作者：[email protected]知道创宇404实验室
日期：2022年12月23日
最近看了一下x86matthew关于hook方法的一篇文章https://www.x86matthew.com/view_post?id=stealth_hook，相对于传统的一些hook方式，个人认为StealthHook的最大优点并不在于不修改内存保护，而是其隐蔽性，这种hook方式是难以检测的，因为其没有直接作用于目标函数。
此hook方式，实际上并没有去hook目标函数，而是通过目标函数内的子函数，去获取了进入目标函数时，栈上保存的返回地址，通过修改这个地址，即可劫持执行流程，在函数返回前，执行我们的代码。
hook样例-CreateFile
下面是其给出的例子。
#include <stdio.h>
#include <windows.h>
DWORD dwGlobal_OrigCreateFileReturnAddr = 0;
DWORD dwGlobal_OrigReferenceAddr = 0;
void __declspec(naked) ModifyReturnValue()
{
// the original return address for the CreateFile call redirects to here
_asm
{
// CreateFile complete - overwrite return value
mov eax, 0x12345678
// continue original execution flow (ecx is safe to overwrite at this point)
mov ecx, dwGlobal_OrigCreateFileReturnAddr
jmp ecx
}
}
void __declspec(naked) HookStub()
{
// the hooked global pointer nested within CreateFile redirects to here
_asm
{
// store original CreateFile return address
mov eax, dword ptr [esp + 0x100]
mov dwGlobal_OrigCreateFileReturnAddr, eax
// overwrite the CreateFile return address
lea eax, ModifyReturnValue
mov dword ptr [esp + 0x100], eax
// continue original execution flow
mov eax, dwGlobal_OrigReferenceAddr
jmp eax
}
}
DWORD InstallHook()
{
BYTE *pModuleBase = NULL;
BYTE *pHookAddr = NULL;
// get base address of kernelbase.dll
pModuleBase = (BYTE*)GetModuleHandle("kernelbase.dll");
if(pModuleBase == NULL)
{
return 1;
}
// get ptr to function reference
pHookAddr = pModuleBase + 0x1DF650;
// store original value
dwGlobal_OrigReferenceAddr = *(DWORD*)pHookAddr;
// overwrite ptr to call HookStub
*(DWORD*)pHookAddr = (DWORD)HookStub;
return 0;
}
int main()
{
HANDLE hFile = NULL;
// create temporary file (without hook)
printf("Creating file #1...\n");
hFile = CreateFile("temp_file_1.txt", GENERIC_WRITE, 0, NULL, CREATE_ALWAYS, FILE_ATTRIBUTE_NORMAL, NULL);
printf("hFile: 0x%X\n\n", hFile);
// install hook
printf("Installing hook...\n\n");
if(InstallHook() != 0)
{
return 1;
}
// create temporary file (with hook)
printf("Creating file #2...\n");
hFile = CreateFile("temp_file_2.txt", GENERIC_WRITE, 0, NULL, CREATE_ALWAYS, FILE_ATTRIBUTE_NORMAL, NULL);
printf("hFile: 0x%X\n\n", hFile);
return 0;
}上面的代码的作用就是钩取了CreatFile这个API函数，修改了其返回值为0x12345678，具体步骤如下。
- Hook了kernelbase.dll+0x1DF650处的函数，这个函数是CreatFile内部会调用的一个子函数。
- 在这个子函数执行前，将栈上CreatFile原本的返回地址保存下来，也就是[esp+0x100]的值，然后替换成了我们自己的函数ModifyReturnValue。
- 子函数执行。
- 最终会执行CreatFile函数最后的ret指令，但是此时栈上的返回地址以被修改，所以会先执行我们的函数，修改了eax，也就是返回值变成了0x12345678。
- 最后mov eax, dwGlobal_OrigReferenceAddr jmp eax，回到真正的返回地址处。
下面来调试一下过程。
先是InstallHook()内部，Hook了一个子函数，其获取EAT中了某一子函数的地址，并且将其替换为了HookStub。
然后到第二次调用CreateFile的开头，我们查看一下，这时候ESP存放的返回地址是多少，实际上等下这里的值是会被修改的。
接着，我们本来会调用CreateFile内部的一个子函数，但是其已被我们hook现在变成了HookStub()函数，我们在HookStub()打断点，发现其对栈偏移100处进行了修改，这个地址保存的就是原CreateFile返回到main函数的返回地址。
HookStub()内部将栈上的地址先进行保存到全局变量，然后修改为了我们自己的一个函数，最后jmp到真正的子函数处。
然后在CreatFile函数内部最后的ret指令处打个断点，发现返回地址已被修改，不会跳转到main函数了，而是跳转到ModifyReturnValue()。
进入ModifyReturnValue()，发现其就是对eax(函数返回值)进行了修改，然后跳转到真正应该返回的地址。
最后结果如下，hook后，调用CreatFile函数的返回值会被修改为0x12345678。
整个过程还是比较清晰，也不是很复杂的hook过程，问题就在于，如何获取到子函数的地址，以及到目标函数的返回地址的栈偏移是多少，因为我们不可能自己去一个一个调试获取。
为了解决这个问题，x86matthew师傅开发了一款工具，用来获取可用的子函数地址，以及栈偏移。
StealthHook工具
其先是注册了一个异常处理函数，用来处理EXCEPTION_SINGLE_STEP异常和EXCEPTION_ACCESS_VIOLATION异常。
LONG WINAPI ExceptionHandler(EXCEPTION_POINTERS* ExceptionInfo)
{
NATIVE_VALUE dwReturnAddress = 0;
// check exception code
if (ExceptionInfo->ExceptionRecord->ExceptionCode == EXCEPTION_SINGLE_STEP)
{
if (dwGlobal_TraceStarted == 0)
{
//打在目标函数的硬件断点和此时的eip是否一致
if (CURRENT_EXCEPTION_INSTRUCTION_PTR != ExceptionInfo->ContextRecord->Dr0)
{
return EXCEPTION_CONTINUE_SEARCH;
}
//获取当前ESP寄存器的值
dwGlobal_InitialStackPtr = CURRENT_EXCEPTION_STACK_PTR;
//返回地址处打硬件断点
ExceptionInfo->ContextRecord->Dr1 = *(NATIVE_VALUE*)dwGlobal_InitialStackPtr;
// initial trace started
dwGlobal_TraceStarted = 1;
}
// set debug control field
ExceptionInfo->ContextRecord->Dr7 = DEBUG_REGISTER_EXEC_DR1;
// check current instruction pointer
if (CURRENT_EXCEPTION_INSTRUCTION_PTR == dwGlobal_Wow64TransitionStub)
{
// we have hit the wow64 transition stub - don't single step here, set a breakpoint on the current return address instead
dwReturnAddress = *(NATIVE_VALUE*)CURRENT_EXCEPTION_STACK_PTR;
ExceptionInfo->ContextRecord->Dr0 = dwReturnAddress;
ExceptionInfo->ContextRecord->Dr7 |= DEBUG_REGISTER_EXEC_DR0;
}
else if (CURRENT_EXCEPTION_INSTRUCTION_PTR == ExceptionInfo->ContextRecord->Dr1)
{
//到达返回地址后，删除所有断点
ExceptionInfo->ContextRecord->Dr7 = 0;
}
else
{
// scan all modules for the current instruction pointer
ScanAllModulesForAddress(CURRENT_EXCEPTION_INSTRUCTION_PTR, CURRENT_EXCEPTION_STACK_PTR);
// single step
ExceptionInfo->ContextRecord->EFlags |= SINGLE_STEP_FLAG;
}
// continue execution
return EXCEPTION_CONTINUE_EXECUTION;
}
else if (ExceptionInfo->ExceptionRecord->ExceptionCode == EXCEPTION_ACCESS_VIOLATION)
{
// access violation - check if the eip matches the expected value
if (CURRENT_EXCEPTION_INSTRUCTION_PTR != OVERWRITE_REFERENCE_ADDRESS_VALUE)
{
return EXCEPTION_CONTINUE_SEARCH;
}
// caught current hook successfully
dwGlobal_CurrHookExecuted = 1;
// restore correct instruction pointer
CURRENT_EXCEPTION_INSTRUCTION_PTR = dwGlobal_OriginalReferenceValue;
// continue execution
return EXCEPTION_CONTINUE_EXECUTION;
}
return EXCEPTION_CONTINUE_SEARCH;
}先不看这个异常处理，后面具体分析。
先看BeginTrace()函数，这个函数的参数就是目标函数的地址。
DWORD BeginTrace(BYTE* pTargetFunction)
{
CONTEXT DebugThreadContext;
// reset values
dwGlobal_TraceStarted = 0;
dwGlobal_SuccessfulHookCount = 0;
dwGlobal_AddressCount = 0;
// set initial debug context - hardware breakpoint on target function
memset((void*)&DebugThreadContext, 0, sizeof(DebugThreadContext));
DebugThreadContext.ContextFlags = CONTEXT_DEBUG_REGISTERS;
DebugThreadContext.Dr0 = (NATIVE_VALUE)pTargetFunction;
DebugThreadContext.Dr7 = DEBUG_REGISTER_EXEC_DR0;
if (SetThreadContext(GetCurrentThread(), &DebugThreadContext) == 0)
{
return 1;
}
// execute the target function
ExecuteTargetFunction();
return 0;
}其在目标函数地址处，打上了硬件断点，这个异常会被我们自己的异常处理函数所捕获，获取了esp寄存器的值，并且在返回地址处又打了个硬件断点。
if (dwGlobal_TraceStarted == 0)
{
//打在目标函数的硬件断点和此时的eip是否一致
if (CURRENT_EXCEPTION_INSTRUCTION_PTR != ExceptionInfo->ContextRecord->Dr0)
{
return EXCEPTION_CONTINUE_SEARCH;
}
//获取当前ESP寄存器的值
dwGlobal_InitialStackPtr = CURRENT_EXCEPTION_STACK_PTR;
//返回地址处打硬件断点
ExceptionInfo->ContextRecord->Dr1 = *(NATIVE_VALUE*)dwGlobal_InitialStackPtr;
// initial trace started
dwGlobal_TraceStarted = 1;
}接着执行，ScanAllModulesForAddress()函数是用来扫描子函数的，其参数是当前eip和当前esp，然后将EFlags设置为了单步执行，意味着后面每执行一条汇编指令，都会触发单步异常，从而进入这个异常处理函数。
// scan all modules for the current instruction pointer
ScanAllModulesForAddress(CURRENT_EXCEPTION_INSTRUCTION_PTR, CURRENT_EXCEPTION_STACK_PTR);
// single step
ExceptionInfo->ContextRecord->EFlags |= SINGLE_STEP_FLAG;当进入到合适的子函数头部中时，就会调用下面的遍历过程，计算出其对应的dll以及函数地址，和栈偏移。下面两个函数，一个遍历模块，一个遍历EAT表，当遍历出子函数时，就会用最初目标函数的的esp-现在的esp，从而得到栈偏移。
DWORD ScanModuleForAddress(BYTE* pModuleBase, char* pModuleName, NATIVE_VALUE dwAddr, NATIVE_VALUE dwStackPtr)
{
IMAGE_DOS_HEADER* pImageDosHeader = NULL;
IMAGE_NT_HEADERS* pImageNtHeader = NULL;
IMAGE_SECTION_HEADER* pCurrSectionHeader = NULL;
DWORD dwReadOffset = 0;
BYTE* pCurrPtr = NULL;
MEMORY_BASIC_INFORMATION MemoryBasicInfo;
DWORD dwStackDelta = 0;
// get dos header
pImageDosHeader = (IMAGE_DOS_HEADER*)pModuleBase;
if (pImageDosHeader->e_magic != 0x5A4D)
{
return 1;
}
// get nt header
pImageNtHeader = (IMAGE_NT_HEADERS*)(pModuleBase + pImageDosHeader->e_lfanew);
if (pImageNtHeader->Signature != IMAGE_NT_SIGNATURE)
{
return 1;
}
// loop through all sections
for (DWORD i = 0; i < pImageNtHeader->FileHeader.NumberOfSections; i++)
{
// get current section header
pCurrSectionHeader = (IMAGE_SECTION_HEADER*)((BYTE*)&pImageNtHeader->OptionalHeader + pImageNtHeader->FileHeader.SizeOfOptionalHeader + (i * sizeof(IMAGE_SECTION_HEADER)));
// ignore executable sections
if (pCurrSectionHeader->Characteristics & IMAGE_SCN_MEM_EXECUTE)
{
continue;
}
// scan current section for the target address
dwReadOffset = pCurrSectionHeader->VirtualAddress;
for (DWORD ii = 0; ii < pCurrSectionHeader->Misc.VirtualSize / sizeof(NATIVE_VALUE); ii++)
{
// check if the current value contains the target address
pCurrPtr = pModuleBase + dwReadOffset;
if (*(NATIVE_VALUE*)pCurrPtr == dwAddr)
{
// found target address - check memory protection
memset((void*)&MemoryBasicInfo, 0, sizeof(MemoryBasicInfo));
if (VirtualQuery(pCurrPtr, &MemoryBasicInfo, sizeof(MemoryBasicInfo)) != 0)
{
// check if the current region is writable
if (MemoryBasicInfo.Protect == PAGE_EXECUTE_READWRITE || MemoryBasicInfo.Protect == PAGE_READWRITE)
{
// ensure the address list is not full
if (dwGlobal_AddressCount >= MAXIMUM_STORED_ADDRESS_COUNT)
{
printf("Error: Address list is full\n");
return 1;
}
// store current address in list
dwGlobal_AddressList[dwGlobal_AddressCount] = (NATIVE_VALUE)pCurrPtr;
dwGlobal_AddressCount++;
// calculate stack delta
dwStackDelta = (DWORD)(dwGlobal_InitialStackPtr - dwStackPtr);
printf("Instruction 0x%p referenced at %s!0x%p (sect: %s, virt_addr: 0x%X, stack delta: 0x%X)\n", (void*)dwAddr, pModuleName, (void*)pCurrPtr, pCurrSectionHeader->Name, dwReadOffset, dwStackDelta);
}
}
}
// increase read offset
dwReadOffset += sizeof(NATIVE_VALUE);
}
}
return 0;
}
DWORD ScanAllModulesForAddress(NATIVE_VALUE dwAddr, NATIVE_VALUE dwStackPtr)
{
DWORD dwPEB = 0;
PEB* pPEB = NULL;
LDR_DATA_TABLE_ENTRY* pCurrEntry = NULL;
LIST_ENTRY* pCurrListEntry = NULL;
DWORD dwEntryOffset = 0;
char szModuleName[512];
DWORD dwStringLength = 0;
// get PEB ptr
#if _WIN64
pPEB = (PEB*)__readgsqword(0x60);
#else
pPEB = (PEB*)__readfsdword(0x30);
#endif
// get InMemoryOrderLinks offset in structure
dwEntryOffset = (DWORD)((BYTE*)&pCurrEntry->InLoadOrderLinks - (BYTE*)pCurrEntry);
// get first link
pCurrListEntry = pPEB->Ldr->InLoadOrderModuleList.Flink;
// enumerate all modules
for (;;)
{
// get ptr to current module entry
pCurrEntry = (LDR_DATA_TABLE_ENTRY*)((BYTE*)pCurrListEntry - dwEntryOffset);
// check if this is the final entry
if (pCurrEntry->DllBase == 0)
{
// end of module list
break;
}
// ignore main exe module
if (pCurrEntry->DllBase != pGlobal_ExeBase)
{
// convert module name to ansi
dwStringLength = pCurrEntry->BaseDllName.Length / sizeof(wchar_t);
if (dwStringLength > sizeof(szModuleName) - 1)
{
dwStringLength = sizeof(szModuleName) - 1;
}
memset(szModuleName, 0, sizeof(szModuleName));
wcstombs(szModuleName, pCurrEntry->BaseDllName.Buffer, dwStringLength);
// scan current module
ScanModuleForAddress((BYTE*)pCurrEntry->DllBase, szModuleName, dwAddr, dwStackPtr);
}
// get next module entry in list
pCurrListEntry = pCurrListEntry->Flink;
}
return 0;
}最终会将所有合适的子函数都保存到dwGlobal_AddressList[dwGlobal_AddressCount]这个全局数组中。
然后会验证一下获取到的这些子函数地址的可用性。
{
// attempt to hook the target function at all referenced instructions found earlier
for (DWORD i = 0; i < dwGlobal_AddressCount; i++)
{
printf("\nOverwriting reference: 0x%p...\n", (void*)dwGlobal_AddressList[i]);
// reset flag
dwGlobal_CurrHookExecuted = 0;
// store original value
dwGlobal_OriginalReferenceValue = *(NATIVE_VALUE*)dwGlobal_AddressList[i];
// overwrite referenced value with placeholder value
*(NATIVE_VALUE*)dwGlobal_AddressList[i] = OVERWRITE_REFERENCE_ADDRESS_VALUE;
printf("Calling target function...\n");
// execute target function
ExecuteTargetFunction();
// restore original value
*(NATIVE_VALUE*)dwGlobal_AddressList[i] = dwGlobal_OriginalReferenceValue;
// check if the hook was executed
if (dwGlobal_CurrHookExecuted == 0)
{
// hook wasn't executed - ignore
printf("Failed to catch hook\n");
}
else
{
// hook was executed - this address can be used to hook the target function
printf("Hook caught successfully!\n");
dwGlobal_SuccessfulHookCount++;
}
}
return 0;
}其将其函数地址修改为OVERWRITE_REFERENCE_ADDRESS_VALUE，导致这个子函数不可用，然后就会触发EXCEPTION_ACCESS_VIOLATION异常，由我们的异常处理函数来处理，主要就是修改dwGlobal_CurrHookExecuted = 1，代表测试成功。
else if (ExceptionInfo->ExceptionRecord->ExceptionCode == EXCEPTION_ACCESS_VIOLATION)
{
// access violation - check if the eip matches the expected value
if (CURRENT_EXCEPTION_INSTRUCTION_PTR != OVERWRITE_REFERENCE_ADDRESS_VALUE)
{
return EXCEPTION_CONTINUE_SEARCH;
}
// caught current hook successfully
dwGlobal_CurrHookExecuted = 1;
// restore correct instruction pointer
CURRENT_EXCEPTION_INSTRUCTION_PTR = dwGlobal_OriginalReferenceValue;
// continue execution
return EXCEPTION_CONTINUE_EXECUTION;
}总结
此hook方式的思路还是很新颖，同样也存在一些缺点，那就是只能在目标函数执行完成后，修改流程，并且可能hook的子函数万一被其他函数也调用了，这时候修改栈上的值，是否会有触发崩溃可能性呢。
通过这个工具的代码，也学到不少东西，异常处理，打硬件断点等等，可惜的是每想要hook一个API函数，都必须要去修改一下源码。
参考
https://www.x86matthew.com/view_post?id=stealth_hook
本文由 Seebug Paper 发布，如需转载请注明来源。本文地址：https://paper.seebug.org/2035/
文章来源: https://paper.seebug.org/2035/
如有侵权请联系:admin#unsafe.sh
如有侵权请联系:admin#unsafe.sh