kern_exec.c

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/*-
 * 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.
 */

#include <sys/cdefs.h>
__FBSDID("$BSDSUniX$");

#include "opt_capsicum.h"
#include "opt_hwpmc_hooks.h"
#include "opt_kdtrace.h"
#include "opt_ktrace.h"
#include "opt_vm.h"

#include <sys/param.h>
#include <sys/capability.h>
#include <sys/systm.h>
#include <sys/capability.h>
#include <sys/eventhandler.h>
#include <sys/lock.h>
#include <sys/mutex.h>
#include <sys/sysproto.h>
#include <sys/signalvar.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/wait.h>
#include <sys/malloc.h>
#include <sys/priv.h>
#include <sys/proc.h>
#include <sys/pioctl.h>
#include <sys/namei.h>
#include <sys/resourcevar.h>
#include <sys/sched.h>
#include <sys/sdt.h>
#include <sys/sf_buf.h>
#include <sys/syscallsubr.h>
#include <sys/sysent.h>
#include <sys/shm.h>
#include <sys/sysctl.h>
#include <sys/vnode.h>
#include <sys/stat.h>
#ifdef KTRACE
#include <sys/ktrace.h>
#endif

#include <vm/vm.h>
#include <vm/vm_param.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/vm_pager.h>

#ifdef  HWPMC_HOOKS
#include <sys/pmckern.h>
#endif

#include <machine/reg.h>

#include <security/audit/audit.h>
#include <security/mac/mac_framework.h>

#ifdef KDTRACE_HOOKS
#include <sys/dtrace_bsd.h>
dtrace_execexit_func_t  dtrace_fasttrap_exec;
#endif

SDT_PROVIDER_DECLARE(proc);
SDT_PROBE_DEFINE1(proc, kernel, , exec, "char *");
SDT_PROBE_DEFINE1(proc, kernel, , exec__failure, "int");
SDT_PROBE_DEFINE1(proc, kernel, , exec__success, "char *");

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

static int sysctl_kern_ps_strings(SYSCTL_HANDLER_ARGS);
static int sysctl_kern_usrstack(SYSCTL_HANDLER_ARGS);
static int sysctl_kern_stackprot(SYSCTL_HANDLER_ARGS);
static int do_execve(struct thread *td, struct image_args *args,
    struct mac *mac_p);

/* XXX This should be vm_size_t. */
SYSCTL_PROC(_kern, KERN_PS_STRINGS, ps_strings, CTLTYPE_ULONG|CTLFLAG_RD,
    NULL, 0, sysctl_kern_ps_strings, "LU", "");

/* XXX This should be vm_size_t. */
SYSCTL_PROC(_kern, KERN_USRSTACK, usrstack, CTLTYPE_ULONG|CTLFLAG_RD|
    CTLFLAG_CAPRD, NULL, 0, sysctl_kern_usrstack, "LU", "");

SYSCTL_PROC(_kern, OID_AUTO, stackprot, CTLTYPE_INT|CTLFLAG_RD,
    NULL, 0, sysctl_kern_stackprot, "I", "");

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

static int disallow_high_osrel;
SYSCTL_INT(_kern, OID_AUTO, disallow_high_osrel, CTLFLAG_RW,
    &disallow_high_osrel, 0,
    "Disallow execution of binaries built for higher version of the world");

static int map_at_zero = 0;
TUNABLE_INT("security.bsd.map_at_zero", &map_at_zero);
SYSCTL_INT(_security_bsd, OID_AUTO, map_at_zero, CTLFLAG_RW, &map_at_zero, 0,
    "Permit processes to map an object at virtual address 0.");

static int
sysctl_kern_ps_strings(SYSCTL_HANDLER_ARGS)
{
        struct proc *p;
        int error;

        p = curproc;
#ifdef SCTL_MASK32
        if (req->flags & SCTL_MASK32) {
                unsigned int val;
                val = (unsigned int)p->p_sysent->sv_psstrings;
                error = SYSCTL_OUT(req, &val, sizeof(val));
        } else
#endif
                error = SYSCTL_OUT(req, &p->p_sysent->sv_psstrings,
                   sizeof(p->p_sysent->sv_psstrings));
        return error;
}

static int
sysctl_kern_usrstack(SYSCTL_HANDLER_ARGS)
{
        struct proc *p;
        int error;

        p = curproc;
#ifdef SCTL_MASK32
        if (req->flags & SCTL_MASK32) {
                unsigned int val;
                val = (unsigned int)p->p_sysent->sv_usrstack;
                error = SYSCTL_OUT(req, &val, sizeof(val));
        } else
#endif
                error = SYSCTL_OUT(req, &p->p_sysent->sv_usrstack,
                    sizeof(p->p_sysent->sv_usrstack));
        return error;
}

static int
sysctl_kern_stackprot(SYSCTL_HANDLER_ARGS)
{
        struct proc *p;

        p = curproc;
        return (SYSCTL_OUT(req, &p->p_sysent->sv_stackprot,
            sizeof(p->p_sysent->sv_stackprot)));
}

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

#ifndef _SYS_SYSPROTO_H_
struct execve_args {
        char    *fname; 
        char    **argv;
        char    **envv; 
};
#endif

int
sys_execve(td, uap)
        struct thread *td;
        struct execve_args /* {
                char *fname;
                char **argv;
                char **envv;
        } */ *uap;
{
        int error;
        struct image_args args;

        error = exec_copyin_args(&args, uap->fname, UIO_USERSPACE,
            uap->argv, uap->envv);
        if (error == 0)
                error = kern_execve(td, &args, NULL);
        return (error);
}

#ifndef _SYS_SYSPROTO_H_
struct fexecve_args {
        int     fd;
        char    **argv;
        char    **envv;
}
#endif
int
sys_fexecve(struct thread *td, struct fexecve_args *uap)
{
        int error;
        struct image_args args;

        error = exec_copyin_args(&args, NULL, UIO_SYSSPACE,
            uap->argv, uap->envv);
        if (error == 0) {
                args.fd = uap->fd;
                error = kern_execve(td, &args, NULL);
        }
        return (error);
}

#ifndef _SYS_SYSPROTO_H_
struct __mac_execve_args {
        char    *fname;
        char    **argv;
        char    **envv;
        struct mac      *mac_p;
};
#endif

int
sys___mac_execve(td, uap)
        struct thread *td;
        struct __mac_execve_args /* {
                char *fname;
                char **argv;
                char **envv;
                struct mac *mac_p;
        } */ *uap;
{
#ifdef MAC
        int error;
        struct image_args args;

        error = exec_copyin_args(&args, uap->fname, UIO_USERSPACE,
            uap->argv, uap->envv);
        if (error == 0)
                error = kern_execve(td, &args, uap->mac_p);
        return (error);
#else
        return (ENOSYS);
#endif
}

/*
 * XXX: kern_execve has the astonishing property of not always returning to
 * the caller.  If sufficiently bad things happen during the call to
 * do_execve(), it can end up calling exit1(); as a result, callers must
 * avoid doing anything which they might need to undo (e.g., allocating
 * memory).
 */
int
kern_execve(td, args, mac_p)
        struct thread *td;
        struct image_args *args;
        struct mac *mac_p;
{
        struct proc *p = td->td_proc;
        struct vmspace *oldvmspace;
        int error;

        AUDIT_ARG_ARGV(args->begin_argv, args->argc,
            args->begin_envv - args->begin_argv);
        AUDIT_ARG_ENVV(args->begin_envv, args->envc,
            args->endp - args->begin_envv);
        if (p->p_flag & P_HADTHREADS) {
                PROC_LOCK(p);
                if (thread_single(SINGLE_BOUNDARY)) {
                        PROC_UNLOCK(p);
                        exec_free_args(args);
                        return (ERESTART);      /* Try again later. */
                }
                PROC_UNLOCK(p);
        }

        KASSERT((td->td_pflags & TDP_EXECVMSPC) == 0, ("nested execve"));
        oldvmspace = td->td_proc->p_vmspace;
        error = do_execve(td, args, mac_p);

        if (p->p_flag & P_HADTHREADS) {
                PROC_LOCK(p);
                /*
                 * If success, we upgrade to SINGLE_EXIT state to
                 * force other threads to suicide.
                 */
                if (error == 0)
                        thread_single(SINGLE_EXIT);
                else
                        thread_single_end();
                PROC_UNLOCK(p);
        }
        if ((td->td_pflags & TDP_EXECVMSPC) != 0) {
                KASSERT(td->td_proc->p_vmspace != oldvmspace,
                    ("oldvmspace still used"));
                vmspace_free(oldvmspace);
                td->td_pflags &= ~TDP_EXECVMSPC;
        }

        return (error);
}

/*
 * In-kernel implementation of execve().  All arguments are assumed to be
 * userspace pointers from the passed thread.
 */
static int
do_execve(td, args, mac_p)
        struct thread *td;
        struct image_args *args;
        struct mac *mac_p;
{
        struct proc *p = td->td_proc;
        struct nameidata nd;
        struct ucred *newcred = NULL, *oldcred;
        struct uidinfo *euip;
        register_t *stack_base;
        int error, i;
        struct image_params image_params, *imgp;
        struct vattr attr;
        int (*img_first)(struct image_params *);
        struct pargs *oldargs = NULL, *newargs = NULL;
        struct sigacts *oldsigacts, *newsigacts;
#ifdef KTRACE
        struct vnode *tracevp = NULL;
        struct ucred *tracecred = NULL;
#endif
        struct vnode *textvp = NULL, *binvp = NULL;
        int credential_changing;
        int vfslocked;
        int textset;
#ifdef MAC
        struct label *interpvplabel = NULL;
        int will_transition;
#endif
#ifdef HWPMC_HOOKS
        struct pmckern_procexec pe;
#endif
        static const char fexecv_proc_title[] = "(fexecv)";

        vfslocked = 0;
        imgp = &image_params;

        /*
         * Lock the process and set the P_INEXEC flag to indicate that
         * it should be left alone until we're done here.  This is
         * necessary to avoid race conditions - e.g. in ptrace() -
         * that might allow a local user to illicitly obtain elevated
         * privileges.
         */
        PROC_LOCK(p);
        KASSERT((p->p_flag & P_INEXEC) == 0,
            ("%s(): process already has P_INEXEC flag", __func__));
        p->p_flag |= P_INEXEC;
        PROC_UNLOCK(p);

        /*
         * Initialize part of the common data
         */
        imgp->proc = p;
        imgp->execlabel = NULL;
        imgp->attr = &attr;
        imgp->entry_addr = 0;
        imgp->reloc_base = 0;
        imgp->vmspace_destroyed = 0;
        imgp->interpreted = 0;
        imgp->opened = 0;
        imgp->interpreter_name = NULL;
        imgp->auxargs = NULL;
        imgp->vp = NULL;
        imgp->object = NULL;
        imgp->firstpage = NULL;
        imgp->ps_strings = 0;
        imgp->auxarg_size = 0;
        imgp->args = args;
        imgp->execpath = imgp->freepath = NULL;
        imgp->execpathp = 0;
        imgp->canary = 0;
        imgp->canarylen = 0;
        imgp->pagesizes = 0;
        imgp->pagesizeslen = 0;
        imgp->stack_prot = 0;

#ifdef MAC
        error = mac_execve_enter(imgp, mac_p);
        if (error)
                goto exec_fail;
#endif

        imgp->image_header = NULL;

        /*
         * Translate the file name. namei() returns a vnode pointer
         *      in ni_vp amoung other things.
         *
         * XXXAUDIT: It would be desirable to also audit the name of the
         * interpreter if this is an interpreted binary.
         */
        if (args->fname != NULL) {
                NDINIT(&nd, LOOKUP, ISOPEN | LOCKLEAF | FOLLOW | SAVENAME
                    | MPSAFE | AUDITVNODE1, UIO_SYSSPACE, args->fname, td);
        }

        SDT_PROBE1(proc, kernel, , exec, args->fname);

interpret:
        if (args->fname != NULL) {
#ifdef CAPABILITY_MODE
                /*
                 * While capability mode can't reach this point via direct
                 * path arguments to execve(), we also don't allow
                 * interpreters to be used in capability mode (for now).
                 * Catch indirect lookups and return a permissions error.
                 */
                if (IN_CAPABILITY_MODE(td)) {
                        error = ECAPMODE;
                        goto exec_fail;
                }
#endif
                error = namei(&nd);
                if (error)
                        goto exec_fail;

                vfslocked = NDHASGIANT(&nd);
                binvp  = nd.ni_vp;
                imgp->vp = binvp;
        } else {
                AUDIT_ARG_FD(args->fd);
                /*
                 * Some might argue that CAP_READ and/or CAP_MMAP should also
                 * be required here; such arguments will be entertained.
                 *
                 * Descriptors opened only with O_EXEC or O_RDONLY are allowed.
                 */
                error = fgetvp_exec(td, args->fd, CAP_FEXECVE, &binvp);
                if (error)
                        goto exec_fail;
                vfslocked = VFS_LOCK_GIANT(binvp->v_mount);
                vn_lock(binvp, LK_EXCLUSIVE | LK_RETRY);
                AUDIT_ARG_VNODE1(binvp);
                imgp->vp = binvp;
        }

        /*
         * Check file permissions (also 'opens' file)
         */
        error = exec_check_permissions(imgp);
        if (error)
                goto exec_fail_dealloc;

        imgp->object = imgp->vp->v_object;
        if (imgp->object != NULL)
                vm_object_reference(imgp->object);

        /*
         * Set VV_TEXT now so no one can write to the executable while we're
         * activating it.
         *
         * Remember if this was set before and unset it in case this is not
         * actually an executable image.
         */
        textset = VOP_IS_TEXT(imgp->vp);
        VOP_SET_TEXT(imgp->vp);

        error = exec_map_first_page(imgp);
        if (error)
                goto exec_fail_dealloc;

        imgp->proc->p_osrel = 0;
        /*
         *      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);

        /*
         *      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) {
                        if (textset == 0)
                                VOP_UNSET_TEXT(imgp->vp);
                        error = ENOEXEC;
                }
                goto exec_fail_dealloc;
        }

        /*
         * Special interpreter operation, cleanup and loop up to try to
         * activate the interpreter.
         */
        if (imgp->interpreted) {
                exec_unmap_first_page(imgp);
                /*
                 * VV_TEXT needs to be unset for scripts.  There is a short
                 * period before we determine that something is a script where
                 * VV_TEXT will be set. The vnode lock is held over this
                 * entire period so nothing should illegitimately be blocked.
                 */
                VOP_UNSET_TEXT(imgp->vp);
                /* free name buffer and old vnode */
                if (args->fname != NULL)
                        NDFREE(&nd, NDF_ONLY_PNBUF);
#ifdef MAC
                mac_execve_interpreter_enter(binvp, &interpvplabel);
#endif
                if (imgp->opened) {
                        VOP_CLOSE(binvp, FREAD, td->td_ucred, td);
                        imgp->opened = 0;
                }
                vput(binvp);
                vm_object_deallocate(imgp->object);
                imgp->object = NULL;
                VFS_UNLOCK_GIANT(vfslocked);
                vfslocked = 0;
                /* set new name to that of the interpreter */
                NDINIT(&nd, LOOKUP, LOCKLEAF | FOLLOW | SAVENAME | MPSAFE,
                    UIO_SYSSPACE, imgp->interpreter_name, td);
                args->fname = imgp->interpreter_name;
                goto interpret;
        }

        /*
         * NB: We unlock the vnode here because it is believed that none
         * of the sv_copyout_strings/sv_fixup operations require the vnode.
         */
        VOP_UNLOCK(imgp->vp, 0);

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

        if (disallow_high_osrel &&
            P_OSREL_MAJOR(p->p_osrel) > P_OSREL_MAJOR(__BSDSUniX_version)) {
                error = ENOEXEC;
                uprintf("Osrel %d for image %s too high\n", p->p_osrel,
                    imgp->execpath != NULL ? imgp->execpath : "<unresolved>");
                vn_lock(imgp->vp, LK_SHARED | LK_RETRY);
                goto exec_fail_dealloc;
        }

        /*
         * Copy out strings (args and env) and initialize stack base
         */
        if (p->p_sysent->sv_copyout_strings)
                stack_base = (*p->p_sysent->sv_copyout_strings)(imgp);
        else
                stack_base = exec_copyout_strings(imgp);

        /*
         * If custom stack fixup routine present for this process
         * let it do the stack setup.
         * Else stuff argument count as first item on stack
         */
        if (p->p_sysent->sv_fixup != NULL)
                (*p->p_sysent->sv_fixup)(&stack_base, imgp);
        else
                suword(--stack_base, imgp->args->argc);

        /*
         * For security and other reasons, the file descriptor table cannot
         * be shared after an exec.
         */
        fdunshare(p, td);

        /*
         * Malloc things before we need locks.
         */
        newcred = crget();
        euip = uifind(attr.va_uid);
        i = imgp->args->begin_envv - imgp->args->begin_argv;
        /* Cache arguments if they fit inside our allowance */
        if (ps_arg_cache_limit >= i + sizeof(struct pargs)) {
                newargs = pargs_alloc(i);
                bcopy(imgp->args->begin_argv, newargs->ar_args, i);
        }

        /* close files on exec */
        fdcloseexec(td);
        vn_lock(imgp->vp, LK_SHARED | LK_RETRY);

        /* Get a reference to the vnode prior to locking the proc */
        VREF(binvp);

        /*
         * For security and other reasons, signal handlers cannot
         * be shared after an exec. The new process gets a copy of the old
         * handlers. In execsigs(), the new process will have its signals
         * reset.
         */
        PROC_LOCK(p);
        oldcred = crcopysafe(p, newcred);
        if (sigacts_shared(p->p_sigacts)) {
                oldsigacts = p->p_sigacts;
                PROC_UNLOCK(p);
                newsigacts = sigacts_alloc();
                sigacts_copy(newsigacts, oldsigacts);
                PROC_LOCK(p);
                p->p_sigacts = newsigacts;
        } else
                oldsigacts = NULL;

        /* Stop profiling */
        stopprofclock(p);

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

        /* name this process - nameiexec(p, ndp) */
        bzero(p->p_comm, sizeof(p->p_comm));
        if (args->fname)
                bcopy(nd.ni_cnd.cn_nameptr, p->p_comm,
                    min(nd.ni_cnd.cn_namelen, MAXCOMLEN));
        else if (vn_commname(binvp, p->p_comm, sizeof(p->p_comm)) != 0)
                bcopy(fexecv_proc_title, p->p_comm, sizeof(fexecv_proc_title));
        bcopy(p->p_comm, td->td_name, sizeof(td->td_name));
#ifdef KTR
        sched_clear_tdname(td);
#endif

        /*
         * mark as execed, wakeup the process that vforked (if any) and tell
         * it that it now has its own resources back
         */
        p->p_flag |= P_EXEC;
        if (p->p_pptr && (p->p_flag & P_PPWAIT)) {
                p->p_flag &= ~(P_PPWAIT | P_PPTRACE);
                cv_broadcast(&p->p_pwait);
        }

        /*
         * Implement image setuid/setgid.
         *
         * Don't honor setuid/setgid if the filesystem prohibits it or if
         * the process is being traced.
         *
         * We disable setuid/setgid/etc in compatibility mode on the basis
         * that most setugid applications are not written with that
         * environment in mind, and will therefore almost certainly operate
         * incorrectly. In principle there's no reason that setugid
         * applications might not be useful in capability mode, so we may want
         * to reconsider this conservative design choice in the future.
         *
         * XXXMAC: For the time being, use NOSUID to also prohibit
         * transitions on the file system.
         */
        credential_changing = 0;
        credential_changing |= (attr.va_mode & S_ISUID) && oldcred->cr_uid !=
            attr.va_uid;
        credential_changing |= (attr.va_mode & S_ISGID) && oldcred->cr_gid !=
            attr.va_gid;
#ifdef MAC
        will_transition = mac_vnode_execve_will_transition(oldcred, imgp->vp,
            interpvplabel, imgp);
        credential_changing |= will_transition;
#endif

        if (credential_changing &&
#ifdef CAPABILITY_MODE
            ((oldcred->cr_flags & CRED_FLAG_CAPMODE) == 0) &&
#endif
            (imgp->vp->v_mount->mnt_flag & MNT_NOSUID) == 0 &&
            (p->p_flag & 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(p);

#ifdef KTRACE
                if (p->p_tracecred != NULL &&
                    priv_check_cred(p->p_tracecred, PRIV_DEBUG_DIFFCRED, 0))
                        ktrprocexec(p, &tracecred, &tracevp);
#endif
                /*
                 * Close any file descriptors 0..2 that reference procfs,
                 * then make sure file descriptors 0..2 are in use.
                 *
                 * setugidsafety() may call closef() and then pfind()
                 * which may grab the process lock.
                 * fdcheckstd() may call falloc() which may block to
                 * allocate memory, so temporarily drop the process lock.
                 */
                PROC_UNLOCK(p);
                VOP_UNLOCK(imgp->vp, 0);
                setugidsafety(td);
                error = fdcheckstd(td);
                vn_lock(imgp->vp, LK_SHARED | LK_RETRY);
                if (error != 0)
                        goto done1;
                PROC_LOCK(p);
                /*
                 * Set the new credentials.
                 */
                if (attr.va_mode & S_ISUID)
                        change_euid(newcred, euip);
                if (attr.va_mode & S_ISGID)
                        change_egid(newcred, attr.va_gid);
#ifdef MAC
                if (will_transition) {
                        mac_vnode_execve_transition(oldcred, newcred, imgp->vp,
                            interpvplabel, imgp);
                }
#endif
                /*
                 * Implement correct POSIX saved-id behavior.
                 *
                 * XXXMAC: Note that the current logic will save the
                 * uid and gid if a MAC domain transition occurs, even
                 * though maybe it shouldn't.
                 */
                change_svuid(newcred, newcred->cr_uid);
                change_svgid(newcred, newcred->cr_gid);
                p->p_ucred = newcred;
                newcred = NULL;
        } else {
                if (oldcred->cr_uid == oldcred->cr_ruid &&
                    oldcred->cr_gid == oldcred->cr_rgid)
                        p->p_flag &= ~P_SUGID;
                /*
                 * Implement correct POSIX saved-id behavior.
                 *
                 * XXX: It's not clear that the existing behavior is
                 * POSIX-compliant.  A number of sources indicate that the
                 * saved uid/gid should only be updated if the new ruid is
                 * not equal to the old ruid, or the new euid is not equal
                 * to the old euid and the new euid is not equal to the old
                 * ruid.  The FreeBSD code always updates the saved uid/gid.
                 * Also, this code uses the new (replaced) euid and egid as
                 * the source, which may or may not be the right ones to use.
                 */
                if (oldcred->cr_svuid != oldcred->cr_uid ||
                    oldcred->cr_svgid != oldcred->cr_gid) {
                        change_svuid(newcred, newcred->cr_uid);
                        change_svgid(newcred, newcred->cr_gid);
                        p->p_ucred = newcred;
                        newcred = NULL;
                }
        }

        /*
         * Store the vp for use in procfs.  This vnode was referenced prior
         * to locking the proc lock.
         */
        textvp = p->p_textvp;
        p->p_textvp = binvp;

#ifdef KDTRACE_HOOKS
        /*
         * Tell the DTrace fasttrap provider about the exec if it
         * has declared an interest.
         */
        if (dtrace_fasttrap_exec)
                dtrace_fasttrap_exec(p);
#endif

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

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

        /*
         * Free any previous argument cache and replace it with
         * the new argument cache, if any.
         */
        oldargs = p->p_args;
        p->p_args = newargs;
        newargs = NULL;

#ifdef  HWPMC_HOOKS
        /*
         * Check if system-wide sampling is in effect or if the
         * current process is using PMCs.  If so, do exec() time
         * processing.  This processing needs to happen AFTER the
         * P_INEXEC flag is cleared.
         *
         * The proc lock needs to be released before taking the PMC
         * SX.
         */
        if (PMC_SYSTEM_SAMPLING_ACTIVE() || PMC_PROC_IS_USING_PMCS(p)) {
                PROC_UNLOCK(p);
                VOP_UNLOCK(imgp->vp, 0);
                pe.pm_credentialschanged = credential_changing;
                pe.pm_entryaddr = imgp->entry_addr;

                PMC_CALL_HOOK_X(td, PMC_FN_PROCESS_EXEC, (void *) &pe);
                vn_lock(imgp->vp, LK_SHARED | LK_RETRY);
        } else
                PROC_UNLOCK(p);
#else  /* !HWPMC_HOOKS */
        PROC_UNLOCK(p);
#endif

        /* Set values passed into the program in registers. */
        if (p->p_sysent->sv_setregs)
                (*p->p_sysent->sv_setregs)(td, imgp, 
                    (u_long)(uintptr_t)stack_base);
        else
                exec_setregs(td, imgp, (u_long)(uintptr_t)stack_base);

        vfs_mark_atime(imgp->vp, td->td_ucred);

        SDT_PROBE1(proc, kernel, , exec__success, args->fname);

done1:
        /*
         * Free any resources malloc'd earlier that we didn't use.
         */
        uifree(euip);
        if (newcred == NULL)
                crfree(oldcred);
        else
                crfree(newcred);
        VOP_UNLOCK(imgp->vp, 0);

        /*
         * Handle deferred decrement of ref counts.
         */
        if (textvp != NULL) {
                int tvfslocked;

                tvfslocked = VFS_LOCK_GIANT(textvp->v_mount);
                vrele(textvp);
                VFS_UNLOCK_GIANT(tvfslocked);
        }
        if (binvp && error != 0)
                vrele(binvp);
#ifdef KTRACE
        if (tracevp != NULL) {
                int tvfslocked;

                tvfslocked = VFS_LOCK_GIANT(tracevp->v_mount);
                vrele(tracevp);
                VFS_UNLOCK_GIANT(tvfslocked);
        }
        if (tracecred != NULL)
                crfree(tracecred);
#endif
        vn_lock(imgp->vp, LK_SHARED | LK_RETRY);
        pargs_drop(oldargs);
        pargs_drop(newargs);
        if (oldsigacts != NULL)
                sigacts_free(oldsigacts);

exec_fail_dealloc:

        /*
         * free various allocated resources
         */
        if (imgp->firstpage != NULL)
                exec_unmap_first_page(imgp);

        if (imgp->vp != NULL) {
                if (args->fname)
                        NDFREE(&nd, NDF_ONLY_PNBUF);
                if (imgp->opened)
                        VOP_CLOSE(imgp->vp, FREAD, td->td_ucred, td);
                vput(imgp->vp);
        }

        if (imgp->object != NULL)
                vm_object_deallocate(imgp->object);

        free(imgp->freepath, M_TEMP);

        if (error == 0) {
                PROC_LOCK(p);
                td->td_dbgflags |= TDB_EXEC;
                PROC_UNLOCK(p);

                /*
                 * Stop the process here if its stop event mask has
                 * the S_EXEC bit set.
                 */
                STOPEVENT(p, S_EXEC, 0);
                goto done2;
        }

exec_fail:
        /* we're done here, clear P_INEXEC */
        PROC_LOCK(p);
        p->p_flag &= ~P_INEXEC;
        PROC_UNLOCK(p);

        SDT_PROBE1(proc, kernel, , exec__failure, error);

done2:
#ifdef MAC
        mac_execve_exit(imgp);
        mac_execve_interpreter_exit(interpvplabel);
#endif
        VFS_UNLOCK_GIANT(vfslocked);
        exec_free_args(args);

        if (error && imgp->vmspace_destroyed) {
                /* sorry, no more process anymore. exit gracefully */
                exit1(td, W_EXITCODE(0, SIGABRT));
                /* NOT REACHED */
        }

#ifdef KTRACE
        if (error == 0)
                ktrprocctor(p);
#endif

        return (error);
}

int
exec_map_first_page(imgp)
        struct image_params *imgp;
{
        int rv, i;
        int initial_pagein;
        vm_page_t ma[VM_INITIAL_PAGEIN];
        vm_object_t object;

        if (imgp->firstpage != NULL)
                exec_unmap_first_page(imgp);

        object = imgp->vp->v_object;
        if (object == NULL)
                return (EACCES);
        VM_OBJECT_LOCK(object);
#if VM_NRESERVLEVEL > 0
        if ((object->flags & OBJ_COLORED) == 0) {
                object->flags |= OBJ_COLORED;
                object->pg_color = 0;
        }
#endif
        ma[0] = vm_page_grab(object, 0, VM_ALLOC_NORMAL | VM_ALLOC_RETRY);
        if (ma[0]->valid != VM_PAGE_BITS_ALL) {
                initial_pagein = VM_INITIAL_PAGEIN;
                if (initial_pagein > object->size)
                        initial_pagein = object->size;
                for (i = 1; i < initial_pagein; i++) {
                        if ((ma[i] = vm_page_next(ma[i - 1])) != NULL) {
                                if (ma[i]->valid)
                                        break;
                                if ((ma[i]->oflags & VPO_BUSY) || ma[i]->busy)
                                        break;
                                vm_page_busy(ma[i]);
                        } else {
                                ma[i] = vm_page_alloc(object, i,
                                    VM_ALLOC_NORMAL | VM_ALLOC_IFNOTCACHED);
                                if (ma[i] == NULL)
                                        break;
                        }
                }
                initial_pagein = i;
                rv = vm_pager_get_pages(object, ma, initial_pagein, 0);
                ma[0] = vm_page_lookup(object, 0);
                if ((rv != VM_PAGER_OK) || (ma[0] == NULL)) {
                        if (ma[0] != NULL) {
                                vm_page_lock(ma[0]);
                                vm_page_free(ma[0]);
                                vm_page_unlock(ma[0]);
                        }
                        VM_OBJECT_UNLOCK(object);
                        return (EIO);
                }
        }
        vm_page_lock(ma[0]);
        vm_page_hold(ma[0]);
        vm_page_unlock(ma[0]);
        vm_page_wakeup(ma[0]);
        VM_OBJECT_UNLOCK(object);

        imgp->firstpage = sf_buf_alloc(ma[0], 0);
        imgp->image_header = (char *)sf_buf_kva(imgp->firstpage);

        return (0);
}

void
exec_unmap_first_page(imgp)
        struct image_params *imgp;
{
        vm_page_t m;

        if (imgp->firstpage != NULL) {
                m = sf_buf_page(imgp->firstpage);
                sf_buf_free(imgp->firstpage);
                imgp->firstpage = NULL;
                vm_page_lock(m);
                vm_page_unhold(m);
                vm_page_unlock(m);
        }
}

/*
 * Destroy old address space, and allocate a new stack
 *      The new stack is only SGROWSIZ large because it is grown
 *      automatically in trap.c.
 */
int
exec_new_vmspace(imgp, sv)
        struct image_params *imgp;
        struct sysentvec *sv;
{
        int error;
        struct proc *p = imgp->proc;
        struct vmspace *vmspace = p->p_vmspace;
        vm_object_t obj;
        vm_offset_t sv_minuser, stack_addr;
        vm_map_t map;
        u_long ssiz;

        imgp->vmspace_destroyed = 1;
        imgp->sysent = sv;

        /* May be called with Giant held */
        EVENTHANDLER_INVOKE(process_exec, p, imgp);

        /*
         * Blow away entire process VM, if address space not shared,
         * otherwise, create a new VM space so that other threads are
         * not disrupted
         */
        map = &vmspace->vm_map;
        if (map_at_zero)
                sv_minuser = sv->sv_minuser;
        else
                sv_minuser = MAX(sv->sv_minuser, PAGE_SIZE);
        if (vmspace->vm_refcnt == 1 && vm_map_min(map) == sv_minuser &&
            vm_map_max(map) == sv->sv_maxuser) {
                shmexit(vmspace);
                pmap_remove_pages(vmspace_pmap(vmspace));
                vm_map_remove(map, vm_map_min(map), vm_map_max(map));
        } else {
                error = vmspace_exec(p, sv_minuser, sv->sv_maxuser);
                if (error)
                        return (error);
                vmspace = p->p_vmspace;
                map = &vmspace->vm_map;
        }

        /* Map a shared page */
        obj = sv->sv_shared_page_obj;
        if (obj != NULL) {
                vm_object_reference(obj);
                error = vm_map_fixed(map, obj, 0,
                    sv->sv_shared_page_base, sv->sv_shared_page_len,
                    VM_PROT_READ | VM_PROT_EXECUTE,
                    VM_PROT_READ | VM_PROT_EXECUTE,
                    MAP_INHERIT_SHARE | MAP_ACC_NO_CHARGE);
                if (error) {
                        vm_object_deallocate(obj);
                        return (error);
                }
        }

        /* Allocate a new stack */
        if (sv->sv_maxssiz != NULL)
                ssiz = *sv->sv_maxssiz;
        else
                ssiz = maxssiz;
        stack_addr = sv->sv_usrstack - ssiz;
        error = vm_map_stack(map, stack_addr, (vm_size_t)ssiz,
            obj != NULL && imgp->stack_prot != 0 ? imgp->stack_prot :
                sv->sv_stackprot,
            VM_PROT_ALL, MAP_STACK_GROWS_DOWN);
        if (error)
                return (error);

#ifdef __ia64__
        /* Allocate a new register stack */
        stack_addr = IA64_BACKINGSTORE;
        error = vm_map_stack(map, stack_addr, (vm_size_t)ssiz,
            sv->sv_stackprot, VM_PROT_ALL, MAP_STACK_GROWS_UP);
        if (error)
                return (error);
#endif

        /* 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 >> PAGE_SHIFT;
        vmspace->vm_maxsaddr = (char *)sv->sv_usrstack - ssiz;

        return (0);
}

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

        bzero(args, sizeof(*args));
        if (argv == NULL)
                return (EFAULT);

        /*
         * Allocate demand-paged memory for the file name, argument, and
         * environment strings.
         */
        error = exec_alloc_args(args);
        if (error != 0)
                return (error);

        /*
         * Copy the file name.
         */
        if (fname != NULL) {
                args->fname = args->buf;
                error = (segflg == UIO_SYSSPACE) ?
                    copystr(fname, args->fname, PATH_MAX, &length) :
                    copyinstr(fname, args->fname, PATH_MAX, &length);
                if (error != 0)
                        goto err_exit;
        } else
                length = 0;

        args->begin_argv = args->buf + length;
        args->endp = args->begin_argv;
        args->stringspace = ARG_MAX;

        /*
         * extract arguments first
         */
        while ((argp = (caddr_t) (intptr_t) fuword(argv++))) {
                if (argp == (caddr_t) -1) {
                        error = EFAULT;
                        goto err_exit;
                }
                if ((error = copyinstr(argp, args->endp,
                    args->stringspace, &length))) {
                        if (error == ENAMETOOLONG) 
                                error = E2BIG;
                        goto err_exit;
                }
                args->stringspace -= length;
                args->endp += length;
                args->argc++;
        }

        args->begin_envv = args->endp;

        /*
         * extract environment strings
         */
        if (envv) {
                while ((envp = (caddr_t)(intptr_t)fuword(envv++))) {
                        if (envp == (caddr_t)-1) {
                                error = EFAULT;
                                goto err_exit;
                        }
                        if ((error = copyinstr(envp, args->endp,
                            args->stringspace, &length))) {
                                if (error == ENAMETOOLONG)
                                        error = E2BIG;
                                goto err_exit;
                        }
                        args->stringspace -= length;
                        args->endp += length;
                        args->envc++;
                }
        }

        return (0);

err_exit:
        exec_free_args(args);
        return (error);
}

/*
 * Allocate temporary demand-paged, zero-filled memory for the file name,
 * argument, and environment strings.  Returns zero if the allocation succeeds
 * and ENOMEM otherwise.
 */
int
exec_alloc_args(struct image_args *args)
{

        args->buf = (char *)kmem_alloc_wait(exec_map, PATH_MAX + ARG_MAX);
        return (args->buf != NULL ? 0 : ENOMEM);
}

void
exec_free_args(struct image_args *args)
{

        if (args->buf != NULL) {
                kmem_free_wakeup(exec_map, (vm_offset_t)args->buf,
                    PATH_MAX + ARG_MAX);
                args->buf = NULL;
        }
        if (args->fname_buf != NULL) {
                free(args->fname_buf, M_TEMP);
                args->fname_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.
 */
register_t *
exec_copyout_strings(imgp)
        struct image_params *imgp;
{
        int argc, envc;
        char **vectp;
        char *stringp;
        uintptr_t destp;
        register_t *stack_base;
        struct ps_strings *arginfo;
        struct proc *p;
        size_t execpath_len;
        int szsigcode, szps;
        char canary[sizeof(long) * 8];

        szps = sizeof(pagesizes[0]) * MAXPAGESIZES;
        /*
         * 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;
        p = imgp->proc;
        szsigcode = 0;
        arginfo = (struct ps_strings *)p->p_sysent->sv_psstrings;
        if (p->p_sysent->sv_sigcode_base == 0) {
                if (p->p_sysent->sv_szsigcode != NULL)
                        szsigcode = *(p->p_sysent->sv_szsigcode);
        }
        destp = (uintptr_t)arginfo;

        /*
         * install sigcode
         */
        if (szsigcode != 0) {
                destp -= szsigcode;
                destp = rounddown2(destp, sizeof(void *));
                copyout(p->p_sysent->sv_sigcode, (void *)destp, szsigcode);
        }

        /*
         * Copy the image path for the rtld.
         */
        if (execpath_len != 0) {
                destp -= execpath_len;
                imgp->execpathp = destp;
                copyout(imgp->execpath, (void *)destp, execpath_len);
        }

        /*
         * Prepare the canary for SSP.
         */
        arc4rand(canary, sizeof(canary), 0);
        destp -= sizeof(canary);
        imgp->canary = destp;
        copyout(canary, (void *)destp, sizeof(canary));
        imgp->canarylen = sizeof(canary);

        /*
         * Prepare the pagesizes array.
         */
        destp -= szps;
        destp = rounddown2(destp, sizeof(void *));
        imgp->pagesizes = destp;
        copyout(pagesizes, (void *)destp, szps);
        imgp->pagesizeslen = szps;

        destp -= ARG_MAX - imgp->args->stringspace;
        destp = rounddown2(destp, sizeof(void *));

        /*
         * If we have a valid auxargs ptr, prepare some room
         * on the stack.
         */
        if (imgp->auxargs) {
                /*
                 * 'AT_COUNT*2' is size for the ELF Auxargs data. This is for
                 * lower compatibility.
                 */
                imgp->auxarg_size = (imgp->auxarg_size) ? imgp->auxarg_size :
                    (AT_COUNT * 2);
                /*
                 * The '+ 2' is for the null pointers at the end of each of
                 * the arg and env vector sets,and imgp->auxarg_size is room
                 * for argument of Runtime loader.
                 */
                vectp = (char **)(destp - (imgp->args->argc +
                    imgp->args->envc + 2 + imgp->auxarg_size)
                    * sizeof(char *));
        } else {
                /*
                 * The '+ 2' is for the null pointers at the end of each of
                 * the arg and env vector sets
                 */
                vectp = (char **)(destp - (imgp->args->argc + imgp->args->envc
                    + 2) * sizeof(char *));
        }

        /*
         * vectp also becomes our initial stack base
         */
        stack_base = (register_t *)vectp;

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

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

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

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

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

        suword(&arginfo->ps_envstr, (long)(intptr_t)vectp);
        suword32(&arginfo->ps_nenvstr, envc);

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

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

        return (stack_base);
}

/*
 * Check permissions of file to execute.
 *      Called with imgp->vp locked.
 *      Return 0 for success or error code on failure.
 */
int
exec_check_permissions(imgp)
        struct image_params *imgp;
{
        struct vnode *vp = imgp->vp;
        struct vattr *attr = imgp->attr;
        struct thread *td;
        int error, writecount;

        td = curthread;

        /* Get file attributes */
        error = VOP_GETATTR(vp, attr, td->td_ucred);
        if (error)
                return (error);

#ifdef MAC
        error = mac_vnode_check_exec(td->td_ucred, imgp->vp, imgp);
        if (error)
                return (error);
#endif

        /*
         * 1) Check if file execution is disabled for the filesystem that
         *    this file resides on.
         * 2) Ensure that at least one execute bit is on. Otherwise, a
         *    privileged user will always succeed, and we don't want this
         *    to happen unless the file really is executable.
         * 3) Ensure that the file is a regular file.
         */
        if ((vp->v_mount->mnt_flag & MNT_NOEXEC) ||
            (attr->va_mode & (S_IXUSR | S_IXGRP | S_IXOTH)) == 0 ||
            (attr->va_type != VREG))
                return (EACCES);

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

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

        /*
         * Check number of open-for-writes on the file and deny execution
         * if there are any.
         */
        error = VOP_GET_WRITECOUNT(vp, &writecount);
        if (error != 0)
                return (error);
        if (writecount != 0)
                return (ETXTBSY);

        /*
         * Call filesystem specific open routine (which does nothing in the
         * general case).
         */
        error = VOP_OPEN(vp, FREAD, td->td_ucred, td, NULL);
        if (error == 0)
                imgp->opened = 1;
        return (error);
}

/*
 * Exec handler registration
 */
int
exec_register(execsw_arg)
        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 = malloc(count * sizeof(*es), M_TEMP, M_WAITOK);
        if (newexecsw == NULL)
                return (ENOMEM);
        xs = newexecsw;
        if (execsw)
                for (es = execsw; *es; es++)
                        *xs++ = *es;
        *xs++ = execsw_arg;
        *xs = NULL;
        if (execsw)
                free(execsw, M_TEMP);
        execsw = newexecsw;
        return (0);
}

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

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

        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 = malloc(count * sizeof(*es), M_TEMP, M_WAITOK);
        if (newexecsw == NULL)
                return (ENOMEM);
        xs = newexecsw;
        for (es = execsw; *es; es++)
                if (*es != execsw_arg)
                        *xs++ = *es;
        *xs = NULL;
        if (execsw)
                free(execsw, M_TEMP);
        execsw = newexecsw;
        return (0);
}