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I using x86dbg and am working on unpacking a target. The unpacking stub appears to be using some anti-debugging techniques - most of which I can detour with a plugin.

However, there are a lot of occurrences of rdtsc in the code. The code is being generated / unpacked throughout execution so I cannot simply search for all instances of the instruction.

I have tried running a trace with a condition to break when rdtsc is found but it is simply way to slow and tedious; especially since rdtsc is sometimes used in loops and it isn't as simple as just noping them out since a comparison takes place much later in the stub (it is also hard to identify where due to the excessive junk code.)

Any help would be greatly appreciated,

Thanks.

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there are a few fake rdtsc drivers floating around

or if you have windbg attached in kernel mode you can toggle cr4.TSD bit and catch the exception iirc there is a script floating for that too but a fleeting google didn't land me that now ill link it later

edit anti rdtsc windbg script by vallejocc

here is a small demo

kd> r cr4
cr4=00000699

kd> r cr4 = 69d
kd> r cr4    
cr4=0000069d
kd> g    

 *** Unhandled exception **0xc0000096**, hit in C:\Windows\system32\svchost.exe -k netsvcs:

 *** enter .exr 03C0F78C for the exception record
 ***  enter .cxr 03C0F7A0 for the context
 *** then kb to get the faulting stack

Break instruction exception - code 80000003 (first chance)
ntdll!RtlUnhandledExceptionFilter2+0x2ab:
001b:7743d10d cc              int     3

kd> .exr 03C0F78C
ExceptionAddress: 6dbb1358
   ExceptionCode: c0000096
  ExceptionFlags: 00000000
NumberParameters: 0

kd> .cxr 03C0F7A0
eax=1d218944 ebx=00000000 ecx=1ee17334 edx=0000021a esi=042708e0 edi=00000000
eip=6dbb1358 esp=03c0fa84 ebp=03c0fb08 iopl=0         nv up ei pl zr na pe nc
cs=001b  ss=0023  ds=0023  es=0023  fs=003b  gs=0000             efl=00010246
001b:6dbb1358 0f31            rdtsc  <<<<<<
kd> kb
  *** Stack trace for last set context - .thread/.cxr resets it
 # ChildEBP RetAddr  Args to Child              
WARNING: Frame IP not in any known module. Following frames may be wrong.
00 03c0fb08 6dbb150f 04270808 002767b0 03c0fb3c 0x6dbb1358
  • Thanks for this response. I think I am going to go the driver route at this point and if it causes some head-aches I may escalate to a kernel mode debugger. Thanks. I am looking at using this driver here deroko.phearless.org/ring0.html – Jeremy Mar 3 '18 at 20:44
  • i edited the post to include the antirdtsc winsbg script's link derokos fakerdtsc is fine – blabb Mar 4 '18 at 7:29

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