122 lines · cpp
1//===-- CFGuardLongjmp.cpp - Longjmp symbols for CFGuard --------*- C++ -*-===//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-exception6//7//===----------------------------------------------------------------------===//8///9/// \file10/// This file contains a machine function pass to insert a symbol after each11/// call to _setjmp and store this in the MachineFunction's LongjmpTargets12/// vector. This will be used to emit the table of valid longjmp targets used13/// by Control Flow Guard.14///15//===----------------------------------------------------------------------===//16 17#include "llvm/ADT/Statistic.h"18#include "llvm/CodeGen/MachineBasicBlock.h"19#include "llvm/CodeGen/MachineFunctionPass.h"20#include "llvm/CodeGen/MachineInstr.h"21#include "llvm/CodeGen/MachineModuleInfo.h"22#include "llvm/CodeGen/MachineOperand.h"23#include "llvm/CodeGen/Passes.h"24#include "llvm/IR/Module.h"25#include "llvm/InitializePasses.h"26 27using namespace llvm;28 29#define DEBUG_TYPE "cfguard-longjmp"30 31STATISTIC(CFGuardLongjmpTargets,32 "Number of Control Flow Guard longjmp targets");33 34namespace {35 36/// MachineFunction pass to insert a symbol after each call to _setjmp and store37/// this in the MachineFunction's LongjmpTargets vector.38class CFGuardLongjmp : public MachineFunctionPass {39public:40 static char ID;41 42 CFGuardLongjmp() : MachineFunctionPass(ID) {43 initializeCFGuardLongjmpPass(*PassRegistry::getPassRegistry());44 }45 46 StringRef getPassName() const override {47 return "Control Flow Guard longjmp targets";48 }49 50 bool runOnMachineFunction(MachineFunction &MF) override;51};52 53} // end anonymous namespace54 55char CFGuardLongjmp::ID = 0;56 57INITIALIZE_PASS(CFGuardLongjmp, "CFGuardLongjmp",58 "Insert symbols at valid longjmp targets for /guard:cf", false,59 false)60FunctionPass *llvm::createCFGuardLongjmpPass() { return new CFGuardLongjmp(); }61 62bool CFGuardLongjmp::runOnMachineFunction(MachineFunction &MF) {63 64 // Skip modules for which the cfguard flag is not set.65 if (!MF.getFunction().getParent()->getModuleFlag("cfguard"))66 return false;67 68 // Skip functions that do not have calls to _setjmp.69 if (!MF.getFunction().callsFunctionThatReturnsTwice())70 return false;71 72 SmallVector<MachineInstr *, 8> SetjmpCalls;73 74 // Iterate over all instructions in the function and add calls to functions75 // that return twice to the list of targets.76 for (MachineBasicBlock &MBB : MF) {77 for (MachineInstr &MI : MBB) {78 79 // Skip instructions that are not calls.80 if (!MI.isCall() || MI.getNumOperands() < 1)81 continue;82 83 // Iterate over operands to find calls to global functions.84 for (MachineOperand &MO : MI.operands()) {85 if (!MO.isGlobal())86 continue;87 88 auto *F = dyn_cast<Function>(MO.getGlobal());89 if (!F)90 continue;91 92 // If the instruction calls a function that returns twice, add93 // it to the list of targets.94 if (F->hasFnAttribute(Attribute::ReturnsTwice)) {95 SetjmpCalls.push_back(&MI);96 break;97 }98 }99 }100 }101 102 if (SetjmpCalls.empty())103 return false;104 105 unsigned SetjmpNum = 0;106 107 // For each possible target, create a new symbol and insert it immediately108 // after the call to setjmp. Add this symbol to the MachineFunction's list109 // of longjmp targets.110 for (MachineInstr *Setjmp : SetjmpCalls) {111 SmallString<128> SymbolName;112 raw_svector_ostream(SymbolName) << "$cfgsj_" << MF.getName() << SetjmpNum++;113 MCSymbol *SjSymbol = MF.getContext().getOrCreateSymbol(SymbolName);114 115 Setjmp->setPostInstrSymbol(MF, SjSymbol);116 MF.addLongjmpTarget(SjSymbol);117 CFGuardLongjmpTargets++;118 }119 120 return true;121}122