377 lines
14 KiB
Python
377 lines
14 KiB
Python
#!/usr/bin/python3
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# Examine the crash files saved by apport to attempt to determine the cause
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# of a segfault. Currently very very simplistic, and only finds commonly
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# understood situations for x86/x86_64.
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#
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# Copyright 2009-2010 Canonical, Ltd.
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# Author: Kees Cook <kees@ubuntu.com>
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#
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# This program is free software; you can redistribute it and/or modify it
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# under the terms of the GNU General Public License as published by the
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# Free Software Foundation; either version 2 of the License, or (at your
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# option) any later version. See http://www.gnu.org/copyleft/gpl.html for
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# the full text of the license.
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import sys, re, logging, io
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class ParseSegv(object):
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def __init__(self, registers, disassembly, maps, debug=False):
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if debug:
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if sys.version > '3':
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logging.basicConfig(level=logging.DEBUG,
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stream=io.TextIOWrapper(sys.stderr, encoding='UTF-8'))
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else:
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logging.basicConfig(level=logging.DEBUG, stream=sys.stderr)
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self.regs = self.parse_regs(registers)
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self.sp = None
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for reg in ['rsp', 'esp']:
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if reg in self.regs:
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self.sp = self.regs[reg]
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self.line, self.pc, self.insn, self.src, self.dest = \
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self.parse_disassembly(disassembly)
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self.stack_vma = None
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self.maps = self.parse_maps(maps)
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def find_vma(self, addr):
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for vma in self.maps:
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if addr >= vma['start'] and addr < vma['end']:
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return vma
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return None
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def parse_maps(self, maps_str):
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maps = []
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for line in maps_str.splitlines():
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items = line.strip().split()
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try:
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span, perms, bits, dev = items[0:4]
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except Exception:
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raise ValueError('Cannot parse maps line: %s' % (line.strip()))
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if len(items) == 5:
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name = None
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else:
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name = items[5]
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start, end = [int(x, 16) for x in span.split('-')]
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if name == '[stack]':
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self.stack_vma = len(maps)
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maps.append({'start': start, 'end': end, 'perms': perms, 'name': name})
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logging.debug('start: %s, end: %s, perms: %s, name: %s', start, end, perms, name)
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return maps
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def parse_regs(self, reg_str):
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regs = dict()
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for line in reg_str.splitlines():
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reg, hexvalue = line.split()[0:2]
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regs[reg] = int(hexvalue, 16)
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logging.debug('%s:0x%08x', reg, regs[reg])
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return regs
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def parse_disassembly(self, disassembly):
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if not self.regs:
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raise ValueError('Registers not loaded yet!?')
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lines = disassembly.splitlines()
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# Throw away possible 'Dump' gdb report line
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if len(lines) > 0 and lines[0].startswith('Dump'):
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lines.pop(0)
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if len(lines) < 1:
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raise ValueError('Failed to load empty disassembly')
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line = lines[0].strip()
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# Drop GDB 7.1's leading $pc mark
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if line.startswith('=>'):
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line = line[2:].strip()
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logging.debug(line)
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pc_str = line.split()[0]
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if pc_str.startswith('0x'):
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pc = int(pc_str.split(':')[0], 16)
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else:
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# Could not identify this instruction line
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raise ValueError('Could not parse PC "%s" from disassembly line: %s' % (pc_str, line))
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logging.debug('pc: 0x%08x', pc)
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full_insn_str = line.split(':', 1)[1].strip()
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# Handle invalid memory
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if 'Cannot access memory at address' in full_insn_str or (full_insn_str == '' and len(lines) == 1):
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return line, pc, None, None, None
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# Handle wrapped lines
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if full_insn_str == '' and lines[1].startswith(' '):
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line = line + ' ' + lines[1].strip()
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full_insn_str = line.split(':', 1)[1].strip()
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insn_parts = full_insn_str.split()
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# Drop call target names "call 0xb7a805af <_Unwind_Find_FDE@plt+111>"
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if insn_parts[-1].endswith('>') and insn_parts[-1].startswith('<'):
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insn_parts.pop(-1)
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# Attempt to find arguments
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args_str = ''
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if len(insn_parts) > 1:
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args_str = insn_parts.pop(-1)
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# Assume remainder is the insn itself
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insn = ' '.join(insn_parts)
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logging.debug('insn: %s', insn)
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args = []
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src = None
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dest = None
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if args_str == '':
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# Could not find insn args
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args = None
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else:
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logging.debug('args: "%s"', args_str)
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for m in re.finditer(r'([^,\(]*(\(:?[^\)]+\))*)', args_str):
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if len(m.group(0)):
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args.append(m.group(0))
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if len(args) > 0:
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src = args[0]
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logging.debug('src: %s', src)
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if len(args) > 1:
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dest = args[1]
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logging.debug('dest: %s', dest)
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# Set up possible implicit memory destinations (stack actions)
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if insn in ['push', 'pop', 'pushl', 'popl', 'call', 'callq', 'ret', 'retq']:
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for reg in ['rsp', 'esp']:
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if reg in self.regs:
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dest = '(%%%s)' % (reg)
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break
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return line, pc, insn, src, dest
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def validate_vma(self, perm, addr, name):
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perm_name = {'x': ['executable', 'executing'], 'r': ['readable', 'reading'], 'w': ['writable', 'writing']}
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vma = self.find_vma(addr)
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if vma is None:
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alarmist = 'unknown'
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if addr < 65536:
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alarmist = 'NULL'
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return False, '%s (0x%08x) not located in a known VMA region (needed %s region)!' % (name, addr, perm_name[perm][0]), '%s %s VMA' % (perm_name[perm][1], alarmist)
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elif perm not in vma['perms']:
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alarmist = ''
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if perm == 'x':
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if 'w' in vma['perms']:
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alarmist = 'writable '
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else:
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alarmist = 'non-writable '
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short = '%s %sVMA %s' % (perm_name[perm][1], alarmist, vma['name'])
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return False, '%s (0x%08x) in non-%s VMA region: 0x%08x-0x%08x %s %s' % (name, addr, perm_name[perm][0], vma['start'], vma['end'], vma['perms'], vma['name']), short
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else:
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return True, '%s (0x%08x) ok' % (name, addr), '%s ok' % (perm_name[perm][1])
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def register_value(self, reg):
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reg_orig = reg
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# print reg
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mask = 0
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if reg.startswith('%'):
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# print('%s -> %s' % (reg, reg[1:]))
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reg = reg[1:]
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if reg in self.regs:
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# print('got %s (%d & %d == %d)' % (reg, self.regs[reg], mask, self.regs[reg] & ~mask))
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return self.regs[reg]
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if len(reg) == 2 and reg.endswith('l'):
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mask |= 0xff00
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# print('%s -> %sx' % (reg, reg[0]))
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reg = '%sx' % reg[0]
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if reg in self.regs:
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# print('got %s (%d & %d == %d)' % (reg, self.regs[reg], mask, self.regs[reg] & ~mask))
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return self.regs[reg] & ~mask
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if len(reg) == 2 and reg.endswith('x'):
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mask |= 0xffff0000
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# print('%s -> e%s' % (reg, reg))
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reg = 'e%s' % reg
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if reg in self.regs:
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# print('got %s (%d & %d == %d)' % (reg, self.regs[reg], mask, self.regs[reg] & ~mask))
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return self.regs[reg] & ~mask
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if len(reg) == 3 and reg.startswith('e'):
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mask |= 0xffffffff00000000
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# print('%s -> r%s' % (reg, reg[1:]))
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reg = 'r%s' % reg[1:]
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if reg in self.regs:
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# print('got %s (%d & %d == %d)' % (reg, self.regs[reg], mask, self.regs[reg] & ~mask))
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return self.regs[reg] & ~mask
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raise ValueError("Could not resolve register '%s'" % (reg_orig))
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def calculate_arg(self, arg):
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# Check for and pre-remove segment offset
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segment = 0
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if arg.startswith('%') and ':' in arg:
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parts = arg.split(':', 1)
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segment = self.regs[parts[0][1:]]
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arg = parts[1]
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# Handle standard offsets
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parts = arg.split('(')
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offset = parts[0]
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# Handle negative signs
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sign = 1
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if offset.startswith('-'):
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sign = -1
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offset = offset[1:]
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# Skip call target dereferences
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if offset.startswith('*'):
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offset = offset[1:]
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if len(offset) > 0:
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if offset.startswith('%'):
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# Handle the *%REG case
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add = self.regs[offset[1:]]
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else:
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if not offset.startswith('0x'):
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raise ValueError('Unknown offset literal: %s' % (parts[0]))
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add = int(offset[2:], 16) * sign
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else:
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add = 0
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def _reg_val(self, text, val=0):
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if text.startswith('%'):
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val = self.regs[text[1:]]
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elif text == "":
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val = 0
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else:
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val = int(text)
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return val
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# (%ebx, %ecx, 4) style
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value = 0
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if len(parts) > 1:
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parens = parts[1][0:-1]
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reg_list = parens.split(',')
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base = 0
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if len(reg_list) > 0:
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base = _reg_val(self, reg_list[0], base)
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index = 0
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if len(reg_list) > 1:
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index = _reg_val(self, reg_list[1], index)
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scale = 1
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if len(reg_list) > 2:
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scale = _reg_val(self, reg_list[2], scale)
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value = base + index * scale
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value = segment + value + add
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if 'esp' in self.regs:
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# 32bit
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return value % 0x100000000
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else:
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# 64bit
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return value % 0x10000000000000000
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def report(self):
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understood = False
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reason = []
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details = ['Segfault happened at: %s' % (self.line)]
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# Verify PC is in an executable region
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valid, out, short = self.validate_vma('x', self.pc, 'PC')
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details.append(out)
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if not valid:
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reason.append(short)
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understood = True
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if self.insn in ['lea', 'leal']:
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# Short-circuit for instructions that do not cause vma access
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details.append('insn (%s) does not access VMA' % (self.insn))
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else:
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# Verify source is readable
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if self.src:
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if ':' not in self.src and (self.src[0] in ['%', '$', '*']) and not self.src.startswith('*%'):
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details.append('source "%s" ok' % (self.src))
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else:
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addr = self.calculate_arg(self.src)
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valid, out, short = self.validate_vma('r', addr, 'source "%s"' % (self.src))
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details.append(out)
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if not valid:
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reason.append(short)
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understood = True
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# Verify destination is writable
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if self.dest:
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if ':' not in self.dest and (self.dest[0] in ['%', '$', '*']):
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details.append('destination "%s" ok' % (self.dest))
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else:
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addr = self.calculate_arg(self.dest)
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valid, out, short = self.validate_vma('w', addr, 'destination "%s"' % (self.dest))
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details.append(out)
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if not valid:
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reason.append(short)
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understood = True
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# Handle I/O port operations
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if self.insn in ['out', 'in'] and not understood:
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reason.append('disallowed I/O port operation on port %d' % (self.register_value(self.src)))
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details.append('disallowed I/O port operation on port %d' % (self.register_value(self.src)))
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understood = True
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# Note position of SP with regard to "[stack]" VMA
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if self.sp is not None:
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if self.stack_vma is not None:
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if self.sp < self.maps[self.stack_vma]['start']:
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details.append("Stack memory exhausted (SP below stack segment)")
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if self.sp >= self.maps[self.stack_vma]['end']:
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details.append("Stack pointer not within stack segment")
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if not understood:
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valid, out, short = self.validate_vma('r', self.sp, 'SP')
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details.append(out)
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if not valid:
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reason.append(short)
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understood = True
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if not understood:
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vma = self.find_vma(self.pc)
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if vma and (vma['name'] == '[vdso]' or vma['name'] == '[vsyscall]'):
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reason.append('Reason could not be automatically determined. (Unhandled exception in kernel code?)')
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details.append('Reason could not be automatically determined. (Unhandled exception in kernel code?)')
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else:
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reason.append('Reason could not be automatically determined.')
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details.append('Reason could not be automatically determined.')
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return understood, '\n'.join(reason), '\n'.join(details)
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def add_info(report):
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# Only interested in segmentation faults...
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if report.get('Signal', '0') != '11':
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return
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needed = ['Signal', 'Architecture', 'Disassembly', 'ProcMaps', 'Registers']
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for field in needed:
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if field not in report:
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report['SegvAnalysis'] = 'Skipped: missing required field "%s"' % (field)
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return
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# Only run on segv for x86 and x86_64...
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if not report['Architecture'] in ['i386', 'amd64']:
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return
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try:
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segv = ParseSegv(report['Registers'], report['Disassembly'], report['ProcMaps'])
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understood, reason, details = segv.report()
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if understood:
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report['SegvReason'] = reason
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report['SegvAnalysis'] = details
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except BaseException as e:
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report['SegvAnalysis'] = 'Failure: %s' % (str(e))
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if __name__ == '__main__':
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if len(sys.argv) != 4 or sys.argv[1] in ['-h', '--help']:
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print('To run self-test, run without any arguments (or with -v)')
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print('To do stand-alone crash parsing:')
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print(' Usage: %s Registers.txt Disassembly.txt ProcMaps.txt' % (sys.argv[0]))
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sys.exit(0)
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segv = ParseSegv(open(sys.argv[1]).read(),
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open(sys.argv[2]).read(),
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open(sys.argv[3]).read())
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understood, reason, details = segv.report()
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print('%s\n\n%s' % (reason, details))
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rc = 0
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if not understood:
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rc = 1
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sys.exit(rc)
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