lib/asan/asan_fake_stack.h

   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 1UL << (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 (1ULL << 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 = (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 1UL << (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            (1 << stack_size_log) * class_id + BytesInSizeClass(class_id) * pos;
 118   }
 119
 120   // Allocate the fake frame.
 121   FakeFrame *Allocate(uptr stack_size_log, uptr class_id, uptr real_stack);
 122
 123   // Deallocate the fake frame: read the saved flag address and write 0 there.
 124   static void Deallocate(uptr x, uptr class_id) {
 125     **SavedFlagPtr(x, class_id) = 0;
 126   }
 127
 128   // Poison the entire FakeStack's shadow with the magic value.
 129   void PoisonAll(u8 magic);
 130
 131   // Return the beginning of the FakeFrame or 0 if the address is not ours.
 132   uptr AddrIsInFakeStack(uptr addr, uptr *frame_beg, uptr *frame_end);
 133   USED uptr AddrIsInFakeStack(uptr addr) {
 134     uptr t1, t2;
 135     return AddrIsInFakeStack(addr, &t1, &t2);
 136   }
 137
 138   // Number of bytes in a fake frame of this size class.
 139   static uptr BytesInSizeClass(uptr class_id) {
 140     return 1UL << (class_id + kMinStackFrameSizeLog);
 141   }
 142
 143   // The fake frame is guaranteed to have a right redzone.
 144   // We use the last word of that redzone to store the address of the flag
 145   // that corresponds to the current frame to make faster deallocation.
 146   static u8 **SavedFlagPtr(uptr x, uptr class_id) {
 147     return reinterpret_cast<u8 **>(x + BytesInSizeClass(class_id) - sizeof(x));
 148   }
 149
 150   uptr stack_size_log() const { return stack_size_log_; }
 151
 152   void HandleNoReturn();
 153   void GC(uptr real_stack);
 154
 155   void ForEachFakeFrame(RangeIteratorCallback callback, void *arg);
 156
 157  private:
 158   FakeStack() { }
 159   static const uptr kFlagsOffset = 4096;  // This is were the flags begin.
 160   // Must match the number of uses of DEFINE_STACK_MALLOC_FREE_WITH_CLASS_ID
 161   COMPILER_CHECK(kNumberOfSizeClasses == 11);
 162   static const uptr kMaxStackMallocSize = 1 << kMaxStackFrameSizeLog;
 163
 164   uptr hint_position_[kNumberOfSizeClasses];
 165   uptr stack_size_log_;
 166   // a bit is set if something was allocated from the corresponding size class.
 167   bool needs_gc_;
 168 };
 169
 170 FakeStack *GetTLSFakeStack();
 171 void SetTLSFakeStack(FakeStack *fs);
 172
 173 }  // namespace __asan
 174
 175 #endif  // ASAN_FAKE_STACK_H