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/Pass.h" 30 #include "llvm/Support/Debug.h" 31 #include "llvm/Support/raw_ostream.h" 32 #include "llvm/Transforms/IPO.h" 33 34 using namespace llvm; 35 36 #define DEBUG_TYPE "cross-dso-cfi" 37 38 STATISTIC(NumTypeIds, "Number of unique type identifiers"); 39 40 namespace { 41 42 struct CrossDSOCFI : public ModulePass { 43 static char ID; 44 CrossDSOCFI() : ModulePass(ID) { 45 initializeCrossDSOCFIPass(*PassRegistry::getPassRegistry()); 46 } 47 48 MDNode *VeryLikelyWeights; 49 50 ConstantInt *extractNumericTypeId(MDNode *MD); 51 void buildCFICheck(Module &M); 52 bool runOnModule(Module &M) override; 53 }; 54 55 } // anonymous namespace 56 57 INITIALIZE_PASS_BEGIN(CrossDSOCFI, "cross-dso-cfi", "Cross-DSO CFI", false, 58 false) 59 INITIALIZE_PASS_END(CrossDSOCFI, "cross-dso-cfi", "Cross-DSO CFI", false, false) 60 char CrossDSOCFI::ID = 0; 61 62 ModulePass *llvm::createCrossDSOCFIPass() { return new CrossDSOCFI; } 63 64 /// Extracts a numeric type identifier from an MDNode containing type metadata. 65 ConstantInt *CrossDSOCFI::extractNumericTypeId(MDNode *MD) { 66 // This check excludes vtables for classes inside anonymous namespaces. 67 auto TM = dyn_cast<ValueAsMetadata>(MD->getOperand(1)); 68 if (!TM) 69 return nullptr; 70 auto C = dyn_cast_or_null<ConstantInt>(TM->getValue()); 71 if (!C) return nullptr; 72 // We are looking for i64 constants. 73 if (C->getBitWidth() != 64) return nullptr; 74 75 return C; 76 } 77 78 /// buildCFICheck - emits __cfi_check for the current module. 79 void CrossDSOCFI::buildCFICheck(Module &M) { 80 // FIXME: verify that __cfi_check ends up near the end of the code section, 81 // but before the jump slots created in LowerTypeTests. 82 SetVector<uint64_t> TypeIds; 83 SmallVector<MDNode *, 2> Types; 84 for (GlobalObject &GO : M.global_objects()) { 85 Types.clear(); 86 GO.getMetadata(LLVMContext::MD_type, Types); 87 for (MDNode *Type : Types) { 88 // Sanity check. GO must not be a function declaration. 89 assert(!isa<Function>(&GO) || !cast<Function>(&GO)->isDeclaration()); 90 91 if (ConstantInt *TypeId = extractNumericTypeId(Type)) 92 TypeIds.insert(TypeId->getZExtValue()); 93 } 94 } 95 96 NamedMDNode *CfiFunctionsMD = M.getNamedMetadata("cfi.functions"); 97 if (CfiFunctionsMD) { 98 for (auto Func : CfiFunctionsMD->operands()) { 99 assert(Func->getNumOperands() >= 2); 100 for (unsigned I = 2; I < Func->getNumOperands(); ++I) 101 if (ConstantInt *TypeId = 102 extractNumericTypeId(cast<MDNode>(Func->getOperand(I).get()))) 103 TypeIds.insert(TypeId->getZExtValue()); 104 } 105 } 106 107 LLVMContext &Ctx = M.getContext(); 108 FunctionCallee C = M.getOrInsertFunction( 109 "__cfi_check", Type::getVoidTy(Ctx), Type::getInt64Ty(Ctx), 110 Type::getInt8PtrTy(Ctx), Type::getInt8PtrTy(Ctx)); 111 Function *F = dyn_cast<Function>(C.getCallee()); 112 // Take over the existing function. The frontend emits a weak stub so that the 113 // linker knows about the symbol; this pass replaces the function body. 114 F->deleteBody(); 115 F->setAlignment(4096); 116 117 Triple T(M.getTargetTriple()); 118 if (T.isARM() || T.isThumb()) 119 F->addFnAttr("target-features", "+thumb-mode"); 120 121 auto args = F->arg_begin(); 122 Value &CallSiteTypeId = *(args++); 123 CallSiteTypeId.setName("CallSiteTypeId"); 124 Value &Addr = *(args++); 125 Addr.setName("Addr"); 126 Value &CFICheckFailData = *(args++); 127 CFICheckFailData.setName("CFICheckFailData"); 128 assert(args == F->arg_end()); 129 130 BasicBlock *BB = BasicBlock::Create(Ctx, "entry", F); 131 BasicBlock *ExitBB = BasicBlock::Create(Ctx, "exit", F); 132 133 BasicBlock *TrapBB = BasicBlock::Create(Ctx, "fail", F); 134 IRBuilder<> IRBFail(TrapBB); 135 FunctionCallee CFICheckFailFn = 136 M.getOrInsertFunction("__cfi_check_fail", Type::getVoidTy(Ctx), 137 Type::getInt8PtrTy(Ctx), Type::getInt8PtrTy(Ctx)); 138 IRBFail.CreateCall(CFICheckFailFn, {&CFICheckFailData, &Addr}); 139 IRBFail.CreateBr(ExitBB); 140 141 IRBuilder<> IRBExit(ExitBB); 142 IRBExit.CreateRetVoid(); 143 144 IRBuilder<> IRB(BB); 145 SwitchInst *SI = IRB.CreateSwitch(&CallSiteTypeId, TrapBB, TypeIds.size()); 146 for (uint64_t TypeId : TypeIds) { 147 ConstantInt *CaseTypeId = ConstantInt::get(Type::getInt64Ty(Ctx), TypeId); 148 BasicBlock *TestBB = BasicBlock::Create(Ctx, "test", F); 149 IRBuilder<> IRBTest(TestBB); 150 Function *BitsetTestFn = Intrinsic::getDeclaration(&M, Intrinsic::type_test); 151 152 Value *Test = IRBTest.CreateCall( 153 BitsetTestFn, {&Addr, MetadataAsValue::get( 154 Ctx, ConstantAsMetadata::get(CaseTypeId))}); 155 BranchInst *BI = IRBTest.CreateCondBr(Test, ExitBB, TrapBB); 156 BI->setMetadata(LLVMContext::MD_prof, VeryLikelyWeights); 157 158 SI->addCase(CaseTypeId, TestBB); 159 ++NumTypeIds; 160 } 161 } 162 163 bool CrossDSOCFI::runOnModule(Module &M) { 164 VeryLikelyWeights = 165 MDBuilder(M.getContext()).createBranchWeights((1U << 20) - 1, 1); 166 if (M.getModuleFlag("Cross-DSO CFI") == nullptr) 167 return false; 168 buildCFICheck(M); 169 return true; 170 } 171 172 PreservedAnalyses CrossDSOCFIPass::run(Module &M, ModuleAnalysisManager &AM) { 173 CrossDSOCFI Impl; 174 bool Changed = Impl.runOnModule(M); 175 if (!Changed) 176 return PreservedAnalyses::all(); 177 return PreservedAnalyses::none(); 178 } 179