devtools: Check for high-entropy ASLR in 64-bit PE executables

check_PE_PIE only checked for DYNAMIC_BASE, this is not enough
for (secure) ASLR on 64-bit.
This commit is contained in:
Wladimir J. van der Laan 2016-06-23 16:52:12 +02:00
parent 08338942b5
commit 9a75d29b6f

View file

@ -12,6 +12,7 @@ import os
READELF_CMD = os.getenv('READELF', '/usr/bin/readelf') READELF_CMD = os.getenv('READELF', '/usr/bin/readelf')
OBJDUMP_CMD = os.getenv('OBJDUMP', '/usr/bin/objdump') OBJDUMP_CMD = os.getenv('OBJDUMP', '/usr/bin/objdump')
NONFATAL = {'HIGH_ENTROPY_VA'} # checks which are non-fatal for now but only generate a warning
def check_ELF_PIE(executable): def check_ELF_PIE(executable):
''' '''
@ -114,26 +115,50 @@ def check_ELF_Canary(executable):
def get_PE_dll_characteristics(executable): def get_PE_dll_characteristics(executable):
''' '''
Get PE DllCharacteristics bits Get PE DllCharacteristics bits.
Returns a tuple (arch,bits) where arch is 'i386:x86-64' or 'i386'
and bits is the DllCharacteristics value.
''' '''
p = subprocess.Popen([OBJDUMP_CMD, '-x', executable], stdout=subprocess.PIPE, stderr=subprocess.PIPE, stdin=subprocess.PIPE) p = subprocess.Popen([OBJDUMP_CMD, '-x', executable], stdout=subprocess.PIPE, stderr=subprocess.PIPE, stdin=subprocess.PIPE)
(stdout, stderr) = p.communicate() (stdout, stderr) = p.communicate()
if p.returncode: if p.returncode:
raise IOError('Error opening file') raise IOError('Error opening file')
arch = ''
bits = 0
for line in stdout.split('\n'): for line in stdout.split('\n'):
tokens = line.split() tokens = line.split()
if len(tokens)>=2 and tokens[0] == 'architecture:':
arch = tokens[1].rstrip(',')
if len(tokens)>=2 and tokens[0] == 'DllCharacteristics': if len(tokens)>=2 and tokens[0] == 'DllCharacteristics':
return int(tokens[1],16) bits = int(tokens[1],16)
return 0 return (arch,bits)
IMAGE_DLL_CHARACTERISTICS_HIGH_ENTROPY_VA = 0x0020
IMAGE_DLL_CHARACTERISTICS_DYNAMIC_BASE = 0x0040
IMAGE_DLL_CHARACTERISTICS_NX_COMPAT = 0x0100
def check_PE_PIE(executable): def check_PE_DYNAMIC_BASE(executable):
'''PIE: DllCharacteristics bit 0x40 signifies dynamicbase (ASLR)''' '''PIE: DllCharacteristics bit 0x40 signifies dynamicbase (ASLR)'''
return bool(get_PE_dll_characteristics(executable) & 0x40) (arch,bits) = get_PE_dll_characteristics(executable)
reqbits = IMAGE_DLL_CHARACTERISTICS_DYNAMIC_BASE
return (bits & reqbits) == reqbits
# On 64 bit, must support high-entropy 64-bit address space layout randomization in addition to DYNAMIC_BASE
# to have secure ASLR.
def check_PE_HIGH_ENTROPY_VA(executable):
'''PIE: DllCharacteristics bit 0x20 signifies high-entropy ASLR'''
(arch,bits) = get_PE_dll_characteristics(executable)
if arch == 'i386:x86-64':
reqbits = IMAGE_DLL_CHARACTERISTICS_HIGH_ENTROPY_VA
else: # Unnecessary on 32-bit
assert(arch == 'i386')
reqbits = 0
return (bits & reqbits) == reqbits
def check_PE_NX(executable): def check_PE_NX(executable):
'''NX: DllCharacteristics bit 0x100 signifies nxcompat (DEP)''' '''NX: DllCharacteristics bit 0x100 signifies nxcompat (DEP)'''
return bool(get_PE_dll_characteristics(executable) & 0x100) (arch,bits) = get_PE_dll_characteristics(executable)
return (bits & IMAGE_DLL_CHARACTERISTICS_NX_COMPAT) == IMAGE_DLL_CHARACTERISTICS_NX_COMPAT
CHECKS = { CHECKS = {
'ELF': [ 'ELF': [
@ -143,7 +168,8 @@ CHECKS = {
('Canary', check_ELF_Canary) ('Canary', check_ELF_Canary)
], ],
'PE': [ 'PE': [
('PIE', check_PE_PIE), ('DYNAMIC_BASE', check_PE_DYNAMIC_BASE),
('HIGH_ENTROPY_VA', check_PE_HIGH_ENTROPY_VA),
('NX', check_PE_NX) ('NX', check_PE_NX)
] ]
} }
@ -168,12 +194,18 @@ if __name__ == '__main__':
continue continue
failed = [] failed = []
warning = []
for (name, func) in CHECKS[etype]: for (name, func) in CHECKS[etype]:
if not func(filename): if not func(filename):
if name in NONFATAL:
warning.append(name)
else:
failed.append(name) failed.append(name)
if failed: if failed:
print('%s: failed %s' % (filename, ' '.join(failed))) print('%s: failed %s' % (filename, ' '.join(failed)))
retval = 1 retval = 1
if warning:
print('%s: warning %s' % (filename, ' '.join(warning)))
except IOError: except IOError:
print('%s: cannot open' % filename) print('%s: cannot open' % filename)
retval = 1 retval = 1