1 //===-- StackProtector.cpp - Stack Protector Insertion --------------------===//
3 // The LLVM Compiler Infrastructure
5 // This file is distributed under the University of Illinois Open Source
6 // License. See LICENSE.TXT for details.
8 //===----------------------------------------------------------------------===//
10 // This pass inserts stack protectors into functions which need them. A variable
11 // with a random value in it is stored onto the stack before the local variables
12 // are allocated. Upon exiting the block, the stored value is checked. If it's
13 // changed, then there was some sort of violation and the program aborts.
15 //===----------------------------------------------------------------------===//
17 #define DEBUG_TYPE "stack-protector"
18 #include "llvm/CodeGen/Passes.h"
19 #include "llvm/ADT/SmallPtrSet.h"
20 #include "llvm/ADT/Statistic.h"
21 #include "llvm/ADT/Triple.h"
22 #include "llvm/Analysis/Dominators.h"
23 #include "llvm/IR/Attributes.h"
24 #include "llvm/IR/Constants.h"
25 #include "llvm/IR/DataLayout.h"
26 #include "llvm/IR/DerivedTypes.h"
27 #include "llvm/IR/Function.h"
28 #include "llvm/IR/GlobalValue.h"
29 #include "llvm/IR/GlobalVariable.h"
30 #include "llvm/IR/Instructions.h"
31 #include "llvm/IR/Intrinsics.h"
32 #include "llvm/IR/Module.h"
33 #include "llvm/Pass.h"
34 #include "llvm/Support/CommandLine.h"
35 #include "llvm/Target/TargetLowering.h"
38 STATISTIC(NumFunProtected, "Number of functions protected");
39 STATISTIC(NumAddrTaken, "Number of local variables that have their address"
43 class StackProtector : public FunctionPass {
44 const TargetMachine *TM;
46 /// TLI - Keep a pointer of a TargetLowering to consult for determining
47 /// target type sizes.
48 const TargetLoweringBase *TLI;
56 /// VisitedPHIs - The set of PHI nodes visited when determining
57 /// if a variable's reference has been taken. This set
58 /// is maintained to ensure we don't visit the same PHI node multiple
60 SmallPtrSet<const PHINode*, 16> VisitedPHIs;
62 /// InsertStackProtectors - Insert code into the prologue and epilogue of
65 /// - The prologue code loads and stores the stack guard onto the stack.
66 /// - The epilogue checks the value stored in the prologue against the
67 /// original value. It calls __stack_chk_fail if they differ.
68 bool InsertStackProtectors();
70 /// CreateFailBB - Create a basic block to jump to when the stack protector
72 BasicBlock *CreateFailBB();
74 /// ContainsProtectableArray - Check whether the type either is an array or
75 /// contains an array of sufficient size so that we need stack protectors
77 bool ContainsProtectableArray(Type *Ty, bool Strong = false,
78 bool InStruct = false) const;
80 /// \brief Check whether a stack allocation has its address taken.
81 bool HasAddressTaken(const Instruction *AI);
83 /// RequiresStackProtector - Check whether or not this function needs a
84 /// stack protector based upon the stack protector level.
85 bool RequiresStackProtector();
87 static char ID; // Pass identification, replacement for typeid.
88 StackProtector() : FunctionPass(ID), TM(0), TLI(0) {
89 initializeStackProtectorPass(*PassRegistry::getPassRegistry());
91 StackProtector(const TargetMachine *TM)
92 : FunctionPass(ID), TM(TM), TLI(0), Trip(TM->getTargetTriple()) {
93 initializeStackProtectorPass(*PassRegistry::getPassRegistry());
96 virtual void getAnalysisUsage(AnalysisUsage &AU) const {
97 AU.addPreserved<DominatorTree>();
100 virtual bool runOnFunction(Function &Fn);
102 } // end anonymous namespace
104 char StackProtector::ID = 0;
105 INITIALIZE_PASS(StackProtector, "stack-protector",
106 "Insert stack protectors", false, false)
108 FunctionPass *llvm::createStackProtectorPass(const TargetMachine *TM) {
109 return new StackProtector(TM);
112 bool StackProtector::runOnFunction(Function &Fn) {
115 DT = getAnalysisIfAvailable<DominatorTree>();
116 TLI = TM->getTargetLowering();
118 if (!RequiresStackProtector()) return false;
121 return InsertStackProtectors();
124 /// ContainsProtectableArray - Check whether the type either is an array or
125 /// contains a char array of sufficient size so that we need stack protectors
127 bool StackProtector::ContainsProtectableArray(Type *Ty, bool Strong,
128 bool InStruct) const {
129 if (!Ty) return false;
130 if (ArrayType *AT = dyn_cast<ArrayType>(Ty)) {
131 // In strong mode any array, regardless of type and size, triggers a
135 const TargetMachine &TM = TLI->getTargetMachine();
136 if (!AT->getElementType()->isIntegerTy(8)) {
137 // If we're on a non-Darwin platform or we're inside of a structure, don't
138 // add stack protectors unless the array is a character array.
139 if (InStruct || !Trip.isOSDarwin())
143 // If an array has more than SSPBufferSize bytes of allocated space, then we
144 // emit stack protectors.
145 if (TM.Options.SSPBufferSize <= TLI->getDataLayout()->getTypeAllocSize(AT))
149 const StructType *ST = dyn_cast<StructType>(Ty);
150 if (!ST) return false;
152 for (StructType::element_iterator I = ST->element_begin(),
153 E = ST->element_end(); I != E; ++I)
154 if (ContainsProtectableArray(*I, Strong, true))
160 bool StackProtector::HasAddressTaken(const Instruction *AI) {
161 for (Value::const_use_iterator UI = AI->use_begin(), UE = AI->use_end();
164 if (const StoreInst *SI = dyn_cast<StoreInst>(U)) {
165 if (AI == SI->getValueOperand())
167 } else if (const PtrToIntInst *SI = dyn_cast<PtrToIntInst>(U)) {
168 if (AI == SI->getOperand(0))
170 } else if (isa<CallInst>(U)) {
172 } else if (isa<InvokeInst>(U)) {
174 } else if (const SelectInst *SI = dyn_cast<SelectInst>(U)) {
175 if (HasAddressTaken(SI))
177 } else if (const PHINode *PN = dyn_cast<PHINode>(U)) {
178 // Keep track of what PHI nodes we have already visited to ensure
179 // they are only visited once.
180 if (VisitedPHIs.insert(PN))
181 if (HasAddressTaken(PN))
183 } else if (const GetElementPtrInst *GEP = dyn_cast<GetElementPtrInst>(U)) {
184 if (HasAddressTaken(GEP))
186 } else if (const BitCastInst *BI = dyn_cast<BitCastInst>(U)) {
187 if (HasAddressTaken(BI))
194 /// \brief Check whether or not this function needs a stack protector based
195 /// upon the stack protector level.
197 /// We use two heuristics: a standard (ssp) and strong (sspstrong).
198 /// The standard heuristic which will add a guard variable to functions that
199 /// call alloca with a either a variable size or a size >= SSPBufferSize,
200 /// functions with character buffers larger than SSPBufferSize, and functions
201 /// with aggregates containing character buffers larger than SSPBufferSize. The
202 /// strong heuristic will add a guard variables to functions that call alloca
203 /// regardless of size, functions with any buffer regardless of type and size,
204 /// functions with aggregates that contain any buffer regardless of type and
205 /// size, and functions that contain stack-based variables that have had their
207 bool StackProtector::RequiresStackProtector() {
209 if (F->getAttributes().hasAttribute(AttributeSet::FunctionIndex,
210 Attribute::StackProtectReq))
212 else if (F->getAttributes().hasAttribute(AttributeSet::FunctionIndex,
213 Attribute::StackProtectStrong))
215 else if (!F->getAttributes().hasAttribute(AttributeSet::FunctionIndex,
216 Attribute::StackProtect))
219 for (Function::iterator I = F->begin(), E = F->end(); I != E; ++I) {
222 for (BasicBlock::iterator
223 II = BB->begin(), IE = BB->end(); II != IE; ++II) {
224 if (AllocaInst *AI = dyn_cast<AllocaInst>(II)) {
225 if (AI->isArrayAllocation()) {
226 // SSP-Strong: Enable protectors for any call to alloca, regardless
231 if (const ConstantInt *CI =
232 dyn_cast<ConstantInt>(AI->getArraySize())) {
233 unsigned BufferSize = TLI->getTargetMachine().Options.SSPBufferSize;
234 if (CI->getLimitedValue(BufferSize) >= BufferSize)
235 // A call to alloca with size >= SSPBufferSize requires
238 } else // A call to alloca with a variable size requires protectors.
242 if (ContainsProtectableArray(AI->getAllocatedType(), Strong))
245 if (Strong && HasAddressTaken(AI)) {
256 /// InsertStackProtectors - Insert code into the prologue and epilogue of the
259 /// - The prologue code loads and stores the stack guard onto the stack.
260 /// - The epilogue checks the value stored in the prologue against the original
261 /// value. It calls __stack_chk_fail if they differ.
262 bool StackProtector::InsertStackProtectors() {
263 BasicBlock *FailBB = 0; // The basic block to jump to if check fails.
264 BasicBlock *FailBBDom = 0; // FailBB's dominator.
265 AllocaInst *AI = 0; // Place on stack that stores the stack guard.
266 Value *StackGuardVar = 0; // The stack guard variable.
268 for (Function::iterator I = F->begin(), E = F->end(); I != E; ) {
269 BasicBlock *BB = I++;
270 ReturnInst *RI = dyn_cast<ReturnInst>(BB->getTerminator());
274 // Insert code into the entry block that stores the __stack_chk_guard
275 // variable onto the stack:
278 // StackGuardSlot = alloca i8*
279 // StackGuard = load __stack_chk_guard
280 // call void @llvm.stackprotect.create(StackGuard, StackGuardSlot)
282 PointerType *PtrTy = Type::getInt8PtrTy(RI->getContext());
283 unsigned AddressSpace, Offset;
284 if (TLI->getStackCookieLocation(AddressSpace, Offset)) {
285 Constant *OffsetVal =
286 ConstantInt::get(Type::getInt32Ty(RI->getContext()), Offset);
288 StackGuardVar = ConstantExpr::getIntToPtr(OffsetVal,
289 PointerType::get(PtrTy, AddressSpace));
290 } else if (Trip.getOS() == llvm::Triple::OpenBSD) {
291 StackGuardVar = M->getOrInsertGlobal("__guard_local", PtrTy);
292 cast<GlobalValue>(StackGuardVar)
293 ->setVisibility(GlobalValue::HiddenVisibility);
295 StackGuardVar = M->getOrInsertGlobal("__stack_chk_guard", PtrTy);
298 BasicBlock &Entry = F->getEntryBlock();
299 Instruction *InsPt = &Entry.front();
301 AI = new AllocaInst(PtrTy, "StackGuardSlot", InsPt);
302 LoadInst *LI = new LoadInst(StackGuardVar, "StackGuard", false, InsPt);
304 Value *Args[] = { LI, AI };
306 Create(Intrinsic::getDeclaration(M, Intrinsic::stackprotector),
309 // Create the basic block to jump to when the guard check fails.
310 FailBB = CreateFailBB();
313 // For each block with a return instruction, convert this:
323 // %1 = load __stack_chk_guard
324 // %2 = load StackGuardSlot
325 // %3 = cmp i1 %1, %2
326 // br i1 %3, label %SP_return, label %CallStackCheckFailBlk
331 // CallStackCheckFailBlk:
332 // call void @__stack_chk_fail()
335 // Split the basic block before the return instruction.
336 BasicBlock *NewBB = BB->splitBasicBlock(RI, "SP_return");
338 if (DT && DT->isReachableFromEntry(BB)) {
339 DT->addNewBlock(NewBB, BB);
340 FailBBDom = FailBBDom ? DT->findNearestCommonDominator(FailBBDom, BB) :BB;
343 // Remove default branch instruction to the new BB.
344 BB->getTerminator()->eraseFromParent();
346 // Move the newly created basic block to the point right after the old basic
347 // block so that it's in the "fall through" position.
348 NewBB->moveAfter(BB);
350 // Generate the stack protector instructions in the old basic block.
351 LoadInst *LI1 = new LoadInst(StackGuardVar, "", false, BB);
352 LoadInst *LI2 = new LoadInst(AI, "", true, BB);
353 ICmpInst *Cmp = new ICmpInst(*BB, CmpInst::ICMP_EQ, LI1, LI2, "");
354 BranchInst::Create(NewBB, FailBB, Cmp, BB);
357 // Return if we didn't modify any basic blocks. I.e., there are no return
358 // statements in the function.
359 if (!FailBB) return false;
362 DT->addNewBlock(FailBB, FailBBDom);
367 /// CreateFailBB - Create a basic block to jump to when the stack protector
369 BasicBlock *StackProtector::CreateFailBB() {
370 LLVMContext &Context = F->getContext();
371 BasicBlock *FailBB = BasicBlock::Create(Context, "CallStackCheckFailBlk", F);
372 if (Trip.getOS() == llvm::Triple::OpenBSD) {
373 Constant *StackChkFail = M->getOrInsertFunction(
374 "__stack_smash_handler", Type::getVoidTy(Context),
375 Type::getInt8PtrTy(Context), NULL);
377 Constant *NameStr = ConstantDataArray::getString(Context, F->getName());
379 new GlobalVariable(*M, NameStr->getType(), true,
380 GlobalVariable::PrivateLinkage, NameStr, "SSH");
382 SmallVector<Constant *, 2> IdxList;
383 IdxList.push_back(ConstantInt::get(Type::getInt8Ty(Context), 0));
384 IdxList.push_back(ConstantInt::get(Type::getInt8Ty(Context), 0));
386 SmallVector<Value *, 1> Args;
387 Args.push_back(ConstantExpr::getGetElementPtr(FuncName, IdxList));
389 CallInst::Create(StackChkFail, Args, "", FailBB);
391 Constant *StackChkFail = M->getOrInsertFunction(
392 "__stack_chk_fail", Type::getVoidTy(Context), NULL);
393 CallInst::Create(StackChkFail, "", FailBB);
395 new UnreachableInst(Context, FailBB);