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Diffstat (limited to 'contrib/llvm/lib/Transforms/Instrumentation/SafeStack.cpp')
| -rw-r--r-- | contrib/llvm/lib/Transforms/Instrumentation/SafeStack.cpp | 760 |
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diff --git a/contrib/llvm/lib/Transforms/Instrumentation/SafeStack.cpp b/contrib/llvm/lib/Transforms/Instrumentation/SafeStack.cpp new file mode 100644 index 0000000..abed465 --- /dev/null +++ b/contrib/llvm/lib/Transforms/Instrumentation/SafeStack.cpp @@ -0,0 +1,760 @@ +//===-- 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); +} |
