| //===- ARMSLSHardening.cpp - Harden Straight Line Missspeculation ---------===// |
| // |
| // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions. |
| // See https://llvm.org/LICENSE.txt for license information. |
| // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception |
| // |
| //===----------------------------------------------------------------------===// |
| // |
| // This file contains a pass to insert code to mitigate against side channel |
| // vulnerabilities that may happen under straight line miss-speculation. |
| // |
| //===----------------------------------------------------------------------===// |
| |
| #include "ARM.h" |
| #include "ARMInstrInfo.h" |
| #include "ARMSubtarget.h" |
| #include "llvm/CodeGen/IndirectThunks.h" |
| #include "llvm/CodeGen/MachineBasicBlock.h" |
| #include "llvm/CodeGen/MachineFunction.h" |
| #include "llvm/CodeGen/MachineFunctionPass.h" |
| #include "llvm/CodeGen/MachineInstr.h" |
| #include "llvm/CodeGen/MachineInstrBuilder.h" |
| #include "llvm/CodeGen/MachineOperand.h" |
| #include "llvm/IR/DebugLoc.h" |
| #include <cassert> |
| |
| using namespace llvm; |
| |
| #define DEBUG_TYPE "arm-sls-hardening" |
| |
| #define ARM_SLS_HARDENING_NAME "ARM sls hardening pass" |
| |
| namespace { |
| |
| class ARMSLSHardening : public MachineFunctionPass { |
| public: |
| const TargetInstrInfo *TII; |
| const ARMSubtarget *ST; |
| |
| static char ID; |
| |
| ARMSLSHardening() : MachineFunctionPass(ID) { |
| initializeARMSLSHardeningPass(*PassRegistry::getPassRegistry()); |
| } |
| |
| bool runOnMachineFunction(MachineFunction &Fn) override; |
| |
| StringRef getPassName() const override { return ARM_SLS_HARDENING_NAME; } |
| |
| void getAnalysisUsage(AnalysisUsage &AU) const override { |
| AU.setPreservesCFG(); |
| MachineFunctionPass::getAnalysisUsage(AU); |
| } |
| |
| private: |
| bool hardenReturnsAndBRs(MachineBasicBlock &MBB) const; |
| bool hardenIndirectCalls(MachineBasicBlock &MBB) const; |
| MachineBasicBlock & |
| ConvertIndirectCallToIndirectJump(MachineBasicBlock &MBB, |
| MachineBasicBlock::iterator) const; |
| }; |
| |
| } // end anonymous namespace |
| |
| char ARMSLSHardening::ID = 0; |
| |
| INITIALIZE_PASS(ARMSLSHardening, "arm-sls-hardening", |
| ARM_SLS_HARDENING_NAME, false, false) |
| |
| static void insertSpeculationBarrier(const ARMSubtarget *ST, |
| MachineBasicBlock &MBB, |
| MachineBasicBlock::iterator MBBI, |
| DebugLoc DL, |
| bool AlwaysUseISBDSB = false) { |
| assert(MBBI != MBB.begin() && |
| "Must not insert SpeculationBarrierEndBB as only instruction in MBB."); |
| assert(std::prev(MBBI)->isBarrier() && |
| "SpeculationBarrierEndBB must only follow unconditional control flow " |
| "instructions."); |
| assert(std::prev(MBBI)->isTerminator() && |
| "SpeculationBarrierEndBB must only follow terminators."); |
| const TargetInstrInfo *TII = ST->getInstrInfo(); |
| assert(ST->hasDataBarrier() || ST->hasSB()); |
| bool ProduceSB = ST->hasSB() && !AlwaysUseISBDSB; |
| unsigned BarrierOpc = |
| ProduceSB ? (ST->isThumb() ? ARM::t2SpeculationBarrierSBEndBB |
| : ARM::SpeculationBarrierSBEndBB) |
| : (ST->isThumb() ? ARM::t2SpeculationBarrierISBDSBEndBB |
| : ARM::SpeculationBarrierISBDSBEndBB); |
| if (MBBI == MBB.end() || !isSpeculationBarrierEndBBOpcode(MBBI->getOpcode())) |
| BuildMI(MBB, MBBI, DL, TII->get(BarrierOpc)); |
| } |
| |
| bool ARMSLSHardening::runOnMachineFunction(MachineFunction &MF) { |
| ST = &MF.getSubtarget<ARMSubtarget>(); |
| TII = MF.getSubtarget().getInstrInfo(); |
| |
| bool Modified = false; |
| for (auto &MBB : MF) { |
| Modified |= hardenReturnsAndBRs(MBB); |
| Modified |= hardenIndirectCalls(MBB); |
| } |
| |
| return Modified; |
| } |
| |
| bool ARMSLSHardening::hardenReturnsAndBRs(MachineBasicBlock &MBB) const { |
| if (!ST->hardenSlsRetBr()) |
| return false; |
| assert(!ST->isThumb1Only()); |
| bool Modified = false; |
| MachineBasicBlock::iterator MBBI = MBB.getFirstTerminator(), E = MBB.end(); |
| MachineBasicBlock::iterator NextMBBI; |
| for (; MBBI != E; MBBI = NextMBBI) { |
| MachineInstr &MI = *MBBI; |
| NextMBBI = std::next(MBBI); |
| if (isIndirectControlFlowNotComingBack(MI)) { |
| assert(MI.isTerminator()); |
| assert(!TII->isPredicated(MI)); |
| insertSpeculationBarrier(ST, MBB, std::next(MBBI), MI.getDebugLoc()); |
| Modified = true; |
| } |
| } |
| return Modified; |
| } |
| |
| static const char SLSBLRNamePrefix[] = "__llvm_slsblr_thunk_"; |
| |
| static const struct ThunkNameRegMode { |
| const char* Name; |
| Register Reg; |
| bool isThumb; |
| } SLSBLRThunks[] = { |
| {"__llvm_slsblr_thunk_arm_r0", ARM::R0, false}, |
| {"__llvm_slsblr_thunk_arm_r1", ARM::R1, false}, |
| {"__llvm_slsblr_thunk_arm_r2", ARM::R2, false}, |
| {"__llvm_slsblr_thunk_arm_r3", ARM::R3, false}, |
| {"__llvm_slsblr_thunk_arm_r4", ARM::R4, false}, |
| {"__llvm_slsblr_thunk_arm_r5", ARM::R5, false}, |
| {"__llvm_slsblr_thunk_arm_r6", ARM::R6, false}, |
| {"__llvm_slsblr_thunk_arm_r7", ARM::R7, false}, |
| {"__llvm_slsblr_thunk_arm_r8", ARM::R8, false}, |
| {"__llvm_slsblr_thunk_arm_r9", ARM::R9, false}, |
| {"__llvm_slsblr_thunk_arm_r10", ARM::R10, false}, |
| {"__llvm_slsblr_thunk_arm_r11", ARM::R11, false}, |
| {"__llvm_slsblr_thunk_arm_sp", ARM::SP, false}, |
| {"__llvm_slsblr_thunk_arm_pc", ARM::PC, false}, |
| {"__llvm_slsblr_thunk_thumb_r0", ARM::R0, true}, |
| {"__llvm_slsblr_thunk_thumb_r1", ARM::R1, true}, |
| {"__llvm_slsblr_thunk_thumb_r2", ARM::R2, true}, |
| {"__llvm_slsblr_thunk_thumb_r3", ARM::R3, true}, |
| {"__llvm_slsblr_thunk_thumb_r4", ARM::R4, true}, |
| {"__llvm_slsblr_thunk_thumb_r5", ARM::R5, true}, |
| {"__llvm_slsblr_thunk_thumb_r6", ARM::R6, true}, |
| {"__llvm_slsblr_thunk_thumb_r7", ARM::R7, true}, |
| {"__llvm_slsblr_thunk_thumb_r8", ARM::R8, true}, |
| {"__llvm_slsblr_thunk_thumb_r9", ARM::R9, true}, |
| {"__llvm_slsblr_thunk_thumb_r10", ARM::R10, true}, |
| {"__llvm_slsblr_thunk_thumb_r11", ARM::R11, true}, |
| {"__llvm_slsblr_thunk_thumb_sp", ARM::SP, true}, |
| {"__llvm_slsblr_thunk_thumb_pc", ARM::PC, true}, |
| }; |
| |
| // An enum for tracking whether Arm and Thumb thunks have been inserted into the |
| // current module so far. |
| enum ArmInsertedThunks { NoThunk = 0, ArmThunk = 1, ThumbThunk = 2 }; |
| |
| inline ArmInsertedThunks &operator|=(ArmInsertedThunks &X, |
| ArmInsertedThunks Y) { |
| return X = static_cast<ArmInsertedThunks>(X | Y); |
| } |
| |
| namespace { |
| struct SLSBLRThunkInserter |
| : ThunkInserter<SLSBLRThunkInserter, ArmInsertedThunks> { |
| const char *getThunkPrefix() { return SLSBLRNamePrefix; } |
| bool mayUseThunk(const MachineFunction &MF) { |
| ComdatThunks &= !MF.getSubtarget<ARMSubtarget>().hardenSlsNoComdat(); |
| return MF.getSubtarget<ARMSubtarget>().hardenSlsBlr(); |
| } |
| ArmInsertedThunks insertThunks(MachineModuleInfo &MMI, MachineFunction &MF, |
| ArmInsertedThunks InsertedThunks); |
| void populateThunk(MachineFunction &MF); |
| |
| private: |
| bool ComdatThunks = true; |
| }; |
| } // namespace |
| |
| ArmInsertedThunks |
| SLSBLRThunkInserter::insertThunks(MachineModuleInfo &MMI, MachineFunction &MF, |
| ArmInsertedThunks InsertedThunks) { |
| if ((InsertedThunks & ArmThunk && |
| !MF.getSubtarget<ARMSubtarget>().isThumb()) || |
| (InsertedThunks & ThumbThunk && |
| MF.getSubtarget<ARMSubtarget>().isThumb())) |
| return NoThunk; |
| // FIXME: It probably would be possible to filter which thunks to produce |
| // based on which registers are actually used in indirect calls in this |
| // function. But would that be a worthwhile optimization? |
| const ARMSubtarget *ST = &MF.getSubtarget<ARMSubtarget>(); |
| for (auto T : SLSBLRThunks) |
| if (ST->isThumb() == T.isThumb) |
| createThunkFunction(MMI, T.Name, ComdatThunks, |
| T.isThumb ? "+thumb-mode" : ""); |
| return ST->isThumb() ? ThumbThunk : ArmThunk; |
| } |
| |
| void SLSBLRThunkInserter::populateThunk(MachineFunction &MF) { |
| assert(MF.getFunction().hasComdat() == ComdatThunks && |
| "ComdatThunks value changed since MF creation"); |
| // FIXME: How to better communicate Register number, rather than through |
| // name and lookup table? |
| assert(MF.getName().starts_with(getThunkPrefix())); |
| auto ThunkIt = llvm::find_if( |
| SLSBLRThunks, [&MF](auto T) { return T.Name == MF.getName(); }); |
| assert(ThunkIt != std::end(SLSBLRThunks)); |
| Register ThunkReg = ThunkIt->Reg; |
| bool isThumb = ThunkIt->isThumb; |
| |
| const TargetInstrInfo *TII = MF.getSubtarget<ARMSubtarget>().getInstrInfo(); |
| MachineBasicBlock *Entry = &MF.front(); |
| Entry->clear(); |
| |
| // These thunks need to consist of the following instructions: |
| // __llvm_slsblr_thunk_(arm/thumb)_rN: |
| // bx rN |
| // barrierInsts |
| Entry->addLiveIn(ThunkReg); |
| if (isThumb) |
| BuildMI(Entry, DebugLoc(), TII->get(ARM::tBX)) |
| .addReg(ThunkReg) |
| .add(predOps(ARMCC::AL)); |
| else |
| BuildMI(Entry, DebugLoc(), TII->get(ARM::BX)) |
| .addReg(ThunkReg); |
| |
| // Make sure the thunks do not make use of the SB extension in case there is |
| // a function somewhere that will call to it that for some reason disabled |
| // the SB extension locally on that function, even though it's enabled for |
| // the module otherwise. Therefore set AlwaysUseISBSDB to true. |
| insertSpeculationBarrier(&MF.getSubtarget<ARMSubtarget>(), *Entry, |
| Entry->end(), DebugLoc(), true /*AlwaysUseISBDSB*/); |
| } |
| |
| MachineBasicBlock &ARMSLSHardening::ConvertIndirectCallToIndirectJump( |
| MachineBasicBlock &MBB, MachineBasicBlock::iterator MBBI) const { |
| // Transform an indirect call to an indirect jump as follows: |
| // Before: |
| // |-----------------------------| |
| // | ... | |
| // | instI | |
| // | BLX rN | |
| // | instJ | |
| // | ... | |
| // |-----------------------------| |
| // |
| // After: |
| // |---------- -------------------------| |
| // | ... | |
| // | instI | |
| // | *call* __llvm_slsblr_thunk_mode_xN | |
| // | instJ | |
| // | ... | |
| // |--------------------------------------| |
| // |
| // __llvm_slsblr_thunk_mode_xN: |
| // |-----------------------------| |
| // | BX rN | |
| // | barrierInsts | |
| // |-----------------------------| |
| // |
| // The __llvm_slsblr_thunk_mode_xN thunks are created by the |
| // SLSBLRThunkInserter. |
| // This function merely needs to transform an indirect call to a direct call |
| // to __llvm_slsblr_thunk_xN. |
| MachineInstr &IndirectCall = *MBBI; |
| assert(isIndirectCall(IndirectCall) && !IndirectCall.isReturn()); |
| int RegOpIdxOnIndirectCall = -1; |
| bool isThumb; |
| switch (IndirectCall.getOpcode()) { |
| case ARM::BLX: // !isThumb2 |
| case ARM::BLX_noip: // !isThumb2 |
| isThumb = false; |
| RegOpIdxOnIndirectCall = 0; |
| break; |
| case ARM::tBLXr: // isThumb2 |
| case ARM::tBLXr_noip: // isThumb2 |
| isThumb = true; |
| RegOpIdxOnIndirectCall = 2; |
| break; |
| default: |
| llvm_unreachable("unhandled Indirect Call"); |
| } |
| |
| Register Reg = IndirectCall.getOperand(RegOpIdxOnIndirectCall).getReg(); |
| // Since linkers are allowed to clobber R12 on function calls, the above |
| // mitigation only works if the original indirect call instruction was not |
| // using R12. Code generation before must make sure that no indirect call |
| // using R12 was produced if the mitigation is enabled. |
| // Also, the transformation is incorrect if the indirect call uses LR, so |
| // also have to avoid that. |
| assert(Reg != ARM::R12 && Reg != ARM::LR); |
| bool RegIsKilled = IndirectCall.getOperand(RegOpIdxOnIndirectCall).isKill(); |
| |
| DebugLoc DL = IndirectCall.getDebugLoc(); |
| |
| MachineFunction &MF = *MBBI->getMF(); |
| auto ThunkIt = llvm::find_if(SLSBLRThunks, [Reg, isThumb](auto T) { |
| return T.Reg == Reg && T.isThumb == isThumb; |
| }); |
| assert(ThunkIt != std::end(SLSBLRThunks)); |
| Module *M = MF.getFunction().getParent(); |
| const GlobalValue *GV = cast<GlobalValue>(M->getNamedValue(ThunkIt->Name)); |
| |
| MachineInstr *BL = |
| isThumb ? BuildMI(MBB, MBBI, DL, TII->get(ARM::tBL)) |
| .addImm(IndirectCall.getOperand(0).getImm()) |
| .addReg(IndirectCall.getOperand(1).getReg()) |
| .addGlobalAddress(GV) |
| : BuildMI(MBB, MBBI, DL, TII->get(ARM::BL)).addGlobalAddress(GV); |
| |
| // Now copy the implicit operands from IndirectCall to BL and copy other |
| // necessary info. |
| // However, both IndirectCall and BL instructions implictly use SP and |
| // implicitly define LR. Blindly copying implicit operands would result in SP |
| // and LR operands to be present multiple times. While this may not be too |
| // much of an issue, let's avoid that for cleanliness, by removing those |
| // implicit operands from the BL created above before we copy over all |
| // implicit operands from the IndirectCall. |
| int ImpLROpIdx = -1; |
| int ImpSPOpIdx = -1; |
| for (unsigned OpIdx = BL->getNumExplicitOperands(); |
| OpIdx < BL->getNumOperands(); OpIdx++) { |
| MachineOperand Op = BL->getOperand(OpIdx); |
| if (!Op.isReg()) |
| continue; |
| if (Op.getReg() == ARM::LR && Op.isDef()) |
| ImpLROpIdx = OpIdx; |
| if (Op.getReg() == ARM::SP && !Op.isDef()) |
| ImpSPOpIdx = OpIdx; |
| } |
| assert(ImpLROpIdx != -1); |
| assert(ImpSPOpIdx != -1); |
| int FirstOpIdxToRemove = std::max(ImpLROpIdx, ImpSPOpIdx); |
| int SecondOpIdxToRemove = std::min(ImpLROpIdx, ImpSPOpIdx); |
| BL->removeOperand(FirstOpIdxToRemove); |
| BL->removeOperand(SecondOpIdxToRemove); |
| // Now copy over the implicit operands from the original IndirectCall |
| BL->copyImplicitOps(MF, IndirectCall); |
| MF.moveAdditionalCallInfo(&IndirectCall, BL); |
| // Also add the register called in the IndirectCall as being used in the |
| // called thunk. |
| BL->addOperand(MachineOperand::CreateReg(Reg, false /*isDef*/, true /*isImp*/, |
| RegIsKilled /*isKill*/)); |
| // Remove IndirectCallinstruction |
| MBB.erase(MBBI); |
| return MBB; |
| } |
| |
| bool ARMSLSHardening::hardenIndirectCalls(MachineBasicBlock &MBB) const { |
| if (!ST->hardenSlsBlr()) |
| return false; |
| bool Modified = false; |
| MachineBasicBlock::iterator MBBI = MBB.begin(), E = MBB.end(); |
| MachineBasicBlock::iterator NextMBBI; |
| for (; MBBI != E; MBBI = NextMBBI) { |
| MachineInstr &MI = *MBBI; |
| NextMBBI = std::next(MBBI); |
| // Tail calls are both indirect calls and "returns". |
| // They are also indirect jumps, so should be handled by sls-harden-retbr, |
| // rather than sls-harden-blr. |
| if (isIndirectCall(MI) && !MI.isReturn()) { |
| ConvertIndirectCallToIndirectJump(MBB, MBBI); |
| Modified = true; |
| } |
| } |
| return Modified; |
| } |
| |
| |
| |
| FunctionPass *llvm::createARMSLSHardeningPass() { |
| return new ARMSLSHardening(); |
| } |
| |
| namespace { |
| class ARMIndirectThunks : public ThunkInserterPass<SLSBLRThunkInserter> { |
| public: |
| static char ID; |
| |
| ARMIndirectThunks() : ThunkInserterPass(ID) {} |
| |
| StringRef getPassName() const override { return "ARM Indirect Thunks"; } |
| }; |
| } // end anonymous namespace |
| |
| char ARMIndirectThunks::ID = 0; |
| |
| FunctionPass *llvm::createARMIndirectThunks() { |
| return new ARMIndirectThunks(); |
| } |
