1 //===-- CrossDSOCFI.cpp - Externalize this module's CFI checks ------------===// 2 // 3 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions. 4 // See https://llvm.org/LICENSE.txt for license information. 5 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception 6 // 7 //===----------------------------------------------------------------------===// 8 // 9 // This pass exports all llvm.bitset's found in the module in the form of a 10 // __cfi_check function, which can be used to verify cross-DSO call targets. 11 // 12 //===----------------------------------------------------------------------===// 13 14 #include "llvm/Transforms/IPO/CrossDSOCFI.h" 15 #include "llvm/ADT/SetVector.h" 16 #include "llvm/ADT/Statistic.h" 17 #include "llvm/IR/Constants.h" 18 #include "llvm/IR/Function.h" 19 #include "llvm/IR/GlobalObject.h" 20 #include "llvm/IR/IRBuilder.h" 21 #include "llvm/IR/Instructions.h" 22 #include "llvm/IR/Intrinsics.h" 23 #include "llvm/IR/MDBuilder.h" 24 #include "llvm/IR/Module.h" 25 #include "llvm/TargetParser/Triple.h" 26 #include "llvm/Transforms/IPO.h" 27 28 using namespace llvm; 29 30 #define DEBUG_TYPE "cross-dso-cfi" 31 32 STATISTIC(NumTypeIds, "Number of unique type identifiers"); 33 34 namespace { 35 36 struct CrossDSOCFI { 37 MDNode *VeryLikelyWeights; 38 39 ConstantInt *extractNumericTypeId(MDNode *MD); 40 void buildCFICheck(Module &M); 41 bool runOnModule(Module &M); 42 }; 43 44 } // anonymous namespace 45 46 /// Extracts a numeric type identifier from an MDNode containing type metadata. 47 ConstantInt *CrossDSOCFI::extractNumericTypeId(MDNode *MD) { 48 // This check excludes vtables for classes inside anonymous namespaces. 49 auto TM = dyn_cast<ValueAsMetadata>(MD->getOperand(1)); 50 if (!TM) 51 return nullptr; 52 auto C = dyn_cast_or_null<ConstantInt>(TM->getValue()); 53 if (!C) return nullptr; 54 // We are looking for i64 constants. 55 if (C->getBitWidth() != 64) return nullptr; 56 57 return C; 58 } 59 60 /// buildCFICheck - emits __cfi_check for the current module. 61 void CrossDSOCFI::buildCFICheck(Module &M) { 62 // FIXME: verify that __cfi_check ends up near the end of the code section, 63 // but before the jump slots created in LowerTypeTests. 64 SetVector<uint64_t> TypeIds; 65 SmallVector<MDNode *, 2> Types; 66 for (GlobalObject &GO : M.global_objects()) { 67 Types.clear(); 68 GO.getMetadata(LLVMContext::MD_type, Types); 69 for (MDNode *Type : Types) 70 if (ConstantInt *TypeId = extractNumericTypeId(Type)) 71 TypeIds.insert(TypeId->getZExtValue()); 72 } 73 74 NamedMDNode *CfiFunctionsMD = M.getNamedMetadata("cfi.functions"); 75 if (CfiFunctionsMD) { 76 for (auto *Func : CfiFunctionsMD->operands()) { 77 assert(Func->getNumOperands() >= 2); 78 for (unsigned I = 2; I < Func->getNumOperands(); ++I) 79 if (ConstantInt *TypeId = 80 extractNumericTypeId(cast<MDNode>(Func->getOperand(I).get()))) 81 TypeIds.insert(TypeId->getZExtValue()); 82 } 83 } 84 85 LLVMContext &Ctx = M.getContext(); 86 FunctionCallee C = M.getOrInsertFunction( 87 "__cfi_check", Type::getVoidTy(Ctx), Type::getInt64Ty(Ctx), 88 Type::getInt8PtrTy(Ctx), Type::getInt8PtrTy(Ctx)); 89 Function *F = cast<Function>(C.getCallee()); 90 // Take over the existing function. The frontend emits a weak stub so that the 91 // linker knows about the symbol; this pass replaces the function body. 92 F->deleteBody(); 93 F->setAlignment(Align(4096)); 94 95 Triple T(M.getTargetTriple()); 96 if (T.isARM() || T.isThumb()) 97 F->addFnAttr("target-features", "+thumb-mode"); 98 99 auto args = F->arg_begin(); 100 Value &CallSiteTypeId = *(args++); 101 CallSiteTypeId.setName("CallSiteTypeId"); 102 Value &Addr = *(args++); 103 Addr.setName("Addr"); 104 Value &CFICheckFailData = *(args++); 105 CFICheckFailData.setName("CFICheckFailData"); 106 assert(args == F->arg_end()); 107 108 BasicBlock *BB = BasicBlock::Create(Ctx, "entry", F); 109 BasicBlock *ExitBB = BasicBlock::Create(Ctx, "exit", F); 110 111 BasicBlock *TrapBB = BasicBlock::Create(Ctx, "fail", F); 112 IRBuilder<> IRBFail(TrapBB); 113 FunctionCallee CFICheckFailFn = 114 M.getOrInsertFunction("__cfi_check_fail", Type::getVoidTy(Ctx), 115 Type::getInt8PtrTy(Ctx), Type::getInt8PtrTy(Ctx)); 116 IRBFail.CreateCall(CFICheckFailFn, {&CFICheckFailData, &Addr}); 117 IRBFail.CreateBr(ExitBB); 118 119 IRBuilder<> IRBExit(ExitBB); 120 IRBExit.CreateRetVoid(); 121 122 IRBuilder<> IRB(BB); 123 SwitchInst *SI = IRB.CreateSwitch(&CallSiteTypeId, TrapBB, TypeIds.size()); 124 for (uint64_t TypeId : TypeIds) { 125 ConstantInt *CaseTypeId = ConstantInt::get(Type::getInt64Ty(Ctx), TypeId); 126 BasicBlock *TestBB = BasicBlock::Create(Ctx, "test", F); 127 IRBuilder<> IRBTest(TestBB); 128 Function *BitsetTestFn = Intrinsic::getDeclaration(&M, Intrinsic::type_test); 129 130 Value *Test = IRBTest.CreateCall( 131 BitsetTestFn, {&Addr, MetadataAsValue::get( 132 Ctx, ConstantAsMetadata::get(CaseTypeId))}); 133 BranchInst *BI = IRBTest.CreateCondBr(Test, ExitBB, TrapBB); 134 BI->setMetadata(LLVMContext::MD_prof, VeryLikelyWeights); 135 136 SI->addCase(CaseTypeId, TestBB); 137 ++NumTypeIds; 138 } 139 } 140 141 bool CrossDSOCFI::runOnModule(Module &M) { 142 VeryLikelyWeights = 143 MDBuilder(M.getContext()).createBranchWeights((1U << 20) - 1, 1); 144 if (M.getModuleFlag("Cross-DSO CFI") == nullptr) 145 return false; 146 buildCFICheck(M); 147 return true; 148 } 149 150 PreservedAnalyses CrossDSOCFIPass::run(Module &M, ModuleAnalysisManager &AM) { 151 CrossDSOCFI Impl; 152 bool Changed = Impl.runOnModule(M); 153 if (!Changed) 154 return PreservedAnalyses::all(); 155 return PreservedAnalyses::none(); 156 } 157