aboutsummaryrefslogtreecommitdiffstats
path: root/arch/x86_64/mm/fault.c
blob: 08dc696f54ee4543fe4aff4cf551f1f7253e2da3 (plain) (blame)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
417
418
419
420
421
422
423
424
425
426
427
428
429
430
431
432
433
434
435
436
437
438
439
440
441
442
443
444
445
446
447
448
449
450
451
452
453
454
455
456
457
458
459
460
461
462
463
464
465
466
467
468
469
470
471
472
473
474
475
476
477
478
479
480
481
482
483
484
485
486
487
488
489
490
491
492
493
494
495
496
497
498
499
500
501
502
503
504
505
506
507
508
509
510
511
512
513
514
515
516
517
518
519
520
521
522
523
524
525
526
527
528
529
530
531
532
533
534
535
536
537
538
539
540
541
542
543
544
545
546
547
548
549
550
551
552
553
554
555
556
557
558
559
560
561
562
563
564
565
566
567
568
569
570
571
572
573
574
575
576
577
578
579
580
581
582
583
584
585
586
587
588
589
590
591
592
593
594
595
596
597
598
599
600
601
602
603
604
605
606
607
608
609
610
611
612
613
614
615
616
617
618
619
620
621
622
623
624
625
626
627
628
629
630
631
632
633
634
635
636
637
638
639
640
641
642
643
644
645
646
647
648
649
650
651
652
653
654
655
656
657
658
659
660
661
662
663
664
665
/*
 *  linux/arch/x86-64/mm/fault.c
 *
 *  Copyright (C) 1995  Linus Torvalds
 *  Copyright (C) 2001,2002 Andi Kleen, SuSE Labs.
 */

#include <linux/config.h>
#include <linux/signal.h>
#include <linux/sched.h>
#include <linux/kernel.h>
#include <linux/errno.h>
#include <linux/string.h>
#include <linux/types.h>
#include <linux/ptrace.h>
#include <linux/mman.h>
#include <linux/mm.h>
#include <linux/smp.h>
#include <linux/smp_lock.h>
#include <linux/interrupt.h>
#include <linux/init.h>
#include <linux/tty.h>
#include <linux/vt_kern.h>		/* For unblank_screen() */
#include <linux/compiler.h>
#include <linux/module.h>
#include <linux/kprobes.h>

#include <asm/system.h>
#include <asm/uaccess.h>
#include <asm/pgalloc.h>
#include <asm/smp.h>
#include <asm/tlbflush.h>
#include <asm/proto.h>
#include <asm/kdebug.h>
#include <asm-generic/sections.h>

/* Page fault error code bits */
#define PF_PROT	(1<<0)		/* or no page found */
#define PF_WRITE	(1<<1)
#define PF_USER	(1<<2)
#define PF_RSVD	(1<<3)
#define PF_INSTR	(1<<4)

#ifdef CONFIG_KPROBES
ATOMIC_NOTIFIER_HEAD(notify_page_fault_chain);

/* Hook to register for page fault notifications */
int register_page_fault_notifier(struct notifier_block *nb)
{
	vmalloc_sync_all();
	return atomic_notifier_chain_register(&notify_page_fault_chain, nb);
}

int unregister_page_fault_notifier(struct notifier_block *nb)
{
	return atomic_notifier_chain_unregister(&notify_page_fault_chain, nb);
}

static inline int notify_page_fault(enum die_val val, const char *str,
			struct pt_regs *regs, long err, int trap, int sig)
{
	struct die_args args = {
		.regs = regs,
		.str = str,
		.err = err,
		.trapnr = trap,
		.signr = sig
	};
	return atomic_notifier_call_chain(&notify_page_fault_chain, val, &args);
}
#else
static inline int notify_page_fault(enum die_val val, const char *str,
			struct pt_regs *regs, long err, int trap, int sig)
{
	return NOTIFY_DONE;
}
#endif

void bust_spinlocks(int yes)
{
	int loglevel_save = console_loglevel;
	if (yes) {
		oops_in_progress = 1;
	} else {
#ifdef CONFIG_VT
		unblank_screen();
#endif
		oops_in_progress = 0;
		/*
		 * OK, the message is on the console.  Now we call printk()
		 * without oops_in_progress set so that printk will give klogd
		 * a poke.  Hold onto your hats...
		 */
		console_loglevel = 15;		/* NMI oopser may have shut the console up */
		printk(" ");
		console_loglevel = loglevel_save;
	}
}

/* Sometimes the CPU reports invalid exceptions on prefetch.
   Check that here and ignore.
   Opcode checker based on code by Richard Brunner */
static noinline int is_prefetch(struct pt_regs *regs, unsigned long addr,
				unsigned long error_code)
{ 
	unsigned char *instr;
	int scan_more = 1;
	int prefetch = 0; 
	unsigned char *max_instr;

	/* If it was a exec fault ignore */
	if (error_code & PF_INSTR)
		return 0;
	
	instr = (unsigned char *)convert_rip_to_linear(current, regs);
	max_instr = instr + 15;

	if (user_mode(regs) && instr >= (unsigned char *)TASK_SIZE)
		return 0;

	while (scan_more && instr < max_instr) { 
		unsigned char opcode;
		unsigned char instr_hi;
		unsigned char instr_lo;

		if (__get_user(opcode, instr))
			break; 

		instr_hi = opcode & 0xf0; 
		instr_lo = opcode & 0x0f; 
		instr++;

		switch (instr_hi) { 
		case 0x20:
		case 0x30:
			/* Values 0x26,0x2E,0x36,0x3E are valid x86
			   prefixes.  In long mode, the CPU will signal
			   invalid opcode if some of these prefixes are
			   present so we will never get here anyway */
			scan_more = ((instr_lo & 7) == 0x6);
			break;
			
		case 0x40:
			/* In AMD64 long mode, 0x40 to 0x4F are valid REX prefixes
			   Need to figure out under what instruction mode the
			   instruction was issued ... */
			/* Could check the LDT for lm, but for now it's good
			   enough to assume that long mode only uses well known
			   segments or kernel. */
			scan_more = (!user_mode(regs)) || (regs->cs == __USER_CS);
			break;
			
		case 0x60:
			/* 0x64 thru 0x67 are valid prefixes in all modes. */
			scan_more = (instr_lo & 0xC) == 0x4;
			break;		
		case 0xF0:
			/* 0xF0, 0xF2, and 0xF3 are valid prefixes in all modes. */
			scan_more = !instr_lo || (instr_lo>>1) == 1;
			break;			
		case 0x00:
			/* Prefetch instruction is 0x0F0D or 0x0F18 */
			scan_more = 0;
			if (__get_user(opcode, instr)) 
				break;
			prefetch = (instr_lo == 0xF) &&
				(opcode == 0x0D || opcode == 0x18);
			break;			
		default:
			scan_more = 0;
			break;
		} 
	}
	return prefetch;
}

static int bad_address(void *p) 
{ 
	unsigned long dummy;
	return __get_user(dummy, (unsigned long *)p);
} 

void dump_pagetable(unsigned long address)
{
	pgd_t *pgd;
	pud_t *pud;
	pmd_t *pmd;
	pte_t *pte;

	asm("movq %%cr3,%0" : "=r" (pgd));

	pgd = __va((unsigned long)pgd & PHYSICAL_PAGE_MASK); 
	pgd += pgd_index(address);
	if (bad_address(pgd)) goto bad;
	printk("PGD %lx ", pgd_val(*pgd));
	if (!pgd_present(*pgd)) goto ret; 

	pud = pud_offset(pgd, address);
	if (bad_address(pud)) goto bad;
	printk("PUD %lx ", pud_val(*pud));
	if (!pud_present(*pud))	goto ret;

	pmd = pmd_offset(pud, address);
	if (bad_address(pmd)) goto bad;
	printk("PMD %lx ", pmd_val(*pmd));
	if (!pmd_present(*pmd))	goto ret;	 

	pte = pte_offset_kernel(pmd, address);
	if (bad_address(pte)) goto bad;
	printk("PTE %lx", pte_val(*pte)); 
ret:
	printk("\n");
	return;
bad:
	printk("BAD\n");
}

static const char errata93_warning[] = 
KERN_ERR "******* Your BIOS seems to not contain a fix for K8 errata #93\n"
KERN_ERR "******* Working around it, but it may cause SEGVs or burn power.\n"
KERN_ERR "******* Please consider a BIOS update.\n"
KERN_ERR "******* Disabling USB legacy in the BIOS may also help.\n";

/* Workaround for K8 erratum #93 & buggy BIOS.
   BIOS SMM functions are required to use a specific workaround
   to avoid corruption of the 64bit RIP register on C stepping K8. 
   A lot of BIOS that didn't get tested properly miss this. 
   The OS sees this as a page fault with the upper 32bits of RIP cleared.
   Try to work around it here.
   Note we only handle faults in kernel here. */

static int is_errata93(struct pt_regs *regs, unsigned long address) 
{
	static int warned;
	if (address != regs->rip)
		return 0;
	if ((address >> 32) != 0) 
		return 0;
	address |= 0xffffffffUL << 32;
	if ((address >= (u64)_stext && address <= (u64)_etext) || 
	    (address >= MODULES_VADDR && address <= MODULES_END)) { 
		if (!warned) {
			printk(errata93_warning); 		
			warned = 1;
		}
		regs->rip = address;
		return 1;
	}
	return 0;
} 

int unhandled_signal(struct task_struct *tsk, int sig)
{
	if (tsk->pid == 1)
		return 1;
	if (tsk->ptrace & PT_PTRACED)
		return 0;
	return (tsk->sighand->action[sig-1].sa.sa_handler == SIG_IGN) ||
		(tsk->sighand->action[sig-1].sa.sa_handler == SIG_DFL);
}

static noinline void pgtable_bad(unsigned long address, struct pt_regs *regs,
				 unsigned long error_code)
{
	unsigned long flags = oops_begin();
	struct task_struct *tsk;

	printk(KERN_ALERT "%s: Corrupted page table at address %lx\n",
	       current->comm, address);
	dump_pagetable(address);
	tsk = current;
	tsk->thread.cr2 = address;
	tsk->thread.trap_no = 14;
	tsk->thread.error_code = error_code;
	__die("Bad pagetable", regs, error_code);
	oops_end(flags);
	do_exit(SIGKILL);
}

/*
 * Handle a fault on the vmalloc area
 *
 * This assumes no large pages in there.
 */
static int vmalloc_fault(unsigned long address)
{
	pgd_t *pgd, *pgd_ref;
	pud_t *pud, *pud_ref;
	pmd_t *pmd, *pmd_ref;
	pte_t *pte, *pte_ref;

	/* Copy kernel mappings over when needed. This can also
	   happen within a race in page table update. In the later
	   case just flush. */

	pgd = pgd_offset(current->mm ?: &init_mm, address);
	pgd_ref = pgd_offset_k(address);
	if (pgd_none(*pgd_ref))
		return -1;
	if (pgd_none(*pgd))
		set_pgd(pgd, *pgd_ref);
	else
		BUG_ON(pgd_page(*pgd) != pgd_page(*pgd_ref));

	/* Below here mismatches are bugs because these lower tables
	   are shared */

	pud = pud_offset(pgd, address);
	pud_ref = pud_offset(pgd_ref, address);
	if (pud_none(*pud_ref))
		return -1;
	if (pud_none(*pud) || pud_page(*pud) != pud_page(*pud_ref))
		BUG();
	pmd = pmd_offset(pud, address);
	pmd_ref = pmd_offset(pud_ref, address);
	if (pmd_none(*pmd_ref))
		return -1;
	if (pmd_none(*pmd) || pmd_page(*pmd) != pmd_page(*pmd_ref))
		BUG();
	pte_ref = pte_offset_kernel(pmd_ref, address);
	if (!pte_present(*pte_ref))
		return -1;
	pte = pte_offset_kernel(pmd, address);
	/* Don't use pte_page here, because the mappings can point
	   outside mem_map, and the NUMA hash lookup cannot handle
	   that. */
	if (!pte_present(*pte) || pte_pfn(*pte) != pte_pfn(*pte_ref))
		BUG();
	return 0;
}

int page_fault_trace = 0;
int exception_trace = 1;

/*
 * This routine handles page faults.  It determines the address,
 * and the problem, and then passes it off to one of the appropriate
 * routines.
 */
asmlinkage void __kprobes do_page_fault(struct pt_regs *regs,
					unsigned long error_code)
{
	struct task_struct *tsk;
	struct mm_struct *mm;
	struct vm_area_struct * vma;
	unsigned long address;
	const struct exception_table_entry *fixup;
	int write;
	unsigned long flags;
	siginfo_t info;

	tsk = current;
	mm = tsk->mm;
	prefetchw(&mm->mmap_sem);

	/* get the address */
	__asm__("movq %%cr2,%0":"=r" (address));

	info.si_code = SEGV_MAPERR;


	/*
	 * We fault-in kernel-space virtual memory on-demand. The
	 * 'reference' page table is init_mm.pgd.
	 *
	 * NOTE! We MUST NOT take any locks for this case. We may
	 * be in an interrupt or a critical region, and should
	 * only copy the information from the master page table,
	 * nothing more.
	 *
	 * This verifies that the fault happens in kernel space
	 * (error_code & 4) == 0, and that the fault was not a
	 * protection error (error_code & 9) == 0.
	 */
	if (unlikely(address >= TASK_SIZE64)) {
		/*
		 * Don't check for the module range here: its PML4
		 * is always initialized because it's shared with the main
		 * kernel text. Only vmalloc may need PML4 syncups.
		 */
		if (!(error_code & (PF_RSVD|PF_USER|PF_PROT)) &&
		      ((address >= VMALLOC_START && address < VMALLOC_END))) {
			if (vmalloc_fault(address) >= 0)
				return;
		}
		if (notify_page_fault(DIE_PAGE_FAULT, "page fault", regs, error_code, 14,
						SIGSEGV) == NOTIFY_STOP)
			return;
		/*
		 * Don't take the mm semaphore here. If we fixup a prefetch
		 * fault we could otherwise deadlock.
		 */
		goto bad_area_nosemaphore;
	}

	if (notify_page_fault(DIE_PAGE_FAULT, "page fault", regs, error_code, 14,
					SIGSEGV) == NOTIFY_STOP)
		return;

	if (likely(regs->eflags & X86_EFLAGS_IF))
		local_irq_enable();

	if (unlikely(page_fault_trace))
		printk("pagefault rip:%lx rsp:%lx cs:%lu ss:%lu address %lx error %lx\n",
		       regs->rip,regs->rsp,regs->cs,regs->ss,address,error_code); 

	if (unlikely(error_code & PF_RSVD))
		pgtable_bad(address, regs, error_code);

	/*
	 * If we're in an interrupt or have no user
	 * context, we must not take the fault..
	 */
	if (unlikely(in_atomic() || !mm))
		goto bad_area_nosemaphore;

 again:
	/* When running in the kernel we expect faults to occur only to
	 * addresses in user space.  All other faults represent errors in the
	 * kernel and should generate an OOPS.  Unfortunatly, in the case of an
	 * erroneous fault occuring in a code path which already holds mmap_sem
	 * we will deadlock attempting to validate the fault against the
	 * address space.  Luckily the kernel only validly references user
	 * space from well defined areas of code, which are listed in the
	 * exceptions table.
	 *
	 * As the vast majority of faults will be valid we will only perform
	 * the source reference check when there is a possibilty of a deadlock.
	 * Attempt to lock the address space, if we cannot we then validate the
	 * source.  If this is invalid we can skip the address space check,
	 * thus avoiding the deadlock.
	 */
	if (!down_read_trylock(&mm->mmap_sem)) {
		if ((error_code & PF_USER) == 0 &&
		    !search_exception_tables(regs->rip))
			goto bad_area_nosemaphore;
		down_read(&mm->mmap_sem);
	}

	vma = find_vma(mm, address);
	if (!vma)
		goto bad_area;
	if (likely(vma->vm_start <= address))
		goto good_area;
	if (!(vma->vm_flags & VM_GROWSDOWN))
		goto bad_area;
	if (error_code & 4) {
		/* Allow userspace just enough access below the stack pointer
		 * to let the 'enter' instruction work.
		 */
		if (address + 65536 + 32 * sizeof(unsigned long) < regs->rsp)
			goto bad_area;
	}
	if (expand_stack(vma, address))
		goto bad_area;
/*
 * Ok, we have a good vm_area for this memory access, so
 * we can handle it..
 */
good_area:
	info.si_code = SEGV_ACCERR;
	write = 0;
	switch (error_code & (PF_PROT|PF_WRITE)) {
		default:	/* 3: write, present */
			/* fall through */
		case PF_WRITE:		/* write, not present */
			if (!(vma->vm_flags & VM_WRITE))
				goto bad_area;
			write++;
			break;
		case PF_PROT:		/* read, present */
			goto bad_area;
		case 0:			/* read, not present */
			if (!(vma->vm_flags & (VM_READ | VM_EXEC)))
				goto bad_area;
	}

	/*
	 * If for any reason at all we couldn't handle the fault,
	 * make sure we exit gracefully rather than endlessly redo
	 * the fault.
	 */
	switch (handle_mm_fault(mm, vma, address, write)) {
	case VM_FAULT_MINOR:
		tsk->min_flt++;
		break;
	case VM_FAULT_MAJOR:
		tsk->maj_flt++;
		break;
	case VM_FAULT_SIGBUS:
		goto do_sigbus;
	default:
		goto out_of_memory;
	}

	up_read(&mm->mmap_sem);
	return;

/*
 * Something tried to access memory that isn't in our memory map..
 * Fix it, but check if it's kernel or user first..
 */
bad_area:
	up_read(&mm->mmap_sem);

bad_area_nosemaphore:
	/* User mode accesses just cause a SIGSEGV */
	if (error_code & PF_USER) {
		if (is_prefetch(regs, address, error_code))
			return;

		/* Work around K8 erratum #100 K8 in compat mode
		   occasionally jumps to illegal addresses >4GB.  We
		   catch this here in the page fault handler because
		   these addresses are not reachable. Just detect this
		   case and return.  Any code segment in LDT is
		   compatibility mode. */
		if ((regs->cs == __USER32_CS || (regs->cs & (1<<2))) &&
		    (address >> 32))
			return;

		if (exception_trace && unhandled_signal(tsk, SIGSEGV)) {
			printk(
		       "%s%s[%d]: segfault at %016lx rip %016lx rsp %016lx error %lx\n",
					tsk->pid > 1 ? KERN_INFO : KERN_EMERG,
					tsk->comm, tsk->pid, address, regs->rip,
					regs->rsp, error_code);
		}
       
		tsk->thread.cr2 = address;
		/* Kernel addresses are always protection faults */
		tsk->thread.error_code = error_code | (address >= TASK_SIZE);
		tsk->thread.trap_no = 14;
		info.si_signo = SIGSEGV;
		info.si_errno = 0;
		/* info.si_code has been set above */
		info.si_addr = (void __user *)address;
		force_sig_info(SIGSEGV, &info, tsk);
		return;
	}

no_context:
	
	/* Are we prepared to handle this kernel fault?  */
	fixup = search_exception_tables(regs->rip);
	if (fixup) {
		regs->rip = fixup->fixup;
		return;
	}

	/* 
	 * Hall of shame of CPU/BIOS bugs.
	 */

 	if (is_prefetch(regs, address, error_code))
 		return;

	if (is_errata93(regs, address))
		return; 

/*
 * Oops. The kernel tried to access some bad page. We'll have to
 * terminate things with extreme prejudice.
 */

	flags = oops_begin();

	if (address < PAGE_SIZE)
		printk(KERN_ALERT "Unable to handle kernel NULL pointer dereference");
	else
		printk(KERN_ALERT "Unable to handle kernel paging request");
	printk(" at %016lx RIP: \n" KERN_ALERT,address);
	printk_address(regs->rip);
	printk("\n");
	dump_pagetable(address);
	tsk->thread.cr2 = address;
	tsk->thread.trap_no = 14;
	tsk->thread.error_code = error_code;
	__die("Oops", regs, error_code);
	/* Executive summary in case the body of the oops scrolled away */
	printk(KERN_EMERG "CR2: %016lx\n", address);
	oops_end(flags);
	do_exit(SIGKILL);

/*
 * We ran out of memory, or some other thing happened to us that made
 * us unable to handle the page fault gracefully.
 */
out_of_memory:
	up_read(&mm->mmap_sem);
	if (current->pid == 1) { 
		yield();
		goto again;
	}
	printk("VM: killing process %s\n", tsk->comm);
	if (error_code & 4)
		do_exit(SIGKILL);
	goto no_context;

do_sigbus:
	up_read(&mm->mmap_sem);

	/* Kernel mode? Handle exceptions or die */
	if (!(error_code & PF_USER))
		goto no_context;

	tsk->thread.cr2 = address;
	tsk->thread.error_code = error_code;
	tsk->thread.trap_no = 14;
	info.si_signo = SIGBUS;
	info.si_errno = 0;
	info.si_code = BUS_ADRERR;
	info.si_addr = (void __user *)address;
	force_sig_info(SIGBUS, &info, tsk);
	return;
}

DEFINE_SPINLOCK(pgd_lock);
struct page *pgd_list;

void vmalloc_sync_all(void)
{
	/* Note that races in the updates of insync and start aren't 
	   problematic:
	   insync can only get set bits added, and updates to start are only
	   improving performance (without affecting correctness if undone). */
	static DECLARE_BITMAP(insync, PTRS_PER_PGD);
	static unsigned long start = VMALLOC_START & PGDIR_MASK;
	unsigned long address;

	for (address = start; address <= VMALLOC_END; address += PGDIR_SIZE) {
		if (!test_bit(pgd_index(address), insync)) {
			const pgd_t *pgd_ref = pgd_offset_k(address);
			struct page *page;

			if (pgd_none(*pgd_ref))
				continue;
			spin_lock(&pgd_lock);
			for (page = pgd_list; page;
			     page = (struct page *)page->index) {
				pgd_t *pgd;
				pgd = (pgd_t *)page_address(page) + pgd_index(address);
				if (pgd_none(*pgd))
					set_pgd(pgd, *pgd_ref);
				else
					BUG_ON(pgd_page(*pgd) != pgd_page(*pgd_ref));
			}
			spin_unlock(&pgd_lock);
			set_bit(pgd_index(address), insync);
		}
		if (address == start)
			start = address + PGDIR_SIZE;
	}
	/* Check that there is no need to do the same for the modules area. */
	BUILD_BUG_ON(!(MODULES_VADDR > __START_KERNEL));
	BUILD_BUG_ON(!(((MODULES_END - 1) & PGDIR_MASK) == 
				(__START_KERNEL & PGDIR_MASK)));
}

static int __init enable_pagefaulttrace(char *str)
{
	page_fault_trace = 1;
	return 1;
}
__setup("pagefaulttrace", enable_pagefaulttrace);