//===- 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/ADT/SmallPtrSet.h"
#include "llvm/ADT/Triple.h"
#include "llvm/Analysis/DomTreeUpdater.h"
#include "llvm/CodeGen/MachineFrameInfo.h"
#include "llvm/IR/Instructions.h"
#include "llvm/Pass.h"
namespace llvm {
class BasicBlock;
class DominatorTree;
class Function;
class Instruction;
class Module;
class TargetLoweringBase;
class TargetMachine;
class Type;
class StackProtector : public FunctionPass {
private:
static constexpr unsigned DefaultSSPBufferSize = 8;
/// A mapping of AllocaInsts to their required SSP layout.
using SSPLayoutMap = DenseMap<const AllocaInst *,
MachineFrameInfo::SSPLayoutKind>;
const TargetMachine *TM = nullptr;
/// TLI - Keep a pointer of a TargetLowering to consult for determining
/// target type sizes.
const TargetLoweringBase *TLI = nullptr;
Triple Trip;
Function *F;
Module *M;
std::optional<DomTreeUpdater> DTU;
/// 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;
/// VisitedPHIs - The set of PHI nodes visited when determining
/// if a variable's reference has been taken. This set
/// is maintained to ensure we don't visit the same PHI node multiple
/// times.
SmallPtrSet<const PHINode *, 16> VisitedPHIs;
// A prologue is generated.
bool HasPrologue = false;
// IR checking code is generated.
bool HasIRCheck = false;
/// InsertStackProtectors - Insert code into the prologue and epilogue of
/// the function.
///
/// - The prologue code loads and stores the stack guard onto the stack.
/// - The epilogue checks the value stored in the prologue against the
/// original value. It calls __stack_chk_fail if they differ.
bool InsertStackProtectors();
/// CreateFailBB - Create a basic block to jump to when the stack protector
/// check fails.
BasicBlock *CreateFailBB();
/// ContainsProtectableArray - Check whether the type either is an array or
/// contains an array of sufficient size so that we need stack protectors
/// for it.
/// \param [out] IsLarge is set to true if a protectable array is found and
/// it is "large" ( >= ssp-buffer-size). In the case of a structure with
/// multiple arrays, this gets set if any of them is large.
bool ContainsProtectableArray(Type *Ty, bool &IsLarge, bool Strong = false,
bool InStruct = false) const;
/// Check whether a stack allocation has its address taken.
bool HasAddressTaken(const Instruction *AI, TypeSize AllocSize);
/// RequiresStackProtector - Check whether or not this function needs a
/// stack protector based upon the stack protector level.
bool RequiresStackProtector();
public:
static char ID; // Pass identification, replacement for typeid.
StackProtector();
void getAnalysisUsage(AnalysisUsage &AU) const override;
// Return true if StackProtector is supposed to be handled by SelectionDAG.
bool shouldEmitSDCheck(const BasicBlock &BB) const;
bool runOnFunction(Function &Fn) override;
void copyToMachineFrameInfo(MachineFrameInfo &MFI) const;
};
} // end namespace llvm
#endif // LLVM_CODEGEN_STACKPROTECTOR_H