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1 //===-- SafeStack.cpp - Safe Stack Insertion ------------------------------===//
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2 //
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3 // The LLVM Compiler Infrastructure
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4 //
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5 // This file is distributed under the University of Illinois Open Source
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6 // License. See LICENSE.TXT for details.
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7 //
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8 //===----------------------------------------------------------------------===//
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9 //
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10 // This pass splits the stack into the safe stack (kept as-is for LLVM backend)
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11 // and the unsafe stack (explicitly allocated and managed through the runtime
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12 // support library).
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13 //
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14 // http://clang.llvm.org/docs/SafeStack.html
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15 //
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16 //===----------------------------------------------------------------------===//
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17
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18 #include "SafeStackColoring.h"
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19 #include "SafeStackLayout.h"
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20 #include "llvm/ADT/Statistic.h"
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21 #include "llvm/ADT/Triple.h"
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22 #include "llvm/Analysis/BranchProbabilityInfo.h"
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23 #include "llvm/Analysis/ScalarEvolution.h"
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24 #include "llvm/Analysis/ScalarEvolutionExpressions.h"
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25 #include "llvm/CodeGen/Passes.h"
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26 #include "llvm/IR/Constants.h"
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27 #include "llvm/IR/DIBuilder.h"
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28 #include "llvm/IR/DataLayout.h"
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29 #include "llvm/IR/DerivedTypes.h"
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30 #include "llvm/IR/Function.h"
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31 #include "llvm/IR/IRBuilder.h"
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32 #include "llvm/IR/InstIterator.h"
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33 #include "llvm/IR/Instructions.h"
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34 #include "llvm/IR/IntrinsicInst.h"
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35 #include "llvm/IR/Intrinsics.h"
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36 #include "llvm/IR/MDBuilder.h"
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37 #include "llvm/IR/Module.h"
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38 #include "llvm/Pass.h"
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39 #include "llvm/Support/CommandLine.h"
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40 #include "llvm/Support/Debug.h"
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41 #include "llvm/Support/Format.h"
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42 #include "llvm/Support/MathExtras.h"
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43 #include "llvm/Support/raw_os_ostream.h"
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44 #include "llvm/Target/TargetLowering.h"
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45 #include "llvm/Target/TargetSubtargetInfo.h"
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46 #include "llvm/Transforms/Utils/BasicBlockUtils.h"
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47 #include "llvm/Transforms/Utils/Local.h"
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48 #include "llvm/Transforms/Utils/ModuleUtils.h"
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49
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50 using namespace llvm;
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51 using namespace llvm::safestack;
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52
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53 #define DEBUG_TYPE "safestack"
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54
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55 namespace llvm {
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56
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57 STATISTIC(NumFunctions, "Total number of functions");
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58 STATISTIC(NumUnsafeStackFunctions, "Number of functions with unsafe stack");
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59 STATISTIC(NumUnsafeStackRestorePointsFunctions,
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60 "Number of functions that use setjmp or exceptions");
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61
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62 STATISTIC(NumAllocas, "Total number of allocas");
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63 STATISTIC(NumUnsafeStaticAllocas, "Number of unsafe static allocas");
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64 STATISTIC(NumUnsafeDynamicAllocas, "Number of unsafe dynamic allocas");
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65 STATISTIC(NumUnsafeByValArguments, "Number of unsafe byval arguments");
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66 STATISTIC(NumUnsafeStackRestorePoints, "Number of setjmps and landingpads");
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67
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68 } // namespace llvm
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69
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70 namespace {
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71
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72 /// Rewrite an SCEV expression for a memory access address to an expression that
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73 /// represents offset from the given alloca.
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74 ///
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75 /// The implementation simply replaces all mentions of the alloca with zero.
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76 class AllocaOffsetRewriter : public SCEVRewriteVisitor<AllocaOffsetRewriter> {
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77 const Value *AllocaPtr;
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78
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79 public:
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80 AllocaOffsetRewriter(ScalarEvolution &SE, const Value *AllocaPtr)
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81 : SCEVRewriteVisitor(SE), AllocaPtr(AllocaPtr) {}
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82
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83 const SCEV *visitUnknown(const SCEVUnknown *Expr) {
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84 if (Expr->getValue() == AllocaPtr)
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85 return SE.getZero(Expr->getType());
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86 return Expr;
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87 }
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88 };
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89
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90 /// The SafeStack pass splits the stack of each function into the safe
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91 /// stack, which is only accessed through memory safe dereferences (as
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92 /// determined statically), and the unsafe stack, which contains all
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93 /// local variables that are accessed in ways that we can't prove to
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94 /// be safe.
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95 class SafeStack : public FunctionPass {
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96 const TargetMachine *TM;
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97 const TargetLoweringBase *TL;
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98 const DataLayout *DL;
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99 ScalarEvolution *SE;
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100
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101 Type *StackPtrTy;
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102 Type *IntPtrTy;
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103 Type *Int32Ty;
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104 Type *Int8Ty;
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105
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106 Value *UnsafeStackPtr = nullptr;
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107
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108 /// Unsafe stack alignment. Each stack frame must ensure that the stack is
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109 /// aligned to this value. We need to re-align the unsafe stack if the
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110 /// alignment of any object on the stack exceeds this value.
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111 ///
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112 /// 16 seems like a reasonable upper bound on the alignment of objects that we
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113 /// might expect to appear on the stack on most common targets.
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114 enum { StackAlignment = 16 };
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115
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116 /// \brief Return the value of the stack canary.
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117 Value *getStackGuard(IRBuilder<> &IRB, Function &F);
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118
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119 /// \brief Load stack guard from the frame and check if it has changed.
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120 void checkStackGuard(IRBuilder<> &IRB, Function &F, ReturnInst &RI,
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121 AllocaInst *StackGuardSlot, Value *StackGuard);
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122
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123 /// \brief Find all static allocas, dynamic allocas, return instructions and
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124 /// stack restore points (exception unwind blocks and setjmp calls) in the
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125 /// given function and append them to the respective vectors.
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126 void findInsts(Function &F, SmallVectorImpl<AllocaInst *> &StaticAllocas,
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127 SmallVectorImpl<AllocaInst *> &DynamicAllocas,
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128 SmallVectorImpl<Argument *> &ByValArguments,
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129 SmallVectorImpl<ReturnInst *> &Returns,
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130 SmallVectorImpl<Instruction *> &StackRestorePoints);
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131
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132 /// \brief Calculate the allocation size of a given alloca. Returns 0 if the
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133 /// size can not be statically determined.
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134 uint64_t getStaticAllocaAllocationSize(const AllocaInst* AI);
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135
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136 /// \brief Allocate space for all static allocas in \p StaticAllocas,
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137 /// replace allocas with pointers into the unsafe stack and generate code to
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138 /// restore the stack pointer before all return instructions in \p Returns.
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139 ///
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140 /// \returns A pointer to the top of the unsafe stack after all unsafe static
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141 /// allocas are allocated.
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142 Value *moveStaticAllocasToUnsafeStack(IRBuilder<> &IRB, Function &F,
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143 ArrayRef<AllocaInst *> StaticAllocas,
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144 ArrayRef<Argument *> ByValArguments,
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145 ArrayRef<ReturnInst *> Returns,
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146 Instruction *BasePointer,
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147 AllocaInst *StackGuardSlot);
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148
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149 /// \brief Generate code to restore the stack after all stack restore points
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150 /// in \p StackRestorePoints.
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151 ///
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152 /// \returns A local variable in which to maintain the dynamic top of the
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153 /// unsafe stack if needed.
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154 AllocaInst *
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155 createStackRestorePoints(IRBuilder<> &IRB, Function &F,
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156 ArrayRef<Instruction *> StackRestorePoints,
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157 Value *StaticTop, bool NeedDynamicTop);
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158
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159 /// \brief Replace all allocas in \p DynamicAllocas with code to allocate
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160 /// space dynamically on the unsafe stack and store the dynamic unsafe stack
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161 /// top to \p DynamicTop if non-null.
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162 void moveDynamicAllocasToUnsafeStack(Function &F, Value *UnsafeStackPtr,
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163 AllocaInst *DynamicTop,
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164 ArrayRef<AllocaInst *> DynamicAllocas);
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165
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166 bool IsSafeStackAlloca(const Value *AllocaPtr, uint64_t AllocaSize);
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167
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168 bool IsMemIntrinsicSafe(const MemIntrinsic *MI, const Use &U,
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169 const Value *AllocaPtr, uint64_t AllocaSize);
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170 bool IsAccessSafe(Value *Addr, uint64_t Size, const Value *AllocaPtr,
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171 uint64_t AllocaSize);
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172
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173 public:
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174 static char ID; // Pass identification, replacement for typeid.
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175 SafeStack(const TargetMachine *TM)
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176 : FunctionPass(ID), TM(TM), TL(nullptr), DL(nullptr) {
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177 initializeSafeStackPass(*PassRegistry::getPassRegistry());
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178 }
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179 SafeStack() : SafeStack(nullptr) {}
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180
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181 void getAnalysisUsage(AnalysisUsage &AU) const override {
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182 AU.addRequired<ScalarEvolutionWrapperPass>();
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183 }
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184
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185 bool doInitialization(Module &M) override {
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186 DL = &M.getDataLayout();
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187
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188 StackPtrTy = Type::getInt8PtrTy(M.getContext());
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189 IntPtrTy = DL->getIntPtrType(M.getContext());
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190 Int32Ty = Type::getInt32Ty(M.getContext());
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191 Int8Ty = Type::getInt8Ty(M.getContext());
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192
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193 return false;
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194 }
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195
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196 bool runOnFunction(Function &F) override;
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197 }; // class SafeStack
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198
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199 uint64_t SafeStack::getStaticAllocaAllocationSize(const AllocaInst* AI) {
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200 uint64_t Size = DL->getTypeAllocSize(AI->getAllocatedType());
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201 if (AI->isArrayAllocation()) {
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202 auto C = dyn_cast<ConstantInt>(AI->getArraySize());
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203 if (!C)
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204 return 0;
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205 Size *= C->getZExtValue();
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206 }
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207 return Size;
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208 }
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209
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210 bool SafeStack::IsAccessSafe(Value *Addr, uint64_t AccessSize,
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211 const Value *AllocaPtr, uint64_t AllocaSize) {
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212 AllocaOffsetRewriter Rewriter(*SE, AllocaPtr);
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213 const SCEV *Expr = Rewriter.visit(SE->getSCEV(Addr));
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214
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215 uint64_t BitWidth = SE->getTypeSizeInBits(Expr->getType());
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216 ConstantRange AccessStartRange = SE->getUnsignedRange(Expr);
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217 ConstantRange SizeRange =
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218 ConstantRange(APInt(BitWidth, 0), APInt(BitWidth, AccessSize));
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219 ConstantRange AccessRange = AccessStartRange.add(SizeRange);
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220 ConstantRange AllocaRange =
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221 ConstantRange(APInt(BitWidth, 0), APInt(BitWidth, AllocaSize));
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222 bool Safe = AllocaRange.contains(AccessRange);
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223
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224 DEBUG(dbgs() << "[SafeStack] "
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225 << (isa<AllocaInst>(AllocaPtr) ? "Alloca " : "ByValArgument ")
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226 << *AllocaPtr << "\n"
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227 << " Access " << *Addr << "\n"
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228 << " SCEV " << *Expr
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229 << " U: " << SE->getUnsignedRange(Expr)
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230 << ", S: " << SE->getSignedRange(Expr) << "\n"
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231 << " Range " << AccessRange << "\n"
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232 << " AllocaRange " << AllocaRange << "\n"
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233 << " " << (Safe ? "safe" : "unsafe") << "\n");
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234
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235 return Safe;
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236 }
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237
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238 bool SafeStack::IsMemIntrinsicSafe(const MemIntrinsic *MI, const Use &U,
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239 const Value *AllocaPtr,
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240 uint64_t AllocaSize) {
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241 // All MemIntrinsics have destination address in Arg0 and size in Arg2.
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242 if (MI->getRawDest() != U) return true;
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243 const auto *Len = dyn_cast<ConstantInt>(MI->getLength());
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244 // Non-constant size => unsafe. FIXME: try SCEV getRange.
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245 if (!Len) return false;
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246 return IsAccessSafe(U, Len->getZExtValue(), AllocaPtr, AllocaSize);
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247 }
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248
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249 /// Check whether a given allocation must be put on the safe
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250 /// stack or not. The function analyzes all uses of AI and checks whether it is
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251 /// only accessed in a memory safe way (as decided statically).
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252 bool SafeStack::IsSafeStackAlloca(const Value *AllocaPtr, uint64_t AllocaSize) {
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253 // Go through all uses of this alloca and check whether all accesses to the
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254 // allocated object are statically known to be memory safe and, hence, the
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255 // object can be placed on the safe stack.
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256 SmallPtrSet<const Value *, 16> Visited;
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257 SmallVector<const Value *, 8> WorkList;
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258 WorkList.push_back(AllocaPtr);
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259
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260 // A DFS search through all uses of the alloca in bitcasts/PHI/GEPs/etc.
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261 while (!WorkList.empty()) {
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262 const Value *V = WorkList.pop_back_val();
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263 for (const Use &UI : V->uses()) {
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264 auto I = cast<const Instruction>(UI.getUser());
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265 assert(V == UI.get());
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266
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267 switch (I->getOpcode()) {
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268 case Instruction::Load: {
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269 if (!IsAccessSafe(UI, DL->getTypeStoreSize(I->getType()), AllocaPtr,
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270 AllocaSize))
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271 return false;
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272 break;
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273 }
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274 case Instruction::VAArg:
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275 // "va-arg" from a pointer is safe.
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276 break;
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277 case Instruction::Store: {
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278 if (V == I->getOperand(0)) {
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279 // Stored the pointer - conservatively assume it may be unsafe.
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280 DEBUG(dbgs() << "[SafeStack] Unsafe alloca: " << *AllocaPtr
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281 << "\n store of address: " << *I << "\n");
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282 return false;
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283 }
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284
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285 if (!IsAccessSafe(UI, DL->getTypeStoreSize(I->getOperand(0)->getType()),
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286 AllocaPtr, AllocaSize))
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287 return false;
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288 break;
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289 }
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290 case Instruction::Ret: {
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291 // Information leak.
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292 return false;
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293 }
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294
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295 case Instruction::Call:
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296 case Instruction::Invoke: {
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297 ImmutableCallSite CS(I);
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298
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299 if (const IntrinsicInst *II = dyn_cast<IntrinsicInst>(I)) {
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300 if (II->getIntrinsicID() == Intrinsic::lifetime_start ||
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301 II->getIntrinsicID() == Intrinsic::lifetime_end)
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302 continue;
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303 }
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304
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305 if (const MemIntrinsic *MI = dyn_cast<MemIntrinsic>(I)) {
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306 if (!IsMemIntrinsicSafe(MI, UI, AllocaPtr, AllocaSize)) {
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307 DEBUG(dbgs() << "[SafeStack] Unsafe alloca: " << *AllocaPtr
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308 << "\n unsafe memintrinsic: " << *I
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309 << "\n");
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310 return false;
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311 }
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312 continue;
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313 }
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314
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315 // LLVM 'nocapture' attribute is only set for arguments whose address
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316 // is not stored, passed around, or used in any other non-trivial way.
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317 // We assume that passing a pointer to an object as a 'nocapture
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318 // readnone' argument is safe.
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319 // FIXME: a more precise solution would require an interprocedural
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320 // analysis here, which would look at all uses of an argument inside
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321 // the function being called.
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322 ImmutableCallSite::arg_iterator B = CS.arg_begin(), E = CS.arg_end();
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323 for (ImmutableCallSite::arg_iterator A = B; A != E; ++A)
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324 if (A->get() == V)
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325 if (!(CS.doesNotCapture(A - B) && (CS.doesNotAccessMemory(A - B) ||
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326 CS.doesNotAccessMemory()))) {
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327 DEBUG(dbgs() << "[SafeStack] Unsafe alloca: " << *AllocaPtr
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328 << "\n unsafe call: " << *I << "\n");
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329 return false;
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330 }
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331 continue;
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332 }
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333
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334 default:
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335 if (Visited.insert(I).second)
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336 WorkList.push_back(cast<const Instruction>(I));
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337 }
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338 }
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339 }
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340
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341 // All uses of the alloca are safe, we can place it on the safe stack.
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342 return true;
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343 }
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344
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345 Value *SafeStack::getStackGuard(IRBuilder<> &IRB, Function &F) {
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346 Value *StackGuardVar = TL->getIRStackGuard(IRB);
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347 if (!StackGuardVar)
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348 StackGuardVar =
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349 F.getParent()->getOrInsertGlobal("__stack_chk_guard", StackPtrTy);
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350 return IRB.CreateLoad(StackGuardVar, "StackGuard");
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351 }
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352
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353 void SafeStack::findInsts(Function &F,
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354 SmallVectorImpl<AllocaInst *> &StaticAllocas,
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355 SmallVectorImpl<AllocaInst *> &DynamicAllocas,
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356 SmallVectorImpl<Argument *> &ByValArguments,
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357 SmallVectorImpl<ReturnInst *> &Returns,
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358 SmallVectorImpl<Instruction *> &StackRestorePoints) {
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359 for (Instruction &I : instructions(&F)) {
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360 if (auto AI = dyn_cast<AllocaInst>(&I)) {
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361 ++NumAllocas;
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362
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363 uint64_t Size = getStaticAllocaAllocationSize(AI);
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364 if (IsSafeStackAlloca(AI, Size))
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365 continue;
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366
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367 if (AI->isStaticAlloca()) {
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368 ++NumUnsafeStaticAllocas;
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369 StaticAllocas.push_back(AI);
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370 } else {
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371 ++NumUnsafeDynamicAllocas;
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372 DynamicAllocas.push_back(AI);
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373 }
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374 } else if (auto RI = dyn_cast<ReturnInst>(&I)) {
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375 Returns.push_back(RI);
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376 } else if (auto CI = dyn_cast<CallInst>(&I)) {
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377 // setjmps require stack restore.
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378 if (CI->getCalledFunction() && CI->canReturnTwice())
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|
379 StackRestorePoints.push_back(CI);
|
|
|
380 } else if (auto LP = dyn_cast<LandingPadInst>(&I)) {
|
|
|
381 // Exception landing pads require stack restore.
|
|
|
382 StackRestorePoints.push_back(LP);
|
|
|
383 } else if (auto II = dyn_cast<IntrinsicInst>(&I)) {
|
|
|
384 if (II->getIntrinsicID() == Intrinsic::gcroot)
|
|
|
385 llvm::report_fatal_error(
|
|
|
386 "gcroot intrinsic not compatible with safestack attribute");
|
|
|
387 }
|
|
|
388 }
|
|
|
389 for (Argument &Arg : F.args()) {
|
|
|
390 if (!Arg.hasByValAttr())
|
|
|
391 continue;
|
|
|
392 uint64_t Size =
|
|
|
393 DL->getTypeStoreSize(Arg.getType()->getPointerElementType());
|
|
|
394 if (IsSafeStackAlloca(&Arg, Size))
|
|
|
395 continue;
|
|
|
396
|
|
|
397 ++NumUnsafeByValArguments;
|
|
|
398 ByValArguments.push_back(&Arg);
|
|
|
399 }
|
|
|
400 }
|
|
|
401
|
|
|
402 AllocaInst *
|
|
|
403 SafeStack::createStackRestorePoints(IRBuilder<> &IRB, Function &F,
|
|
|
404 ArrayRef<Instruction *> StackRestorePoints,
|
|
|
405 Value *StaticTop, bool NeedDynamicTop) {
|
|
|
406 assert(StaticTop && "The stack top isn't set.");
|
|
|
407
|
|
|
408 if (StackRestorePoints.empty())
|
|
|
409 return nullptr;
|
|
|
410
|
|
|
411 // We need the current value of the shadow stack pointer to restore
|
|
|
412 // after longjmp or exception catching.
|
|
|
413
|
|
|
414 // FIXME: On some platforms this could be handled by the longjmp/exception
|
|
|
415 // runtime itself.
|
|
|
416
|
|
|
417 AllocaInst *DynamicTop = nullptr;
|
|
|
418 if (NeedDynamicTop) {
|
|
|
419 // If we also have dynamic alloca's, the stack pointer value changes
|
|
|
420 // throughout the function. For now we store it in an alloca.
|
|
|
421 DynamicTop = IRB.CreateAlloca(StackPtrTy, /*ArraySize=*/nullptr,
|
|
|
422 "unsafe_stack_dynamic_ptr");
|
|
|
423 IRB.CreateStore(StaticTop, DynamicTop);
|
|
|
424 }
|
|
|
425
|
|
|
426 // Restore current stack pointer after longjmp/exception catch.
|
|
|
427 for (Instruction *I : StackRestorePoints) {
|
|
|
428 ++NumUnsafeStackRestorePoints;
|
|
|
429
|
|
|
430 IRB.SetInsertPoint(I->getNextNode());
|
|
|
431 Value *CurrentTop = DynamicTop ? IRB.CreateLoad(DynamicTop) : StaticTop;
|
|
|
432 IRB.CreateStore(CurrentTop, UnsafeStackPtr);
|
|
|
433 }
|
|
|
434
|
|
|
435 return DynamicTop;
|
|
|
436 }
|
|
|
437
|
|
|
438 void SafeStack::checkStackGuard(IRBuilder<> &IRB, Function &F, ReturnInst &RI,
|
|
|
439 AllocaInst *StackGuardSlot, Value *StackGuard) {
|
|
|
440 Value *V = IRB.CreateLoad(StackGuardSlot);
|
|
|
441 Value *Cmp = IRB.CreateICmpNE(StackGuard, V);
|
|
|
442
|
|
|
443 auto SuccessProb = BranchProbabilityInfo::getBranchProbStackProtector(true);
|
|
|
444 auto FailureProb = BranchProbabilityInfo::getBranchProbStackProtector(false);
|
|
|
445 MDNode *Weights = MDBuilder(F.getContext())
|
|
|
446 .createBranchWeights(SuccessProb.getNumerator(),
|
|
|
447 FailureProb.getNumerator());
|
|
|
448 Instruction *CheckTerm =
|
|
|
449 SplitBlockAndInsertIfThen(Cmp, &RI,
|
|
|
450 /* Unreachable */ true, Weights);
|
|
|
451 IRBuilder<> IRBFail(CheckTerm);
|
|
|
452 // FIXME: respect -fsanitize-trap / -ftrap-function here?
|
|
|
453 Constant *StackChkFail = F.getParent()->getOrInsertFunction(
|
|
|
454 "__stack_chk_fail", IRB.getVoidTy(), nullptr);
|
|
|
455 IRBFail.CreateCall(StackChkFail, {});
|
|
|
456 }
|
|
|
457
|
|
|
458 /// We explicitly compute and set the unsafe stack layout for all unsafe
|
|
|
459 /// static alloca instructions. We save the unsafe "base pointer" in the
|
|
|
460 /// prologue into a local variable and restore it in the epilogue.
|
|
|
461 Value *SafeStack::moveStaticAllocasToUnsafeStack(
|
|
|
462 IRBuilder<> &IRB, Function &F, ArrayRef<AllocaInst *> StaticAllocas,
|
|
|
463 ArrayRef<Argument *> ByValArguments, ArrayRef<ReturnInst *> Returns,
|
|
|
464 Instruction *BasePointer, AllocaInst *StackGuardSlot) {
|
|
|
465 if (StaticAllocas.empty() && ByValArguments.empty())
|
|
|
466 return BasePointer;
|
|
|
467
|
|
|
468 DIBuilder DIB(*F.getParent());
|
|
|
469
|
|
|
470 StackColoring SSC(F, StaticAllocas);
|
|
|
471 SSC.run();
|
|
|
472 SSC.removeAllMarkers();
|
|
|
473
|
|
|
474 // Unsafe stack always grows down.
|
|
|
475 StackLayout SSL(StackAlignment);
|
|
|
476 if (StackGuardSlot) {
|
|
|
477 Type *Ty = StackGuardSlot->getAllocatedType();
|
|
|
478 unsigned Align =
|
|
|
479 std::max(DL->getPrefTypeAlignment(Ty), StackGuardSlot->getAlignment());
|
|
|
480 SSL.addObject(StackGuardSlot, getStaticAllocaAllocationSize(StackGuardSlot),
|
|
|
481 Align, SSC.getFullLiveRange());
|
|
|
482 }
|
|
|
483
|
|
|
484 for (Argument *Arg : ByValArguments) {
|
|
|
485 Type *Ty = Arg->getType()->getPointerElementType();
|
|
|
486 uint64_t Size = DL->getTypeStoreSize(Ty);
|
|
|
487 if (Size == 0)
|
|
|
488 Size = 1; // Don't create zero-sized stack objects.
|
|
|
489
|
|
|
490 // Ensure the object is properly aligned.
|
|
|
491 unsigned Align = std::max((unsigned)DL->getPrefTypeAlignment(Ty),
|
|
|
492 Arg->getParamAlignment());
|
|
|
493 SSL.addObject(Arg, Size, Align, SSC.getFullLiveRange());
|
|
|
494 }
|
|
|
495
|
|
|
496 for (AllocaInst *AI : StaticAllocas) {
|
|
|
497 Type *Ty = AI->getAllocatedType();
|
|
|
498 uint64_t Size = getStaticAllocaAllocationSize(AI);
|
|
|
499 if (Size == 0)
|
|
|
500 Size = 1; // Don't create zero-sized stack objects.
|
|
|
501
|
|
|
502 // Ensure the object is properly aligned.
|
|
|
503 unsigned Align =
|
|
|
504 std::max((unsigned)DL->getPrefTypeAlignment(Ty), AI->getAlignment());
|
|
|
505
|
|
|
506 SSL.addObject(AI, Size, Align, SSC.getLiveRange(AI));
|
|
|
507 }
|
|
|
508
|
|
|
509 SSL.computeLayout();
|
|
|
510 unsigned FrameAlignment = SSL.getFrameAlignment();
|
|
|
511
|
|
|
512 // FIXME: tell SSL that we start at a less-then-MaxAlignment aligned location
|
|
|
513 // (AlignmentSkew).
|
|
|
514 if (FrameAlignment > StackAlignment) {
|
|
|
515 // Re-align the base pointer according to the max requested alignment.
|
|
|
516 assert(isPowerOf2_32(FrameAlignment));
|
|
|
517 IRB.SetInsertPoint(BasePointer->getNextNode());
|
|
|
518 BasePointer = cast<Instruction>(IRB.CreateIntToPtr(
|
|
|
519 IRB.CreateAnd(IRB.CreatePtrToInt(BasePointer, IntPtrTy),
|
|
|
520 ConstantInt::get(IntPtrTy, ~uint64_t(FrameAlignment - 1))),
|
|
|
521 StackPtrTy));
|
|
|
522 }
|
|
|
523
|
|
|
524 IRB.SetInsertPoint(BasePointer->getNextNode());
|
|
|
525
|
|
|
526 if (StackGuardSlot) {
|
|
|
527 unsigned Offset = SSL.getObjectOffset(StackGuardSlot);
|
|
|
528 Value *Off = IRB.CreateGEP(BasePointer, // BasePointer is i8*
|
|
|
529 ConstantInt::get(Int32Ty, -Offset));
|
|
|
530 Value *NewAI =
|
|
|
531 IRB.CreateBitCast(Off, StackGuardSlot->getType(), "StackGuardSlot");
|
|
|
532
|
|
|
533 // Replace alloc with the new location.
|
|
|
534 StackGuardSlot->replaceAllUsesWith(NewAI);
|
|
|
535 StackGuardSlot->eraseFromParent();
|
|
|
536 }
|
|
|
537
|
|
|
538 for (Argument *Arg : ByValArguments) {
|
|
|
539 unsigned Offset = SSL.getObjectOffset(Arg);
|
|
|
540 Type *Ty = Arg->getType()->getPointerElementType();
|
|
|
541
|
|
|
542 uint64_t Size = DL->getTypeStoreSize(Ty);
|
|
|
543 if (Size == 0)
|
|
|
544 Size = 1; // Don't create zero-sized stack objects.
|
|
|
545
|
|
|
546 Value *Off = IRB.CreateGEP(BasePointer, // BasePointer is i8*
|
|
|
547 ConstantInt::get(Int32Ty, -Offset));
|
|
|
548 Value *NewArg = IRB.CreateBitCast(Off, Arg->getType(),
|
|
|
549 Arg->getName() + ".unsafe-byval");
|
|
|
550
|
|
|
551 // Replace alloc with the new location.
|
|
|
552 replaceDbgDeclare(Arg, BasePointer, BasePointer->getNextNode(), DIB,
|
|
|
553 /*Deref=*/true, -Offset);
|
|
|
554 Arg->replaceAllUsesWith(NewArg);
|
|
|
555 IRB.SetInsertPoint(cast<Instruction>(NewArg)->getNextNode());
|
|
|
556 IRB.CreateMemCpy(Off, Arg, Size, Arg->getParamAlignment());
|
|
|
557 }
|
|
|
558
|
|
|
559 // Allocate space for every unsafe static AllocaInst on the unsafe stack.
|
|
|
560 for (AllocaInst *AI : StaticAllocas) {
|
|
|
561 IRB.SetInsertPoint(AI);
|
|
|
562 unsigned Offset = SSL.getObjectOffset(AI);
|
|
|
563
|
|
|
564 uint64_t Size = getStaticAllocaAllocationSize(AI);
|
|
|
565 if (Size == 0)
|
|
|
566 Size = 1; // Don't create zero-sized stack objects.
|
|
|
567
|
|
|
568 replaceDbgDeclareForAlloca(AI, BasePointer, DIB, /*Deref=*/true, -Offset);
|
|
|
569 replaceDbgValueForAlloca(AI, BasePointer, DIB, -Offset);
|
|
|
570
|
|
|
571 // Replace uses of the alloca with the new location.
|
|
|
572 // Insert address calculation close to each use to work around PR27844.
|
|
|
573 std::string Name = std::string(AI->getName()) + ".unsafe";
|
|
|
574 while (!AI->use_empty()) {
|
|
|
575 Use &U = *AI->use_begin();
|
|
|
576 Instruction *User = cast<Instruction>(U.getUser());
|
|
|
577
|
|
|
578 Instruction *InsertBefore;
|
|
|
579 if (auto *PHI = dyn_cast<PHINode>(User))
|
|
|
580 InsertBefore = PHI->getIncomingBlock(U)->getTerminator();
|
|
|
581 else
|
|
|
582 InsertBefore = User;
|
|
|
583
|
|
|
584 IRBuilder<> IRBUser(InsertBefore);
|
|
|
585 Value *Off = IRBUser.CreateGEP(BasePointer, // BasePointer is i8*
|
|
|
586 ConstantInt::get(Int32Ty, -Offset));
|
|
|
587 Value *Replacement = IRBUser.CreateBitCast(Off, AI->getType(), Name);
|
|
|
588
|
|
|
589 if (auto *PHI = dyn_cast<PHINode>(User)) {
|
|
|
590 // PHI nodes may have multiple incoming edges from the same BB (why??),
|
|
|
591 // all must be updated at once with the same incoming value.
|
|
|
592 auto *BB = PHI->getIncomingBlock(U);
|
|
|
593 for (unsigned I = 0; I < PHI->getNumIncomingValues(); ++I)
|
|
|
594 if (PHI->getIncomingBlock(I) == BB)
|
|
|
595 PHI->setIncomingValue(I, Replacement);
|
|
|
596 } else {
|
|
|
597 U.set(Replacement);
|
|
|
598 }
|
|
|
599 }
|
|
|
600
|
|
|
601 AI->eraseFromParent();
|
|
|
602 }
|
|
|
603
|
|
|
604 // Re-align BasePointer so that our callees would see it aligned as
|
|
|
605 // expected.
|
|
|
606 // FIXME: no need to update BasePointer in leaf functions.
|
|
|
607 unsigned FrameSize = alignTo(SSL.getFrameSize(), StackAlignment);
|
|
|
608
|
|
|
609 // Update shadow stack pointer in the function epilogue.
|
|
|
610 IRB.SetInsertPoint(BasePointer->getNextNode());
|
|
|
611
|
|
|
612 Value *StaticTop =
|
|
|
613 IRB.CreateGEP(BasePointer, ConstantInt::get(Int32Ty, -FrameSize),
|
|
|
614 "unsafe_stack_static_top");
|
|
|
615 IRB.CreateStore(StaticTop, UnsafeStackPtr);
|
|
|
616 return StaticTop;
|
|
|
617 }
|
|
|
618
|
|
|
619 void SafeStack::moveDynamicAllocasToUnsafeStack(
|
|
|
620 Function &F, Value *UnsafeStackPtr, AllocaInst *DynamicTop,
|
|
|
621 ArrayRef<AllocaInst *> DynamicAllocas) {
|
|
|
622 DIBuilder DIB(*F.getParent());
|
|
|
623
|
|
|
624 for (AllocaInst *AI : DynamicAllocas) {
|
|
|
625 IRBuilder<> IRB(AI);
|
|
|
626
|
|
|
627 // Compute the new SP value (after AI).
|
|
|
628 Value *ArraySize = AI->getArraySize();
|
|
|
629 if (ArraySize->getType() != IntPtrTy)
|
|
|
630 ArraySize = IRB.CreateIntCast(ArraySize, IntPtrTy, false);
|
|
|
631
|
|
|
632 Type *Ty = AI->getAllocatedType();
|
|
|
633 uint64_t TySize = DL->getTypeAllocSize(Ty);
|
|
|
634 Value *Size = IRB.CreateMul(ArraySize, ConstantInt::get(IntPtrTy, TySize));
|
|
|
635
|
|
|
636 Value *SP = IRB.CreatePtrToInt(IRB.CreateLoad(UnsafeStackPtr), IntPtrTy);
|
|
|
637 SP = IRB.CreateSub(SP, Size);
|
|
|
638
|
|
|
639 // Align the SP value to satisfy the AllocaInst, type and stack alignments.
|
|
|
640 unsigned Align = std::max(
|
|
|
641 std::max((unsigned)DL->getPrefTypeAlignment(Ty), AI->getAlignment()),
|
|
|
642 (unsigned)StackAlignment);
|
|
|
643
|
|
|
644 assert(isPowerOf2_32(Align));
|
|
|
645 Value *NewTop = IRB.CreateIntToPtr(
|
|
|
646 IRB.CreateAnd(SP, ConstantInt::get(IntPtrTy, ~uint64_t(Align - 1))),
|
|
|
647 StackPtrTy);
|
|
|
648
|
|
|
649 // Save the stack pointer.
|
|
|
650 IRB.CreateStore(NewTop, UnsafeStackPtr);
|
|
|
651 if (DynamicTop)
|
|
|
652 IRB.CreateStore(NewTop, DynamicTop);
|
|
|
653
|
|
|
654 Value *NewAI = IRB.CreatePointerCast(NewTop, AI->getType());
|
|
|
655 if (AI->hasName() && isa<Instruction>(NewAI))
|
|
|
656 NewAI->takeName(AI);
|
|
|
657
|
|
|
658 replaceDbgDeclareForAlloca(AI, NewAI, DIB, /*Deref=*/true);
|
|
|
659 AI->replaceAllUsesWith(NewAI);
|
|
|
660 AI->eraseFromParent();
|
|
|
661 }
|
|
|
662
|
|
|
663 if (!DynamicAllocas.empty()) {
|
|
|
664 // Now go through the instructions again, replacing stacksave/stackrestore.
|
|
|
665 for (inst_iterator It = inst_begin(&F), Ie = inst_end(&F); It != Ie;) {
|
|
|
666 Instruction *I = &*(It++);
|
|
|
667 auto II = dyn_cast<IntrinsicInst>(I);
|
|
|
668 if (!II)
|
|
|
669 continue;
|
|
|
670
|
|
|
671 if (II->getIntrinsicID() == Intrinsic::stacksave) {
|
|
|
672 IRBuilder<> IRB(II);
|
|
|
673 Instruction *LI = IRB.CreateLoad(UnsafeStackPtr);
|
|
|
674 LI->takeName(II);
|
|
|
675 II->replaceAllUsesWith(LI);
|
|
|
676 II->eraseFromParent();
|
|
|
677 } else if (II->getIntrinsicID() == Intrinsic::stackrestore) {
|
|
|
678 IRBuilder<> IRB(II);
|
|
|
679 Instruction *SI = IRB.CreateStore(II->getArgOperand(0), UnsafeStackPtr);
|
|
|
680 SI->takeName(II);
|
|
|
681 assert(II->use_empty());
|
|
|
682 II->eraseFromParent();
|
|
|
683 }
|
|
|
684 }
|
|
|
685 }
|
|
|
686 }
|
|
|
687
|
|
|
688 bool SafeStack::runOnFunction(Function &F) {
|
|
|
689 DEBUG(dbgs() << "[SafeStack] Function: " << F.getName() << "\n");
|
|
|
690
|
|
|
691 if (!F.hasFnAttribute(Attribute::SafeStack)) {
|
|
|
692 DEBUG(dbgs() << "[SafeStack] safestack is not requested"
|
|
|
693 " for this function\n");
|
|
|
694 return false;
|
|
|
695 }
|
|
|
696
|
|
|
697 if (F.isDeclaration()) {
|
|
|
698 DEBUG(dbgs() << "[SafeStack] function definition"
|
|
|
699 " is not available\n");
|
|
|
700 return false;
|
|
|
701 }
|
|
|
702
|
|
|
703 if (!TM)
|
|
|
704 report_fatal_error("Target machine is required");
|
|
|
705 TL = TM->getSubtargetImpl(F)->getTargetLowering();
|
|
|
706 SE = &getAnalysis<ScalarEvolutionWrapperPass>().getSE();
|
|
|
707
|
|
|
708 ++NumFunctions;
|
|
|
709
|
|
|
710 SmallVector<AllocaInst *, 16> StaticAllocas;
|
|
|
711 SmallVector<AllocaInst *, 4> DynamicAllocas;
|
|
|
712 SmallVector<Argument *, 4> ByValArguments;
|
|
|
713 SmallVector<ReturnInst *, 4> Returns;
|
|
|
714
|
|
|
715 // Collect all points where stack gets unwound and needs to be restored
|
|
|
716 // This is only necessary because the runtime (setjmp and unwind code) is
|
|
|
717 // not aware of the unsafe stack and won't unwind/restore it properly.
|
|
|
718 // To work around this problem without changing the runtime, we insert
|
|
|
719 // instrumentation to restore the unsafe stack pointer when necessary.
|
|
|
720 SmallVector<Instruction *, 4> StackRestorePoints;
|
|
|
721
|
|
|
722 // Find all static and dynamic alloca instructions that must be moved to the
|
|
|
723 // unsafe stack, all return instructions and stack restore points.
|
|
|
724 findInsts(F, StaticAllocas, DynamicAllocas, ByValArguments, Returns,
|
|
|
725 StackRestorePoints);
|
|
|
726
|
|
|
727 if (StaticAllocas.empty() && DynamicAllocas.empty() &&
|
|
|
728 ByValArguments.empty() && StackRestorePoints.empty())
|
|
|
729 return false; // Nothing to do in this function.
|
|
|
730
|
|
|
731 if (!StaticAllocas.empty() || !DynamicAllocas.empty() ||
|
|
|
732 !ByValArguments.empty())
|
|
|
733 ++NumUnsafeStackFunctions; // This function has the unsafe stack.
|
|
|
734
|
|
|
735 if (!StackRestorePoints.empty())
|
|
|
736 ++NumUnsafeStackRestorePointsFunctions;
|
|
|
737
|
|
|
738 IRBuilder<> IRB(&F.front(), F.begin()->getFirstInsertionPt());
|
|
|
739 UnsafeStackPtr = TL->getSafeStackPointerLocation(IRB);
|
|
|
740
|
|
|
741 // Load the current stack pointer (we'll also use it as a base pointer).
|
|
|
742 // FIXME: use a dedicated register for it ?
|
|
|
743 Instruction *BasePointer =
|
|
|
744 IRB.CreateLoad(UnsafeStackPtr, false, "unsafe_stack_ptr");
|
|
|
745 assert(BasePointer->getType() == StackPtrTy);
|
|
|
746
|
|
|
747 AllocaInst *StackGuardSlot = nullptr;
|
|
|
748 // FIXME: implement weaker forms of stack protector.
|
|
|
749 if (F.hasFnAttribute(Attribute::StackProtect) ||
|
|
|
750 F.hasFnAttribute(Attribute::StackProtectStrong) ||
|
|
|
751 F.hasFnAttribute(Attribute::StackProtectReq)) {
|
|
|
752 Value *StackGuard = getStackGuard(IRB, F);
|
|
|
753 StackGuardSlot = IRB.CreateAlloca(StackPtrTy, nullptr);
|
|
|
754 IRB.CreateStore(StackGuard, StackGuardSlot);
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755
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756 for (ReturnInst *RI : Returns) {
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757 IRBuilder<> IRBRet(RI);
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758 checkStackGuard(IRBRet, F, *RI, StackGuardSlot, StackGuard);
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759 }
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760 }
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761
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762 // The top of the unsafe stack after all unsafe static allocas are
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|
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763 // allocated.
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764 Value *StaticTop =
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765 moveStaticAllocasToUnsafeStack(IRB, F, StaticAllocas, ByValArguments,
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|
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766 Returns, BasePointer, StackGuardSlot);
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767
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768 // Safe stack object that stores the current unsafe stack top. It is updated
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769 // as unsafe dynamic (non-constant-sized) allocas are allocated and freed.
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770 // This is only needed if we need to restore stack pointer after longjmp
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|
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771 // or exceptions, and we have dynamic allocations.
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772 // FIXME: a better alternative might be to store the unsafe stack pointer
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|
|
773 // before setjmp / invoke instructions.
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774 AllocaInst *DynamicTop = createStackRestorePoints(
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775 IRB, F, StackRestorePoints, StaticTop, !DynamicAllocas.empty());
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776
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777 // Handle dynamic allocas.
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778 moveDynamicAllocasToUnsafeStack(F, UnsafeStackPtr, DynamicTop,
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779 DynamicAllocas);
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|
|
780
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|
|
781 // Restore the unsafe stack pointer before each return.
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782 for (ReturnInst *RI : Returns) {
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783 IRB.SetInsertPoint(RI);
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|
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784 IRB.CreateStore(BasePointer, UnsafeStackPtr);
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785 }
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786
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787 DEBUG(dbgs() << "[SafeStack] safestack applied\n");
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788 return true;
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789 }
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|
790
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|
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791 } // anonymous namespace
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792
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793 char SafeStack::ID = 0;
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|
|
794 INITIALIZE_TM_PASS_BEGIN(SafeStack, "safe-stack",
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|
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795 "Safe Stack instrumentation pass", false, false)
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|
|
796 INITIALIZE_TM_PASS_END(SafeStack, "safe-stack",
|
|
|
797 "Safe Stack instrumentation pass", false, false)
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|
|
798
|
|
|
799 FunctionPass *llvm::createSafeStackPass(const llvm::TargetMachine *TM) {
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|
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800 return new SafeStack(TM);
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|
|
801 }
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