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/Analysis.h"
19 #include "llvm/CodeGen/Passes.h"
20 #include "llvm/ADT/SmallPtrSet.h"
21 #include "llvm/ADT/Statistic.h"
22 #include "llvm/ADT/Triple.h"
23 #include "llvm/Analysis/Dominators.h"
24 #include "llvm/Analysis/ValueTracking.h"
25 #include "llvm/IR/Attributes.h"
26 #include "llvm/IR/Constants.h"
27 #include "llvm/IR/DataLayout.h"
28 #include "llvm/IR/DerivedTypes.h"
29 #include "llvm/IR/Function.h"
30 #include "llvm/IR/GlobalValue.h"
31 #include "llvm/IR/GlobalVariable.h"
32 #include "llvm/IR/Instructions.h"
33 #include "llvm/IR/IntrinsicInst.h"
34 #include "llvm/IR/Intrinsics.h"
35 #include "llvm/IR/Module.h"
36 #include "llvm/Pass.h"
37 #include "llvm/Support/CommandLine.h"
38 #include "llvm/Target/TargetLowering.h"
42 STATISTIC(NumFunProtected, "Number of functions protected");
43 STATISTIC(NumAddrTaken, "Number of local variables that have their address"
47 EnableSelectionDAGSP("enable-selectiondag-sp", cl::init(true),
51 class StackProtector : public FunctionPass {
52 const TargetMachine *TM;
54 /// TLI - Keep a pointer of a TargetLowering to consult for determining
55 /// target type sizes.
56 const TargetLoweringBase *TLI;
64 /// \brief The minimum size of buffers that will receive stack smashing
65 /// protection when -fstack-protection is used.
66 unsigned SSPBufferSize;
68 /// VisitedPHIs - The set of PHI nodes visited when determining
69 /// if a variable's reference has been taken. This set
70 /// is maintained to ensure we don't visit the same PHI node multiple
72 SmallPtrSet<const PHINode*, 16> VisitedPHIs;
74 /// InsertStackProtectors - Insert code into the prologue and epilogue of
77 /// - The prologue code loads and stores the stack guard onto the stack.
78 /// - The epilogue checks the value stored in the prologue against the
79 /// original value. It calls __stack_chk_fail if they differ.
80 bool InsertStackProtectors();
82 /// CreateFailBB - Create a basic block to jump to when the stack protector
84 BasicBlock *CreateFailBB();
86 /// ContainsProtectableArray - Check whether the type either is an array or
87 /// contains an array of sufficient size so that we need stack protectors
89 bool ContainsProtectableArray(Type *Ty, bool Strong = false,
90 bool InStruct = false) const;
92 /// \brief Check whether a stack allocation has its address taken.
93 bool HasAddressTaken(const Instruction *AI);
95 /// RequiresStackProtector - Check whether or not this function needs a
96 /// stack protector based upon the stack protector level.
97 bool RequiresStackProtector();
99 static char ID; // Pass identification, replacement for typeid.
100 StackProtector() : FunctionPass(ID), TM(0), TLI(0), SSPBufferSize(0) {
101 initializeStackProtectorPass(*PassRegistry::getPassRegistry());
103 StackProtector(const TargetMachine *TM)
104 : FunctionPass(ID), TM(TM), TLI(0), Trip(TM->getTargetTriple()),
106 initializeStackProtectorPass(*PassRegistry::getPassRegistry());
109 virtual void getAnalysisUsage(AnalysisUsage &AU) const {
110 AU.addPreserved<DominatorTree>();
113 virtual bool runOnFunction(Function &Fn);
115 } // end anonymous namespace
117 char StackProtector::ID = 0;
118 INITIALIZE_PASS(StackProtector, "stack-protector",
119 "Insert stack protectors", false, false)
121 FunctionPass *llvm::createStackProtectorPass(const TargetMachine *TM) {
122 return new StackProtector(TM);
125 bool StackProtector::runOnFunction(Function &Fn) {
128 DT = getAnalysisIfAvailable<DominatorTree>();
129 TLI = TM->getTargetLowering();
131 if (!RequiresStackProtector()) return false;
134 Fn.getAttributes().getAttribute(AttributeSet::FunctionIndex,
135 "stack-protector-buffer-size");
136 if (Attr.isStringAttribute())
137 SSPBufferSize = atoi(Attr.getValueAsString().data());
140 return InsertStackProtectors();
143 /// ContainsProtectableArray - Check whether the type either is an array or
144 /// contains a char array of sufficient size so that we need stack protectors
146 bool StackProtector::ContainsProtectableArray(Type *Ty, bool Strong,
147 bool InStruct) const {
148 if (!Ty) return false;
149 if (ArrayType *AT = dyn_cast<ArrayType>(Ty)) {
150 // In strong mode any array, regardless of type and size, triggers a
154 if (!AT->getElementType()->isIntegerTy(8)) {
155 // If we're on a non-Darwin platform or we're inside of a structure, don't
156 // add stack protectors unless the array is a character array.
157 if (InStruct || !Trip.isOSDarwin())
161 // If an array has more than SSPBufferSize bytes of allocated space, then we
162 // emit stack protectors.
163 if (SSPBufferSize <= TLI->getDataLayout()->getTypeAllocSize(AT))
167 const StructType *ST = dyn_cast<StructType>(Ty);
168 if (!ST) return false;
170 for (StructType::element_iterator I = ST->element_begin(),
171 E = ST->element_end(); I != E; ++I)
172 if (ContainsProtectableArray(*I, Strong, true))
178 bool StackProtector::HasAddressTaken(const Instruction *AI) {
179 for (Value::const_use_iterator UI = AI->use_begin(), UE = AI->use_end();
182 if (const StoreInst *SI = dyn_cast<StoreInst>(U)) {
183 if (AI == SI->getValueOperand())
185 } else if (const PtrToIntInst *SI = dyn_cast<PtrToIntInst>(U)) {
186 if (AI == SI->getOperand(0))
188 } else if (isa<CallInst>(U)) {
190 } else if (isa<InvokeInst>(U)) {
192 } else if (const SelectInst *SI = dyn_cast<SelectInst>(U)) {
193 if (HasAddressTaken(SI))
195 } else if (const PHINode *PN = dyn_cast<PHINode>(U)) {
196 // Keep track of what PHI nodes we have already visited to ensure
197 // they are only visited once.
198 if (VisitedPHIs.insert(PN))
199 if (HasAddressTaken(PN))
201 } else if (const GetElementPtrInst *GEP = dyn_cast<GetElementPtrInst>(U)) {
202 if (HasAddressTaken(GEP))
204 } else if (const BitCastInst *BI = dyn_cast<BitCastInst>(U)) {
205 if (HasAddressTaken(BI))
212 /// \brief Check whether or not this function needs a stack protector based
213 /// upon the stack protector level.
215 /// We use two heuristics: a standard (ssp) and strong (sspstrong).
216 /// The standard heuristic which will add a guard variable to functions that
217 /// call alloca with a either a variable size or a size >= SSPBufferSize,
218 /// functions with character buffers larger than SSPBufferSize, and functions
219 /// with aggregates containing character buffers larger than SSPBufferSize. The
220 /// strong heuristic will add a guard variables to functions that call alloca
221 /// regardless of size, functions with any buffer regardless of type and size,
222 /// functions with aggregates that contain any buffer regardless of type and
223 /// size, and functions that contain stack-based variables that have had their
225 bool StackProtector::RequiresStackProtector() {
227 if (F->getAttributes().hasAttribute(AttributeSet::FunctionIndex,
228 Attribute::StackProtectReq))
230 else if (F->getAttributes().hasAttribute(AttributeSet::FunctionIndex,
231 Attribute::StackProtectStrong))
233 else if (!F->getAttributes().hasAttribute(AttributeSet::FunctionIndex,
234 Attribute::StackProtect))
237 for (Function::iterator I = F->begin(), E = F->end(); I != E; ++I) {
240 for (BasicBlock::iterator
241 II = BB->begin(), IE = BB->end(); II != IE; ++II) {
242 if (AllocaInst *AI = dyn_cast<AllocaInst>(II)) {
243 if (AI->isArrayAllocation()) {
244 // SSP-Strong: Enable protectors for any call to alloca, regardless
249 if (const ConstantInt *CI =
250 dyn_cast<ConstantInt>(AI->getArraySize())) {
251 if (CI->getLimitedValue(SSPBufferSize) >= SSPBufferSize)
252 // A call to alloca with size >= SSPBufferSize requires
256 // A call to alloca with a variable size requires protectors.
261 if (ContainsProtectableArray(AI->getAllocatedType(), Strong))
264 if (Strong && HasAddressTaken(AI)) {
275 static bool InstructionWillNotHaveChain(const Instruction *I) {
276 return !I->mayHaveSideEffects() && !I->mayReadFromMemory() &&
277 isSafeToSpeculativelyExecute(I);
280 /// Identify if RI has a previous instruction in the "Tail Position" and return
281 /// it. Otherwise return 0.
283 /// This is based off of the code in llvm::isInTailCallPosition. The difference
284 /// is that it inverts the first part of llvm::isInTailCallPosition since
285 /// isInTailCallPosition is checking if a call is in a tail call position, and
286 /// we are searching for an unknown tail call that might be in the tail call
287 /// position. Once we find the call though, the code uses the same refactored
288 /// code, returnTypeIsEligibleForTailCall.
289 static CallInst *FindPotentialTailCall(BasicBlock *BB, ReturnInst *RI,
290 const TargetLoweringBase *TLI) {
291 // Establish a reasonable upper bound on the maximum amount of instructions we
292 // will look through to find a tail call.
293 unsigned SearchCounter = 0;
294 const unsigned MaxSearch = 4;
295 bool NoInterposingChain = true;
297 for (BasicBlock::reverse_iterator I = llvm::next(BB->rbegin()), E = BB->rend();
298 I != E && SearchCounter < MaxSearch; ++I) {
299 Instruction *Inst = &*I;
301 // Skip over debug intrinsics and do not allow them to affect our MaxSearch
303 if (isa<DbgInfoIntrinsic>(Inst))
306 // If we find a call and the following conditions are satisifed, then we
307 // have found a tail call that satisfies at least the target independent
308 // requirements of a tail call:
310 // 1. The call site has the tail marker.
312 // 2. The call site either will not cause the creation of a chain or if a
313 // chain is necessary there are no instructions in between the callsite and
314 // the call which would create an interposing chain.
316 // 3. The return type of the function does not impede tail call
318 if (CallInst *CI = dyn_cast<CallInst>(Inst)) {
319 if (CI->isTailCall() &&
320 (InstructionWillNotHaveChain(CI) || NoInterposingChain) &&
321 returnTypeIsEligibleForTailCall(BB->getParent(), CI, RI, *TLI))
325 // If we did not find a call see if we have an instruction that may create
326 // an interposing chain.
327 NoInterposingChain = NoInterposingChain && InstructionWillNotHaveChain(Inst);
329 // Increment max search.
336 /// Insert code into the entry block that stores the __stack_chk_guard
337 /// variable onto the stack:
340 /// StackGuardSlot = alloca i8*
341 /// StackGuard = load __stack_chk_guard
342 /// call void @llvm.stackprotect.create(StackGuard, StackGuardSlot)
344 /// Returns true if the platform/triple supports the stackprotectorcreate pseudo
346 static bool CreatePrologue(Function *F, Module *M, ReturnInst *RI,
347 const TargetLoweringBase *TLI, const Triple &Trip,
348 AllocaInst *&AI, Value *&StackGuardVar) {
349 bool SupportsSelectionDAGSP = false;
350 PointerType *PtrTy = Type::getInt8PtrTy(RI->getContext());
351 unsigned AddressSpace, Offset;
352 if (TLI->getStackCookieLocation(AddressSpace, Offset)) {
353 Constant *OffsetVal =
354 ConstantInt::get(Type::getInt32Ty(RI->getContext()), Offset);
356 StackGuardVar = ConstantExpr::getIntToPtr(OffsetVal,
357 PointerType::get(PtrTy,
359 } else if (Trip.getOS() == llvm::Triple::OpenBSD) {
360 StackGuardVar = M->getOrInsertGlobal("__guard_local", PtrTy);
361 cast<GlobalValue>(StackGuardVar)
362 ->setVisibility(GlobalValue::HiddenVisibility);
364 SupportsSelectionDAGSP = true;
365 StackGuardVar = M->getOrInsertGlobal("__stack_chk_guard", PtrTy);
368 BasicBlock &Entry = F->getEntryBlock();
369 Instruction *InsPt = &Entry.front();
371 AI = new AllocaInst(PtrTy, "StackGuardSlot", InsPt);
372 LoadInst *LI = new LoadInst(StackGuardVar, "StackGuard", false, InsPt);
374 Value *Args[] = { LI, AI };
376 Create(Intrinsic::getDeclaration(M, Intrinsic::stackprotector),
379 return SupportsSelectionDAGSP;
382 /// InsertStackProtectors - Insert code into the prologue and epilogue of the
385 /// - The prologue code loads and stores the stack guard onto the stack.
386 /// - The epilogue checks the value stored in the prologue against the original
387 /// value. It calls __stack_chk_fail if they differ.
388 bool StackProtector::InsertStackProtectors() {
389 bool HasPrologue = false;
390 bool SupportsSelectionDAGSP =
391 EnableSelectionDAGSP && !TM->Options.EnableFastISel;
392 AllocaInst *AI = 0; // Place on stack that stores the stack guard.
393 Value *StackGuardVar = 0; // The stack guard variable.
395 for (Function::iterator I = F->begin(), E = F->end(); I != E; ) {
396 BasicBlock *BB = I++;
397 ReturnInst *RI = dyn_cast<ReturnInst>(BB->getTerminator());
403 SupportsSelectionDAGSP &= CreatePrologue(F, M, RI, TLI, Trip, AI,
407 if (SupportsSelectionDAGSP) {
408 // Since we have a potential tail call, insert the special stack check
410 Instruction *InsertionPt = 0;
411 if (CallInst *CI = FindPotentialTailCall(BB, RI, TLI)) {
415 // At this point we know that BB has a return statement so it *DOES*
416 // have a terminator.
417 assert(InsertionPt != 0 && "BB must have a terminator instruction at "
421 Function *Intrinsic =
422 Intrinsic::getDeclaration(M, Intrinsic::stackprotectorcheck);
423 Value *Args[] = { StackGuardVar };
424 CallInst::Create(Intrinsic, Args, "", InsertionPt);
427 // If we do not support SelectionDAG based tail calls, generate IR level
430 // For each block with a return instruction, convert this:
440 // %1 = load __stack_chk_guard
441 // %2 = load StackGuardSlot
442 // %3 = cmp i1 %1, %2
443 // br i1 %3, label %SP_return, label %CallStackCheckFailBlk
448 // CallStackCheckFailBlk:
449 // call void @__stack_chk_fail()
452 // Create the FailBB. We duplicate the BB every time since the MI tail
453 // merge pass will merge together all of the various BB into one including
454 // fail BB generated by the stack protector pseudo instruction.
455 BasicBlock *FailBB = CreateFailBB();
457 // Split the basic block before the return instruction.
458 BasicBlock *NewBB = BB->splitBasicBlock(RI, "SP_return");
460 // Update the dominator tree if we need to.
461 if (DT && DT->isReachableFromEntry(BB)) {
462 DT->addNewBlock(NewBB, BB);
463 DT->addNewBlock(FailBB, BB);
466 // Remove default branch instruction to the new BB.
467 BB->getTerminator()->eraseFromParent();
469 // Move the newly created basic block to the point right after the old
470 // basic block so that it's in the "fall through" position.
471 NewBB->moveAfter(BB);
473 // Generate the stack protector instructions in the old basic block.
474 LoadInst *LI1 = new LoadInst(StackGuardVar, "", false, BB);
475 LoadInst *LI2 = new LoadInst(AI, "", true, BB);
476 ICmpInst *Cmp = new ICmpInst(*BB, CmpInst::ICMP_EQ, LI1, LI2, "");
477 BranchInst::Create(NewBB, FailBB, Cmp, BB);
481 // Return if we didn't modify any basic blocks. I.e., there are no return
482 // statements in the function.
489 /// CreateFailBB - Create a basic block to jump to when the stack protector
491 BasicBlock *StackProtector::CreateFailBB() {
492 LLVMContext &Context = F->getContext();
493 BasicBlock *FailBB = BasicBlock::Create(Context, "CallStackCheckFailBlk", F);
494 if (Trip.getOS() == llvm::Triple::OpenBSD) {
495 Constant *StackChkFail = M->getOrInsertFunction(
496 "__stack_smash_handler", Type::getVoidTy(Context),
497 Type::getInt8PtrTy(Context), NULL);
499 Constant *NameStr = ConstantDataArray::getString(Context, F->getName());
501 new GlobalVariable(*M, NameStr->getType(), true,
502 GlobalVariable::PrivateLinkage, NameStr, "SSH");
504 SmallVector<Constant *, 2> IdxList;
505 IdxList.push_back(ConstantInt::get(Type::getInt8Ty(Context), 0));
506 IdxList.push_back(ConstantInt::get(Type::getInt8Ty(Context), 0));
508 SmallVector<Value *, 1> Args;
509 Args.push_back(ConstantExpr::getGetElementPtr(FuncName, IdxList));
511 CallInst::Create(StackChkFail, Args, "", FailBB);
513 Constant *StackChkFail = M->getOrInsertFunction(
514 "__stack_chk_fail", Type::getVoidTy(Context), NULL);
515 CallInst::Create(StackChkFail, "", FailBB);
517 new UnreachableInst(Context, FailBB);