Set higher baud rate of COM1 on connect

CERT-Polska · Aug 7, 2024 · f8226f6 · f8226f6
1 parent 7636df0
commit f8226f6
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Showing 3 changed files with 66 additions and 0 deletions.
diff --git a/drakshell/guest/drakshell.c b/drakshell/guest/drakshell.c
@@ -225,6 +225,8 @@ static bool req_download_file(HANDLE hComm)
 }
 
 void __attribute__((noinline)) __attribute__((force_align_arg_pointer)) drakshell_main() {
+    DCB dcb = { .DCBlength = sizeof(DCB) };
+
     if(!load_winapi()) {
         // Failed to load some WinAPI functions
         return;
@@ -249,6 +251,21 @@ void __attribute__((noinline)) __attribute__((force_align_arg_pointer)) drakshel
         return;
     }
 
+    if(!GetCommState(hComm, &dcb))
+    {
+        OutputDebugStringW(L"Failed to get mode of COM1");
+        return;
+    }
+
+    dcb.BaudRate = 115200;
+    dcb.fParity = false;
+
+    if(!SetCommState(hComm, &dcb))
+    {
+        OutputDebugStringW(L"Failed to set mode of COM1");
+        return;
+    }
+
     OutputDebugStringW(L"I'm connected");
 
     while(true) {

diff --git a/drakshell/guest/include/nt_loader.h b/drakshell/guest/include/nt_loader.h
@@ -42,6 +42,37 @@ typedef char* LPSTR;
 typedef wchar_t* LPWSTR;
 typedef bool BOOL;
 
+typedef struct _DCB {
+    DWORD DCBlength;
+    DWORD BaudRate;
+    DWORD fBinary : 1;
+    DWORD fParity : 1;
+    DWORD fOutxCtsFlow : 1;
+    DWORD fOutxDsrFlow : 1;
+    DWORD fDtrControl : 2;
+    DWORD fDsrSensitivity : 1;
+    DWORD fTXContinueOnXoff : 1;
+    DWORD fOutX : 1;
+    DWORD fInX : 1;
+    DWORD fErrorChar : 1;
+    DWORD fNull : 1;
+    DWORD fRtsControl : 2;
+    DWORD fAbortOnError : 1;
+    DWORD fDummy2 : 17;
+    WORD  wReserved;
+    WORD  XonLim;
+    WORD  XoffLim;
+    BYTE  ByteSize;
+    BYTE  Parity;
+    BYTE  StopBits;
+    char  XonChar;
+    char  XoffChar;
+    char  ErrorChar;
+    char  EofChar;
+    char  EvtChar;
+    WORD  wReserved1;
+} DCB, *LPDCB;
+
 #define WINAPI __attribute__((ms_abi))
 
 typedef int (WINAPI* PCreateThread)(
@@ -149,5 +180,19 @@ typedef DWORD (WINAPI* PGetLastError)();
 extern PGetLastError pGetLastError;
 #define GetLastError (*pGetLastError)
 
+typedef BOOL (WINAPI* PGetCommState)(
+    HANDLE hFile,
+    LPDCB  lpDCB
+);
+extern PGetCommState pGetCommState;
+#define GetCommState (*pGetCommState)
+
+typedef BOOL (WINAPI* PSetCommState)(
+    HANDLE hFile,
+    LPDCB  lpDCB
+);
+extern PSetCommState pSetCommState;
+#define SetCommState (*pSetCommState)
+
 extern void* get_func_from_peb(const wchar_t* libraryName, const char* procName);
 extern bool load_winapi();
diff --git a/drakshell/guest/nt_loader.c b/drakshell/guest/nt_loader.c
@@ -218,6 +218,8 @@ PExitThread pExitThread;
 PSleep pSleep;
 PVirtualFree pVirtualFree;
 PGetLastError pGetLastError;
+PGetCommState pGetCommState;
+PSetCommState pSetCommState;
 
 bool load_winapi() {
     HANDLE hKernel32, hUser32;
@@ -244,6 +246,8 @@ bool load_winapi() {
     pSleep = GetProcAddress(hKernel32, "Sleep");
     pVirtualFree = GetProcAddress(hKernel32, "VirtualFree");
     pGetLastError = GetProcAddress(hKernel32, "GetLastError");
+    pGetCommState = GetProcAddress(hKernel32, "GetCommState");
+    pSetCommState = GetProcAddress(hKernel32, "SetCommState");
 
     return true;
 }