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 #include "llvm/CodeGen/StackProtector.h"
18 #include "llvm/ADT/SmallPtrSet.h"
19 #include "llvm/ADT/Statistic.h"
20 #include "llvm/Analysis/BranchProbabilityInfo.h"
21 #include "llvm/Analysis/EHPersonalities.h"
22 #include "llvm/Analysis/ValueTracking.h"
23 #include "llvm/CodeGen/Passes.h"
24 #include "llvm/IR/Attributes.h"
25 #include "llvm/IR/Constants.h"
26 #include "llvm/IR/DataLayout.h"
27 #include "llvm/IR/DebugInfo.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/IRBuilder.h"
33 #include "llvm/IR/Instructions.h"
34 #include "llvm/IR/IntrinsicInst.h"
35 #include "llvm/IR/Intrinsics.h"
36 #include "llvm/IR/MDBuilder.h"
37 #include "llvm/IR/Module.h"
38 #include "llvm/Support/CommandLine.h"
39 #include "llvm/Target/TargetSubtargetInfo.h"
43 #define DEBUG_TYPE "stack-protector"
45 STATISTIC(NumFunProtected, "Number of functions protected");
46 STATISTIC(NumAddrTaken, "Number of local variables that have their address"
49 static cl::opt<bool> EnableSelectionDAGSP("enable-selectiondag-sp",
50 cl::init(true), cl::Hidden);
52 char StackProtector::ID = 0;
53 INITIALIZE_TM_PASS(StackProtector, "stack-protector", "Insert stack protectors",
56 FunctionPass *llvm::createStackProtectorPass(const TargetMachine *TM) {
57 return new StackProtector(TM);
60 StackProtector::SSPLayoutKind
61 StackProtector::getSSPLayout(const AllocaInst *AI) const {
62 return AI ? Layout.lookup(AI) : SSPLK_None;
65 void StackProtector::adjustForColoring(const AllocaInst *From,
66 const AllocaInst *To) {
67 // When coloring replaces one alloca with another, transfer the SSPLayoutKind
68 // tag from the remapped to the target alloca. The remapped alloca should
69 // have a size smaller than or equal to the replacement alloca.
70 SSPLayoutMap::iterator I = Layout.find(From);
71 if (I != Layout.end()) {
72 SSPLayoutKind Kind = I->second;
75 // Transfer the tag, but make sure that SSPLK_AddrOf does not overwrite
76 // SSPLK_SmallArray or SSPLK_LargeArray, and make sure that
77 // SSPLK_SmallArray does not overwrite SSPLK_LargeArray.
79 if (I == Layout.end())
80 Layout.insert(std::make_pair(To, Kind));
81 else if (I->second != SSPLK_LargeArray && Kind != SSPLK_AddrOf)
86 bool StackProtector::runOnFunction(Function &Fn) {
89 DominatorTreeWrapperPass *DTWP =
90 getAnalysisIfAvailable<DominatorTreeWrapperPass>();
91 DT = DTWP ? &DTWP->getDomTree() : nullptr;
92 TLI = TM->getSubtargetImpl(Fn)->getTargetLowering();
96 Attribute Attr = Fn.getFnAttribute("stack-protector-buffer-size");
97 if (Attr.isStringAttribute() &&
98 Attr.getValueAsString().getAsInteger(10, SSPBufferSize))
99 return false; // Invalid integer string
101 if (!RequiresStackProtector())
104 // TODO(etienneb): Functions with funclets are not correctly supported now.
105 // Do nothing if this is funclet-based personality.
106 if (Fn.hasPersonalityFn()) {
107 EHPersonality Personality = classifyEHPersonality(Fn.getPersonalityFn());
108 if (isFuncletEHPersonality(Personality))
113 return InsertStackProtectors();
116 /// \param [out] IsLarge is set to true if a protectable array is found and
117 /// it is "large" ( >= ssp-buffer-size). In the case of a structure with
118 /// multiple arrays, this gets set if any of them is large.
119 bool StackProtector::ContainsProtectableArray(Type *Ty, bool &IsLarge,
121 bool InStruct) const {
124 if (ArrayType *AT = dyn_cast<ArrayType>(Ty)) {
125 if (!AT->getElementType()->isIntegerTy(8)) {
126 // If we're on a non-Darwin platform or we're inside of a structure, don't
127 // add stack protectors unless the array is a character array.
128 // However, in strong mode any array, regardless of type and size,
129 // triggers a protector.
130 if (!Strong && (InStruct || !Trip.isOSDarwin()))
134 // If an array has more than SSPBufferSize bytes of allocated space, then we
135 // emit stack protectors.
136 if (SSPBufferSize <= M->getDataLayout().getTypeAllocSize(AT)) {
142 // Require a protector for all arrays in strong mode
146 const StructType *ST = dyn_cast<StructType>(Ty);
150 bool NeedsProtector = false;
151 for (StructType::element_iterator I = ST->element_begin(),
152 E = ST->element_end();
154 if (ContainsProtectableArray(*I, IsLarge, Strong, true)) {
155 // If the element is a protectable array and is large (>= SSPBufferSize)
156 // then we are done. If the protectable array is not large, then
157 // keep looking in case a subsequent element is a large array.
160 NeedsProtector = true;
163 return NeedsProtector;
166 bool StackProtector::HasAddressTaken(const Instruction *AI) {
167 for (const User *U : AI->users()) {
168 if (const StoreInst *SI = dyn_cast<StoreInst>(U)) {
169 if (AI == SI->getValueOperand())
171 } else if (const PtrToIntInst *SI = dyn_cast<PtrToIntInst>(U)) {
172 if (AI == SI->getOperand(0))
174 } else if (isa<CallInst>(U)) {
176 } else if (isa<InvokeInst>(U)) {
178 } else if (const SelectInst *SI = dyn_cast<SelectInst>(U)) {
179 if (HasAddressTaken(SI))
181 } else if (const PHINode *PN = dyn_cast<PHINode>(U)) {
182 // Keep track of what PHI nodes we have already visited to ensure
183 // they are only visited once.
184 if (VisitedPHIs.insert(PN).second)
185 if (HasAddressTaken(PN))
187 } else if (const GetElementPtrInst *GEP = dyn_cast<GetElementPtrInst>(U)) {
188 if (HasAddressTaken(GEP))
190 } else if (const BitCastInst *BI = dyn_cast<BitCastInst>(U)) {
191 if (HasAddressTaken(BI))
198 /// \brief Check whether or not this function needs a stack protector based
199 /// upon the stack protector level.
201 /// We use two heuristics: a standard (ssp) and strong (sspstrong).
202 /// The standard heuristic which will add a guard variable to functions that
203 /// call alloca with a either a variable size or a size >= SSPBufferSize,
204 /// functions with character buffers larger than SSPBufferSize, and functions
205 /// with aggregates containing character buffers larger than SSPBufferSize. The
206 /// strong heuristic will add a guard variables to functions that call alloca
207 /// regardless of size, functions with any buffer regardless of type and size,
208 /// functions with aggregates that contain any buffer regardless of type and
209 /// size, and functions that contain stack-based variables that have had their
211 bool StackProtector::RequiresStackProtector() {
213 bool NeedsProtector = false;
214 for (const BasicBlock &BB : *F)
215 for (const Instruction &I : BB)
216 if (const CallInst *CI = dyn_cast<CallInst>(&I))
217 if (CI->getCalledFunction() ==
218 Intrinsic::getDeclaration(F->getParent(),
219 Intrinsic::stackprotector))
222 if (F->hasFnAttribute(Attribute::SafeStack))
225 if (F->hasFnAttribute(Attribute::StackProtectReq)) {
226 NeedsProtector = true;
227 Strong = true; // Use the same heuristic as strong to determine SSPLayout
228 } else if (F->hasFnAttribute(Attribute::StackProtectStrong))
230 else if (HasPrologue)
231 NeedsProtector = true;
232 else if (!F->hasFnAttribute(Attribute::StackProtect))
235 for (const BasicBlock &BB : *F) {
236 for (const Instruction &I : BB) {
237 if (const AllocaInst *AI = dyn_cast<AllocaInst>(&I)) {
238 if (AI->isArrayAllocation()) {
239 if (const auto *CI = dyn_cast<ConstantInt>(AI->getArraySize())) {
240 if (CI->getLimitedValue(SSPBufferSize) >= SSPBufferSize) {
241 // A call to alloca with size >= SSPBufferSize requires
243 Layout.insert(std::make_pair(AI, SSPLK_LargeArray));
244 NeedsProtector = true;
246 // Require protectors for all alloca calls in strong mode.
247 Layout.insert(std::make_pair(AI, SSPLK_SmallArray));
248 NeedsProtector = true;
251 // A call to alloca with a variable size requires protectors.
252 Layout.insert(std::make_pair(AI, SSPLK_LargeArray));
253 NeedsProtector = true;
258 bool IsLarge = false;
259 if (ContainsProtectableArray(AI->getAllocatedType(), IsLarge, Strong)) {
260 Layout.insert(std::make_pair(AI, IsLarge ? SSPLK_LargeArray
261 : SSPLK_SmallArray));
262 NeedsProtector = true;
266 if (Strong && HasAddressTaken(AI)) {
268 Layout.insert(std::make_pair(AI, SSPLK_AddrOf));
269 NeedsProtector = true;
275 return NeedsProtector;
278 /// Create a stack guard loading and populate whether SelectionDAG SSP is
280 static Value *getStackGuard(const TargetLoweringBase *TLI, Module *M,
282 bool *SupportsSelectionDAGSP = nullptr) {
283 if (Value *Guard = TLI->getIRStackGuard(B))
284 return B.CreateLoad(Guard, true, "StackGuard");
286 // Use SelectionDAG SSP handling, since there isn't an IR guard.
288 // This is more or less weird, since we optionally output whether we
289 // should perform a SelectionDAG SP here. The reason is that it's strictly
290 // defined as !TLI->getIRStackGuard(B), where getIRStackGuard is also
291 // mutating. There is no way to get this bit without mutating the IR, so
292 // getting this bit has to happen in this right time.
294 // We could have define a new function TLI::supportsSelectionDAGSP(), but that
295 // will put more burden on the backends' overriding work, especially when it
296 // actually conveys the same information getIRStackGuard() already gives.
297 if (SupportsSelectionDAGSP)
298 *SupportsSelectionDAGSP = true;
299 TLI->insertSSPDeclarations(*M);
300 return B.CreateCall(Intrinsic::getDeclaration(M, Intrinsic::stackguard));
303 /// Insert code into the entry block that stores the stack guard
304 /// variable onto the stack:
307 /// StackGuardSlot = alloca i8*
308 /// StackGuard = <stack guard>
309 /// call void @llvm.stackprotector(StackGuard, StackGuardSlot)
311 /// Returns true if the platform/triple supports the stackprotectorcreate pseudo
313 static bool CreatePrologue(Function *F, Module *M, ReturnInst *RI,
314 const TargetLoweringBase *TLI, AllocaInst *&AI) {
315 bool SupportsSelectionDAGSP = false;
316 IRBuilder<> B(&F->getEntryBlock().front());
317 PointerType *PtrTy = Type::getInt8PtrTy(RI->getContext());
318 AI = B.CreateAlloca(PtrTy, nullptr, "StackGuardSlot");
320 Value *GuardSlot = getStackGuard(TLI, M, B, &SupportsSelectionDAGSP);
321 B.CreateCall(Intrinsic::getDeclaration(M, Intrinsic::stackprotector),
323 return SupportsSelectionDAGSP;
326 /// InsertStackProtectors - Insert code into the prologue and epilogue of the
329 /// - The prologue code loads and stores the stack guard onto the stack.
330 /// - The epilogue checks the value stored in the prologue against the original
331 /// value. It calls __stack_chk_fail if they differ.
332 bool StackProtector::InsertStackProtectors() {
333 bool SupportsSelectionDAGSP =
334 EnableSelectionDAGSP && !TM->Options.EnableFastISel;
335 AllocaInst *AI = nullptr; // Place on stack that stores the stack guard.
337 for (Function::iterator I = F->begin(), E = F->end(); I != E;) {
338 BasicBlock *BB = &*I++;
339 ReturnInst *RI = dyn_cast<ReturnInst>(BB->getTerminator());
343 // Generate prologue instrumentation if not already generated.
346 SupportsSelectionDAGSP &= CreatePrologue(F, M, RI, TLI, AI);
349 // SelectionDAG based code generation. Nothing else needs to be done here.
350 // The epilogue instrumentation is postponed to SelectionDAG.
351 if (SupportsSelectionDAGSP)
354 // Set HasIRCheck to true, so that SelectionDAG will not generate its own
355 // version. SelectionDAG called 'shouldEmitSDCheck' to check whether
356 // instrumentation has already been generated.
359 // Generate epilogue instrumentation. The epilogue intrumentation can be
360 // function-based or inlined depending on which mechanism the target is
362 if (Value* GuardCheck = TLI->getSSPStackGuardCheck(*M)) {
363 // Generate the function-based epilogue instrumentation.
364 // The target provides a guard check function, generate a call to it.
366 LoadInst *Guard = B.CreateLoad(AI, true, "Guard");
367 CallInst *Call = B.CreateCall(GuardCheck, {Guard});
368 llvm::Function *Function = cast<llvm::Function>(GuardCheck);
369 Call->setAttributes(Function->getAttributes());
370 Call->setCallingConv(Function->getCallingConv());
372 // Generate the epilogue with inline instrumentation.
373 // If we do not support SelectionDAG based tail calls, generate IR level
376 // For each block with a return instruction, convert this:
386 // %1 = <stack guard>
387 // %2 = load StackGuardSlot
388 // %3 = cmp i1 %1, %2
389 // br i1 %3, label %SP_return, label %CallStackCheckFailBlk
394 // CallStackCheckFailBlk:
395 // call void @__stack_chk_fail()
398 // Create the FailBB. We duplicate the BB every time since the MI tail
399 // merge pass will merge together all of the various BB into one including
400 // fail BB generated by the stack protector pseudo instruction.
401 BasicBlock *FailBB = CreateFailBB();
403 // Split the basic block before the return instruction.
404 BasicBlock *NewBB = BB->splitBasicBlock(RI->getIterator(), "SP_return");
406 // Update the dominator tree if we need to.
407 if (DT && DT->isReachableFromEntry(BB)) {
408 DT->addNewBlock(NewBB, BB);
409 DT->addNewBlock(FailBB, BB);
412 // Remove default branch instruction to the new BB.
413 BB->getTerminator()->eraseFromParent();
415 // Move the newly created basic block to the point right after the old
416 // basic block so that it's in the "fall through" position.
417 NewBB->moveAfter(BB);
419 // Generate the stack protector instructions in the old basic block.
421 Value *Guard = getStackGuard(TLI, M, B);
422 LoadInst *LI2 = B.CreateLoad(AI, true);
423 Value *Cmp = B.CreateICmpEQ(Guard, LI2);
425 BranchProbabilityInfo::getBranchProbStackProtector(true);
427 BranchProbabilityInfo::getBranchProbStackProtector(false);
428 MDNode *Weights = MDBuilder(F->getContext())
429 .createBranchWeights(SuccessProb.getNumerator(),
430 FailureProb.getNumerator());
431 B.CreateCondBr(Cmp, NewBB, FailBB, Weights);
435 // Return if we didn't modify any basic blocks. i.e., there are no return
436 // statements in the function.
440 /// CreateFailBB - Create a basic block to jump to when the stack protector
442 BasicBlock *StackProtector::CreateFailBB() {
443 LLVMContext &Context = F->getContext();
444 BasicBlock *FailBB = BasicBlock::Create(Context, "CallStackCheckFailBlk", F);
445 IRBuilder<> B(FailBB);
446 B.SetCurrentDebugLocation(DebugLoc::get(0, 0, F->getSubprogram()));
447 if (Trip.isOSOpenBSD()) {
448 Constant *StackChkFail =
449 M->getOrInsertFunction("__stack_smash_handler",
450 Type::getVoidTy(Context),
451 Type::getInt8PtrTy(Context), nullptr);
453 B.CreateCall(StackChkFail, B.CreateGlobalStringPtr(F->getName(), "SSH"));
455 Constant *StackChkFail =
456 M->getOrInsertFunction("__stack_chk_fail", Type::getVoidTy(Context),
458 B.CreateCall(StackChkFail, {});
460 B.CreateUnreachable();
464 bool StackProtector::shouldEmitSDCheck(const BasicBlock &BB) const {
465 return HasPrologue && !HasIRCheck && dyn_cast<ReturnInst>(BB.getTerminator());