| //===- SafeStack.cpp - Safe Stack Insertion -------------------------------===// |
| // |
| // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions. |
| // See https://llvm.org/LICENSE.txt for license information. |
| // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception |
| // |
| //===----------------------------------------------------------------------===// |
| // |
| // 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 "SafeStackColoring.h" |
| #include "SafeStackLayout.h" |
| #include "llvm/ADT/APInt.h" |
| #include "llvm/ADT/ArrayRef.h" |
| #include "llvm/ADT/SmallPtrSet.h" |
| #include "llvm/ADT/SmallVector.h" |
| #include "llvm/ADT/Statistic.h" |
| #include "llvm/Analysis/AssumptionCache.h" |
| #include "llvm/Analysis/BranchProbabilityInfo.h" |
| #include "llvm/Analysis/InlineCost.h" |
| #include "llvm/Analysis/LoopInfo.h" |
| #include "llvm/Analysis/ScalarEvolution.h" |
| #include "llvm/Analysis/ScalarEvolutionExpressions.h" |
| #include "llvm/Analysis/TargetLibraryInfo.h" |
| #include "llvm/CodeGen/TargetLowering.h" |
| #include "llvm/CodeGen/TargetPassConfig.h" |
| #include "llvm/CodeGen/TargetSubtargetInfo.h" |
| #include "llvm/IR/Argument.h" |
| #include "llvm/IR/Attributes.h" |
| #include "llvm/IR/CallSite.h" |
| #include "llvm/IR/ConstantRange.h" |
| #include "llvm/IR/Constants.h" |
| #include "llvm/IR/DIBuilder.h" |
| #include "llvm/IR/DataLayout.h" |
| #include "llvm/IR/DerivedTypes.h" |
| #include "llvm/IR/Dominators.h" |
| #include "llvm/IR/Function.h" |
| #include "llvm/IR/IRBuilder.h" |
| #include "llvm/IR/InstIterator.h" |
| #include "llvm/IR/Instruction.h" |
| #include "llvm/IR/Instructions.h" |
| #include "llvm/IR/IntrinsicInst.h" |
| #include "llvm/IR/Intrinsics.h" |
| #include "llvm/IR/MDBuilder.h" |
| #include "llvm/IR/Module.h" |
| #include "llvm/IR/Type.h" |
| #include "llvm/IR/Use.h" |
| #include "llvm/IR/User.h" |
| #include "llvm/IR/Value.h" |
| #include "llvm/InitializePasses.h" |
| #include "llvm/Pass.h" |
| #include "llvm/Support/Casting.h" |
| #include "llvm/Support/Debug.h" |
| #include "llvm/Support/ErrorHandling.h" |
| #include "llvm/Support/MathExtras.h" |
| #include "llvm/Support/raw_ostream.h" |
| #include "llvm/Target/TargetMachine.h" |
| #include "llvm/Transforms/Utils/BasicBlockUtils.h" |
| #include "llvm/Transforms/Utils/Cloning.h" |
| #include "llvm/Transforms/Utils/Local.h" |
| #include <algorithm> |
| #include <cassert> |
| #include <cstdint> |
| #include <string> |
| #include <utility> |
| |
| using namespace llvm; |
| using namespace llvm::safestack; |
| |
| #define DEBUG_TYPE "safe-stack" |
| |
| 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 |
| |
| /// Use __safestack_pointer_address even if the platform has a faster way of |
| /// access safe stack pointer. |
| static cl::opt<bool> |
| SafeStackUsePointerAddress("safestack-use-pointer-address", |
| cl::init(false), cl::Hidden); |
| |
| |
| 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 { |
| Function &F; |
| 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 }; |
| |
| /// Return the value of the stack canary. |
| Value *getStackGuard(IRBuilder<> &IRB, Function &F); |
| |
| /// Load stack guard from the frame and check if it has changed. |
| void checkStackGuard(IRBuilder<> &IRB, Function &F, ReturnInst &RI, |
| AllocaInst *StackGuardSlot, Value *StackGuard); |
| |
| /// 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); |
| |
| /// Calculate the allocation size of a given alloca. Returns 0 if the |
| /// size can not be statically determined. |
| uint64_t getStaticAllocaAllocationSize(const AllocaInst* AI); |
| |
| /// 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, |
| Instruction *BasePointer, |
| AllocaInst *StackGuardSlot); |
| |
| /// 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); |
| |
| /// 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); |
| |
| bool ShouldInlinePointerAddress(CallSite &CS); |
| void TryInlinePointerAddress(); |
| |
| public: |
| SafeStack(Function &F, const TargetLoweringBase &TL, const DataLayout &DL, |
| ScalarEvolution &SE) |
| : F(F), TL(TL), DL(DL), SE(SE), |
| StackPtrTy(Type::getInt8PtrTy(F.getContext())), |
| IntPtrTy(DL.getIntPtrType(F.getContext())), |
| Int32Ty(Type::getInt32Ty(F.getContext())), |
| Int8Ty(Type::getInt8Ty(F.getContext())) {} |
| |
| // Run the transformation on the associated function. |
| // Returns whether the function was changed. |
| bool run(); |
| }; |
| |
| 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); |
| |
| LLVM_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) { |
| if (auto MTI = dyn_cast<MemTransferInst>(MI)) { |
| if (MTI->getRawSource() != U && MTI->getRawDest() != U) |
| return true; |
| } else { |
| 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. |
| LLVM_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 (I->isLifetimeStartOrEnd()) |
| continue; |
| |
| if (const MemIntrinsic *MI = dyn_cast<MemIntrinsic>(I)) { |
| if (!IsMemIntrinsicSafe(MI, UI, AllocaPtr, AllocaSize)) { |
| LLVM_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()))) { |
| LLVM_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::getStackGuard(IRBuilder<> &IRB, Function &F) { |
| Value *StackGuardVar = TL.getIRStackGuard(IRB); |
| if (!StackGuardVar) |
| StackGuardVar = |
| F.getParent()->getOrInsertGlobal("__stack_chk_guard", StackPtrTy); |
| return IRB.CreateLoad(StackPtrTy, StackGuardVar, "StackGuard"); |
| } |
| |
| 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) |
| 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) { |
| assert(StaticTop && "The stack top isn't set."); |
| |
| 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"); |
| 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(StackPtrTy, DynamicTop) : StaticTop; |
| IRB.CreateStore(CurrentTop, UnsafeStackPtr); |
| } |
| |
| return DynamicTop; |
| } |
| |
| void SafeStack::checkStackGuard(IRBuilder<> &IRB, Function &F, ReturnInst &RI, |
| AllocaInst *StackGuardSlot, Value *StackGuard) { |
| Value *V = IRB.CreateLoad(StackPtrTy, StackGuardSlot); |
| Value *Cmp = IRB.CreateICmpNE(StackGuard, V); |
| |
| auto SuccessProb = BranchProbabilityInfo::getBranchProbStackProtector(true); |
| auto FailureProb = BranchProbabilityInfo::getBranchProbStackProtector(false); |
| MDNode *Weights = MDBuilder(F.getContext()) |
| .createBranchWeights(SuccessProb.getNumerator(), |
| FailureProb.getNumerator()); |
| Instruction *CheckTerm = |
| SplitBlockAndInsertIfThen(Cmp, &RI, |
| /* Unreachable */ true, Weights); |
| IRBuilder<> IRBFail(CheckTerm); |
| // FIXME: respect -fsanitize-trap / -ftrap-function here? |
| FunctionCallee StackChkFail = |
| F.getParent()->getOrInsertFunction("__stack_chk_fail", IRB.getVoidTy()); |
| IRBFail.CreateCall(StackChkFail, {}); |
| } |
| |
| /// 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. |
| Value *SafeStack::moveStaticAllocasToUnsafeStack( |
| IRBuilder<> &IRB, Function &F, ArrayRef<AllocaInst *> StaticAllocas, |
| ArrayRef<Argument *> ByValArguments, ArrayRef<ReturnInst *> Returns, |
| Instruction *BasePointer, AllocaInst *StackGuardSlot) { |
| if (StaticAllocas.empty() && ByValArguments.empty()) |
| return BasePointer; |
| |
| DIBuilder DIB(*F.getParent()); |
| |
| StackColoring SSC(F, StaticAllocas); |
| SSC.run(); |
| SSC.removeAllMarkers(); |
| |
| // Unsafe stack always grows down. |
| StackLayout SSL(StackAlignment); |
| if (StackGuardSlot) { |
| Type *Ty = StackGuardSlot->getAllocatedType(); |
| unsigned Align = |
| std::max(DL.getPrefTypeAlignment(Ty), StackGuardSlot->getAlignment()); |
| SSL.addObject(StackGuardSlot, getStaticAllocaAllocationSize(StackGuardSlot), |
| Align, SSC.getFullLiveRange()); |
| } |
| |
| 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()); |
| SSL.addObject(Arg, Size, Align, SSC.getFullLiveRange()); |
| } |
| |
| for (AllocaInst *AI : StaticAllocas) { |
| 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()); |
| |
| SSL.addObject(AI, Size, Align, SSC.getLiveRange(AI)); |
| } |
| |
| SSL.computeLayout(); |
| unsigned FrameAlignment = SSL.getFrameAlignment(); |
| |
| // FIXME: tell SSL that we start at a less-then-MaxAlignment aligned location |
| // (AlignmentSkew). |
| if (FrameAlignment > StackAlignment) { |
| // Re-align the base pointer according to the max requested alignment. |
| assert(isPowerOf2_32(FrameAlignment)); |
| IRB.SetInsertPoint(BasePointer->getNextNode()); |
| BasePointer = cast<Instruction>(IRB.CreateIntToPtr( |
| IRB.CreateAnd(IRB.CreatePtrToInt(BasePointer, IntPtrTy), |
| ConstantInt::get(IntPtrTy, ~uint64_t(FrameAlignment - 1))), |
| StackPtrTy)); |
| } |
| |
| IRB.SetInsertPoint(BasePointer->getNextNode()); |
| |
| if (StackGuardSlot) { |
| unsigned Offset = SSL.getObjectOffset(StackGuardSlot); |
| Value *Off = IRB.CreateGEP(Int8Ty, BasePointer, // BasePointer is i8* |
| ConstantInt::get(Int32Ty, -Offset)); |
| Value *NewAI = |
| IRB.CreateBitCast(Off, StackGuardSlot->getType(), "StackGuardSlot"); |
| |
| // Replace alloc with the new location. |
| StackGuardSlot->replaceAllUsesWith(NewAI); |
| StackGuardSlot->eraseFromParent(); |
| } |
| |
| for (Argument *Arg : ByValArguments) { |
| unsigned Offset = SSL.getObjectOffset(Arg); |
| MaybeAlign Align(SSL.getObjectAlignment(Arg)); |
| Type *Ty = Arg->getType()->getPointerElementType(); |
| |
| uint64_t Size = DL.getTypeStoreSize(Ty); |
| if (Size == 0) |
| Size = 1; // Don't create zero-sized stack objects. |
| |
| Value *Off = IRB.CreateGEP(Int8Ty, BasePointer, // BasePointer is i8* |
| ConstantInt::get(Int32Ty, -Offset)); |
| Value *NewArg = IRB.CreateBitCast(Off, Arg->getType(), |
| Arg->getName() + ".unsafe-byval"); |
| |
| // Replace alloc with the new location. |
| replaceDbgDeclare(Arg, BasePointer, BasePointer->getNextNode(), DIB, |
| DIExpression::ApplyOffset, -Offset); |
| Arg->replaceAllUsesWith(NewArg); |
| IRB.SetInsertPoint(cast<Instruction>(NewArg)->getNextNode()); |
| IRB.CreateMemCpy(Off, Align, Arg, Arg->getParamAlign(), Size); |
| } |
| |
| // Allocate space for every unsafe static AllocaInst on the unsafe stack. |
| for (AllocaInst *AI : StaticAllocas) { |
| IRB.SetInsertPoint(AI); |
| unsigned Offset = SSL.getObjectOffset(AI); |
| |
| replaceDbgDeclareForAlloca(AI, BasePointer, DIB, DIExpression::ApplyOffset, |
| -Offset); |
| replaceDbgValueForAlloca(AI, BasePointer, DIB, -Offset); |
| |
| // Replace uses of the alloca with the new location. |
| // Insert address calculation close to each use to work around PR27844. |
| std::string Name = std::string(AI->getName()) + ".unsafe"; |
| while (!AI->use_empty()) { |
| Use &U = *AI->use_begin(); |
| Instruction *User = cast<Instruction>(U.getUser()); |
| |
| Instruction *InsertBefore; |
| if (auto *PHI = dyn_cast<PHINode>(User)) |
| InsertBefore = PHI->getIncomingBlock(U)->getTerminator(); |
| else |
| InsertBefore = User; |
| |
| IRBuilder<> IRBUser(InsertBefore); |
| Value *Off = IRBUser.CreateGEP(Int8Ty, BasePointer, // BasePointer is i8* |
| ConstantInt::get(Int32Ty, -Offset)); |
| Value *Replacement = IRBUser.CreateBitCast(Off, AI->getType(), Name); |
| |
| if (auto *PHI = dyn_cast<PHINode>(User)) |
| // PHI nodes may have multiple incoming edges from the same BB (why??), |
| // all must be updated at once with the same incoming value. |
| PHI->setIncomingValueForBlock(PHI->getIncomingBlock(U), Replacement); |
| else |
| U.set(Replacement); |
| } |
| |
| AI->eraseFromParent(); |
| } |
| |
| // Re-align BasePointer so that our callees would see it aligned as |
| // expected. |
| // FIXME: no need to update BasePointer in leaf functions. |
| unsigned FrameSize = alignTo(SSL.getFrameSize(), StackAlignment); |
| |
| // Update shadow stack pointer in the function epilogue. |
| IRB.SetInsertPoint(BasePointer->getNextNode()); |
| |
| Value *StaticTop = |
| IRB.CreateGEP(Int8Ty, BasePointer, ConstantInt::get(Int32Ty, -FrameSize), |
| "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(StackPtrTy, 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, DIExpression::ApplyOffset, 0); |
| 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(StackPtrTy, 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::ShouldInlinePointerAddress(CallSite &CS) { |
| Function *Callee = CS.getCalledFunction(); |
| if (CS.hasFnAttr(Attribute::AlwaysInline) && isInlineViable(*Callee)) |
| return true; |
| if (Callee->isInterposable() || Callee->hasFnAttribute(Attribute::NoInline) || |
| CS.isNoInline()) |
| return false; |
| return true; |
| } |
| |
| void SafeStack::TryInlinePointerAddress() { |
| if (!isa<CallInst>(UnsafeStackPtr)) |
| return; |
| |
| if(F.hasOptNone()) |
| return; |
| |
| CallSite CS(UnsafeStackPtr); |
| Function *Callee = CS.getCalledFunction(); |
| if (!Callee || Callee->isDeclaration()) |
| return; |
| |
| if (!ShouldInlinePointerAddress(CS)) |
| return; |
| |
| InlineFunctionInfo IFI; |
| InlineFunction(CS, IFI); |
| } |
| |
| bool SafeStack::run() { |
| assert(F.hasFnAttribute(Attribute::SafeStack) && |
| "Can't run SafeStack on a function without the attribute"); |
| assert(!F.isDeclaration() && "Can't run SafeStack on a function declaration"); |
| |
| ++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 properly. |
| // 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()); |
| // Calls must always have a debug location, or else inlining breaks. So |
| // we explicitly set a artificial debug location here. |
| if (DISubprogram *SP = F.getSubprogram()) |
| IRB.SetCurrentDebugLocation(DebugLoc::get(SP->getScopeLine(), 0, SP)); |
| if (SafeStackUsePointerAddress) { |
| FunctionCallee Fn = F.getParent()->getOrInsertFunction( |
| "__safestack_pointer_address", StackPtrTy->getPointerTo(0)); |
| UnsafeStackPtr = IRB.CreateCall(Fn); |
| } else { |
| UnsafeStackPtr = TL.getSafeStackPointerLocation(IRB); |
| } |
| |
| // 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(StackPtrTy, UnsafeStackPtr, false, "unsafe_stack_ptr"); |
| assert(BasePointer->getType() == StackPtrTy); |
| |
| AllocaInst *StackGuardSlot = nullptr; |
| // FIXME: implement weaker forms of stack protector. |
| if (F.hasFnAttribute(Attribute::StackProtect) || |
| F.hasFnAttribute(Attribute::StackProtectStrong) || |
| F.hasFnAttribute(Attribute::StackProtectReq)) { |
| Value *StackGuard = getStackGuard(IRB, F); |
| StackGuardSlot = IRB.CreateAlloca(StackPtrTy, nullptr); |
| IRB.CreateStore(StackGuard, StackGuardSlot); |
| |
| for (ReturnInst *RI : Returns) { |
| IRBuilder<> IRBRet(RI); |
| checkStackGuard(IRBRet, F, *RI, StackGuardSlot, StackGuard); |
| } |
| } |
| |
| // The top of the unsafe stack after all unsafe static allocas are |
| // allocated. |
| Value *StaticTop = |
| moveStaticAllocasToUnsafeStack(IRB, F, StaticAllocas, ByValArguments, |
| Returns, BasePointer, StackGuardSlot); |
| |
| // 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); |
| |
| // Restore the unsafe stack pointer before each return. |
| for (ReturnInst *RI : Returns) { |
| IRB.SetInsertPoint(RI); |
| IRB.CreateStore(BasePointer, UnsafeStackPtr); |
| } |
| |
| TryInlinePointerAddress(); |
| |
| LLVM_DEBUG(dbgs() << "[SafeStack] safestack applied\n"); |
| return true; |
| } |
| |
| class SafeStackLegacyPass : public FunctionPass { |
| const TargetMachine *TM = nullptr; |
| |
| public: |
| static char ID; // Pass identification, replacement for typeid.. |
| |
| SafeStackLegacyPass() : FunctionPass(ID) { |
| initializeSafeStackLegacyPassPass(*PassRegistry::getPassRegistry()); |
| } |
| |
| void getAnalysisUsage(AnalysisUsage &AU) const override { |
| AU.addRequired<TargetPassConfig>(); |
| AU.addRequired<TargetLibraryInfoWrapperPass>(); |
| AU.addRequired<AssumptionCacheTracker>(); |
| } |
| |
| bool runOnFunction(Function &F) override { |
| LLVM_DEBUG(dbgs() << "[SafeStack] Function: " << F.getName() << "\n"); |
| |
| if (!F.hasFnAttribute(Attribute::SafeStack)) { |
| LLVM_DEBUG(dbgs() << "[SafeStack] safestack is not requested" |
| " for this function\n"); |
| return false; |
| } |
| |
| if (F.isDeclaration()) { |
| LLVM_DEBUG(dbgs() << "[SafeStack] function definition" |
| " is not available\n"); |
| return false; |
| } |
| |
| TM = &getAnalysis<TargetPassConfig>().getTM<TargetMachine>(); |
| auto *TL = TM->getSubtargetImpl(F)->getTargetLowering(); |
| if (!TL) |
| report_fatal_error("TargetLowering instance is required"); |
| |
| auto *DL = &F.getParent()->getDataLayout(); |
| auto &TLI = getAnalysis<TargetLibraryInfoWrapperPass>().getTLI(F); |
| auto &ACT = getAnalysis<AssumptionCacheTracker>().getAssumptionCache(F); |
| |
| // Compute DT and LI only for functions that have the attribute. |
| // This is only useful because the legacy pass manager doesn't let us |
| // compute analyzes lazily. |
| // In the backend pipeline, nothing preserves DT before SafeStack, so we |
| // would otherwise always compute it wastefully, even if there is no |
| // function with the safestack attribute. |
| DominatorTree DT(F); |
| LoopInfo LI(DT); |
| |
| ScalarEvolution SE(F, TLI, ACT, DT, LI); |
| |
| return SafeStack(F, *TL, *DL, SE).run(); |
| } |
| }; |
| |
| } // end anonymous namespace |
| |
| char SafeStackLegacyPass::ID = 0; |
| |
| INITIALIZE_PASS_BEGIN(SafeStackLegacyPass, DEBUG_TYPE, |
| "Safe Stack instrumentation pass", false, false) |
| INITIALIZE_PASS_DEPENDENCY(TargetPassConfig) |
| INITIALIZE_PASS_END(SafeStackLegacyPass, DEBUG_TYPE, |
| "Safe Stack instrumentation pass", false, false) |
| |
| FunctionPass *llvm::createSafeStackPass() { return new SafeStackLegacyPass(); } |
