root/arch/x86/kernel/traps.c

DEFINITIONS

1. cond_local_irq_enable
2. cond_local_irq_disable
3. ist_enter
4. ist_exit
5. ist_begin_non_atomic
6. ist_end_non_atomic
7. is_valid_bugaddr
8. fixup_bug
9. do_trap_no_signal
10. show_signal
11. do_trap
12. do_error_trap
13. DO_ERROR
14. do_double_fault
15. do_bounds
16. do_general_protection
17. do_int3
18. sync_regs
19. fixup_bad_iret
20. is_sysenter_singlestep
21. do_debug
22. math_error
23. do_coprocessor_error
24. do_simd_coprocessor_error
25. do_spurious_interrupt_bug
26. do_device_not_available
27. do_iret_error
28. trap_init

   1 /*
   2  *  Copyright (C) 1991, 1992  Linus Torvalds
   3  *  Copyright (C) 2000, 2001, 2002 Andi Kleen, SuSE Labs
   4  *
   5  *  Pentium III FXSR, SSE support
   6  *      Gareth Hughes <gareth@valinux.com>, May 2000
   7  */
   8 
   9 /*
  10  * Handle hardware traps and faults.
  11  */
  12 
  13 #define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
  14 
  15 #include <linux/context_tracking.h>
  16 #include <linux/interrupt.h>
  17 #include <linux/kallsyms.h>
  18 #include <linux/spinlock.h>
  19 #include <linux/kprobes.h>
  20 #include <linux/uaccess.h>
  21 #include <linux/kdebug.h>
  22 #include <linux/kgdb.h>
  23 #include <linux/kernel.h>
  24 #include <linux/export.h>
  25 #include <linux/ptrace.h>
  26 #include <linux/uprobes.h>
  27 #include <linux/string.h>
  28 #include <linux/delay.h>
  29 #include <linux/errno.h>
  30 #include <linux/kexec.h>
  31 #include <linux/sched.h>
  32 #include <linux/sched/task_stack.h>
  33 #include <linux/timer.h>
  34 #include <linux/init.h>
  35 #include <linux/bug.h>
  36 #include <linux/nmi.h>
  37 #include <linux/mm.h>
  38 #include <linux/smp.h>
  39 #include <linux/io.h>
  40 
  41 #if defined(CONFIG_EDAC)
  42 #include <linux/edac.h>
  43 #endif
  44 
  45 #include <asm/stacktrace.h>
  46 #include <asm/processor.h>
  47 #include <asm/debugreg.h>
  48 #include <linux/atomic.h>
  49 #include <asm/text-patching.h>
  50 #include <asm/ftrace.h>
  51 #include <asm/traps.h>
  52 #include <asm/desc.h>
  53 #include <asm/fpu/internal.h>
  54 #include <asm/cpu_entry_area.h>
  55 #include <asm/mce.h>
  56 #include <asm/fixmap.h>
  57 #include <asm/mach_traps.h>
  58 #include <asm/alternative.h>
  59 #include <asm/fpu/xstate.h>
  60 #include <asm/trace/mpx.h>
  61 #include <asm/mpx.h>
  62 #include <asm/vm86.h>
  63 #include <asm/umip.h>
  64 
  65 #ifdef CONFIG_X86_64
  66 #include <asm/x86_init.h>
  67 #include <asm/pgalloc.h>
  68 #include <asm/proto.h>
  69 #else
  70 #include <asm/processor-flags.h>
  71 #include <asm/setup.h>
  72 #include <asm/proto.h>
  73 #endif
  74 
  75 DECLARE_BITMAP(system_vectors, NR_VECTORS);
  76 
  77 static inline void cond_local_irq_enable(struct pt_regs *regs)
  78 {
  79         if (regs->flags & X86_EFLAGS_IF)
  80                 local_irq_enable();
  81 }
  82 
  83 static inline void cond_local_irq_disable(struct pt_regs *regs)
  84 {
  85         if (regs->flags & X86_EFLAGS_IF)
  86                 local_irq_disable();
  87 }
  88 
  89 /*
  90  * In IST context, we explicitly disable preemption.  This serves two
  91  * purposes: it makes it much less likely that we would accidentally
  92  * schedule in IST context and it will force a warning if we somehow
  93  * manage to schedule by accident.
  94  */
  95 void ist_enter(struct pt_regs *regs)
  96 {
  97         if (user_mode(regs)) {
  98                 RCU_LOCKDEP_WARN(!rcu_is_watching(), "entry code didn't wake RCU");
  99         } else {
 100                 /*
 101                  * We might have interrupted pretty much anything.  In
 102                  * fact, if we're a machine check, we can even interrupt
 103                  * NMI processing.  We don't want in_nmi() to return true,
 104                  * but we need to notify RCU.
 105                  */
 106                 rcu_nmi_enter();
 107         }
 108 
 109         preempt_disable();
 110 
 111         /* This code is a bit fragile.  Test it. */
 112         RCU_LOCKDEP_WARN(!rcu_is_watching(), "ist_enter didn't work");
 113 }
 114 NOKPROBE_SYMBOL(ist_enter);
 115 
 116 void ist_exit(struct pt_regs *regs)
 117 {
 118         preempt_enable_no_resched();
 119 
 120         if (!user_mode(regs))
 121                 rcu_nmi_exit();
 122 }
 123 
 124 /**
 125  * ist_begin_non_atomic() - begin a non-atomic section in an IST exception
 126  * @regs:       regs passed to the IST exception handler
 127  *
 128  * IST exception handlers normally cannot schedule.  As a special
 129  * exception, if the exception interrupted userspace code (i.e.
 130  * user_mode(regs) would return true) and the exception was not
 131  * a double fault, it can be safe to schedule.  ist_begin_non_atomic()
 132  * begins a non-atomic section within an ist_enter()/ist_exit() region.
 133  * Callers are responsible for enabling interrupts themselves inside
 134  * the non-atomic section, and callers must call ist_end_non_atomic()
 135  * before ist_exit().
 136  */
 137 void ist_begin_non_atomic(struct pt_regs *regs)
 138 {
 139         BUG_ON(!user_mode(regs));
 140 
 141         /*
 142          * Sanity check: we need to be on the normal thread stack.  This
 143          * will catch asm bugs and any attempt to use ist_preempt_enable
 144          * from double_fault.
 145          */
 146         BUG_ON(!on_thread_stack());
 147 
 148         preempt_enable_no_resched();
 149 }
 150 
 151 /**
 152  * ist_end_non_atomic() - begin a non-atomic section in an IST exception
 153  *
 154  * Ends a non-atomic section started with ist_begin_non_atomic().
 155  */
 156 void ist_end_non_atomic(void)
 157 {
 158         preempt_disable();
 159 }
 160 
 161 int is_valid_bugaddr(unsigned long addr)
 162 {
 163         unsigned short ud;
 164 
 165         if (addr < TASK_SIZE_MAX)
 166                 return 0;
 167 
 168         if (probe_kernel_address((unsigned short *)addr, ud))
 169                 return 0;
 170 
 171         return ud == INSN_UD0 || ud == INSN_UD2;
 172 }
 173 
 174 int fixup_bug(struct pt_regs *regs, int trapnr)
 175 {
 176         if (trapnr != X86_TRAP_UD)
 177                 return 0;
 178 
 179         switch (report_bug(regs->ip, regs)) {
 180         case BUG_TRAP_TYPE_NONE:
 181         case BUG_TRAP_TYPE_BUG:
 182                 break;
 183 
 184         case BUG_TRAP_TYPE_WARN:
 185                 regs->ip += LEN_UD2;
 186                 return 1;
 187         }
 188 
 189         return 0;
 190 }
 191 
 192 static nokprobe_inline int
 193 do_trap_no_signal(struct task_struct *tsk, int trapnr, const char *str,
 194                   struct pt_regs *regs, long error_code)
 195 {
 196         if (v8086_mode(regs)) {
 197                 /*
 198                  * Traps 0, 1, 3, 4, and 5 should be forwarded to vm86.
 199                  * On nmi (interrupt 2), do_trap should not be called.
 200                  */
 201                 if (trapnr < X86_TRAP_UD) {
 202                         if (!handle_vm86_trap((struct kernel_vm86_regs *) regs,
 203                                                 error_code, trapnr))
 204                                 return 0;
 205                 }
 206         } else if (!user_mode(regs)) {
 207                 if (fixup_exception(regs, trapnr, error_code, 0))
 208                         return 0;
 209 
 210                 tsk->thread.error_code = error_code;
 211                 tsk->thread.trap_nr = trapnr;
 212                 die(str, regs, error_code);
 213         }
 214 
 215         /*
 216          * We want error_code and trap_nr set for userspace faults and
 217          * kernelspace faults which result in die(), but not
 218          * kernelspace faults which are fixed up.  die() gives the
 219          * process no chance to handle the signal and notice the
 220          * kernel fault information, so that won't result in polluting
 221          * the information about previously queued, but not yet
 222          * delivered, faults.  See also do_general_protection below.
 223          */
 224         tsk->thread.error_code = error_code;
 225         tsk->thread.trap_nr = trapnr;
 226 
 227         return -1;
 228 }
 229 
 230 static void show_signal(struct task_struct *tsk, int signr,
 231                         const char *type, const char *desc,
 232                         struct pt_regs *regs, long error_code)
 233 {
 234         if (show_unhandled_signals && unhandled_signal(tsk, signr) &&
 235             printk_ratelimit()) {
 236                 pr_info("%s[%d] %s%s ip:%lx sp:%lx error:%lx",
 237                         tsk->comm, task_pid_nr(tsk), type, desc,
 238                         regs->ip, regs->sp, error_code);
 239                 print_vma_addr(KERN_CONT " in ", regs->ip);
 240                 pr_cont("\n");
 241         }
 242 }
 243 
 244 static void
 245 do_trap(int trapnr, int signr, char *str, struct pt_regs *regs,
 246         long error_code, int sicode, void __user *addr)
 247 {
 248         struct task_struct *tsk = current;
 249 
 250 
 251         if (!do_trap_no_signal(tsk, trapnr, str, regs, error_code))
 252                 return;
 253 
 254         show_signal(tsk, signr, "trap ", str, regs, error_code);
 255 
 256         if (!sicode)
 257                 force_sig(signr);
 258         else
 259                 force_sig_fault(signr, sicode, addr);
 260 }
 261 NOKPROBE_SYMBOL(do_trap);
 262 
 263 static void do_error_trap(struct pt_regs *regs, long error_code, char *str,
 264         unsigned long trapnr, int signr, int sicode, void __user *addr)
 265 {
 266         RCU_LOCKDEP_WARN(!rcu_is_watching(), "entry code didn't wake RCU");
 267 
 268         /*
 269          * WARN*()s end up here; fix them up before we call the
 270          * notifier chain.
 271          */
 272         if (!user_mode(regs) && fixup_bug(regs, trapnr))
 273                 return;
 274 
 275         if (notify_die(DIE_TRAP, str, regs, error_code, trapnr, signr) !=
 276                         NOTIFY_STOP) {
 277                 cond_local_irq_enable(regs);
 278                 do_trap(trapnr, signr, str, regs, error_code, sicode, addr);
 279         }
 280 }
 281 
 282 #define IP ((void __user *)uprobe_get_trap_addr(regs))
 283 #define DO_ERROR(trapnr, signr, sicode, addr, str, name)                   \
 284 dotraplinkage void do_##name(struct pt_regs *regs, long error_code)        \
 285 {                                                                          \
 286         do_error_trap(regs, error_code, str, trapnr, signr, sicode, addr); \
 287 }
 288 
 289 DO_ERROR(X86_TRAP_DE,     SIGFPE,  FPE_INTDIV,   IP, "divide error",        divide_error)
 290 DO_ERROR(X86_TRAP_OF,     SIGSEGV,          0, NULL, "overflow",            overflow)
 291 DO_ERROR(X86_TRAP_UD,     SIGILL,  ILL_ILLOPN,   IP, "invalid opcode",      invalid_op)
 292 DO_ERROR(X86_TRAP_OLD_MF, SIGFPE,           0, NULL, "coprocessor segment overrun", coprocessor_segment_overrun)
 293 DO_ERROR(X86_TRAP_TS,     SIGSEGV,          0, NULL, "invalid TSS",         invalid_TSS)
 294 DO_ERROR(X86_TRAP_NP,     SIGBUS,           0, NULL, "segment not present", segment_not_present)
 295 DO_ERROR(X86_TRAP_SS,     SIGBUS,           0, NULL, "stack segment",       stack_segment)
 296 DO_ERROR(X86_TRAP_AC,     SIGBUS,  BUS_ADRALN, NULL, "alignment check",     alignment_check)
 297 #undef IP
 298 
 299 #ifdef CONFIG_VMAP_STACK
 300 __visible void __noreturn handle_stack_overflow(const char *message,
 301                                                 struct pt_regs *regs,
 302                                                 unsigned long fault_address)
 303 {
 304         printk(KERN_EMERG "BUG: stack guard page was hit at %p (stack is %p..%p)\n",
 305                  (void *)fault_address, current->stack,
 306                  (char *)current->stack + THREAD_SIZE - 1);
 307         die(message, regs, 0);
 308 
 309         /* Be absolutely certain we don't return. */
 310         panic("%s", message);
 311 }
 312 #endif
 313 
 314 #ifdef CONFIG_X86_64
 315 /* Runs on IST stack */
 316 dotraplinkage void do_double_fault(struct pt_regs *regs, long error_code, unsigned long cr2)
 317 {
 318         static const char str[] = "double fault";
 319         struct task_struct *tsk = current;
 320 
 321 #ifdef CONFIG_X86_ESPFIX64
 322         extern unsigned char native_irq_return_iret[];
 323 
 324         /*
 325          * If IRET takes a non-IST fault on the espfix64 stack, then we
 326          * end up promoting it to a doublefault.  In that case, take
 327          * advantage of the fact that we're not using the normal (TSS.sp0)
 328          * stack right now.  We can write a fake #GP(0) frame at TSS.sp0
 329          * and then modify our own IRET frame so that, when we return,
 330          * we land directly at the #GP(0) vector with the stack already
 331          * set up according to its expectations.
 332          *
 333          * The net result is that our #GP handler will think that we
 334          * entered from usermode with the bad user context.
 335          *
 336          * No need for ist_enter here because we don't use RCU.
 337          */
 338         if (((long)regs->sp >> P4D_SHIFT) == ESPFIX_PGD_ENTRY &&
 339                 regs->cs == __KERNEL_CS &&
 340                 regs->ip == (unsigned long)native_irq_return_iret)
 341         {
 342                 struct pt_regs *gpregs = (struct pt_regs *)this_cpu_read(cpu_tss_rw.x86_tss.sp0) - 1;
 343 
 344                 /*
 345                  * regs->sp points to the failing IRET frame on the
 346                  * ESPFIX64 stack.  Copy it to the entry stack.  This fills
 347                  * in gpregs->ss through gpregs->ip.
 348                  *
 349                  */
 350                 memmove(&gpregs->ip, (void *)regs->sp, 5*8);
 351                 gpregs->orig_ax = 0;  /* Missing (lost) #GP error code */
 352 
 353                 /*
 354                  * Adjust our frame so that we return straight to the #GP
 355                  * vector with the expected RSP value.  This is safe because
 356                  * we won't enable interupts or schedule before we invoke
 357                  * general_protection, so nothing will clobber the stack
 358                  * frame we just set up.
 359                  *
 360                  * We will enter general_protection with kernel GSBASE,
 361                  * which is what the stub expects, given that the faulting
 362                  * RIP will be the IRET instruction.
 363                  */
 364                 regs->ip = (unsigned long)general_protection;
 365                 regs->sp = (unsigned long)&gpregs->orig_ax;
 366 
 367                 return;
 368         }
 369 #endif
 370 
 371         ist_enter(regs);
 372         notify_die(DIE_TRAP, str, regs, error_code, X86_TRAP_DF, SIGSEGV);
 373 
 374         tsk->thread.error_code = error_code;
 375         tsk->thread.trap_nr = X86_TRAP_DF;
 376 
 377 #ifdef CONFIG_VMAP_STACK
 378         /*
 379          * If we overflow the stack into a guard page, the CPU will fail
 380          * to deliver #PF and will send #DF instead.  Similarly, if we
 381          * take any non-IST exception while too close to the bottom of
 382          * the stack, the processor will get a page fault while
 383          * delivering the exception and will generate a double fault.
 384          *
 385          * According to the SDM (footnote in 6.15 under "Interrupt 14 -
 386          * Page-Fault Exception (#PF):
 387          *
 388          *   Processors update CR2 whenever a page fault is detected. If a
 389          *   second page fault occurs while an earlier page fault is being
 390          *   delivered, the faulting linear address of the second fault will
 391          *   overwrite the contents of CR2 (replacing the previous
 392          *   address). These updates to CR2 occur even if the page fault
 393          *   results in a double fault or occurs during the delivery of a
 394          *   double fault.
 395          *
 396          * The logic below has a small possibility of incorrectly diagnosing
 397          * some errors as stack overflows.  For example, if the IDT or GDT
 398          * gets corrupted such that #GP delivery fails due to a bad descriptor
 399          * causing #GP and we hit this condition while CR2 coincidentally
 400          * points to the stack guard page, we'll think we overflowed the
 401          * stack.  Given that we're going to panic one way or another
 402          * if this happens, this isn't necessarily worth fixing.
 403          *
 404          * If necessary, we could improve the test by only diagnosing
 405          * a stack overflow if the saved RSP points within 47 bytes of
 406          * the bottom of the stack: if RSP == tsk_stack + 48 and we
 407          * take an exception, the stack is already aligned and there
 408          * will be enough room SS, RSP, RFLAGS, CS, RIP, and a
 409          * possible error code, so a stack overflow would *not* double
 410          * fault.  With any less space left, exception delivery could
 411          * fail, and, as a practical matter, we've overflowed the
 412          * stack even if the actual trigger for the double fault was
 413          * something else.
 414          */
 415         if ((unsigned long)task_stack_page(tsk) - 1 - cr2 < PAGE_SIZE)
 416                 handle_stack_overflow("kernel stack overflow (double-fault)", regs, cr2);
 417 #endif
 418 
 419 #ifdef CONFIG_DOUBLEFAULT
 420         df_debug(regs, error_code);
 421 #endif
 422         /*
 423          * This is always a kernel trap and never fixable (and thus must
 424          * never return).
 425          */
 426         for (;;)
 427                 die(str, regs, error_code);
 428 }
 429 #endif
 430 
 431 dotraplinkage void do_bounds(struct pt_regs *regs, long error_code)
 432 {
 433         const struct mpx_bndcsr *bndcsr;
 434 
 435         RCU_LOCKDEP_WARN(!rcu_is_watching(), "entry code didn't wake RCU");
 436         if (notify_die(DIE_TRAP, "bounds", regs, error_code,
 437                         X86_TRAP_BR, SIGSEGV) == NOTIFY_STOP)
 438                 return;
 439         cond_local_irq_enable(regs);
 440 
 441         if (!user_mode(regs))
 442                 die("bounds", regs, error_code);
 443 
 444         if (!cpu_feature_enabled(X86_FEATURE_MPX)) {
 445                 /* The exception is not from Intel MPX */
 446                 goto exit_trap;
 447         }
 448 
 449         /*
 450          * We need to look at BNDSTATUS to resolve this exception.
 451          * A NULL here might mean that it is in its 'init state',
 452          * which is all zeros which indicates MPX was not
 453          * responsible for the exception.
 454          */
 455         bndcsr = get_xsave_field_ptr(XFEATURE_BNDCSR);
 456         if (!bndcsr)
 457                 goto exit_trap;
 458 
 459         trace_bounds_exception_mpx(bndcsr);
 460         /*
 461          * The error code field of the BNDSTATUS register communicates status
 462          * information of a bound range exception #BR or operation involving
 463          * bound directory.
 464          */
 465         switch (bndcsr->bndstatus & MPX_BNDSTA_ERROR_CODE) {
 466         case 2: /* Bound directory has invalid entry. */
 467                 if (mpx_handle_bd_fault())
 468                         goto exit_trap;
 469                 break; /* Success, it was handled */
 470         case 1: /* Bound violation. */
 471         {
 472                 struct task_struct *tsk = current;
 473                 struct mpx_fault_info mpx;
 474 
 475                 if (mpx_fault_info(&mpx, regs)) {
 476                         /*
 477                          * We failed to decode the MPX instruction.  Act as if
 478                          * the exception was not caused by MPX.
 479                          */
 480                         goto exit_trap;
 481                 }
 482                 /*
 483                  * Success, we decoded the instruction and retrieved
 484                  * an 'mpx' containing the address being accessed
 485                  * which caused the exception.  This information
 486                  * allows and application to possibly handle the
 487                  * #BR exception itself.
 488                  */
 489                 if (!do_trap_no_signal(tsk, X86_TRAP_BR, "bounds", regs,
 490                                        error_code))
 491                         break;
 492 
 493                 show_signal(tsk, SIGSEGV, "trap ", "bounds", regs, error_code);
 494 
 495                 force_sig_bnderr(mpx.addr, mpx.lower, mpx.upper);
 496                 break;
 497         }
 498         case 0: /* No exception caused by Intel MPX operations. */
 499                 goto exit_trap;
 500         default:
 501                 die("bounds", regs, error_code);
 502         }
 503 
 504         return;
 505 
 506 exit_trap:
 507         /*
 508          * This path out is for all the cases where we could not
 509          * handle the exception in some way (like allocating a
 510          * table or telling userspace about it.  We will also end
 511          * up here if the kernel has MPX turned off at compile
 512          * time..
 513          */
 514         do_trap(X86_TRAP_BR, SIGSEGV, "bounds", regs, error_code, 0, NULL);
 515 }
 516 
 517 dotraplinkage void
 518 do_general_protection(struct pt_regs *regs, long error_code)
 519 {
 520         const char *desc = "general protection fault";
 521         struct task_struct *tsk;
 522 
 523         RCU_LOCKDEP_WARN(!rcu_is_watching(), "entry code didn't wake RCU");
 524         cond_local_irq_enable(regs);
 525 
 526         if (static_cpu_has(X86_FEATURE_UMIP)) {
 527                 if (user_mode(regs) && fixup_umip_exception(regs))
 528                         return;
 529         }
 530 
 531         if (v8086_mode(regs)) {
 532                 local_irq_enable();
 533                 handle_vm86_fault((struct kernel_vm86_regs *) regs, error_code);
 534                 return;
 535         }
 536 
 537         tsk = current;
 538         if (!user_mode(regs)) {
 539                 if (fixup_exception(regs, X86_TRAP_GP, error_code, 0))
 540                         return;
 541 
 542                 tsk->thread.error_code = error_code;
 543                 tsk->thread.trap_nr = X86_TRAP_GP;
 544 
 545                 /*
 546                  * To be potentially processing a kprobe fault and to
 547                  * trust the result from kprobe_running(), we have to
 548                  * be non-preemptible.
 549                  */
 550                 if (!preemptible() && kprobe_running() &&
 551                     kprobe_fault_handler(regs, X86_TRAP_GP))
 552                         return;
 553 
 554                 if (notify_die(DIE_GPF, desc, regs, error_code,
 555                                X86_TRAP_GP, SIGSEGV) != NOTIFY_STOP)
 556                         die(desc, regs, error_code);
 557                 return;
 558         }
 559 
 560         tsk->thread.error_code = error_code;
 561         tsk->thread.trap_nr = X86_TRAP_GP;
 562 
 563         show_signal(tsk, SIGSEGV, "", desc, regs, error_code);
 564 
 565         force_sig(SIGSEGV);
 566 }
 567 NOKPROBE_SYMBOL(do_general_protection);
 568 
 569 dotraplinkage void notrace do_int3(struct pt_regs *regs, long error_code)
 570 {
 571 #ifdef CONFIG_DYNAMIC_FTRACE
 572         /*
 573          * ftrace must be first, everything else may cause a recursive crash.
 574          * See note by declaration of modifying_ftrace_code in ftrace.c
 575          */
 576         if (unlikely(atomic_read(&modifying_ftrace_code)) &&
 577             ftrace_int3_handler(regs))
 578                 return;
 579 #endif
 580         if (poke_int3_handler(regs))
 581                 return;
 582 
 583         /*
 584          * Use ist_enter despite the fact that we don't use an IST stack.
 585          * We can be called from a kprobe in non-CONTEXT_KERNEL kernel
 586          * mode or even during context tracking state changes.
 587          *
 588          * This means that we can't schedule.  That's okay.
 589          */
 590         ist_enter(regs);
 591         RCU_LOCKDEP_WARN(!rcu_is_watching(), "entry code didn't wake RCU");
 592 #ifdef CONFIG_KGDB_LOW_LEVEL_TRAP
 593         if (kgdb_ll_trap(DIE_INT3, "int3", regs, error_code, X86_TRAP_BP,
 594                                 SIGTRAP) == NOTIFY_STOP)
 595                 goto exit;
 596 #endif /* CONFIG_KGDB_LOW_LEVEL_TRAP */
 597 
 598 #ifdef CONFIG_KPROBES
 599         if (kprobe_int3_handler(regs))
 600                 goto exit;
 601 #endif
 602 
 603         if (notify_die(DIE_INT3, "int3", regs, error_code, X86_TRAP_BP,
 604                         SIGTRAP) == NOTIFY_STOP)
 605                 goto exit;
 606 
 607         cond_local_irq_enable(regs);
 608         do_trap(X86_TRAP_BP, SIGTRAP, "int3", regs, error_code, 0, NULL);
 609         cond_local_irq_disable(regs);
 610 
 611 exit:
 612         ist_exit(regs);
 613 }
 614 NOKPROBE_SYMBOL(do_int3);
 615 
 616 #ifdef CONFIG_X86_64
 617 /*
 618  * Help handler running on a per-cpu (IST or entry trampoline) stack
 619  * to switch to the normal thread stack if the interrupted code was in
 620  * user mode. The actual stack switch is done in entry_64.S
 621  */
 622 asmlinkage __visible notrace struct pt_regs *sync_regs(struct pt_regs *eregs)
 623 {
 624         struct pt_regs *regs = (struct pt_regs *)this_cpu_read(cpu_current_top_of_stack) - 1;
 625         if (regs != eregs)
 626                 *regs = *eregs;
 627         return regs;
 628 }
 629 NOKPROBE_SYMBOL(sync_regs);
 630 
 631 struct bad_iret_stack {
 632         void *error_entry_ret;
 633         struct pt_regs regs;
 634 };
 635 
 636 asmlinkage __visible notrace
 637 struct bad_iret_stack *fixup_bad_iret(struct bad_iret_stack *s)
 638 {
 639         /*
 640          * This is called from entry_64.S early in handling a fault
 641          * caused by a bad iret to user mode.  To handle the fault
 642          * correctly, we want to move our stack frame to where it would
 643          * be had we entered directly on the entry stack (rather than
 644          * just below the IRET frame) and we want to pretend that the
 645          * exception came from the IRET target.
 646          */
 647         struct bad_iret_stack *new_stack =
 648                 (struct bad_iret_stack *)this_cpu_read(cpu_tss_rw.x86_tss.sp0) - 1;
 649 
 650         /* Copy the IRET target to the new stack. */
 651         memmove(&new_stack->regs.ip, (void *)s->regs.sp, 5*8);
 652 
 653         /* Copy the remainder of the stack from the current stack. */
 654         memmove(new_stack, s, offsetof(struct bad_iret_stack, regs.ip));
 655 
 656         BUG_ON(!user_mode(&new_stack->regs));
 657         return new_stack;
 658 }
 659 NOKPROBE_SYMBOL(fixup_bad_iret);
 660 #endif
 661 
 662 static bool is_sysenter_singlestep(struct pt_regs *regs)
 663 {
 664         /*
 665          * We don't try for precision here.  If we're anywhere in the region of
 666          * code that can be single-stepped in the SYSENTER entry path, then
 667          * assume that this is a useless single-step trap due to SYSENTER
 668          * being invoked with TF set.  (We don't know in advance exactly
 669          * which instructions will be hit because BTF could plausibly
 670          * be set.)
 671          */
 672 #ifdef CONFIG_X86_32
 673         return (regs->ip - (unsigned long)__begin_SYSENTER_singlestep_region) <
 674                 (unsigned long)__end_SYSENTER_singlestep_region -
 675                 (unsigned long)__begin_SYSENTER_singlestep_region;
 676 #elif defined(CONFIG_IA32_EMULATION)
 677         return (regs->ip - (unsigned long)entry_SYSENTER_compat) <
 678                 (unsigned long)__end_entry_SYSENTER_compat -
 679                 (unsigned long)entry_SYSENTER_compat;
 680 #else
 681         return false;
 682 #endif
 683 }
 684 
 685 /*
 686  * Our handling of the processor debug registers is non-trivial.
 687  * We do not clear them on entry and exit from the kernel. Therefore
 688  * it is possible to get a watchpoint trap here from inside the kernel.
 689  * However, the code in ./ptrace.c has ensured that the user can
 690  * only set watchpoints on userspace addresses. Therefore the in-kernel
 691  * watchpoint trap can only occur in code which is reading/writing
 692  * from user space. Such code must not hold kernel locks (since it
 693  * can equally take a page fault), therefore it is safe to call
 694  * force_sig_info even though that claims and releases locks.
 695  *
 696  * Code in ./signal.c ensures that the debug control register
 697  * is restored before we deliver any signal, and therefore that
 698  * user code runs with the correct debug control register even though
 699  * we clear it here.
 700  *
 701  * Being careful here means that we don't have to be as careful in a
 702  * lot of more complicated places (task switching can be a bit lazy
 703  * about restoring all the debug state, and ptrace doesn't have to
 704  * find every occurrence of the TF bit that could be saved away even
 705  * by user code)
 706  *
 707  * May run on IST stack.
 708  */
 709 dotraplinkage void do_debug(struct pt_regs *regs, long error_code)
 710 {
 711         struct task_struct *tsk = current;
 712         int user_icebp = 0;
 713         unsigned long dr6;
 714         int si_code;
 715 
 716         ist_enter(regs);
 717 
 718         get_debugreg(dr6, 6);
 719         /*
 720          * The Intel SDM says:
 721          *
 722          *   Certain debug exceptions may clear bits 0-3. The remaining
 723          *   contents of the DR6 register are never cleared by the
 724          *   processor. To avoid confusion in identifying debug
 725          *   exceptions, debug handlers should clear the register before
 726          *   returning to the interrupted task.
 727          *
 728          * Keep it simple: clear DR6 immediately.
 729          */
 730         set_debugreg(0, 6);
 731 
 732         /* Filter out all the reserved bits which are preset to 1 */
 733         dr6 &= ~DR6_RESERVED;
 734 
 735         /*
 736          * The SDM says "The processor clears the BTF flag when it
 737          * generates a debug exception."  Clear TIF_BLOCKSTEP to keep
 738          * TIF_BLOCKSTEP in sync with the hardware BTF flag.
 739          */
 740         clear_tsk_thread_flag(tsk, TIF_BLOCKSTEP);
 741 
 742         if (unlikely(!user_mode(regs) && (dr6 & DR_STEP) &&
 743                      is_sysenter_singlestep(regs))) {
 744                 dr6 &= ~DR_STEP;
 745                 if (!dr6)
 746                         goto exit;
 747                 /*
 748                  * else we might have gotten a single-step trap and hit a
 749                  * watchpoint at the same time, in which case we should fall
 750                  * through and handle the watchpoint.
 751                  */
 752         }
 753 
 754         /*
 755          * If dr6 has no reason to give us about the origin of this trap,
 756          * then it's very likely the result of an icebp/int01 trap.
 757          * User wants a sigtrap for that.
 758          */
 759         if (!dr6 && user_mode(regs))
 760                 user_icebp = 1;
 761 
 762         /* Store the virtualized DR6 value */
 763         tsk->thread.debugreg6 = dr6;
 764 
 765 #ifdef CONFIG_KPROBES
 766         if (kprobe_debug_handler(regs))
 767                 goto exit;
 768 #endif
 769 
 770         if (notify_die(DIE_DEBUG, "debug", regs, (long)&dr6, error_code,
 771                                                         SIGTRAP) == NOTIFY_STOP)
 772                 goto exit;
 773 
 774         /*
 775          * Let others (NMI) know that the debug stack is in use
 776          * as we may switch to the interrupt stack.
 777          */
 778         debug_stack_usage_inc();
 779 
 780         /* It's safe to allow irq's after DR6 has been saved */
 781         cond_local_irq_enable(regs);
 782 
 783         if (v8086_mode(regs)) {
 784                 handle_vm86_trap((struct kernel_vm86_regs *) regs, error_code,
 785                                         X86_TRAP_DB);
 786                 cond_local_irq_disable(regs);
 787                 debug_stack_usage_dec();
 788                 goto exit;
 789         }
 790 
 791         if (WARN_ON_ONCE((dr6 & DR_STEP) && !user_mode(regs))) {
 792                 /*
 793                  * Historical junk that used to handle SYSENTER single-stepping.
 794                  * This should be unreachable now.  If we survive for a while
 795                  * without anyone hitting this warning, we'll turn this into
 796                  * an oops.
 797                  */
 798                 tsk->thread.debugreg6 &= ~DR_STEP;
 799                 set_tsk_thread_flag(tsk, TIF_SINGLESTEP);
 800                 regs->flags &= ~X86_EFLAGS_TF;
 801         }
 802         si_code = get_si_code(tsk->thread.debugreg6);
 803         if (tsk->thread.debugreg6 & (DR_STEP | DR_TRAP_BITS) || user_icebp)
 804                 send_sigtrap(regs, error_code, si_code);
 805         cond_local_irq_disable(regs);
 806         debug_stack_usage_dec();
 807 
 808 exit:
 809         ist_exit(regs);
 810 }
 811 NOKPROBE_SYMBOL(do_debug);
 812 
 813 /*
 814  * Note that we play around with the 'TS' bit in an attempt to get
 815  * the correct behaviour even in the presence of the asynchronous
 816  * IRQ13 behaviour
 817  */
 818 static void math_error(struct pt_regs *regs, int error_code, int trapnr)
 819 {
 820         struct task_struct *task = current;
 821         struct fpu *fpu = &task->thread.fpu;
 822         int si_code;
 823         char *str = (trapnr == X86_TRAP_MF) ? "fpu exception" :
 824                                                 "simd exception";
 825 
 826         cond_local_irq_enable(regs);
 827 
 828         if (!user_mode(regs)) {
 829                 if (fixup_exception(regs, trapnr, error_code, 0))
 830                         return;
 831 
 832                 task->thread.error_code = error_code;
 833                 task->thread.trap_nr = trapnr;
 834 
 835                 if (notify_die(DIE_TRAP, str, regs, error_code,
 836                                         trapnr, SIGFPE) != NOTIFY_STOP)
 837                         die(str, regs, error_code);
 838                 return;
 839         }
 840 
 841         /*
 842          * Save the info for the exception handler and clear the error.
 843          */
 844         fpu__save(fpu);
 845 
 846         task->thread.trap_nr    = trapnr;
 847         task->thread.error_code = error_code;
 848 
 849         si_code = fpu__exception_code(fpu, trapnr);
 850         /* Retry when we get spurious exceptions: */
 851         if (!si_code)
 852                 return;
 853 
 854         force_sig_fault(SIGFPE, si_code,
 855                         (void __user *)uprobe_get_trap_addr(regs));
 856 }
 857 
 858 dotraplinkage void do_coprocessor_error(struct pt_regs *regs, long error_code)
 859 {
 860         RCU_LOCKDEP_WARN(!rcu_is_watching(), "entry code didn't wake RCU");
 861         math_error(regs, error_code, X86_TRAP_MF);
 862 }
 863 
 864 dotraplinkage void
 865 do_simd_coprocessor_error(struct pt_regs *regs, long error_code)
 866 {
 867         RCU_LOCKDEP_WARN(!rcu_is_watching(), "entry code didn't wake RCU");
 868         math_error(regs, error_code, X86_TRAP_XF);
 869 }
 870 
 871 dotraplinkage void
 872 do_spurious_interrupt_bug(struct pt_regs *regs, long error_code)
 873 {
 874         cond_local_irq_enable(regs);
 875 }
 876 
 877 dotraplinkage void
 878 do_device_not_available(struct pt_regs *regs, long error_code)
 879 {
 880         unsigned long cr0 = read_cr0();
 881 
 882         RCU_LOCKDEP_WARN(!rcu_is_watching(), "entry code didn't wake RCU");
 883 
 884 #ifdef CONFIG_MATH_EMULATION
 885         if (!boot_cpu_has(X86_FEATURE_FPU) && (cr0 & X86_CR0_EM)) {
 886                 struct math_emu_info info = { };
 887 
 888                 cond_local_irq_enable(regs);
 889 
 890                 info.regs = regs;
 891                 math_emulate(&info);
 892                 return;
 893         }
 894 #endif
 895 
 896         /* This should not happen. */
 897         if (WARN(cr0 & X86_CR0_TS, "CR0.TS was set")) {
 898                 /* Try to fix it up and carry on. */
 899                 write_cr0(cr0 & ~X86_CR0_TS);
 900         } else {
 901                 /*
 902                  * Something terrible happened, and we're better off trying
 903                  * to kill the task than getting stuck in a never-ending
 904                  * loop of #NM faults.
 905                  */
 906                 die("unexpected #NM exception", regs, error_code);
 907         }
 908 }
 909 NOKPROBE_SYMBOL(do_device_not_available);
 910 
 911 #ifdef CONFIG_X86_32
 912 dotraplinkage void do_iret_error(struct pt_regs *regs, long error_code)
 913 {
 914         RCU_LOCKDEP_WARN(!rcu_is_watching(), "entry code didn't wake RCU");
 915         local_irq_enable();
 916 
 917         if (notify_die(DIE_TRAP, "iret exception", regs, error_code,
 918                         X86_TRAP_IRET, SIGILL) != NOTIFY_STOP) {
 919                 do_trap(X86_TRAP_IRET, SIGILL, "iret exception", regs, error_code,
 920                         ILL_BADSTK, (void __user *)NULL);
 921         }
 922 }
 923 #endif
 924 
 925 void __init trap_init(void)
 926 {
 927         /* Init cpu_entry_area before IST entries are set up */
 928         setup_cpu_entry_areas();
 929 
 930         idt_setup_traps();
 931 
 932         /*
 933          * Set the IDT descriptor to a fixed read-only location, so that the
 934          * "sidt" instruction will not leak the location of the kernel, and
 935          * to defend the IDT against arbitrary memory write vulnerabilities.
 936          * It will be reloaded in cpu_init() */
 937         cea_set_pte(CPU_ENTRY_AREA_RO_IDT_VADDR, __pa_symbol(idt_table),
 938                     PAGE_KERNEL_RO);
 939         idt_descr.address = CPU_ENTRY_AREA_RO_IDT;
 940 
 941         /*
 942          * Should be a barrier for any external CPU state:
 943          */
 944         cpu_init();
 945 
 946         idt_setup_ist_traps();
 947 
 948         x86_init.irqs.trap_init();
 949 
 950         idt_setup_debugidt_traps();
 951 }