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Timekeeping In VMware Virtual Machines

Timekeeping In VMware Virtual Machines
Posted Sep 2, 2015
Authored by B3mB4m

The rdtsc (Read Time-Stamp Counter) instruction is used to determine how many CPU ticks took place since the processor was reset. It is commonly used as a timing defense (anti-debugging technique). This is assembler that demonstrates this functionality.

tags | shellcode
SHA-256 | 9bfdca451768b6da9c782a6982027fffa643051d6ce5acb5bcfddea28faba675

Timekeeping In VMware Virtual Machines

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;Timekeeping in VMware Virtual Machines
;Description

;The rdtsc (Read Time-Stamp Counter) instruction is used to determine how many CPU ticks took place since the processor was reset.
;It is commonly used as a timing defense (anti-debugging technique).

;Coded By B3mB4m
;Concat : b3mb4m@tuta.io

extern printf
section .text
global main
main:
mov ebx,0x0A

loop:
push ebp ;Set stack frame
mov ebp,esp
xor edi,edi
xor ecx,ecx

rdtsc
add edi,eax
rdtsc
sub eax,edi

push eax
add [total],eax

push dword printformat
call printf
add esp, 8

mov esp, ebp
pop ebp

dec ebx
jnz loop
jz average

average:
xor eax,eax
xor edx,edx
mov eax,[total]
mov ecx,0x0A
div ecx

;Divinded : EDX:EAX
;Quotient : EAX
;Remainder : EDX

push eax
push dword printformat2
call printf


cmp eax,0xc8
jg vm
jl notvm


vm:
xor ebx,ebx
push ebx
push vmdetect
call printf
jmp exit

notvm:
xor ebx,ebx
push ebx
push vmnotpresent
call printf
jmp exit

exit:

xor eax,eax
inc al
int 0x80


section .data
vmdetect: db "VM Detected", 10, 0
vmnotpresent db "VM not present", 10, 0
printformat: db "RDTSC difference : %d", 10, 0
printformat2: db "RDTSC average : %d ", 10, 0
total: dd 0



;nasm -f elf testvm.asm
;gcc -m32 -o testvm testvm.o
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