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//===-- CFGuardLongjmp.cpp - Longjmp symbols for CFGuard --------*- C++ -*-===//
//
// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
// See https://llvm.org/LICENSE.txt for license information.
// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
//
//===----------------------------------------------------------------------===//
///
/// \file
/// This file contains a machine function pass to insert a symbol after each
/// call to _setjmp and store this in the MachineFunction's LongjmpTargets
/// vector. This will be used to emit the table of valid longjmp targets used
/// by Control Flow Guard.
///
//===----------------------------------------------------------------------===//
#include "llvm/ADT/Statistic.h"
#include "llvm/CodeGen/MachineBasicBlock.h"
#include "llvm/CodeGen/MachineFunctionPass.h"
#include "llvm/CodeGen/MachineInstr.h"
#include "llvm/CodeGen/MachineModuleInfo.h"
#include "llvm/CodeGen/MachineOperand.h"
#include "llvm/CodeGen/Passes.h"
#include "llvm/InitializePasses.h"
using namespace llvm;
#define DEBUG_TYPE "cfguard-longjmp"
STATISTIC(CFGuardLongjmpTargets,
"Number of Control Flow Guard longjmp targets");
namespace {
/// MachineFunction pass to insert a symbol after each call to _setjmp and store
/// this in the MachineFunction's LongjmpTargets vector.
class CFGuardLongjmp : public MachineFunctionPass {
public:
static char ID;
CFGuardLongjmp() : MachineFunctionPass(ID) {
initializeCFGuardLongjmpPass(*PassRegistry::getPassRegistry());
}
StringRef getPassName() const override {
return "Control Flow Guard longjmp targets";
}
bool runOnMachineFunction(MachineFunction &MF) override;
};
} // end anonymous namespace
char CFGuardLongjmp::ID = 0;
INITIALIZE_PASS(CFGuardLongjmp, "CFGuardLongjmp",
"Insert symbols at valid longjmp targets for /guard:cf", false,
false)
FunctionPass *llvm::createCFGuardLongjmpPass() { return new CFGuardLongjmp(); }
bool CFGuardLongjmp::runOnMachineFunction(MachineFunction &MF) {
// Skip modules for which the cfguard flag is not set.
if (!MF.getMMI().getModule()->getModuleFlag("cfguard"))
return false;
// Skip functions that do not have calls to _setjmp.
if (!MF.getFunction().callsFunctionThatReturnsTwice())
return false;
SmallVector<MachineInstr *, 8> SetjmpCalls;
// Iterate over all instructions in the function and add calls to functions
// that return twice to the list of targets.
for (MachineBasicBlock &MBB : MF) {
for (MachineInstr &MI : MBB) {
// Skip instructions that are not calls.
if (!MI.isCall() || MI.getNumOperands() < 1)
continue;
// Iterate over operands to find calls to global functions.
for (MachineOperand &MO : MI.operands()) {
if (!MO.isGlobal())
continue;
auto *F = dyn_cast<Function>(MO.getGlobal());
if (!F)
continue;
// If the instruction calls a function that returns twice, add
// it to the list of targets.
if (F->hasFnAttribute(Attribute::ReturnsTwice)) {
SetjmpCalls.push_back(&MI);
break;
}
}
}
}
if (SetjmpCalls.empty())
return false;
unsigned SetjmpNum = 0;
// For each possible target, create a new symbol and insert it immediately
// after the call to setjmp. Add this symbol to the MachineFunction's list
// of longjmp targets.
for (MachineInstr *Setjmp : SetjmpCalls) {
SmallString<128> SymbolName;
raw_svector_ostream(SymbolName) << "$cfgsj_" << MF.getName() << SetjmpNum++;
MCSymbol *SjSymbol = MF.getContext().getOrCreateSymbol(SymbolName);
Setjmp->setPostInstrSymbol(MF, SjSymbol);
MF.addLongjmpTarget(SjSymbol);
CFGuardLongjmpTargets++;
}
return true;
}
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