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Linux/arch/x86/mm/fault.c

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  1 /*
  2  *  Copyright (C) 1995  Linus Torvalds
  3  *  Copyright (C) 2001, 2002 Andi Kleen, SuSE Labs.
  4  *  Copyright (C) 2008-2009, Red Hat Inc., Ingo Molnar
  5  */
  6 #include <linux/magic.h>                /* STACK_END_MAGIC              */
  7 #include <linux/sched.h>                /* test_thread_flag(), ...      */
  8 #include <linux/kdebug.h>               /* oops_begin/end, ...          */
  9 #include <linux/module.h>               /* search_exception_table       */
 10 #include <linux/bootmem.h>              /* max_low_pfn                  */
 11 #include <linux/kprobes.h>              /* __kprobes, ...               */
 12 #include <linux/mmiotrace.h>            /* kmmio_handler, ...           */
 13 #include <linux/perf_event.h>           /* perf_sw_event                */
 14 #include <linux/hugetlb.h>              /* hstate_index_to_shift        */
 15 #include <linux/prefetch.h>             /* prefetchw                    */
 16 #include <linux/context_tracking.h>     /* exception_enter(), ...       */
 17 
 18 #include <asm/traps.h>                  /* dotraplinkage, ...           */
 19 #include <asm/pgalloc.h>                /* pgd_*(), ...                 */
 20 #include <asm/kmemcheck.h>              /* kmemcheck_*(), ...           */
 21 #include <asm/fixmap.h>                 /* VSYSCALL_START               */
 22 
 23 #define CREATE_TRACE_POINTS
 24 #include <asm/trace/exceptions.h>
 25 
 26 /*
 27  * Page fault error code bits:
 28  *
 29  *   bit 0 ==    0: no page found       1: protection fault
 30  *   bit 1 ==    0: read access         1: write access
 31  *   bit 2 ==    0: kernel-mode access  1: user-mode access
 32  *   bit 3 ==                           1: use of reserved bit detected
 33  *   bit 4 ==                           1: fault was an instruction fetch
 34  */
 35 enum x86_pf_error_code {
 36 
 37         PF_PROT         =               1 << 0,
 38         PF_WRITE        =               1 << 1,
 39         PF_USER         =               1 << 2,
 40         PF_RSVD         =               1 << 3,
 41         PF_INSTR        =               1 << 4,
 42 };
 43 
 44 /*
 45  * Returns 0 if mmiotrace is disabled, or if the fault is not
 46  * handled by mmiotrace:
 47  */
 48 static inline int __kprobes
 49 kmmio_fault(struct pt_regs *regs, unsigned long addr)
 50 {
 51         if (unlikely(is_kmmio_active()))
 52                 if (kmmio_handler(regs, addr) == 1)
 53                         return -1;
 54         return 0;
 55 }
 56 
 57 static inline int __kprobes kprobes_fault(struct pt_regs *regs)
 58 {
 59         int ret = 0;
 60 
 61         /* kprobe_running() needs smp_processor_id() */
 62         if (kprobes_built_in() && !user_mode_vm(regs)) {
 63                 preempt_disable();
 64                 if (kprobe_running() && kprobe_fault_handler(regs, 14))
 65                         ret = 1;
 66                 preempt_enable();
 67         }
 68 
 69         return ret;
 70 }
 71 
 72 /*
 73  * Prefetch quirks:
 74  *
 75  * 32-bit mode:
 76  *
 77  *   Sometimes AMD Athlon/Opteron CPUs report invalid exceptions on prefetch.
 78  *   Check that here and ignore it.
 79  *
 80  * 64-bit mode:
 81  *
 82  *   Sometimes the CPU reports invalid exceptions on prefetch.
 83  *   Check that here and ignore it.
 84  *
 85  * Opcode checker based on code by Richard Brunner.
 86  */
 87 static inline int
 88 check_prefetch_opcode(struct pt_regs *regs, unsigned char *instr,
 89                       unsigned char opcode, int *prefetch)
 90 {
 91         unsigned char instr_hi = opcode & 0xf0;
 92         unsigned char instr_lo = opcode & 0x0f;
 93 
 94         switch (instr_hi) {
 95         case 0x20:
 96         case 0x30:
 97                 /*
 98                  * Values 0x26,0x2E,0x36,0x3E are valid x86 prefixes.
 99                  * In X86_64 long mode, the CPU will signal invalid
100                  * opcode if some of these prefixes are present so
101                  * X86_64 will never get here anyway
102                  */
103                 return ((instr_lo & 7) == 0x6);
104 #ifdef CONFIG_X86_64
105         case 0x40:
106                 /*
107                  * In AMD64 long mode 0x40..0x4F are valid REX prefixes
108                  * Need to figure out under what instruction mode the
109                  * instruction was issued. Could check the LDT for lm,
110                  * but for now it's good enough to assume that long
111                  * mode only uses well known segments or kernel.
112                  */
113                 return (!user_mode(regs) || user_64bit_mode(regs));
114 #endif
115         case 0x60:
116                 /* 0x64 thru 0x67 are valid prefixes in all modes. */
117                 return (instr_lo & 0xC) == 0x4;
118         case 0xF0:
119                 /* 0xF0, 0xF2, 0xF3 are valid prefixes in all modes. */
120                 return !instr_lo || (instr_lo>>1) == 1;
121         case 0x00:
122                 /* Prefetch instruction is 0x0F0D or 0x0F18 */
123                 if (probe_kernel_address(instr, opcode))
124                         return 0;
125 
126                 *prefetch = (instr_lo == 0xF) &&
127                         (opcode == 0x0D || opcode == 0x18);
128                 return 0;
129         default:
130                 return 0;
131         }
132 }
133 
134 static int
135 is_prefetch(struct pt_regs *regs, unsigned long error_code, unsigned long addr)
136 {
137         unsigned char *max_instr;
138         unsigned char *instr;
139         int prefetch = 0;
140 
141         /*
142          * If it was a exec (instruction fetch) fault on NX page, then
143          * do not ignore the fault:
144          */
145         if (error_code & PF_INSTR)
146                 return 0;
147 
148         instr = (void *)convert_ip_to_linear(current, regs);
149         max_instr = instr + 15;
150 
151         if (user_mode(regs) && instr >= (unsigned char *)TASK_SIZE)
152                 return 0;
153 
154         while (instr < max_instr) {
155                 unsigned char opcode;
156 
157                 if (probe_kernel_address(instr, opcode))
158                         break;
159 
160                 instr++;
161 
162                 if (!check_prefetch_opcode(regs, instr, opcode, &prefetch))
163                         break;
164         }
165         return prefetch;
166 }
167 
168 static void
169 force_sig_info_fault(int si_signo, int si_code, unsigned long address,
170                      struct task_struct *tsk, int fault)
171 {
172         unsigned lsb = 0;
173         siginfo_t info;
174 
175         info.si_signo   = si_signo;
176         info.si_errno   = 0;
177         info.si_code    = si_code;
178         info.si_addr    = (void __user *)address;
179         if (fault & VM_FAULT_HWPOISON_LARGE)
180                 lsb = hstate_index_to_shift(VM_FAULT_GET_HINDEX(fault)); 
181         if (fault & VM_FAULT_HWPOISON)
182                 lsb = PAGE_SHIFT;
183         info.si_addr_lsb = lsb;
184 
185         force_sig_info(si_signo, &info, tsk);
186 }
187 
188 DEFINE_SPINLOCK(pgd_lock);
189 LIST_HEAD(pgd_list);
190 
191 #ifdef CONFIG_X86_32
192 static inline pmd_t *vmalloc_sync_one(pgd_t *pgd, unsigned long address)
193 {
194         unsigned index = pgd_index(address);
195         pgd_t *pgd_k;
196         pud_t *pud, *pud_k;
197         pmd_t *pmd, *pmd_k;
198 
199         pgd += index;
200         pgd_k = init_mm.pgd + index;
201 
202         if (!pgd_present(*pgd_k))
203                 return NULL;
204 
205         /*
206          * set_pgd(pgd, *pgd_k); here would be useless on PAE
207          * and redundant with the set_pmd() on non-PAE. As would
208          * set_pud.
209          */
210         pud = pud_offset(pgd, address);
211         pud_k = pud_offset(pgd_k, address);
212         if (!pud_present(*pud_k))
213                 return NULL;
214 
215         pmd = pmd_offset(pud, address);
216         pmd_k = pmd_offset(pud_k, address);
217         if (!pmd_present(*pmd_k))
218                 return NULL;
219 
220         if (!pmd_present(*pmd))
221                 set_pmd(pmd, *pmd_k);
222         else
223                 BUG_ON(pmd_page(*pmd) != pmd_page(*pmd_k));
224 
225         return pmd_k;
226 }
227 
228 void vmalloc_sync_all(void)
229 {
230         unsigned long address;
231 
232         if (SHARED_KERNEL_PMD)
233                 return;
234 
235         for (address = VMALLOC_START & PMD_MASK;
236              address >= TASK_SIZE && address < FIXADDR_TOP;
237              address += PMD_SIZE) {
238                 struct page *page;
239 
240                 spin_lock(&pgd_lock);
241                 list_for_each_entry(page, &pgd_list, lru) {
242                         spinlock_t *pgt_lock;
243                         pmd_t *ret;
244 
245                         /* the pgt_lock only for Xen */
246                         pgt_lock = &pgd_page_get_mm(page)->page_table_lock;
247 
248                         spin_lock(pgt_lock);
249                         ret = vmalloc_sync_one(page_address(page), address);
250                         spin_unlock(pgt_lock);
251 
252                         if (!ret)
253                                 break;
254                 }
255                 spin_unlock(&pgd_lock);
256         }
257 }
258 
259 /*
260  * 32-bit:
261  *
262  *   Handle a fault on the vmalloc or module mapping area
263  */
264 static noinline __kprobes int vmalloc_fault(unsigned long address)
265 {
266         unsigned long pgd_paddr;
267         pmd_t *pmd_k;
268         pte_t *pte_k;
269 
270         /* Make sure we are in vmalloc area: */
271         if (!(address >= VMALLOC_START && address < VMALLOC_END))
272                 return -1;
273 
274         WARN_ON_ONCE(in_nmi());
275 
276         /*
277          * Synchronize this task's top level page-table
278          * with the 'reference' page table.
279          *
280          * Do _not_ use "current" here. We might be inside
281          * an interrupt in the middle of a task switch..
282          */
283         pgd_paddr = read_cr3();
284         pmd_k = vmalloc_sync_one(__va(pgd_paddr), address);
285         if (!pmd_k)
286                 return -1;
287 
288         pte_k = pte_offset_kernel(pmd_k, address);
289         if (!pte_present(*pte_k))
290                 return -1;
291 
292         return 0;
293 }
294 
295 /*
296  * Did it hit the DOS screen memory VA from vm86 mode?
297  */
298 static inline void
299 check_v8086_mode(struct pt_regs *regs, unsigned long address,
300                  struct task_struct *tsk)
301 {
302         unsigned long bit;
303 
304         if (!v8086_mode(regs))
305                 return;
306 
307         bit = (address - 0xA0000) >> PAGE_SHIFT;
308         if (bit < 32)
309                 tsk->thread.screen_bitmap |= 1 << bit;
310 }
311 
312 static bool low_pfn(unsigned long pfn)
313 {
314         return pfn < max_low_pfn;
315 }
316 
317 static void dump_pagetable(unsigned long address)
318 {
319         pgd_t *base = __va(read_cr3());
320         pgd_t *pgd = &base[pgd_index(address)];
321         pmd_t *pmd;
322         pte_t *pte;
323 
324 #ifdef CONFIG_X86_PAE
325         printk("*pdpt = %016Lx ", pgd_val(*pgd));
326         if (!low_pfn(pgd_val(*pgd) >> PAGE_SHIFT) || !pgd_present(*pgd))
327                 goto out;
328 #endif
329         pmd = pmd_offset(pud_offset(pgd, address), address);
330         printk(KERN_CONT "*pde = %0*Lx ", sizeof(*pmd) * 2, (u64)pmd_val(*pmd));
331 
332         /*
333          * We must not directly access the pte in the highpte
334          * case if the page table is located in highmem.
335          * And let's rather not kmap-atomic the pte, just in case
336          * it's allocated already:
337          */
338         if (!low_pfn(pmd_pfn(*pmd)) || !pmd_present(*pmd) || pmd_large(*pmd))
339                 goto out;
340 
341         pte = pte_offset_kernel(pmd, address);
342         printk("*pte = %0*Lx ", sizeof(*pte) * 2, (u64)pte_val(*pte));
343 out:
344         printk("\n");
345 }
346 
347 #else /* CONFIG_X86_64: */
348 
349 void vmalloc_sync_all(void)
350 {
351         sync_global_pgds(VMALLOC_START & PGDIR_MASK, VMALLOC_END);
352 }
353 
354 /*
355  * 64-bit:
356  *
357  *   Handle a fault on the vmalloc area
358  *
359  * This assumes no large pages in there.
360  */
361 static noinline __kprobes int vmalloc_fault(unsigned long address)
362 {
363         pgd_t *pgd, *pgd_ref;
364         pud_t *pud, *pud_ref;
365         pmd_t *pmd, *pmd_ref;
366         pte_t *pte, *pte_ref;
367 
368         /* Make sure we are in vmalloc area: */
369         if (!(address >= VMALLOC_START && address < VMALLOC_END))
370                 return -1;
371 
372         WARN_ON_ONCE(in_nmi());
373 
374         /*
375          * Copy kernel mappings over when needed. This can also
376          * happen within a race in page table update. In the later
377          * case just flush:
378          */
379         pgd = pgd_offset(current->active_mm, address);
380         pgd_ref = pgd_offset_k(address);
381         if (pgd_none(*pgd_ref))
382                 return -1;
383 
384         if (pgd_none(*pgd)) {
385                 set_pgd(pgd, *pgd_ref);
386                 arch_flush_lazy_mmu_mode();
387         } else {
388                 BUG_ON(pgd_page_vaddr(*pgd) != pgd_page_vaddr(*pgd_ref));
389         }
390 
391         /*
392          * Below here mismatches are bugs because these lower tables
393          * are shared:
394          */
395 
396         pud = pud_offset(pgd, address);
397         pud_ref = pud_offset(pgd_ref, address);
398         if (pud_none(*pud_ref))
399                 return -1;
400 
401         if (pud_none(*pud) || pud_page_vaddr(*pud) != pud_page_vaddr(*pud_ref))
402                 BUG();
403 
404         pmd = pmd_offset(pud, address);
405         pmd_ref = pmd_offset(pud_ref, address);
406         if (pmd_none(*pmd_ref))
407                 return -1;
408 
409         if (pmd_none(*pmd) || pmd_page(*pmd) != pmd_page(*pmd_ref))
410                 BUG();
411 
412         pte_ref = pte_offset_kernel(pmd_ref, address);
413         if (!pte_present(*pte_ref))
414                 return -1;
415 
416         pte = pte_offset_kernel(pmd, address);
417 
418         /*
419          * Don't use pte_page here, because the mappings can point
420          * outside mem_map, and the NUMA hash lookup cannot handle
421          * that:
422          */
423         if (!pte_present(*pte) || pte_pfn(*pte) != pte_pfn(*pte_ref))
424                 BUG();
425 
426         return 0;
427 }
428 
429 #ifdef CONFIG_CPU_SUP_AMD
430 static const char errata93_warning[] =
431 KERN_ERR 
432 "******* Your BIOS seems to not contain a fix for K8 errata #93\n"
433 "******* Working around it, but it may cause SEGVs or burn power.\n"
434 "******* Please consider a BIOS update.\n"
435 "******* Disabling USB legacy in the BIOS may also help.\n";
436 #endif
437 
438 /*
439  * No vm86 mode in 64-bit mode:
440  */
441 static inline void
442 check_v8086_mode(struct pt_regs *regs, unsigned long address,
443                  struct task_struct *tsk)
444 {
445 }
446 
447 static int bad_address(void *p)
448 {
449         unsigned long dummy;
450 
451         return probe_kernel_address((unsigned long *)p, dummy);
452 }
453 
454 static void dump_pagetable(unsigned long address)
455 {
456         pgd_t *base = __va(read_cr3() & PHYSICAL_PAGE_MASK);
457         pgd_t *pgd = base + pgd_index(address);
458         pud_t *pud;
459         pmd_t *pmd;
460         pte_t *pte;
461 
462         if (bad_address(pgd))
463                 goto bad;
464 
465         printk("PGD %lx ", pgd_val(*pgd));
466 
467         if (!pgd_present(*pgd))
468                 goto out;
469 
470         pud = pud_offset(pgd, address);
471         if (bad_address(pud))
472                 goto bad;
473 
474         printk("PUD %lx ", pud_val(*pud));
475         if (!pud_present(*pud) || pud_large(*pud))
476                 goto out;
477 
478         pmd = pmd_offset(pud, address);
479         if (bad_address(pmd))
480                 goto bad;
481 
482         printk("PMD %lx ", pmd_val(*pmd));
483         if (!pmd_present(*pmd) || pmd_large(*pmd))
484                 goto out;
485 
486         pte = pte_offset_kernel(pmd, address);
487         if (bad_address(pte))
488                 goto bad;
489 
490         printk("PTE %lx", pte_val(*pte));
491 out:
492         printk("\n");
493         return;
494 bad:
495         printk("BAD\n");
496 }
497 
498 #endif /* CONFIG_X86_64 */
499 
500 /*
501  * Workaround for K8 erratum #93 & buggy BIOS.
502  *
503  * BIOS SMM functions are required to use a specific workaround
504  * to avoid corruption of the 64bit RIP register on C stepping K8.
505  *
506  * A lot of BIOS that didn't get tested properly miss this.
507  *
508  * The OS sees this as a page fault with the upper 32bits of RIP cleared.
509  * Try to work around it here.
510  *
511  * Note we only handle faults in kernel here.
512  * Does nothing on 32-bit.
513  */
514 static int is_errata93(struct pt_regs *regs, unsigned long address)
515 {
516 #if defined(CONFIG_X86_64) && defined(CONFIG_CPU_SUP_AMD)
517         if (boot_cpu_data.x86_vendor != X86_VENDOR_AMD
518             || boot_cpu_data.x86 != 0xf)
519                 return 0;
520 
521         if (address != regs->ip)
522                 return 0;
523 
524         if ((address >> 32) != 0)
525                 return 0;
526 
527         address |= 0xffffffffUL << 32;
528         if ((address >= (u64)_stext && address <= (u64)_etext) ||
529             (address >= MODULES_VADDR && address <= MODULES_END)) {
530                 printk_once(errata93_warning);
531                 regs->ip = address;
532                 return 1;
533         }
534 #endif
535         return 0;
536 }
537 
538 /*
539  * Work around K8 erratum #100 K8 in compat mode occasionally jumps
540  * to illegal addresses >4GB.
541  *
542  * We catch this in the page fault handler because these addresses
543  * are not reachable. Just detect this case and return.  Any code
544  * segment in LDT is compatibility mode.
545  */
546 static int is_errata100(struct pt_regs *regs, unsigned long address)
547 {
548 #ifdef CONFIG_X86_64
549         if ((regs->cs == __USER32_CS || (regs->cs & (1<<2))) && (address >> 32))
550                 return 1;
551 #endif
552         return 0;
553 }
554 
555 static int is_f00f_bug(struct pt_regs *regs, unsigned long address)
556 {
557 #ifdef CONFIG_X86_F00F_BUG
558         unsigned long nr;
559 
560         /*
561          * Pentium F0 0F C7 C8 bug workaround:
562          */
563         if (boot_cpu_has_bug(X86_BUG_F00F)) {
564                 nr = (address - idt_descr.address) >> 3;
565 
566                 if (nr == 6) {
567                         do_invalid_op(regs, 0);
568                         return 1;
569                 }
570         }
571 #endif
572         return 0;
573 }
574 
575 static const char nx_warning[] = KERN_CRIT
576 "kernel tried to execute NX-protected page - exploit attempt? (uid: %d)\n";
577 
578 static void
579 show_fault_oops(struct pt_regs *regs, unsigned long error_code,
580                 unsigned long address)
581 {
582         if (!oops_may_print())
583                 return;
584 
585         if (error_code & PF_INSTR) {
586                 unsigned int level;
587                 pgd_t *pgd;
588                 pte_t *pte;
589 
590                 pgd = __va(read_cr3() & PHYSICAL_PAGE_MASK);
591                 pgd += pgd_index(address);
592 
593                 pte = lookup_address_in_pgd(pgd, address, &level);
594 
595                 if (pte && pte_present(*pte) && !pte_exec(*pte))
596                         printk(nx_warning, from_kuid(&init_user_ns, current_uid()));
597         }
598 
599         printk(KERN_ALERT "BUG: unable to handle kernel ");
600         if (address < PAGE_SIZE)
601                 printk(KERN_CONT "NULL pointer dereference");
602         else
603                 printk(KERN_CONT "paging request");
604 
605         printk(KERN_CONT " at %p\n", (void *) address);
606         printk(KERN_ALERT "IP:");
607         printk_address(regs->ip);
608 
609         dump_pagetable(address);
610 }
611 
612 static noinline void
613 pgtable_bad(struct pt_regs *regs, unsigned long error_code,
614             unsigned long address)
615 {
616         struct task_struct *tsk;
617         unsigned long flags;
618         int sig;
619 
620         flags = oops_begin();
621         tsk = current;
622         sig = SIGKILL;
623 
624         printk(KERN_ALERT "%s: Corrupted page table at address %lx\n",
625                tsk->comm, address);
626         dump_pagetable(address);
627 
628         tsk->thread.cr2         = address;
629         tsk->thread.trap_nr     = X86_TRAP_PF;
630         tsk->thread.error_code  = error_code;
631 
632         if (__die("Bad pagetable", regs, error_code))
633                 sig = 0;
634 
635         oops_end(flags, regs, sig);
636 }
637 
638 static noinline void
639 no_context(struct pt_regs *regs, unsigned long error_code,
640            unsigned long address, int signal, int si_code)
641 {
642         struct task_struct *tsk = current;
643         unsigned long *stackend;
644         unsigned long flags;
645         int sig;
646 
647         /* Are we prepared to handle this kernel fault? */
648         if (fixup_exception(regs)) {
649                 /*
650                  * Any interrupt that takes a fault gets the fixup. This makes
651                  * the below recursive fault logic only apply to a faults from
652                  * task context.
653                  */
654                 if (in_interrupt())
655                         return;
656 
657                 /*
658                  * Per the above we're !in_interrupt(), aka. task context.
659                  *
660                  * In this case we need to make sure we're not recursively
661                  * faulting through the emulate_vsyscall() logic.
662                  */
663                 if (current_thread_info()->sig_on_uaccess_error && signal) {
664                         tsk->thread.trap_nr = X86_TRAP_PF;
665                         tsk->thread.error_code = error_code | PF_USER;
666                         tsk->thread.cr2 = address;
667 
668                         /* XXX: hwpoison faults will set the wrong code. */
669                         force_sig_info_fault(signal, si_code, address, tsk, 0);
670                 }
671 
672                 /*
673                  * Barring that, we can do the fixup and be happy.
674                  */
675                 return;
676         }
677 
678         /*
679          * 32-bit:
680          *
681          *   Valid to do another page fault here, because if this fault
682          *   had been triggered by is_prefetch fixup_exception would have
683          *   handled it.
684          *
685          * 64-bit:
686          *
687          *   Hall of shame of CPU/BIOS bugs.
688          */
689         if (is_prefetch(regs, error_code, address))
690                 return;
691 
692         if (is_errata93(regs, address))
693                 return;
694 
695         /*
696          * Oops. The kernel tried to access some bad page. We'll have to
697          * terminate things with extreme prejudice:
698          */
699         flags = oops_begin();
700 
701         show_fault_oops(regs, error_code, address);
702 
703         stackend = end_of_stack(tsk);
704         if (tsk != &init_task && *stackend != STACK_END_MAGIC)
705                 printk(KERN_EMERG "Thread overran stack, or stack corrupted\n");
706 
707         tsk->thread.cr2         = address;
708         tsk->thread.trap_nr     = X86_TRAP_PF;
709         tsk->thread.error_code  = error_code;
710 
711         sig = SIGKILL;
712         if (__die("Oops", regs, error_code))
713                 sig = 0;
714 
715         /* Executive summary in case the body of the oops scrolled away */
716         printk(KERN_DEFAULT "CR2: %016lx\n", address);
717 
718         oops_end(flags, regs, sig);
719 }
720 
721 /*
722  * Print out info about fatal segfaults, if the show_unhandled_signals
723  * sysctl is set:
724  */
725 static inline void
726 show_signal_msg(struct pt_regs *regs, unsigned long error_code,
727                 unsigned long address, struct task_struct *tsk)
728 {
729         if (!unhandled_signal(tsk, SIGSEGV))
730                 return;
731 
732         if (!printk_ratelimit())
733                 return;
734 
735         printk("%s%s[%d]: segfault at %lx ip %p sp %p error %lx",
736                 task_pid_nr(tsk) > 1 ? KERN_INFO : KERN_EMERG,
737                 tsk->comm, task_pid_nr(tsk), address,
738                 (void *)regs->ip, (void *)regs->sp, error_code);
739 
740         print_vma_addr(KERN_CONT " in ", regs->ip);
741 
742         printk(KERN_CONT "\n");
743 }
744 
745 static void
746 __bad_area_nosemaphore(struct pt_regs *regs, unsigned long error_code,
747                        unsigned long address, int si_code)
748 {
749         struct task_struct *tsk = current;
750 
751         /* User mode accesses just cause a SIGSEGV */
752         if (error_code & PF_USER) {
753                 /*
754                  * It's possible to have interrupts off here:
755                  */
756                 local_irq_enable();
757 
758                 /*
759                  * Valid to do another page fault here because this one came
760                  * from user space:
761                  */
762                 if (is_prefetch(regs, error_code, address))
763                         return;
764 
765                 if (is_errata100(regs, address))
766                         return;
767 
768 #ifdef CONFIG_X86_64
769                 /*
770                  * Instruction fetch faults in the vsyscall page might need
771                  * emulation.
772                  */
773                 if (unlikely((error_code & PF_INSTR) &&
774                              ((address & ~0xfff) == VSYSCALL_START))) {
775                         if (emulate_vsyscall(regs, address))
776                                 return;
777                 }
778 #endif
779                 /* Kernel addresses are always protection faults: */
780                 if (address >= TASK_SIZE)
781                         error_code |= PF_PROT;
782 
783                 if (likely(show_unhandled_signals))
784                         show_signal_msg(regs, error_code, address, tsk);
785 
786                 tsk->thread.cr2         = address;
787                 tsk->thread.error_code  = error_code;
788                 tsk->thread.trap_nr     = X86_TRAP_PF;
789 
790                 force_sig_info_fault(SIGSEGV, si_code, address, tsk, 0);
791 
792                 return;
793         }
794 
795         if (is_f00f_bug(regs, address))
796                 return;
797 
798         no_context(regs, error_code, address, SIGSEGV, si_code);
799 }
800 
801 static noinline void
802 bad_area_nosemaphore(struct pt_regs *regs, unsigned long error_code,
803                      unsigned long address)
804 {
805         __bad_area_nosemaphore(regs, error_code, address, SEGV_MAPERR);
806 }
807 
808 static void
809 __bad_area(struct pt_regs *regs, unsigned long error_code,
810            unsigned long address, int si_code)
811 {
812         struct mm_struct *mm = current->mm;
813 
814         /*
815          * Something tried to access memory that isn't in our memory map..
816          * Fix it, but check if it's kernel or user first..
817          */
818         up_read(&mm->mmap_sem);
819 
820         __bad_area_nosemaphore(regs, error_code, address, si_code);
821 }
822 
823 static noinline void
824 bad_area(struct pt_regs *regs, unsigned long error_code, unsigned long address)
825 {
826         __bad_area(regs, error_code, address, SEGV_MAPERR);
827 }
828 
829 static noinline void
830 bad_area_access_error(struct pt_regs *regs, unsigned long error_code,
831                       unsigned long address)
832 {
833         __bad_area(regs, error_code, address, SEGV_ACCERR);
834 }
835 
836 static void
837 do_sigbus(struct pt_regs *regs, unsigned long error_code, unsigned long address,
838           unsigned int fault)
839 {
840         struct task_struct *tsk = current;
841         struct mm_struct *mm = tsk->mm;
842         int code = BUS_ADRERR;
843 
844         up_read(&mm->mmap_sem);
845 
846         /* Kernel mode? Handle exceptions or die: */
847         if (!(error_code & PF_USER)) {
848                 no_context(regs, error_code, address, SIGBUS, BUS_ADRERR);
849                 return;
850         }
851 
852         /* User-space => ok to do another page fault: */
853         if (is_prefetch(regs, error_code, address))
854                 return;
855 
856         tsk->thread.cr2         = address;
857         tsk->thread.error_code  = error_code;
858         tsk->thread.trap_nr     = X86_TRAP_PF;
859 
860 #ifdef CONFIG_MEMORY_FAILURE
861         if (fault & (VM_FAULT_HWPOISON|VM_FAULT_HWPOISON_LARGE)) {
862                 printk(KERN_ERR
863         "MCE: Killing %s:%d due to hardware memory corruption fault at %lx\n",
864                         tsk->comm, tsk->pid, address);
865                 code = BUS_MCEERR_AR;
866         }
867 #endif
868         force_sig_info_fault(SIGBUS, code, address, tsk, fault);
869 }
870 
871 static noinline void
872 mm_fault_error(struct pt_regs *regs, unsigned long error_code,
873                unsigned long address, unsigned int fault)
874 {
875         if (fatal_signal_pending(current) && !(error_code & PF_USER)) {
876                 up_read(&current->mm->mmap_sem);
877                 no_context(regs, error_code, address, 0, 0);
878                 return;
879         }
880 
881         if (fault & VM_FAULT_OOM) {
882                 /* Kernel mode? Handle exceptions or die: */
883                 if (!(error_code & PF_USER)) {
884                         up_read(&current->mm->mmap_sem);
885                         no_context(regs, error_code, address,
886                                    SIGSEGV, SEGV_MAPERR);
887                         return;
888                 }
889 
890                 up_read(&current->mm->mmap_sem);
891 
892                 /*
893                  * We ran out of memory, call the OOM killer, and return the
894                  * userspace (which will retry the fault, or kill us if we got
895                  * oom-killed):
896                  */
897                 pagefault_out_of_memory();
898         } else {
899                 if (fault & (VM_FAULT_SIGBUS|VM_FAULT_HWPOISON|
900                              VM_FAULT_HWPOISON_LARGE))
901                         do_sigbus(regs, error_code, address, fault);
902                 else
903                         BUG();
904         }
905 }
906 
907 static int spurious_fault_check(unsigned long error_code, pte_t *pte)
908 {
909         if ((error_code & PF_WRITE) && !pte_write(*pte))
910                 return 0;
911 
912         if ((error_code & PF_INSTR) && !pte_exec(*pte))
913                 return 0;
914 
915         return 1;
916 }
917 
918 /*
919  * Handle a spurious fault caused by a stale TLB entry.
920  *
921  * This allows us to lazily refresh the TLB when increasing the
922  * permissions of a kernel page (RO -> RW or NX -> X).  Doing it
923  * eagerly is very expensive since that implies doing a full
924  * cross-processor TLB flush, even if no stale TLB entries exist
925  * on other processors.
926  *
927  * There are no security implications to leaving a stale TLB when
928  * increasing the permissions on a page.
929  */
930 static noinline __kprobes int
931 spurious_fault(unsigned long error_code, unsigned long address)
932 {
933         pgd_t *pgd;
934         pud_t *pud;
935         pmd_t *pmd;
936         pte_t *pte;
937         int ret;
938 
939         /* Reserved-bit violation or user access to kernel space? */
940         if (error_code & (PF_USER | PF_RSVD))
941                 return 0;
942 
943         pgd = init_mm.pgd + pgd_index(address);
944         if (!pgd_present(*pgd))
945                 return 0;
946 
947         pud = pud_offset(pgd, address);
948         if (!pud_present(*pud))
949                 return 0;
950 
951         if (pud_large(*pud))
952                 return spurious_fault_check(error_code, (pte_t *) pud);
953 
954         pmd = pmd_offset(pud, address);
955         if (!pmd_present(*pmd))
956                 return 0;
957 
958         if (pmd_large(*pmd))
959                 return spurious_fault_check(error_code, (pte_t *) pmd);
960 
961         pte = pte_offset_kernel(pmd, address);
962         if (!pte_present(*pte))
963                 return 0;
964 
965         ret = spurious_fault_check(error_code, pte);
966         if (!ret)
967                 return 0;
968 
969         /*
970          * Make sure we have permissions in PMD.
971          * If not, then there's a bug in the page tables:
972          */
973         ret = spurious_fault_check(error_code, (pte_t *) pmd);
974         WARN_ONCE(!ret, "PMD has incorrect permission bits\n");
975 
976         return ret;
977 }
978 
979 int show_unhandled_signals = 1;
980 
981 static inline int
982 access_error(unsigned long error_code, struct vm_area_struct *vma)
983 {
984         if (error_code & PF_WRITE) {
985                 /* write, present and write, not present: */
986                 if (unlikely(!(vma->vm_flags & VM_WRITE)))
987                         return 1;
988                 return 0;
989         }
990 
991         /* read, present: */
992         if (unlikely(error_code & PF_PROT))
993                 return 1;
994 
995         /* read, not present: */
996         if (unlikely(!(vma->vm_flags & (VM_READ | VM_EXEC | VM_WRITE))))
997                 return 1;
998 
999         return 0;
1000 }
1001 
1002 static int fault_in_kernel_space(unsigned long address)
1003 {
1004         return address >= TASK_SIZE_MAX;
1005 }
1006 
1007 static inline bool smap_violation(int error_code, struct pt_regs *regs)
1008 {
1009         if (!IS_ENABLED(CONFIG_X86_SMAP))
1010                 return false;
1011 
1012         if (!static_cpu_has(X86_FEATURE_SMAP))
1013                 return false;
1014 
1015         if (error_code & PF_USER)
1016                 return false;
1017 
1018         if (!user_mode_vm(regs) && (regs->flags & X86_EFLAGS_AC))
1019                 return false;
1020 
1021         return true;
1022 }
1023 
1024 /*
1025  * This routine handles page faults.  It determines the address,
1026  * and the problem, and then passes it off to one of the appropriate
1027  * routines.
1028  *
1029  * This function must have noinline because both callers
1030  * {,trace_}do_page_fault() have notrace on. Having this an actual function
1031  * guarantees there's a function trace entry.
1032  */
1033 static void __kprobes noinline
1034 __do_page_fault(struct pt_regs *regs, unsigned long error_code,
1035                 unsigned long address)
1036 {
1037         struct vm_area_struct *vma;
1038         struct task_struct *tsk;
1039         struct mm_struct *mm;
1040         int fault;
1041         unsigned int flags = FAULT_FLAG_ALLOW_RETRY | FAULT_FLAG_KILLABLE;
1042 
1043         tsk = current;
1044         mm = tsk->mm;
1045 
1046         /*
1047          * Detect and handle instructions that would cause a page fault for
1048          * both a tracked kernel page and a userspace page.
1049          */
1050         if (kmemcheck_active(regs))
1051                 kmemcheck_hide(regs);
1052         prefetchw(&mm->mmap_sem);
1053 
1054         if (unlikely(kmmio_fault(regs, address)))
1055                 return;
1056 
1057         /*
1058          * We fault-in kernel-space virtual memory on-demand. The
1059          * 'reference' page table is init_mm.pgd.
1060          *
1061          * NOTE! We MUST NOT take any locks for this case. We may
1062          * be in an interrupt or a critical region, and should
1063          * only copy the information from the master page table,
1064          * nothing more.
1065          *
1066          * This verifies that the fault happens in kernel space
1067          * (error_code & 4) == 0, and that the fault was not a
1068          * protection error (error_code & 9) == 0.
1069          */
1070         if (unlikely(fault_in_kernel_space(address))) {
1071                 if (!(error_code & (PF_RSVD | PF_USER | PF_PROT))) {
1072                         if (vmalloc_fault(address) >= 0)
1073                                 return;
1074 
1075                         if (kmemcheck_fault(regs, address, error_code))
1076                                 return;
1077                 }
1078 
1079                 /* Can handle a stale RO->RW TLB: */
1080                 if (spurious_fault(error_code, address))
1081                         return;
1082 
1083                 /* kprobes don't want to hook the spurious faults: */
1084                 if (kprobes_fault(regs))
1085                         return;
1086                 /*
1087                  * Don't take the mm semaphore here. If we fixup a prefetch
1088                  * fault we could otherwise deadlock:
1089                  */
1090                 bad_area_nosemaphore(regs, error_code, address);
1091 
1092                 return;
1093         }
1094 
1095         /* kprobes don't want to hook the spurious faults: */
1096         if (unlikely(kprobes_fault(regs)))
1097                 return;
1098 
1099         if (unlikely(error_code & PF_RSVD))
1100                 pgtable_bad(regs, error_code, address);
1101 
1102         if (unlikely(smap_violation(error_code, regs))) {
1103                 bad_area_nosemaphore(regs, error_code, address);
1104                 return;
1105         }
1106 
1107         /*
1108          * If we're in an interrupt, have no user context or are running
1109          * in an atomic region then we must not take the fault:
1110          */
1111         if (unlikely(in_atomic() || !mm)) {
1112                 bad_area_nosemaphore(regs, error_code, address);
1113                 return;
1114         }
1115 
1116         /*
1117          * It's safe to allow irq's after cr2 has been saved and the
1118          * vmalloc fault has been handled.
1119          *
1120          * User-mode registers count as a user access even for any
1121          * potential system fault or CPU buglet:
1122          */
1123         if (user_mode_vm(regs)) {
1124                 local_irq_enable();
1125                 error_code |= PF_USER;
1126                 flags |= FAULT_FLAG_USER;
1127         } else {
1128                 if (regs->flags & X86_EFLAGS_IF)
1129                         local_irq_enable();
1130         }
1131 
1132         perf_sw_event(PERF_COUNT_SW_PAGE_FAULTS, 1, regs, address);
1133 
1134         if (error_code & PF_WRITE)
1135                 flags |= FAULT_FLAG_WRITE;
1136 
1137         /*
1138          * When running in the kernel we expect faults to occur only to
1139          * addresses in user space.  All other faults represent errors in
1140          * the kernel and should generate an OOPS.  Unfortunately, in the
1141          * case of an erroneous fault occurring in a code path which already
1142          * holds mmap_sem we will deadlock attempting to validate the fault
1143          * against the address space.  Luckily the kernel only validly
1144          * references user space from well defined areas of code, which are
1145          * listed in the exceptions table.
1146          *
1147          * As the vast majority of faults will be valid we will only perform
1148          * the source reference check when there is a possibility of a
1149          * deadlock. Attempt to lock the address space, if we cannot we then
1150          * validate the source. If this is invalid we can skip the address
1151          * space check, thus avoiding the deadlock:
1152          */
1153         if (unlikely(!down_read_trylock(&mm->mmap_sem))) {
1154                 if ((error_code & PF_USER) == 0 &&
1155                     !search_exception_tables(regs->ip)) {
1156                         bad_area_nosemaphore(regs, error_code, address);
1157                         return;
1158                 }
1159 retry:
1160                 down_read(&mm->mmap_sem);
1161         } else {
1162                 /*
1163                  * The above down_read_trylock() might have succeeded in
1164                  * which case we'll have missed the might_sleep() from
1165                  * down_read():
1166                  */
1167                 might_sleep();
1168         }
1169 
1170         vma = find_vma(mm, address);
1171         if (unlikely(!vma)) {
1172                 bad_area(regs, error_code, address);
1173                 return;
1174         }
1175         if (likely(vma->vm_start <= address))
1176                 goto good_area;
1177         if (unlikely(!(vma->vm_flags & VM_GROWSDOWN))) {
1178                 bad_area(regs, error_code, address);
1179                 return;
1180         }
1181         if (error_code & PF_USER) {
1182                 /*
1183                  * Accessing the stack below %sp is always a bug.
1184                  * The large cushion allows instructions like enter
1185                  * and pusha to work. ("enter $65535, $31" pushes
1186                  * 32 pointers and then decrements %sp by 65535.)
1187                  */
1188                 if (unlikely(address + 65536 + 32 * sizeof(unsigned long) < regs->sp)) {
1189                         bad_area(regs, error_code, address);
1190                         return;
1191                 }
1192         }
1193         if (unlikely(expand_stack(vma, address))) {
1194                 bad_area(regs, error_code, address);
1195                 return;
1196         }
1197 
1198         /*
1199          * Ok, we have a good vm_area for this memory access, so
1200          * we can handle it..
1201          */
1202 good_area:
1203         if (unlikely(access_error(error_code, vma))) {
1204                 bad_area_access_error(regs, error_code, address);
1205                 return;
1206         }
1207 
1208         /*
1209          * If for any reason at all we couldn't handle the fault,
1210          * make sure we exit gracefully rather than endlessly redo
1211          * the fault:
1212          */
1213         fault = handle_mm_fault(mm, vma, address, flags);
1214 
1215         /*
1216          * If we need to retry but a fatal signal is pending, handle the
1217          * signal first. We do not need to release the mmap_sem because it
1218          * would already be released in __lock_page_or_retry in mm/filemap.c.
1219          */
1220         if (unlikely((fault & VM_FAULT_RETRY) && fatal_signal_pending(current)))
1221                 return;
1222 
1223         if (unlikely(fault & VM_FAULT_ERROR)) {
1224                 mm_fault_error(regs, error_code, address, fault);
1225                 return;
1226         }
1227 
1228         /*
1229          * Major/minor page fault accounting is only done on the
1230          * initial attempt. If we go through a retry, it is extremely
1231          * likely that the page will be found in page cache at that point.
1232          */
1233         if (flags & FAULT_FLAG_ALLOW_RETRY) {
1234                 if (fault & VM_FAULT_MAJOR) {
1235                         tsk->maj_flt++;
1236                         perf_sw_event(PERF_COUNT_SW_PAGE_FAULTS_MAJ, 1,
1237                                       regs, address);
1238                 } else {
1239                         tsk->min_flt++;
1240                         perf_sw_event(PERF_COUNT_SW_PAGE_FAULTS_MIN, 1,
1241                                       regs, address);
1242                 }
1243                 if (fault & VM_FAULT_RETRY) {
1244                         /* Clear FAULT_FLAG_ALLOW_RETRY to avoid any risk
1245                          * of starvation. */
1246                         flags &= ~FAULT_FLAG_ALLOW_RETRY;
1247                         flags |= FAULT_FLAG_TRIED;
1248                         goto retry;
1249                 }
1250         }
1251 
1252         check_v8086_mode(regs, address, tsk);
1253 
1254         up_read(&mm->mmap_sem);
1255 }
1256 
1257 dotraplinkage void __kprobes notrace
1258 do_page_fault(struct pt_regs *regs, unsigned long error_code)
1259 {
1260         unsigned long address = read_cr2(); /* Get the faulting address */
1261         enum ctx_state prev_state;
1262 
1263         /*
1264          * We must have this function tagged with __kprobes, notrace and call
1265          * read_cr2() before calling anything else. To avoid calling any kind
1266          * of tracing machinery before we've observed the CR2 value.
1267          *
1268          * exception_{enter,exit}() contain all sorts of tracepoints.
1269          */
1270 
1271         prev_state = exception_enter();
1272         __do_page_fault(regs, error_code, address);
1273         exception_exit(prev_state);
1274 }
1275 
1276 #ifdef CONFIG_TRACING
1277 static void trace_page_fault_entries(unsigned long address, struct pt_regs *regs,
1278                                      unsigned long error_code)
1279 {
1280         if (user_mode(regs))
1281                 trace_page_fault_user(address, regs, error_code);
1282         else
1283                 trace_page_fault_kernel(address, regs, error_code);
1284 }
1285 
1286 dotraplinkage void __kprobes notrace
1287 trace_do_page_fault(struct pt_regs *regs, unsigned long error_code)
1288 {
1289         /*
1290          * The exception_enter and tracepoint processing could
1291          * trigger another page faults (user space callchain
1292          * reading) and destroy the original cr2 value, so read
1293          * the faulting address now.
1294          */
1295         unsigned long address = read_cr2();
1296         enum ctx_state prev_state;
1297 
1298         prev_state = exception_enter();
1299         trace_page_fault_entries(address, regs, error_code);
1300         __do_page_fault(regs, error_code, address);
1301         exception_exit(prev_state);
1302 }
1303 #endif /* CONFIG_TRACING */
1304 

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