# This file is Copyright 2019 Volatility Foundation and licensed under the Volatility Software License 1.0
# which is available at https://www.volatilityfoundation.org/license/vsl-v1.0
#
import logging
from typing import Optional, Tuple
from volatility3.framework import constants, interfaces
from volatility3.framework.automagic import symbol_cache, symbol_finder
from volatility3.framework.layers import intel, scanners
from volatility3.framework.symbols import linux
vollog = logging.getLogger(__name__)
[docs]
class LinuxIntelStacker(interfaces.automagic.StackerLayerInterface):
stack_order = 35
exclusion_list = ["mac", "windows"]
[docs]
@classmethod
def stack(
cls,
context: interfaces.context.ContextInterface,
layer_name: str,
progress_callback: constants.ProgressCallback = None,
) -> Optional[interfaces.layers.DataLayerInterface]:
"""Attempts to identify linux within this layer."""
# Bail out by default unless we can stack properly
layer = context.layers[layer_name]
join = interfaces.configuration.path_join
# Never stack on top of an intel layer
# FIXME: Find a way to improve this check
if isinstance(layer, intel.Intel):
return None
linux_banners = symbol_cache.load_cache_manager().get_identifier_dictionary(
operating_system="linux"
)
# If we have no banners, don't bother scanning
if not linux_banners:
vollog.info(
"No Linux banners found - if this is a linux plugin, please check your symbol files location"
)
return None
mss = scanners.MultiStringScanner([x for x in linux_banners if x is not None])
for _, banner in layer.scan(
context=context, scanner=mss, progress_callback=progress_callback
):
dtb = None
vollog.debug(f"Identified banner: {repr(banner)}")
isf_path = linux_banners.get(banner, None)
if isf_path:
table_name = context.symbol_space.free_table_name("LintelStacker")
table = linux.LinuxKernelIntermedSymbols(
context,
"temporary." + table_name,
name=table_name,
isf_url=isf_path,
)
context.symbol_space.append(table)
kaslr_shift, aslr_shift = cls.find_aslr(
context, table_name, layer_name, progress_callback=progress_callback
)
if "init_top_pgt" in table.symbols:
layer_class = intel.LinuxIntel32e
dtb_symbol_name = "init_top_pgt"
elif "init_level4_pgt" in table.symbols:
layer_class = intel.LinuxIntel32e
dtb_symbol_name = "init_level4_pgt"
elif "pkmap_count" in table.symbols and table.get_symbol(
"pkmap_count"
).type.count in (512, 2048):
layer_class = intel.LinuxIntelPAE
dtb_symbol_name = "swapper_pg_dir"
else:
layer_class = intel.LinuxIntel
dtb_symbol_name = "swapper_pg_dir"
dtb = cls.virtual_to_physical_address(
table.get_symbol(dtb_symbol_name).address + kaslr_shift
)
# Build the new layer
new_layer_name = context.layers.free_layer_name("IntelLayer")
config_path = join("IntelHelper", new_layer_name)
context.config[join(config_path, "memory_layer")] = layer_name
context.config[join(config_path, "page_map_offset")] = dtb
context.config[
join(config_path, LinuxSymbolFinder.banner_config_key)
] = str(banner, "latin-1")
layer = layer_class(
context,
config_path=config_path,
name=new_layer_name,
metadata={"os": "Linux"},
)
layer.config["kernel_virtual_offset"] = aslr_shift
if layer and dtb:
vollog.debug(f"DTB was found at: 0x{dtb:0x}")
return layer
vollog.debug("No suitable linux banner could be matched")
return None
[docs]
@classmethod
def find_aslr(
cls,
context: interfaces.context.ContextInterface,
symbol_table: str,
layer_name: str,
progress_callback: constants.ProgressCallback = None,
) -> Tuple[int, int]:
"""Determines the offset of the actual DTB in physical space and its
symbol offset."""
init_task_symbol = symbol_table + constants.BANG + "init_task"
init_task_json_address = context.symbol_space.get_symbol(
init_task_symbol
).address
swapper_signature = rb"swapper(\/0|\x00\x00)\x00\x00\x00\x00\x00\x00"
module = context.module(symbol_table, layer_name, 0)
address_mask = context.symbol_space[symbol_table].config.get(
"symbol_mask", None
)
task_symbol = module.get_type("task_struct")
comm_child_offset = task_symbol.relative_child_offset("comm")
for offset in context.layers[layer_name].scan(
scanner=scanners.RegExScanner(swapper_signature),
context=context,
progress_callback=progress_callback,
):
init_task_address = offset - comm_child_offset
init_task = module.object(
object_type="task_struct", offset=init_task_address, absolute=True
)
if init_task.pid != 0:
continue
elif (
init_task.has_member("state")
and init_task.state.cast("unsigned int") != 0
):
continue
elif init_task.active_mm.cast("long unsigned int") == module.get_symbol(
"init_mm"
).address and init_task.tasks.next.cast(
"long unsigned int"
) == init_task.tasks.prev.cast(
"long unsigned int"
):
# The idle task steals `mm` from previously running task, i.e.,
# `init_mm` is only used as long as no CPU has ever been idle.
# This catches cases where we found a fragment of the
# unrelocated ELF file instead of the running kernel.
continue
# This we get for free
aslr_shift = (
int.from_bytes(
init_task.files.cast("bytes", length=init_task.files.vol.size),
byteorder=init_task.files.vol.data_format.byteorder,
)
- module.get_symbol("init_files").address
)
kaslr_shift = init_task_address - cls.virtual_to_physical_address(
init_task_json_address
)
if address_mask:
aslr_shift = aslr_shift & address_mask
if aslr_shift & 0xFFF != 0 or kaslr_shift & 0xFFF != 0:
continue
vollog.debug(
f"Linux ASLR shift values determined: physical {kaslr_shift:0x} virtual {aslr_shift:0x}"
)
return kaslr_shift, aslr_shift
# We don't throw an exception, because we may legitimately not have an ASLR shift, but we report it
vollog.debug("Scanners could not determine any ASLR shifts, using 0 for both")
return 0, 0
[docs]
@classmethod
def virtual_to_physical_address(cls, addr: int) -> int:
"""Converts a virtual linux address to a physical one (does not account
of ASLR)"""
if addr > 0xFFFFFFFF80000000:
return addr - 0xFFFFFFFF80000000
return addr - 0xC0000000
[docs]
class LinuxSymbolFinder(symbol_finder.SymbolFinder):
"""Linux symbol loader based on uname signature strings."""
banner_config_key = "kernel_banner"
operating_system = "linux"
symbol_class = "volatility3.framework.symbols.linux.LinuxKernelIntermedSymbols"
exclusion_list = ["mac", "windows"]
[docs]
@classmethod
def find_aslr(cls, *args):
return LinuxIntelStacker.find_aslr(*args)[1]