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