dotnet: add support for basic blocks

CHANGELOG.md

@@ -3,6 +3,7 @@
 ## master (unreleased)
 
 ### New Features
+- dotnet: add support for basic blocks #1326 @mike-hunhoff
 
 ### Breaking Changes
 

capa/features/extractors/dnfile/basicblock.py

@@ -0,0 +1,45 @@
+# 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.
+
+from typing import Tuple, Iterator
+
+from dncil.cil.instruction import Instruction
+
+from capa.features.common import Feature, Characteristic
+from capa.features.address import Address
+from capa.features.basicblock import BasicBlock
+from capa.features.extractors.base_extractor import BBHandle, FunctionHandle
+
+
+def extract_bb_stackstring(fh: FunctionHandle, bbh: BBHandle) -> Iterator[Tuple[Feature, Address]]:
+    """extract stackstring indicators from basic block"""
+    raise NotImplementedError
+
+
+def extract_bb_tight_loop(fh: FunctionHandle, bbh: BBHandle) -> Iterator[Tuple[Feature, Address]]:
+    """extract tight loop indicators from a basic block"""
+    first: Instruction = bbh.inner.instructions[0]
+    last: Instruction = bbh.inner.instructions[-1]
+
+    if any((last.is_br(), last.is_cond_br(), last.is_leave())):
+        if last.operand == first.offset:
+            yield Characteristic("tight loop"), bbh.address
+
+
+def extract_features(fh: FunctionHandle, bbh: BBHandle) -> Iterator[Tuple[Feature, Address]]:
+    """extract basic block features"""
+    for bb_handler in BASIC_BLOCK_HANDLERS:
+        for feature, addr in bb_handler(fh, bbh):
+            yield feature, addr
+    yield BasicBlock(), bbh.address
+
+
+BASIC_BLOCK_HANDLERS = (
+    extract_bb_tight_loop,
+    # extract_bb_stackstring,
+)

capa/features/extractors/dnfile/extractor.py

@@ -8,19 +8,21 @@
 
 from __future__ import annotations
 
-from typing import Dict, List, Tuple, Union, Iterator, Optional
+from typing import Set, Dict, List, Tuple, Union, Iterator, Optional
 
 import dnfile
 from dncil.cil.opcode import OpCodes
+from dncil.cil.instruction import Instruction
 
 import capa.features.extractors
 import capa.features.extractors.dotnetfile
 import capa.features.extractors.dnfile.file
 import capa.features.extractors.dnfile.insn
 import capa.features.extractors.dnfile.function
+import capa.features.extractors.dnfile.basicblock
 from capa.features.common import Feature
 from capa.features.address import NO_ADDRESS, Address, DNTokenAddress, DNTokenOffsetAddress
-from capa.features.extractors.dnfile.types import DnType, DnUnmanagedMethod
+from capa.features.extractors.dnfile.types import DnType, DnBasicBlock, DnUnmanagedMethod
 from capa.features.extractors.base_extractor import BBHandle, InsnHandle, FunctionHandle, FeatureExtractor
 from capa.features.extractors.dnfile.helpers import (
     get_dotnet_types,
@@ -98,7 +100,13 @@ def get_functions(self) -> Iterator[FunctionHandle]:
             fh: FunctionHandle = FunctionHandle(
                 address=DNTokenAddress(token),
                 inner=method,
-                ctx={"pe": self.pe, "calls_from": set(), "calls_to": set(), "cache": self.token_cache},
+                ctx={
+                    "pe": self.pe,
+                    "calls_from": set(),
+                    "calls_to": set(),
+                    "blocks": list(),
+                    "cache": self.token_cache,
+                },
             )
 
             # method tokens should be unique
@@ -127,26 +135,100 @@ def get_functions(self) -> Iterator[FunctionHandle]:
                 # those calls to other MethodDef methods e.g. calls to imported MemberRef methods
                 fh.ctx["calls_from"].add(address)
 
+        # calculate basic blocks
+        for fh in methods.values():
+            # calculate basic block leaders where,
+            #   1. The first instruction of the intermediate code is a leader
+            #   2. Instructions that are targets of unconditional or conditional jump/goto statements are leaders
+            #   3. Instructions that immediately follow unconditional or conditional jump/goto statements are considered leaders
+            #   https://www.geeksforgeeks.org/basic-blocks-in-compiler-design/
+
+            leaders: Set[int] = set()
+            for idx, insn in enumerate(fh.inner.instructions):
+                if idx == 0:
+                    # add #1
+                    leaders.add(insn.offset)
+
+                if any((insn.is_br(), insn.is_cond_br(), insn.is_leave())):
+                    # add #2
+                    leaders.add(insn.operand)
+                    # add #3
+                    try:
+                        leaders.add(fh.inner.instructions[idx + 1].offset)
+                    except IndexError:
+                        # may encounter branch at end of method
+                        continue
+
+            # build basic blocks using leaders
+            bb_curr: Optional[DnBasicBlock] = None
+            for idx, insn in enumerate(fh.inner.instructions):
+                if insn.offset in leaders:
+                    # new leader, new basic block
+                    bb_curr = DnBasicBlock(instructions=[insn])
+                    fh.ctx["blocks"].append(bb_curr)
+                    continue
+
+                assert bb_curr is not None
+                bb_curr.instructions.append(insn)
+
+            # create mapping of first instruction to basic block
+            bb_map: Dict[int, DnBasicBlock] = {}
+            for bb in fh.ctx["blocks"]:
+                if len(bb.instructions) == 0:
+                    # TODO: consider error?
+                    continue
+                bb_map[bb.instructions[0].offset] = bb
+
+            # connect basic blocks
+            for idx, bb in enumerate(fh.ctx["blocks"]):
+                if len(bb.instructions) == 0:
+                    # TODO: consider error?
+                    continue
+
+                last = bb.instructions[-1]
+
+                # connect branches to other basic blocks
+                if any((last.is_br(), last.is_cond_br(), last.is_leave())):
+                    bb_branch: Optional[DnBasicBlock] = bb_map.get(last.operand, None)
+                    if bb_branch is not None:
+                        # TODO: consider None error?
+                        bb.succs.append(bb_branch)
+                        bb_branch.preds.append(bb)
+
+                if any((last.is_br(), last.is_leave())):
+                    # no fallthrough
+                    continue
+
+                # connect fallthrough
+                try:
+                    bb_next: DnBasicBlock = fh.ctx["blocks"][idx + 1]
+                    bb.succs.append(bb_next)
+                    bb_next.preds.append(bb)
+                except IndexError:
+                    continue
+
         yield from methods.values()
 
     def extract_function_features(self, fh) -> Iterator[Tuple[Feature, Address]]:
         yield from capa.features.extractors.dnfile.function.extract_features(fh)
 
-    def get_basic_blocks(self, f) -> Iterator[BBHandle]:
-        # each dotnet method is considered 1 basic block
-        yield BBHandle(
-            address=f.address,
-            inner=f.inner,
-        )
+    def get_basic_blocks(self, fh) -> Iterator[BBHandle]:
+        for bb in fh.ctx["blocks"]:
+            yield BBHandle(
+                address=DNTokenOffsetAddress(
+                    fh.address, bb.instructions[0].offset - (fh.inner.offset + fh.inner.header_size)
+                ),
+                inner=bb,
+            )
 
     def extract_basic_block_features(self, fh, bbh):
         # we don't support basic block features
-        yield from []
+        yield from capa.features.extractors.dnfile.basicblock.extract_features(fh, bbh)
 
     def get_instructions(self, fh, bbh):
         for insn in bbh.inner.instructions:
             yield InsnHandle(
-                address=DNTokenOffsetAddress(bbh.address, insn.offset - (fh.inner.offset + fh.inner.header_size)),
+                address=DNTokenOffsetAddress(fh.address, insn.offset - (fh.inner.offset + fh.inner.header_size)),
                 inner=insn,
             )
 

capa/features/extractors/dnfile/function.py

@@ -13,6 +13,7 @@
 
 from capa.features.common import Feature, Characteristic
 from capa.features.address import Address
+from capa.features.extractors import loops
 from capa.features.extractors.base_extractor import FunctionHandle
 
 logger = logging.getLogger(__name__)
@@ -38,7 +39,13 @@ def extract_recursive_call(fh: FunctionHandle) -> Iterator[Tuple[Characteristic,
 
 def extract_function_loop(fh: FunctionHandle) -> Iterator[Tuple[Characteristic, Address]]:
     """extract loop indicators from a function"""
-    raise NotImplementedError()
+    edges = []
+    for bb in fh.ctx["blocks"]:
+        for succ in bb.succs:
+            edges.append((bb.instructions[0].offset, succ.instructions[0].offset))
+
+    if loops.has_loop(edges):
+        yield Characteristic("loop"), fh.address
 
 
 def extract_features(fh: FunctionHandle) -> Iterator[Tuple[Feature, Address]]:
@@ -47,4 +54,9 @@ def extract_features(fh: FunctionHandle) -> Iterator[Tuple[Feature, Address]]:
             yield feature, addr
 
 
-FUNCTION_HANDLERS = (extract_function_calls_to, extract_function_calls_from, extract_recursive_call)
+FUNCTION_HANDLERS = (
+    extract_function_calls_to,
+    extract_function_calls_from,
+    extract_recursive_call,
+    extract_function_loop,
+)

capa/features/extractors/dnfile/types.py

@@ -6,8 +6,10 @@
 #  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.
 
-from enum import Enum
-from typing import Union, Optional
+from typing import TYPE_CHECKING, Dict, List, Optional
+
+if TYPE_CHECKING:
+    from dncil.cil.instruction import Instruction
 
 
 class DnType(object):
@@ -73,3 +75,10 @@ def __repr__(self):
     @staticmethod
     def format_name(module, method):
         return f"{module}.{method}"
+
+
+class DnBasicBlock:
+    def __init__(self, preds=None, succs=None, instructions=None):
+        self.succs: List[DnBasicBlock] = succs or []
+        self.preds: List[DnBasicBlock] = preds or []
+        self.instructions: List[Instruction] = instructions or []

tests/fixtures.py

@@ -371,7 +371,7 @@ def get_function_by_token(extractor, token: int) -> FunctionHandle:
 def get_basic_block(extractor, fh: FunctionHandle, va: int) -> BBHandle:
     for bbh in extractor.get_basic_blocks(fh):
         if isinstance(extractor, DnfileFeatureExtractor):
-            addr = bbh.inner.offset
+            addr = bbh.inner.instructions[0].offset
         else:
             addr = bbh.address
         if addr == va:
@@ -741,9 +741,9 @@ def parametrize(params, values, **kwargs):
         ("hello-world", "file", capa.features.common.Class("System.Console"), True),
         ("hello-world", "file", capa.features.common.Namespace("System.Diagnostics"), True),
         ("hello-world", "function=0x250", capa.features.common.String("Hello World!"), True),
-        ("hello-world", "function=0x250, bb=0x250, insn=0x252", capa.features.common.String("Hello World!"), True),
-        ("hello-world", "function=0x250, bb=0x250, insn=0x257", capa.features.common.Class("System.Console"), True),
-        ("hello-world", "function=0x250, bb=0x250, insn=0x257", capa.features.common.Namespace("System"), True),
+        ("hello-world", "function=0x250, bb=0x251, insn=0x252", capa.features.common.String("Hello World!"), True),
+        ("hello-world", "function=0x250, bb=0x251, insn=0x257", capa.features.common.Class("System.Console"), True),
+        ("hello-world", "function=0x250, bb=0x251, insn=0x257", capa.features.common.Namespace("System"), True),
         ("hello-world", "function=0x250", capa.features.insn.API("System.Console::WriteLine"), True),
         ("hello-world", "file", capa.features.file.Import("System.Console::WriteLine"), True),
         ("_1c444", "file", capa.features.common.String(r"SOFTWARE\Microsoft\Windows\CurrentVersion\Uninstall"), True),
@@ -758,6 +758,8 @@ def parametrize(params, values, **kwargs):
         ("_1c444", "token=0x6000018", capa.features.common.Characteristic("calls to"), False),
         ("_1c444", "token=0x600001D", capa.features.common.Characteristic("calls from"), True),
         ("_1c444", "token=0x600000F", capa.features.common.Characteristic("calls from"), False),
+        ("_1c444", "token=0x600001D", capa.features.common.Characteristic("loop"), True),
+        ("_1c444", "token=0x0600008C", capa.features.common.Characteristic("loop"), False),
         ("_1c444", "function=0x1F68", capa.features.insn.Number(0x0), True),
         ("_1c444", "function=0x1F68", capa.features.insn.Number(0x1), False),
         ("_692f", "token=0x6000004", capa.features.insn.API("System.Linq.Enumerable::First"), True),  # generic method
@@ -773,7 +775,7 @@ def parametrize(params, values, **kwargs):
         ("_1c444", "token=0x6000020", capa.features.common.Class("Reqss.Reqss"), True),  # ldftn
         (
             "_1c444",
-            "function=0x1F59, bb=0x1F59, insn=0x1F5B",
+            "function=0x1F59, bb=0x1F5A, insn=0x1F5B",
             capa.features.common.Characteristic("unmanaged call"),
             True,
         ),
@@ -782,11 +784,11 @@ def parametrize(params, values, **kwargs):
         ("_1c444", "token=0x6000088", capa.features.common.Characteristic("unmanaged call"), False),
         (
             "_1c444",
-            "function=0x1F68, bb=0x1F68, insn=0x1FF9",
+            "function=0x1F68, bb=0x1F74, insn=0x1FF9",
             capa.features.insn.API("System.Drawing.Image::FromHbitmap"),
             True,
         ),
-        ("_1c444", "function=0x1F68, bb=0x1F68, insn=0x1FF9", capa.features.insn.API("FromHbitmap"), False),
+        ("_1c444", "function=0x1F68, bb=0x1F74, insn=0x1FF9", capa.features.insn.API("FromHbitmap"), False),
         (
             "_1c444",
             "token=0x600002B",
@@ -954,6 +956,7 @@ def parametrize(params, values, **kwargs):
     ("mimikatz", "file", capa.features.file.Import("cabinet.FCIAddFile"), True),
 ]
 
+
 FEATURE_COUNT_TESTS = [
     ("mimikatz", "function=0x40E5C2", capa.features.basicblock.BasicBlock(), 7),
     ("mimikatz", "function=0x4702FD", capa.features.common.Characteristic("calls from"), 0),
@@ -962,8 +965,9 @@ def parametrize(params, values, **kwargs):
     ("mimikatz", "function=0x40B1F1", capa.features.common.Characteristic("calls to"), 3),
 ]
 
-
 FEATURE_COUNT_TESTS_DOTNET = [
+    ("_1c444", "token=0x06000072", capa.features.basicblock.BasicBlock(), 1),
+    ("_1c444", "token=0x0600008C", capa.features.basicblock.BasicBlock(), 10),
     ("_1c444", "token=0x600001D", capa.features.common.Characteristic("calls to"), 1),
     ("_1c444", "token=0x600001D", capa.features.common.Characteristic("calls from"), 9),
 ]