Hello everyone (sorry my English). There was a time, and decided to write something unusual on VB6, namely to try to write a driver. I must say before that I never wrote a driver and have no programming experience in kernel mode. The driver, according to my idea, will have to read the memory is not available in user mode, namely in the range 0x80000000 - 0xffffffff (in default mode, without IMAGE_FILE_LARGE_ADDRESS_AWARE). Immediately give the driver source code which is obtained:
<--Created using ToHtml.com on 2019-02-28 09:02:08 UTC -->
So, the driver must have an entry point DriverEntry, which causes the controller I/O driver is loaded. In the parameters of a pointer to an object-driver and a pointer to a string containing the name of the registry key corresponding to the loadable driver. In the Init procedure, we create two lines, one with the name of the device, the other with reference to the device name. Because we can not use the runtime kernel mode, it is necessary to create a string in the form of a static array, wrapped in a user-defined type, thereby VB6 allocates memory for the array on the stack. If you use a string that will inevitably be caused by one of the functions for runtime and copy assignment line, and we can not allow that. Then we can call IoCreateDevice, which creates a device object. Device object is the recipient of I/O requests and to him we will access when calling CreateFile function from user mode.
The first parameter is a pointer to an object-driver; the second parameter is 0, then since we do not have the structure of the expansion device, and we do not need to allocate memory; the third parameter we pass the name of the device, it is we need to implement access to the device; fourth parameter passed to the device type (see below). in the fifth, we pass 0 as we have "non-standard device"; in the sixth pass False, because We do not need single-user mode; the last parameter - the output. As the name of the device we have to use a string like DeviceDeviceName (where DeviceName - TrickMemReader), is the name we need to ensure that we can create a link to it, which in turn need to access the device from user mode.
Device type - FILE_DEVICE_MEMREADER. All non-standard devices must be of type or FILE_DEVICE_UNKNOWN, or the number of 0x8000 - 0xffff. I created FILE_DEVICE_MEMREADER constant with a value of 0x8000, which corresponds to the first free number. On success, the device is created and filled structure DEVICE_OBJECT. After the need to create a connection between the device name of the kernel mode and user mode. As the name we use DosDevicesTrickMemReader, from user mode, we will refer to it via the link '\.TrickMemReader". The link is created through IoCreateSymbolicLink. Next we define callback-procedure that will be called when certain events occur:
DriverUnload - deinitialize driver;
DriverCreateClose - when opening and closing device;
DriverDeviceControl - when calling DeviceIoControl.
And So. Now we return STATUS_SUCCESS, which corresponds to the successful implementation.* Now consider the procedure DriverUnload. It's simple - we remove the connection and set up the device. In the processing functions of opening and closing device DriverCreateClose, the status of the request, we return a success, and return the IRP packet I/O manager. Exchange of data between an application and device via the IRP-packets. IRP-package consists of 2 parts: a header and a stack of variable length. Part of the structure represented by the type of IRP. So now we add functionality to our driver function DriverDeviceControl. In this function I/O Manager will send IRP-data packet transmitted from the client application, which we will generate a call to DeviceIoControl. The parameters we pass 2 Long numbers: 1st address, where produce reading, 2nd number of bytes to read. Also one of the parameters passed to IRP-bag, when calling DeviceIoControl, a control code input / output (IOCTL), which represents the structure of the device type, function number, the type of data and the type of access. You can define several such codes for different operations and use them. I defined the code so IOCTL_READ_MEMORY = 0x80002000, 8000 - corresponds to the type of our device (FILE_DEVICE_MEMREADER); function number = 0x800, values below are reserved for user-defined functions allowed values 0x800 - 0xFFF; the type of data transmission - 0x0 (METHOD_BUFFERED), it means that we will receive / transmit data through the buffer that is specified SystemBuffer IRP-package); access type - FILE_ANY_ACCESS.
So, as a function of DriverDeviceControl we get a pointer to the I/O stack IRP-query using the IoGetCurrentIrpStackLocation, which returns the parameter of lpCurStackLocation. When Successes (if non-zero pointer) is copied to the local structure IO_STACK_LOCATION parameters are referenced by the pointer. Now we check the IOCTL-code field AssociatedIrp, which is a union (in VB6 no associations) which stores a pointer to SystemBuffer. Because we have the type of data corresponds METHOD_BUFFERED, in parameter SystemBuffer contains a pointer to the buffer with the parameters (address and size) DeviceIoControl, in this buffer, we can also recover data that is written to the output buffer DeviceIoControl. Now, if we have data contains the correct values (IOCTL and SystemBuffer), then we copy into local variables (lpPointer, DataSize). Next, check the size of the buffer. Size of the system I/O buffer is contained in the parameter DeviceIoControl.OutputBufferLength. If the requested number of bytes is not larger than the size of the system buffer, then everything is fine. Now we need to calculate the number of memory pages occupied by the data that we want to copy. To do this, we define the virtual address of the beginning of the page corresponding to pass a pointer, and because page size is a multiple of 4 KB (0x1000) we simply vanish 12-bit pointer. Next, we check in the cycle will not be whether an exception is thrown Page fault using the MmIsAddressValid. If the page is not in memory, the function returns False. Thus we check the number of pages that you want us to take a piece of memory and the number of pages that we can read. Then we calculate the actual size of the data that we will be able to read and, if necessary, adjust the size. Next to the title of IRP-package we copy the data size that we can read and a successful status. IoStatus.Information field matches the value returned by DeviceIoControl parameter lpBytesReturned. Next copy in SystemBuffer right amount of bytes using RtlMoveMemory and return IRP-package I/O manager. Return the status of a successful operation. In all other cases, return error STATUS_INVALID_PARAMETER and zero data size. All the driver code is ready.
Proceed to the compilation. Because we can not use the runtime, all the API-functions, we declare a TLB, so that they fall into the import:
<--Created using ToHtml.com on 2019-02-28 09:03:56 UTC --> PS. InterlockedExchange - I left because first driver had a bit of a different structure, subsequently left the ad in the TLB. In the driver, it does not fall into imports.
To the driver worked to do three things:
In the field Subsystem, structure IMAGE_OPTIONAL_HEADER PE-driver file should be the value that corresponds to IMAGE_SUBSYSTEM_NATIVE kernel-mode driver.
Specify as the entry point of our procedure DriverEntry
Add a relocation section, in order that the driver can be loaded at any address.
Exclude MSVBVM60 of imports.
For the first 3 points are added to the compilation keys vbp-file with the following contents:
Compile the project with all the default optimization. To exclude the runtime of the import, I use a utility Patch, I used here. I'm a little modify it, as initially could not start the driver and long puzzled because of what it does, and the reason was the checksum. After exclusion of the import library checksum has changed, and I do not update it. And EXE, DLL, etc. this field is not checked, and the driver checks. To check the watch imports in any viewer PE:
As you can see there is no runtime. What we required.
To test driver I wrote a simple program that loads the driver and works with him.
<--Created using ToHtml.com on 2019-02-28 09:04:55 UTC -->
The driver must be in the same folder as the program. Code is commented, so I will not describe his work.
To debug a driver you want to use the kernel-mode debugger. Debug going on a virtual system (VMware) - Windows XP. As a debugger take Syser, choose our driver and click Load. The system stops and we go to the debugger:
We are in the beginning of the function DriverEntry. The first "CALL" corresponds to a function call Init. If we follow step by step (F8) what's inside, we see how to complete the structure and called RtlInitUnicodeString for the device name and a symbolic link. The second "CALL" corresponds to the function "NT_SUCCESS", look it returns TRUE (in the register EAX) and code jumps after checking (TEST EAX, EAX) zero (False) on:
As can be seen code pushes the stack parameters for the IoCreateDevice from last to first using the instructions "PUSH". We start checking parameters. Check the name of the device (the third parameter - PUSH 0f8a2c010), for example, type "d 0f8a2c010" (which means to view a memory dump at f8a2c010, addresses are valid only for the current debugging) and see the contents:
the first 8 bytes - this is our variable DeviceName. The first two words - respectively the length of the line and the maximum length of the string in bytes. Next double word - a pointer to a string, look (d f8a2c0d8 consider the byte order little-endian):
there Unicode string with the name of the device. If you look at parameter Device (last output parameter - PUSH 0f8a2c020), we can see that it is different from the name on the 0x10 byte. Now look at the declaration of variables, the variable "Device" is declared after the DeviceName and DeviceLink, a total length of 8 + 8 = 0x10 bytes. Ie the order of the variables in the memory corresponds to the order in the ad code. Check the first non-const parameter ESI, in the beginning it is copied to the value at ESP + 0xC. Register ESP - points to the top of the stack. If you walk to the top function DriverEntry, you can see the preservation of the stack of two registers ESI and EDI (by agreement StdCall these registers are saved in the list, ie, the procedure should not change them after the call). DriverObject transmitted in the first variable, i.e. closest to the top of the stack, and after all the settings saved return address - ie DriverObject parameter before executing the first instruction in the DriverEntry function is located at ESP + 4 (the stack grows downward addresses), after two instructions "PUSH" he accordingly shifted by 8 bytes, as a result DriverObject located at ESP + 0C, all right . Correct settings, you can call the function. Hit F10 to not go inside and look IoCreateDevice value of the EAX register after the call, there must be a non-negative integer that indicates that the function worked without error. I have it returned 0 (STATUS_SUCCESS), everything is fine. Next comes the familiar procedure at 0xF8A2B750 - NT_SUCCESS:
If successful, go jump on 0xf8a2b7bf, where there is the pushing of the stack parameters for the function IoCreateSymbolicLink. Parameter DeviceName we have checked, check DeviceLink:
What you need. Hit F10, test EAX, if successful go further if it fails, remove the device and exit with an error. Procedure at 0xf8a2bbb0 - it GetAddr, which simply returns its this value:
Next there is copying of addresses at offsets DriverObject, if you look at the declaration you can see that at offset 0x34 is written address DriverUnload, at offset 0x38 - MajorFunction (0), etc. Recorded values correspond to the address of the function in our driver. Then there is zero EAX (the returned value) and exit from the procedure DriverEntry. Everything works without error, go ahead. So, to track the performance of the driver we will put a breakpoint on the function DriverDeviceControl. Address it is possible to take on the newly written offsets in the structure of DRIVER_OBJECT or find easy viewing and by analyzing the code. In my test, the address is 0xf8a2b870, go to him (. 0xf8a2b870) and press F9, set breakpoints. On the contrary instructions to set a marker:
Now, when this function is called the debugger will stop code execution and enables us to step through the code. Function "DriverCreateClose" and "DriverUnload" I will not describe, because everything is simple. Hit F5, thereby continuing to perform normally. We were immediately transferred back to Windows. Now we run our test application, enter any address (eg 81234567) and click on the button Read. Our challenge intercepts debugger and we can continue to test the function code DriverDeviceControl. Details inside I will not describe the code will focus on the copy:
Immediately look at the stack (register ESP), we see that the correct parameters are passed. In any case, do a dump, then compare:
Press F5 - and return to Windows. We look at the dump is already in our program:
As you can see everything is fine copy. Let's try to copy the data to a page boundary, so that one page was missing. Experimental method was found such a page that's what we get:
As we can see that the data is copied correctly, which did not work there, we displayed a question mark. The output parameter DeviceIoControl we actually returns the number of bytes read, we use it to display a question mark. _________________________________________________________________
As you can see on VB6, you can write a simple driver, and if you use inline assembly can be more serious and write something. Thank you for your attention. Good Luck!
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