llvm/lib/Target/X86/X86IndirectBranchTracking.cpp

   1 //===---- X86IndirectBranchTracking.cpp - Enables CET IBT mechanism -------===//
   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 file defines a pass that enables Indirect Branch Tracking (IBT) as part
  10 // of Control-Flow Enforcement Technology (CET).
  11 // The pass adds ENDBR (End Branch) machine instructions at the beginning of
  12 // each basic block or function that is referenced by an indrect jump/call
  13 // instruction.
  14 // The ENDBR instructions have a NOP encoding and as such are ignored in
  15 // targets that do not support CET IBT mechanism.
  16 //===----------------------------------------------------------------------===//
  17
  18 #include "X86.h"
  19 #include "X86InstrInfo.h"
  20 #include "X86Subtarget.h"
  21 #include "X86TargetMachine.h"
  22 #include "llvm/ADT/Statistic.h"
  23 #include "llvm/CodeGen/MachineFunctionPass.h"
  24 #include "llvm/CodeGen/MachineInstrBuilder.h"
  25 #include "llvm/CodeGen/MachineModuleInfo.h"
  26
  27 using namespace llvm;
  28
  29 #define DEBUG_TYPE "x86-indirect-branch-tracking"
  30
  31 cl::opt<bool> IndirectBranchTracking(
  32     "x86-indirect-branch-tracking", cl::init(false), cl::Hidden,
  33     cl::desc("Enable X86 indirect branch tracking pass."));
  34
  35 STATISTIC(NumEndBranchAdded, "Number of ENDBR instructions added");
  36
  37 namespace {
  38 class X86IndirectBranchTrackingPass : public MachineFunctionPass {
  39 public:
  40   X86IndirectBranchTrackingPass() : MachineFunctionPass(ID) {}
  41
  42   StringRef getPassName() const override {
  43     return "X86 Indirect Branch Tracking";
  44   }
  45
  46   bool runOnMachineFunction(MachineFunction &MF) override;
  47
  48 private:
  49   static char ID;
  50
  51   /// Machine instruction info used throughout the class.
  52   const X86InstrInfo *TII = nullptr;
  53
  54   /// Endbr opcode for the current machine function.
  55   unsigned int EndbrOpcode = 0;
  56
  57   /// Adds a new ENDBR instruction to the beginning of the MBB.
  58   /// The function will not add it if already exists.
  59   /// It will add ENDBR32 or ENDBR64 opcode, depending on the target.
  60   /// \returns true if the ENDBR was added and false otherwise.
  61   bool addENDBR(MachineBasicBlock &MBB, MachineBasicBlock::iterator I) const;
  62 };
  63
  64 } // end anonymous namespace
  65
  66 char X86IndirectBranchTrackingPass::ID = 0;
  67
  68 FunctionPass *llvm::createX86IndirectBranchTrackingPass() {
  69   return new X86IndirectBranchTrackingPass();
  70 }
  71
  72 bool X86IndirectBranchTrackingPass::addENDBR(
  73     MachineBasicBlock &MBB, MachineBasicBlock::iterator I) const {
  74   assert(TII && "Target instruction info was not initialized");
  75   assert((X86::ENDBR64 == EndbrOpcode || X86::ENDBR32 == EndbrOpcode) &&
  76          "Unexpected Endbr opcode");
  77
  78   // If the MBB/I is empty or the current instruction is not ENDBR,
  79   // insert ENDBR instruction to the location of I.
  80   if (I == MBB.end() || I->getOpcode() != EndbrOpcode) {
  81     BuildMI(MBB, I, MBB.findDebugLoc(I), TII->get(EndbrOpcode));
  82     ++NumEndBranchAdded;
  83     return true;
  84   }
  85   return false;
  86 }
  87
  88 static bool IsCallReturnTwice(llvm::MachineOperand &MOp) {
  89   if (!MOp.isGlobal())
  90     return false;
  91   auto *CalleeFn = dyn_cast<Function>(MOp.getGlobal());
  92   if (!CalleeFn)
  93     return false;
  94   AttributeList Attrs = CalleeFn->getAttributes();
  95   return Attrs.hasFnAttr(Attribute::ReturnsTwice);
  96 }
  97
  98 bool X86IndirectBranchTrackingPass::runOnMachineFunction(MachineFunction &MF) {
  99   const X86Subtarget &SubTarget = MF.getSubtarget<X86Subtarget>();
 100
 101   // Check that the cf-protection-branch is enabled.
 102   Metadata *isCFProtectionSupported =
 103       MF.getMMI().getModule()->getModuleFlag("cf-protection-branch");
 104   // NB: We need to enable IBT in jitted code if JIT compiler is CET
 105   // enabled.
 106   const X86TargetMachine *TM =
 107       static_cast<const X86TargetMachine *>(&MF.getTarget());
 108 #ifdef __CET__
 109   bool isJITwithCET = TM->isJIT();
 110 #else
 111   bool isJITwithCET = false;
 112 #endif
 113   if (!isCFProtectionSupported && !IndirectBranchTracking && !isJITwithCET)
 114     return false;
 115
 116   // True if the current MF was changed and false otherwise.
 117   bool Changed = false;
 118
 119   TII = SubTarget.getInstrInfo();
 120   EndbrOpcode = SubTarget.is64Bit() ? X86::ENDBR64 : X86::ENDBR32;
 121
 122   // Large code model, non-internal function or function whose address
 123   // was taken, can be accessed through indirect calls. Mark the first
 124   // BB with ENDBR instruction unless nocf_check attribute is used.
 125   if ((TM->getCodeModel() == CodeModel::Large ||
 126        MF.getFunction().hasAddressTaken() ||
 127        !MF.getFunction().hasLocalLinkage()) &&
 128       !MF.getFunction().doesNoCfCheck()) {
 129     auto MBB = MF.begin();
 130     Changed |= addENDBR(*MBB, MBB->begin());
 131   }
 132
 133   for (auto &MBB : MF) {
 134     // Find all basic blocks that their address was taken (for example
 135     // in the case of indirect jump) and add ENDBR instruction.
 136     if (MBB.hasAddressTaken())
 137       Changed |= addENDBR(MBB, MBB.begin());
 138
 139     for (MachineBasicBlock::iterator I = MBB.begin(); I != MBB.end(); ++I) {
 140       if (I->isCall() && IsCallReturnTwice(I->getOperand(0)))
 141         Changed |= addENDBR(MBB, std::next(I));
 142     }
 143
 144     // Exception handle may indirectly jump to catch pad, So we should add
 145     // ENDBR before catch pad instructions. For SjLj exception model, it will
 146     // create a new BB(new landingpad) indirectly jump to the old landingpad.
 147     if (TM->Options.ExceptionModel == ExceptionHandling::SjLj) {
 148       for (MachineBasicBlock::iterator I = MBB.begin(); I != MBB.end(); ++I) {
 149         // New Landingpad BB without EHLabel.
 150         if (MBB.isEHPad()) {
 151           if (I->isDebugInstr())
 152             continue;
 153           Changed |= addENDBR(MBB, I);
 154           break;
 155         } else if (I->isEHLabel()) {
 156           // Old Landingpad BB (is not Landingpad now) with
 157           // the the old "callee" EHLabel.
 158           MCSymbol *Sym = I->getOperand(0).getMCSymbol();
 159           if (!MF.hasCallSiteLandingPad(Sym))
 160             continue;
 161           Changed |= addENDBR(MBB, std::next(I));
 162           break;
 163         }
 164       }
 165     } else if (MBB.isEHPad()){
 166       for (MachineBasicBlock::iterator I = MBB.begin(); I != MBB.end(); ++I) {
 167         if (!I->isEHLabel())
 168           continue;
 169         Changed |= addENDBR(MBB, std::next(I));
 170         break;
 171       }
 172     }
 173   }
 174   return Changed;
 175 }