Move SafeStack to CodeGen.
It depends on the target machinery, that's not available for
instrumentation passes.
llvm-svn: 258942
diff --git a/llvm/lib/CodeGen/SafeStack.cpp b/llvm/lib/CodeGen/SafeStack.cpp
new file mode 100644
index 0000000..7adcdea
--- /dev/null
+++ b/llvm/lib/CodeGen/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/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/CodeGen/Passes.h"
+#include "llvm/IR/Constants.h"
+#include "llvm/IR/DIBuilder.h"
+#include "llvm/IR/DataLayout.h"
+#include "llvm/IR/DerivedTypes.h"
+#include "llvm/IR/Function.h"
+#include "llvm/IR/IRBuilder.h"
+#include "llvm/IR/InstIterator.h"
+#include "llvm/IR/Instructions.h"
+#include "llvm/IR/IntrinsicInst.h"
+#include "llvm/IR/Intrinsics.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 = alignTo(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 = alignTo(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 = alignTo(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);
+}