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author | Dimitry Andric <dim@FreeBSD.org> | 2019-12-20 19:53:05 +0000 |
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committer | Dimitry Andric <dim@FreeBSD.org> | 2019-12-20 19:53:05 +0000 |
commit | 0b57cec536236d46e3dba9bd041533462f33dbb7 (patch) | |
tree | 56229dbdbbf76d18580f72f789003db17246c8d9 /contrib/llvm-project/llvm/lib/CodeGen/SafeStack.cpp | |
parent | 718ef55ec7785aae63f98f8ca05dc07ed399c16d (diff) | |
download | src-0b57cec536236d46e3dba9bd041533462f33dbb7.tar.gz src-0b57cec536236d46e3dba9bd041533462f33dbb7.zip |
Move all sources from the llvm project into contrib/llvm-project.
This uses the new layout of the upstream repository, which was recently
migrated to GitHub, and converted into a "monorepo". That is, most of
the earlier separate sub-projects with their own branches and tags were
consolidated into one top-level directory, and are now branched and
tagged together.
Updating the vendor area to match this layout is next.
Notes
Notes:
svn path=/head/; revision=355940
Diffstat (limited to 'contrib/llvm-project/llvm/lib/CodeGen/SafeStack.cpp')
-rw-r--r-- | contrib/llvm-project/llvm/lib/CodeGen/SafeStack.cpp | 902 |
1 files changed, 902 insertions, 0 deletions
diff --git a/contrib/llvm-project/llvm/lib/CodeGen/SafeStack.cpp b/contrib/llvm-project/llvm/lib/CodeGen/SafeStack.cpp new file mode 100644 index 000000000000..a6bc7330e2cc --- /dev/null +++ b/contrib/llvm-project/llvm/lib/CodeGen/SafeStack.cpp @@ -0,0 +1,902 @@ +//===- SafeStack.cpp - Safe Stack Insertion -------------------------------===// +// +// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions. +// See https://llvm.org/LICENSE.txt for license information. +// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception +// +//===----------------------------------------------------------------------===// +// +// This pass splits the stack into the safe stack (kept as-is for LLVM backend) +// and the unsafe stack (explicitly allocated and managed through the runtime +// support library). +// +// http://clang.llvm.org/docs/SafeStack.html +// +//===----------------------------------------------------------------------===// + +#include "SafeStackColoring.h" +#include "SafeStackLayout.h" +#include "llvm/ADT/APInt.h" +#include "llvm/ADT/ArrayRef.h" +#include "llvm/ADT/SmallPtrSet.h" +#include "llvm/ADT/SmallVector.h" +#include "llvm/ADT/Statistic.h" +#include "llvm/Analysis/AssumptionCache.h" +#include "llvm/Analysis/BranchProbabilityInfo.h" +#include "llvm/Analysis/InlineCost.h" +#include "llvm/Analysis/LoopInfo.h" +#include "llvm/Analysis/ScalarEvolution.h" +#include "llvm/Analysis/ScalarEvolutionExpressions.h" +#include "llvm/Analysis/TargetLibraryInfo.h" +#include "llvm/Transforms/Utils/Local.h" +#include "llvm/CodeGen/TargetLowering.h" +#include "llvm/CodeGen/TargetPassConfig.h" +#include "llvm/CodeGen/TargetSubtargetInfo.h" +#include "llvm/IR/Argument.h" +#include "llvm/IR/Attributes.h" +#include "llvm/IR/CallSite.h" +#include "llvm/IR/ConstantRange.h" +#include "llvm/IR/Constants.h" +#include "llvm/IR/DIBuilder.h" +#include "llvm/IR/DataLayout.h" +#include "llvm/IR/DerivedTypes.h" +#include "llvm/IR/Dominators.h" +#include "llvm/IR/Function.h" +#include "llvm/IR/IRBuilder.h" +#include "llvm/IR/InstIterator.h" +#include "llvm/IR/Instruction.h" +#include "llvm/IR/Instructions.h" +#include "llvm/IR/IntrinsicInst.h" +#include "llvm/IR/Intrinsics.h" +#include "llvm/IR/MDBuilder.h" +#include "llvm/IR/Module.h" +#include "llvm/IR/Type.h" +#include "llvm/IR/Use.h" +#include "llvm/IR/User.h" +#include "llvm/IR/Value.h" +#include "llvm/Pass.h" +#include "llvm/Support/Casting.h" +#include "llvm/Support/Debug.h" +#include "llvm/Support/ErrorHandling.h" +#include "llvm/Support/MathExtras.h" +#include "llvm/Support/raw_ostream.h" +#include "llvm/Target/TargetMachine.h" +#include "llvm/Transforms/Utils/BasicBlockUtils.h" +#include "llvm/Transforms/Utils/Cloning.h" +#include <algorithm> +#include <cassert> +#include <cstdint> +#include <string> +#include <utility> + +using namespace llvm; +using namespace llvm::safestack; + +#define DEBUG_TYPE "safe-stack" + +namespace llvm { + +STATISTIC(NumFunctions, "Total number of functions"); +STATISTIC(NumUnsafeStackFunctions, "Number of functions with unsafe stack"); +STATISTIC(NumUnsafeStackRestorePointsFunctions, + "Number of functions that use setjmp or exceptions"); + +STATISTIC(NumAllocas, "Total number of allocas"); +STATISTIC(NumUnsafeStaticAllocas, "Number of unsafe static allocas"); +STATISTIC(NumUnsafeDynamicAllocas, "Number of unsafe dynamic allocas"); +STATISTIC(NumUnsafeByValArguments, "Number of unsafe byval arguments"); +STATISTIC(NumUnsafeStackRestorePoints, "Number of setjmps and landingpads"); + +} // namespace llvm + +/// Use __safestack_pointer_address even if the platform has a faster way of +/// access safe stack pointer. +static cl::opt<bool> + SafeStackUsePointerAddress("safestack-use-pointer-address", + cl::init(false), cl::Hidden); + + +namespace { + +/// Rewrite an SCEV expression for a memory access address to an expression that +/// represents offset from the given alloca. +/// +/// The implementation simply replaces all mentions of the alloca with zero. +class AllocaOffsetRewriter : public SCEVRewriteVisitor<AllocaOffsetRewriter> { + const Value *AllocaPtr; + +public: + AllocaOffsetRewriter(ScalarEvolution &SE, const Value *AllocaPtr) + : SCEVRewriteVisitor(SE), AllocaPtr(AllocaPtr) {} + + const SCEV *visitUnknown(const SCEVUnknown *Expr) { + if (Expr->getValue() == AllocaPtr) + return SE.getZero(Expr->getType()); + return Expr; + } +}; + +/// The SafeStack pass splits the stack of each function into the safe +/// stack, which is only accessed through memory safe dereferences (as +/// determined statically), and the unsafe stack, which contains all +/// local variables that are accessed in ways that we can't prove to +/// be safe. +class SafeStack { + Function &F; + const TargetLoweringBase &TL; + const DataLayout &DL; + ScalarEvolution &SE; + + Type *StackPtrTy; + Type *IntPtrTy; + Type *Int32Ty; + Type *Int8Ty; + + Value *UnsafeStackPtr = nullptr; + + /// Unsafe stack alignment. Each stack frame must ensure that the stack is + /// aligned to this value. We need to re-align the unsafe stack if the + /// alignment of any object on the stack exceeds this value. + /// + /// 16 seems like a reasonable upper bound on the alignment of objects that we + /// might expect to appear on the stack on most common targets. + enum { StackAlignment = 16 }; + + /// Return the value of the stack canary. + Value *getStackGuard(IRBuilder<> &IRB, Function &F); + + /// Load stack guard from the frame and check if it has changed. + void checkStackGuard(IRBuilder<> &IRB, Function &F, ReturnInst &RI, + AllocaInst *StackGuardSlot, Value *StackGuard); + + /// Find all static allocas, dynamic allocas, return instructions and + /// stack restore points (exception unwind blocks and setjmp calls) in the + /// given function and append them to the respective vectors. + void findInsts(Function &F, SmallVectorImpl<AllocaInst *> &StaticAllocas, + SmallVectorImpl<AllocaInst *> &DynamicAllocas, + SmallVectorImpl<Argument *> &ByValArguments, + SmallVectorImpl<ReturnInst *> &Returns, + SmallVectorImpl<Instruction *> &StackRestorePoints); + + /// Calculate the allocation size of a given alloca. Returns 0 if the + /// size can not be statically determined. + uint64_t getStaticAllocaAllocationSize(const AllocaInst* AI); + + /// Allocate space for all static allocas in \p StaticAllocas, + /// replace allocas with pointers into the unsafe stack and generate code to + /// restore the stack pointer before all return instructions in \p Returns. + /// + /// \returns A pointer to the top of the unsafe stack after all unsafe static + /// allocas are allocated. + Value *moveStaticAllocasToUnsafeStack(IRBuilder<> &IRB, Function &F, + ArrayRef<AllocaInst *> StaticAllocas, + ArrayRef<Argument *> ByValArguments, + ArrayRef<ReturnInst *> Returns, + Instruction *BasePointer, + AllocaInst *StackGuardSlot); + + /// Generate code to restore the stack after all stack restore points + /// in \p StackRestorePoints. + /// + /// \returns A local variable in which to maintain the dynamic top of the + /// unsafe stack if needed. + AllocaInst * + createStackRestorePoints(IRBuilder<> &IRB, Function &F, + ArrayRef<Instruction *> StackRestorePoints, + Value *StaticTop, bool NeedDynamicTop); + + /// Replace all allocas in \p DynamicAllocas with code to allocate + /// space dynamically on the unsafe stack and store the dynamic unsafe stack + /// top to \p DynamicTop if non-null. + void moveDynamicAllocasToUnsafeStack(Function &F, Value *UnsafeStackPtr, + AllocaInst *DynamicTop, + ArrayRef<AllocaInst *> DynamicAllocas); + + bool IsSafeStackAlloca(const Value *AllocaPtr, uint64_t AllocaSize); + + bool IsMemIntrinsicSafe(const MemIntrinsic *MI, const Use &U, + const Value *AllocaPtr, uint64_t AllocaSize); + bool IsAccessSafe(Value *Addr, uint64_t Size, const Value *AllocaPtr, + uint64_t AllocaSize); + + bool ShouldInlinePointerAddress(CallSite &CS); + void TryInlinePointerAddress(); + +public: + SafeStack(Function &F, const TargetLoweringBase &TL, const DataLayout &DL, + ScalarEvolution &SE) + : F(F), TL(TL), DL(DL), SE(SE), + StackPtrTy(Type::getInt8PtrTy(F.getContext())), + IntPtrTy(DL.getIntPtrType(F.getContext())), + Int32Ty(Type::getInt32Ty(F.getContext())), + Int8Ty(Type::getInt8Ty(F.getContext())) {} + + // Run the transformation on the associated function. + // Returns whether the function was changed. + bool run(); +}; + +uint64_t SafeStack::getStaticAllocaAllocationSize(const AllocaInst* AI) { + uint64_t Size = DL.getTypeAllocSize(AI->getAllocatedType()); + if (AI->isArrayAllocation()) { + auto C = dyn_cast<ConstantInt>(AI->getArraySize()); + if (!C) + return 0; + Size *= C->getZExtValue(); + } + return Size; +} + +bool SafeStack::IsAccessSafe(Value *Addr, uint64_t AccessSize, + const Value *AllocaPtr, uint64_t AllocaSize) { + AllocaOffsetRewriter Rewriter(SE, AllocaPtr); + const SCEV *Expr = Rewriter.visit(SE.getSCEV(Addr)); + + uint64_t BitWidth = SE.getTypeSizeInBits(Expr->getType()); + ConstantRange AccessStartRange = SE.getUnsignedRange(Expr); + ConstantRange SizeRange = + ConstantRange(APInt(BitWidth, 0), APInt(BitWidth, AccessSize)); + ConstantRange AccessRange = AccessStartRange.add(SizeRange); + ConstantRange AllocaRange = + ConstantRange(APInt(BitWidth, 0), APInt(BitWidth, AllocaSize)); + bool Safe = AllocaRange.contains(AccessRange); + + LLVM_DEBUG( + dbgs() << "[SafeStack] " + << (isa<AllocaInst>(AllocaPtr) ? "Alloca " : "ByValArgument ") + << *AllocaPtr << "\n" + << " Access " << *Addr << "\n" + << " SCEV " << *Expr + << " U: " << SE.getUnsignedRange(Expr) + << ", S: " << SE.getSignedRange(Expr) << "\n" + << " Range " << AccessRange << "\n" + << " AllocaRange " << AllocaRange << "\n" + << " " << (Safe ? "safe" : "unsafe") << "\n"); + + return Safe; +} + +bool SafeStack::IsMemIntrinsicSafe(const MemIntrinsic *MI, const Use &U, + const Value *AllocaPtr, + uint64_t AllocaSize) { + if (auto MTI = dyn_cast<MemTransferInst>(MI)) { + if (MTI->getRawSource() != U && MTI->getRawDest() != U) + return true; + } else { + if (MI->getRawDest() != U) + return true; + } + + const auto *Len = dyn_cast<ConstantInt>(MI->getLength()); + // Non-constant size => unsafe. FIXME: try SCEV getRange. + if (!Len) return false; + return IsAccessSafe(U, Len->getZExtValue(), AllocaPtr, AllocaSize); +} + +/// Check whether a given allocation must be put on the safe +/// stack or not. The function analyzes all uses of AI and checks whether it is +/// only accessed in a memory safe way (as decided statically). +bool SafeStack::IsSafeStackAlloca(const Value *AllocaPtr, uint64_t AllocaSize) { + // Go through all uses of this alloca and check whether all accesses to the + // allocated object are statically known to be memory safe and, hence, the + // object can be placed on the safe stack. + SmallPtrSet<const Value *, 16> Visited; + SmallVector<const Value *, 8> WorkList; + WorkList.push_back(AllocaPtr); + + // A DFS search through all uses of the alloca in bitcasts/PHI/GEPs/etc. + while (!WorkList.empty()) { + const Value *V = WorkList.pop_back_val(); + for (const Use &UI : V->uses()) { + auto I = cast<const Instruction>(UI.getUser()); + assert(V == UI.get()); + + switch (I->getOpcode()) { + case Instruction::Load: + if (!IsAccessSafe(UI, DL.getTypeStoreSize(I->getType()), AllocaPtr, + AllocaSize)) + return false; + break; + + case Instruction::VAArg: + // "va-arg" from a pointer is safe. + break; + case Instruction::Store: + if (V == I->getOperand(0)) { + // Stored the pointer - conservatively assume it may be unsafe. + LLVM_DEBUG(dbgs() + << "[SafeStack] Unsafe alloca: " << *AllocaPtr + << "\n store of address: " << *I << "\n"); + return false; + } + + if (!IsAccessSafe(UI, DL.getTypeStoreSize(I->getOperand(0)->getType()), + AllocaPtr, AllocaSize)) + return false; + break; + + case Instruction::Ret: + // Information leak. + return false; + + case Instruction::Call: + case Instruction::Invoke: { + ImmutableCallSite CS(I); + + if (I->isLifetimeStartOrEnd()) + continue; + + if (const MemIntrinsic *MI = dyn_cast<MemIntrinsic>(I)) { + if (!IsMemIntrinsicSafe(MI, UI, AllocaPtr, AllocaSize)) { + LLVM_DEBUG(dbgs() + << "[SafeStack] Unsafe alloca: " << *AllocaPtr + << "\n unsafe memintrinsic: " << *I << "\n"); + return false; + } + continue; + } + + // LLVM 'nocapture' attribute is only set for arguments whose address + // is not stored, passed around, or used in any other non-trivial way. + // We assume that passing a pointer to an object as a 'nocapture + // readnone' argument is safe. + // FIXME: a more precise solution would require an interprocedural + // analysis here, which would look at all uses of an argument inside + // the function being called. + ImmutableCallSite::arg_iterator B = CS.arg_begin(), E = CS.arg_end(); + for (ImmutableCallSite::arg_iterator A = B; A != E; ++A) + if (A->get() == V) + if (!(CS.doesNotCapture(A - B) && (CS.doesNotAccessMemory(A - B) || + CS.doesNotAccessMemory()))) { + LLVM_DEBUG(dbgs() << "[SafeStack] Unsafe alloca: " << *AllocaPtr + << "\n unsafe call: " << *I << "\n"); + return false; + } + continue; + } + + default: + if (Visited.insert(I).second) + WorkList.push_back(cast<const Instruction>(I)); + } + } + } + + // All uses of the alloca are safe, we can place it on the safe stack. + return true; +} + +Value *SafeStack::getStackGuard(IRBuilder<> &IRB, Function &F) { + Value *StackGuardVar = TL.getIRStackGuard(IRB); + if (!StackGuardVar) + StackGuardVar = + F.getParent()->getOrInsertGlobal("__stack_chk_guard", StackPtrTy); + return IRB.CreateLoad(StackPtrTy, StackGuardVar, "StackGuard"); +} + +void SafeStack::findInsts(Function &F, + SmallVectorImpl<AllocaInst *> &StaticAllocas, + SmallVectorImpl<AllocaInst *> &DynamicAllocas, + SmallVectorImpl<Argument *> &ByValArguments, + SmallVectorImpl<ReturnInst *> &Returns, + SmallVectorImpl<Instruction *> &StackRestorePoints) { + for (Instruction &I : instructions(&F)) { + if (auto AI = dyn_cast<AllocaInst>(&I)) { + ++NumAllocas; + + uint64_t Size = getStaticAllocaAllocationSize(AI); + if (IsSafeStackAlloca(AI, Size)) + continue; + + if (AI->isStaticAlloca()) { + ++NumUnsafeStaticAllocas; + StaticAllocas.push_back(AI); + } else { + ++NumUnsafeDynamicAllocas; + DynamicAllocas.push_back(AI); + } + } else if (auto RI = dyn_cast<ReturnInst>(&I)) { + Returns.push_back(RI); + } else if (auto CI = dyn_cast<CallInst>(&I)) { + // setjmps require stack restore. + if (CI->getCalledFunction() && CI->canReturnTwice()) + StackRestorePoints.push_back(CI); + } else if (auto LP = dyn_cast<LandingPadInst>(&I)) { + // Exception landing pads require stack restore. + StackRestorePoints.push_back(LP); + } else if (auto II = dyn_cast<IntrinsicInst>(&I)) { + if (II->getIntrinsicID() == Intrinsic::gcroot) + report_fatal_error( + "gcroot intrinsic not compatible with safestack attribute"); + } + } + for (Argument &Arg : F.args()) { + if (!Arg.hasByValAttr()) + continue; + uint64_t Size = + DL.getTypeStoreSize(Arg.getType()->getPointerElementType()); + if (IsSafeStackAlloca(&Arg, Size)) + continue; + + ++NumUnsafeByValArguments; + ByValArguments.push_back(&Arg); + } +} + +AllocaInst * +SafeStack::createStackRestorePoints(IRBuilder<> &IRB, Function &F, + ArrayRef<Instruction *> StackRestorePoints, + Value *StaticTop, bool NeedDynamicTop) { + assert(StaticTop && "The stack top isn't set."); + + if (StackRestorePoints.empty()) + return nullptr; + + // We need the current value of the shadow stack pointer to restore + // after longjmp or exception catching. + + // FIXME: On some platforms this could be handled by the longjmp/exception + // runtime itself. + + AllocaInst *DynamicTop = nullptr; + if (NeedDynamicTop) { + // If we also have dynamic alloca's, the stack pointer value changes + // throughout the function. For now we store it in an alloca. + DynamicTop = IRB.CreateAlloca(StackPtrTy, /*ArraySize=*/nullptr, + "unsafe_stack_dynamic_ptr"); + IRB.CreateStore(StaticTop, DynamicTop); + } + + // Restore current stack pointer after longjmp/exception catch. + for (Instruction *I : StackRestorePoints) { + ++NumUnsafeStackRestorePoints; + + IRB.SetInsertPoint(I->getNextNode()); + Value *CurrentTop = + DynamicTop ? IRB.CreateLoad(StackPtrTy, DynamicTop) : StaticTop; + IRB.CreateStore(CurrentTop, UnsafeStackPtr); + } + + return DynamicTop; +} + +void SafeStack::checkStackGuard(IRBuilder<> &IRB, Function &F, ReturnInst &RI, + AllocaInst *StackGuardSlot, Value *StackGuard) { + Value *V = IRB.CreateLoad(StackPtrTy, StackGuardSlot); + Value *Cmp = IRB.CreateICmpNE(StackGuard, V); + + auto SuccessProb = BranchProbabilityInfo::getBranchProbStackProtector(true); + auto FailureProb = BranchProbabilityInfo::getBranchProbStackProtector(false); + MDNode *Weights = MDBuilder(F.getContext()) + .createBranchWeights(SuccessProb.getNumerator(), + FailureProb.getNumerator()); + Instruction *CheckTerm = + SplitBlockAndInsertIfThen(Cmp, &RI, + /* Unreachable */ true, Weights); + IRBuilder<> IRBFail(CheckTerm); + // FIXME: respect -fsanitize-trap / -ftrap-function here? + FunctionCallee StackChkFail = + F.getParent()->getOrInsertFunction("__stack_chk_fail", IRB.getVoidTy()); + IRBFail.CreateCall(StackChkFail, {}); +} + +/// We explicitly compute and set the unsafe stack layout for all unsafe +/// static alloca instructions. We save the unsafe "base pointer" in the +/// prologue into a local variable and restore it in the epilogue. +Value *SafeStack::moveStaticAllocasToUnsafeStack( + IRBuilder<> &IRB, Function &F, ArrayRef<AllocaInst *> StaticAllocas, + ArrayRef<Argument *> ByValArguments, ArrayRef<ReturnInst *> Returns, + Instruction *BasePointer, AllocaInst *StackGuardSlot) { + if (StaticAllocas.empty() && ByValArguments.empty()) + return BasePointer; + + DIBuilder DIB(*F.getParent()); + + StackColoring SSC(F, StaticAllocas); + SSC.run(); + SSC.removeAllMarkers(); + + // Unsafe stack always grows down. + StackLayout SSL(StackAlignment); + if (StackGuardSlot) { + Type *Ty = StackGuardSlot->getAllocatedType(); + unsigned Align = + std::max(DL.getPrefTypeAlignment(Ty), StackGuardSlot->getAlignment()); + SSL.addObject(StackGuardSlot, getStaticAllocaAllocationSize(StackGuardSlot), + Align, SSC.getFullLiveRange()); + } + + for (Argument *Arg : ByValArguments) { + Type *Ty = Arg->getType()->getPointerElementType(); + uint64_t Size = DL.getTypeStoreSize(Ty); + if (Size == 0) + Size = 1; // Don't create zero-sized stack objects. + + // Ensure the object is properly aligned. + unsigned Align = std::max((unsigned)DL.getPrefTypeAlignment(Ty), + Arg->getParamAlignment()); + SSL.addObject(Arg, Size, Align, SSC.getFullLiveRange()); + } + + for (AllocaInst *AI : StaticAllocas) { + Type *Ty = AI->getAllocatedType(); + uint64_t Size = getStaticAllocaAllocationSize(AI); + if (Size == 0) + Size = 1; // Don't create zero-sized stack objects. + + // Ensure the object is properly aligned. + unsigned Align = + std::max((unsigned)DL.getPrefTypeAlignment(Ty), AI->getAlignment()); + + SSL.addObject(AI, Size, Align, SSC.getLiveRange(AI)); + } + + SSL.computeLayout(); + unsigned FrameAlignment = SSL.getFrameAlignment(); + + // FIXME: tell SSL that we start at a less-then-MaxAlignment aligned location + // (AlignmentSkew). + if (FrameAlignment > StackAlignment) { + // Re-align the base pointer according to the max requested alignment. + assert(isPowerOf2_32(FrameAlignment)); + IRB.SetInsertPoint(BasePointer->getNextNode()); + BasePointer = cast<Instruction>(IRB.CreateIntToPtr( + IRB.CreateAnd(IRB.CreatePtrToInt(BasePointer, IntPtrTy), + ConstantInt::get(IntPtrTy, ~uint64_t(FrameAlignment - 1))), + StackPtrTy)); + } + + IRB.SetInsertPoint(BasePointer->getNextNode()); + + if (StackGuardSlot) { + unsigned Offset = SSL.getObjectOffset(StackGuardSlot); + Value *Off = IRB.CreateGEP(Int8Ty, BasePointer, // BasePointer is i8* + ConstantInt::get(Int32Ty, -Offset)); + Value *NewAI = + IRB.CreateBitCast(Off, StackGuardSlot->getType(), "StackGuardSlot"); + + // Replace alloc with the new location. + StackGuardSlot->replaceAllUsesWith(NewAI); + StackGuardSlot->eraseFromParent(); + } + + for (Argument *Arg : ByValArguments) { + unsigned Offset = SSL.getObjectOffset(Arg); + unsigned Align = SSL.getObjectAlignment(Arg); + Type *Ty = Arg->getType()->getPointerElementType(); + + uint64_t Size = DL.getTypeStoreSize(Ty); + if (Size == 0) + Size = 1; // Don't create zero-sized stack objects. + + Value *Off = IRB.CreateGEP(Int8Ty, BasePointer, // BasePointer is i8* + ConstantInt::get(Int32Ty, -Offset)); + Value *NewArg = IRB.CreateBitCast(Off, Arg->getType(), + Arg->getName() + ".unsafe-byval"); + + // Replace alloc with the new location. + replaceDbgDeclare(Arg, BasePointer, BasePointer->getNextNode(), DIB, + DIExpression::ApplyOffset, -Offset); + Arg->replaceAllUsesWith(NewArg); + IRB.SetInsertPoint(cast<Instruction>(NewArg)->getNextNode()); + IRB.CreateMemCpy(Off, Align, Arg, Arg->getParamAlignment(), Size); + } + + // Allocate space for every unsafe static AllocaInst on the unsafe stack. + for (AllocaInst *AI : StaticAllocas) { + IRB.SetInsertPoint(AI); + unsigned Offset = SSL.getObjectOffset(AI); + + replaceDbgDeclareForAlloca(AI, BasePointer, DIB, DIExpression::ApplyOffset, + -Offset); + replaceDbgValueForAlloca(AI, BasePointer, DIB, -Offset); + + // Replace uses of the alloca with the new location. + // Insert address calculation close to each use to work around PR27844. + std::string Name = std::string(AI->getName()) + ".unsafe"; + while (!AI->use_empty()) { + Use &U = *AI->use_begin(); + Instruction *User = cast<Instruction>(U.getUser()); + + Instruction *InsertBefore; + if (auto *PHI = dyn_cast<PHINode>(User)) + InsertBefore = PHI->getIncomingBlock(U)->getTerminator(); + else + InsertBefore = User; + + IRBuilder<> IRBUser(InsertBefore); + Value *Off = IRBUser.CreateGEP(Int8Ty, BasePointer, // BasePointer is i8* + ConstantInt::get(Int32Ty, -Offset)); + Value *Replacement = IRBUser.CreateBitCast(Off, AI->getType(), Name); + + if (auto *PHI = dyn_cast<PHINode>(User)) + // PHI nodes may have multiple incoming edges from the same BB (why??), + // all must be updated at once with the same incoming value. + PHI->setIncomingValueForBlock(PHI->getIncomingBlock(U), Replacement); + else + U.set(Replacement); + } + + AI->eraseFromParent(); + } + + // Re-align BasePointer so that our callees would see it aligned as + // expected. + // FIXME: no need to update BasePointer in leaf functions. + unsigned FrameSize = alignTo(SSL.getFrameSize(), StackAlignment); + + // Update shadow stack pointer in the function epilogue. + IRB.SetInsertPoint(BasePointer->getNextNode()); + + Value *StaticTop = + IRB.CreateGEP(Int8Ty, BasePointer, ConstantInt::get(Int32Ty, -FrameSize), + "unsafe_stack_static_top"); + IRB.CreateStore(StaticTop, UnsafeStackPtr); + return StaticTop; +} + +void SafeStack::moveDynamicAllocasToUnsafeStack( + Function &F, Value *UnsafeStackPtr, AllocaInst *DynamicTop, + ArrayRef<AllocaInst *> DynamicAllocas) { + DIBuilder DIB(*F.getParent()); + + for (AllocaInst *AI : DynamicAllocas) { + IRBuilder<> IRB(AI); + + // Compute the new SP value (after AI). + Value *ArraySize = AI->getArraySize(); + if (ArraySize->getType() != IntPtrTy) + ArraySize = IRB.CreateIntCast(ArraySize, IntPtrTy, false); + + Type *Ty = AI->getAllocatedType(); + uint64_t TySize = DL.getTypeAllocSize(Ty); + Value *Size = IRB.CreateMul(ArraySize, ConstantInt::get(IntPtrTy, TySize)); + + Value *SP = IRB.CreatePtrToInt(IRB.CreateLoad(StackPtrTy, UnsafeStackPtr), + IntPtrTy); + SP = IRB.CreateSub(SP, Size); + + // Align the SP value to satisfy the AllocaInst, type and stack alignments. + unsigned Align = std::max( + std::max((unsigned)DL.getPrefTypeAlignment(Ty), AI->getAlignment()), + (unsigned)StackAlignment); + + assert(isPowerOf2_32(Align)); + Value *NewTop = IRB.CreateIntToPtr( + IRB.CreateAnd(SP, ConstantInt::get(IntPtrTy, ~uint64_t(Align - 1))), + StackPtrTy); + + // Save the stack pointer. + IRB.CreateStore(NewTop, UnsafeStackPtr); + if (DynamicTop) + IRB.CreateStore(NewTop, DynamicTop); + + Value *NewAI = IRB.CreatePointerCast(NewTop, AI->getType()); + if (AI->hasName() && isa<Instruction>(NewAI)) + NewAI->takeName(AI); + + replaceDbgDeclareForAlloca(AI, NewAI, DIB, DIExpression::ApplyOffset, 0); + AI->replaceAllUsesWith(NewAI); + AI->eraseFromParent(); + } + + if (!DynamicAllocas.empty()) { + // Now go through the instructions again, replacing stacksave/stackrestore. + for (inst_iterator It = inst_begin(&F), Ie = inst_end(&F); It != Ie;) { + Instruction *I = &*(It++); + auto II = dyn_cast<IntrinsicInst>(I); + if (!II) + continue; + + if (II->getIntrinsicID() == Intrinsic::stacksave) { + IRBuilder<> IRB(II); + Instruction *LI = IRB.CreateLoad(StackPtrTy, UnsafeStackPtr); + LI->takeName(II); + II->replaceAllUsesWith(LI); + II->eraseFromParent(); + } else if (II->getIntrinsicID() == Intrinsic::stackrestore) { + IRBuilder<> IRB(II); + Instruction *SI = IRB.CreateStore(II->getArgOperand(0), UnsafeStackPtr); + SI->takeName(II); + assert(II->use_empty()); + II->eraseFromParent(); + } + } + } +} + +bool SafeStack::ShouldInlinePointerAddress(CallSite &CS) { + Function *Callee = CS.getCalledFunction(); + if (CS.hasFnAttr(Attribute::AlwaysInline) && isInlineViable(*Callee)) + return true; + if (Callee->isInterposable() || Callee->hasFnAttribute(Attribute::NoInline) || + CS.isNoInline()) + return false; + return true; +} + +void SafeStack::TryInlinePointerAddress() { + if (!isa<CallInst>(UnsafeStackPtr)) + return; + + if(F.hasOptNone()) + return; + + CallSite CS(UnsafeStackPtr); + Function *Callee = CS.getCalledFunction(); + if (!Callee || Callee->isDeclaration()) + return; + + if (!ShouldInlinePointerAddress(CS)) + return; + + InlineFunctionInfo IFI; + InlineFunction(CS, IFI); +} + +bool SafeStack::run() { + assert(F.hasFnAttribute(Attribute::SafeStack) && + "Can't run SafeStack on a function without the attribute"); + assert(!F.isDeclaration() && "Can't run SafeStack on a function declaration"); + + ++NumFunctions; + + SmallVector<AllocaInst *, 16> StaticAllocas; + SmallVector<AllocaInst *, 4> DynamicAllocas; + SmallVector<Argument *, 4> ByValArguments; + SmallVector<ReturnInst *, 4> Returns; + + // Collect all points where stack gets unwound and needs to be restored + // This is only necessary because the runtime (setjmp and unwind code) is + // not aware of the unsafe stack and won't unwind/restore it properly. + // To work around this problem without changing the runtime, we insert + // instrumentation to restore the unsafe stack pointer when necessary. + SmallVector<Instruction *, 4> StackRestorePoints; + + // Find all static and dynamic alloca instructions that must be moved to the + // unsafe stack, all return instructions and stack restore points. + findInsts(F, StaticAllocas, DynamicAllocas, ByValArguments, Returns, + StackRestorePoints); + + if (StaticAllocas.empty() && DynamicAllocas.empty() && + ByValArguments.empty() && StackRestorePoints.empty()) + return false; // Nothing to do in this function. + + if (!StaticAllocas.empty() || !DynamicAllocas.empty() || + !ByValArguments.empty()) + ++NumUnsafeStackFunctions; // This function has the unsafe stack. + + if (!StackRestorePoints.empty()) + ++NumUnsafeStackRestorePointsFunctions; + + IRBuilder<> IRB(&F.front(), F.begin()->getFirstInsertionPt()); + // Calls must always have a debug location, or else inlining breaks. So + // we explicitly set a artificial debug location here. + if (DISubprogram *SP = F.getSubprogram()) + IRB.SetCurrentDebugLocation(DebugLoc::get(SP->getScopeLine(), 0, SP)); + if (SafeStackUsePointerAddress) { + FunctionCallee Fn = F.getParent()->getOrInsertFunction( + "__safestack_pointer_address", StackPtrTy->getPointerTo(0)); + UnsafeStackPtr = IRB.CreateCall(Fn); + } else { + UnsafeStackPtr = TL.getSafeStackPointerLocation(IRB); + } + + // Load the current stack pointer (we'll also use it as a base pointer). + // FIXME: use a dedicated register for it ? + Instruction *BasePointer = + IRB.CreateLoad(StackPtrTy, UnsafeStackPtr, false, "unsafe_stack_ptr"); + assert(BasePointer->getType() == StackPtrTy); + + AllocaInst *StackGuardSlot = nullptr; + // FIXME: implement weaker forms of stack protector. + if (F.hasFnAttribute(Attribute::StackProtect) || + F.hasFnAttribute(Attribute::StackProtectStrong) || + F.hasFnAttribute(Attribute::StackProtectReq)) { + Value *StackGuard = getStackGuard(IRB, F); + StackGuardSlot = IRB.CreateAlloca(StackPtrTy, nullptr); + IRB.CreateStore(StackGuard, StackGuardSlot); + + for (ReturnInst *RI : Returns) { + IRBuilder<> IRBRet(RI); + checkStackGuard(IRBRet, F, *RI, StackGuardSlot, StackGuard); + } + } + + // The top of the unsafe stack after all unsafe static allocas are + // allocated. + Value *StaticTop = + moveStaticAllocasToUnsafeStack(IRB, F, StaticAllocas, ByValArguments, + Returns, BasePointer, StackGuardSlot); + + // Safe stack object that stores the current unsafe stack top. It is updated + // as unsafe dynamic (non-constant-sized) allocas are allocated and freed. + // This is only needed if we need to restore stack pointer after longjmp + // or exceptions, and we have dynamic allocations. + // FIXME: a better alternative might be to store the unsafe stack pointer + // before setjmp / invoke instructions. + AllocaInst *DynamicTop = createStackRestorePoints( + IRB, F, StackRestorePoints, StaticTop, !DynamicAllocas.empty()); + + // Handle dynamic allocas. + moveDynamicAllocasToUnsafeStack(F, UnsafeStackPtr, DynamicTop, + DynamicAllocas); + + // Restore the unsafe stack pointer before each return. + for (ReturnInst *RI : Returns) { + IRB.SetInsertPoint(RI); + IRB.CreateStore(BasePointer, UnsafeStackPtr); + } + + TryInlinePointerAddress(); + + LLVM_DEBUG(dbgs() << "[SafeStack] safestack applied\n"); + return true; +} + +class SafeStackLegacyPass : public FunctionPass { + const TargetMachine *TM = nullptr; + +public: + static char ID; // Pass identification, replacement for typeid.. + + SafeStackLegacyPass() : FunctionPass(ID) { + initializeSafeStackLegacyPassPass(*PassRegistry::getPassRegistry()); + } + + void getAnalysisUsage(AnalysisUsage &AU) const override { + AU.addRequired<TargetPassConfig>(); + AU.addRequired<TargetLibraryInfoWrapperPass>(); + AU.addRequired<AssumptionCacheTracker>(); + } + + bool runOnFunction(Function &F) override { + LLVM_DEBUG(dbgs() << "[SafeStack] Function: " << F.getName() << "\n"); + + if (!F.hasFnAttribute(Attribute::SafeStack)) { + LLVM_DEBUG(dbgs() << "[SafeStack] safestack is not requested" + " for this function\n"); + return false; + } + + if (F.isDeclaration()) { + LLVM_DEBUG(dbgs() << "[SafeStack] function definition" + " is not available\n"); + return false; + } + + TM = &getAnalysis<TargetPassConfig>().getTM<TargetMachine>(); + auto *TL = TM->getSubtargetImpl(F)->getTargetLowering(); + if (!TL) + report_fatal_error("TargetLowering instance is required"); + + auto *DL = &F.getParent()->getDataLayout(); + auto &TLI = getAnalysis<TargetLibraryInfoWrapperPass>().getTLI(); + auto &ACT = getAnalysis<AssumptionCacheTracker>().getAssumptionCache(F); + + // Compute DT and LI only for functions that have the attribute. + // This is only useful because the legacy pass manager doesn't let us + // compute analyzes lazily. + // In the backend pipeline, nothing preserves DT before SafeStack, so we + // would otherwise always compute it wastefully, even if there is no + // function with the safestack attribute. + DominatorTree DT(F); + LoopInfo LI(DT); + + ScalarEvolution SE(F, TLI, ACT, DT, LI); + + return SafeStack(F, *TL, *DL, SE).run(); + } +}; + +} // end anonymous namespace + +char SafeStackLegacyPass::ID = 0; + +INITIALIZE_PASS_BEGIN(SafeStackLegacyPass, DEBUG_TYPE, + "Safe Stack instrumentation pass", false, false) +INITIALIZE_PASS_DEPENDENCY(TargetPassConfig) +INITIALIZE_PASS_END(SafeStackLegacyPass, DEBUG_TYPE, + "Safe Stack instrumentation pass", false, false) + +FunctionPass *llvm::createSafeStackPass() { return new SafeStackLegacyPass(); } |