// Copyright 2014 The Crashpad Authors
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
// http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.
#include "snapshot/mac/mach_o_image_symbol_table_reader.h"
#include <mach-o/loader.h>
#include <mach-o/nlist.h>
#include <sys/types.h>
#include <memory>
#include <utility>
#include "base/logging.h"
#include "base/strings/stringprintf.h"
#include "util/mac/checked_mach_address_range.h"
#include "util/process/process_memory_mac.h"
namespace crashpad {
namespace internal {
//! \brief The internal implementation for MachOImageSymbolTableReader.
//!
//! Initialization is broken into more than one function that needs to share
//! data, so member variables are used. However, much of this data is irrelevant
//! after initialization is completed, so rather than doing it in
//! MachOImageSymbolTableReader, it’s handled by this class, which is a “friend”
//! of MachOImageSymbolTableReader.
class MachOImageSymbolTableReaderInitializer {
public:
MachOImageSymbolTableReaderInitializer(
ProcessReaderMac* process_reader,
const MachOImageSegmentReader* linkedit_segment,
const std::string& module_info)
: module_info_(module_info),
linkedit_range_(),
process_reader_(process_reader),
linkedit_segment_(linkedit_segment) {
linkedit_range_.SetRange(process_reader_->Is64Bit(),
linkedit_segment->Address(),
linkedit_segment->Size());
DCHECK(linkedit_range_.IsValid());
}
MachOImageSymbolTableReaderInitializer(
const MachOImageSymbolTableReaderInitializer&) = delete;
MachOImageSymbolTableReaderInitializer& operator=(
const MachOImageSymbolTableReaderInitializer&) = delete;
~MachOImageSymbolTableReaderInitializer() {}
//! \brief Reads the symbol table from another process.
//!
//! \sa MachOImageSymbolTableReader::Initialize()
bool Initialize(const process_types::symtab_command* symtab_command,
const process_types::dysymtab_command* dysymtab_command,
MachOImageSymbolTableReader::SymbolInformationMap*
external_defined_symbols) {
mach_vm_address_t symtab_address =
AddressForLinkEditComponent(symtab_command->symoff);
uint32_t symbol_count = symtab_command->nsyms;
size_t nlist_size = process_types::nlist::ExpectedSize(process_reader_);
mach_vm_size_t symtab_size = symbol_count * nlist_size;
if (!IsInLinkEditSegment(symtab_address, symtab_size, "symtab")) {
return false;
}
// If a dysymtab is present, use it to filter the symtab for just the
// portion used for extdefsym. If no dysymtab is present, the entire symtab
// will need to be consulted.
uint32_t skip_count = 0;
if (dysymtab_command) {
if (dysymtab_command->iextdefsym >= symtab_command->nsyms ||
dysymtab_command->iextdefsym + dysymtab_command->nextdefsym >
symtab_command->nsyms) {
LOG(WARNING) << base::StringPrintf(
"dysymtab extdefsym %u + %u > symtab nsyms %u",
dysymtab_command->iextdefsym,
dysymtab_command->nextdefsym,
symtab_command->nsyms) << module_info_;
return false;
}
skip_count = dysymtab_command->iextdefsym;
mach_vm_size_t skip_size = skip_count * nlist_size;
symtab_address += skip_size;
symtab_size -= skip_size;
symbol_count = dysymtab_command->nextdefsym;
}
mach_vm_address_t strtab_address =
AddressForLinkEditComponent(symtab_command->stroff);
mach_vm_size_t strtab_size = symtab_command->strsize;
if (!IsInLinkEditSegment(strtab_address, strtab_size, "strtab")) {
return false;
}
std::unique_ptr<process_types::nlist[]> symbols(
new process_types::nlist[symtab_command->nsyms]);
if (!process_types::nlist::ReadArrayInto(
process_reader_, symtab_address, symbol_count, &symbols[0])) {
LOG(WARNING) << "could not read symbol table" << module_info_;
return false;
}
std::unique_ptr<ProcessMemoryMac::MappedMemory> string_table;
for (size_t symbol_index = 0; symbol_index < symbol_count; ++symbol_index) {
const process_types::nlist& symbol = symbols[symbol_index];
std::string symbol_info = base::StringPrintf(", symbol index %zu%s",
skip_count + symbol_index,
module_info_.c_str());
bool valid_symbol = true;
if ((symbol.n_type & N_STAB) == 0 && (symbol.n_type & N_PEXT) == 0 &&
(symbol.n_type & N_EXT)) {
uint8_t symbol_type = symbol.n_type & N_TYPE;
if (symbol_type == N_ABS || symbol_type == N_SECT) {
if (symbol.n_strx >= strtab_size) {
LOG(WARNING) << base::StringPrintf(
"string at 0x%x out of bounds (0x%llx)",
symbol.n_strx,
strtab_size) << symbol_info;
return false;
}
if (!string_table) {
string_table = process_reader_->Memory()->ReadMapped(
strtab_address, strtab_size);
if (!string_table) {
LOG(WARNING) << "could not read string table" << module_info_;
return false;
}
}
std::string name;
if (!string_table->ReadCString(symbol.n_strx, &name)) {
LOG(WARNING) << "could not read string" << symbol_info;
return false;
}
if (symbol_type == N_ABS && symbol.n_sect != NO_SECT) {
LOG(WARNING) << base::StringPrintf("N_ABS symbol %s in section %u",
name.c_str(),
symbol.n_sect) << symbol_info;
return false;
}
if (symbol_type == N_SECT && symbol.n_sect == NO_SECT) {
LOG(WARNING) << base::StringPrintf(
"N_SECT symbol %s in section NO_SECT",
name.c_str()) << symbol_info;
return false;
}
MachOImageSymbolTableReader::SymbolInformation this_symbol_info;
this_symbol_info.value = symbol.n_value;
this_symbol_info.section = symbol.n_sect;
if (!external_defined_symbols->insert(
std::make_pair(name, this_symbol_info)).second) {
LOG(WARNING) << "duplicate symbol " << name << symbol_info;
return false;
}
} else {
// External indirect symbols may be found in the portion of the symbol
// table used for external symbols as opposed to indirect symbols when
// the indirect symbols are also external. These can be produced by
// Xcode 5.1 ld64-236.3/src/ld/LinkEditClassic.hpp
// ld::tool::SymbolTableAtom<>::addGlobal(). Indirect symbols are not
// currently supported by this symbol table reader, so ignore them
// without failing or logging a message when encountering them. See
// https://groups.google.com/a/chromium.org/d/topic/crashpad-dev/k7QkLwO71Zo
valid_symbol = symbol_type == N_INDR;
}
} else {
valid_symbol = false;
}
if (!valid_symbol && dysymtab_command) {
LOG(WARNING) << "non-external symbol with type " << symbol.n_type
<< " in extdefsym" << symbol_info;
return false;
}
}
return true;
}
private:
//! \brief Computes the address for data in the `__LINKEDIT` segment
//! identified by its file offset in a Mach-O image.
//!
//! \param[in] fileoff The file offset relative to the beginning of an image’s
//! `mach_header` or `mach_header_64` of the data in the `__LINKEDIT`
//! segment.
//!
//! \return The address, in the remote process’ address space, of the
//! requested data.
mach_vm_address_t AddressForLinkEditComponent(uint32_t fileoff) const {
return linkedit_range_.Base() + fileoff - linkedit_segment_->fileoff();
}
//! \brief Determines whether an address range is located within the
//! `__LINKEDIT` segment.
//!
//! \param[in] address The base address of the range to check.
//! \param[in] size The size of the range to check.
//! \param[in] tag A string that identifies the range being checked. This is
//! used only for logging.
//!
//! \return `true` if the range identified by \a address + \a size lies
//! entirely within the `__LINKEDIT` segment. `false` if that range is
//! invalid, or if that range is not contained by the `__LINKEDIT`
//! segment, with an appropriate message logged.
bool IsInLinkEditSegment(mach_vm_address_t address,
mach_vm_size_t size,
const char* tag) const {
CheckedMachAddressRange subrange(process_reader_->Is64Bit(), address, size);
if (!subrange.IsValid()) {
LOG(WARNING) << base::StringPrintf("invalid %s range (0x%llx + 0x%llx)",
tag,
address,
size) << module_info_;
return false;
}
if (!linkedit_range_.ContainsRange(subrange)) {
LOG(WARNING) << base::StringPrintf(
"%s at 0x%llx + 0x%llx outside of " SEG_LINKEDIT
" segment at 0x%llx + 0x%llx",
tag,
address,
size,
linkedit_range_.Base(),
linkedit_range_.Size()) << module_info_;
return false;
}
return true;
}
std::string module_info_;
CheckedMachAddressRange linkedit_range_;
ProcessReaderMac* process_reader_; // weak
const MachOImageSegmentReader* linkedit_segment_; // weak
};
} // namespace internal
MachOImageSymbolTableReader::MachOImageSymbolTableReader()
: external_defined_symbols_(), initialized_() {
}
MachOImageSymbolTableReader::~MachOImageSymbolTableReader() {
}
bool MachOImageSymbolTableReader::Initialize(
ProcessReaderMac* process_reader,
const process_types::symtab_command* symtab_command,
const process_types::dysymtab_command* dysymtab_command,
const MachOImageSegmentReader* linkedit_segment,
const std::string& module_info) {
INITIALIZATION_STATE_SET_INITIALIZING(initialized_);
internal::MachOImageSymbolTableReaderInitializer initializer(process_reader,
linkedit_segment,
module_info);
if (!initializer.Initialize(
symtab_command, dysymtab_command, &external_defined_symbols_)) {
return false;
}
INITIALIZATION_STATE_SET_VALID(initialized_);
return true;
}
const MachOImageSymbolTableReader::SymbolInformation*
MachOImageSymbolTableReader::LookUpExternalDefinedSymbol(
const std::string& name) const {
INITIALIZATION_STATE_DCHECK_VALID(initialized_);
const auto& iterator = external_defined_symbols_.find(name);
if (iterator == external_defined_symbols_.end()) {
return nullptr;
}
return &iterator->second;
}
} // namespace crashpad
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