1 //===-- hwasan_dynamic_shadow.cpp -------------------------------*- C++ -*-===//
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
7 //===----------------------------------------------------------------------===//
10 /// This file is a part of HWAddressSanitizer. It reserves dynamic shadow memory
11 /// region and handles ifunc resolver case, when necessary.
13 //===----------------------------------------------------------------------===//
16 #include "hwasan_dynamic_shadow.h"
17 #include "hwasan_mapping.h"
18 #include "sanitizer_common/sanitizer_common.h"
19 #include "sanitizer_common/sanitizer_posix.h"
24 // The code in this file needs to run in an unrelocated binary. It should not
25 // access any external symbol, including its own non-hidden globals.
29 static void UnmapFromTo(uptr from, uptr to) {
33 uptr res = internal_munmap(reinterpret_cast<void *>(from), to - from);
34 if (UNLIKELY(internal_iserror(res))) {
35 Report("ERROR: %s failed to unmap 0x%zx (%zd) bytes at address %p\n",
36 SanitizerToolName, to - from, to - from, from);
37 CHECK("unable to unmap" && 0);
41 // Returns an address aligned to kShadowBaseAlignment, such that
42 // 2**kShadowBaseAlingment on the left and shadow_size_bytes bytes on the right
43 // of it are mapped no access.
44 static uptr MapDynamicShadow(uptr shadow_size_bytes) {
45 const uptr granularity = GetMmapGranularity();
46 const uptr min_alignment = granularity << kShadowScale;
47 const uptr alignment = 1ULL << kShadowBaseAlignment;
48 CHECK_GE(alignment, min_alignment);
50 const uptr left_padding = 1ULL << kShadowBaseAlignment;
51 const uptr shadow_size =
52 RoundUpTo(shadow_size_bytes, granularity);
53 const uptr map_size = shadow_size + left_padding + alignment;
55 const uptr map_start = (uptr)MmapNoAccess(map_size);
56 CHECK_NE(map_start, ~(uptr)0);
58 const uptr shadow_start = RoundUpTo(map_start + left_padding, alignment);
60 UnmapFromTo(map_start, shadow_start - left_padding);
61 UnmapFromTo(shadow_start + shadow_size, map_start + map_size);
66 } // namespace __hwasan
71 INTERFACE_ATTRIBUTE void __hwasan_shadow();
72 decltype(__hwasan_shadow)* __hwasan_premap_shadow();
78 // Conservative upper limit.
79 static uptr PremapShadowSize() {
80 return RoundUpTo(GetMaxVirtualAddress() >> kShadowScale,
81 GetMmapGranularity());
84 static uptr PremapShadow() {
85 return MapDynamicShadow(PremapShadowSize());
88 static bool IsPremapShadowAvailable() {
89 const uptr shadow = reinterpret_cast<uptr>(&__hwasan_shadow);
90 const uptr resolver = reinterpret_cast<uptr>(&__hwasan_premap_shadow);
91 // shadow == resolver is how Android KitKat and older handles ifunc.
92 // shadow == 0 just in case.
93 return shadow != 0 && shadow != resolver;
96 static uptr FindPremappedShadowStart(uptr shadow_size_bytes) {
97 const uptr granularity = GetMmapGranularity();
98 const uptr shadow_start = reinterpret_cast<uptr>(&__hwasan_shadow);
99 const uptr premap_shadow_size = PremapShadowSize();
100 const uptr shadow_size = RoundUpTo(shadow_size_bytes, granularity);
102 // We may have mapped too much. Release extra memory.
103 UnmapFromTo(shadow_start + shadow_size, shadow_start + premap_shadow_size);
107 } // namespace __hwasan
111 decltype(__hwasan_shadow)* __hwasan_premap_shadow() {
112 // The resolver might be called multiple times. Map the shadow just once.
113 static __sanitizer::uptr shadow = 0;
115 shadow = __hwasan::PremapShadow();
116 return reinterpret_cast<decltype(__hwasan_shadow)*>(shadow);
119 // __hwasan_shadow is a "function" that has the same address as the first byte
120 // of the shadow mapping.
121 INTERFACE_ATTRIBUTE __attribute__((ifunc("__hwasan_premap_shadow")))
122 void __hwasan_shadow();
124 extern __attribute((weak, visibility("hidden"))) ElfW(Rela) __rela_iplt_start[],
131 void InitShadowGOT() {
132 // Call the ifunc resolver for __hwasan_shadow and fill in its GOT entry. This
133 // needs to be done before other ifunc resolvers (which are handled by libc)
134 // because a resolver might read __hwasan_shadow.
135 typedef ElfW(Addr) (*ifunc_resolver_t)(void);
136 for (ElfW(Rela) *r = __rela_iplt_start; r != __rela_iplt_end; ++r) {
137 ElfW(Addr)* offset = reinterpret_cast<ElfW(Addr)*>(r->r_offset);
138 ElfW(Addr) resolver = r->r_addend;
139 if (resolver == reinterpret_cast<ElfW(Addr)>(&__hwasan_premap_shadow)) {
140 *offset = reinterpret_cast<ifunc_resolver_t>(resolver)();
146 uptr FindDynamicShadowStart(uptr shadow_size_bytes) {
147 if (IsPremapShadowAvailable())
148 return FindPremappedShadowStart(shadow_size_bytes);
149 return MapDynamicShadow(shadow_size_bytes);
152 } // namespace __hwasan
156 void InitShadowGOT() {}
158 uptr FindDynamicShadowStart(uptr shadow_size_bytes) {
159 return MapDynamicShadow(shadow_size_bytes);
162 } // namespace __hwasan
164 #endif // SANITIZER_ANDROID