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change_classifier.cc
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change_classifier.cc
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// Copyright 2011-2024 Google LLC
//
// 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
//
// https://www.apache.org/licenses/LICENSE-2.0
//
// 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.
#include "third_party/zynamics/bindiff/change_classifier.h"
#include "third_party/zynamics/bindiff/call_graph.h"
#include "third_party/zynamics/bindiff/flow_graph.h"
#include "third_party/zynamics/bindiff/match/context.h"
namespace security::bindiff {
namespace {
bool InstructionsChanged(const FlowGraph& primary, const FlowGraph& secondary,
const BasicBlockFixedPoint& fixed_point) {
const int matched_instruction_count =
fixed_point.GetInstructionMatches().size();
const auto primary_instructions =
primary.GetInstructions(fixed_point.GetPrimaryVertex());
const auto secondary_instructions =
secondary.GetInstructions(fixed_point.GetSecondaryVertex());
return secondary_instructions.second - secondary_instructions.first !=
matched_instruction_count ||
primary_instructions.second - primary_instructions.first !=
matched_instruction_count;
}
bool IsBranchInversion(const FlowGraph& primary, const FlowGraph& secondary,
const BasicBlockFixedPoint& fixed_point) {
const auto& instruction_matches = fixed_point.GetInstructionMatches();
const int matched_instruction_count = instruction_matches.size();
auto primary_instructions =
primary.GetInstructions(fixed_point.GetPrimaryVertex());
auto secondary_instructions =
secondary.GetInstructions(fixed_point.GetSecondaryVertex());
const int primary_changed =
std::abs(secondary_instructions.second - secondary_instructions.first -
matched_instruction_count);
const int secondary_changed =
std::abs(primary_instructions.second - primary_instructions.first -
matched_instruction_count);
if (primary_changed > 1 || secondary_changed > 1) {
return false;
}
if (!instruction_matches.empty()) {
for (auto i = instruction_matches.cbegin(),
end = --instruction_matches.cend();
i != end &&
primary_instructions.first != primary_instructions.second &&
secondary_instructions.first != secondary_instructions.second;
++i, ++primary_instructions.first, ++secondary_instructions.first) {
if (&*primary_instructions.first != i->first ||
&*secondary_instructions.first != i->second) {
return false;
}
}
// Return false if the single matched instruction is the branch instruction.
if (instruction_matches.size() == 1) {
if (instruction_matches.begin()->first ==
&*--primary_instructions.second) {
return false;
}
}
}
int primary_out_edges = 0;
int secondary_out_edges = 0;
for (auto [it, end] =
out_edges(fixed_point.GetPrimaryVertex(), primary.GetGraph());
it != end; ++it, ++primary_out_edges) {
// Intentionally empty
}
for (auto [it, end] =
out_edges(fixed_point.GetSecondaryVertex(), secondary.GetGraph());
it != end; ++it, ++secondary_out_edges) {
// Intentionally empty
}
if (primary_out_edges != secondary_out_edges || primary_out_edges < 2 ||
secondary_out_edges < 2) {
return false;
}
return true;
}
} // namespace
void ClassifyChanges(FixedPoint* fixed_point) {
const FlowGraph& primary = *fixed_point->GetPrimary();
const FlowGraph& secondary = *fixed_point->GetSecondary();
// Check for structural changes.
if (primary.GetBasicBlockCount() != secondary.GetBasicBlockCount() ||
boost::num_edges(primary.GetGraph()) !=
boost::num_edges(secondary.GetGraph())) {
fixed_point->SetFlag(CHANGE_STRUCTURAL);
}
// If we haven't already diagnosed a structural change due to differing
// basic block or edge count check that all edges have been matched.
if (!fixed_point->HasFlag(CHANGE_STRUCTURAL)) {
// We only need to iterate primary edges since edge count is equal at this
// point.
FlowGraph::EdgeIterator edge, end;
for (auto [edge, end] = boost::edges(primary.GetGraph()); edge != end;
++edge) {
if (primary.GetFixedPoint(boost::source(*edge, primary.GetGraph())) ==
nullptr ||
primary.GetFixedPoint(boost::target(*edge, primary.GetGraph())) ==
nullptr) {
fixed_point->SetFlag(CHANGE_STRUCTURAL);
break;
}
}
}
// Check for instruction changes, branch inversions and call target changes.
const auto& basic_block_fixed_points =
fixed_point->GetBasicBlockFixedPoints();
for (const auto& basic_block : basic_block_fixed_points) {
if (InstructionsChanged(primary, secondary, basic_block)) {
fixed_point->SetFlag(CHANGE_INSTRUCTIONS);
// Branch inversions
if (!(fixed_point->GetFlags() & CHANGE_BRANCHINVERSION)) {
if (IsBranchInversion(primary, secondary, basic_block)) {
fixed_point->SetFlag(CHANGE_BRANCHINVERSION);
}
}
}
if (!(fixed_point->GetFlags() & CHANGE_CALLS)) { // Call target changes
auto call_targets_primary =
primary.GetCallTargets(basic_block.GetPrimaryVertex());
auto call_targets_secondary =
secondary.GetCallTargets(basic_block.GetSecondaryVertex());
if (call_targets_primary.second - call_targets_primary.first ==
call_targets_secondary.second - call_targets_secondary.first) {
for (; call_targets_primary.first != call_targets_primary.second &&
call_targets_secondary.first != call_targets_secondary.second;
++call_targets_primary.first, ++call_targets_secondary.first) {
const CallGraph::Vertex vertex1 =
primary.GetCallGraph()->GetVertex(*call_targets_primary.first);
const CallGraph::Vertex vertex2 = secondary.GetCallGraph()->GetVertex(
*call_targets_secondary.first);
if (vertex1 == CallGraph::kInvalidVertex ||
vertex2 == CallGraph::kInvalidVertex) {
continue;
}
const FlowGraph* target_primary =
primary.GetCallGraph()->GetFlowGraph(vertex1);
const FlowGraph* target_secondary =
secondary.GetCallGraph()->GetFlowGraph(vertex2);
if (!target_primary || !target_secondary) {
fixed_point->SetFlag(CHANGE_CALLS);
break;
}
const FixedPoint* target_fixed_point =
target_primary->GetFixedPoint();
if (!target_fixed_point ||
target_fixed_point->GetSecondary() != target_secondary) {
fixed_point->SetFlag(CHANGE_CALLS);
break;
}
}
}
}
}
// Check for changes in entry point.
// TODO(cblichmann): Set this only if it is the only change (i.e. no other
// instructions have been modified).
if (primary.GetBasicBlockCount()) {
const auto* basic_block_fixed_point = primary.GetFixedPoint(
primary.GetVertex(primary.GetEntryPointAddress()));
if (!basic_block_fixed_point ||
secondary.GetVertex(secondary.GetEntryPointAddress()) !=
basic_block_fixed_point->GetSecondaryVertex() ||
InstructionsChanged(primary, secondary, *basic_block_fixed_point)) {
fixed_point->SetFlag(CHANGE_ENTRYPOINT);
}
}
// Check for loop changes.
if (primary.GetLoopCount() != secondary.GetLoopCount()) {
fixed_point->SetFlag(CHANGE_LOOPS);
}
// TODO(cblichmann): Check for changes in operands.
}
void ClassifyChanges(MatchingContext* context) {
for (auto& fixed_point : context->fixed_points_) {
ClassifyChanges(const_cast<FixedPoint*>(&fixed_point));
}
}
std::string GetChangeDescription(int change_flags) {
std::string result("GIOJELC");
for (int i = 0; i < CHANGE_COUNT; ++i) {
if (!(change_flags & (1 << i))) {
result[i] = '-';
}
}
return result;
}
} // namespace security::bindiff