usr.sbin/makefs/ffs: Remove m_buf::b_is_hammer2

[dragonfly.git] / sys / kern / kern_exec.c

/*
 * Copyright (c) 1993, David Greenman
 * All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer.
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in the
 *    documentation and/or other materials provided with the distribution.
 *
 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
 * ARE DISCLAIMED.  IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
 * SUCH DAMAGE.
 *
 * $FreeBSD: src/sys/kern/kern_exec.c,v 1.107.2.15 2002/07/30 15:40:46 nectar Exp $
 */

#include <sys/param.h>
#include <sys/systm.h>
#include <sys/sysmsg.h>
#include <sys/kernel.h>
#include <sys/mount.h>
#include <sys/filedesc.h>
#include <sys/fcntl.h>
#include <sys/acct.h>
#include <sys/exec.h>
#include <sys/imgact.h>
#include <sys/imgact_elf.h>
#include <sys/kern_syscall.h>
#include <sys/wait.h>
#include <sys/malloc.h>
#include <sys/proc.h>
#include <sys/priv.h>
#include <sys/ktrace.h>
#include <sys/signalvar.h>
#include <sys/pioctl.h>
#include <sys/nlookup.h>
#include <sys/sysent.h>
#include <sys/shm.h>
#include <sys/sysctl.h>
#include <sys/vnode.h>
#include <sys/vmmeter.h>
#include <sys/libkern.h>

#include <cpu/lwbuf.h>

#include <vm/vm.h>
#include <vm/vm_param.h>
#include <sys/lock.h>
#include <vm/pmap.h>
#include <vm/vm_page.h>
#include <vm/vm_map.h>
#include <vm/vm_kern.h>
#include <vm/vm_extern.h>
#include <vm/vm_object.h>
#include <vm/vnode_pager.h>
#include <vm/vm_pager.h>

#include <sys/reg.h>

#include <sys/objcache.h>
#include <sys/refcount.h>
#include <sys/thread2.h>
#include <vm/vm_page2.h>

MALLOC_DEFINE(M_PARGS, "proc-args", "Process arguments");
MALLOC_DEFINE(M_EXECARGS, "exec-args", "Exec arguments");

enum exec_path_segflg {
        PATH_SYSSPACE,
        PATH_USERSPACE,
};

static register_t *exec_copyout_strings(struct image_params *);
static int      exec_copyin_args(struct image_args *, char *,
                                 enum exec_path_segflg, char **, char **);
static void     exec_free_args(struct image_args *);
static void     print_execve_args(struct image_args *args);

/* XXX This should be vm_size_t. */
__read_mostly static u_long ps_strings = PS_STRINGS;
SYSCTL_ULONG(_kern, KERN_PS_STRINGS, ps_strings, CTLFLAG_RD, &ps_strings, 0, "");

/* XXX This should be vm_size_t. */
__read_mostly static u_long usrstack = USRSTACK;
SYSCTL_ULONG(_kern, KERN_USRSTACK, usrstack, CTLFLAG_RD, &usrstack, 0, "");

__read_mostly u_long ps_arg_cache_limit = PAGE_SIZE / 16;
SYSCTL_LONG(_kern, OID_AUTO, ps_arg_cache_limit, CTLFLAG_RW, 
    &ps_arg_cache_limit, 0, "");

__read_mostly int ps_argsopen = 1;
SYSCTL_INT(_kern, OID_AUTO, ps_argsopen, CTLFLAG_RW, &ps_argsopen, 0, "");

__read_mostly static int ktrace_suid = 0;
SYSCTL_INT(_kern, OID_AUTO, ktrace_suid, CTLFLAG_RW, &ktrace_suid, 0, "");

__read_mostly static int debug_execve_args = 0;
SYSCTL_INT(_kern, OID_AUTO, debug_execve_args, CTLFLAG_RW, &debug_execve_args,
    0, "");

/*
 * Exec arguments object cache
 */
__read_mostly static struct objcache *exec_objcache;

static
void
exec_objcache_init(void *arg __unused)
{
        int cluster_limit;
        size_t limsize;

        /*
         * Maximum number of concurrent execs.  This can be limiting on
         * systems with a lot of cpu cores but it also eats a significant
         * amount of memory.
         */
        cluster_limit = (ncpus < 16) ? 16 : ncpus;
        limsize = kmem_lim_size();
        if (limsize > 7 * 1024)
                cluster_limit *= 2;
        if (limsize > 15 * 1024)
                cluster_limit *= 2;

        exec_objcache = objcache_create_mbacked(
                                        M_EXECARGS, PATH_MAX + ARG_MAX,
                                        cluster_limit, 8,
                                        NULL, NULL, NULL);
}
SYSINIT(exec_objcache, SI_BOOT2_MACHDEP, SI_ORDER_ANY, exec_objcache_init, 0);

/*
 * stackgap_random specifies if the stackgap should have a random size added
 * to it.  It must be a power of 2.  If non-zero, the stack gap will be 
 * calculated as: ALIGN(karc4random() & (stackgap_random - 1)).
 */
__read_mostly static int stackgap_random = 1024;

static int
sysctl_kern_stackgap(SYSCTL_HANDLER_ARGS)
{
        int error, new_val;
        new_val = stackgap_random;
        error = sysctl_handle_int(oidp, &new_val, 0, req);
        if (error != 0 || req->newptr == NULL)
                return (error);
        if (new_val > 0 && ((new_val > 16 * PAGE_SIZE) || !powerof2(new_val)))
                return (EINVAL);
        stackgap_random = new_val;

        return(0);
}

SYSCTL_PROC(_kern, OID_AUTO, stackgap_random, CTLFLAG_RW|CTLTYPE_INT,
        0, 0, sysctl_kern_stackgap, "I",
        "Max random stack gap (power of 2), static gap if negative");

static void
print_execve_args(struct image_args *args)
{
        char *cp;
        int ndx;

        cp = args->begin_argv;
        for (ndx = 0; ndx < args->argc; ndx++) {
                kprintf("\targv[%d]: %s\n", ndx, cp);
                while (*cp++ != '\0');
        }
        for (ndx = 0; ndx < args->envc; ndx++) {
                kprintf("\tenvv[%d]: %s\n", ndx, cp);
                while (*cp++ != '\0');
        }
}

/*
 * Each of the items is a pointer to a `const struct execsw', hence the
 * double pointer here.
 */
__read_mostly static const struct execsw **execsw;

/*
 * Replace current vmspace with a new binary.
 * Returns 0 on success, > 0 on recoverable error (use as errno).
 * Returns -1 on lethal error which demands killing of the current
 * process!
 */
int
kern_execve(struct nlookupdata *nd, struct file *fp, char fileflags,
            struct image_args *args)
{
        static const char *proctitle = "(execve)";
        register_t *stack_base;
        struct thread *td = curthread;
        struct lwp *lp = td->td_lwp;
        struct proc *p = td->td_proc;
        struct vnode *ovp;
        struct pargs *pa;
        struct sigacts *ops;
        struct sigacts *nps;
        struct image_params image_params, *imgp;
        struct filedesc *fds;
        struct nchandle *nch;
        struct nlookupdata nd_interpreter;
        struct vattr_lite lva;
        int error, len, i;
        int (*img_first) (struct image_params *);

        if (debug_execve_args) {
                kprintf("%s()\n", __func__);
                print_execve_args(args);
        }

        KKASSERT(p);
        lwkt_gettoken(&p->p_token);
        imgp = &image_params;

        /*
         * NOTE: P_INEXEC is handled by exec_new_vmspace() now.  We make
         * no modifications to the process at all until we get there.
         *
         * Note that multiple threads may be trying to exec at the same
         * time.  exec_new_vmspace() handles that too.
         */

        /*
         * Initialize part of the common data
         */
        imgp->proc = p;
        imgp->args = args;
        imgp->lvap = &lva;
        imgp->entry_addr = 0;
        imgp->resident = 0;
        imgp->vmspace_destroyed = 0;
        imgp->interpreted = 0;
        imgp->interpreter_name[0] = 0;
        imgp->auxargs = NULL;
        imgp->vp = NULL;
        imgp->firstpage = NULL;
        imgp->ps_strings = 0;
        imgp->execpath = imgp->freepath = NULL;
        imgp->execpathp = 0;
        imgp->image_header = NULL;

interpret:

        if (nd) {
                /*
                 * Translate the file name to a vnode.  Unlock the cache
                 * entry to improve parallelism for programs exec'd in
                 * parallel.
                 */
                nch = &nd->nl_nch;
                nd->nl_flags |= NLC_SHAREDLOCK;
                if ((error = nlookup(nd)) != 0)
                        goto failed;

                error = cache_vget(nch, nd->nl_cred, LK_SHARED, &imgp->vp);
                KKASSERT(nd->nl_flags & NLC_NCPISLOCKED);
                nd->nl_flags &= ~NLC_NCPISLOCKED;
                cache_unlock(nch);
        } else {
                nch = &fp->f_nchandle;
                imgp->vp = fp->f_data;
                error = vget(imgp->vp, LK_SHARED);
        }
        if (error) {
                imgp->vp = NULL;
                goto failed;
        }

        /*
         * Check file permissions (also 'opens' file).
         * Include also the top level mount in the check.
         */
        error = exec_check_permissions(imgp, nch->mount);
        if (error) {
                vn_unlock(imgp->vp);
                goto failed;
        }

        error = exec_map_first_page(imgp);
        vn_unlock(imgp->vp);
        if (error)
                goto failed;

        imgp->proc->p_osrel = 0;

        if (debug_execve_args && imgp->interpreted) {
                kprintf("    target is interpreted -- recursive pass\n");
                kprintf("    interpreter: %s\n", imgp->interpreter_name);
                print_execve_args(args);
        }

        /*
         *      If the current process has a special image activator it
         *      wants to try first, call it.  For example, emulating shell
         *      scripts differently.
         */
        error = -1;
        if ((img_first = imgp->proc->p_sysent->sv_imgact_try) != NULL)
                error = img_first(imgp);

        /*
         *      If the vnode has a registered vmspace, exec the vmspace
         */
        if (error == -1 && imgp->vp->v_resident)
                error = exec_resident_imgact(imgp);

        /*
         *      Loop through the list of image activators, calling each one.
         *      An activator returns -1 if there is no match, 0 on success,
         *      and an error otherwise.
         */
        for (i = 0; error == -1 && execsw[i]; ++i) {
                if (execsw[i]->ex_imgact == NULL ||
                    execsw[i]->ex_imgact == img_first) {
                        continue;
                }
                error = (*execsw[i]->ex_imgact)(imgp);
        }

        if (error) {
                if (error == -1)
                        error = ENOEXEC;
                goto failed;
        }

        /*
         * Special interpreter operation, cleanup and loop up to try to
         * activate the interpreter.
         */
        if (imgp->interpreted) {
                exec_unmap_first_page(imgp);
                vrele(imgp->vp);
                imgp->vp = NULL;

                nd = &nd_interpreter;
                error = nlookup_init(nd, imgp->interpreter_name,
                                     UIO_SYSSPACE, NLC_FOLLOW);
                if (error)
                        goto failed;

                if (fp && (fileflags & UF_EXCLOSE)) {
                        /*
                         * Fexecve'ing an interpreted file opened with
                         * O_CLOEXEC flag, return ENOENT.
                         */
                        error = ENOENT;
                        goto failed;
                }

                goto interpret;
        }

        /*
         * Do the best to calculate the full path to the image file
         */
        if (imgp->auxargs != NULL &&
            ((args->fname != NULL && args->fname[0] == '/') ||
             vn_fullpath(imgp->proc, imgp->vp, &imgp->execpath,
                         &imgp->freepath, 0) != 0))
        {
                imgp->execpath = args->fname;
        }

        /*
         * Copy out strings (args and env) and initialize stack base
         */
        stack_base = exec_copyout_strings(imgp);
        p->p_vmspace->vm_minsaddr = (char *)stack_base;

        /*
         * If custom stack fixup routine present for this process
         * let it do the stack setup.  If we are running a resident
         * image there is no auxinfo or other image activator context
         * so don't try to add fixups to the stack.
         *
         * Else stuff argument count as first item on stack
         */
        if (p->p_sysent->sv_fixup && imgp->resident == 0)
                (*p->p_sysent->sv_fixup)(&stack_base, imgp);
        else
                suword64(--stack_base, imgp->args->argc);

        /*
         * For security and other reasons, the file descriptor table cannot
         * be shared after an exec.
         */
        if (p->p_fd->fd_refcnt > 1) {
                if ((error = fdcopy(p, &fds)) != 0)
                        goto failed;

                fdfree(p, fds);
        }

        /*
         * For security and other reasons, signal handlers cannot
         * be shared after an exec. The new proces gets a copy of the old
         * handlers. In execsigs(), the new process will have its signals
         * reset.
         */
        ops = p->p_sigacts;
        if (ops->ps_refcnt > 1) {
                nps = kmalloc(sizeof(*nps), M_SUBPROC, M_WAITOK);
                bcopy(ops, nps, sizeof(*nps));
                refcount_init(&nps->ps_refcnt, 1);
                p->p_sigacts = nps;
                if (refcount_release(&ops->ps_refcnt)) {
                        kfree(ops, M_SUBPROC);
                        ops = NULL;
                }
        }

        /*
         * Clean up shared pages, the new program will allocate fresh
         * copies as needed.  This is also for security purposes and
         * to ensure (for example) that things like sys_lpmap->blockallsigs
         * state is properly reset on exec.
         */
        lwp_userunmap(lp);
        proc_userunmap(p);

        /*
         * For security and other reasons virtual kernels cannot be
         * inherited by an exec.  This also allows a virtual kernel
         * to fork/exec unrelated applications.
         */
        if (p->p_vkernel)
                vkernel_exit(p);

        /* Stop profiling */
        stopprofclock(p);

        /* close files on exec */
        fdcloseexec(p);

        /* reset caught signals */
        execsigs(p);

        /* name this process */
        if (nch->ncp) {
                len = min(nch->ncp->nc_nlen, MAXCOMLEN);
                bcopy(nch->ncp->nc_name, p->p_comm, len);
        } else {
                len = sizeof(proctitle) - 1;
                bcopy(proctitle, p->p_comm, len);
        }
        p->p_comm[len] = 0;
        bcopy(p->p_comm, lp->lwp_thread->td_comm, MAXCOMLEN+1);

        /*
         * mark as execed, wakeup the process that vforked (if any) and tell
         * it that it now has its own resources back
         *
         * We are using the P_PPWAIT as an interlock so an atomic op is
         * necessary to synchronize with the parent's cpu.
         */
        p->p_flags |= P_EXEC;
        if (p->p_pptr && (p->p_flags & P_PPWAIT)) {
                if (p->p_pptr->p_upmap)
                        atomic_add_int(&p->p_pptr->p_upmap->invfork, -1);
                atomic_clear_int(&p->p_flags, P_PPWAIT);
                wakeup(p->p_pptr);
        }

        /*
         * Implement image setuid/setgid.
         *
         * Don't honor setuid/setgid if the filesystem prohibits it or if
         * the process is being traced.
         */
        if ((((lva.va_mode & VSUID) && p->p_ucred->cr_uid != lva.va_uid) ||
             ((lva.va_mode & VSGID) && p->p_ucred->cr_gid != lva.va_gid)) &&
            (imgp->vp->v_mount->mnt_flag & MNT_NOSUID) == 0 &&
            (p->p_flags & P_TRACED) == 0) {
                /*
                 * Turn off syscall tracing for set-id programs, except for
                 * root.  Record any set-id flags first to make sure that
                 * we do not regain any tracing during a possible block.
                 */
                setsugid();
                if (p->p_tracenode && ktrace_suid == 0 &&
                    priv_check(td, PRIV_ROOT) != 0) {
                        ktrdestroy(&p->p_tracenode);
                        p->p_traceflag = 0;
                }

                /* Clear any PROC_PDEATHSIG_CTL setting */
                p->p_deathsig = 0;

                /* Close any file descriptors 0..2 that reference procfs */
                setugidsafety(p);
                /* Make sure file descriptors 0..2 are in use. */
                error = fdcheckstd(lp);
                if (error != 0)
                        goto failed;

                /*
                 * Set the new credentials.
                 */
                cratom_proc(p);
                if (lva.va_mode & VSUID)
                        change_euid(lva.va_uid);
                if (lva.va_mode & VSGID)
                        p->p_ucred->cr_gid = lva.va_gid;

                /* Clear local varsym variables */
                varsymset_clean(&p->p_varsymset);
        } else {
                if (p->p_ucred->cr_uid == p->p_ucred->cr_ruid &&
                    p->p_ucred->cr_gid == p->p_ucred->cr_rgid)
                        p->p_flags &= ~P_SUGID;
        }

        /*
         * Implement correct POSIX saved-id behavior.
         */
        if (p->p_ucred->cr_svuid != p->p_ucred->cr_uid ||
            p->p_ucred->cr_svgid != p->p_ucred->cr_gid) {
                cratom_proc(p);
                p->p_ucred->cr_svuid = p->p_ucred->cr_uid;
                p->p_ucred->cr_svgid = p->p_ucred->cr_gid;
        }

        /*
         * Store the vp for use in procfs.  Be sure to keep p_textvp
         * consistent if we block during the switch-over.
         */
        ovp = p->p_textvp;
        vref(imgp->vp);                 /* ref new vp */
        p->p_textvp = imgp->vp;
        if (ovp)                        /* release old vp */
                vrele(ovp);

        /* Release old namecache handle to text file */
        if (p->p_textnch.ncp)
                cache_drop(&p->p_textnch);
        if (nch->mount)
                cache_copy(nch, &p->p_textnch);

        /*
         * Notify others that we exec'd, and clear the P_INEXEC flag
         * as we're now a bona fide freshly-execed process.
         */
        KNOTE(&p->p_klist, NOTE_EXEC);
        p->p_flags &= ~P_INEXEC;
        if (p->p_stops)
                wakeup(&p->p_stype);

        /*
         * If tracing the process, trap to debugger so breakpoints
         *      can be set before the program executes.
         */
        STOPEVENT(p, S_EXEC, 0);

        if (p->p_flags & P_TRACED)
                ksignal(p, SIGTRAP);

        /* clear "fork but no exec" flag, as we _are_ execing */
        p->p_acflag &= ~AFORK;

        /* Set values passed into the program in registers. */
        exec_setregs(imgp->entry_addr, (u_long)(uintptr_t)stack_base,
                     imgp->ps_strings);

        /* Set the access time on the vnode */
        vn_mark_atime(imgp->vp, td);

        /*
         * Free any previous argument cache
         */
        pa = p->p_args;
        p->p_args = NULL;
        if (pa && refcount_release(&pa->ar_ref)) {
                kfree(pa, M_PARGS);
                pa = NULL;
        }

        /*
         * Cache arguments if they fit inside our allowance
         */
        i = imgp->args->begin_envv - imgp->args->begin_argv;
        if (sizeof(struct pargs) + i <= ps_arg_cache_limit) {
                pa = kmalloc(sizeof(struct pargs) + i, M_PARGS, M_WAITOK);
                refcount_init(&pa->ar_ref, 1);
                pa->ar_length = i;
                bcopy(imgp->args->begin_argv, pa->ar_args, i);
                KKASSERT(p->p_args == NULL);
                p->p_args = pa;
        }

failed:

        /*
         * free various allocated resources
         */
        if (imgp->firstpage)
                exec_unmap_first_page(imgp);
        if (imgp->vp)
                vrele(imgp->vp);
        if (imgp->freepath)
                kfree(imgp->freepath, M_TEMP);
        if (nd == &nd_interpreter)
                nlookup_done(nd);

        if (error == 0) {
                ++mycpu->gd_cnt.v_exec;
                lwkt_reltoken(&p->p_token);
                return (0);
        }

        /*
         * we're done here, clear P_INEXEC if we were the ones that
         * set it.  Otherwise if vmspace_destroyed is still set we
         * raced another thread and that thread is responsible for
         * clearing it.
         */
        if (imgp->vmspace_destroyed & 2) {
                p->p_flags &= ~P_INEXEC;
                if (p->p_stops)
                        wakeup(&p->p_stype);
        }
        lwkt_reltoken(&p->p_token);
        if (imgp->vmspace_destroyed) {
                /*
                 * Sorry, no more process anymore. exit gracefully.
                 * However we can't die right here, because our
                 * caller might have to clean up, so indicate a
                 * lethal error by returning -1.
                 */
                return (-1);
        } else {
                return (error);
        }
}

/*
 * execve() system call.
 */
int
sys_execve(struct sysmsg *sysmsg, const struct execve_args *uap)
{
        struct nlookupdata nd;
        struct image_args args;
        int error;

        bzero(&args, sizeof(args));

        error = nlookup_init(&nd, uap->fname, UIO_USERSPACE, NLC_FOLLOW);
        if (error == 0) {
                error = exec_copyin_args(&args, uap->fname, PATH_USERSPACE,
                                         uap->argv, uap->envv);
        }
        if (error == 0)
                error = kern_execve(&nd, NULL, 0, &args);
        nlookup_done(&nd);
        exec_free_args(&args);

        if (error < 0) {
                /* We hit a lethal error condition.  Let's die now. */
                exit1(W_EXITCODE(0, SIGABRT));
                /* NOTREACHED */
        }

        /*
         * The syscall result is returned in registers to the new program.
         * Linux will register %edx as an atexit function and we must be
         * sure to set it to 0.  XXX
         */
        if (error == 0)
                sysmsg->sysmsg_result64 = 0;

        return (error);
}

/*
 * fexecve() system call.
 */
int
sys_fexecve(struct sysmsg *sysmsg, const struct fexecve_args *uap)
{
        struct image_args args;
        struct thread *td = curthread;
        struct file *fp;
        char fileflags;
        char fname[32]; /* "/dev/fd/xxx" */
        int error;

        if ((error = holdvnode2(td, uap->fd, &fp, &fileflags)) != 0)
                return (error);

        /*
         * Require a descriptor opened only with O_RDONLY or O_EXEC.
         * XXX: missing O_EXEC support
         */
        if ((fp->f_flag & FWRITE) != 0 || (fp->f_flag & FREAD) == 0) {
                error = EBADF;
                goto done;
        }

        /*
         * The 'fname' argument is required when executing an
         * interpreted program because the interpreter must know
         * the script path.  Supply it with '/dev/fd/xxx'.
         */
        ksnprintf(fname, sizeof(fname), "/dev/fd/%d", uap->fd);
        bzero(&args, sizeof(args));
        error = exec_copyin_args(&args, fname, PATH_SYSSPACE,
                                 uap->argv, uap->envv);
        if (error == 0)
                error = kern_execve(NULL, fp, fileflags, &args);
        exec_free_args(&args);

        if (error < 0) {
                /* We hit a lethal error condition.  Let's die now. */
                exit1(W_EXITCODE(0, SIGABRT));
                /* NOTREACHED */
        }

        /*
         * The syscall result is returned in registers to the new program.
         * Linux will register %edx as an atexit function and we must be
         * sure to set it to 0.  XXX
         */
        if (error == 0)
                sysmsg->sysmsg_result64 = 0;

done:
        fdrop(fp);
        return (error);
}

int
exec_map_page(struct image_params *imgp, vm_pindex_t pageno,
              struct lwbuf **plwb, const char **pdata)
{
        int rv;
        vm_page_t ma;
        vm_page_t m;
        vm_object_t object;

        /*
         * The file has to be mappable.
         */
        if ((object = imgp->vp->v_object) == NULL)
                return (EIO);

        if (pageno >= object->size)
                return (EIO);

        /*
         * Shortcut using shared locks, improve concurrent execs.
         */
        vm_object_hold_shared(object);
        m = vm_page_lookup(object, pageno);
        if (m) {
                if ((m->valid & VM_PAGE_BITS_ALL) == VM_PAGE_BITS_ALL) {
                        vm_page_hold(m);
                        vm_page_sleep_busy(m, FALSE, "execpg");
                        if ((m->valid & VM_PAGE_BITS_ALL) == VM_PAGE_BITS_ALL &&
                            m->object == object && m->pindex == pageno) {
                                vm_object_drop(object);
                                goto done;
                        }
                        vm_page_unhold(m);
                }
        }
        vm_object_drop(object);

        /*
         * Do it the hard way
         */
        vm_object_hold(object);
        m = vm_page_grab(object, pageno, VM_ALLOC_NORMAL | VM_ALLOC_RETRY);
        while ((m->valid & VM_PAGE_BITS_ALL) != VM_PAGE_BITS_ALL) {
                ma = m;

                /*
                 * get_pages unbusies all the requested pages except the
                 * primary page (at index 0 in this case).  The primary
                 * page may have been wired during the pagein (e.g. by
                 * the buffer cache) so vnode_pager_freepage() must be
                 * used to properly release it.
                 */
                rv = vm_pager_get_page(object, pageno, &ma, 1);
                m = vm_page_lookup(object, pageno);

                if (rv != VM_PAGER_OK || m == NULL || m->valid == 0) {
                        if (m) {
                                vm_page_protect(m, VM_PROT_NONE);
                                vnode_pager_freepage(m);
                        }
                        vm_object_drop(object);
                        return EIO;
                }
        }
        vm_page_hold(m);
        vm_page_wakeup(m);      /* unbusy the page */
        vm_object_drop(object);

done:
        *plwb = lwbuf_alloc(m, *plwb);
        *pdata = (void *)lwbuf_kva(*plwb);

        return (0);
}

/*
 * Map the first page of an executable image.
 *
 * NOTE: If the mapping fails we have to NULL-out firstpage which may
 *       still be pointing to our supplied lwp structure.
 */
int
exec_map_first_page(struct image_params *imgp)
{
        int err;

        if (imgp->firstpage)
                exec_unmap_first_page(imgp);

        imgp->firstpage = &imgp->firstpage_cache;
        err = exec_map_page(imgp, 0, &imgp->firstpage, &imgp->image_header);

        if (err) {
                imgp->firstpage = NULL;
                return err;
        }

        return 0;
}

void
exec_unmap_page(struct lwbuf *lwb)
{
        vm_page_t m;

        crit_enter();
        if (lwb != NULL) {
                m = lwbuf_page(lwb);
                lwbuf_free(lwb);
                vm_page_unhold(m);
        }
        crit_exit();
}

void
exec_unmap_first_page(struct image_params *imgp)
{
        exec_unmap_page(imgp->firstpage);
        imgp->firstpage = NULL;
        imgp->image_header = NULL;
}

/*
 * Destroy old address space, and allocate a new stack
 *      The new stack is only SGROWSIZ large because it is grown
 *      automatically in trap.c.
 *
 * This is the point of no return.
 */
int
exec_new_vmspace(struct image_params *imgp, struct vmspace *vmcopy)
{
        struct vmspace *vmspace = imgp->proc->p_vmspace;
        vm_offset_t stack_addr = USRSTACK - maxssiz;
        struct lwp *lp;
        struct proc *p;
        vm_map_t map;
        int error;

        /*
         * Indicate that we cannot gracefully error out any more, kill
         * any other threads present, and set P_INEXEC to indicate that
         * we are now messing with the process structure proper.
         *
         * If killalllwps() races return an error which coupled with
         * vmspace_destroyed will cause us to exit.  This is what we
         * want since another thread is patiently waiting for us to exit
         * in that case.
         */
        lp = curthread->td_lwp;
        p = lp->lwp_proc;
        imgp->vmspace_destroyed = 1;

        if (curthread->td_proc->p_nthreads > 1) {
                error = killalllwps(1);
                if (error)
                        return (error);
        }
        imgp->vmspace_destroyed |= 2;   /* we are responsible for P_INEXEC */
        p->p_flags |= P_INEXEC;

        /*
         * Tell procfs to release its hold on the process.  It
         * will return EAGAIN.
         */
        if (p->p_stops)
                wakeup(&p->p_stype);

        /*
         * After setting P_INEXEC wait for any remaining references to
         * the process (p) to go away.
         *
         * In particular, a vfork/exec sequence will replace p->p_vmspace
         * and we must interlock anyone trying to access the space (aka
         * procfs or sys_process.c calling procfs_domem()).
         *
         * If P_PPWAIT is set the parent vfork()'d and has a PHOLD() on us.
         */
        PSTALL(p, "exec1", ((p->p_flags & P_PPWAIT) ? 1 : 0));

        /*
         * Blow away entire process VM, if address space not shared,
         * otherwise, create a new VM space so that other threads are
         * not disrupted.  If we are execing a resident vmspace we
         * create a duplicate of it and remap the stack.
         */
        map = &vmspace->vm_map;
        if (vmcopy) {
                vmspace_exec(imgp->proc, vmcopy);
                vmspace = imgp->proc->p_vmspace;
                pmap_remove_pages(vmspace_pmap(vmspace), stack_addr, USRSTACK);
                map = &vmspace->vm_map;
        } else if (vmspace_getrefs(vmspace) == 1) {
                shmexit(vmspace);
                pmap_remove_pages(vmspace_pmap(vmspace),
                                  0, VM_MAX_USER_ADDRESS);
                vm_map_remove(map, 0, VM_MAX_USER_ADDRESS);
        } else {
                vmspace_exec(imgp->proc, NULL);
                vmspace = imgp->proc->p_vmspace;
                map = &vmspace->vm_map;
        }

        /*
         * Really make sure lwp-specific and process-specific mappings
         * are gone.
         *
         * Once we've done that, and because we are the only LWP left, with
         * no TID-dependent mappings, we can reset the TID to 1 (the RB tree
         * will remain consistent since it has only one entry).  This way
         * the exec'd program gets a nice deterministic tid of 1.
         */
        lwp_userunmap(lp);
        proc_userunmap(p);
        lp->lwp_tid = 1;
        p->p_lasttid = 1;

        /*
         * Allocate a new stack, generally make the stack non-executable
         * but allow the program to adjust that (the program may desire to
         * use areas of the stack for executable code).
         */
        error = vm_map_stack(&vmspace->vm_map, &stack_addr, (vm_size_t)maxssiz,
                             0,
                             VM_PROT_READ|VM_PROT_WRITE,
                             VM_PROT_READ|VM_PROT_WRITE|VM_PROT_EXECUTE,
                             0);
        if (error)
                return (error);

        /*
         * vm_ssize and vm_maxsaddr are somewhat antiquated concepts in the
         * VM_STACK case, but they are still used to monitor the size of the
         * process stack so we can check the stack rlimit.
         */
        vmspace->vm_ssize = sgrowsiz;           /* in bytes */
        vmspace->vm_maxsaddr = (char *)USRSTACK - maxssiz;

        return(0);
}

/*
 * Copy out argument and environment strings from the old process
 *      address space into the temporary string buffer.
 */
static int
exec_copyin_args(struct image_args *args, char *fname,
                 enum exec_path_segflg segflg, char **argv, char **envv)
{
        char    *argp, *envp;
        int     error = 0;
        size_t  length;

        args->buf = objcache_get(exec_objcache, M_WAITOK);
        if (args->buf == NULL)
                return (ENOMEM);

        args->begin_argv = args->buf;
        args->endp = args->begin_argv;
        args->space = ARG_MAX;

        args->fname = args->buf + ARG_MAX;

        /*
         * Copy the file name.
         */
        if (segflg == PATH_SYSSPACE)
                error = copystr(fname, args->fname, PATH_MAX, &length);
        else
                error = copyinstr(fname, args->fname, PATH_MAX, &length);
        if (error)
                return (error);

        /*
         * Extract argument strings.  argv may not be NULL.  The argv
         * array is terminated by a NULL entry.  We special-case the
         * situation where argv[0] is NULL by passing { filename, NULL }
         * to the new program to guarentee that the interpreter knows what
         * file to open in case we exec an interpreted file.   Note that
         * a NULL argv[0] terminates the argv[] array.
         *
         * XXX the special-casing of argv[0] is historical and needs to be
         * revisited.
         */
        if (argv == NULL)
                error = EFAULT;
        if (error == 0) {
                while ((argp = (caddr_t)(intptr_t)
                               fuword64((uintptr_t *)argv++)) != NULL) {
                        if (argp == (caddr_t)-1) {
                                error = EFAULT;
                                break;
                        }
                        error = copyinstr(argp, args->endp,
                                          args->space, &length);
                        if (error) {
                                if (error == ENAMETOOLONG)
                                        error = E2BIG;
                                break;
                        }
                        args->space -= length;
                        args->endp += length;
                        args->argc++;
                }
                if (args->argc == 0 && error == 0) {
                        length = strlen(args->fname) + 1;
                        if (length > args->space) {
                                error = E2BIG;
                        } else {
                                bcopy(args->fname, args->endp, length);
                                args->space -= length;
                                args->endp += length;
                                args->argc++;
                        }
                }
        }       

        args->begin_envv = args->endp;

        /*
         * extract environment strings.  envv may be NULL.
         */
        if (envv && error == 0) {
                while ((envp = (caddr_t)(intptr_t)
                               fuword64((uintptr_t *)envv++))) {
                        if (envp == (caddr_t) -1) {
                                error = EFAULT;
                                break;
                        }
                        error = copyinstr(envp, args->endp,
                                          args->space, &length);
                        if (error) {
                                if (error == ENAMETOOLONG)
                                        error = E2BIG;
                                break;
                        }
                        args->space -= length;
                        args->endp += length;
                        args->envc++;
                }
        }

        return (error);
}

static void
exec_free_args(struct image_args *args)
{
        if (args->buf) {
                objcache_put(exec_objcache, args->buf);
                args->buf = NULL;
        }
}

/*
 * Copy strings out to the new process address space, constructing
 * new arg and env vector tables. Return a pointer to the base
 * so that it can be used as the initial stack pointer.
 *
 * The format is, roughly:
 *
 *      [argv[]]                        <-- vectp
 *      [envp[]]
 *      [ELF_Auxargs]
 *
 *      [args & env]                    <-- destp
 *      [sgap]
 *      [SPARE_USRSPACE]
 *      [execpath]
 *      [szsigcode]   RO|NX
 *      [ps_strings]  RO|NX             Top of user stack
 *
 */
static register_t *
exec_copyout_strings(struct image_params *imgp)
{
        int argc, envc, sgap;
        int gap;
        int argsenvspace;
        char **vectp;
        char *stringp, *destp, *szsigbase;
        register_t *stack_base;
        struct ps_strings *arginfo;
        size_t execpath_len;
        int szsigcode;

        /*
         * Calculate string base and vector table pointers.
         * Also deal with signal trampoline code for this exec type.
         */
        if (imgp->execpath != NULL && imgp->auxargs != NULL)
                execpath_len = strlen(imgp->execpath) + 1;
        else
                execpath_len = 0;
        arginfo = (struct ps_strings *)PS_STRINGS;
        szsigcode = *(imgp->proc->p_sysent->sv_szsigcode);

        argsenvspace = roundup((ARG_MAX - imgp->args->space), sizeof(char *));
        gap = stackgap_random;
        cpu_ccfence();
        if (gap != 0) {
                if (gap < 0)
                        sgap = ALIGN(-gap);
                else
                        sgap = ALIGN(karc4random() & (gap - 1));
        } else {
                sgap = 0;
        }

        /*
         * Calculate destp, which points to [args & env] and above.
         */
        szsigbase = (char *)(intptr_t)
                    trunc_page64((intptr_t)arginfo - szsigcode);
        szsigbase -= SZSIGCODE_EXTRA_BYTES;
        destp = szsigbase -
                roundup(execpath_len, sizeof(char *)) -
                SPARE_USRSPACE -
                sgap -
                argsenvspace;

        /*
         * install sigcode
         */
        if (szsigcode)
                copyout(imgp->proc->p_sysent->sv_sigcode, szsigbase, szsigcode);

        /*
         * Copy the image path for the rtld
         */
        if (execpath_len) {
                imgp->execpathp = (uintptr_t)szsigbase -
                                  roundup(execpath_len, sizeof(char *));
                copyout(imgp->execpath, (void *)imgp->execpathp, execpath_len);
        }

        /*
         * Calculate base for argv[], envp[], and ELF_Auxargs.
         */
        vectp = (char **)destp - (AT_COUNT * 2);
        vectp -= imgp->args->argc + imgp->args->envc + 2;

        stack_base = (register_t *)vectp;

        stringp = imgp->args->begin_argv;
        argc = imgp->args->argc;
        envc = imgp->args->envc;

        /*
         * Copy out strings - arguments and environment (at destp)
         */
        copyout(stringp, destp, ARG_MAX - imgp->args->space);

        /*
         * Fill in "ps_strings" struct for ps, w, etc.
         */
        suword64((void *)&arginfo->ps_argvstr, (uint64_t)(intptr_t)vectp);
        suword32((void *)&arginfo->ps_nargvstr, argc);

        /*
         * Fill in argument portion of vector table.
         */
        for (; argc > 0; --argc) {
                suword64((void *)vectp++, (uintptr_t)destp);
                while (*stringp++ != 0)
                        destp++;
                destp++;
        }

        /* a null vector table pointer separates the argp's from the envp's */
        suword64((void *)vectp++, 0);

        suword64((void *)&arginfo->ps_envstr, (uintptr_t)vectp);
        suword32((void *)&arginfo->ps_nenvstr, envc);

        /*
         * Fill in environment portion of vector table.
         */
        for (; envc > 0; --envc) {
                suword64((void *)vectp++, (uintptr_t)destp);
                while (*stringp++ != 0)
                        destp++;
                destp++;
        }

        /* end of vector table is a null pointer */
        suword64((void *)vectp, 0);

        /*
         * Make the signal trampoline executable and read-only.
         */
        vm_map_protect(&imgp->proc->p_vmspace->vm_map,
                       (vm_offset_t)szsigbase,
                       (vm_offset_t)szsigbase + PAGE_SIZE,
                       VM_PROT_READ|VM_PROT_EXECUTE, FALSE);

        return (stack_base);
}

/*
 * Check permissions of file to execute.
 *      Return 0 for success or error code on failure.
 */
int
exec_check_permissions(struct image_params *imgp, struct mount *topmnt)
{
        struct proc *p = imgp->proc;
        struct vnode *vp = imgp->vp;
        struct vattr_lite *lvap = imgp->lvap;
        int error;

        /* Get file attributes */
        error = VOP_GETATTR_LITE(vp, lvap);
        if (error)
                return (error);

        /*
         * 1) Check if file execution is disabled for the filesystem that this
         *      file resides on.
         * 2) Insure that at least one execute bit is on - otherwise root
         *      will always succeed, and we don't want to happen unless the
         *      file really is executable.
         * 3) Insure that the file is a regular file.
         */
        if ((vp->v_mount->mnt_flag & MNT_NOEXEC) ||
            ((topmnt != NULL) && (topmnt->mnt_flag & MNT_NOEXEC)) ||
            ((lvap->va_mode & 0111) == 0) ||
            (lvap->va_type != VREG)) {
                return (EACCES);
        }

        /*
         * Zero length files can't be exec'd
         */
        if (lvap->va_size == 0)
                return (ENOEXEC);

        /*
         *  Check for execute permission to file based on current credentials.
         */
        error = VOP_EACCESS(vp, VEXEC, p->p_ucred);
        if (error)
                return (error);

        /*
         * Check number of open-for-writes on the file and deny execution
         * if there are any.
         */
        if (vp->v_writecount)
                return (ETXTBSY);

        /*
         * Call filesystem specific open routine, which allows us to read,
         * write, and mmap the file.  Without the VOP_OPEN we can only
         * stat the file.
         */
        error = VOP_OPEN(vp, FREAD, p->p_ucred, NULL);
        if (error)
                return (error);

        return (0);
}

/*
 * Exec handler registration
 */
int
exec_register(const struct execsw *execsw_arg)
{
        const struct execsw **es, **xs, **newexecsw;
        int count = 2;  /* New slot and trailing NULL */

        if (execsw)
                for (es = execsw; *es; es++)
                        count++;
        newexecsw = kmalloc(count * sizeof(*es), M_TEMP, M_WAITOK);
        xs = newexecsw;
        if (execsw)
                for (es = execsw; *es; es++)
                        *xs++ = *es;
        *xs++ = execsw_arg;
        *xs = NULL;
        if (execsw)
                kfree(execsw, M_TEMP);
        execsw = newexecsw;
        return 0;
}

int
exec_unregister(const struct execsw *execsw_arg)
{
        const struct execsw **es, **xs, **newexecsw;
        int count = 1;

        if (execsw == NULL)
                panic("unregister with no handlers left?");

        for (es = execsw; *es; es++) {
                if (*es == execsw_arg)
                        break;
        }
        if (*es == NULL)
                return ENOENT;
        for (es = execsw; *es; es++)
                if (*es != execsw_arg)
                        count++;
        newexecsw = kmalloc(count * sizeof(*es), M_TEMP, M_WAITOK);
        xs = newexecsw;
        for (es = execsw; *es; es++)
                if (*es != execsw_arg)
                        *xs++ = *es;
        *xs = NULL;
        if (execsw)
                kfree(execsw, M_TEMP);
        execsw = newexecsw;
        return 0;
}