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1 //===- SafeStack.cpp - Safe Stack Insertion -------------------------------===//
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120
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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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121
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20 #include "llvm/ADT/APInt.h"
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21 #include "llvm/ADT/ArrayRef.h"
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22 #include "llvm/ADT/SmallPtrSet.h"
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23 #include "llvm/ADT/SmallVector.h"
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120
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24 #include "llvm/ADT/Statistic.h"
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121
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25 #include "llvm/Analysis/AssumptionCache.h"
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120
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26 #include "llvm/Analysis/BranchProbabilityInfo.h"
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134
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27 #include "llvm/Analysis/InlineCost.h"
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121
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28 #include "llvm/Analysis/LoopInfo.h"
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120
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29 #include "llvm/Analysis/ScalarEvolution.h"
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30 #include "llvm/Analysis/ScalarEvolutionExpressions.h"
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121
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31 #include "llvm/Analysis/TargetLibraryInfo.h"
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134
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32 #include "llvm/CodeGen/TargetLowering.h"
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121
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33 #include "llvm/CodeGen/TargetPassConfig.h"
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134
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34 #include "llvm/CodeGen/TargetSubtargetInfo.h"
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121
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35 #include "llvm/IR/Argument.h"
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36 #include "llvm/IR/Attributes.h"
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37 #include "llvm/IR/CallSite.h"
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38 #include "llvm/IR/ConstantRange.h"
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120
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39 #include "llvm/IR/Constants.h"
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40 #include "llvm/IR/DIBuilder.h"
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41 #include "llvm/IR/DataLayout.h"
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42 #include "llvm/IR/DerivedTypes.h"
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121
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43 #include "llvm/IR/Dominators.h"
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120
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44 #include "llvm/IR/Function.h"
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45 #include "llvm/IR/IRBuilder.h"
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46 #include "llvm/IR/InstIterator.h"
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121
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47 #include "llvm/IR/Instruction.h"
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120
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48 #include "llvm/IR/Instructions.h"
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49 #include "llvm/IR/IntrinsicInst.h"
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50 #include "llvm/IR/Intrinsics.h"
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51 #include "llvm/IR/MDBuilder.h"
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52 #include "llvm/IR/Module.h"
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121
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53 #include "llvm/IR/Type.h"
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54 #include "llvm/IR/Use.h"
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55 #include "llvm/IR/User.h"
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56 #include "llvm/IR/Value.h"
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120
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57 #include "llvm/Pass.h"
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121
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58 #include "llvm/Support/Casting.h"
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120
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59 #include "llvm/Support/Debug.h"
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121
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60 #include "llvm/Support/ErrorHandling.h"
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120
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61 #include "llvm/Support/MathExtras.h"
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121
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62 #include "llvm/Support/raw_ostream.h"
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63 #include "llvm/Target/TargetMachine.h"
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120
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64 #include "llvm/Transforms/Utils/BasicBlockUtils.h"
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134
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65 #include "llvm/Transforms/Utils/Cloning.h"
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120
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66 #include "llvm/Transforms/Utils/Local.h"
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121
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67 #include <algorithm>
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68 #include <cassert>
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69 #include <cstdint>
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70 #include <string>
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71 #include <utility>
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120
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72
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73 using namespace llvm;
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74 using namespace llvm::safestack;
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75
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121
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76 #define DEBUG_TYPE "safe-stack"
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120
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77
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78 namespace llvm {
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79
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80 STATISTIC(NumFunctions, "Total number of functions");
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81 STATISTIC(NumUnsafeStackFunctions, "Number of functions with unsafe stack");
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82 STATISTIC(NumUnsafeStackRestorePointsFunctions,
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83 "Number of functions that use setjmp or exceptions");
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84
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85 STATISTIC(NumAllocas, "Total number of allocas");
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86 STATISTIC(NumUnsafeStaticAllocas, "Number of unsafe static allocas");
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87 STATISTIC(NumUnsafeDynamicAllocas, "Number of unsafe dynamic allocas");
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88 STATISTIC(NumUnsafeByValArguments, "Number of unsafe byval arguments");
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89 STATISTIC(NumUnsafeStackRestorePoints, "Number of setjmps and landingpads");
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90
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91 } // namespace llvm
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92
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134
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93 /// Use __safestack_pointer_address even if the platform has a faster way of
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94 /// access safe stack pointer.
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95 static cl::opt<bool>
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96 SafeStackUsePointerAddress("safestack-use-pointer-address",
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97 cl::init(false), cl::Hidden);
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98
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99
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120
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100 namespace {
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101
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102 /// Rewrite an SCEV expression for a memory access address to an expression that
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103 /// represents offset from the given alloca.
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104 ///
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105 /// The implementation simply replaces all mentions of the alloca with zero.
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106 class AllocaOffsetRewriter : public SCEVRewriteVisitor<AllocaOffsetRewriter> {
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107 const Value *AllocaPtr;
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108
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109 public:
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110 AllocaOffsetRewriter(ScalarEvolution &SE, const Value *AllocaPtr)
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111 : SCEVRewriteVisitor(SE), AllocaPtr(AllocaPtr) {}
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112
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113 const SCEV *visitUnknown(const SCEVUnknown *Expr) {
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114 if (Expr->getValue() == AllocaPtr)
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115 return SE.getZero(Expr->getType());
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116 return Expr;
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117 }
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118 };
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119
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120 /// The SafeStack pass splits the stack of each function into the safe
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121 /// stack, which is only accessed through memory safe dereferences (as
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122 /// determined statically), and the unsafe stack, which contains all
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123 /// local variables that are accessed in ways that we can't prove to
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124 /// be safe.
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121
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125 class SafeStack {
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126 Function &F;
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127 const TargetLoweringBase &TL;
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128 const DataLayout &DL;
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129 ScalarEvolution &SE;
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120
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130
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131 Type *StackPtrTy;
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132 Type *IntPtrTy;
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133 Type *Int32Ty;
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134 Type *Int8Ty;
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135
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136 Value *UnsafeStackPtr = nullptr;
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137
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138 /// Unsafe stack alignment. Each stack frame must ensure that the stack is
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139 /// aligned to this value. We need to re-align the unsafe stack if the
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140 /// alignment of any object on the stack exceeds this value.
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141 ///
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142 /// 16 seems like a reasonable upper bound on the alignment of objects that we
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143 /// might expect to appear on the stack on most common targets.
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144 enum { StackAlignment = 16 };
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145
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146 /// \brief Return the value of the stack canary.
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147 Value *getStackGuard(IRBuilder<> &IRB, Function &F);
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148
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149 /// \brief Load stack guard from the frame and check if it has changed.
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150 void checkStackGuard(IRBuilder<> &IRB, Function &F, ReturnInst &RI,
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151 AllocaInst *StackGuardSlot, Value *StackGuard);
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152
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153 /// \brief Find all static allocas, dynamic allocas, return instructions and
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154 /// stack restore points (exception unwind blocks and setjmp calls) in the
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155 /// given function and append them to the respective vectors.
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156 void findInsts(Function &F, SmallVectorImpl<AllocaInst *> &StaticAllocas,
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157 SmallVectorImpl<AllocaInst *> &DynamicAllocas,
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158 SmallVectorImpl<Argument *> &ByValArguments,
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159 SmallVectorImpl<ReturnInst *> &Returns,
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160 SmallVectorImpl<Instruction *> &StackRestorePoints);
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161
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162 /// \brief Calculate the allocation size of a given alloca. Returns 0 if the
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163 /// size can not be statically determined.
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164 uint64_t getStaticAllocaAllocationSize(const AllocaInst* AI);
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165
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166 /// \brief Allocate space for all static allocas in \p StaticAllocas,
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167 /// replace allocas with pointers into the unsafe stack and generate code to
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168 /// restore the stack pointer before all return instructions in \p Returns.
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169 ///
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170 /// \returns A pointer to the top of the unsafe stack after all unsafe static
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171 /// allocas are allocated.
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172 Value *moveStaticAllocasToUnsafeStack(IRBuilder<> &IRB, Function &F,
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173 ArrayRef<AllocaInst *> StaticAllocas,
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174 ArrayRef<Argument *> ByValArguments,
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175 ArrayRef<ReturnInst *> Returns,
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176 Instruction *BasePointer,
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177 AllocaInst *StackGuardSlot);
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178
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179 /// \brief Generate code to restore the stack after all stack restore points
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180 /// in \p StackRestorePoints.
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181 ///
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182 /// \returns A local variable in which to maintain the dynamic top of the
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183 /// unsafe stack if needed.
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184 AllocaInst *
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185 createStackRestorePoints(IRBuilder<> &IRB, Function &F,
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186 ArrayRef<Instruction *> StackRestorePoints,
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187 Value *StaticTop, bool NeedDynamicTop);
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188
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189 /// \brief Replace all allocas in \p DynamicAllocas with code to allocate
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190 /// space dynamically on the unsafe stack and store the dynamic unsafe stack
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191 /// top to \p DynamicTop if non-null.
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192 void moveDynamicAllocasToUnsafeStack(Function &F, Value *UnsafeStackPtr,
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193 AllocaInst *DynamicTop,
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194 ArrayRef<AllocaInst *> DynamicAllocas);
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195
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196 bool IsSafeStackAlloca(const Value *AllocaPtr, uint64_t AllocaSize);
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197
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198 bool IsMemIntrinsicSafe(const MemIntrinsic *MI, const Use &U,
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199 const Value *AllocaPtr, uint64_t AllocaSize);
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200 bool IsAccessSafe(Value *Addr, uint64_t Size, const Value *AllocaPtr,
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201 uint64_t AllocaSize);
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202
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134
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203 bool ShouldInlinePointerAddress(CallSite &CS);
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204 void TryInlinePointerAddress();
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205
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120
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206 public:
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207 SafeStack(Function &F, const TargetLoweringBase &TL, const DataLayout &DL,
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208 ScalarEvolution &SE)
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209 : F(F), TL(TL), DL(DL), SE(SE),
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210 StackPtrTy(Type::getInt8PtrTy(F.getContext())),
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211 IntPtrTy(DL.getIntPtrType(F.getContext())),
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212 Int32Ty(Type::getInt32Ty(F.getContext())),
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213 Int8Ty(Type::getInt8Ty(F.getContext())) {}
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120
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214
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121
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215 // Run the transformation on the associated function.
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216 // Returns whether the function was changed.
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217 bool run();
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218 };
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120
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219
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220 uint64_t SafeStack::getStaticAllocaAllocationSize(const AllocaInst* AI) {
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121
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221 uint64_t Size = DL.getTypeAllocSize(AI->getAllocatedType());
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120
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222 if (AI->isArrayAllocation()) {
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223 auto C = dyn_cast<ConstantInt>(AI->getArraySize());
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224 if (!C)
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225 return 0;
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226 Size *= C->getZExtValue();
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227 }
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228 return Size;
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229 }
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230
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231 bool SafeStack::IsAccessSafe(Value *Addr, uint64_t AccessSize,
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232 const Value *AllocaPtr, uint64_t AllocaSize) {
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121
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233 AllocaOffsetRewriter Rewriter(SE, AllocaPtr);
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234 const SCEV *Expr = Rewriter.visit(SE.getSCEV(Addr));
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120
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235
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121
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236 uint64_t BitWidth = SE.getTypeSizeInBits(Expr->getType());
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237 ConstantRange AccessStartRange = SE.getUnsignedRange(Expr);
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120
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238 ConstantRange SizeRange =
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239 ConstantRange(APInt(BitWidth, 0), APInt(BitWidth, AccessSize));
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240 ConstantRange AccessRange = AccessStartRange.add(SizeRange);
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241 ConstantRange AllocaRange =
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242 ConstantRange(APInt(BitWidth, 0), APInt(BitWidth, AllocaSize));
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243 bool Safe = AllocaRange.contains(AccessRange);
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244
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245 DEBUG(dbgs() << "[SafeStack] "
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246 << (isa<AllocaInst>(AllocaPtr) ? "Alloca " : "ByValArgument ")
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247 << *AllocaPtr << "\n"
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248 << " Access " << *Addr << "\n"
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249 << " SCEV " << *Expr
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121
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250 << " U: " << SE.getUnsignedRange(Expr)
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251 << ", S: " << SE.getSignedRange(Expr) << "\n"
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120
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252 << " Range " << AccessRange << "\n"
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253 << " AllocaRange " << AllocaRange << "\n"
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254 << " " << (Safe ? "safe" : "unsafe") << "\n");
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255
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256 return Safe;
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257 }
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258
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259 bool SafeStack::IsMemIntrinsicSafe(const MemIntrinsic *MI, const Use &U,
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260 const Value *AllocaPtr,
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261 uint64_t AllocaSize) {
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262 // All MemIntrinsics have destination address in Arg0 and size in Arg2.
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263 if (MI->getRawDest() != U) return true;
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264 const auto *Len = dyn_cast<ConstantInt>(MI->getLength());
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265 // Non-constant size => unsafe. FIXME: try SCEV getRange.
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266 if (!Len) return false;
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267 return IsAccessSafe(U, Len->getZExtValue(), AllocaPtr, AllocaSize);
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268 }
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269
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270 /// Check whether a given allocation must be put on the safe
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271 /// stack or not. The function analyzes all uses of AI and checks whether it is
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272 /// only accessed in a memory safe way (as decided statically).
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273 bool SafeStack::IsSafeStackAlloca(const Value *AllocaPtr, uint64_t AllocaSize) {
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274 // Go through all uses of this alloca and check whether all accesses to the
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275 // allocated object are statically known to be memory safe and, hence, the
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276 // object can be placed on the safe stack.
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277 SmallPtrSet<const Value *, 16> Visited;
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278 SmallVector<const Value *, 8> WorkList;
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279 WorkList.push_back(AllocaPtr);
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280
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281 // A DFS search through all uses of the alloca in bitcasts/PHI/GEPs/etc.
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282 while (!WorkList.empty()) {
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283 const Value *V = WorkList.pop_back_val();
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284 for (const Use &UI : V->uses()) {
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285 auto I = cast<const Instruction>(UI.getUser());
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286 assert(V == UI.get());
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287
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288 switch (I->getOpcode()) {
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121
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289 case Instruction::Load:
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290 if (!IsAccessSafe(UI, DL.getTypeStoreSize(I->getType()), AllocaPtr,
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120
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291 AllocaSize))
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292 return false;
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293 break;
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121
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294
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120
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295 case Instruction::VAArg:
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296 // "va-arg" from a pointer is safe.
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297 break;
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121
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298 case Instruction::Store:
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120
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299 if (V == I->getOperand(0)) {
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300 // Stored the pointer - conservatively assume it may be unsafe.
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301 DEBUG(dbgs() << "[SafeStack] Unsafe alloca: " << *AllocaPtr
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302 << "\n store of address: " << *I << "\n");
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303 return false;
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304 }
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305
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121
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306 if (!IsAccessSafe(UI, DL.getTypeStoreSize(I->getOperand(0)->getType()),
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120
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307 AllocaPtr, AllocaSize))
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308 return false;
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309 break;
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121
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310
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311 case Instruction::Ret:
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120
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312 // Information leak.
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313 return false;
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314
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315 case Instruction::Call:
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316 case Instruction::Invoke: {
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317 ImmutableCallSite CS(I);
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318
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319 if (const IntrinsicInst *II = dyn_cast<IntrinsicInst>(I)) {
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320 if (II->getIntrinsicID() == Intrinsic::lifetime_start ||
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321 II->getIntrinsicID() == Intrinsic::lifetime_end)
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322 continue;
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323 }
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324
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325 if (const MemIntrinsic *MI = dyn_cast<MemIntrinsic>(I)) {
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326 if (!IsMemIntrinsicSafe(MI, UI, AllocaPtr, AllocaSize)) {
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327 DEBUG(dbgs() << "[SafeStack] Unsafe alloca: " << *AllocaPtr
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328 << "\n unsafe memintrinsic: " << *I
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329 << "\n");
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330 return false;
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331 }
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332 continue;
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333 }
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334
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335 // LLVM 'nocapture' attribute is only set for arguments whose address
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336 // is not stored, passed around, or used in any other non-trivial way.
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337 // We assume that passing a pointer to an object as a 'nocapture
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338 // readnone' argument is safe.
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339 // FIXME: a more precise solution would require an interprocedural
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340 // analysis here, which would look at all uses of an argument inside
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341 // the function being called.
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342 ImmutableCallSite::arg_iterator B = CS.arg_begin(), E = CS.arg_end();
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343 for (ImmutableCallSite::arg_iterator A = B; A != E; ++A)
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344 if (A->get() == V)
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345 if (!(CS.doesNotCapture(A - B) && (CS.doesNotAccessMemory(A - B) ||
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346 CS.doesNotAccessMemory()))) {
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347 DEBUG(dbgs() << "[SafeStack] Unsafe alloca: " << *AllocaPtr
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348 << "\n unsafe call: " << *I << "\n");
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349 return false;
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350 }
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351 continue;
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352 }
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353
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354 default:
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355 if (Visited.insert(I).second)
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356 WorkList.push_back(cast<const Instruction>(I));
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357 }
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358 }
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359 }
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360
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361 // All uses of the alloca are safe, we can place it on the safe stack.
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362 return true;
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363 }
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364
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365 Value *SafeStack::getStackGuard(IRBuilder<> &IRB, Function &F) {
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121
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366 Value *StackGuardVar = TL.getIRStackGuard(IRB);
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120
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367 if (!StackGuardVar)
|
|
|
368 StackGuardVar =
|
|
|
369 F.getParent()->getOrInsertGlobal("__stack_chk_guard", StackPtrTy);
|
|
|
370 return IRB.CreateLoad(StackGuardVar, "StackGuard");
|
|
|
371 }
|
|
|
372
|
|
|
373 void SafeStack::findInsts(Function &F,
|
|
|
374 SmallVectorImpl<AllocaInst *> &StaticAllocas,
|
|
|
375 SmallVectorImpl<AllocaInst *> &DynamicAllocas,
|
|
|
376 SmallVectorImpl<Argument *> &ByValArguments,
|
|
|
377 SmallVectorImpl<ReturnInst *> &Returns,
|
|
|
378 SmallVectorImpl<Instruction *> &StackRestorePoints) {
|
|
|
379 for (Instruction &I : instructions(&F)) {
|
|
|
380 if (auto AI = dyn_cast<AllocaInst>(&I)) {
|
|
|
381 ++NumAllocas;
|
|
|
382
|
|
|
383 uint64_t Size = getStaticAllocaAllocationSize(AI);
|
|
|
384 if (IsSafeStackAlloca(AI, Size))
|
|
|
385 continue;
|
|
|
386
|
|
|
387 if (AI->isStaticAlloca()) {
|
|
|
388 ++NumUnsafeStaticAllocas;
|
|
|
389 StaticAllocas.push_back(AI);
|
|
|
390 } else {
|
|
|
391 ++NumUnsafeDynamicAllocas;
|
|
|
392 DynamicAllocas.push_back(AI);
|
|
|
393 }
|
|
|
394 } else if (auto RI = dyn_cast<ReturnInst>(&I)) {
|
|
|
395 Returns.push_back(RI);
|
|
|
396 } else if (auto CI = dyn_cast<CallInst>(&I)) {
|
|
|
397 // setjmps require stack restore.
|
|
|
398 if (CI->getCalledFunction() && CI->canReturnTwice())
|
|
|
399 StackRestorePoints.push_back(CI);
|
|
|
400 } else if (auto LP = dyn_cast<LandingPadInst>(&I)) {
|
|
|
401 // Exception landing pads require stack restore.
|
|
|
402 StackRestorePoints.push_back(LP);
|
|
|
403 } else if (auto II = dyn_cast<IntrinsicInst>(&I)) {
|
|
|
404 if (II->getIntrinsicID() == Intrinsic::gcroot)
|
|
121
|
405 report_fatal_error(
|
|
120
|
406 "gcroot intrinsic not compatible with safestack attribute");
|
|
|
407 }
|
|
|
408 }
|
|
|
409 for (Argument &Arg : F.args()) {
|
|
|
410 if (!Arg.hasByValAttr())
|
|
|
411 continue;
|
|
|
412 uint64_t Size =
|
|
121
|
413 DL.getTypeStoreSize(Arg.getType()->getPointerElementType());
|
|
120
|
414 if (IsSafeStackAlloca(&Arg, Size))
|
|
|
415 continue;
|
|
|
416
|
|
|
417 ++NumUnsafeByValArguments;
|
|
|
418 ByValArguments.push_back(&Arg);
|
|
|
419 }
|
|
|
420 }
|
|
|
421
|
|
|
422 AllocaInst *
|
|
|
423 SafeStack::createStackRestorePoints(IRBuilder<> &IRB, Function &F,
|
|
|
424 ArrayRef<Instruction *> StackRestorePoints,
|
|
|
425 Value *StaticTop, bool NeedDynamicTop) {
|
|
|
426 assert(StaticTop && "The stack top isn't set.");
|
|
|
427
|
|
|
428 if (StackRestorePoints.empty())
|
|
|
429 return nullptr;
|
|
|
430
|
|
|
431 // We need the current value of the shadow stack pointer to restore
|
|
|
432 // after longjmp or exception catching.
|
|
|
433
|
|
|
434 // FIXME: On some platforms this could be handled by the longjmp/exception
|
|
|
435 // runtime itself.
|
|
|
436
|
|
|
437 AllocaInst *DynamicTop = nullptr;
|
|
|
438 if (NeedDynamicTop) {
|
|
|
439 // If we also have dynamic alloca's, the stack pointer value changes
|
|
|
440 // throughout the function. For now we store it in an alloca.
|
|
|
441 DynamicTop = IRB.CreateAlloca(StackPtrTy, /*ArraySize=*/nullptr,
|
|
|
442 "unsafe_stack_dynamic_ptr");
|
|
|
443 IRB.CreateStore(StaticTop, DynamicTop);
|
|
|
444 }
|
|
|
445
|
|
|
446 // Restore current stack pointer after longjmp/exception catch.
|
|
|
447 for (Instruction *I : StackRestorePoints) {
|
|
|
448 ++NumUnsafeStackRestorePoints;
|
|
|
449
|
|
|
450 IRB.SetInsertPoint(I->getNextNode());
|
|
|
451 Value *CurrentTop = DynamicTop ? IRB.CreateLoad(DynamicTop) : StaticTop;
|
|
|
452 IRB.CreateStore(CurrentTop, UnsafeStackPtr);
|
|
|
453 }
|
|
|
454
|
|
|
455 return DynamicTop;
|
|
|
456 }
|
|
|
457
|
|
|
458 void SafeStack::checkStackGuard(IRBuilder<> &IRB, Function &F, ReturnInst &RI,
|
|
|
459 AllocaInst *StackGuardSlot, Value *StackGuard) {
|
|
|
460 Value *V = IRB.CreateLoad(StackGuardSlot);
|
|
|
461 Value *Cmp = IRB.CreateICmpNE(StackGuard, V);
|
|
|
462
|
|
|
463 auto SuccessProb = BranchProbabilityInfo::getBranchProbStackProtector(true);
|
|
|
464 auto FailureProb = BranchProbabilityInfo::getBranchProbStackProtector(false);
|
|
|
465 MDNode *Weights = MDBuilder(F.getContext())
|
|
|
466 .createBranchWeights(SuccessProb.getNumerator(),
|
|
|
467 FailureProb.getNumerator());
|
|
|
468 Instruction *CheckTerm =
|
|
|
469 SplitBlockAndInsertIfThen(Cmp, &RI,
|
|
|
470 /* Unreachable */ true, Weights);
|
|
|
471 IRBuilder<> IRBFail(CheckTerm);
|
|
|
472 // FIXME: respect -fsanitize-trap / -ftrap-function here?
|
|
|
473 Constant *StackChkFail = F.getParent()->getOrInsertFunction(
|
|
121
|
474 "__stack_chk_fail", IRB.getVoidTy());
|
|
120
|
475 IRBFail.CreateCall(StackChkFail, {});
|
|
|
476 }
|
|
|
477
|
|
|
478 /// We explicitly compute and set the unsafe stack layout for all unsafe
|
|
|
479 /// static alloca instructions. We save the unsafe "base pointer" in the
|
|
|
480 /// prologue into a local variable and restore it in the epilogue.
|
|
|
481 Value *SafeStack::moveStaticAllocasToUnsafeStack(
|
|
|
482 IRBuilder<> &IRB, Function &F, ArrayRef<AllocaInst *> StaticAllocas,
|
|
|
483 ArrayRef<Argument *> ByValArguments, ArrayRef<ReturnInst *> Returns,
|
|
|
484 Instruction *BasePointer, AllocaInst *StackGuardSlot) {
|
|
|
485 if (StaticAllocas.empty() && ByValArguments.empty())
|
|
|
486 return BasePointer;
|
|
|
487
|
|
|
488 DIBuilder DIB(*F.getParent());
|
|
|
489
|
|
|
490 StackColoring SSC(F, StaticAllocas);
|
|
|
491 SSC.run();
|
|
|
492 SSC.removeAllMarkers();
|
|
|
493
|
|
|
494 // Unsafe stack always grows down.
|
|
|
495 StackLayout SSL(StackAlignment);
|
|
|
496 if (StackGuardSlot) {
|
|
|
497 Type *Ty = StackGuardSlot->getAllocatedType();
|
|
|
498 unsigned Align =
|
|
121
|
499 std::max(DL.getPrefTypeAlignment(Ty), StackGuardSlot->getAlignment());
|
|
120
|
500 SSL.addObject(StackGuardSlot, getStaticAllocaAllocationSize(StackGuardSlot),
|
|
|
501 Align, SSC.getFullLiveRange());
|
|
|
502 }
|
|
|
503
|
|
|
504 for (Argument *Arg : ByValArguments) {
|
|
|
505 Type *Ty = Arg->getType()->getPointerElementType();
|
|
121
|
506 uint64_t Size = DL.getTypeStoreSize(Ty);
|
|
120
|
507 if (Size == 0)
|
|
|
508 Size = 1; // Don't create zero-sized stack objects.
|
|
|
509
|
|
|
510 // Ensure the object is properly aligned.
|
|
121
|
511 unsigned Align = std::max((unsigned)DL.getPrefTypeAlignment(Ty),
|
|
120
|
512 Arg->getParamAlignment());
|
|
|
513 SSL.addObject(Arg, Size, Align, SSC.getFullLiveRange());
|
|
|
514 }
|
|
|
515
|
|
|
516 for (AllocaInst *AI : StaticAllocas) {
|
|
|
517 Type *Ty = AI->getAllocatedType();
|
|
|
518 uint64_t Size = getStaticAllocaAllocationSize(AI);
|
|
|
519 if (Size == 0)
|
|
|
520 Size = 1; // Don't create zero-sized stack objects.
|
|
|
521
|
|
|
522 // Ensure the object is properly aligned.
|
|
|
523 unsigned Align =
|
|
121
|
524 std::max((unsigned)DL.getPrefTypeAlignment(Ty), AI->getAlignment());
|
|
120
|
525
|
|
|
526 SSL.addObject(AI, Size, Align, SSC.getLiveRange(AI));
|
|
|
527 }
|
|
|
528
|
|
|
529 SSL.computeLayout();
|
|
|
530 unsigned FrameAlignment = SSL.getFrameAlignment();
|
|
|
531
|
|
|
532 // FIXME: tell SSL that we start at a less-then-MaxAlignment aligned location
|
|
|
533 // (AlignmentSkew).
|
|
|
534 if (FrameAlignment > StackAlignment) {
|
|
|
535 // Re-align the base pointer according to the max requested alignment.
|
|
|
536 assert(isPowerOf2_32(FrameAlignment));
|
|
|
537 IRB.SetInsertPoint(BasePointer->getNextNode());
|
|
|
538 BasePointer = cast<Instruction>(IRB.CreateIntToPtr(
|
|
|
539 IRB.CreateAnd(IRB.CreatePtrToInt(BasePointer, IntPtrTy),
|
|
|
540 ConstantInt::get(IntPtrTy, ~uint64_t(FrameAlignment - 1))),
|
|
|
541 StackPtrTy));
|
|
|
542 }
|
|
|
543
|
|
|
544 IRB.SetInsertPoint(BasePointer->getNextNode());
|
|
|
545
|
|
|
546 if (StackGuardSlot) {
|
|
|
547 unsigned Offset = SSL.getObjectOffset(StackGuardSlot);
|
|
|
548 Value *Off = IRB.CreateGEP(BasePointer, // BasePointer is i8*
|
|
|
549 ConstantInt::get(Int32Ty, -Offset));
|
|
|
550 Value *NewAI =
|
|
|
551 IRB.CreateBitCast(Off, StackGuardSlot->getType(), "StackGuardSlot");
|
|
|
552
|
|
|
553 // Replace alloc with the new location.
|
|
|
554 StackGuardSlot->replaceAllUsesWith(NewAI);
|
|
|
555 StackGuardSlot->eraseFromParent();
|
|
|
556 }
|
|
|
557
|
|
|
558 for (Argument *Arg : ByValArguments) {
|
|
|
559 unsigned Offset = SSL.getObjectOffset(Arg);
|
|
134
|
560 unsigned Align = SSL.getObjectAlignment(Arg);
|
|
120
|
561 Type *Ty = Arg->getType()->getPointerElementType();
|
|
|
562
|
|
121
|
563 uint64_t Size = DL.getTypeStoreSize(Ty);
|
|
120
|
564 if (Size == 0)
|
|
|
565 Size = 1; // Don't create zero-sized stack objects.
|
|
|
566
|
|
|
567 Value *Off = IRB.CreateGEP(BasePointer, // BasePointer is i8*
|
|
|
568 ConstantInt::get(Int32Ty, -Offset));
|
|
|
569 Value *NewArg = IRB.CreateBitCast(Off, Arg->getType(),
|
|
|
570 Arg->getName() + ".unsafe-byval");
|
|
|
571
|
|
|
572 // Replace alloc with the new location.
|
|
|
573 replaceDbgDeclare(Arg, BasePointer, BasePointer->getNextNode(), DIB,
|
|
134
|
574 DIExpression::NoDeref, -Offset, DIExpression::NoDeref);
|
|
120
|
575 Arg->replaceAllUsesWith(NewArg);
|
|
|
576 IRB.SetInsertPoint(cast<Instruction>(NewArg)->getNextNode());
|
|
134
|
577 IRB.CreateMemCpy(Off, Align, Arg, Arg->getParamAlignment(), Size);
|
|
120
|
578 }
|
|
|
579
|
|
|
580 // Allocate space for every unsafe static AllocaInst on the unsafe stack.
|
|
|
581 for (AllocaInst *AI : StaticAllocas) {
|
|
|
582 IRB.SetInsertPoint(AI);
|
|
|
583 unsigned Offset = SSL.getObjectOffset(AI);
|
|
|
584
|
|
|
585 uint64_t Size = getStaticAllocaAllocationSize(AI);
|
|
|
586 if (Size == 0)
|
|
|
587 Size = 1; // Don't create zero-sized stack objects.
|
|
|
588
|
|
134
|
589 replaceDbgDeclareForAlloca(AI, BasePointer, DIB, DIExpression::NoDeref,
|
|
|
590 -Offset, DIExpression::NoDeref);
|
|
120
|
591 replaceDbgValueForAlloca(AI, BasePointer, DIB, -Offset);
|
|
|
592
|
|
|
593 // Replace uses of the alloca with the new location.
|
|
|
594 // Insert address calculation close to each use to work around PR27844.
|
|
|
595 std::string Name = std::string(AI->getName()) + ".unsafe";
|
|
|
596 while (!AI->use_empty()) {
|
|
|
597 Use &U = *AI->use_begin();
|
|
|
598 Instruction *User = cast<Instruction>(U.getUser());
|
|
|
599
|
|
|
600 Instruction *InsertBefore;
|
|
|
601 if (auto *PHI = dyn_cast<PHINode>(User))
|
|
|
602 InsertBefore = PHI->getIncomingBlock(U)->getTerminator();
|
|
|
603 else
|
|
|
604 InsertBefore = User;
|
|
|
605
|
|
|
606 IRBuilder<> IRBUser(InsertBefore);
|
|
|
607 Value *Off = IRBUser.CreateGEP(BasePointer, // BasePointer is i8*
|
|
|
608 ConstantInt::get(Int32Ty, -Offset));
|
|
|
609 Value *Replacement = IRBUser.CreateBitCast(Off, AI->getType(), Name);
|
|
|
610
|
|
|
611 if (auto *PHI = dyn_cast<PHINode>(User)) {
|
|
|
612 // PHI nodes may have multiple incoming edges from the same BB (why??),
|
|
|
613 // all must be updated at once with the same incoming value.
|
|
|
614 auto *BB = PHI->getIncomingBlock(U);
|
|
|
615 for (unsigned I = 0; I < PHI->getNumIncomingValues(); ++I)
|
|
|
616 if (PHI->getIncomingBlock(I) == BB)
|
|
|
617 PHI->setIncomingValue(I, Replacement);
|
|
|
618 } else {
|
|
|
619 U.set(Replacement);
|
|
|
620 }
|
|
|
621 }
|
|
|
622
|
|
|
623 AI->eraseFromParent();
|
|
|
624 }
|
|
|
625
|
|
|
626 // Re-align BasePointer so that our callees would see it aligned as
|
|
|
627 // expected.
|
|
|
628 // FIXME: no need to update BasePointer in leaf functions.
|
|
|
629 unsigned FrameSize = alignTo(SSL.getFrameSize(), StackAlignment);
|
|
|
630
|
|
|
631 // Update shadow stack pointer in the function epilogue.
|
|
|
632 IRB.SetInsertPoint(BasePointer->getNextNode());
|
|
|
633
|
|
|
634 Value *StaticTop =
|
|
|
635 IRB.CreateGEP(BasePointer, ConstantInt::get(Int32Ty, -FrameSize),
|
|
|
636 "unsafe_stack_static_top");
|
|
|
637 IRB.CreateStore(StaticTop, UnsafeStackPtr);
|
|
|
638 return StaticTop;
|
|
|
639 }
|
|
|
640
|
|
|
641 void SafeStack::moveDynamicAllocasToUnsafeStack(
|
|
|
642 Function &F, Value *UnsafeStackPtr, AllocaInst *DynamicTop,
|
|
|
643 ArrayRef<AllocaInst *> DynamicAllocas) {
|
|
|
644 DIBuilder DIB(*F.getParent());
|
|
|
645
|
|
|
646 for (AllocaInst *AI : DynamicAllocas) {
|
|
|
647 IRBuilder<> IRB(AI);
|
|
|
648
|
|
|
649 // Compute the new SP value (after AI).
|
|
|
650 Value *ArraySize = AI->getArraySize();
|
|
|
651 if (ArraySize->getType() != IntPtrTy)
|
|
|
652 ArraySize = IRB.CreateIntCast(ArraySize, IntPtrTy, false);
|
|
|
653
|
|
|
654 Type *Ty = AI->getAllocatedType();
|
|
121
|
655 uint64_t TySize = DL.getTypeAllocSize(Ty);
|
|
120
|
656 Value *Size = IRB.CreateMul(ArraySize, ConstantInt::get(IntPtrTy, TySize));
|
|
|
657
|
|
|
658 Value *SP = IRB.CreatePtrToInt(IRB.CreateLoad(UnsafeStackPtr), IntPtrTy);
|
|
|
659 SP = IRB.CreateSub(SP, Size);
|
|
|
660
|
|
|
661 // Align the SP value to satisfy the AllocaInst, type and stack alignments.
|
|
|
662 unsigned Align = std::max(
|
|
121
|
663 std::max((unsigned)DL.getPrefTypeAlignment(Ty), AI->getAlignment()),
|
|
120
|
664 (unsigned)StackAlignment);
|
|
|
665
|
|
|
666 assert(isPowerOf2_32(Align));
|
|
|
667 Value *NewTop = IRB.CreateIntToPtr(
|
|
|
668 IRB.CreateAnd(SP, ConstantInt::get(IntPtrTy, ~uint64_t(Align - 1))),
|
|
|
669 StackPtrTy);
|
|
|
670
|
|
|
671 // Save the stack pointer.
|
|
|
672 IRB.CreateStore(NewTop, UnsafeStackPtr);
|
|
|
673 if (DynamicTop)
|
|
|
674 IRB.CreateStore(NewTop, DynamicTop);
|
|
|
675
|
|
|
676 Value *NewAI = IRB.CreatePointerCast(NewTop, AI->getType());
|
|
|
677 if (AI->hasName() && isa<Instruction>(NewAI))
|
|
|
678 NewAI->takeName(AI);
|
|
|
679
|
|
134
|
680 replaceDbgDeclareForAlloca(AI, NewAI, DIB, DIExpression::NoDeref, 0,
|
|
|
681 DIExpression::NoDeref);
|
|
120
|
682 AI->replaceAllUsesWith(NewAI);
|
|
|
683 AI->eraseFromParent();
|
|
|
684 }
|
|
|
685
|
|
|
686 if (!DynamicAllocas.empty()) {
|
|
|
687 // Now go through the instructions again, replacing stacksave/stackrestore.
|
|
|
688 for (inst_iterator It = inst_begin(&F), Ie = inst_end(&F); It != Ie;) {
|
|
|
689 Instruction *I = &*(It++);
|
|
|
690 auto II = dyn_cast<IntrinsicInst>(I);
|
|
|
691 if (!II)
|
|
|
692 continue;
|
|
|
693
|
|
|
694 if (II->getIntrinsicID() == Intrinsic::stacksave) {
|
|
|
695 IRBuilder<> IRB(II);
|
|
|
696 Instruction *LI = IRB.CreateLoad(UnsafeStackPtr);
|
|
|
697 LI->takeName(II);
|
|
|
698 II->replaceAllUsesWith(LI);
|
|
|
699 II->eraseFromParent();
|
|
|
700 } else if (II->getIntrinsicID() == Intrinsic::stackrestore) {
|
|
|
701 IRBuilder<> IRB(II);
|
|
|
702 Instruction *SI = IRB.CreateStore(II->getArgOperand(0), UnsafeStackPtr);
|
|
|
703 SI->takeName(II);
|
|
|
704 assert(II->use_empty());
|
|
|
705 II->eraseFromParent();
|
|
|
706 }
|
|
|
707 }
|
|
|
708 }
|
|
|
709 }
|
|
|
710
|
|
134
|
711 bool SafeStack::ShouldInlinePointerAddress(CallSite &CS) {
|
|
|
712 Function *Callee = CS.getCalledFunction();
|
|
|
713 if (CS.hasFnAttr(Attribute::AlwaysInline) && isInlineViable(*Callee))
|
|
|
714 return true;
|
|
|
715 if (Callee->isInterposable() || Callee->hasFnAttribute(Attribute::NoInline) ||
|
|
|
716 CS.isNoInline())
|
|
|
717 return false;
|
|
|
718 return true;
|
|
|
719 }
|
|
|
720
|
|
|
721 void SafeStack::TryInlinePointerAddress() {
|
|
|
722 if (!isa<CallInst>(UnsafeStackPtr))
|
|
|
723 return;
|
|
|
724
|
|
|
725 if(F.hasFnAttribute(Attribute::OptimizeNone))
|
|
|
726 return;
|
|
|
727
|
|
|
728 CallSite CS(UnsafeStackPtr);
|
|
|
729 Function *Callee = CS.getCalledFunction();
|
|
|
730 if (!Callee || Callee->isDeclaration())
|
|
|
731 return;
|
|
|
732
|
|
|
733 if (!ShouldInlinePointerAddress(CS))
|
|
|
734 return;
|
|
|
735
|
|
|
736 InlineFunctionInfo IFI;
|
|
|
737 InlineFunction(CS, IFI);
|
|
|
738 }
|
|
|
739
|
|
121
|
740 bool SafeStack::run() {
|
|
|
741 assert(F.hasFnAttribute(Attribute::SafeStack) &&
|
|
|
742 "Can't run SafeStack on a function without the attribute");
|
|
|
743 assert(!F.isDeclaration() && "Can't run SafeStack on a function declaration");
|
|
120
|
744
|
|
|
745 ++NumFunctions;
|
|
|
746
|
|
|
747 SmallVector<AllocaInst *, 16> StaticAllocas;
|
|
|
748 SmallVector<AllocaInst *, 4> DynamicAllocas;
|
|
|
749 SmallVector<Argument *, 4> ByValArguments;
|
|
|
750 SmallVector<ReturnInst *, 4> Returns;
|
|
|
751
|
|
|
752 // Collect all points where stack gets unwound and needs to be restored
|
|
|
753 // This is only necessary because the runtime (setjmp and unwind code) is
|
|
|
754 // not aware of the unsafe stack and won't unwind/restore it properly.
|
|
|
755 // To work around this problem without changing the runtime, we insert
|
|
|
756 // instrumentation to restore the unsafe stack pointer when necessary.
|
|
|
757 SmallVector<Instruction *, 4> StackRestorePoints;
|
|
|
758
|
|
|
759 // Find all static and dynamic alloca instructions that must be moved to the
|
|
|
760 // unsafe stack, all return instructions and stack restore points.
|
|
|
761 findInsts(F, StaticAllocas, DynamicAllocas, ByValArguments, Returns,
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|
|
762 StackRestorePoints);
|
|
|
763
|
|
|
764 if (StaticAllocas.empty() && DynamicAllocas.empty() &&
|
|
|
765 ByValArguments.empty() && StackRestorePoints.empty())
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|
|
766 return false; // Nothing to do in this function.
|
|
|
767
|
|
|
768 if (!StaticAllocas.empty() || !DynamicAllocas.empty() ||
|
|
|
769 !ByValArguments.empty())
|
|
|
770 ++NumUnsafeStackFunctions; // This function has the unsafe stack.
|
|
|
771
|
|
|
772 if (!StackRestorePoints.empty())
|
|
|
773 ++NumUnsafeStackRestorePointsFunctions;
|
|
|
774
|
|
|
775 IRBuilder<> IRB(&F.front(), F.begin()->getFirstInsertionPt());
|
|
134
|
776 if (SafeStackUsePointerAddress) {
|
|
|
777 Value *Fn = F.getParent()->getOrInsertFunction(
|
|
|
778 "__safestack_pointer_address", StackPtrTy->getPointerTo(0));
|
|
|
779 UnsafeStackPtr = IRB.CreateCall(Fn);
|
|
|
780 } else {
|
|
|
781 UnsafeStackPtr = TL.getSafeStackPointerLocation(IRB);
|
|
|
782 }
|
|
120
|
783
|
|
|
784 // Load the current stack pointer (we'll also use it as a base pointer).
|
|
|
785 // FIXME: use a dedicated register for it ?
|
|
|
786 Instruction *BasePointer =
|
|
|
787 IRB.CreateLoad(UnsafeStackPtr, false, "unsafe_stack_ptr");
|
|
|
788 assert(BasePointer->getType() == StackPtrTy);
|
|
|
789
|
|
|
790 AllocaInst *StackGuardSlot = nullptr;
|
|
|
791 // FIXME: implement weaker forms of stack protector.
|
|
|
792 if (F.hasFnAttribute(Attribute::StackProtect) ||
|
|
|
793 F.hasFnAttribute(Attribute::StackProtectStrong) ||
|
|
|
794 F.hasFnAttribute(Attribute::StackProtectReq)) {
|
|
|
795 Value *StackGuard = getStackGuard(IRB, F);
|
|
|
796 StackGuardSlot = IRB.CreateAlloca(StackPtrTy, nullptr);
|
|
|
797 IRB.CreateStore(StackGuard, StackGuardSlot);
|
|
|
798
|
|
|
799 for (ReturnInst *RI : Returns) {
|
|
|
800 IRBuilder<> IRBRet(RI);
|
|
|
801 checkStackGuard(IRBRet, F, *RI, StackGuardSlot, StackGuard);
|
|
|
802 }
|
|
|
803 }
|
|
|
804
|
|
|
805 // The top of the unsafe stack after all unsafe static allocas are
|
|
|
806 // allocated.
|
|
|
807 Value *StaticTop =
|
|
|
808 moveStaticAllocasToUnsafeStack(IRB, F, StaticAllocas, ByValArguments,
|
|
|
809 Returns, BasePointer, StackGuardSlot);
|
|
|
810
|
|
|
811 // Safe stack object that stores the current unsafe stack top. It is updated
|
|
|
812 // as unsafe dynamic (non-constant-sized) allocas are allocated and freed.
|
|
|
813 // This is only needed if we need to restore stack pointer after longjmp
|
|
|
814 // or exceptions, and we have dynamic allocations.
|
|
|
815 // FIXME: a better alternative might be to store the unsafe stack pointer
|
|
|
816 // before setjmp / invoke instructions.
|
|
|
817 AllocaInst *DynamicTop = createStackRestorePoints(
|
|
|
818 IRB, F, StackRestorePoints, StaticTop, !DynamicAllocas.empty());
|
|
|
819
|
|
|
820 // Handle dynamic allocas.
|
|
|
821 moveDynamicAllocasToUnsafeStack(F, UnsafeStackPtr, DynamicTop,
|
|
|
822 DynamicAllocas);
|
|
|
823
|
|
|
824 // Restore the unsafe stack pointer before each return.
|
|
|
825 for (ReturnInst *RI : Returns) {
|
|
|
826 IRB.SetInsertPoint(RI);
|
|
|
827 IRB.CreateStore(BasePointer, UnsafeStackPtr);
|
|
|
828 }
|
|
|
829
|
|
134
|
830 TryInlinePointerAddress();
|
|
|
831
|
|
120
|
832 DEBUG(dbgs() << "[SafeStack] safestack applied\n");
|
|
|
833 return true;
|
|
|
834 }
|
|
|
835
|
|
121
|
836 class SafeStackLegacyPass : public FunctionPass {
|
|
|
837 const TargetMachine *TM = nullptr;
|
|
|
838
|
|
|
839 public:
|
|
|
840 static char ID; // Pass identification, replacement for typeid..
|
|
|
841
|
|
|
842 SafeStackLegacyPass() : FunctionPass(ID) {
|
|
|
843 initializeSafeStackLegacyPassPass(*PassRegistry::getPassRegistry());
|
|
|
844 }
|
|
|
845
|
|
|
846 void getAnalysisUsage(AnalysisUsage &AU) const override {
|
|
|
847 AU.addRequired<TargetPassConfig>();
|
|
|
848 AU.addRequired<TargetLibraryInfoWrapperPass>();
|
|
|
849 AU.addRequired<AssumptionCacheTracker>();
|
|
|
850 }
|
|
|
851
|
|
|
852 bool runOnFunction(Function &F) override {
|
|
|
853 DEBUG(dbgs() << "[SafeStack] Function: " << F.getName() << "\n");
|
|
|
854
|
|
|
855 if (!F.hasFnAttribute(Attribute::SafeStack)) {
|
|
|
856 DEBUG(dbgs() << "[SafeStack] safestack is not requested"
|
|
|
857 " for this function\n");
|
|
|
858 return false;
|
|
|
859 }
|
|
|
860
|
|
|
861 if (F.isDeclaration()) {
|
|
|
862 DEBUG(dbgs() << "[SafeStack] function definition"
|
|
|
863 " is not available\n");
|
|
|
864 return false;
|
|
|
865 }
|
|
120
|
866
|
|
121
|
867 TM = &getAnalysis<TargetPassConfig>().getTM<TargetMachine>();
|
|
|
868 auto *TL = TM->getSubtargetImpl(F)->getTargetLowering();
|
|
|
869 if (!TL)
|
|
|
870 report_fatal_error("TargetLowering instance is required");
|
|
|
871
|
|
|
872 auto *DL = &F.getParent()->getDataLayout();
|
|
|
873 auto &TLI = getAnalysis<TargetLibraryInfoWrapperPass>().getTLI();
|
|
|
874 auto &ACT = getAnalysis<AssumptionCacheTracker>().getAssumptionCache(F);
|
|
|
875
|
|
|
876 // Compute DT and LI only for functions that have the attribute.
|
|
|
877 // This is only useful because the legacy pass manager doesn't let us
|
|
|
878 // compute analyzes lazily.
|
|
|
879 // In the backend pipeline, nothing preserves DT before SafeStack, so we
|
|
|
880 // would otherwise always compute it wastefully, even if there is no
|
|
|
881 // function with the safestack attribute.
|
|
|
882 DominatorTree DT(F);
|
|
|
883 LoopInfo LI(DT);
|
|
120
|
884
|
|
121
|
885 ScalarEvolution SE(F, TLI, ACT, DT, LI);
|
|
|
886
|
|
|
887 return SafeStack(F, *TL, *DL, SE).run();
|
|
|
888 }
|
|
|
889 };
|
|
|
890
|
|
|
891 } // end anonymous namespace
|
|
|
892
|
|
|
893 char SafeStackLegacyPass::ID = 0;
|
|
|
894
|
|
|
895 INITIALIZE_PASS_BEGIN(SafeStackLegacyPass, DEBUG_TYPE,
|
|
|
896 "Safe Stack instrumentation pass", false, false)
|
|
|
897 INITIALIZE_PASS_DEPENDENCY(TargetPassConfig)
|
|
|
898 INITIALIZE_PASS_END(SafeStackLegacyPass, DEBUG_TYPE,
|
|
|
899 "Safe Stack instrumentation pass", false, false)
|
|
|
900
|
|
|
901 FunctionPass *llvm::createSafeStackPass() { return new SafeStackLegacyPass(); }
|
