ourvxd
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I will introduce you some basic aspects about
the VxD programming (don't you think I have much
more idea than you, this is my first W95 VxD :-)
First you must know that a VxD can do everything
we want, no more Ring3 restrictions, you can
stop completely the system, read or write any
memory address, hook all interrupts or exceptions,
take control of the IO ports, for that reason
I recomend you to reverse a little WinIce so you
could see how these great programmers do it, also
is a good idea study a little VxDMonitor,FileMonitor
and RegMonitor all from Bryce Cogswell and Mark
Russinovich, BTW I have been able to create my
VxD thanks to they sourcers, M$ documentation about
this makes laught.
A VxD has two parts, one is the Initialization Part
of Code that is discardable, so when the VxD has been
loaded and initializated, the memory area of this code
(and it data) is freed, and a locked (permanent) part
that is only released when the VxD is unloaded.
At the initialization you must perform the critical
actions like hooking int,s ,devices, API,s ,etc.
Well no more words and lets see it with an example,
lets try to intercept timing functions of W95 so
we will use it as a TSR for reversing purposes.
I will use Hedit 2.0 because it is a 'small'
program (although 340Kb is a little overbloated)
so everyone could download the program and follow
the example easily. Hedit get the system time and
then compares it with another stored value and
if the system_time is lower than the stored value
a good guy is asummed, so we can tell the program
we are in the year 1088 and then we will be good guys
(quite obvious).
If you read my WinIce essay, you will remember that
W95 uses the Old Int 21h service 2Ah in order to get
the system time, so we will path these service.
Our VxD will check all time requests by hooking the
Int 21h service 2Ah and then will check if the caller
is Hedit gives it a good guy date otherwise lets DOS
give the correct date. Easy is it?
BTW, I have also added a complete service list with
the codes, so you can monitor (or intercept) every
call to a service using next function:
?mov?eax,Service_ID
?mov?esi,Our_New_Procedure
?VmmCall?Hook_Device_Service
?jc?Not_Installed
?mov?[Real_Proc],esi
Our_New_Proc:
?Do ?something
?jmp?[Real_Proc]
????? THE SOURCE (vxdbody.asm)
.386p
?.xlist
?include?vmm.inc
?include vwin32.inc
.list
;===============================================================
;???????????????????????? S O M E?? E Q U =============================
VXDBODYName????????????? EQU???? <'VXDBODY VXD????? '> ;Must be 16 chars
VXDBODYRev?????????????? EQU???? 00H
VXDBODY_MAJOR_VERSION??? EQU???? 1
VXDBODY_MINOR_VERSION??? EQU???? 0
ErrorCode?????????????? EQU 0FFFFFFFFh
;===================================================
; ???? P U B L I C?? D A T A
;======================================================
VXD_LOCKED_DATA_SEG
FLAGS?? dd 0
SYS_VM? dd 0
LD????? dd 0
VXD_LOCKED_DATA_ENDS
;===================================
;D E V I C E?? D E C L A R A T I O N
;===================================
VXD_LOCKED_CODE_SEG
DECLARE_VIRTUAL_DEVICE VXDBODY,? \
??????? VXDBODY_MAJOR_VERSION,?? \
??????? VXDBODY_MINOR_VERSION,?? \
??????? VXDBODY_Control, ,?????? \
?UNDEFINED_INIT_ORDER
;=================
;M A I N?? C O D E
;=================
public VXDBODY_Control
VXDBODY_Control PROC NEAR
??????? Control_Dispatch SYS_DYNAMIC_DEVICE_INIT,?????? VXDBODY_Device_Init
??????? Control_Dispatch SYS_DYNAMIC_DEVICE_EXIT,?????? VXDBODY_Device_Exit
??????? Control_Dispatch W32_DEVICEIOCONTROL,?????????? VXDBODY_ioctl
?clc
?ret
VXDBODY_Control ENDP
Public VXDBODY_ioctl
BeginProc VXDBODY_ioctl
?mov?ecx,[esi].dwIoControlCode?; get ioctl code
??????? cmp???? ecx,1
??????? je????? Function1
??????? cmp???? ecx,2
??????? je????? Function2
??????? jmp???? RetSuccess
Function1:
??????? ;Here everything you want
??????? ;No more Ring3 limitations
??????? jmp???? RetSuccess
Function2:
??????? ;Here other function
??????? ;and so on.
??????? jmp???? RetSuccess
RetSuccess:
??????? xor???? eax, eax???? ;return zero = success
?clc
?ret
RetFail:
??????? mov???? eax,ErrorCode
??????? stc
??????? ret
EndProc VXDBODY_ioctl
BeginProc Our_Int_Handler
??????? pushad
??????? mov???? eax,[ebp.Client_EAX]
??????? cmp???? ax,2A00h??????????????? ;Get_System_Time DOS function?
??????? jne???? Let_DOS_Work
???????
??????? xor???? eax,eax
??????? mov???? FLAGS,eax??;Must be zero
??????? VxDCall VWIN32_GetCurrentProcessHandle
??????? mov???? eax,[eax+38h]
??????? or????? al,7
??????? mov???? LD,eax??? ??;Store the Local Descriptor
??????? VmmCall Get_Sys_VM_Handle
??????? mov???? SYS_VM,ebx
??????? VmmCall _SelectorMapFlat
??????? add???? eax,0F2h??????? ;Now eax points to the caller name
??????? mov???? ebx,[eax]
??????? cmp???? ebx,'ideH'????? ;Hedit inverted
??????? jne???? Let_DOS_Work
??????? mov???? bl,[eax+4]
??????? cmp???? bl,'t'
??????? jne???? Let_DOS_Work
??????? mov???? [ebp.Client_AX],1????? ;Day of week
??????? mov???? [ebp.Client_CX],1088?? ;Year
??????? mov???? [ebp.Client_DX],0101h? ;Day and Month
Is_Hedit:
??????? popad
??????? clc???? ;consume the interrupt
??????? ret
Let_DOS_Work:
??????? popad
?? ?stc?? ; don't consume the interrupt
?? ?ret
EndProc Our_Int_Handler
Public VXDBODY_Device_Exit
BeginProc VXDBODY_Device_Exit
??????? mov???? eax, 21h
??????? mov???? esi, OFFSET32 Our_Int_Handler
??????? VMMCall UnHook_V86_Int_Chain
?clc
?ret
EndProc VXDBODY_Device_Exit
VXD_LOCKED_CODE_ENDS
VXD_ICODE_SEG
BeginProc VXDBODY_Device_Init
??????? mov???? eax, 21h
??????? mov???? esi, OFFSET32 Our_Int_Handler
?? ?VMMCall Hook_V86_Int_Chain
?clc
?ret
EndProc VXDBODY_Device_Init
VXD_ICODE_ENDS
end
??THE DEFINITIONS (vxdbody.def)
VXD VXDBODY DYNAMIC
SEGMENTS
?_LPTEXT??CLASS 'LCODE'?? PRELOAD NONDISCARDABLE
?_LTEXT??CLASS 'LCODE'?? PRELOAD NONDISCARDABLE
?_LDATA??CLASS 'LCODE'?? PRELOAD NONDISCARDABLE
?_TEXT??CLASS 'LCODE'?? PRELOAD NONDISCARDABLE
?_DATA??CLASS 'LCODE'?? PRELOAD NONDISCARDABLE
?CONST??CLASS 'LCODE'?? PRELOAD NONDISCARDABLE
?_TLS??CLASS 'LCODE'?? PRELOAD NONDISCARDABLE
?_BSS??CLASS 'LCODE'?? PRELOAD NONDISCARDABLE
??????? _MSGTABLE?CLASS 'MCODE'?PRELOAD NONDISCARDABLE IOPL
??????? _MSGDATA?CLASS 'MCODE'?PRELOAD NONDISCARDABLE IOPL
??????? _IMSGTABLE?CLASS 'MCODE'?PRELOAD DISCARDABLE IOPL
??????? _IMSGDATA?CLASS 'MCODE'?PRELOAD DISCARDABLE IOPL
??????? _ITEXT??CLASS 'ICODE'?? DISCARDABLE
?_IDATA??CLASS 'ICODE'?? DISCARDABLE
?_PTEXT??CLASS 'PCODE'?? NONDISCARDABLE
?_PDATA??CLASS 'PDATA'?? NONDISCARDABLE SHARED
?_STEXT??CLASS 'SCODE'?? RESIDENT
?_SDATA??CLASS 'SCODE'?? RESIDENT
?_DBOSTART?CLASS 'DBOCODE' PRELOAD NONDISCARDABLE CONFORMING
?_DBOCODE?CLASS 'DBOCODE' PRELOAD NONDISCARDABLE CONFORMING
?_DBODATA?CLASS 'DBOCODE' PRELOAD NONDISCARDABLE CONFORMING
?_16ICODE?CLASS '16ICODE' PRELOAD DISCARDABLE
?_RCODE??CLASS 'RCODE'
EXPORTS
??????? VXDBODY_DDB
??THE MAKEFILE (makefile.?? )
OBJECTS = vxdbody.obj
vxdbody.vxd:???? $(OBJECTS) vxdbody.def
??????? LINK.EXE @<<
-VXD -OUT:vxdbody.VXD
-DEF:vxdbody.def
-MERGE:.data=_LDATA -MERGE:.bss=_LDATA -MERGE:_PDATA=_PTEXT
-COMMENT:"vxdbody VXD"
$(OBJECTS)
<<
???????
.asm.obj:
??????? set ML=-coff -DBLD_COFF -DIS_32 -nologo -W3 -Zd -c -Cx -DMASM6 -DINITLOG -DDEBLEVEL=1 -DDEBUG -Fl
?ml -Fo$*.obj $<
vxdbody.obj:???? vxdbody.asm
Also I attach a simple programm that opens our vxd and closes it,
and (not implemented yet) sends orders to our vxd.
Soon more (but you must work at your own)
+rcg 1998
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