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112 lines
3.8 KiB
C++
112 lines
3.8 KiB
C++
//===---- KCFI.cpp - Implements Kernel Control-Flow Integrity (KCFI) ------===//
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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 pass implements Kernel Control-Flow Integrity (KCFI) indirect call
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// check lowering. For each call instruction with a cfi-type attribute, it
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// emits an arch-specific check before the call, and bundles the check and
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// the call to prevent unintentional modifications.
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//
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//===----------------------------------------------------------------------===//
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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/MachineInstrBundle.h"
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#include "llvm/CodeGen/MachineModuleInfo.h"
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#include "llvm/CodeGen/TargetInstrInfo.h"
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#include "llvm/CodeGen/TargetLowering.h"
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#include "llvm/CodeGen/TargetSubtargetInfo.h"
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#include "llvm/InitializePasses.h"
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using namespace llvm;
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#define DEBUG_TYPE "kcfi"
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#define KCFI_PASS_NAME "Insert KCFI indirect call checks"
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STATISTIC(NumKCFIChecksAdded, "Number of indirect call checks added");
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namespace {
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class KCFI : public MachineFunctionPass {
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public:
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static char ID;
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KCFI() : MachineFunctionPass(ID) {}
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StringRef getPassName() const override { return KCFI_PASS_NAME; }
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bool runOnMachineFunction(MachineFunction &MF) override;
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private:
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/// Machine instruction info used throughout the class.
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const TargetInstrInfo *TII = nullptr;
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/// Target lowering for arch-specific parts.
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const TargetLowering *TLI = nullptr;
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/// Emits a KCFI check before an indirect call.
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/// \returns true if the check was added and false otherwise.
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bool emitCheck(MachineBasicBlock &MBB,
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MachineBasicBlock::instr_iterator I) const;
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};
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char KCFI::ID = 0;
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} // end anonymous namespace
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INITIALIZE_PASS(KCFI, DEBUG_TYPE, KCFI_PASS_NAME, false, false)
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FunctionPass *llvm::createKCFIPass() { return new KCFI(); }
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bool KCFI::emitCheck(MachineBasicBlock &MBB,
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MachineBasicBlock::instr_iterator MBBI) const {
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assert(TII && "Target instruction info was not initialized");
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assert(TLI && "Target lowering was not initialized");
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// If the call instruction is bundled, we can only emit a check safely if
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// it's the first instruction in the bundle.
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if (MBBI->isBundled() && !std::prev(MBBI)->isBundle())
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report_fatal_error("Cannot emit a KCFI check for a bundled call");
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// Emit a KCFI check for the call instruction at MBBI. The implementation
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// must unfold memory operands if applicable.
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MachineInstr *Check = TLI->EmitKCFICheck(MBB, MBBI, TII);
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// Clear the original call's CFI type.
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assert(MBBI->isCall() && "Unexpected instruction type");
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MBBI->setCFIType(*MBB.getParent(), 0);
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// If not already bundled, bundle the check and the call to prevent
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// further changes.
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if (!MBBI->isBundled())
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finalizeBundle(MBB, Check->getIterator(), std::next(MBBI->getIterator()));
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++NumKCFIChecksAdded;
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return true;
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}
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bool KCFI::runOnMachineFunction(MachineFunction &MF) {
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const Module *M = MF.getMMI().getModule();
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if (!M->getModuleFlag("kcfi"))
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return false;
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const auto &SubTarget = MF.getSubtarget();
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TII = SubTarget.getInstrInfo();
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TLI = SubTarget.getTargetLowering();
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bool Changed = false;
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for (MachineBasicBlock &MBB : MF) {
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// Use instr_iterator because we don't want to skip bundles.
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for (MachineBasicBlock::instr_iterator MII = MBB.instr_begin(),
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MIE = MBB.instr_end();
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MII != MIE; ++MII) {
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if (MII->isCall() && MII->getCFIType())
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Changed |= emitCheck(MBB, MII);
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}
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}
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return Changed;
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}
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