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$$ Author: Javier Vicente Vallejo
$$ Twitter: @vallejocc
$$ Web:
$$ $$>a<anti_antidebug_rdtsc.wdbg
$$ This script works in similar way than anti-rdtsc tools that install a driver.
$$ The script enables flag 2 of cr4: TSD Time Stamp Disable. In this way rdtsc is a privileged instruction.
$$ After that, it enables the option for stopping when user mode exception (gflag +sue +soe, gflags 0x20000001).
$$ Then we enable 0xc0000096 -> privileged instruction.
$$ In this way, when rdtsc is executed by an application, an exception will occur and windbg will catch the exception.
$$ In that moment, the script checks the ins code of rdtsc, 0x310f. If it is a rdtsc instruction, it skips the instruction ip = ip+2.
$$ Finally it sets edx = 0, and eax = last_counter+1.
$$ Applications execution rdtsc will see an increment of 1 each rdtsc execution.
$$set rdtsc as priv instruction, then catch exceptions for priv instructions and skip rdtsc(eip=eip+2) and set edx:eax = last rdtsc returned value +1
$$use $t9 for counter
r $t9 = 0
$$rdtsc = privileged instruction
r cr4 = cr4 | 4
$$Stop on exception
!gflag +soe
$$Stop on unhandled user-mode exception
!gflag +sue
$$disable access violation (we have enabled exception in user mode, and access violation will cause lot of exceptions)
sxd av
$$we enable to catch privileged instructions execution (we have converted rdtsc in priv ins with cr4)
$$in this moment we check if it is rdtsc, and in this case, we jump over the instruction and we set eax=0 edx=0
sxe -c ".if((poi(eip)&0x0000ffff)==0x310f){.printf \"rdtsc\r\n\";r eip = eip+2;r eax=@$t9;r edx=0;r $t9=@$t9+1; gh;}" c0000096