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/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 }