1 //===-- CrossDSOCFI.cpp - Externalize this module's CFI checks ------------===//
2 //
3 // The LLVM Compiler Infrastructure
4 //
5 // This file is distributed under the University of Illinois Open Source
6 // License. See LICENSE.TXT for details.
7 //
8 //===----------------------------------------------------------------------===//
9 //
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.
12 //
13 //===----------------------------------------------------------------------===//
14
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"
35
36 using namespace llvm;
37
38 #define DEBUG_TYPE "cross-dso-cfi"
39
40 STATISTIC(NumTypeIds, "Number of unique type identifiers");
41
42 namespace {
43
44 struct CrossDSOCFI : public ModulePass {
45 static char ID;
CrossDSOCFI__anon7f7616920111::CrossDSOCFI46 CrossDSOCFI() : ModulePass(ID) {
47 initializeCrossDSOCFIPass(*PassRegistry::getPassRegistry());
48 }
49
50 MDNode *VeryLikelyWeights;
51
52 ConstantInt *extractNumericTypeId(MDNode *MD);
53 void buildCFICheck(Module &M);
54 bool runOnModule(Module &M) override;
55 };
56
57 } // anonymous namespace
58
59 INITIALIZE_PASS_BEGIN(CrossDSOCFI, "cross-dso-cfi", "Cross-DSO CFI", false,
60 false)
61 INITIALIZE_PASS_END(CrossDSOCFI, "cross-dso-cfi", "Cross-DSO CFI", false, false)
62 char CrossDSOCFI::ID = 0;
63
createCrossDSOCFIPass()64 ModulePass *llvm::createCrossDSOCFIPass() { return new CrossDSOCFI; }
65
66 /// Extracts a numeric type identifier from an MDNode containing type metadata.
extractNumericTypeId(MDNode * MD)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));
70 if (!TM)
71 return nullptr;
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;
76
77 return C;
78 }
79
80 /// buildCFICheck - emits __cfi_check for the current module.
buildCFICheck(Module & M)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()) {
87 Types.clear();
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());
92
93 if (ConstantInt *TypeId = extractNumericTypeId(Type))
94 TypeIds.insert(TypeId->getZExtValue());
95 }
96 }
97
98 LLVMContext &Ctx = M.getContext();
99 Constant *C = M.getOrInsertFunction(
100 "__cfi_check", Type::getVoidTy(Ctx), Type::getInt64Ty(Ctx),
101 Type::getInt8PtrTy(Ctx), Type::getInt8PtrTy(Ctx), nullptr);
102 Function *F = dyn_cast<Function>(C);
103 F->setAlignment(4096);
104 auto args = F->arg_begin();
105 Value &CallSiteTypeId = *(args++);
106 CallSiteTypeId.setName("CallSiteTypeId");
107 Value &Addr = *(args++);
108 Addr.setName("Addr");
109 Value &CFICheckFailData = *(args++);
110 CFICheckFailData.setName("CFICheckFailData");
111 assert(args == F->arg_end());
112
113 BasicBlock *BB = BasicBlock::Create(Ctx, "entry", F);
114 BasicBlock *ExitBB = BasicBlock::Create(Ctx, "exit", F);
115
116 BasicBlock *TrapBB = BasicBlock::Create(Ctx, "fail", F);
117 IRBuilder<> IRBFail(TrapBB);
118 Constant *CFICheckFailFn = M.getOrInsertFunction(
119 "__cfi_check_fail", Type::getVoidTy(Ctx), Type::getInt8PtrTy(Ctx),
120 Type::getInt8PtrTy(Ctx), nullptr);
121 IRBFail.CreateCall(CFICheckFailFn, {&CFICheckFailData, &Addr});
122 IRBFail.CreateBr(ExitBB);
123
124 IRBuilder<> IRBExit(ExitBB);
125 IRBExit.CreateRetVoid();
126
127 IRBuilder<> IRB(BB);
128 SwitchInst *SI = IRB.CreateSwitch(&CallSiteTypeId, TrapBB, TypeIds.size());
129 for (uint64_t TypeId : TypeIds) {
130 ConstantInt *CaseTypeId = ConstantInt::get(Type::getInt64Ty(Ctx), TypeId);
131 BasicBlock *TestBB = BasicBlock::Create(Ctx, "test", F);
132 IRBuilder<> IRBTest(TestBB);
133 Function *BitsetTestFn = Intrinsic::getDeclaration(&M, Intrinsic::type_test);
134
135 Value *Test = IRBTest.CreateCall(
136 BitsetTestFn, {&Addr, MetadataAsValue::get(
137 Ctx, ConstantAsMetadata::get(CaseTypeId))});
138 BranchInst *BI = IRBTest.CreateCondBr(Test, ExitBB, TrapBB);
139 BI->setMetadata(LLVMContext::MD_prof, VeryLikelyWeights);
140
141 SI->addCase(CaseTypeId, TestBB);
142 ++NumTypeIds;
143 }
144 }
145
runOnModule(Module & M)146 bool CrossDSOCFI::runOnModule(Module &M) {
147 if (skipModule(M))
148 return false;
149
150 VeryLikelyWeights =
151 MDBuilder(M.getContext()).createBranchWeights((1U << 20) - 1, 1);
152 if (M.getModuleFlag("Cross-DSO CFI") == nullptr)
153 return false;
154 buildCFICheck(M);
155 return true;
156 }
157
run(Module & M,AnalysisManager<Module> & AM)158 PreservedAnalyses CrossDSOCFIPass::run(Module &M, AnalysisManager<Module> &AM) {
159 CrossDSOCFI Impl;
160 bool Changed = Impl.runOnModule(M);
161 if (!Changed)
162 return PreservedAnalyses::all();
163 return PreservedAnalyses::none();
164 }
165