From a5f0c7f1b95390bae67d8bcf107a30b5f0a95c32 Mon Sep 17 00:00:00 2001
From: Mike Auty <mike.auty@gmail.com>
Date: Sun, 25 Aug 2019 13:39:27 +0100
Subject: [PATCH] Don't forget the linear layer.

---
 volatility/framework/layers/linear.py | 62 +++++++++++++++++++++++++++
 1 file changed, 62 insertions(+)
 create mode 100644 volatility/framework/layers/linear.py

diff --git a/volatility/framework/layers/linear.py b/volatility/framework/layers/linear.py
new file mode 100644
index 000000000..be9323c22
--- /dev/null
+++ b/volatility/framework/layers/linear.py
@@ -0,0 +1,62 @@
+import functools
+from typing import List, Optional, Tuple
+
+from volatility.framework import exceptions, interfaces
+
+
+class LinearlyMappedLayer(interfaces.layers.TranslationLayerInterface):
+    """Class to differentiate Linearly Mapped layers (where a => b implies that a + c => b + c)"""
+
+    ### Translation layer convenience function
+
+    def translate(self, offset: int, ignore_errors: bool = False) -> Tuple[Optional[int], Optional[str]]:
+        mapping = list(self.mapping(offset, 0, ignore_errors))
+        if len(mapping) == 1:
+            original_offset, mapped_offset, _, layer = mapping[0]
+            if original_offset != offset:
+                raise exceptions.LayerException(self.name,
+                                                "Layer {} claims to map linearly but does not".format(self.name))
+        else:
+            if ignore_errors:
+                # We should only hit this if we ignored errors, but check anyway
+                return None, None
+            raise exceptions.InvalidAddressException(self.name, offset,
+                                                     "Cannot translate {} in layer {}".format(offset, self.name))
+        return mapped_offset, layer
+
+    # ## Read/Write functions for mapped pages
+    # Redefine read here for speed reasons (so we don't call a processing method
+
+    @functools.lru_cache(maxsize = 512)
+    def read(self, offset: int, length: int, pad: bool = False) -> bytes:
+        """Reads an offset for length bytes and returns 'bytes' (not 'str') of length size"""
+        current_offset = offset
+        output = []  # type: List[bytes]
+        for (offset, mapped_offset, mapped_length, layer) in self.mapping(offset, length, ignore_errors = pad):
+            if not pad and offset > current_offset:
+                raise exceptions.InvalidAddressException(
+                    self.name, current_offset, "Layer {} cannot map offset: {}".format(self.name, current_offset))
+            elif offset > current_offset:
+                output += [b"\x00" * (offset - current_offset)]
+                current_offset = offset
+            elif offset < current_offset:
+                raise exceptions.LayerException(self.name, "Mapping returned an overlapping element")
+            if mapped_length > 0:
+                output += [self._context.layers.read(layer, mapped_offset, mapped_length, pad)]
+            current_offset += mapped_length
+        recovered_data = b"".join(output)
+        return recovered_data + b"\x00" * (length - len(recovered_data))
+
+    def write(self, offset: int, value: bytes) -> None:
+        """Writes a value at offset, distributing the writing across any underlying mapping"""
+        current_offset = offset
+        length = len(value)
+        for (offset, mapped_offset, length, layer) in self.mapping(offset, length):
+            if offset > current_offset:
+                raise exceptions.InvalidAddressException(
+                    self.name, current_offset, "Layer {} cannot map offset: {}".format(self.name, current_offset))
+            elif offset < current_offset:
+                raise exceptions.LayerException(self.name, "Mapping returned an overlapping element")
+            self._context.layers.write(layer, mapped_offset, value[:length])
+            value = value[length:]
+            current_offset += length