1 //===-- CrossDSOCFI.cpp - Externalize this module's CFI checks ------------===//
3 // The LLVM Compiler Infrastructure
5 // This file is distributed under the University of Illinois Open Source
6 // License. See LICENSE.TXT for details.
8 //===----------------------------------------------------------------------===//
10 // This pass exports all llvm.bitset's found in the module in the form of a
11 // __cfi_check function, which can be used to verify cross-DSO call targets.
13 //===----------------------------------------------------------------------===//
15 #include "llvm/Transforms/IPO/CrossDSOCFI.h"
16 #include "llvm/ADT/DenseSet.h"
17 #include "llvm/ADT/EquivalenceClasses.h"
18 #include "llvm/ADT/Statistic.h"
19 #include "llvm/IR/Constant.h"
20 #include "llvm/IR/Constants.h"
21 #include "llvm/IR/Function.h"
22 #include "llvm/IR/GlobalObject.h"
23 #include "llvm/IR/GlobalVariable.h"
24 #include "llvm/IR/IRBuilder.h"
25 #include "llvm/IR/Instructions.h"
26 #include "llvm/IR/Intrinsics.h"
27 #include "llvm/IR/MDBuilder.h"
28 #include "llvm/IR/Module.h"
29 #include "llvm/IR/Operator.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 #include "llvm/Transforms/Utils/BasicBlockUtils.h"
38 #define DEBUG_TYPE "cross-dso-cfi"
40 STATISTIC(NumTypeIds, "Number of unique type identifiers");
44 struct CrossDSOCFI : public ModulePass {
46 CrossDSOCFI() : ModulePass(ID) {
47 initializeCrossDSOCFIPass(*PassRegistry::getPassRegistry());
50 MDNode *VeryLikelyWeights;
52 ConstantInt *extractNumericTypeId(MDNode *MD);
53 void buildCFICheck(Module &M);
54 bool runOnModule(Module &M) override;
57 } // anonymous namespace
59 INITIALIZE_PASS_BEGIN(CrossDSOCFI, "cross-dso-cfi", "Cross-DSO CFI", false,
61 INITIALIZE_PASS_END(CrossDSOCFI, "cross-dso-cfi", "Cross-DSO CFI", false, false)
62 char CrossDSOCFI::ID = 0;
64 ModulePass *llvm::createCrossDSOCFIPass() { return new CrossDSOCFI; }
66 /// Extracts a numeric type identifier from an MDNode containing type metadata.
67 ConstantInt *CrossDSOCFI::extractNumericTypeId(MDNode *MD) {
68 // This check excludes vtables for classes inside anonymous namespaces.
69 auto TM = dyn_cast<ValueAsMetadata>(MD->getOperand(1));
72 auto C = dyn_cast_or_null<ConstantInt>(TM->getValue());
73 if (!C) return nullptr;
74 // We are looking for i64 constants.
75 if (C->getBitWidth() != 64) return nullptr;
80 /// buildCFICheck - emits __cfi_check for the current module.
81 void CrossDSOCFI::buildCFICheck(Module &M) {
82 // FIXME: verify that __cfi_check ends up near the end of the code section,
83 // but before the jump slots created in LowerTypeTests.
84 llvm::DenseSet<uint64_t> TypeIds;
85 SmallVector<MDNode *, 2> Types;
86 for (GlobalObject &GO : M.global_objects()) {
88 GO.getMetadata(LLVMContext::MD_type, Types);
89 for (MDNode *Type : Types) {
90 // Sanity check. GO must not be a function declaration.
91 assert(!isa<Function>(&GO) || !cast<Function>(&GO)->isDeclaration());
93 if (ConstantInt *TypeId = extractNumericTypeId(Type))
94 TypeIds.insert(TypeId->getZExtValue());
98 NamedMDNode *CfiFunctionsMD = M.getNamedMetadata("cfi.functions");
100 for (auto Func : CfiFunctionsMD->operands()) {
101 assert(Func->getNumOperands() >= 2);
102 for (unsigned I = 2; I < Func->getNumOperands(); ++I)
103 if (ConstantInt *TypeId =
104 extractNumericTypeId(cast<MDNode>(Func->getOperand(I).get())))
105 TypeIds.insert(TypeId->getZExtValue());
109 LLVMContext &Ctx = M.getContext();
110 Constant *C = M.getOrInsertFunction(
111 "__cfi_check", Type::getVoidTy(Ctx), Type::getInt64Ty(Ctx),
112 Type::getInt8PtrTy(Ctx), Type::getInt8PtrTy(Ctx));
113 Function *F = dyn_cast<Function>(C);
114 // Take over the existing function. The frontend emits a weak stub so that the
115 // linker knows about the symbol; this pass replaces the function body.
117 F->setAlignment(4096);
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());
127 BasicBlock *BB = BasicBlock::Create(Ctx, "entry", F);
128 BasicBlock *ExitBB = BasicBlock::Create(Ctx, "exit", F);
130 BasicBlock *TrapBB = BasicBlock::Create(Ctx, "fail", F);
131 IRBuilder<> IRBFail(TrapBB);
132 Constant *CFICheckFailFn = M.getOrInsertFunction(
133 "__cfi_check_fail", Type::getVoidTy(Ctx), Type::getInt8PtrTy(Ctx),
134 Type::getInt8PtrTy(Ctx));
135 IRBFail.CreateCall(CFICheckFailFn, {&CFICheckFailData, &Addr});
136 IRBFail.CreateBr(ExitBB);
138 IRBuilder<> IRBExit(ExitBB);
139 IRBExit.CreateRetVoid();
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);
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);
155 SI->addCase(CaseTypeId, TestBB);
160 bool CrossDSOCFI::runOnModule(Module &M) {
165 MDBuilder(M.getContext()).createBranchWeights((1U << 20) - 1, 1);
166 if (M.getModuleFlag("Cross-DSO CFI") == nullptr)
172 PreservedAnalyses CrossDSOCFIPass::run(Module &M, ModuleAnalysisManager &AM) {
174 bool Changed = Impl.runOnModule(M);
176 return PreservedAnalyses::all();
177 return PreservedAnalyses::none();