1 //===---- X86IndirectBranchTracking.cpp - Enables CET IBT mechanism -------===//
3 // The LLVM Compiler Infrastructure
5 // This file is distributed under the University of Illinois Open Source
6 // License. See LICENSE.TXT for details.
8 //===----------------------------------------------------------------------===//
10 // This file defines a pass that enables Indirect Branch Tracking (IBT) as part
11 // of Control-Flow Enforcement Technology (CET).
12 // The pass adds ENDBR (End Branch) machine instructions at the beginning of
13 // each basic block or function that is referenced by an indrect jump/call
15 // The ENDBR instructions have a NOP encoding and as such are ignored in
16 // targets that do not support CET IBT mechanism.
17 //===----------------------------------------------------------------------===//
20 #include "X86InstrInfo.h"
21 #include "X86Subtarget.h"
22 #include "llvm/ADT/Statistic.h"
23 #include "llvm/CodeGen/MachineFunctionPass.h"
24 #include "llvm/CodeGen/MachineInstrBuilder.h"
25 #include "llvm/CodeGen/MachineJumpTableInfo.h"
26 #include "llvm/CodeGen/MachineModuleInfo.h"
30 #define DEBUG_TYPE "x86-indirect-branch-tracking"
32 static cl::opt<bool> IndirectBranchTracking(
33 "x86-indirect-branch-tracking", cl::init(false), cl::Hidden,
34 cl::desc("Enable X86 indirect branch tracking pass."));
36 STATISTIC(NumEndBranchAdded, "Number of ENDBR instructions added");
39 class X86IndirectBranchTrackingPass : public MachineFunctionPass {
41 X86IndirectBranchTrackingPass() : MachineFunctionPass(ID) {}
43 StringRef getPassName() const override {
44 return "X86 Indirect Branch Tracking";
47 bool runOnMachineFunction(MachineFunction &MF) override;
52 /// Machine instruction info used throughout the class.
53 const X86InstrInfo *TII;
55 /// Endbr opcode for the current machine function.
56 unsigned int EndbrOpcode;
58 /// Adds a new ENDBR instruction to the begining of the MBB.
59 /// The function will not add it if already exists.
60 /// It will add ENDBR32 or ENDBR64 opcode, depending on the target.
61 void addENDBR(MachineBasicBlock &MBB) const;
64 } // end anonymous namespace
66 char X86IndirectBranchTrackingPass::ID = 0;
68 FunctionPass *llvm::createX86IndirectBranchTrackingPass() {
69 return new X86IndirectBranchTrackingPass();
72 void X86IndirectBranchTrackingPass::addENDBR(MachineBasicBlock &MBB) const {
73 assert(TII && "Target instruction info was not initialized");
74 assert((X86::ENDBR64 == EndbrOpcode || X86::ENDBR32 == EndbrOpcode) &&
75 "Unexpected Endbr opcode");
77 auto MI = MBB.begin();
78 // If the MBB is empty or the first instruction is not ENDBR,
79 // add the ENDBR instruction to the beginning of the MBB.
80 if (MI == MBB.end() || EndbrOpcode != MI->getOpcode()) {
81 BuildMI(MBB, MI, MBB.findDebugLoc(MI), TII->get(EndbrOpcode));
86 bool X86IndirectBranchTrackingPass::runOnMachineFunction(MachineFunction &MF) {
87 const X86Subtarget &SubTarget = MF.getSubtarget<X86Subtarget>();
89 // Make sure that the target supports ENDBR instruction.
90 if (!SubTarget.hasIBT())
93 // Check that the cf-protection-branch is enabled.
94 Metadata *isCFProtectionSupported =
95 MF.getMMI().getModule()->getModuleFlag("cf-protection-branch");
96 if (!isCFProtectionSupported && !IndirectBranchTracking)
99 // True if the current MF was changed and false otherwise.
100 bool Changed = false;
102 TII = SubTarget.getInstrInfo();
103 EndbrOpcode = SubTarget.is64Bit() ? X86::ENDBR64 : X86::ENDBR32;
105 // Non-internal function or function whose address was taken, can be
106 // invoked through indirect calls. Mark the first BB with ENDBR instruction.
107 // TODO: Do not add ENDBR instruction in case notrack attribute is used.
108 if (MF.getFunction().hasAddressTaken() ||
109 !MF.getFunction().hasLocalLinkage()) {
110 auto MBB = MF.begin();
115 for (auto &MBB : MF) {
116 // Find all basic blocks that thier address was taken (for example
117 // in the case of indirect jump) and add ENDBR instruction.
118 if (MBB.hasAddressTaken()) {
124 // Adds ENDBR instructions to MBB destinations of the jump table.
125 // TODO: In case of more than 50 destinations, do not add ENDBR and
126 // instead add DS_PREFIX.
127 if (MachineJumpTableInfo *JTI = MF.getJumpTableInfo()) {
128 for (const auto &JT : JTI->getJumpTables()) {
129 for (auto *MBB : JT.MBBs) {
130 // This assert verifies the assumption that this MBB has an indirect
131 // jump terminator in one of its predecessor.
132 // Jump tables are generated when lowering switch-case statements or
133 // setjmp/longjump functions. As a result only indirect jumps use jump
136 bool hasIndirectJumpTerm = false;
137 for (auto &PredMBB : MBB->predecessors())
138 for (auto &TermI : PredMBB->terminators())
139 if (TermI.isIndirectBranch())
140 hasIndirectJumpTerm = true;
141 assert(hasIndirectJumpTerm &&
142 "The MBB is not the destination of an indirect jump");
143 (void)hasIndirectJumpTerm;