StackProtector.h

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//===- StackProtector.h - Stack Protector Insertion -------------*- C++ -*-===//
//
// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
// See https://llvm.org/LICENSE.txt for license information.
// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
//
//===----------------------------------------------------------------------===//
//
// This pass inserts stack protectors into functions which need them. A variable
// with a random value in it is stored onto the stack before the local variables
// are allocated. Upon exiting the block, the stored value is checked. If it's
// changed, then there was some sort of violation and the program aborts.
//
//===----------------------------------------------------------------------===//
 
#ifndef LLVM_CODEGEN_STACKPROTECTOR_H
#define LLVM_CODEGEN_STACKPROTECTOR_H
 
#include "llvm/Analysis/DomTreeUpdater.h"
#include "llvm/CodeGen/MachineFrameInfo.h"
#include "llvm/IR/Instructions.h"
#include "llvm/IR/PassManager.h"
#include "llvm/Pass.h"
#include "llvm/TargetParser/Triple.h"
 
namespace llvm {
 
class BasicBlock;
class Function;
class Module;
class TargetLoweringBase;
class TargetMachine;
 
class SSPLayoutInfo {
  friend class StackProtectorPass;
  friend class SSPLayoutAnalysis;
  friend class StackProtector;
  static constexpr unsigned DefaultSSPBufferSize = 8;
 
  /// A mapping of AllocaInsts to their required SSP layout.
  using SSPLayoutMap =
      DenseMap<const AllocaInst *, MachineFrameInfo::SSPLayoutKind>;
 
  /// Layout - Mapping of allocations to the required SSPLayoutKind.
  /// StackProtector analysis will update this map when determining if an
  /// AllocaInst triggers a stack protector.
  SSPLayoutMap Layout;
 
  /// The minimum size of buffers that will receive stack smashing
  /// protection when -fstack-protection is used.
  unsigned SSPBufferSize = DefaultSSPBufferSize;
 
  bool RequireStackProtector = false;
 
  // A prologue is generated.
  bool HasPrologue = false;
 
  // IR checking code is generated.
  bool HasIRCheck = false;
 
public:
  // Return true if StackProtector is supposed to be handled by SelectionDAG.
  bool shouldEmitSDCheck(const BasicBlock &BB) const;
 
  void copyToMachineFrameInfo(MachineFrameInfo &MFI) const;
};
 
class SSPLayoutAnalysis : public AnalysisInfoMixin<SSPLayoutAnalysis> {
  friend AnalysisInfoMixin<SSPLayoutAnalysis>;
  using SSPLayoutMap = SSPLayoutInfo::SSPLayoutMap;
 
  static AnalysisKey Key;
 
public:
  using Result = SSPLayoutInfo;
 
  Result run(Function &F, FunctionAnalysisManager &FAM);
 
  /// Check whether or not \p F needs a stack protector based upon the stack
  /// protector level.
  static bool requiresStackProtector(Function *F,
                                     SSPLayoutMap *Layout = nullptr);
};
 
class StackProtectorPass : public PassInfoMixin<StackProtectorPass> {
  const TargetMachine *TM;
 
public:
  explicit StackProtectorPass(const TargetMachine &TM) : TM(&TM) {}
  PreservedAnalyses run(Function &F, FunctionAnalysisManager &FAM);
};
 
class StackProtector : public FunctionPass {
private:
  /// A mapping of AllocaInsts to their required SSP layout.
  using SSPLayoutMap = SSPLayoutInfo::SSPLayoutMap;
 
  const TargetMachine *TM = nullptr;
 
  Function *F = nullptr;
  Module *M = nullptr;
 
  std::optional<DomTreeUpdater> DTU;
 
  SSPLayoutInfo LayoutInfo;
 
public:
  static char ID; // Pass identification, replacement for typeid.
 
  StackProtector();
 
  SSPLayoutInfo &getLayoutInfo() { return LayoutInfo; }
 
  void getAnalysisUsage(AnalysisUsage &AU) const override;
 
  // Return true if StackProtector is supposed to be handled by SelectionDAG.
  bool shouldEmitSDCheck(const BasicBlock &BB) const {
    return LayoutInfo.shouldEmitSDCheck(BB);
  }
 
  bool runOnFunction(Function &Fn) override;
 
  void copyToMachineFrameInfo(MachineFrameInfo &MFI) const {
    LayoutInfo.copyToMachineFrameInfo(MFI);
  }
 
  /// Check whether or not \p F needs a stack protector based upon the stack
  /// protector level.
  static bool requiresStackProtector(Function *F,
                                     SSPLayoutMap *Layout = nullptr) {
    return SSPLayoutAnalysis::requiresStackProtector(F, Layout);
  }
};
 
} // end namespace llvm
 
#endif // LLVM_CODEGEN_STACKPROTECTOR_H