sandboxed-api/sandboxed_api/sandbox2/unwind/unwind.cc

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// Copyright 2019 Google LLC
//
// 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
//
// https://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 "sandboxed_api/sandbox2/unwind/unwind.h"
#include <cxxabi.h>
#include <cstddef>
#include <cstdint>
#include <cstdio>
#include <cstdlib>
#include <map>
#include <memory>
#include <string>
#include <vector>
#include "absl/cleanup/cleanup.h"
#include "absl/status/statusor.h"
#include "absl/strings/match.h"
#include "absl/strings/str_cat.h"
#include "libunwind-ptrace.h"
#include "sandboxed_api/sandbox2/comms.h"
#include "sandboxed_api/sandbox2/unwind/ptrace_hook.h"
#include "sandboxed_api/sandbox2/unwind/unwind.pb.h"
#include "sandboxed_api/sandbox2/util/maps_parser.h"
#include "sandboxed_api/sandbox2/util/minielf.h"
#include "sandboxed_api/util/file_helpers.h"
#include "sandboxed_api/util/raw_logging.h"
#include "sandboxed_api/util/status_macros.h"
#include "sandboxed_api/util/strerror.h"
namespace sandbox2 {
namespace {
std::string DemangleSymbol(const std::string& maybe_mangled) {
int status;
size_t length;
std::unique_ptr<char, decltype(&std::free)> symbol(
abi::__cxa_demangle(maybe_mangled.c_str(), /*output_buffer=*/nullptr,
&length, &status),
std::free);
if (symbol && status == 0) {
return std::string(symbol.get(), length);
}
return maybe_mangled;
}
absl::StatusOr<std::vector<uintptr_t>> RunLibUnwind(pid_t pid, int max_frames) {
static unw_addr_space_t as =
unw_create_addr_space(&_UPT_accessors, 0 /* byte order */);
if (as == nullptr) {
return absl::InternalError("unw_create_addr_space() failed");
}
void* context = _UPT_create(pid);
if (context == nullptr) {
return absl::InternalError("_UPT_create() failed");
}
absl::Cleanup context_cleanup = [&context] { _UPT_destroy(context); };
unw_cursor_t cursor;
if (int rc = unw_init_remote(&cursor, as, context); rc < 0) {
// Could be UNW_EINVAL (8), UNW_EUNSPEC (1) or UNW_EBADREG (3).
return absl::InternalError(
absl::StrCat("unw_init_remote() failed with error ", rc));
}
std::vector<uintptr_t> ips;
for (int i = 0; i < max_frames; ++i) {
unw_word_t ip;
int rc = unw_get_reg(&cursor, UNW_REG_IP, &ip);
if (rc < 0) {
// Could be UNW_EUNSPEC or UNW_EBADREG.
SAPI_RAW_LOG(WARNING, "unw_get_reg() failed with error %d", rc);
break;
}
ips.push_back(ip);
rc = unw_step(&cursor);
// Non-error condition: UNW_ESUCCESS (0).
if (rc < 0) {
// If anything but UNW_ESTOPUNWIND (-5), there has been an error.
// However since we can't do anything about it and it appears that
// this happens every time we don't log this.
break;
}
}
return ips;
}
absl::StatusOr<std::vector<std::string>> SymbolizeStacktrace(
pid_t pid, const std::vector<uintptr_t>& ips) {
SAPI_ASSIGN_OR_RETURN(auto addr_to_symbol, LoadSymbolsMap(pid));
std::vector<std::string> stack_trace;
stack_trace.reserve(ips.size());
// Symbolize stacktrace
for (uintptr_t ip : ips) {
const std::string symbol =
GetSymbolAt(addr_to_symbol, static_cast<uint64_t>(ip));
stack_trace.push_back(absl::StrCat(symbol, "(0x", absl::Hex(ip), ")"));
}
return stack_trace;
}
} // namespace
std::string GetSymbolAt(const SymbolMap& addr_to_symbol, uint64_t addr) {
auto entry_for_next_symbol = addr_to_symbol.lower_bound(addr);
if (entry_for_next_symbol != addr_to_symbol.end() &&
entry_for_next_symbol != addr_to_symbol.begin()) {
// Matches the addr exactly:
if (entry_for_next_symbol->first == addr) {
return DemangleSymbol(entry_for_next_symbol->second);
}
// Might be inside a function, return symbol+offset;
const auto entry_for_previous_symbol = --entry_for_next_symbol;
if (!entry_for_previous_symbol->second.empty()) {
return absl::StrCat(DemangleSymbol(entry_for_previous_symbol->second),
"+0x",
absl::Hex(addr - entry_for_previous_symbol->first));
}
}
return "";
}
absl::StatusOr<SymbolMap> LoadSymbolsMap(pid_t pid) {
const std::string maps_filename = absl::StrCat("/proc/", pid, "/maps");
std::string maps_content;
SAPI_RETURN_IF_ERROR(sapi::file::GetContents(maps_filename, &maps_content,
sapi::file::Defaults()));
SAPI_ASSIGN_OR_RETURN(std::vector<MapsEntry> maps,
ParseProcMaps(maps_content));
// Get symbols for each file entry in the maps entry.
// This is not a very efficient way, so we might want to optimize it.
SymbolMap addr_to_symbol;
for (const MapsEntry& entry : maps) {
if (!entry.is_executable ||
entry.inode == 0 || // Only parse file-backed entries
entry.path.empty() ||
absl::EndsWith(entry.path, " (deleted)") // Skip deleted files
) {
continue;
}
// Store details about start + end of this map.
// The maps entries are ordered and thus sorted with increasing adresses.
// This means if there is a symbol @ entry.end, it will be overwritten in
// the next iteration.
std::string map = absl::StrCat("map:", entry.path);
if (entry.pgoff) {
absl::StrAppend(&map, "+0x", absl::Hex(entry.pgoff));
}
addr_to_symbol[entry.start] = map;
addr_to_symbol[entry.end] = "";
absl::StatusOr<ElfFile> elf =
ElfFile::ParseFromFile(entry.path, ElfFile::kLoadSymbols);
if (!elf.ok()) {
SAPI_RAW_LOG(WARNING, "Could not load symbols for %s: %s",
entry.path.c_str(),
std::string(elf.status().message()).c_str());
continue;
}
for (const ElfFile::Symbol& symbol : elf->symbols()) {
if (elf->position_independent()) {
if (symbol.address >= entry.pgoff &&
symbol.address - entry.pgoff < entry.end - entry.start) {
addr_to_symbol[symbol.address + entry.start - entry.pgoff] =
symbol.name;
}
} else {
if (symbol.address >= entry.start && symbol.address < entry.end) {
addr_to_symbol[symbol.address] = symbol.name;
}
}
}
}
return addr_to_symbol;
}
bool RunLibUnwindAndSymbolizer(Comms* comms) {
UnwindSetup setup;
if (!comms->RecvProtoBuf(&setup)) {
return false;
}
EnablePtraceEmulationWithUserRegs(setup.regs());
absl::StatusOr<std::vector<uintptr_t>> ips =
RunLibUnwind(setup.pid(), setup.default_max_frames());
absl::StatusOr<std::vector<std::string>> stack_trace;
if (ips.ok()) {
stack_trace = SymbolizeStacktrace(setup.pid(), *ips);
} else {
stack_trace = ips.status();
}
if (!comms->SendStatus(stack_trace.status())) {
return false;
}
if (!stack_trace.ok()) {
return true;
}
UnwindResult msg;
*msg.mutable_stacktrace() = {stack_trace->begin(), stack_trace->end()};
*msg.mutable_ip() = {ips->begin(), ips->end()};
return comms->SendProtoBuf(msg);
}
absl::StatusOr<std::vector<std::string>> RunLibUnwindAndSymbolizer(
pid_t pid, int max_frames) {
SAPI_ASSIGN_OR_RETURN(std::vector<uintptr_t> ips,
RunLibUnwind(pid, max_frames));
return SymbolizeStacktrace(pid, ips);
}
} // namespace sandbox2