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//===---- AArch64KCFI.cpp - Implements KCFI -------------------------------===//
//
// 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
//
//===----------------------------------------------------------------------===//
//
// This file implements KCFI indirect call checking.
//
//===----------------------------------------------------------------------===//
#include "AArch64.h"
#include "AArch64InstrInfo.h"
#include "AArch64Subtarget.h"
#include "AArch64TargetMachine.h"
#include "llvm/ADT/Statistic.h"
#include "llvm/CodeGen/MachineFunctionPass.h"
#include "llvm/CodeGen/MachineInstrBuilder.h"
#include "llvm/CodeGen/MachineInstrBundle.h"
#include "llvm/CodeGen/MachineModuleInfo.h"
using namespace llvm;
#define DEBUG_TYPE "aarch64-kcfi"
#define AARCH64_KCFI_PASS_NAME "Insert KCFI indirect call checks"
STATISTIC(NumKCFIChecksAdded, "Number of indirect call checks added");
namespace {
class AArch64KCFI : public MachineFunctionPass {
public:
static char ID;
AArch64KCFI() : MachineFunctionPass(ID) {}
StringRef getPassName() const override { return AARCH64_KCFI_PASS_NAME; }
bool runOnMachineFunction(MachineFunction &MF) override;
private:
/// Machine instruction info used throughout the class.
const AArch64InstrInfo *TII = nullptr;
/// Emits a KCFI check before an indirect call.
/// \returns true if the check was added and false otherwise.
bool emitCheck(MachineBasicBlock &MBB,
MachineBasicBlock::instr_iterator I) const;
};
char AArch64KCFI::ID = 0;
} // end anonymous namespace
INITIALIZE_PASS(AArch64KCFI, DEBUG_TYPE, AARCH64_KCFI_PASS_NAME, false, false)
FunctionPass *llvm::createAArch64KCFIPass() { return new AArch64KCFI(); }
bool AArch64KCFI::emitCheck(MachineBasicBlock &MBB,
MachineBasicBlock::instr_iterator MBBI) const {
assert(TII && "Target instruction info was not initialized");
// If the call instruction is bundled, we can only emit a check safely if
// it's the first instruction in the bundle.
if (MBBI->isBundled() && !std::prev(MBBI)->isBundle())
report_fatal_error("Cannot emit a KCFI check for a bundled call");
switch (MBBI->getOpcode()) {
case AArch64::BLR:
case AArch64::BLRNoIP:
case AArch64::TCRETURNri:
case AArch64::TCRETURNriBTI:
break;
default:
llvm_unreachable("Unexpected CFI call opcode");
}
MachineOperand &Target = MBBI->getOperand(0);
assert(Target.isReg() && "Invalid target operand for an indirect call");
Target.setIsRenamable(false);
MachineInstr *Check =
BuildMI(MBB, MBBI, MBBI->getDebugLoc(), TII->get(AArch64::KCFI_CHECK))
.addReg(Target.getReg())
.addImm(MBBI->getCFIType())
.getInstr();
MBBI->setCFIType(*MBB.getParent(), 0);
// If not already bundled, bundle the check and the call to prevent
// further changes.
if (!MBBI->isBundled())
finalizeBundle(MBB, Check->getIterator(), std::next(MBBI->getIterator()));
++NumKCFIChecksAdded;
return true;
}
bool AArch64KCFI::runOnMachineFunction(MachineFunction &MF) {
const Module *M = MF.getMMI().getModule();
if (!M->getModuleFlag("kcfi"))
return false;
const auto &SubTarget = MF.getSubtarget<AArch64Subtarget>();
TII = SubTarget.getInstrInfo();
bool Changed = false;
for (MachineBasicBlock &MBB : MF) {
for (MachineBasicBlock::instr_iterator MII = MBB.instr_begin(),
MIE = MBB.instr_end();
MII != MIE; ++MII) {
if (MII->isCall() && MII->getCFIType())
Changed |= emitCheck(MBB, MII);
}
}
return Changed;
}
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