Ignore machine-check MSRs

[freebsd-src/fkvm-freebsd.git] / sys / kern / sys_process.c

/*-
 * Copyright (c) 1994, Sean Eric Fagan
 * 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.
 * 3. All advertising materials mentioning features or use of this software
 *    must display the following acknowledgement:
 *      This product includes software developed by Sean Eric Fagan.
 * 4. The name of the author may not be used to endorse or promote products
 *    derived from this software without specific prior written permission.
 *
 * 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("$FreeBSD$");

#include "opt_compat.h"

#include <sys/param.h>
#include <sys/systm.h>
#include <sys/lock.h>
#include <sys/mutex.h>
#include <sys/syscallsubr.h>
#include <sys/sysproto.h>
#include <sys/proc.h>
#include <sys/vnode.h>
#include <sys/ptrace.h>
#include <sys/sx.h>
#include <sys/malloc.h>
#include <sys/signalvar.h>

#include <machine/reg.h>

#include <security/audit/audit.h>

#include <vm/vm.h>
#include <vm/pmap.h>
#include <vm/vm_extern.h>
#include <vm/vm_map.h>
#include <vm/vm_kern.h>
#include <vm/vm_object.h>
#include <vm/vm_page.h>

#ifdef COMPAT_IA32
#include <sys/procfs.h>
#include <machine/fpu.h>
#include <compat/ia32/ia32_reg.h>

extern struct sysentvec ia32_freebsd_sysvec;

struct ptrace_io_desc32 {
        int             piod_op;
        u_int32_t       piod_offs;
        u_int32_t       piod_addr;
        u_int32_t       piod_len;
};
#endif

/*
 * Functions implemented using PROC_ACTION():
 *
 * proc_read_regs(proc, regs)
 *      Get the current user-visible register set from the process
 *      and copy it into the regs structure (<machine/reg.h>).
 *      The process is stopped at the time read_regs is called.
 *
 * proc_write_regs(proc, regs)
 *      Update the current register set from the passed in regs
 *      structure.  Take care to avoid clobbering special CPU
 *      registers or privileged bits in the PSL.
 *      Depending on the architecture this may have fix-up work to do,
 *      especially if the IAR or PCW are modified.
 *      The process is stopped at the time write_regs is called.
 *
 * proc_read_fpregs, proc_write_fpregs
 *      deal with the floating point register set, otherwise as above.
 *
 * proc_read_dbregs, proc_write_dbregs
 *      deal with the processor debug register set, otherwise as above.
 *
 * proc_sstep(proc)
 *      Arrange for the process to trap after executing a single instruction.
 */

#define PROC_ACTION(action) do {                                        \
        int error;                                                      \
                                                                        \
        PROC_LOCK_ASSERT(td->td_proc, MA_OWNED);                        \
        if ((td->td_proc->p_flag & P_INMEM) == 0)                       \
                error = EIO;                                            \
        else                                                            \
                error = (action);                                       \
        return (error);                                                 \
} while(0)

int
proc_read_regs(struct thread *td, struct reg *regs)
{

        PROC_ACTION(fill_regs(td, regs));
}

int
proc_write_regs(struct thread *td, struct reg *regs)
{

        PROC_ACTION(set_regs(td, regs));
}

int
proc_read_dbregs(struct thread *td, struct dbreg *dbregs)
{

        PROC_ACTION(fill_dbregs(td, dbregs));
}

int
proc_write_dbregs(struct thread *td, struct dbreg *dbregs)
{

        PROC_ACTION(set_dbregs(td, dbregs));
}

/*
 * Ptrace doesn't support fpregs at all, and there are no security holes
 * or translations for fpregs, so we can just copy them.
 */
int
proc_read_fpregs(struct thread *td, struct fpreg *fpregs)
{

        PROC_ACTION(fill_fpregs(td, fpregs));
}

int
proc_write_fpregs(struct thread *td, struct fpreg *fpregs)
{

        PROC_ACTION(set_fpregs(td, fpregs));
}

#ifdef COMPAT_IA32
/* For 32 bit binaries, we need to expose the 32 bit regs layouts. */
int
proc_read_regs32(struct thread *td, struct reg32 *regs32)
{

        PROC_ACTION(fill_regs32(td, regs32));
}

int
proc_write_regs32(struct thread *td, struct reg32 *regs32)
{

        PROC_ACTION(set_regs32(td, regs32));
}

int
proc_read_dbregs32(struct thread *td, struct dbreg32 *dbregs32)
{

        PROC_ACTION(fill_dbregs32(td, dbregs32));
}

int
proc_write_dbregs32(struct thread *td, struct dbreg32 *dbregs32)
{

        PROC_ACTION(set_dbregs32(td, dbregs32));
}

int
proc_read_fpregs32(struct thread *td, struct fpreg32 *fpregs32)
{

        PROC_ACTION(fill_fpregs32(td, fpregs32));
}

int
proc_write_fpregs32(struct thread *td, struct fpreg32 *fpregs32)
{

        PROC_ACTION(set_fpregs32(td, fpregs32));
}
#endif

int
proc_sstep(struct thread *td)
{

        PROC_ACTION(ptrace_single_step(td));
}

int
proc_rwmem(struct proc *p, struct uio *uio)
{
        vm_map_t map;
        vm_object_t backing_object, object = NULL;
        vm_offset_t pageno = 0;         /* page number */
        vm_prot_t reqprot;
        int error, fault_flags, writing;

        /*
         * Assert that someone has locked this vmspace.  (Should be
         * curthread but we can't assert that.)  This keeps the process
         * from exiting out from under us until this operation completes.
         */
        KASSERT(p->p_lock >= 1, ("%s: process %p (pid %d) not held", __func__,
            p, p->p_pid));

        /*
         * The map we want...
         */
        map = &p->p_vmspace->vm_map;

        writing = uio->uio_rw == UIO_WRITE;
        reqprot = writing ? (VM_PROT_WRITE | VM_PROT_OVERRIDE_WRITE) :
            VM_PROT_READ;
        fault_flags = writing ? VM_FAULT_DIRTY : VM_FAULT_NORMAL; 

        /*
         * Only map in one page at a time.  We don't have to, but it
         * makes things easier.  This way is trivial - right?
         */
        do {
                vm_map_t tmap;
                vm_offset_t uva;
                int page_offset;                /* offset into page */
                vm_map_entry_t out_entry;
                vm_prot_t out_prot;
                boolean_t wired;
                vm_pindex_t pindex;
                u_int len;
                vm_page_t m;

                object = NULL;

                uva = (vm_offset_t)uio->uio_offset;

                /*
                 * Get the page number of this segment.
                 */
                pageno = trunc_page(uva);
                page_offset = uva - pageno;

                /*
                 * How many bytes to copy
                 */
                len = min(PAGE_SIZE - page_offset, uio->uio_resid);

                /*
                 * Fault the page on behalf of the process
                 */
                error = vm_fault(map, pageno, reqprot, fault_flags);
                if (error) {
                        error = EFAULT;
                        break;
                }

                /*
                 * Now we need to get the page.  out_entry, out_prot, wired,
                 * and single_use aren't used.  One would think the vm code
                 * would be a *bit* nicer...  We use tmap because
                 * vm_map_lookup() can change the map argument.
                 */
                tmap = map;
                error = vm_map_lookup(&tmap, pageno, reqprot, &out_entry,
                    &object, &pindex, &out_prot, &wired);
                if (error) {
                        error = EFAULT;
                        break;
                }
                VM_OBJECT_LOCK(object);
                while ((m = vm_page_lookup(object, pindex)) == NULL &&
                    !writing &&
                    (backing_object = object->backing_object) != NULL) {
                        /*
                         * Allow fallback to backing objects if we are reading.
                         */
                        VM_OBJECT_LOCK(backing_object);
                        pindex += OFF_TO_IDX(object->backing_object_offset);
                        VM_OBJECT_UNLOCK(object);
                        object = backing_object;
                }
                VM_OBJECT_UNLOCK(object);
                if (m == NULL) {
                        vm_map_lookup_done(tmap, out_entry);
                        error = EFAULT;
                        break;
                }

                /*
                 * Hold the page in memory.
                 */
                vm_page_lock_queues();
                vm_page_hold(m);
                vm_page_unlock_queues();

                /*
                 * We're done with tmap now.
                 */
                vm_map_lookup_done(tmap, out_entry);

                /*
                 * Now do the i/o move.
                 */
                error = uiomove_fromphys(&m, page_offset, len, uio);

                /*
                 * Release the page.
                 */
                vm_page_lock_queues();
                vm_page_unhold(m);
                vm_page_unlock_queues();

        } while (error == 0 && uio->uio_resid > 0);

        return (error);
}

/*
 * Process debugging system call.
 */
#ifndef _SYS_SYSPROTO_H_
struct ptrace_args {
        int     req;
        pid_t   pid;
        caddr_t addr;
        int     data;
};
#endif

#ifdef COMPAT_IA32
/*
 * This CPP subterfuge is to try and reduce the number of ifdefs in
 * the body of the code.
 *   COPYIN(uap->addr, &r.reg, sizeof r.reg);
 * becomes either:
 *   copyin(uap->addr, &r.reg, sizeof r.reg);
 * or
 *   copyin(uap->addr, &r.reg32, sizeof r.reg32);
 * .. except this is done at runtime.
 */
#define COPYIN(u, k, s)         wrap32 ? \
        copyin(u, k ## 32, s ## 32) : \
        copyin(u, k, s)
#define COPYOUT(k, u, s)        wrap32 ? \
        copyout(k ## 32, u, s ## 32) : \
        copyout(k, u, s)
#else
#define COPYIN(u, k, s)         copyin(u, k, s)
#define COPYOUT(k, u, s)        copyout(k, u, s)
#endif
int
ptrace(struct thread *td, struct ptrace_args *uap)
{
        /*
         * XXX this obfuscation is to reduce stack usage, but the register
         * structs may be too large to put on the stack anyway.
         */
        union {
                struct ptrace_io_desc piod;
                struct ptrace_lwpinfo pl;
                struct dbreg dbreg;
                struct fpreg fpreg;
                struct reg reg;
#ifdef COMPAT_IA32
                struct dbreg32 dbreg32;
                struct fpreg32 fpreg32;
                struct reg32 reg32;
                struct ptrace_io_desc32 piod32;
#endif
        } r;
        void *addr;
        int error = 0;
#ifdef COMPAT_IA32
        int wrap32 = 0;

        if (td->td_proc->p_sysent == &ia32_freebsd_sysvec)
                wrap32 = 1;
#endif
        AUDIT_ARG(pid, uap->pid);
        AUDIT_ARG(cmd, uap->req);
        AUDIT_ARG(addr, uap->addr);
        AUDIT_ARG(value, uap->data);
        addr = &r;
        switch (uap->req) {
        case PT_GETREGS:
        case PT_GETFPREGS:
        case PT_GETDBREGS:
        case PT_LWPINFO:
                break;
        case PT_SETREGS:
                error = COPYIN(uap->addr, &r.reg, sizeof r.reg);
                break;
        case PT_SETFPREGS:
                error = COPYIN(uap->addr, &r.fpreg, sizeof r.fpreg);
                break;
        case PT_SETDBREGS:
                error = COPYIN(uap->addr, &r.dbreg, sizeof r.dbreg);
                break;
        case PT_IO:
                error = COPYIN(uap->addr, &r.piod, sizeof r.piod);
                break;
        default:
                addr = uap->addr;
                break;
        }
        if (error)
                return (error);

        error = kern_ptrace(td, uap->req, uap->pid, addr, uap->data);
        if (error)
                return (error);

        switch (uap->req) {
        case PT_IO:
                error = COPYOUT(&r.piod, uap->addr, sizeof r.piod);
                break;
        case PT_GETREGS:
                error = COPYOUT(&r.reg, uap->addr, sizeof r.reg);
                break;
        case PT_GETFPREGS:
                error = COPYOUT(&r.fpreg, uap->addr, sizeof r.fpreg);
                break;
        case PT_GETDBREGS:
                error = COPYOUT(&r.dbreg, uap->addr, sizeof r.dbreg);
                break;
        case PT_LWPINFO:
                error = copyout(&r.pl, uap->addr, uap->data);
                break;
        }

        return (error);
}
#undef COPYIN
#undef COPYOUT

#ifdef COMPAT_IA32
/*
 *   PROC_READ(regs, td2, addr);
 * becomes either:
 *   proc_read_regs(td2, addr);
 * or
 *   proc_read_regs32(td2, addr);
 * .. except this is done at runtime.  There is an additional
 * complication in that PROC_WRITE disallows 32 bit consumers
 * from writing to 64 bit address space targets.
 */
#define PROC_READ(w, t, a)      wrap32 ? \
        proc_read_ ## w ## 32(t, a) : \
        proc_read_ ## w (t, a)
#define PROC_WRITE(w, t, a)     wrap32 ? \
        (safe ? proc_write_ ## w ## 32(t, a) : EINVAL ) : \
        proc_write_ ## w (t, a)
#else
#define PROC_READ(w, t, a)      proc_read_ ## w (t, a)
#define PROC_WRITE(w, t, a)     proc_write_ ## w (t, a)
#endif

int
kern_ptrace(struct thread *td, int req, pid_t pid, void *addr, int data)
{
        struct iovec iov;
        struct uio uio;
        struct proc *curp, *p, *pp;
        struct thread *td2 = NULL;
        struct ptrace_io_desc *piod = NULL;
        struct ptrace_lwpinfo *pl;
        int error, write, tmp, num;
        int proctree_locked = 0;
        lwpid_t tid = 0, *buf;
#ifdef COMPAT_IA32
        int wrap32 = 0, safe = 0;
        struct ptrace_io_desc32 *piod32 = NULL;
#endif

        curp = td->td_proc;

        /* Lock proctree before locking the process. */
        switch (req) {
        case PT_TRACE_ME:
        case PT_ATTACH:
        case PT_STEP:
        case PT_CONTINUE:
        case PT_TO_SCE:
        case PT_TO_SCX:
        case PT_SYSCALL:
        case PT_DETACH:
                sx_xlock(&proctree_lock);
                proctree_locked = 1;
                break;
        default:
                break;
        }

        write = 0;
        if (req == PT_TRACE_ME) {
                p = td->td_proc;
                PROC_LOCK(p);
        } else {
                if (pid <= PID_MAX) {
                        if ((p = pfind(pid)) == NULL) {
                                if (proctree_locked)
                                        sx_xunlock(&proctree_lock);
                                return (ESRCH);
                        }
                } else {
                        /* this is slow, should be optimized */
                        sx_slock(&allproc_lock);
                        FOREACH_PROC_IN_SYSTEM(p) {
                                PROC_LOCK(p);
                                FOREACH_THREAD_IN_PROC(p, td2) {
                                        if (td2->td_tid == pid)
                                                break;
                                }
                                if (td2 != NULL)
                                        break; /* proc lock held */
                                PROC_UNLOCK(p);
                        }
                        sx_sunlock(&allproc_lock);
                        if (p == NULL) {
                                if (proctree_locked)
                                        sx_xunlock(&proctree_lock);
                                return (ESRCH);
                        }
                        tid = pid;
                        pid = p->p_pid;
                }
        }
        AUDIT_ARG(process, p);

        if ((p->p_flag & P_WEXIT) != 0) {
                error = ESRCH;
                goto fail;
        }
        if ((error = p_cansee(td, p)) != 0)
                goto fail;

        if ((error = p_candebug(td, p)) != 0)
                goto fail;

        /*
         * System processes can't be debugged.
         */
        if ((p->p_flag & P_SYSTEM) != 0) {
                error = EINVAL;
                goto fail;
        }

        if (tid == 0) {
                if ((p->p_flag & P_STOPPED_TRACE) != 0) {
                        KASSERT(p->p_xthread != NULL, ("NULL p_xthread"));
                        td2 = p->p_xthread;
                } else {
                        td2 = FIRST_THREAD_IN_PROC(p);
                }
                tid = td2->td_tid;
        }

#ifdef COMPAT_IA32
        /*
         * Test if we're a 32 bit client and what the target is.
         * Set the wrap controls accordingly.
         */
        if (td->td_proc->p_sysent == &ia32_freebsd_sysvec) {
                if (td2->td_proc->p_sysent == &ia32_freebsd_sysvec)
                        safe = 1;
                wrap32 = 1;
        }
#endif
        /*
         * Permissions check
         */
        switch (req) {
        case PT_TRACE_ME:
                /* Always legal. */
                break;

        case PT_ATTACH:
                /* Self */
                if (p->p_pid == td->td_proc->p_pid) {
                        error = EINVAL;
                        goto fail;
                }

                /* Already traced */
                if (p->p_flag & P_TRACED) {
                        error = EBUSY;
                        goto fail;
                }

                /* Can't trace an ancestor if you're being traced. */
                if (curp->p_flag & P_TRACED) {
                        for (pp = curp->p_pptr; pp != NULL; pp = pp->p_pptr) {
                                if (pp == p) {
                                        error = EINVAL;
                                        goto fail;
                                }
                        }
                }


                /* OK */
                break;

        case PT_CLEARSTEP:
                /* Allow thread to clear single step for itself */
                if (td->td_tid == tid)
                        break;

                /* FALLTHROUGH */
        default:
                /* not being traced... */
                if ((p->p_flag & P_TRACED) == 0) {
                        error = EPERM;
                        goto fail;
                }

                /* not being traced by YOU */
                if (p->p_pptr != td->td_proc) {
                        error = EBUSY;
                        goto fail;
                }

                /* not currently stopped */
                if ((p->p_flag & (P_STOPPED_SIG | P_STOPPED_TRACE)) == 0 ||
                    p->p_suspcount != p->p_numthreads  ||
                    (p->p_flag & P_WAITED) == 0) {
                        error = EBUSY;
                        goto fail;
                }

                if ((p->p_flag & P_STOPPED_TRACE) == 0) {
                        static int count = 0;
                        if (count++ == 0)
                                printf("P_STOPPED_TRACE not set.\n");
                }

                /* OK */
                break;
        }

        /* Keep this process around until we finish this request. */
        _PHOLD(p);

#ifdef FIX_SSTEP
        /*
         * Single step fixup ala procfs
         */
        FIX_SSTEP(td2);
#endif

        /*
         * Actually do the requests
         */

        td->td_retval[0] = 0;

        switch (req) {
        case PT_TRACE_ME:
                /* set my trace flag and "owner" so it can read/write me */
                p->p_flag |= P_TRACED;
                p->p_oppid = p->p_pptr->p_pid;
                break;

        case PT_ATTACH:
                /* security check done above */
                p->p_flag |= P_TRACED;
                p->p_oppid = p->p_pptr->p_pid;
                if (p->p_pptr != td->td_proc)
                        proc_reparent(p, td->td_proc);
                data = SIGSTOP;
                goto sendsig;   /* in PT_CONTINUE below */

        case PT_CLEARSTEP:
                error = ptrace_clear_single_step(td2);
                break;

        case PT_SETSTEP:
                error = ptrace_single_step(td2);
                break;

        case PT_SUSPEND:
                thread_lock(td2);
                td2->td_flags |= TDF_DBSUSPEND;
                thread_unlock(td2);
                break;

        case PT_RESUME:
                thread_lock(td2);
                td2->td_flags &= ~TDF_DBSUSPEND;
                thread_unlock(td2);
                break;

        case PT_STEP:
        case PT_CONTINUE:
        case PT_TO_SCE:
        case PT_TO_SCX:
        case PT_SYSCALL:
        case PT_DETACH:
                /* Zero means do not send any signal */
                if (data < 0 || data > _SIG_MAXSIG) {
                        error = EINVAL;
                        break;
                }

                switch (req) {
                case PT_STEP:
                        error = ptrace_single_step(td2);
                        if (error)
                                goto out;
                        break;
                case PT_TO_SCE:
                        p->p_stops |= S_PT_SCE;
                        break;
                case PT_TO_SCX:
                        p->p_stops |= S_PT_SCX;
                        break;
                case PT_SYSCALL:
                        p->p_stops |= S_PT_SCE | S_PT_SCX;
                        break;
                }

                if (addr != (void *)1) {
                        error = ptrace_set_pc(td2, (u_long)(uintfptr_t)addr);
                        if (error)
                                break;
                }

                if (req == PT_DETACH) {
                        /* reset process parent */
                        if (p->p_oppid != p->p_pptr->p_pid) {
                                struct proc *pp;

                                PROC_LOCK(p->p_pptr);
                                sigqueue_take(p->p_ksi);
                                PROC_UNLOCK(p->p_pptr);

                                PROC_UNLOCK(p);
                                pp = pfind(p->p_oppid);
                                if (pp == NULL)
                                        pp = initproc;
                                else
                                        PROC_UNLOCK(pp);
                                PROC_LOCK(p);
                                proc_reparent(p, pp);
                                if (pp == initproc)
                                        p->p_sigparent = SIGCHLD;
                        }
                        p->p_flag &= ~(P_TRACED | P_WAITED);
                        p->p_oppid = 0;

                        /* should we send SIGCHLD? */
                        /* childproc_continued(p); */
                }

        sendsig:
                if (proctree_locked) {
                        sx_xunlock(&proctree_lock);
                        proctree_locked = 0;
                }
                p->p_xstat = data;
                p->p_xthread = NULL;
                if ((p->p_flag & (P_STOPPED_SIG | P_STOPPED_TRACE)) != 0) {
                        /* deliver or queue signal */
                        thread_lock(td2);
                        td2->td_flags &= ~TDF_XSIG;
                        thread_unlock(td2);
                        td2->td_xsig = data;

                        if (req == PT_DETACH) {
                                struct thread *td3;
                                FOREACH_THREAD_IN_PROC(p, td3) {
                                        thread_lock(td3);
                                        td3->td_flags &= ~TDF_DBSUSPEND; 
                                        thread_unlock(td3);
                                }
                        }
                        /*
                         * unsuspend all threads, to not let a thread run,
                         * you should use PT_SUSPEND to suspend it before
                         * continuing process.
                         */
                        PROC_SLOCK(p);
                        p->p_flag &= ~(P_STOPPED_TRACE|P_STOPPED_SIG|P_WAITED);
                        thread_unsuspend(p);
                        PROC_SUNLOCK(p);
                } else {
                        if (data)
                                psignal(p, data);
                }
                break;

        case PT_WRITE_I:
        case PT_WRITE_D:
                write = 1;
                /* FALLTHROUGH */
        case PT_READ_I:
        case PT_READ_D:
                PROC_UNLOCK(p);
                tmp = 0;
                /* write = 0 set above */
                iov.iov_base = write ? (caddr_t)&data : (caddr_t)&tmp;
                iov.iov_len = sizeof(int);
                uio.uio_iov = &iov;
                uio.uio_iovcnt = 1;
                uio.uio_offset = (off_t)(uintptr_t)addr;
                uio.uio_resid = sizeof(int);
                uio.uio_segflg = UIO_SYSSPACE;  /* i.e.: the uap */
                uio.uio_rw = write ? UIO_WRITE : UIO_READ;
                uio.uio_td = td;
                error = proc_rwmem(p, &uio);
                if (uio.uio_resid != 0) {
                        /*
                         * XXX proc_rwmem() doesn't currently return ENOSPC,
                         * so I think write() can bogusly return 0.
                         * XXX what happens for short writes?  We don't want
                         * to write partial data.
                         * XXX proc_rwmem() returns EPERM for other invalid
                         * addresses.  Convert this to EINVAL.  Does this
                         * clobber returns of EPERM for other reasons?
                         */
                        if (error == 0 || error == ENOSPC || error == EPERM)
                                error = EINVAL; /* EOF */
                }
                if (!write)
                        td->td_retval[0] = tmp;
                PROC_LOCK(p);
                break;

        case PT_IO:
#ifdef COMPAT_IA32
                if (wrap32) {
                        piod32 = addr;
                        iov.iov_base = (void *)(uintptr_t)piod32->piod_addr;
                        iov.iov_len = piod32->piod_len;
                        uio.uio_offset = (off_t)(uintptr_t)piod32->piod_offs;
                        uio.uio_resid = piod32->piod_len;
                } else
#endif
                {
                        piod = addr;
                        iov.iov_base = piod->piod_addr;
                        iov.iov_len = piod->piod_len;
                        uio.uio_offset = (off_t)(uintptr_t)piod->piod_offs;
                        uio.uio_resid = piod->piod_len;
                }
                uio.uio_iov = &iov;
                uio.uio_iovcnt = 1;
                uio.uio_segflg = UIO_USERSPACE;
                uio.uio_td = td;
#ifdef COMPAT_IA32
                tmp = wrap32 ? piod32->piod_op : piod->piod_op;
#else
                tmp = piod->piod_op;
#endif
                switch (tmp) {
                case PIOD_READ_D:
                case PIOD_READ_I:
                        uio.uio_rw = UIO_READ;
                        break;
                case PIOD_WRITE_D:
                case PIOD_WRITE_I:
                        uio.uio_rw = UIO_WRITE;
                        break;
                default:
                        error = EINVAL;
                        goto out;
                }
                PROC_UNLOCK(p);
                error = proc_rwmem(p, &uio);
#ifdef COMPAT_IA32
                if (wrap32)
                        piod32->piod_len -= uio.uio_resid;
                else
#endif
                        piod->piod_len -= uio.uio_resid;
                PROC_LOCK(p);
                break;

        case PT_KILL:
                data = SIGKILL;
                goto sendsig;   /* in PT_CONTINUE above */

        case PT_SETREGS:
                error = PROC_WRITE(regs, td2, addr);
                break;

        case PT_GETREGS:
                error = PROC_READ(regs, td2, addr);
                break;

        case PT_SETFPREGS:
                error = PROC_WRITE(fpregs, td2, addr);
                break;

        case PT_GETFPREGS:
                error = PROC_READ(fpregs, td2, addr);
                break;

        case PT_SETDBREGS:
                error = PROC_WRITE(dbregs, td2, addr);
                break;

        case PT_GETDBREGS:
                error = PROC_READ(dbregs, td2, addr);
                break;

        case PT_LWPINFO:
                if (data <= 0 || data > sizeof(*pl)) {
                        error = EINVAL;
                        break;
                }
                pl = addr;
                pl->pl_lwpid = td2->td_tid;
                if (td2->td_flags & TDF_XSIG)
                        pl->pl_event = PL_EVENT_SIGNAL;
                else
                        pl->pl_event = 0;
                pl->pl_flags = 0;
                pl->pl_sigmask = td2->td_sigmask;
                pl->pl_siglist = td2->td_siglist;
                break;

        case PT_GETNUMLWPS:
                td->td_retval[0] = p->p_numthreads;
                break;

        case PT_GETLWPLIST:
                if (data <= 0) {
                        error = EINVAL;
                        break;
                }
                num = imin(p->p_numthreads, data);
                PROC_UNLOCK(p);
                buf = malloc(num * sizeof(lwpid_t), M_TEMP, M_WAITOK);
                tmp = 0;
                PROC_LOCK(p);
                FOREACH_THREAD_IN_PROC(p, td2) {
                        if (tmp >= num)
                                break;
                        buf[tmp++] = td2->td_tid;
                }
                PROC_UNLOCK(p);
                error = copyout(buf, addr, tmp * sizeof(lwpid_t));
                free(buf, M_TEMP);
                if (!error)
                        td->td_retval[0] = tmp;
                PROC_LOCK(p);
                break;

        default:
#ifdef __HAVE_PTRACE_MACHDEP
                if (req >= PT_FIRSTMACH) {
                        PROC_UNLOCK(p);
                        error = cpu_ptrace(td2, req, addr, data);
                        PROC_LOCK(p);
                } else
#endif
                        /* Unknown request. */
                        error = EINVAL;
                break;
        }

out:
        /* Drop our hold on this process now that the request has completed. */
        _PRELE(p);
fail:
        PROC_UNLOCK(p);
        if (proctree_locked)
                sx_xunlock(&proctree_lock);
        return (error);
}
#undef PROC_READ
#undef PROC_WRITE

/*
 * Stop a process because of a debugging event;
 * stay stopped until p->p_step is cleared
 * (cleared by PIOCCONT in procfs).
 */
void
stopevent(struct proc *p, unsigned int event, unsigned int val)
{

        PROC_LOCK_ASSERT(p, MA_OWNED);
        p->p_step = 1;
        do {
                p->p_xstat = val;
                p->p_xthread = NULL;
                p->p_stype = event;     /* Which event caused the stop? */
                wakeup(&p->p_stype);    /* Wake up any PIOCWAIT'ing procs */
                msleep(&p->p_step, &p->p_mtx, PWAIT, "stopevent", 0);
        } while (p->p_step);
}