| // Copyright 2017 Google 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 |
| // |
| // http://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 "syzygy/instrument/transforms/security_cookie_check_hook_transform.h" |
| |
| #include "syzygy/pe/pe_utils.h" |
| |
| namespace instrument { |
| namespace transforms { |
| |
| using block_graph::Displacement; |
| using block_graph::Operand; |
| |
| const char SecurityCookieCheckHookTransform::kTransformName[] = |
| "SecurityCookieCheckHookTransform"; |
| |
| const char SecurityCookieCheckHookTransform::kReportGsFailure[] = |
| "__report_gsfailure"; |
| |
| const char SecurityCookieCheckHookTransform::kSyzygyReportGsFailure[] = |
| "__syzygy_report_gsfailure"; |
| |
| const uint32_t SecurityCookieCheckHookTransform::kInvalidUserAddress = |
| 0xdeadbeef; |
| |
| bool SecurityCookieCheckHookTransform::TransformBlockGraph( |
| const TransformPolicyInterface* policy, |
| BlockGraph* block_graph, |
| BlockGraph::Block* header_block) { |
| BlockGraph::Block* report_gsfailure = nullptr; |
| BlockGraph::BlockMap& blocks = block_graph->blocks_mutable(); |
| for (auto& block : blocks) { |
| std::string name(block.second.name()); |
| if (name == kReportGsFailure) { |
| report_gsfailure = &block.second; |
| break; |
| } |
| } |
| |
| if (report_gsfailure == nullptr) { |
| LOG(ERROR) << "Could not find " << kReportGsFailure << "."; |
| return false; |
| } |
| |
| if (report_gsfailure->referrers().size() != 1) { |
| // We bail out if we don't have a single referrer as the only |
| // expected referrer is supposed to be __security_cookie_check. |
| // If there is more than one, we would rather bail out than take |
| // a chance at modifying the behavior of the PE image. |
| LOG(ERROR) << "Only a single referrer to " << kReportGsFailure |
| << " is expected."; |
| return false; |
| } |
| |
| LOG(INFO) << "Found a " << kReportGsFailure |
| << " implementation, hooking it now."; |
| BlockGraph::Section* section_text = block_graph->FindOrAddSection( |
| pe::kCodeSectionName, pe::kCodeCharacteristics); |
| |
| // All of the below is needed to build the instrumentation via the assembler. |
| BasicBlockSubGraph bbsg; |
| BasicBlockSubGraph::BlockDescription* block_desc = bbsg.AddBlockDescription( |
| kSyzygyReportGsFailure, nullptr, BlockGraph::CODE_BLOCK, |
| section_text->id(), 1, 0); |
| |
| BasicCodeBlock* bb = bbsg.AddBasicCodeBlock(kSyzygyReportGsFailure); |
| block_desc->basic_block_order.push_back(bb); |
| BasicBlockAssembler assm(bb->instructions().begin(), &bb->instructions()); |
| assm.mov(Operand(Displacement(kInvalidUserAddress)), assm::eax); |
| |
| // Condense into a block. |
| BlockBuilder block_builder(block_graph); |
| if (!block_builder.Merge(&bbsg)) { |
| LOG(ERROR) << "Failed to build " << kSyzygyReportGsFailure << " block."; |
| return false; |
| } |
| |
| DCHECK_EQ(1u, block_builder.new_blocks().size()); |
| |
| // Transfer the referrers to the new block, and delete the old one. |
| BlockGraph::Block* syzygy_report_gsfailure = |
| block_builder.new_blocks().front(); |
| report_gsfailure->TransferReferrers( |
| 0, syzygy_report_gsfailure, |
| BlockGraph::Block::kTransferInternalReferences); |
| |
| report_gsfailure->RemoveAllReferences(); |
| if (!block_graph->RemoveBlock(report_gsfailure)) { |
| LOG(ERROR) << "Removing " << kReportGsFailure << " failed."; |
| return false; |
| } |
| |
| return true; |
| } |
| |
| } // namespace transforms |
| } // namespace instrument |