Unseen Debugger Detection (Ollydbg)

[upb]

LPVOID AddrZwQueryInformationProcess = (LPVOID)-1;
BYTE SavedByteZwQueryInformationProcess = 0;

bool DisableZwQueryInformationProcessDebugPort(void)
{
DWORD numread;
BYTE bFE = 0xFE;
HMODULE ntdll = GetModuleHandle("ntdll.dll");
AddrZwQueryInformationProcess = GetProcAddress(ntdll, "NtQueryInformationProcess");
ReadProcessMemory(hproc, AddrZwQueryInformationProcess, &SavedByteZwQueryInformationProcess, 1, &numread);
WriteProcessMemory(hproc, AddrZwQueryInformationProcess, &bFE, 1, &numread);
return true;
}

bool ZwQueryInformationProcessTracer(DEBUG_EVENT evt)
{
DWORD numread;
BYTE bFE = 0xFE;

ReadProcessMemory(hproc, AddrZwQueryInformationProcess, &SavedByteZwQueryInformationProcess, 1, &numread);
WriteProcessMemory(hproc, AddrZwQueryInformationProcess, &bFE, 1, &numread);

return false; // end trace
}


in debug loop:
if (evt.u.Exception.ExceptionRecord.ExceptionCode == EXCEPTION_ILLEGAL_INSTRUCTION &&
evt.u.Exception.ExceptionRecord.ExceptionAddress == AddrZwQueryInformationProcess)
{
hthread = ThreadIdToHandle(evt.dwThreadId);

DWORD stack[6];
DWORD numread;
ReadProcessMemory(hproc, (LPVOID)ctx.Esp, &stack, sizeof(DWORD) * 6, &numread);
MsgBoxF("ZwQueryInformationProcess trapped >%08X (%08X, %08X, %08X)", stack[0], stack[1], stack[2], stack[3]);
if (stack[2] == 7)
{
DWORD d0 = 0;
WriteProcessMemory(hproc, (LPVOID)stack[3], &d0, 1, &numread);
d0 = ctx.Esp - 4 * 3;
WriteProcessMemory(hproc, (LPVOID)(ctx.Esp + 3 * 4), &d0, sizeof(DWORD), &numread);
}
WriteProcessMemory(hproc, AddrZwQueryInformationProcess, &SavedByteZwQueryInformationProcess, 1, &numread);
StartTrace(hthread, ZwQueryInformationProcessTracer);
ContinueStatus = DBG_CONTINUE;
} else

// note: plz do not rip this code 1:1 into any pulumbium tutorials