Luna/kernel/src/sys/signal.cpp

#include "Log.h"
#include "Pledge.h"
#include "memory/MemoryManager.h"
#include "sys/Syscall.h"
#include "thread/Scheduler.h"
#include <bits/signal.h>

Result<u64> sys_sigreturn(Registers* regs, SyscallArgs)
{
    auto* current = Scheduler::current();

    current->sigreturn(regs);

    // Since we could be returning to anywhere in the program, we don't want to be changing the return value register
    // (RAX on x86_64). But our syscall framework doesn't allow that, so we just set it to its current value.
    return current->return_register();
}

Result<u64> sys_sigaction(Registers*, SyscallArgs args)
{
    auto* current = Scheduler::current();
    TRY(check_pledge(current, Promise::p_stdio));

    int signo = (int)args[0];
    const struct sigaction* act = (const struct sigaction*)args[1];
    struct sigaction* oldact = (struct sigaction*)args[2];
    void* sigreturn = (void*)args[3];

    if (signo > NSIG) return err(EINVAL);
    if (signo <= 0) return err(EINVAL);

    if (oldact)
    {
        if (!MemoryManager::copy_to_user_typed(oldact, &current->signal_handlers[signo - 1])) return err(EFAULT);
    }

    if (act)
    {
        struct sigaction kact;
        if (!MemoryManager::copy_from_user_typed(act, &kact)) return err(EFAULT);
        kact.__sa_sigreturn = sigreturn;

        current->signal_handlers[signo - 1] = kact;
    }

    return 0;
}

Result<u64> sys_kill(Registers*, SyscallArgs args)
{
    auto* current = Scheduler::current();
    TRY(check_pledge(current, Promise::p_proc));

    pid_t pid = (pid_t)args[0];
    int signo = (int)args[1];

    auto send_signal = [&](Thread* target) -> Result<void> {
        if (current->auth.euid != 0 && current->auth.euid != target->auth.euid &&
            current->auth.egid != target->auth.egid)
            return err(EPERM);
        if (target->is_kernel) return {};
        if (signo == 0) return {};

        target->send_signal(signo);

        return {};
    };

    if (pid > 0)
    {
        auto* target = TRY(Result<Thread*>::from_option(Scheduler::find_by_pid(pid), ESRCH));
        TRY(send_signal(target));
    }
    else if (pid == 0)
    {
        int errno = -1;
        bool pgid_exists = false;
        Scheduler::for_each_in_process_group(current->pgid, [&](Thread* target) {
            pgid_exists = true;
            auto rc = send_signal(target);
            if (rc.has_error())
            {
                errno = rc.error();
                return false;
            }
            return true;
        });
        if (errno > 0) return err(errno);
        if (!pgid_exists) return err(ESRCH);
    }
    else if (pid == -1)
    {
        for (auto* thread : g_threads)
        {
            // We ignore permission errors here.
            if (thread != current && thread->id != 1) send_signal(thread);
        }
    }
    else if (pid < -1)
    {
        int errno = -1;
        bool pgid_exists = false;
        Scheduler::for_each_in_process_group(-pid, [&](Thread* target) {
            pgid_exists = true;
            auto rc = send_signal(target);
            if (rc.has_error())
            {
                errno = rc.error();
                return false;
            }
            return true;
        });
        if (errno > 0) return err(errno);
        if (!pgid_exists) return err(ESRCH);
    }

    return 0;
}

Result<u64> sys_sigprocmask(Registers*, SyscallArgs args)
{
    auto* current = Scheduler::current();
    TRY(check_pledge(current, Promise::p_stdio));

    int how = (int)args[0];
    const sigset_t* set = (const sigset_t*)args[1];
    sigset_t* oldset = (sigset_t*)args[2];

    if (oldset)
    {
        sigset_t mask = current->signal_mask.value();
        if (!MemoryManager::copy_to_user_typed(oldset, &mask)) return err(EFAULT);
    }

    if (set)
    {
        sigset_t kset;
        if (!MemoryManager::copy_from_user_typed(set, &kset)) return err(EFAULT);

        switch (how)
        {
        case SIG_BLOCK: current->signal_mask = current->signal_mask.value() | kset; break;
        case SIG_UNBLOCK: current->signal_mask = current->signal_mask.value() & ~kset; break;
        case SIG_SETMASK: current->signal_mask = kset; break;
        default: return err(EINVAL);
        }
    }

    return 0;
}

Result<u64> sys_pause(Registers* regs, SyscallArgs)
{
    auto* current = Scheduler::current();
    while (1)
    {
        kernel_wait_for_event();
        if (current->interrupted)
        {
            if (current->will_ignore_pending_signal())
            {
                current->process_pending_signals(regs);
                continue;
            }
            return err(EINTR);
        }
    }
}

Result<u64> sys_sigsuspend(Registers* regs, SyscallArgs args)
{
    const sigset_t* set = (const sigset_t*)args[0];

    auto* current = Scheduler::current();

    sigset_t kset;
    if (!MemoryManager::copy_from_user_typed(set, &kset)) return err(EFAULT);

    sigset_t oldset = current->signal_mask.value();
    current->signal_mask = kset;

    while (1)
    {
        kernel_wait_for_event();
        if (current->interrupted)
        {
            if (current->will_ignore_pending_signal())
            {
                current->process_pending_signals(regs);
                continue;
            }
            current->signal_mask = oldset;
            return err(EINTR);
        }
    }
}