/*
 * Copyright (C) 2015 Thomas Meyer (thomas@m3y3r.de)
 * Copyright (C) 2002- 2007 Jeff Dike (jdike@{addtoit,linux.intel}.com)
 * Licensed under the GPL
 */

#include <stdlib.h>
#include <unistd.h>
#include <sched.h>
#include <errno.h>
#include <string.h>
#include <sys/mman.h>
#include <sys/wait.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 <linux/threads.h>

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

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++)
                printk(UM_KERN_ERR "\t%d - %lx\n", 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 "wait_stub_done : continue failed, "
                               "errno = %d\n", 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 "wait_stub_done : failed to wait for SIGTRAP, "
               "pid = %d, n = %d, errno = %d, status = 0x%x\n", pid, n, errno,
               status);
        fatal_sigsegv();
}

extern unsigned long current_stub_stack(void);

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

        err = get_fp_registers(pid, aux_fp_regs);
        if (err < 0) {
                printk(UM_KERN_ERR "save_fp_registers returned %d\n",
                       err);
                fatal_sigsegv();
        }
        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));

        err = put_fp_registers(pid, aux_fp_regs);
        if (err < 0) {
                printk(UM_KERN_ERR "put_fp_registers returned %d\n",
                       err);
                fatal_sigsegv();
        }
}

static void handle_segv(int pid, struct uml_pt_regs *regs, unsigned long *aux_fp_regs)
{
        get_skas_faultinfo(pid, &regs->faultinfo, aux_fp_regs);
        segv(regs->faultinfo, 0, 1, NULL);
}

/*
 * To use the same value of using_sysemu as the caller, ask it that value
 * (in local_using_sysemu
 */
static void handle_trap(int pid, struct uml_pt_regs *regs,
                        int local_using_sysemu)
{
        int err, status;

        if ((UPT_IP(regs) >= STUB_START) && (UPT_IP(regs) < STUB_END))
                fatal_sigsegv();

        if (!local_using_sysemu)
        {
                err = ptrace(PTRACE_POKEUSER, pid, PT_SYSCALL_NR_OFFSET,
                             __NR_getpid);
                if (err < 0) {
                        printk(UM_KERN_ERR "handle_trap - nullifying syscall "
                               "failed, errno = %d\n", errno);
                        fatal_sigsegv();
                }

                err = ptrace(PTRACE_SYSCALL, pid, 0, 0);
                if (err < 0) {
                        printk(UM_KERN_ERR "handle_trap - continuing to end of "
                               "syscall failed, errno = %d\n", errno);
                        fatal_sigsegv();
                }

                CATCH_EINTR(err = waitpid(pid, &status, WUNTRACED | __WALL));
                if ((err < 0) || !WIFSTOPPED(status) ||
                    (WSTOPSIG(status) != SIGTRAP + 0x80)) {
                        err = ptrace_dump_regs(pid);
                        if (err)
                                printk(UM_KERN_ERR "Failed to get registers "
                                       "from process, errno = %d\n", -err);
                        printk(UM_KERN_ERR "handle_trap - failed to wait at "
                               "end of syscall, errno = %d, status = %d\n",
                               errno, status);
                        fatal_sigsegv();
                }
        }

        handle_syscall(regs);
}

extern char __syscall_stub_start[];

/**
 * userspace_tramp() - userspace trampoline
 * @stack:      pointer to the new userspace stack page, can be NULL, if? FIXME:
 *
 * The userspace trampoline is used to setup a new userspace process in start_userspace() after it was clone()'ed.
 * This function will run on a temporary stack page.
 * It ptrace()'es itself, then
 * Two pages are mapped into the userspace address space:
 * - STUB_CODE (with EXEC), which contains the skas stub code
 * - STUB_DATA (with R/W), which contains a data page that is used to transfer certain data between the UML userspace process and the UML kernel.
 * Also for the userspace process a SIGSEGV handler is installed to catch pagefaults in the userspace process.
 * And last the process stops itself to give control to the UML kernel for this userspace process.
 *
 * Return: Always zero, otherwise the current userspace process is ended with non null exit() call
 */
static int userspace_tramp(void *stack)
{
        void *addr;
        int fd;
        unsigned long long offset;

        ptrace(PTRACE_TRACEME, 0, 0, 0);

        signal(SIGTERM, SIG_DFL);
        signal(SIGWINCH, SIG_IGN);

        /*
         * This has a pte, but it can't be mapped in with the usual
         * tlb_flush mechanism because this is part of that mechanism
         */
        fd = phys_mapping(to_phys(__syscall_stub_start), &offset);
        addr = mmap64((void *) STUB_CODE, UM_KERN_PAGE_SIZE,
                      PROT_EXEC, MAP_FIXED | MAP_PRIVATE, fd, offset);
        if (addr == MAP_FAILED) {
                printk(UM_KERN_ERR "mapping mmap stub at 0x%lx failed, "
                       "errno = %d\n", STUB_CODE, errno);
                exit(1);
        }

        if (stack != NULL) {
                fd = phys_mapping(to_phys(stack), &offset);
                addr = mmap((void *) STUB_DATA,
                            UM_KERN_PAGE_SIZE, PROT_READ | PROT_WRITE,
                            MAP_FIXED | MAP_SHARED, fd, offset);
                if (addr == MAP_FAILED) {
                        printk(UM_KERN_ERR "mapping segfault stack "
                               "at 0x%lx failed, errno = %d\n",
                               STUB_DATA, errno);
                        exit(1);
                }
        }
        if (stack != NULL) {
                struct sigaction sa;

                unsigned long v = STUB_CODE +
                                  (unsigned long) stub_segv_handler -
                                  (unsigned long) __syscall_stub_start;

                set_sigstack((void *) STUB_DATA, UM_KERN_PAGE_SIZE);
                sigemptyset(&sa.sa_mask);
                sa.sa_flags = SA_ONSTACK | SA_NODEFER | SA_SIGINFO;
                sa.sa_sigaction = (void *) v;
                sa.sa_restorer = NULL;
                if (sigaction(SIGSEGV, &sa, NULL) < 0) {
                        printk(UM_KERN_ERR "userspace_tramp - setting SIGSEGV "
                               "handler failed - errno = %d\n", errno);
                        exit(1);
                }
        }

        kill(os_getpid(), SIGSTOP);
        return 0;
}

int userspace_pid[NR_CPUS];

/**
 * start_userspace() - prepare a new userspace process
 * @stub_stack: pointer to the stub stack. Can be NULL, if? FIXME:
 *
 * 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(unsigned long stub_stack)
{
        void *stack;
        unsigned long sp;
        int pid, status, n, flags, 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 "start_userspace : mmap failed, "
                       "errno = %d\n", 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 - sizeof(void *);

        flags = CLONE_FILES | SIGCHLD;

        /* clone into new userspace process */
        pid = clone(userspace_tramp, (void *) sp, flags, (void *) stub_stack);
        if (pid < 0) {
                err = -errno;
                printk(UM_KERN_ERR "start_userspace : clone failed, "
                       "errno = %d\n", errno);
                return err;
        }

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

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

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

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

        return pid;

 out_kill:
        os_kill_ptraced_process(pid, 1);
        return err;
}

void userspace(struct uml_pt_regs *regs, unsigned long *aux_fp_regs)
{
        int err, status, op, pid = userspace_pid[0];
        /* To prevent races if using_sysemu changes under us.*/
        int local_using_sysemu;
        siginfo_t si;

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

        while (1) {

                /*
                 * 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 "userspace - ptrace set regs "
                               "failed, errno = %d\n", errno);
                        fatal_sigsegv();
                }

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

                /* Now we set local_using_sysemu to be used for one loop */
                local_using_sysemu = get_using_sysemu();

                op = SELECT_PTRACE_OPERATION(local_using_sysemu,
                                             singlestepping(NULL));

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

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

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

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

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

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

                        ptrace(PTRACE_GETSIGINFO, pid, 0, (struct siginfo *)&si);

                        switch (sig) {
                        case SIGSEGV:
                                if (PTRACE_FULL_FAULTINFO) {
                                        get_skas_faultinfo(pid,
                                                           &regs->faultinfo, aux_fp_regs);
                                        (*sig_info[SIGSEGV])(SIGSEGV, (struct siginfo *)&si,
                                                             regs);
                                }
                                else handle_segv(pid, regs, aux_fp_regs);
                                break;
                        case SIGTRAP + 0x80:
                                handle_trap(pid, regs, local_using_sysemu);
                                break;
                        case SIGTRAP:
                                relay_signal(SIGTRAP, (struct siginfo *)&si, regs);
                                break;
                        case SIGALRM:
                                break;
                        case SIGIO:
                        case SIGILL:
                        case SIGBUS:
                        case SIGFPE:
                        case SIGWINCH:
                                block_signals();
                                (*sig_info[sig])(sig, (struct siginfo *)&si, regs);
                                unblock_signals();
                                break;
                        default:
                                printk(UM_KERN_ERR "userspace - child stopped "
                                       "with signal %d\n", sig);
                                fatal_sigsegv();
                        }
                        pid = userspace_pid[0];
                        interrupt_end();

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

static unsigned long thread_regs[MAX_REG_NR];
static unsigned long thread_fp_regs[FP_SIZE];

static int __init init_thread_regs(void)
{
        get_safe_registers(thread_regs, thread_fp_regs);
        /* Set parent's instruction pointer to start of clone-stub */
        thread_regs[REGS_IP_INDEX] = STUB_CODE +
                                (unsigned long) stub_clone_handler -
                                (unsigned long) __syscall_stub_start;
        thread_regs[REGS_SP_INDEX] = STUB_DATA + UM_KERN_PAGE_SIZE -
                sizeof(void *);
#ifdef __SIGNAL_FRAMESIZE
        thread_regs[REGS_SP_INDEX] -= __SIGNAL_FRAMESIZE;
#endif
        return 0;
}

__initcall(init_thread_regs);

int copy_context_skas0(unsigned long new_stack, int pid)
{
        int err;
        unsigned long current_stack = current_stub_stack();
        struct stub_data *data = (struct stub_data *) current_stack;
        struct stub_data *child_data = (struct stub_data *) new_stack;
        unsigned long long new_offset;
        int new_fd = phys_mapping(to_phys((void *)new_stack), &new_offset);

        /*
         * prepare offset and fd of child's stack as argument for parent's
         * and child's mmap2 calls
         */
        *data = ((struct stub_data) {
                        .offset = MMAP_OFFSET(new_offset),
                        .fd     = new_fd
        });

        err = ptrace_setregs(pid, thread_regs);
        if (err < 0) {
                err = -errno;
                printk(UM_KERN_ERR "copy_context_skas0 : PTRACE_SETREGS "
                       "failed, pid = %d, errno = %d\n", pid, -err);
                return err;
        }

        err = put_fp_registers(pid, thread_fp_regs);
        if (err < 0) {
                printk(UM_KERN_ERR "copy_context_skas0 : put_fp_registers "
                       "failed, pid = %d, err = %d\n", pid, err);
                return err;
        }

        /* set a well known return code for detection of child write failure */
        child_data->err = 12345678;

        /*
         * Wait, until parent has finished its work: read child's pid from
         * parent's stack, and check, if bad result.
         */
        err = ptrace(PTRACE_CONT, pid, 0, 0);
        if (err) {
                err = -errno;
                printk(UM_KERN_ERR "Failed to continue new process, pid = %d, "
                       "errno = %d\n", pid, errno);
                return err;
        }

        wait_stub_done(pid);

        pid = data->err;
        if (pid < 0) {
                printk(UM_KERN_ERR "copy_context_skas0 - stub-parent reports "
                       "error %d\n", -pid);
                return pid;
        }

        /*
         * Wait, until child has finished too: read child's result from
         * child's stack and check it.
         */
        wait_stub_done(pid);
        if (child_data->err != STUB_DATA) {
                printk(UM_KERN_ERR "copy_context_skas0 - stub-child reports "
                       "error %ld\n", child_data->err);
                err = child_data->err;
                goto out_kill;
        }

        if (ptrace(PTRACE_OLDSETOPTIONS, pid, NULL,
                   (void *)PTRACE_O_TRACESYSGOOD) < 0) {
                err = -errno;
                printk(UM_KERN_ERR "copy_context_skas0 : PTRACE_OLDSETOPTIONS "
                       "failed, errno = %d\n", errno);
                goto out_kill;
        }

        return pid;

 out_kill:
        os_kill_ptraced_process(pid, 1);
        return err;
}

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

static jmp_buf initial_jmpbuf;

/* XXX Make these percpu */
static void (*cb_proc)(void *arg);
static void *cb_arg;
static 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 "
                       "start_idle_thread - %d\n", 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;

        block_signals();
        if (UML_SETJMP(&here) == 0)
                UML_LONGJMP(&initial_jmpbuf, INIT_JMP_CALLBACK);
        unblock_signals();

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

void halt_skas(void)
{
        block_signals();
        UML_LONGJMP(&initial_jmpbuf, INIT_JMP_HALT);
}

void reboot_skas(void)
{
        block_signals();
        UML_LONGJMP(&initial_jmpbuf, INIT_JMP_REBOOT);
}

void __switch_mm(struct mm_id *mm_idp)
{
        userspace_pid[0] = mm_idp->u.pid;
}