xref: /freebsd/contrib/llvm-project/compiler-rt/lib/hwasan/hwasan_dynamic_shadow.cpp (revision 6ba2210ee039f2f12878c217bcf058e9c8b26b29)
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 #if SANITIZER_ANDROID
28 extern "C" {
29 
30 INTERFACE_ATTRIBUTE void __hwasan_shadow();
31 decltype(__hwasan_shadow)* __hwasan_premap_shadow();
32 
33 }  // extern "C"
34 
35 namespace __hwasan {
36 
37 // Conservative upper limit.
38 static uptr PremapShadowSize() {
39   return RoundUpTo(GetMaxVirtualAddress() >> kShadowScale,
40                    GetMmapGranularity());
41 }
42 
43 static uptr PremapShadow() {
44   return MapDynamicShadow(PremapShadowSize(), kShadowScale,
45                           kShadowBaseAlignment, kHighMemEnd);
46 }
47 
48 static bool IsPremapShadowAvailable() {
49   const uptr shadow = reinterpret_cast<uptr>(&__hwasan_shadow);
50   const uptr resolver = reinterpret_cast<uptr>(&__hwasan_premap_shadow);
51   // shadow == resolver is how Android KitKat and older handles ifunc.
52   // shadow == 0 just in case.
53   return shadow != 0 && shadow != resolver;
54 }
55 
56 static uptr FindPremappedShadowStart(uptr shadow_size_bytes) {
57   const uptr granularity = GetMmapGranularity();
58   const uptr shadow_start = reinterpret_cast<uptr>(&__hwasan_shadow);
59   const uptr premap_shadow_size = PremapShadowSize();
60   const uptr shadow_size = RoundUpTo(shadow_size_bytes, granularity);
61 
62   // We may have mapped too much. Release extra memory.
63   UnmapFromTo(shadow_start + shadow_size, shadow_start + premap_shadow_size);
64   return shadow_start;
65 }
66 
67 }  // namespace __hwasan
68 
69 extern "C" {
70 
71 decltype(__hwasan_shadow)* __hwasan_premap_shadow() {
72   // The resolver might be called multiple times. Map the shadow just once.
73   static __sanitizer::uptr shadow = 0;
74   if (!shadow)
75     shadow = __hwasan::PremapShadow();
76   return reinterpret_cast<decltype(__hwasan_shadow)*>(shadow);
77 }
78 
79 // __hwasan_shadow is a "function" that has the same address as the first byte
80 // of the shadow mapping.
81 INTERFACE_ATTRIBUTE __attribute__((ifunc("__hwasan_premap_shadow")))
82 void __hwasan_shadow();
83 
84 extern __attribute((weak, visibility("hidden"))) ElfW(Rela) __rela_iplt_start[],
85     __rela_iplt_end[];
86 
87 }  // extern "C"
88 
89 namespace __hwasan {
90 
91 void InitShadowGOT() {
92   // Call the ifunc resolver for __hwasan_shadow and fill in its GOT entry. This
93   // needs to be done before other ifunc resolvers (which are handled by libc)
94   // because a resolver might read __hwasan_shadow.
95   typedef ElfW(Addr) (*ifunc_resolver_t)(void);
96   for (ElfW(Rela) *r = __rela_iplt_start; r != __rela_iplt_end; ++r) {
97     ElfW(Addr)* offset = reinterpret_cast<ElfW(Addr)*>(r->r_offset);
98     ElfW(Addr) resolver = r->r_addend;
99     if (resolver == reinterpret_cast<ElfW(Addr)>(&__hwasan_premap_shadow)) {
100       *offset = reinterpret_cast<ifunc_resolver_t>(resolver)();
101       break;
102     }
103   }
104 }
105 
106 uptr FindDynamicShadowStart(uptr shadow_size_bytes) {
107   if (IsPremapShadowAvailable())
108     return FindPremappedShadowStart(shadow_size_bytes);
109   return MapDynamicShadow(shadow_size_bytes, kShadowScale, kShadowBaseAlignment,
110                           kHighMemEnd);
111 }
112 
113 }  // namespace __hwasan
114 #else
115 namespace __hwasan {
116 
117 void InitShadowGOT() {}
118 
119 uptr FindDynamicShadowStart(uptr shadow_size_bytes) {
120   return MapDynamicShadow(shadow_size_bytes, kShadowScale, kShadowBaseAlignment,
121                           kHighMemEnd);
122 }
123 
124 }  // namespace __hwasan
125 
126 #endif  // SANITIZER_ANDROID
127