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 144