libsanitizer/asan/asan_fake_stack.h

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