Statement construction for mixed-scope rules

CHANGELOG.md

@@ -11,6 +11,7 @@
 - Add support for flavor-based rule scopes @yelhamer
 - Add ProcessesAddress and ThreadAddress #1612 @yelhamer
 - Add dynamic capability extraction @yelhamer
+- Add support for mixed-scopes rules @yelhamer
 
 ### Breaking Changes
 

capa/features/common.py

@@ -458,6 +458,13 @@ def evaluate(self, ctx, **kwargs):
 FORMAT_SC32 = "sc32"
 FORMAT_SC64 = "sc64"
 FORMAT_CAPE = "cape"
+STATIC_FORMATS = (
+    FORMAT_SC32,
+    FORMAT_SC64,
+    FORMAT_PE,
+    FORMAT_ELF,
+    FORMAT_DOTNET,
+)
 DYNAMIC_FORMATS = (FORMAT_CAPE,)
 FORMAT_FREEZE = "freeze"
 FORMAT_RESULT = "result"

capa/helpers.py

@@ -8,6 +8,8 @@
 import json
 import inspect
 import logging
+import weakref
+import functools
 import contextlib
 import importlib.util
 from typing import NoReturn
@@ -130,6 +132,25 @@ def new_print(*args, **kwargs):
         inspect.builtins.print = old_print  # type: ignore
 
 
+def weak_lru(maxsize=128, typed=False):
+    """
+    LRU Cache decorator that keeps a weak reference to 'self'
+    """
+
+    def wrapper(func):
+        @functools.lru_cache(maxsize, typed)
+        def _func(_self, *args, **kwargs):
+            return func(_self(), *args, **kwargs)
+
+        @functools.wraps(func)
+        def inner(self, *args, **kwargs):
+            return _func(weakref.ref(self), *args, **kwargs)
+
+        return inner
+
+    return wrapper
+
+
 def log_unsupported_format_error():
     logger.error("-" * 80)
     logger.error(" Input file does not appear to be a PE or ELF file.")

capa/main.py

@@ -20,6 +20,7 @@
 import itertools
 import contextlib
 import collections
+from enum import Enum
 from typing import Any, Dict, List, Tuple, Callable, Optional
 from pathlib import Path
 
@@ -78,6 +79,8 @@
     FORMAT_DOTNET,
     FORMAT_FREEZE,
     FORMAT_RESULT,
+    STATIC_FORMATS,
+    DYNAMIC_FORMATS,
 )
 from capa.features.address import NO_ADDRESS, Address
 from capa.features.extractors.base_extractor import (
@@ -113,6 +116,15 @@
 logger = logging.getLogger("capa")
 
 
+class ExecutionContext(str, Enum):
+    STATIC = "static"
+    DYNAMIC = "dynamic"
+
+
+STATIC_CONTEXT = ExecutionContext.STATIC
+DYNAMIC_CONTEXT = ExecutionContext.DYNAMIC
+
+
 @contextlib.contextmanager
 def timing(msg: str):
     t0 = time.time()
@@ -823,6 +835,7 @@ def get_rules(
     rule_paths: List[RulePath],
     cache_dir=None,
     on_load_rule: Callable[[RulePath, int, int], None] = on_load_rule_default,
+    analysis_context: Optional[ExecutionContext] = None,
 ) -> RuleSet:
     """
     args:
@@ -861,7 +874,14 @@ def get_rules(
             rules.append(rule)
             logger.debug("loaded rule: '%s' with scope: %s", rule.name, rule.scopes)
 
-    ruleset = capa.rules.RuleSet(rules)
+    # filter rules according to the execution context
+    if analysis_context is STATIC_CONTEXT:
+        ruleset = capa.rules.RuleSet(rules, rules_filter_func=lambda rule: rule.scopes.static)
+    elif analysis_context is DYNAMIC_CONTEXT:
+        ruleset = capa.rules.RuleSet(rules, rules_filter_func=lambda rule: rule.scopes.dynamic)
+    else:
+        # default: load all rules
+        ruleset = capa.rules.RuleSet(rules)
 
     capa.rules.cache.cache_ruleset(cache_dir, ruleset)
 
@@ -1382,7 +1402,15 @@ def main(argv: Optional[List[str]] = None):
         else:
             cache_dir = capa.rules.cache.get_default_cache_directory()
 
-        rules = get_rules(args.rules, cache_dir=cache_dir)
+        if format_ in STATIC_FORMATS:
+            analysis_context = STATIC_CONTEXT
+        elif format_ in DYNAMIC_FORMATS:
+            analysis_context = DYNAMIC_CONTEXT
+        else:
+            # freeze or result formats
+            analysis_context = None
+
+        rules = get_rules(args.rules, cache_dir=cache_dir, analysis_context=analysis_context)
 
         logger.debug(
             "successfully loaded %s rules",