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Refactor stack trace handling

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- Drop `delim` argument from the `GetStackTrace()` family of functions.
  We only ever used plain spaces.
- Use an `std::vector<std::string>` for the symbolized stack frames and
  adjust the unwind proto accordingly.

This change now prints each stack frame on its own line while skipping
duplicate ones:

```
I20200717 11:47:16.811381 3636246 monitor.cc:326] Stack trace: [
I20200717 11:47:16.811415 3636246 monitor.cc:337]   map:/lib/x86_64-linux-gnu/libc-2.30.so+0xceee7(0x7fb871602ee7)
I20200717 11:47:16.811420 3636246 monitor.cc:337]   Rot13File+0x130(0x55ed24615995)
I20200717 11:47:16.811424 3636246 monitor.cc:337]   ffi_call_unix64+0x55(0x55ed2461f2dd)
I20200717 11:47:16.811429 3636246 monitor.cc:337]   map:[stack]+0x1ec80(0x7ffee4257c80)
I20200717 11:47:16.811455 3636246 monitor.cc:339]   (last frame repeated 196 times)
I20200717 11:47:16.811460 3636246 monitor.cc:347] ]
```

PiperOrigin-RevId: 322089140
Change-Id: I05b0de2f4118fed90fe920c06bbd70ea0d1119e2
This commit is contained in:
Christian Blichmann 2020-07-20 00:24:12 -07:00 committed by Copybara-Service
parent f7d3f442df
commit eb62bae167
9 changed files with 189 additions and 125 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

28
sandboxed_api/sandbox2/monitor.cc
View File

@ -314,15 +314,20 @@ void Monitor::SetAdditionalResultInfo(std::unique_ptr<Regs> regs) {
result_.SetRegs(std::move(regs));
result_.SetProgName(util::GetProgName(pid));
result_.SetProcMaps(ReadProcMaps(pid_));
if (ShouldCollectStackTrace()) {
if (!ShouldCollectStackTrace()) {
LOG(INFO) << "Stack traces have been disabled";
return;
}
auto* ns = policy_->GetNamespace();
const Mounts empty_mounts;
result_.SetStackTrace(
result_.set_stack_trace(
GetStackTrace(result_.GetRegs(), ns ? ns->mounts() : empty_mounts));
LOG(INFO) << "Stack trace: " << result_.GetStackTrace();
} else {
LOG(INFO) << "Stack traces have been disabled";
LOG(INFO) << "Stack trace: [";
for (const auto& frame : CompactStackTrace(result_.stack_trace())) {
LOG(INFO) << " " << frame;
}
LOG(INFO) << "]";
}
void Monitor::KillSandboxee() {
@ -873,12 +878,15 @@ void Monitor::StateProcessStopped(pid_t pid, int status) {
executor_->libunwind_sbox_for_pid_ == 0 &&
policy_->GetNamespace())) {
Regs regs(pid);
auto status = regs.Fetch();
if (status.ok()) {
VLOG(0) << "SANDBOX STACK : PID: " << pid << ", ["
<< GetStackTrace(&regs, policy_->GetNamespace()->mounts()) << "]";
} else {
if (auto status = regs.Fetch(); !status.ok()) {
LOG(WARNING) << "FAILED TO GET SANDBOX STACK : " << status;
} else if (SAPI_VLOG_IS_ON(0)) {
VLOG(0) << "SANDBOX STACK: PID: " << pid << ", [";
for (const auto& frame :
GetStackTrace(&regs, policy_->GetNamespace()->mounts())) {
VLOG(0) << " " << frame;
}
VLOG(0) << "]";
}
should_dump_stack_ = false;
}

5
sandboxed_api/sandbox2/result.cc
View File

@ -17,6 +17,7 @@
#include "sandboxed_api/sandbox2/result.h"
#include "absl/strings/str_cat.h"
#include "absl/strings/str_join.h"
#include "sandboxed_api/sandbox2/syscall.h"
#include "sandboxed_api/sandbox2/util.h"
@ -42,6 +43,10 @@ Result& Result::operator=(const Result& other) {
return *this;
}
std::string Result::GetStackTrace() const {
return absl::StrJoin(stack_trace_, " ");
}
absl::Status Result::ToStatus() const {
switch (final_status()) {
case OK:

11
sandboxed_api/sandbox2/result.h
View File

@ -111,8 +111,8 @@ class Result {
// The stacktrace must be sometimes fetched before SetExitStatusCode is
// called, because after WIFEXITED() or WIFSIGNALED() the process is just a
// zombie.
void SetStackTrace(const std::string& stack_trace) {
stack_trace_ = stack_trace;
void set_stack_trace(std::vector<std::string> value) {
stack_trace_ = std::move(value);
}
void SetRegs(std::unique_ptr<Regs> regs) { regs_ = std::move(regs); }
@ -135,7 +135,10 @@ class Result {
return syscall_ ? syscall_->arch() : Syscall::kUnknown;
}
const std::string& GetStackTrace() const { return stack_trace_; }
const std::vector<std::string> stack_trace() { return stack_trace_; }
// Returns the stack trace as a space-delimited string.
std::string GetStackTrace() const;
const Regs* GetRegs() const { return regs_.get(); }
@ -177,7 +180,7 @@ class Result {
uintptr_t reason_code_ = 0;
// Might contain stack-trace of the process, especially if it failed with
// syscall violation, or was terminated by a signal.
std::string stack_trace_;
std::vector<std::string> stack_trace_;
// Might contain the register values of the process, similar to the stack.
// trace
std::unique_ptr<Regs> regs_;

89
sandboxed_api/sandbox2/stack_trace.cc
View File

@ -62,8 +62,7 @@ class StackTracePeer {
const Mounts& mounts);
static bool LaunchLibunwindSandbox(const Regs* regs, const Mounts& mounts,
UnwindResult* result,
const std::string& delim);
UnwindResult* result);
};
std::unique_ptr<Policy> StackTracePeer::GetPolicy(pid_t target_pid,
@ -106,9 +105,8 @@ std::unique_ptr<Policy> StackTracePeer::GetPolicy(pid_t target_pid,
.AddPolicyOnSyscall(
__NR_process_vm_readv,
{
// The pid technically is a 64bit int, however
// Linux usually uses max 16 bit, so we are fine
// with comparing only 32 bits here.
// The pid technically is a 64bit int, however Linux usually uses
// max 16 bit, so we are fine with comparing only 32 bits here.
ARG_32(0),
JEQ32(static_cast<unsigned int>(target_pid), ALLOW),
JEQ32(static_cast<unsigned int>(1), ALLOW),
@ -139,25 +137,23 @@ std::unique_ptr<Policy> StackTracePeer::GetPolicy(pid_t target_pid,
}
}
auto policy_or = builder.TryBuild();
if (!policy_or.ok()) {
auto policy = builder.TryBuild();
if (!policy.ok()) {
LOG(ERROR) << "Creating stack unwinder sandbox policy failed";
return nullptr;
}
std::unique_ptr<Policy> policy = std::move(policy_or).value();
auto keep_capabilities = absl::make_unique<std::vector<int>>();
keep_capabilities->push_back(CAP_SYS_PTRACE);
policy->AllowUnsafeKeepCapabilities(std::move(keep_capabilities));
(*policy)->AllowUnsafeKeepCapabilities(std::move(keep_capabilities));
// Use no special namespace flags when cloning. We will join an existing
// user namespace and will unshare() afterwards (See forkserver.cc).
policy->GetNamespace()->clone_flags_ = 0;
return policy;
(*policy)->GetNamespace()->clone_flags_ = 0;
return std::move(*policy);
}
bool StackTracePeer::LaunchLibunwindSandbox(const Regs* regs,
const Mounts& mounts,
sandbox2::UnwindResult* result,
const std::string& delim) {
sandbox2::UnwindResult* result) {
const pid_t pid = regs->pid();
// Tell executor to use this special internal mode.
@ -240,17 +236,17 @@ bool StackTracePeer::LaunchLibunwindSandbox(const Regs* regs,
if (!policy) {
return false;
}
auto comms = executor->ipc()->comms();
Sandbox2 s2(std::move(executor), std::move(policy));
auto* comms = executor->ipc()->comms();
Sandbox2 sandbox(std::move(executor), std::move(policy));
VLOG(1) << "Running libunwind sandbox";
s2.RunAsync();
sandbox.RunAsync();
UnwindSetup msg;
msg.set_pid(pid);
msg.set_regs(reinterpret_cast<const char*>(&regs->user_regs_),
sizeof(regs->user_regs_));
msg.set_default_max_frames(kDefaultMaxFrames);
msg.set_delim(delim.c_str(), delim.size());
bool success = true;
if (!comms->SendProtoBuf(msg)) {
@ -264,23 +260,22 @@ bool StackTracePeer::LaunchLibunwindSandbox(const Regs* regs,
}
if (!success) {
s2.Kill();
sandbox.Kill();
}
auto s2_result = s2.AwaitResult();
auto sandbox_result = sandbox.AwaitResult();
LOG(INFO) << "Libunwind execution status: " << s2_result.ToString();
LOG(INFO) << "Libunwind execution status: " << sandbox_result.ToString();
return success && s2_result.final_status() == Result::OK;
return success && sandbox_result.final_status() == Result::OK;
}
std::string GetStackTrace(const Regs* regs, const Mounts& mounts,
const std::string& delim) {
std::vector<std::string> GetStackTrace(const Regs* regs, const Mounts& mounts) {
if (absl::GetFlag(FLAGS_sandbox_disable_all_stack_traces)) {
return "[Stacktraces disabled]";
return {"[Stacktraces disabled]"};
}
if (!regs) {
LOG(WARNING) << "Could not obtain stacktrace, regs == nullptr";
return "[ERROR (noregs)]";
return {"[ERROR (noregs)]"};
}
#if defined(THREAD_SANITIZER) || defined(ADDRESS_SANITIZER) || \
@ -301,26 +296,50 @@ std::string GetStackTrace(const Regs* regs, const Mounts& mounts,
<< "Sanitizer build, using non-sandboxed libunwind";
LOG_IF(WARNING, coverage_enabled)
<< "Coverage build, using non-sandboxed libunwind";
return UnsafeGetStackTrace(regs->pid(), delim);
return UnsafeGetStackTrace(regs->pid());
}
if (!absl::GetFlag(FLAGS_sandbox_libunwind_crash_handler)) {
return UnsafeGetStackTrace(regs->pid(), delim);
return UnsafeGetStackTrace(regs->pid());
}
UnwindResult res;
if (!StackTracePeer::LaunchLibunwindSandbox(regs, mounts, &res, delim)) {
return "";
UnwindResult res;
if (!StackTracePeer::LaunchLibunwindSandbox(regs, mounts, &res)) {
return {};
}
return res.stacktrace();
return {res.stacktrace().begin(), res.stacktrace().end()};
}
std::string UnsafeGetStackTrace(pid_t pid, const std::string& delim) {
std::vector<std::string> UnsafeGetStackTrace(pid_t pid) {
LOG(WARNING) << "Using non-sandboxed libunwind";
std::string stack_trace;
std::vector<uintptr_t> ips;
RunLibUnwindAndSymbolizer(pid, &stack_trace, &ips, kDefaultMaxFrames, delim);
return stack_trace;
return RunLibUnwindAndSymbolizer(pid, &ips, kDefaultMaxFrames);
}
std::vector<std::string> CompactStackTrace(
const std::vector<std::string>& stack_trace) {
std::vector<std::string> compact_trace;
compact_trace.reserve(stack_trace.size() / 2);
const std::string* prev = nullptr;
int seen = 0;
auto add_repeats = [&compact_trace](int seen) {
if (seen != 0) {
compact_trace.push_back(
absl::StrCat("(previous frame repeated ", seen, " times)"));
}
};
for (const auto& frame : stack_trace) {
if (prev && frame == *prev) {
++seen;
} else {
prev = &frame;
add_repeats(seen);
seen = 0;
compact_trace.push_back(frame);
}
}
add_repeats(seen);
return compact_trace;
}
} // namespace sandbox2

21
sandboxed_api/sandbox2/stack_trace.h
View File

@ -20,9 +20,11 @@
#define SANDBOXED_API_SANDBOX2_STACK_TRACE_H_
#include <sys/types.h>
#include <cstddef>
#include <memory>
#include <string>
#include <vector>
#include "sandboxed_api/sandbox2/mounts.h"
#include "sandboxed_api/sandbox2/policy.h"
@ -33,13 +35,24 @@ namespace sandbox2 {
// Maximum depth of analyzed call stack.
constexpr size_t kDefaultMaxFrames = 200;
// Returns the stack-trace of the PID=pid, delimited by the delim argument.
std::string GetStackTrace(const Regs* regs, const Mounts& mounts,
const std::string& delim = " ");
// Returns the stack-trace of the PID=pid, one line per frame.
std::vector<std::string> GetStackTrace(const Regs* regs, const Mounts& mounts);
// Similar to GetStackTrace() but without using the sandbox to isolate
// libunwind.
std::string UnsafeGetStackTrace(pid_t pid, const std::string& delim = " ");
std::vector<std::string> UnsafeGetStackTrace(pid_t pid);
// Returns a stack trace that collapses duplicate stack frames and annotates
// them with a repetition count.
// Example:
// _start _start
// main main
// recursive_call recursive_call
// recursive_call (previous frame repeated 2 times)
// recursive_call tail_call
// tail_call
std::vector<std::string> CompactStackTrace(
const std::vector<std::string>& stack_trace);
} // namespace sandbox2

27
sandboxed_api/sandbox2/stack_trace_test.cc
View File

@ -42,8 +42,10 @@ ABSL_DECLARE_FLAG(bool, sandbox_libunwind_crash_handler);
namespace sandbox2 {
namespace {
using ::testing::ElementsAre;
using ::testing::Eq;
using ::testing::HasSubstr;
using ::testing::IsEmpty;
using ::testing::Not;
// Temporarily overrides a flag, restores the original flag value when it goes
@ -190,5 +192,30 @@ TEST(StackTraceTest, SymbolizationTrustedFilesOnly) {
ASSERT_THAT(result.GetStackTrace(), Not(HasSubstr("CrashMe")));
}
TEST(StackTraceTest, CompactStackTrace) {
EXPECT_THAT(CompactStackTrace({}), IsEmpty());
EXPECT_THAT(CompactStackTrace({"_start"}), ElementsAre("_start"));
EXPECT_THAT(CompactStackTrace({
"_start",
"main",
"recursive_call",
"recursive_call",
"recursive_call",
"tail_call",
}),
ElementsAre("_start", "main", "recursive_call",
"(previous frame repeated 2 times)", "tail_call"));
EXPECT_THAT(CompactStackTrace({
"_start",
"main",
"recursive_call",
"recursive_call",
"recursive_call",
"recursive_call",
}),
ElementsAre("_start", "main", "recursive_call",
"(previous frame repeated 3 times)"));
}
} // namespace
} // namespace sandbox2

81
sandboxed_api/sandbox2/unwind/unwind.cc
View File

@ -71,28 +71,30 @@ std::string GetSymbolAt(const std::map<uint64_t, std::string>& addr_to_symbol,
} // namespace
void GetIPList(pid_t pid, std::vector<uintptr_t>* ips, int max_frames) {
ips->clear();
std::vector<uintptr_t> GetIPList(pid_t pid, int max_frames) {
unw_cursor_t cursor;
static unw_addr_space_t as =
unw_create_addr_space(&_UPT_accessors, 0 /* byte order */);
if (as == nullptr) {
SAPI_RAW_LOG(WARNING, "unw_create_addr_space() failed");
return;
return {};
}
auto* ui = reinterpret_cast<struct UPT_info*>(_UPT_create(pid));
std::unique_ptr<struct UPT_info, void (*)(void*)> ui(
reinterpret_cast<struct UPT_info*>(_UPT_create(pid)), _UPT_destroy);
if (ui == nullptr) {
SAPI_RAW_LOG(WARNING, "_UPT_create() failed");
return;
return {};
}
int rc = unw_init_remote(&cursor, as, ui);
int rc = unw_init_remote(&cursor, as, ui.get());
if (rc < 0) {
// Could be UNW_EINVAL (8), UNW_EUNSPEC (1) or UNW_EBADREG (3).
SAPI_RAW_LOG(WARNING, "unw_init_remote() failed with error %d", rc);
} else {
return {};
}
std::vector<uintptr_t> ips;
for (int i = 0; i < max_frames; i++) {
unw_word_t ip;
rc = unw_get_reg(&cursor, UNW_REG_IP, &ip);
@ -101,7 +103,7 @@ void GetIPList(pid_t pid, std::vector<uintptr_t>* ips, int max_frames) {
SAPI_RAW_LOG(WARNING, "unw_get_reg() failed with error %d", rc);
break;
}
ips->push_back(ip);
ips.push_back(ip);
rc = unw_step(&cursor);
// Non-error condition: UNW_ESUCCESS (0).
if (rc < 0) {
@ -111,40 +113,34 @@ void GetIPList(pid_t pid, std::vector<uintptr_t>* ips, int max_frames) {
break;
}
}
}
// This is only needed if _UPT_create() has been successful.
_UPT_destroy(ui);
return ips;
}
bool RunLibUnwindAndSymbolizer(Comms* comms) {
UnwindSetup pb_setup;
if (!comms->RecvProtoBuf(&pb_setup)) {
UnwindSetup setup;
if (!comms->RecvProtoBuf(&setup)) {
return false;
}
std::string data = pb_setup.regs();
const std::string& data = setup.regs();
InstallUserRegs(data.c_str(), data.length());
ArmPtraceEmulation();
UnwindResult msg;
std::string stack_trace;
std::vector<uintptr_t> ips;
std::vector<std::string> stack_trace =
RunLibUnwindAndSymbolizer(setup.pid(), &ips, setup.default_max_frames());
RunLibUnwindAndSymbolizer(pb_setup.pid(), &stack_trace, &ips,
pb_setup.default_max_frames(), pb_setup.delim());
for (const auto& i : ips) {
msg.add_ip(i);
}
msg.set_stacktrace(stack_trace.c_str(), stack_trace.size());
UnwindResult msg;
*msg.mutable_stacktrace() = {stack_trace.begin(), stack_trace.end()};
*msg.mutable_ip() = {ips.begin(), ips.end()};
return comms->SendProtoBuf(msg);
}
void RunLibUnwindAndSymbolizer(pid_t pid, std::string* stack_trace_out,
std::vector<uintptr_t>* ips, int max_frames,
const std::string& delim) {
std::vector<std::string> RunLibUnwindAndSymbolizer(pid_t pid,
std::vector<uintptr_t>* ips,
int max_frames) {
// Run libunwind.
GetIPList(pid, ips, max_frames);
*ips = GetIPList(pid, max_frames);
// Open /proc/pid/maps.
std::string path_maps = absl::StrCat("/proc/", pid, "/maps");
@ -157,7 +153,7 @@ void RunLibUnwindAndSymbolizer(pid_t pid, std::string* stack_trace_out,
if (!f) {
// Could not open maps file.
SAPI_RAW_LOG(ERROR, "Could not open %s", path_maps);
return;
return {};
}
constexpr static size_t kBufferSize = 10 * 1024 * 1024;
@ -166,21 +162,20 @@ void RunLibUnwindAndSymbolizer(pid_t pid, std::string* stack_trace_out,
if (bytes_read == 0) {
// Could not read the whole maps file.
SAPI_RAW_PLOG(ERROR, "Could not read maps file");
return;
return {};
}
maps_content.resize(bytes_read);
auto maps_or = ParseProcMaps(maps_content);
if (!maps_or.ok()) {
auto maps = ParseProcMaps(maps_content);
if (!maps.ok()) {
SAPI_RAW_LOG(ERROR, "Could not parse /proc/%d/maps", pid);
return;
return {};
}
auto maps = std::move(maps_or).value();
// Get symbols for each file entry in the maps entry.
// This is not a very efficient way, so we might want to optimize it.
std::map<uint64_t, std::string> addr_to_symbol;
for (const auto& entry : maps) {
for (const auto& entry : *maps) {
if (!entry.path.empty()) {
// Store details about start + end of this map.
// The maps entries are ordered and thus sorted with increasing adresses.
@ -216,17 +211,15 @@ void RunLibUnwindAndSymbolizer(pid_t pid, std::string* stack_trace_out,
}
}
std::string stack_trace;
std::vector<std::string> stack_trace;
stack_trace.reserve(ips->size());
// Symbolize stacktrace.
for (auto i = ips->begin(); i != ips->end(); ++i) {
if (i != ips->begin()) {
stack_trace += delim;
for (const auto& 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), ")"));
}
std::string symbol = GetSymbolAt(addr_to_symbol, static_cast<uint64_t>(*i));
absl::StrAppend(&stack_trace, symbol, "(0x", absl::Hex(*i), ")");
}
*stack_trace_out = stack_trace;
return stack_trace;
}
} // namespace sandbox2

8
sandboxed_api/sandbox2/unwind/unwind.h
View File

@ -25,12 +25,12 @@
namespace sandbox2 {
void GetIPList(pid_t pid, std::vector<uintptr_t>* ips, int max_frames);
// Runs libunwind and the symbolizer and sends the results via comms.
bool RunLibUnwindAndSymbolizer(Comms* comms);
void RunLibUnwindAndSymbolizer(pid_t pid, std::string* stack_trace_out,
std::vector<uintptr_t>* ips, int max_frames,
const std::string& delim);
std::vector<std::string> RunLibUnwindAndSymbolizer(pid_t pid,
std::vector<uintptr_t>* ips,
int max_frames);
} // namespace sandbox2

10
sandboxed_api/sandbox2/unwind/unwind.proto
View File

@ -18,22 +18,18 @@ syntax = "proto3";
package sandbox2;
message UnwindSetup {
// Required
// Process ID of the process to unwind
// Process ID of the process to unwind. Required.
uint64 pid = 1;
// Register content for the process to unwind
bytes regs = 2;
// Optional
// Maximum number of stack frames to unwind
uint64 default_max_frames = 3;
// Delimiter used in the result to separate the stack frames
bytes delim = 4;
}
message UnwindResult {
// Readable stacktrace, symbolized, each framed separated by the delim
// specified in the UnwindSetup message
bytes stacktrace = 1;
// Readable stacktrace, symbolized, one frame per line
repeated string stacktrace = 1;
// Stack frames
repeated uint64 ip = 2;
}