#!/usr/bin/python

# me_cleaner -  Tool for partial deblobbing of Intel ME/TXE firmware images
# Copyright (C) 2016, 2017 Nicola Corna <nicola@corna.info>
#
# This program 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 3 of the License, or
# (at your option) any later version.
#
# This program 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.
#

import sys
import itertools
import binascii
import hashlib
from struct import pack, unpack


unremovable_modules = ("BUP", "ROMP")


def get_chunks_offsets(llut, me_start):
    chunk_count = unpack("<I", llut[0x04:0x08])[0]
    huffman_stream_end = sum(unpack("<II", llut[0x10:0x18])) + me_start
    nonzero_offsets = [huffman_stream_end]
    offsets = []

    for i in range(0, chunk_count):
        chunk = llut[0x40 + i * 4:0x44 + i * 4]
        offset = 0

        if chunk[3] != 0x80:
            offset = unpack("<I", chunk[0:3] + b"\x00")[0] + me_start

        offsets.append([offset, 0])
        if offset != 0:
            nonzero_offsets.append(offset)

    nonzero_offsets.sort()

    for i in offsets:
        if i[0] != 0:
            i[1] = nonzero_offsets[nonzero_offsets.index(i[0]) + 1]

    return offsets


def fill_range(f, start, end, fill):
    block = fill * 4096
    f.seek(start)
    f.writelines(itertools.repeat(block, (end - start) // 4096))
    f.write(block[:(end - start) % 4096])


def remove_modules(f, mod_headers, ftpr_offset):
    comp_str = ("Uncomp.", "Huffman", "LZMA")
    unremovable_huff_chunks = []
    chunks_offsets = []
    base = 0
    chunk_size = 0

    for mod_header in mod_headers:
        name = mod_header[0x04:0x14].rstrip(b"\x00").decode("ascii")
        offset = unpack("<I", mod_header[0x38:0x3C])[0] + ftpr_offset
        size = unpack("<I", mod_header[0x40:0x44])[0]
        flags = unpack("<I", mod_header[0x50:0x54])[0]
        comp_type = (flags >> 4) & 7

        sys.stdout.write(" {:<16} ({:<7}, ".format(name, comp_str[comp_type]))

        if comp_type == 0x00 or comp_type == 0x02:
            sys.stdout.write("0x{:06x} - 0x{:06x}): "
                             .format(offset, offset + size))

            if name in unremovable_modules:
                print("NOT removed, essential")
            else:
                fill_range(f, offset, offset + size, b"\xff")
                print("removed")

        elif comp_type == 0x01:
            sys.stdout.write("fragmented data    ): ")
            if not chunks_offsets:
                f.seek(offset)
                llut = f.read(4)
                if llut == b"LLUT":
                    llut += f.read(0x3c)

                    chunk_count = unpack("<I", llut[0x4:0x8])[0]
                    base = unpack("<I", llut[0x8:0xc])[0] + 0x10000000
                    huff_data_len = unpack("<I", llut[0x10:0x14])[0]
                    chunk_size = unpack("<I", llut[0x30:0x34])[0]

                    llut += f.read(chunk_count * 4 + huff_data_len)
                    chunks_offsets = get_chunks_offsets(llut, me_start)
                else:
                    sys.exit("Huffman modules found, but LLUT is not present")

            if name in unremovable_modules:
                print("NOT removed, essential")
                module_base = unpack("<I", mod_header[0x34:0x38])[0]
                module_size = unpack("<I", mod_header[0x3c:0x40])[0]
                first_chunk_num = (module_base - base) // chunk_size
                last_chunk_num = first_chunk_num + module_size // chunk_size

                unremovable_huff_chunks += \
                    [x for x in chunks_offsets[first_chunk_num:
                     last_chunk_num + 1] if x[0] != 0]
            else:
                print("removed")

        else:
            sys.stdout.write("0x{:06x} - 0x{:06x}): unknown compression, "
                             "skipping".format(offset, offset + size))

    if chunks_offsets:
        removable_huff_chunks = []

        for chunk in chunks_offsets:
            if all(not(unremovable_chk[0] <= chunk[0] < unremovable_chk[1] or
                       unremovable_chk[0] < chunk[1] <= unremovable_chk[1])
                   for unremovable_chk in unremovable_huff_chunks):
                removable_huff_chunks.append(chunk)

        for removable_chunk in removable_huff_chunks:
            if removable_chunk[1] > removable_chunk[0]:
                fill_range(f, removable_chunk[0], removable_chunk[1], b"\xff")


def check_partition_signature(f, offset):
    f.seek(offset)
    header = f.read(0x80)
    modulus = int(binascii.hexlify(f.read(0x100)[::-1]), 16)
    public_exponent = int(binascii.hexlify(f.read(0x4)[::-1]), 16)
    signature = int(binascii.hexlify(f.read(0x100)[::-1]), 16)

    header_len = unpack("<I", header[0x4:0x8])[0] * 4
    manifest_len = unpack("<I", header[0x18:0x1c])[0] * 4
    f.seek(offset + header_len)

    sha256 = hashlib.sha256()
    sha256.update(header)
    sha256.update(f.read(manifest_len - header_len))

    decrypted_sig = pow(signature, public_exponent, modulus)

    return "{:#x}".format(decrypted_sig).endswith(sha256.hexdigest())   # FIXME


if len(sys.argv) != 2 or sys.argv[1] == "-h" or sys.argv[1] == "--help":
    print("Usage: \n"
          " me_cleaner.py me_or_txe_image.bin\n"
          "or\n"
          " me_cleaner.py full_dump.bin")
else:
    with open(sys.argv[1], "r+b") as f:
        f.seek(0x10)
        magic = f.read(4)

        if magic == b"$FPT":
            print("ME/TXE image detected")
            me_start = 0
            f.seek(0, 2)
            me_end = f.tell()

        elif magic == b"\x5a\xa5\xf0\x0f":
            print("Full image detected")
            f.seek(0x14)
            flmap0 = unpack("<I", f.read(4))[0]
            nr = flmap0 >> 24 & 0x7
            frba = flmap0 >> 12 & 0xff0
            if nr >= 2:
                f.seek(frba + 0x8)
                flreg2 = unpack("<I", f.read(4))[0]
                me_start = (flreg2 & 0x1fff) << 12
                me_end = flreg2 >> 4 & 0x1fff000 | 0xfff

                if me_start >= me_end:
                    sys.exit("The ME/TXE region in this image has been "
                             "disabled")

                f.seek(me_start + 0x10)
                if f.read(4) != b"$FPT":
                    sys.exit("The ME/TXE region is corrupted or missing")

                print("The ME/TXE region goes from {:#x} to {:#x}"
                      .format(me_start, me_end))
            else:
                sys.exit("This image does not contains a ME/TXE firmware "
                         "(NR = {})".format(nr))
        else:
            sys.exit("Unknown image")

        print("Found FPT header at {:#x}".format(me_start + 0x10))

        f.seek(me_start + 0x14)
        entries = unpack("<I", f.read(4))[0]
        print("Found {} partition(s)".format(entries))

        f.seek(me_start + 0x14)
        header_len = unpack("B", f.read(1))[0]

        f.seek(me_start + 0x30)
        partitions = f.read(entries * 0x20)

        ftpr_header = b""

        for i in range(entries):
            if partitions[i * 0x20:(i * 0x20) + 4] == b"FTPR":
                ftpr_header = partitions[i * 0x20:(i + 1) * 0x20]
                break

        if ftpr_header == b"":
            sys.exit("FTPR header not found, this image doesn't seem to be "
                     "valid")

        ftpr_offset, ftpr_lenght = unpack("<II", ftpr_header[0x08:0x10])
        ftpr_offset += me_start
        print("Found FTPR header: FTPR partition spans from {:#x} to {:#x}"
              .format(ftpr_offset, ftpr_offset + ftpr_lenght))
        print("Removing extra partitions...")

        fill_range(f, me_start + 0x30, ftpr_offset, b"\xff")
        fill_range(f, ftpr_offset + ftpr_lenght, me_end, b"\xff")

        print("Removing extra partition entries in FPT...")
        f.seek(me_start + 0x30)
        f.write(ftpr_header)
        f.seek(me_start + 0x14)
        f.write(pack("<I", 1))

        print("Removing EFFS presence flag...")
        f.seek(me_start + 0x24)
        flags = unpack("<I", f.read(4))[0]
        flags &= ~(0x00000001)
        f.seek(me_start + 0x24)
        f.write(pack("<I", flags))

        f.seek(me_start, 0)
        header = bytearray(f.read(0x30))
        checksum = (0x100 - (sum(header) - header[0x1b]) & 0xff) & 0xff

        print("Correcting checksum (0x{:02x})...".format(checksum))
        # The checksum is just the two's complement of the sum of the first
        # 0x30 bytes (except for 0x1b, the checksum itself). In other words,
        # the sum of the first 0x30 bytes must be always 0x00.
        f.seek(me_start + 0x1b)
        f.write(pack("B", checksum))

        f.seek(ftpr_offset)
        if f.read(4) == b"$CPD":
            me11 = True
            num_entries = unpack("<I", f.read(4))[0]
            f.seek(ftpr_offset + 0x10 + num_entries * 0x18 + 0x24)
        else:
            me11 = False
            f.seek(ftpr_offset + 0x24)

        version = unpack("<HHHH", f.read(0x08))
        print("ME/TXE firmware version {}"
              .format('.'.join(str(i) for i in version)))

        if not me11:
            print("Reading FTPR modules list...")
            f.seek(ftpr_offset + 0x1c)
            tag = f.read(4)

            if tag == b"$MN2":
                f.seek(ftpr_offset + 0x20)
                num_modules = unpack("<I", f.read(4))[0]
                f.seek(ftpr_offset + 0x290)
                data = f.read(0x84)

                module_header_size = 0
                if data[0x0:0x4] == b"$MME":
                    if data[0x60:0x64] == b"$MME":
                        module_header_size = 0x60
                    elif data[0x80:0x84] == b"$MME":
                        module_header_size = 0x80

                if module_header_size != 0:
                    f.seek(ftpr_offset + 0x290)
                    mod_headers = [f.read(module_header_size)
                                   for i in range(0, num_modules)]

                    if all(mod_h.startswith(b"$MME") for mod_h in mod_headers):
                        remove_modules(f, mod_headers, ftpr_offset)
                    else:
                        print("Found less modules than expected in the FTPR "
                              "partition; skipping modules removal")
                else:
                    print("Can't find the module header size; skipping "
                          "modules removal")
            else:
                print("Wrong FTPR partition tag ({}); skipping modules removal"
                      .format(tag))
        else:
            print("Modules removal in ME v11 or greater is not yet supported")

        sys.stdout.write("Checking FTPR RSA signature... ")
        if check_partition_signature(f, ftpr_offset):
            print("VALID")
        else:
            print("INVALID!!")
            sys.exit("The FTPR partition signature is not valid. Is the input "
                     "ME/TXE image valid?")

        print("Done! Good luck!")