signal.cpp

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// SPDX-License-Identifier: GPL-3.0-or-later
 
#include "mos/tasks/signal.hpp"
 
#include "mos/platform/platform.hpp"
#include "mos/syslog/printk.hpp"
#include "mos/tasks/process.hpp"
#include "mos/tasks/schedule.hpp"
#include "mos/tasks/thread.hpp"
 
#include <errno.h>
#include <limits.h>
#include <mos/lib/structures/list.hpp>
#include <mos/lib/sync/spinlock.hpp>
#include <mos/tasks/signal_types.h>
#include <mos_stdlib.hpp>
#include <mos_string.hpp>
 
static int sigset_add(sigset_t *sigset, int sig)
{
    MOS_ASSERT(sig >= 1 && sig <= SIGNAL_MAX_N);
 
    const int signo = sig - 1;
    char *const ptr = (char *) sigset;
    ptr[signo / CHAR_BIT] |= (1 << (signo % CHAR_BIT));
    return 0;
}
 
static int sigset_del(sigset_t *sigset, int sig)
{
    MOS_ASSERT(sig >= 1 && sig <= SIGNAL_MAX_N);
 
    const int signo = sig - 1;
    char *const ptr = (char *) sigset;
    ptr[signo / CHAR_BIT] &= ~(1 << (signo % CHAR_BIT));
    return 0;
}
 
static int sigset_test(const sigset_t *sigset, int sig)
{
    MOS_ASSERT(sig >= 1 && sig <= SIGNAL_MAX_N);
 
    const int signo = sig - 1;
    const char *ptr = (const char *) sigset;
    return (ptr[signo / CHAR_BIT] & (1 << (signo % CHAR_BIT))) != 0;
}
 
[[noreturn]] static void signal_do_coredump(signal_t signal)
{
    process_exit(std::move(current_process), 0, signal);
    MOS_UNREACHABLE();
}
 
[[noreturn]] static void signal_do_terminate(signal_t signal)
{
    if (current_thread == current_process->main_thread)
        process_exit(std::move(current_process), 0, signal);
    else
        thread_exit(std::move(current_thread));
    MOS_UNREACHABLE();
}
 
static void signal_do_ignore(signal_t signal)
{
    pr_dinfo2(signal, "thread %pt ignoring signal %d", current_thread, signal);
}
 
static bool is_fatal_signal(signal_t signal)
{
    switch (signal)
    {
        case SIGILL:
        case SIGTRAP:
        case SIGABRT:
        case SIGKILL:
        case SIGSEGV: return true;
 
        case SIGINT:
        case SIGTERM:
        case SIGCHLD:
        case SIGPIPE: return false;
 
        default: MOS_UNREACHABLE_X("handle this signal %d", signal); break;
    }
}
 
long signal_send_to_thread(Thread *target, signal_t signal)
{
    if (target->mode == THREAD_MODE_KERNEL && !is_fatal_signal(signal))
    {
        pr_emerg("signal_send_to_thread(%pt, %d): cannot send non-fatal signal to kernel thread", target, signal);
        return -EINVAL;
    }
 
    spinlock_acquire(&target->signal_info.lock);
 
    bool has_pending = false; // true if the signal is already pending
    list_foreach(sigpending_t, pending, target->signal_info.pending)
    {
        has_pending |= pending->signal == signal;
        if (has_pending)
            break;
    }
 
    if (!has_pending)
    {
        sigpending_t *sigdesc = mos::create<sigpending_t>();
        linked_list_init(list_node(sigdesc));
        sigdesc->signal = signal;
        list_node_append(&target->signal_info.pending, list_node(sigdesc));
    }
 
    spinlock_release(&target->signal_info.lock);
 
    if (target != current_thread)
        scheduler_wake_thread(target);
 
    return 0;
}
 
long signal_send_to_process(Process *target, signal_t signal)
{
    if (target->pid == 1 && signal == SIGKILL)
    {
        pr_emerg("signal_send_to_process(%pp, %d): cannot send SIGKILL to init", target, signal);
        return -EINVAL;
    }
 
    if (target->pid == 2)
    {
        pr_emerg("signal_send_to_process(%pp, %d): cannot send signal to kthreadd", target, signal);
        return -EINVAL;
    }
 
    Thread *target_thread = NULL;
    for (const auto &thread : target->thread_list)
    {
        if (thread->state == THREAD_STATE_RUNNING || thread->state == THREAD_STATE_READY || thread->state == THREAD_STATE_CREATED)
        {
            target_thread = thread;
            break;
        }
    }
 
    if (!target_thread)
    {
        for (const auto &thread : target->thread_list)
        {
            if (thread->state == THREAD_STATE_BLOCKED)
            {
                target_thread = thread;
                break;
            }
        }
    }
 
    if (!target_thread)
    {
        pr_emerg("signal_send_to_process(%pp, %d): no thread to send signal to", target, signal);
        return -EINVAL;
    }
 
    signal_send_to_thread(target_thread, signal);
 
    return 0;
}
 
static signal_t signal_get_next_pending(void)
{
    signal_t signal = 0;
 
    MOS_ASSERT(spinlock_is_locked(&current_thread->signal_info.lock));
    list_foreach(sigpending_t, pending, current_thread->signal_info.pending)
    {
        if (sigset_test(&current_thread->signal_info.mask, pending->signal))
        {
            // if a fatal signal is pending but also masked, kill the thread
            if (is_fatal_signal(pending->signal))
            {
                pr_emerg("thread %pt received fatal signal %d but it was masked, terminating", current_thread, pending->signal);
                signal_do_terminate(pending->signal);
            }
            continue; // signal is masked, skip it
        }
 
        list_remove(pending);
        signal = pending->signal;
        delete pending;
        break;
    }
 
    return signal;
}
 
static void do_signal_exit_to_user_prepare(platform_regs_t *regs, signal_t next_signal, const sigaction_t *action)
{
    if (action->handler == SIG_DFL)
    {
        if (current_process->pid == 1 && !is_fatal_signal(next_signal))
            goto done; // init only receives signals it wants
 
        switch (next_signal)
        {
            case SIGINT: signal_do_terminate(next_signal); break;
            case SIGILL: signal_do_coredump(next_signal); break;
            case SIGTRAP: signal_do_coredump(next_signal); break;
            case SIGABRT: signal_do_coredump(next_signal); break;
            case SIGKILL: signal_do_terminate(next_signal); break;
            case SIGSEGV: signal_do_coredump(next_signal); break;
            case SIGTERM: signal_do_terminate(next_signal); break;
            case SIGCHLD: signal_do_ignore(next_signal); break;
            case SIGPIPE: signal_do_terminate(next_signal); break;
 
            default: MOS_UNREACHABLE_X("handle this signal %d", next_signal); break;
        }
 
    // the default handler returns
    done:
        return;
    }
 
    if (action->handler == SIG_IGN)
    {
        signal_do_ignore(next_signal);
        return;
    }
 
    const bool was_masked = sigset_test(&current_thread->signal_info.mask, next_signal);
    if (!was_masked)
        sigset_add(&current_thread->signal_info.mask, next_signal);
 
    const sigreturn_data_t data = {
        .signal = next_signal,
        .was_masked = was_masked,
    };
 
    platform_jump_to_signal_handler(regs, &data, action); // save previous register states onto user stack
}
 
void signal_exit_to_user_prepare(platform_regs_t *regs)
{
    MOS_ASSERT(current_thread);
 
    spinlock_acquire(&current_thread->signal_info.lock);
    const signal_t next_signal = signal_get_next_pending();
    spinlock_release(&current_thread->signal_info.lock);
 
    if (!next_signal)
        return; // no pending signal, leave asap
 
    const sigaction_t action = current_process->signal_info.handlers[next_signal];
 
    do_signal_exit_to_user_prepare(regs, next_signal, &action);
}
 
void signal_exit_to_user_prepare_syscall(platform_regs_t *regs, reg_t syscall_nr, reg_t syscall_ret)
{
    MOS_ASSERT(current_thread);
 
    spinlock_acquire(&current_thread->signal_info.lock);
    const signal_t next_signal = signal_get_next_pending();
    spinlock_release(&current_thread->signal_info.lock);
 
    const sigaction_t action = current_process->signal_info.handlers[next_signal];
 
    reg_t real_ret = syscall_ret;
    if (syscall_ret == (reg_t) -ERESTARTSYS)
    {
        MOS_ASSERT(next_signal);
        real_ret = -EINTR;
 
        if (action.sa_flags & SA_RESTART)
        {
            pr_dinfo2(signal, "thread %pt will restart syscall %lu after signal %d", current_thread, syscall_nr, next_signal);
            platform_syscall_setup_restart_context(regs, syscall_nr);
            goto really_prepare;
        }
        // else: fall through, return -EINTR
    }
 
    platform_syscall_store_retval(regs, real_ret);
 
    if (!next_signal)
        return; // no pending signal, leave asap
 
really_prepare:
    do_signal_exit_to_user_prepare(regs, next_signal, &action);
}
 
void signal_on_returned(sigreturn_data_t *data)
{
    if (!data->was_masked)
        sigset_del(&current_thread->signal_info.mask, data->signal);
}
 
bool signal_has_pending(void)
{
    bool has_pending = false;
    spinlock_acquire(&current_thread->signal_info.lock);
    list_foreach(sigpending_t, pending, current_thread->signal_info.pending)
    {
        if (sigset_test(&current_thread->signal_info.mask, pending->signal))
            continue; // signal is masked, skip it
        has_pending = true;
        break;
    }
 
    spinlock_release(&current_thread->signal_info.lock);
    return has_pending;
}