sys/amd64/amd64/trap.c

   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  * AMD64 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_stack.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/pioctl.h>
  62 #include <sys/ptrace.h>
  63 #include <sys/kdb.h>
  64 #include <sys/kernel.h>
  65 #include <sys/ktr.h>
  66 #include <sys/lock.h>
  67 #include <sys/mutex.h>
  68 #include <sys/resourcevar.h>
  69 #include <sys/signalvar.h>
  70 #include <sys/syscall.h>
  71 #include <sys/sysctl.h>
  72 #include <sys/sysent.h>
  73 #include <sys/uio.h>
  74 #include <sys/vmmeter.h>
  75 #ifdef HWPMC_HOOKS
  76 #include <sys/pmckern.h>
  77 PMC_SOFT_DEFINE( , , page_fault, all);
  78 PMC_SOFT_DEFINE( , , page_fault, read);
  79 PMC_SOFT_DEFINE( , , page_fault, write);
  80 #endif
  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
 102 #ifdef KDTRACE_HOOKS
 103 #include <sys/dtrace_bsd.h>
 104 #endif
 105
 106 extern inthand_t IDTVEC(bpt), IDTVEC(bpt_pti), IDTVEC(dbg),
 107     IDTVEC(fast_syscall), IDTVEC(fast_syscall_pti), IDTVEC(fast_syscall32),
 108     IDTVEC(int0x80_syscall_pti), IDTVEC(int0x80_syscall);
 109
 110 void __noinline trap(struct trapframe *frame);
 111 void trap_check(struct trapframe *frame);
 112 void dblfault_handler(struct trapframe *frame);
 113
 114 static int trap_pfault(struct trapframe *, int);
 115 static void trap_fatal(struct trapframe *, vm_offset_t);
 116 #ifdef KDTRACE_HOOKS
 117 static bool trap_user_dtrace(struct trapframe *,
 118     int (**hook)(struct trapframe *));
 119 #endif
 120
 121 static const char UNKNOWN[] = "unknown";
 122 static const char *const trap_msg[] = {
 123         [0] =                   UNKNOWN,                        /* unused */
 124         [T_PRIVINFLT] =         "privileged instruction fault",
 125         [2] =                   UNKNOWN,                        /* unused */
 126         [T_BPTFLT] =            "breakpoint instruction fault",
 127         [4] =                   UNKNOWN,                        /* unused */
 128         [5] =                   UNKNOWN,                        /* unused */
 129         [T_ARITHTRAP] =         "arithmetic trap",
 130         [7] =                   UNKNOWN,                        /* unused */
 131         [8] =                   UNKNOWN,                        /* unused */
 132         [T_PROTFLT] =           "general protection fault",
 133         [T_TRCTRAP] =           "debug exception",
 134         [11] =                  UNKNOWN,                        /* unused */
 135         [T_PAGEFLT] =           "page fault",
 136         [13] =                  UNKNOWN,                        /* unused */
 137         [T_ALIGNFLT] =          "alignment fault",
 138         [15] =                  UNKNOWN,                        /* unused */
 139         [16] =                  UNKNOWN,                        /* unused */
 140         [17] =                  UNKNOWN,                        /* unused */
 141         [T_DIVIDE] =            "integer divide fault",
 142         [T_NMI] =               "non-maskable interrupt trap",
 143         [T_OFLOW] =             "overflow trap",
 144         [T_BOUND] =             "FPU bounds check fault",
 145         [T_DNA] =               "FPU device not available",
 146         [T_DOUBLEFLT] =         "double fault",
 147         [T_FPOPFLT] =           "FPU operand fetch fault",
 148         [T_TSSFLT] =            "invalid TSS fault",
 149         [T_SEGNPFLT] =          "segment not present fault",
 150         [T_STKFLT] =            "stack fault",
 151         [T_MCHK] =              "machine check trap",
 152         [T_XMMFLT] =            "SIMD floating-point exception",
 153         [T_RESERVED] =          "reserved (unknown) fault",
 154         [31] =                  UNKNOWN,                        /* reserved */
 155         [T_DTRACE_RET] =        "DTrace pid return trap",
 156 };
 157
 158 static int prot_fault_translation;
 159 SYSCTL_INT(_machdep, OID_AUTO, prot_fault_translation, CTLFLAG_RWTUN,
 160     &prot_fault_translation, 0,
 161     "Select signal to deliver on protection fault");
 162 static int uprintf_signal;
 163 SYSCTL_INT(_machdep, OID_AUTO, uprintf_signal, CTLFLAG_RWTUN,
 164     &uprintf_signal, 0,
 165     "Print debugging information on trap signal to ctty");
 166
 167 /*
 168  * Control L1D flush on return from NMI.
 169  *
 170  * Tunable  can be set to the following values:
 171  * 0 - only enable flush on return from NMI if required by vmm.ko (default)
 172  * >1 - always flush on return from NMI.
 173  *
 174  * Post-boot, the sysctl indicates if flushing is currently enabled.
 175  */
 176 int nmi_flush_l1d_sw;
 177 SYSCTL_INT(_machdep, OID_AUTO, nmi_flush_l1d_sw, CTLFLAG_RWTUN,
 178     &nmi_flush_l1d_sw, 0,
 179     "Flush L1 Data Cache on NMI exit, software bhyve L1TF mitigation assist");
 180
 181 /*
 182  * Exception, fault, and trap interface to the FreeBSD kernel.
 183  * This common code is called from assembly language IDT gate entry
 184  * routines that prepare a suitable stack frame, and restore this
 185  * frame after the exception has been processed.
 186  */
 187
 188 void
 189 trap(struct trapframe *frame)
 190 {
 191         ksiginfo_t ksi;
 192         struct thread *td;
 193         struct proc *p;
 194         register_t addr, dr6;
 195         int signo, ucode;
 196         u_int type;
 197
 198         td = curthread;
 199         p = td->td_proc;
 200         signo = 0;
 201         ucode = 0;
 202         addr = 0;
 203         dr6 = 0;
 204
 205         VM_CNT_INC(v_trap);
 206         type = frame->tf_trapno;
 207
 208 #ifdef SMP
 209         /* Handler for NMI IPIs used for stopping CPUs. */
 210         if (type == T_NMI && ipi_nmi_handler() == 0)
 211                 return;
 212 #endif
 213
 214 #ifdef KDB
 215         if (kdb_active) {
 216                 kdb_reenter();
 217                 return;
 218         }
 219 #endif
 220
 221         if (type == T_RESERVED) {
 222                 trap_fatal(frame, 0);
 223                 return;
 224         }
 225
 226         if (type == T_NMI) {
 227 #ifdef HWPMC_HOOKS
 228                 /*
 229                  * CPU PMCs interrupt using an NMI.  If the PMC module is
 230                  * active, pass the 'rip' value to the PMC module's interrupt
 231                  * handler.  A non-zero return value from the handler means that
 232                  * the NMI was consumed by it and we can return immediately.
 233                  */
 234                 if (pmc_intr != NULL &&
 235                     (*pmc_intr)(frame) != 0)
 236                         return;
 237 #endif
 238
 239 #ifdef STACK
 240                 if (stack_nmi_handler(frame) != 0)
 241                         return;
 242 #endif
 243         }
 244
 245         if ((frame->tf_rflags & PSL_I) == 0) {
 246                 /*
 247                  * Buggy application or kernel code has disabled
 248                  * interrupts and then trapped.  Enabling interrupts
 249                  * now is wrong, but it is better than running with
 250                  * interrupts disabled until they are accidentally
 251                  * enabled later.
 252                  */
 253                 if (TRAPF_USERMODE(frame))
 254                         uprintf(
 255                             "pid %ld (%s): trap %d with interrupts disabled\n",
 256                             (long)curproc->p_pid, curthread->td_name, type);
 257                 else if (type != T_NMI && type != T_BPTFLT &&
 258                     type != T_TRCTRAP) {
 259                         /*
 260                          * XXX not quite right, since this may be for a
 261                          * multiple fault in user mode.
 262                          */
 263                         printf("kernel trap %d with interrupts disabled\n",
 264                             type);
 265
 266                         /*
 267                          * We shouldn't enable interrupts while holding a
 268                          * spin lock.
 269                          */
 270                         if (td->td_md.md_spinlock_count == 0)
 271                                 enable_intr();
 272                 }
 273         }
 274
 275         if (TRAPF_USERMODE(frame)) {
 276                 /* user trap */
 277
 278                 td->td_pticks = 0;
 279                 td->td_frame = frame;
 280                 addr = frame->tf_rip;
 281                 if (td->td_cowgen != p->p_cowgen)
 282                         thread_cow_update(td);
 283
 284                 switch (type) {
 285                 case T_PRIVINFLT:       /* privileged instruction fault */
 286                         signo = SIGILL;
 287                         ucode = ILL_PRVOPC;
 288                         break;
 289
 290                 case T_BPTFLT:          /* bpt instruction fault */
 291 #ifdef KDTRACE_HOOKS
 292                         if (trap_user_dtrace(frame, &dtrace_pid_probe_ptr))
 293                                 return;
 294 #else
 295                         enable_intr();
 296 #endif
 297                         signo = SIGTRAP;
 298                         ucode = TRAP_BRKPT;
 299                         break;
 300
 301                 case T_TRCTRAP:         /* debug exception */
 302                         enable_intr();
 303                         signo = SIGTRAP;
 304                         ucode = TRAP_TRACE;
 305                         dr6 = rdr6();
 306                         if ((dr6 & DBREG_DR6_BS) != 0) {
 307                                 PROC_LOCK(td->td_proc);
 308                                 if ((td->td_dbgflags & TDB_STEP) != 0) {
 309                                         td->td_frame->tf_rflags &= ~PSL_T;
 310                                         td->td_dbgflags &= ~TDB_STEP;
 311                                 }
 312                                 PROC_UNLOCK(td->td_proc);
 313                         }
 314                         break;
 315
 316                 case T_ARITHTRAP:       /* arithmetic trap */
 317                         ucode = fputrap_x87();
 318                         if (ucode == -1)
 319                                 return;
 320                         signo = SIGFPE;
 321                         break;
 322
 323                 case T_PROTFLT:         /* general protection fault */
 324                         signo = SIGBUS;
 325                         ucode = BUS_OBJERR;
 326                         break;
 327                 case T_STKFLT:          /* stack fault */
 328                 case T_SEGNPFLT:        /* segment not present fault */
 329                         signo = SIGBUS;
 330                         ucode = BUS_ADRERR;
 331                         break;
 332                 case T_TSSFLT:          /* invalid TSS fault */
 333                         signo = SIGBUS;
 334                         ucode = BUS_OBJERR;
 335                         break;
 336                 case T_ALIGNFLT:
 337                         signo = SIGBUS;
 338                         ucode = BUS_ADRALN;
 339                         break;
 340                 case T_DOUBLEFLT:       /* double fault */
 341                 default:
 342                         signo = SIGBUS;
 343                         ucode = BUS_OBJERR;
 344                         break;
 345
 346                 case T_PAGEFLT:         /* page fault */
 347                         /*
 348                          * Emulator can take care about this trap?
 349                          */
 350                         if (*p->p_sysent->sv_trap != NULL &&
 351                             (*p->p_sysent->sv_trap)(td) == 0)
 352                                 return;
 353
 354                         addr = frame->tf_addr;
 355                         signo = trap_pfault(frame, TRUE);
 356                         if (signo == -1)
 357                                 return;
 358                         if (signo == 0)
 359                                 goto userret;
 360                         if (signo == SIGSEGV) {
 361                                 ucode = SEGV_MAPERR;
 362                         } else if (prot_fault_translation == 0) {
 363                                 /*
 364                                  * Autodetect.  This check also covers
 365                                  * the images without the ABI-tag ELF
 366                                  * note.
 367                                  */
 368                                 if (SV_CURPROC_ABI() == SV_ABI_FREEBSD &&
 369                                     p->p_osrel >= P_OSREL_SIGSEGV) {
 370                                         signo = SIGSEGV;
 371                                         ucode = SEGV_ACCERR;
 372                                 } else {
 373                                         signo = SIGBUS;
 374                                         ucode = T_PAGEFLT;
 375                                 }
 376                         } else if (prot_fault_translation == 1) {
 377                                 /*
 378                                  * Always compat mode.
 379                                  */
 380                                 signo = SIGBUS;
 381                                 ucode = T_PAGEFLT;
 382                         } else {
 383                                 /*
 384                                  * Always SIGSEGV mode.
 385                                  */
 386                                 signo = SIGSEGV;
 387                                 ucode = SEGV_ACCERR;
 388                         }
 389                         break;
 390
 391                 case T_DIVIDE:          /* integer divide fault */
 392                         ucode = FPE_INTDIV;
 393                         signo = SIGFPE;
 394                         break;
 395
 396 #ifdef DEV_ISA
 397                 case T_NMI:
 398                         nmi_handle_intr(type, frame);
 399                         return;
 400 #endif
 401
 402                 case T_OFLOW:           /* integer overflow fault */
 403                         ucode = FPE_INTOVF;
 404                         signo = SIGFPE;
 405                         break;
 406
 407                 case T_BOUND:           /* bounds check fault */
 408                         ucode = FPE_FLTSUB;
 409                         signo = SIGFPE;
 410                         break;
 411
 412                 case T_DNA:
 413                         /* transparent fault (due to context switch "late") */
 414                         KASSERT(PCB_USER_FPU(td->td_pcb),
 415                             ("kernel FPU ctx has leaked"));
 416                         fpudna();
 417                         return;
 418
 419                 case T_FPOPFLT:         /* FPU operand fetch fault */
 420                         ucode = ILL_COPROC;
 421                         signo = SIGILL;
 422                         break;
 423
 424                 case T_XMMFLT:          /* SIMD floating-point exception */
 425                         ucode = fputrap_sse();
 426                         if (ucode == -1)
 427                                 return;
 428                         signo = SIGFPE;
 429                         break;
 430 #ifdef KDTRACE_HOOKS
 431                 case T_DTRACE_RET:
 432                         (void)trap_user_dtrace(frame, &dtrace_return_probe_ptr);
 433                         return;
 434 #endif
 435                 }
 436         } else {
 437                 /* kernel trap */
 438
 439                 KASSERT(cold || td->td_ucred != NULL,
 440                     ("kernel trap doesn't have ucred"));
 441                 switch (type) {
 442                 case T_PAGEFLT:                 /* page fault */
 443                         (void) trap_pfault(frame, FALSE);
 444                         return;
 445
 446                 case T_DNA:
 447                         if (PCB_USER_FPU(td->td_pcb))
 448                                 panic("Unregistered use of FPU in kernel");
 449                         fpudna();
 450                         return;
 451
 452                 case T_ARITHTRAP:       /* arithmetic trap */
 453                 case T_XMMFLT:          /* SIMD floating-point exception */
 454                 case T_FPOPFLT:         /* FPU operand fetch fault */
 455                         /*
 456                          * For now, supporting kernel handler
 457                          * registration for FPU traps is overkill.
 458                          */
 459                         trap_fatal(frame, 0);
 460                         return;
 461
 462                 case T_STKFLT:          /* stack fault */
 463                 case T_PROTFLT:         /* general protection fault */
 464                 case T_SEGNPFLT:        /* segment not present fault */
 465                         if (td->td_intr_nesting_level != 0)
 466                                 break;
 467
 468                         /*
 469                          * Invalid segment selectors and out of bounds
 470                          * %rip's and %rsp's can be set up in user mode.
 471                          * This causes a fault in kernel mode when the
 472                          * kernel tries to return to user mode.  We want
 473                          * to get this fault so that we can fix the
 474                          * problem here and not have to check all the
 475                          * selectors and pointers when the user changes
 476                          * them.
 477                          *
 478                          * In case of PTI, the IRETQ faulted while the
 479                          * kernel used the pti stack, and exception
 480                          * frame records %rsp value pointing to that
 481                          * stack.  If we return normally to
 482                          * doreti_iret_fault, the trapframe is
 483                          * reconstructed on pti stack, and calltrap()
 484                          * called on it as well.  Due to the very
 485                          * limited pti stack size, kernel does not
 486                          * survive for too long.  Switch to the normal
 487                          * thread stack for the trap handling.
 488                          *
 489                          * Magic '5' is the number of qwords occupied by
 490                          * the hardware trap frame.
 491                          */
 492                         if (frame->tf_rip == (long)doreti_iret) {
 493                                 frame->tf_rip = (long)doreti_iret_fault;
 494                                 if ((PCPU_GET(curpmap)->pm_ucr3 !=
 495                                     PMAP_NO_CR3) &&
 496                                     (frame->tf_rsp == (uintptr_t)PCPU_GET(
 497                                     pti_rsp0) - 5 * sizeof(register_t))) {
 498                                         frame->tf_rsp = PCPU_GET(rsp0) - 5 *
 499                                             sizeof(register_t);
 500                                 }
 501                                 return;
 502                         }
 503                         if (frame->tf_rip == (long)ld_ds) {
 504                                 frame->tf_rip = (long)ds_load_fault;
 505                                 return;
 506                         }
 507                         if (frame->tf_rip == (long)ld_es) {
 508                                 frame->tf_rip = (long)es_load_fault;
 509                                 return;
 510                         }
 511                         if (frame->tf_rip == (long)ld_fs) {
 512                                 frame->tf_rip = (long)fs_load_fault;
 513                                 return;
 514                         }
 515                         if (frame->tf_rip == (long)ld_gs) {
 516                                 frame->tf_rip = (long)gs_load_fault;
 517                                 return;
 518                         }
 519                         if (frame->tf_rip == (long)ld_gsbase) {
 520                                 frame->tf_rip = (long)gsbase_load_fault;
 521                                 return;
 522                         }
 523                         if (frame->tf_rip == (long)ld_fsbase) {
 524                                 frame->tf_rip = (long)fsbase_load_fault;
 525                                 return;
 526                         }
 527                         if (curpcb->pcb_onfault != NULL) {
 528                                 frame->tf_rip = (long)curpcb->pcb_onfault;
 529                                 return;
 530                         }
 531                         break;
 532
 533                 case T_TSSFLT:
 534                         /*
 535                          * PSL_NT can be set in user mode and isn't cleared
 536                          * automatically when the kernel is entered.  This
 537                          * causes a TSS fault when the kernel attempts to
 538                          * `iret' because the TSS link is uninitialized.  We
 539                          * want to get this fault so that we can fix the
 540                          * problem here and not every time the kernel is
 541                          * entered.
 542                          */
 543                         if (frame->tf_rflags & PSL_NT) {
 544                                 frame->tf_rflags &= ~PSL_NT;
 545                                 return;
 546                         }
 547                         break;
 548
 549                 case T_TRCTRAP:  /* debug exception */
 550                         /* Clear any pending debug events. */
 551                         dr6 = rdr6();
 552                         load_dr6(0);
 553
 554                         /*
 555                          * Ignore debug register exceptions due to
 556                          * accesses in the user's address space, which
 557                          * can happen under several conditions such as
 558                          * if a user sets a watchpoint on a buffer and
 559                          * then passes that buffer to a system call.
 560                          * We still want to get TRCTRAPS for addresses
 561                          * in kernel space because that is useful when
 562                          * debugging the kernel.
 563                          */
 564                         if (user_dbreg_trap(dr6))
 565                                 return;
 566
 567                         /*
 568                          * Malicious user code can configure a debug
 569                          * register watchpoint to trap on data access
 570                          * to the top of stack and then execute 'pop
 571                          * %ss; int 3'.  Due to exception deferral for
 572                          * 'pop %ss', the CPU will not interrupt 'int
 573                          * 3' to raise the DB# exception for the debug
 574                          * register but will postpone the DB# until
 575                          * execution of the first instruction of the
 576                          * BP# handler (in kernel mode).  Normally the
 577                          * previous check would ignore DB# exceptions
 578                          * for watchpoints on user addresses raised in
 579                          * kernel mode.  However, some CPU errata
 580                          * include cases where DB# exceptions do not
 581                          * properly set bits in %dr6, e.g. Haswell
 582                          * HSD23 and Skylake-X SKZ24.
 583                          *
 584                          * A deferred DB# can also be raised on the
 585                          * first instructions of system call entry
 586                          * points or single-step traps via similar use
 587                          * of 'pop %ss' or 'mov xxx, %ss'.
 588                          */
 589                         if (pti) {
 590                                 if (frame->tf_rip ==
 591                                     (uintptr_t)IDTVEC(fast_syscall_pti) ||
 592 #ifdef COMPAT_FREEBSD32
 593                                     frame->tf_rip ==
 594                                     (uintptr_t)IDTVEC(int0x80_syscall_pti) ||
 595 #endif
 596                                     frame->tf_rip == (uintptr_t)IDTVEC(bpt_pti))
 597                                         return;
 598                         } else {
 599                                 if (frame->tf_rip ==
 600                                     (uintptr_t)IDTVEC(fast_syscall) ||
 601 #ifdef COMPAT_FREEBSD32
 602                                     frame->tf_rip ==
 603                                     (uintptr_t)IDTVEC(int0x80_syscall) ||
 604 #endif
 605                                     frame->tf_rip == (uintptr_t)IDTVEC(bpt))
 606                                         return;
 607                         }
 608                         if (frame->tf_rip == (uintptr_t)IDTVEC(dbg) ||
 609                             /* Needed for AMD. */
 610                             frame->tf_rip == (uintptr_t)IDTVEC(fast_syscall32))
 611                                 return;
 612                         /*
 613                          * FALLTHROUGH (TRCTRAP kernel mode, kernel address)
 614                          */
 615                 case T_BPTFLT:
 616                         /*
 617                          * If KDB is enabled, let it handle the debugger trap.
 618                          * Otherwise, debugger traps "can't happen".
 619                          */
 620 #ifdef KDB
 621                         if (kdb_trap(type, dr6, frame))
 622                                 return;
 623 #endif
 624                         break;
 625
 626 #ifdef DEV_ISA
 627                 case T_NMI:
 628                         nmi_handle_intr(type, frame);
 629                         return;
 630 #endif
 631                 }
 632
 633                 trap_fatal(frame, 0);
 634                 return;
 635         }
 636
 637         /* Translate fault for emulators (e.g. Linux) */
 638         if (*p->p_sysent->sv_transtrap != NULL)
 639                 signo = (*p->p_sysent->sv_transtrap)(signo, type);
 640
 641         ksiginfo_init_trap(&ksi);
 642         ksi.ksi_signo = signo;
 643         ksi.ksi_code = ucode;
 644         ksi.ksi_trapno = type;
 645         ksi.ksi_addr = (void *)addr;
 646         if (uprintf_signal) {
 647                 uprintf("pid %d comm %s: signal %d err %lx code %d type %d "
 648                     "addr 0x%lx rsp 0x%lx rip 0x%lx "
 649                     "<%02x %02x %02x %02x %02x %02x %02x %02x>\n",
 650                     p->p_pid, p->p_comm, signo, frame->tf_err, ucode, type,
 651                     addr, frame->tf_rsp, frame->tf_rip,
 652                     fubyte((void *)(frame->tf_rip + 0)),
 653                     fubyte((void *)(frame->tf_rip + 1)),
 654                     fubyte((void *)(frame->tf_rip + 2)),
 655                     fubyte((void *)(frame->tf_rip + 3)),
 656                     fubyte((void *)(frame->tf_rip + 4)),
 657                     fubyte((void *)(frame->tf_rip + 5)),
 658                     fubyte((void *)(frame->tf_rip + 6)),
 659                     fubyte((void *)(frame->tf_rip + 7)));
 660         }
 661         KASSERT((read_rflags() & PSL_I) != 0, ("interrupts disabled"));
 662         trapsignal(td, &ksi);
 663
 664 userret:
 665         userret(td, frame);
 666         KASSERT(PCB_USER_FPU(td->td_pcb),
 667             ("Return from trap with kernel FPU ctx leaked"));
 668 }
 669
 670 /*
 671  * Ensure that we ignore any DTrace-induced faults. This function cannot
 672  * be instrumented, so it cannot generate such faults itself.
 673  */
 674 void
 675 trap_check(struct trapframe *frame)
 676 {
 677
 678 #ifdef KDTRACE_HOOKS
 679         if (dtrace_trap_func != NULL &&
 680             (*dtrace_trap_func)(frame, frame->tf_trapno) != 0)
 681                 return;
 682 #endif
 683         trap(frame);
 684 }
 685
 686 static bool
 687 trap_is_smap(struct trapframe *frame)
 688 {
 689
 690         /*
 691          * A page fault on a userspace address is classified as
 692          * SMAP-induced if:
 693          * - SMAP is supported;
 694          * - kernel mode accessed present data page;
 695          * - rflags.AC was cleared.
 696          * Kernel must never access user space with rflags.AC cleared
 697          * if SMAP is enabled.
 698          */
 699         return ((cpu_stdext_feature & CPUID_STDEXT_SMAP) != 0 &&
 700             (frame->tf_err & (PGEX_P | PGEX_U | PGEX_I | PGEX_RSV)) ==
 701             PGEX_P && (frame->tf_rflags & PSL_AC) == 0);
 702 }
 703
 704 static bool
 705 trap_is_pti(struct trapframe *frame)
 706 {
 707
 708         return (PCPU_GET(curpmap)->pm_ucr3 != PMAP_NO_CR3 &&
 709             pg_nx != 0 && (frame->tf_err & (PGEX_P | PGEX_W |
 710             PGEX_U | PGEX_I)) == (PGEX_P | PGEX_U | PGEX_I) &&
 711             (curpcb->pcb_saved_ucr3 & ~CR3_PCID_MASK) ==
 712             (PCPU_GET(curpmap)->pm_cr3 & ~CR3_PCID_MASK));
 713 }
 714
 715 static int
 716 trap_pfault(struct trapframe *frame, int usermode)
 717 {
 718         struct thread *td;
 719         struct proc *p;
 720         vm_map_t map;
 721         vm_offset_t va;
 722         int rv;
 723         vm_prot_t ftype;
 724         vm_offset_t eva;
 725
 726         td = curthread;
 727         p = td->td_proc;
 728         eva = frame->tf_addr;
 729
 730         if (__predict_false((td->td_pflags & TDP_NOFAULTING) != 0)) {
 731                 /*
 732                  * Due to both processor errata and lazy TLB invalidation when
 733                  * access restrictions are removed from virtual pages, memory
 734                  * accesses that are allowed by the physical mapping layer may
 735                  * nonetheless cause one spurious page fault per virtual page.
 736                  * When the thread is executing a "no faulting" section that
 737                  * is bracketed by vm_fault_{disable,enable}_pagefaults(),
 738                  * every page fault is treated as a spurious page fault,
 739                  * unless it accesses the same virtual address as the most
 740                  * recent page fault within the same "no faulting" section.
 741                  */
 742                 if (td->td_md.md_spurflt_addr != eva ||
 743                     (td->td_pflags & TDP_RESETSPUR) != 0) {
 744                         /*
 745                          * Do nothing to the TLB.  A stale TLB entry is
 746                          * flushed automatically by a page fault.
 747                          */
 748                         td->td_md.md_spurflt_addr = eva;
 749                         td->td_pflags &= ~TDP_RESETSPUR;
 750                         return (0);
 751                 }
 752         } else {
 753                 /*
 754                  * If we get a page fault while in a critical section, then
 755                  * it is most likely a fatal kernel page fault.  The kernel
 756                  * is already going to panic trying to get a sleep lock to
 757                  * do the VM lookup, so just consider it a fatal trap so the
 758                  * kernel can print out a useful trap message and even get
 759                  * to the debugger.
 760                  *
 761                  * If we get a page fault while holding a non-sleepable
 762                  * lock, then it is most likely a fatal kernel page fault.
 763                  * If WITNESS is enabled, then it's going to whine about
 764                  * bogus LORs with various VM locks, so just skip to the
 765                  * fatal trap handling directly.
 766                  */
 767                 if (td->td_critnest != 0 ||
 768                     WITNESS_CHECK(WARN_SLEEPOK | WARN_GIANTOK, NULL,
 769                     "Kernel page fault") != 0) {
 770                         trap_fatal(frame, eva);
 771                         return (-1);
 772                 }
 773         }
 774         va = trunc_page(eva);
 775         if (va >= VM_MIN_KERNEL_ADDRESS) {
 776                 /*
 777                  * Don't allow user-mode faults in kernel address space.
 778                  */
 779                 if (usermode)
 780                         return (SIGSEGV);
 781
 782                 map = kernel_map;
 783         } else {
 784                 map = &p->p_vmspace->vm_map;
 785
 786                 /*
 787                  * When accessing a usermode address, kernel must be
 788                  * ready to accept the page fault, and provide a
 789                  * handling routine.  Since accessing the address
 790                  * without the handler is a bug, do not try to handle
 791                  * it normally, and panic immediately.
 792                  *
 793                  * If SMAP is enabled, filter SMAP faults also,
 794                  * because illegal access might occur to the mapped
 795                  * user address, causing infinite loop.
 796                  */
 797                 if (!usermode && (td->td_intr_nesting_level != 0 ||
 798                     trap_is_smap(frame) || curpcb->pcb_onfault == NULL)) {
 799                         trap_fatal(frame, eva);
 800                         return (-1);
 801                 }
 802         }
 803
 804         /*
 805          * If the trap was caused by errant bits in the PTE then panic.
 806          */
 807         if (frame->tf_err & PGEX_RSV) {
 808                 trap_fatal(frame, eva);
 809                 return (-1);
 810         }
 811
 812         /*
 813          * User-mode protection key violation (PKU).  May happen
 814          * either from usermode or from kernel if copyin accessed
 815          * key-protected mapping.
 816          */
 817         if ((frame->tf_err & PGEX_PK) != 0) {
 818                 if (eva > VM_MAXUSER_ADDRESS) {
 819                         trap_fatal(frame, eva);
 820                         return (-1);
 821                 }
 822                 rv = KERN_PROTECTION_FAILURE;
 823                 goto after_vmfault;
 824         }
 825
 826         /*
 827          * If nx protection of the usermode portion of kernel page
 828          * tables caused trap, panic.
 829          */
 830         if (usermode && trap_is_pti(frame))
 831                 panic("PTI: pid %d comm %s tf_err %#lx", p->p_pid,
 832                     p->p_comm, frame->tf_err);
 833
 834         /*
 835          * PGEX_I is defined only if the execute disable bit capability is
 836          * supported and enabled.
 837          */
 838         if (frame->tf_err & PGEX_W)
 839                 ftype = VM_PROT_WRITE;
 840         else if ((frame->tf_err & PGEX_I) && pg_nx != 0)
 841                 ftype = VM_PROT_EXECUTE;
 842         else
 843                 ftype = VM_PROT_READ;
 844
 845         /* Fault in the page. */
 846         rv = vm_fault(map, va, ftype, VM_FAULT_NORMAL);
 847         if (rv == KERN_SUCCESS) {
 848 #ifdef HWPMC_HOOKS
 849                 if (ftype == VM_PROT_READ || ftype == VM_PROT_WRITE) {
 850                         PMC_SOFT_CALL_TF( , , page_fault, all, frame);
 851                         if (ftype == VM_PROT_READ)
 852                                 PMC_SOFT_CALL_TF( , , page_fault, read,
 853                                     frame);
 854                         else
 855                                 PMC_SOFT_CALL_TF( , , page_fault, write,
 856                                     frame);
 857                 }
 858 #endif
 859                 return (0);
 860         }
 861 after_vmfault:
 862         if (!usermode) {
 863                 if (td->td_intr_nesting_level == 0 &&
 864                     curpcb->pcb_onfault != NULL) {
 865                         frame->tf_rip = (long)curpcb->pcb_onfault;
 866                         return (0);
 867                 }
 868                 trap_fatal(frame, eva);
 869                 return (-1);
 870         }
 871         return ((rv == KERN_PROTECTION_FAILURE) ? SIGBUS : SIGSEGV);
 872 }
 873
 874 static void
 875 trap_fatal(frame, eva)
 876         struct trapframe *frame;
 877         vm_offset_t eva;
 878 {
 879         int code, ss;
 880         u_int type;
 881         struct soft_segment_descriptor softseg;
 882 #ifdef KDB
 883         bool handled;
 884 #endif
 885
 886         code = frame->tf_err;
 887         type = frame->tf_trapno;
 888         sdtossd(&gdt[NGDT * PCPU_GET(cpuid) + IDXSEL(frame->tf_cs & 0xffff)],
 889             &softseg);
 890
 891         printf("\n\nFatal trap %d: %s while in %s mode\n", type,
 892             type < nitems(trap_msg) ? trap_msg[type] : UNKNOWN,
 893             TRAPF_USERMODE(frame) ? "user" : "kernel");
 894 #ifdef SMP
 895         /* two separate prints in case of a trap on an unmapped page */
 896         printf("cpuid = %d; ", PCPU_GET(cpuid));
 897         printf("apic id = %02x\n", PCPU_GET(apic_id));
 898 #endif
 899         if (type == T_PAGEFLT) {
 900                 printf("fault virtual address   = 0x%lx\n", eva);
 901                 printf("fault code              = %s %s %s%s%s, %s\n",
 902                         code & PGEX_U ? "user" : "supervisor",
 903                         code & PGEX_W ? "write" : "read",
 904                         code & PGEX_I ? "instruction" : "data",
 905                         code & PGEX_PK ? " prot key" : "",
 906                         code & PGEX_SGX ? " SGX" : "",
 907                         code & PGEX_RSV ? "reserved bits in PTE" :
 908                         code & PGEX_P ? "protection violation" : "page not present");
 909         }
 910         printf("instruction pointer     = 0x%lx:0x%lx\n",
 911                frame->tf_cs & 0xffff, frame->tf_rip);
 912         ss = frame->tf_ss & 0xffff;
 913         printf("stack pointer           = 0x%x:0x%lx\n", ss, frame->tf_rsp);
 914         printf("frame pointer           = 0x%x:0x%lx\n", ss, frame->tf_rbp);
 915         printf("code segment            = base 0x%lx, limit 0x%lx, type 0x%x\n",
 916                softseg.ssd_base, softseg.ssd_limit, softseg.ssd_type);
 917         printf("                        = DPL %d, pres %d, long %d, def32 %d, gran %d\n",
 918                softseg.ssd_dpl, softseg.ssd_p, softseg.ssd_long, softseg.ssd_def32,
 919                softseg.ssd_gran);
 920         printf("processor eflags        = ");
 921         if (frame->tf_rflags & PSL_T)
 922                 printf("trace trap, ");
 923         if (frame->tf_rflags & PSL_I)
 924                 printf("interrupt enabled, ");
 925         if (frame->tf_rflags & PSL_NT)
 926                 printf("nested task, ");
 927         if (frame->tf_rflags & PSL_RF)
 928                 printf("resume, ");
 929         printf("IOPL = %ld\n", (frame->tf_rflags & PSL_IOPL) >> 12);
 930         printf("current process         = %d (%s)\n",
 931             curproc->p_pid, curthread->td_name);
 932
 933 #ifdef KDB
 934         if (debugger_on_trap) {
 935                 kdb_why = KDB_WHY_TRAP;
 936                 handled = kdb_trap(type, 0, frame);
 937                 kdb_why = KDB_WHY_UNSET;
 938                 if (handled)
 939                         return;
 940         }
 941 #endif
 942         printf("trap number             = %d\n", type);
 943         panic("%s", type < nitems(trap_msg) ? trap_msg[type] :
 944             "unknown/reserved trap");
 945 }
 946
 947 #ifdef KDTRACE_HOOKS
 948 /*
 949  * Invoke a userspace DTrace hook.  The hook pointer is cleared when no
 950  * userspace probes are enabled, so we must synchronize with DTrace to ensure
 951  * that a trapping thread is able to call the hook before it is cleared.
 952  */
 953 static bool
 954 trap_user_dtrace(struct trapframe *frame, int (**hookp)(struct trapframe *))
 955 {
 956         int (*hook)(struct trapframe *);
 957
 958         hook = (int (*)(struct trapframe *))atomic_load_ptr(hookp);
 959         enable_intr();
 960         if (hook != NULL)
 961                 return ((hook)(frame) == 0);
 962         return (false);
 963 }
 964 #endif
 965
 966 /*
 967  * Double fault handler. Called when a fault occurs while writing
 968  * a frame for a trap/exception onto the stack. This usually occurs
 969  * when the stack overflows (such is the case with infinite recursion,
 970  * for example).
 971  */
 972 void
 973 dblfault_handler(struct trapframe *frame)
 974 {
 975 #ifdef KDTRACE_HOOKS
 976         if (dtrace_doubletrap_func != NULL)
 977                 (*dtrace_doubletrap_func)();
 978 #endif
 979         printf("\nFatal double fault\n"
 980             "rip %#lx rsp %#lx rbp %#lx\n"
 981             "rax %#lx rdx %#lx rbx %#lx\n"
 982             "rcx %#lx rsi %#lx rdi %#lx\n"
 983             "r8 %#lx r9 %#lx r10 %#lx\n"
 984             "r11 %#lx r12 %#lx r13 %#lx\n"
 985             "r14 %#lx r15 %#lx rflags %#lx\n"
 986             "cs %#lx ss %#lx ds %#hx es %#hx fs %#hx gs %#hx\n"
 987             "fsbase %#lx gsbase %#lx kgsbase %#lx\n",
 988             frame->tf_rip, frame->tf_rsp, frame->tf_rbp,
 989             frame->tf_rax, frame->tf_rdx, frame->tf_rbx,
 990             frame->tf_rcx, frame->tf_rdi, frame->tf_rsi,
 991             frame->tf_r8, frame->tf_r9, frame->tf_r10,
 992             frame->tf_r11, frame->tf_r12, frame->tf_r13,
 993             frame->tf_r14, frame->tf_r15, frame->tf_rflags,
 994             frame->tf_cs, frame->tf_ss, frame->tf_ds, frame->tf_es,
 995             frame->tf_fs, frame->tf_gs,
 996             rdmsr(MSR_FSBASE), rdmsr(MSR_GSBASE), rdmsr(MSR_KGSBASE));
 997 #ifdef SMP
 998         /* two separate prints in case of a trap on an unmapped page */
 999         printf("cpuid = %d; ", PCPU_GET(cpuid));
1000         printf("apic id = %02x\n", PCPU_GET(apic_id));
1001 #endif
1002         panic("double fault");
1003 }
1004
1005 static int __noinline
1006 cpu_fetch_syscall_args_fallback(struct thread *td, struct syscall_args *sa)
1007 {
1008         struct proc *p;
1009         struct trapframe *frame;
1010         register_t *argp;
1011         caddr_t params;
1012         int reg, regcnt, error;
1013
1014         p = td->td_proc;
1015         frame = td->td_frame;
1016         reg = 0;
1017         regcnt = NARGREGS;
1018
1019         sa->code = frame->tf_rax;
1020
1021         if (sa->code == SYS_syscall || sa->code == SYS___syscall) {
1022                 sa->code = frame->tf_rdi;
1023                 reg++;
1024                 regcnt--;
1025         }
1026
1027         if (sa->code >= p->p_sysent->sv_size)
1028                 sa->callp = &p->p_sysent->sv_table[0];
1029         else
1030                 sa->callp = &p->p_sysent->sv_table[sa->code];
1031
1032         sa->narg = sa->callp->sy_narg;
1033         KASSERT(sa->narg <= nitems(sa->args), ("Too many syscall arguments!"));
1034         argp = &frame->tf_rdi;
1035         argp += reg;
1036         memcpy(sa->args, argp, sizeof(sa->args[0]) * NARGREGS);
1037         if (sa->narg > regcnt) {
1038                 params = (caddr_t)frame->tf_rsp + sizeof(register_t);
1039                 error = copyin(params, &sa->args[regcnt],
1040                     (sa->narg - regcnt) * sizeof(sa->args[0]));
1041                 if (__predict_false(error != 0))
1042                         return (error);
1043         }
1044
1045         td->td_retval[0] = 0;
1046         td->td_retval[1] = frame->tf_rdx;
1047
1048         return (0);
1049 }
1050
1051 int
1052 cpu_fetch_syscall_args(struct thread *td)
1053 {
1054         struct proc *p;
1055         struct trapframe *frame;
1056         struct syscall_args *sa;
1057
1058         p = td->td_proc;
1059         frame = td->td_frame;
1060         sa = &td->td_sa;
1061
1062         sa->code = frame->tf_rax;
1063
1064         if (__predict_false(sa->code == SYS_syscall ||
1065             sa->code == SYS___syscall ||
1066             sa->code >= p->p_sysent->sv_size))
1067                 return (cpu_fetch_syscall_args_fallback(td, sa));
1068
1069         sa->callp = &p->p_sysent->sv_table[sa->code];
1070         sa->narg = sa->callp->sy_narg;
1071         KASSERT(sa->narg <= nitems(sa->args), ("Too many syscall arguments!"));
1072
1073         if (__predict_false(sa->narg > NARGREGS))
1074                 return (cpu_fetch_syscall_args_fallback(td, sa));
1075
1076         memcpy(sa->args, &frame->tf_rdi, sizeof(sa->args[0]) * NARGREGS);
1077
1078         td->td_retval[0] = 0;
1079         td->td_retval[1] = frame->tf_rdx;
1080
1081         return (0);
1082 }
1083
1084 #include "../../kern/subr_syscall.c"
1085
1086 static void (*syscall_ret_l1d_flush)(void);
1087 int syscall_ret_l1d_flush_mode;
1088
1089 static void
1090 flush_l1d_hw(void)
1091 {
1092
1093         wrmsr(MSR_IA32_FLUSH_CMD, IA32_FLUSH_CMD_L1D);
1094 }
1095
1096 static void __inline
1097 amd64_syscall_ret_flush_l1d_inline(int error)
1098 {
1099         void (*p)(void);
1100
1101         if (error != 0 && error != EEXIST && error != EAGAIN &&
1102             error != EXDEV && error != ENOENT && error != ENOTCONN &&
1103             error != EINPROGRESS) {
1104                 p = syscall_ret_l1d_flush;
1105                 if (p != NULL)
1106                         p();
1107         }
1108 }
1109
1110 void
1111 amd64_syscall_ret_flush_l1d(int error)
1112 {
1113
1114         amd64_syscall_ret_flush_l1d_inline(error);
1115 }
1116
1117 void
1118 amd64_syscall_ret_flush_l1d_recalc(void)
1119 {
1120         bool l1d_hw;
1121
1122         l1d_hw = (cpu_stdext_feature3 & CPUID_STDEXT3_L1D_FLUSH) != 0;
1123 again:
1124         switch (syscall_ret_l1d_flush_mode) {
1125         case 0:
1126                 syscall_ret_l1d_flush = NULL;
1127                 break;
1128         case 1:
1129                 syscall_ret_l1d_flush = l1d_hw ? flush_l1d_hw :
1130                     flush_l1d_sw_abi;
1131                 break;
1132         case 2:
1133                 syscall_ret_l1d_flush = l1d_hw ? flush_l1d_hw : NULL;
1134                 break;
1135         case 3:
1136                 syscall_ret_l1d_flush = flush_l1d_sw_abi;
1137                 break;
1138         default:
1139                 syscall_ret_l1d_flush_mode = 1;
1140                 goto again;
1141         }
1142 }
1143
1144 static int
1145 machdep_syscall_ret_flush_l1d(SYSCTL_HANDLER_ARGS)
1146 {
1147         int error, val;
1148
1149         val = syscall_ret_l1d_flush_mode;
1150         error = sysctl_handle_int(oidp, &val, 0, req);
1151         if (error != 0 || req->newptr == NULL)
1152                 return (error);
1153         syscall_ret_l1d_flush_mode = val;
1154         amd64_syscall_ret_flush_l1d_recalc();
1155         return (0);
1156 }
1157 SYSCTL_PROC(_machdep, OID_AUTO, syscall_ret_flush_l1d, CTLTYPE_INT |
1158     CTLFLAG_RWTUN | CTLFLAG_NOFETCH | CTLFLAG_MPSAFE, NULL, 0,
1159     machdep_syscall_ret_flush_l1d, "I",
1160     "Flush L1D on syscall return with error (0 - off, 1 - on, "
1161     "2 - use hw only, 3 - use sw only");
1162
1163
1164 /*
1165  * System call handler for native binaries.  The trap frame is already
1166  * set up by the assembler trampoline and a pointer to it is saved in
1167  * td_frame.
1168  */
1169 void
1170 amd64_syscall(struct thread *td, int traced)
1171 {
1172         int error;
1173         ksiginfo_t ksi;
1174
1175 #ifdef DIAGNOSTIC
1176         if (!TRAPF_USERMODE(td->td_frame)) {
1177                 panic("syscall");
1178                 /* NOT REACHED */
1179         }
1180 #endif
1181         error = syscallenter(td);
1182
1183         /*
1184          * Traced syscall.
1185          */
1186         if (__predict_false(traced)) {
1187                 td->td_frame->tf_rflags &= ~PSL_T;
1188                 ksiginfo_init_trap(&ksi);
1189                 ksi.ksi_signo = SIGTRAP;
1190                 ksi.ksi_code = TRAP_TRACE;
1191                 ksi.ksi_addr = (void *)td->td_frame->tf_rip;
1192                 trapsignal(td, &ksi);
1193         }
1194
1195         KASSERT(PCB_USER_FPU(td->td_pcb),
1196             ("System call %s returning with kernel FPU ctx leaked",
1197              syscallname(td->td_proc, td->td_sa.code)));
1198         KASSERT(td->td_pcb->pcb_save == get_pcb_user_save_td(td),
1199             ("System call %s returning with mangled pcb_save",
1200              syscallname(td->td_proc, td->td_sa.code)));
1201         KASSERT(pmap_not_in_di(),
1202             ("System call %s returning with leaked invl_gen %lu",
1203             syscallname(td->td_proc, td->td_sa.code),
1204             td->td_md.md_invl_gen.gen));
1205
1206         syscallret(td, error);
1207
1208         /*
1209          * If the user-supplied value of %rip is not a canonical
1210          * address, then some CPUs will trigger a ring 0 #GP during
1211          * the sysret instruction.  However, the fault handler would
1212          * execute in ring 0 with the user's %gs and %rsp which would
1213          * not be safe.  Instead, use the full return path which
1214          * catches the problem safely.
1215          */
1216         if (__predict_false(td->td_frame->tf_rip >= VM_MAXUSER_ADDRESS))
1217                 set_pcb_flags(td->td_pcb, PCB_FULL_IRET);
1218
1219         amd64_syscall_ret_flush_l1d_inline(error);
1220 }