forked from OSchip/llvm-project
744 lines
28 KiB
C++
744 lines
28 KiB
C++
//===-- SafeStack.cpp - Safe Stack Insertion ------------------------------===//
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//
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// The LLVM Compiler Infrastructure
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//
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// This file is distributed under the University of Illinois Open Source
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// License. See LICENSE.TXT for details.
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//
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//===----------------------------------------------------------------------===//
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//
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// This pass splits the stack into the safe stack (kept as-is for LLVM backend)
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// and the unsafe stack (explicitly allocated and managed through the runtime
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// support library).
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//
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// http://clang.llvm.org/docs/SafeStack.html
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//
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//===----------------------------------------------------------------------===//
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#include "llvm/Transforms/Instrumentation.h"
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#include "llvm/ADT/Statistic.h"
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#include "llvm/ADT/Triple.h"
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#include "llvm/Analysis/ScalarEvolution.h"
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#include "llvm/Analysis/ScalarEvolutionExpressions.h"
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#include "llvm/CodeGen/Passes.h"
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#include "llvm/IR/Constants.h"
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#include "llvm/IR/DataLayout.h"
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#include "llvm/IR/DerivedTypes.h"
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#include "llvm/IR/DIBuilder.h"
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#include "llvm/IR/Function.h"
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#include "llvm/IR/InstIterator.h"
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#include "llvm/IR/Instructions.h"
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#include "llvm/IR/IntrinsicInst.h"
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#include "llvm/IR/Intrinsics.h"
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#include "llvm/IR/IRBuilder.h"
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#include "llvm/IR/Module.h"
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#include "llvm/Pass.h"
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#include "llvm/Support/CommandLine.h"
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#include "llvm/Support/Debug.h"
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#include "llvm/Support/Format.h"
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#include "llvm/Support/MathExtras.h"
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#include "llvm/Support/raw_os_ostream.h"
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#include "llvm/Target/TargetLowering.h"
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#include "llvm/Target/TargetSubtargetInfo.h"
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#include "llvm/Transforms/Utils/Local.h"
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#include "llvm/Transforms/Utils/ModuleUtils.h"
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using namespace llvm;
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#define DEBUG_TYPE "safestack"
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namespace llvm {
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STATISTIC(NumFunctions, "Total number of functions");
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STATISTIC(NumUnsafeStackFunctions, "Number of functions with unsafe stack");
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STATISTIC(NumUnsafeStackRestorePointsFunctions,
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"Number of functions that use setjmp or exceptions");
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STATISTIC(NumAllocas, "Total number of allocas");
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STATISTIC(NumUnsafeStaticAllocas, "Number of unsafe static allocas");
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STATISTIC(NumUnsafeDynamicAllocas, "Number of unsafe dynamic allocas");
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STATISTIC(NumUnsafeByValArguments, "Number of unsafe byval arguments");
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STATISTIC(NumUnsafeStackRestorePoints, "Number of setjmps and landingpads");
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} // namespace llvm
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namespace {
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/// Rewrite an SCEV expression for a memory access address to an expression that
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/// represents offset from the given alloca.
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///
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/// The implementation simply replaces all mentions of the alloca with zero.
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class AllocaOffsetRewriter : public SCEVRewriteVisitor<AllocaOffsetRewriter> {
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const Value *AllocaPtr;
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public:
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AllocaOffsetRewriter(ScalarEvolution &SE, const Value *AllocaPtr)
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: SCEVRewriteVisitor(SE), AllocaPtr(AllocaPtr) {}
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const SCEV *visitUnknown(const SCEVUnknown *Expr) {
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if (Expr->getValue() == AllocaPtr)
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return SE.getZero(Expr->getType());
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return Expr;
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}
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};
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/// The SafeStack pass splits the stack of each function into the safe
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/// stack, which is only accessed through memory safe dereferences (as
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/// determined statically), and the unsafe stack, which contains all
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/// local variables that are accessed in ways that we can't prove to
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/// be safe.
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class SafeStack : public FunctionPass {
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const TargetMachine *TM;
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const TargetLoweringBase *TL;
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const DataLayout *DL;
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ScalarEvolution *SE;
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Type *StackPtrTy;
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Type *IntPtrTy;
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Type *Int32Ty;
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Type *Int8Ty;
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Value *UnsafeStackPtr = nullptr;
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/// Unsafe stack alignment. Each stack frame must ensure that the stack is
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/// aligned to this value. We need to re-align the unsafe stack if the
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/// alignment of any object on the stack exceeds this value.
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///
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/// 16 seems like a reasonable upper bound on the alignment of objects that we
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/// might expect to appear on the stack on most common targets.
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enum { StackAlignment = 16 };
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/// \brief Build a value representing a pointer to the unsafe stack pointer.
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Value *getOrCreateUnsafeStackPtr(IRBuilder<> &IRB, Function &F);
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/// \brief Find all static allocas, dynamic allocas, return instructions and
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/// stack restore points (exception unwind blocks and setjmp calls) in the
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/// given function and append them to the respective vectors.
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void findInsts(Function &F, SmallVectorImpl<AllocaInst *> &StaticAllocas,
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SmallVectorImpl<AllocaInst *> &DynamicAllocas,
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SmallVectorImpl<Argument *> &ByValArguments,
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SmallVectorImpl<ReturnInst *> &Returns,
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SmallVectorImpl<Instruction *> &StackRestorePoints);
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/// \brief Calculate the allocation size of a given alloca. Returns 0 if the
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/// size can not be statically determined.
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uint64_t getStaticAllocaAllocationSize(const AllocaInst* AI);
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/// \brief Allocate space for all static allocas in \p StaticAllocas,
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/// replace allocas with pointers into the unsafe stack and generate code to
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/// restore the stack pointer before all return instructions in \p Returns.
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///
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/// \returns A pointer to the top of the unsafe stack after all unsafe static
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/// allocas are allocated.
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Value *moveStaticAllocasToUnsafeStack(IRBuilder<> &IRB, Function &F,
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ArrayRef<AllocaInst *> StaticAllocas,
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ArrayRef<Argument *> ByValArguments,
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ArrayRef<ReturnInst *> Returns);
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/// \brief Generate code to restore the stack after all stack restore points
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/// in \p StackRestorePoints.
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///
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/// \returns A local variable in which to maintain the dynamic top of the
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/// unsafe stack if needed.
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AllocaInst *
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createStackRestorePoints(IRBuilder<> &IRB, Function &F,
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ArrayRef<Instruction *> StackRestorePoints,
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Value *StaticTop, bool NeedDynamicTop);
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/// \brief Replace all allocas in \p DynamicAllocas with code to allocate
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/// space dynamically on the unsafe stack and store the dynamic unsafe stack
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/// top to \p DynamicTop if non-null.
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void moveDynamicAllocasToUnsafeStack(Function &F, Value *UnsafeStackPtr,
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AllocaInst *DynamicTop,
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ArrayRef<AllocaInst *> DynamicAllocas);
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bool IsSafeStackAlloca(const Value *AllocaPtr, uint64_t AllocaSize);
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bool IsMemIntrinsicSafe(const MemIntrinsic *MI, const Use &U,
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const Value *AllocaPtr, uint64_t AllocaSize);
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bool IsAccessSafe(Value *Addr, uint64_t Size, const Value *AllocaPtr,
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uint64_t AllocaSize);
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public:
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static char ID; // Pass identification, replacement for typeid.
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SafeStack(const TargetMachine *TM)
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: FunctionPass(ID), TM(TM), TL(nullptr), DL(nullptr) {
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initializeSafeStackPass(*PassRegistry::getPassRegistry());
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}
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SafeStack() : SafeStack(nullptr) {}
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void getAnalysisUsage(AnalysisUsage &AU) const override {
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AU.addRequired<ScalarEvolutionWrapperPass>();
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}
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bool doInitialization(Module &M) override {
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DL = &M.getDataLayout();
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StackPtrTy = Type::getInt8PtrTy(M.getContext());
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IntPtrTy = DL->getIntPtrType(M.getContext());
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Int32Ty = Type::getInt32Ty(M.getContext());
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Int8Ty = Type::getInt8Ty(M.getContext());
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return false;
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}
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bool runOnFunction(Function &F) override;
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}; // class SafeStack
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uint64_t SafeStack::getStaticAllocaAllocationSize(const AllocaInst* AI) {
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uint64_t Size = DL->getTypeAllocSize(AI->getAllocatedType());
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if (AI->isArrayAllocation()) {
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auto C = dyn_cast<ConstantInt>(AI->getArraySize());
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if (!C)
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return 0;
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Size *= C->getZExtValue();
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}
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return Size;
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}
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bool SafeStack::IsAccessSafe(Value *Addr, uint64_t AccessSize,
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const Value *AllocaPtr, uint64_t AllocaSize) {
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AllocaOffsetRewriter Rewriter(*SE, AllocaPtr);
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const SCEV *Expr = Rewriter.visit(SE->getSCEV(Addr));
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uint64_t BitWidth = SE->getTypeSizeInBits(Expr->getType());
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ConstantRange AccessStartRange = SE->getUnsignedRange(Expr);
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ConstantRange SizeRange =
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ConstantRange(APInt(BitWidth, 0), APInt(BitWidth, AccessSize));
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ConstantRange AccessRange = AccessStartRange.add(SizeRange);
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ConstantRange AllocaRange =
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ConstantRange(APInt(BitWidth, 0), APInt(BitWidth, AllocaSize));
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bool Safe = AllocaRange.contains(AccessRange);
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DEBUG(dbgs() << "[SafeStack] "
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<< (isa<AllocaInst>(AllocaPtr) ? "Alloca " : "ByValArgument ")
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<< *AllocaPtr << "\n"
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<< " Access " << *Addr << "\n"
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<< " SCEV " << *Expr
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<< " U: " << SE->getUnsignedRange(Expr)
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<< ", S: " << SE->getSignedRange(Expr) << "\n"
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<< " Range " << AccessRange << "\n"
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<< " AllocaRange " << AllocaRange << "\n"
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<< " " << (Safe ? "safe" : "unsafe") << "\n");
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return Safe;
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}
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bool SafeStack::IsMemIntrinsicSafe(const MemIntrinsic *MI, const Use &U,
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const Value *AllocaPtr,
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uint64_t AllocaSize) {
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// All MemIntrinsics have destination address in Arg0 and size in Arg2.
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if (MI->getRawDest() != U) return true;
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const auto *Len = dyn_cast<ConstantInt>(MI->getLength());
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// Non-constant size => unsafe. FIXME: try SCEV getRange.
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if (!Len) return false;
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return IsAccessSafe(U, Len->getZExtValue(), AllocaPtr, AllocaSize);
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}
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/// Check whether a given allocation must be put on the safe
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/// stack or not. The function analyzes all uses of AI and checks whether it is
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/// only accessed in a memory safe way (as decided statically).
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bool SafeStack::IsSafeStackAlloca(const Value *AllocaPtr, uint64_t AllocaSize) {
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// Go through all uses of this alloca and check whether all accesses to the
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// allocated object are statically known to be memory safe and, hence, the
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// object can be placed on the safe stack.
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SmallPtrSet<const Value *, 16> Visited;
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SmallVector<const Value *, 8> WorkList;
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WorkList.push_back(AllocaPtr);
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// A DFS search through all uses of the alloca in bitcasts/PHI/GEPs/etc.
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while (!WorkList.empty()) {
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const Value *V = WorkList.pop_back_val();
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for (const Use &UI : V->uses()) {
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auto I = cast<const Instruction>(UI.getUser());
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assert(V == UI.get());
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switch (I->getOpcode()) {
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case Instruction::Load: {
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if (!IsAccessSafe(UI, DL->getTypeStoreSize(I->getType()), AllocaPtr,
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AllocaSize))
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return false;
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break;
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}
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case Instruction::VAArg:
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// "va-arg" from a pointer is safe.
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break;
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case Instruction::Store: {
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if (V == I->getOperand(0)) {
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// Stored the pointer - conservatively assume it may be unsafe.
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DEBUG(dbgs() << "[SafeStack] Unsafe alloca: " << *AllocaPtr
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<< "\n store of address: " << *I << "\n");
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return false;
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}
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if (!IsAccessSafe(UI, DL->getTypeStoreSize(I->getOperand(0)->getType()),
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AllocaPtr, AllocaSize))
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return false;
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break;
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}
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case Instruction::Ret: {
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// Information leak.
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return false;
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}
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case Instruction::Call:
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case Instruction::Invoke: {
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ImmutableCallSite CS(I);
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if (const IntrinsicInst *II = dyn_cast<IntrinsicInst>(I)) {
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if (II->getIntrinsicID() == Intrinsic::lifetime_start ||
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II->getIntrinsicID() == Intrinsic::lifetime_end)
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continue;
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}
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if (const MemIntrinsic *MI = dyn_cast<MemIntrinsic>(I)) {
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if (!IsMemIntrinsicSafe(MI, UI, AllocaPtr, AllocaSize)) {
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DEBUG(dbgs() << "[SafeStack] Unsafe alloca: " << *AllocaPtr
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<< "\n unsafe memintrinsic: " << *I
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<< "\n");
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return false;
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}
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continue;
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}
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// LLVM 'nocapture' attribute is only set for arguments whose address
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// is not stored, passed around, or used in any other non-trivial way.
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// We assume that passing a pointer to an object as a 'nocapture
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// readnone' argument is safe.
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// FIXME: a more precise solution would require an interprocedural
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// analysis here, which would look at all uses of an argument inside
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// the function being called.
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ImmutableCallSite::arg_iterator B = CS.arg_begin(), E = CS.arg_end();
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for (ImmutableCallSite::arg_iterator A = B; A != E; ++A)
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if (A->get() == V)
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if (!(CS.doesNotCapture(A - B) && (CS.doesNotAccessMemory(A - B) ||
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CS.doesNotAccessMemory()))) {
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DEBUG(dbgs() << "[SafeStack] Unsafe alloca: " << *AllocaPtr
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<< "\n unsafe call: " << *I << "\n");
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return false;
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}
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continue;
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}
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default:
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if (Visited.insert(I).second)
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WorkList.push_back(cast<const Instruction>(I));
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}
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}
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}
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// All uses of the alloca are safe, we can place it on the safe stack.
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return true;
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}
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Value *SafeStack::getOrCreateUnsafeStackPtr(IRBuilder<> &IRB, Function &F) {
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// Check if there is a target-specific location for the unsafe stack pointer.
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if (TL)
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if (Value *V = TL->getSafeStackPointerLocation(IRB))
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return V;
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// Otherwise, assume the target links with compiler-rt, which provides a
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// thread-local variable with a magic name.
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Module &M = *F.getParent();
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const char *UnsafeStackPtrVar = "__safestack_unsafe_stack_ptr";
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auto UnsafeStackPtr =
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dyn_cast_or_null<GlobalVariable>(M.getNamedValue(UnsafeStackPtrVar));
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if (!UnsafeStackPtr) {
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// The global variable is not defined yet, define it ourselves.
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// We use the initial-exec TLS model because we do not support the
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// variable living anywhere other than in the main executable.
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UnsafeStackPtr = new GlobalVariable(
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M, StackPtrTy, false, GlobalValue::ExternalLinkage, nullptr,
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UnsafeStackPtrVar, nullptr, GlobalValue::InitialExecTLSModel);
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} else {
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// The variable exists, check its type and attributes.
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if (UnsafeStackPtr->getValueType() != StackPtrTy)
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report_fatal_error(Twine(UnsafeStackPtrVar) + " must have void* type");
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if (!UnsafeStackPtr->isThreadLocal())
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report_fatal_error(Twine(UnsafeStackPtrVar) + " must be thread-local");
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}
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return UnsafeStackPtr;
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}
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void SafeStack::findInsts(Function &F,
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SmallVectorImpl<AllocaInst *> &StaticAllocas,
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SmallVectorImpl<AllocaInst *> &DynamicAllocas,
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SmallVectorImpl<Argument *> &ByValArguments,
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SmallVectorImpl<ReturnInst *> &Returns,
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SmallVectorImpl<Instruction *> &StackRestorePoints) {
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for (Instruction &I : instructions(&F)) {
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if (auto AI = dyn_cast<AllocaInst>(&I)) {
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++NumAllocas;
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uint64_t Size = getStaticAllocaAllocationSize(AI);
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if (IsSafeStackAlloca(AI, Size))
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continue;
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if (AI->isStaticAlloca()) {
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++NumUnsafeStaticAllocas;
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StaticAllocas.push_back(AI);
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} else {
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++NumUnsafeDynamicAllocas;
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DynamicAllocas.push_back(AI);
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}
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} else if (auto RI = dyn_cast<ReturnInst>(&I)) {
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Returns.push_back(RI);
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} else if (auto CI = dyn_cast<CallInst>(&I)) {
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// setjmps require stack restore.
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if (CI->getCalledFunction() && CI->canReturnTwice())
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StackRestorePoints.push_back(CI);
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} else if (auto LP = dyn_cast<LandingPadInst>(&I)) {
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// Exception landing pads require stack restore.
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StackRestorePoints.push_back(LP);
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} else if (auto II = dyn_cast<IntrinsicInst>(&I)) {
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if (II->getIntrinsicID() == Intrinsic::gcroot)
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llvm::report_fatal_error(
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"gcroot intrinsic not compatible with safestack attribute");
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}
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}
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for (Argument &Arg : F.args()) {
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if (!Arg.hasByValAttr())
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continue;
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uint64_t Size =
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DL->getTypeStoreSize(Arg.getType()->getPointerElementType());
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if (IsSafeStackAlloca(&Arg, Size))
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continue;
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++NumUnsafeByValArguments;
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ByValArguments.push_back(&Arg);
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}
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}
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AllocaInst *
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SafeStack::createStackRestorePoints(IRBuilder<> &IRB, Function &F,
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ArrayRef<Instruction *> StackRestorePoints,
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Value *StaticTop, bool NeedDynamicTop) {
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if (StackRestorePoints.empty())
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return nullptr;
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// We need the current value of the shadow stack pointer to restore
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// after longjmp or exception catching.
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// FIXME: On some platforms this could be handled by the longjmp/exception
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// runtime itself.
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AllocaInst *DynamicTop = nullptr;
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if (NeedDynamicTop)
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// If we also have dynamic alloca's, the stack pointer value changes
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// throughout the function. For now we store it in an alloca.
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DynamicTop = IRB.CreateAlloca(StackPtrTy, /*ArraySize=*/nullptr,
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"unsafe_stack_dynamic_ptr");
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if (!StaticTop)
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// We need the original unsafe stack pointer value, even if there are
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// no unsafe static allocas.
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StaticTop = IRB.CreateLoad(UnsafeStackPtr, false, "unsafe_stack_ptr");
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if (NeedDynamicTop)
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IRB.CreateStore(StaticTop, DynamicTop);
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// Restore current stack pointer after longjmp/exception catch.
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for (Instruction *I : StackRestorePoints) {
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++NumUnsafeStackRestorePoints;
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IRB.SetInsertPoint(I->getNextNode());
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Value *CurrentTop = DynamicTop ? IRB.CreateLoad(DynamicTop) : StaticTop;
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IRB.CreateStore(CurrentTop, UnsafeStackPtr);
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}
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return DynamicTop;
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}
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Value *SafeStack::moveStaticAllocasToUnsafeStack(
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IRBuilder<> &IRB, Function &F, ArrayRef<AllocaInst *> StaticAllocas,
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ArrayRef<Argument *> ByValArguments, ArrayRef<ReturnInst *> Returns) {
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if (StaticAllocas.empty() && ByValArguments.empty())
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return nullptr;
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DIBuilder DIB(*F.getParent());
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// We explicitly compute and set the unsafe stack layout for all unsafe
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// static alloca instructions. We save the unsafe "base pointer" in the
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// prologue into a local variable and restore it in the epilogue.
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// Load the current stack pointer (we'll also use it as a base pointer).
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// FIXME: use a dedicated register for it ?
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Instruction *BasePointer =
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IRB.CreateLoad(UnsafeStackPtr, false, "unsafe_stack_ptr");
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assert(BasePointer->getType() == StackPtrTy);
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for (ReturnInst *RI : Returns) {
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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);
|
|
}
|