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696d846a MO |
1 | //===-- ubsan_type_hash_itanium.cc ----------------------------------------===// |
2 | // | |
3 | // This file is distributed under the University of Illinois Open Source | |
4 | // License. See LICENSE.TXT for details. | |
5 | // | |
6 | //===----------------------------------------------------------------------===// | |
7 | // | |
8 | // Implementation of type hashing/lookup for Itanium C++ ABI. | |
9 | // | |
10 | //===----------------------------------------------------------------------===// | |
11 | ||
12 | #include "sanitizer_common/sanitizer_platform.h" | |
13 | #include "ubsan_platform.h" | |
14 | #if CAN_SANITIZE_UB && !SANITIZER_WINDOWS | |
15 | #include "ubsan_type_hash.h" | |
16 | ||
17 | #include "sanitizer_common/sanitizer_common.h" | |
18 | ||
19 | // The following are intended to be binary compatible with the definitions | |
20 | // given in the Itanium ABI. We make no attempt to be ODR-compatible with | |
21 | // those definitions, since existing ABI implementations aren't. | |
22 | ||
23 | namespace std { | |
24 | class type_info { | |
25 | public: | |
26 | virtual ~type_info(); | |
27 | ||
28 | const char *__type_name; | |
29 | }; | |
30 | } | |
31 | ||
32 | namespace __cxxabiv1 { | |
33 | ||
34 | /// Type info for classes with no bases, and base class for type info for | |
35 | /// classes with bases. | |
36 | class __class_type_info : public std::type_info { | |
37 | ~__class_type_info() override; | |
38 | }; | |
39 | ||
40 | /// Type info for classes with simple single public inheritance. | |
41 | class __si_class_type_info : public __class_type_info { | |
42 | public: | |
43 | ~__si_class_type_info() override; | |
44 | ||
45 | const __class_type_info *__base_type; | |
46 | }; | |
47 | ||
48 | class __base_class_type_info { | |
49 | public: | |
50 | const __class_type_info *__base_type; | |
51 | long __offset_flags; | |
52 | ||
53 | enum __offset_flags_masks { | |
54 | __virtual_mask = 0x1, | |
55 | __public_mask = 0x2, | |
56 | __offset_shift = 8 | |
57 | }; | |
58 | }; | |
59 | ||
60 | /// Type info for classes with multiple, virtual, or non-public inheritance. | |
61 | class __vmi_class_type_info : public __class_type_info { | |
62 | public: | |
63 | ~__vmi_class_type_info() override; | |
64 | ||
65 | unsigned int flags; | |
66 | unsigned int base_count; | |
67 | __base_class_type_info base_info[1]; | |
68 | }; | |
69 | ||
70 | } | |
71 | ||
72 | namespace abi = __cxxabiv1; | |
73 | ||
10189819 MO |
74 | using namespace __sanitizer; |
75 | ||
696d846a MO |
76 | // We implement a simple two-level cache for type-checking results. For each |
77 | // (vptr,type) pair, a hash is computed. This hash is assumed to be globally | |
78 | // unique; if it collides, we will get false negatives, but: | |
79 | // * such a collision would have to occur on the *first* bad access, | |
80 | // * the probability of such a collision is low (and for a 64-bit target, is | |
81 | // negligible), and | |
82 | // * the vptr, and thus the hash, can be affected by ASLR, so multiple runs | |
83 | // give better coverage. | |
84 | // | |
85 | // The first caching layer is a small hash table with no chaining; buckets are | |
86 | // reused as needed. The second caching layer is a large hash table with open | |
87 | // chaining. We can freely evict from either layer since this is just a cache. | |
88 | // | |
89 | // FIXME: Make these hash table accesses thread-safe. The races here are benign: | |
90 | // assuming the unsequenced loads and stores don't misbehave too badly, | |
91 | // the worst case is false negatives or poor cache behavior, not false | |
92 | // positives or crashes. | |
93 | ||
94 | /// Find a bucket to store the given hash value in. | |
95 | static __ubsan::HashValue *getTypeCacheHashTableBucket(__ubsan::HashValue V) { | |
96 | static const unsigned HashTableSize = 65537; | |
97 | static __ubsan::HashValue __ubsan_vptr_hash_set[HashTableSize]; | |
98 | ||
99 | unsigned First = (V & 65535) ^ 1; | |
100 | unsigned Probe = First; | |
101 | for (int Tries = 5; Tries; --Tries) { | |
102 | if (!__ubsan_vptr_hash_set[Probe] || __ubsan_vptr_hash_set[Probe] == V) | |
103 | return &__ubsan_vptr_hash_set[Probe]; | |
104 | Probe += ((V >> 16) & 65535) + 1; | |
105 | if (Probe >= HashTableSize) | |
106 | Probe -= HashTableSize; | |
107 | } | |
108 | // FIXME: Pick a random entry from the probe sequence to evict rather than | |
109 | // just taking the first. | |
110 | return &__ubsan_vptr_hash_set[First]; | |
111 | } | |
112 | ||
113 | /// \brief Determine whether \p Derived has a \p Base base class subobject at | |
114 | /// offset \p Offset. | |
115 | static bool isDerivedFromAtOffset(const abi::__class_type_info *Derived, | |
116 | const abi::__class_type_info *Base, | |
117 | sptr Offset) { | |
10189819 MO |
118 | if (Derived->__type_name == Base->__type_name || |
119 | (SANITIZER_NON_UNIQUE_TYPEINFO && | |
120 | !internal_strcmp(Derived->__type_name, Base->__type_name))) | |
696d846a MO |
121 | return Offset == 0; |
122 | ||
123 | if (const abi::__si_class_type_info *SI = | |
124 | dynamic_cast<const abi::__si_class_type_info*>(Derived)) | |
125 | return isDerivedFromAtOffset(SI->__base_type, Base, Offset); | |
126 | ||
127 | const abi::__vmi_class_type_info *VTI = | |
128 | dynamic_cast<const abi::__vmi_class_type_info*>(Derived); | |
129 | if (!VTI) | |
130 | // No base class subobjects. | |
131 | return false; | |
132 | ||
133 | // Look for a base class which is derived from \p Base at the right offset. | |
134 | for (unsigned int base = 0; base != VTI->base_count; ++base) { | |
135 | // FIXME: Curtail the recursion if this base can't possibly contain the | |
136 | // given offset. | |
137 | sptr OffsetHere = VTI->base_info[base].__offset_flags >> | |
138 | abi::__base_class_type_info::__offset_shift; | |
139 | if (VTI->base_info[base].__offset_flags & | |
140 | abi::__base_class_type_info::__virtual_mask) | |
141 | // For now, just punt on virtual bases and say 'yes'. | |
142 | // FIXME: OffsetHere is the offset in the vtable of the virtual base | |
143 | // offset. Read the vbase offset out of the vtable and use it. | |
144 | return true; | |
145 | if (isDerivedFromAtOffset(VTI->base_info[base].__base_type, | |
146 | Base, Offset - OffsetHere)) | |
147 | return true; | |
148 | } | |
149 | ||
150 | return false; | |
151 | } | |
152 | ||
153 | /// \brief Find the derived-most dynamic base class of \p Derived at offset | |
154 | /// \p Offset. | |
155 | static const abi::__class_type_info *findBaseAtOffset( | |
156 | const abi::__class_type_info *Derived, sptr Offset) { | |
157 | if (!Offset) | |
158 | return Derived; | |
159 | ||
160 | if (const abi::__si_class_type_info *SI = | |
161 | dynamic_cast<const abi::__si_class_type_info*>(Derived)) | |
162 | return findBaseAtOffset(SI->__base_type, Offset); | |
163 | ||
164 | const abi::__vmi_class_type_info *VTI = | |
165 | dynamic_cast<const abi::__vmi_class_type_info*>(Derived); | |
166 | if (!VTI) | |
167 | // No base class subobjects. | |
10189819 | 168 | return nullptr; |
696d846a MO |
169 | |
170 | for (unsigned int base = 0; base != VTI->base_count; ++base) { | |
171 | sptr OffsetHere = VTI->base_info[base].__offset_flags >> | |
172 | abi::__base_class_type_info::__offset_shift; | |
173 | if (VTI->base_info[base].__offset_flags & | |
174 | abi::__base_class_type_info::__virtual_mask) | |
175 | // FIXME: Can't handle virtual bases yet. | |
176 | continue; | |
177 | if (const abi::__class_type_info *Base = | |
178 | findBaseAtOffset(VTI->base_info[base].__base_type, | |
179 | Offset - OffsetHere)) | |
180 | return Base; | |
181 | } | |
182 | ||
10189819 | 183 | return nullptr; |
696d846a MO |
184 | } |
185 | ||
186 | namespace { | |
187 | ||
188 | struct VtablePrefix { | |
189 | /// The offset from the vptr to the start of the most-derived object. | |
190 | /// This will only be greater than zero in some virtual base class vtables | |
191 | /// used during object con-/destruction, and will usually be exactly zero. | |
192 | sptr Offset; | |
193 | /// The type_info object describing the most-derived class type. | |
194 | std::type_info *TypeInfo; | |
195 | }; | |
196 | VtablePrefix *getVtablePrefix(void *Vtable) { | |
197 | VtablePrefix *Vptr = reinterpret_cast<VtablePrefix*>(Vtable); | |
696d846a | 198 | VtablePrefix *Prefix = Vptr - 1; |
5d3805fc JJ |
199 | if (!IsAccessibleMemoryRange((uptr)Prefix, sizeof(VtablePrefix))) |
200 | return nullptr; | |
696d846a MO |
201 | if (!Prefix->TypeInfo) |
202 | // This can't possibly be a valid vtable. | |
10189819 | 203 | return nullptr; |
696d846a MO |
204 | return Prefix; |
205 | } | |
206 | ||
207 | } | |
208 | ||
209 | bool __ubsan::checkDynamicType(void *Object, void *Type, HashValue Hash) { | |
210 | // A crash anywhere within this function probably means the vptr is corrupted. | |
211 | // FIXME: Perform these checks more cautiously. | |
212 | ||
213 | // Check whether this is something we've evicted from the cache. | |
214 | HashValue *Bucket = getTypeCacheHashTableBucket(Hash); | |
215 | if (*Bucket == Hash) { | |
216 | __ubsan_vptr_type_cache[Hash % VptrTypeCacheSize] = Hash; | |
217 | return true; | |
218 | } | |
219 | ||
220 | void *VtablePtr = *reinterpret_cast<void **>(Object); | |
221 | VtablePrefix *Vtable = getVtablePrefix(VtablePtr); | |
222 | if (!Vtable) | |
223 | return false; | |
10189819 MO |
224 | if (Vtable->Offset < -VptrMaxOffsetToTop || Vtable->Offset > VptrMaxOffsetToTop) { |
225 | // Too large or too small offset are signs of Vtable corruption. | |
226 | return false; | |
227 | } | |
696d846a MO |
228 | |
229 | // Check that this is actually a type_info object for a class type. | |
230 | abi::__class_type_info *Derived = | |
231 | dynamic_cast<abi::__class_type_info*>(Vtable->TypeInfo); | |
232 | if (!Derived) | |
233 | return false; | |
234 | ||
235 | abi::__class_type_info *Base = (abi::__class_type_info*)Type; | |
236 | if (!isDerivedFromAtOffset(Derived, Base, -Vtable->Offset)) | |
237 | return false; | |
238 | ||
239 | // Success. Cache this result. | |
240 | __ubsan_vptr_type_cache[Hash % VptrTypeCacheSize] = Hash; | |
241 | *Bucket = Hash; | |
242 | return true; | |
243 | } | |
244 | ||
245 | __ubsan::DynamicTypeInfo | |
246 | __ubsan::getDynamicTypeInfoFromVtable(void *VtablePtr) { | |
247 | VtablePrefix *Vtable = getVtablePrefix(VtablePtr); | |
248 | if (!Vtable) | |
10189819 MO |
249 | return DynamicTypeInfo(nullptr, 0, nullptr); |
250 | if (Vtable->Offset < -VptrMaxOffsetToTop || Vtable->Offset > VptrMaxOffsetToTop) | |
251 | return DynamicTypeInfo(nullptr, Vtable->Offset, nullptr); | |
696d846a MO |
252 | const abi::__class_type_info *ObjectType = findBaseAtOffset( |
253 | static_cast<const abi::__class_type_info*>(Vtable->TypeInfo), | |
254 | -Vtable->Offset); | |
255 | return DynamicTypeInfo(Vtable->TypeInfo->__type_name, -Vtable->Offset, | |
256 | ObjectType ? ObjectType->__type_name : "<unknown>"); | |
257 | } | |
258 | ||
259 | #endif // CAN_SANITIZE_UB && !SANITIZER_WINDOWS |