diff options
Diffstat (limited to 'lib/sanitizer_common/sanitizer_stoptheworld_linux_libcdep.cpp')
| -rw-r--r-- | lib/sanitizer_common/sanitizer_stoptheworld_linux_libcdep.cpp | 573 |
1 files changed, 573 insertions, 0 deletions
diff --git a/lib/sanitizer_common/sanitizer_stoptheworld_linux_libcdep.cpp b/lib/sanitizer_common/sanitizer_stoptheworld_linux_libcdep.cpp new file mode 100644 index 000000000000..651d5056dd9d --- /dev/null +++ b/lib/sanitizer_common/sanitizer_stoptheworld_linux_libcdep.cpp @@ -0,0 +1,573 @@ +//===-- sanitizer_stoptheworld_linux_libcdep.cpp --------------------------===// +// +// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions. +// See https://llvm.org/LICENSE.txt for license information. +// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception +// +//===----------------------------------------------------------------------===// +// +// See sanitizer_stoptheworld.h for details. +// This implementation was inspired by Markus Gutschke's linuxthreads.cc. +// +//===----------------------------------------------------------------------===// + +#include "sanitizer_platform.h" + +#if SANITIZER_LINUX && (defined(__x86_64__) || defined(__mips__) || \ + defined(__aarch64__) || defined(__powerpc64__) || \ + defined(__s390__) || defined(__i386__) || \ + defined(__arm__)) + +#include "sanitizer_stoptheworld.h" + +#include "sanitizer_platform_limits_posix.h" +#include "sanitizer_atomic.h" + +#include <errno.h> +#include <sched.h> // for CLONE_* definitions +#include <stddef.h> +#include <sys/prctl.h> // for PR_* definitions +#include <sys/ptrace.h> // for PTRACE_* definitions +#include <sys/types.h> // for pid_t +#include <sys/uio.h> // for iovec +#include <elf.h> // for NT_PRSTATUS +#if defined(__aarch64__) && !SANITIZER_ANDROID +// GLIBC 2.20+ sys/user does not include asm/ptrace.h +# include <asm/ptrace.h> +#endif +#include <sys/user.h> // for user_regs_struct +#if SANITIZER_ANDROID && SANITIZER_MIPS +# include <asm/reg.h> // for mips SP register in sys/user.h +#endif +#include <sys/wait.h> // for signal-related stuff + +#ifdef sa_handler +# undef sa_handler +#endif + +#ifdef sa_sigaction +# undef sa_sigaction +#endif + +#include "sanitizer_common.h" +#include "sanitizer_flags.h" +#include "sanitizer_libc.h" +#include "sanitizer_linux.h" +#include "sanitizer_mutex.h" +#include "sanitizer_placement_new.h" + +// Sufficiently old kernel headers don't provide this value, but we can still +// call prctl with it. If the runtime kernel is new enough, the prctl call will +// have the desired effect; if the kernel is too old, the call will error and we +// can ignore said error. +#ifndef PR_SET_PTRACER +#define PR_SET_PTRACER 0x59616d61 +#endif + +// This module works by spawning a Linux task which then attaches to every +// thread in the caller process with ptrace. This suspends the threads, and +// PTRACE_GETREGS can then be used to obtain their register state. The callback +// supplied to StopTheWorld() is run in the tracer task while the threads are +// suspended. +// The tracer task must be placed in a different thread group for ptrace to +// work, so it cannot be spawned as a pthread. Instead, we use the low-level +// clone() interface (we want to share the address space with the caller +// process, so we prefer clone() over fork()). +// +// We don't use any libc functions, relying instead on direct syscalls. There +// are two reasons for this: +// 1. calling a library function while threads are suspended could cause a +// deadlock, if one of the treads happens to be holding a libc lock; +// 2. it's generally not safe to call libc functions from the tracer task, +// because clone() does not set up a thread-local storage for it. Any +// thread-local variables used by libc will be shared between the tracer task +// and the thread which spawned it. + +namespace __sanitizer { + +class SuspendedThreadsListLinux : public SuspendedThreadsList { + public: + SuspendedThreadsListLinux() { thread_ids_.reserve(1024); } + + tid_t GetThreadID(uptr index) const; + uptr ThreadCount() const; + bool ContainsTid(tid_t thread_id) const; + void Append(tid_t tid); + + PtraceRegistersStatus GetRegistersAndSP(uptr index, uptr *buffer, + uptr *sp) const; + uptr RegisterCount() const; + + private: + InternalMmapVector<tid_t> thread_ids_; +}; + +// Structure for passing arguments into the tracer thread. +struct TracerThreadArgument { + StopTheWorldCallback callback; + void *callback_argument; + // The tracer thread waits on this mutex while the parent finishes its + // preparations. + BlockingMutex mutex; + // Tracer thread signals its completion by setting done. + atomic_uintptr_t done; + uptr parent_pid; +}; + +// This class handles thread suspending/unsuspending in the tracer thread. +class ThreadSuspender { + public: + explicit ThreadSuspender(pid_t pid, TracerThreadArgument *arg) + : arg(arg) + , pid_(pid) { + CHECK_GE(pid, 0); + } + bool SuspendAllThreads(); + void ResumeAllThreads(); + void KillAllThreads(); + SuspendedThreadsListLinux &suspended_threads_list() { + return suspended_threads_list_; + } + TracerThreadArgument *arg; + private: + SuspendedThreadsListLinux suspended_threads_list_; + pid_t pid_; + bool SuspendThread(tid_t thread_id); +}; + +bool ThreadSuspender::SuspendThread(tid_t tid) { + // Are we already attached to this thread? + // Currently this check takes linear time, however the number of threads is + // usually small. + if (suspended_threads_list_.ContainsTid(tid)) return false; + int pterrno; + if (internal_iserror(internal_ptrace(PTRACE_ATTACH, tid, nullptr, nullptr), + &pterrno)) { + // Either the thread is dead, or something prevented us from attaching. + // Log this event and move on. + VReport(1, "Could not attach to thread %zu (errno %d).\n", (uptr)tid, + pterrno); + return false; + } else { + VReport(2, "Attached to thread %zu.\n", (uptr)tid); + // The thread is not guaranteed to stop before ptrace returns, so we must + // wait on it. Note: if the thread receives a signal concurrently, + // we can get notification about the signal before notification about stop. + // In such case we need to forward the signal to the thread, otherwise + // the signal will be missed (as we do PTRACE_DETACH with arg=0) and + // any logic relying on signals will break. After forwarding we need to + // continue to wait for stopping, because the thread is not stopped yet. + // We do ignore delivery of SIGSTOP, because we want to make stop-the-world + // as invisible as possible. + for (;;) { + int status; + uptr waitpid_status; + HANDLE_EINTR(waitpid_status, internal_waitpid(tid, &status, __WALL)); + int wperrno; + if (internal_iserror(waitpid_status, &wperrno)) { + // Got a ECHILD error. I don't think this situation is possible, but it + // doesn't hurt to report it. + VReport(1, "Waiting on thread %zu failed, detaching (errno %d).\n", + (uptr)tid, wperrno); + internal_ptrace(PTRACE_DETACH, tid, nullptr, nullptr); + return false; + } + if (WIFSTOPPED(status) && WSTOPSIG(status) != SIGSTOP) { + internal_ptrace(PTRACE_CONT, tid, nullptr, + (void*)(uptr)WSTOPSIG(status)); + continue; + } + break; + } + suspended_threads_list_.Append(tid); + return true; + } +} + +void ThreadSuspender::ResumeAllThreads() { + for (uptr i = 0; i < suspended_threads_list_.ThreadCount(); i++) { + pid_t tid = suspended_threads_list_.GetThreadID(i); + int pterrno; + if (!internal_iserror(internal_ptrace(PTRACE_DETACH, tid, nullptr, nullptr), + &pterrno)) { + VReport(2, "Detached from thread %d.\n", tid); + } else { + // Either the thread is dead, or we are already detached. + // The latter case is possible, for instance, if this function was called + // from a signal handler. + VReport(1, "Could not detach from thread %d (errno %d).\n", tid, pterrno); + } + } +} + +void ThreadSuspender::KillAllThreads() { + for (uptr i = 0; i < suspended_threads_list_.ThreadCount(); i++) + internal_ptrace(PTRACE_KILL, suspended_threads_list_.GetThreadID(i), + nullptr, nullptr); +} + +bool ThreadSuspender::SuspendAllThreads() { + ThreadLister thread_lister(pid_); + bool retry = true; + InternalMmapVector<tid_t> threads; + threads.reserve(128); + for (int i = 0; i < 30 && retry; ++i) { + retry = false; + switch (thread_lister.ListThreads(&threads)) { + case ThreadLister::Error: + ResumeAllThreads(); + return false; + case ThreadLister::Incomplete: + retry = true; + break; + case ThreadLister::Ok: + break; + } + for (tid_t tid : threads) { + if (SuspendThread(tid)) + retry = true; + } + } + return suspended_threads_list_.ThreadCount(); +} + +// Pointer to the ThreadSuspender instance for use in signal handler. +static ThreadSuspender *thread_suspender_instance = nullptr; + +// Synchronous signals that should not be blocked. +static const int kSyncSignals[] = { SIGABRT, SIGILL, SIGFPE, SIGSEGV, SIGBUS, + SIGXCPU, SIGXFSZ }; + +static void TracerThreadDieCallback() { + // Generally a call to Die() in the tracer thread should be fatal to the + // parent process as well, because they share the address space. + // This really only works correctly if all the threads are suspended at this + // point. So we correctly handle calls to Die() from within the callback, but + // not those that happen before or after the callback. Hopefully there aren't + // a lot of opportunities for that to happen... + ThreadSuspender *inst = thread_suspender_instance; + if (inst && stoptheworld_tracer_pid == internal_getpid()) { + inst->KillAllThreads(); + thread_suspender_instance = nullptr; + } +} + +// Signal handler to wake up suspended threads when the tracer thread dies. +static void TracerThreadSignalHandler(int signum, __sanitizer_siginfo *siginfo, + void *uctx) { + SignalContext ctx(siginfo, uctx); + Printf("Tracer caught signal %d: addr=0x%zx pc=0x%zx sp=0x%zx\n", signum, + ctx.addr, ctx.pc, ctx.sp); + ThreadSuspender *inst = thread_suspender_instance; + if (inst) { + if (signum == SIGABRT) + inst->KillAllThreads(); + else + inst->ResumeAllThreads(); + RAW_CHECK(RemoveDieCallback(TracerThreadDieCallback)); + thread_suspender_instance = nullptr; + atomic_store(&inst->arg->done, 1, memory_order_relaxed); + } + internal__exit((signum == SIGABRT) ? 1 : 2); +} + +// Size of alternative stack for signal handlers in the tracer thread. +static const int kHandlerStackSize = 8192; + +// This function will be run as a cloned task. +static int TracerThread(void* argument) { + TracerThreadArgument *tracer_thread_argument = + (TracerThreadArgument *)argument; + + internal_prctl(PR_SET_PDEATHSIG, SIGKILL, 0, 0, 0); + // Check if parent is already dead. + if (internal_getppid() != tracer_thread_argument->parent_pid) + internal__exit(4); + + // Wait for the parent thread to finish preparations. + tracer_thread_argument->mutex.Lock(); + tracer_thread_argument->mutex.Unlock(); + + RAW_CHECK(AddDieCallback(TracerThreadDieCallback)); + + ThreadSuspender thread_suspender(internal_getppid(), tracer_thread_argument); + // Global pointer for the signal handler. + thread_suspender_instance = &thread_suspender; + + // Alternate stack for signal handling. + InternalMmapVector<char> handler_stack_memory(kHandlerStackSize); + stack_t handler_stack; + internal_memset(&handler_stack, 0, sizeof(handler_stack)); + handler_stack.ss_sp = handler_stack_memory.data(); + handler_stack.ss_size = kHandlerStackSize; + internal_sigaltstack(&handler_stack, nullptr); + + // Install our handler for synchronous signals. Other signals should be + // blocked by the mask we inherited from the parent thread. + for (uptr i = 0; i < ARRAY_SIZE(kSyncSignals); i++) { + __sanitizer_sigaction act; + internal_memset(&act, 0, sizeof(act)); + act.sigaction = TracerThreadSignalHandler; + act.sa_flags = SA_ONSTACK | SA_SIGINFO; + internal_sigaction_norestorer(kSyncSignals[i], &act, 0); + } + + int exit_code = 0; + if (!thread_suspender.SuspendAllThreads()) { + VReport(1, "Failed suspending threads.\n"); + exit_code = 3; + } else { + tracer_thread_argument->callback(thread_suspender.suspended_threads_list(), + tracer_thread_argument->callback_argument); + thread_suspender.ResumeAllThreads(); + exit_code = 0; + } + RAW_CHECK(RemoveDieCallback(TracerThreadDieCallback)); + thread_suspender_instance = nullptr; + atomic_store(&tracer_thread_argument->done, 1, memory_order_relaxed); + return exit_code; +} + +class ScopedStackSpaceWithGuard { + public: + explicit ScopedStackSpaceWithGuard(uptr stack_size) { + stack_size_ = stack_size; + guard_size_ = GetPageSizeCached(); + // FIXME: Omitting MAP_STACK here works in current kernels but might break + // in the future. + guard_start_ = (uptr)MmapOrDie(stack_size_ + guard_size_, + "ScopedStackWithGuard"); + CHECK(MprotectNoAccess((uptr)guard_start_, guard_size_)); + } + ~ScopedStackSpaceWithGuard() { + UnmapOrDie((void *)guard_start_, stack_size_ + guard_size_); + } + void *Bottom() const { + return (void *)(guard_start_ + stack_size_ + guard_size_); + } + + private: + uptr stack_size_; + uptr guard_size_; + uptr guard_start_; +}; + +// We have a limitation on the stack frame size, so some stuff had to be moved +// into globals. +static __sanitizer_sigset_t blocked_sigset; +static __sanitizer_sigset_t old_sigset; + +class StopTheWorldScope { + public: + StopTheWorldScope() { + // Make this process dumpable. Processes that are not dumpable cannot be + // attached to. + process_was_dumpable_ = internal_prctl(PR_GET_DUMPABLE, 0, 0, 0, 0); + if (!process_was_dumpable_) + internal_prctl(PR_SET_DUMPABLE, 1, 0, 0, 0); + } + + ~StopTheWorldScope() { + // Restore the dumpable flag. + if (!process_was_dumpable_) + internal_prctl(PR_SET_DUMPABLE, 0, 0, 0, 0); + } + + private: + int process_was_dumpable_; +}; + +// When sanitizer output is being redirected to file (i.e. by using log_path), +// the tracer should write to the parent's log instead of trying to open a new +// file. Alert the logging code to the fact that we have a tracer. +struct ScopedSetTracerPID { + explicit ScopedSetTracerPID(uptr tracer_pid) { + stoptheworld_tracer_pid = tracer_pid; + stoptheworld_tracer_ppid = internal_getpid(); + } + ~ScopedSetTracerPID() { + stoptheworld_tracer_pid = 0; + stoptheworld_tracer_ppid = 0; + } +}; + +void StopTheWorld(StopTheWorldCallback callback, void *argument) { + StopTheWorldScope in_stoptheworld; + // Prepare the arguments for TracerThread. + struct TracerThreadArgument tracer_thread_argument; + tracer_thread_argument.callback = callback; + tracer_thread_argument.callback_argument = argument; + tracer_thread_argument.parent_pid = internal_getpid(); + atomic_store(&tracer_thread_argument.done, 0, memory_order_relaxed); + const uptr kTracerStackSize = 2 * 1024 * 1024; + ScopedStackSpaceWithGuard tracer_stack(kTracerStackSize); + // Block the execution of TracerThread until after we have set ptrace + // permissions. + tracer_thread_argument.mutex.Lock(); + // Signal handling story. + // We don't want async signals to be delivered to the tracer thread, + // so we block all async signals before creating the thread. An async signal + // handler can temporary modify errno, which is shared with this thread. + // We ought to use pthread_sigmask here, because sigprocmask has undefined + // behavior in multithreaded programs. However, on linux sigprocmask is + // equivalent to pthread_sigmask with the exception that pthread_sigmask + // does not allow to block some signals used internally in pthread + // implementation. We are fine with blocking them here, we are really not + // going to pthread_cancel the thread. + // The tracer thread should not raise any synchronous signals. But in case it + // does, we setup a special handler for sync signals that properly kills the + // parent as well. Note: we don't pass CLONE_SIGHAND to clone, so handlers + // in the tracer thread won't interfere with user program. Double note: if a + // user does something along the lines of 'kill -11 pid', that can kill the + // process even if user setup own handler for SEGV. + // Thing to watch out for: this code should not change behavior of user code + // in any observable way. In particular it should not override user signal + // handlers. + internal_sigfillset(&blocked_sigset); + for (uptr i = 0; i < ARRAY_SIZE(kSyncSignals); i++) + internal_sigdelset(&blocked_sigset, kSyncSignals[i]); + int rv = internal_sigprocmask(SIG_BLOCK, &blocked_sigset, &old_sigset); + CHECK_EQ(rv, 0); + uptr tracer_pid = internal_clone( + TracerThread, tracer_stack.Bottom(), + CLONE_VM | CLONE_FS | CLONE_FILES | CLONE_UNTRACED, + &tracer_thread_argument, nullptr /* parent_tidptr */, + nullptr /* newtls */, nullptr /* child_tidptr */); + internal_sigprocmask(SIG_SETMASK, &old_sigset, 0); + int local_errno = 0; + if (internal_iserror(tracer_pid, &local_errno)) { + VReport(1, "Failed spawning a tracer thread (errno %d).\n", local_errno); + tracer_thread_argument.mutex.Unlock(); + } else { + ScopedSetTracerPID scoped_set_tracer_pid(tracer_pid); + // On some systems we have to explicitly declare that we want to be traced + // by the tracer thread. + internal_prctl(PR_SET_PTRACER, tracer_pid, 0, 0, 0); + // Allow the tracer thread to start. + tracer_thread_argument.mutex.Unlock(); + // NOTE: errno is shared between this thread and the tracer thread. + // internal_waitpid() may call syscall() which can access/spoil errno, + // so we can't call it now. Instead we for the tracer thread to finish using + // the spin loop below. Man page for sched_yield() says "In the Linux + // implementation, sched_yield() always succeeds", so let's hope it does not + // spoil errno. Note that this spin loop runs only for brief periods before + // the tracer thread has suspended us and when it starts unblocking threads. + while (atomic_load(&tracer_thread_argument.done, memory_order_relaxed) == 0) + sched_yield(); + // Now the tracer thread is about to exit and does not touch errno, + // wait for it. + for (;;) { + uptr waitpid_status = internal_waitpid(tracer_pid, nullptr, __WALL); + if (!internal_iserror(waitpid_status, &local_errno)) + break; + if (local_errno == EINTR) + continue; + VReport(1, "Waiting on the tracer thread failed (errno %d).\n", + local_errno); + break; + } + } +} + +// Platform-specific methods from SuspendedThreadsList. +#if SANITIZER_ANDROID && defined(__arm__) +typedef pt_regs regs_struct; +#define REG_SP ARM_sp + +#elif SANITIZER_LINUX && defined(__arm__) +typedef user_regs regs_struct; +#define REG_SP uregs[13] + +#elif defined(__i386__) || defined(__x86_64__) +typedef user_regs_struct regs_struct; +#if defined(__i386__) +#define REG_SP esp +#else +#define REG_SP rsp +#endif + +#elif defined(__powerpc__) || defined(__powerpc64__) +typedef pt_regs regs_struct; +#define REG_SP gpr[PT_R1] + +#elif defined(__mips__) +typedef struct user regs_struct; +# if SANITIZER_ANDROID +# define REG_SP regs[EF_R29] +# else +# define REG_SP regs[EF_REG29] +# endif + +#elif defined(__aarch64__) +typedef struct user_pt_regs regs_struct; +#define REG_SP sp +#define ARCH_IOVEC_FOR_GETREGSET + +#elif defined(__s390__) +typedef _user_regs_struct regs_struct; +#define REG_SP gprs[15] +#define ARCH_IOVEC_FOR_GETREGSET + +#else +#error "Unsupported architecture" +#endif // SANITIZER_ANDROID && defined(__arm__) + +tid_t SuspendedThreadsListLinux::GetThreadID(uptr index) const { + CHECK_LT(index, thread_ids_.size()); + return thread_ids_[index]; +} + +uptr SuspendedThreadsListLinux::ThreadCount() const { + return thread_ids_.size(); +} + +bool SuspendedThreadsListLinux::ContainsTid(tid_t thread_id) const { + for (uptr i = 0; i < thread_ids_.size(); i++) { + if (thread_ids_[i] == thread_id) return true; + } + return false; +} + +void SuspendedThreadsListLinux::Append(tid_t tid) { + thread_ids_.push_back(tid); +} + +PtraceRegistersStatus SuspendedThreadsListLinux::GetRegistersAndSP( + uptr index, uptr *buffer, uptr *sp) const { + pid_t tid = GetThreadID(index); + regs_struct regs; + int pterrno; +#ifdef ARCH_IOVEC_FOR_GETREGSET + struct iovec regset_io; + regset_io.iov_base = ®s; + regset_io.iov_len = sizeof(regs_struct); + bool isErr = internal_iserror(internal_ptrace(PTRACE_GETREGSET, tid, + (void*)NT_PRSTATUS, (void*)®set_io), + &pterrno); +#else + bool isErr = internal_iserror(internal_ptrace(PTRACE_GETREGS, tid, nullptr, + ®s), &pterrno); +#endif + if (isErr) { + VReport(1, "Could not get registers from thread %d (errno %d).\n", tid, + pterrno); + // ESRCH means that the given thread is not suspended or already dead. + // Therefore it's unsafe to inspect its data (e.g. walk through stack) and + // we should notify caller about this. + return pterrno == ESRCH ? REGISTERS_UNAVAILABLE_FATAL + : REGISTERS_UNAVAILABLE; + } + + *sp = regs.REG_SP; + internal_memcpy(buffer, ®s, sizeof(regs)); + return REGISTERS_AVAILABLE; +} + +uptr SuspendedThreadsListLinux::RegisterCount() const { + return sizeof(regs_struct) / sizeof(uptr); +} +} // namespace __sanitizer + +#endif // SANITIZER_LINUX && (defined(__x86_64__) || defined(__mips__) + // || defined(__aarch64__) || defined(__powerpc64__) + // || defined(__s390__) || defined(__i386__) || defined(__arm__) |