peutils.py

# -*- coding: Latin-1 -*-
"""peutils, Portable Executable utilities module


Copyright (c) 2005, 2006, 2007 Ero Carrera <ero@dkbza.org>

All rights reserved.

For detailed copyright information see the file COPYING in
the root of the distribution archive.
"""

import os
import re
import string
import urllib
import pefile

__author__ = 'Ero Carrera'
__version__ = pefile.__version__
__contact__ = 'ero@dkbza.org'




class SignatureDatabase:
    """This class loads and keeps a parsed PEiD signature database.
    
    Usage:
        
        sig_db = SignatureDatabase('/path/to/signature/file')
    
    and/or
        
        sig_db = SignatureDatabase()
        sig_db.load('/path/to/signature/file')
    
    Signature databases can be combined by performing multiple loads.
    
    The filename parameter can be a URL too. In that case the
    signature database will be downloaded from that location.
    """
    
    def __init__(self, filename=None, data=None):
        
        # RegExp to match a signature block
        #
        self.parse_sig = re.compile(
            '\[(.*?)\]\s+?signature\s*=\s*(.*?)(\s+\?\?)*\s*ep_only\s*=\s*(\w+)(?:\s*section_start_only\s*=\s*(\w+)|)', re.S)
        
        # Signature information
        #
        # Signatures are stored as trees using dictionaries
        # The keys are the byte values while the values for
        # each key are either:
        #
        # - Other dictionaries of the same form for further
        #   bytes in the signature
        #
        # - A dictionary with a string as a key (packer name)
        #   and None as value to indicate a full signature
        #
        self.signature_tree_eponly_true = dict ()
        self.signature_count_eponly_true = 0
        self.signature_tree_eponly_false = dict ()
        self.signature_count_eponly_false = 0
        self.signature_tree_section_start = dict ()
        self.signature_count_section_start = 0
        
        # The depth (length) of the longest signature
        #
        self.max_depth = 0
        
        self.__load(filename=filename, data=data)
    
    def generate_section_signatures(self, pe, name, sig_length=512):
        """Generates signatures for all the sections in a PE file.
        
        If the section contains any data a signature will be created
        for it. The signature name will be a combination of the
        parameter 'name' and the section number and its name.
        """
        
        section_signatures = list()
        
        for idx, section in enumerate(pe.sections):
            
            if section.SizeOfRawData < sig_length:
                continue
            
            #offset = pe.get_offset_from_rva(section.VirtualAddress)
            offset = section.PointerToRawData
            
            sig_name = '%s Section(%d/%d,%s)' % (
                name, idx + 1, len(pe.sections),
                ''.join([c for c in section.Name if c in string.printable]))
            
            section_signatures.append(
                self.__generate_signature(
                    pe, offset, sig_name, ep_only=False,
                    section_start_only=True,
                    sig_length=sig_length) )
        
        return '\n'.join(section_signatures)+'\n'
    
    
    
    def generate_ep_signature(self, pe, name, sig_length=512):
        """Generate signatures for the entry point of a PE file.
        
        Creates a signature whose name will be the parameter 'name'
        and the section number and its name.
        """
        
        offset = pe.get_offset_from_rva(pe.OPTIONAL_HEADER.AddressOfEntryPoint)
        
        return self.__generate_signature(
            pe, offset, name, ep_only=True, sig_length=sig_length)
        
    
    
    def __generate_signature(self, pe, offset, name, ep_only=False,
            section_start_only=False, sig_length=512):
        
        data = pe.__data__[offset:offset+sig_length]
        
        signature_bytes = ' '.join(['%02x' % ord(c) for c in data])
        
        if ep_only == True:
            ep_only = 'true'
        else:
            ep_only = 'false'
        
        if section_start_only == True:
            section_start_only = 'true'
        else:
            section_start_only = 'false'
        
        signature = '[%s]\nsignature = %s\nep_only = %s\nsection_start_only = %s\n' % (
            name, signature_bytes, ep_only, section_start_only)
        
        return signature
    
    def match(self, pe, ep_only=True, section_start_only=False):
        """Matches and returns the exact match(es).
        
        If ep_only is True the result will be a string with
        the packer name. Otherwise it will be a list of the
        form (file_ofsset, packer_name). Specifying where
        in the file the signature was found.
        """
        
        matches = self.__match(pe, ep_only, section_start_only)
        
        # The last match (the most precise) from the
        # list of matches (if any) is returned
        #
        if matches:
            if ep_only == False:
                # Get the most exact match for each list of matches
                # at a given offset
                #
                return [(match[0], match[1][-1]) for match in matches]
            
            return matches[1][-1]
        
        return None
    
    def match_all(self, pe, ep_only=True, section_start_only=False):
        """Matches and returns all the likely matches."""
        
        matches = self.__match(pe, ep_only, section_start_only)
        
        if matches:
            if ep_only == False:
                # Get the most exact match for each list of matches
                # at a given offset
                #
                return matches
            
            return matches[1]
        
        return None
    
    def __match(self, pe, ep_only, section_start_only):
        
        # Load the corresponding set of signatures
        # Either the one for ep_only equal to True or
        # to False
        #
        if section_start_only is True:
            
            # Fetch the data of the executable as it'd
            # look once loaded in memory
            #
            try :
                data = pe.__data__
            except Exception, excp :
                raise
            
            # Load the corresponding tree of signatures
            #
            signatures = self.signature_tree_section_start
            
            # Set the starting address to start scanning from
            #
            scan_addresses = [section.PointerToRawData for section in pe.sections]
        
        elif ep_only is True:
            
            # Fetch the data of the executable as it'd
            # look once loaded in memory
            #
            try :
                data = pe.get_memory_mapped_image()
            except Exception, excp :
                raise
            
            # Load the corresponding tree of signatures
            #
            signatures = self.signature_tree_eponly_true
            
            # Fetch the entry point of the PE file and the data
            # at the entry point
            #
            ep = pe.OPTIONAL_HEADER.AddressOfEntryPoint
            
            # Set the starting address to start scanning from
            #
            scan_addresses = [ep]
        
        else:
            
            data = pe.__data__
            
            signatures = self.signature_tree_eponly_false
            
            scan_addresses = xrange( len(data) )
        
        # For each start address, check if any signature matches
        #
        matches = []
        for idx in scan_addresses:
            result = self.__match_signature_tree(
                signatures,
                data[idx:idx+self.max_depth])
            if result:
                matches.append( (idx, result) )
        
        # Return only the matched items found at the entry point if
        # ep_only is True (matches will have only one element in that
        # case)
        #
        if ep_only is True:
            if matches:
                return matches[0]
        
        return matches
        
    
    def __match_signature_tree(self, signature_tree, data, depth = 0):
        """Recursive function to find matches along the signature tree.
        
        signature_tree  is the part of the tree left to walk
        data    is the data being checked against the signature tree
        depth   keeps track of how far we have gone down the tree
        """
        
        
        matched_names = list ()
        match = signature_tree
        
        # Walk the bytes in the data and match them
        # against the signature
        #
        for idx, byte in enumerate ( [ord (b) for b in data] ):
            
            # If the tree is exhausted...
            #
            if match is None :
                break
            
            # Get the next byte in the tree
            #
            match_next = match.get(byte, None)
        
            
            # If None is among the values for the key
            # it means that a signature in the database
            # ends here and that there's an exact match.
            #
            if None in match.values():
                # idx represent how deep we are in the tree
                #
                #names = [idx+depth]
                names = list()
                
                # For each of the item pairs we check
                # if it has an element other than None,
                # if not then we have an exact signature
                #
                for item in match.items():
                    if item[1] is None :
                        names.append (item[0])
                matched_names.append(names)
            
            # If a wildcard is found keep scanning the signature
            # ignoring the byte.
            #
            if match.has_key ('??') :
                match_tree_alternate = match.get ('??', None)
                data_remaining = data[idx + 1 :]
                if data_remaining:
                    matched_names.extend(
                        self.__match_signature_tree(
                            match_tree_alternate, data_remaining, idx+depth+1))
            
            match = match_next
        
        # If we have any more packer name in the end of the signature tree
        # add them to the matches
        #
        if match is not None and None in match.values():
            #names = [idx + depth + 1]
            names = list()
            for item in match.items() :
                if item[1] is None:
                    names.append(item[0])
            matched_names.append(names)
        
        return matched_names
    
    def load(self , filename=None, data=None):
        """Load a PEiD signature file.
        
        Invoking this method on different files combines the signatures.
        """
        
        self.__load(filename=filename, data=data)
    
    def __load(self, filename=None, data=None):
        
        
        if filename is not None:
            # If the path does not exist, attempt to open a URL
            #
            if not os.path.exists(filename):
                try:
                    sig_f = urllib.urlopen(filename)
                    sig_data = sig_f.read()
                    sig_f.close()
                except IOError:
                    # Let this be raised back to the user...
                    raise
            else:
                # Get the data for a file
                #
                sig_f = file( filename, 'rt' )
                sig_data = sig_f.read()
                sig_f.close()
        else:
            sig_data = data
        
        # Helper function to parse the signature bytes
        #
        def to_byte(value) :
            if value == '??' or value == '?0' :
                return value
            return int (value, 16)
        
        
        # Parse all the signatures in the file
        #
        matches = self.parse_sig.findall(sig_data)
        
        # For each signature, get the details and load it into the
        # signature tree
        #
        for packer_name, signature, superfluous_wildcards, ep_only, section_start_only in matches:
            
            ep_only = ep_only.strip().lower()
            
            signature = signature.replace('\\n', '').strip()
            
            signature_bytes = [to_byte(b) for b in signature.split()]
            
            if ep_only == 'true':
                ep_only = True
            else:
                ep_only = False
            
            if section_start_only == 'true':
                section_start_only = True
            else:
                section_start_only = False
            
            
            depth = 0
            
            if section_start_only is True:
                
                tree = self.signature_tree_section_start
                self.signature_count_section_start += 1
            
            else:
                if ep_only is True :
                    tree = self.signature_tree_eponly_true
                    self.signature_count_eponly_true += 1
                else :
                    tree = self.signature_tree_eponly_false
                    self.signature_count_eponly_false += 1
            
            for idx, byte in enumerate (signature_bytes) :
                
                if idx+1 == len(signature_bytes):
                    
                    tree[byte] = tree.get( byte, dict() )
                    tree[byte][packer_name] = None
                
                else :
                    
                    tree[byte] = tree.get ( byte, dict() )
                
                tree = tree[byte]
                depth += 1
            
            if depth > self.max_depth:
                self.max_depth = depth