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
30extern "C" {
31
32INTERFACE_ATTRIBUTE void __hwasan_shadow();
33decltype(__hwasan_shadow)* __hwasan_premap_shadow();
34
35} // extern "C"
36
37namespace __hwasan {
38
39// We cannot call anything in libc here (see comment above), so we need to
40// assume the biggest allowed page size.
41// Android max page size is defined as 16k here:
42// https://android.googlesource.com/platform/bionic/+/main/libc/platform/bionic/page.h#41
43static constexpr uptr kMaxGranularity = 16384;
44
45// Conservative upper limit.
46static uptr PremapShadowSize() {
47 return RoundUpTo(GetMaxVirtualAddress() >> kShadowScale, kMaxGranularity);
48}
49
50static uptr PremapShadow() {
51 return MapDynamicShadow(PremapShadowSize(), kShadowScale,
52 kShadowBaseAlignment, kHighMemEnd, kMaxGranularity);
53}
54
55static bool IsPremapShadowAvailable() {
56 const uptr shadow = reinterpret_cast<uptr>(&__hwasan_shadow);
57 const uptr resolver = reinterpret_cast<uptr>(&__hwasan_premap_shadow);
58 // shadow == resolver is how Android KitKat and older handles ifunc.
59 // shadow == 0 just in case.
60 return shadow != 0 && shadow != resolver;
61}
62
63static uptr FindPremappedShadowStart(uptr shadow_size_bytes) {
64 const uptr granularity = kMaxGranularity;
65 const uptr shadow_start = reinterpret_cast<uptr>(&__hwasan_shadow);
66 const uptr premap_shadow_size = PremapShadowSize();
67 const uptr shadow_size = RoundUpTo(shadow_size_bytes, granularity);
68
69 // We may have mapped too much. Release extra memory.
70 UnmapFromTo(shadow_start + shadow_size, shadow_start + premap_shadow_size);
71 return shadow_start;
72}
73
74} // namespace __hwasan
75
76extern "C" {
77
78decltype(__hwasan_shadow)* __hwasan_premap_shadow() {
79 // The resolver might be called multiple times. Map the shadow just once.
80 static __sanitizer::uptr shadow = 0;
81 if (!shadow)
82 shadow = __hwasan::PremapShadow();
83 return reinterpret_cast<decltype(__hwasan_shadow)*>(shadow);
84}
85
86// __hwasan_shadow is a "function" that has the same address as the first byte
87// of the shadow mapping.
88INTERFACE_ATTRIBUTE __attribute__((ifunc("__hwasan_premap_shadow")))
89void __hwasan_shadow();
90
91extern __attribute((weak, visibility("hidden"))) ElfW(Rela) __rela_iplt_start[],
92 __rela_iplt_end[];
93
94} // extern "C"
95
96namespace __hwasan {
97
98void InitShadowGOT() {
99 // Call the ifunc resolver for __hwasan_shadow and fill in its GOT entry. This
100 // needs to be done before other ifunc resolvers (which are handled by libc)
101 // because a resolver might read __hwasan_shadow.
102 typedef ElfW(Addr) (*ifunc_resolver_t)(void);
103 for (ElfW(Rela) *r = __rela_iplt_start; r != __rela_iplt_end; ++r) {
104 ElfW(Addr)* offset = reinterpret_cast<ElfW(Addr)*>(r->r_offset);
105 ElfW(Addr) resolver = r->r_addend;
106 if (resolver == reinterpret_cast<ElfW(Addr)>(&__hwasan_premap_shadow)) {
107 *offset = reinterpret_cast<ifunc_resolver_t>(resolver)();
108 break;
109 }
110 }
111}
112
113uptr FindDynamicShadowStart(uptr shadow_size_bytes) {
114 if (IsPremapShadowAvailable())
115 return FindPremappedShadowStart(shadow_size_bytes);
116 return MapDynamicShadow(shadow_size_bytes, kShadowScale, kShadowBaseAlignment,
117 kHighMemEnd, kMaxGranularity);
118}
119
120} // namespace __hwasan
121
122#elif SANITIZER_FUCHSIA
123
124namespace __hwasan {
125
126void InitShadowGOT() {}
127
128} // namespace __hwasan
129
130#else
131namespace __hwasan {
132
133void InitShadowGOT() {}
134
135uptr FindDynamicShadowStart(uptr shadow_size_bytes) {
136# if defined(HWASAN_ALIASING_MODE)
137 constexpr uptr kAliasSize = 1ULL << kAddressTagShift;
138 constexpr uptr kNumAliases = 1ULL << kTagBits;
139 return MapDynamicShadowAndAliases(shadow_size: shadow_size_bytes, alias_size: kAliasSize, num_aliases: kNumAliases,
140 ring_buffer_size: RingBufferSize());
141# endif
142 return MapDynamicShadow(shadow_size_bytes, shadow_scale: kShadowScale, min_shadow_base_alignment: kShadowBaseAlignment,
143 high_mem_end&: kHighMemEnd, granularity: GetMmapGranularity());
144}
145
146} // namespace __hwasan
147
148#endif // SANITIZER_ANDROID
149