| //===-- SafeStack.cpp - Safe Stack Insertion ------------------------------===// |
| // |
| // The LLVM Compiler Infrastructure |
| // |
| // This file is distributed under the University of Illinois Open Source |
| // License. See LICENSE.TXT for details. |
| // |
| //===----------------------------------------------------------------------===// |
| // |
| // This pass splits the stack into the safe stack (kept as-is for LLVM backend) |
| // and the unsafe stack (explicitly allocated and managed through the runtime |
| // support library). |
| // |
| // http://clang.llvm.org/docs/SafeStack.html |
| // |
| //===----------------------------------------------------------------------===// |
| |
| #include "llvm/Transforms/Instrumentation.h" |
| #include "llvm/ADT/Statistic.h" |
| #include "llvm/ADT/Triple.h" |
| #include "llvm/Analysis/ScalarEvolution.h" |
| #include "llvm/Analysis/ScalarEvolutionExpressions.h" |
| #include "llvm/CodeGen/Passes.h" |
| #include "llvm/IR/Constants.h" |
| #include "llvm/IR/DataLayout.h" |
| #include "llvm/IR/DerivedTypes.h" |
| #include "llvm/IR/DIBuilder.h" |
| #include "llvm/IR/Function.h" |
| #include "llvm/IR/InstIterator.h" |
| #include "llvm/IR/Instructions.h" |
| #include "llvm/IR/IntrinsicInst.h" |
| #include "llvm/IR/Intrinsics.h" |
| #include "llvm/IR/IRBuilder.h" |
| #include "llvm/IR/Module.h" |
| #include "llvm/Pass.h" |
| #include "llvm/Support/CommandLine.h" |
| #include "llvm/Support/Debug.h" |
| #include "llvm/Support/Format.h" |
| #include "llvm/Support/MathExtras.h" |
| #include "llvm/Support/raw_os_ostream.h" |
| #include "llvm/Target/TargetLowering.h" |
| #include "llvm/Target/TargetSubtargetInfo.h" |
| #include "llvm/Transforms/Utils/Local.h" |
| #include "llvm/Transforms/Utils/ModuleUtils.h" |
| |
| using namespace llvm; |
| |
| #define DEBUG_TYPE "safestack" |
| |
| enum UnsafeStackPtrStorageVal { ThreadLocalUSP, SingleThreadUSP }; |
| |
| static cl::opt<UnsafeStackPtrStorageVal> USPStorage("safe-stack-usp-storage", |
| cl::Hidden, cl::init(ThreadLocalUSP), |
| cl::desc("Type of storage for the unsafe stack pointer"), |
| cl::values(clEnumValN(ThreadLocalUSP, "thread-local", |
| "Thread-local storage"), |
| clEnumValN(SingleThreadUSP, "single-thread", |
| "Non-thread-local storage"), |
| clEnumValEnd)); |
| |
| namespace llvm { |
| |
| STATISTIC(NumFunctions, "Total number of functions"); |
| STATISTIC(NumUnsafeStackFunctions, "Number of functions with unsafe stack"); |
| STATISTIC(NumUnsafeStackRestorePointsFunctions, |
| "Number of functions that use setjmp or exceptions"); |
| |
| STATISTIC(NumAllocas, "Total number of allocas"); |
| STATISTIC(NumUnsafeStaticAllocas, "Number of unsafe static allocas"); |
| STATISTIC(NumUnsafeDynamicAllocas, "Number of unsafe dynamic allocas"); |
| STATISTIC(NumUnsafeByValArguments, "Number of unsafe byval arguments"); |
| STATISTIC(NumUnsafeStackRestorePoints, "Number of setjmps and landingpads"); |
| |
| } // namespace llvm |
| |
| namespace { |
| |
| /// Rewrite an SCEV expression for a memory access address to an expression that |
| /// represents offset from the given alloca. |
| /// |
| /// The implementation simply replaces all mentions of the alloca with zero. |
| class AllocaOffsetRewriter : public SCEVRewriteVisitor<AllocaOffsetRewriter> { |
| const Value *AllocaPtr; |
| |
| public: |
| AllocaOffsetRewriter(ScalarEvolution &SE, const Value *AllocaPtr) |
| : SCEVRewriteVisitor(SE), AllocaPtr(AllocaPtr) {} |
| |
| const SCEV *visitUnknown(const SCEVUnknown *Expr) { |
| if (Expr->getValue() == AllocaPtr) |
| return SE.getZero(Expr->getType()); |
| return Expr; |
| } |
| }; |
| |
| /// The SafeStack pass splits the stack of each function into the safe |
| /// stack, which is only accessed through memory safe dereferences (as |
| /// determined statically), and the unsafe stack, which contains all |
| /// local variables that are accessed in ways that we can't prove to |
| /// be safe. |
| class SafeStack : public FunctionPass { |
| const TargetMachine *TM; |
| const TargetLoweringBase *TL; |
| const DataLayout *DL; |
| ScalarEvolution *SE; |
| |
| Type *StackPtrTy; |
| Type *IntPtrTy; |
| Type *Int32Ty; |
| Type *Int8Ty; |
| |
| Value *UnsafeStackPtr = nullptr; |
| |
| /// Unsafe stack alignment. Each stack frame must ensure that the stack is |
| /// aligned to this value. We need to re-align the unsafe stack if the |
| /// alignment of any object on the stack exceeds this value. |
| /// |
| /// 16 seems like a reasonable upper bound on the alignment of objects that we |
| /// might expect to appear on the stack on most common targets. |
| enum { StackAlignment = 16 }; |
| |
| /// \brief Build a value representing a pointer to the unsafe stack pointer. |
| Value *getOrCreateUnsafeStackPtr(IRBuilder<> &IRB, Function &F); |
| |
| /// \brief Find all static allocas, dynamic allocas, return instructions and |
| /// stack restore points (exception unwind blocks and setjmp calls) in the |
| /// given function and append them to the respective vectors. |
| void findInsts(Function &F, SmallVectorImpl<AllocaInst *> &StaticAllocas, |
| SmallVectorImpl<AllocaInst *> &DynamicAllocas, |
| SmallVectorImpl<Argument *> &ByValArguments, |
| SmallVectorImpl<ReturnInst *> &Returns, |
| SmallVectorImpl<Instruction *> &StackRestorePoints); |
| |
| /// \brief Calculate the allocation size of a given alloca. Returns 0 if the |
| /// size can not be statically determined. |
| uint64_t getStaticAllocaAllocationSize(const AllocaInst* AI); |
| |
| /// \brief Allocate space for all static allocas in \p StaticAllocas, |
| /// replace allocas with pointers into the unsafe stack and generate code to |
| /// restore the stack pointer before all return instructions in \p Returns. |
| /// |
| /// \returns A pointer to the top of the unsafe stack after all unsafe static |
| /// allocas are allocated. |
| Value *moveStaticAllocasToUnsafeStack(IRBuilder<> &IRB, Function &F, |
| ArrayRef<AllocaInst *> StaticAllocas, |
| ArrayRef<Argument *> ByValArguments, |
| ArrayRef<ReturnInst *> Returns); |
| |
| /// \brief Generate code to restore the stack after all stack restore points |
| /// in \p StackRestorePoints. |
| /// |
| /// \returns A local variable in which to maintain the dynamic top of the |
| /// unsafe stack if needed. |
| AllocaInst * |
| createStackRestorePoints(IRBuilder<> &IRB, Function &F, |
| ArrayRef<Instruction *> StackRestorePoints, |
| Value *StaticTop, bool NeedDynamicTop); |
| |
| /// \brief Replace all allocas in \p DynamicAllocas with code to allocate |
| /// space dynamically on the unsafe stack and store the dynamic unsafe stack |
| /// top to \p DynamicTop if non-null. |
| void moveDynamicAllocasToUnsafeStack(Function &F, Value *UnsafeStackPtr, |
| AllocaInst *DynamicTop, |
| ArrayRef<AllocaInst *> DynamicAllocas); |
| |
| bool IsSafeStackAlloca(const Value *AllocaPtr, uint64_t AllocaSize); |
| |
| bool IsMemIntrinsicSafe(const MemIntrinsic *MI, const Use &U, |
| const Value *AllocaPtr, uint64_t AllocaSize); |
| bool IsAccessSafe(Value *Addr, uint64_t Size, const Value *AllocaPtr, |
| uint64_t AllocaSize); |
| |
| public: |
| static char ID; // Pass identification, replacement for typeid. |
| SafeStack(const TargetMachine *TM) |
| : FunctionPass(ID), TM(TM), TL(nullptr), DL(nullptr) { |
| initializeSafeStackPass(*PassRegistry::getPassRegistry()); |
| } |
| SafeStack() : SafeStack(nullptr) {} |
| |
| void getAnalysisUsage(AnalysisUsage &AU) const override { |
| AU.addRequired<ScalarEvolutionWrapperPass>(); |
| } |
| |
| bool doInitialization(Module &M) override { |
| DL = &M.getDataLayout(); |
| |
| StackPtrTy = Type::getInt8PtrTy(M.getContext()); |
| IntPtrTy = DL->getIntPtrType(M.getContext()); |
| Int32Ty = Type::getInt32Ty(M.getContext()); |
| Int8Ty = Type::getInt8Ty(M.getContext()); |
| |
| return false; |
| } |
| |
| bool runOnFunction(Function &F) override; |
| }; // class SafeStack |
| |
| uint64_t SafeStack::getStaticAllocaAllocationSize(const AllocaInst* AI) { |
| uint64_t Size = DL->getTypeAllocSize(AI->getAllocatedType()); |
| if (AI->isArrayAllocation()) { |
| auto C = dyn_cast<ConstantInt>(AI->getArraySize()); |
| if (!C) |
| return 0; |
| Size *= C->getZExtValue(); |
| } |
| return Size; |
| } |
| |
| bool SafeStack::IsAccessSafe(Value *Addr, uint64_t AccessSize, |
| const Value *AllocaPtr, uint64_t AllocaSize) { |
| AllocaOffsetRewriter Rewriter(*SE, AllocaPtr); |
| const SCEV *Expr = Rewriter.visit(SE->getSCEV(Addr)); |
| |
| uint64_t BitWidth = SE->getTypeSizeInBits(Expr->getType()); |
| ConstantRange AccessStartRange = SE->getUnsignedRange(Expr); |
| ConstantRange SizeRange = |
| ConstantRange(APInt(BitWidth, 0), APInt(BitWidth, AccessSize)); |
| ConstantRange AccessRange = AccessStartRange.add(SizeRange); |
| ConstantRange AllocaRange = |
| ConstantRange(APInt(BitWidth, 0), APInt(BitWidth, AllocaSize)); |
| bool Safe = AllocaRange.contains(AccessRange); |
| |
| DEBUG(dbgs() << "[SafeStack] " |
| << (isa<AllocaInst>(AllocaPtr) ? "Alloca " : "ByValArgument ") |
| << *AllocaPtr << "\n" |
| << " Access " << *Addr << "\n" |
| << " SCEV " << *Expr |
| << " U: " << SE->getUnsignedRange(Expr) |
| << ", S: " << SE->getSignedRange(Expr) << "\n" |
| << " Range " << AccessRange << "\n" |
| << " AllocaRange " << AllocaRange << "\n" |
| << " " << (Safe ? "safe" : "unsafe") << "\n"); |
| |
| return Safe; |
| } |
| |
| bool SafeStack::IsMemIntrinsicSafe(const MemIntrinsic *MI, const Use &U, |
| const Value *AllocaPtr, |
| uint64_t AllocaSize) { |
| // All MemIntrinsics have destination address in Arg0 and size in Arg2. |
| if (MI->getRawDest() != U) return true; |
| const auto *Len = dyn_cast<ConstantInt>(MI->getLength()); |
| // Non-constant size => unsafe. FIXME: try SCEV getRange. |
| if (!Len) return false; |
| return IsAccessSafe(U, Len->getZExtValue(), AllocaPtr, AllocaSize); |
| } |
| |
| /// Check whether a given allocation must be put on the safe |
| /// stack or not. The function analyzes all uses of AI and checks whether it is |
| /// only accessed in a memory safe way (as decided statically). |
| bool SafeStack::IsSafeStackAlloca(const Value *AllocaPtr, uint64_t AllocaSize) { |
| // Go through all uses of this alloca and check whether all accesses to the |
| // allocated object are statically known to be memory safe and, hence, the |
| // object can be placed on the safe stack. |
| SmallPtrSet<const Value *, 16> Visited; |
| SmallVector<const Value *, 8> WorkList; |
| WorkList.push_back(AllocaPtr); |
| |
| // A DFS search through all uses of the alloca in bitcasts/PHI/GEPs/etc. |
| while (!WorkList.empty()) { |
| const Value *V = WorkList.pop_back_val(); |
| for (const Use &UI : V->uses()) { |
| auto I = cast<const Instruction>(UI.getUser()); |
| assert(V == UI.get()); |
| |
| switch (I->getOpcode()) { |
| case Instruction::Load: { |
| if (!IsAccessSafe(UI, DL->getTypeStoreSize(I->getType()), AllocaPtr, |
| AllocaSize)) |
| return false; |
| break; |
| } |
| case Instruction::VAArg: |
| // "va-arg" from a pointer is safe. |
| break; |
| case Instruction::Store: { |
| if (V == I->getOperand(0)) { |
| // Stored the pointer - conservatively assume it may be unsafe. |
| DEBUG(dbgs() << "[SafeStack] Unsafe alloca: " << *AllocaPtr |
| << "\n store of address: " << *I << "\n"); |
| return false; |
| } |
| |
| if (!IsAccessSafe(UI, DL->getTypeStoreSize(I->getOperand(0)->getType()), |
| AllocaPtr, AllocaSize)) |
| return false; |
| break; |
| } |
| case Instruction::Ret: { |
| // Information leak. |
| return false; |
| } |
| |
| case Instruction::Call: |
| case Instruction::Invoke: { |
| ImmutableCallSite CS(I); |
| |
| if (const IntrinsicInst *II = dyn_cast<IntrinsicInst>(I)) { |
| if (II->getIntrinsicID() == Intrinsic::lifetime_start || |
| II->getIntrinsicID() == Intrinsic::lifetime_end) |
| continue; |
| } |
| |
| if (const MemIntrinsic *MI = dyn_cast<MemIntrinsic>(I)) { |
| if (!IsMemIntrinsicSafe(MI, UI, AllocaPtr, AllocaSize)) { |
| DEBUG(dbgs() << "[SafeStack] Unsafe alloca: " << *AllocaPtr |
| << "\n unsafe memintrinsic: " << *I |
| << "\n"); |
| return false; |
| } |
| continue; |
| } |
| |
| // LLVM 'nocapture' attribute is only set for arguments whose address |
| // is not stored, passed around, or used in any other non-trivial way. |
| // We assume that passing a pointer to an object as a 'nocapture |
| // readnone' argument is safe. |
| // FIXME: a more precise solution would require an interprocedural |
| // analysis here, which would look at all uses of an argument inside |
| // the function being called. |
| ImmutableCallSite::arg_iterator B = CS.arg_begin(), E = CS.arg_end(); |
| for (ImmutableCallSite::arg_iterator A = B; A != E; ++A) |
| if (A->get() == V) |
| if (!(CS.doesNotCapture(A - B) && (CS.doesNotAccessMemory(A - B) || |
| CS.doesNotAccessMemory()))) { |
| DEBUG(dbgs() << "[SafeStack] Unsafe alloca: " << *AllocaPtr |
| << "\n unsafe call: " << *I << "\n"); |
| return false; |
| } |
| continue; |
| } |
| |
| default: |
| if (Visited.insert(I).second) |
| WorkList.push_back(cast<const Instruction>(I)); |
| } |
| } |
| } |
| |
| // All uses of the alloca are safe, we can place it on the safe stack. |
| return true; |
| } |
| |
| Value *SafeStack::getOrCreateUnsafeStackPtr(IRBuilder<> &IRB, Function &F) { |
| // Check if there is a target-specific location for the unsafe stack pointer. |
| if (TL) |
| if (Value *V = TL->getSafeStackPointerLocation(IRB)) |
| return V; |
| |
| // Otherwise, assume the target links with compiler-rt, which provides a |
| // thread-local variable with a magic name. |
| Module &M = *F.getParent(); |
| const char *UnsafeStackPtrVar = "__safestack_unsafe_stack_ptr"; |
| auto UnsafeStackPtr = |
| dyn_cast_or_null<GlobalVariable>(M.getNamedValue(UnsafeStackPtrVar)); |
| |
| bool UseTLS = USPStorage == ThreadLocalUSP; |
| |
| if (!UnsafeStackPtr) { |
| auto TLSModel = UseTLS ? |
| GlobalValue::InitialExecTLSModel : |
| GlobalValue::NotThreadLocal; |
| // The global variable is not defined yet, define it ourselves. |
| // We use the initial-exec TLS model because we do not support the |
| // variable living anywhere other than in the main executable. |
| UnsafeStackPtr = new GlobalVariable( |
| M, StackPtrTy, false, GlobalValue::ExternalLinkage, nullptr, |
| UnsafeStackPtrVar, nullptr, TLSModel); |
| } else { |
| // The variable exists, check its type and attributes. |
| if (UnsafeStackPtr->getValueType() != StackPtrTy) |
| report_fatal_error(Twine(UnsafeStackPtrVar) + " must have void* type"); |
| if (UseTLS != UnsafeStackPtr->isThreadLocal()) |
| report_fatal_error(Twine(UnsafeStackPtrVar) + " must " + |
| (UseTLS ? "" : "not ") + "be thread-local"); |
| } |
| return UnsafeStackPtr; |
| } |
| |
| void SafeStack::findInsts(Function &F, |
| SmallVectorImpl<AllocaInst *> &StaticAllocas, |
| SmallVectorImpl<AllocaInst *> &DynamicAllocas, |
| SmallVectorImpl<Argument *> &ByValArguments, |
| SmallVectorImpl<ReturnInst *> &Returns, |
| SmallVectorImpl<Instruction *> &StackRestorePoints) { |
| for (Instruction &I : instructions(&F)) { |
| if (auto AI = dyn_cast<AllocaInst>(&I)) { |
| ++NumAllocas; |
| |
| uint64_t Size = getStaticAllocaAllocationSize(AI); |
| if (IsSafeStackAlloca(AI, Size)) |
| continue; |
| |
| if (AI->isStaticAlloca()) { |
| ++NumUnsafeStaticAllocas; |
| StaticAllocas.push_back(AI); |
| } else { |
| ++NumUnsafeDynamicAllocas; |
| DynamicAllocas.push_back(AI); |
| } |
| } else if (auto RI = dyn_cast<ReturnInst>(&I)) { |
| Returns.push_back(RI); |
| } else if (auto CI = dyn_cast<CallInst>(&I)) { |
| // setjmps require stack restore. |
| if (CI->getCalledFunction() && CI->canReturnTwice()) |
| StackRestorePoints.push_back(CI); |
| } else if (auto LP = dyn_cast<LandingPadInst>(&I)) { |
| // Exception landing pads require stack restore. |
| StackRestorePoints.push_back(LP); |
| } else if (auto II = dyn_cast<IntrinsicInst>(&I)) { |
| if (II->getIntrinsicID() == Intrinsic::gcroot) |
| llvm::report_fatal_error( |
| "gcroot intrinsic not compatible with safestack attribute"); |
| } |
| } |
| for (Argument &Arg : F.args()) { |
| if (!Arg.hasByValAttr()) |
| continue; |
| uint64_t Size = |
| DL->getTypeStoreSize(Arg.getType()->getPointerElementType()); |
| if (IsSafeStackAlloca(&Arg, Size)) |
| continue; |
| |
| ++NumUnsafeByValArguments; |
| ByValArguments.push_back(&Arg); |
| } |
| } |
| |
| AllocaInst * |
| SafeStack::createStackRestorePoints(IRBuilder<> &IRB, Function &F, |
| ArrayRef<Instruction *> StackRestorePoints, |
| Value *StaticTop, bool NeedDynamicTop) { |
| if (StackRestorePoints.empty()) |
| return nullptr; |
| |
| // We need the current value of the shadow stack pointer to restore |
| // after longjmp or exception catching. |
| |
| // FIXME: On some platforms this could be handled by the longjmp/exception |
| // runtime itself. |
| |
| AllocaInst *DynamicTop = nullptr; |
| if (NeedDynamicTop) |
| // If we also have dynamic alloca's, the stack pointer value changes |
| // throughout the function. For now we store it in an alloca. |
| DynamicTop = IRB.CreateAlloca(StackPtrTy, /*ArraySize=*/nullptr, |
| "unsafe_stack_dynamic_ptr"); |
| |
| if (!StaticTop) |
| // We need the original unsafe stack pointer value, even if there are |
| // no unsafe static allocas. |
| StaticTop = IRB.CreateLoad(UnsafeStackPtr, false, "unsafe_stack_ptr"); |
| |
| if (NeedDynamicTop) |
| IRB.CreateStore(StaticTop, DynamicTop); |
| |
| // Restore current stack pointer after longjmp/exception catch. |
| for (Instruction *I : StackRestorePoints) { |
| ++NumUnsafeStackRestorePoints; |
| |
| IRB.SetInsertPoint(I->getNextNode()); |
| Value *CurrentTop = DynamicTop ? IRB.CreateLoad(DynamicTop) : StaticTop; |
| IRB.CreateStore(CurrentTop, UnsafeStackPtr); |
| } |
| |
| return DynamicTop; |
| } |
| |
| Value *SafeStack::moveStaticAllocasToUnsafeStack( |
| IRBuilder<> &IRB, Function &F, ArrayRef<AllocaInst *> StaticAllocas, |
| ArrayRef<Argument *> ByValArguments, ArrayRef<ReturnInst *> Returns) { |
| if (StaticAllocas.empty() && ByValArguments.empty()) |
| return nullptr; |
| |
| DIBuilder DIB(*F.getParent()); |
| |
| // We explicitly compute and set the unsafe stack layout for all unsafe |
| // static alloca instructions. We save the unsafe "base pointer" in the |
| // prologue into a local variable and restore it in the epilogue. |
| |
| // Load the current stack pointer (we'll also use it as a base pointer). |
| // FIXME: use a dedicated register for it ? |
| Instruction *BasePointer = |
| IRB.CreateLoad(UnsafeStackPtr, false, "unsafe_stack_ptr"); |
| assert(BasePointer->getType() == StackPtrTy); |
| |
| for (ReturnInst *RI : Returns) { |
| IRB.SetInsertPoint(RI); |
| IRB.CreateStore(BasePointer, UnsafeStackPtr); |
| } |
| |
| // Compute maximum alignment among static objects on the unsafe stack. |
| unsigned MaxAlignment = 0; |
| for (Argument *Arg : ByValArguments) { |
| Type *Ty = Arg->getType()->getPointerElementType(); |
| unsigned Align = std::max((unsigned)DL->getPrefTypeAlignment(Ty), |
| Arg->getParamAlignment()); |
| if (Align > MaxAlignment) |
| MaxAlignment = Align; |
| } |
| for (AllocaInst *AI : StaticAllocas) { |
| Type *Ty = AI->getAllocatedType(); |
| unsigned Align = |
| std::max((unsigned)DL->getPrefTypeAlignment(Ty), AI->getAlignment()); |
| if (Align > MaxAlignment) |
| MaxAlignment = Align; |
| } |
| |
| if (MaxAlignment > StackAlignment) { |
| // Re-align the base pointer according to the max requested alignment. |
| assert(isPowerOf2_32(MaxAlignment)); |
| IRB.SetInsertPoint(BasePointer->getNextNode()); |
| BasePointer = cast<Instruction>(IRB.CreateIntToPtr( |
| IRB.CreateAnd(IRB.CreatePtrToInt(BasePointer, IntPtrTy), |
| ConstantInt::get(IntPtrTy, ~uint64_t(MaxAlignment - 1))), |
| StackPtrTy)); |
| } |
| |
| int64_t StaticOffset = 0; // Current stack top. |
| IRB.SetInsertPoint(BasePointer->getNextNode()); |
| |
| for (Argument *Arg : ByValArguments) { |
| Type *Ty = Arg->getType()->getPointerElementType(); |
| |
| uint64_t Size = DL->getTypeStoreSize(Ty); |
| if (Size == 0) |
| Size = 1; // Don't create zero-sized stack objects. |
| |
| // Ensure the object is properly aligned. |
| unsigned Align = std::max((unsigned)DL->getPrefTypeAlignment(Ty), |
| Arg->getParamAlignment()); |
| |
| // Add alignment. |
| // NOTE: we ensure that BasePointer itself is aligned to >= Align. |
| StaticOffset += Size; |
| StaticOffset = RoundUpToAlignment(StaticOffset, Align); |
| |
| Value *Off = IRB.CreateGEP(BasePointer, // BasePointer is i8* |
| ConstantInt::get(Int32Ty, -StaticOffset)); |
| Value *NewArg = IRB.CreateBitCast(Off, Arg->getType(), |
| Arg->getName() + ".unsafe-byval"); |
| |
| // Replace alloc with the new location. |
| replaceDbgDeclare(Arg, BasePointer, BasePointer->getNextNode(), DIB, |
| /*Deref=*/true, -StaticOffset); |
| Arg->replaceAllUsesWith(NewArg); |
| IRB.SetInsertPoint(cast<Instruction>(NewArg)->getNextNode()); |
| IRB.CreateMemCpy(Off, Arg, Size, Arg->getParamAlignment()); |
| } |
| |
| // Allocate space for every unsafe static AllocaInst on the unsafe stack. |
| for (AllocaInst *AI : StaticAllocas) { |
| IRB.SetInsertPoint(AI); |
| |
| Type *Ty = AI->getAllocatedType(); |
| uint64_t Size = getStaticAllocaAllocationSize(AI); |
| if (Size == 0) |
| Size = 1; // Don't create zero-sized stack objects. |
| |
| // Ensure the object is properly aligned. |
| unsigned Align = |
| std::max((unsigned)DL->getPrefTypeAlignment(Ty), AI->getAlignment()); |
| |
| // Add alignment. |
| // NOTE: we ensure that BasePointer itself is aligned to >= Align. |
| StaticOffset += Size; |
| StaticOffset = RoundUpToAlignment(StaticOffset, Align); |
| |
| Value *Off = IRB.CreateGEP(BasePointer, // BasePointer is i8* |
| ConstantInt::get(Int32Ty, -StaticOffset)); |
| Value *NewAI = IRB.CreateBitCast(Off, AI->getType(), AI->getName()); |
| if (AI->hasName() && isa<Instruction>(NewAI)) |
| cast<Instruction>(NewAI)->takeName(AI); |
| |
| // Replace alloc with the new location. |
| replaceDbgDeclareForAlloca(AI, BasePointer, DIB, /*Deref=*/true, -StaticOffset); |
| AI->replaceAllUsesWith(NewAI); |
| AI->eraseFromParent(); |
| } |
| |
| // Re-align BasePointer so that our callees would see it aligned as |
| // expected. |
| // FIXME: no need to update BasePointer in leaf functions. |
| StaticOffset = RoundUpToAlignment(StaticOffset, StackAlignment); |
| |
| // Update shadow stack pointer in the function epilogue. |
| IRB.SetInsertPoint(BasePointer->getNextNode()); |
| |
| Value *StaticTop = |
| IRB.CreateGEP(BasePointer, ConstantInt::get(Int32Ty, -StaticOffset), |
| "unsafe_stack_static_top"); |
| IRB.CreateStore(StaticTop, UnsafeStackPtr); |
| return StaticTop; |
| } |
| |
| void SafeStack::moveDynamicAllocasToUnsafeStack( |
| Function &F, Value *UnsafeStackPtr, AllocaInst *DynamicTop, |
| ArrayRef<AllocaInst *> DynamicAllocas) { |
| DIBuilder DIB(*F.getParent()); |
| |
| for (AllocaInst *AI : DynamicAllocas) { |
| IRBuilder<> IRB(AI); |
| |
| // Compute the new SP value (after AI). |
| Value *ArraySize = AI->getArraySize(); |
| if (ArraySize->getType() != IntPtrTy) |
| ArraySize = IRB.CreateIntCast(ArraySize, IntPtrTy, false); |
| |
| Type *Ty = AI->getAllocatedType(); |
| uint64_t TySize = DL->getTypeAllocSize(Ty); |
| Value *Size = IRB.CreateMul(ArraySize, ConstantInt::get(IntPtrTy, TySize)); |
| |
| Value *SP = IRB.CreatePtrToInt(IRB.CreateLoad(UnsafeStackPtr), IntPtrTy); |
| SP = IRB.CreateSub(SP, Size); |
| |
| // Align the SP value to satisfy the AllocaInst, type and stack alignments. |
| unsigned Align = std::max( |
| std::max((unsigned)DL->getPrefTypeAlignment(Ty), AI->getAlignment()), |
| (unsigned)StackAlignment); |
| |
| assert(isPowerOf2_32(Align)); |
| Value *NewTop = IRB.CreateIntToPtr( |
| IRB.CreateAnd(SP, ConstantInt::get(IntPtrTy, ~uint64_t(Align - 1))), |
| StackPtrTy); |
| |
| // Save the stack pointer. |
| IRB.CreateStore(NewTop, UnsafeStackPtr); |
| if (DynamicTop) |
| IRB.CreateStore(NewTop, DynamicTop); |
| |
| Value *NewAI = IRB.CreatePointerCast(NewTop, AI->getType()); |
| if (AI->hasName() && isa<Instruction>(NewAI)) |
| NewAI->takeName(AI); |
| |
| replaceDbgDeclareForAlloca(AI, NewAI, DIB, /*Deref=*/true); |
| AI->replaceAllUsesWith(NewAI); |
| AI->eraseFromParent(); |
| } |
| |
| if (!DynamicAllocas.empty()) { |
| // Now go through the instructions again, replacing stacksave/stackrestore. |
| for (inst_iterator It = inst_begin(&F), Ie = inst_end(&F); It != Ie;) { |
| Instruction *I = &*(It++); |
| auto II = dyn_cast<IntrinsicInst>(I); |
| if (!II) |
| continue; |
| |
| if (II->getIntrinsicID() == Intrinsic::stacksave) { |
| IRBuilder<> IRB(II); |
| Instruction *LI = IRB.CreateLoad(UnsafeStackPtr); |
| LI->takeName(II); |
| II->replaceAllUsesWith(LI); |
| II->eraseFromParent(); |
| } else if (II->getIntrinsicID() == Intrinsic::stackrestore) { |
| IRBuilder<> IRB(II); |
| Instruction *SI = IRB.CreateStore(II->getArgOperand(0), UnsafeStackPtr); |
| SI->takeName(II); |
| assert(II->use_empty()); |
| II->eraseFromParent(); |
| } |
| } |
| } |
| } |
| |
| bool SafeStack::runOnFunction(Function &F) { |
| DEBUG(dbgs() << "[SafeStack] Function: " << F.getName() << "\n"); |
| |
| if (!F.hasFnAttribute(Attribute::SafeStack)) { |
| DEBUG(dbgs() << "[SafeStack] safestack is not requested" |
| " for this function\n"); |
| return false; |
| } |
| |
| if (F.isDeclaration()) { |
| DEBUG(dbgs() << "[SafeStack] function definition" |
| " is not available\n"); |
| return false; |
| } |
| |
| TL = TM ? TM->getSubtargetImpl(F)->getTargetLowering() : nullptr; |
| SE = &getAnalysis<ScalarEvolutionWrapperPass>().getSE(); |
| |
| { |
| // Make sure the regular stack protector won't run on this function |
| // (safestack attribute takes precedence). |
| AttrBuilder B; |
| B.addAttribute(Attribute::StackProtect) |
| .addAttribute(Attribute::StackProtectReq) |
| .addAttribute(Attribute::StackProtectStrong); |
| F.removeAttributes( |
| AttributeSet::FunctionIndex, |
| AttributeSet::get(F.getContext(), AttributeSet::FunctionIndex, B)); |
| } |
| |
| ++NumFunctions; |
| |
| SmallVector<AllocaInst *, 16> StaticAllocas; |
| SmallVector<AllocaInst *, 4> DynamicAllocas; |
| SmallVector<Argument *, 4> ByValArguments; |
| SmallVector<ReturnInst *, 4> Returns; |
| |
| // Collect all points where stack gets unwound and needs to be restored |
| // This is only necessary because the runtime (setjmp and unwind code) is |
| // not aware of the unsafe stack and won't unwind/restore it prorerly. |
| // To work around this problem without changing the runtime, we insert |
| // instrumentation to restore the unsafe stack pointer when necessary. |
| SmallVector<Instruction *, 4> StackRestorePoints; |
| |
| // Find all static and dynamic alloca instructions that must be moved to the |
| // unsafe stack, all return instructions and stack restore points. |
| findInsts(F, StaticAllocas, DynamicAllocas, ByValArguments, Returns, |
| StackRestorePoints); |
| |
| if (StaticAllocas.empty() && DynamicAllocas.empty() && |
| ByValArguments.empty() && StackRestorePoints.empty()) |
| return false; // Nothing to do in this function. |
| |
| if (!StaticAllocas.empty() || !DynamicAllocas.empty() || |
| !ByValArguments.empty()) |
| ++NumUnsafeStackFunctions; // This function has the unsafe stack. |
| |
| if (!StackRestorePoints.empty()) |
| ++NumUnsafeStackRestorePointsFunctions; |
| |
| IRBuilder<> IRB(&F.front(), F.begin()->getFirstInsertionPt()); |
| UnsafeStackPtr = getOrCreateUnsafeStackPtr(IRB, F); |
| |
| // The top of the unsafe stack after all unsafe static allocas are allocated. |
| Value *StaticTop = moveStaticAllocasToUnsafeStack(IRB, F, StaticAllocas, |
| ByValArguments, Returns); |
| |
| // Safe stack object that stores the current unsafe stack top. It is updated |
| // as unsafe dynamic (non-constant-sized) allocas are allocated and freed. |
| // This is only needed if we need to restore stack pointer after longjmp |
| // or exceptions, and we have dynamic allocations. |
| // FIXME: a better alternative might be to store the unsafe stack pointer |
| // before setjmp / invoke instructions. |
| AllocaInst *DynamicTop = createStackRestorePoints( |
| IRB, F, StackRestorePoints, StaticTop, !DynamicAllocas.empty()); |
| |
| // Handle dynamic allocas. |
| moveDynamicAllocasToUnsafeStack(F, UnsafeStackPtr, DynamicTop, |
| DynamicAllocas); |
| |
| DEBUG(dbgs() << "[SafeStack] safestack applied\n"); |
| return true; |
| } |
| |
| } // anonymous namespace |
| |
| char SafeStack::ID = 0; |
| INITIALIZE_TM_PASS_BEGIN(SafeStack, "safe-stack", |
| "Safe Stack instrumentation pass", false, false) |
| INITIALIZE_TM_PASS_END(SafeStack, "safe-stack", |
| "Safe Stack instrumentation pass", false, false) |
| |
| FunctionPass *llvm::createSafeStackPass(const llvm::TargetMachine *TM) { |
| return new SafeStack(TM); |
| } |
