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android_system_core/debuggerd/handler/debuggerd_handler.cpp

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/*
* Copyright 2008 The Android Open Source Project
*
* 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 "debuggerd/handler.h"
#include <errno.h>
#include <fcntl.h>
#include <inttypes.h>
#include <linux/futex.h>
#include <pthread.h>
#include <sched.h>
#include <signal.h>
#include <stddef.h>
#include <stdint.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <sys/capability.h>
#include <sys/mman.h>
#include <sys/prctl.h>
#include <sys/socket.h>
#include <sys/syscall.h>
#include <sys/uio.h>
#include <sys/un.h>
#include <sys/wait.h>
#include <unistd.h>
#include <android-base/macros.h>
#include <android-base/parsebool.h>
#include <android-base/properties.h>
#include <android-base/unique_fd.h>
#include <async_safe/log.h>
#include <bionic/reserved_signals.h>
#include <libdebuggerd/utility.h>
#include "dump_type.h"
#include "protocol.h"
#include "handler/fallback.h"
using ::android::base::ParseBool;
using ::android::base::ParseBoolResult;
using ::android::base::Pipe;
// We muck with our fds in a 'thread' that doesn't share the same fd table.
// Close fds in that thread with a raw close syscall instead of going through libc.
struct FdsanBypassCloser {
static void Close(int fd) {
syscall(__NR_close, fd);
}
};
using unique_fd = android::base::unique_fd_impl<FdsanBypassCloser>;
// see man(2) prctl, specifically the section about PR_GET_NAME
#define MAX_TASK_NAME_LEN (16)
#if defined(__LP64__)
#define CRASH_DUMP_NAME "crash_dump64"
#else
#define CRASH_DUMP_NAME "crash_dump32"
#endif
#define CRASH_DUMP_PATH "/apex/com.android.runtime/bin/" CRASH_DUMP_NAME
// Wrappers that directly invoke the respective syscalls, in case the cached values are invalid.
#pragma GCC poison getpid gettid
static pid_t __getpid() {
return syscall(__NR_getpid);
}
static pid_t __gettid() {
return syscall(__NR_gettid);
}
static bool property_parse_bool(const char* name) {
const prop_info* pi = __system_property_find(name);
if (!pi) return false;
bool cookie = false;
__system_property_read_callback(
pi,
[](void* cookie, const char*, const char* value, uint32_t) {
*reinterpret_cast<bool*>(cookie) = ParseBool(value) == ParseBoolResult::kTrue;
},
&cookie);
return cookie;
}
static bool is_permissive_mte() {
// Environment variable for testing or local use from shell.
char* permissive_env = getenv("MTE_PERMISSIVE");
char process_sysprop_name[512];
async_safe_format_buffer(process_sysprop_name, sizeof(process_sysprop_name),
"persist.device_config.memory_safety_native.permissive.process.%s",
getprogname());
// DO NOT REPLACE this with GetBoolProperty. That uses std::string which allocates, so it is
// not async-safe (and this functiong gets used in a signal handler).
return property_parse_bool("persist.sys.mte.permissive") ||
property_parse_bool("persist.device_config.memory_safety_native.permissive.default") ||
property_parse_bool(process_sysprop_name) ||
(permissive_env && ParseBool(permissive_env) == ParseBoolResult::kTrue);
}
static inline void futex_wait(volatile void* ftx, int value) {
syscall(__NR_futex, ftx, FUTEX_WAIT, value, nullptr, nullptr, 0);
}
class ErrnoRestorer {
public:
ErrnoRestorer() : saved_errno_(errno) {
}
~ErrnoRestorer() {
errno = saved_errno_;
}
private:
int saved_errno_;
};
extern "C" void* android_fdsan_get_fd_table();
extern "C" void debuggerd_fallback_handler(siginfo_t*, ucontext_t*, void*);
static debuggerd_callbacks_t g_callbacks;
// Mutex to ensure only one crashing thread dumps itself.
static pthread_mutex_t crash_mutex = PTHREAD_MUTEX_INITIALIZER;
// Don't use async_safe_fatal because it exits via abort, which might put us back into
// a signal handler.
static void __noreturn __printflike(1, 2) fatal(const char* fmt, ...) {
va_list args;
va_start(args, fmt);
async_safe_format_log_va_list(ANDROID_LOG_FATAL, "libc", fmt, args);
_exit(1);
}
static void __noreturn __printflike(1, 2) fatal_errno(const char* fmt, ...) {
int err = errno;
va_list args;
va_start(args, fmt);
char buf[256];
async_safe_format_buffer_va_list(buf, sizeof(buf), fmt, args);
fatal("%s: %s", buf, strerror(err));
}
static bool get_main_thread_name(char* buf, size_t len) {
unique_fd fd(open("/proc/self/comm", O_RDONLY | O_CLOEXEC));
if (fd == -1) {
return false;
}
ssize_t rc = read(fd, buf, len);
if (rc == -1) {
return false;
} else if (rc == 0) {
// Should never happen?
return false;
}
// There's a trailing newline, replace it with a NUL.
buf[rc - 1] = '\0';
return true;
}
/*
* Writes a summary of the signal to the log file. We do this so that, if
* for some reason we're not able to contact debuggerd, there is still some
* indication of the failure in the log.
*
* We could be here as a result of native heap corruption, or while a
* mutex is being held, so we don't want to use any libc functions that
* could allocate memory or hold a lock.
*/
static void log_signal_summary(const siginfo_t* si) {
char main_thread_name[MAX_TASK_NAME_LEN + 1];
if (!get_main_thread_name(main_thread_name, sizeof(main_thread_name))) {
strncpy(main_thread_name, "<unknown>", sizeof(main_thread_name));
}
if (si->si_signo == BIONIC_SIGNAL_DEBUGGER) {
async_safe_format_log(ANDROID_LOG_INFO, "libc", "Requested dump for pid %d (%s)", __getpid(),
main_thread_name);
return;
}
// Many signals don't have a sender or extra detail, but some do...
pid_t self_pid = __getpid();
char sender_desc[32] = {}; // " from pid 1234, uid 666"
if (signal_has_sender(si, self_pid)) {
get_signal_sender(sender_desc, sizeof(sender_desc), si);
}
char extra_desc[32] = {}; // ", fault addr 0x1234" or ", syscall 1234"
if (si->si_signo == SIGSYS && si->si_code == SYS_SECCOMP) {
async_safe_format_buffer(extra_desc, sizeof(extra_desc), ", syscall %d", si->si_syscall);
} else if (signal_has_si_addr(si)) {
async_safe_format_buffer(extra_desc, sizeof(extra_desc), ", fault addr %p", si->si_addr);
}
char thread_name[MAX_TASK_NAME_LEN + 1]; // one more for termination
if (prctl(PR_GET_NAME, reinterpret_cast<unsigned long>(thread_name), 0, 0, 0) != 0) {
strcpy(thread_name, "<name unknown>");
} else {
// short names are null terminated by prctl, but the man page
// implies that 16 byte names are not.
thread_name[MAX_TASK_NAME_LEN] = 0;
}
async_safe_format_log(ANDROID_LOG_FATAL, "libc",
"Fatal signal %d (%s), code %d (%s%s)%s in tid %d (%s), pid %d (%s)",
si->si_signo, get_signame(si), si->si_code, get_sigcode(si), sender_desc,
extra_desc, __gettid(), thread_name, self_pid, main_thread_name);
}
/*
* Returns true if the handler for signal "signum" has SA_SIGINFO set.
*/
static bool have_siginfo(int signum) {
struct sigaction old_action;
if (sigaction(signum, nullptr, &old_action) < 0) {
async_safe_format_log(ANDROID_LOG_WARN, "libc", "Failed testing for SA_SIGINFO: %s",
strerror(errno));
return false;
}
return (old_action.sa_flags & SA_SIGINFO) != 0;
}
static void raise_caps() {
// Raise CapInh to match CapPrm, so that we can set the ambient bits.
__user_cap_header_struct capheader;
memset(&capheader, 0, sizeof(capheader));
capheader.version = _LINUX_CAPABILITY_VERSION_3;
capheader.pid = 0;
__user_cap_data_struct capdata[2];
if (capget(&capheader, &capdata[0]) == -1) {
fatal_errno("capget failed");
}
if (capdata[0].permitted != capdata[0].inheritable ||
capdata[1].permitted != capdata[1].inheritable) {
capdata[0].inheritable = capdata[0].permitted;
capdata[1].inheritable = capdata[1].permitted;
if (capset(&capheader, &capdata[0]) == -1) {
async_safe_format_log(ANDROID_LOG_ERROR, "libc", "capset failed: %s", strerror(errno));
}
}
// Set the ambient capability bits so that crash_dump gets all of our caps and can ptrace us.
uint64_t capmask = capdata[0].inheritable;
capmask |= static_cast<uint64_t>(capdata[1].inheritable) << 32;
for (unsigned long i = 0; i < 64; ++i) {
if (capmask & (1ULL << i)) {
if (prctl(PR_CAP_AMBIENT, PR_CAP_AMBIENT_RAISE, i, 0, 0) != 0) {
async_safe_format_log(ANDROID_LOG_ERROR, "libc",
"failed to raise ambient capability %lu: %s", i, strerror(errno));
}
}
}
}
static pid_t __fork() {
return clone(nullptr, nullptr, 0, nullptr);
}
// Double-clone, with CLONE_FILES to share the file descriptor table for kcmp validation.
// Returns 0 in the orphaned child, the pid of the orphan in the original process, or -1 on failure.
static void create_vm_process() {
pid_t first = clone(nullptr, nullptr, CLONE_FILES, nullptr);
if (first == -1) {
fatal_errno("failed to clone vm process");
} else if (first == 0) {
drop_capabilities();
if (clone(nullptr, nullptr, CLONE_FILES, nullptr) == -1) {
_exit(errno);
}
// crash_dump is ptracing both sides of the fork; it'll let the parent exit,
// but keep the orphan stopped to peek at its memory.
// There appears to be a bug in the kernel where our death causes SIGHUP to
// be sent to our process group if we exit while it has stopped jobs (e.g.
// because of wait_for_debugger). Use setsid to create a new process group to
// avoid hitting this.
setsid();
_exit(0);
}
int status;
if (TEMP_FAILURE_RETRY(waitpid(first, &status, __WCLONE)) != first) {
fatal_errno("failed to waitpid in double fork");
} else if (!WIFEXITED(status)) {
fatal("intermediate process didn't exit cleanly in double fork (status = %d)", status);
} else if (WEXITSTATUS(status)) {
fatal("second clone failed: %s", strerror(WEXITSTATUS(status)));
}
}
struct debugger_thread_info {
pid_t crashing_tid;
pid_t pseudothread_tid;
siginfo_t* siginfo;
void* ucontext;
debugger_process_info process_info;
};
// Logging and contacting debuggerd requires free file descriptors, which we might not have.
// Work around this by spawning a "thread" that shares its parent's address space, but not its file
// descriptor table, so that we can close random file descriptors without affecting the original
// process. Note that this doesn't go through pthread_create, so TLS is shared with the spawning
// process.
static void* pseudothread_stack;
static DebuggerdDumpType get_dump_type(const debugger_thread_info* thread_info) {
if (thread_info->siginfo->si_signo == BIONIC_SIGNAL_DEBUGGER &&
thread_info->siginfo->si_value.sival_int) {
return kDebuggerdNativeBacktrace;
}
return kDebuggerdTombstoneProto;
}
static int debuggerd_dispatch_pseudothread(void* arg) {
debugger_thread_info* thread_info = static_cast<debugger_thread_info*>(arg);
for (int i = 0; i < 1024; ++i) {
// Don't use close to avoid bionic's file descriptor ownership checks.
syscall(__NR_close, i);
}
int devnull = TEMP_FAILURE_RETRY(open("/dev/null", O_RDWR));
if (devnull == -1) {
fatal_errno("failed to open /dev/null");
} else if (devnull != 0) {
fatal_errno("expected /dev/null fd to be 0, actually %d", devnull);
}
// devnull will be 0.
TEMP_FAILURE_RETRY(dup2(devnull, 1));
TEMP_FAILURE_RETRY(dup2(devnull, 2));
unique_fd input_read, input_write;
unique_fd output_read, output_write;
if (!Pipe(&input_read, &input_write) != 0 || !Pipe(&output_read, &output_write)) {
fatal_errno("failed to create pipe");
}
uint32_t version;
ssize_t expected;
// ucontext_t is absurdly large on AArch64, so piece it together manually with writev.
struct iovec iovs[4] = {
{.iov_base = &version, .iov_len = sizeof(version)},
{.iov_base = thread_info->siginfo, .iov_len = sizeof(siginfo_t)},
{.iov_base = thread_info->ucontext, .iov_len = sizeof(ucontext_t)},
};
constexpr size_t kHeaderSize = sizeof(version) + sizeof(siginfo_t) + sizeof(ucontext_t);
if (thread_info->process_info.fdsan_table) {
// Dynamic executables always use version 4. There is no need to increment the version number if
// the format changes, because the sender (linker) and receiver (crash_dump) are version locked.
version = 4;
expected = sizeof(CrashInfoHeader) + sizeof(CrashInfoDataDynamic);
static_assert(sizeof(CrashInfoHeader) + sizeof(CrashInfoDataDynamic) ==
kHeaderSize + sizeof(thread_info->process_info),
"Wire protocol structs do not match the data sent.");
#define ASSERT_SAME_OFFSET(MEMBER1, MEMBER2) \
static_assert(sizeof(CrashInfoHeader) + offsetof(CrashInfoDataDynamic, MEMBER1) == \
kHeaderSize + offsetof(debugger_process_info, MEMBER2), \
"Wire protocol offset does not match data sent: " #MEMBER1);
ASSERT_SAME_OFFSET(fdsan_table_address, fdsan_table);
ASSERT_SAME_OFFSET(gwp_asan_state, gwp_asan_state);
ASSERT_SAME_OFFSET(gwp_asan_metadata, gwp_asan_metadata);
ASSERT_SAME_OFFSET(scudo_stack_depot, scudo_stack_depot);
ASSERT_SAME_OFFSET(scudo_region_info, scudo_region_info);
ASSERT_SAME_OFFSET(scudo_ring_buffer, scudo_ring_buffer);
ASSERT_SAME_OFFSET(scudo_ring_buffer_size, scudo_ring_buffer_size);
ASSERT_SAME_OFFSET(recoverable_gwp_asan_crash, recoverable_gwp_asan_crash);
#undef ASSERT_SAME_OFFSET
iovs[3] = {.iov_base = &thread_info->process_info,
.iov_len = sizeof(thread_info->process_info)};
} else {
// Static executables always use version 1.
version = 1;
expected = sizeof(CrashInfoHeader) + sizeof(CrashInfoDataStatic);
static_assert(
sizeof(CrashInfoHeader) + sizeof(CrashInfoDataStatic) == kHeaderSize + sizeof(uintptr_t),
"Wire protocol structs do not match the data sent.");
iovs[3] = {.iov_base = &thread_info->process_info.abort_msg, .iov_len = sizeof(uintptr_t)};
}
errno = 0;
if (fcntl(output_write.get(), F_SETPIPE_SZ, expected) < static_cast<int>(expected)) {
fatal_errno("failed to set pipe buffer size");
}
ssize_t rc = TEMP_FAILURE_RETRY(writev(output_write.get(), iovs, arraysize(iovs)));
if (rc == -1) {
fatal_errno("failed to write crash info");
} else if (rc != expected) {
fatal("failed to write crash info, wrote %zd bytes, expected %zd", rc, expected);
}
// Don't use fork(2) to avoid calling pthread_atfork handlers.
pid_t crash_dump_pid = __fork();
if (crash_dump_pid == -1) {
async_safe_format_log(ANDROID_LOG_FATAL, "libc",
"failed to fork in debuggerd signal handler: %s", strerror(errno));
} else if (crash_dump_pid == 0) {
TEMP_FAILURE_RETRY(dup2(input_write.get(), STDOUT_FILENO));
TEMP_FAILURE_RETRY(dup2(output_read.get(), STDIN_FILENO));
input_read.reset();
input_write.reset();
output_read.reset();
output_write.reset();
raise_caps();
char main_tid[10];
char pseudothread_tid[10];
char debuggerd_dump_type[10];
async_safe_format_buffer(main_tid, sizeof(main_tid), "%d", thread_info->crashing_tid);
async_safe_format_buffer(pseudothread_tid, sizeof(pseudothread_tid), "%d",
thread_info->pseudothread_tid);
async_safe_format_buffer(debuggerd_dump_type, sizeof(debuggerd_dump_type), "%d",
get_dump_type(thread_info));
execle(CRASH_DUMP_PATH, CRASH_DUMP_NAME, main_tid, pseudothread_tid, debuggerd_dump_type,
nullptr, nullptr);
async_safe_format_log(ANDROID_LOG_FATAL, "libc", "failed to exec crash_dump helper: %s",
strerror(errno));
return 1;
}
input_write.reset();
output_read.reset();
// crash_dump will ptrace and pause all of our threads, and then write to the pipe to tell
// us to fork off a process to read memory from.
char buf[4];
rc = TEMP_FAILURE_RETRY(read(input_read.get(), &buf, sizeof(buf)));
bool success = false;
if (rc == 1 && buf[0] == '\1') {
// crash_dump successfully started, and is ptracing us.
// Fork off a copy of our address space for it to use.
create_vm_process();
success = true;
} else {
// Something went wrong, log it.
if (rc == -1) {
async_safe_format_log(ANDROID_LOG_FATAL, "libc", "read of IPC pipe failed: %s",
strerror(errno));
} else if (rc == 0) {
async_safe_format_log(ANDROID_LOG_FATAL, "libc",
"crash_dump helper failed to exec, or was killed");
} else if (rc != 1) {
async_safe_format_log(ANDROID_LOG_FATAL, "libc",
"read of IPC pipe returned unexpected value: %zd", rc);
} else if (buf[0] != '\1') {
async_safe_format_log(ANDROID_LOG_FATAL, "libc", "crash_dump helper reported failure");
}
}
// Don't leave a zombie child.
int status;
if (TEMP_FAILURE_RETRY(waitpid(crash_dump_pid, &status, 0)) == -1) {
async_safe_format_log(ANDROID_LOG_FATAL, "libc", "failed to wait for crash_dump helper: %s",
strerror(errno));
} else if (WIFSTOPPED(status) || WIFSIGNALED(status)) {
async_safe_format_log(ANDROID_LOG_FATAL, "libc", "crash_dump helper crashed or stopped");
}
if (success) {
if (thread_info->siginfo->si_signo != BIONIC_SIGNAL_DEBUGGER) {
// For crashes, we don't need to minimize pause latency.
// Wait for the dump to complete before having the process exit, to avoid being murdered by
// ActivityManager or init.
TEMP_FAILURE_RETRY(read(input_read, &buf, sizeof(buf)));
}
}
return success ? 0 : 1;
}
static void resend_signal(siginfo_t* info) {
// Signals can either be fatal or nonfatal.
// For fatal signals, crash_dump will send us the signal we crashed with
// before resuming us, so that processes using waitpid on us will see that we
// exited with the correct exit status (e.g. so that sh will report
// "Segmentation fault" instead of "Killed"). For this to work, we need
// to deregister our signal handler for that signal before continuing.
if (info->si_signo != BIONIC_SIGNAL_DEBUGGER) {
signal(info->si_signo, SIG_DFL);
int rc = syscall(SYS_rt_tgsigqueueinfo, __getpid(), __gettid(), info->si_signo, info);
if (rc != 0) {
fatal_errno("failed to resend signal during crash");
}
}
}
// Handler that does crash dumping by forking and doing the processing in the child.
// Do this by ptracing the relevant thread, and then execing debuggerd to do the actual dump.
static void debuggerd_signal_handler(int signal_number, siginfo_t* info, void* context) {
// Make sure we don't change the value of errno, in case a signal comes in between the process
// making a syscall and checking errno.
ErrnoRestorer restorer;
auto *ucontext = static_cast<ucontext_t*>(context);
// It's possible somebody cleared the SA_SIGINFO flag, which would mean
// our "info" arg holds an undefined value.
if (!have_siginfo(signal_number)) {
info = nullptr;
}
struct siginfo dummy_info = {};
if (!info) {
memset(&dummy_info, 0, sizeof(dummy_info));
dummy_info.si_signo = signal_number;
dummy_info.si_code = SI_USER;
dummy_info.si_pid = __getpid();
dummy_info.si_uid = getuid();
info = &dummy_info;
} else if (info->si_code >= 0 || info->si_code == SI_TKILL) {
// rt_tgsigqueueinfo(2)'s documentation appears to be incorrect on kernels
// that contain commit 66dd34a (3.9+). The manpage claims to only allow
// negative si_code values that are not SI_TKILL, but 66dd34a changed the
// check to allow all si_code values in calls coming from inside the house.
}
debugger_process_info process_info = {};
uintptr_t si_val = reinterpret_cast<uintptr_t>(info->si_ptr);
if (signal_number == BIONIC_SIGNAL_DEBUGGER) {
if (info->si_code == SI_QUEUE && info->si_pid == __getpid()) {
// Allow for the abort message to be explicitly specified via the sigqueue value.
// Keep the bottom bit intact for representing whether we want a backtrace or a tombstone.
if (si_val != kDebuggerdFallbackSivalUintptrRequestDump) {
process_info.abort_msg = reinterpret_cast<void*>(si_val & ~1);
info->si_ptr = reinterpret_cast<void*>(si_val & 1);
}
}
} else if (g_callbacks.get_process_info) {
process_info = g_callbacks.get_process_info();
}
// GWP-ASan catches use-after-free and heap-buffer-overflow by using PROT_NONE
// guard pages, which lead to SEGV. Normally, debuggerd prints a bug report
// and the process terminates, but in some cases, we actually want to print
// the bug report and let the signal handler return, and restart the process.
// In order to do that, we need to disable GWP-ASan's guard pages. The
// following callbacks handle this case.
gwp_asan_callbacks_t gwp_asan_callbacks = g_callbacks.get_gwp_asan_callbacks();
if (signal_number == SIGSEGV && signal_has_si_addr(info) &&
gwp_asan_callbacks.debuggerd_needs_gwp_asan_recovery &&
gwp_asan_callbacks.debuggerd_gwp_asan_pre_crash_report &&
gwp_asan_callbacks.debuggerd_gwp_asan_post_crash_report &&
gwp_asan_callbacks.debuggerd_needs_gwp_asan_recovery(info->si_addr)) {
gwp_asan_callbacks.debuggerd_gwp_asan_pre_crash_report(info->si_addr);
process_info.recoverable_gwp_asan_crash = true;
}
// If sival_int is ~0, it means that the fallback handler has been called
// once before and this function is being called again to dump the stack
// of a specific thread. It is possible that the prctl call might return 1,
// then return 0 in subsequent calls, so check the sival_int to determine if
// the fallback handler should be called first.
bool no_new_privs = prctl(PR_GET_NO_NEW_PRIVS, 0, 0, 0, 0) == 1;
if (si_val == kDebuggerdFallbackSivalUintptrRequestDump || no_new_privs) {
// This check might be racy if another thread sets NO_NEW_PRIVS, but this should be unlikely,
// you can only set NO_NEW_PRIVS to 1, and the effect should be at worst a single missing
// ANR trace.
debuggerd_fallback_handler(info, ucontext, process_info.abort_msg);
if (no_new_privs && process_info.recoverable_gwp_asan_crash) {
gwp_asan_callbacks.debuggerd_gwp_asan_post_crash_report(info->si_addr);
return;
}
resend_signal(info);
return;
}
// Only allow one thread to handle a signal at a time.
int ret = pthread_mutex_lock(&crash_mutex);
if (ret != 0) {
async_safe_format_log(ANDROID_LOG_INFO, "libc", "pthread_mutex_lock failed: %s", strerror(ret));
return;
}
log_signal_summary(info);
// If we got here due to the signal BIONIC_SIGNAL_DEBUGGER, it's possible
// this is not the main thread, which can cause the intercept logic to fail
// since the intercept is only looking for the main thread. In this case,
// setting crashing_tid to pid instead of the current thread's tid avoids
// the problem.
debugger_thread_info thread_info = {
.crashing_tid = (signal_number == BIONIC_SIGNAL_DEBUGGER) ? __getpid() : __gettid(),
.pseudothread_tid = -1,
.siginfo = info,
.ucontext = context,
.process_info = process_info,
};
// Set PR_SET_DUMPABLE to 1, so that crash_dump can ptrace us.
int orig_dumpable = prctl(PR_GET_DUMPABLE);
if (prctl(PR_SET_DUMPABLE, 1) != 0) {
fatal_errno("failed to set dumpable");
}
// On kernels with yama_ptrace enabled, also allow any process to attach.
bool restore_orig_ptracer = true;
if (prctl(PR_SET_PTRACER, PR_SET_PTRACER_ANY) != 0) {
if (errno == EINVAL) {
// This kernel does not support PR_SET_PTRACER_ANY, or Yama is not enabled.
restore_orig_ptracer = false;
} else {
fatal_errno("failed to set traceable");
}
}
// Essentially pthread_create without CLONE_FILES, so we still work during file descriptor
// exhaustion.
pid_t child_pid =
clone(debuggerd_dispatch_pseudothread, pseudothread_stack,
CLONE_THREAD | CLONE_SIGHAND | CLONE_VM | CLONE_CHILD_SETTID | CLONE_CHILD_CLEARTID,
&thread_info, nullptr, nullptr, &thread_info.pseudothread_tid);
if (child_pid == -1) {
fatal_errno("failed to spawn debuggerd dispatch thread");
}
// Wait for the child to start...
futex_wait(&thread_info.pseudothread_tid, -1);
// and then wait for it to terminate.
futex_wait(&thread_info.pseudothread_tid, child_pid);
// Restore PR_SET_DUMPABLE to its original value.
if (prctl(PR_SET_DUMPABLE, orig_dumpable) != 0) {
fatal_errno("failed to restore dumpable");
}
// Restore PR_SET_PTRACER to its original value.
if (restore_orig_ptracer && prctl(PR_SET_PTRACER, 0) != 0) {
fatal_errno("failed to restore traceable");
}
if (info->si_signo == BIONIC_SIGNAL_DEBUGGER) {
// If the signal is fatal, don't unlock the mutex to prevent other crashing threads from
// starting to dump right before our death.
pthread_mutex_unlock(&crash_mutex);
} else if (process_info.recoverable_gwp_asan_crash) {
gwp_asan_callbacks.debuggerd_gwp_asan_post_crash_report(info->si_addr);
pthread_mutex_unlock(&crash_mutex);
}
#ifdef __aarch64__
else if (info->si_signo == SIGSEGV &&
(info->si_code == SEGV_MTESERR || info->si_code == SEGV_MTEAERR) &&
is_permissive_mte()) {
// If we are in permissive MTE mode, we do not crash, but instead disable MTE on this thread,
// and then let the failing instruction be retried. The second time should work (except
// if there is another non-MTE fault).
int tagged_addr_ctrl = prctl(PR_GET_TAGGED_ADDR_CTRL, 0, 0, 0, 0);
if (tagged_addr_ctrl < 0) {
fatal_errno("failed to PR_GET_TAGGED_ADDR_CTRL");
}
tagged_addr_ctrl = (tagged_addr_ctrl & ~PR_MTE_TCF_MASK) | PR_MTE_TCF_NONE;
if (prctl(PR_SET_TAGGED_ADDR_CTRL, tagged_addr_ctrl, 0, 0, 0) < 0) {
fatal_errno("failed to PR_SET_TAGGED_ADDR_CTRL");
}
async_safe_format_log(ANDROID_LOG_ERROR, "libc",
"MTE ERROR DETECTED BUT RUNNING IN PERMISSIVE MODE. CONTINUING.");
pthread_mutex_unlock(&crash_mutex);
} else if (info->si_signo == SIGSEGV && info->si_code == SEGV_MTEAERR && getppid() == 1) {
// Back channel to init (see system/core/init/service.cpp) to signal that
// this process crashed due to an ASYNC MTE fault and should be considered
// for upgrade to SYNC mode. We are re-using the ART profiler signal, which
// is always handled (ignored in native processes, handled for generating a
// dump in ART processes), so a process will never crash from this signal
// except from here.
// The kernel is not particularly receptive to adding this information:
// https://lore.kernel.org/all/20220909180617.374238-1-fmayer@google.com/, so we work around
// like this.
info->si_signo = BIONIC_SIGNAL_ART_PROFILER;
resend_signal(info);
}
#endif
else {
// Resend the signal, so that either the debugger or the parent's waitpid sees it.
resend_signal(info);
}
}
void debuggerd_init(debuggerd_callbacks_t* callbacks) {
if (callbacks) {
g_callbacks = *callbacks;
}
size_t thread_stack_pages = 8;
void* thread_stack_allocation = mmap(nullptr, PAGE_SIZE * (thread_stack_pages + 2), PROT_NONE,
MAP_ANONYMOUS | MAP_PRIVATE, -1, 0);
if (thread_stack_allocation == MAP_FAILED) {
fatal_errno("failed to allocate debuggerd thread stack");
}
char* stack = static_cast<char*>(thread_stack_allocation) + PAGE_SIZE;
if (mprotect(stack, PAGE_SIZE * thread_stack_pages, PROT_READ | PROT_WRITE) != 0) {
fatal_errno("failed to mprotect debuggerd thread stack");
}
// Stack grows negatively, set it to the last byte in the page...
stack = (stack + thread_stack_pages * PAGE_SIZE - 1);
// and align it.
stack -= 15;
pseudothread_stack = stack;
struct sigaction action;
memset(&action, 0, sizeof(action));
sigfillset(&action.sa_mask);
action.sa_sigaction = debuggerd_signal_handler;
action.sa_flags = SA_RESTART | SA_SIGINFO;
// Use the alternate signal stack if available so we can catch stack overflows.
action.sa_flags |= SA_ONSTACK;
#define SA_EXPOSE_TAGBITS 0x00000800
// Request that the kernel set tag bits in the fault address. This is necessary for diagnosing MTE
// faults.
action.sa_flags |= SA_EXPOSE_TAGBITS;
debuggerd_register_handlers(&action);
}
// When debuggerd's signal handler is the first handler called, it's great at
// handling the recoverable GWP-ASan mode. For apps, sigchain (from libart) is
// always the first signal handler, and so the following function is what
// sigchain must call before processing the signal. This allows for processing
// of a potentially recoverable GWP-ASan crash. If the signal requires GWP-ASan
// recovery, then dump a report (via the regular debuggerd hanndler), and patch
// up the allocator, and allow the process to continue (indicated by returning
// 'true'). If the crash has nothing to do with GWP-ASan, or recovery isn't
// possible, return 'false'.
bool debuggerd_handle_signal(int signal_number, siginfo_t* info, void* context) {
if (signal_number != SIGSEGV || !signal_has_si_addr(info)) return false;
gwp_asan_callbacks_t gwp_asan_callbacks = g_callbacks.get_gwp_asan_callbacks();
if (gwp_asan_callbacks.debuggerd_needs_gwp_asan_recovery == nullptr ||
gwp_asan_callbacks.debuggerd_gwp_asan_pre_crash_report == nullptr ||
gwp_asan_callbacks.debuggerd_gwp_asan_post_crash_report == nullptr ||
!gwp_asan_callbacks.debuggerd_needs_gwp_asan_recovery(info->si_addr)) {
return false;
}
// Only dump a crash report for the first GWP-ASan crash. ActivityManager
// doesn't like it when an app crashes multiple times, and is even more strict
// about an app crashing multiple times in a short time period. While the app
// won't crash fully when we do GWP-ASan recovery, ActivityManager still gets
// the information about the crash through the DropBoxManager service. If an
// app has multiple back-to-back GWP-ASan crashes, this would lead to the app
// being killed, which defeats the purpose of having the recoverable mode. To
// mitigate against this, only generate a debuggerd crash report for the first
// GWP-ASan crash encountered. We still need to do the patching up of the
// allocator though, so do that.
static pthread_mutex_t first_crash_mutex = PTHREAD_MUTEX_INITIALIZER;
pthread_mutex_lock(&first_crash_mutex);
static bool first_crash = true;
if (first_crash) {
// `debuggerd_signal_handler` will call
// `debuggerd_gwp_asan_(pre|post)_crash_report`, so no need to manually call
// them here.
debuggerd_signal_handler(signal_number, info, context);
first_crash = false;
} else {
gwp_asan_callbacks.debuggerd_gwp_asan_pre_crash_report(info->si_addr);
gwp_asan_callbacks.debuggerd_gwp_asan_post_crash_report(info->si_addr);
}
pthread_mutex_unlock(&first_crash_mutex);
return true;
}
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