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