1 //===-- asan_fake_stack.h ---------------------------------------*- C++ -*-===// 2 // 3 // The LLVM Compiler Infrastructure 4 // 5 // This file is distributed under the University of Illinois Open Source 6 // License. See LICENSE.TXT for details. 7 // 8 //===----------------------------------------------------------------------===// 9 // 10 // This file is a part of AddressSanitizer, an address sanity checker. 11 // 12 // ASan-private header for asan_fake_stack.cc, implements FakeStack. 13 //===----------------------------------------------------------------------===// 14 15 #ifndef ASAN_FAKE_STACK_H 16 #define ASAN_FAKE_STACK_H 17 18 #include "sanitizer_common/sanitizer_common.h" 19 20 namespace __asan { 21 22 // Fake stack frame contains local variables of one function. 23 struct FakeFrame { 24 uptr magic; // Modified by the instrumented code. 25 uptr descr; // Modified by the instrumented code. 26 uptr pc; // Modified by the instrumented code. 27 uptr real_stack; 28 }; 29 30 // For each thread we create a fake stack and place stack objects on this fake 31 // stack instead of the real stack. The fake stack is not really a stack but 32 // a fast malloc-like allocator so that when a function exits the fake stack 33 // is not popped but remains there for quite some time until gets used again. 34 // So, we poison the objects on the fake stack when function returns. 35 // It helps us find use-after-return bugs. 36 // 37 // The FakeStack objects is allocated by a single mmap call and has no other 38 // pointers. The size of the fake stack depends on the actual thread stack size 39 // and thus can not be a constant. 40 // stack_size is a power of two greater or equal to the thread's stack size; 41 // we store it as its logarithm (stack_size_log). 42 // FakeStack has kNumberOfSizeClasses (11) size classes, each size class 43 // is a power of two, starting from 64 bytes. Each size class occupies 44 // stack_size bytes and thus can allocate 45 // NumberOfFrames=(stack_size/BytesInSizeClass) fake frames (also a power of 2). 46 // For each size class we have NumberOfFrames allocation flags, 47 // each flag indicates whether the given frame is currently allocated. 48 // All flags for size classes 0 .. 10 are stored in a single contiguous region 49 // followed by another contiguous region which contains the actual memory for 50 // size classes. The addresses are computed by GetFlags and GetFrame without 51 // any memory accesses solely based on 'this' and stack_size_log. 52 // Allocate() flips the appropriate allocation flag atomically, thus achieving 53 // async-signal safety. 54 // This allocator does not have quarantine per se, but it tries to allocate the 55 // frames in round robin fasion to maximize the delay between a deallocation 56 // and the next allocation. 57 class FakeStack { 58 static const uptr kMinStackFrameSizeLog = 6; // Min frame is 64B. 59 static const uptr kMaxStackFrameSizeLog = 16; // Max stack frame is 64K. 60 61 public: 62 static const uptr kNumberOfSizeClasses = 63 kMaxStackFrameSizeLog - kMinStackFrameSizeLog + 1; 64 65 // CTOR: create the FakeStack as a single mmap-ed object. 66 static FakeStack *Create(uptr stack_size_log); 67 68 void Destroy(int tid); 69 70 // stack_size_log is at least 15 (stack_size >= 32K). 71 static uptr SizeRequiredForFlags(uptr stack_size_log) { 72 return ((uptr)1) << (stack_size_log + 1 - kMinStackFrameSizeLog); 73 } 74 75 // Each size class occupies stack_size bytes. 76 static uptr SizeRequiredForFrames(uptr stack_size_log) { 77 return (((uptr)1) << stack_size_log) * kNumberOfSizeClasses; 78 } 79 80 // Number of bytes requires for the whole object. 81 static uptr RequiredSize(uptr stack_size_log) { 82 return kFlagsOffset + SizeRequiredForFlags(stack_size_log) + 83 SizeRequiredForFrames(stack_size_log); 84 } 85 86 // Offset of the given flag from the first flag. 87 // The flags for class 0 begin at offset 000000000 88 // The flags for class 1 begin at offset 100000000 89 // ....................2................ 110000000 90 // ....................3................ 111000000 91 // and so on. 92 static uptr FlagsOffset(uptr stack_size_log, uptr class_id) { 93 uptr t = kNumberOfSizeClasses - 1 - class_id; 94 const uptr all_ones = (((uptr)1) << (kNumberOfSizeClasses - 1)) - 1; 95 return ((all_ones >> t) << t) << (stack_size_log - 15); 96 } 97 98 static uptr NumberOfFrames(uptr stack_size_log, uptr class_id) { 99 return ((uptr)1) << (stack_size_log - kMinStackFrameSizeLog - class_id); 100 } 101 102 // Divide n by the numbe of frames in size class. 103 static uptr ModuloNumberOfFrames(uptr stack_size_log, uptr class_id, uptr n) { 104 return n & (NumberOfFrames(stack_size_log, class_id) - 1); 105 } 106 107 // The the pointer to the flags of the given class_id. 108 u8 *GetFlags(uptr stack_size_log, uptr class_id) { 109 return reinterpret_cast<u8 *>(this) + kFlagsOffset + 110 FlagsOffset(stack_size_log, class_id); 111 } 112 113 // Get frame by class_id and pos. 114 u8 *GetFrame(uptr stack_size_log, uptr class_id, uptr pos) { 115 return reinterpret_cast<u8 *>(this) + kFlagsOffset + 116 SizeRequiredForFlags(stack_size_log) + 117 (((uptr)1) << stack_size_log) * class_id + 118 BytesInSizeClass(class_id) * pos; 119 } 120 121 // Allocate the fake frame. 122 FakeFrame *Allocate(uptr stack_size_log, uptr class_id, uptr real_stack); 123 124 // Deallocate the fake frame: read the saved flag address and write 0 there. 125 static void Deallocate(uptr x, uptr class_id) { 126 **SavedFlagPtr(x, class_id) = 0; 127 } 128 129 // Poison the entire FakeStack's shadow with the magic value. 130 void PoisonAll(u8 magic); 131 132 // Return the beginning of the FakeFrame or 0 if the address is not ours. 133 uptr AddrIsInFakeStack(uptr addr, uptr *frame_beg, uptr *frame_end); 134 USED uptr AddrIsInFakeStack(uptr addr) { 135 uptr t1, t2; 136 return AddrIsInFakeStack(addr, &t1, &t2); 137 } 138 139 // Number of bytes in a fake frame of this size class. 140 static uptr BytesInSizeClass(uptr class_id) { 141 return ((uptr)1) << (class_id + kMinStackFrameSizeLog); 142 } 143 144 // The fake frame is guaranteed to have a right redzone. 145 // We use the last word of that redzone to store the address of the flag 146 // that corresponds to the current frame to make faster deallocation. 147 static u8 **SavedFlagPtr(uptr x, uptr class_id) { 148 return reinterpret_cast<u8 **>(x + BytesInSizeClass(class_id) - sizeof(x)); 149 } 150 151 uptr stack_size_log() const { return stack_size_log_; } 152 153 void HandleNoReturn(); 154 void GC(uptr real_stack); 155 156 void ForEachFakeFrame(RangeIteratorCallback callback, void *arg); 157 158 private: 159 FakeStack() { } 160 static const uptr kFlagsOffset = 4096; // This is were the flags begin. 161 // Must match the number of uses of DEFINE_STACK_MALLOC_FREE_WITH_CLASS_ID 162 COMPILER_CHECK(kNumberOfSizeClasses == 11); 163 static const uptr kMaxStackMallocSize = ((uptr)1) << kMaxStackFrameSizeLog; 164 165 uptr hint_position_[kNumberOfSizeClasses]; 166 uptr stack_size_log_; 167 // a bit is set if something was allocated from the corresponding size class. 168 bool needs_gc_; 169 }; 170 171 FakeStack *GetTLSFakeStack(); 172 void SetTLSFakeStack(FakeStack *fs); 173 174 } // namespace __asan 175 176 #endif // ASAN_FAKE_STACK_H 177
