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#!/usr/bin/env python3
# Copyright (c) 2015-2020 The Bitcoin Core developers
# Distributed under the MIT software license, see the accompanying
# file COPYING or http://www.opensource.org/licenses/mit-license.php.
'''
Perform basic security checks on a series of executables.
Exit status will be 0 if successful, and the program will be silent.
Otherwise the exit status will be 1 and it will log which executables failed which checks.
'''
import sys
from typing import List
import lief #type:ignore
def check_ELF_RELRO(binary) -> bool:
'''
Check for read-only relocations.
GNU_RELRO program header must exist
Dynamic section must have BIND_NOW flag
'''
have_gnu_relro = False
for segment in binary.segments:
# Note: not checking p_flags == PF_R: here as linkers set the permission differently
# This does not affect security: the permission flags of the GNU_RELRO program
# header are ignored, the PT_LOAD header determines the effective permissions.
# However, the dynamic linker need to write to this area so these are RW.
# Glibc itself takes care of mprotecting this area R after relocations are finished.
# See also https://marc.info/?l=binutils&m=1498883354122353
if segment.type == lief.ELF.SEGMENT_TYPES.GNU_RELRO:
have_gnu_relro = True
have_bindnow = False
try:
flags = binary.get(lief.ELF.DYNAMIC_TAGS.FLAGS)
if flags.value & lief.ELF.DYNAMIC_FLAGS.BIND_NOW:
have_bindnow = True
except:
have_bindnow = False
return have_gnu_relro and have_bindnow
def check_ELF_Canary(binary) -> bool:
'''
Check for use of stack canary
'''
return binary.has_symbol('__stack_chk_fail')
def check_ELF_separate_code(binary):
'''
Check that sections are appropriately separated in virtual memory,
based on their permissions. This checks for missing -Wl,-z,separate-code
and potentially other problems.
'''
R = lief.ELF.SEGMENT_FLAGS.R
W = lief.ELF.SEGMENT_FLAGS.W
E = lief.ELF.SEGMENT_FLAGS.X
EXPECTED_FLAGS = {
# Read + execute
'.init': R | E,
'.plt': R | E,
'.plt.got': R | E,
'.plt.sec': R | E,
'.text': R | E,
'.fini': R | E,
# Read-only data
'.interp': R,
'.note.gnu.property': R,
'.note.gnu.build-id': R,
'.note.ABI-tag': R,
'.gnu.hash': R,
'.dynsym': R,
'.dynstr': R,
'.gnu.version': R,
'.gnu.version_r': R,
'.rela.dyn': R,
'.rela.plt': R,
'.rodata': R,
'.eh_frame_hdr': R,
'.eh_frame': R,
'.qtmetadata': R,
'.gcc_except_table': R,
'.stapsdt.base': R,
# Writable data
'.init_array': R | W,
'.fini_array': R | W,
'.dynamic': R | W,
'.got': R | W,
'.data': R | W,
'.bss': R | W,
}
if binary.header.machine_type == lief.ELF.ARCH.PPC64:
# .plt is RW on ppc64 even with separate-code
EXPECTED_FLAGS['.plt'] = R | W
# For all LOAD program headers get mapping to the list of sections,
# and for each section, remember the flags of the associated program header.
flags_per_section = {}
for segment in binary.segments:
if segment.type == lief.ELF.SEGMENT_TYPES.LOAD:
for section in segment.sections:
assert(section.name not in flags_per_section)
flags_per_section[section.name] = segment.flags
# Spot-check ELF LOAD program header flags per section
# If these sections exist, check them against the expected R/W/E flags
for (section, flags) in flags_per_section.items():
if section in EXPECTED_FLAGS:
if int(EXPECTED_FLAGS[section]) != int(flags):
return False
return True
def check_PE_DYNAMIC_BASE(binary) -> bool:
'''PIE: DllCharacteristics bit 0x40 signifies dynamicbase (ASLR)'''
return lief.PE.DLL_CHARACTERISTICS.DYNAMIC_BASE in binary.optional_header.dll_characteristics_lists
# 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(binary) -> bool:
'''PIE: DllCharacteristics bit 0x20 signifies high-entropy ASLR'''
return lief.PE.DLL_CHARACTERISTICS.HIGH_ENTROPY_VA in binary.optional_header.dll_characteristics_lists
def check_PE_RELOC_SECTION(binary) -> bool:
'''Check for a reloc section. This is required for functional ASLR.'''
return binary.has_relocations
def check_MACHO_NOUNDEFS(binary) -> bool:
'''
Check for no undefined references.
'''
return binary.header.has(lief.MachO.HEADER_FLAGS.NOUNDEFS)
def check_MACHO_LAZY_BINDINGS(binary) -> bool:
'''
Check for no lazy bindings.
We don't use or check for MH_BINDATLOAD. See #18295.
'''
return binary.dyld_info.lazy_bind == (0,0)
def check_MACHO_Canary(binary) -> bool:
'''
Check for use of stack canary
'''
return binary.has_symbol('___stack_chk_fail')
def check_PIE(binary) -> bool:
'''
Check for position independent executable (PIE),
allowing for address space randomization.
'''
return binary.is_pie
def check_NX(binary) -> bool:
'''
Check for no stack execution
'''
return binary.has_nx
def check_control_flow(binary) -> bool:
'''
Check for control flow instrumentation
'''
content = binary.get_content_from_virtual_address(binary.entrypoint, 4, lief.Binary.VA_TYPES.AUTO)
if content == [243, 15, 30, 250]: # endbr64
return True
return False
CHECKS = {
'ELF': [
('PIE', check_PIE),
('NX', check_NX),
('RELRO', check_ELF_RELRO),
('Canary', check_ELF_Canary),
('separate_code', check_ELF_separate_code),
],
'PE': [
('PIE', check_PIE),
('DYNAMIC_BASE', check_PE_DYNAMIC_BASE),
('HIGH_ENTROPY_VA', check_PE_HIGH_ENTROPY_VA),
('NX', check_NX),
('RELOC_SECTION', check_PE_RELOC_SECTION)
],
'MACHO': [
('PIE', check_PIE),
('NOUNDEFS', check_MACHO_NOUNDEFS),
('NX', check_NX),
('LAZY_BINDINGS', check_MACHO_LAZY_BINDINGS),
('Canary', check_MACHO_Canary),
('CONTROL_FLOW', check_control_flow),
]
}
if __name__ == '__main__':
retval: int = 0
for filename in sys.argv[1:]:
try:
binary = lief.parse(filename)
etype = binary.format.name
if etype == lief.EXE_FORMATS.UNKNOWN:
print(f'{filename}: unknown executable format')
retval = 1
continue
failed: List[str] = []
for (name, func) in CHECKS[etype]:
if not func(binary):
failed.append(name)
if failed:
print(f'{filename}: failed {" ".join(failed)}')
retval = 1
except IOError:
print(f'{filename}: cannot open')
retval = 1
sys.exit(retval)
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