libsanitizer/asan/asan_premap_shadow.cc

   1 //===-- asan_premap_shadow.cc ---------------------------------------------===//
   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 // Reserve shadow memory with an ifunc resolver.
  11 //===----------------------------------------------------------------------===//
  12
  13 #include "asan_mapping.h"
  14
  15 #if ASAN_PREMAP_SHADOW
  16
  17 #include "asan_premap_shadow.h"
  18 #include "sanitizer_common/sanitizer_posix.h"
  19
  20 namespace __asan {
  21
  22 // The code in this file needs to run in an unrelocated binary. It may not
  23 // access any external symbol, including its own non-hidden globals.
  24
  25 // Conservative upper limit.
  26 uptr PremapShadowSize() {
  27   uptr granularity = GetMmapGranularity();
  28   return RoundUpTo(GetMaxVirtualAddress() >> SHADOW_SCALE, granularity);
  29 }
  30
  31 // Returns an address aligned to 8 pages, such that one page on the left and
  32 // PremapShadowSize() bytes on the right of it are mapped r/o.
  33 uptr PremapShadow() {
  34   uptr granularity = GetMmapGranularity();
  35   uptr alignment = granularity * 8;
  36   uptr left_padding = granularity;
  37   uptr shadow_size = PremapShadowSize();
  38   uptr map_size = shadow_size + left_padding + alignment;
  39
  40   uptr map_start = (uptr)MmapNoAccess(map_size);
  41   CHECK_NE(map_start, ~(uptr)0);
  42
  43   uptr shadow_start = RoundUpTo(map_start + left_padding, alignment);
  44   uptr shadow_end = shadow_start + shadow_size;
  45   internal_munmap(reinterpret_cast<void *>(map_start),
  46                   shadow_start - left_padding - map_start);
  47   internal_munmap(reinterpret_cast<void *>(shadow_end),
  48                   map_start + map_size - shadow_end);
  49   return shadow_start;
  50 }
  51
  52 bool PremapShadowFailed() {
  53   uptr shadow = reinterpret_cast<uptr>(&__asan_shadow);
  54   uptr resolver = reinterpret_cast<uptr>(&__asan_premap_shadow);
  55   // shadow == resolver is how Android KitKat and older handles ifunc.
  56   // shadow == 0 just in case.
  57   if (shadow == 0 || shadow == resolver)
  58     return true;
  59   return false;
  60 }
  61 } // namespace __asan
  62
  63 extern "C" {
  64 decltype(__asan_shadow)* __asan_premap_shadow() {
  65   // The resolver may be called multiple times. Map the shadow just once.
  66   static uptr premapped_shadow = 0;
  67   if (!premapped_shadow) premapped_shadow = __asan::PremapShadow();
  68   return reinterpret_cast<decltype(__asan_shadow)*>(premapped_shadow);
  69 }
  70
  71 // __asan_shadow is a "function" that has the same address as the first byte of
  72 // the shadow mapping.
  73 INTERFACE_ATTRIBUTE __attribute__((ifunc("__asan_premap_shadow"))) void
  74 __asan_shadow();
  75 }
  76
  77 #endif // ASAN_PREMAP_SHADOW