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.h"
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"
20 
21 #include <elf.h>
22 #include <link.h>
23 
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.
26 
27 namespace __hwasan {
28 
29 static void UnmapFromTo(uptr from, uptr to) {
30   if (to == from)
31     return;
32   CHECK(to >= from);
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);
38   }
39 }
40 
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);
49 
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;
54 
55   const uptr map_start = (uptr)MmapNoAccess(map_size);
56   CHECK_NE(map_start, ~(uptr)0);
57 
58   const uptr shadow_start = RoundUpTo(map_start + left_padding, alignment);
59 
60   UnmapFromTo(map_start, shadow_start - left_padding);
61   UnmapFromTo(shadow_start + shadow_size, map_start + map_size);
62 
63   return shadow_start;
64 }
65 
66 }  // namespace __hwasan
67 
68 #if SANITIZER_ANDROID
69 extern "C" {
70 
71 INTERFACE_ATTRIBUTE void __hwasan_shadow();
72 decltype(__hwasan_shadow)* __hwasan_premap_shadow();
73 
74 }  // extern "C"
75 
76 namespace __hwasan {
77 
78 // Conservative upper limit.
79 static uptr PremapShadowSize() {
80   return RoundUpTo(GetMaxVirtualAddress() >> kShadowScale,
81                    GetMmapGranularity());
82 }
83 
84 static uptr PremapShadow() {
85   return MapDynamicShadow(PremapShadowSize());
86 }
87 
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;
94 }
95 
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);
101 
102   // We may have mapped too much. Release extra memory.
103   UnmapFromTo(shadow_start + shadow_size, shadow_start + premap_shadow_size);
104   return shadow_start;
105 }
106 
107 }  // namespace __hwasan
108 
109 extern "C" {
110 
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;
114   if (!shadow)
115     shadow = __hwasan::PremapShadow();
116   return reinterpret_cast<decltype(__hwasan_shadow)*>(shadow);
117 }
118 
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();
123 
124 extern __attribute((weak, visibility("hidden"))) ElfW(Rela) __rela_iplt_start[],
125     __rela_iplt_end[];
126 
127 }  // extern "C"
128 
129 namespace __hwasan {
130 
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)();
141       break;
142     }
143   }
144 }
145 
146 uptr FindDynamicShadowStart(uptr shadow_size_bytes) {
147   if (IsPremapShadowAvailable())
148     return FindPremappedShadowStart(shadow_size_bytes);
149   return MapDynamicShadow(shadow_size_bytes);
150 }
151 
152 }  // namespace __hwasan
153 #else
154 namespace __hwasan {
155 
156 void InitShadowGOT() {}
157 
158 uptr FindDynamicShadowStart(uptr shadow_size_bytes) {
159   return MapDynamicShadow(shadow_size_bytes);
160 }
161 
162 }  // namespace __hwasan
163 
164 #endif  // SANITIZER_ANDROID
165