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121 lines
4.1 KiB
C++
121 lines
4.1 KiB
C++
//===---- X86IndirectBranchTracking.cpp - Enables CET IBT mechanism -------===//
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//
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// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
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// See https://llvm.org/LICENSE.txt for license information.
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// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
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//
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//===----------------------------------------------------------------------===//
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//
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// This file defines a pass that enables Indirect Branch Tracking (IBT) as part
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// of Control-Flow Enforcement Technology (CET).
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// The pass adds ENDBR (End Branch) machine instructions at the beginning of
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// each basic block or function that is referenced by an indrect jump/call
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// instruction.
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// The ENDBR instructions have a NOP encoding and as such are ignored in
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// targets that do not support CET IBT mechanism.
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//===----------------------------------------------------------------------===//
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#include "X86.h"
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#include "X86InstrInfo.h"
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#include "X86Subtarget.h"
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#include "llvm/ADT/Statistic.h"
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#include "llvm/CodeGen/MachineFunctionPass.h"
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#include "llvm/CodeGen/MachineInstrBuilder.h"
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#include "llvm/CodeGen/MachineModuleInfo.h"
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using namespace llvm;
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#define DEBUG_TYPE "x86-indirect-branch-tracking"
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static cl::opt<bool> IndirectBranchTracking(
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"x86-indirect-branch-tracking", cl::init(false), cl::Hidden,
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cl::desc("Enable X86 indirect branch tracking pass."));
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STATISTIC(NumEndBranchAdded, "Number of ENDBR instructions added");
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namespace {
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class X86IndirectBranchTrackingPass : public MachineFunctionPass {
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public:
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X86IndirectBranchTrackingPass() : MachineFunctionPass(ID) {}
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StringRef getPassName() const override {
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return "X86 Indirect Branch Tracking";
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}
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bool runOnMachineFunction(MachineFunction &MF) override;
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private:
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static char ID;
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/// Machine instruction info used throughout the class.
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const X86InstrInfo *TII;
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/// Endbr opcode for the current machine function.
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unsigned int EndbrOpcode;
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/// Adds a new ENDBR instruction to the begining of the MBB.
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/// The function will not add it if already exists.
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/// It will add ENDBR32 or ENDBR64 opcode, depending on the target.
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/// \returns true if the ENDBR was added and false otherwise.
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bool addENDBR(MachineBasicBlock &MBB) const;
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};
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} // end anonymous namespace
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char X86IndirectBranchTrackingPass::ID = 0;
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FunctionPass *llvm::createX86IndirectBranchTrackingPass() {
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return new X86IndirectBranchTrackingPass();
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}
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bool X86IndirectBranchTrackingPass::addENDBR(MachineBasicBlock &MBB) const {
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assert(TII && "Target instruction info was not initialized");
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assert((X86::ENDBR64 == EndbrOpcode || X86::ENDBR32 == EndbrOpcode) &&
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"Unexpected Endbr opcode");
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auto MI = MBB.begin();
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// If the MBB is empty or the first instruction is not ENDBR,
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// add the ENDBR instruction to the beginning of the MBB.
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if (MI == MBB.end() || EndbrOpcode != MI->getOpcode()) {
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BuildMI(MBB, MI, MBB.findDebugLoc(MI), TII->get(EndbrOpcode));
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NumEndBranchAdded++;
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return true;
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}
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return false;
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}
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bool X86IndirectBranchTrackingPass::runOnMachineFunction(MachineFunction &MF) {
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const X86Subtarget &SubTarget = MF.getSubtarget<X86Subtarget>();
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// Check that the cf-protection-branch is enabled.
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Metadata *isCFProtectionSupported =
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MF.getMMI().getModule()->getModuleFlag("cf-protection-branch");
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if (!isCFProtectionSupported && !IndirectBranchTracking)
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return false;
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// True if the current MF was changed and false otherwise.
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bool Changed = false;
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TII = SubTarget.getInstrInfo();
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EndbrOpcode = SubTarget.is64Bit() ? X86::ENDBR64 : X86::ENDBR32;
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// Non-internal function or function whose address was taken, can be
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// accessed through indirect calls. Mark the first BB with ENDBR instruction
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// unless nocf_check attribute is used.
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if ((MF.getFunction().hasAddressTaken() ||
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!MF.getFunction().hasLocalLinkage()) &&
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!MF.getFunction().doesNoCfCheck()) {
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auto MBB = MF.begin();
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Changed |= addENDBR(*MBB);
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}
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for (auto &MBB : MF)
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// Find all basic blocks that their address was taken (for example
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// in the case of indirect jump) and add ENDBR instruction.
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if (MBB.hasAddressTaken())
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Changed |= addENDBR(MBB);
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return Changed;
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}
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