From ca39b20c6dcf750cf8e8e4d4ab58ae19f346ba9b Mon Sep 17 00:00:00 2001
From: Mike Auty <mike.auty@gmail.com>
Date: Sun, 26 Sep 2021 01:35:52 +0100
Subject: [PATCH] Layers: Implement AVML file support

---
 volatility3/framework/layers/avml.py | 282 +++++++++++++++++++++++++++
 1 file changed, 282 insertions(+)
 create mode 100644 volatility3/framework/layers/avml.py

diff --git a/volatility3/framework/layers/avml.py b/volatility3/framework/layers/avml.py
new file mode 100644
index 000000000..aca3b037f
--- /dev/null
+++ b/volatility3/framework/layers/avml.py
@@ -0,0 +1,282 @@
+"""Functions that read AVML files.
+
+The user of the file doesn't have to worry about the compression,
+but random access is not allowed."""
+import io
+import struct
+from typing import Tuple, List, Optional
+
+from volatility3.framework import exceptions, interfaces, constants
+from volatility3.framework.layers import segmented
+
+try:
+    import snappy
+
+    HAS_SNAPPY = True
+except ImportError:
+    HAS_SNAPPY = False
+
+
+class SnappyFraming:
+    def __init__(self):
+        pass
+
+    # crc32-c (Castagnoli) (crc32c_poly=0x1EDC6F41)
+    crc32c_table = [
+        0x00000000, 0xF26B8303, 0xE13B70F7, 0x1350F3F4,
+        0xC79A971F, 0x35F1141C, 0x26A1E7E8, 0xD4CA64EB,
+        0x8AD958CF, 0x78B2DBCC, 0x6BE22838, 0x9989AB3B,
+        0x4D43CFD0, 0xBF284CD3, 0xAC78BF27, 0x5E133C24,
+        0x105EC76F, 0xE235446C, 0xF165B798, 0x030E349B,
+        0xD7C45070, 0x25AFD373, 0x36FF2087, 0xC494A384,
+        0x9A879FA0, 0x68EC1CA3, 0x7BBCEF57, 0x89D76C54,
+        0x5D1D08BF, 0xAF768BBC, 0xBC267848, 0x4E4DFB4B,
+        0x20BD8EDE, 0xD2D60DDD, 0xC186FE29, 0x33ED7D2A,
+        0xE72719C1, 0x154C9AC2, 0x061C6936, 0xF477EA35,
+        0xAA64D611, 0x580F5512, 0x4B5FA6E6, 0xB93425E5,
+        0x6DFE410E, 0x9F95C20D, 0x8CC531F9, 0x7EAEB2FA,
+        0x30E349B1, 0xC288CAB2, 0xD1D83946, 0x23B3BA45,
+        0xF779DEAE, 0x05125DAD, 0x1642AE59, 0xE4292D5A,
+        0xBA3A117E, 0x4851927D, 0x5B016189, 0xA96AE28A,
+        0x7DA08661, 0x8FCB0562, 0x9C9BF696, 0x6EF07595,
+        0x417B1DBC, 0xB3109EBF, 0xA0406D4B, 0x522BEE48,
+        0x86E18AA3, 0x748A09A0, 0x67DAFA54, 0x95B17957,
+        0xCBA24573, 0x39C9C670, 0x2A993584, 0xD8F2B687,
+        0x0C38D26C, 0xFE53516F, 0xED03A29B, 0x1F682198,
+        0x5125DAD3, 0xA34E59D0, 0xB01EAA24, 0x42752927,
+        0x96BF4DCC, 0x64D4CECF, 0x77843D3B, 0x85EFBE38,
+        0xDBFC821C, 0x2997011F, 0x3AC7F2EB, 0xC8AC71E8,
+        0x1C661503, 0xEE0D9600, 0xFD5D65F4, 0x0F36E6F7,
+        0x61C69362, 0x93AD1061, 0x80FDE395, 0x72966096,
+        0xA65C047D, 0x5437877E, 0x4767748A, 0xB50CF789,
+        0xEB1FCBAD, 0x197448AE, 0x0A24BB5A, 0xF84F3859,
+        0x2C855CB2, 0xDEEEDFB1, 0xCDBE2C45, 0x3FD5AF46,
+        0x7198540D, 0x83F3D70E, 0x90A324FA, 0x62C8A7F9,
+        0xB602C312, 0x44694011, 0x5739B3E5, 0xA55230E6,
+        0xFB410CC2, 0x092A8FC1, 0x1A7A7C35, 0xE811FF36,
+        0x3CDB9BDD, 0xCEB018DE, 0xDDE0EB2A, 0x2F8B6829,
+        0x82F63B78, 0x709DB87B, 0x63CD4B8F, 0x91A6C88C,
+        0x456CAC67, 0xB7072F64, 0xA457DC90, 0x563C5F93,
+        0x082F63B7, 0xFA44E0B4, 0xE9141340, 0x1B7F9043,
+        0xCFB5F4A8, 0x3DDE77AB, 0x2E8E845F, 0xDCE5075C,
+        0x92A8FC17, 0x60C37F14, 0x73938CE0, 0x81F80FE3,
+        0x55326B08, 0xA759E80B, 0xB4091BFF, 0x466298FC,
+        0x1871A4D8, 0xEA1A27DB, 0xF94AD42F, 0x0B21572C,
+        0xDFEB33C7, 0x2D80B0C4, 0x3ED04330, 0xCCBBC033,
+        0xA24BB5A6, 0x502036A5, 0x4370C551, 0xB11B4652,
+        0x65D122B9, 0x97BAA1BA, 0x84EA524E, 0x7681D14D,
+        0x2892ED69, 0xDAF96E6A, 0xC9A99D9E, 0x3BC21E9D,
+        0xEF087A76, 0x1D63F975, 0x0E330A81, 0xFC588982,
+        0xB21572C9, 0x407EF1CA, 0x532E023E, 0xA145813D,
+        0x758FE5D6, 0x87E466D5, 0x94B49521, 0x66DF1622,
+        0x38CC2A06, 0xCAA7A905, 0xD9F75AF1, 0x2B9CD9F2,
+        0xFF56BD19, 0x0D3D3E1A, 0x1E6DCDEE, 0xEC064EED,
+        0xC38D26C4, 0x31E6A5C7, 0x22B65633, 0xD0DDD530,
+        0x0417B1DB, 0xF67C32D8, 0xE52CC12C, 0x1747422F,
+        0x49547E0B, 0xBB3FFD08, 0xA86F0EFC, 0x5A048DFF,
+        0x8ECEE914, 0x7CA56A17, 0x6FF599E3, 0x9D9E1AE0,
+        0xD3D3E1AB, 0x21B862A8, 0x32E8915C, 0xC083125F,
+        0x144976B4, 0xE622F5B7, 0xF5720643, 0x07198540,
+        0x590AB964, 0xAB613A67, 0xB831C993, 0x4A5A4A90,
+        0x9E902E7B, 0x6CFBAD78, 0x7FAB5E8C, 0x8DC0DD8F,
+        0xE330A81A, 0x115B2B19, 0x020BD8ED, 0xF0605BEE,
+        0x24AA3F05, 0xD6C1BC06, 0xC5914FF2, 0x37FACCF1,
+        0x69E9F0D5, 0x9B8273D6, 0x88D28022, 0x7AB90321,
+        0xAE7367CA, 0x5C18E4C9, 0x4F48173D, 0xBD23943E,
+        0xF36E6F75, 0x0105EC76, 0x12551F82, 0xE03E9C81,
+        0x34F4F86A, 0xC69F7B69, 0xD5CF889D, 0x27A40B9E,
+        0x79B737BA, 0x8BDCB4B9, 0x988C474D, 0x6AE7C44E,
+        0xBE2DA0A5, 0x4C4623A6, 0x5F16D052, 0xAD7D5351,
+    ]
+
+    def masked_crc32c(self, buf: bytes) -> int:
+        crc = 0xffffffff
+        for c in buf:
+            crc = (crc >> 8) ^ self.crc32c_table[(crc ^ c) & 0xFF]
+        crc = (~crc) & 0xffffffff
+        # reverse endianness
+        crc = struct.unpack(">I", struct.pack("<I", crc))[0]
+        return (((crc >> 15) | (crc << 17)) + 0xa282ead8) & 0xffffffff
+
+    def decompress(self, source_data: bytes) -> io.BytesIO:
+        offset = 0
+        data = io.BytesIO()
+        while offset < len(source_data):
+            header_structure = "<IIQQQ"
+            header_size = struct.calcsize(header_structure)
+            header_data = source_data[offset:offset + header_size]
+            magic, version, start, end, padding = struct.unpack(header_structure, header_data)
+            print(magic, version, start, end, padding)
+            if magic not in [0x4c4d5641]:
+                raise RuntimeError("File not in AVML or LiME format")
+            chunk_data = source_data[offset + header_size: offset + header_size + (end - start)]
+            chunk, consumed = self.read_snappy_data(chunk_data, end - start)
+            data.seek(start)
+            data.write(chunk)
+            # TODO: Check whatever the remaining 8 bytes are
+            offset += header_size + consumed + 8
+        data.seek(0)
+        return data
+
+    def read_snappy_data(self, data: bytes, limit: int) -> Tuple[bytes, int]:
+        """Decompresses data up to the size limit provided
+
+        Args:
+            data: Input data
+            limit: The maximum size of decompressed data
+
+        Returns:
+            Tuple of decompressed data, and number of compressed bytes consumed
+        """
+        decompressed = bytearray()
+        offset = 0
+        crc_len = 4
+        chunk_header_struct = '<L'
+        chunk_header_len = struct.calcsize(chunk_header_struct)
+        while len(decompressed) <= limit:
+            if offset + chunk_header_len < len(data):
+                chunk_header = data[offset:offset + chunk_header_len]
+                chunk_header_val = struct.unpack('<L', chunk_header)[0]
+                chunk_type, chunk_size = chunk_header_val & 0xff, chunk_header_val >> 8
+                if chunk_type == 0xff:
+                    if data[offset + chunk_header_len:offset + chunk_header_len + chunk_size] != b'sNaPpY':
+                        raise ValueError(f"Snappy header missing at offset: {offset}")
+                elif chunk_type in [0x00, 0x01]:
+                    # CRC + (Un)compressed data
+                    start = offset + chunk_header_len
+                    chunk_crc = data[start: start + crc_len]
+                    chunk_data = data[start + crc_len: start + chunk_size]
+                    if chunk_type == 0x00:
+                        # Compressed data
+                        chunk_data = snappy.decompress(chunk_data)
+                    # TODO: Verify CRC
+                    decompressed.extend(chunk_data)
+                elif chunk_type in range(0x2, 0x80):
+                    # Unskippable
+                    raise ValueError(f"Unskippable chunk of type {chunk_type} found: {offset}")
+                offset += chunk_header_len + chunk_size
+        return decompressed, offset
+
+
+class AVMLLayer(segmented.NonLinearlySegmentedLayer):
+    """A Lime format TranslationLayer.
+
+    Lime is generally used to store physical memory images where there
+    are large holes in the physical layer
+    """
+
+    def __init__(self, *args, **kwargs):
+        self._compressed = {}
+        super().__init__(*args, **kwargs)
+
+    @classmethod
+    def _check_header(cls, layer: interfaces.layers.DataLayerInterface):
+        header_structure = "<II"
+        magic, version = struct.unpack(header_structure,
+                                       layer.read(layer.minimum_address, struct.calcsize(header_structure)))
+        if magic not in [0x4c4d5641] or version != 2:
+            raise exceptions.LayerException("File not completely in AVML format")
+
+    def _load_segments(self) -> None:
+        base_layer = self.context.layers[self._base_layer]
+        offset = base_layer.minimum_address
+        while offset + 4 < base_layer.maximum_address:
+            avml_header_structure = "<IIQQQ"
+            avml_header_size = struct.calcsize(avml_header_structure)
+            avml_header_data = base_layer.read(offset, avml_header_size)
+            magic, version, start, end, padding = struct.unpack(avml_header_structure, avml_header_data)
+
+            if magic not in [0x4c4d5641] or version != 2:
+                raise exceptions.LayerException("File not completely in AVML format")
+            chunk_data = base_layer.read(offset + avml_header_size,
+                                         min(end - start,
+                                             base_layer.maximum_address - (offset + avml_header_size)))
+            segments, consumed = self._read_snappy_frames(chunk_data, end - start)
+            # The returned segments are accurate the chunk_data that was passed in, but needs shifting
+            for (thing, mapped_offset, size, mapped_size, compressed) in segments:
+                self._segments.append((thing + start, offset + mapped_offset + avml_header_size, size, mapped_size))
+                self._compressed[offset + mapped_offset + avml_header_size] = compressed
+
+            # TODO: Check whatever the remaining 8 bytes are
+            offset += avml_header_size + consumed + 8
+
+    def _read_snappy_frames(self, data: bytes, expected_length: int) -> Tuple[
+        List[Tuple[int, int, int, int, bool]], int]:
+        """
+        Reads a framed-format snappy stream
+
+        Args:
+            data: The stream to read
+            expected_length: How big the decompressed stream is expected to be (termination limit)
+
+        Returns:
+            (offset, mapped_offset, length, mapped_length, compressed) relative to the data chunk (ie, not relative to the file start)
+        """
+        segments = []
+        decompressed_len = 0
+        offset = 0
+        crc_len = 4
+        frame_header_struct = '<L'
+        frame_header_len = struct.calcsize(frame_header_struct)
+        while decompressed_len <= expected_length:
+            if offset + frame_header_len < len(data):
+                frame_header = data[offset:offset + frame_header_len]
+                frame_header_val = struct.unpack('<L', frame_header)[0]
+                frame_type, frame_size = frame_header_val & 0xff, frame_header_val >> 8
+                if frame_type == 0xff:
+                    if data[offset + frame_header_len:offset + frame_header_len + frame_size] != b'sNaPpY':
+                        raise ValueError(f"Snappy header missing at offset: {offset}")
+                elif frame_type in [0x00, 0x01]:
+                    # CRC + (Un)compressed data
+                    mapped_start = offset + frame_header_len
+                    frame_crc = data[mapped_start: mapped_start + crc_len]
+                    frame_data = data[mapped_start + crc_len: mapped_start + frame_size]
+                    if frame_type == 0x00:
+                        # Compressed data
+                        frame_data = snappy.decompress(frame_data)
+                    # TODO: Verify CRC
+                    segments.append((decompressed_len, mapped_start + crc_len, len(frame_data), frame_size - crc_len,
+                                     frame_type == 0x00))
+                    decompressed_len += len(frame_data)
+                elif frame_type in range(0x2, 0x80):
+                    # Unskippable
+                    raise exceptions.LayerException(f"Unskippable chunk of type {frame_type} found: {offset}")
+                offset += frame_header_len + frame_size
+        return segments, offset
+
+    def _decode_data(self, data: bytes, mapped_offset: int, offset: int, output_length: int) -> bytes:
+        start_offset, _, _, _ = self._find_segment(offset)
+        if self._compressed[mapped_offset]:
+            decoded_data = snappy.decompress(data)
+        else:
+            decoded_data = data
+        decoded_data = decoded_data[offset - start_offset:]
+        decoded_data = decoded_data[:output_length]
+        return decoded_data
+
+
+class AVMLStacker(interfaces.automagic.StackerLayerInterface):
+    stack_order = 10
+
+    @classmethod
+    def stack(cls,
+              context: interfaces.context.ContextInterface,
+              layer_name: str,
+              progress_callback: constants.ProgressCallback = None) -> Optional[interfaces.layers.DataLayerInterface]:
+        try:
+            AVMLLayer._check_header(context.layers[layer_name])
+        except exceptions.LayerException:
+            return None
+        new_name = context.layers.free_layer_name("AVMLLayer")
+        context.config[interfaces.configuration.path_join(new_name, "base_layer")] = layer_name
+        return AVMLLayer(context, new_name, new_name)
+
+
+if __name__ == '__main__':
+    import sys
+
+    source_data = open(sys.argv[1], 'br').read()
+
+    sf = SnappyFraming()
+    with open('outputfile', 'wb') as fp:
+        fp.write(sf.decompress(source_data).read())