The Design and Implementation of the FreeBSD Operating System, Second Edition
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FreeBSD/Linux Kernel Cross Reference
sys/i386/i386/sys_machdep.c

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    1 /*-
    2  * Copyright (c) 1990 The Regents of the University of California.
    3  * All rights reserved.
    4  *
    5  * Redistribution and use in source and binary forms, with or without
    6  * modification, are permitted provided that the following conditions
    7  * are met:
    8  * 1. Redistributions of source code must retain the above copyright
    9  *    notice, this list of conditions and the following disclaimer.
   10  * 2. Redistributions in binary form must reproduce the above copyright
   11  *    notice, this list of conditions and the following disclaimer in the
   12  *    documentation and/or other materials provided with the distribution.
   13  * 4. Neither the name of the University nor the names of its contributors
   14  *    may be used to endorse or promote products derived from this software
   15  *    without specific prior written permission.
   16  *
   17  * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
   18  * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
   19  * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
   20  * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
   21  * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
   22  * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
   23  * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
   24  * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
   25  * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
   26  * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
   27  * SUCH DAMAGE.
   28  *
   29  *      from: @(#)sys_machdep.c 5.5 (Berkeley) 1/19/91
   30  */
   31 
   32 #include <sys/cdefs.h>
   33 __FBSDID("$FreeBSD: releng/10.1/sys/i386/i386/sys_machdep.c 267714 2014-06-22 08:32:31Z kib $");
   34 
   35 #include "opt_capsicum.h"
   36 #include "opt_kstack_pages.h"
   37 
   38 #include <sys/param.h>
   39 #include <sys/capability.h>
   40 #include <sys/systm.h>
   41 #include <sys/lock.h>
   42 #include <sys/malloc.h>
   43 #include <sys/mutex.h>
   44 #include <sys/priv.h>
   45 #include <sys/proc.h>
   46 #include <sys/smp.h>
   47 #include <sys/sysproto.h>
   48 
   49 #include <vm/vm.h>
   50 #include <vm/pmap.h>
   51 #include <vm/vm_map.h>
   52 #include <vm/vm_extern.h>
   53 
   54 #include <machine/cpu.h>
   55 #include <machine/pcb.h>
   56 #include <machine/pcb_ext.h>
   57 #include <machine/proc.h>
   58 #include <machine/sysarch.h>
   59 
   60 #include <security/audit/audit.h>
   61 
   62 #ifdef XEN 
   63 #include <machine/xen/xenfunc.h>
   64 
   65 void i386_reset_ldt(struct proc_ldt *pldt); 
   66 
   67 void 
   68 i386_reset_ldt(struct proc_ldt *pldt) 
   69 { 
   70         xen_set_ldt((vm_offset_t)pldt->ldt_base, pldt->ldt_len); 
   71 } 
   72 #else  
   73 #define i386_reset_ldt(x) 
   74 #endif 
   75 
   76 #include <vm/vm_kern.h>         /* for kernel_map */
   77 
   78 #define MAX_LD 8192
   79 #define LD_PER_PAGE 512
   80 #define NEW_MAX_LD(num)  ((num + LD_PER_PAGE) & ~(LD_PER_PAGE-1))
   81 #define SIZE_FROM_LARGEST_LD(num) (NEW_MAX_LD(num) << 3)
   82 #define NULL_LDT_BASE   ((caddr_t)NULL)
   83 
   84 #ifdef SMP
   85 static void set_user_ldt_rv(struct vmspace *vmsp);
   86 #endif
   87 static int i386_set_ldt_data(struct thread *, int start, int num,
   88         union descriptor *descs);
   89 static int i386_ldt_grow(struct thread *td, int len);
   90 
   91 #ifndef _SYS_SYSPROTO_H_
   92 struct sysarch_args {
   93         int op;
   94         char *parms;
   95 };
   96 #endif
   97 
   98 int
   99 sysarch(td, uap)
  100         struct thread *td;
  101         register struct sysarch_args *uap;
  102 {
  103         int error;
  104         union descriptor *lp;
  105         union {
  106                 struct i386_ldt_args largs;
  107                 struct i386_ioperm_args iargs;
  108         } kargs;
  109         uint32_t base;
  110         struct segment_descriptor sd, *sdp;
  111 
  112         AUDIT_ARG_CMD(uap->op);
  113 
  114 #ifdef CAPABILITY_MODE
  115         /*
  116          * When adding new operations, add a new case statement here to
  117          * explicitly indicate whether or not the operation is safe to
  118          * perform in capability mode.
  119          */
  120         if (IN_CAPABILITY_MODE(td)) {
  121                 switch (uap->op) {
  122                 case I386_GET_LDT:
  123                 case I386_SET_LDT:
  124                 case I386_GET_IOPERM:
  125                 case I386_GET_FSBASE:
  126                 case I386_SET_FSBASE:
  127                 case I386_GET_GSBASE:
  128                 case I386_SET_GSBASE:
  129                         break;
  130 
  131                 case I386_SET_IOPERM:
  132                 default:
  133 #ifdef KTRACE
  134                         if (KTRPOINT(td, KTR_CAPFAIL))
  135                                 ktrcapfail(CAPFAIL_SYSCALL, NULL, NULL);
  136 #endif
  137                         return (ECAPMODE);
  138                 }
  139         }
  140 #endif
  141 
  142         switch (uap->op) {
  143         case I386_GET_IOPERM:
  144         case I386_SET_IOPERM:
  145                 if ((error = copyin(uap->parms, &kargs.iargs,
  146                     sizeof(struct i386_ioperm_args))) != 0)
  147                         return (error);
  148                 break;
  149         case I386_GET_LDT:
  150         case I386_SET_LDT:
  151                 if ((error = copyin(uap->parms, &kargs.largs,
  152                     sizeof(struct i386_ldt_args))) != 0)
  153                         return (error);
  154                 if (kargs.largs.num > MAX_LD || kargs.largs.num <= 0)
  155                         return (EINVAL);
  156                 break;
  157         default:
  158                 break;
  159         }
  160 
  161         switch(uap->op) {
  162         case I386_GET_LDT:
  163                 error = i386_get_ldt(td, &kargs.largs);
  164                 break;
  165         case I386_SET_LDT:
  166                 if (kargs.largs.descs != NULL) {
  167                         lp = (union descriptor *)malloc(
  168                             kargs.largs.num * sizeof(union descriptor),
  169                             M_TEMP, M_WAITOK);
  170                         error = copyin(kargs.largs.descs, lp,
  171                             kargs.largs.num * sizeof(union descriptor));
  172                         if (error == 0)
  173                                 error = i386_set_ldt(td, &kargs.largs, lp);
  174                         free(lp, M_TEMP);
  175                 } else {
  176                         error = i386_set_ldt(td, &kargs.largs, NULL);
  177                 }
  178                 break;
  179         case I386_GET_IOPERM:
  180                 error = i386_get_ioperm(td, &kargs.iargs);
  181                 if (error == 0)
  182                         error = copyout(&kargs.iargs, uap->parms,
  183                             sizeof(struct i386_ioperm_args));
  184                 break;
  185         case I386_SET_IOPERM:
  186                 error = i386_set_ioperm(td, &kargs.iargs);
  187                 break;
  188         case I386_VM86:
  189                 error = vm86_sysarch(td, uap->parms);
  190                 break;
  191         case I386_GET_FSBASE:
  192                 sdp = &td->td_pcb->pcb_fsd;
  193                 base = sdp->sd_hibase << 24 | sdp->sd_lobase;
  194                 error = copyout(&base, uap->parms, sizeof(base));
  195                 break;
  196         case I386_SET_FSBASE:
  197                 error = copyin(uap->parms, &base, sizeof(base));
  198                 if (!error) {
  199                         /*
  200                          * Construct a descriptor and store it in the pcb for
  201                          * the next context switch.  Also store it in the gdt
  202                          * so that the load of tf_fs into %fs will activate it
  203                          * at return to userland.
  204                          */
  205                         sd.sd_lobase = base & 0xffffff;
  206                         sd.sd_hibase = (base >> 24) & 0xff;
  207 #ifdef XEN
  208                         /* need to do nosegneg like Linux */
  209                         sd.sd_lolimit = (HYPERVISOR_VIRT_START >> 12) & 0xffff;
  210 #else                   
  211                         sd.sd_lolimit = 0xffff; /* 4GB limit, wraps around */
  212 #endif
  213                         sd.sd_hilimit = 0xf;
  214                         sd.sd_type  = SDT_MEMRWA;
  215                         sd.sd_dpl   = SEL_UPL;
  216                         sd.sd_p     = 1;
  217                         sd.sd_xx    = 0;
  218                         sd.sd_def32 = 1;
  219                         sd.sd_gran  = 1;
  220                         critical_enter();
  221                         td->td_pcb->pcb_fsd = sd;
  222 #ifdef XEN
  223                         HYPERVISOR_update_descriptor(vtomach(&PCPU_GET(fsgs_gdt)[0]),
  224                             *(uint64_t *)&sd);
  225 #else
  226                         PCPU_GET(fsgs_gdt)[0] = sd;
  227 #endif
  228                         critical_exit();
  229                         td->td_frame->tf_fs = GSEL(GUFS_SEL, SEL_UPL);
  230                 }
  231                 break;
  232         case I386_GET_GSBASE:
  233                 sdp = &td->td_pcb->pcb_gsd;
  234                 base = sdp->sd_hibase << 24 | sdp->sd_lobase;
  235                 error = copyout(&base, uap->parms, sizeof(base));
  236                 break;
  237         case I386_SET_GSBASE:
  238                 error = copyin(uap->parms, &base, sizeof(base));
  239                 if (!error) {
  240                         /*
  241                          * Construct a descriptor and store it in the pcb for
  242                          * the next context switch.  Also store it in the gdt
  243                          * because we have to do a load_gs() right now.
  244                          */
  245                         sd.sd_lobase = base & 0xffffff;
  246                         sd.sd_hibase = (base >> 24) & 0xff;
  247 
  248 #ifdef XEN
  249                         /* need to do nosegneg like Linux */
  250                         sd.sd_lolimit = (HYPERVISOR_VIRT_START >> 12) & 0xffff;
  251 #else   
  252                         sd.sd_lolimit = 0xffff; /* 4GB limit, wraps around */
  253 #endif
  254                         sd.sd_hilimit = 0xf;
  255                         sd.sd_type  = SDT_MEMRWA;
  256                         sd.sd_dpl   = SEL_UPL;
  257                         sd.sd_p     = 1;
  258                         sd.sd_xx    = 0;
  259                         sd.sd_def32 = 1;
  260                         sd.sd_gran  = 1;
  261                         critical_enter();
  262                         td->td_pcb->pcb_gsd = sd;
  263 #ifdef XEN
  264                         HYPERVISOR_update_descriptor(vtomach(&PCPU_GET(fsgs_gdt)[1]),
  265                             *(uint64_t *)&sd);
  266 #else                   
  267                         PCPU_GET(fsgs_gdt)[1] = sd;
  268 #endif
  269                         critical_exit();
  270                         load_gs(GSEL(GUGS_SEL, SEL_UPL));
  271                 }
  272                 break;
  273         default:
  274                 error = EINVAL;
  275                 break;
  276         }
  277         return (error);
  278 }
  279 
  280 int
  281 i386_extend_pcb(struct thread *td)
  282 {
  283         int i, offset;
  284         u_long *addr;
  285         struct pcb_ext *ext;
  286         struct soft_segment_descriptor ssd = {
  287                 0,                      /* segment base address (overwritten) */
  288                 ctob(IOPAGES + 1) - 1,  /* length */
  289                 SDT_SYS386TSS,          /* segment type */
  290                 0,                      /* priority level */
  291                 1,                      /* descriptor present */
  292                 0, 0,
  293                 0,                      /* default 32 size */
  294                 0                       /* granularity */
  295         };
  296 
  297         ext = (struct pcb_ext *)kmem_malloc(kernel_arena, ctob(IOPAGES+1),
  298             M_WAITOK | M_ZERO);
  299         /* -16 is so we can convert a trapframe into vm86trapframe inplace */
  300         ext->ext_tss.tss_esp0 = td->td_kstack + ctob(KSTACK_PAGES) -
  301             sizeof(struct pcb) - 16;
  302         ext->ext_tss.tss_ss0 = GSEL(GDATA_SEL, SEL_KPL);
  303         /*
  304          * The last byte of the i/o map must be followed by an 0xff byte.
  305          * We arbitrarily allocate 16 bytes here, to keep the starting
  306          * address on a doubleword boundary.
  307          */
  308         offset = PAGE_SIZE - 16;
  309         ext->ext_tss.tss_ioopt = 
  310             (offset - ((unsigned)&ext->ext_tss - (unsigned)ext)) << 16;
  311         ext->ext_iomap = (caddr_t)ext + offset;
  312         ext->ext_vm86.vm86_intmap = (caddr_t)ext + offset - 32;
  313 
  314         addr = (u_long *)ext->ext_vm86.vm86_intmap;
  315         for (i = 0; i < (ctob(IOPAGES) + 32 + 16) / sizeof(u_long); i++)
  316                 *addr++ = ~0;
  317 
  318         ssd.ssd_base = (unsigned)&ext->ext_tss;
  319         ssd.ssd_limit -= ((unsigned)&ext->ext_tss - (unsigned)ext);
  320         ssdtosd(&ssd, &ext->ext_tssd);
  321 
  322         KASSERT(td == curthread, ("giving TSS to !curthread"));
  323         KASSERT(td->td_pcb->pcb_ext == 0, ("already have a TSS!"));
  324 
  325         /* Switch to the new TSS. */
  326         critical_enter();
  327         td->td_pcb->pcb_ext = ext;
  328         PCPU_SET(private_tss, 1);
  329         *PCPU_GET(tss_gdt) = ext->ext_tssd;
  330         ltr(GSEL(GPROC0_SEL, SEL_KPL));
  331         critical_exit();
  332 
  333         return 0;
  334 }
  335 
  336 int
  337 i386_set_ioperm(td, uap)
  338         struct thread *td;
  339         struct i386_ioperm_args *uap;
  340 {
  341         int i, error;
  342         char *iomap;
  343 
  344         if ((error = priv_check(td, PRIV_IO)) != 0)
  345                 return (error);
  346         if ((error = securelevel_gt(td->td_ucred, 0)) != 0)
  347                 return (error);
  348         /*
  349          * XXX 
  350          * While this is restricted to root, we should probably figure out
  351          * whether any other driver is using this i/o address, as so not to
  352          * cause confusion.  This probably requires a global 'usage registry'.
  353          */
  354 
  355         if (td->td_pcb->pcb_ext == 0)
  356                 if ((error = i386_extend_pcb(td)) != 0)
  357                         return (error);
  358         iomap = (char *)td->td_pcb->pcb_ext->ext_iomap;
  359 
  360         if (uap->start + uap->length > IOPAGES * PAGE_SIZE * NBBY)
  361                 return (EINVAL);
  362 
  363         for (i = uap->start; i < uap->start + uap->length; i++) {
  364                 if (uap->enable)
  365                         iomap[i >> 3] &= ~(1 << (i & 7));
  366                 else
  367                         iomap[i >> 3] |= (1 << (i & 7));
  368         }
  369         return (error);
  370 }
  371 
  372 int
  373 i386_get_ioperm(td, uap)
  374         struct thread *td;
  375         struct i386_ioperm_args *uap;
  376 {
  377         int i, state;
  378         char *iomap;
  379 
  380         if (uap->start >= IOPAGES * PAGE_SIZE * NBBY)
  381                 return (EINVAL);
  382 
  383         if (td->td_pcb->pcb_ext == 0) {
  384                 uap->length = 0;
  385                 goto done;
  386         }
  387 
  388         iomap = (char *)td->td_pcb->pcb_ext->ext_iomap;
  389 
  390         i = uap->start;
  391         state = (iomap[i >> 3] >> (i & 7)) & 1;
  392         uap->enable = !state;
  393         uap->length = 1;
  394 
  395         for (i = uap->start + 1; i < IOPAGES * PAGE_SIZE * NBBY; i++) {
  396                 if (state != ((iomap[i >> 3] >> (i & 7)) & 1))
  397                         break;
  398                 uap->length++;
  399         }
  400 
  401 done:
  402         return (0);
  403 }
  404 
  405 /*
  406  * Update the GDT entry pointing to the LDT to point to the LDT of the
  407  * current process. Manage dt_lock holding/unholding autonomously.
  408  */   
  409 void
  410 set_user_ldt(struct mdproc *mdp)
  411 {
  412         struct proc_ldt *pldt;
  413         int dtlocked;
  414 
  415         dtlocked = 0;
  416         if (!mtx_owned(&dt_lock)) {
  417                 mtx_lock_spin(&dt_lock);
  418                 dtlocked = 1;
  419         }
  420 
  421         pldt = mdp->md_ldt;
  422 #ifdef XEN
  423         i386_reset_ldt(pldt);
  424         PCPU_SET(currentldt, (int)pldt);
  425 #else   
  426 #ifdef SMP
  427         gdt[PCPU_GET(cpuid) * NGDT + GUSERLDT_SEL].sd = pldt->ldt_sd;
  428 #else
  429         gdt[GUSERLDT_SEL].sd = pldt->ldt_sd;
  430 #endif
  431         lldt(GSEL(GUSERLDT_SEL, SEL_KPL));
  432         PCPU_SET(currentldt, GSEL(GUSERLDT_SEL, SEL_KPL));
  433 #endif /* XEN */ 
  434         if (dtlocked)
  435                 mtx_unlock_spin(&dt_lock);
  436 }
  437 
  438 #ifdef SMP
  439 static void
  440 set_user_ldt_rv(struct vmspace *vmsp)
  441 {
  442         struct thread *td;
  443 
  444         td = curthread;
  445         if (vmsp != td->td_proc->p_vmspace)
  446                 return;
  447 
  448         set_user_ldt(&td->td_proc->p_md);
  449 }
  450 #endif
  451 
  452 #ifdef XEN
  453 
  454 /* 
  455  * dt_lock must be held. Returns with dt_lock held. 
  456  */ 
  457 struct proc_ldt * 
  458 user_ldt_alloc(struct mdproc *mdp, int len) 
  459 { 
  460         struct proc_ldt *pldt, *new_ldt; 
  461  
  462         mtx_assert(&dt_lock, MA_OWNED); 
  463         mtx_unlock_spin(&dt_lock); 
  464         new_ldt = malloc(sizeof(struct proc_ldt), 
  465                 M_SUBPROC, M_WAITOK); 
  466  
  467         new_ldt->ldt_len = len = NEW_MAX_LD(len); 
  468         new_ldt->ldt_base = (caddr_t)kmem_malloc(kernel_arena, 
  469             round_page(len * sizeof(union descriptor)), M_WAITOK);
  470         new_ldt->ldt_refcnt = 1; 
  471         new_ldt->ldt_active = 0; 
  472  
  473         mtx_lock_spin(&dt_lock);
  474         if ((pldt = mdp->md_ldt)) { 
  475                 if (len > pldt->ldt_len) 
  476                         len = pldt->ldt_len; 
  477                 bcopy(pldt->ldt_base, new_ldt->ldt_base, 
  478                     len * sizeof(union descriptor)); 
  479         } else { 
  480                 bcopy(ldt, new_ldt->ldt_base, PAGE_SIZE); 
  481         } 
  482         mtx_unlock_spin(&dt_lock);  /* XXX kill once pmap locking fixed. */
  483         pmap_map_readonly(kernel_pmap, (vm_offset_t)new_ldt->ldt_base, 
  484                           new_ldt->ldt_len*sizeof(union descriptor)); 
  485         mtx_lock_spin(&dt_lock);  /* XXX kill once pmap locking fixed. */
  486         return (new_ldt);
  487 } 
  488 #else
  489 /*
  490  * dt_lock must be held. Returns with dt_lock held.
  491  */
  492 struct proc_ldt *
  493 user_ldt_alloc(struct mdproc *mdp, int len)
  494 {
  495         struct proc_ldt *pldt, *new_ldt;
  496 
  497         mtx_assert(&dt_lock, MA_OWNED);
  498         mtx_unlock_spin(&dt_lock);
  499         new_ldt = malloc(sizeof(struct proc_ldt),
  500                 M_SUBPROC, M_WAITOK);
  501 
  502         new_ldt->ldt_len = len = NEW_MAX_LD(len);
  503         new_ldt->ldt_base = (caddr_t)kmem_malloc(kernel_arena,
  504             len * sizeof(union descriptor), M_WAITOK);
  505         new_ldt->ldt_refcnt = 1;
  506         new_ldt->ldt_active = 0;
  507 
  508         mtx_lock_spin(&dt_lock);
  509         gdt_segs[GUSERLDT_SEL].ssd_base = (unsigned)new_ldt->ldt_base;
  510         gdt_segs[GUSERLDT_SEL].ssd_limit = len * sizeof(union descriptor) - 1;
  511         ssdtosd(&gdt_segs[GUSERLDT_SEL], &new_ldt->ldt_sd);
  512 
  513         if ((pldt = mdp->md_ldt) != NULL) {
  514                 if (len > pldt->ldt_len)
  515                         len = pldt->ldt_len;
  516                 bcopy(pldt->ldt_base, new_ldt->ldt_base,
  517                     len * sizeof(union descriptor));
  518         } else
  519                 bcopy(ldt, new_ldt->ldt_base, sizeof(ldt));
  520         
  521         return (new_ldt);
  522 }
  523 #endif /* !XEN */
  524 
  525 /*
  526  * Must be called with dt_lock held.  Returns with dt_lock unheld.
  527  */
  528 void
  529 user_ldt_free(struct thread *td)
  530 {
  531         struct mdproc *mdp = &td->td_proc->p_md;
  532         struct proc_ldt *pldt;
  533 
  534         mtx_assert(&dt_lock, MA_OWNED);
  535         if ((pldt = mdp->md_ldt) == NULL) {
  536                 mtx_unlock_spin(&dt_lock);
  537                 return;
  538         }
  539 
  540         if (td == curthread) {
  541 #ifdef XEN
  542                 i386_reset_ldt(&default_proc_ldt);
  543                 PCPU_SET(currentldt, (int)&default_proc_ldt);
  544 #else
  545                 lldt(_default_ldt);
  546                 PCPU_SET(currentldt, _default_ldt);
  547 #endif
  548         }
  549 
  550         mdp->md_ldt = NULL;
  551         user_ldt_deref(pldt);
  552 }
  553 
  554 void
  555 user_ldt_deref(struct proc_ldt *pldt)
  556 {
  557 
  558         mtx_assert(&dt_lock, MA_OWNED);
  559         if (--pldt->ldt_refcnt == 0) {
  560                 mtx_unlock_spin(&dt_lock);
  561                 kmem_free(kernel_arena, (vm_offset_t)pldt->ldt_base,
  562                         pldt->ldt_len * sizeof(union descriptor));
  563                 free(pldt, M_SUBPROC);
  564         } else
  565                 mtx_unlock_spin(&dt_lock);
  566 }
  567 
  568 /*
  569  * Note for the authors of compat layers (linux, etc): copyout() in
  570  * the function below is not a problem since it presents data in
  571  * arch-specific format (i.e. i386-specific in this case), not in
  572  * the OS-specific one.
  573  */
  574 int
  575 i386_get_ldt(td, uap)
  576         struct thread *td;
  577         struct i386_ldt_args *uap;
  578 {
  579         int error = 0;
  580         struct proc_ldt *pldt;
  581         int nldt, num;
  582         union descriptor *lp;
  583 
  584 #ifdef  DEBUG
  585         printf("i386_get_ldt: start=%d num=%d descs=%p\n",
  586             uap->start, uap->num, (void *)uap->descs);
  587 #endif
  588 
  589         mtx_lock_spin(&dt_lock);
  590         if ((pldt = td->td_proc->p_md.md_ldt) != NULL) {
  591                 nldt = pldt->ldt_len;
  592                 lp = &((union descriptor *)(pldt->ldt_base))[uap->start];
  593                 mtx_unlock_spin(&dt_lock);
  594                 num = min(uap->num, nldt);
  595         } else {
  596                 mtx_unlock_spin(&dt_lock);
  597                 nldt = sizeof(ldt)/sizeof(ldt[0]);
  598                 num = min(uap->num, nldt);
  599                 lp = &ldt[uap->start];
  600         }
  601 
  602         if ((uap->start > (unsigned int)nldt) ||
  603             ((unsigned int)num > (unsigned int)nldt) ||
  604             ((unsigned int)(uap->start + num) > (unsigned int)nldt))
  605                 return(EINVAL);
  606 
  607         error = copyout(lp, uap->descs, num * sizeof(union descriptor));
  608         if (!error)
  609                 td->td_retval[0] = num;
  610 
  611         return(error);
  612 }
  613 
  614 int
  615 i386_set_ldt(td, uap, descs)
  616         struct thread *td;
  617         struct i386_ldt_args *uap;
  618         union descriptor *descs;
  619 {
  620         int error = 0, i;
  621         int largest_ld;
  622         struct mdproc *mdp = &td->td_proc->p_md;
  623         struct proc_ldt *pldt;
  624         union descriptor *dp;
  625 
  626 #ifdef  DEBUG
  627         printf("i386_set_ldt: start=%d num=%d descs=%p\n",
  628             uap->start, uap->num, (void *)uap->descs);
  629 #endif
  630 
  631         if (descs == NULL) {
  632                 /* Free descriptors */
  633                 if (uap->start == 0 && uap->num == 0) {
  634                         /*
  635                          * Treat this as a special case, so userland needn't
  636                          * know magic number NLDT.
  637                          */
  638                         uap->start = NLDT;
  639                         uap->num = MAX_LD - NLDT;
  640                 }
  641                 if (uap->num == 0)
  642                         return (EINVAL);
  643                 mtx_lock_spin(&dt_lock);
  644                 if ((pldt = mdp->md_ldt) == NULL ||
  645                     uap->start >= pldt->ldt_len) {
  646                         mtx_unlock_spin(&dt_lock);
  647                         return (0);
  648                 }
  649                 largest_ld = uap->start + uap->num;
  650                 if (largest_ld > pldt->ldt_len)
  651                         largest_ld = pldt->ldt_len;
  652                 i = largest_ld - uap->start;
  653                 bzero(&((union descriptor *)(pldt->ldt_base))[uap->start],
  654                     sizeof(union descriptor) * i);
  655                 mtx_unlock_spin(&dt_lock);
  656                 return (0);
  657         }
  658 
  659         if (!(uap->start == LDT_AUTO_ALLOC && uap->num == 1)) {
  660                 /* verify range of descriptors to modify */
  661                 largest_ld = uap->start + uap->num;
  662                 if (uap->start >= MAX_LD || largest_ld > MAX_LD) {
  663                         return (EINVAL);
  664                 }
  665         }
  666 
  667         /* Check descriptors for access violations */
  668         for (i = 0; i < uap->num; i++) {
  669                 dp = &descs[i];
  670 
  671                 switch (dp->sd.sd_type) {
  672                 case SDT_SYSNULL:       /* system null */ 
  673                         dp->sd.sd_p = 0;
  674                         break;
  675                 case SDT_SYS286TSS: /* system 286 TSS available */
  676                 case SDT_SYSLDT:    /* system local descriptor table */
  677                 case SDT_SYS286BSY: /* system 286 TSS busy */
  678                 case SDT_SYSTASKGT: /* system task gate */
  679                 case SDT_SYS286IGT: /* system 286 interrupt gate */
  680                 case SDT_SYS286TGT: /* system 286 trap gate */
  681                 case SDT_SYSNULL2:  /* undefined by Intel */ 
  682                 case SDT_SYS386TSS: /* system 386 TSS available */
  683                 case SDT_SYSNULL3:  /* undefined by Intel */
  684                 case SDT_SYS386BSY: /* system 386 TSS busy */
  685                 case SDT_SYSNULL4:  /* undefined by Intel */ 
  686                 case SDT_SYS386IGT: /* system 386 interrupt gate */
  687                 case SDT_SYS386TGT: /* system 386 trap gate */
  688                 case SDT_SYS286CGT: /* system 286 call gate */ 
  689                 case SDT_SYS386CGT: /* system 386 call gate */
  690                         /* I can't think of any reason to allow a user proc
  691                          * to create a segment of these types.  They are
  692                          * for OS use only.
  693                          */
  694                         return (EACCES);
  695                         /*NOTREACHED*/
  696 
  697                 /* memory segment types */
  698                 case SDT_MEMEC:   /* memory execute only conforming */
  699                 case SDT_MEMEAC:  /* memory execute only accessed conforming */
  700                 case SDT_MEMERC:  /* memory execute read conforming */
  701                 case SDT_MEMERAC: /* memory execute read accessed conforming */
  702                          /* Must be "present" if executable and conforming. */
  703                         if (dp->sd.sd_p == 0)
  704                                 return (EACCES);
  705                         break;
  706                 case SDT_MEMRO:   /* memory read only */
  707                 case SDT_MEMROA:  /* memory read only accessed */
  708                 case SDT_MEMRW:   /* memory read write */
  709                 case SDT_MEMRWA:  /* memory read write accessed */
  710                 case SDT_MEMROD:  /* memory read only expand dwn limit */
  711                 case SDT_MEMRODA: /* memory read only expand dwn lim accessed */
  712                 case SDT_MEMRWD:  /* memory read write expand dwn limit */  
  713                 case SDT_MEMRWDA: /* memory read write expand dwn lim acessed */
  714                 case SDT_MEME:    /* memory execute only */ 
  715                 case SDT_MEMEA:   /* memory execute only accessed */
  716                 case SDT_MEMER:   /* memory execute read */
  717                 case SDT_MEMERA:  /* memory execute read accessed */
  718                         break;
  719                 default:
  720                         return(EINVAL);
  721                         /*NOTREACHED*/
  722                 }
  723 
  724                 /* Only user (ring-3) descriptors may be present. */
  725                 if ((dp->sd.sd_p != 0) && (dp->sd.sd_dpl != SEL_UPL))
  726                         return (EACCES);
  727         }
  728 
  729         if (uap->start == LDT_AUTO_ALLOC && uap->num == 1) {
  730                 /* Allocate a free slot */
  731                 mtx_lock_spin(&dt_lock);
  732                 if ((pldt = mdp->md_ldt) == NULL) {
  733                         if ((error = i386_ldt_grow(td, NLDT + 1))) {
  734                                 mtx_unlock_spin(&dt_lock);
  735                                 return (error);
  736                         }
  737                         pldt = mdp->md_ldt;
  738                 }
  739 again:
  740                 /*
  741                  * start scanning a bit up to leave room for NVidia and
  742                  * Wine, which still user the "Blat" method of allocation.
  743                  */
  744                 dp = &((union descriptor *)(pldt->ldt_base))[NLDT];
  745                 for (i = NLDT; i < pldt->ldt_len; ++i) {
  746                         if (dp->sd.sd_type == SDT_SYSNULL)
  747                                 break;
  748                         dp++;
  749                 }
  750                 if (i >= pldt->ldt_len) {
  751                         if ((error = i386_ldt_grow(td, pldt->ldt_len+1))) {
  752                                 mtx_unlock_spin(&dt_lock);
  753                                 return (error);
  754                         }
  755                         goto again;
  756                 }
  757                 uap->start = i;
  758                 error = i386_set_ldt_data(td, i, 1, descs);
  759                 mtx_unlock_spin(&dt_lock);
  760         } else {
  761                 largest_ld = uap->start + uap->num;
  762                 mtx_lock_spin(&dt_lock);
  763                 if (!(error = i386_ldt_grow(td, largest_ld))) {
  764                         error = i386_set_ldt_data(td, uap->start, uap->num,
  765                             descs);
  766                 }
  767                 mtx_unlock_spin(&dt_lock);
  768         }
  769         if (error == 0)
  770                 td->td_retval[0] = uap->start;
  771         return (error);
  772 }
  773 #ifdef XEN
  774 static int
  775 i386_set_ldt_data(struct thread *td, int start, int num,
  776         union descriptor *descs)
  777 {
  778         struct mdproc *mdp = &td->td_proc->p_md;
  779         struct proc_ldt *pldt = mdp->md_ldt;
  780 
  781         mtx_assert(&dt_lock, MA_OWNED);
  782 
  783         while (num) {
  784                 xen_update_descriptor(
  785                     &((union descriptor *)(pldt->ldt_base))[start],
  786                     descs);
  787                 num--;
  788                 start++;
  789                 descs++;
  790         }
  791         return (0);
  792 }
  793 #else
  794 static int
  795 i386_set_ldt_data(struct thread *td, int start, int num,
  796         union descriptor *descs)
  797 {
  798         struct mdproc *mdp = &td->td_proc->p_md;
  799         struct proc_ldt *pldt = mdp->md_ldt;
  800 
  801         mtx_assert(&dt_lock, MA_OWNED);
  802 
  803         /* Fill in range */
  804         bcopy(descs,
  805             &((union descriptor *)(pldt->ldt_base))[start],
  806             num * sizeof(union descriptor));
  807         return (0);
  808 }
  809 #endif /* !XEN */
  810 
  811 static int
  812 i386_ldt_grow(struct thread *td, int len) 
  813 {
  814         struct mdproc *mdp = &td->td_proc->p_md;
  815         struct proc_ldt *new_ldt, *pldt;
  816         caddr_t old_ldt_base = NULL_LDT_BASE;
  817         int old_ldt_len = 0;
  818 
  819         mtx_assert(&dt_lock, MA_OWNED);
  820 
  821         if (len > MAX_LD)
  822                 return (ENOMEM);
  823         if (len < NLDT + 1)
  824                 len = NLDT + 1;
  825 
  826         /* Allocate a user ldt. */
  827         if ((pldt = mdp->md_ldt) == NULL || len > pldt->ldt_len) {
  828                 new_ldt = user_ldt_alloc(mdp, len);
  829                 if (new_ldt == NULL)
  830                         return (ENOMEM);
  831                 pldt = mdp->md_ldt;
  832 
  833                 if (pldt != NULL) {
  834                         if (new_ldt->ldt_len <= pldt->ldt_len) {
  835                                 /*
  836                                  * We just lost the race for allocation, so
  837                                  * free the new object and return.
  838                                  */
  839                                 mtx_unlock_spin(&dt_lock);
  840                                 kmem_free(kernel_arena,
  841                                    (vm_offset_t)new_ldt->ldt_base,
  842                                    new_ldt->ldt_len * sizeof(union descriptor));
  843                                 free(new_ldt, M_SUBPROC);
  844                                 mtx_lock_spin(&dt_lock);
  845                                 return (0);
  846                         }
  847 
  848                         /*
  849                          * We have to substitute the current LDT entry for
  850                          * curproc with the new one since its size grew.
  851                          */
  852                         old_ldt_base = pldt->ldt_base;
  853                         old_ldt_len = pldt->ldt_len;
  854                         pldt->ldt_sd = new_ldt->ldt_sd;
  855                         pldt->ldt_base = new_ldt->ldt_base;
  856                         pldt->ldt_len = new_ldt->ldt_len;
  857                 } else
  858                         mdp->md_ldt = pldt = new_ldt;
  859 #ifdef SMP
  860                 /*
  861                  * Signal other cpus to reload ldt.  We need to unlock dt_lock
  862                  * here because other CPU will contest on it since their
  863                  * curthreads won't hold the lock and will block when trying
  864                  * to acquire it.
  865                  */
  866                 mtx_unlock_spin(&dt_lock);
  867                 smp_rendezvous(NULL, (void (*)(void *))set_user_ldt_rv,
  868                     NULL, td->td_proc->p_vmspace);
  869 #else
  870                 set_user_ldt(&td->td_proc->p_md);
  871                 mtx_unlock_spin(&dt_lock);
  872 #endif
  873                 if (old_ldt_base != NULL_LDT_BASE) {
  874                         kmem_free(kernel_arena, (vm_offset_t)old_ldt_base,
  875                             old_ldt_len * sizeof(union descriptor));
  876                         free(new_ldt, M_SUBPROC);
  877                 }
  878                 mtx_lock_spin(&dt_lock);
  879         }
  880         return (0);
  881 }

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