ARRAY_TYPE:
+ SafePrintFixedArray(FixedArray::cast(*this), os);- 对应：d8 入口改成 BFS 平铺
src/d8/d8.cc：
diff
+void Shell::LoadBytecode(...)
+std::deque<i::Handle<i::SharedFunctionInfo>> queue;
+std::unordered_set<i::Address> seen;
+while (!queue.empty()) { ... }
+global_template->Set(isolate, "loadBytecode",
+ FunctionTemplate::New(isolate, LoadBytecode));0x08 稳定性
修 Handle 生命周期和字节码迭代稳定性
diff
- i::HandleScope inner_scope(isolateInternal);
+ // No inner HandleScope here --- child handles stored in queue/all_sfis
+ // must survive across iterations. outer_scope keeps them all alive.
...
- i::BytecodeArray handle_storage = *hbca;
- i::Handle<i::BytecodeArray> handle(
- reinterpret_cast<i::Address*>(&handle_storage));
- i::interpreter::BytecodeArrayIterator iterator(handle);
+ // Use hbca directly --- it's a proper Handle rooted in print_scope.
+ i::interpreter::BytecodeArrayIterator iterator(hbca);
...
+ // Re-derive base_address each iteration (GC-safe)
+ i::Address base_address = hbca->GetFirstBytecodeAddress();调试可见性 + SFI 入队条件
diff
+ printf("[DBG] root SFI ptr = 0x%p\n", reinterpret_cast<void*>(root->ptr()));
+ printf("[DBG] root HasBytecodeArray = %d\n", root_has_bc);
...
+ printf("[DBG] cp[%d] raw=0x%p smi=%d\n", cp_index,
+ reinterpret_cast<void*>(obj.ptr()), obj.IsSmi());
...
- if (obj.IsSharedFunctionInfo()) {
+ if (!obj.IsSmi() && obj.IsSharedFunctionInfo()) {常量池可读性增强
diff
+const int kMaxLiteralElementsToPrint = 1024;
+std::function<void(i::Object, int)> print_compact_obj;
...
+if (value.IsArrayBoilerplateDescription()) { ... }
+if (value.IsFixedArray()) { ... }
+if (value.IsFixedDoubleArray()) { ... }
...
+print_compact_obj(obj, 0);其它
src/objects/string.cc：
diff
-if (len > kMaxShortPrintLength) {
+// if (len > kMaxShortPrintLength) {
...
-accumulator->Add("%c", c);
+accumulator->Add("\\u%04x", c);0x09 将反编译结果初步还原成可读js
- 喂给
jsc2js/View8（这里你可能要手动改一下，懒得贴了），我记得好像还要处理一下常量池？
来来回回折腾了三天，最开始啥都不懂硬生生肝出来了，基本都是需要什么去问什么去学什么 hhhhhhh 现在还真是方便啊
写完跑路