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;
CrossDSOCFI__anon8cdb5fbe0111::CrossDSOCFI40 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
createCrossDSOCFIPass()58 ModulePass *llvm::createCrossDSOCFIPass() { return new CrossDSOCFI; }
59
60 /// Extracts a numeric type identifier from an MDNode containing type metadata.
extractNumericTypeId(MDNode * MD)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.
buildCFICheck(Module & M)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
runOnModule(Module & M)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
run(Module & M,ModuleAnalysisManager & AM)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