/* * 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 #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include #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; // 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(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 function 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 bool parse_uint_with_error_reporting(const char* s, const char* name, int* v) { if (android::base::ParseInt(s, v) && *v >= 0) { return true; } async_safe_format_log(ANDROID_LOG_ERROR, "libc", "invalid %s: %s", name, s); return false; } // We cannot use base::GetIntProperty, because that internally uses // std::string, which allocates. static bool property_parse_int(const char* name, int* out) { const prop_info* pi = __system_property_find(name); if (!pi) return false; struct cookie_t { int* out; bool empty; } cookie{out, true}; __system_property_read_callback( pi, [](void* raw_cookie, const char* name, const char* value, uint32_t) { // Property is set to empty value, ignoring. if (!*value) return; cookie_t* cookie = reinterpret_cast(raw_cookie); if (parse_uint_with_error_reporting(value, name, cookie->out)) cookie->empty = false; }, &cookie); return !cookie.empty; } static int permissive_mte_renable_timer() { if (char* env = getenv("MTE_PERMISSIVE_REENABLE_TIME_CPUMS")) { int v; if (parse_uint_with_error_reporting(env, "MTE_PERMISSIVE_REENABLE_TIME_CPUMS", &v)) return v; } char process_sysprop_name[512]; async_safe_format_buffer(process_sysprop_name, sizeof(process_sysprop_name), "persist.sys.mte.permissive_reenable_timer.process.%s", getprogname()); int v; if (property_parse_int(process_sysprop_name, &v)) return v; if (property_parse_int("persist.sys.mte.permissive_reenable_timer.default", &v)) return v; char process_deviceconf_sysprop_name[512]; async_safe_format_buffer( process_deviceconf_sysprop_name, sizeof(process_deviceconf_sysprop_name), "persist.device_config.memory_safety_native.permissive_reenable_timer.process.%s", getprogname()); if (property_parse_int(process_deviceconf_sysprop_name, &v)) return v; if (property_parse_int( "persist.device_config.memory_safety_native.permissive_reenable_timer.default", &v)) return v; return 0; } 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, "", 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(thread_name), 0, 0, 0) != 0) { strcpy(thread_name, ""); } 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(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)); } } } } // 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 const char* get_unwind_type(const debugger_thread_info* thread_info) { if (thread_info->siginfo->si_signo == BIONIC_SIGNAL_DEBUGGER) { return "Unwind request"; } return "Crash due to signal"; } static int debuggerd_dispatch_pseudothread(void* arg) { debugger_thread_info* thread_info = static_cast(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(scudo_stack_depot_size, scudo_stack_depot_size); ASSERT_SAME_OFFSET(recoverable_crash, recoverable_crash); ASSERT_SAME_OFFSET(crash_detail_page, crash_detail_page); #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(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", "%s: failed to exec crash_dump helper: %s", get_unwind_type(thread_info), 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", "%s: read of IPC pipe failed: %s", get_unwind_type(thread_info), strerror(errno)); } else if (rc == 0) { async_safe_format_log(ANDROID_LOG_FATAL, "libc", "%s: crash_dump helper failed to exec, or was killed", get_unwind_type(thread_info)); } else if (rc != 1) { async_safe_format_log(ANDROID_LOG_FATAL, "libc", "%s: read of IPC pipe returned unexpected value: %zd", get_unwind_type(thread_info), rc); } else if (buf[0] != '\1') { async_safe_format_log(ANDROID_LOG_FATAL, "libc", "%s: crash_dump helper reported failure", get_unwind_type(thread_info)); } } // 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", "%s: failed to wait for crash_dump helper: %s", get_unwind_type(thread_info), strerror(errno)); } else if (WIFSTOPPED(status) || WIFSIGNALED(status)) { async_safe_format_log(ANDROID_LOG_FATAL, "libc", "%s: crash_dump helper crashed or stopped", get_unwind_type(thread_info)); } 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(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 = {}; if (g_callbacks.get_process_info) { process_info = g_callbacks.get_process_info(); } uintptr_t si_val = reinterpret_cast(info->si_ptr); if (signal_number == BIONIC_SIGNAL_DEBUGGER) { // Applications can set abort messages via android_set_abort_message without // actually aborting; ignore those messages in non-fatal dumps. process_info.abort_msg = nullptr; 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(si_val & ~1); info->si_ptr = reinterpret_cast(si_val & 1); } } } gwp_asan_callbacks_t gwp_asan_callbacks = {}; bool recoverable_gwp_asan_crash = false; if (g_callbacks.get_gwp_asan_callbacks != nullptr) { // 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 = 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); recoverable_gwp_asan_crash = true; process_info.recoverable_crash = true; } } if (info->si_signo == SIGSEGV && (info->si_code == SEGV_MTESERR || info->si_code == SEGV_MTEAERR) && is_permissive_mte()) { process_info.recoverable_crash = true; // 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"); } int previous = tagged_addr_ctrl & PR_MTE_TCF_MASK; 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"); } if (int reenable_timer = permissive_mte_renable_timer()) { async_safe_format_log(ANDROID_LOG_ERROR, "libc", "MTE ERROR DETECTED BUT RUNNING IN PERMISSIVE MODE. CONTINUING WITH " "MTE DISABLED FOR %d MS OF CPU TIME.", reenable_timer); timer_t timerid{}; struct sigevent sev {}; sev.sigev_signo = BIONIC_ENABLE_MTE; sev.sigev_notify = SIGEV_THREAD_ID; sev.sigev_value.sival_int = previous; sev.sigev_notify_thread_id = __gettid(); // This MUST be CLOCK_THREAD_CPUTIME_ID. If we used CLOCK_MONOTONIC we could get stuck // in an endless loop of re-running the same instruction, calling this signal handler, // and re-enabling MTE before we had a chance to re-run the instruction. if (timer_create(CLOCK_THREAD_CPUTIME_ID, &sev, &timerid) == -1) { fatal_errno("timer_create() failed"); } struct itimerspec its {}; its.it_value.tv_sec = reenable_timer / 1000; its.it_value.tv_nsec = (reenable_timer % 1000) * 1000000; if (timer_settime(timerid, 0, &its, nullptr) == -1) { fatal_errno("timer_settime() failed"); } } else { async_safe_format_log( ANDROID_LOG_ERROR, "libc", "MTE ERROR DETECTED BUT RUNNING IN PERMISSIVE MODE. CONTINUING WITH MTE DISABLED."); } pthread_mutex_unlock(&crash_mutex); } // 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 && 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_crash) { if (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_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, getpagesize() * (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(thread_stack_allocation) + getpagesize(); if (mprotect(stack, getpagesize() * 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 * getpagesize() - 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; // 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); } bool debuggerd_handle_gwp_asan_signal(int signal_number, siginfo_t* info, void* context) { if (g_callbacks.get_gwp_asan_callbacks == nullptr) 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; } // When debuggerd's signal handler is the first handler called, it's great at // handling the recoverable GWP-ASan and permissive MTE modes. 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 or MTE // crash. If the signal requires recovery, then dump a report (via the regular // debuggerd hanndler), and patch up the allocator (in the case of GWP-ASan) or // disable MTE on the thread, and allow the process to continue (indicated by // returning 'true'). If the crash has nothing to do with GWP-ASan/MTE, or // recovery isn't possible, return 'false'. bool debuggerd_handle_signal(int signal_number, siginfo_t* info, void* context) { if (signal_number != SIGSEGV) return false; if (info->si_code == SEGV_MTEAERR || info->si_code == SEGV_MTESERR) { if (!is_permissive_mte()) return false; // Because permissive MTE disables MTE for the entire thread, we're less // worried about getting a whole bunch of crashes in a row. ActivityManager // doesn't like multiple native crashes for an app in a short period of time // (see the comment about recoverable GWP-ASan in // `debuggerd_handle_gwp_asan_signal`), but that shouldn't happen if MTE is // disabled for the entire thread. This might need to be changed if there's // some low-hanging bug that happens across multiple threads in quick // succession. debuggerd_signal_handler(signal_number, info, context); return true; } if (!signal_has_si_addr(info)) return false; return debuggerd_handle_gwp_asan_signal(signal_number, info, context); }