llvm/lib/Transforms/IPO/CrossDSOCFI.cpp

   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/InitializePasses.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
  35 using namespace llvm;
  36
  37 #define DEBUG_TYPE "cross-dso-cfi"
  38
  39 STATISTIC(NumTypeIds, "Number of unique type identifiers");
  40
  41 namespace {
  42
  43 struct CrossDSOCFI : public ModulePass {
  44   static char ID;
  45   CrossDSOCFI() : ModulePass(ID) {
  46     initializeCrossDSOCFIPass(*PassRegistry::getPassRegistry());
  47   }
  48
  49   MDNode *VeryLikelyWeights;
  50
  51   ConstantInt *extractNumericTypeId(MDNode *MD);
  52   void buildCFICheck(Module &M);
  53   bool runOnModule(Module &M) override;
  54 };
  55
  56 } // anonymous namespace
  57
  58 INITIALIZE_PASS_BEGIN(CrossDSOCFI, "cross-dso-cfi", "Cross-DSO CFI", false,
  59                       false)
  60 INITIALIZE_PASS_END(CrossDSOCFI, "cross-dso-cfi", "Cross-DSO CFI", false, false)
  61 char CrossDSOCFI::ID = 0;
  62
  63 ModulePass *llvm::createCrossDSOCFIPass() { return new CrossDSOCFI; }
  64
  65 /// Extracts a numeric type identifier from an MDNode containing type metadata.
  66 ConstantInt *CrossDSOCFI::extractNumericTypeId(MDNode *MD) {
  67   // This check excludes vtables for classes inside anonymous namespaces.
  68   auto TM = dyn_cast<ValueAsMetadata>(MD->getOperand(1));
  69   if (!TM)
  70     return nullptr;
  71   auto C = dyn_cast_or_null<ConstantInt>(TM->getValue());
  72   if (!C) return nullptr;
  73   // We are looking for i64 constants.
  74   if (C->getBitWidth() != 64) return nullptr;
  75
  76   return C;
  77 }
  78
  79 /// buildCFICheck - emits __cfi_check for the current module.
  80 void CrossDSOCFI::buildCFICheck(Module &M) {
  81   // FIXME: verify that __cfi_check ends up near the end of the code section,
  82   // but before the jump slots created in LowerTypeTests.
  83   SetVector<uint64_t> TypeIds;
  84   SmallVector<MDNode *, 2> Types;
  85   for (GlobalObject &GO : M.global_objects()) {
  86     Types.clear();
  87     GO.getMetadata(LLVMContext::MD_type, Types);
  88     for (MDNode *Type : Types)
  89       if (ConstantInt *TypeId = extractNumericTypeId(Type))
  90         TypeIds.insert(TypeId->getZExtValue());
  91   }
  92
  93   NamedMDNode *CfiFunctionsMD = M.getNamedMetadata("cfi.functions");
  94   if (CfiFunctionsMD) {
  95     for (auto Func : CfiFunctionsMD->operands()) {
  96       assert(Func->getNumOperands() >= 2);
  97       for (unsigned I = 2; I < Func->getNumOperands(); ++I)
  98         if (ConstantInt *TypeId =
  99                 extractNumericTypeId(cast<MDNode>(Func->getOperand(I).get())))
 100           TypeIds.insert(TypeId->getZExtValue());
 101     }
 102   }
 103
 104   LLVMContext &Ctx = M.getContext();
 105   FunctionCallee C = M.getOrInsertFunction(
 106       "__cfi_check", Type::getVoidTy(Ctx), Type::getInt64Ty(Ctx),
 107       Type::getInt8PtrTy(Ctx), Type::getInt8PtrTy(Ctx));
 108   Function *F = cast<Function>(C.getCallee());
 109   // Take over the existing function. The frontend emits a weak stub so that the
 110   // linker knows about the symbol; this pass replaces the function body.
 111   F->deleteBody();
 112   F->setAlignment(Align(4096));
 113
 114   Triple T(M.getTargetTriple());
 115   if (T.isARM() || T.isThumb())
 116     F->addFnAttr("target-features", "+thumb-mode");
 117
 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());
 126
 127   BasicBlock *BB = BasicBlock::Create(Ctx, "entry", F);
 128   BasicBlock *ExitBB = BasicBlock::Create(Ctx, "exit", F);
 129
 130   BasicBlock *TrapBB = BasicBlock::Create(Ctx, "fail", F);
 131   IRBuilder<> IRBFail(TrapBB);
 132   FunctionCallee CFICheckFailFn =
 133       M.getOrInsertFunction("__cfi_check_fail", Type::getVoidTy(Ctx),
 134                             Type::getInt8PtrTy(Ctx), Type::getInt8PtrTy(Ctx));
 135   IRBFail.CreateCall(CFICheckFailFn, {&CFICheckFailData, &Addr});
 136   IRBFail.CreateBr(ExitBB);
 137
 138   IRBuilder<> IRBExit(ExitBB);
 139   IRBExit.CreateRetVoid();
 140
 141   IRBuilder<> IRB(BB);
 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);
 148
 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);
 154
 155     SI->addCase(CaseTypeId, TestBB);
 156     ++NumTypeIds;
 157   }
 158 }
 159
 160 bool CrossDSOCFI::runOnModule(Module &M) {
 161   VeryLikelyWeights =
 162     MDBuilder(M.getContext()).createBranchWeights((1U << 20) - 1, 1);
 163   if (M.getModuleFlag("Cross-DSO CFI") == nullptr)
 164     return false;
 165   buildCFICheck(M);
 166   return true;
 167 }
 168
 169 PreservedAnalyses CrossDSOCFIPass::run(Module &M, ModuleAnalysisManager &AM) {
 170   CrossDSOCFI Impl;
 171   bool Changed = Impl.runOnModule(M);
 172   if (!Changed)
 173     return PreservedAnalyses::all();
 174   return PreservedAnalyses::none();
 175 }