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/ADT/Triple.h" 18 #include "llvm/IR/Constant.h" 19 #include "llvm/IR/Constants.h" 20 #include "llvm/IR/Function.h" 21 #include "llvm/IR/GlobalObject.h" 22 #include "llvm/IR/GlobalVariable.h" 23 #include "llvm/IR/IRBuilder.h" 24 #include "llvm/IR/Instructions.h" 25 #include "llvm/IR/Intrinsics.h" 26 #include "llvm/IR/MDBuilder.h" 27 #include "llvm/IR/Module.h" 28 #include "llvm/IR/Operator.h" 29 #include "llvm/InitializePasses.h" 30 #include "llvm/Pass.h" 31 #include "llvm/Support/Debug.h" 32 #include "llvm/Support/raw_ostream.h" 33 #include "llvm/Transforms/IPO.h" 34 35 using namespace llvm; 36 37 #define DEBUG_TYPE "cross-dso-cfi" 38 39 STATISTIC(NumTypeIds, "Number of unique type identifiers"); 40 41 namespace { 42 43 struct CrossDSOCFI : public ModulePass { 44 static char ID; 45 CrossDSOCFI() : ModulePass(ID) { 46 initializeCrossDSOCFIPass(*PassRegistry::getPassRegistry()); 47 } 48 49 MDNode *VeryLikelyWeights; 50 51 ConstantInt *extractNumericTypeId(MDNode *MD); 52 void buildCFICheck(Module &M); 53 bool runOnModule(Module &M) override; 54 }; 55 56 } // anonymous namespace 57 58 INITIALIZE_PASS_BEGIN(CrossDSOCFI, "cross-dso-cfi", "Cross-DSO CFI", false, 59 false) 60 INITIALIZE_PASS_END(CrossDSOCFI, "cross-dso-cfi", "Cross-DSO CFI", false, false) 61 char CrossDSOCFI::ID = 0; 62 63 ModulePass *llvm::createCrossDSOCFIPass() { return new CrossDSOCFI; } 64 65 /// Extracts a numeric type identifier from an MDNode containing type metadata. 66 ConstantInt *CrossDSOCFI::extractNumericTypeId(MDNode *MD) { 67 // This check excludes vtables for classes inside anonymous namespaces. 68 auto TM = dyn_cast<ValueAsMetadata>(MD->getOperand(1)); 69 if (!TM) 70 return nullptr; 71 auto C = dyn_cast_or_null<ConstantInt>(TM->getValue()); 72 if (!C) return nullptr; 73 // We are looking for i64 constants. 74 if (C->getBitWidth() != 64) return nullptr; 75 76 return C; 77 } 78 79 /// buildCFICheck - emits __cfi_check for the current module. 80 void CrossDSOCFI::buildCFICheck(Module &M) { 81 // FIXME: verify that __cfi_check ends up near the end of the code section, 82 // but before the jump slots created in LowerTypeTests. 83 SetVector<uint64_t> TypeIds; 84 SmallVector<MDNode *, 2> Types; 85 for (GlobalObject &GO : M.global_objects()) { 86 Types.clear(); 87 GO.getMetadata(LLVMContext::MD_type, Types); 88 for (MDNode *Type : Types) 89 if (ConstantInt *TypeId = extractNumericTypeId(Type)) 90 TypeIds.insert(TypeId->getZExtValue()); 91 } 92 93 NamedMDNode *CfiFunctionsMD = M.getNamedMetadata("cfi.functions"); 94 if (CfiFunctionsMD) { 95 for (auto Func : CfiFunctionsMD->operands()) { 96 assert(Func->getNumOperands() >= 2); 97 for (unsigned I = 2; I < Func->getNumOperands(); ++I) 98 if (ConstantInt *TypeId = 99 extractNumericTypeId(cast<MDNode>(Func->getOperand(I).get()))) 100 TypeIds.insert(TypeId->getZExtValue()); 101 } 102 } 103 104 LLVMContext &Ctx = M.getContext(); 105 FunctionCallee C = M.getOrInsertFunction( 106 "__cfi_check", Type::getVoidTy(Ctx), Type::getInt64Ty(Ctx), 107 Type::getInt8PtrTy(Ctx), Type::getInt8PtrTy(Ctx)); 108 Function *F = cast<Function>(C.getCallee()); 109 // Take over the existing function. The frontend emits a weak stub so that the 110 // linker knows about the symbol; this pass replaces the function body. 111 F->deleteBody(); 112 F->setAlignment(Align(4096)); 113 114 Triple T(M.getTargetTriple()); 115 if (T.isARM() || T.isThumb()) 116 F->addFnAttr("target-features", "+thumb-mode"); 117 118 auto args = F->arg_begin(); 119 Value &CallSiteTypeId = *(args++); 120 CallSiteTypeId.setName("CallSiteTypeId"); 121 Value &Addr = *(args++); 122 Addr.setName("Addr"); 123 Value &CFICheckFailData = *(args++); 124 CFICheckFailData.setName("CFICheckFailData"); 125 assert(args == F->arg_end()); 126 127 BasicBlock *BB = BasicBlock::Create(Ctx, "entry", F); 128 BasicBlock *ExitBB = BasicBlock::Create(Ctx, "exit", F); 129 130 BasicBlock *TrapBB = BasicBlock::Create(Ctx, "fail", F); 131 IRBuilder<> IRBFail(TrapBB); 132 FunctionCallee CFICheckFailFn = 133 M.getOrInsertFunction("__cfi_check_fail", Type::getVoidTy(Ctx), 134 Type::getInt8PtrTy(Ctx), Type::getInt8PtrTy(Ctx)); 135 IRBFail.CreateCall(CFICheckFailFn, {&CFICheckFailData, &Addr}); 136 IRBFail.CreateBr(ExitBB); 137 138 IRBuilder<> IRBExit(ExitBB); 139 IRBExit.CreateRetVoid(); 140 141 IRBuilder<> IRB(BB); 142 SwitchInst *SI = IRB.CreateSwitch(&CallSiteTypeId, TrapBB, TypeIds.size()); 143 for (uint64_t TypeId : TypeIds) { 144 ConstantInt *CaseTypeId = ConstantInt::get(Type::getInt64Ty(Ctx), TypeId); 145 BasicBlock *TestBB = BasicBlock::Create(Ctx, "test", F); 146 IRBuilder<> IRBTest(TestBB); 147 Function *BitsetTestFn = Intrinsic::getDeclaration(&M, Intrinsic::type_test); 148 149 Value *Test = IRBTest.CreateCall( 150 BitsetTestFn, {&Addr, MetadataAsValue::get( 151 Ctx, ConstantAsMetadata::get(CaseTypeId))}); 152 BranchInst *BI = IRBTest.CreateCondBr(Test, ExitBB, TrapBB); 153 BI->setMetadata(LLVMContext::MD_prof, VeryLikelyWeights); 154 155 SI->addCase(CaseTypeId, TestBB); 156 ++NumTypeIds; 157 } 158 } 159 160 bool CrossDSOCFI::runOnModule(Module &M) { 161 VeryLikelyWeights = 162 MDBuilder(M.getContext()).createBranchWeights((1U << 20) - 1, 1); 163 if (M.getModuleFlag("Cross-DSO CFI") == nullptr) 164 return false; 165 buildCFICheck(M); 166 return true; 167 } 168 169 PreservedAnalyses CrossDSOCFIPass::run(Module &M, ModuleAnalysisManager &AM) { 170 CrossDSOCFI Impl; 171 bool Changed = Impl.runOnModule(M); 172 if (!Changed) 173 return PreservedAnalyses::all(); 174 return PreservedAnalyses::none(); 175 } 176