tools/llvm-cfi-verify/lib/GraphBuilder.h

   1 //===- GraphBuilder.h -------------------------------------------*- C++ -*-===//
   2 //
   3 //                      The LLVM Compiler Infrastructure
   4 //
   5 // This file is distributed under the University of Illinois Open Source
   6 // License. See LICENSE.TXT for details.
   7 //
   8 //===----------------------------------------------------------------------===//
   9
  10 #ifndef LLVM_CFI_VERIFY_GRAPH_BUILDER_H
  11 #define LLVM_CFI_VERIFY_GRAPH_BUILDER_H
  12
  13 #include "FileAnalysis.h"
  14
  15 #include "llvm/ADT/DenseMap.h"
  16 #include "llvm/BinaryFormat/ELF.h"
  17 #include "llvm/MC/MCAsmInfo.h"
  18 #include "llvm/MC/MCContext.h"
  19 #include "llvm/MC/MCDisassembler/MCDisassembler.h"
  20 #include "llvm/MC/MCInst.h"
  21 #include "llvm/MC/MCInstPrinter.h"
  22 #include "llvm/MC/MCInstrAnalysis.h"
  23 #include "llvm/MC/MCInstrDesc.h"
  24 #include "llvm/MC/MCInstrInfo.h"
  25 #include "llvm/MC/MCObjectFileInfo.h"
  26 #include "llvm/MC/MCRegisterInfo.h"
  27 #include "llvm/MC/MCSubtargetInfo.h"
  28 #include "llvm/Object/Binary.h"
  29 #include "llvm/Object/COFF.h"
  30 #include "llvm/Object/ELFObjectFile.h"
  31 #include "llvm/Object/ObjectFile.h"
  32 #include "llvm/Support/Casting.h"
  33 #include "llvm/Support/CommandLine.h"
  34 #include "llvm/Support/Error.h"
  35 #include "llvm/Support/MemoryBuffer.h"
  36 #include "llvm/Support/TargetRegistry.h"
  37 #include "llvm/Support/TargetSelect.h"
  38 #include "llvm/Support/raw_ostream.h"
  39
  40 #include <functional>
  41 #include <set>
  42 #include <string>
  43 #include <unordered_map>
  44
  45 using Instr = llvm::cfi_verify::FileAnalysis::Instr;
  46
  47 namespace llvm {
  48 namespace cfi_verify {
  49
  50 extern unsigned long long SearchLengthForUndef;
  51 extern unsigned long long SearchLengthForConditionalBranch;
  52
  53 struct ConditionalBranchNode {
  54   uint64_t Address;
  55   uint64_t Target;
  56   uint64_t Fallthrough;
  57   // Does this conditional branch look like it's used for CFI protection? i.e.
  58   //  - The exit point of a basic block whos entry point is {target|fallthrough}
  59   //    is a CFI trap, and...
  60   //  - The exit point of the other basic block is an undirect CF instruction.
  61   bool CFIProtection;
  62   bool IndirectCFIsOnTargetPath;
  63 };
  64
  65 // The canonical graph result structure returned by GraphBuilder. The members
  66 // in this structure encapsulate all possible code paths to the instruction
  67 // located at `BaseAddress`.
  68 struct GraphResult {
  69   uint64_t BaseAddress;
  70
  71   // Map between an instruction address, and the address of the next instruction
  72   // that will be executed. This map will contain all keys in the range:
  73   //   - [orphaned node, base address)
  74   //   - [conditional branch node {target|fallthrough}, base address)
  75   DenseMap<uint64_t, uint64_t> IntermediateNodes;
  76
  77   // A list of orphaned nodes. A node is an 'orphan' if it meets any of the
  78   // following criteria:
  79   //   - The length of the path from the base to this node has exceeded
  80   //     `SearchLengthForConditionalBranch`.
  81   //   - The node has no cross references to it.
  82   //   - The path from the base to this node is cyclic.
  83   std::vector<uint64_t> OrphanedNodes;
  84
  85   // A list of top-level conditional branches that exist at the top of any
  86   // non-orphan paths from the base.
  87   std::vector<ConditionalBranchNode> ConditionalBranchNodes;
  88
  89   // Returns an in-order list of the path between the address provided and the
  90   // base. The provided address must be part of this graph, and must not be a
  91   // conditional branch.
  92   std::vector<uint64_t> flattenAddress(uint64_t Address) const;
  93
  94   // Print the DOT representation of this result.
  95   void printToDOT(const FileAnalysis &Analysis, raw_ostream &OS) const;
  96 };
  97
  98 class GraphBuilder {
  99 public:
 100   // Build the control flow graph for a provided control flow node. This method
 101   // will enumerate all branch nodes that can lead to this node, and place them
 102   // into GraphResult::ConditionalBranchNodes. It will also provide any orphaned
 103   // (i.e. the upwards traversal did not make it to a branch node) flows to the
 104   // provided node in GraphResult::OrphanedNodes.
 105   static GraphResult buildFlowGraph(const FileAnalysis &Analysis,
 106                                     uint64_t Address);
 107
 108 private:
 109   // Implementation function that actually builds the flow graph. Retrieves a
 110   // list of cross references to instruction referenced in `Address`. If any of
 111   // these XRefs are conditional branches, it will build the other potential
 112   // path (fallthrough or target) using `buildFlowsToUndefined`. Otherwise, this
 113   // function will recursively call itself where `Address` in the recursive call
 114   // is now the XRef. If any XRef is an orphan, it is added to
 115   // `Result.OrphanedNodes`. `OpenedNodes` keeps track of the list of nodes
 116   // in the current path and is used for cycle-checking. If the path is found
 117   // to be cyclic, it will be added to `Result.OrphanedNodes`.
 118   static void buildFlowGraphImpl(const FileAnalysis &Analysis,
 119                                  DenseSet<uint64_t> &OpenedNodes,
 120                                  GraphResult &Result, uint64_t Address,
 121                                  uint64_t Depth);
 122
 123   // Utilised by buildFlowGraphImpl to build the tree out from the provided
 124   // conditional branch node to an undefined instruction. The provided
 125   // conditional branch node must have exactly one of its subtrees set, and will
 126   // update the node's CFIProtection field if a deterministic flow can be found
 127   // to an undefined instruction.
 128   static void buildFlowsToUndefined(const FileAnalysis &Analysis,
 129                                     GraphResult &Result,
 130                                     ConditionalBranchNode &BranchNode,
 131                                     const Instr &BranchInstrMeta);
 132 };
 133
 134 } // end namespace cfi_verify
 135 } // end namespace llvm
 136
 137 #endif // LLVM_CFI_VERIFY_GRAPH_BUILDER_H