// SPDX-License-Identifier: GPL-2.0
/*
 * Copyright (C) 2021 Benjamin Berg <benjamin@sipsolutions.net>
 * Copyright (C) 2015 Thomas Meyer (thomas@m3y3r.de)
 * Copyright (C) 2002- 2007 Jeff Dike (jdike@{addtoit,linux.intel}.com)
 */

#include <stdlib.h>
#include <stdbool.h>
#include <unistd.h>
#include <sched.h>
#include <errno.h>
#include <string.h>
#include <fcntl.h>
#include <mem_user.h>
#include <sys/mman.h>
#include <sys/wait.h>
#include <sys/stat.h>
#include <sys/socket.h>
#include <asm/unistd.h>
#include <as-layout.h>
#include <init.h>
#include <kern_util.h>
#include <mem.h>
#include <os.h>
#include <ptrace_user.h>
#include <registers.h>
#include <skas.h>
#include <sysdep/stub.h>
#include <sysdep/mcontext.h>
#include <linux/futex.h>
#include <linux/threads.h>
#include <timetravel.h>
#include <asm-generic/rwonce.h>
#include "../internal.h"

int is_skas_winch(int pid, int fd, void *data)
{
        return pid == getpgrp();
}

static const char *ptrace_reg_name(int idx)
{
#define R(n) case HOST_##n: return #n

        switch (idx) {
#ifdef __x86_64__
        R(BX);
        R(CX);
        R(DI);
        R(SI);
        R(DX);
        R(BP);
        R(AX);
        R(R8);
        R(R9);
        R(R10);
        R(R11);
        R(R12);
        R(R13);
        R(R14);
        R(R15);
        R(ORIG_AX);
        R(CS);
        R(SS);
        R(EFLAGS);
#elif defined(__i386__)
        R(IP);
        R(SP);
        R(EFLAGS);
        R(AX);
        R(BX);
        R(CX);
        R(DX);
        R(SI);
        R(DI);
        R(BP);
        R(CS);
        R(SS);
        R(DS);
        R(FS);
        R(ES);
        R(GS);
        R(ORIG_AX);
#endif
        }
        return "";
}

static int ptrace_dump_regs(int pid)
{
        unsigned long regs[MAX_REG_NR];
        int i;

        if (ptrace(PTRACE_GETREGS, pid, 0, regs) < 0)
                return -errno;

        printk(UM_KERN_ERR "Stub registers -\n");
        for (i = 0; i < ARRAY_SIZE(regs); i++) {
                const char *regname = ptrace_reg_name(i);

                printk(UM_KERN_ERR "\t%s\t(%2d): %lx\n", regname, i, regs[i]);
        }

        return 0;
}

/*
 * Signals that are OK to receive in the stub - we'll just continue it.
 * SIGWINCH will happen when UML is inside a detached screen.
 */
#define STUB_SIG_MASK ((1 << SIGALRM) | (1 << SIGWINCH))

/* Signals that the stub will finish with - anything else is an error */
#define STUB_DONE_MASK (1 << SIGTRAP)

void wait_stub_done(int pid)
{
        int n, status, err;

        while (1) {
                CATCH_EINTR(n = waitpid(pid, &status, WUNTRACED | __WALL));
                if ((n < 0) || !WIFSTOPPED(status))
                        goto bad_wait;

                if (((1 << WSTOPSIG(status)) & STUB_SIG_MASK) == 0)
                        break;

                err = ptrace(PTRACE_CONT, pid, 0, 0);
                if (err) {
                        printk(UM_KERN_ERR "%s : continue failed, errno = %d\n",
                               __func__, errno);
                        fatal_sigsegv();
                }
        }

        if (((1 << WSTOPSIG(status)) & STUB_DONE_MASK) != 0)
                return;

bad_wait:
        err = ptrace_dump_regs(pid);
        if (err)
                printk(UM_KERN_ERR "Failed to get registers from stub, errno = %d\n",
                       -err);
        printk(UM_KERN_ERR "%s : failed to wait for SIGTRAP, pid = %d, n = %d, errno = %d, status = 0x%x\n",
               __func__, pid, n, errno, status);
        fatal_sigsegv();
}

void wait_stub_done_seccomp(struct mm_id *mm_idp, int running, int wait_sigsys)
{
        struct stub_data *data = (void *)mm_idp->stack;
        int ret;

        do {
                const char byte = 0;
                struct iovec iov = {
                        .iov_base = (void *)&byte,
                        .iov_len = sizeof(byte),
                };
                union {
                        char data[CMSG_SPACE(sizeof(mm_idp->syscall_fd_map))];
                        struct cmsghdr align;
                } ctrl;
                struct msghdr msgh = {
                        .msg_iov = &iov,
                        .msg_iovlen = 1,
                };

                if (!running) {
                        if (mm_idp->syscall_fd_num) {
                                unsigned int fds_size =
                                        sizeof(int) * mm_idp->syscall_fd_num;
                                struct cmsghdr *cmsg;

                                msgh.msg_control = ctrl.data;
                                msgh.msg_controllen = CMSG_SPACE(fds_size);
                                cmsg = CMSG_FIRSTHDR(&msgh);
                                cmsg->cmsg_level = SOL_SOCKET;
                                cmsg->cmsg_type = SCM_RIGHTS;
                                cmsg->cmsg_len = CMSG_LEN(fds_size);
                                memcpy(CMSG_DATA(cmsg), mm_idp->syscall_fd_map,
                                       fds_size);

                                CATCH_EINTR(syscall(__NR_sendmsg, mm_idp->sock,
                                                &msgh, 0));
                        }

                        data->signal = 0;
                        data->futex = FUTEX_IN_CHILD;
                        CATCH_EINTR(syscall(__NR_futex, &data->futex,
                                            FUTEX_WAKE, 1, NULL, NULL, 0));
                }

                do {
                        /*
                         * We need to check whether the child is still alive
                         * before and after the FUTEX_WAIT call. Before, in
                         * case it just died but we still updated data->futex
                         * to FUTEX_IN_CHILD. And after, in case it died while
                         * we were waiting (and SIGCHLD woke us up, see the
                         * IRQ handler in mmu.c).
                         *
                         * Either way, if PID is negative, then we have no
                         * choice but to kill the task.
                         */
                        if (__READ_ONCE(mm_idp->pid) < 0)
                                goto out_kill;

                        ret = syscall(__NR_futex, &data->futex,
                                      FUTEX_WAIT, FUTEX_IN_CHILD,
                                      NULL, NULL, 0);
                        if (ret < 0 && errno != EINTR && errno != EAGAIN) {
                                printk(UM_KERN_ERR "%s : FUTEX_WAIT failed, errno = %d\n",
                                       __func__, errno);
                                goto out_kill;
                        }
                } while (data->futex == FUTEX_IN_CHILD);

                if (__READ_ONCE(mm_idp->pid) < 0)
                        goto out_kill;

                running = 0;

                /* We may receive a SIGALRM before SIGSYS, iterate again. */
        } while (wait_sigsys && data->signal == SIGALRM);

        if (data->mctx_offset > sizeof(data->sigstack) - sizeof(mcontext_t)) {
                printk(UM_KERN_ERR "%s : invalid mcontext offset", __func__);
                goto out_kill;
        }

        if (wait_sigsys && data->signal != SIGSYS) {
                printk(UM_KERN_ERR "%s : expected SIGSYS but got %d",
                       __func__, data->signal);
                goto out_kill;
        }

        return;

out_kill:
        printk(UM_KERN_ERR "%s : failed to wait for stub, pid = %d, errno = %d\n",
               __func__, mm_idp->pid, errno);
        /* This is not true inside start_userspace */
        if (current_mm_id() == mm_idp)
                fatal_sigsegv();
}

extern unsigned long current_stub_stack(void);

static void get_skas_faultinfo(int pid, struct faultinfo *fi)
{
        int err;

        err = ptrace(PTRACE_CONT, pid, 0, SIGSEGV);
        if (err) {
                printk(UM_KERN_ERR "Failed to continue stub, pid = %d, "
                       "errno = %d\n", pid, errno);
                fatal_sigsegv();
        }
        wait_stub_done(pid);

        /*
         * faultinfo is prepared by the stub_segv_handler at start of
         * the stub stack page. We just have to copy it.
         */
        memcpy(fi, (void *)current_stub_stack(), sizeof(*fi));
}

static void handle_trap(struct uml_pt_regs *regs)
{
        if ((UPT_IP(regs) >= STUB_START) && (UPT_IP(regs) < STUB_END))
                fatal_sigsegv();

        handle_syscall(regs);
}

extern char __syscall_stub_start[];

static int stub_exe_fd;

struct tramp_data {
        struct stub_data *stub_data;
        /* 0 is inherited, 1 is the kernel side */
        int sockpair[2];
};

#ifndef CLOSE_RANGE_CLOEXEC
#define CLOSE_RANGE_CLOEXEC     (1U << 2)
#endif

static int userspace_tramp(void *data)
{
        struct tramp_data *tramp_data = data;
        char *const argv[] = { "uml-userspace", NULL };
        unsigned long long offset;
        struct stub_init_data init_data = {
                .seccomp = using_seccomp,
                .stub_start = STUB_START,
        };
        int ret;

        if (using_seccomp) {
                init_data.signal_handler = STUB_CODE +
                                           (unsigned long) stub_signal_interrupt -
                                           (unsigned long) __syscall_stub_start;
                init_data.signal_restorer = STUB_CODE +
                                           (unsigned long) stub_signal_restorer -
                                           (unsigned long) __syscall_stub_start;
        } else {
                init_data.signal_handler = STUB_CODE +
                                           (unsigned long) stub_segv_handler -
                                           (unsigned long) __syscall_stub_start;
                init_data.signal_restorer = 0;
        }

        init_data.stub_code_fd = phys_mapping(uml_to_phys(__syscall_stub_start),
                                              &offset);
        init_data.stub_code_offset = MMAP_OFFSET(offset);

        init_data.stub_data_fd = phys_mapping(uml_to_phys(tramp_data->stub_data),
                                              &offset);
        init_data.stub_data_offset = MMAP_OFFSET(offset);

        /*
         * Avoid leaking unneeded FDs to the stub by setting CLOEXEC on all FDs
         * and then unsetting it on all memory related FDs.
         * This is not strictly necessary from a safety perspective.
         */
        syscall(__NR_close_range, 0, ~0U, CLOSE_RANGE_CLOEXEC);

        fcntl(init_data.stub_data_fd, F_SETFD, 0);

        /* dup2 signaling FD/socket to STDIN */
        if (dup2(tramp_data->sockpair[0], 0) < 0)
                exit(3);
        close(tramp_data->sockpair[0]);

        /* Write init_data and close write side */
        ret = write(tramp_data->sockpair[1], &init_data, sizeof(init_data));
        close(tramp_data->sockpair[1]);

        if (ret != sizeof(init_data))
                exit(4);

        /* Raw execveat for compatibility with older libc versions */
        syscall(__NR_execveat, stub_exe_fd, (unsigned long)"",
                (unsigned long)argv, NULL, AT_EMPTY_PATH);

        exit(5);
}

extern char stub_exe_start[];
extern char stub_exe_end[];

extern char *tempdir;

#define STUB_EXE_NAME_TEMPLATE "/uml-userspace-XXXXXX"

#ifndef MFD_EXEC
#define MFD_EXEC 0x0010U
#endif

static int __init init_stub_exe_fd(void)
{
        size_t written = 0;
        char *tmpfile = NULL;

        stub_exe_fd = memfd_create("uml-userspace",
                                   MFD_EXEC | MFD_CLOEXEC | MFD_ALLOW_SEALING);

        if (stub_exe_fd < 0) {
                printk(UM_KERN_INFO "Could not create executable memfd, using temporary file!");

                tmpfile = malloc(strlen(tempdir) +
                                  strlen(STUB_EXE_NAME_TEMPLATE) + 1);
                if (tmpfile == NULL)
                        panic("Failed to allocate memory for stub binary name");

                strcpy(tmpfile, tempdir);
                strcat(tmpfile, STUB_EXE_NAME_TEMPLATE);

                stub_exe_fd = mkstemp(tmpfile);
                if (stub_exe_fd < 0)
                        panic("Could not create temporary file for stub binary: %d",
                              -errno);
        }

        while (written < stub_exe_end - stub_exe_start) {
                ssize_t res = write(stub_exe_fd, stub_exe_start + written,
                                    stub_exe_end - stub_exe_start - written);
                if (res < 0) {
                        if (errno == EINTR)
                                continue;

                        if (tmpfile)
                                unlink(tmpfile);
                        panic("Failed write stub binary: %d", -errno);
                }

                written += res;
        }

        if (!tmpfile) {
                fcntl(stub_exe_fd, F_ADD_SEALS,
                      F_SEAL_WRITE | F_SEAL_SHRINK | F_SEAL_GROW | F_SEAL_SEAL);
        } else {
                if (fchmod(stub_exe_fd, 00500) < 0) {
                        unlink(tmpfile);
                        panic("Could not make stub binary executable: %d",
                              -errno);
                }

                close(stub_exe_fd);
                stub_exe_fd = open(tmpfile, O_RDONLY | O_CLOEXEC | O_NOFOLLOW);
                if (stub_exe_fd < 0) {
                        unlink(tmpfile);
                        panic("Could not reopen stub binary: %d", -errno);
                }

                unlink(tmpfile);
                free(tmpfile);
        }

        return 0;
}
__initcall(init_stub_exe_fd);

int using_seccomp;

/**
 * start_userspace() - prepare a new userspace process
 * @mm_id: The corresponding struct mm_id
 *
 * Setups a new temporary stack page that is used while userspace_tramp() runs
 * Clones the kernel process into a new userspace process, with FDs only.
 *
 * Return: When positive: the process id of the new userspace process,
 *         when negative: an error number.
 * FIXME: can PIDs become negative?!
 */
int start_userspace(struct mm_id *mm_id)
{
        struct stub_data *proc_data = (void *)mm_id->stack;
        struct tramp_data tramp_data = {
                .stub_data = proc_data,
        };
        void *stack;
        unsigned long sp;
        int status, n, err;

        /* setup a temporary stack page */
        stack = mmap(NULL, UM_KERN_PAGE_SIZE,
                     PROT_READ | PROT_WRITE | PROT_EXEC,
                     MAP_PRIVATE | MAP_ANONYMOUS, -1, 0);
        if (stack == MAP_FAILED) {
                err = -errno;
                printk(UM_KERN_ERR "%s : mmap failed, errno = %d\n",
                       __func__, errno);
                return err;
        }

        /* set stack pointer to the end of the stack page, so it can grow downwards */
        sp = (unsigned long)stack + UM_KERN_PAGE_SIZE;

        /* socket pair for init data and SECCOMP FD passing (no CLOEXEC here) */
        if (socketpair(AF_UNIX, SOCK_STREAM, 0, tramp_data.sockpair)) {
                err = -errno;
                printk(UM_KERN_ERR "%s : socketpair failed, errno = %d\n",
                       __func__, errno);
                return err;
        }

        if (using_seccomp)
                proc_data->futex = FUTEX_IN_CHILD;

        mm_id->pid = clone(userspace_tramp, (void *) sp,
                    CLONE_VFORK | CLONE_VM | SIGCHLD,
                    (void *)&tramp_data);
        if (mm_id->pid < 0) {
                err = -errno;
                printk(UM_KERN_ERR "%s : clone failed, errno = %d\n",
                       __func__, errno);
                goto out_close;
        }

        if (using_seccomp) {
                wait_stub_done_seccomp(mm_id, 1, 1);
        } else {
                do {
                        CATCH_EINTR(n = waitpid(mm_id->pid, &status,
                                                WUNTRACED | __WALL));
                        if (n < 0) {
                                err = -errno;
                                printk(UM_KERN_ERR "%s : wait failed, errno = %d\n",
                                       __func__, errno);
                                goto out_kill;
                        }
                } while (WIFSTOPPED(status) && (WSTOPSIG(status) == SIGALRM));

                if (!WIFSTOPPED(status) || (WSTOPSIG(status) != SIGSTOP)) {
                        err = -EINVAL;
                        printk(UM_KERN_ERR "%s : expected SIGSTOP, got status = %d\n",
                               __func__, status);
                        goto out_kill;
                }

                if (ptrace(PTRACE_SETOPTIONS, mm_id->pid, NULL,
                           (void *) PTRACE_O_TRACESYSGOOD) < 0) {
                        err = -errno;
                        printk(UM_KERN_ERR "%s : PTRACE_SETOPTIONS failed, errno = %d\n",
                               __func__, errno);
                        goto out_kill;
                }
        }

        if (munmap(stack, UM_KERN_PAGE_SIZE) < 0) {
                err = -errno;
                printk(UM_KERN_ERR "%s : munmap failed, errno = %d\n",
                       __func__, errno);
                goto out_kill;
        }

        close(tramp_data.sockpair[0]);
        if (using_seccomp)
                mm_id->sock = tramp_data.sockpair[1];
        else
                close(tramp_data.sockpair[1]);

        return 0;

out_kill:
        os_kill_ptraced_process(mm_id->pid, 1);
out_close:
        close(tramp_data.sockpair[0]);
        close(tramp_data.sockpair[1]);

        mm_id->pid = -1;

        return err;
}

static int unscheduled_userspace_iterations;
extern unsigned long tt_extra_sched_jiffies;

void userspace(struct uml_pt_regs *regs)
{
        int err, status, op;
        siginfo_t si_local;
        siginfo_t *si;
        int sig;

        /* Handle any immediate reschedules or signals */
        interrupt_end();

        while (1) {
                struct mm_id *mm_id = current_mm_id();

                /*
                 * At any given time, only one CPU thread can enter the
                 * turnstile to operate on the same stub process, including
                 * executing stub system calls (mmap and munmap).
                 */
                enter_turnstile(mm_id);

                /*
                 * When we are in time-travel mode, userspace can theoretically
                 * do a *lot* of work without being scheduled. The problem with
                 * this is that it will prevent kernel bookkeeping (primarily
                 * the RCU) from running and this can for example cause OOM
                 * situations.
                 *
                 * This code accounts a jiffie against the scheduling clock
                 * after the defined userspace iterations in the same thread.
                 * By doing so the situation is effectively prevented.
                 */
                if (time_travel_mode == TT_MODE_INFCPU ||
                    time_travel_mode == TT_MODE_EXTERNAL) {
#ifdef CONFIG_UML_MAX_USERSPACE_ITERATIONS
                        if (CONFIG_UML_MAX_USERSPACE_ITERATIONS &&
                            unscheduled_userspace_iterations++ >
                            CONFIG_UML_MAX_USERSPACE_ITERATIONS) {
                                tt_extra_sched_jiffies += 1;
                                unscheduled_userspace_iterations = 0;
                        }
#endif
                }

                time_travel_print_bc_msg();

                current_mm_sync();

                if (using_seccomp) {
                        struct stub_data *proc_data = (void *) mm_id->stack;

                        err = set_stub_state(regs, proc_data, singlestepping());
                        if (err) {
                                printk(UM_KERN_ERR "%s - failed to set regs: %d",
                                       __func__, err);
                                fatal_sigsegv();
                        }

                        /* Must have been reset by the syscall caller */
                        if (proc_data->restart_wait != 0)
                                panic("Programming error: Flag to only run syscalls in child was not cleared!");

                        /* Mark pending syscalls for flushing */
                        proc_data->syscall_data_len = mm_id->syscall_data_len;

                        wait_stub_done_seccomp(mm_id, 0, 0);

                        sig = proc_data->signal;

                        if (sig == SIGTRAP && proc_data->err != 0) {
                                printk(UM_KERN_ERR "%s - Error flushing stub syscalls",
                                       __func__);
                                syscall_stub_dump_error(mm_id);
                                mm_id->syscall_data_len = proc_data->err;
                                fatal_sigsegv();
                        }

                        mm_id->syscall_data_len = 0;
                        mm_id->syscall_fd_num = 0;

                        err = get_stub_state(regs, proc_data, NULL);
                        if (err) {
                                printk(UM_KERN_ERR "%s - failed to get regs: %d",
                                       __func__, err);
                                fatal_sigsegv();
                        }

                        if (proc_data->si_offset > sizeof(proc_data->sigstack) - sizeof(*si))
                                panic("%s - Invalid siginfo offset from child", __func__);

                        si = &si_local;
                        memcpy(si, &proc_data->sigstack[proc_data->si_offset], sizeof(*si));

                        regs->is_user = 1;

                        /* Fill in ORIG_RAX and extract fault information */
                        PT_SYSCALL_NR(regs->gp) = si->si_syscall;
                        if (sig == SIGSEGV) {
                                mcontext_t *mcontext = (void *)&proc_data->sigstack[proc_data->mctx_offset];

                                GET_FAULTINFO_FROM_MC(regs->faultinfo, mcontext);
                        }
                } else {
                        int pid = mm_id->pid;

                        /* Flush out any pending syscalls */
                        err = syscall_stub_flush(mm_id);
                        if (err) {
                                if (err == -ENOMEM)
                                        report_enomem();

                                printk(UM_KERN_ERR "%s - Error flushing stub syscalls: %d",
                                        __func__, -err);
                                fatal_sigsegv();
                        }

                        /*
                         * This can legitimately fail if the process loads a
                         * bogus value into a segment register.  It will
                         * segfault and PTRACE_GETREGS will read that value
                         * out of the process.  However, PTRACE_SETREGS will
                         * fail.  In this case, there is nothing to do but
                         * just kill the process.
                         */
                        if (ptrace(PTRACE_SETREGS, pid, 0, regs->gp)) {
                                printk(UM_KERN_ERR "%s - ptrace set regs failed, errno = %d\n",
                                       __func__, errno);
                                fatal_sigsegv();
                        }

                        if (put_fp_registers(pid, regs->fp)) {
                                printk(UM_KERN_ERR "%s - ptrace set fp regs failed, errno = %d\n",
                                       __func__, errno);
                                fatal_sigsegv();
                        }

                        if (singlestepping())
                                op = PTRACE_SYSEMU_SINGLESTEP;
                        else
                                op = PTRACE_SYSEMU;

                        if (ptrace(op, pid, 0, 0)) {
                                printk(UM_KERN_ERR "%s - ptrace continue failed, op = %d, errno = %d\n",
                                       __func__, op, errno);
                                fatal_sigsegv();
                        }

                        CATCH_EINTR(err = waitpid(pid, &status, WUNTRACED | __WALL));
                        if (err < 0) {
                                printk(UM_KERN_ERR "%s - wait failed, errno = %d\n",
                                       __func__, errno);
                                fatal_sigsegv();
                        }

                        regs->is_user = 1;
                        if (ptrace(PTRACE_GETREGS, pid, 0, regs->gp)) {
                                printk(UM_KERN_ERR "%s - PTRACE_GETREGS failed, errno = %d\n",
                                       __func__, errno);
                                fatal_sigsegv();
                        }

                        if (get_fp_registers(pid, regs->fp)) {
                                printk(UM_KERN_ERR "%s -  get_fp_registers failed, errno = %d\n",
                                       __func__, errno);
                                fatal_sigsegv();
                        }

                        if (WIFSTOPPED(status)) {
                                sig = WSTOPSIG(status);

                                /*
                                 * These signal handlers need the si argument
                                 * and SIGSEGV needs the faultinfo.
                                 * The SIGIO and SIGALARM handlers which constitute
                                 * the majority of invocations, do not use it.
                                 */
                                switch (sig) {
                                case SIGSEGV:
                                        get_skas_faultinfo(pid,
                                                           &regs->faultinfo);
                                        fallthrough;
                                case SIGTRAP:
                                case SIGILL:
                                case SIGBUS:
                                case SIGFPE:
                                case SIGWINCH:
                                        ptrace(PTRACE_GETSIGINFO, pid, 0,
                                               (struct siginfo *)&si_local);
                                        si = &si_local;
                                        break;
                                default:
                                        si = NULL;
                                        break;
                                }
                        } else {
                                sig = 0;
                        }
                }

                exit_turnstile(mm_id);

                UPT_SYSCALL_NR(regs) = -1; /* Assume: It's not a syscall */

                if (sig) {
                        switch (sig) {
                        case SIGSEGV:
                                if (using_seccomp || PTRACE_FULL_FAULTINFO)
                                        (*sig_info[SIGSEGV])(SIGSEGV,
                                                             (struct siginfo *)si,
                                                             regs, NULL);
                                else
                                        segv(regs->faultinfo, 0, 1, NULL, NULL);

                                break;
                        case SIGSYS:
                                handle_syscall(regs);
                                break;
                        case SIGTRAP + 0x80:
                                handle_trap(regs);
                                break;
                        case SIGTRAP:
                                relay_signal(SIGTRAP, (struct siginfo *)si, regs, NULL);
                                break;
                        case SIGALRM:
                                break;
                        case SIGIO:
                        case SIGILL:
                        case SIGBUS:
                        case SIGFPE:
                        case SIGWINCH:
                                block_signals_trace();
                                (*sig_info[sig])(sig, (struct siginfo *)si, regs, NULL);
                                unblock_signals_trace();
                                break;
                        default:
                                printk(UM_KERN_ERR "%s - child stopped with signal %d\n",
                                       __func__, sig);
                                fatal_sigsegv();
                        }
                        interrupt_end();

                        /* Avoid -ERESTARTSYS handling in host */
                        if (PT_SYSCALL_NR_OFFSET != PT_SYSCALL_RET_OFFSET)
                                PT_SYSCALL_NR(regs->gp) = -1;
                }
        }
}

void new_thread(void *stack, jmp_buf *buf, void (*handler)(void))
{
        (*buf)[0].JB_IP = (unsigned long) handler;
        (*buf)[0].JB_SP = (unsigned long) stack + UM_THREAD_SIZE -
                sizeof(void *);
}

#define INIT_JMP_NEW_THREAD 0
#define INIT_JMP_CALLBACK 1
#define INIT_JMP_HALT 2
#define INIT_JMP_REBOOT 3

void switch_threads(jmp_buf *me, jmp_buf *you)
{
        unscheduled_userspace_iterations = 0;

        if (UML_SETJMP(me) == 0)
                UML_LONGJMP(you, 1);
}

static jmp_buf initial_jmpbuf;

static __thread void (*cb_proc)(void *arg);
static __thread void *cb_arg;
static __thread jmp_buf *cb_back;

int start_idle_thread(void *stack, jmp_buf *switch_buf)
{
        int n;

        set_handler(SIGWINCH);

        /*
         * Can't use UML_SETJMP or UML_LONGJMP here because they save
         * and restore signals, with the possible side-effect of
         * trying to handle any signals which came when they were
         * blocked, which can't be done on this stack.
         * Signals must be blocked when jumping back here and restored
         * after returning to the jumper.
         */
        n = setjmp(initial_jmpbuf);
        switch (n) {
        case INIT_JMP_NEW_THREAD:
                (*switch_buf)[0].JB_IP = (unsigned long) uml_finishsetup;
                (*switch_buf)[0].JB_SP = (unsigned long) stack +
                        UM_THREAD_SIZE - sizeof(void *);
                break;
        case INIT_JMP_CALLBACK:
                (*cb_proc)(cb_arg);
                longjmp(*cb_back, 1);
                break;
        case INIT_JMP_HALT:
                kmalloc_ok = 0;
                return 0;
        case INIT_JMP_REBOOT:
                kmalloc_ok = 0;
                return 1;
        default:
                printk(UM_KERN_ERR "Bad sigsetjmp return in %s - %d\n",
                       __func__, n);
                fatal_sigsegv();
        }
        longjmp(*switch_buf, 1);

        /* unreachable */
        printk(UM_KERN_ERR "impossible long jump!");
        fatal_sigsegv();
        return 0;
}

void initial_thread_cb_skas(void (*proc)(void *), void *arg)
{
        jmp_buf here;

        cb_proc = proc;
        cb_arg = arg;
        cb_back = &here;

        initial_jmpbuf_lock();
        if (UML_SETJMP(&here) == 0)
                UML_LONGJMP(&initial_jmpbuf, INIT_JMP_CALLBACK);
        initial_jmpbuf_unlock();

        cb_proc = NULL;
        cb_arg = NULL;
        cb_back = NULL;
}

void halt_skas(void)
{
        initial_jmpbuf_lock();
        UML_LONGJMP(&initial_jmpbuf, INIT_JMP_HALT);
        /* unreachable */
}

static bool noreboot;

static int __init noreboot_cmd_param(char *str, int *add)
{
        *add = 0;
        noreboot = true;
        return 0;
}

__uml_setup("noreboot", noreboot_cmd_param,
"noreboot\n"
"    Rather than rebooting, exit always, akin to QEMU's -no-reboot option.\n"
"    This is useful if you're using CONFIG_PANIC_TIMEOUT in order to catch\n"
"    crashes in CI\n\n");

void reboot_skas(void)
{
        initial_jmpbuf_lock();
        UML_LONGJMP(&initial_jmpbuf, noreboot ? INIT_JMP_HALT : INIT_JMP_REBOOT);
        /* unreachable */
}