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_PASS_BEGIN(StackProtector, "stack-protector",
62 "Insert stack protectors", false, true)
63 INITIALIZE_PASS_DEPENDENCY(TargetPassConfig)
64 INITIALIZE_PASS_END(StackProtector, "stack-protector",
65 "Insert stack protectors", false, true)
67 FunctionPass *llvm::createStackProtectorPass() { return new StackProtector(); }
69 StackProtector::SSPLayoutKind
70 StackProtector::getSSPLayout(const AllocaInst *AI) const {
71 return AI ? Layout.lookup(AI) : SSPLK_None;
74 void StackProtector::adjustForColoring(const AllocaInst *From,
75 const AllocaInst *To) {
76 // When coloring replaces one alloca with another, transfer the SSPLayoutKind
77 // tag from the remapped to the target alloca. The remapped alloca should
78 // have a size smaller than or equal to the replacement alloca.
79 SSPLayoutMap::iterator I = Layout.find(From);
80 if (I != Layout.end()) {
81 SSPLayoutKind Kind = I->second;
84 // Transfer the tag, but make sure that SSPLK_AddrOf does not overwrite
85 // SSPLK_SmallArray or SSPLK_LargeArray, and make sure that
86 // SSPLK_SmallArray does not overwrite SSPLK_LargeArray.
88 if (I == Layout.end())
89 Layout.insert(std::make_pair(To, Kind));
90 else if (I->second != SSPLK_LargeArray && Kind != SSPLK_AddrOf)
95 bool StackProtector::runOnFunction(Function &Fn) {
98 DominatorTreeWrapperPass *DTWP =
99 getAnalysisIfAvailable<DominatorTreeWrapperPass>();
100 DT = DTWP ? &DTWP->getDomTree() : nullptr;
101 TM = &getAnalysis<TargetPassConfig>().getTM<TargetMachine>();
102 Trip = TM->getTargetTriple();
103 TLI = TM->getSubtargetImpl(Fn)->getTargetLowering();
107 Attribute Attr = Fn.getFnAttribute("stack-protector-buffer-size");
108 if (Attr.isStringAttribute() &&
109 Attr.getValueAsString().getAsInteger(10, SSPBufferSize))
110 return false; // Invalid integer string
112 if (!RequiresStackProtector())
115 // TODO(etienneb): Functions with funclets are not correctly supported now.
116 // Do nothing if this is funclet-based personality.
117 if (Fn.hasPersonalityFn()) {
118 EHPersonality Personality = classifyEHPersonality(Fn.getPersonalityFn());
119 if (isFuncletEHPersonality(Personality))
124 return InsertStackProtectors();
127 /// \param [out] IsLarge is set to true if a protectable array is found and
128 /// it is "large" ( >= ssp-buffer-size). In the case of a structure with
129 /// multiple arrays, this gets set if any of them is large.
130 bool StackProtector::ContainsProtectableArray(Type *Ty, bool &IsLarge,
132 bool InStruct) const {
135 if (ArrayType *AT = dyn_cast<ArrayType>(Ty)) {
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 // However, in strong mode any array, regardless of type and size,
140 // triggers a protector.
141 if (!Strong && (InStruct || !Trip.isOSDarwin()))
145 // If an array has more than SSPBufferSize bytes of allocated space, then we
146 // emit stack protectors.
147 if (SSPBufferSize <= M->getDataLayout().getTypeAllocSize(AT)) {
153 // Require a protector for all arrays in strong mode
157 const StructType *ST = dyn_cast<StructType>(Ty);
161 bool NeedsProtector = false;
162 for (StructType::element_iterator I = ST->element_begin(),
163 E = ST->element_end();
165 if (ContainsProtectableArray(*I, IsLarge, Strong, true)) {
166 // If the element is a protectable array and is large (>= SSPBufferSize)
167 // then we are done. If the protectable array is not large, then
168 // keep looking in case a subsequent element is a large array.
171 NeedsProtector = true;
174 return NeedsProtector;
177 bool StackProtector::HasAddressTaken(const Instruction *AI) {
178 for (const User *U : AI->users()) {
179 if (const StoreInst *SI = dyn_cast<StoreInst>(U)) {
180 if (AI == SI->getValueOperand())
182 } else if (const PtrToIntInst *SI = dyn_cast<PtrToIntInst>(U)) {
183 if (AI == SI->getOperand(0))
185 } else if (isa<CallInst>(U)) {
187 } else if (isa<InvokeInst>(U)) {
189 } else if (const SelectInst *SI = dyn_cast<SelectInst>(U)) {
190 if (HasAddressTaken(SI))
192 } else if (const PHINode *PN = dyn_cast<PHINode>(U)) {
193 // Keep track of what PHI nodes we have already visited to ensure
194 // they are only visited once.
195 if (VisitedPHIs.insert(PN).second)
196 if (HasAddressTaken(PN))
198 } else if (const GetElementPtrInst *GEP = dyn_cast<GetElementPtrInst>(U)) {
199 if (HasAddressTaken(GEP))
201 } else if (const BitCastInst *BI = dyn_cast<BitCastInst>(U)) {
202 if (HasAddressTaken(BI))
209 /// \brief Check whether or not this function needs a stack protector based
210 /// upon the stack protector level.
212 /// We use two heuristics: a standard (ssp) and strong (sspstrong).
213 /// The standard heuristic which will add a guard variable to functions that
214 /// call alloca with a either a variable size or a size >= SSPBufferSize,
215 /// functions with character buffers larger than SSPBufferSize, and functions
216 /// with aggregates containing character buffers larger than SSPBufferSize. The
217 /// strong heuristic will add a guard variables to functions that call alloca
218 /// regardless of size, functions with any buffer regardless of type and size,
219 /// functions with aggregates that contain any buffer regardless of type and
220 /// size, and functions that contain stack-based variables that have had their
222 bool StackProtector::RequiresStackProtector() {
224 bool NeedsProtector = false;
225 for (const BasicBlock &BB : *F)
226 for (const Instruction &I : BB)
227 if (const CallInst *CI = dyn_cast<CallInst>(&I))
228 if (CI->getCalledFunction() ==
229 Intrinsic::getDeclaration(F->getParent(),
230 Intrinsic::stackprotector))
233 if (F->hasFnAttribute(Attribute::SafeStack))
236 // We are constructing the OptimizationRemarkEmitter on the fly rather than
237 // using the analysis pass to avoid building DominatorTree and LoopInfo which
238 // are not available this late in the IR pipeline.
239 OptimizationRemarkEmitter ORE(F);
241 if (F->hasFnAttribute(Attribute::StackProtectReq)) {
242 ORE.emit(OptimizationRemark(DEBUG_TYPE, "StackProtectorRequested", F)
243 << "Stack protection applied to function "
244 << ore::NV("Function", F)
245 << " due to a function attribute or command-line switch");
246 NeedsProtector = true;
247 Strong = true; // Use the same heuristic as strong to determine SSPLayout
248 } else if (F->hasFnAttribute(Attribute::StackProtectStrong))
250 else if (HasPrologue)
251 NeedsProtector = true;
252 else if (!F->hasFnAttribute(Attribute::StackProtect))
255 for (const BasicBlock &BB : *F) {
256 for (const Instruction &I : BB) {
257 if (const AllocaInst *AI = dyn_cast<AllocaInst>(&I)) {
258 if (AI->isArrayAllocation()) {
259 OptimizationRemark Remark(DEBUG_TYPE, "StackProtectorAllocaOrArray",
262 << "Stack protection applied to function "
263 << ore::NV("Function", F)
264 << " due to a call to alloca or use of a variable length array";
265 if (const auto *CI = dyn_cast<ConstantInt>(AI->getArraySize())) {
266 if (CI->getLimitedValue(SSPBufferSize) >= SSPBufferSize) {
267 // A call to alloca with size >= SSPBufferSize requires
269 Layout.insert(std::make_pair(AI, SSPLK_LargeArray));
271 NeedsProtector = true;
273 // Require protectors for all alloca calls in strong mode.
274 Layout.insert(std::make_pair(AI, SSPLK_SmallArray));
276 NeedsProtector = true;
279 // A call to alloca with a variable size requires protectors.
280 Layout.insert(std::make_pair(AI, SSPLK_LargeArray));
282 NeedsProtector = true;
287 bool IsLarge = false;
288 if (ContainsProtectableArray(AI->getAllocatedType(), IsLarge, Strong)) {
289 Layout.insert(std::make_pair(AI, IsLarge ? SSPLK_LargeArray
290 : SSPLK_SmallArray));
291 ORE.emit(OptimizationRemark(DEBUG_TYPE, "StackProtectorBuffer", &I)
292 << "Stack protection applied to function "
293 << ore::NV("Function", F)
294 << " due to a stack allocated buffer or struct containing a "
296 NeedsProtector = true;
300 if (Strong && HasAddressTaken(AI)) {
302 Layout.insert(std::make_pair(AI, SSPLK_AddrOf));
304 OptimizationRemark(DEBUG_TYPE, "StackProtectorAddressTaken", &I)
305 << "Stack protection applied to function "
306 << ore::NV("Function", F)
307 << " due to the address of a local variable being taken");
308 NeedsProtector = true;
314 return NeedsProtector;
317 /// Create a stack guard loading and populate whether SelectionDAG SSP is
319 static Value *getStackGuard(const TargetLoweringBase *TLI, Module *M,
321 bool *SupportsSelectionDAGSP = nullptr) {
322 if (Value *Guard = TLI->getIRStackGuard(B))
323 return B.CreateLoad(Guard, true, "StackGuard");
325 // Use SelectionDAG SSP handling, since there isn't an IR guard.
327 // This is more or less weird, since we optionally output whether we
328 // should perform a SelectionDAG SP here. The reason is that it's strictly
329 // defined as !TLI->getIRStackGuard(B), where getIRStackGuard is also
330 // mutating. There is no way to get this bit without mutating the IR, so
331 // getting this bit has to happen in this right time.
333 // We could have define a new function TLI::supportsSelectionDAGSP(), but that
334 // will put more burden on the backends' overriding work, especially when it
335 // actually conveys the same information getIRStackGuard() already gives.
336 if (SupportsSelectionDAGSP)
337 *SupportsSelectionDAGSP = true;
338 TLI->insertSSPDeclarations(*M);
339 return B.CreateCall(Intrinsic::getDeclaration(M, Intrinsic::stackguard));
342 /// Insert code into the entry block that stores the stack guard
343 /// variable onto the stack:
346 /// StackGuardSlot = alloca i8*
347 /// StackGuard = <stack guard>
348 /// call void @llvm.stackprotector(StackGuard, StackGuardSlot)
350 /// Returns true if the platform/triple supports the stackprotectorcreate pseudo
352 static bool CreatePrologue(Function *F, Module *M, ReturnInst *RI,
353 const TargetLoweringBase *TLI, AllocaInst *&AI) {
354 bool SupportsSelectionDAGSP = false;
355 IRBuilder<> B(&F->getEntryBlock().front());
356 PointerType *PtrTy = Type::getInt8PtrTy(RI->getContext());
357 AI = B.CreateAlloca(PtrTy, nullptr, "StackGuardSlot");
359 Value *GuardSlot = getStackGuard(TLI, M, B, &SupportsSelectionDAGSP);
360 B.CreateCall(Intrinsic::getDeclaration(M, Intrinsic::stackprotector),
362 return SupportsSelectionDAGSP;
365 /// InsertStackProtectors - Insert code into the prologue and epilogue of the
368 /// - The prologue code loads and stores the stack guard onto the stack.
369 /// - The epilogue checks the value stored in the prologue against the original
370 /// value. It calls __stack_chk_fail if they differ.
371 bool StackProtector::InsertStackProtectors() {
372 bool SupportsSelectionDAGSP =
373 EnableSelectionDAGSP && !TM->Options.EnableFastISel;
374 AllocaInst *AI = nullptr; // Place on stack that stores the stack guard.
376 for (Function::iterator I = F->begin(), E = F->end(); I != E;) {
377 BasicBlock *BB = &*I++;
378 ReturnInst *RI = dyn_cast<ReturnInst>(BB->getTerminator());
382 // Generate prologue instrumentation if not already generated.
385 SupportsSelectionDAGSP &= CreatePrologue(F, M, RI, TLI, AI);
388 // SelectionDAG based code generation. Nothing else needs to be done here.
389 // The epilogue instrumentation is postponed to SelectionDAG.
390 if (SupportsSelectionDAGSP)
393 // Set HasIRCheck to true, so that SelectionDAG will not generate its own
394 // version. SelectionDAG called 'shouldEmitSDCheck' to check whether
395 // instrumentation has already been generated.
398 // Generate epilogue instrumentation. The epilogue intrumentation can be
399 // function-based or inlined depending on which mechanism the target is
401 if (Value* GuardCheck = TLI->getSSPStackGuardCheck(*M)) {
402 // Generate the function-based epilogue instrumentation.
403 // The target provides a guard check function, generate a call to it.
405 LoadInst *Guard = B.CreateLoad(AI, true, "Guard");
406 CallInst *Call = B.CreateCall(GuardCheck, {Guard});
407 llvm::Function *Function = cast<llvm::Function>(GuardCheck);
408 Call->setAttributes(Function->getAttributes());
409 Call->setCallingConv(Function->getCallingConv());
411 // Generate the epilogue with inline instrumentation.
412 // If we do not support SelectionDAG based tail calls, generate IR level
415 // For each block with a return instruction, convert this:
425 // %1 = <stack guard>
426 // %2 = load StackGuardSlot
427 // %3 = cmp i1 %1, %2
428 // br i1 %3, label %SP_return, label %CallStackCheckFailBlk
433 // CallStackCheckFailBlk:
434 // call void @__stack_chk_fail()
437 // Create the FailBB. We duplicate the BB every time since the MI tail
438 // merge pass will merge together all of the various BB into one including
439 // fail BB generated by the stack protector pseudo instruction.
440 BasicBlock *FailBB = CreateFailBB();
442 // Split the basic block before the return instruction.
443 BasicBlock *NewBB = BB->splitBasicBlock(RI->getIterator(), "SP_return");
445 // Update the dominator tree if we need to.
446 if (DT && DT->isReachableFromEntry(BB)) {
447 DT->addNewBlock(NewBB, BB);
448 DT->addNewBlock(FailBB, BB);
451 // Remove default branch instruction to the new BB.
452 BB->getTerminator()->eraseFromParent();
454 // Move the newly created basic block to the point right after the old
455 // basic block so that it's in the "fall through" position.
456 NewBB->moveAfter(BB);
458 // Generate the stack protector instructions in the old basic block.
460 Value *Guard = getStackGuard(TLI, M, B);
461 LoadInst *LI2 = B.CreateLoad(AI, true);
462 Value *Cmp = B.CreateICmpEQ(Guard, LI2);
464 BranchProbabilityInfo::getBranchProbStackProtector(true);
466 BranchProbabilityInfo::getBranchProbStackProtector(false);
467 MDNode *Weights = MDBuilder(F->getContext())
468 .createBranchWeights(SuccessProb.getNumerator(),
469 FailureProb.getNumerator());
470 B.CreateCondBr(Cmp, NewBB, FailBB, Weights);
474 // Return if we didn't modify any basic blocks. i.e., there are no return
475 // statements in the function.
479 /// CreateFailBB - Create a basic block to jump to when the stack protector
481 BasicBlock *StackProtector::CreateFailBB() {
482 LLVMContext &Context = F->getContext();
483 BasicBlock *FailBB = BasicBlock::Create(Context, "CallStackCheckFailBlk", F);
484 IRBuilder<> B(FailBB);
485 B.SetCurrentDebugLocation(DebugLoc::get(0, 0, F->getSubprogram()));
486 if (Trip.isOSOpenBSD()) {
487 Constant *StackChkFail =
488 M->getOrInsertFunction("__stack_smash_handler",
489 Type::getVoidTy(Context),
490 Type::getInt8PtrTy(Context));
492 B.CreateCall(StackChkFail, B.CreateGlobalStringPtr(F->getName(), "SSH"));
494 Constant *StackChkFail =
495 M->getOrInsertFunction("__stack_chk_fail", Type::getVoidTy(Context));
497 B.CreateCall(StackChkFail, {});
499 B.CreateUnreachable();
503 bool StackProtector::shouldEmitSDCheck(const BasicBlock &BB) const {
504 return HasPrologue && !HasIRCheck && dyn_cast<ReturnInst>(BB.getTerminator());