1 //===-- ubsan_type_hash_itanium.cc ----------------------------------------===//
3 // The LLVM Compiler Infrastructure
5 // This file is distributed under the University of Illinois Open Source
6 // License. See LICENSE.TXT for details.
8 //===----------------------------------------------------------------------===//
10 // Implementation of type hashing/lookup for Itanium C++ ABI.
12 //===----------------------------------------------------------------------===//
14 #include "sanitizer_common/sanitizer_platform.h"
15 #include "ubsan_platform.h"
16 #if CAN_SANITIZE_UB && !SANITIZER_WINDOWS
17 #include "ubsan_type_hash.h"
19 #include "sanitizer_common/sanitizer_common.h"
21 // The following are intended to be binary compatible with the definitions
22 // given in the Itanium ABI. We make no attempt to be ODR-compatible with
23 // those definitions, since existing ABI implementations aren't.
30 const char *__type_name;
34 namespace __cxxabiv1 {
36 /// Type info for classes with no bases, and base class for type info for
37 /// classes with bases.
38 class __class_type_info : public std::type_info {
39 ~__class_type_info() override;
42 /// Type info for classes with simple single public inheritance.
43 class __si_class_type_info : public __class_type_info {
45 ~__si_class_type_info() override;
47 const __class_type_info *__base_type;
50 class __base_class_type_info {
52 const __class_type_info *__base_type;
55 enum __offset_flags_masks {
62 /// Type info for classes with multiple, virtual, or non-public inheritance.
63 class __vmi_class_type_info : public __class_type_info {
65 ~__vmi_class_type_info() override;
68 unsigned int base_count;
69 __base_class_type_info base_info[1];
74 namespace abi = __cxxabiv1;
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
82 // * the vptr, and thus the hash, can be affected by ASLR, so multiple runs
83 // give better coverage.
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.
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.
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];
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;
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];
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,
118 if (Derived->__type_name == Base->__type_name)
121 if (const abi::__si_class_type_info *SI =
122 dynamic_cast<const abi::__si_class_type_info*>(Derived))
123 return isDerivedFromAtOffset(SI->__base_type, Base, Offset);
125 const abi::__vmi_class_type_info *VTI =
126 dynamic_cast<const abi::__vmi_class_type_info*>(Derived);
128 // No base class subobjects.
131 // Look for a base class which is derived from \p Base at the right offset.
132 for (unsigned int base = 0; base != VTI->base_count; ++base) {
133 // FIXME: Curtail the recursion if this base can't possibly contain the
135 sptr OffsetHere = VTI->base_info[base].__offset_flags >>
136 abi::__base_class_type_info::__offset_shift;
137 if (VTI->base_info[base].__offset_flags &
138 abi::__base_class_type_info::__virtual_mask)
139 // For now, just punt on virtual bases and say 'yes'.
140 // FIXME: OffsetHere is the offset in the vtable of the virtual base
141 // offset. Read the vbase offset out of the vtable and use it.
143 if (isDerivedFromAtOffset(VTI->base_info[base].__base_type,
144 Base, Offset - OffsetHere))
151 /// \brief Find the derived-most dynamic base class of \p Derived at offset
153 static const abi::__class_type_info *findBaseAtOffset(
154 const abi::__class_type_info *Derived, sptr Offset) {
158 if (const abi::__si_class_type_info *SI =
159 dynamic_cast<const abi::__si_class_type_info*>(Derived))
160 return findBaseAtOffset(SI->__base_type, Offset);
162 const abi::__vmi_class_type_info *VTI =
163 dynamic_cast<const abi::__vmi_class_type_info*>(Derived);
165 // No base class subobjects.
168 for (unsigned int base = 0; base != VTI->base_count; ++base) {
169 sptr OffsetHere = VTI->base_info[base].__offset_flags >>
170 abi::__base_class_type_info::__offset_shift;
171 if (VTI->base_info[base].__offset_flags &
172 abi::__base_class_type_info::__virtual_mask)
173 // FIXME: Can't handle virtual bases yet.
175 if (const abi::__class_type_info *Base =
176 findBaseAtOffset(VTI->base_info[base].__base_type,
177 Offset - OffsetHere))
186 struct VtablePrefix {
187 /// The offset from the vptr to the start of the most-derived object.
188 /// This will only be greater than zero in some virtual base class vtables
189 /// used during object con-/destruction, and will usually be exactly zero.
191 /// The type_info object describing the most-derived class type.
192 std::type_info *TypeInfo;
194 VtablePrefix *getVtablePrefix(void *Vtable) {
195 VtablePrefix *Vptr = reinterpret_cast<VtablePrefix*>(Vtable);
198 VtablePrefix *Prefix = Vptr - 1;
199 if (!Prefix->TypeInfo)
200 // This can't possibly be a valid vtable.
207 bool __ubsan::checkDynamicType(void *Object, void *Type, HashValue Hash) {
208 // A crash anywhere within this function probably means the vptr is corrupted.
209 // FIXME: Perform these checks more cautiously.
211 // Check whether this is something we've evicted from the cache.
212 HashValue *Bucket = getTypeCacheHashTableBucket(Hash);
213 if (*Bucket == Hash) {
214 __ubsan_vptr_type_cache[Hash % VptrTypeCacheSize] = Hash;
218 void *VtablePtr = *reinterpret_cast<void **>(Object);
219 VtablePrefix *Vtable = getVtablePrefix(VtablePtr);
223 // Check that this is actually a type_info object for a class type.
224 abi::__class_type_info *Derived =
225 dynamic_cast<abi::__class_type_info*>(Vtable->TypeInfo);
229 abi::__class_type_info *Base = (abi::__class_type_info*)Type;
230 if (!isDerivedFromAtOffset(Derived, Base, -Vtable->Offset))
233 // Success. Cache this result.
234 __ubsan_vptr_type_cache[Hash % VptrTypeCacheSize] = Hash;
239 __ubsan::DynamicTypeInfo
240 __ubsan::getDynamicTypeInfoFromVtable(void *VtablePtr) {
241 VtablePrefix *Vtable = getVtablePrefix(VtablePtr);
243 return DynamicTypeInfo(0, 0, 0);
244 const abi::__class_type_info *ObjectType = findBaseAtOffset(
245 static_cast<const abi::__class_type_info*>(Vtable->TypeInfo),
247 return DynamicTypeInfo(Vtable->TypeInfo->__type_name, -Vtable->Offset,
248 ObjectType ? ObjectType->__type_name : "<unknown>");
251 #endif // CAN_SANITIZE_UB && !SANITIZER_WINDOWS