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devtools: Add security check for separate_code
Check that sections are appropriately separated in virtual memory, based on their (expected) permissions. This checks for missing -Wl,-z,separate-code and potentially other problems. Co-authored-by: fanquake <fanquake@gmail.com>
This commit is contained in:
Wladimir J. van der Laan
fanquake
parent
2e9e6377f1
commit
65d0f1a533
@ -40,25 +40,48 @@ def get_ELF_program_headers(executable):
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stdout = run_command([READELF_CMD, '-l', '-W', executable])
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in_headers = False
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count = 0
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headers = []
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for line in stdout.splitlines():
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if line.startswith('Program Headers:'):
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in_headers = True
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count = 0
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if line == '':
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in_headers = False
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if in_headers:
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if count == 1: # header line
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ofs_typ = line.find('Type')
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ofs_offset = line.find('Offset')
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ofs_flags = line.find('Flg')
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ofs_align = line.find('Align')
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if ofs_typ == -1 or ofs_offset == -1 or ofs_flags == -1 or ofs_align == -1:
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header = [x.strip() for x in line.split()]
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ofs_typ = header.index('Type')
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ofs_flags = header.index('Flg')
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# assert readelf output is what we expect
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if ofs_typ == -1 or ofs_flags == -1:
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raise ValueError('Cannot parse elfread -lW output')
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elif count > 1:
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typ = line[ofs_typ:ofs_offset].rstrip()
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flags = line[ofs_flags:ofs_align].rstrip()
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headers.append((typ, flags))
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splitline = [x.strip() for x in line.split()]
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typ = splitline[ofs_typ]
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if not typ.startswith('[R'): # skip [Requesting ...]
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splitline = [x.strip() for x in line.split()]
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flags = splitline[ofs_flags]
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# check for 'R', ' E'
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if splitline[ofs_flags + 1] is 'E':
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flags += ' E'
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headers.append((typ, flags, []))
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count += 1
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if line.startswith(' Section to Segment mapping:'):
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in_mapping = True
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count = 0
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if line == '':
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in_mapping = False
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if in_mapping:
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if count == 1: # header line
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ofs_segment = line.find('Segment')
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ofs_sections = line.find('Sections...')
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if ofs_segment == -1 or ofs_sections == -1:
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raise ValueError('Cannot parse elfread -lW output')
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elif count > 1:
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segment = int(line[ofs_segment:ofs_sections].strip())
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sections = line[ofs_sections:].strip().split()
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headers[segment][2].extend(sections)
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count += 1
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return headers
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@ -68,7 +91,7 @@ def check_ELF_NX(executable) -> bool:
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'''
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have_wx = False
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have_gnu_stack = False
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for (typ, flags) in get_ELF_program_headers(executable):
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for (typ, flags, _) in get_ELF_program_headers(executable):
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if typ == 'GNU_STACK':
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have_gnu_stack = True
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if 'W' in flags and 'E' in flags: # section is both writable and executable
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@ -82,7 +105,7 @@ def check_ELF_RELRO(executable) -> bool:
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Dynamic section must have BIND_NOW flag
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'''
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have_gnu_relro = False
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for (typ, flags) in get_ELF_program_headers(executable):
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for (typ, flags, _) in get_ELF_program_headers(executable):
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# Note: not checking flags == 'R': here as linkers set the permission differently
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# This does not affect security: the permission flags of the GNU_RELRO program
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# header are ignored, the PT_LOAD header determines the effective permissions.
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@ -113,6 +136,62 @@ def check_ELF_Canary(executable) -> bool:
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ok = True
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return ok
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def check_ELF_separate_code(executable):
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'''
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Check that sections are appropriately separated in virtual memory,
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based on their permissions. This checks for missing -Wl,-z,separate-code
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and potentially other problems.
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'''
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EXPECTED_FLAGS = {
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# Read + execute
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'.init': 'R E',
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'.plt': 'R E',
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'.plt.got': 'R E',
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'.plt.sec': 'R E',
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'.text': 'R E',
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'.fini': 'R E',
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# Read-only data
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'.interp': 'R',
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'.note.gnu.property': 'R',
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'.note.gnu.build-id': 'R',
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'.note.ABI-tag': 'R',
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'.gnu.hash': 'R',
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'.dynsym': 'R',
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'.dynstr': 'R',
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'.gnu.version': 'R',
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'.gnu.version_r': 'R',
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'.rela.dyn': 'R',
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'.rela.plt': 'R',
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'.rodata': 'R',
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'.eh_frame_hdr': 'R',
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'.eh_frame': 'R',
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'.qtmetadata': 'R',
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'.gcc_except_table': 'R',
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'.stapsdt.base': 'R',
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# Writable data
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'.init_array': 'RW',
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'.fini_array': 'RW',
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'.dynamic': 'RW',
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'.got': 'RW',
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'.data': 'RW',
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'.bss': 'RW',
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}
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# For all LOAD program headers get mapping to the list of sections,
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# and for each section, remember the flags of the associated program header.
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flags_per_section = {}
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for (typ, flags, sections) in get_ELF_program_headers(executable):
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if typ == 'LOAD':
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for section in sections:
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assert(section not in flags_per_section)
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flags_per_section[section] = flags
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# Spot-check ELF LOAD program header flags per section
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# If these sections exist, check them against the expected R/W/E flags
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for (section, flags) in flags_per_section.items():
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if section in EXPECTED_FLAGS:
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if EXPECTED_FLAGS[section] != flags:
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return False
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return True
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def get_PE_dll_characteristics(executable) -> int:
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'''Get PE DllCharacteristics bits'''
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stdout = run_command([OBJDUMP_CMD, '-x', executable])
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@ -225,7 +304,8 @@ CHECKS = {
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('PIE', check_ELF_PIE),
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('NX', check_ELF_NX),
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('RELRO', check_ELF_RELRO),
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('Canary', check_ELF_Canary)
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('Canary', check_ELF_Canary),
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('separate_code', check_ELF_separate_code),
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],
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'PE': [
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('DYNAMIC_BASE', check_PE_DYNAMIC_BASE),
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@ -31,15 +31,17 @@ class TestSecurityChecks(unittest.TestCase):
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cc = 'gcc'
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write_testcode(source)
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self.assertEqual(call_security_check(cc, source, executable, ['-Wl,-zexecstack','-fno-stack-protector','-Wl,-znorelro','-no-pie','-fno-PIE']),
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self.assertEqual(call_security_check(cc, source, executable, ['-Wl,-zexecstack','-fno-stack-protector','-Wl,-znorelro','-no-pie','-fno-PIE', '-Wl,-z,separate-code']),
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(1, executable+': failed PIE NX RELRO Canary'))
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self.assertEqual(call_security_check(cc, source, executable, ['-Wl,-znoexecstack','-fno-stack-protector','-Wl,-znorelro','-no-pie','-fno-PIE']),
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self.assertEqual(call_security_check(cc, source, executable, ['-Wl,-znoexecstack','-fno-stack-protector','-Wl,-znorelro','-no-pie','-fno-PIE', '-Wl,-z,separate-code']),
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(1, executable+': failed PIE RELRO Canary'))
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self.assertEqual(call_security_check(cc, source, executable, ['-Wl,-znoexecstack','-fstack-protector-all','-Wl,-znorelro','-no-pie','-fno-PIE']),
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self.assertEqual(call_security_check(cc, source, executable, ['-Wl,-znoexecstack','-fstack-protector-all','-Wl,-znorelro','-no-pie','-fno-PIE', '-Wl,-z,separate-code']),
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(1, executable+': failed PIE RELRO'))
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self.assertEqual(call_security_check(cc, source, executable, ['-Wl,-znoexecstack','-fstack-protector-all','-Wl,-znorelro','-pie','-fPIE']),
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self.assertEqual(call_security_check(cc, source, executable, ['-Wl,-znoexecstack','-fstack-protector-all','-Wl,-znorelro','-pie','-fPIE', '-Wl,-z,separate-code']),
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(1, executable+': failed RELRO'))
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self.assertEqual(call_security_check(cc, source, executable, ['-Wl,-znoexecstack','-fstack-protector-all','-Wl,-zrelro','-Wl,-z,now','-pie','-fPIE']),
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self.assertEqual(call_security_check(cc, source, executable, ['-Wl,-znoexecstack','-fstack-protector-all','-Wl,-zrelro','-Wl,-z,now','-pie','-fPIE', '-Wl,-z,noseparate-code']),
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(1, executable+': failed separate_code'))
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self.assertEqual(call_security_check(cc, source, executable, ['-Wl,-znoexecstack','-fstack-protector-all','-Wl,-zrelro','-Wl,-z,now','-pie','-fPIE', '-Wl,-z,separate-code']),
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(0, ''))
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def test_PE(self):
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