reverse engineering of bedaisy.sys (battleyes kernel driver)
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README.md

BEDaisy

reverse engineering of bedaisy.sys (battleyes kernel driver). By registering on image load callbacks and IAT hooking BEDaisy's MmGetSystemRoutineAddress we can simply hook any imports we want and have control flow over subsequent functions. Write up can be found here: https://back.engineering/post/battleye/

APCS

The below function will be executed in each thread that bedaisy registers an APC on.

__int64 __usercall apc_callback@<rax>(char _CL@<cl>, char _BH@<bh>, __int64 *a3@<r9>)
{
  __int64 v4; // rbx

  __asm { rcl     bh, cl }
  v4 = *a3;
  *(_DWORD *)(v4 + 2160) = RtlWalkFrameChain(*a3 + 0x70, 256i64, 0i64);
  return KeSetEvent(v4 + 88, 0i64, 0i64);
}

Registeration of APCS:

    status = PsLookupThreadByThreadId(thread_id, &some_pethread);
    v17 = 0;
    if ( (int)status >= 0 )
    {
      allocated_pool = ExAllocatePool(0x200i64, 0x878i64);
      allocated_pool_1 = allocated_pool;
      allocated_pool_2 = allocated_pool;
      if ( allocated_pool )
      {
        allocated_pool_plus_58 = allocated_pool + 0x58;
        KeInitializeEvent((PRKEVENT)(allocated_pool + 0x58), NotificationEvent, 0);
        __asm { rcl     cx, 0C6h }
        LOBYTE(v77) = 0;
        KeInitializeApc(allocated_pool_2, some_pethread, 0i64, j_apc_callback, 0i64, 0i64, v77, 0i64);
        if ( (unsigned __int8)KeInsertQueueApc(allocated_pool_2, allocated_pool_2, 0i64, 2i64) )

HWID

BEDaisy opens a handle to DR0 (disk.sys).

02646022	190.98799133	[GoodEye]ZwOpenFile called from: 0xFFFFF804DEFDB904	
02646023	190.98799133	[GoodEye]     - ZwOpenFile(\Device\Harddisk0\DR0)	
02646024	190.98869324	[GoodEye]     - ZwOpenFile handle result: 0xFFFFFFFF80003E28

BEDaisy then sends a few IOCTL's to disk.sys using ZwDeviceIoControlFile

02646049	190.99142456	[GoodEye]ZwDeviceIoControlFile Called From 0xFFFFF804DEFDB94A	
02646050	190.99143982	[GoodEye]     - FileHandle: 0xFFFFFFFF80003E28	
02646051	190.99143982	[GoodEye]     - IoControlCode: 0x00000000002D1400	
02646052	190.99143982	[GoodEye]     - OutputBufferLength: 0x0000000000000008	
02646053	190.99143982	[GoodEye]     - InoutBufferLength: 0x000000000000000C

02646059	190.99192810	[GoodEye]ZwDeviceIoControlFile Called From 0xFFFFF804DEFDB960	
02646060	190.99192810	[GoodEye]     - FileHandle: 0xFFFFFFFF80003E28	
02646061	190.99192810	[GoodEye]     - IoControlCode: 0x00000000002D1400	
02646062	190.99192810	[GoodEye]     - OutputBufferLength: 0x0000000000000000	
02646063	190.99194336	[GoodEye]     - InoutBufferLength: 0x000000000000000C

02646072	190.99209595	[GoodEye]ZwDeviceIoControlFile Called From 0xFFFFF804DEFDB9B1	
02646073	190.99211121	[GoodEye]     - FileHandle: 0xFFFFFFFF80003E28	
02646074	190.99211121	[GoodEye]     - IoControlCode: 0x000000000007C088	
02646075	190.99211121	[GoodEye]     - OutputBufferLength: 0x0000000000000211	
02646076	190.99211121	[GoodEye]     - InoutBufferLength: 0x0000000000000021	

IRP

BEDaisy checks the IRP's of every single loaded driver. Below is the checks done on dxgkrnl.sys on windows 10-2004. Base address of dxgkrnl.sys is 0xfffff80498f10000.

00042942	92.55983734	[GoodEye]gh_wcsnicmp called from: 0xFFFFF804DEFDD874	
00042943	92.55983734	[GoodEye]     - string1: C:\Windows\System32\drivers\dxgkrnl.sys	
00042944	92.55983734	[GoodEye]     - string2: C:\Windows\System32\drivers\dxgkrnl.sys	
00042945	92.55983734	[GoodEye]     - count: 0x27	
00042946	92.55996704	[GoodEye]MmIsAddressValid Called From: 0xFFFFF804DEFDD8B6	
00042947	92.55996704	[GoodEye]     - NonPaged VirtualAddress: 0xFFFFF80498F10000	// base address of dxgkrnl.sys
00042951	92.56208801	[GoodEye]MmIsAddressValid Called From: 0xFFFFF804DEFE1116	
00042952	92.56209564	[GoodEye]     - NonPaged VirtualAddress: 0xFFFFF8049905E400	// address of DxgkCreateClose
00042953	92.56209564	[GoodEye]MmIsAddressValid Called From: 0xFFFFF804DEFE1116	
00042956	92.56209564	[GoodEye]     - NonPaged VirtualAddress: 0xFFFFF8049905E400	// address of DxgkCreateClose
00042957	92.56209564	[GoodEye]MmIsAddressValid Called From: 0xFFFFF804DEFE1116	
00042980	92.56213379	[GoodEye]     - NonPaged VirtualAddress: 0xFFFFF80498F516A0	// address of DxgkDeviceIoctl
00042981	92.56213379	[GoodEye]MmIsAddressValid Called From: 0xFFFFF804DEFE1116	
00042982	92.56213379	[GoodEye]     - NonPaged VirtualAddress: 0xFFFFF80499059670	// address of DxgkInternalDeviceIoctl

Imports

All import addresses are stored in the .data section of the driver and can easily be changed to hook imported functions.