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+//===-- StackProtector.cpp - 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.
+//
+//===----------------------------------------------------------------------===//
+
+#define DEBUG_TYPE "stack-protector"
+#include "llvm/CodeGen/Passes.h"
+#include "llvm/ADT/SmallPtrSet.h"
+#include "llvm/ADT/Statistic.h"
+#include "llvm/ADT/Triple.h"
+#include "llvm/Analysis/Dominators.h"
+#include "llvm/IR/Attributes.h"
+#include "llvm/IR/Constants.h"
+#include "llvm/IR/DataLayout.h"
+#include "llvm/IR/DerivedTypes.h"
+#include "llvm/IR/Function.h"
+#include "llvm/IR/Instructions.h"
+#include "llvm/IR/Intrinsics.h"
+#include "llvm/IR/Module.h"
+#include "llvm/Pass.h"
+#include "llvm/Support/CommandLine.h"
+#include "llvm/Target/TargetLowering.h"
+using namespace llvm;
+
+STATISTIC(NumFunProtected, "Number of functions protected");
+STATISTIC(NumAddrTaken, "Number of local variables that have their address"
+ " taken.");
+
+namespace {
+ class StackProtector : public FunctionPass {
+ /// TLI - Keep a pointer of a TargetLowering to consult for determining
+ /// target type sizes.
+ const TargetLoweringBase *TLI;
+
+ Function *F;
+ Module *M;
+
+ DominatorTree *DT;
+
+ /// 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.
+ bool ContainsProtectableArray(Type *Ty, 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();
+ public:
+ static char ID; // Pass identification, replacement for typeid.
+ StackProtector() : FunctionPass(ID), TLI(0) {
+ initializeStackProtectorPass(*PassRegistry::getPassRegistry());
+ }
+ StackProtector(const TargetLoweringBase *tli)
+ : FunctionPass(ID), TLI(tli) {
+ initializeStackProtectorPass(*PassRegistry::getPassRegistry());
+ }
+
+ virtual void getAnalysisUsage(AnalysisUsage &AU) const {
+ AU.addPreserved<DominatorTree>();
+ }
+
+ virtual bool runOnFunction(Function &Fn);
+ };
+} // end anonymous namespace
+
+char StackProtector::ID = 0;
+INITIALIZE_PASS(StackProtector, "stack-protector",
+ "Insert stack protectors", false, false)
+
+FunctionPass *llvm::createStackProtectorPass(const TargetLoweringBase *tli) {
+ return new StackProtector(tli);
+}
+
+bool StackProtector::runOnFunction(Function &Fn) {
+ F = &Fn;
+ M = F->getParent();
+ DT = getAnalysisIfAvailable<DominatorTree>();
+
+ if (!RequiresStackProtector()) return false;
+
+ ++NumFunProtected;
+ return InsertStackProtectors();
+}
+
+/// ContainsProtectableArray - Check whether the type either is an array or
+/// contains a char array of sufficient size so that we need stack protectors
+/// for it.
+bool StackProtector::ContainsProtectableArray(Type *Ty, bool Strong,
+ bool InStruct) const {
+ if (!Ty) return false;
+ if (ArrayType *AT = dyn_cast<ArrayType>(Ty)) {
+ // In strong mode any array, regardless of type and size, triggers a
+ // protector
+ if (Strong)
+ return true;
+ const TargetMachine &TM = TLI->getTargetMachine();
+ if (!AT->getElementType()->isIntegerTy(8)) {
+ Triple Trip(TM.getTargetTriple());
+
+ // If we're on a non-Darwin platform or we're inside of a structure, don't
+ // add stack protectors unless the array is a character array.
+ if (InStruct || !Trip.isOSDarwin())
+ return false;
+ }
+
+ // If an array has more than SSPBufferSize bytes of allocated space, then we
+ // emit stack protectors.
+ if (TM.Options.SSPBufferSize <= TLI->getDataLayout()->getTypeAllocSize(AT))
+ return true;
+ }
+
+ const StructType *ST = dyn_cast<StructType>(Ty);
+ if (!ST) return false;
+
+ for (StructType::element_iterator I = ST->element_begin(),
+ E = ST->element_end(); I != E; ++I)
+ if (ContainsProtectableArray(*I, Strong, true))
+ return true;
+
+ return false;
+}
+
+bool StackProtector::HasAddressTaken(const Instruction *AI) {
+ for (Value::const_use_iterator UI = AI->use_begin(), UE = AI->use_end();
+ UI != UE; ++UI) {
+ const User *U = *UI;
+ if (const StoreInst *SI = dyn_cast<StoreInst>(U)) {
+ if (AI == SI->getValueOperand())
+ return true;
+ } else if (const PtrToIntInst *SI = dyn_cast<PtrToIntInst>(U)) {
+ if (AI == SI->getOperand(0))
+ return true;
+ } else if (isa<CallInst>(U)) {
+ return true;
+ } else if (isa<InvokeInst>(U)) {
+ return true;
+ } else if (const SelectInst *SI = dyn_cast<SelectInst>(U)) {
+ if (HasAddressTaken(SI))
+ return true;
+ } else if (const PHINode *PN = dyn_cast<PHINode>(U)) {
+ // Keep track of what PHI nodes we have already visited to ensure
+ // they are only visited once.
+ if (VisitedPHIs.insert(PN))
+ if (HasAddressTaken(PN))
+ return true;
+ } else if (const GetElementPtrInst *GEP = dyn_cast<GetElementPtrInst>(U)) {
+ if (HasAddressTaken(GEP))
+ return true;
+ } else if (const BitCastInst *BI = dyn_cast<BitCastInst>(U)) {
+ if (HasAddressTaken(BI))
+ return true;
+ }
+ }
+ return false;
+}
+
+/// \brief Check whether or not this function needs a stack protector based
+/// upon the stack protector level.
+///
+/// We use two heuristics: a standard (ssp) and strong (sspstrong).
+/// The standard heuristic which will add a guard variable to functions that
+/// call alloca with a either a variable size or a size >= SSPBufferSize,
+/// functions with character buffers larger than SSPBufferSize, and functions
+/// with aggregates containing character buffers larger than SSPBufferSize. The
+/// strong heuristic will add a guard variables to functions that call alloca
+/// regardless of size, functions with any buffer regardless of type and size,
+/// functions with aggregates that contain any buffer regardless of type and
+/// size, and functions that contain stack-based variables that have had their
+/// address taken.
+bool StackProtector::RequiresStackProtector() {
+ bool Strong = false;
+ if (F->getAttributes().hasAttribute(AttributeSet::FunctionIndex,
+ Attribute::StackProtectReq))
+ return true;
+ else if (F->getAttributes().hasAttribute(AttributeSet::FunctionIndex,
+ Attribute::StackProtectStrong))
+ Strong = true;
+ else if (!F->getAttributes().hasAttribute(AttributeSet::FunctionIndex,
+ Attribute::StackProtect))
+ return false;
+
+ for (Function::iterator I = F->begin(), E = F->end(); I != E; ++I) {
+ BasicBlock *BB = I;
+
+ for (BasicBlock::iterator
+ II = BB->begin(), IE = BB->end(); II != IE; ++II) {
+ if (AllocaInst *AI = dyn_cast<AllocaInst>(II)) {
+ if (AI->isArrayAllocation()) {
+ // SSP-Strong: Enable protectors for any call to alloca, regardless
+ // of size.
+ if (Strong)
+ return true;
+
+ if (const ConstantInt *CI =
+ dyn_cast<ConstantInt>(AI->getArraySize())) {
+ unsigned BufferSize = TLI->getTargetMachine().Options.SSPBufferSize;
+ if (CI->getLimitedValue(BufferSize) >= BufferSize)
+ // A call to alloca with size >= SSPBufferSize requires
+ // stack protectors.
+ return true;
+ } else // A call to alloca with a variable size requires protectors.
+ return true;
+ }
+
+ if (ContainsProtectableArray(AI->getAllocatedType(), Strong))
+ return true;
+
+ if (Strong && HasAddressTaken(AI)) {
+ ++NumAddrTaken;
+ return true;
+ }
+ }
+ }
+ }
+
+ return 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 StackProtector::InsertStackProtectors() {
+ BasicBlock *FailBB = 0; // The basic block to jump to if check fails.
+ BasicBlock *FailBBDom = 0; // FailBB's dominator.
+ AllocaInst *AI = 0; // Place on stack that stores the stack guard.
+ Value *StackGuardVar = 0; // The stack guard variable.
+
+ for (Function::iterator I = F->begin(), E = F->end(); I != E; ) {
+ BasicBlock *BB = I++;
+ ReturnInst *RI = dyn_cast<ReturnInst>(BB->getTerminator());
+ if (!RI) continue;
+
+ if (!FailBB) {
+ // Insert code into the entry block that stores the __stack_chk_guard
+ // variable onto the stack:
+ //
+ // entry:
+ // StackGuardSlot = alloca i8*
+ // StackGuard = load __stack_chk_guard
+ // call void @llvm.stackprotect.create(StackGuard, StackGuardSlot)
+ //
+ PointerType *PtrTy = Type::getInt8PtrTy(RI->getContext());
+ unsigned AddressSpace, Offset;
+ if (TLI->getStackCookieLocation(AddressSpace, Offset)) {
+ Constant *OffsetVal =
+ ConstantInt::get(Type::getInt32Ty(RI->getContext()), Offset);
+
+ StackGuardVar = ConstantExpr::getIntToPtr(OffsetVal,
+ PointerType::get(PtrTy, AddressSpace));
+ } else {
+ StackGuardVar = M->getOrInsertGlobal("__stack_chk_guard", PtrTy);
+ }
+
+ BasicBlock &Entry = F->getEntryBlock();
+ Instruction *InsPt = &Entry.front();
+
+ AI = new AllocaInst(PtrTy, "StackGuardSlot", InsPt);
+ LoadInst *LI = new LoadInst(StackGuardVar, "StackGuard", false, InsPt);
+
+ Value *Args[] = { LI, AI };
+ CallInst::
+ Create(Intrinsic::getDeclaration(M, Intrinsic::stackprotector),
+ Args, "", InsPt);
+
+ // Create the basic block to jump to when the guard check fails.
+ FailBB = CreateFailBB();
+ }
+
+ // For each block with a return instruction, convert this:
+ //
+ // return:
+ // ...
+ // ret ...
+ //
+ // into this:
+ //
+ // return:
+ // ...
+ // %1 = load __stack_chk_guard
+ // %2 = load StackGuardSlot
+ // %3 = cmp i1 %1, %2
+ // br i1 %3, label %SP_return, label %CallStackCheckFailBlk
+ //
+ // SP_return:
+ // ret ...
+ //
+ // CallStackCheckFailBlk:
+ // call void @__stack_chk_fail()
+ // unreachable
+
+ // Split the basic block before the return instruction.
+ BasicBlock *NewBB = BB->splitBasicBlock(RI, "SP_return");
+
+ if (DT && DT->isReachableFromEntry(BB)) {
+ DT->addNewBlock(NewBB, BB);
+ FailBBDom = FailBBDom ? DT->findNearestCommonDominator(FailBBDom, BB) :BB;
+ }
+
+ // Remove default branch instruction to the new BB.
+ BB->getTerminator()->eraseFromParent();
+
+ // Move the newly created basic block to the point right after the old basic
+ // block so that it's in the "fall through" position.
+ NewBB->moveAfter(BB);
+
+ // Generate the stack protector instructions in the old basic block.
+ LoadInst *LI1 = new LoadInst(StackGuardVar, "", false, BB);
+ LoadInst *LI2 = new LoadInst(AI, "", true, BB);
+ ICmpInst *Cmp = new ICmpInst(*BB, CmpInst::ICMP_EQ, LI1, LI2, "");
+ BranchInst::Create(NewBB, FailBB, Cmp, BB);
+ }
+
+ // Return if we didn't modify any basic blocks. I.e., there are no return
+ // statements in the function.
+ if (!FailBB) return false;
+
+ if (DT && FailBBDom)
+ DT->addNewBlock(FailBB, FailBBDom);
+
+ return true;
+}
+
+/// CreateFailBB - Create a basic block to jump to when the stack protector
+/// check fails.
+BasicBlock *StackProtector::CreateFailBB() {
+ BasicBlock *FailBB = BasicBlock::Create(F->getContext(),
+ "CallStackCheckFailBlk", F);
+ Constant *StackChkFail =
+ M->getOrInsertFunction("__stack_chk_fail",
+ Type::getVoidTy(F->getContext()), NULL);
+ CallInst::Create(StackChkFail, "", FailBB);
+ new UnreachableInst(F->getContext(), FailBB);
+ return FailBB;
+}
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