1//===-- ubsan_type_hash_itanium.cc ----------------------------------------===// 2// 3// The LLVM Compiler Infrastructure 4// 5// This file is distributed under the University of Illinois Open Source 6// License. See LICENSE.TXT for details. 7// 8//===----------------------------------------------------------------------===// 9// 10// Implementation of type hashing/lookup for Itanium C++ ABI. 11// 12//===----------------------------------------------------------------------===// 13 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" 18 19#include "sanitizer_common/sanitizer_common.h" 20 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. 24 25namespace std { 26 class type_info { 27 public: 28 virtual ~type_info(); 29 30 const char *__type_name; 31 }; 32} 33 34namespace __cxxabiv1 { 35 36/// Type info for classes with no bases, and base class for type info for 37/// classes with bases. 38class __class_type_info : public std::type_info { 39 ~__class_type_info() override; 40}; 41 42/// Type info for classes with simple single public inheritance. 43class __si_class_type_info : public __class_type_info { 44public: 45 ~__si_class_type_info() override; 46 47 const __class_type_info *__base_type; 48}; 49 50class __base_class_type_info { 51public: 52 const __class_type_info *__base_type; 53 long __offset_flags; 54 55 enum __offset_flags_masks { 56 __virtual_mask = 0x1, 57 __public_mask = 0x2, 58 __offset_shift = 8 59 }; 60}; 61 62/// Type info for classes with multiple, virtual, or non-public inheritance. 63class __vmi_class_type_info : public __class_type_info { 64public: 65 ~__vmi_class_type_info() override; 66 67 unsigned int flags; 68 unsigned int base_count; 69 __base_class_type_info base_info[1]; 70}; 71 72} 73 74namespace abi = __cxxabiv1; 75 76using namespace __sanitizer; 77 78// We implement a simple two-level cache for type-checking results. For each 79// (vptr,type) pair, a hash is computed. This hash is assumed to be globally 80// unique; if it collides, we will get false negatives, but: 81// * such a collision would have to occur on the *first* bad access, 82// * the probability of such a collision is low (and for a 64-bit target, is 83// negligible), and 84// * the vptr, and thus the hash, can be affected by ASLR, so multiple runs 85// give better coverage. 86// 87// The first caching layer is a small hash table with no chaining; buckets are 88// reused as needed. The second caching layer is a large hash table with open 89// chaining. We can freely evict from either layer since this is just a cache. 90// 91// FIXME: Make these hash table accesses thread-safe. The races here are benign: 92// assuming the unsequenced loads and stores don't misbehave too badly, 93// the worst case is false negatives or poor cache behavior, not false 94// positives or crashes. 95 96/// Find a bucket to store the given hash value in. 97static __ubsan::HashValue *getTypeCacheHashTableBucket(__ubsan::HashValue V) { 98 static const unsigned HashTableSize = 65537; 99 static __ubsan::HashValue __ubsan_vptr_hash_set[HashTableSize]; 100 101 unsigned First = (V & 65535) ^ 1; 102 unsigned Probe = First; 103 for (int Tries = 5; Tries; --Tries) { 104 if (!__ubsan_vptr_hash_set[Probe] || __ubsan_vptr_hash_set[Probe] == V) 105 return &__ubsan_vptr_hash_set[Probe]; 106 Probe += ((V >> 16) & 65535) + 1; 107 if (Probe >= HashTableSize) 108 Probe -= HashTableSize; 109 } 110 // FIXME: Pick a random entry from the probe sequence to evict rather than 111 // just taking the first. 112 return &__ubsan_vptr_hash_set[First]; 113} 114 115/// \brief Determine whether \p Derived has a \p Base base class subobject at 116/// offset \p Offset. 117static bool isDerivedFromAtOffset(const abi::__class_type_info *Derived, 118 const abi::__class_type_info *Base, 119 sptr Offset) { 120 if (Derived->__type_name == Base->__type_name || 121 (SANITIZER_NON_UNIQUE_TYPEINFO && 122 !internal_strcmp(Derived->__type_name, Base->__type_name))) 123 return Offset == 0; 124 125 if (const abi::__si_class_type_info *SI = 126 dynamic_cast<const abi::__si_class_type_info*>(Derived)) 127 return isDerivedFromAtOffset(SI->__base_type, Base, Offset); 128 129 const abi::__vmi_class_type_info *VTI = 130 dynamic_cast<const abi::__vmi_class_type_info*>(Derived); 131 if (!VTI) 132 // No base class subobjects. 133 return false; 134 135 // Look for a base class which is derived from \p Base at the right offset. 136 for (unsigned int base = 0; base != VTI->base_count; ++base) { 137 // FIXME: Curtail the recursion if this base can't possibly contain the 138 // given offset. 139 sptr OffsetHere = VTI->base_info[base].__offset_flags >> 140 abi::__base_class_type_info::__offset_shift; 141 if (VTI->base_info[base].__offset_flags & 142 abi::__base_class_type_info::__virtual_mask) 143 // For now, just punt on virtual bases and say 'yes'. 144 // FIXME: OffsetHere is the offset in the vtable of the virtual base 145 // offset. Read the vbase offset out of the vtable and use it. 146 return true; 147 if (isDerivedFromAtOffset(VTI->base_info[base].__base_type, 148 Base, Offset - OffsetHere)) 149 return true; 150 } 151 152 return false; 153} 154 155/// \brief Find the derived-most dynamic base class of \p Derived at offset 156/// \p Offset. 157static const abi::__class_type_info *findBaseAtOffset( 158 const abi::__class_type_info *Derived, sptr Offset) { 159 if (!Offset) 160 return Derived; 161 162 if (const abi::__si_class_type_info *SI = 163 dynamic_cast<const abi::__si_class_type_info*>(Derived)) 164 return findBaseAtOffset(SI->__base_type, Offset); 165 166 const abi::__vmi_class_type_info *VTI = 167 dynamic_cast<const abi::__vmi_class_type_info*>(Derived); 168 if (!VTI) 169 // No base class subobjects. 170 return nullptr; 171 172 for (unsigned int base = 0; base != VTI->base_count; ++base) { 173 sptr OffsetHere = VTI->base_info[base].__offset_flags >> 174 abi::__base_class_type_info::__offset_shift; 175 if (VTI->base_info[base].__offset_flags & 176 abi::__base_class_type_info::__virtual_mask) 177 // FIXME: Can't handle virtual bases yet. 178 continue; 179 if (const abi::__class_type_info *Base = 180 findBaseAtOffset(VTI->base_info[base].__base_type, 181 Offset - OffsetHere)) 182 return Base; 183 } 184 185 return nullptr; 186} 187 188namespace { 189 190struct VtablePrefix { 191 /// The offset from the vptr to the start of the most-derived object. 192 /// This will only be greater than zero in some virtual base class vtables 193 /// used during object con-/destruction, and will usually be exactly zero. 194 sptr Offset; 195 /// The type_info object describing the most-derived class type. 196 std::type_info *TypeInfo; 197}; 198VtablePrefix *getVtablePrefix(void *Vtable) { 199 VtablePrefix *Vptr = reinterpret_cast<VtablePrefix*>(Vtable); 200 VtablePrefix *Prefix = Vptr - 1; 201 if (!IsAccessibleMemoryRange((uptr)Prefix, sizeof(VtablePrefix))) 202 return nullptr; 203 if (!Prefix->TypeInfo) 204 // This can't possibly be a valid vtable. 205 return nullptr; 206 return Prefix; 207} 208 209} 210 211bool __ubsan::checkDynamicType(void *Object, void *Type, HashValue Hash) { 212 // A crash anywhere within this function probably means the vptr is corrupted. 213 // FIXME: Perform these checks more cautiously. 214 215 // Check whether this is something we've evicted from the cache. 216 HashValue *Bucket = getTypeCacheHashTableBucket(Hash); 217 if (*Bucket == Hash) { 218 __ubsan_vptr_type_cache[Hash % VptrTypeCacheSize] = Hash; 219 return true; 220 } 221 222 void *VtablePtr = *reinterpret_cast<void **>(Object); 223 VtablePrefix *Vtable = getVtablePrefix(VtablePtr); 224 if (!Vtable) 225 return false; 226 if (Vtable->Offset < -VptrMaxOffsetToTop || Vtable->Offset > VptrMaxOffsetToTop) { 227 // Too large or too small offset are signs of Vtable corruption. 228 return false; 229 } 230 231 // Check that this is actually a type_info object for a class type. 232 abi::__class_type_info *Derived = 233 dynamic_cast<abi::__class_type_info*>(Vtable->TypeInfo); 234 if (!Derived) 235 return false; 236 237 abi::__class_type_info *Base = (abi::__class_type_info*)Type; 238 if (!isDerivedFromAtOffset(Derived, Base, -Vtable->Offset)) 239 return false; 240 241 // Success. Cache this result. 242 __ubsan_vptr_type_cache[Hash % VptrTypeCacheSize] = Hash; 243 *Bucket = Hash; 244 return true; 245} 246 247__ubsan::DynamicTypeInfo 248__ubsan::getDynamicTypeInfoFromVtable(void *VtablePtr) { 249 VtablePrefix *Vtable = getVtablePrefix(VtablePtr); 250 if (!Vtable) 251 return DynamicTypeInfo(nullptr, 0, nullptr); 252 if (Vtable->Offset < -VptrMaxOffsetToTop || Vtable->Offset > VptrMaxOffsetToTop) 253 return DynamicTypeInfo(nullptr, Vtable->Offset, nullptr); 254 const abi::__class_type_info *ObjectType = findBaseAtOffset( 255 static_cast<const abi::__class_type_info*>(Vtable->TypeInfo), 256 -Vtable->Offset); 257 return DynamicTypeInfo(Vtable->TypeInfo->__type_name, -Vtable->Offset, 258 ObjectType ? ObjectType->__type_name : "<unknown>"); 259} 260 261#endif // CAN_SANITIZE_UB && !SANITIZER_WINDOWS 262