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# Source:
# https://github.com/zcutlip/bowcaster/blob/master/src/bowcaster/encoders/mips.py
#
# Copyright (c) 2013 Zachary Cutlip <uid000@gmail.com>,
# 2013 Tactical Network Solutions, LLC
#
#
# Permission is hereby granted, free of charge, to any person obtaining a copy of
# this software and associated documentation files (the "Software"), to deal in
# the Software without restriction, including without limitation the rights to
# use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies
# of the Software, and to permit persons to whom the Software is furnished to do
# so, subject to the following conditions:
#
# The above copyright notice and this permission notice shall be included in all
# copies or substantial portions of the Software.
#
# THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
# IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
# FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
# AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
# LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
# OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
# SOFTWARE.
from __future__ import absolute_import
from __future__ import division
import six
from pwnlib import asm
from pwnlib import shellcraft
from pwnlib.context import context
from pwnlib.encoders.encoder import Encoder
from pwnlib.util.fiddling import xor_key
decoders = {
'little': b''.join([
b'SIZ2SIZ1\x0e\x24', # li t6,-5
b'\x27\x70\xc0\x01', # nor t6,t6,zero
b'\xa3\xff\x0b\x24', # li t3,-93
b'\x26\x40\xce\x01', # xor t0,t6,t6
b'\xff\xff\x08\x21', # addi t0,t0,-1
b'\xff\xff\x10\x05', # bltzal t0,14 <next>
b'\x82\x82\x08\x28', # slti t0,zero,-32126
b'\xe0\xff\xfd\x23', # addi sp,ra,-32
b'\x27\x58\x60\x01', # nor t3,t3,zero
b'\x21\xc8\xeb\x03', # addu t9,ra,t3
b'\x82\x82\x17\x28', # slti s7,zero,-32126
b'\xfc\xff\x31\x8f', # lw s1,-4(t9)
b'\xfb\xff\x0c\x24', # li t4,-5
b'\x27\x60\x80\x01', # nor t4,t4,zero
b'\xfd\xff\x8f\x21', # addi t7,t4,-3
b'\xfc\xff\x28\x8f', # lw t0,-4(t9)
b'\x21\xb8\xef\x02', # addu s7,s7,t7
b'\x26\x18\x11\x01', # xor v1,t0,s1
b'\x2b\xf0\xee\x02', # sltu s8,s7,t6
b'\xfc\xff\x23\xaf', # sw v1,-4(t9)
b'\xfa\xff\x1e\x14', # bne zero,s8,3c <loop>
b'\x21\xc8\x2c\x03', # addu t9,t9,t4
b'\xfd\xff\x86\x21', # addi a2,t4,-3
b'\xf8\xff\xa6\xaf', # sw a2,-8(sp)
b'\x26\x28\xce\x01', # xor a1,t6,t6
b'\xfc\xff\xa5\xaf', # sw a1,-4(sp)
b'\xf8\xff\xa4\x27', # addiu a0,sp,-8
b'\x46\x10\x02\x24', # li v0,4166
b'\x0c\x54\x4a\x01' # syscall 0x52950
]),
'big': b''.join([
b'\x24\x0eSIZ1SIZ2', # li t6,-5
b'\x01\xc0\x70\x27', # nor t6,t6,zero
b'\x24\x0b\xff\xa3', # li t3,-93
b'\x01\xce\x40\x26', # xor t0,t6,t6
b'\x21\x08\xff\xff', # addi t0,t0,-1
b'\x05\x10\xff\xff', # bltzal t0,14 <next>
b'\x28\x08\x82\x82', # slti t0,zero,-32126
b'\x23\xfd\xff\xe0', # addi sp,ra,-32
b'\x01\x60\x58\x27', # nor t3,t3,zero
b'\x03\xeb\xc8\x21', # addu t9,ra,t3
b'\x28\x17\x82\x82', # slti s7,zero,-32126
b'\x8f\x31\xff\xfc', # lw s1,-4(t9)
b'\x24\x0c\xff\xfb', # li t4,-5
b'\x01\x80\x60\x27', # nor t4,t4,zero
b'\x21\x8f\xff\xfd', # addi t7,t4,-3
b'\x8f\x28\xff\xfc', # lw t0,-4(t9)
b'\x02\xef\xb8\x21', # addu s7,s7,t7
b'\x01\x11\x18\x26', # xor v1,t0,s1
b'\x02\xee\xf0\x2b', # sltu s8,s7,t6
b'\xaf\x23\xff\xfc', # sw v1,-4(t9)
b'\x14\x1e\xff\xfa', # bne zero,s8,3c <loop>
b'\x03\x2c\xc8\x21', # addu t9,t9,t4
b'\x21\x86\xff\xfd', # addi a2,t4,-3
b'\xaf\xa6\xff\xf8', # sw a2,-8(sp)
b'\x01\xce\x28\x26', # xor a1,t6,t6
b'\xaf\xa5\xff\xfc', # sw a1,-4(sp)
b'\x27\xa4\xff\xf8', # addiu a0,sp,-8
b'\x24\x02\x10\x46', # li v0,4166
b'\x01\x4a\x54\x0c' # syscall 0x52950
])
}
class MipsXorEncoder(Encoder):
r"""Generates an XOR decoder for MIPS.
>>> context.clear(arch='mips')
>>> shellcode = asm(shellcraft.sh())
>>> avoid = b'/bin/sh\x00'
>>> encoded = pwnlib.encoders.mips.xor.encode(shellcode, avoid)
>>> assert not any(c in encoded for c in avoid)
>>> p = run_shellcode(encoded)
>>> p.sendline(b'echo hello; exit')
>>> p.recvline()
b'hello\n'
"""
arch = 'mips'
blacklist = cannot_avoid = set(b''.join(v for v in decoders.values()))
def __call__(self, raw_bytes, avoid, pcreg=''):
assert 0 == len(raw_bytes) % context.bytes, "Payload is not aligned"
size = (len(raw_bytes) // 4) + 1
assert size < 0x10000, "Payload is too long"
size = size ^ 0xffff
sizelo = size & 0xff
sizehi = size >> 8
decoder = decoders[context.endian]
decoder = decoder.replace(b'SIZ1', six.int2byte(sizehi))
decoder = decoder.replace(b'SIZ2', six.int2byte(sizelo))
key, data = xor_key(raw_bytes, avoid=avoid)
return decoder + key + data
encode = MipsXorEncoder()
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