cc682/NetRoc
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为了避免自己的某个dll模块被别人检测出来，有时候希望在自己加载一个dll之后，或者将dll注入到他人进程之后避免被检查出来。这就需要想办法抹掉这个dll的模块信息，使得Toolhelp、psapi等枚举模块的API无法枚举它。
我们可以先简单看看Windows枚举进程内模块的办法吧：
首先是BOOL EnumProcessModules( HANDLE hProcess, HMODULE* lphModule, DWORD cb, LPDWORD lpcbNeeded);
EnumProcessModules实际调用EnumProcessModulesInternal进行枚举。下面是vista下psapi的代码片断：
.text:514024B8 push ebx
.text:514024B9 push 18h
.text:514024BB lea eax, [ebp+stProcessBasicInfo]
.text:514024BE push eax
.text:514024BF push ebx ;ebx=0
.text:514024C0 push [ebp+hProcess]
.text:514024C3 call ds:__imp__NtQueryInformationProcess@20 ; NtQueryInformationProcess(x,x,x,x,x)
.text:514024C9 cmp eax, ebx
.text:514024CB jge short loc_514024E0
调用NtQueryInformationProcess获得ProcessBasicInformation，在PROCESS_BASIC_INFORMATION结构中取得PEB地址。然后读取指定进程PEB中的数据
text:514024E0 loc_514024E0: ; CODE XREF: EnumProcessModulesInternal(x,x,x,x,x)+24j
.text:514024E0 mov eax, [ebp+stProcessBasicInfo.PebBaseAddress]
.text:514024E3 cmp eax, ebx
.text:514024E5 jnz short loc_514024EE
.text:514024E7 push 8000000Dh
.text:514024EC jmp short loc_514024CE
.text:514024EE ; ---------------------------------------------------------------------------
.text:514024EE
.text:514024EE loc_514024EE: ; CODE XREF: EnumProcessModulesInternal(x,x,x,x,x)+3Ej
.text:514024EE push ebx ; lpNumberOfBytesRead
.text:514024EF push 4 ; nSize
.text:514024F1 lea ecx, [ebp+Ldr]
.text:514024F4 push ecx ; lpBuffer
.text:514024F5 add eax, 0Ch
.text:514024F8 push eax ; lpBaseAddress
.text:514024F9 push [ebp+hProcess] ; hProcess
.text:514024FC mov edi, ds:__imp__ReadProcessMemory@20 ; ReadProcessMemory(x,x,x,x,x)
.text:51402502 call edi ; ReadProcessMemory(x,x,x,x,x) ; ReadProcessMemory(x,x,x,x,x)
这里读取的是PEB地址+0C处的四个字节。
通过WinDbg我们可以看看nt!_PEB的结构
0: kd> dt nt!_PEB
+0x000 InheritedAddressSpace : UChar
+0x001 ReadImageFileExecOptions : UChar
+0x002 BeingDebugged : UChar
+0x003 SpareBool : UChar
+0x004 Mutant : Ptr32 Void
+0x008 ImageBaseAddress : Ptr32 Void
+0x00c Ldr : Ptr32 _PEB_LDR_DATA
+0x010 ProcessParameters : Ptr32 _RTL_USER_PROCESS_PARAMETERS
……
+0C处是一个_PEB_LDR_DATA结构指针，里面包含了和LDR相关的一些数据，进程的模块链表就保存在Ldr中。下面是_PEB_LDR_DATA的结构：
0: kd> dt nt!_PEB_LDR_DATA
+0x000 Length : Uint4B
+0x004 Initialized : UChar
+0x008 SsHandle : Ptr32 Void
+0x00c InLoadOrderModuleList : _LIST_ENTRY
+0x014 InMemoryOrderModuleList : _LIST_ENTRY
+0x01c InInitializationOrderModuleList : _LIST_ENTRY
+0x024 EntryInProgress : Ptr32 Void
其中，InLoadOrderModuleList、InMemoryOrderModuleList、InInitializationOrderModuleList就是进程当前已加载模块的链表，只是按照不同的方式排序。EnumProcessModules是通过InMemoryOrderModuleList链表枚举的，而根据Win2k代码，ToolHelp32函数是通过InLoadOrderModuleList枚举。这三个_LIST_ENTRY都是在一个RTL_PROCESS_MODULE_INFORMATION结构中的成员。这个结构在2k代码中有引用，不过没有确切的定义，下面是ReactOS中的定义，不过看起来我的vista PSAPI中使用的结构已经有所变化了，这里只作参考。
//
// Loader Data Table Entry
//
typedef struct _LDR_DATA_TABLE_ENTRY
{
LIST_ENTRY InLoadOrderLinks;
LIST_ENTRY InMemoryOrderModuleList;
LIST_ENTRY InInitializationOrderModuleList;
PVOID DllBase;
PVOID EntryPoint;
ULONG SizeOfImage;
UNICODE_STRING FullDllName;
UNICODE_STRING BaseDllName;
ULONG Flags;
USHORT LoadCount;
USHORT TlsIndex;
union
{
LIST_ENTRY HashLinks;
PVOID SectionPointer;
};
ULONG CheckSum;
union
{
ULONG TimeDateStamp;
PVOID LoadedImports;
};
PVOID EntryPointActivationContext;
PVOID PatchInformation;
} LDR_DATA_TABLE_ENTRY, *PLDR_DATA_TABLE_ENTRY;
到这里，隐藏模块的方法就已经明了了：通过PEB取得Ldr数据，拿到三个模块链表，并将要隐藏的模块断链即可。下面是主要代码实现：
BOOL HideMyself()
{
HMODULE hMod = GetModuleHandle( _T( "ntdll.dll"));
HMODULE hModMyself = GetModuleHandle( _T("dll.dll"));
pfnNtQueryInformationProcess p = (pfnNtQueryInformationProcess)::GetProcAddress( hMod, "NtQueryInformationProcess");
PROCESS_BASIC_INFORMATION stInfo = {0};
DWORD dwRetnLen = 0;
DWORD dw = p( GetCurrentProcess(), 0, &stInfo, sizeof(stInfo), &dwRetnLen);
PPEB pPeb = stInfo.PebBaseAddress;
PLIST_ENTRY ListHead, Current;
PLDR_DATA_TABLE_ENTRY pstEntry = NULL;
ListHead = &( stInfo.PebBaseAddress->Ldr->InLoadOrderModuleList);
Current = ListHead->Flink;
while ( Current != ListHead)
{
pstEntry = CONTAINING_RECORD( Current, LDR_DATA_TABLE_ENTRY, InLoadOrderLinks);
//DebugOutW( L"Module:%s, base:0x%X\r\n", pstEntry->FullDllName.Buffer, pstEntry->EntryPoint);
if ( pstEntry->DllBase == hModMyself)
{
pstEntry->InLoadOrderLinks.Flink->Blink = pstEntry->InLoadOrderLinks.Blink;
pstEntry->InLoadOrderLinks.Blink->Flink = pstEntry->InLoadOrderLinks.Flink;
DebugOut( _T( "Hide injected dll."));
break;
}
Current = pstEntry->InLoadOrderLinks.Flink;
}
ListHead = &( stInfo.PebBaseAddress->Ldr->InMemoryOrderModuleList);
Current = ListHead->Flink;
while ( Current != ListHead)
{
pstEntry = CONTAINING_RECORD( Current, LDR_DATA_TABLE_ENTRY, InMemoryOrderModuleList);
DebugOutW( L"Module:%s, base:0x%X\r\n", pstEntry->FullDllName.Buffer, pstEntry->EntryPoint);
if ( pstEntry->DllBase == hModMyself)
{
pstEntry->InMemoryOrderModuleList.Flink->Blink = pstEntry->InMemoryOrderModuleList.Blink;
pstEntry->InMemoryOrderModuleList.Blink->Flink = pstEntry->InMemoryOrderModuleList.Flink;
DebugOut( _T( "Hide injected dll."));
break;
}
Current = pstEntry->InMemoryOrderModuleList.Flink;
}
DebugOutW( L"\r\n");
ListHead = &( stInfo.PebBaseAddress->Ldr->InInitializationOrderModuleList);
Current = ListHead->Flink;
while ( Current != ListHead)
{
pstEntry = CONTAINING_RECORD( Current, LDR_DATA_TABLE_ENTRY, InInitializationOrderModuleList);
DebugOutW( L"Module:%s, base:0x%X\r\n", pstEntry->FullDllName.Buffer, pstEntry->EntryPoint);
if ( pstEntry->DllBase == hModMyself)
{
pstEntry->InInitializationOrderModuleList.Flink->Blink = pstEntry->InInitializationOrderModuleList.Blink;
pstEntry->InInitializationOrderModuleList.Blink->Flink = pstEntry->InInitializationOrderModuleList.Flink;
DebugOut( _T( "Hide injected dll."));
break;
}
Current = pstEntry->InInitializationOrderModuleList.Flink;
}
//DebugOut( _T("Out HideMyself\r\n"));
return TRUE;
}
这样处理之后，通过常规的枚举进程方式已经枚举不到隐藏模块，ProcessExplorer也无法枚举。但是，通过枚举进程内存空间等非常规方法，仍然是可以找到的。关于PSAPI和Toolhelp函数枚举模块的原理，可以逆向Windows代码，或者查找网上的代码看看就明白了。