| //==-- X86LoadValueInjectionLoadHardening.cpp - LVI load hardening for x86 --=// |
| // |
| // 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 |
| // |
| //===----------------------------------------------------------------------===// |
| /// |
| /// Description: This pass finds Load Value Injection (LVI) gadgets consisting |
| /// of a load from memory (i.e., SOURCE), and any operation that may transmit |
| /// the value loaded from memory over a covert channel, or use the value loaded |
| /// from memory to determine a branch/call target (i.e., SINK). After finding |
| /// all such gadgets in a given function, the pass minimally inserts LFENCE |
| /// instructions in such a manner that the following property is satisfied: for |
| /// all SOURCE+SINK pairs, all paths in the CFG from SOURCE to SINK contain at |
| /// least one LFENCE instruction. The algorithm that implements this minimal |
| /// insertion is influenced by an academic paper that minimally inserts memory |
| /// fences for high-performance concurrent programs: |
| /// http://www.cs.ucr.edu/~lesani/companion/oopsla15/OOPSLA15.pdf |
| /// The algorithm implemented in this pass is as follows: |
| /// 1. Build a condensed CFG (i.e., a GadgetGraph) consisting only of the |
| /// following components: |
| /// - SOURCE instructions (also includes function arguments) |
| /// - SINK instructions |
| /// - Basic block entry points |
| /// - Basic block terminators |
| /// - LFENCE instructions |
| /// 2. Analyze the GadgetGraph to determine which SOURCE+SINK pairs (i.e., |
| /// gadgets) are already mitigated by existing LFENCEs. If all gadgets have been |
| /// mitigated, go to step 6. |
| /// 3. Use a heuristic or plugin to approximate minimal LFENCE insertion. |
| /// 4. Insert one LFENCE along each CFG edge that was cut in step 3. |
| /// 5. Go to step 2. |
| /// 6. If any LFENCEs were inserted, return `true` from runOnFunction() to tell |
| /// LLVM that the function was modified. |
| /// |
| //===----------------------------------------------------------------------===// |
| |
| #include "ImmutableGraph.h" |
| #include "X86.h" |
| #include "X86Subtarget.h" |
| #include "X86TargetMachine.h" |
| #include "llvm/ADT/DenseMap.h" |
| #include "llvm/ADT/DenseSet.h" |
| #include "llvm/ADT/SmallSet.h" |
| #include "llvm/ADT/Statistic.h" |
| #include "llvm/ADT/StringRef.h" |
| #include "llvm/CodeGen/MachineBasicBlock.h" |
| #include "llvm/CodeGen/MachineDominanceFrontier.h" |
| #include "llvm/CodeGen/MachineDominators.h" |
| #include "llvm/CodeGen/MachineFunction.h" |
| #include "llvm/CodeGen/MachineFunctionPass.h" |
| #include "llvm/CodeGen/MachineInstr.h" |
| #include "llvm/CodeGen/MachineInstrBuilder.h" |
| #include "llvm/CodeGen/MachineLoopInfo.h" |
| #include "llvm/CodeGen/MachineRegisterInfo.h" |
| #include "llvm/CodeGen/RDFGraph.h" |
| #include "llvm/CodeGen/RDFLiveness.h" |
| #include "llvm/InitializePasses.h" |
| #include "llvm/Support/CommandLine.h" |
| #include "llvm/Support/DOTGraphTraits.h" |
| #include "llvm/Support/Debug.h" |
| #include "llvm/Support/DynamicLibrary.h" |
| #include "llvm/Support/GraphWriter.h" |
| #include "llvm/Support/raw_ostream.h" |
| |
| using namespace llvm; |
| |
| #define PASS_KEY "x86-lvi-load" |
| #define DEBUG_TYPE PASS_KEY |
| |
| STATISTIC(NumFences, "Number of LFENCEs inserted for LVI mitigation"); |
| STATISTIC(NumFunctionsConsidered, "Number of functions analyzed"); |
| STATISTIC(NumFunctionsMitigated, "Number of functions for which mitigations " |
| "were deployed"); |
| STATISTIC(NumGadgets, "Number of LVI gadgets detected during analysis"); |
| |
| static cl::opt<std::string> OptimizePluginPath( |
| PASS_KEY "-opt-plugin", |
| cl::desc("Specify a plugin to optimize LFENCE insertion"), cl::Hidden); |
| |
| static cl::opt<bool> NoConditionalBranches( |
| PASS_KEY "-no-cbranch", |
| cl::desc("Don't treat conditional branches as disclosure gadgets. This " |
| "may improve performance, at the cost of security."), |
| cl::init(false), cl::Hidden); |
| |
| static cl::opt<bool> EmitDot( |
| PASS_KEY "-dot", |
| cl::desc( |
| "For each function, emit a dot graph depicting potential LVI gadgets"), |
| cl::init(false), cl::Hidden); |
| |
| static cl::opt<bool> EmitDotOnly( |
| PASS_KEY "-dot-only", |
| cl::desc("For each function, emit a dot graph depicting potential LVI " |
| "gadgets, and do not insert any fences"), |
| cl::init(false), cl::Hidden); |
| |
| static cl::opt<bool> EmitDotVerify( |
| PASS_KEY "-dot-verify", |
| cl::desc("For each function, emit a dot graph to stdout depicting " |
| "potential LVI gadgets, used for testing purposes only"), |
| cl::init(false), cl::Hidden); |
| |
| static cl::opt<bool> NoFixedLoads( |
| PASS_KEY "-no-fixed", |
| cl::desc("Don't mitigate RIP-relative or RSP-relative loads. This " |
| "may improve performance, at the cost of security."), |
| cl::init(false), cl::Hidden); |
| |
| static llvm::sys::DynamicLibrary OptimizeDL{}; |
| typedef int (*OptimizeCutT)(unsigned int *nodes, unsigned int nodes_size, |
| unsigned int *edges, int *edge_values, |
| int *cut_edges /* out */, unsigned int edges_size); |
| static OptimizeCutT OptimizeCut = nullptr; |
| |
| #define ARG_NODE nullptr |
| #define GADGET_EDGE ((int)(-1)) |
| #define WEIGHT(EdgeValue) ((double)(2 * (EdgeValue) + 1)) |
| |
| namespace { |
| |
| class X86LoadValueInjectionLoadHardeningPass : public MachineFunctionPass { |
| public: |
| X86LoadValueInjectionLoadHardeningPass() : MachineFunctionPass(ID) {} |
| |
| StringRef getPassName() const override { |
| return "X86 Load Value Injection (LVI) Load Hardening"; |
| } |
| void getAnalysisUsage(AnalysisUsage &AU) const override; |
| bool runOnMachineFunction(MachineFunction &MF) override; |
| |
| static char ID; |
| |
| private: |
| struct MachineGadgetGraph : ImmutableGraph<MachineInstr *, int> { |
| using GraphT = ImmutableGraph<MachineInstr *, int>; |
| using Node = typename GraphT::Node; |
| using Edge = typename GraphT::Edge; |
| using size_type = typename GraphT::size_type; |
| MachineGadgetGraph(Node *Nodes, size_type NodesSize, Edge *Edges, |
| size_type EdgesSize, int NumFences = 0, |
| int NumGadgets = 0) |
| : GraphT{Nodes, NodesSize, Edges, EdgesSize}, NumFences{NumFences}, |
| NumGadgets{NumGadgets} {} |
| MachineFunction &getMF() { // FIXME: This function should be cleaner |
| for (Node *NI = nodes_begin(), *const NE = nodes_end(); NI != NE; ++NI) { |
| if (NI->value()) { |
| return *NI->value()->getMF(); |
| } |
| } |
| llvm_unreachable("Could not find a valid node"); |
| } |
| static inline bool isCFGEdge(Edge &E) { return E.value() != GADGET_EDGE; } |
| static inline bool isGadgetEdge(Edge &E) { |
| return E.value() == GADGET_EDGE; |
| } |
| int NumFences; |
| int NumGadgets; |
| }; |
| friend struct llvm::DOTGraphTraits<MachineGadgetGraph *>; |
| using GTraits = llvm::GraphTraits<MachineGadgetGraph *>; |
| using GraphBuilder = ImmutableGraphBuilder<MachineGadgetGraph>; |
| using EdgeSet = MachineGadgetGraph::EdgeSet; |
| using Gadget = std::pair<MachineInstr *, MachineInstr *>; |
| |
| const X86Subtarget *STI; |
| const TargetInstrInfo *TII; |
| const TargetRegisterInfo *TRI; |
| |
| int hardenLoads(MachineFunction &MF, bool Fixed) const; |
| std::unique_ptr<MachineGadgetGraph> |
| getGadgetGraph(MachineFunction &MF, const MachineLoopInfo &MLI, |
| const MachineDominatorTree &MDT, |
| const MachineDominanceFrontier &MDF, bool FixedLoads) const; |
| std::unique_ptr<MachineGadgetGraph> |
| elimEdges(std::unique_ptr<MachineGadgetGraph> Graph) const; |
| void cutEdges(MachineGadgetGraph &G, EdgeSet &CutEdges /* out */) const; |
| int insertFences(MachineGadgetGraph &G, |
| EdgeSet &CutEdges /* in, out */) const; |
| |
| bool instrUsesRegToAccessMemory(const MachineInstr &I, unsigned Reg) const; |
| bool instrUsesRegToBranch(const MachineInstr &I, unsigned Reg) const; |
| template <unsigned K> bool hasLoadFrom(const MachineInstr &MI) const; |
| bool instrAccessesStackSlot(const MachineInstr &MI) const; |
| bool instrAccessesConstantPool(const MachineInstr &MI) const; |
| bool instrAccessesGOT(const MachineInstr &MI) const; |
| inline bool instrIsFixedAccess(const MachineInstr &MI) const { |
| return instrAccessesConstantPool(MI) || instrAccessesStackSlot(MI) || |
| instrAccessesGOT(MI); |
| } |
| inline bool isFence(const MachineInstr *MI) const { |
| return MI && (MI->getOpcode() == X86::LFENCE || |
| (STI->useLVIControlFlowIntegrity() && MI->isCall())); |
| } |
| }; |
| |
| } // end anonymous namespace |
| |
| namespace llvm { |
| |
| template <> |
| struct GraphTraits<X86LoadValueInjectionLoadHardeningPass::MachineGadgetGraph *> |
| : GraphTraits<ImmutableGraph<MachineInstr *, int> *> {}; |
| |
| template <> |
| struct DOTGraphTraits< |
| X86LoadValueInjectionLoadHardeningPass::MachineGadgetGraph *> |
| : DefaultDOTGraphTraits { |
| using GraphType = X86LoadValueInjectionLoadHardeningPass::MachineGadgetGraph; |
| using Traits = X86LoadValueInjectionLoadHardeningPass::GTraits; |
| using NodeRef = typename Traits::NodeRef; |
| using EdgeRef = typename Traits::EdgeRef; |
| using ChildIteratorType = typename Traits::ChildIteratorType; |
| using ChildEdgeIteratorType = typename Traits::ChildEdgeIteratorType; |
| |
| DOTGraphTraits(bool isSimple = false) : DefaultDOTGraphTraits(isSimple) {} |
| |
| static std::string getGraphName(GraphType *G) { |
| std::string GraphName{"Speculative gadgets for \""}; |
| GraphName += G->getMF().getName(); |
| GraphName += "\" function"; |
| return GraphName; |
| } |
| |
| std::string getNodeLabel(NodeRef Node, GraphType *) { |
| std::string str; |
| raw_string_ostream str_stream{str}; |
| if (Node->value() == ARG_NODE) |
| return "ARGS"; |
| str_stream << *Node->value(); |
| return str_stream.str(); |
| } |
| |
| static std::string getNodeAttributes(NodeRef Node, GraphType *) { |
| MachineInstr *MI = Node->value(); |
| if (MI == ARG_NODE) |
| return "color = blue"; |
| else if (MI->getOpcode() == X86::LFENCE) |
| return "color = green"; |
| else |
| return ""; |
| } |
| |
| static std::string getEdgeAttributes(NodeRef, ChildIteratorType E, |
| GraphType *) { |
| int EdgeVal = (*E.getCurrent()).value(); |
| return EdgeVal >= 0 ? "label = " + std::to_string(EdgeVal) |
| : "color = red, style = \"dashed\""; |
| } |
| }; |
| |
| } // end namespace llvm |
| |
| char X86LoadValueInjectionLoadHardeningPass::ID = 0; |
| |
| void X86LoadValueInjectionLoadHardeningPass::getAnalysisUsage( |
| AnalysisUsage &AU) const { |
| MachineFunctionPass::getAnalysisUsage(AU); |
| AU.addRequired<MachineLoopInfo>(); |
| AU.addRequired<MachineDominatorTree>(); |
| AU.addRequired<MachineDominanceFrontier>(); |
| AU.setPreservesCFG(); |
| } |
| |
| bool X86LoadValueInjectionLoadHardeningPass::runOnMachineFunction( |
| MachineFunction &MF) { |
| LLVM_DEBUG(dbgs() << "***** " << getPassName() << " : " << MF.getName() |
| << " *****\n"); |
| STI = &MF.getSubtarget<X86Subtarget>(); |
| if (!STI->useLVILoadHardening() || !STI->is64Bit()) |
| return false; // FIXME: support 32-bit |
| |
| // Don't skip functions with the "optnone" attr but participate in opt-bisect. |
| const Function &F = MF.getFunction(); |
| if (!F.hasOptNone() && skipFunction(F)) |
| return false; |
| |
| ++NumFunctionsConsidered; |
| TII = STI->getInstrInfo(); |
| TRI = STI->getRegisterInfo(); |
| LLVM_DEBUG(dbgs() << "Hardening data-dependent loads...\n"); |
| int FencesInserted = hardenLoads(MF, false); |
| LLVM_DEBUG(dbgs() << "Hardening data-dependent loads... Done\n"); |
| if (!NoFixedLoads) { |
| LLVM_DEBUG(dbgs() << "Hardening fixed loads...\n"); |
| FencesInserted += hardenLoads(MF, true); |
| LLVM_DEBUG(dbgs() << "Hardening fixed loads... Done\n"); |
| } |
| if (FencesInserted > 0) |
| ++NumFunctionsMitigated; |
| NumFences += FencesInserted; |
| return (FencesInserted > 0); |
| } |
| |
| // Apply the mitigation to `MF`, return the number of fences inserted. |
| // If `FixedLoads` is `true`, then the mitigation will be applied to fixed |
| // loads; otherwise, mitigation will be applied to non-fixed loads. |
| int X86LoadValueInjectionLoadHardeningPass::hardenLoads(MachineFunction &MF, |
| bool FixedLoads) const { |
| int FencesInserted = 0; |
| |
| LLVM_DEBUG(dbgs() << "Building gadget graph...\n"); |
| const auto &MLI = getAnalysis<MachineLoopInfo>(); |
| const auto &MDT = getAnalysis<MachineDominatorTree>(); |
| const auto &MDF = getAnalysis<MachineDominanceFrontier>(); |
| std::unique_ptr<MachineGadgetGraph> Graph = |
| getGadgetGraph(MF, MLI, MDT, MDF, FixedLoads); |
| LLVM_DEBUG(dbgs() << "Building gadget graph... Done\n"); |
| if (Graph == nullptr) |
| return 0; // didn't find any gadgets |
| |
| if (EmitDotVerify) { |
| WriteGraph(outs(), Graph.get()); |
| return 0; |
| } |
| |
| if (EmitDot || EmitDotOnly) { |
| LLVM_DEBUG(dbgs() << "Emitting gadget graph...\n"); |
| std::error_code FileError; |
| std::string FileName = "lvi."; |
| if (FixedLoads) |
| FileName += "fixed."; |
| FileName += Graph->getMF().getName(); |
| FileName += ".dot"; |
| raw_fd_ostream FileOut(FileName, FileError); |
| if (FileError) |
| errs() << FileError.message(); |
| WriteGraph(FileOut, Graph.get()); |
| FileOut.close(); |
| LLVM_DEBUG(dbgs() << "Emitting gadget graph... Done\n"); |
| if (EmitDotOnly) |
| return 0; |
| } |
| |
| do { |
| LLVM_DEBUG(dbgs() << "Eliminating mitigated paths...\n"); |
| std::unique_ptr<MachineGadgetGraph> ElimGraph = elimEdges(std::move(Graph)); |
| LLVM_DEBUG(dbgs() << "Eliminating mitigated paths... Done\n"); |
| if (ElimGraph->NumGadgets == 0) |
| break; |
| |
| EdgeSet CutEdges{*ElimGraph}; |
| LLVM_DEBUG(dbgs() << "Cutting edges...\n"); |
| cutEdges(*ElimGraph, CutEdges); |
| LLVM_DEBUG(dbgs() << "Cutting edges... Done\n"); |
| |
| LLVM_DEBUG(dbgs() << "Inserting LFENCEs...\n"); |
| FencesInserted += insertFences(*ElimGraph, CutEdges); |
| LLVM_DEBUG(dbgs() << "Inserting LFENCEs... Done\n"); |
| |
| Graph.reset(GraphBuilder::trim( |
| *ElimGraph, MachineGadgetGraph::NodeSet{*ElimGraph}, CutEdges)); |
| } while (true); |
| |
| return FencesInserted; |
| } |
| |
| std::unique_ptr<X86LoadValueInjectionLoadHardeningPass::MachineGadgetGraph> |
| X86LoadValueInjectionLoadHardeningPass::getGadgetGraph( |
| MachineFunction &MF, const MachineLoopInfo &MLI, |
| const MachineDominatorTree &MDT, const MachineDominanceFrontier &MDF, |
| bool FixedLoads) const { |
| using namespace rdf; |
| |
| // Build the Register Dataflow Graph using the RDF framework |
| TargetOperandInfo TOI{*TII}; |
| DataFlowGraph DFG{MF, *TII, *TRI, MDT, MDF, TOI}; |
| DFG.build(); |
| Liveness L{MF.getRegInfo(), DFG}; |
| L.computePhiInfo(); |
| |
| GraphBuilder Builder; |
| using GraphIter = typename GraphBuilder::NodeRef; |
| DenseMap<MachineInstr *, GraphIter> NodeMap; |
| int FenceCount = 0; |
| auto MaybeAddNode = [&NodeMap, &Builder](MachineInstr *MI) { |
| auto Ref = NodeMap.find(MI); |
| if (Ref == NodeMap.end()) { |
| auto I = Builder.addVertex(MI); |
| NodeMap[MI] = I; |
| return std::pair<GraphIter, bool>{I, true}; |
| } else { |
| return std::pair<GraphIter, bool>{Ref->getSecond(), false}; |
| } |
| }; |
| |
| // Analyze all machine instructions to find gadgets and LFENCEs, adding |
| // each interesting value to `Nodes` |
| DenseSet<std::pair<GraphIter, GraphIter>> GadgetEdgeSet; |
| auto AnalyzeDef = [&](NodeAddr<DefNode *> Def) { |
| MachineInstr *MI = Def.Addr->getFlags() & NodeAttrs::PhiRef |
| ? ARG_NODE |
| : Def.Addr->getOp().getParent(); |
| auto AnalyzeUse = [&](NodeAddr<UseNode *> Use) { |
| assert(!(Use.Addr->getFlags() & NodeAttrs::PhiRef)); |
| MachineOperand &UseMO = Use.Addr->getOp(); |
| MachineInstr &UseMI = *UseMO.getParent(); |
| assert(UseMO.isReg()); |
| // We naively assume that an instruction propagates any loaded Uses |
| // to all Defs, unless the instruction is a call |
| if (UseMI.isCall()) |
| return false; |
| if (instrUsesRegToAccessMemory(UseMI, UseMO.getReg()) || |
| (!NoConditionalBranches && |
| instrUsesRegToBranch(UseMI, UseMO.getReg()))) { // found a gadget! |
| // add the root of this chain |
| auto GadgetBegin = MaybeAddNode(MI); |
| // and the instruction that (transitively) discloses the root |
| auto GadgetEnd = MaybeAddNode(&UseMI); |
| if (GadgetEdgeSet.insert({GadgetBegin.first, GadgetEnd.first}).second) |
| Builder.addEdge(GADGET_EDGE, GadgetBegin.first, GadgetEnd.first); |
| if (UseMI.mayLoad()) // FIXME: This should be more precise |
| return false; // stop traversing further uses of `Reg` |
| } |
| return true; |
| }; |
| SmallSet<NodeId, 8> NodesVisited; |
| std::function<void(NodeAddr<DefNode *>)> AnalyzeDefUseChain = |
| [&](NodeAddr<DefNode *> Def) { |
| if (Def.Addr->getAttrs() & NodeAttrs::Dead) |
| return; |
| RegisterRef DefReg = DFG.getPRI().normalize(Def.Addr->getRegRef(DFG)); |
| NodeList Uses; |
| for (auto UseID : L.getAllReachedUses(DefReg, Def)) { |
| auto Use = DFG.addr<UseNode *>(UseID); |
| if (Use.Addr->getFlags() & NodeAttrs::PhiRef) { // phi node |
| NodeAddr<PhiNode *> Phi = Use.Addr->getOwner(DFG); |
| for (auto I : L.getRealUses(Phi.Id)) { |
| if (DFG.getPRI().alias(RegisterRef(I.first), DefReg)) { |
| for (auto UA : I.second) { |
| auto PhiUse = DFG.addr<UseNode *>(UA.first); |
| Uses.push_back(PhiUse); |
| } |
| } |
| } |
| } else { // not a phi node |
| Uses.push_back(Use); |
| } |
| } |
| for (auto N : Uses) { |
| NodeAddr<UseNode *> Use{N}; |
| if (NodesVisited.insert(Use.Id).second && AnalyzeUse(Use)) { |
| NodeAddr<InstrNode *> Owner{Use.Addr->getOwner(DFG)}; |
| NodeList Defs = Owner.Addr->members_if(DataFlowGraph::IsDef, DFG); |
| std::for_each(Defs.begin(), Defs.end(), AnalyzeDefUseChain); |
| } |
| } |
| }; |
| AnalyzeDefUseChain(Def); |
| }; |
| |
| LLVM_DEBUG(dbgs() << "Analyzing def-use chains to find gadgets\n"); |
| // Analyze function arguments |
| if (!FixedLoads) { // only need to analyze function args once |
| NodeAddr<BlockNode *> EntryBlock = DFG.getFunc().Addr->getEntryBlock(DFG); |
| for (NodeAddr<PhiNode *> ArgPhi : |
| EntryBlock.Addr->members_if(DataFlowGraph::IsPhi, DFG)) { |
| NodeList Defs = ArgPhi.Addr->members_if(DataFlowGraph::IsDef, DFG); |
| std::for_each(Defs.begin(), Defs.end(), AnalyzeDef); |
| } |
| } |
| // Analyze every instruction in MF |
| for (NodeAddr<BlockNode *> BA : DFG.getFunc().Addr->members(DFG)) { |
| for (NodeAddr<StmtNode *> SA : |
| BA.Addr->members_if(DataFlowGraph::IsCode<NodeAttrs::Stmt>, DFG)) { |
| MachineInstr *MI = SA.Addr->getCode(); |
| if (isFence(MI)) { |
| MaybeAddNode(MI); |
| ++FenceCount; |
| } else if (MI->mayLoad() && ((FixedLoads && instrIsFixedAccess(*MI)) || |
| (!FixedLoads && !instrIsFixedAccess(*MI)))) { |
| NodeList Defs = SA.Addr->members_if(DataFlowGraph::IsDef, DFG); |
| std::for_each(Defs.begin(), Defs.end(), AnalyzeDef); |
| } |
| } |
| } |
| int GadgetCount = static_cast<int>(GadgetEdgeSet.size()); |
| LLVM_DEBUG(dbgs() << "Found " << FenceCount << " fences\n"); |
| LLVM_DEBUG(dbgs() << "Found " << GadgetCount << " gadgets\n"); |
| if (GadgetCount == 0) |
| return nullptr; |
| NumGadgets += GadgetCount; |
| |
| // Traverse CFG to build the rest of the graph |
| SmallSet<MachineBasicBlock *, 8> BlocksVisited; |
| std::function<void(MachineBasicBlock *, GraphIter, unsigned)> TraverseCFG = |
| [&](MachineBasicBlock *MBB, GraphIter GI, unsigned ParentDepth) { |
| unsigned LoopDepth = MLI.getLoopDepth(MBB); |
| if (!MBB->empty()) { |
| // Always add the first instruction in each block |
| auto NI = MBB->begin(); |
| auto BeginBB = MaybeAddNode(&*NI); |
| Builder.addEdge(ParentDepth, GI, BeginBB.first); |
| if (!BlocksVisited.insert(MBB).second) |
| return; |
| |
| // Add any instructions within the block that are gadget components |
| GI = BeginBB.first; |
| while (++NI != MBB->end()) { |
| auto Ref = NodeMap.find(&*NI); |
| if (Ref != NodeMap.end()) { |
| Builder.addEdge(LoopDepth, GI, Ref->getSecond()); |
| GI = Ref->getSecond(); |
| } |
| } |
| |
| // Always add the terminator instruction, if one exists |
| auto T = MBB->getFirstTerminator(); |
| if (T != MBB->end()) { |
| auto EndBB = MaybeAddNode(&*T); |
| if (EndBB.second) |
| Builder.addEdge(LoopDepth, GI, EndBB.first); |
| GI = EndBB.first; |
| } |
| } |
| for (MachineBasicBlock *Succ : MBB->successors()) |
| TraverseCFG(Succ, GI, LoopDepth); |
| }; |
| // ARG_NODE is a pseudo-instruction that represents MF args in the GadgetGraph |
| GraphIter ArgNode = MaybeAddNode(ARG_NODE).first; |
| TraverseCFG(&MF.front(), ArgNode, 0); |
| std::unique_ptr<MachineGadgetGraph> G{Builder.get(FenceCount, GadgetCount)}; |
| LLVM_DEBUG(dbgs() << "Found " << GTraits::size(G.get()) << " nodes\n"); |
| return G; |
| } |
| |
| std::unique_ptr<X86LoadValueInjectionLoadHardeningPass::MachineGadgetGraph> |
| X86LoadValueInjectionLoadHardeningPass::elimEdges( |
| std::unique_ptr<MachineGadgetGraph> Graph) const { |
| MachineGadgetGraph::NodeSet ElimNodes{*Graph}; |
| MachineGadgetGraph::EdgeSet ElimEdges{*Graph}; |
| |
| if (Graph->NumFences > 0) { // eliminate fences |
| for (auto EI = Graph->edges_begin(), EE = Graph->edges_end(); EI != EE; |
| ++EI) { |
| GTraits::NodeRef Dest = GTraits::edge_dest(*EI); |
| if (isFence(Dest->value())) { |
| ElimNodes.insert(Dest); |
| ElimEdges.insert(EI); |
| std::for_each( |
| GTraits::child_edge_begin(Dest), GTraits::child_edge_end(Dest), |
| [&ElimEdges](GTraits::EdgeRef E) { ElimEdges.insert(&E); }); |
| } |
| } |
| LLVM_DEBUG(dbgs() << "Eliminated " << ElimNodes.count() |
| << " fence nodes\n"); |
| } |
| |
| // eliminate gadget edges that are mitigated |
| int NumGadgets = 0; |
| MachineGadgetGraph::NodeSet Visited{*Graph}, GadgetSinks{*Graph}; |
| MachineGadgetGraph::EdgeSet ElimGadgets{*Graph}; |
| for (auto NI = GTraits::nodes_begin(Graph.get()), |
| NE = GTraits::nodes_end(Graph.get()); |
| NI != NE; ++NI) { |
| // collect the gadgets for this node |
| for (auto EI = GTraits::child_edge_begin(*NI), |
| EE = GTraits::child_edge_end(*NI); |
| EI != EE; ++EI) { |
| if (MachineGadgetGraph::isGadgetEdge(*EI)) { |
| ++NumGadgets; |
| ElimGadgets.insert(EI); |
| GadgetSinks.insert(GTraits::edge_dest(*EI)); |
| } |
| } |
| if (GadgetSinks.empty()) |
| continue; |
| std::function<void(GTraits::NodeRef, bool)> TraverseDFS = |
| [&](GTraits::NodeRef N, bool FirstNode) { |
| if (!FirstNode) { |
| Visited.insert(N); |
| if (GadgetSinks.contains(N)) { |
| for (auto CEI = GTraits::child_edge_begin(*NI), |
| CEE = GTraits::child_edge_end(*NI); |
| CEI != CEE; ++CEI) { |
| if (MachineGadgetGraph::isGadgetEdge(*CEI) && |
| GTraits::edge_dest(*CEI) == N) |
| ElimGadgets.erase(CEI); |
| } |
| } |
| } |
| for (auto CEI = GTraits::child_edge_begin(N), |
| CEE = GTraits::child_edge_end(N); |
| CEI != CEE; ++CEI) { |
| GTraits::NodeRef Dest = GTraits::edge_dest(*CEI); |
| if (MachineGadgetGraph::isCFGEdge(*CEI) && |
| !Visited.contains(Dest) && !ElimEdges.contains(CEI)) |
| TraverseDFS(Dest, false); |
| } |
| }; |
| TraverseDFS(*NI, true); |
| Visited.clear(); |
| GadgetSinks.clear(); |
| } |
| LLVM_DEBUG(dbgs() << "Eliminated " << ElimGadgets.count() |
| << " gadget edges\n"); |
| ElimEdges |= ElimGadgets; |
| |
| if (!(ElimEdges.empty() && ElimNodes.empty())) { |
| int NumRemainingGadgets = NumGadgets - ElimGadgets.count(); |
| Graph.reset(GraphBuilder::trim(*Graph, ElimNodes, ElimEdges, |
| 0 /* NumFences */, NumRemainingGadgets)); |
| } else { |
| Graph->NumFences = 0; |
| Graph->NumGadgets = NumGadgets; |
| } |
| return Graph; |
| } |
| |
| void X86LoadValueInjectionLoadHardeningPass::cutEdges( |
| MachineGadgetGraph &G, |
| MachineGadgetGraph::EdgeSet &CutEdges /* out */) const { |
| if (!OptimizePluginPath.empty()) { |
| if (!OptimizeDL.isValid()) { |
| std::string ErrorMsg{}; |
| OptimizeDL = llvm::sys::DynamicLibrary::getPermanentLibrary( |
| OptimizePluginPath.c_str(), &ErrorMsg); |
| if (!ErrorMsg.empty()) |
| report_fatal_error("Failed to load opt plugin: \"" + ErrorMsg + '\"'); |
| OptimizeCut = (OptimizeCutT)OptimizeDL.getAddressOfSymbol("optimize_cut"); |
| if (!OptimizeCut) |
| report_fatal_error("Invalid optimization plugin"); |
| } |
| auto *Nodes = new unsigned int[G.nodes_size() + 1 /* terminator node */]; |
| auto *Edges = new unsigned int[G.edges_size()]; |
| auto *EdgeCuts = new int[G.edges_size()]; |
| auto *EdgeValues = new int[G.edges_size()]; |
| for (auto *NI = G.nodes_begin(), *NE = G.nodes_end(); NI != NE; ++NI) { |
| Nodes[std::distance(G.nodes_begin(), NI)] = |
| std::distance(G.edges_begin(), GTraits::child_edge_begin(NI)); |
| } |
| Nodes[G.nodes_size()] = G.edges_size(); // terminator node |
| for (auto *EI = G.edges_begin(), *EE = G.edges_end(); EI != EE; ++EI) { |
| Edges[std::distance(G.edges_begin(), EI)] = |
| std::distance(G.nodes_begin(), GTraits::edge_dest(*EI)); |
| EdgeValues[std::distance(G.edges_begin(), EI)] = EI->value(); |
| } |
| OptimizeCut(Nodes, G.nodes_size(), Edges, EdgeValues, EdgeCuts, |
| G.edges_size()); |
| for (int I = 0; I < G.edges_size(); ++I) { |
| if (EdgeCuts[I]) |
| CutEdges.set(I); |
| } |
| delete[] Nodes; |
| delete[] Edges; |
| delete[] EdgeCuts; |
| delete[] EdgeValues; |
| } else { // Use the default greedy heuristic |
| // Find the cheapest CFG edge that will eliminate a gadget (by being egress |
| // from a SOURCE node or ingress to a SINK node), and cut it. |
| MachineGadgetGraph::NodeSet GadgetSinks{G}; |
| MachineGadgetGraph::Edge *CheapestSoFar = nullptr; |
| for (auto NI = GTraits::nodes_begin(&G), NE = GTraits::nodes_end(&G); |
| NI != NE; ++NI) { |
| for (auto EI = GTraits::child_edge_begin(*NI), |
| EE = GTraits::child_edge_end(*NI); |
| EI != EE; ++EI) { |
| if (MachineGadgetGraph::isGadgetEdge(*EI)) { |
| // NI is a SOURCE node. Look for a cheap egress edge |
| for (auto EEI = GTraits::child_edge_begin(*NI); EEI != EE; ++EEI) { |
| if (MachineGadgetGraph::isCFGEdge(*EEI)) { |
| if (!CheapestSoFar || EEI->value() < CheapestSoFar->value()) |
| CheapestSoFar = EEI; |
| } |
| } |
| GadgetSinks.insert(GTraits::edge_dest(*EI)); |
| } else { // EI is a CFG edge |
| if (GadgetSinks.contains(GTraits::edge_dest(*EI))) { |
| // The dest is a SINK node. Hence EI is an ingress edge |
| if (!CheapestSoFar || EI->value() < CheapestSoFar->value()) |
| CheapestSoFar = EI; |
| } |
| } |
| } |
| } |
| assert(CheapestSoFar && "Failed to cut an edge"); |
| CutEdges.insert(CheapestSoFar); |
| } |
| LLVM_DEBUG(dbgs() << "Cut " << CutEdges.count() << " edges\n"); |
| } |
| |
| int X86LoadValueInjectionLoadHardeningPass::insertFences( |
| MachineGadgetGraph &G, EdgeSet &CutEdges /* in, out */) const { |
| int FencesInserted = 0, AdditionalEdgesCut = 0; |
| auto CutAllCFGEdges = [&CutEdges, &AdditionalEdgesCut](GTraits::NodeRef N) { |
| for (auto CEI = GTraits::child_edge_begin(N), |
| CEE = GTraits::child_edge_end(N); |
| CEI != CEE; ++CEI) { |
| if (MachineGadgetGraph::isCFGEdge(*CEI) && !CutEdges.contains(CEI)) { |
| CutEdges.insert(CEI); |
| ++AdditionalEdgesCut; |
| } |
| } |
| }; |
| for (auto NI = GTraits::nodes_begin(&G), NE = GTraits::nodes_end(&G); |
| NI != NE; ++NI) { |
| for (auto CEI = GTraits::child_edge_begin(*NI), |
| CEE = GTraits::child_edge_end(*NI); |
| CEI != CEE; ++CEI) { |
| if (CutEdges.contains(CEI)) { |
| MachineInstr *MI = (*NI)->value(), *Prev; |
| MachineBasicBlock *MBB; |
| MachineBasicBlock::iterator InsertionPt; |
| if (MI == ARG_NODE) { // insert LFENCE at beginning of entry block |
| MBB = &G.getMF().front(); |
| InsertionPt = MBB->begin(); |
| Prev = nullptr; |
| } else if (MI->isBranch()) { // insert the LFENCE before the branch |
| MBB = MI->getParent(); |
| InsertionPt = MI; |
| Prev = MI->getPrevNode(); |
| CutAllCFGEdges(*NI); |
| } else { // insert the LFENCE after the instruction |
| MBB = MI->getParent(); |
| InsertionPt = MI->getNextNode() ? MI->getNextNode() : MBB->end(); |
| Prev = InsertionPt == MBB->end() |
| ? (MBB->empty() ? nullptr : &MBB->back()) |
| : InsertionPt->getPrevNode(); |
| } |
| if ((InsertionPt == MBB->end() || !isFence(&*InsertionPt)) && |
| (!Prev || !isFence(Prev))) { |
| BuildMI(*MBB, InsertionPt, DebugLoc(), TII->get(X86::LFENCE)); |
| ++FencesInserted; |
| } |
| } |
| } |
| } |
| LLVM_DEBUG(dbgs() << "Inserted " << FencesInserted << " fences\n"); |
| LLVM_DEBUG(dbgs() << "Cut an additional " << AdditionalEdgesCut |
| << " edges during fence insertion\n"); |
| return FencesInserted; |
| } |
| |
| bool X86LoadValueInjectionLoadHardeningPass::instrUsesRegToAccessMemory( |
| const MachineInstr &MI, unsigned Reg) const { |
| if (!MI.mayLoadOrStore() || MI.getOpcode() == X86::MFENCE || |
| MI.getOpcode() == X86::SFENCE || MI.getOpcode() == X86::LFENCE) |
| return false; |
| |
| // FIXME: This does not handle pseudo loading instruction like TCRETURN* |
| const MCInstrDesc &Desc = MI.getDesc(); |
| int MemRefBeginIdx = X86II::getMemoryOperandNo(Desc.TSFlags); |
| if (MemRefBeginIdx < 0) { |
| LLVM_DEBUG(dbgs() << "Warning: unable to obtain memory operand for loading " |
| "instruction:\n"; |
| MI.print(dbgs()); dbgs() << '\n';); |
| return false; |
| } |
| MemRefBeginIdx += X86II::getOperandBias(Desc); |
| |
| const MachineOperand &BaseMO = |
| MI.getOperand(MemRefBeginIdx + X86::AddrBaseReg); |
| const MachineOperand &IndexMO = |
| MI.getOperand(MemRefBeginIdx + X86::AddrIndexReg); |
| return (BaseMO.isReg() && BaseMO.getReg() != X86::NoRegister && |
| TRI->regsOverlap(BaseMO.getReg(), Reg)) || |
| (IndexMO.isReg() && IndexMO.getReg() != X86::NoRegister && |
| TRI->regsOverlap(IndexMO.getReg(), Reg)); |
| } |
| |
| bool X86LoadValueInjectionLoadHardeningPass::instrUsesRegToBranch( |
| const MachineInstr &MI, unsigned Reg) const { |
| if (!MI.isConditionalBranch()) |
| return false; |
| for (const MachineOperand &Use : MI.uses()) |
| if (Use.isReg() && Use.getReg() == Reg) |
| return true; |
| return false; |
| } |
| |
| template <unsigned K> |
| bool X86LoadValueInjectionLoadHardeningPass::hasLoadFrom( |
| const MachineInstr &MI) const { |
| for (auto &MMO : MI.memoperands()) { |
| const PseudoSourceValue *PSV = MMO->getPseudoValue(); |
| if (PSV && PSV->kind() == K && MMO->isLoad()) |
| return true; |
| } |
| return false; |
| } |
| |
| bool X86LoadValueInjectionLoadHardeningPass::instrAccessesStackSlot( |
| const MachineInstr &MI) const { |
| // Check the PSV first |
| if (hasLoadFrom<PseudoSourceValue::PSVKind::FixedStack>(MI)) |
| return true; |
| // Some loads are not marked with a PSV, so we always need to double check |
| const MCInstrDesc &Desc = MI.getDesc(); |
| int MemRefBeginIdx = X86II::getMemoryOperandNo(Desc.TSFlags); |
| if (MemRefBeginIdx < 0) |
| return false; |
| MemRefBeginIdx += X86II::getOperandBias(Desc); |
| return MI.getOperand(MemRefBeginIdx + X86::AddrBaseReg).isFI() && |
| MI.getOperand(MemRefBeginIdx + X86::AddrScaleAmt).isImm() && |
| MI.getOperand(MemRefBeginIdx + X86::AddrIndexReg).isReg() && |
| MI.getOperand(MemRefBeginIdx + X86::AddrDisp).isImm() && |
| MI.getOperand(MemRefBeginIdx + X86::AddrScaleAmt).getImm() == 1 && |
| MI.getOperand(MemRefBeginIdx + X86::AddrIndexReg).getReg() == |
| X86::NoRegister && |
| MI.getOperand(MemRefBeginIdx + X86::AddrDisp).getImm() == 0; |
| } |
| |
| bool X86LoadValueInjectionLoadHardeningPass::instrAccessesConstantPool( |
| const MachineInstr &MI) const { |
| if (hasLoadFrom<PseudoSourceValue::PSVKind::ConstantPool>(MI)) |
| return true; |
| const MCInstrDesc &Desc = MI.getDesc(); |
| int MemRefBeginIdx = X86II::getMemoryOperandNo(Desc.TSFlags); |
| if (MemRefBeginIdx < 0) |
| return false; |
| MemRefBeginIdx += X86II::getOperandBias(Desc); |
| return MI.getOperand(MemRefBeginIdx + X86::AddrBaseReg).isReg() && |
| MI.getOperand(MemRefBeginIdx + X86::AddrScaleAmt).isImm() && |
| MI.getOperand(MemRefBeginIdx + X86::AddrIndexReg).isReg() && |
| MI.getOperand(MemRefBeginIdx + X86::AddrDisp).isCPI() && |
| (MI.getOperand(MemRefBeginIdx + X86::AddrBaseReg).getReg() == |
| X86::RIP || |
| MI.getOperand(MemRefBeginIdx + X86::AddrBaseReg).getReg() == |
| X86::NoRegister) && |
| MI.getOperand(MemRefBeginIdx + X86::AddrScaleAmt).getImm() == 1 && |
| MI.getOperand(MemRefBeginIdx + X86::AddrIndexReg).getReg() == |
| X86::NoRegister; |
| } |
| |
| bool X86LoadValueInjectionLoadHardeningPass::instrAccessesGOT( |
| const MachineInstr &MI) const { |
| if (hasLoadFrom<PseudoSourceValue::PSVKind::GOT>(MI)) |
| return true; |
| const MCInstrDesc &Desc = MI.getDesc(); |
| int MemRefBeginIdx = X86II::getMemoryOperandNo(Desc.TSFlags); |
| if (MemRefBeginIdx < 0) |
| return false; |
| MemRefBeginIdx += X86II::getOperandBias(Desc); |
| return MI.getOperand(MemRefBeginIdx + X86::AddrBaseReg).isReg() && |
| MI.getOperand(MemRefBeginIdx + X86::AddrScaleAmt).isImm() && |
| MI.getOperand(MemRefBeginIdx + X86::AddrIndexReg).isReg() && |
| MI.getOperand(MemRefBeginIdx + X86::AddrDisp).getTargetFlags() == |
| X86II::MO_GOTPCREL && |
| MI.getOperand(MemRefBeginIdx + X86::AddrBaseReg).getReg() == |
| X86::RIP && |
| MI.getOperand(MemRefBeginIdx + X86::AddrScaleAmt).getImm() == 1 && |
| MI.getOperand(MemRefBeginIdx + X86::AddrIndexReg).getReg() == |
| X86::NoRegister; |
| } |
| |
| INITIALIZE_PASS_BEGIN(X86LoadValueInjectionLoadHardeningPass, PASS_KEY, |
| "X86 LVI load hardening", false, false) |
| INITIALIZE_PASS_DEPENDENCY(MachineLoopInfo) |
| INITIALIZE_PASS_DEPENDENCY(MachineDominatorTree) |
| INITIALIZE_PASS_DEPENDENCY(MachineDominanceFrontier) |
| INITIALIZE_PASS_END(X86LoadValueInjectionLoadHardeningPass, PASS_KEY, |
| "X86 LVI load hardening", false, false) |
| |
| FunctionPass *llvm::createX86LoadValueInjectionLoadHardeningPass() { |
| return new X86LoadValueInjectionLoadHardeningPass(); |
| } |
