1 //===-- ASanStackFrameLayout.cpp - helper for AddressSanitizer ------------===// 2 // 3 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions. 4 // See https://llvm.org/LICENSE.txt for license information. 5 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception 6 // 7 //===----------------------------------------------------------------------===// 8 // 9 // Definition of ComputeASanStackFrameLayout (see ASanStackFrameLayout.h). 10 // 11 //===----------------------------------------------------------------------===// 12 #include "llvm/Transforms/Utils/ASanStackFrameLayout.h" 13 #include "llvm/ADT/SmallString.h" 14 #include "llvm/IR/DebugInfo.h" 15 #include "llvm/Support/MathExtras.h" 16 #include "llvm/Support/ScopedPrinter.h" 17 #include "llvm/Support/raw_ostream.h" 18 #include <algorithm> 19 20 namespace llvm { 21 22 // We sort the stack variables by alignment (largest first) to minimize 23 // unnecessary large gaps due to alignment. 24 // It is tempting to also sort variables by size so that larger variables 25 // have larger redzones at both ends. But reordering will make report analysis 26 // harder, especially when temporary unnamed variables are present. 27 // So, until we can provide more information (type, line number, etc) 28 // for the stack variables we avoid reordering them too much. 29 static inline bool CompareVars(const ASanStackVariableDescription &a, 30 const ASanStackVariableDescription &b) { 31 return a.Alignment > b.Alignment; 32 } 33 34 // We also force minimal alignment for all vars to kMinAlignment so that vars 35 // with e.g. alignment 1 and alignment 16 do not get reordered by CompareVars. 36 static const size_t kMinAlignment = 16; 37 38 // We want to add a full redzone after every variable. 39 // The larger the variable Size the larger is the redzone. 40 // The resulting frame size is a multiple of Alignment. 41 static size_t VarAndRedzoneSize(size_t Size, size_t Granularity, 42 size_t Alignment) { 43 size_t Res = 0; 44 if (Size <= 4) Res = 16; 45 else if (Size <= 16) Res = 32; 46 else if (Size <= 128) Res = Size + 32; 47 else if (Size <= 512) Res = Size + 64; 48 else if (Size <= 4096) Res = Size + 128; 49 else Res = Size + 256; 50 return alignTo(std::max(Res, 2 * Granularity), Alignment); 51 } 52 53 ASanStackFrameLayout 54 ComputeASanStackFrameLayout(SmallVectorImpl<ASanStackVariableDescription> &Vars, 55 size_t Granularity, size_t MinHeaderSize) { 56 assert(Granularity >= 8 && Granularity <= 64 && 57 (Granularity & (Granularity - 1)) == 0); 58 assert(MinHeaderSize >= 16 && (MinHeaderSize & (MinHeaderSize - 1)) == 0 && 59 MinHeaderSize >= Granularity); 60 const size_t NumVars = Vars.size(); 61 assert(NumVars > 0); 62 for (size_t i = 0; i < NumVars; i++) 63 Vars[i].Alignment = std::max(Vars[i].Alignment, kMinAlignment); 64 65 llvm::stable_sort(Vars, CompareVars); 66 67 ASanStackFrameLayout Layout; 68 Layout.Granularity = Granularity; 69 Layout.FrameAlignment = std::max(Granularity, Vars[0].Alignment); 70 size_t Offset = std::max(std::max(MinHeaderSize, Granularity), 71 Vars[0].Alignment); 72 assert((Offset % Granularity) == 0); 73 for (size_t i = 0; i < NumVars; i++) { 74 bool IsLast = i == NumVars - 1; 75 size_t Alignment = std::max(Granularity, Vars[i].Alignment); 76 (void)Alignment; // Used only in asserts. 77 size_t Size = Vars[i].Size; 78 assert((Alignment & (Alignment - 1)) == 0); 79 assert(Layout.FrameAlignment >= Alignment); 80 assert((Offset % Alignment) == 0); 81 assert(Size > 0); 82 size_t NextAlignment = IsLast ? Granularity 83 : std::max(Granularity, Vars[i + 1].Alignment); 84 size_t SizeWithRedzone = VarAndRedzoneSize(Size, Granularity, 85 NextAlignment); 86 Vars[i].Offset = Offset; 87 Offset += SizeWithRedzone; 88 } 89 if (Offset % MinHeaderSize) { 90 Offset += MinHeaderSize - (Offset % MinHeaderSize); 91 } 92 Layout.FrameSize = Offset; 93 assert((Layout.FrameSize % MinHeaderSize) == 0); 94 return Layout; 95 } 96 97 SmallString<64> ComputeASanStackFrameDescription( 98 const SmallVectorImpl<ASanStackVariableDescription> &Vars) { 99 SmallString<2048> StackDescriptionStorage; 100 raw_svector_ostream StackDescription(StackDescriptionStorage); 101 StackDescription << Vars.size(); 102 103 for (const auto &Var : Vars) { 104 std::string Name = Var.Name; 105 if (Var.Line) { 106 Name += ":"; 107 Name += to_string(Var.Line); 108 } 109 StackDescription << " " << Var.Offset << " " << Var.Size << " " 110 << Name.size() << " " << Name; 111 } 112 return StackDescription.str(); 113 } 114 115 SmallVector<uint8_t, 64> 116 GetShadowBytes(const SmallVectorImpl<ASanStackVariableDescription> &Vars, 117 const ASanStackFrameLayout &Layout) { 118 assert(Vars.size() > 0); 119 SmallVector<uint8_t, 64> SB; 120 SB.clear(); 121 const size_t Granularity = Layout.Granularity; 122 SB.resize(Vars[0].Offset / Granularity, kAsanStackLeftRedzoneMagic); 123 for (const auto &Var : Vars) { 124 SB.resize(Var.Offset / Granularity, kAsanStackMidRedzoneMagic); 125 126 SB.resize(SB.size() + Var.Size / Granularity, 0); 127 if (Var.Size % Granularity) 128 SB.push_back(Var.Size % Granularity); 129 } 130 SB.resize(Layout.FrameSize / Granularity, kAsanStackRightRedzoneMagic); 131 return SB; 132 } 133 134 SmallVector<uint8_t, 64> GetShadowBytesAfterScope( 135 const SmallVectorImpl<ASanStackVariableDescription> &Vars, 136 const ASanStackFrameLayout &Layout) { 137 SmallVector<uint8_t, 64> SB = GetShadowBytes(Vars, Layout); 138 const size_t Granularity = Layout.Granularity; 139 140 for (const auto &Var : Vars) { 141 assert(Var.LifetimeSize <= Var.Size); 142 const size_t LifetimeShadowSize = 143 (Var.LifetimeSize + Granularity - 1) / Granularity; 144 const size_t Offset = Var.Offset / Granularity; 145 std::fill(SB.begin() + Offset, SB.begin() + Offset + LifetimeShadowSize, 146 kAsanStackUseAfterScopeMagic); 147 } 148 149 return SB; 150 } 151 152 } // llvm namespace 153