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250 lines
8.4 KiB
C++
250 lines
8.4 KiB
C++
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//===-- ubsan_type_hash_itanium.cc ----------------------------------------===//
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//
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// This file is distributed under the University of Illinois Open Source
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// License. See LICENSE.TXT for details.
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//
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//===----------------------------------------------------------------------===//
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//
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// Implementation of type hashing/lookup for Itanium C++ ABI.
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//
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//===----------------------------------------------------------------------===//
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#include "sanitizer_common/sanitizer_platform.h"
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#include "ubsan_platform.h"
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#if CAN_SANITIZE_UB && !SANITIZER_WINDOWS
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#include "ubsan_type_hash.h"
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#include "sanitizer_common/sanitizer_common.h"
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// The following are intended to be binary compatible with the definitions
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// given in the Itanium ABI. We make no attempt to be ODR-compatible with
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// those definitions, since existing ABI implementations aren't.
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namespace std {
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class type_info {
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public:
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virtual ~type_info();
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const char *__type_name;
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};
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}
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namespace __cxxabiv1 {
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/// Type info for classes with no bases, and base class for type info for
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/// classes with bases.
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class __class_type_info : public std::type_info {
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~__class_type_info() override;
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};
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/// Type info for classes with simple single public inheritance.
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class __si_class_type_info : public __class_type_info {
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public:
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~__si_class_type_info() override;
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const __class_type_info *__base_type;
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};
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class __base_class_type_info {
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public:
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const __class_type_info *__base_type;
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long __offset_flags;
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enum __offset_flags_masks {
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__virtual_mask = 0x1,
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__public_mask = 0x2,
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__offset_shift = 8
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};
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};
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/// Type info for classes with multiple, virtual, or non-public inheritance.
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class __vmi_class_type_info : public __class_type_info {
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public:
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~__vmi_class_type_info() override;
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unsigned int flags;
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unsigned int base_count;
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__base_class_type_info base_info[1];
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};
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}
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namespace abi = __cxxabiv1;
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// We implement a simple two-level cache for type-checking results. For each
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// (vptr,type) pair, a hash is computed. This hash is assumed to be globally
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// unique; if it collides, we will get false negatives, but:
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// * such a collision would have to occur on the *first* bad access,
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// * the probability of such a collision is low (and for a 64-bit target, is
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// negligible), and
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// * the vptr, and thus the hash, can be affected by ASLR, so multiple runs
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// give better coverage.
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//
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// The first caching layer is a small hash table with no chaining; buckets are
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// reused as needed. The second caching layer is a large hash table with open
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// chaining. We can freely evict from either layer since this is just a cache.
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//
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// FIXME: Make these hash table accesses thread-safe. The races here are benign:
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// assuming the unsequenced loads and stores don't misbehave too badly,
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// the worst case is false negatives or poor cache behavior, not false
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// positives or crashes.
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/// Find a bucket to store the given hash value in.
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static __ubsan::HashValue *getTypeCacheHashTableBucket(__ubsan::HashValue V) {
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static const unsigned HashTableSize = 65537;
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static __ubsan::HashValue __ubsan_vptr_hash_set[HashTableSize];
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unsigned First = (V & 65535) ^ 1;
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unsigned Probe = First;
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for (int Tries = 5; Tries; --Tries) {
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if (!__ubsan_vptr_hash_set[Probe] || __ubsan_vptr_hash_set[Probe] == V)
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return &__ubsan_vptr_hash_set[Probe];
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Probe += ((V >> 16) & 65535) + 1;
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if (Probe >= HashTableSize)
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Probe -= HashTableSize;
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}
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// FIXME: Pick a random entry from the probe sequence to evict rather than
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// just taking the first.
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return &__ubsan_vptr_hash_set[First];
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}
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/// \brief Determine whether \p Derived has a \p Base base class subobject at
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/// offset \p Offset.
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static bool isDerivedFromAtOffset(const abi::__class_type_info *Derived,
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const abi::__class_type_info *Base,
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sptr Offset) {
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if (Derived->__type_name == Base->__type_name)
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return Offset == 0;
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if (const abi::__si_class_type_info *SI =
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dynamic_cast<const abi::__si_class_type_info*>(Derived))
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return isDerivedFromAtOffset(SI->__base_type, Base, Offset);
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const abi::__vmi_class_type_info *VTI =
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dynamic_cast<const abi::__vmi_class_type_info*>(Derived);
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if (!VTI)
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// No base class subobjects.
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return false;
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// Look for a base class which is derived from \p Base at the right offset.
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for (unsigned int base = 0; base != VTI->base_count; ++base) {
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// FIXME: Curtail the recursion if this base can't possibly contain the
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// given offset.
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sptr OffsetHere = VTI->base_info[base].__offset_flags >>
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abi::__base_class_type_info::__offset_shift;
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if (VTI->base_info[base].__offset_flags &
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abi::__base_class_type_info::__virtual_mask)
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// For now, just punt on virtual bases and say 'yes'.
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// FIXME: OffsetHere is the offset in the vtable of the virtual base
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// offset. Read the vbase offset out of the vtable and use it.
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return true;
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if (isDerivedFromAtOffset(VTI->base_info[base].__base_type,
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Base, Offset - OffsetHere))
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return true;
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}
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return false;
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}
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/// \brief Find the derived-most dynamic base class of \p Derived at offset
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/// \p Offset.
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static const abi::__class_type_info *findBaseAtOffset(
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const abi::__class_type_info *Derived, sptr Offset) {
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if (!Offset)
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return Derived;
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if (const abi::__si_class_type_info *SI =
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dynamic_cast<const abi::__si_class_type_info*>(Derived))
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return findBaseAtOffset(SI->__base_type, Offset);
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const abi::__vmi_class_type_info *VTI =
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dynamic_cast<const abi::__vmi_class_type_info*>(Derived);
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if (!VTI)
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// No base class subobjects.
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return 0;
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for (unsigned int base = 0; base != VTI->base_count; ++base) {
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sptr OffsetHere = VTI->base_info[base].__offset_flags >>
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abi::__base_class_type_info::__offset_shift;
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if (VTI->base_info[base].__offset_flags &
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abi::__base_class_type_info::__virtual_mask)
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// FIXME: Can't handle virtual bases yet.
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continue;
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if (const abi::__class_type_info *Base =
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findBaseAtOffset(VTI->base_info[base].__base_type,
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Offset - OffsetHere))
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return Base;
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}
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return 0;
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}
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namespace {
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struct VtablePrefix {
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/// The offset from the vptr to the start of the most-derived object.
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/// This will only be greater than zero in some virtual base class vtables
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/// used during object con-/destruction, and will usually be exactly zero.
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sptr Offset;
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/// The type_info object describing the most-derived class type.
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std::type_info *TypeInfo;
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};
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VtablePrefix *getVtablePrefix(void *Vtable) {
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VtablePrefix *Vptr = reinterpret_cast<VtablePrefix*>(Vtable);
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if (!Vptr)
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return 0;
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VtablePrefix *Prefix = Vptr - 1;
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if (!Prefix->TypeInfo)
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// This can't possibly be a valid vtable.
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return 0;
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return Prefix;
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}
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}
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bool __ubsan::checkDynamicType(void *Object, void *Type, HashValue Hash) {
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// A crash anywhere within this function probably means the vptr is corrupted.
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// FIXME: Perform these checks more cautiously.
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// Check whether this is something we've evicted from the cache.
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HashValue *Bucket = getTypeCacheHashTableBucket(Hash);
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if (*Bucket == Hash) {
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__ubsan_vptr_type_cache[Hash % VptrTypeCacheSize] = Hash;
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return true;
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}
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void *VtablePtr = *reinterpret_cast<void **>(Object);
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VtablePrefix *Vtable = getVtablePrefix(VtablePtr);
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if (!Vtable)
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return false;
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// Check that this is actually a type_info object for a class type.
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abi::__class_type_info *Derived =
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dynamic_cast<abi::__class_type_info*>(Vtable->TypeInfo);
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if (!Derived)
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return false;
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abi::__class_type_info *Base = (abi::__class_type_info*)Type;
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if (!isDerivedFromAtOffset(Derived, Base, -Vtable->Offset))
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return false;
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// Success. Cache this result.
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__ubsan_vptr_type_cache[Hash % VptrTypeCacheSize] = Hash;
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*Bucket = Hash;
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return true;
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}
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__ubsan::DynamicTypeInfo
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__ubsan::getDynamicTypeInfoFromVtable(void *VtablePtr) {
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VtablePrefix *Vtable = getVtablePrefix(VtablePtr);
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if (!Vtable)
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return DynamicTypeInfo(0, 0, 0);
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const abi::__class_type_info *ObjectType = findBaseAtOffset(
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static_cast<const abi::__class_type_info*>(Vtable->TypeInfo),
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-Vtable->Offset);
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return DynamicTypeInfo(Vtable->TypeInfo->__type_name, -Vtable->Offset,
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ObjectType ? ObjectType->__type_name : "<unknown>");
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}
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#endif // CAN_SANITIZE_UB && !SANITIZER_WINDOWS
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