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//==-- 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 runOnMachineFunction()
/// 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/STLExtras.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 llvm::sys::DynamicLibrary OptimizeDL;
typedef int (*OptimizeCutT)(unsigned int *Nodes, unsigned int NodesSize,
unsigned int *Edges, int *EdgeValues,
int *CutEdges /* out */, unsigned int EdgesSize);
static OptimizeCutT OptimizeCut = nullptr;
namespace {
struct MachineGadgetGraph : ImmutableGraph<MachineInstr *, int> {
static constexpr int GadgetEdgeSentinel = -1;
static constexpr MachineInstr *const ArgNodeSentinel = nullptr;
using GraphT = ImmutableGraph<MachineInstr *, int>;
using Node = typename GraphT::Node;
using Edge = typename GraphT::Edge;
using size_type = typename GraphT::size_type;
MachineGadgetGraph(std::unique_ptr<Node[]> Nodes,
std::unique_ptr<Edge[]> Edges, size_type NodesSize,
size_type EdgesSize, int NumFences = 0, int NumGadgets = 0)
: GraphT(std::move(Nodes), std::move(Edges), NodesSize, EdgesSize),
NumFences(NumFences), NumGadgets(NumGadgets) {}
static inline bool isCFGEdge(const Edge &E) {
return E.getValue() != GadgetEdgeSentinel;
}
static inline bool isGadgetEdge(const Edge &E) {
return E.getValue() == GadgetEdgeSentinel;
}
int NumFences;
int NumGadgets;
};
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:
using GraphBuilder = ImmutableGraphBuilder<MachineGadgetGraph>;
using Edge = MachineGadgetGraph::Edge;
using Node = MachineGadgetGraph::Node;
using EdgeSet = MachineGadgetGraph::EdgeSet;
using NodeSet = MachineGadgetGraph::NodeSet;
const X86Subtarget *STI;
const TargetInstrInfo *TII;
const TargetRegisterInfo *TRI;
std::unique_ptr<MachineGadgetGraph>
getGadgetGraph(MachineFunction &MF, const MachineLoopInfo &MLI,
const MachineDominatorTree &MDT,
const MachineDominanceFrontier &MDF) const;
int hardenLoadsWithPlugin(MachineFunction &MF,
std::unique_ptr<MachineGadgetGraph> Graph) const;
int hardenLoadsWithHeuristic(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 {
return MI && (MI->getOpcode() == X86::LFENCE ||
(STI->useLVIControlFlowIntegrity() && MI->isCall()));
}
};
} // end anonymous namespace
namespace llvm {
template <>
struct GraphTraits<MachineGadgetGraph *>
: GraphTraits<ImmutableGraph<MachineInstr *, int> *> {};
template <>
struct DOTGraphTraits<MachineGadgetGraph *> : DefaultDOTGraphTraits {
using GraphType = MachineGadgetGraph;
using Traits = llvm::GraphTraits<GraphType *>;
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) {}
std::string getNodeLabel(NodeRef Node, GraphType *) {
if (Node->getValue() == MachineGadgetGraph::ArgNodeSentinel)
return "ARGS";
std::string Str;
raw_string_ostream OS(Str);
OS << *Node->getValue();
return OS.str();
}
static std::string getNodeAttributes(NodeRef Node, GraphType *) {
MachineInstr *MI = Node->getValue();
if (MI == MachineGadgetGraph::ArgNodeSentinel)
return "color = blue";
if (MI->getOpcode() == X86::LFENCE)
return "color = green";
return "";
}
static std::string getEdgeAttributes(NodeRef, ChildIteratorType E,
GraphType *) {
int EdgeVal = (*E.getCurrent()).getValue();
return EdgeVal >= 0 ? "label = " + std::to_string(EdgeVal)
: "color = red, style = \"dashed\"";
}
};
} // end namespace llvm
constexpr MachineInstr *MachineGadgetGraph::ArgNodeSentinel;
constexpr int MachineGadgetGraph::GadgetEdgeSentinel;
char X86LoadValueInjectionLoadHardeningPass::ID = 0;
void X86LoadValueInjectionLoadHardeningPass::getAnalysisUsage(
AnalysisUsage &AU) const {
MachineFunctionPass::getAnalysisUsage(AU);
AU.addRequired<MachineLoopInfo>();
AU.addRequired<MachineDominatorTree>();
AU.addRequired<MachineDominanceFrontier>();
AU.setPreservesCFG();
}
static void writeGadgetGraph(raw_ostream &OS, MachineFunction &MF,
MachineGadgetGraph *G) {
WriteGraph(OS, G, /*ShortNames*/ false,
"Speculative gadgets for \"" + MF.getName() + "\" function");
}
bool X86LoadValueInjectionLoadHardeningPass::runOnMachineFunction(
MachineFunction &MF) {
LLVM_DEBUG(dbgs() << "***** " << getPassName() << " : " << MF.getName()
<< " *****\n");
STI = &MF.getSubtarget<X86Subtarget>();
if (!STI->useLVILoadHardening())
return false;
// FIXME: support 32-bit
if (!STI->is64Bit())
report_fatal_error("LVI load hardening is only supported on 64-bit", false);
// 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() << "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);
LLVM_DEBUG(dbgs() << "Building gadget graph... Done\n");
if (Graph == nullptr)
return false; // didn't find any gadgets
if (EmitDotVerify) {
writeGadgetGraph(outs(), MF, Graph.get());
return false;
}
if (EmitDot || EmitDotOnly) {
LLVM_DEBUG(dbgs() << "Emitting gadget graph...\n");
std::error_code FileError;
std::string FileName = "lvi.";
FileName += MF.getName();
FileName += ".dot";
raw_fd_ostream FileOut(FileName, FileError);
if (FileError)
errs() << FileError.message();
writeGadgetGraph(FileOut, MF, Graph.get());
FileOut.close();
LLVM_DEBUG(dbgs() << "Emitting gadget graph... Done\n");
if (EmitDotOnly)
return false;
}
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 = hardenLoadsWithHeuristic(MF, std::move(Graph));
}
if (FencesInserted > 0)
++NumFunctionsMitigated;
NumFences += FencesInserted;
return (FencesInserted > 0);
}
std::unique_ptr<MachineGadgetGraph>
X86LoadValueInjectionLoadHardeningPass::getGadgetGraph(
MachineFunction &MF, const MachineLoopInfo &MLI,
const MachineDominatorTree &MDT,
const MachineDominanceFrontier &MDF) 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::BuilderNodeRef;
DenseMap<MachineInstr *, GraphIter> NodeMap;
int FenceCount = 0, GadgetCount = 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};
}
return std::pair<GraphIter, bool>{Ref->getSecond(), false};
};
// The `Transmitters` map memoizes transmitters found for each def. If a def
// has not yet been analyzed, then it will not appear in the map. If a def
// has been analyzed and was determined not to have any transmitters, then
// its list of transmitters will be empty.
DenseMap<NodeId, std::vector<NodeId>> Transmitters;
// Analyze all machine instructions to find gadgets and LFENCEs, adding
// each interesting value to `Nodes`
auto AnalyzeDef = [&](NodeAddr<DefNode *> SourceDef) {
SmallSet<NodeId, 8> UsesVisited, DefsVisited;
std::function<void(NodeAddr<DefNode *>)> AnalyzeDefUseChain =
[&](NodeAddr<DefNode *> Def) {
if (Transmitters.find(Def.Id) != Transmitters.end())
return; // Already analyzed `Def`
// Use RDF to find all the uses of `Def`
rdf::NodeSet Uses;
RegisterRef DefReg = Def.Addr->getRegRef(DFG);
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)
Uses.emplace(UA.first);
}
}
} else { // not a phi node
Uses.emplace(UseID);
}
}
// For each use of `Def`, we want to know whether:
// (1) The use can leak the Def'ed value,
// (2) The use can further propagate the Def'ed value to more defs
for (auto UseID : Uses) {
if (!UsesVisited.insert(UseID).second)
continue; // Already visited this use of `Def`
auto Use = DFG.addr<UseNode *>(UseID);
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, in which
// case all arguments will be treated as gadget sources during
// analysis of the callee function.
if (UseMI.isCall())
continue;
// Check whether this use can transmit (leak) its value.
if (instrUsesRegToAccessMemory(UseMI, UseMO.getReg()) ||
(!NoConditionalBranches &&
instrUsesRegToBranch(UseMI, UseMO.getReg()))) {
Transmitters[Def.Id].push_back(Use.Addr->getOwner(DFG).Id);
if (UseMI.mayLoad())
continue; // Found a transmitting load -- no need to continue
// traversing its defs (i.e., this load will become
// a new gadget source anyways).
}
// Check whether the use propagates to more defs.
NodeAddr<InstrNode *> Owner{Use.Addr->getOwner(DFG)};
rdf::NodeList AnalyzedChildDefs;
for (auto &ChildDef :
Owner.Addr->members_if(DataFlowGraph::IsDef, DFG)) {
if (!DefsVisited.insert(ChildDef.Id).second)
continue; // Already visited this def
if (Def.Addr->getAttrs() & NodeAttrs::Dead)
continue;
if (Def.Id == ChildDef.Id)
continue; // `Def` uses itself (e.g., increment loop counter)
AnalyzeDefUseChain(ChildDef);
// `Def` inherits all of its child defs' transmitters.
for (auto TransmitterId : Transmitters[ChildDef.Id])
Transmitters[Def.Id].push_back(TransmitterId);
}
}
// Note that this statement adds `Def.Id` to the map if no
// transmitters were found for `Def`.
auto &DefTransmitters = Transmitters[Def.Id];
// Remove duplicate transmitters
llvm::sort(DefTransmitters);
DefTransmitters.erase(
std::unique(DefTransmitters.begin(), DefTransmitters.end()),
DefTransmitters.end());
};
// Find all of the transmitters
AnalyzeDefUseChain(SourceDef);
auto &SourceDefTransmitters = Transmitters[SourceDef.Id];
if (SourceDefTransmitters.empty())
return; // No transmitters for `SourceDef`
MachineInstr *Source = SourceDef.Addr->getFlags() & NodeAttrs::PhiRef
? MachineGadgetGraph::ArgNodeSentinel
: SourceDef.Addr->getOp().getParent();
auto GadgetSource = MaybeAddNode(Source);
// Each transmitter is a sink for `SourceDef`.
for (auto TransmitterId : SourceDefTransmitters) {
MachineInstr *Sink = DFG.addr<StmtNode *>(TransmitterId).Addr->getCode();
auto GadgetSink = MaybeAddNode(Sink);
// Add the gadget edge to the graph.
Builder.addEdge(MachineGadgetGraph::GadgetEdgeSentinel,
GadgetSource.first, GadgetSink.first);
++GadgetCount;
}
};
LLVM_DEBUG(dbgs() << "Analyzing def-use chains to find gadgets\n");
// Analyze function arguments
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);
llvm::for_each(Defs, 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()) {
NodeList Defs = SA.Addr->members_if(DataFlowGraph::IsDef, DFG);
llvm::for_each(Defs, AnalyzeDef);
}
}
}
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);
};
// ArgNodeSentinel is a pseudo-instruction that represents MF args in the
// GadgetGraph
GraphIter ArgNode = MaybeAddNode(MachineGadgetGraph::ArgNodeSentinel).first;
TraverseCFG(&MF.front(), ArgNode, 0);
std::unique_ptr<MachineGadgetGraph> G{Builder.get(FenceCount, GadgetCount)};
LLVM_DEBUG(dbgs() << "Found " << G->nodes_size() << " nodes\n");
return G;
}
// Returns the number of remaining gadget edges that could not be eliminated
int X86LoadValueInjectionLoadHardeningPass::elimMitigatedEdgesAndNodes(
MachineGadgetGraph &G, EdgeSet &ElimEdges /* in, out */,
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 Edge &E : G.edges()) {
const Node *Dest = E.getDest();
if (isFence(Dest->getValue())) {
ElimNodes.insert(*Dest);
ElimEdges.insert(E);
for (const Edge &DE : Dest->edges())
ElimEdges.insert(DE);
}
}
}
// Find and eliminate gadget edges that have been mitigated.
int MitigatedGadgets = 0, RemainingGadgets = 0;
NodeSet ReachableNodes{G};
for (const Node &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 Node *, bool)> FindReachableNodes =
[&](const Node *N, bool FirstNode) {
if (!FirstNode)
ReachableNodes.insert(*N);
for (const Edge &E : N->edges()) {
const 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 Edge &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 {
NodeSet ElimNodes{*Graph};
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 Node &N : Graph->nodes()) {
Nodes[Graph->getNodeIndex(N)] = Graph->getEdgeIndex(*N.edges_begin());
}
Nodes[Graph->nodes_size()] = Graph->edges_size(); // terminator node
for (const Edge &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, NodeSet{*Graph}, CutEdges);
} while (true);
return FencesInserted;
}
int X86LoadValueInjectionLoadHardeningPass::hardenLoadsWithHeuristic(
MachineFunction &MF, std::unique_ptr<MachineGadgetGraph> Graph) const {
// If `MF` does not have any fences, then no gadgets would have been
// mitigated at this point.
if (Graph->NumFences > 0) {
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");
EdgeSet CutEdges{*Graph};
// Begin by collecting all ingress CFG edges for each node
DenseMap<const Node *, SmallVector<const Edge *, 2>> IngressEdgeMap;
for (const Edge &E : Graph->edges())
if (MachineGadgetGraph::isCFGEdge(E))
IngressEdgeMap[E.getDest()].push_back(&E);
// For each gadget edge, make cuts that guarantee the gadget will be
// mitigated. A computationally efficient way to achieve this is to either:
// (a) cut all egress CFG edges from the gadget source, or
// (b) cut all ingress CFG edges to the gadget sink.
//
// Moreover, the algorithm tries not to make a cut into a loop by preferring
// to make a (b)-type cut if the gadget source resides at a greater loop depth
// than the gadget sink, or an (a)-type cut otherwise.
for (const Node &N : Graph->nodes()) {
for (const Edge &E : N.edges()) {
if (!MachineGadgetGraph::isGadgetEdge(E))
continue;
SmallVector<const Edge *, 2> EgressEdges;
SmallVector<const Edge *, 2> &IngressEdges = IngressEdgeMap[E.getDest()];
for (const Edge &EgressEdge : N.edges())
if (MachineGadgetGraph::isCFGEdge(EgressEdge))
EgressEdges.push_back(&EgressEdge);
int EgressCutCost = 0, IngressCutCost = 0;
for (const Edge *EgressEdge : EgressEdges)
if (!CutEdges.contains(*EgressEdge))
EgressCutCost += EgressEdge->getValue();
for (const Edge *IngressEdge : IngressEdges)
if (!CutEdges.contains(*IngressEdge))
IngressCutCost += IngressEdge->getValue();
auto &EdgesToCut =
IngressCutCost < EgressCutCost ? IngressEdges : EgressEdges;
for (const Edge *E : EdgesToCut)
CutEdges.insert(*E);
}
}
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 Node &N : G.nodes()) {
for (const Edge &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 Edge &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 ||
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;
}
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();
}
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