diff options
Diffstat (limited to 'lib/CodeGen/ShadowStackGC.cpp')
| -rw-r--r-- | lib/CodeGen/ShadowStackGC.cpp | 412 |
1 files changed, 7 insertions, 405 deletions
diff --git a/lib/CodeGen/ShadowStackGC.cpp b/lib/CodeGen/ShadowStackGC.cpp index 0be00f0..b12e943 100644 --- a/lib/CodeGen/ShadowStackGC.cpp +++ b/lib/CodeGen/ShadowStackGC.cpp @@ -38,416 +38,18 @@ using namespace llvm; #define DEBUG_TYPE "shadowstackgc" namespace { - - class ShadowStackGC : public GCStrategy { - /// RootChain - This is the global linked-list that contains the chain of GC - /// roots. - GlobalVariable *Head; - - /// StackEntryTy - Abstract type of a link in the shadow stack. - /// - StructType *StackEntryTy; - StructType *FrameMapTy; - - /// Roots - GC roots in the current function. Each is a pair of the - /// intrinsic call and its corresponding alloca. - std::vector<std::pair<CallInst*,AllocaInst*> > Roots; - - public: - ShadowStackGC(); - - bool initializeCustomLowering(Module &M) override; - bool performCustomLowering(Function &F) override; - - private: - bool IsNullValue(Value *V); - Constant *GetFrameMap(Function &F); - Type* GetConcreteStackEntryType(Function &F); - void CollectRoots(Function &F); - static GetElementPtrInst *CreateGEP(LLVMContext &Context, - IRBuilder<> &B, Value *BasePtr, - int Idx1, const char *Name); - static GetElementPtrInst *CreateGEP(LLVMContext &Context, - IRBuilder<> &B, Value *BasePtr, - int Idx1, int Idx2, const char *Name); - }; - +class ShadowStackGC : public GCStrategy { +public: + ShadowStackGC(); +}; } static GCRegistry::Add<ShadowStackGC> -X("shadow-stack", "Very portable GC for uncooperative code generators"); - -namespace { - /// EscapeEnumerator - This is a little algorithm to find all escape points - /// from a function so that "finally"-style code can be inserted. In addition - /// to finding the existing return and unwind instructions, it also (if - /// necessary) transforms any call instructions into invokes and sends them to - /// a landing pad. - /// - /// It's wrapped up in a state machine using the same transform C# uses for - /// 'yield return' enumerators, This transform allows it to be non-allocating. - class EscapeEnumerator { - Function &F; - const char *CleanupBBName; - - // State. - int State; - Function::iterator StateBB, StateE; - IRBuilder<> Builder; - - public: - EscapeEnumerator(Function &F, const char *N = "cleanup") - : F(F), CleanupBBName(N), State(0), Builder(F.getContext()) {} - - IRBuilder<> *Next() { - switch (State) { - default: - return nullptr; - - case 0: - StateBB = F.begin(); - StateE = F.end(); - State = 1; - - case 1: - // Find all 'return', 'resume', and 'unwind' instructions. - while (StateBB != StateE) { - BasicBlock *CurBB = StateBB++; - - // Branches and invokes do not escape, only unwind, resume, and return - // do. - TerminatorInst *TI = CurBB->getTerminator(); - if (!isa<ReturnInst>(TI) && !isa<ResumeInst>(TI)) - continue; - - Builder.SetInsertPoint(TI->getParent(), TI); - return &Builder; - } - - State = 2; - - // Find all 'call' instructions. - SmallVector<Instruction*,16> Calls; - for (Function::iterator BB = F.begin(), - E = F.end(); BB != E; ++BB) - for (BasicBlock::iterator II = BB->begin(), - EE = BB->end(); II != EE; ++II) - if (CallInst *CI = dyn_cast<CallInst>(II)) - if (!CI->getCalledFunction() || - !CI->getCalledFunction()->getIntrinsicID()) - Calls.push_back(CI); - - if (Calls.empty()) - return nullptr; + X("shadow-stack", "Very portable GC for uncooperative code generators"); - // Create a cleanup block. - LLVMContext &C = F.getContext(); - BasicBlock *CleanupBB = BasicBlock::Create(C, CleanupBBName, &F); - Type *ExnTy = StructType::get(Type::getInt8PtrTy(C), - Type::getInt32Ty(C), nullptr); - Constant *PersFn = - F.getParent()-> - getOrInsertFunction("__gcc_personality_v0", - FunctionType::get(Type::getInt32Ty(C), true)); - LandingPadInst *LPad = LandingPadInst::Create(ExnTy, PersFn, 1, - "cleanup.lpad", - CleanupBB); - LPad->setCleanup(true); - ResumeInst *RI = ResumeInst::Create(LPad, CleanupBB); +void llvm::linkShadowStackGC() {} - // Transform the 'call' instructions into 'invoke's branching to the - // cleanup block. Go in reverse order to make prettier BB names. - SmallVector<Value*,16> Args; - for (unsigned I = Calls.size(); I != 0; ) { - CallInst *CI = cast<CallInst>(Calls[--I]); - - // Split the basic block containing the function call. - BasicBlock *CallBB = CI->getParent(); - BasicBlock *NewBB = - CallBB->splitBasicBlock(CI, CallBB->getName() + ".cont"); - - // Remove the unconditional branch inserted at the end of CallBB. - CallBB->getInstList().pop_back(); - NewBB->getInstList().remove(CI); - - // Create a new invoke instruction. - Args.clear(); - CallSite CS(CI); - Args.append(CS.arg_begin(), CS.arg_end()); - - InvokeInst *II = InvokeInst::Create(CI->getCalledValue(), - NewBB, CleanupBB, - Args, CI->getName(), CallBB); - II->setCallingConv(CI->getCallingConv()); - II->setAttributes(CI->getAttributes()); - CI->replaceAllUsesWith(II); - delete CI; - } - - Builder.SetInsertPoint(RI->getParent(), RI); - return &Builder; - } - } - }; -} - -// ----------------------------------------------------------------------------- - -void llvm::linkShadowStackGC() { } - -ShadowStackGC::ShadowStackGC() : Head(nullptr), StackEntryTy(nullptr) { +ShadowStackGC::ShadowStackGC() { InitRoots = true; CustomRoots = true; } - -Constant *ShadowStackGC::GetFrameMap(Function &F) { - // doInitialization creates the abstract type of this value. - Type *VoidPtr = Type::getInt8PtrTy(F.getContext()); - - // Truncate the ShadowStackDescriptor if some metadata is null. - unsigned NumMeta = 0; - SmallVector<Constant*, 16> Metadata; - for (unsigned I = 0; I != Roots.size(); ++I) { - Constant *C = cast<Constant>(Roots[I].first->getArgOperand(1)); - if (!C->isNullValue()) - NumMeta = I + 1; - Metadata.push_back(ConstantExpr::getBitCast(C, VoidPtr)); - } - Metadata.resize(NumMeta); - - Type *Int32Ty = Type::getInt32Ty(F.getContext()); - - Constant *BaseElts[] = { - ConstantInt::get(Int32Ty, Roots.size(), false), - ConstantInt::get(Int32Ty, NumMeta, false), - }; - - Constant *DescriptorElts[] = { - ConstantStruct::get(FrameMapTy, BaseElts), - ConstantArray::get(ArrayType::get(VoidPtr, NumMeta), Metadata) - }; - - Type *EltTys[] = { DescriptorElts[0]->getType(),DescriptorElts[1]->getType()}; - StructType *STy = StructType::create(EltTys, "gc_map."+utostr(NumMeta)); - - Constant *FrameMap = ConstantStruct::get(STy, DescriptorElts); - - // FIXME: Is this actually dangerous as WritingAnLLVMPass.html claims? Seems - // that, short of multithreaded LLVM, it should be safe; all that is - // necessary is that a simple Module::iterator loop not be invalidated. - // Appending to the GlobalVariable list is safe in that sense. - // - // All of the output passes emit globals last. The ExecutionEngine - // explicitly supports adding globals to the module after - // initialization. - // - // Still, if it isn't deemed acceptable, then this transformation needs - // to be a ModulePass (which means it cannot be in the 'llc' pipeline - // (which uses a FunctionPassManager (which segfaults (not asserts) if - // provided a ModulePass))). - Constant *GV = new GlobalVariable(*F.getParent(), FrameMap->getType(), true, - GlobalVariable::InternalLinkage, - FrameMap, "__gc_" + F.getName()); - - Constant *GEPIndices[2] = { - ConstantInt::get(Type::getInt32Ty(F.getContext()), 0), - ConstantInt::get(Type::getInt32Ty(F.getContext()), 0) - }; - return ConstantExpr::getGetElementPtr(GV, GEPIndices); -} - -Type* ShadowStackGC::GetConcreteStackEntryType(Function &F) { - // doInitialization creates the generic version of this type. - std::vector<Type*> EltTys; - EltTys.push_back(StackEntryTy); - for (size_t I = 0; I != Roots.size(); I++) - EltTys.push_back(Roots[I].second->getAllocatedType()); - - return StructType::create(EltTys, "gc_stackentry."+F.getName().str()); -} - -/// doInitialization - If this module uses the GC intrinsics, find them now. If -/// not, exit fast. -bool ShadowStackGC::initializeCustomLowering(Module &M) { - // struct FrameMap { - // int32_t NumRoots; // Number of roots in stack frame. - // int32_t NumMeta; // Number of metadata descriptors. May be < NumRoots. - // void *Meta[]; // May be absent for roots without metadata. - // }; - std::vector<Type*> EltTys; - // 32 bits is ok up to a 32GB stack frame. :) - EltTys.push_back(Type::getInt32Ty(M.getContext())); - // Specifies length of variable length array. - EltTys.push_back(Type::getInt32Ty(M.getContext())); - FrameMapTy = StructType::create(EltTys, "gc_map"); - PointerType *FrameMapPtrTy = PointerType::getUnqual(FrameMapTy); - - // struct StackEntry { - // ShadowStackEntry *Next; // Caller's stack entry. - // FrameMap *Map; // Pointer to constant FrameMap. - // void *Roots[]; // Stack roots (in-place array, so we pretend). - // }; - - StackEntryTy = StructType::create(M.getContext(), "gc_stackentry"); - - EltTys.clear(); - EltTys.push_back(PointerType::getUnqual(StackEntryTy)); - EltTys.push_back(FrameMapPtrTy); - StackEntryTy->setBody(EltTys); - PointerType *StackEntryPtrTy = PointerType::getUnqual(StackEntryTy); - - // Get the root chain if it already exists. - Head = M.getGlobalVariable("llvm_gc_root_chain"); - if (!Head) { - // If the root chain does not exist, insert a new one with linkonce - // linkage! - Head = new GlobalVariable(M, StackEntryPtrTy, false, - GlobalValue::LinkOnceAnyLinkage, - Constant::getNullValue(StackEntryPtrTy), - "llvm_gc_root_chain"); - } else if (Head->hasExternalLinkage() && Head->isDeclaration()) { - Head->setInitializer(Constant::getNullValue(StackEntryPtrTy)); - Head->setLinkage(GlobalValue::LinkOnceAnyLinkage); - } - - return true; -} - -bool ShadowStackGC::IsNullValue(Value *V) { - if (Constant *C = dyn_cast<Constant>(V)) - return C->isNullValue(); - return false; -} - -void ShadowStackGC::CollectRoots(Function &F) { - // FIXME: Account for original alignment. Could fragment the root array. - // Approach 1: Null initialize empty slots at runtime. Yuck. - // Approach 2: Emit a map of the array instead of just a count. - - assert(Roots.empty() && "Not cleaned up?"); - - SmallVector<std::pair<CallInst*, AllocaInst*>, 16> MetaRoots; - - for (Function::iterator BB = F.begin(), E = F.end(); BB != E; ++BB) - for (BasicBlock::iterator II = BB->begin(), E = BB->end(); II != E;) - if (IntrinsicInst *CI = dyn_cast<IntrinsicInst>(II++)) - if (Function *F = CI->getCalledFunction()) - if (F->getIntrinsicID() == Intrinsic::gcroot) { - std::pair<CallInst*, AllocaInst*> Pair = std::make_pair( - CI, cast<AllocaInst>(CI->getArgOperand(0)->stripPointerCasts())); - if (IsNullValue(CI->getArgOperand(1))) - Roots.push_back(Pair); - else - MetaRoots.push_back(Pair); - } - - // Number roots with metadata (usually empty) at the beginning, so that the - // FrameMap::Meta array can be elided. - Roots.insert(Roots.begin(), MetaRoots.begin(), MetaRoots.end()); -} - -GetElementPtrInst * -ShadowStackGC::CreateGEP(LLVMContext &Context, IRBuilder<> &B, Value *BasePtr, - int Idx, int Idx2, const char *Name) { - Value *Indices[] = { ConstantInt::get(Type::getInt32Ty(Context), 0), - ConstantInt::get(Type::getInt32Ty(Context), Idx), - ConstantInt::get(Type::getInt32Ty(Context), Idx2) }; - Value* Val = B.CreateGEP(BasePtr, Indices, Name); - - assert(isa<GetElementPtrInst>(Val) && "Unexpected folded constant"); - - return dyn_cast<GetElementPtrInst>(Val); -} - -GetElementPtrInst * -ShadowStackGC::CreateGEP(LLVMContext &Context, IRBuilder<> &B, Value *BasePtr, - int Idx, const char *Name) { - Value *Indices[] = { ConstantInt::get(Type::getInt32Ty(Context), 0), - ConstantInt::get(Type::getInt32Ty(Context), Idx) }; - Value *Val = B.CreateGEP(BasePtr, Indices, Name); - - assert(isa<GetElementPtrInst>(Val) && "Unexpected folded constant"); - - return dyn_cast<GetElementPtrInst>(Val); -} - -/// runOnFunction - Insert code to maintain the shadow stack. -bool ShadowStackGC::performCustomLowering(Function &F) { - LLVMContext &Context = F.getContext(); - - // Find calls to llvm.gcroot. - CollectRoots(F); - - // If there are no roots in this function, then there is no need to add a - // stack map entry for it. - if (Roots.empty()) - return false; - - // Build the constant map and figure the type of the shadow stack entry. - Value *FrameMap = GetFrameMap(F); - Type *ConcreteStackEntryTy = GetConcreteStackEntryType(F); - - // Build the shadow stack entry at the very start of the function. - BasicBlock::iterator IP = F.getEntryBlock().begin(); - IRBuilder<> AtEntry(IP->getParent(), IP); - - Instruction *StackEntry = AtEntry.CreateAlloca(ConcreteStackEntryTy, nullptr, - "gc_frame"); - - while (isa<AllocaInst>(IP)) ++IP; - AtEntry.SetInsertPoint(IP->getParent(), IP); - - // Initialize the map pointer and load the current head of the shadow stack. - Instruction *CurrentHead = AtEntry.CreateLoad(Head, "gc_currhead"); - Instruction *EntryMapPtr = CreateGEP(Context, AtEntry, StackEntry, - 0,1,"gc_frame.map"); - AtEntry.CreateStore(FrameMap, EntryMapPtr); - - // After all the allocas... - for (unsigned I = 0, E = Roots.size(); I != E; ++I) { - // For each root, find the corresponding slot in the aggregate... - Value *SlotPtr = CreateGEP(Context, AtEntry, StackEntry, 1 + I, "gc_root"); - - // And use it in lieu of the alloca. - AllocaInst *OriginalAlloca = Roots[I].second; - SlotPtr->takeName(OriginalAlloca); - OriginalAlloca->replaceAllUsesWith(SlotPtr); - } - - // Move past the original stores inserted by GCStrategy::InitRoots. This isn't - // really necessary (the collector would never see the intermediate state at - // runtime), but it's nicer not to push the half-initialized entry onto the - // shadow stack. - while (isa<StoreInst>(IP)) ++IP; - AtEntry.SetInsertPoint(IP->getParent(), IP); - - // Push the entry onto the shadow stack. - Instruction *EntryNextPtr = CreateGEP(Context, AtEntry, - StackEntry,0,0,"gc_frame.next"); - Instruction *NewHeadVal = CreateGEP(Context, AtEntry, - StackEntry, 0, "gc_newhead"); - AtEntry.CreateStore(CurrentHead, EntryNextPtr); - AtEntry.CreateStore(NewHeadVal, Head); - - // For each instruction that escapes... - EscapeEnumerator EE(F, "gc_cleanup"); - while (IRBuilder<> *AtExit = EE.Next()) { - // Pop the entry from the shadow stack. Don't reuse CurrentHead from - // AtEntry, since that would make the value live for the entire function. - Instruction *EntryNextPtr2 = CreateGEP(Context, *AtExit, StackEntry, 0, 0, - "gc_frame.next"); - Value *SavedHead = AtExit->CreateLoad(EntryNextPtr2, "gc_savedhead"); - AtExit->CreateStore(SavedHead, Head); - } - - // Delete the original allocas (which are no longer used) and the intrinsic - // calls (which are no longer valid). Doing this last avoids invalidating - // iterators. - for (unsigned I = 0, E = Roots.size(); I != E; ++I) { - Roots[I].first->eraseFromParent(); - Roots[I].second->eraseFromParent(); - } - - Roots.clear(); - return true; -} |