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

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    1 /*-
    2  * SPDX-License-Identifier: BSD-4-Clause
    3  *
    4  * Copyright (C) 1994, David Greenman
    5  * Copyright (c) 1990, 1993
    6  *      The Regents of the University of California.  All rights reserved.
    7  *
    8  * This code is derived from software contributed to Berkeley by
    9  * the University of Utah, and William Jolitz.
   10  *
   11  * Redistribution and use in source and binary forms, with or without
   12  * modification, are permitted provided that the following conditions
   13  * are met:
   14  * 1. Redistributions of source code must retain the above copyright
   15  *    notice, this list of conditions and the following disclaimer.
   16  * 2. Redistributions in binary form must reproduce the above copyright
   17  *    notice, this list of conditions and the following disclaimer in the
   18  *    documentation and/or other materials provided with the distribution.
   19  * 3. All advertising materials mentioning features or use of this software
   20  *    must display the following acknowledgement:
   21  *      This product includes software developed by the University of
   22  *      California, Berkeley and its contributors.
   23  * 4. Neither the name of the University nor the names of its contributors
   24  *    may be used to endorse or promote products derived from this software
   25  *    without specific prior written permission.
   26  *
   27  * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
   28  * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
   29  * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
   30  * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
   31  * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
   32  * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
   33  * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
   34  * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
   35  * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
   36  * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
   37  * SUCH DAMAGE.
   38  *
   39  *      from: @(#)trap.c        7.4 (Berkeley) 5/13/91
   40  */
   41 
   42 #include <sys/cdefs.h>
   43 __FBSDID("$FreeBSD$");
   44 
   45 /*
   46  * 386 Trap and System call handling
   47  */
   48 
   49 #include "opt_clock.h"
   50 #include "opt_compat.h"
   51 #include "opt_cpu.h"
   52 #include "opt_hwpmc_hooks.h"
   53 #include "opt_isa.h"
   54 #include "opt_kdb.h"
   55 #include "opt_trap.h"
   56 
   57 #include <sys/param.h>
   58 #include <sys/bus.h>
   59 #include <sys/systm.h>
   60 #include <sys/proc.h>
   61 #include <sys/ptrace.h>
   62 #include <sys/kdb.h>
   63 #include <sys/kernel.h>
   64 #include <sys/ktr.h>
   65 #include <sys/lock.h>
   66 #include <sys/mutex.h>
   67 #include <sys/resourcevar.h>
   68 #include <sys/signalvar.h>
   69 #include <sys/syscall.h>
   70 #include <sys/sysctl.h>
   71 #include <sys/sysent.h>
   72 #include <sys/uio.h>
   73 #include <sys/vmmeter.h>
   74 #ifdef HWPMC_HOOKS
   75 #include <sys/pmckern.h>
   76 PMC_SOFT_DEFINE( , , page_fault, all);
   77 PMC_SOFT_DEFINE( , , page_fault, read);
   78 PMC_SOFT_DEFINE( , , page_fault, write);
   79 #endif
   80 #include <security/audit/audit.h>
   81 
   82 #include <vm/vm.h>
   83 #include <vm/vm_param.h>
   84 #include <vm/pmap.h>
   85 #include <vm/vm_kern.h>
   86 #include <vm/vm_map.h>
   87 #include <vm/vm_page.h>
   88 #include <vm/vm_extern.h>
   89 
   90 #include <machine/cpu.h>
   91 #include <machine/intr_machdep.h>
   92 #include <x86/mca.h>
   93 #include <machine/md_var.h>
   94 #include <machine/pcb.h>
   95 #ifdef SMP
   96 #include <machine/smp.h>
   97 #endif
   98 #include <machine/stack.h>
   99 #include <machine/trap.h>
  100 #include <machine/tss.h>
  101 #include <machine/vm86.h>
  102 
  103 #ifdef POWERFAIL_NMI
  104 #include <sys/syslog.h>
  105 #include <machine/clock.h>
  106 #endif
  107 
  108 #ifdef KDTRACE_HOOKS
  109 #include <sys/dtrace_bsd.h>
  110 #endif
  111 
  112 void trap(struct trapframe *frame);
  113 void syscall(struct trapframe *frame);
  114 
  115 static int trap_pfault(struct trapframe *, bool, vm_offset_t, int *, int *);
  116 static void trap_fatal(struct trapframe *, vm_offset_t);
  117 #ifdef KDTRACE_HOOKS
  118 static bool trap_user_dtrace(struct trapframe *,
  119     int (**hook)(struct trapframe *));
  120 #endif
  121 void dblfault_handler(void);
  122 
  123 extern inthand_t IDTVEC(bpt), IDTVEC(dbg), IDTVEC(int0x80_syscall);
  124 extern uint64_t pg_nx;
  125 
  126 struct trap_data {
  127         bool            ei;
  128         const char      *msg;
  129 };
  130 
  131 static const struct trap_data trap_data[] = {
  132         [T_PRIVINFLT] = { .ei = true,   .msg = "privileged instruction fault" },
  133         [T_BPTFLT] =    { .ei = false,  .msg = "breakpoint instruction fault" },
  134         [T_ARITHTRAP] = { .ei = true,   .msg = "arithmetic trap" },
  135         [T_PROTFLT] =   { .ei = true,   .msg = "general protection fault" },
  136         [T_TRCTRAP] =   { .ei = false,  .msg = "debug exception" },
  137         [T_PAGEFLT] =   { .ei = true,   .msg = "page fault" },
  138         [T_ALIGNFLT] =  { .ei = true,   .msg = "alignment fault" },
  139         [T_DIVIDE] =    { .ei = true,   .msg = "integer divide fault" },
  140         [T_NMI] =       { .ei = false,  .msg = "non-maskable interrupt trap" },
  141         [T_OFLOW] =     { .ei = true,   .msg = "overflow trap" },
  142         [T_BOUND] =     { .ei = true,   .msg = "FPU bounds check fault" },
  143         [T_DNA] =       { .ei = true,   .msg = "FPU device not available" },
  144         [T_DOUBLEFLT] = { .ei = false,  .msg = "double fault" },
  145         [T_FPOPFLT] =   { .ei = true,   .msg = "FPU operand fetch fault" },
  146         [T_TSSFLT] =    { .ei = true,   .msg = "invalid TSS fault" },
  147         [T_SEGNPFLT] =  { .ei = true,   .msg = "segment not present fault" },
  148         [T_STKFLT] =    { .ei = true,   .msg = "stack fault" },
  149         [T_MCHK] =      { .ei = true,   .msg = "machine check trap" },
  150         [T_XMMFLT] =    { .ei = true,   .msg = "SIMD floating-point exception" },
  151         [T_DTRACE_RET] ={ .ei = true,   .msg = "DTrace pid return trap" },
  152 };
  153 
  154 static bool
  155 trap_enable_intr(int trapno)
  156 {
  157 
  158         MPASS(trapno > 0);
  159         if (trapno < nitems(trap_data) && trap_data[trapno].msg != NULL)
  160                 return (trap_data[trapno].ei);
  161         return (false);
  162 }
  163 
  164 static const char *
  165 trap_msg(int trapno)
  166 {
  167         const char *res;
  168         static const char unkn[] = "UNKNOWN";
  169 
  170         res = NULL;
  171         if (trapno < nitems(trap_data))
  172                 res = trap_data[trapno].msg;
  173         if (res == NULL)
  174                 res = unkn;
  175         return (res);
  176 }
  177 
  178 #if defined(I586_CPU) && !defined(NO_F00F_HACK)
  179 int has_f00f_bug = 0;           /* Initialized so that it can be patched. */
  180 #endif
  181 
  182 static int uprintf_signal;
  183 SYSCTL_INT(_machdep, OID_AUTO, uprintf_signal, CTLFLAG_RW,
  184     &uprintf_signal, 0,
  185     "Print debugging information on trap signal to ctty");
  186 
  187 /*
  188  * Exception, fault, and trap interface to the FreeBSD kernel.
  189  * This common code is called from assembly language IDT gate entry
  190  * routines that prepare a suitable stack frame, and restore this
  191  * frame after the exception has been processed.
  192  */
  193 
  194 void
  195 trap(struct trapframe *frame)
  196 {
  197         ksiginfo_t ksi;
  198         struct thread *td;
  199         struct proc *p;
  200         int pf, signo, ucode;
  201         u_int type;
  202         register_t addr, dr6;
  203         vm_offset_t eva;
  204 #ifdef POWERFAIL_NMI
  205         static int lastalert = 0;
  206 #endif
  207 
  208         td = curthread;
  209         p = td->td_proc;
  210         dr6 = 0;
  211 
  212         VM_CNT_INC(v_trap);
  213         type = frame->tf_trapno;
  214 
  215         KASSERT((read_eflags() & PSL_I) == 0,
  216             ("trap: interrupts enabled, type %d frame %p", type, frame));
  217 
  218 #ifdef SMP
  219         /* Handler for NMI IPIs used for stopping CPUs. */
  220         if (type == T_NMI && ipi_nmi_handler() == 0)
  221                 return;
  222 #endif /* SMP */
  223 
  224 #ifdef KDB
  225         if (kdb_active) {
  226                 kdb_reenter();
  227                 return;
  228         }
  229 #endif
  230 
  231         if (type == T_RESERVED) {
  232                 trap_fatal(frame, 0);
  233                 return;
  234         }
  235 
  236         if (type == T_NMI) {
  237 #ifdef HWPMC_HOOKS
  238                 /*
  239                  * CPU PMCs interrupt using an NMI so we check for that first.
  240                  * If the HWPMC module is active, 'pmc_hook' will point to
  241                  * the function to be called.  A non-zero return value from the
  242                  * hook means that the NMI was consumed by it and that we can
  243                  * return immediately.
  244                  */
  245                 if (pmc_intr != NULL &&
  246                     (*pmc_intr)(frame) != 0)
  247                         return;
  248 #endif
  249         }
  250 
  251         if (type == T_MCHK) {
  252                 mca_intr();
  253                 return;
  254         }
  255 
  256 #ifdef KDTRACE_HOOKS
  257         /*
  258          * A trap can occur while DTrace executes a probe. Before
  259          * executing the probe, DTrace blocks re-scheduling and sets
  260          * a flag in its per-cpu flags to indicate that it doesn't
  261          * want to fault. On returning from the probe, the no-fault
  262          * flag is cleared and finally re-scheduling is enabled.
  263          */
  264         if ((type == T_PROTFLT || type == T_PAGEFLT) &&
  265             dtrace_trap_func != NULL && (*dtrace_trap_func)(frame, type))
  266                 return;
  267 #endif
  268 
  269         /*
  270          * We must not allow context switches until %cr2 is read.
  271          * Also, for some Cyrix CPUs, %cr2 is clobbered by interrupts.
  272          * All faults use interrupt gates, so %cr2 can be safely read
  273          * now, before optional enable of the interrupts below.
  274          */
  275         if (type == T_PAGEFLT)
  276                 eva = rcr2();
  277 
  278         /*
  279          * Buggy application or kernel code has disabled interrupts
  280          * and then trapped.  Enabling interrupts now is wrong, but it
  281          * is better than running with interrupts disabled until they
  282          * are accidentally enabled later.
  283          */
  284         if ((frame->tf_eflags & PSL_I) == 0 && TRAPF_USERMODE(frame) &&
  285             (curpcb->pcb_flags & PCB_VM86CALL) == 0)
  286                 uprintf("pid %ld (%s): trap %d with interrupts disabled\n",
  287                     (long)curproc->p_pid, curthread->td_name, type);
  288 
  289         /*
  290          * Conditionally reenable interrupts.  If we hold a spin lock,
  291          * then we must not reenable interrupts.  This might be a
  292          * spurious page fault.
  293          */
  294         if (trap_enable_intr(type) && td->td_md.md_spinlock_count == 0 &&
  295             frame->tf_eip != (int)cpu_switch_load_gs)
  296                 enable_intr();
  297 
  298         if (TRAPF_USERMODE(frame) && (curpcb->pcb_flags & PCB_VM86CALL) == 0) {
  299                 /* user trap */
  300 
  301                 td->td_pticks = 0;
  302                 td->td_frame = frame;
  303                 addr = frame->tf_eip;
  304                 if (td->td_cowgen != p->p_cowgen)
  305                         thread_cow_update(td);
  306 
  307                 switch (type) {
  308                 case T_PRIVINFLT:       /* privileged instruction fault */
  309                         signo = SIGILL;
  310                         ucode = ILL_PRVOPC;
  311                         break;
  312 
  313                 case T_BPTFLT:          /* bpt instruction fault */
  314 #ifdef KDTRACE_HOOKS
  315                         if (trap_user_dtrace(frame, &dtrace_pid_probe_ptr))
  316                                 return;
  317 #else
  318                         enable_intr();
  319 #endif
  320                         signo = SIGTRAP;
  321                         ucode = TRAP_BRKPT;
  322                         break;
  323 
  324                 case T_TRCTRAP:         /* debug exception */
  325                         enable_intr();
  326 user_trctrap_out:
  327                         signo = SIGTRAP;
  328                         ucode = TRAP_TRACE;
  329                         dr6 = rdr6();
  330                         if ((dr6 & DBREG_DR6_BS) != 0) {
  331                                 PROC_LOCK(td->td_proc);
  332                                 if ((td->td_dbgflags & TDB_STEP) != 0) {
  333                                         td->td_frame->tf_eflags &= ~PSL_T;
  334                                         td->td_dbgflags &= ~TDB_STEP;
  335                                 }
  336                                 PROC_UNLOCK(td->td_proc);
  337                         }
  338                         break;
  339 
  340                 case T_ARITHTRAP:       /* arithmetic trap */
  341                         ucode = npxtrap_x87();
  342                         if (ucode == -1)
  343                                 return;
  344                         signo = SIGFPE;
  345                         break;
  346 
  347                 /*
  348                  * The following two traps can happen in vm86 mode,
  349                  * and, if so, we want to handle them specially.
  350                  */
  351                 case T_PROTFLT:         /* general protection fault */
  352                 case T_STKFLT:          /* stack fault */
  353                         if (frame->tf_eflags & PSL_VM) {
  354                                 signo = vm86_emulate((struct vm86frame *)frame);
  355                                 ucode = 0;      /* XXXKIB: better code ? */
  356                                 if (signo == SIGTRAP) {
  357                                         load_dr6(rdr6() | 0x4000);
  358                                         goto user_trctrap_out;
  359                                 }
  360                                 if (signo == 0)
  361                                         goto user;
  362                                 break;
  363                         }
  364                         signo = SIGBUS;
  365                         ucode = (type == T_PROTFLT) ? BUS_OBJERR : BUS_ADRERR;
  366                         break;
  367                 case T_SEGNPFLT:        /* segment not present fault */
  368                         signo = SIGBUS;
  369                         ucode = BUS_ADRERR;
  370                         break;
  371                 case T_TSSFLT:          /* invalid TSS fault */
  372                         signo = SIGBUS;
  373                         ucode = BUS_OBJERR;
  374                         break;
  375                 case T_ALIGNFLT:
  376                         signo = SIGBUS;
  377                         ucode = BUS_ADRALN;
  378                         break;
  379                 case T_DOUBLEFLT:       /* double fault */
  380                 default:
  381                         signo = SIGBUS;
  382                         ucode = BUS_OBJERR;
  383                         break;
  384 
  385                 case T_PAGEFLT:         /* page fault */
  386                         addr = eva;
  387                         pf = trap_pfault(frame, true, eva, &signo, &ucode);
  388 #if defined(I586_CPU) && !defined(NO_F00F_HACK)
  389                         if (pf == -2) {
  390                                 /*
  391                                  * The f00f hack workaround has triggered, so
  392                                  * treat the fault as an illegal instruction 
  393                                  * (T_PRIVINFLT) instead of a page fault.
  394                                  */
  395                                 type = frame->tf_trapno = T_PRIVINFLT;
  396                                 break;
  397                         }
  398 #endif
  399                         if (pf == -1)
  400                                 return;
  401                         if (pf == 0)
  402                                 goto user;
  403                         break;
  404 
  405                 case T_DIVIDE:          /* integer divide fault */
  406                         ucode = FPE_INTDIV;
  407                         signo = SIGFPE;
  408                         break;
  409 
  410                 case T_NMI:
  411 #ifdef POWERFAIL_NMI
  412 #ifndef TIMER_FREQ
  413 #  define TIMER_FREQ 1193182
  414 #endif
  415                         if (time_second - lastalert > 10) {
  416                                 log(LOG_WARNING, "NMI: power fail\n");
  417                                 sysbeep(880, hz);
  418                                 lastalert = time_second;
  419                         }
  420                         return;
  421 #else /* !POWERFAIL_NMI */
  422                         nmi_handle_intr(type, frame);
  423                         return;
  424 #endif /* POWERFAIL_NMI */
  425 
  426                 case T_OFLOW:           /* integer overflow fault */
  427                         ucode = FPE_INTOVF;
  428                         signo = SIGFPE;
  429                         break;
  430 
  431                 case T_BOUND:           /* bounds check fault */
  432                         ucode = FPE_FLTSUB;
  433                         signo = SIGFPE;
  434                         break;
  435 
  436                 case T_DNA:
  437                         KASSERT(PCB_USER_FPU(td->td_pcb),
  438                             ("kernel FPU ctx has leaked"));
  439                         /* transparent fault (due to context switch "late") */
  440                         if (npxdna())
  441                                 return;
  442                         uprintf("pid %d killed due to lack of floating point\n",
  443                                 p->p_pid);
  444                         signo = SIGKILL;
  445                         ucode = 0;
  446                         break;
  447 
  448                 case T_FPOPFLT:         /* FPU operand fetch fault */
  449                         ucode = ILL_COPROC;
  450                         signo = SIGILL;
  451                         break;
  452 
  453                 case T_XMMFLT:          /* SIMD floating-point exception */
  454                         ucode = npxtrap_sse();
  455                         if (ucode == -1)
  456                                 return;
  457                         signo = SIGFPE;
  458                         break;
  459 #ifdef KDTRACE_HOOKS
  460                 case T_DTRACE_RET:
  461                         (void)trap_user_dtrace(frame, &dtrace_return_probe_ptr);
  462                         return;
  463 #endif
  464                 }
  465         } else {
  466                 /* kernel trap */
  467 
  468                 KASSERT(cold || td->td_ucred != NULL,
  469                     ("kernel trap doesn't have ucred"));
  470                 switch (type) {
  471                 case T_PAGEFLT:                 /* page fault */
  472                         (void)trap_pfault(frame, false, eva, NULL, NULL);
  473                         return;
  474 
  475                 case T_DNA:
  476                         if (PCB_USER_FPU(td->td_pcb))
  477                                 panic("Unregistered use of FPU in kernel");
  478                         if (npxdna())
  479                                 return;
  480                         break;
  481 
  482                 case T_ARITHTRAP:       /* arithmetic trap */
  483                 case T_XMMFLT:          /* SIMD floating-point exception */
  484                 case T_FPOPFLT:         /* FPU operand fetch fault */
  485                         /*
  486                          * XXXKIB for now disable any FPU traps in kernel
  487                          * handler registration seems to be overkill
  488                          */
  489                         trap_fatal(frame, 0);
  490                         return;
  491 
  492                         /*
  493                          * The following two traps can happen in
  494                          * vm86 mode, and, if so, we want to handle
  495                          * them specially.
  496                          */
  497                 case T_PROTFLT:         /* general protection fault */
  498                 case T_STKFLT:          /* stack fault */
  499                         if (frame->tf_eflags & PSL_VM) {
  500                                 signo = vm86_emulate((struct vm86frame *)frame);
  501                                 if (signo == SIGTRAP) {
  502                                         type = T_TRCTRAP;
  503                                         load_dr6(rdr6() | 0x4000);
  504                                         goto kernel_trctrap;
  505                                 }
  506                                 if (signo != 0)
  507                                         /*
  508                                          * returns to original process
  509                                          */
  510                                         vm86_trap((struct vm86frame *)frame);
  511                                 return;
  512                         }
  513                         /* FALL THROUGH */
  514                 case T_SEGNPFLT:        /* segment not present fault */
  515                         if (curpcb->pcb_flags & PCB_VM86CALL)
  516                                 break;
  517 
  518                         /*
  519                          * Invalid %fs's and %gs's can be created using
  520                          * procfs or PT_SETREGS or by invalidating the
  521                          * underlying LDT entry.  This causes a fault
  522                          * in kernel mode when the kernel attempts to
  523                          * switch contexts.  Lose the bad context
  524                          * (XXX) so that we can continue, and generate
  525                          * a signal.
  526                          */
  527                         if (frame->tf_eip == (int)cpu_switch_load_gs) {
  528                                 curpcb->pcb_gs = 0;
  529 #if 0                           
  530                                 PROC_LOCK(p);
  531                                 kern_psignal(p, SIGBUS);
  532                                 PROC_UNLOCK(p);
  533 #endif                          
  534                                 return;
  535                         }
  536 
  537                         if (td->td_intr_nesting_level != 0)
  538                                 break;
  539 
  540                         /*
  541                          * Invalid segment selectors and out of bounds
  542                          * %eip's and %esp's can be set up in user mode.
  543                          * This causes a fault in kernel mode when the
  544                          * kernel tries to return to user mode.  We want
  545                          * to get this fault so that we can fix the
  546                          * problem here and not have to check all the
  547                          * selectors and pointers when the user changes
  548                          * them.
  549                          *
  550                          * N.B. Comparing to long mode, 32-bit mode
  551                          * does not push %esp on the trap frame,
  552                          * because iretl faulted while in ring 0.  As
  553                          * the consequence, there is no need to fixup
  554                          * the stack pointer for doreti_iret_fault,
  555                          * the fixup and the complimentary trap() call
  556                          * are executed on the main thread stack, not
  557                          * on the trampoline stack.
  558                          */
  559                         if (frame->tf_eip == (int)doreti_iret + setidt_disp) {
  560                                 frame->tf_eip = (int)doreti_iret_fault +
  561                                     setidt_disp;
  562                                 return;
  563                         }
  564                         if (type == T_STKFLT)
  565                                 break;
  566 
  567                         if (frame->tf_eip == (int)doreti_popl_ds +
  568                             setidt_disp) {
  569                                 frame->tf_eip = (int)doreti_popl_ds_fault +
  570                                     setidt_disp;
  571                                 return;
  572                         }
  573                         if (frame->tf_eip == (int)doreti_popl_es +
  574                             setidt_disp) {
  575                                 frame->tf_eip = (int)doreti_popl_es_fault +
  576                                     setidt_disp;
  577                                 return;
  578                         }
  579                         if (frame->tf_eip == (int)doreti_popl_fs +
  580                             setidt_disp) {
  581                                 frame->tf_eip = (int)doreti_popl_fs_fault +
  582                                     setidt_disp;
  583                                 return;
  584                         }
  585                         if (curpcb->pcb_onfault != NULL) {
  586                                 frame->tf_eip = (int)curpcb->pcb_onfault;
  587                                 return;
  588                         }
  589                         break;
  590 
  591                 case T_TSSFLT:
  592                         /*
  593                          * PSL_NT can be set in user mode and isn't cleared
  594                          * automatically when the kernel is entered.  This
  595                          * causes a TSS fault when the kernel attempts to
  596                          * `iret' because the TSS link is uninitialized.  We
  597                          * want to get this fault so that we can fix the
  598                          * problem here and not every time the kernel is
  599                          * entered.
  600                          */
  601                         if (frame->tf_eflags & PSL_NT) {
  602                                 frame->tf_eflags &= ~PSL_NT;
  603                                 return;
  604                         }
  605                         break;
  606 
  607                 case T_TRCTRAP:  /* debug exception */
  608 kernel_trctrap:
  609                         /* Clear any pending debug events. */
  610                         dr6 = rdr6();
  611                         load_dr6(0);
  612 
  613                         /*
  614                          * Ignore debug register exceptions due to
  615                          * accesses in the user's address space, which
  616                          * can happen under several conditions such as
  617                          * if a user sets a watchpoint on a buffer and
  618                          * then passes that buffer to a system call.
  619                          * We still want to get TRCTRAPS for addresses
  620                          * in kernel space because that is useful when
  621                          * debugging the kernel.
  622                          */
  623                         if (user_dbreg_trap(dr6) &&
  624                            !(curpcb->pcb_flags & PCB_VM86CALL))
  625                                 return;
  626 
  627                         /*
  628                          * Malicious user code can configure a debug
  629                          * register watchpoint to trap on data access
  630                          * to the top of stack and then execute 'pop
  631                          * %ss; int 3'.  Due to exception deferral for
  632                          * 'pop %ss', the CPU will not interrupt 'int
  633                          * 3' to raise the DB# exception for the debug
  634                          * register but will postpone the DB# until
  635                          * execution of the first instruction of the
  636                          * BP# handler (in kernel mode).  Normally the
  637                          * previous check would ignore DB# exceptions
  638                          * for watchpoints on user addresses raised in
  639                          * kernel mode.  However, some CPU errata
  640                          * include cases where DB# exceptions do not
  641                          * properly set bits in %dr6, e.g. Haswell
  642                          * HSD23 and Skylake-X SKZ24.
  643                          *
  644                          * A deferred DB# can also be raised on the
  645                          * first instructions of system call entry
  646                          * points or single-step traps via similar use
  647                          * of 'pop %ss' or 'mov xxx, %ss'.
  648                          */
  649                         if (frame->tf_eip ==
  650                             (uintptr_t)IDTVEC(int0x80_syscall) + setidt_disp ||
  651                             frame->tf_eip == (uintptr_t)IDTVEC(bpt) +
  652                             setidt_disp ||
  653                             frame->tf_eip == (uintptr_t)IDTVEC(dbg) +
  654                             setidt_disp)
  655                                 return;
  656                         /*
  657                          * FALLTHROUGH (TRCTRAP kernel mode, kernel address)
  658                          */
  659                 case T_BPTFLT:
  660                         /*
  661                          * If KDB is enabled, let it handle the debugger trap.
  662                          * Otherwise, debugger traps "can't happen".
  663                          */
  664 #ifdef KDB
  665                         if (kdb_trap(type, dr6, frame))
  666                                 return;
  667 #endif
  668                         break;
  669 
  670                 case T_NMI:
  671 #ifdef POWERFAIL_NMI
  672                         if (time_second - lastalert > 10) {
  673                                 log(LOG_WARNING, "NMI: power fail\n");
  674                                 sysbeep(880, hz);
  675                                 lastalert = time_second;
  676                         }
  677                         return;
  678 #else /* !POWERFAIL_NMI */
  679                         nmi_handle_intr(type, frame);
  680                         return;
  681 #endif /* POWERFAIL_NMI */
  682                 }
  683 
  684                 trap_fatal(frame, eva);
  685                 return;
  686         }
  687 
  688         /* Translate fault for emulators (e.g. Linux) */
  689         if (*p->p_sysent->sv_transtrap != NULL)
  690                 signo = (*p->p_sysent->sv_transtrap)(signo, type);
  691 
  692         ksiginfo_init_trap(&ksi);
  693         ksi.ksi_signo = signo;
  694         ksi.ksi_code = ucode;
  695         ksi.ksi_addr = (void *)addr;
  696         ksi.ksi_trapno = type;
  697         if (uprintf_signal) {
  698                 uprintf("pid %d comm %s: signal %d err %x code %d type %d "
  699                     "addr 0x%x ss 0x%04x esp 0x%08x cs 0x%04x eip 0x%08x "
  700                     "<%02x %02x %02x %02x %02x %02x %02x %02x>\n",
  701                     p->p_pid, p->p_comm, signo, frame->tf_err, ucode, type,
  702                     addr, frame->tf_ss, frame->tf_esp, frame->tf_cs,
  703                     frame->tf_eip,
  704                     fubyte((void *)(frame->tf_eip + 0)),
  705                     fubyte((void *)(frame->tf_eip + 1)),
  706                     fubyte((void *)(frame->tf_eip + 2)),
  707                     fubyte((void *)(frame->tf_eip + 3)),
  708                     fubyte((void *)(frame->tf_eip + 4)),
  709                     fubyte((void *)(frame->tf_eip + 5)),
  710                     fubyte((void *)(frame->tf_eip + 6)),
  711                     fubyte((void *)(frame->tf_eip + 7)));
  712         }
  713         KASSERT((read_eflags() & PSL_I) != 0, ("interrupts disabled"));
  714         trapsignal(td, &ksi);
  715 
  716 user:
  717         userret(td, frame);
  718         KASSERT(PCB_USER_FPU(td->td_pcb),
  719             ("Return from trap with kernel FPU ctx leaked"));
  720 }
  721 
  722 /*
  723  * Handle all details of a page fault.
  724  * Returns:
  725  * -2 if the fault was caused by triggered workaround for Intel Pentium
  726  *    0xf00f bug.
  727  * -1 if this fault was fatal, typically from kernel mode
  728  *    (cannot happen, but we need to return something).
  729  * 0  if this fault was handled by updating either the user or kernel
  730  *    page table, execution can continue.
  731  * 1  if this fault was from usermode and it was not handled, a synchronous
  732  *    signal should be delivered to the thread.  *signo returns the signal
  733  *    number, *ucode gives si_code.
  734  */
  735 static int
  736 trap_pfault(struct trapframe *frame, bool usermode, vm_offset_t eva,
  737     int *signo, int *ucode)
  738 {
  739         struct thread *td;
  740         struct proc *p;
  741         vm_map_t map;
  742         int rv;
  743         vm_prot_t ftype;
  744 
  745         MPASS(!usermode || (signo != NULL && ucode != NULL));
  746 
  747         td = curthread;
  748         p = td->td_proc;
  749 
  750         if (__predict_false((td->td_pflags & TDP_NOFAULTING) != 0)) {
  751                 /*
  752                  * Due to both processor errata and lazy TLB invalidation when
  753                  * access restrictions are removed from virtual pages, memory
  754                  * accesses that are allowed by the physical mapping layer may
  755                  * nonetheless cause one spurious page fault per virtual page. 
  756                  * When the thread is executing a "no faulting" section that
  757                  * is bracketed by vm_fault_{disable,enable}_pagefaults(),
  758                  * every page fault is treated as a spurious page fault,
  759                  * unless it accesses the same virtual address as the most
  760                  * recent page fault within the same "no faulting" section.
  761                  */
  762                 if (td->td_md.md_spurflt_addr != eva ||
  763                     (td->td_pflags & TDP_RESETSPUR) != 0) {
  764                         /*
  765                          * Do nothing to the TLB.  A stale TLB entry is
  766                          * flushed automatically by a page fault.
  767                          */
  768                         td->td_md.md_spurflt_addr = eva;
  769                         td->td_pflags &= ~TDP_RESETSPUR;
  770                         return (0);
  771                 }
  772         } else {
  773                 /*
  774                  * If we get a page fault while in a critical section, then
  775                  * it is most likely a fatal kernel page fault.  The kernel
  776                  * is already going to panic trying to get a sleep lock to
  777                  * do the VM lookup, so just consider it a fatal trap so the
  778                  * kernel can print out a useful trap message and even get
  779                  * to the debugger.
  780                  *
  781                  * If we get a page fault while holding a non-sleepable
  782                  * lock, then it is most likely a fatal kernel page fault.
  783                  * If WITNESS is enabled, then it's going to whine about
  784                  * bogus LORs with various VM locks, so just skip to the
  785                  * fatal trap handling directly.
  786                  */
  787                 if (td->td_critnest != 0 ||
  788                     WITNESS_CHECK(WARN_SLEEPOK | WARN_GIANTOK, NULL,
  789                     "Kernel page fault") != 0) {
  790                         trap_fatal(frame, eva);
  791                         return (-1);
  792                 }
  793         }
  794         if (eva >= PMAP_TRM_MIN_ADDRESS) {
  795                 /*
  796                  * Don't allow user-mode faults in kernel address space.
  797                  * An exception:  if the faulting address is the invalid
  798                  * instruction entry in the IDT, then the Intel Pentium
  799                  * F00F bug workaround was triggered, and we need to
  800                  * treat it is as an illegal instruction, and not a page
  801                  * fault.
  802                  */
  803 #if defined(I586_CPU) && !defined(NO_F00F_HACK)
  804                 if ((eva == (unsigned int)&idt[6]) && has_f00f_bug) {
  805                         *ucode = ILL_PRVOPC;
  806                         *signo = SIGILL;
  807                         return (-2);
  808                 }
  809 #endif
  810                 if (usermode) {
  811                         *signo = SIGSEGV;
  812                         *ucode = SEGV_MAPERR;
  813                         return (1);
  814                 }
  815                 trap_fatal(frame, eva);
  816                 return (-1);
  817         } else {
  818                 map = usermode ? &p->p_vmspace->vm_map : kernel_map;
  819 
  820                 /*
  821                  * Kernel cannot access a user-space address directly
  822                  * because user pages are not mapped.  Also, page
  823                  * faults must not be caused during the interrupts.
  824                  */
  825                 if (!usermode && td->td_intr_nesting_level != 0) {
  826                         trap_fatal(frame, eva);
  827                         return (-1);
  828                 }
  829         }
  830 
  831         /*
  832          * If the trap was caused by errant bits in the PTE then panic.
  833          */
  834         if (frame->tf_err & PGEX_RSV) {
  835                 trap_fatal(frame, eva);
  836                 return (-1);
  837         }
  838 
  839         /*
  840          * PGEX_I is defined only if the execute disable bit capability is
  841          * supported and enabled.
  842          */
  843         if (frame->tf_err & PGEX_W)
  844                 ftype = VM_PROT_WRITE;
  845         else if ((frame->tf_err & PGEX_I) && pg_nx != 0)
  846                 ftype = VM_PROT_EXECUTE;
  847         else
  848                 ftype = VM_PROT_READ;
  849 
  850         /* Fault in the page. */
  851         rv = vm_fault_trap(map, eva, ftype, VM_FAULT_NORMAL, signo, ucode);
  852         if (rv == KERN_SUCCESS) {
  853 #ifdef HWPMC_HOOKS
  854                 if (ftype == VM_PROT_READ || ftype == VM_PROT_WRITE) {
  855                         PMC_SOFT_CALL_TF( , , page_fault, all, frame);
  856                         if (ftype == VM_PROT_READ)
  857                                 PMC_SOFT_CALL_TF( , , page_fault, read,
  858                                     frame);
  859                         else
  860                                 PMC_SOFT_CALL_TF( , , page_fault, write,
  861                                     frame);
  862                 }
  863 #endif
  864                 return (0);
  865         }
  866         if (usermode)
  867                 return (1);
  868         if (td->td_intr_nesting_level == 0 &&
  869             curpcb->pcb_onfault != NULL) {
  870                 frame->tf_eip = (int)curpcb->pcb_onfault;
  871                 return (0);
  872         }
  873         trap_fatal(frame, eva);
  874         return (-1);
  875 }
  876 
  877 static void
  878 trap_fatal(frame, eva)
  879         struct trapframe *frame;
  880         vm_offset_t eva;
  881 {
  882         int code, ss, esp;
  883         u_int type;
  884         struct soft_segment_descriptor softseg;
  885 #ifdef KDB
  886         bool handled;
  887 #endif
  888 
  889         code = frame->tf_err;
  890         type = frame->tf_trapno;
  891         sdtossd(&gdt[IDXSEL(frame->tf_cs & 0xffff)].sd, &softseg);
  892 
  893         printf("\n\nFatal trap %d: %s while in %s mode\n", type, trap_msg(type),
  894             frame->tf_eflags & PSL_VM ? "vm86" :
  895             ISPL(frame->tf_cs) == SEL_UPL ? "user" : "kernel");
  896 #ifdef SMP
  897         /* two separate prints in case of a trap on an unmapped page */
  898         printf("cpuid = %d; ", PCPU_GET(cpuid));
  899         printf("apic id = %02x\n", PCPU_GET(apic_id));
  900 #endif
  901         if (type == T_PAGEFLT) {
  902                 printf("fault virtual address   = 0x%x\n", eva);
  903                 printf("fault code              = %s %s%s, %s\n",
  904                         code & PGEX_U ? "user" : "supervisor",
  905                         code & PGEX_W ? "write" : "read",
  906                         pg_nx != 0 ?
  907                         (code & PGEX_I ? " instruction" : " data") :
  908                         "",
  909                         code & PGEX_RSV ? "reserved bits in PTE" :
  910                         code & PGEX_P ? "protection violation" : "page not present");
  911         } else {
  912                 printf("error code              = %#x\n", code);
  913         }
  914         printf("instruction pointer     = 0x%x:0x%x\n",
  915                frame->tf_cs & 0xffff, frame->tf_eip);
  916         if (TF_HAS_STACKREGS(frame)) {
  917                 ss = frame->tf_ss & 0xffff;
  918                 esp = frame->tf_esp;
  919         } else {
  920                 ss = GSEL(GDATA_SEL, SEL_KPL);
  921                 esp = (int)&frame->tf_esp;
  922         }
  923         printf("stack pointer           = 0x%x:0x%x\n", ss, esp);
  924         printf("frame pointer           = 0x%x:0x%x\n", ss, frame->tf_ebp);
  925         printf("code segment            = base 0x%x, limit 0x%x, type 0x%x\n",
  926                softseg.ssd_base, softseg.ssd_limit, softseg.ssd_type);
  927         printf("                        = DPL %d, pres %d, def32 %d, gran %d\n",
  928                softseg.ssd_dpl, softseg.ssd_p, softseg.ssd_def32,
  929                softseg.ssd_gran);
  930         printf("processor eflags        = ");
  931         if (frame->tf_eflags & PSL_T)
  932                 printf("trace trap, ");
  933         if (frame->tf_eflags & PSL_I)
  934                 printf("interrupt enabled, ");
  935         if (frame->tf_eflags & PSL_NT)
  936                 printf("nested task, ");
  937         if (frame->tf_eflags & PSL_RF)
  938                 printf("resume, ");
  939         if (frame->tf_eflags & PSL_VM)
  940                 printf("vm86, ");
  941         printf("IOPL = %d\n", (frame->tf_eflags & PSL_IOPL) >> 12);
  942         printf("current process         = %d (%s)\n",
  943             curproc->p_pid, curthread->td_name);
  944 
  945 #ifdef KDB
  946         if (debugger_on_trap) {
  947                 kdb_why = KDB_WHY_TRAP;
  948                 frame->tf_err = eva;    /* smuggle fault address to ddb */
  949                 handled = kdb_trap(type, 0, frame);
  950                 frame->tf_err = code;   /* restore error code */
  951                 kdb_why = KDB_WHY_UNSET;
  952                 if (handled)
  953                         return;
  954         }
  955 #endif
  956         printf("trap number             = %d\n", type);
  957         if (trap_msg(type) != NULL)
  958                 panic("%s", trap_msg(type));
  959         else
  960                 panic("unknown/reserved trap");
  961 }
  962 
  963 #ifdef KDTRACE_HOOKS
  964 /*
  965  * Invoke a userspace DTrace hook.  The hook pointer is cleared when no
  966  * userspace probes are enabled, so we must synchronize with DTrace to ensure
  967  * that a trapping thread is able to call the hook before it is cleared.
  968  */
  969 static bool
  970 trap_user_dtrace(struct trapframe *frame, int (**hookp)(struct trapframe *))
  971 {
  972         int (*hook)(struct trapframe *);
  973 
  974         hook = atomic_load_ptr(hookp);
  975         enable_intr();
  976         if (hook != NULL)
  977                 return ((hook)(frame) == 0);
  978         return (false);
  979 }
  980 #endif
  981 
  982 /*
  983  * Double fault handler. Called when a fault occurs while writing
  984  * a frame for a trap/exception onto the stack. This usually occurs
  985  * when the stack overflows (such is the case with infinite recursion,
  986  * for example).
  987  *
  988  * XXX Note that the current PTD gets replaced by IdlePTD when the
  989  * task switch occurs. This means that the stack that was active at
  990  * the time of the double fault is not available at <kstack> unless
  991  * the machine was idle when the double fault occurred. The downside
  992  * of this is that "trace <ebp>" in ddb won't work.
  993  */
  994 void
  995 dblfault_handler(void)
  996 {
  997 #ifdef KDTRACE_HOOKS
  998         if (dtrace_doubletrap_func != NULL)
  999                 (*dtrace_doubletrap_func)();
 1000 #endif
 1001         printf("\nFatal double fault:\n");
 1002         printf("eip = 0x%x\n", PCPU_GET(common_tssp)->tss_eip);
 1003         printf("esp = 0x%x\n", PCPU_GET(common_tssp)->tss_esp);
 1004         printf("ebp = 0x%x\n", PCPU_GET(common_tssp)->tss_ebp);
 1005 #ifdef SMP
 1006         /* two separate prints in case of a trap on an unmapped page */
 1007         printf("cpuid = %d; ", PCPU_GET(cpuid));
 1008         printf("apic id = %02x\n", PCPU_GET(apic_id));
 1009 #endif
 1010         panic("double fault");
 1011 }
 1012 
 1013 int
 1014 cpu_fetch_syscall_args(struct thread *td)
 1015 {
 1016         struct proc *p;
 1017         struct trapframe *frame;
 1018         struct syscall_args *sa;
 1019         caddr_t params;
 1020         long tmp;
 1021         int error;
 1022 #ifdef COMPAT_43
 1023         u_int32_t eip;
 1024         int cs;
 1025 #endif
 1026 
 1027         p = td->td_proc;
 1028         frame = td->td_frame;
 1029         sa = &td->td_sa;
 1030 
 1031 #ifdef COMPAT_43
 1032         if (__predict_false(frame->tf_cs == 7 && frame->tf_eip == 2)) {
 1033                 /*
 1034                  * In lcall $7,$0 after int $0x80.  Convert the user
 1035                  * frame to what it would be for a direct int 0x80 instead
 1036                  * of lcall $7,$0, by popping the lcall return address.
 1037                  */
 1038                 error = fueword32((void *)frame->tf_esp, &eip);
 1039                 if (error == -1)
 1040                         return (EFAULT);
 1041                 cs = fuword16((void *)(frame->tf_esp + sizeof(u_int32_t)));
 1042                 if (cs == -1)
 1043                         return (EFAULT);
 1044 
 1045                 /*
 1046                  * Unwind in-kernel frame after all stack frame pieces
 1047                  * were successfully read.
 1048                  */
 1049                 frame->tf_eip = eip;
 1050                 frame->tf_cs = cs;
 1051                 frame->tf_esp += 2 * sizeof(u_int32_t);
 1052                 frame->tf_err = 7;      /* size of lcall $7,$0 */
 1053         }
 1054 #endif
 1055 
 1056         sa->code = frame->tf_eax;
 1057         params = (caddr_t)frame->tf_esp + sizeof(uint32_t);
 1058 
 1059         /*
 1060          * Need to check if this is a 32 bit or 64 bit syscall.
 1061          */
 1062         if (sa->code == SYS_syscall) {
 1063                 /*
 1064                  * Code is first argument, followed by actual args.
 1065                  */
 1066                 error = fueword(params, &tmp);
 1067                 if (error == -1)
 1068                         return (EFAULT);
 1069                 sa->code = tmp;
 1070                 params += sizeof(uint32_t);
 1071         } else if (sa->code == SYS___syscall) {
 1072                 /*
 1073                  * Like syscall, but code is a quad, so as to maintain
 1074                  * quad alignment for the rest of the arguments.
 1075                  */
 1076                 error = fueword(params, &tmp);
 1077                 if (error == -1)
 1078                         return (EFAULT);
 1079                 sa->code = tmp;
 1080                 params += sizeof(quad_t);
 1081         }
 1082 
 1083         if (sa->code >= p->p_sysent->sv_size)
 1084                 sa->callp = &p->p_sysent->sv_table[0];
 1085         else
 1086                 sa->callp = &p->p_sysent->sv_table[sa->code];
 1087 
 1088         if (params != NULL && sa->callp->sy_narg != 0)
 1089                 error = copyin(params, (caddr_t)sa->args,
 1090                     (u_int)(sa->callp->sy_narg * sizeof(uint32_t)));
 1091         else
 1092                 error = 0;
 1093 
 1094         if (error == 0) {
 1095                 td->td_retval[0] = 0;
 1096                 td->td_retval[1] = frame->tf_edx;
 1097         }
 1098                 
 1099         return (error);
 1100 }
 1101 
 1102 #include "../../kern/subr_syscall.c"
 1103 
 1104 /*
 1105  * syscall - system call request C handler.  A system call is
 1106  * essentially treated as a trap by reusing the frame layout.
 1107  */
 1108 void
 1109 syscall(struct trapframe *frame)
 1110 {
 1111         struct thread *td;
 1112         register_t orig_tf_eflags;
 1113         ksiginfo_t ksi;
 1114 
 1115 #ifdef DIAGNOSTIC
 1116         if (!(TRAPF_USERMODE(frame) &&
 1117             (curpcb->pcb_flags & PCB_VM86CALL) == 0)) {
 1118                 panic("syscall");
 1119                 /* NOT REACHED */
 1120         }
 1121 #endif
 1122         orig_tf_eflags = frame->tf_eflags;
 1123 
 1124         td = curthread;
 1125         td->td_frame = frame;
 1126 
 1127         syscallenter(td);
 1128 
 1129         /*
 1130          * Traced syscall.
 1131          */
 1132         if ((orig_tf_eflags & PSL_T) && !(orig_tf_eflags & PSL_VM)) {
 1133                 frame->tf_eflags &= ~PSL_T;
 1134                 ksiginfo_init_trap(&ksi);
 1135                 ksi.ksi_signo = SIGTRAP;
 1136                 ksi.ksi_code = TRAP_TRACE;
 1137                 ksi.ksi_addr = (void *)frame->tf_eip;
 1138                 trapsignal(td, &ksi);
 1139         }
 1140 
 1141         KASSERT(PCB_USER_FPU(td->td_pcb),
 1142             ("System call %s returning with kernel FPU ctx leaked",
 1143              syscallname(td->td_proc, td->td_sa.code)));
 1144         KASSERT(td->td_pcb->pcb_save == get_pcb_user_save_td(td),
 1145             ("System call %s returning with mangled pcb_save",
 1146              syscallname(td->td_proc, td->td_sa.code)));
 1147 
 1148         syscallret(td);
 1149 }

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