libsanitizer/hwasan/hwasan_dynamic_shadow.cpp

   1 //===-- hwasan_dynamic_shadow.cpp -------------------------------*- C++ -*-===//
   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 /// \file
  10 /// This file is a part of HWAddressSanitizer. It reserves dynamic shadow memory
  11 /// region and handles ifunc resolver case, when necessary.
  12 ///
  13 //===----------------------------------------------------------------------===//
  14
  15 #include "hwasan_dynamic_shadow.h"
  16
  17 #include <elf.h>
  18 #include <link.h>
  19
  20 #include "hwasan.h"
  21 #include "hwasan_mapping.h"
  22 #include "hwasan_thread_list.h"
  23 #include "sanitizer_common/sanitizer_common.h"
  24 #include "sanitizer_common/sanitizer_posix.h"
  25
  26 // The code in this file needs to run in an unrelocated binary. It should not
  27 // access any external symbol, including its own non-hidden globals.
  28
  29 #if SANITIZER_ANDROID
  30 extern "C" {
  31
  32 INTERFACE_ATTRIBUTE void __hwasan_shadow();
  33 decltype(__hwasan_shadow)* __hwasan_premap_shadow();
  34
  35 }  // extern "C"
  36
  37 namespace __hwasan {
  38
  39 // Conservative upper limit.
  40 static uptr PremapShadowSize() {
  41   return RoundUpTo(GetMaxVirtualAddress() >> kShadowScale,
  42                    GetMmapGranularity());
  43 }
  44
  45 static uptr PremapShadow() {
  46   return MapDynamicShadow(PremapShadowSize(), kShadowScale,
  47                           kShadowBaseAlignment, kHighMemEnd);
  48 }
  49
  50 static bool IsPremapShadowAvailable() {
  51   const uptr shadow = reinterpret_cast<uptr>(&__hwasan_shadow);
  52   const uptr resolver = reinterpret_cast<uptr>(&__hwasan_premap_shadow);
  53   // shadow == resolver is how Android KitKat and older handles ifunc.
  54   // shadow == 0 just in case.
  55   return shadow != 0 && shadow != resolver;
  56 }
  57
  58 static uptr FindPremappedShadowStart(uptr shadow_size_bytes) {
  59   const uptr granularity = GetMmapGranularity();
  60   const uptr shadow_start = reinterpret_cast<uptr>(&__hwasan_shadow);
  61   const uptr premap_shadow_size = PremapShadowSize();
  62   const uptr shadow_size = RoundUpTo(shadow_size_bytes, granularity);
  63
  64   // We may have mapped too much. Release extra memory.
  65   UnmapFromTo(shadow_start + shadow_size, shadow_start + premap_shadow_size);
  66   return shadow_start;
  67 }
  68
  69 }  // namespace __hwasan
  70
  71 extern "C" {
  72
  73 decltype(__hwasan_shadow)* __hwasan_premap_shadow() {
  74   // The resolver might be called multiple times. Map the shadow just once.
  75   static __sanitizer::uptr shadow = 0;
  76   if (!shadow)
  77     shadow = __hwasan::PremapShadow();
  78   return reinterpret_cast<decltype(__hwasan_shadow)*>(shadow);
  79 }
  80
  81 // __hwasan_shadow is a "function" that has the same address as the first byte
  82 // of the shadow mapping.
  83 INTERFACE_ATTRIBUTE __attribute__((ifunc("__hwasan_premap_shadow")))
  84 void __hwasan_shadow();
  85
  86 extern __attribute((weak, visibility("hidden"))) ElfW(Rela) __rela_iplt_start[],
  87     __rela_iplt_end[];
  88
  89 }  // extern "C"
  90
  91 namespace __hwasan {
  92
  93 void InitShadowGOT() {
  94   // Call the ifunc resolver for __hwasan_shadow and fill in its GOT entry. This
  95   // needs to be done before other ifunc resolvers (which are handled by libc)
  96   // because a resolver might read __hwasan_shadow.
  97   typedef ElfW(Addr) (*ifunc_resolver_t)(void);
  98   for (ElfW(Rela) *r = __rela_iplt_start; r != __rela_iplt_end; ++r) {
  99     ElfW(Addr)* offset = reinterpret_cast<ElfW(Addr)*>(r->r_offset);
 100     ElfW(Addr) resolver = r->r_addend;
 101     if (resolver == reinterpret_cast<ElfW(Addr)>(&__hwasan_premap_shadow)) {
 102       *offset = reinterpret_cast<ifunc_resolver_t>(resolver)();
 103       break;
 104     }
 105   }
 106 }
 107
 108 uptr FindDynamicShadowStart(uptr shadow_size_bytes) {
 109   if (IsPremapShadowAvailable())
 110     return FindPremappedShadowStart(shadow_size_bytes);
 111   return MapDynamicShadow(shadow_size_bytes, kShadowScale, kShadowBaseAlignment,
 112                           kHighMemEnd);
 113 }
 114
 115 }  // namespace __hwasan
 116
 117 #elif SANITIZER_FUCHSIA
 118
 119 namespace __hwasan {
 120
 121 void InitShadowGOT() {}
 122
 123 }  // namespace __hwasan
 124
 125 #else
 126 namespace __hwasan {
 127
 128 void InitShadowGOT() {}
 129
 130 uptr FindDynamicShadowStart(uptr shadow_size_bytes) {
 131 #  if defined(HWASAN_ALIASING_MODE)
 132   constexpr uptr kAliasSize = 1ULL << kAddressTagShift;
 133   constexpr uptr kNumAliases = 1ULL << kTagBits;
 134   return MapDynamicShadowAndAliases(shadow_size_bytes, kAliasSize, kNumAliases,
 135                                     RingBufferSize());
 136 #  endif
 137   return MapDynamicShadow(shadow_size_bytes, kShadowScale, kShadowBaseAlignment,
 138                           kHighMemEnd);
 139 }
 140
 141 }  // namespace __hwasan
 142
 143 #endif  // SANITIZER_ANDROID