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/ADT/SmallPtrSet.h"
18 #include "llvm/ADT/Statistic.h"
19 #include "llvm/Analysis/BranchProbabilityInfo.h"
20 #include "llvm/Analysis/EHPersonalities.h"
21 #include "llvm/Analysis/OptimizationDiagnosticInfo.h"
22 #include "llvm/CodeGen/Passes.h"
23 #include "llvm/CodeGen/StackProtector.h"
24 #include "llvm/IR/Attributes.h"
25 #include "llvm/IR/BasicBlock.h"
26 #include "llvm/IR/Constants.h"
27 #include "llvm/IR/DataLayout.h"
28 #include "llvm/IR/DebugInfo.h"
29 #include "llvm/IR/DebugLoc.h"
30 #include "llvm/IR/DerivedTypes.h"
31 #include "llvm/IR/Function.h"
32 #include "llvm/IR/IRBuilder.h"
33 #include "llvm/IR/Instruction.h"
34 #include "llvm/IR/Instructions.h"
35 #include "llvm/IR/Intrinsics.h"
36 #include "llvm/IR/MDBuilder.h"
37 #include "llvm/IR/Module.h"
38 #include "llvm/IR/Type.h"
39 #include "llvm/IR/User.h"
40 #include "llvm/Pass.h"
41 #include "llvm/Support/Casting.h"
42 #include "llvm/Support/CommandLine.h"
43 #include "llvm/Target/TargetLowering.h"
44 #include "llvm/Target/TargetMachine.h"
45 #include "llvm/Target/TargetOptions.h"
46 #include "llvm/Target/TargetSubtargetInfo.h"
51 #define DEBUG_TYPE "stack-protector"
53 STATISTIC(NumFunProtected, "Number of functions protected");
54 STATISTIC(NumAddrTaken, "Number of local variables that have their address"
57 static cl::opt<bool> EnableSelectionDAGSP("enable-selectiondag-sp",
58 cl::init(true), cl::Hidden);
60 char StackProtector::ID = 0;
61 INITIALIZE_TM_PASS(StackProtector, "stack-protector", "Insert stack protectors",
64 FunctionPass *llvm::createStackProtectorPass(const TargetMachine *TM) {
65 return new StackProtector(TM);
68 StackProtector::SSPLayoutKind
69 StackProtector::getSSPLayout(const AllocaInst *AI) const {
70 return AI ? Layout.lookup(AI) : SSPLK_None;
73 void StackProtector::adjustForColoring(const AllocaInst *From,
74 const AllocaInst *To) {
75 // When coloring replaces one alloca with another, transfer the SSPLayoutKind
76 // tag from the remapped to the target alloca. The remapped alloca should
77 // have a size smaller than or equal to the replacement alloca.
78 SSPLayoutMap::iterator I = Layout.find(From);
79 if (I != Layout.end()) {
80 SSPLayoutKind Kind = I->second;
83 // Transfer the tag, but make sure that SSPLK_AddrOf does not overwrite
84 // SSPLK_SmallArray or SSPLK_LargeArray, and make sure that
85 // SSPLK_SmallArray does not overwrite SSPLK_LargeArray.
87 if (I == Layout.end())
88 Layout.insert(std::make_pair(To, Kind));
89 else if (I->second != SSPLK_LargeArray && Kind != SSPLK_AddrOf)
94 bool StackProtector::runOnFunction(Function &Fn) {
97 DominatorTreeWrapperPass *DTWP =
98 getAnalysisIfAvailable<DominatorTreeWrapperPass>();
99 DT = DTWP ? &DTWP->getDomTree() : nullptr;
100 TLI = TM->getSubtargetImpl(Fn)->getTargetLowering();
104 Attribute Attr = Fn.getFnAttribute("stack-protector-buffer-size");
105 if (Attr.isStringAttribute() &&
106 Attr.getValueAsString().getAsInteger(10, SSPBufferSize))
107 return false; // Invalid integer string
109 if (!RequiresStackProtector())
112 // TODO(etienneb): Functions with funclets are not correctly supported now.
113 // Do nothing if this is funclet-based personality.
114 if (Fn.hasPersonalityFn()) {
115 EHPersonality Personality = classifyEHPersonality(Fn.getPersonalityFn());
116 if (isFuncletEHPersonality(Personality))
121 return InsertStackProtectors();
124 /// \param [out] IsLarge is set to true if a protectable array is found and
125 /// it is "large" ( >= ssp-buffer-size). In the case of a structure with
126 /// multiple arrays, this gets set if any of them is large.
127 bool StackProtector::ContainsProtectableArray(Type *Ty, bool &IsLarge,
129 bool InStruct) const {
132 if (ArrayType *AT = dyn_cast<ArrayType>(Ty)) {
133 if (!AT->getElementType()->isIntegerTy(8)) {
134 // If we're on a non-Darwin platform or we're inside of a structure, don't
135 // add stack protectors unless the array is a character array.
136 // However, in strong mode any array, regardless of type and size,
137 // triggers a protector.
138 if (!Strong && (InStruct || !Trip.isOSDarwin()))
142 // If an array has more than SSPBufferSize bytes of allocated space, then we
143 // emit stack protectors.
144 if (SSPBufferSize <= M->getDataLayout().getTypeAllocSize(AT)) {
150 // Require a protector for all arrays in strong mode
154 const StructType *ST = dyn_cast<StructType>(Ty);
158 bool NeedsProtector = false;
159 for (StructType::element_iterator I = ST->element_begin(),
160 E = ST->element_end();
162 if (ContainsProtectableArray(*I, IsLarge, Strong, true)) {
163 // If the element is a protectable array and is large (>= SSPBufferSize)
164 // then we are done. If the protectable array is not large, then
165 // keep looking in case a subsequent element is a large array.
168 NeedsProtector = true;
171 return NeedsProtector;
174 bool StackProtector::HasAddressTaken(const Instruction *AI) {
175 for (const User *U : AI->users()) {
176 if (const StoreInst *SI = dyn_cast<StoreInst>(U)) {
177 if (AI == SI->getValueOperand())
179 } else if (const PtrToIntInst *SI = dyn_cast<PtrToIntInst>(U)) {
180 if (AI == SI->getOperand(0))
182 } else if (isa<CallInst>(U)) {
184 } else if (isa<InvokeInst>(U)) {
186 } else if (const SelectInst *SI = dyn_cast<SelectInst>(U)) {
187 if (HasAddressTaken(SI))
189 } else if (const PHINode *PN = dyn_cast<PHINode>(U)) {
190 // Keep track of what PHI nodes we have already visited to ensure
191 // they are only visited once.
192 if (VisitedPHIs.insert(PN).second)
193 if (HasAddressTaken(PN))
195 } else if (const GetElementPtrInst *GEP = dyn_cast<GetElementPtrInst>(U)) {
196 if (HasAddressTaken(GEP))
198 } else if (const BitCastInst *BI = dyn_cast<BitCastInst>(U)) {
199 if (HasAddressTaken(BI))
206 /// \brief Check whether or not this function needs a stack protector based
207 /// upon the stack protector level.
209 /// We use two heuristics: a standard (ssp) and strong (sspstrong).
210 /// The standard heuristic which will add a guard variable to functions that
211 /// call alloca with a either a variable size or a size >= SSPBufferSize,
212 /// functions with character buffers larger than SSPBufferSize, and functions
213 /// with aggregates containing character buffers larger than SSPBufferSize. The
214 /// strong heuristic will add a guard variables to functions that call alloca
215 /// regardless of size, functions with any buffer regardless of type and size,
216 /// functions with aggregates that contain any buffer regardless of type and
217 /// size, and functions that contain stack-based variables that have had their
219 bool StackProtector::RequiresStackProtector() {
221 bool NeedsProtector = false;
222 for (const BasicBlock &BB : *F)
223 for (const Instruction &I : BB)
224 if (const CallInst *CI = dyn_cast<CallInst>(&I))
225 if (CI->getCalledFunction() ==
226 Intrinsic::getDeclaration(F->getParent(),
227 Intrinsic::stackprotector))
230 if (F->hasFnAttribute(Attribute::SafeStack))
233 // We are constructing the OptimizationRemarkEmitter on the fly rather than
234 // using the analysis pass to avoid building DominatorTree and LoopInfo which
235 // are not available this late in the IR pipeline.
236 OptimizationRemarkEmitter ORE(F);
238 if (F->hasFnAttribute(Attribute::StackProtectReq)) {
239 ORE.emit(OptimizationRemark(DEBUG_TYPE, "StackProtectorRequested", F)
240 << "Stack protection applied to function "
241 << ore::NV("Function", F)
242 << " due to a function attribute or command-line switch");
243 NeedsProtector = true;
244 Strong = true; // Use the same heuristic as strong to determine SSPLayout
245 } else if (F->hasFnAttribute(Attribute::StackProtectStrong))
247 else if (HasPrologue)
248 NeedsProtector = true;
249 else if (!F->hasFnAttribute(Attribute::StackProtect))
252 for (const BasicBlock &BB : *F) {
253 for (const Instruction &I : BB) {
254 if (const AllocaInst *AI = dyn_cast<AllocaInst>(&I)) {
255 if (AI->isArrayAllocation()) {
256 OptimizationRemark Remark(DEBUG_TYPE, "StackProtectorAllocaOrArray",
259 << "Stack protection applied to function "
260 << ore::NV("Function", F)
261 << " due to a call to alloca or use of a variable length array";
262 if (const auto *CI = dyn_cast<ConstantInt>(AI->getArraySize())) {
263 if (CI->getLimitedValue(SSPBufferSize) >= SSPBufferSize) {
264 // A call to alloca with size >= SSPBufferSize requires
266 Layout.insert(std::make_pair(AI, SSPLK_LargeArray));
268 NeedsProtector = true;
270 // Require protectors for all alloca calls in strong mode.
271 Layout.insert(std::make_pair(AI, SSPLK_SmallArray));
273 NeedsProtector = true;
276 // A call to alloca with a variable size requires protectors.
277 Layout.insert(std::make_pair(AI, SSPLK_LargeArray));
279 NeedsProtector = true;
284 bool IsLarge = false;
285 if (ContainsProtectableArray(AI->getAllocatedType(), IsLarge, Strong)) {
286 Layout.insert(std::make_pair(AI, IsLarge ? SSPLK_LargeArray
287 : SSPLK_SmallArray));
288 ORE.emit(OptimizationRemark(DEBUG_TYPE, "StackProtectorBuffer", &I)
289 << "Stack protection applied to function "
290 << ore::NV("Function", F)
291 << " due to a stack allocated buffer or struct containing a "
293 NeedsProtector = true;
297 if (Strong && HasAddressTaken(AI)) {
299 Layout.insert(std::make_pair(AI, SSPLK_AddrOf));
301 OptimizationRemark(DEBUG_TYPE, "StackProtectorAddressTaken", &I)
302 << "Stack protection applied to function "
303 << ore::NV("Function", F)
304 << " due to the address of a local variable being taken");
305 NeedsProtector = true;
311 return NeedsProtector;
314 /// Create a stack guard loading and populate whether SelectionDAG SSP is
316 static Value *getStackGuard(const TargetLoweringBase *TLI, Module *M,
318 bool *SupportsSelectionDAGSP = nullptr) {
319 if (Value *Guard = TLI->getIRStackGuard(B))
320 return B.CreateLoad(Guard, true, "StackGuard");
322 // Use SelectionDAG SSP handling, since there isn't an IR guard.
324 // This is more or less weird, since we optionally output whether we
325 // should perform a SelectionDAG SP here. The reason is that it's strictly
326 // defined as !TLI->getIRStackGuard(B), where getIRStackGuard is also
327 // mutating. There is no way to get this bit without mutating the IR, so
328 // getting this bit has to happen in this right time.
330 // We could have define a new function TLI::supportsSelectionDAGSP(), but that
331 // will put more burden on the backends' overriding work, especially when it
332 // actually conveys the same information getIRStackGuard() already gives.
333 if (SupportsSelectionDAGSP)
334 *SupportsSelectionDAGSP = true;
335 TLI->insertSSPDeclarations(*M);
336 return B.CreateCall(Intrinsic::getDeclaration(M, Intrinsic::stackguard));
339 /// Insert code into the entry block that stores the stack guard
340 /// variable onto the stack:
343 /// StackGuardSlot = alloca i8*
344 /// StackGuard = <stack guard>
345 /// call void @llvm.stackprotector(StackGuard, StackGuardSlot)
347 /// Returns true if the platform/triple supports the stackprotectorcreate pseudo
349 static bool CreatePrologue(Function *F, Module *M, ReturnInst *RI,
350 const TargetLoweringBase *TLI, AllocaInst *&AI) {
351 bool SupportsSelectionDAGSP = false;
352 IRBuilder<> B(&F->getEntryBlock().front());
353 PointerType *PtrTy = Type::getInt8PtrTy(RI->getContext());
354 AI = B.CreateAlloca(PtrTy, nullptr, "StackGuardSlot");
356 Value *GuardSlot = getStackGuard(TLI, M, B, &SupportsSelectionDAGSP);
357 B.CreateCall(Intrinsic::getDeclaration(M, Intrinsic::stackprotector),
359 return SupportsSelectionDAGSP;
362 /// InsertStackProtectors - Insert code into the prologue and epilogue of the
365 /// - The prologue code loads and stores the stack guard onto the stack.
366 /// - The epilogue checks the value stored in the prologue against the original
367 /// value. It calls __stack_chk_fail if they differ.
368 bool StackProtector::InsertStackProtectors() {
369 bool SupportsSelectionDAGSP =
370 EnableSelectionDAGSP && !TM->Options.EnableFastISel;
371 AllocaInst *AI = nullptr; // Place on stack that stores the stack guard.
373 for (Function::iterator I = F->begin(), E = F->end(); I != E;) {
374 BasicBlock *BB = &*I++;
375 ReturnInst *RI = dyn_cast<ReturnInst>(BB->getTerminator());
379 // Generate prologue instrumentation if not already generated.
382 SupportsSelectionDAGSP &= CreatePrologue(F, M, RI, TLI, AI);
385 // SelectionDAG based code generation. Nothing else needs to be done here.
386 // The epilogue instrumentation is postponed to SelectionDAG.
387 if (SupportsSelectionDAGSP)
390 // Set HasIRCheck to true, so that SelectionDAG will not generate its own
391 // version. SelectionDAG called 'shouldEmitSDCheck' to check whether
392 // instrumentation has already been generated.
395 // Generate epilogue instrumentation. The epilogue intrumentation can be
396 // function-based or inlined depending on which mechanism the target is
398 if (Value* GuardCheck = TLI->getSSPStackGuardCheck(*M)) {
399 // Generate the function-based epilogue instrumentation.
400 // The target provides a guard check function, generate a call to it.
402 LoadInst *Guard = B.CreateLoad(AI, true, "Guard");
403 CallInst *Call = B.CreateCall(GuardCheck, {Guard});
404 llvm::Function *Function = cast<llvm::Function>(GuardCheck);
405 Call->setAttributes(Function->getAttributes());
406 Call->setCallingConv(Function->getCallingConv());
408 // Generate the epilogue with inline instrumentation.
409 // If we do not support SelectionDAG based tail calls, generate IR level
412 // For each block with a return instruction, convert this:
422 // %1 = <stack guard>
423 // %2 = load StackGuardSlot
424 // %3 = cmp i1 %1, %2
425 // br i1 %3, label %SP_return, label %CallStackCheckFailBlk
430 // CallStackCheckFailBlk:
431 // call void @__stack_chk_fail()
434 // Create the FailBB. We duplicate the BB every time since the MI tail
435 // merge pass will merge together all of the various BB into one including
436 // fail BB generated by the stack protector pseudo instruction.
437 BasicBlock *FailBB = CreateFailBB();
439 // Split the basic block before the return instruction.
440 BasicBlock *NewBB = BB->splitBasicBlock(RI->getIterator(), "SP_return");
442 // Update the dominator tree if we need to.
443 if (DT && DT->isReachableFromEntry(BB)) {
444 DT->addNewBlock(NewBB, BB);
445 DT->addNewBlock(FailBB, BB);
448 // Remove default branch instruction to the new BB.
449 BB->getTerminator()->eraseFromParent();
451 // Move the newly created basic block to the point right after the old
452 // basic block so that it's in the "fall through" position.
453 NewBB->moveAfter(BB);
455 // Generate the stack protector instructions in the old basic block.
457 Value *Guard = getStackGuard(TLI, M, B);
458 LoadInst *LI2 = B.CreateLoad(AI, true);
459 Value *Cmp = B.CreateICmpEQ(Guard, LI2);
461 BranchProbabilityInfo::getBranchProbStackProtector(true);
463 BranchProbabilityInfo::getBranchProbStackProtector(false);
464 MDNode *Weights = MDBuilder(F->getContext())
465 .createBranchWeights(SuccessProb.getNumerator(),
466 FailureProb.getNumerator());
467 B.CreateCondBr(Cmp, NewBB, FailBB, Weights);
471 // Return if we didn't modify any basic blocks. i.e., there are no return
472 // statements in the function.
476 /// CreateFailBB - Create a basic block to jump to when the stack protector
478 BasicBlock *StackProtector::CreateFailBB() {
479 LLVMContext &Context = F->getContext();
480 BasicBlock *FailBB = BasicBlock::Create(Context, "CallStackCheckFailBlk", F);
481 IRBuilder<> B(FailBB);
482 B.SetCurrentDebugLocation(DebugLoc::get(0, 0, F->getSubprogram()));
483 if (Trip.isOSOpenBSD()) {
484 Constant *StackChkFail =
485 M->getOrInsertFunction("__stack_smash_handler",
486 Type::getVoidTy(Context),
487 Type::getInt8PtrTy(Context));
489 B.CreateCall(StackChkFail, B.CreateGlobalStringPtr(F->getName(), "SSH"));
491 Constant *StackChkFail =
492 M->getOrInsertFunction("__stack_chk_fail", Type::getVoidTy(Context));
494 B.CreateCall(StackChkFail, {});
496 B.CreateUnreachable();
500 bool StackProtector::shouldEmitSDCheck(const BasicBlock &BB) const {
501 return HasPrologue && !HasIRCheck && dyn_cast<ReturnInst>(BB.getTerminator());