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//===-- StackProtector.h - Stack Protector Insertion ----------------------===//
// The LLVM Compiler Infrastructure
// This file is distributed under the University of Illinois Open Source
// License. See LICENSE.TXT for details.
// 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.
#include "llvm/ADT/SmallPtrSet.h"
#include "llvm/ADT/Triple.h"
#include "llvm/IR/Dominators.h"
#include "llvm/IR/ValueMap.h"
#include "llvm/Pass.h"
#include "llvm/Target/TargetLowering.h"
namespace llvm {
class Function;
class Module;
class PHINode;
class StackProtector : public FunctionPass {
/// SSPLayoutKind. Stack Smashing Protection (SSP) rules require that
/// vulnerable stack allocations are located close the stack protector.
enum SSPLayoutKind {
SSPLK_None, ///< Did not trigger a stack protector. No effect on data
///< layout.
SSPLK_LargeArray, ///< Array or nested array >= SSP-buffer-size. Closest
///< to the stack protector.
SSPLK_SmallArray, ///< Array or nested array < SSP-buffer-size. 2nd closest
///< to the stack protector.
SSPLK_AddrOf ///< The address of this allocation is exposed and
///< triggered protection. 3rd closest to the protector.
/// A mapping of AllocaInsts to their required SSP layout.
typedef ValueMap<const AllocaInst *, SSPLayoutKind> SSPLayoutMap;
const TargetMachine *TM;
/// TLI - Keep a pointer of a TargetLowering to consult for determining
/// target type sizes.
const TargetLoweringBase *TLI;
const Triple Trip;
Function *F;
Module *M;
DominatorTree *DT;
/// 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;
/// \brief The minimum size of buffers that will receive stack smashing
/// protection when -fstack-protection is used.
unsigned SSPBufferSize;
/// 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;
/// 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;
/// \brief Check whether a stack allocation has its address taken.
bool HasAddressTaken(const Instruction *AI);
/// RequiresStackProtector - Check whether or not this function needs a
/// stack protector based upon the stack protector level.
bool RequiresStackProtector();
static char ID; // Pass identification, replacement for typeid.
: FunctionPass(ID), TM(nullptr), TLI(nullptr), SSPBufferSize(0) {
StackProtector(const TargetMachine *TM)
: FunctionPass(ID), TM(TM), TLI(nullptr), Trip(TM->getTargetTriple()),
SSPBufferSize(8) {
void getAnalysisUsage(AnalysisUsage &AU) const override {
SSPLayoutKind getSSPLayout(const AllocaInst *AI) const;
void adjustForColoring(const AllocaInst *From, const AllocaInst *To);
bool runOnFunction(Function &Fn) override;
} // end namespace llvm