Volatility apihooks.py - Inline interrupt hooks

# Volatility
# Copyright (C) 2007-2013 Volatility Foundation
#
# Authors:
# Michael Hale Ligh <michael.ligh@mnin.org>
#
# This file is part of Volatility.
#
# Volatility is free software; you can redistribute it and/or modify
# it under the terms of the GNU General Public License as published by
# the Free Software Foundation; either version 2 of the License, or
# (at your option) any later version.
#
# Volatility is distributed in the hope that it will be useful,
# but WITHOUT ANY WARRANTY; without even the implied warranty of
# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
# GNU General Public License for more details.
#
# You should have received a copy of the GNU General Public License
# along with Volatility.  If not, see <http://www.gnu.org/licenses/>.
#

import re, ntpath
import volatility.utils as utils
import volatility.obj as obj
import volatility.debug as debug
import volatility.win32.tasks as tasks
import volatility.win32.modules as modules
import volatility.plugins.malware.malfind as malfind
import volatility.plugins.malware.idt as idt
import volatility.plugins.overlays.basic as basic
import volatility.plugins.procdump as procdump
import volatility.exceptions as exceptions

try:
    import distorm3
    has_distorm3 = True
except ImportError:
    has_distorm3 = False

#--------------------------------------------------------------------------------
# Constants
#--------------------------------------------------------------------------------

# hook modes
HOOK_MODE_USER = 1
HOOK_MODE_KERNEL = 2

# hook types
HOOKTYPE_IAT = 4
HOOKTYPE_EAT = 8
HOOKTYPE_INLINE = 16
HOOKTYPE_NT_SYSCALL = 32
HOOKTYPE_CODEPAGE_KERNEL = 64
HOOKTYPE_IDT = 128
HOOKTYPE_IRP = 256
HOOKTYPE_WINSOCK = 512

# names for hook types
hook_type_strings = {
    HOOKTYPE_IAT             : "Import Address Table (IAT)",
    HOOKTYPE_EAT             : "Export Address Table (EAT)",
    HOOKTYPE_INLINE          : "Inline/Trampoline",
    HOOKTYPE_NT_SYSCALL      : "NT Syscall",
    HOOKTYPE_CODEPAGE_KERNEL : "Unknown Code Page Call",
    HOOKTYPE_WINSOCK         : "Winsock Procedure Table Hook",
}

WINSOCK_TABLE = [
    '_WSPAccept',
    '_WSPAddressToString',
    '_WSPAsyncSelect',
    '_WSPBind',
    '_WSPCancelBlockingCall',
    '_WSPCleanup',
    '_WSPCloseSocket',
    '_WSPConnect',
    '_WSPDuplicateSocket',
    '_WSPEnumNetworkEvents',
    '_WSPEventSelect',
    '_WSPGetOverlappedResult',
    '_WSPGetPeerName',
    '_WSPGetSockName',
    '_WSPGetSockOpt',
    '_WSPGetQOSByName',
    '_WSPIoctl',
    '_WSPJoinLeaf',
    '_WSPListen',
    '_WSPRecv',
    '_WSPRecvDisconnect',
    '_WSPRecvFrom',
    '_WSPSelect',
    '_WSPSend',
    '_WSPSendDisconnect',
    '_WSPSendTo',
    '_WSPSetSockOpt',
    '_WSPShutdown',
    '_WSPSocket',
    '_WSPStringToAddress',
]

#--------------------------------------------------------------------------------
# Profile Modifications
#--------------------------------------------------------------------------------

class MalwareWSPVTypes(obj.ProfileModification):
    before = ['WindowsOverlay']
    conditions = {'os': lambda x : x == 'windows',
                  'memory_model': lambda x: x == '32bit'}
    def modification(self, profile):
        profile.vtypes.update({
            '_SOCK_PROC_TABLE' : [ None, {
            'Functions' : [ 0x0, ['array', 30, ['address']]],
            }]})

#--------------------------------------------------------------------------------
# Module Group Class
#--------------------------------------------------------------------------------

class ModuleGroup(object):
    """A class to assist with module lookups"""

    def __init__(self, mod_list):
        """Initialize.

        @param mod_list: a list of _LDR_DATA_TABLE_ENTRY objects.
        This can be a generator.
        """

        self.mods = list(mod_list)
        self.mod_name = {}
        self.mod_fast = [(mod.DllBase, mod.DllBase + mod.SizeOfImage, mod) for mod in self.mods]

        for mod in self.mods:
            name = str(mod.BaseDllName or '').lower()
            if name in self.mod_name:
                self.mod_name[name].append(mod)
            else:
                self.mod_name[name] = [mod]

    def find_module(self, address):
        """Find a module by an address it contains.

        @param address: location in process or kernel AS to
        find an owning module.

        When performing thousands of lookups, this method
        is actually quicker than tasks.find_module.
        """

        for base, end, mod in self.mod_fast:
            if address >= base and address <= end:
                return mod

        return obj.NoneObject("")

#--------------------------------------------------------------------------------
# Hook Class
#--------------------------------------------------------------------------------

class Hook(object):
    """A class for API hooks. It helps organize the many
    pieces of information required to report on the hook."""

    def __init__(self, hook_type, hook_mode, function_name,
                        function_address = None, hook_address = None,
                        hook_module = None, victim_module = None):
        """
        Initalize a hook class instance.

        @params hook_type: one of the HOOK_TYPE_* constants
        @params hook_mode: one of the HOOK_MODE_* constants

        @params function_name: name of the function being hooked

        @params function_address: address of the hooked function in
            process or kernel memory.

        @params hook_address: address where the hooked function
            actually points.

        @params hook_module: the _LDR_DATA_TABLE_ENTRY of the
            hooking module (owner of the hook_address). note:
            this can be None if the module cannot be identified.

        @params victim_module: the _LDR_DATA_TABLE_ENTRY of the
            module being hooked (contains the function_address).
            note: this can be a string if checking IAT hooks.

        """
        self.hook_mode = hook_mode
        self.hook_type = hook_type
        self.function_name = function_name
        self.function_address = function_address
        self.hook_address = hook_address
        self.hook_module = hook_module
        self.victim_module = victim_module
        # List of tuples: address, data pairs
        self.disassembled_hops = []

    def add_hop_chunk(self, address, data):
        """Support disassembly for multiple hops"""
        self.disassembled_hops.append((address, data))

    def _module_name(self, module):
        """Return a sanitized module name"""

        # The module can't be identified
        if not module:
            return '<unknown>'

        # The module is a string name like "ntdll.dll"
        if isinstance(module, basic.String) or isinstance(module, str):
            return str(module)

        # The module is a _LDR_DATA_TABLE_ENTRY
        return str(module.BaseDllName or '') or str(module.FullDllName or '') or '<unknown>'

    @property
    def Type(self):
        """Translate the hook type into a string"""
        return hook_type_strings.get(self.hook_type, "")

    @property
    def Mode(self):
        """Translate the hook mode into a string"""
        if self.hook_mode == HOOK_MODE_USER:
            return "Usermode"
        else:
            return "Kernelmode"

    @property
    def Function(self):
        """Return the function name if its available"""
        return str(self.function_name) or '<unknown>'

    @property
    def Detail(self):
        """The detail depends on the hook type"""
        if self.hook_type == HOOKTYPE_IAT:
            return "{0}!{1}".format(self.VictimModule, self.Function)
        elif self.hook_type == HOOKTYPE_EAT:
            return "{0} at {1:#x}".format(self.Function, self.hook_address)
        elif self.hook_type == HOOKTYPE_INLINE:
            return "{0}!{1} at {2:#x}".format(self.VictimModule, self.Function, self.function_address)
        else:
            return self.Function

    @property
    def HookModule(self):
        """Name of the hooking module"""
        return self._module_name(self.hook_module)

    @property
    def VictimModule(self):
        """Name of the victim module"""
        return self._module_name(self.victim_module)

#--------------------------------------------------------------------------------
# Whitelist Rules
#--------------------------------------------------------------------------------

# The values of each dictionary item is a list of tuples which are regexes
# in the format (process, srd_mod, dst_mod, function). If you specify
# (".*", ".*", ".*", ".*") then you essentially whitelist all possible hooks
# of the given type.

whitelist_rules = {
    HOOK_MODE_USER | HOOKTYPE_IAT : [
    # Ignore hooks that point inside C runtime libraries
    (".*", ".*", "(msvcr|msvcp).+\.dll", ".*"),
    # Ignore hooks of WMI that point inside advapi32.dll
    (".*", "wmi.dll", "advapi32.dll", ".*"),
    # Ignore hooks of winsock that point inside ws2 and   mswsock
    (".*", "WSOCK32.dll", "(WS2_32|MSWSOCK)\.dll", ".*"),
    # Ignore hooks of SCHANNEL* that point inside secur32.dll
    (".*", "schannel.dll", "secur32.dll", ".*"),
    # Ignore hooks of Secur32* that point inside SSPICLI
    (".*", "Secur32.dll", "SSPICLI.DLL", ".*"),
    # Ignore hooks that point inside known modules
    (".*", ".*", "(kernel32|gdi32|advapi32|ntdll|shimeng|kernelbase|shlwapi|user32|cfgmgr32)", ".*"),
    # Handle some known forwarded imports
    (".*", ".*", ".*", "((Enter|Delete|Leave)CriticalSection|(Get|Set)LastError|Heap(ReAlloc|Free|Size|Alloc)|Rtl(Unwind|MoveMemory))"),
    # Ignore sfc hooks going to sfc_os
    (".*", "sfc\.dll", "sfc_os\.dll", ".*"),
    # Ignore netapi32 hooks pointing at netutils or samcli
    (".*", "netapi32\.dll", "(netutils|samcli)\.dll", ".*"),
    (".*", "setupapi\.dll", "devrtl\.dll", ".*"),
    ],
    HOOK_MODE_USER | HOOKTYPE_EAT : [
    # These modules have so many hooks its really not useful to check
    (".*", "(msvcp|msvcr|mfc|wbemcomn|fastprox)", ".*", ".*"),
    ],
    HOOK_MODE_USER | HOOKTYPE_INLINE : [
    # Ignore hooks in the pywin32 service process
    ("pythonservice", ".*", ".*", ".*"),
    # Many legit hooks land inside these modules
    (".*", ".*", "(msvcr|advapi32|version|wbemcomn|ntdll|kernel32|kernelbase|sechost|ole32|shlwapi|user32|gdi32|ws2_32|shell32)", ".*"),
    # Ignore hooks of the c runtime DLLs
    (".*", "(msvc(p|r)\d{2}|mfc\d{2})\.dll", ".*", ".*"),
    # This is a global variable
    (".*", "msvcrt\.dll", ".*", "_acmdln"),
    # Ignore hooks of MD5Final, MD5Init, MD5Update that point inside advapi32
    (".*", ".*", "advapi32.dll", "MD5.+"),
    # Ignore hooks of common firefox components
    ("firefox\.exe", ".*", "(xul|mozcrt|nspr4)", ".*"),
    # Ignore hooks created by Parallels VM software
    (".*", "user32.dll", "prl_hook.dll", ".*"),
    # Ignore DLL registration functions
    (".*", ".*", ".*", "(DllCanUnloadNow|DllRegisterServer|DllUnregisterServer)"),
    # Ignore netapi32 hooks pointing at netutils
    (".*", "netapi32\.dll", "netutils\.dll", ".*"),
    ],
    HOOK_MODE_KERNEL | HOOKTYPE_IAT : [
    (".*", ".*", "(win32k\.sys|hal\.dll|dump_wmilib\.sys|ntkrnlpa\.exe|ntoskrnl\.exe)", ".*"),
    # Ignore hooks of the SCSI module which point inside the dump_scsiport module
    (".*", "scsiport\.sys", "dump_scsiport\.sys", ".*"),
    # Ignore other storage port hooks
    (".*", "storport\.sys", "dump_storport\.sys", ".*"),
    ],
    HOOK_MODE_KERNEL | HOOKTYPE_EAT : [
    ],
    HOOK_MODE_KERNEL | HOOKTYPE_INLINE : [
    # Ignore kernel hooks that point inside these modules
    (".*", ".*", "(hal.dll|ndis.sys|ntkrnlpa.exe|ntoskrnl.exe)", ".*"),
    ],
}

class ApiHooks(procdump.ProcExeDump):
    """Detect API hooks in process and kernel memory"""

    def __init__(self, config, *args, **kwargs):
        procdump.ProcExeDump.__init__(self, config, *args, **kwargs)
        config.remove_option("DUMP-DIR")

        config.add_option("NO-WHITELIST", short_option = 'N', default = False,
                action = 'store_true',
                help = 'No whitelist (show all hooks, can be verbose)')

        config.add_option("SKIP-KERNEL", short_option = 'R', default = False,
                action = 'store_true',
                help = 'Skip kernel mode checks')

        config.add_option("SKIP-PROCESS", short_option = 'P', default = False,
                action = 'store_true',
                help = 'Skip process checks')

        config.add_option("QUICK", short_option = 'Q', default = False,
                action = 'store_true',
                help = 'Work faster by only analyzing critical processes and dlls')

        self.compiled_rules = self.compile()

        # When the --quick option is set, we only scan the processes
        # and dlls in these lists. Feel free to adjust them for
        # your own purposes.
        self.critical_process = ["explorer.exe", "svchost.exe", "lsass.exe",
            "services.exe", "winlogon.exe", "csrss.exe", "smss.exe",
            "wininit.exe", "iexplore.exe", "firefox.exe", "spoolsv.exe"]

        self.critical_dlls = ["ntdll.dll", "kernel32.dll", "ws2_32.dll",
            "advapi32.dll", "secur32.dll", "crypt32.dll", "user32.dll",
            "gdi32.dll", "shell32.dll", "shlwapi.dll", "lsasrv.dll",
            "cryptdll.dll", "wsock32.dll", "mswsock.dll", "urlmon.dll",
            "csrsrv.dll", "winsrv.dll", "wininet.dll"]

        # When scanning for calls to unknown code pages (UCP), only
        # analyze the following drivers. This is based on an analysis of
        # the modules rootkits are most likely to infect, but feel free
        # to adjust it for your own purposes.
        self.ucpscan_modules = ["tcpip.sys", "ntfs.sys", "fastfast.sys",
            "wanarp.sys", "ndis.sys", "atapi.sys", "ntoskrnl.exe",
            "ntkrnlpa.exe", "ntkrnlmp.exe"]

    @staticmethod
    def is_valid_profile(profile):
        return (profile.metadata.get('os', 'unknown') == 'windows' and
                profile.metadata.get('memory_model', '32bit') == '32bit')

    def compile(self):
        """
        Precompile the regular expression rules. Its quicker
        if we do this once per plugin run, rather than once per
        API hook that needs checking.
        """
        ret = dict()
        for key, rules in whitelist_rules.items():
            for rule in rules:
                ruleset = ((re.compile(rule[0], re.I), # Process name
                            re.compile(rule[1], re.I), # Source module
                            re.compile(rule[2], re.I), # Destination module
                            re.compile(rule[3], re.I), # Function name
                            ))
                if ret.has_key(key):
                    ret[key].append(ruleset)
                else:
                    ret[key] = [ruleset]
        return ret

    def whitelist(self, rule_key, process, src_mod, dst_mod, function):
        """Check if an API hook should be ignored due to whitelisting.

        @param rule_key: a key from the whitelist_rules dictionary which
            describes the type of hook (i.e. Usermode IAT or Kernel Inline).

        @param process: name of the suspected victim process.

        @param src_mod: name of the source module whose function has been
            hooked. this varies depending on whether we're dealing with IAT
            EAT, inline, etc.

        @param dst_mod: name of the module that is the destination of the
            hook pointer. this is usually the rootkit dll, exe, or sys,
            however, in many cases there is no module name since the rootkit
            is trying to be stealthy.

        @param function: name of the function that has been hooked.
        """
        # There are no whitelist rules for this hook type
        if rule_key not in self.compiled_rules:
            return False

        for rule in self.compiled_rules[rule_key]:
            if (rule[0].search(process) != None and
                    rule[1].search(src_mod) != None and
                    rule[2].search(dst_mod) != None and
                    rule[3].search(function) != None):
                return True

        return False

    def get_idt(self):
        """
        Build IDT to check for inline hooks that use interrupts, whitelist interrupts
        that are handled by common kernel mode modules

        @returns: Dictionary of idt index and handler address
        """
        idt_data={}
        for n, _, addr, module in idt.IDT(self._config).calculate():
            for rule in self.compiled_rules[HOOK_MODE_KERNEL | HOOKTYPE_INLINE]:
                if module:
                    module_name = str(module.BaseDllName or '')
                else:
                    module_name = "UNKNOWN"
                if rule[2].search(module_name) is None:
                    idt_data[n] = addr
                else:
                    idt_data[n] = None
        return idt_data


    @staticmethod
    def check_syscall(addr_space, module, module_group):
        """
        Enumerate syscall hooks in ntdll.dll. A syscall hook is one
        that modifies the function prologue of an NT API function
        (i.e. ntdll!NtCreateFile) or swaps the location of the sysenter
        with a malicious address.

        @param addr_space: a process AS for the process containing the
        ntdll.dll module.

        @param module: the _LDR_DATA_TABLE_ENTRY for ntdll.dll

        @param module_group: a ModuleGroup instance for the process.
        """

        # Resolve the real location of KiFastSystem Call for comparison
        KiFastSystemCall = module.getprocaddress("KiFastSystemCall")
        KiIntSystemCall = module.getprocaddress("KiIntSystemCall")

        if not KiFastSystemCall or not KiIntSystemCall:
            #debug.debug("Abort check_syscall, can't find KiFastSystemCall")
            return

        # Add the RVA to make it absolute
        KiFastSystemCall += module.DllBase
        KiIntSystemCall += module.DllBase

        # Check each exported function if its an NT syscall
        for _, f, n in module.exports():

            # Ignore forwarded exports
            if not f:
                #debug.debug("Skipping forwarded export {0}".format(n or ''))
                continue

            function_address = module.DllBase + f

            if not addr_space.is_valid_address(function_address):
                #debug.debug("Function address {0:#x} for {1} is paged".format(
                #    function_address, n or ''))
                continue

            # Read enough of the function prologue for two instructions
            data = addr_space.zread(function_address, 24)

            instructions = []

            for op in distorm3.Decompose(function_address, data, distorm3.Decode32Bits):
                if not op.valid:
                    break
                if len(instructions) == 3:
                    break
                instructions.append(op)

            i0 = instructions[0]
            i1 = instructions[1]
            i2 = instructions[2]

            # They both must be properly decomposed and have two operands
            if (not i0 or not i0.valid or len(i0.operands) != 2 or
                    not i1 or not i1.valid or len(i1.operands) != 2):
                #debug.debug("Error decomposing prologue for {0} at {1:#x}".format(
                #    n or '', function_address))
                continue

            # Now check the instruction and operand types
            if (i0.mnemonic == "MOV" and i0.operands[0].type == 'Register' and
                    i0.operands[0].name == 'EAX' and i0.operands[1].type == 'Immediate' and
                    i1.mnemonic == "MOV" and i1.operands[0].type == 'Register' and
                    i1.operands[0].name == 'EDX' and i0.operands[1].type == 'Immediate'):

                if i2.operands[0].type == "Register":
                    # KiFastSystemCall is already in the register
                    syscall_address = i1.operands[1].value
                else:
                    # Pointer to where KiFastSystemCall is stored
                    syscall_address = obj.Object('address',
                        offset = i1.operands[1].value, vm = addr_space)

                if syscall_address not in [KiFastSystemCall, KiIntSystemCall]:
                    hook_module = module_group.find_module(syscall_address)
                    hook = Hook(hook_type = HOOKTYPE_NT_SYSCALL,
                                hook_mode = HOOK_MODE_USER,
                                function_name = n or '',
                                function_address = function_address,
                                hook_address = syscall_address,
                                hook_module = hook_module,
                                victim_module = module,
                                )
                    # Add the bytes that will later be disassembled in the
                    # output to show exactly how the hook works. The first
                    # hop is the ntdll!Nt* API and the next hop is the rootkit.
                    hook.add_hop_chunk(function_address, data)
                    hook.add_hop_chunk(syscall_address, addr_space.zread(syscall_address, 24))
                    yield hook

    def check_ucpcall(self, addr_space, module, module_group):
        """Scan for calls to unknown code pages.

        @param addr_space: a kernel AS

        @param module: the _LDR_DATA_TABLE_ENTRY to scan

        @param module_group: a ModuleGroup instance for the process.
        """

        try:
            dos_header = obj.Object("_IMAGE_DOS_HEADER",
                offset = module.DllBase, vm = addr_space)

            nt_header = dos_header.get_nt_header()
        except (ValueError, exceptions.SanityCheckException), _why:
            #debug.debug('get_nt_header() failed: {0}'.format(why))
            return

        # Parse the PE sections for this driver
        for sec in nt_header.get_sections(self._config.UNSAFE):

            # Only check executable sections
            if not sec.Characteristics & 0x20000000:
                continue

            # Calculate the virtual address of this PE section in memory
            sec_va = module.DllBase + sec.VirtualAddress

            # Extract the section's data and make sure its not all zeros
            data = addr_space.zread(sec_va, sec.Misc.VirtualSize)

            if data == "\x00" * len(data):
                continue

            # Disassemble instructions in the section
            for op in distorm3.DecomposeGenerator(sec_va, data, distorm3.Decode32Bits):

                if (op.valid and ((op.flowControl == 'FC_CALL' and
                        op.mnemonic == "CALL") or
                        (op.flowControl == 'FC_UNC_BRANCH' and
                        op.mnemonic == "JMP")) and
                        op.operands[0].type == 'AbsoluteMemoryAddress'):

                    # This is ADDR, which is the IAT location
                    const = op.operands[0].disp & 0xFFFFFFFF

                    # Abort if ADDR is not a valid address
                    if not addr_space.is_valid_address(const):
                        continue

                    # This is what [ADDR] points to - the absolute destination
                    call_dest = obj.Object("address", offset = const, vm = addr_space)

                    # Abort if [ADDR] is not a valid address
                    if not addr_space.is_valid_address(call_dest):
                        continue

                    check1 = module_group.find_module(const)
                    check2 = module_group.find_module(call_dest)

                    # If ADDR or [ADDR] point to an unknown code page
                    if not check1 or not check2:
                        hook = Hook(hook_type = HOOKTYPE_CODEPAGE_KERNEL,
                                    hook_mode = HOOK_MODE_KERNEL,
                                    function_name = "",
                                    function_address = op.address,
                                    hook_address = call_dest,
                                    )
                        # Add the location we found the call
                        hook.add_hop_chunk(op.address,
                            data[op.address - sec_va : op.address - sec_va + 24])

                        # Add the rootkit stub
                        hook.add_hop_chunk(call_dest, addr_space.zread(call_dest, 24))
                        yield hook

    def check_wsp(self, addr_space, module, module_group):
        """
        Check for hooks of non-exported WSP* functions. The
        mswsock.dll module contains a global variable which
        points to all the internal Winsock functions. We find
        the function table by the reference from the exported
        WSPStartup API.

        .text:6C88922E 8B 7D 50          mov     edi, [ebp+lpProcTable]
        .text:6C889231 6A 1E             push    1Eh
        .text:6C889233 59                pop     ecx
        .text:6C889234 BE 40 64 8B 6C    mov     esi, offset _SockProcTable
        .text:6C889239 F3 A5             rep movsd

        @param addr_space: process AS

        @param module: the _LDR_DATA_TABLE_ENTRY for mswsock.dll

        @param module_group: a ModuleGroup instance for the process.
        """

        WSPStartup = module.getprocaddress("WSPStartup")

        if not WSPStartup:
            #debug.debug("Abort check_wsp, can't find WSPStartup")
            return

        WSPStartup += module.DllBase

        # Opcode pattern to look for
        signature = "\x6A\x1E\x59\xBE"

        # Read enough bytes of the function to find our signature
        data = addr_space.zread(WSPStartup, 300)

        if data == "\x00" * len(data):
            #debug.debug("WSPStartup prologue is paged")
            return

        offset = data.find(signature)

        if offset == -1:
            #debug.debug("Can't find {0} in WSPStartup".format(repr(signature)))
            return

        # Dereference the pointer as our _SockProcTable
        p = obj.Object("address",
            offset = WSPStartup + offset + len(signature),
            vm = addr_space)

        p = p.dereference_as("_SOCK_PROC_TABLE")

        # Enumerate functions in the procedure table
        for i, function_address in enumerate(p.Functions):

            function_owner = module_group.find_module(function_address)

            # The function points outside of mwsock, its hooked
            if function_owner != module:

                hook = Hook(hook_type = HOOKTYPE_WINSOCK,
                            hook_mode = HOOK_MODE_USER,
                            function_name = WINSOCK_TABLE[i],
                            function_address = function_address,
                            hook_module = function_owner,
                            victim_module = module
                            )
                hook.add_hop_chunk(function_address,
                    addr_space.zread(function_address, 12))

                yield hook
            else:
                # The function points inside mwsock, check inline
                ret = self.check_inline(function_address, addr_space,
                    module.DllBase, module.DllBase + module.SizeOfImage,
                    self.idt)

                if not ret:
                    #debug.debug("Cannot analyze {0}".format(WINSOCK_TABLE[i]))
                    continue

                (hooked, data, hook_address) = ret

                if hooked:
                    hook_module = module_group.find_module(hook_address)
                    if hook_module != module:
                        hook = Hook(hook_type = HOOKTYPE_WINSOCK,
                                    hook_mode = HOOK_MODE_USER,
                                    function_name = WINSOCK_TABLE[i],
                                    function_address = function_address,
                                    hook_module = hook_module,
                                    hook_address = hook_address,
                                    victim_module = module
                                    )
                        hook.add_hop_chunk(function_address, data)
                        hook.add_hop_chunk(hook_address, addr_space.zread(hook_address, 12))
                        yield hook

    @staticmethod
    def check_inline(va, addr_space, mem_start, mem_end, idt = None):
        """
        Check for inline API hooks. We check for direct and indirect
        calls, direct and indirect jumps, and PUSH/RET combinations.

        @param va: the virtual address of the function to check

        @param addr_space: process or kernel AS where the function resides

        @param mem_start: base address of the module containing the
            function being checked.

        @param mem_end: end address of the module containing the func
            being checked.

        @param idt: whitelisted IDT interrupt handlers removed from the
            dict. Not required for compatibility reasons.

        @returns: a tuple of (hooked, data, hook_address)
        """

        data = addr_space.zread(va, 24)

        if data == "\x00" * len(data):
            #debug.debug("Cannot read function prologue at {0:#x}".format(va))
            return None

        outside_module = lambda x: x != None and (x < mem_start or x > mem_end)

        # Number of instructions disassembled so far
        n = 0
        # Destination address of hooks
        d = None
        # Save the last PUSH before a CALL
        push_val = None
        # Save the general purpose registers
        regs = {}

        for op in distorm3.Decompose(va, data, distorm3.Decode32Bits):

            # Quit the loop when we have three instructions or when
            # a decomposition error is encountered, whichever is first.
            if not op.valid or n == 3:
                break

            if op.flowControl == 'FC_CALL':
                # Clear the push value
                if push_val:
                    push_val = None
                if op.mnemonic == "CALL" and op.operands[0].type == 'AbsoluteMemoryAddress':
                    # Check for CALL [ADDR]
                    const = op.operands[0].disp & 0xFFFFFFFF
                    d = obj.Object("unsigned int", offset = const, vm = addr_space)
                    if outside_module(d):
                        break
                elif op.operands[0].type == 'Immediate':
                    # Check for CALL ADDR
                    d = op.operands[0].value & 0xFFFFFFFF
                    if outside_module(d):
                        break
                elif op.operands[0].type == 'Register':
                    # Check for CALL REG
                    d = regs.get(op.operands[0].name)
                    if d and outside_module(d):
                        break
            elif op.flowControl == 'FC_UNC_BRANCH' and op.mnemonic == "JMP":
                # Clear the push value
                if push_val:
                    push_val = None
                if op.size > 2:
                    if op.operands[0].type == 'AbsoluteMemoryAddress':
                        # Check for JMP [ADDR]
                        const = op.operands[0].disp & 0xFFFFFFFF
                        d = obj.Object("unsigned int", offset = const, vm = addr_space)
                        if outside_module(d):
                            break
                    elif op.operands[0].type == 'Immediate':
                        # Check for JMP ADDR
                        d = op.operands[0].value & 0xFFFFFFFF
                        if outside_module(d):
                            break
                elif op.size == 2 and op.operands[0].type == 'Register':
                    # Check for JMP REG
                    d = regs.get(op.operands[0].name)
                    if d and outside_module(d):
                        break
            elif op.flowControl == 'FC_NONE':
                # Check for PUSH followed by a RET
                if (op.mnemonic == "PUSH" and
                        op.operands[0].type == 'Immediate' and op.size == 5):
                    # Set the push value
                    push_val = op.operands[0].value & 0xFFFFFFFF
                # Check for moving imm values into a register
                if (op.mnemonic == "MOV" and op.operands[0].type == 'Register'
                        and op.operands[1].type == 'Immediate'):
                    # Clear the push value
                    if push_val:
                        push_val = None
                    # Save the value put into the register
                    regs[op.operands[0].name] = op.operands[1].value
            elif op.flowControl == 'FC_RET':
                if push_val:
                    d = push_val
                    if outside_module(d):
                        break
                # This causes us to stop disassembling when
                # reaching the end of a function
                break
            elif op.flowControl == "FC_INT" and idt:
                # Clear the push value
                if push_val:
                    push_val = None
                # Check for INT, ignore INT3
                if op.mnemonic == "INT" and op.size > 1 and op.operands[0].type == 'Immediate':
                    # Check interrupt handler address
                    d = idt[op.operands[0].value]
                    if d and outside_module(d):
                        break
            n += 1

        # Check EIP after the function prologue
        if outside_module(d):
            return True, data, d
        else:
            return False, data, d

    def gather_stuff(self, _addr_space, module):
        """Use the Volatility object classes to enumerate
        imports and exports. This function can be overriden
        to use pefile instead for speed testing"""

        # This is a dictionary where keys are the names of imported
        # modules and values are lists of tuples (ord, addr, name).
        imports = {}
        exports = [(o, module.DllBase + f, n) for o, f, n in module.exports()]

        for dll, o, f, n in module.imports():
            dll = dll.lower()
            if dll in imports:
                imports[dll].append((o, f, n))
            else:
                imports[dll] = [(o, f, n)]

        return imports, exports

    def get_hooks(self, hook_mode, addr_space, module, module_group):
        """Enumerate IAT, EAT, Inline hooks. Also acts as a dispatcher
        for NT syscall, UCP scans, and winsock procedure table hooks.

        @param hook_mode: one of the HOOK_MODE_* constants

        @param addr_space: a process AS or kernel AS

        @param module: an _LDR_DATA_TABLE_ENTRY for the module being
        checked for hooks.

        @param module_group: a ModuleGroup instance for the process.
        """

        # We start with the module base name. If that's not available,
        # trim the full name down to its base name.
        module_name = (str(module.BaseDllName or '') or
                       ntpath.basename(str(module.FullDllName or '')))

        # Lowercase for string matching
        module_name = module_name.lower()

        if hook_mode == HOOK_MODE_USER:
            if module_name == "ntdll.dll":
                for hook in self.check_syscall(addr_space, module, module_group):
                    yield hook
            elif module_name == "mswsock.dll":
                for hook in self.check_wsp(addr_space, module, module_group):
                    yield hook
        else:
            if module_name in self.ucpscan_modules:
                for hook in self.check_ucpcall(addr_space, module, module_group):
                    yield hook

        imports, exports = \
            self.gather_stuff(addr_space, module)

        for dll, functions in imports.items():

            valid_owners = module_group.mod_name.get(dll, [])
            if not valid_owners:
                #debug.debug("Cannot find any modules named {0}".format(dll))
                continue

            for (_, f, n) in functions:

                if not f:
                    #debug.debug("IAT function {0} is paged or ordinal".format(n or ''))
                    continue

                if not addr_space.is_valid_address(f):
                    continue

                function_owner = module_group.find_module(f)

                if function_owner not in valid_owners:
                    hook = Hook(hook_type = HOOKTYPE_IAT,
                                hook_mode = hook_mode,
                                function_name = n or '',
                                hook_address = f,
                                hook_module = function_owner,
                                victim_module = dll, # only for IAT hooks
                                )
                    # Add the rootkit code
                    hook.add_hop_chunk(f, addr_space.zread(f, 24))
                    yield hook

        for _, f, n in exports:

            if not f:
                #debug.debug("EAT function {0} is paged".format(n or ''))
                continue

            function_address = f

            if not addr_space.is_valid_address(function_address):
                continue

            # Get the module containing the function
            function_owner = module_group.find_module(function_address)

            # This is a check for EAT hooks
            if function_owner != module:
                hook = Hook(hook_type = HOOKTYPE_EAT,
                            hook_mode = hook_mode,
                            function_name = n or '',
                            hook_address = function_address,
                            hook_module = function_owner,
                            )
                hook.add_hop_chunk(function_address,
                    addr_space.zread(function_address, 24))
                yield hook

                # No need to check for inline hooks if EAT is hooked
                continue

            ret = self.check_inline(function_address, addr_space,
                module.DllBase, module.DllBase + module.SizeOfImage,
                self.idt)

            if ret == None:
                #debug.debug("Cannot analyze {0}".format(n or ''))
                continue

            (hooked, data, dest_addr) = ret

            if not hooked:
                continue

            if not addr_space.is_valid_address(dest_addr):
                continue

            function_owner = module_group.find_module(dest_addr)
            if function_owner != module:
                # only do this for kernel hooks
                #if params['mode'] == HOOK_MODE_KERNEL:
                #    if owner:
                #        if self.in_data_section(owner, status['destaddr']):
                #            continue

                hook = Hook(hook_type = HOOKTYPE_INLINE,
                            hook_mode = hook_mode,
                            function_name = n or '',
                            function_address = function_address,
                            hook_address = dest_addr,
                            hook_module = function_owner,
                            victim_module = module,
                            )
                # Add the function prologue
                hook.add_hop_chunk(function_address, data)
                # Add the first redirection
                hook.add_hop_chunk(dest_addr, addr_space.zread(dest_addr, 24))
                yield hook

    def calculate(self):

        addr_space = utils.load_as(self._config)

        if not has_distorm3:
            debug.error("Install distorm3 code.google.com/p/distorm/")

        if not self.is_valid_profile(addr_space.profile):
            debug.error("This command does not support the selected profile.")

        self.idt = self.get_idt()

        if not self._config.SKIP_PROCESS:
            for proc in self.filter_tasks(tasks.pslist(addr_space)):
                process_name = str(proc.ImageFileName).lower()

                if (self._config.QUICK and
                        process_name not in self.critical_process):
                    #debug.debug("Skipping non-critical process {0} ({1})".format(
                    #    process_name, proc.UniqueProcessId))
                    continue

                process_space = proc.get_process_address_space()
                if not process_space:
                    #debug.debug("Cannot acquire process AS for {0} ({1})".format(
                    #    process_name, proc.UniqueProcessId))
                    continue

                module_group = ModuleGroup(proc.get_load_modules())

                for dll in module_group.mods:

                    if not process_space.is_valid_address(dll.DllBase):
                        continue

                    dll_name = str(dll.BaseDllName or '').lower()

                    if (self._config.QUICK and
                            dll_name not in self.critical_dlls and
                            dll.DllBase != proc.Peb.ImageBaseAddress):
                        #debug.debug("Skipping non-critical dll {0} at {1:#x}".format(
                        #    dll_name, dll.DllBase))
                        continue

                    #debug.debug("Analyzing {0}!{1}".format(process_name, dll_name))

                    for hook in self.get_hooks(HOOK_MODE_USER,
                            process_space, dll, module_group):
                        yield proc, dll, hook

        if not self._config.SKIP_KERNEL:
            process_list = list(tasks.pslist(addr_space))
            module_group = ModuleGroup(modules.lsmod(addr_space))

            for mod in module_group.mods:

                #module_name = str(mod.BaseDllName or '')
                #debug.debug("Analyzing {0}".format(module_name))

                kernel_space = tasks.find_space(addr_space,
                    process_list, mod.DllBase)

                if not kernel_space:
                    #debug.debug("No kernel AS for {0} at {1:#x}".format(
                    #    module_name, mod.DllBase))
                    continue

                for hook in self.get_hooks(HOOK_MODE_KERNEL,
                        kernel_space, mod, module_group):
                    yield None, mod, hook

    def render_text(self, outfd, data):
        for process, module, hook in data:

            if not self._config.NO_WHITELIST:

                if process:
                    process_name = str(process.ImageFileName)
                else:
                    process_name = ''

                if self.whitelist(hook.hook_mode | hook.hook_type,
                                    process_name, hook.VictimModule,
                                    hook.HookModule, hook.Function):
                    #debug.debug("Skipping whitelisted function: {0} {1} {2} {3}".format(
                    #    process_name, hook.VictimModule, hook.HookModule,
                    #    hook.Function))
                    continue

            outfd.write("*" * 72 + "\n")
            outfd.write("Hook mode: {0}\n".format(hook.Mode))
            outfd.write("Hook type: {0}\n".format(hook.Type))

            if process:
                outfd.write('Process: {0} ({1})\n'.format(
                    process.UniqueProcessId, process.ImageFileName))

            outfd.write("Victim module: {0} ({1:#x} - {2:#x})\n".format(
                str(module.BaseDllName or '') or ntpath.basename(str(module.FullDllName or '')),
                module.DllBase, module.DllBase + module.SizeOfImage))

            outfd.write("Function: {0}\n".format(hook.Detail))
            outfd.write("Hook address: {0:#x}\n".format(hook.hook_address))
            outfd.write("Hooking module: {0}\n\n".format(hook.HookModule))

            for n, info in enumerate(hook.disassembled_hops):
                (address, data) = info
                s = ["{0:#x} {1:<16} {2}".format(o, h, i)
                        for o, i, h in
                        malfind.Disassemble(data, int(address))
                    ]
                outfd.write("Disassembly({0}):\n{1}".format(n, "\n".join(s)))
                outfd.write("\n\n")