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Interfacing To The Spy Device

Now that you know how w2k_mem.exe is used, it's time to see how it works. Rather than discuss command line parsing and dispatching, let's see how this application communicates with the spy device inside w2k_spy.sys.

Device I/O Control Revisited

The kernel-mode side of IOCTL communication has already been shown in Listings 4-6 and 4-7. The spy device simply sits waiting for I/O Request Packets (IRPs) and handles some of them, especially those tagged IRP_MJ_DEVICE_CONTROL, which request some forbidden actions to be executed, at least forbidden in the context of the user-mode application that sends these requests. It does so by calling the Win32 API function DeviceIoControl(), prototyped in Listing 4-27. The dwIoControlCode, lpInBuffer, nInBufferSize, lpOutBuffer, nOutBufferSize, and lpBytesReturned arguments should look familiar to you. In fact, they correspond 1:1 to the dCode, pInput, dInput, pOutput, dOutput, and pdInfo arguments of the SpyDispatcher() function in Listing 4-7. The remaining arguments are explained quickly. hDevice is the handle to the spy device, and lpOverlapped optionally points to an OVERLAPPED structure required for asynchronous IOCTL. We are not going to send asynchronous requests, so this argument will always be NULL.

Listing 4-28 is a collection of wrapper functions that perform basic IOCTL operations. The most basic function is IoControl(), which calls DeviceIoControl() and tests the reported output data size. Because w2k_mem.exe sizes its output buffers accurately, the number of output bytes should always be equal to the buffer size. ReadBinary() is a simplified version of IoControl() for IOCTL functions that don't require input data. ReadCpuInfo(), ReadSegment(), and ReadPhysical() are specifically tailored to the spy functions SPY_IO_CPU_INFO, SPY_IO_SEGMENT, and SPY_IO_PHYSICAL, because these are the most frequently used IOCTL functions. Encapsulating them in C functions makes the code much more readable.

Listing 4-27. Prototype of DeviceIoControl()

BOOL WINAPI DeviceIoControl (HANDLE      hDevice,
DWORD       dwIoControlCode,
                             PVOID       lpInBuffer,
                             DWORD       nInBufferSize,
                             PVOID       lpOutBuffer,
                             DWORD       nOutBufferSize,
                             PDWORD      lpBytesReturned,
                             POVERLAPPED lpOverlapped);

Listing 4-28. Various IOCTL Wrappers

BOOL WINAPI IoControl (HANDLE hDevice,
                       DWORD  dCode,
                       PVOID  pInput,
                       DWORD  dInput,
                       PVOID  pOutput,
                       DWORD  dOutput)
    {
    DWORD dData = 0;

    return DeviceIoControl (hDevice, dCode,
                            pInput,  dInput,
                            pOutput, dOutput,
                            &dData,  NULL)
           &&
           (dData == dOutput);
    }

// -----------------------------------------------------------------

BOOL WINAPI ReadBinary (HANDLE hDevice,
                        DWORD  dCode,
                        PVOID  pOutput,
                        DWORD  dOutput)
    {
    return IoControl (hDevice, dCode, NULL, 0, pOutput, dOutput);
    }

// -----------------------------------------------------------------

BOOL WINAPI ReadCpuInfo (HANDLE        hDevice,
                         PSPY_CPU_INFO psci)
    {
    return IoControl (hDevice, SPY_IO_CPU_INFO,
                      NULL,    0,
                      psci,    SPY_CPU_INFO_);
    }// -----------------------------------------------------------------

BOOL WINAPI ReadSegment (HANDLE       hDevice,
                         DWORD        dSelector,
                         PSPY_SEGMENT pss)
    {
    return IoControl (hDevice,    SPY_IO_SEGMENT,
                      &dSelector, DWORD_,
                      pss,        SPY_SEGMENT_);
    }

// -----------------------------------------------------------------

BOOL WINAPI ReadPhysical (HANDLE            hDevice,
                          PVOID             pLinear,
                          PPHYSICAL_ADDRESS ppa)
    {
    return IoControl (hDevice,  SPY_IO_PHYSICAL,
                      &pLinear, PVOID_,
                      ppa,      PHYSICAL_ADDRESS_)
           &&
           (ppa->LowPart || ppa->HighPart);
    }

All functions shown so far in this section require a spy device handle. It's time that I show how to obtain it. It is actually a quite simple Win32 operation, similar to opening a file. Listing 4-29 shows the implementation of the command handler inside w2k_mem.exe. This code uses the API functions w2kFilePath(), w2kServiceLoad(), and w2kServiceUnload(), exported by the "SBS Windows 2000 Utility Library" w2k_lib.dll, included on the companion CD of this book. If you have read the section about the Windows 2000 Service Control Manager in Chapter 3, you already know w2kServiceLoad() and w2kServiceUnload() from Listing 3-8. These powerful functions load and unload kernel-mode device drivers on the fly and handle benign error situations, such as gracefully loading a driver that is already loaded. w2kFilePath() is a helpful utility function that derives a file path from a base path, given a file name or file extension. w2k_mem.exe calls it to obtain a fully qualified path to the spy driver executable that matches its own path.

Listing 4-29. Controlling the Spy Device

WORD awSpyFile      [] = SW(DRV_FILENAME);
WORD awSpyDevice    [] = SW(DRV_MODULE);
WORD awSpyDisplay   [] = SW(DRV_NAME);
WORD awSpyPath      [] = SW(DRV_PATH);

// -----------------------------------------------------------------

void WINAPI Execute (PPWORD ppwArguments,
                     DWORD  dArguments)
    {
    SPY_VERSION_INFO svi;
    DWORD            dOptions, dRequest, dReceive;
    WORD             awPath [MAX_PATH] = L"?";
    SC_HANDLE        hControl          = NULL;
    HANDLE           hDevice           = NULL;
    _printf (L"\r\nLoading \"%s\" (%s) ...\r\n",
             awSpyDisplay, awSpyDevice);

    if (w2kFilePath (NULL, awSpyFile, awPath, MAX_PATH))
        {
        _printf (L"Driver: \"%s\"\r\n",
                 awPath);

        hControl = w2kServiceLoad (awSpyDevice, awSpyDisplay,
                                   awPath, TRUE);
        }
    if (hControl != NULL)
        {
        _printf (L"Opening \"%s\" ...\r\n",
                 awSpyPath);

        hDevice = CreateFile (awSpyPath, GENERIC_READ,
                              FILE_SHARE_READ | FILE_SHARE_WRITE,
                              NULL, OPEN_EXISTING,
                              FILE_ATTRIBUTE_NORMAL, NULL);
        }
    if (hDevice != INVALID_HANDLE_VALUE)
        {
        if (ReadBinary (hDevice, SPY_IO_VERSION_INFO,
                        &svi, SPY_VERSION_INFO_))
            {
            _printf (L"\r\n%s V%lu.%02lu ready\r\n",
                     svi.awName,
                     svi.dVersion / 100, svi.dVersion % 100);
            }
        dOptions = COMMAND_OPTION_NONE;
        dRequest = CommandParse (hDevice, ppwArguments, dArguments,
                                 TRUE, &dOptions);

        dOptions = COMMAND_OPTION_NONE;
        dReceive = CommandParse (hDevice, ppwArguments, dArguments,
                                 FALSE, &dOptions);
        if (dRequest)
            {
            _printf (awSummary,
                     dRequest, (dRequest == 1 ? awByte : awBytes),                     
                     dReceive, (dReceive == 1 ? awByte : awBytes));
            }
        _printf (L"\r\nClosing the spy device ...\r\n");
        CloseHandle (hDevice);
        }
    else
        {
        _printf (L"Spy device not available.\r\n");
        }
    if ((hControl != NULL) && gfSpyUnload)
        {
        _printf (L"Unloading the spy device ...\r\n");
        w2kServiceUnload (hControl, awSpyDevice);
        }
    return;
    }

Please note the four global string definitions at the top of Listing 4-29. The constants DRV_FILENAME, DRV_MODULE, DRV_NAME, and DRV_PATH are drawn from the header file of the spy device driver, w2k_spy.h. Table 4-4 lists their current values. You will not find device-specific definitions in the source files of w2k_mem.exe. w2k_spy.h provides everything a client application needs. This is very important: If any device-specific definitions change in the future, there is no need to update any application files. Just rebuild the application with the updated spy header file, and everything will fall into place.

The w2kFilePath() call near the beginning of Listing 4-29 guarantees that the w2k_spy.sys file specified by the global string awSpyFile (cf. Table 4-4) is always loaded from the directory where w2k_mem.exe resides. Next, the code in Listing 4-29 passes the global strings awSpyDevice and awSpyDisplay (cf. Table 4-4) to w2kServiceLoad(), attempting to load and start the spy device driver. If the driver was not loaded yet, these strings will be stored in the driver's property list and can be retrieved by other applications; otherwise, the current property settings are retained. Although the w2kServiceLoad() call in Listing 4-29 returns a handle, this is not a handle that can be used in any IOCTL calls. To get a handle to the spy device, the Win32 multipurpose function CreateFile() must be used. This function opens or creates almost anything that can be opened or created on Windows 2000. You certainly have called this function a million times to get a file handle. CreateFile() can also open kernel-mode devices if the symbolic link name of the device is supplied in the format \\.\<SymbolicLink> for the lpFileName argument. The symbolic link of the spy device is named w2k_spy, so the first CreateFile() argument must be \\.\w2k_spy, which is the value of the global string variable awSpyPath according to Table 4-4.

Table 4-4. Device-Specific String Definitions

w2k_spy CONSTANT

w2k_mem VARIABLE

VALUE

DRV_FILENAME

awSpyFile

w2k_spy.sys

DRV_MODULE

awSpyDevice

w2k_spy

DRV_NAME

awSpyDisplay

SBS Windows 2000 Spy Device

DRV_PATH

awSpyPath

\\.\w2k_spy


If CreateFile() succeeds, it returns a device handle that can be passed to DeviceIoControl(). The Execute() function in Listing 4-29 uses this handle immediately to query the version information of the spy device, which it displays on the screen if the IOCTL call succeeds. Next, the CommandParse() function is invoked twice with a different BOOL value for the fourth argument. The first call simply checks the command line for invalid parameters and displays any errors, and the second call actually executes all commands. I do not want to discuss in detail the command parser. The remaining code in Listing 4-29 is cleanup code that closes handles and optionally unloads the spy drives. The source code of w2k_mem.exe contains other interesting code snippets, but I will not discuss them here. Please see the files w2k_mem.c and w2k_mem.h in the \src\w2k_mem directory on the sample CD for further details.

The only notable thing left is the gfSpyUnload flag tested before unloading the spy driver. I have set this global flag to FALSE, so the driver will not be unloaded automatically. This enhances the performance of w2k_mem.exe and other w2k_spy. sys clients because loading a driver takes some time. The first client has to take the loading overhead, but all successors will benefit from having the driver already in memory. This setting also avoids conflict situations involving competitive clients, in which one client attempts to unload the driver while another one is still using it. Of course, Windows 2000 will not unload the driver unless all handles to its devices are closed, but it will put it into a STOP_PENDING state that will not allow new clients to access the device. However, if you don't run w2k_spy.sys in a multiclient environment, and you are updating the device driver frequently, you should probably set the gfSpyUnload flag to TRUE.

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