volatility3/volatility/framework/plugins/linux/check_syscall.py

# 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
#
"""A module containing a collection of plugins that produce data typically
found in Linux's /proc file system."""
import logging
from typing import List

from volatility.framework import exceptions, interfaces, contexts
from volatility.framework import renderers, constants
from volatility.framework.automagic import linux
from volatility.framework.configuration import requirements
from volatility.framework.interfaces import plugins
from volatility.framework.renderers import format_hints

vollog = logging.getLogger(__name__)

try:
    import capstone

    has_capstone = True
except ImportError:
    has_capstone = False


class Check_syscall(plugins.PluginInterface):
    """Check system call table for hooks."""

    @classmethod
    def get_requirements(cls) -> List[interfaces.configuration.RequirementInterface]:
        return [
            requirements.TranslationLayerRequirement(name = 'primary',
                                                     description = 'Memory layer for the kernel',
                                                     architectures = ["Intel32", "Intel64"]),
            requirements.SymbolTableRequirement(name = "vmlinux", description = "Linux kernel symbols")
        ]

    def _get_table_size_next_symbol(self, table_addr, ptr_sz, vmlinux):
        """Returns the size of the table based on the next symbol."""
        ret = 0

        sym_table = self.context.symbol_space[vmlinux.name]

        sorted_symbols = sorted([(sym_table.get_symbol(sn).address, sn) for sn in sym_table.symbols])

        sym_address = 0

        for tmp_sym_address, sym_name in sorted_symbols:
            if tmp_sym_address > table_addr:
                sym_address = tmp_sym_address
                break

        if sym_address > 0:
            ret = int((sym_address - table_addr) / ptr_sz)

        return ret

    def _get_table_size_meta(self, vmlinux):
        """returns the number of symbols that start with __syscall_meta__ this
        is a fast way to determine the number of system calls, but not the most
        accurate."""

        return len(
            [sym for sym in self.context.symbol_space[vmlinux.name].symbols if sym.startswith("__syscall_meta__")])

    def _get_table_info_other(self, table_addr, ptr_sz, vmlinux):
        table_size_meta = self._get_table_size_meta(vmlinux)
        table_size_syms = self._get_table_size_next_symbol(table_addr, ptr_sz, vmlinux)

        sizes = [size for size in [table_size_meta, table_size_syms] if size > 0]

        table_size = min(sizes)

        return table_size

    def _get_table_info_disassembly(self, ptr_sz, vmlinux):
        """Find the size of the system call table by disassembling functions
        that immediately reference it in their first isntruction This is in the
        form 'cmp reg,NR_syscalls'."""
        table_size = 0

        if not has_capstone:
            return table_size

        if ptr_sz == 4:
            syscall_entry_func = "sysenter_do_call"
            mode = capstone.CS_MODE_32
        else:
            syscall_entry_func = "system_call_fastpath"
            mode = capstone.CS_MODE_64

        md = capstone.Cs(capstone.CS_ARCH_X86, mode)

        try:
            func_addr = self.context.symbol_space.get_symbol(vmlinux.name + constants.BANG + syscall_entry_func).address
        except exceptions.SymbolError as e:
            # if we can't find the disassemble function then bail and rely on a different method
            return 0

        data = self.context.layers.read(self.config['primary'], func_addr, 6)

        for (address, size, mnemonic, op_str) in md.disasm_lite(data, func_addr):
            if mnemonic == 'CMP':
                table_size = int(op_str.split(",")[1].strip()) & 0xffff
                break

        return table_size

    def _get_table_info(self, vmlinux, table_name, ptr_sz):
        table_sym = self.context.symbol_space.get_symbol(vmlinux.name + constants.BANG + table_name)

        table_size = self._get_table_info_disassembly(ptr_sz, vmlinux)

        if table_size == 0:
            table_size = self._get_table_info_other(table_sym.address, ptr_sz, vmlinux)

            if table_size == 0:
                vollog.error("Unable to get system call table size")
                return 0, 0

        return table_sym.address, table_size

    # TODO - add finding and parsing unistd.h once cached file enumeration is added
    def _generator(self):
        linux.LinuxUtilities.aslr_mask_symbol_table(self.context, self.config['vmlinux'], self.config['primary'])

        vmlinux = contexts.Module(self.context,
                                  self.config['vmlinux'],
                                  self.config['primary'],
                                  0,
                                  absolute_symbol_addresses = True)

        ptr_sz = vmlinux.get_type("pointer").size
        if ptr_sz == 4:
            table_name = "32bit"
        else:
            table_name = "64bit"

        try:
            table_info = self._get_table_info(vmlinux, "sys_call_table", ptr_sz)
        except exceptions.SymbolError:
            vollog.error("Unable to find the system call table. Exiting.")
            return

        tables = [(table_name, table_info)]

        # this table is only present on 64 bit systems with 32 bit emulation
        # enabled in order to support 32 bit programs and libraries
        # if the symbol isn't there then the support isn't in the kernel and so we skip it
        try:
            ia32_symbol = self.context.symbol_space.get_symbol(vmlinux.name + constants.BANG + "ia32_sys_call_table")
        except exceptions.SymbolError:
            ia32_symbol = None

        if ia32_symbol != None:
            ia32_info = self._get_table_info(vmlinux, "ia32_sys_call_table", ptr_sz)
            tables.append(("32bit", ia32_info))

        for (table_name, (tableaddr, tblsz)) in tables:
            table = vmlinux.object(object_type = "array",
                                   subtype = vmlinux.get_type("pointer"),
                                   offset = tableaddr,
                                   count = tblsz)

            for (i, call_addr) in enumerate(table):
                if not call_addr:
                    continue

                symbols = list(self.context.symbol_space.get_symbols_by_location(call_addr))

                if len(symbols) > 0:
                    sym_name = str(symbols[0].split(constants.BANG)[1]) if constants.BANG in symbols[0] else \
                        str(symbols[0])
                else:
                    sym_name = "UNKNOWN"

                yield (0, (format_hints.Hex(tableaddr), table_name, i, format_hints.Hex(call_addr), sym_name))

    def run(self):

        return renderers.TreeGrid([("Table Address", format_hints.Hex), ("Table Name", str), ("Index", int),
                                   ("Handler Address", format_hints.Hex), ("Handler Symbol", str)], self._generator())