diff options
Diffstat (limited to 'llvm/lib/Target/X86/X86LoadValueInjectionLoadHardening.cpp')
| -rw-r--r-- | llvm/lib/Target/X86/X86LoadValueInjectionLoadHardening.cpp | 309 |
1 files changed, 306 insertions, 3 deletions
diff --git a/llvm/lib/Target/X86/X86LoadValueInjectionLoadHardening.cpp b/llvm/lib/Target/X86/X86LoadValueInjectionLoadHardening.cpp index 563b225c5ef..50f8b3477ac 100644 --- a/llvm/lib/Target/X86/X86LoadValueInjectionLoadHardening.cpp +++ b/llvm/lib/Target/X86/X86LoadValueInjectionLoadHardening.cpp @@ -9,7 +9,30 @@ /// 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). +/// 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 runOnMachineFunction() +/// to tell LLVM that the function was modified. /// //===----------------------------------------------------------------------===// @@ -37,6 +60,7 @@ #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" @@ -45,11 +69,16 @@ 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 " @@ -74,6 +103,12 @@ static cl::opt<bool> EmitDotVerify( "potential LVI gadgets, used for testing purposes only"), 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; + namespace { struct MachineGadgetGraph : ImmutableGraph<MachineInstr *, int> { @@ -125,7 +160,19 @@ private: getGadgetGraph(MachineFunction &MF, const MachineLoopInfo &MLI, const MachineDominatorTree &MDT, const MachineDominanceFrontier &MDF) const; - + int hardenLoadsWithPlugin(MachineFunction &MF, + std::unique_ptr<MachineGadgetGraph> Graph) const; + int hardenLoadsWithGreedyHeuristic( + MachineFunction &MF, std::unique_ptr<MachineGadgetGraph> Graph) const; + int elimMitigatedEdgesAndNodes(MachineGadgetGraph &G, + EdgeSet &ElimEdges /* in, out */, + NodeSet &ElimNodes /* in, out */) const; + std::unique_ptr<MachineGadgetGraph> + trimMitigatedEdges(std::unique_ptr<MachineGadgetGraph> Graph) const; + void findAndCutEdges(MachineGadgetGraph &G, + EdgeSet &CutEdges /* out */) const; + int insertFences(MachineFunction &MF, MachineGadgetGraph &G, + EdgeSet &CutEdges /* in, out */) const; bool instrUsesRegToAccessMemory(const MachineInstr &I, unsigned Reg) const; bool instrUsesRegToBranch(const MachineInstr &I, unsigned Reg) const; inline bool isFence(const MachineInstr *MI) const { @@ -252,7 +299,27 @@ bool X86LoadValueInjectionLoadHardeningPass::runOnMachineFunction( return false; } - return 0; + int FencesInserted; + 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"); + } + FencesInserted = hardenLoadsWithPlugin(MF, std::move(Graph)); + } else { // Use the default greedy heuristic + FencesInserted = hardenLoadsWithGreedyHeuristic(MF, std::move(Graph)); + } + + if (FencesInserted > 0) + ++NumFunctionsMitigated; + NumFences += FencesInserted; + return (FencesInserted > 0); } std::unique_ptr<MachineGadgetGraph> @@ -471,6 +538,242 @@ X86LoadValueInjectionLoadHardeningPass::getGadgetGraph( return G; } +// Returns the number of remaining gadget edges that could not be eliminated +int X86LoadValueInjectionLoadHardeningPass::elimMitigatedEdgesAndNodes( + MachineGadgetGraph &G, MachineGadgetGraph::EdgeSet &ElimEdges /* in, out */, + MachineGadgetGraph::NodeSet &ElimNodes /* in, out */) const { + if (G.NumFences > 0) { + // Eliminate fences and CFG edges that ingress and egress the fence, as + // they are trivially mitigated. + for (const auto &E : G.edges()) { + const MachineGadgetGraph::Node *Dest = E.getDest(); + if (isFence(Dest->getValue())) { + ElimNodes.insert(*Dest); + ElimEdges.insert(E); + for (const auto &DE : Dest->edges()) + ElimEdges.insert(DE); + } + } + } + + // Find and eliminate gadget edges that have been mitigated. + int MitigatedGadgets = 0, RemainingGadgets = 0; + MachineGadgetGraph::NodeSet ReachableNodes{G}; + for (const auto &RootN : G.nodes()) { + if (llvm::none_of(RootN.edges(), MachineGadgetGraph::isGadgetEdge)) + continue; // skip this node if it isn't a gadget source + + // Find all of the nodes that are CFG-reachable from RootN using DFS + ReachableNodes.clear(); + std::function<void(const MachineGadgetGraph::Node *, bool)> + FindReachableNodes = + [&](const MachineGadgetGraph::Node *N, bool FirstNode) { + if (!FirstNode) + ReachableNodes.insert(*N); + for (const auto &E : N->edges()) { + const MachineGadgetGraph::Node *Dest = E.getDest(); + if (MachineGadgetGraph::isCFGEdge(E) && + !ElimEdges.contains(E) && !ReachableNodes.contains(*Dest)) + FindReachableNodes(Dest, false); + } + }; + FindReachableNodes(&RootN, true); + + // Any gadget whose sink is unreachable has been mitigated + for (const auto &E : RootN.edges()) { + if (MachineGadgetGraph::isGadgetEdge(E)) { + if (ReachableNodes.contains(*E.getDest())) { + // This gadget's sink is reachable + ++RemainingGadgets; + } else { // This gadget's sink is unreachable, and therefore mitigated + ++MitigatedGadgets; + ElimEdges.insert(E); + } + } + } + } + return RemainingGadgets; +} + +std::unique_ptr<MachineGadgetGraph> +X86LoadValueInjectionLoadHardeningPass::trimMitigatedEdges( + std::unique_ptr<MachineGadgetGraph> Graph) const { + MachineGadgetGraph::NodeSet ElimNodes{*Graph}; + MachineGadgetGraph::EdgeSet ElimEdges{*Graph}; + int RemainingGadgets = + elimMitigatedEdgesAndNodes(*Graph, ElimEdges, ElimNodes); + if (ElimEdges.empty() && ElimNodes.empty()) { + Graph->NumFences = 0; + Graph->NumGadgets = RemainingGadgets; + } else { + Graph = GraphBuilder::trim(*Graph, ElimNodes, ElimEdges, 0 /* NumFences */, + RemainingGadgets); + } + return Graph; +} + +int X86LoadValueInjectionLoadHardeningPass::hardenLoadsWithPlugin( + MachineFunction &MF, std::unique_ptr<MachineGadgetGraph> Graph) const { + int FencesInserted = 0; + + do { + LLVM_DEBUG(dbgs() << "Eliminating mitigated paths...\n"); + Graph = trimMitigatedEdges(std::move(Graph)); + LLVM_DEBUG(dbgs() << "Eliminating mitigated paths... Done\n"); + if (Graph->NumGadgets == 0) + break; + + LLVM_DEBUG(dbgs() << "Cutting edges...\n"); + EdgeSet CutEdges{*Graph}; + auto Nodes = std::make_unique<unsigned int[]>(Graph->nodes_size() + + 1 /* terminator node */); + auto Edges = std::make_unique<unsigned int[]>(Graph->edges_size()); + auto EdgeCuts = std::make_unique<int[]>(Graph->edges_size()); + auto EdgeValues = std::make_unique<int[]>(Graph->edges_size()); + for (const auto &N : Graph->nodes()) { + Nodes[Graph->getNodeIndex(N)] = Graph->getEdgeIndex(*N.edges_begin()); + } + Nodes[Graph->nodes_size()] = Graph->edges_size(); // terminator node + for (const auto &E : Graph->edges()) { + Edges[Graph->getEdgeIndex(E)] = Graph->getNodeIndex(*E.getDest()); + EdgeValues[Graph->getEdgeIndex(E)] = E.getValue(); + } + OptimizeCut(Nodes.get(), Graph->nodes_size(), Edges.get(), EdgeValues.get(), + EdgeCuts.get(), Graph->edges_size()); + for (int I = 0; I < Graph->edges_size(); ++I) + if (EdgeCuts[I]) + CutEdges.set(I); + LLVM_DEBUG(dbgs() << "Cutting edges... Done\n"); + LLVM_DEBUG(dbgs() << "Cut " << CutEdges.count() << " edges\n"); + + LLVM_DEBUG(dbgs() << "Inserting LFENCEs...\n"); + FencesInserted += insertFences(MF, *Graph, CutEdges); + LLVM_DEBUG(dbgs() << "Inserting LFENCEs... Done\n"); + LLVM_DEBUG(dbgs() << "Inserted " << FencesInserted << " fences\n"); + + Graph = GraphBuilder::trim(*Graph, MachineGadgetGraph::NodeSet{*Graph}, + CutEdges); + } while (true); + + return FencesInserted; +} + +int X86LoadValueInjectionLoadHardeningPass::hardenLoadsWithGreedyHeuristic( + MachineFunction &MF, std::unique_ptr<MachineGadgetGraph> Graph) const { + LLVM_DEBUG(dbgs() << "Eliminating mitigated paths...\n"); + Graph = trimMitigatedEdges(std::move(Graph)); + LLVM_DEBUG(dbgs() << "Eliminating mitigated paths... Done\n"); + if (Graph->NumGadgets == 0) + return 0; + + LLVM_DEBUG(dbgs() << "Cutting edges...\n"); + MachineGadgetGraph::NodeSet ElimNodes{*Graph}, GadgetSinks{*Graph}; + MachineGadgetGraph::EdgeSet ElimEdges{*Graph}, CutEdges{*Graph}; + auto IsCFGEdge = [&ElimEdges, &CutEdges](const MachineGadgetGraph::Edge &E) { + return !ElimEdges.contains(E) && !CutEdges.contains(E) && + MachineGadgetGraph::isCFGEdge(E); + }; + auto IsGadgetEdge = [&ElimEdges, + &CutEdges](const MachineGadgetGraph::Edge &E) { + return !ElimEdges.contains(E) && !CutEdges.contains(E) && + MachineGadgetGraph::isGadgetEdge(E); + }; + + // FIXME: this is O(E^2), we could probably do better. + do { + // 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. + const MachineGadgetGraph::Edge *CheapestSoFar = nullptr; + + // First, collect all gadget source and sink nodes. + MachineGadgetGraph::NodeSet GadgetSources{*Graph}, GadgetSinks{*Graph}; + for (const auto &N : Graph->nodes()) { + if (ElimNodes.contains(N)) + continue; + for (const auto &E : N.edges()) { + if (IsGadgetEdge(E)) { + GadgetSources.insert(N); + GadgetSinks.insert(*E.getDest()); + } + } + } + + // Next, look for the cheapest CFG edge which, when cut, is guaranteed to + // mitigate at least one gadget by either: + // (a) being egress from a gadget source, or + // (b) being ingress to a gadget sink. + for (const auto &N : Graph->nodes()) { + if (ElimNodes.contains(N)) + continue; + for (const auto &E : N.edges()) { + if (IsCFGEdge(E)) { + if (GadgetSources.contains(N) || GadgetSinks.contains(*E.getDest())) { + if (!CheapestSoFar || E.getValue() < CheapestSoFar->getValue()) + CheapestSoFar = &E; + } + } + } + } + + assert(CheapestSoFar && "Failed to cut an edge"); + CutEdges.insert(*CheapestSoFar); + ElimEdges.insert(*CheapestSoFar); + } while (elimMitigatedEdgesAndNodes(*Graph, ElimEdges, ElimNodes)); + LLVM_DEBUG(dbgs() << "Cutting edges... Done\n"); + LLVM_DEBUG(dbgs() << "Cut " << CutEdges.count() << " edges\n"); + + LLVM_DEBUG(dbgs() << "Inserting LFENCEs...\n"); + int FencesInserted = insertFences(MF, *Graph, CutEdges); + LLVM_DEBUG(dbgs() << "Inserting LFENCEs... Done\n"); + LLVM_DEBUG(dbgs() << "Inserted " << FencesInserted << " fences\n"); + + return FencesInserted; +} + +int X86LoadValueInjectionLoadHardeningPass::insertFences( + MachineFunction &MF, MachineGadgetGraph &G, + EdgeSet &CutEdges /* in, out */) const { + int FencesInserted = 0; + for (const auto &N : G.nodes()) { + for (const auto &E : N.edges()) { + if (CutEdges.contains(E)) { + MachineInstr *MI = N.getValue(), *Prev; + MachineBasicBlock *MBB; // Insert an LFENCE in this MBB + MachineBasicBlock::iterator InsertionPt; // ...at this point + if (MI == MachineGadgetGraph::ArgNodeSentinel) { + // insert LFENCE at beginning of entry block + MBB = &MF.front(); + InsertionPt = MBB->begin(); + Prev = nullptr; + } else if (MI->isBranch()) { // insert the LFENCE before the branch + MBB = MI->getParent(); + InsertionPt = MI; + Prev = MI->getPrevNode(); + // Remove all egress CFG edges from this branch because the inserted + // LFENCE prevents gadgets from crossing the branch. + for (const auto &E : N.edges()) { + if (MachineGadgetGraph::isCFGEdge(E)) + CutEdges.insert(E); + } + } 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(); + } + // Ensure this insertion is not redundant (two LFENCEs in sequence). + if ((InsertionPt == MBB->end() || !isFence(&*InsertionPt)) && + (!Prev || !isFence(Prev))) { + BuildMI(*MBB, InsertionPt, DebugLoc(), TII->get(X86::LFENCE)); + ++FencesInserted; + } + } + } + } + return FencesInserted; +} + bool X86LoadValueInjectionLoadHardeningPass::instrUsesRegToAccessMemory( const MachineInstr &MI, unsigned Reg) const { if (!MI.mayLoadOrStore() || MI.getOpcode() == X86::MFENCE || |
