// SPDX-License-Identifier: GPL-2.0
/*
 * Copyright (C) 2015 Anton Ivanov (aivanov@{brocade.com,kot-begemot.co.uk})
 * Copyright (C) 2015 Thomas Meyer (thomas@m3y3r.de)
 * Copyright (C) 2004 PathScale, Inc
 * Copyright (C) 2004 - 2007 Jeff Dike (jdike@{addtoit,linux.intel}.com)
 */

#include <stdlib.h>
#include <stdarg.h>
#include <stdbool.h>
#include <errno.h>
#include <signal.h>
#include <string.h>
#include <strings.h>
#include <as-layout.h>
#include <kern_util.h>
#include <os.h>
#include <skas.h>
#include <sysdep/mcontext.h>
#include <um_malloc.h>
#include <sys/ucontext.h>
#include <timetravel.h>
#include "internal.h"

void (*sig_info[NSIG])(int, struct siginfo *, struct uml_pt_regs *, void *mc) = {
        [SIGTRAP]       = relay_signal,
        [SIGFPE]        = relay_signal,
        [SIGILL]        = relay_signal,
        [SIGWINCH]      = winch,
        [SIGBUS]        = relay_signal,
        [SIGSEGV]       = segv_handler,
        [SIGIO]         = sigio_handler,
        [SIGCHLD]       = sigchld_handler,
};

static void sig_handler_common(int sig, struct siginfo *si, mcontext_t *mc)
{
        struct uml_pt_regs r;

        r.is_user = 0;
        if (sig == SIGSEGV) {
                /* For segfaults, we want the data from the sigcontext. */
                get_regs_from_mc(&r, mc);
                GET_FAULTINFO_FROM_MC(r.faultinfo, mc);
        }

        /* enable signals if sig isn't IRQ signal */
        if ((sig != SIGIO) && (sig != SIGWINCH) && (sig != SIGCHLD))
                unblock_signals_trace();

        (*sig_info[sig])(sig, si, &r, mc);
}

/*
 * These are the asynchronous signals.  SIGPROF is excluded because we want to
 * be able to profile all of UML, not just the non-critical sections.  If
 * profiling is not thread-safe, then that is not my problem.  We can disable
 * profiling when SMP is enabled in that case.
 */
#define SIGIO_BIT 0
#define SIGIO_MASK (1 << SIGIO_BIT)

#define SIGALRM_BIT 1
#define SIGALRM_MASK (1 << SIGALRM_BIT)

#define SIGCHLD_BIT 2
#define SIGCHLD_MASK (1 << SIGCHLD_BIT)

__thread int signals_enabled;
#if IS_ENABLED(CONFIG_UML_TIME_TRAVEL_SUPPORT)
static int signals_blocked, signals_blocked_pending;
#endif
static __thread unsigned int signals_pending;
static __thread unsigned int signals_active;

static void sig_handler(int sig, struct siginfo *si, mcontext_t *mc)
{
        int enabled = signals_enabled;

#if IS_ENABLED(CONFIG_UML_TIME_TRAVEL_SUPPORT)
        if ((signals_blocked ||
             __atomic_load_n(&signals_blocked_pending, __ATOMIC_SEQ_CST)) &&
            (sig == SIGIO)) {
                /* increment so unblock will do another round */
                __atomic_add_fetch(&signals_blocked_pending, 1,
                                   __ATOMIC_SEQ_CST);
                return;
        }
#endif

        if (!enabled && (sig == SIGIO)) {
                /*
                 * In TT_MODE_EXTERNAL, need to still call time-travel
                 * handlers. This will mark signals_pending by itself
                 * (only if necessary.)
                 * Note we won't get here if signals are hard-blocked
                 * (which is handled above), in that case the hard-
                 * unblock will handle things.
                 */
                if (time_travel_mode == TT_MODE_EXTERNAL)
                        sigio_run_timetravel_handlers();
                else
                        signals_pending |= SIGIO_MASK;
                return;
        }

        if (!enabled && (sig == SIGCHLD)) {
                signals_pending |= SIGCHLD_MASK;
                return;
        }

        block_signals_trace();

        sig_handler_common(sig, si, mc);

        um_set_signals_trace(enabled);
}

static void timer_real_alarm_handler(mcontext_t *mc)
{
        struct uml_pt_regs regs;

        if (mc != NULL)
                get_regs_from_mc(&regs, mc);
        else
                memset(&regs, 0, sizeof(regs));
        timer_handler(SIGALRM, NULL, &regs);
}

static void timer_alarm_handler(int sig, struct siginfo *unused_si, mcontext_t *mc)
{
        int enabled;

        enabled = signals_enabled;
        if (!signals_enabled) {
                signals_pending |= SIGALRM_MASK;
                return;
        }

        block_signals_trace();

        signals_active |= SIGALRM_MASK;

        timer_real_alarm_handler(mc);

        signals_active &= ~SIGALRM_MASK;

        um_set_signals_trace(enabled);
}

void deliver_alarm(void) {
    timer_alarm_handler(SIGALRM, NULL, NULL);
}

void timer_set_signal_handler(void)
{
        set_handler(SIGALRM);
}

int timer_alarm_pending(void)
{
        return !!(signals_pending & SIGALRM_MASK);
}

void set_sigstack(void *sig_stack, int size)
{
        stack_t stack = {
                .ss_flags = 0,
                .ss_sp = sig_stack,
                .ss_size = size
        };

        if (sigaltstack(&stack, NULL) != 0)
                panic("enabling signal stack failed, errno = %d\n", errno);
}

static void sigusr1_handler(int sig, struct siginfo *unused_si, mcontext_t *mc)
{
        uml_pm_wake();
}

void register_pm_wake_signal(void)
{
        set_handler(SIGUSR1);
}

static void (*handlers[_NSIG])(int sig, struct siginfo *si, mcontext_t *mc) = {
        [SIGSEGV] = sig_handler,
        [SIGBUS] = sig_handler,
        [SIGILL] = sig_handler,
        [SIGFPE] = sig_handler,
        [SIGTRAP] = sig_handler,

        [SIGIO] = sig_handler,
        [SIGWINCH] = sig_handler,
        /* SIGCHLD is only actually registered in seccomp mode. */
        [SIGCHLD] = sig_handler,
        [SIGALRM] = timer_alarm_handler,

        [SIGUSR1] = sigusr1_handler,
};

static void hard_handler(int sig, siginfo_t *si, void *p)
{
        ucontext_t *uc = p;
        mcontext_t *mc = &uc->uc_mcontext;
        int save_errno = errno;

        (*handlers[sig])(sig, (struct siginfo *)si, mc);

        errno = save_errno;
}

void set_handler(int sig)
{
        struct sigaction action;
        int flags = SA_SIGINFO | SA_ONSTACK;
        sigset_t sig_mask;

        action.sa_sigaction = hard_handler;

        /* block irq ones */
        sigemptyset(&action.sa_mask);
        sigaddset(&action.sa_mask, SIGIO);
        sigaddset(&action.sa_mask, SIGWINCH);
        sigaddset(&action.sa_mask, SIGALRM);
        if (using_seccomp)
                sigaddset(&action.sa_mask, SIGCHLD);

        if (sig == SIGSEGV)
                flags |= SA_NODEFER;

        if (sigismember(&action.sa_mask, sig))
                flags |= SA_RESTART; /* if it's an irq signal */

        action.sa_flags = flags;
        action.sa_restorer = NULL;
        if (sigaction(sig, &action, NULL) < 0)
                panic("sigaction failed - errno = %d\n", errno);

        sigemptyset(&sig_mask);
        sigaddset(&sig_mask, sig);
        if (sigprocmask(SIG_UNBLOCK, &sig_mask, NULL) < 0)
                panic("sigprocmask failed - errno = %d\n", errno);
}

void send_sigio_to_self(void)
{
        kill(os_getpid(), SIGIO);
}

int change_sig(int signal, int on)
{
        sigset_t sigset;

        sigemptyset(&sigset);
        sigaddset(&sigset, signal);
        if (sigprocmask(on ? SIG_UNBLOCK : SIG_BLOCK, &sigset, NULL) < 0)
                return -errno;

        return 0;
}

static inline void __block_signals(void)
{
        if (!signals_enabled)
                return;

        os_local_ipi_disable();
        barrier();
        signals_enabled = 0;
}

static inline void __unblock_signals(void)
{
        if (signals_enabled)
                return;

        signals_enabled = 1;
        barrier();
        os_local_ipi_enable();
}

void block_signals(void)
{
        __block_signals();
        /*
         * This must return with signals disabled, so this barrier
         * ensures that writes are flushed out before the return.
         * This might matter if gcc figures out how to inline this and
         * decides to shuffle this code into the caller.
         */
        barrier();
}

void unblock_signals(void)
{
        int save_pending;

        if (signals_enabled == 1)
                return;

        __unblock_signals();

#if IS_ENABLED(CONFIG_UML_TIME_TRAVEL_SUPPORT)
        deliver_time_travel_irqs();
#endif

        /*
         * We loop because the IRQ handler returns with interrupts off.  So,
         * interrupts may have arrived and we need to re-enable them and
         * recheck signals_pending.
         */
        while (1) {
                /*
                 * Save and reset save_pending after enabling signals.  This
                 * way, signals_pending won't be changed while we're reading it.
                 *
                 * Setting signals_enabled and reading signals_pending must
                 * happen in this order, so have the barrier here.
                 */
                barrier();

                save_pending = signals_pending;
                if (save_pending == 0)
                        return;

                signals_pending = 0;

                /*
                 * We have pending interrupts, so disable signals, as the
                 * handlers expect them off when they are called.  They will
                 * be enabled again above. We need to trace this, as we're
                 * expected to be enabling interrupts already, but any more
                 * tracing that happens inside the handlers we call for the
                 * pending signals will mess up the tracing state.
                 */
                __block_signals();
                um_trace_signals_off();

                /*
                 * Deal with SIGIO first because the alarm handler might
                 * schedule, leaving the pending SIGIO stranded until we come
                 * back here.
                 *
                 * SIGIO's handler doesn't use siginfo or mcontext,
                 * so they can be NULL.
                 */
                if (save_pending & SIGIO_MASK)
                        sig_handler_common(SIGIO, NULL, NULL);

                if (save_pending & SIGCHLD_MASK) {
                        struct uml_pt_regs regs = {};

                        sigchld_handler(SIGCHLD, NULL, &regs, NULL);
                }

                /* Do not reenter the handler */

                if ((save_pending & SIGALRM_MASK) && (!(signals_active & SIGALRM_MASK)))
                        timer_real_alarm_handler(NULL);

                /* Rerun the loop only if there is still pending SIGIO and not in TIMER handler */

                if (!(signals_pending & SIGIO_MASK) && (signals_active & SIGALRM_MASK))
                        return;

                /* Re-enable signals and trace that we're doing so. */
                um_trace_signals_on();
                __unblock_signals();
        }
}

int um_get_signals(void)
{
        return signals_enabled;
}

int um_set_signals(int enable)
{
        int ret;
        if (signals_enabled == enable)
                return enable;

        ret = signals_enabled;
        if (enable)
                unblock_signals();
        else block_signals();

        return ret;
}

int um_set_signals_trace(int enable)
{
        int ret;
        if (signals_enabled == enable)
                return enable;

        ret = signals_enabled;
        if (enable)
                unblock_signals_trace();
        else
                block_signals_trace();

        return ret;
}

#if IS_ENABLED(CONFIG_UML_TIME_TRAVEL_SUPPORT)
void mark_sigio_pending(void)
{
        /*
         * It would seem that this should be atomic so
         * it isn't a read-modify-write with a signal
         * that could happen in the middle, losing the
         * value set by the signal.
         *
         * However, this function is only called when in
         * time-travel=ext simulation mode, in which case
         * the only signal ever pending is SIGIO, which
         * is blocked while this can be called, and the
         * timer signal (SIGALRM) cannot happen.
         */
        signals_pending |= SIGIO_MASK;
}

void block_signals_hard(void)
{
        signals_blocked++;
        barrier();
}

void unblock_signals_hard(void)
{
        static bool unblocking;

        if (!signals_blocked)
                panic("unblocking signals while not blocked");

        if (--signals_blocked)
                return;
        /*
         * Must be set to 0 before we check pending so the
         * SIGIO handler will run as normal unless we're still
         * going to process signals_blocked_pending.
         */
        barrier();

        /*
         * Note that block_signals_hard()/unblock_signals_hard() can be called
         * within the unblock_signals()/sigio_run_timetravel_handlers() below.
         * This would still be prone to race conditions since it's actually a
         * call _within_ e.g. vu_req_read_message(), where we observed this
         * issue, which loops. Thus, if the inner call handles the recorded
         * pending signals, we can get out of the inner call with the real
         * signal hander no longer blocked, and still have a race. Thus don't
         * handle unblocking in the inner call, if it happens, but only in
         * the outermost call - 'unblocking' serves as an ownership for the
         * signals_blocked_pending decrement.
         */
        if (unblocking)
                return;
        unblocking = true;

        while (__atomic_load_n(&signals_blocked_pending, __ATOMIC_SEQ_CST)) {
                if (signals_enabled) {
                        /* signals are enabled so we can touch this */
                        signals_pending |= SIGIO_MASK;
                        /*
                         * this is a bit inefficient, but that's
                         * not really important
                         */
                        block_signals();
                        unblock_signals();
                } else {
                        /*
                         * we need to run time-travel handlers even
                         * if not enabled
                         */
                        sigio_run_timetravel_handlers();
                }

                /*
                 * The decrement of signals_blocked_pending must be atomic so
                 * that the signal handler will either happen before or after
                 * the decrement, not during a read-modify-write:
                 *  - If it happens before, it can increment it and we'll
                 *    decrement it and do another round in the loop.
                 *  - If it happens after it'll see 0 for both signals_blocked
                 *    and signals_blocked_pending and thus run the handler as
                 *    usual (subject to signals_enabled, but that's unrelated.)
                 *
                 * Note that a call to unblock_signals_hard() within the calls
                 * to unblock_signals() or sigio_run_timetravel_handlers() above
                 * will do nothing due to the 'unblocking' state, so this cannot
                 * underflow as the only one decrementing will be the outermost
                 * one.
                 */
                if (__atomic_sub_fetch(&signals_blocked_pending, 1,
                                       __ATOMIC_SEQ_CST) < 0)
                        panic("signals_blocked_pending underflow");
        }

        unblocking = false;
}
#endif