Emulation in the Analysis Loop
Aside from manual emulation, automatic emulation is also possible in the analysis loop.
For example, the aaaa command performs the ESIL emulation stage, among others.
To disable or enable ESIL analysis, set the anal.esil configuration variable.
Furthermore, emu.write allows the ESIL VM to modify memory. However, enabling it
might be quite dangerous, especially when analyzing malware. Regardless, it is
still sometimes required, particularly when deobfuscating or unpacking code. To
show the emulation process, you can set asm.emu variable which will show
calculated register and memory values as comments in the disassembly:
[0x00001660]> e asm.emu=true
[0x00001660]> pdf
. (fcn) fcn.00001660 40
| fcn.00001660 ();
| ; CALL XREF from 0x00001713 (entry2.fini)
| 0x00001660 lea rdi, obj.__progname ; 0x207220 ; rdi=0x207220 -> 0x464c457f
| 0x00001667 push rbp ; rsp=0xfffffffffffffff8
| 0x00001668 lea rax, obj.__progname ; 0x207220 ; rax=0x207220 -> 0x464c457f
| 0x0000166f cmp rax, rdi ; zf=0x1 -> 0x2464c45 ; cf=0x0 ; pf=0x1 -> 0x2464c45 ; sf=0x0 ; of=0x0
| 0x00001672 mov rbp, rsp ; rbp=0xfffffffffffffff8
| .-< 0x00001675 je 0x1690 ; rip=0x1690 -> 0x1f0fc35d ; likely
| | 0x00001677 mov rax, qword [reloc._ITM_deregisterTMCloneTable] ; [0x206fd8:8]=0 ; rax=0x0
| | 0x0000167e test rax, rax ; zf=0x1 -> 0x2464c45 ; pf=0x1 -> 0x2464c45 ; sf=0x0 ; cf=0x0 ; of=0x0
|.--< 0x00001681 je 0x1690 ; rip=0x1690 -> 0x1f0fc35d ; likely
||| 0x00001683 pop rbp ; rbp=0xffffffffffffffff -> 0x4c457fff ; rsp=0x0
||| 0x00001684 jmp rax ; rip=0x0 ..
|``-> 0x00001690 pop rbp ; rbp=0x10102464c457f ; rsp=0x8 -> 0x464c457f
` 0x00001691 ret ; rip=0x0 ; rsp=0x10 -> 0x3e0003
Note the comments containing likely, which indicate conditional jumps likely to be taken by ESIL emulation.
Apart from the basic ESIL VM setup, you can change its behavior with other options located in the emu. and esil. configuration namespaces.
Debugging with ESIL
The debugger APIs can be configured to use different backends, to communicate with a local or remote GDB server, use the native debugger, a specific virtualization or emulation engine like Unicorn or BOCHS, but there's also an ESIL backend.
[0x00000000]> dL
0 --- bf LGPL3
1 --- bochs LGPL3
2 --- esil LGPL3
3 --- evm LGPL3
4 --- gdb LGPL3
5 --- io MIT
6 dbg native LGPL3
7 --- null MIT
8 --- qnx LGPL3
9 --- rap LGPL3
[0x00000000]> dL esil
[0x00000000]>
After this command, you can use any of the d sub-commands to change register values, step or skip instructions, set breakpoints, etc. but using the internal emulation logic of ESIL.