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TOMOYO Linux Cross Reference
Linux/arch/x86/kernel/traps.c

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  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, tsk);
258         else
259                 force_sig_fault(signr, sicode, addr, tsk);
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)
317 {
318         static const char str[] = "double fault";
319         struct task_struct *tsk = current;
320 #ifdef CONFIG_VMAP_STACK
321         unsigned long cr2;
322 #endif
323 
324 #ifdef CONFIG_X86_ESPFIX64
325         extern unsigned char native_irq_return_iret[];
326 
327         /*
328          * If IRET takes a non-IST fault on the espfix64 stack, then we
329          * end up promoting it to a doublefault.  In that case, take
330          * advantage of the fact that we're not using the normal (TSS.sp0)
331          * stack right now.  We can write a fake #GP(0) frame at TSS.sp0
332          * and then modify our own IRET frame so that, when we return,
333          * we land directly at the #GP(0) vector with the stack already
334          * set up according to its expectations.
335          *
336          * The net result is that our #GP handler will think that we
337          * entered from usermode with the bad user context.
338          *
339          * No need for ist_enter here because we don't use RCU.
340          */
341         if (((long)regs->sp >> P4D_SHIFT) == ESPFIX_PGD_ENTRY &&
342                 regs->cs == __KERNEL_CS &&
343                 regs->ip == (unsigned long)native_irq_return_iret)
344         {
345                 struct pt_regs *gpregs = (struct pt_regs *)this_cpu_read(cpu_tss_rw.x86_tss.sp0) - 1;
346 
347                 /*
348                  * regs->sp points to the failing IRET frame on the
349                  * ESPFIX64 stack.  Copy it to the entry stack.  This fills
350                  * in gpregs->ss through gpregs->ip.
351                  *
352                  */
353                 memmove(&gpregs->ip, (void *)regs->sp, 5*8);
354                 gpregs->orig_ax = 0;  /* Missing (lost) #GP error code */
355 
356                 /*
357                  * Adjust our frame so that we return straight to the #GP
358                  * vector with the expected RSP value.  This is safe because
359                  * we won't enable interupts or schedule before we invoke
360                  * general_protection, so nothing will clobber the stack
361                  * frame we just set up.
362                  *
363                  * We will enter general_protection with kernel GSBASE,
364                  * which is what the stub expects, given that the faulting
365                  * RIP will be the IRET instruction.
366                  */
367                 regs->ip = (unsigned long)general_protection;
368                 regs->sp = (unsigned long)&gpregs->orig_ax;
369 
370                 return;
371         }
372 #endif
373 
374         ist_enter(regs);
375         notify_die(DIE_TRAP, str, regs, error_code, X86_TRAP_DF, SIGSEGV);
376 
377         tsk->thread.error_code = error_code;
378         tsk->thread.trap_nr = X86_TRAP_DF;
379 
380 #ifdef CONFIG_VMAP_STACK
381         /*
382          * If we overflow the stack into a guard page, the CPU will fail
383          * to deliver #PF and will send #DF instead.  Similarly, if we
384          * take any non-IST exception while too close to the bottom of
385          * the stack, the processor will get a page fault while
386          * delivering the exception and will generate a double fault.
387          *
388          * According to the SDM (footnote in 6.15 under "Interrupt 14 -
389          * Page-Fault Exception (#PF):
390          *
391          *   Processors update CR2 whenever a page fault is detected. If a
392          *   second page fault occurs while an earlier page fault is being
393          *   delivered, the faulting linear address of the second fault will
394          *   overwrite the contents of CR2 (replacing the previous
395          *   address). These updates to CR2 occur even if the page fault
396          *   results in a double fault or occurs during the delivery of a
397          *   double fault.
398          *
399          * The logic below has a small possibility of incorrectly diagnosing
400          * some errors as stack overflows.  For example, if the IDT or GDT
401          * gets corrupted such that #GP delivery fails due to a bad descriptor
402          * causing #GP and we hit this condition while CR2 coincidentally
403          * points to the stack guard page, we'll think we overflowed the
404          * stack.  Given that we're going to panic one way or another
405          * if this happens, this isn't necessarily worth fixing.
406          *
407          * If necessary, we could improve the test by only diagnosing
408          * a stack overflow if the saved RSP points within 47 bytes of
409          * the bottom of the stack: if RSP == tsk_stack + 48 and we
410          * take an exception, the stack is already aligned and there
411          * will be enough room SS, RSP, RFLAGS, CS, RIP, and a
412          * possible error code, so a stack overflow would *not* double
413          * fault.  With any less space left, exception delivery could
414          * fail, and, as a practical matter, we've overflowed the
415          * stack even if the actual trigger for the double fault was
416          * something else.
417          */
418         cr2 = read_cr2();
419         if ((unsigned long)task_stack_page(tsk) - 1 - cr2 < PAGE_SIZE)
420                 handle_stack_overflow("kernel stack overflow (double-fault)", regs, cr2);
421 #endif
422 
423 #ifdef CONFIG_DOUBLEFAULT
424         df_debug(regs, error_code);
425 #endif
426         /*
427          * This is always a kernel trap and never fixable (and thus must
428          * never return).
429          */
430         for (;;)
431                 die(str, regs, error_code);
432 }
433 #endif
434 
435 dotraplinkage void do_bounds(struct pt_regs *regs, long error_code)
436 {
437         const struct mpx_bndcsr *bndcsr;
438 
439         RCU_LOCKDEP_WARN(!rcu_is_watching(), "entry code didn't wake RCU");
440         if (notify_die(DIE_TRAP, "bounds", regs, error_code,
441                         X86_TRAP_BR, SIGSEGV) == NOTIFY_STOP)
442                 return;
443         cond_local_irq_enable(regs);
444 
445         if (!user_mode(regs))
446                 die("bounds", regs, error_code);
447 
448         if (!cpu_feature_enabled(X86_FEATURE_MPX)) {
449                 /* The exception is not from Intel MPX */
450                 goto exit_trap;
451         }
452 
453         /*
454          * We need to look at BNDSTATUS to resolve this exception.
455          * A NULL here might mean that it is in its 'init state',
456          * which is all zeros which indicates MPX was not
457          * responsible for the exception.
458          */
459         bndcsr = get_xsave_field_ptr(XFEATURE_MASK_BNDCSR);
460         if (!bndcsr)
461                 goto exit_trap;
462 
463         trace_bounds_exception_mpx(bndcsr);
464         /*
465          * The error code field of the BNDSTATUS register communicates status
466          * information of a bound range exception #BR or operation involving
467          * bound directory.
468          */
469         switch (bndcsr->bndstatus & MPX_BNDSTA_ERROR_CODE) {
470         case 2: /* Bound directory has invalid entry. */
471                 if (mpx_handle_bd_fault())
472                         goto exit_trap;
473                 break; /* Success, it was handled */
474         case 1: /* Bound violation. */
475         {
476                 struct task_struct *tsk = current;
477                 struct mpx_fault_info mpx;
478 
479                 if (mpx_fault_info(&mpx, regs)) {
480                         /*
481                          * We failed to decode the MPX instruction.  Act as if
482                          * the exception was not caused by MPX.
483                          */
484                         goto exit_trap;
485                 }
486                 /*
487                  * Success, we decoded the instruction and retrieved
488                  * an 'mpx' containing the address being accessed
489                  * which caused the exception.  This information
490                  * allows and application to possibly handle the
491                  * #BR exception itself.
492                  */
493                 if (!do_trap_no_signal(tsk, X86_TRAP_BR, "bounds", regs,
494                                        error_code))
495                         break;
496 
497                 show_signal(tsk, SIGSEGV, "trap ", "bounds", regs, error_code);
498 
499                 force_sig_bnderr(mpx.addr, mpx.lower, mpx.upper);
500                 break;
501         }
502         case 0: /* No exception caused by Intel MPX operations. */
503                 goto exit_trap;
504         default:
505                 die("bounds", regs, error_code);
506         }
507 
508         return;
509 
510 exit_trap:
511         /*
512          * This path out is for all the cases where we could not
513          * handle the exception in some way (like allocating a
514          * table or telling userspace about it.  We will also end
515          * up here if the kernel has MPX turned off at compile
516          * time..
517          */
518         do_trap(X86_TRAP_BR, SIGSEGV, "bounds", regs, error_code, 0, NULL);
519 }
520 
521 dotraplinkage void
522 do_general_protection(struct pt_regs *regs, long error_code)
523 {
524         const char *desc = "general protection fault";
525         struct task_struct *tsk;
526 
527         RCU_LOCKDEP_WARN(!rcu_is_watching(), "entry code didn't wake RCU");
528         cond_local_irq_enable(regs);
529 
530         if (static_cpu_has(X86_FEATURE_UMIP)) {
531                 if (user_mode(regs) && fixup_umip_exception(regs))
532                         return;
533         }
534 
535         if (v8086_mode(regs)) {
536                 local_irq_enable();
537                 handle_vm86_fault((struct kernel_vm86_regs *) regs, error_code);
538                 return;
539         }
540 
541         tsk = current;
542         if (!user_mode(regs)) {
543                 if (fixup_exception(regs, X86_TRAP_GP, error_code, 0))
544                         return;
545 
546                 tsk->thread.error_code = error_code;
547                 tsk->thread.trap_nr = X86_TRAP_GP;
548 
549                 /*
550                  * To be potentially processing a kprobe fault and to
551                  * trust the result from kprobe_running(), we have to
552                  * be non-preemptible.
553                  */
554                 if (!preemptible() && kprobe_running() &&
555                     kprobe_fault_handler(regs, X86_TRAP_GP))
556                         return;
557 
558                 if (notify_die(DIE_GPF, desc, regs, error_code,
559                                X86_TRAP_GP, SIGSEGV) != NOTIFY_STOP)
560                         die(desc, regs, error_code);
561                 return;
562         }
563 
564         tsk->thread.error_code = error_code;
565         tsk->thread.trap_nr = X86_TRAP_GP;
566 
567         show_signal(tsk, SIGSEGV, "", desc, regs, error_code);
568 
569         force_sig(SIGSEGV, tsk);
570 }
571 NOKPROBE_SYMBOL(do_general_protection);
572 
573 dotraplinkage void notrace do_int3(struct pt_regs *regs, long error_code)
574 {
575 #ifdef CONFIG_DYNAMIC_FTRACE
576         /*
577          * ftrace must be first, everything else may cause a recursive crash.
578          * See note by declaration of modifying_ftrace_code in ftrace.c
579          */
580         if (unlikely(atomic_read(&modifying_ftrace_code)) &&
581             ftrace_int3_handler(regs))
582                 return;
583 #endif
584         if (poke_int3_handler(regs))
585                 return;
586 
587         /*
588          * Use ist_enter despite the fact that we don't use an IST stack.
589          * We can be called from a kprobe in non-CONTEXT_KERNEL kernel
590          * mode or even during context tracking state changes.
591          *
592          * This means that we can't schedule.  That's okay.
593          */
594         ist_enter(regs);
595         RCU_LOCKDEP_WARN(!rcu_is_watching(), "entry code didn't wake RCU");
596 #ifdef CONFIG_KGDB_LOW_LEVEL_TRAP
597         if (kgdb_ll_trap(DIE_INT3, "int3", regs, error_code, X86_TRAP_BP,
598                                 SIGTRAP) == NOTIFY_STOP)
599                 goto exit;
600 #endif /* CONFIG_KGDB_LOW_LEVEL_TRAP */
601 
602 #ifdef CONFIG_KPROBES
603         if (kprobe_int3_handler(regs))
604                 goto exit;
605 #endif
606 
607         if (notify_die(DIE_INT3, "int3", regs, error_code, X86_TRAP_BP,
608                         SIGTRAP) == NOTIFY_STOP)
609                 goto exit;
610 
611         cond_local_irq_enable(regs);
612         do_trap(X86_TRAP_BP, SIGTRAP, "int3", regs, error_code, 0, NULL);
613         cond_local_irq_disable(regs);
614 
615 exit:
616         ist_exit(regs);
617 }
618 NOKPROBE_SYMBOL(do_int3);
619 
620 #ifdef CONFIG_X86_64
621 /*
622  * Help handler running on a per-cpu (IST or entry trampoline) stack
623  * to switch to the normal thread stack if the interrupted code was in
624  * user mode. The actual stack switch is done in entry_64.S
625  */
626 asmlinkage __visible notrace struct pt_regs *sync_regs(struct pt_regs *eregs)
627 {
628         struct pt_regs *regs = (struct pt_regs *)this_cpu_read(cpu_current_top_of_stack) - 1;
629         if (regs != eregs)
630                 *regs = *eregs;
631         return regs;
632 }
633 NOKPROBE_SYMBOL(sync_regs);
634 
635 struct bad_iret_stack {
636         void *error_entry_ret;
637         struct pt_regs regs;
638 };
639 
640 asmlinkage __visible notrace
641 struct bad_iret_stack *fixup_bad_iret(struct bad_iret_stack *s)
642 {
643         /*
644          * This is called from entry_64.S early in handling a fault
645          * caused by a bad iret to user mode.  To handle the fault
646          * correctly, we want to move our stack frame to where it would
647          * be had we entered directly on the entry stack (rather than
648          * just below the IRET frame) and we want to pretend that the
649          * exception came from the IRET target.
650          */
651         struct bad_iret_stack *new_stack =
652                 (struct bad_iret_stack *)this_cpu_read(cpu_tss_rw.x86_tss.sp0) - 1;
653 
654         /* Copy the IRET target to the new stack. */
655         memmove(&new_stack->regs.ip, (void *)s->regs.sp, 5*8);
656 
657         /* Copy the remainder of the stack from the current stack. */
658         memmove(new_stack, s, offsetof(struct bad_iret_stack, regs.ip));
659 
660         BUG_ON(!user_mode(&new_stack->regs));
661         return new_stack;
662 }
663 NOKPROBE_SYMBOL(fixup_bad_iret);
664 #endif
665 
666 static bool is_sysenter_singlestep(struct pt_regs *regs)
667 {
668         /*
669          * We don't try for precision here.  If we're anywhere in the region of
670          * code that can be single-stepped in the SYSENTER entry path, then
671          * assume that this is a useless single-step trap due to SYSENTER
672          * being invoked with TF set.  (We don't know in advance exactly
673          * which instructions will be hit because BTF could plausibly
674          * be set.)
675          */
676 #ifdef CONFIG_X86_32
677         return (regs->ip - (unsigned long)__begin_SYSENTER_singlestep_region) <
678                 (unsigned long)__end_SYSENTER_singlestep_region -
679                 (unsigned long)__begin_SYSENTER_singlestep_region;
680 #elif defined(CONFIG_IA32_EMULATION)
681         return (regs->ip - (unsigned long)entry_SYSENTER_compat) <
682                 (unsigned long)__end_entry_SYSENTER_compat -
683                 (unsigned long)entry_SYSENTER_compat;
684 #else
685         return false;
686 #endif
687 }
688 
689 /*
690  * Our handling of the processor debug registers is non-trivial.
691  * We do not clear them on entry and exit from the kernel. Therefore
692  * it is possible to get a watchpoint trap here from inside the kernel.
693  * However, the code in ./ptrace.c has ensured that the user can
694  * only set watchpoints on userspace addresses. Therefore the in-kernel
695  * watchpoint trap can only occur in code which is reading/writing
696  * from user space. Such code must not hold kernel locks (since it
697  * can equally take a page fault), therefore it is safe to call
698  * force_sig_info even though that claims and releases locks.
699  *
700  * Code in ./signal.c ensures that the debug control register
701  * is restored before we deliver any signal, and therefore that
702  * user code runs with the correct debug control register even though
703  * we clear it here.
704  *
705  * Being careful here means that we don't have to be as careful in a
706  * lot of more complicated places (task switching can be a bit lazy
707  * about restoring all the debug state, and ptrace doesn't have to
708  * find every occurrence of the TF bit that could be saved away even
709  * by user code)
710  *
711  * May run on IST stack.
712  */
713 dotraplinkage void do_debug(struct pt_regs *regs, long error_code)
714 {
715         struct task_struct *tsk = current;
716         int user_icebp = 0;
717         unsigned long dr6;
718         int si_code;
719 
720         ist_enter(regs);
721 
722         get_debugreg(dr6, 6);
723         /*
724          * The Intel SDM says:
725          *
726          *   Certain debug exceptions may clear bits 0-3. The remaining
727          *   contents of the DR6 register are never cleared by the
728          *   processor. To avoid confusion in identifying debug
729          *   exceptions, debug handlers should clear the register before
730          *   returning to the interrupted task.
731          *
732          * Keep it simple: clear DR6 immediately.
733          */
734         set_debugreg(0, 6);
735 
736         /* Filter out all the reserved bits which are preset to 1 */
737         dr6 &= ~DR6_RESERVED;
738 
739         /*
740          * The SDM says "The processor clears the BTF flag when it
741          * generates a debug exception."  Clear TIF_BLOCKSTEP to keep
742          * TIF_BLOCKSTEP in sync with the hardware BTF flag.
743          */
744         clear_tsk_thread_flag(tsk, TIF_BLOCKSTEP);
745 
746         if (unlikely(!user_mode(regs) && (dr6 & DR_STEP) &&
747                      is_sysenter_singlestep(regs))) {
748                 dr6 &= ~DR_STEP;
749                 if (!dr6)
750                         goto exit;
751                 /*
752                  * else we might have gotten a single-step trap and hit a
753                  * watchpoint at the same time, in which case we should fall
754                  * through and handle the watchpoint.
755                  */
756         }
757 
758         /*
759          * If dr6 has no reason to give us about the origin of this trap,
760          * then it's very likely the result of an icebp/int01 trap.
761          * User wants a sigtrap for that.
762          */
763         if (!dr6 && user_mode(regs))
764                 user_icebp = 1;
765 
766         /* Store the virtualized DR6 value */
767         tsk->thread.debugreg6 = dr6;
768 
769 #ifdef CONFIG_KPROBES
770         if (kprobe_debug_handler(regs))
771                 goto exit;
772 #endif
773 
774         if (notify_die(DIE_DEBUG, "debug", regs, (long)&dr6, error_code,
775                                                         SIGTRAP) == NOTIFY_STOP)
776                 goto exit;
777 
778         /*
779          * Let others (NMI) know that the debug stack is in use
780          * as we may switch to the interrupt stack.
781          */
782         debug_stack_usage_inc();
783 
784         /* It's safe to allow irq's after DR6 has been saved */
785         cond_local_irq_enable(regs);
786 
787         if (v8086_mode(regs)) {
788                 handle_vm86_trap((struct kernel_vm86_regs *) regs, error_code,
789                                         X86_TRAP_DB);
790                 cond_local_irq_disable(regs);
791                 debug_stack_usage_dec();
792                 goto exit;
793         }
794 
795         if (WARN_ON_ONCE((dr6 & DR_STEP) && !user_mode(regs))) {
796                 /*
797                  * Historical junk that used to handle SYSENTER single-stepping.
798                  * This should be unreachable now.  If we survive for a while
799                  * without anyone hitting this warning, we'll turn this into
800                  * an oops.
801                  */
802                 tsk->thread.debugreg6 &= ~DR_STEP;
803                 set_tsk_thread_flag(tsk, TIF_SINGLESTEP);
804                 regs->flags &= ~X86_EFLAGS_TF;
805         }
806         si_code = get_si_code(tsk->thread.debugreg6);
807         if (tsk->thread.debugreg6 & (DR_STEP | DR_TRAP_BITS) || user_icebp)
808                 send_sigtrap(tsk, regs, error_code, si_code);
809         cond_local_irq_disable(regs);
810         debug_stack_usage_dec();
811 
812 exit:
813         ist_exit(regs);
814 }
815 NOKPROBE_SYMBOL(do_debug);
816 
817 /*
818  * Note that we play around with the 'TS' bit in an attempt to get
819  * the correct behaviour even in the presence of the asynchronous
820  * IRQ13 behaviour
821  */
822 static void math_error(struct pt_regs *regs, int error_code, int trapnr)
823 {
824         struct task_struct *task = current;
825         struct fpu *fpu = &task->thread.fpu;
826         int si_code;
827         char *str = (trapnr == X86_TRAP_MF) ? "fpu exception" :
828                                                 "simd exception";
829 
830         cond_local_irq_enable(regs);
831 
832         if (!user_mode(regs)) {
833                 if (fixup_exception(regs, trapnr, error_code, 0))
834                         return;
835 
836                 task->thread.error_code = error_code;
837                 task->thread.trap_nr = trapnr;
838 
839                 if (notify_die(DIE_TRAP, str, regs, error_code,
840                                         trapnr, SIGFPE) != NOTIFY_STOP)
841                         die(str, regs, error_code);
842                 return;
843         }
844 
845         /*
846          * Save the info for the exception handler and clear the error.
847          */
848         fpu__save(fpu);
849 
850         task->thread.trap_nr    = trapnr;
851         task->thread.error_code = error_code;
852 
853         si_code = fpu__exception_code(fpu, trapnr);
854         /* Retry when we get spurious exceptions: */
855         if (!si_code)
856                 return;
857 
858         force_sig_fault(SIGFPE, si_code,
859                         (void __user *)uprobe_get_trap_addr(regs), task);
860 }
861 
862 dotraplinkage void do_coprocessor_error(struct pt_regs *regs, long error_code)
863 {
864         RCU_LOCKDEP_WARN(!rcu_is_watching(), "entry code didn't wake RCU");
865         math_error(regs, error_code, X86_TRAP_MF);
866 }
867 
868 dotraplinkage void
869 do_simd_coprocessor_error(struct pt_regs *regs, long error_code)
870 {
871         RCU_LOCKDEP_WARN(!rcu_is_watching(), "entry code didn't wake RCU");
872         math_error(regs, error_code, X86_TRAP_XF);
873 }
874 
875 dotraplinkage void
876 do_spurious_interrupt_bug(struct pt_regs *regs, long error_code)
877 {
878         cond_local_irq_enable(regs);
879 }
880 
881 dotraplinkage void
882 do_device_not_available(struct pt_regs *regs, long error_code)
883 {
884         unsigned long cr0 = read_cr0();
885 
886         RCU_LOCKDEP_WARN(!rcu_is_watching(), "entry code didn't wake RCU");
887 
888 #ifdef CONFIG_MATH_EMULATION
889         if (!boot_cpu_has(X86_FEATURE_FPU) && (cr0 & X86_CR0_EM)) {
890                 struct math_emu_info info = { };
891 
892                 cond_local_irq_enable(regs);
893 
894                 info.regs = regs;
895                 math_emulate(&info);
896                 return;
897         }
898 #endif
899 
900         /* This should not happen. */
901         if (WARN(cr0 & X86_CR0_TS, "CR0.TS was set")) {
902                 /* Try to fix it up and carry on. */
903                 write_cr0(cr0 & ~X86_CR0_TS);
904         } else {
905                 /*
906                  * Something terrible happened, and we're better off trying
907                  * to kill the task than getting stuck in a never-ending
908                  * loop of #NM faults.
909                  */
910                 die("unexpected #NM exception", regs, error_code);
911         }
912 }
913 NOKPROBE_SYMBOL(do_device_not_available);
914 
915 #ifdef CONFIG_X86_32
916 dotraplinkage void do_iret_error(struct pt_regs *regs, long error_code)
917 {
918         RCU_LOCKDEP_WARN(!rcu_is_watching(), "entry code didn't wake RCU");
919         local_irq_enable();
920 
921         if (notify_die(DIE_TRAP, "iret exception", regs, error_code,
922                         X86_TRAP_IRET, SIGILL) != NOTIFY_STOP) {
923                 do_trap(X86_TRAP_IRET, SIGILL, "iret exception", regs, error_code,
924                         ILL_BADSTK, (void __user *)NULL);
925         }
926 }
927 #endif
928 
929 void __init trap_init(void)
930 {
931         /* Init cpu_entry_area before IST entries are set up */
932         setup_cpu_entry_areas();
933 
934         idt_setup_traps();
935 
936         /*
937          * Set the IDT descriptor to a fixed read-only location, so that the
938          * "sidt" instruction will not leak the location of the kernel, and
939          * to defend the IDT against arbitrary memory write vulnerabilities.
940          * It will be reloaded in cpu_init() */
941         cea_set_pte(CPU_ENTRY_AREA_RO_IDT_VADDR, __pa_symbol(idt_table),
942                     PAGE_KERNEL_RO);
943         idt_descr.address = CPU_ENTRY_AREA_RO_IDT;
944 
945         /*
946          * Should be a barrier for any external CPU state:
947          */
948         cpu_init();
949 
950         idt_setup_ist_traps();
951 
952         x86_init.irqs.trap_init();
953 
954         idt_setup_debugidt_traps();
955 }
956 

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