capa/scripts/show-features.py

#!/usr/bin/env python2
"""
Copyright (C) 2020 Mandiant, Inc. All Rights Reserved.
Licensed under the Apache License, Version 2.0 (the "License");
 you may not use this file except in compliance with the License.
You may obtain a copy of the License at: [package root]/LICENSE.txt
Unless required by applicable law or agreed to in writing, software distributed under the License
 is distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
See the License for the specific language governing permissions and limitations under the License.

show-features

Show the features that capa extracts from the given sample,
to assist with the development of rules.

If you have a function with a capability that you'd like to detect,
you can run this tool and grep for the function/basic block/instruction addresses
to see what capa picks up.
This way, you can verify that capa successfully notices the features you'd reference.

Example::

    $ python scripts/show-features.py /tmp/suspicious.dll_
    ...
    file: 0x10004e4d: export(__entry)
    file: 0x10004706: export(Install)
    file: 0x10004c2b: export(uninstallA)
    file: 0x10005034: import(kernel32.GetStartupInfoA)
    file: 0x10005034: import(GetStartupInfoA)
    file: 0x10005048: import(kernel32.SetLastError)
    file: 0x00004e10: string(Y29ubmVjdA==)
    file: 0x00004e28: string(practicalmalwareanalysis.com)
    file: 0x00004e68: string(serve.html)
    file: 0x00004eb8: string(dW5zdXBwb3J0)
    file: 0x00004ec8: string(c2xlZXA=)
    func: 0x100012c2: characteristic(calls to)
    func: 0x10001000: characteristic(loop)
    bb  : 0x10001000: basic block
    insn: 0x10001000: mnemonic(push)
    insn: 0x10001001: mnemonic(push)
    insn: 0x10001002: mnemonic(push)
    insn: 0x10001003: mnemonic(push)
    insn: 0x10001004: mnemonic(push)
    insn: 0x10001005: mnemonic(push)
    insn: 0x10001006: mnemonic(xor)
    insn: 0x10001008: number(0x1)
    insn: 0x10001008: mnemonic(mov)
    bb  : 0x1000100a: basic block
    bb  : 0x1000100a: characteristic(tight loop)
    insn: 0x1000100a: mnemonic(movzx)
    insn: 0x1000100d: mnemonic(mov)
    insn: 0x1000100f: offset(0x1000A7C8)
    insn: 0x1000100f: mnemonic(mov)
    insn: 0x10001015: offset(0x100075C8)
    insn: 0x10001015: mnemonic(mov)
    insn: 0x1000101b: mnemonic(mov)
    insn: 0x1000101d: number(0x80)
    insn: 0x1000101d: mnemonic(and)
    insn: 0x10001020: mnemonic(neg)
    insn: 0x10001022: mnemonic(sbb)
    insn: 0x10001024: number(0x1B)
    insn: 0x10001024: mnemonic(and)
    insn: 0x10001027: number(0x1)
    insn: 0x10001027: mnemonic(shl)
    ...
"""
import os
import sys
import logging
import os.path
import argparse

import capa.main
import capa.rules
import capa.engine
import capa.helpers
import capa.features
import capa.exceptions
import capa.features.common
import capa.features.freeze
from capa.helpers import log_unsupported_runtime_error

logger = logging.getLogger("capa.show-features")


def main(argv=None):
    if argv is None:
        argv = sys.argv[1:]

    parser = argparse.ArgumentParser(description="Show the features that capa extracts from the given sample")
    capa.main.install_common_args(parser, wanted={"format", "sample", "signatures", "backend"})

    parser.add_argument("-F", "--function", type=lambda x: int(x, 0x10), help="Show features for specific function")
    args = parser.parse_args(args=argv)
    capa.main.handle_common_args(args)

    try:
        taste = capa.helpers.get_file_taste(args.sample)
    except IOError as e:
        logger.error("%s", str(e))
        return -1

    try:
        sig_paths = capa.main.get_signatures(args.signatures)
    except (IOError) as e:
        logger.error("%s", str(e))
        return -1

    if (args.format == "freeze") or (args.format == "auto" and capa.features.freeze.is_freeze(taste)):
        with open(args.sample, "rb") as f:
            extractor = capa.features.freeze.load(f.read())
    else:
        should_save_workspace = os.environ.get("CAPA_SAVE_WORKSPACE") not in ("0", "no", "NO", "n", None)
        try:
            extractor = capa.main.get_extractor(
                args.sample, args.format, args.backend, sig_paths, should_save_workspace
            )
        except capa.exceptions.UnsupportedFormatError:
            capa.helpers.log_unsupported_format_error()
            return -1
        except capa.exceptions.UnsupportedRuntimeError:
            log_unsupported_runtime_error()
            return -1

    if not args.function:
        for feature, va in extractor.extract_file_features():
            if va:
                print("file: 0x%08x: %s" % (va, feature))
            else:
                print("file: 0x00000000: %s" % (feature))

    functions = extractor.get_functions()

    if args.function:
        if args.format == "freeze":
            functions = tuple(filter(lambda f: f == args.function, functions))
        else:
            functions = tuple(filter(lambda f: int(f) == args.function, functions))

            if args.function not in [int(f) for f in functions]:
                print("0x%X not a function" % args.function)
                return -1

        if len(functions) == 0:
            print("0x%X not a function")
            return -1

    print_features(functions, extractor)

    return 0


def ida_main():
    import idc

    import capa.features.extractors.ida.extractor

    function = idc.get_func_attr(idc.here(), idc.FUNCATTR_START)
    print("getting features for current function 0x%X" % function)

    extractor = capa.features.extractors.ida.extractor.IdaFeatureExtractor()

    if not function:
        for feature, va in extractor.extract_file_features():
            if va:
                print("file: 0x%08x: %s" % (va, feature))
            else:
                print("file: 0x00000000: %s" % (feature))
        return

    functions = extractor.get_functions()

    if function:
        functions = tuple(filter(lambda f: f.start_ea == function, functions))

        if len(functions) == 0:
            print("0x%X not a function" % function)
            return -1

    print_features(functions, extractor)

    return 0


def print_features(functions, extractor):
    for f in functions:
        function_address = int(f)

        if extractor.is_library_function(function_address):
            function_name = extractor.get_function_name(function_address)
            logger.debug("skipping library function 0x%x (%s)", function_address, function_name)
            continue

        print("func: 0x%08x" % (function_address))

        for feature, va in extractor.extract_function_features(f):
            if capa.features.common.is_global_feature(feature):
                continue

            print("func: 0x%08x: %s" % (va, feature))

        for bb in extractor.get_basic_blocks(f):
            for feature, va in extractor.extract_basic_block_features(f, bb):
                if capa.features.common.is_global_feature(feature):
                    continue

                print("bb  : 0x%08x: %s" % (va, feature))

            for insn in extractor.get_instructions(f, bb):
                for feature, va in extractor.extract_insn_features(f, bb, insn):
                    if capa.features.common.is_global_feature(feature):
                        continue

                    try:
                        print("insn: 0x%08x: %s" % (va, feature))
                    except UnicodeEncodeError:
                        # may be an issue while piping to less and encountering non-ascii characters
                        continue


if __name__ == "__main__":
    if capa.main.is_runtime_ida():
        ida_main()
    else:
        sys.exit(main())