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import subprocess
import sys
import re
function_intro_re = re.compile(r'^(?P<addr>[0-9a-fA-F]{8}) <(?P<name>[a-zA-Z0-9\._]+)>:$')
insn_re = re.compile(r'^\s+(?P<addr>[0-9a-fA-F]+):\s+(?P<insn>[0-9a-fA-F ]+)\s+\t(?P<op>.*)$')
class Instruction:
def __init__(self, addr, insn, op):
self.addr = long(addr, 16)
self.insn = insn
args = op.split('\t', 1)
self.op = args[0].strip()
if len(args) == 2:
comment = args[1].strip().split(';', 1)
else:
comment = args
self.args = comment[0].strip()
if len(comment) == 2:
self.comment = comment[1].strip()
else:
self.comment = ''
def __repr__(self):
return '<insn %r>' % (self.__dict__)
def literal_branch_target(t):
return ' <' in t
class Function:
def __init__(self, addr, name):
self.name = name
self.addr = long(addr, 16)
self.insns = []
self.calls = []
def __repr__(self):
return '<%s %d instructions>' % (self.name, len(self.insns))
def add_insn(self, insn):
self.insns.append(Instruction(**insn))
def contains_addr(self, addr):
if self.insns:
return addr >= self.addr and addr <= self.insns[-1].addr
else:
return addr == self.addr
def dump(self):
print self.name + ':'
for insn in self.insns:
print ' ', '%04x' % insn.addr + ':', insn.op, insn.args, '\t;', insn.comment
def get_literal_word(self, addr):
for insn in self.insns:
if insn.addr == addr and insn.op == '.word':
w = int(insn.args, 16)
if w & 0x80000000:
w = -(w ^ 0xffffffff) + 1
return w
return None
def analyse(self, prog):
self.stack_guess = None
regs = {}
for insn in self.insns:
# stack adjustment with literal
if insn.op == 'sub' and insn.args.startswith('sp, ') and self.stack_guess is None:
sz = int(insn.args.split('#', 1)[1])
self.stack_guess = sz
# literal pool loads
if insn.op == 'ldr' and ', [pc, #' in insn.args:
reg, offset = insn.args.split(', [pc, #')
offset = int(offset.replace(']', ''))
word = self.get_literal_word(insn.addr + offset + 2)
if word is not None:
regs[reg] = word
if insn.op == 'add' and insn.args.startswith('sp, r') and self.stack_guess is None:
reg = insn.args.split(', ')[1]
if reg in regs:
self.stack_guess = regs[reg]
# static branches
if insn.op[0] == 'b' and literal_branch_target(insn.args):
target = long(insn.args.split(' <', 1)[0], 16)
targetf = prog.function_at_addr(target)
if targetf and targetf != self:
self.calls.append(targetf)
if self.stack_guess is None:
self.stack_guess = 0
def stack_usage(self, hints, warns, prog, depth = 0):
hinted_calls = []
if self.stack_guess:
print ' ' * depth, 'stack:', self.name, self.stack_guess, 'bytes'
our_hints = [h for h in hints if h and h[0] == self.name]
if our_hints:
hints = [h[1:] for h in our_hints]
hinted_calls = [prog.function_by_name(h[0]) for h in hints if h]
else:
if self.name in warns:
print ' WARN: no calls hints for fn-ptr caller', self.name
if self.calls + hinted_calls:
call_usage = max([f.stack_usage(hints, warns, prog, depth + 1) for f in self.calls + hinted_calls])
else:
call_usage = 0
return self.stack_guess + call_usage
class Program:
def __init__(self):
self.functions = []
# sequence of tuples naming a call sequence known to occur
# this allows working out calls through pointers
self.call_hints = []
# function names to warn on if we don't have callees
self.call_warns = set()
def read_elf(self, elf):
current_fn = None
for x in subprocess.Popen(['arm-none-eabi-objdump', '-d', elf],
stdout = subprocess.PIPE).stdout:
x = x.rstrip('\n')
m = function_intro_re.match(x)
if m:
fn = Function(**m.groupdict())
current_fn = fn
self.functions.append(fn)
m = insn_re.match(x)
if m:
assert current_fn
current_fn.add_insn(m.groupdict())
def analyse(self):
for f in self.functions:
f.analyse(self)
def function_by_name(self, name):
fns = [fn for fn in self.functions if fn.name == name]
if len(fns) == 0:
return None
elif len(fns) == 1:
return fns[0]
else:
print 'warn: more than one function named', name
return None
def function_at_addr(self, addr):
for f in self.functions:
if f.addr == addr:
return f
return None
def add_call_hint(self, *seq):
self.call_hints.append(seq)
def add_call_warn(self, fn):
self.call_warns.add(fn)
def measure_stack(self, name):
fn = self.function_by_name(name)
if fn is None:
return 0
return fn.stack_usage(self.call_hints, self.call_warns, self)
_, exe, fn = sys.argv
p = Program()
p.read_elf(exe)
p.analyse()
# calls which indirect through fn ptrs
p.add_call_warn('cf_blockwise_accumulate')
p.add_call_warn('cf_blockwise_accumulate_final')
# hints to resolve those
p.add_call_hint('cf_sha224_update', 'cf_blockwise_accumulate', 'cf_blockwise_accumulate_final', 'sha256_update_block')
p.add_call_hint('cf_sha256_update', 'cf_blockwise_accumulate', 'cf_blockwise_accumulate_final', 'sha256_update_block')
p.add_call_hint('cf_sha384_update', 'cf_blockwise_accumulate', 'cf_blockwise_accumulate_final', 'sha512_update_block')
p.add_call_hint('cf_sha512_update', 'cf_blockwise_accumulate', 'cf_blockwise_accumulate_final', 'sha512_update_block')
p.add_call_hint('cf_norx32_encrypt', 'input', 'cf_blockwise_accumulate', 'cf_blockwise_accumulate_final', 'input_block')
p.add_call_hint('cf_norx32_decrypt', 'input', 'cf_blockwise_accumulate', 'cf_blockwise_accumulate_final', 'input_block')
p.add_call_hint('cf_cbcmac_stream_update', 'cf_blockwise_accumulate', 'cf_blockwise_accumulate_final', 'cbcmac_process')
p.add_call_hint('cf_cmac_stream_update', 'cf_blockwise_accumulate', 'cf_blockwise_accumulate_final', 'cmac_process_final_pad')
p.add_call_hint('cf_cmac_stream_update', 'cf_blockwise_accumulate_final', 'cmac_process')
p.add_call_hint('cf_cmac_stream_update', 'cf_blockwise_accumulate_final', 'cmac_process_final_nopad')
print 'stack', fn, '=', p.measure_stack(fn)
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