xref: /linux/fs/proc/kcore.c (revision 69bfec7548f4c1595bac0e3ddfc0458a5af31f4c) 
1 // SPDX-License-Identifier: GPL-2.0
2 /*
3  *	fs/proc/kcore.c kernel ELF core dumper
4  *
5  *	Modelled on fs/exec.c:aout_core_dump()
6  *	Jeremy Fitzhardinge <jeremy@sw.oz.au>
7  *	ELF version written by David Howells <David.Howells@nexor.co.uk>
8  *	Modified and incorporated into 2.3.x by Tigran Aivazian <tigran@veritas.com>
9  *	Support to dump vmalloc'd areas (ELF only), Tigran Aivazian <tigran@veritas.com>
10  *	Safe accesses to vmalloc/direct-mapped discontiguous areas, Kanoj Sarcar <kanoj@sgi.com>
11  */
12 
13 #include <linux/crash_core.h>
14 #include <linux/mm.h>
15 #include <linux/proc_fs.h>
16 #include <linux/kcore.h>
17 #include <linux/user.h>
18 #include <linux/capability.h>
19 #include <linux/elf.h>
20 #include <linux/elfcore.h>
21 #include <linux/vmalloc.h>
22 #include <linux/highmem.h>
23 #include <linux/printk.h>
24 #include <linux/memblock.h>
25 #include <linux/init.h>
26 #include <linux/slab.h>
27 #include <linux/uaccess.h>
28 #include <asm/io.h>
29 #include <linux/list.h>
30 #include <linux/ioport.h>
31 #include <linux/memory.h>
32 #include <linux/sched/task.h>
33 #include <linux/security.h>
34 #include <asm/sections.h>
35 #include "internal.h"
36 
37 #define CORE_STR "CORE"
38 
39 #ifndef ELF_CORE_EFLAGS
40 #define ELF_CORE_EFLAGS	0
41 #endif
42 
43 static struct proc_dir_entry *proc_root_kcore;
44 
45 
46 #ifndef kc_vaddr_to_offset
47 #define	kc_vaddr_to_offset(v) ((v) - PAGE_OFFSET)
48 #endif
49 #ifndef	kc_offset_to_vaddr
50 #define	kc_offset_to_vaddr(o) ((o) + PAGE_OFFSET)
51 #endif
52 
53 static LIST_HEAD(kclist_head);
54 static DECLARE_RWSEM(kclist_lock);
55 static int kcore_need_update = 1;
56 
57 /*
58  * Returns > 0 for RAM pages, 0 for non-RAM pages, < 0 on error
59  * Same as oldmem_pfn_is_ram in vmcore
60  */
61 static int (*mem_pfn_is_ram)(unsigned long pfn);
62 
63 int __init register_mem_pfn_is_ram(int (*fn)(unsigned long pfn))
64 {
65 	if (mem_pfn_is_ram)
66 		return -EBUSY;
67 	mem_pfn_is_ram = fn;
68 	return 0;
69 }
70 
71 static int pfn_is_ram(unsigned long pfn)
72 {
73 	if (mem_pfn_is_ram)
74 		return mem_pfn_is_ram(pfn);
75 	else
76 		return 1;
77 }
78 
79 /* This doesn't grab kclist_lock, so it should only be used at init time. */
80 void __init kclist_add(struct kcore_list *new, void *addr, size_t size,
81 		       int type)
82 {
83 	new->addr = (unsigned long)addr;
84 	new->size = size;
85 	new->type = type;
86 
87 	list_add_tail(&new->list, &kclist_head);
88 }
89 
90 static size_t get_kcore_size(int *nphdr, size_t *phdrs_len, size_t *notes_len,
91 			     size_t *data_offset)
92 {
93 	size_t try, size;
94 	struct kcore_list *m;
95 
96 	*nphdr = 1; /* PT_NOTE */
97 	size = 0;
98 
99 	list_for_each_entry(m, &kclist_head, list) {
100 		try = kc_vaddr_to_offset((size_t)m->addr + m->size);
101 		if (try > size)
102 			size = try;
103 		*nphdr = *nphdr + 1;
104 	}
105 
106 	*phdrs_len = *nphdr * sizeof(struct elf_phdr);
107 	*notes_len = (4 * sizeof(struct elf_note) +
108 		      3 * ALIGN(sizeof(CORE_STR), 4) +
109 		      VMCOREINFO_NOTE_NAME_BYTES +
110 		      ALIGN(sizeof(struct elf_prstatus), 4) +
111 		      ALIGN(sizeof(struct elf_prpsinfo), 4) +
112 		      ALIGN(arch_task_struct_size, 4) +
113 		      ALIGN(vmcoreinfo_size, 4));
114 	*data_offset = PAGE_ALIGN(sizeof(struct elfhdr) + *phdrs_len +
115 				  *notes_len);
116 	return *data_offset + size;
117 }
118 
119 #ifdef CONFIG_HIGHMEM
120 /*
121  * If no highmem, we can assume [0...max_low_pfn) continuous range of memory
122  * because memory hole is not as big as !HIGHMEM case.
123  * (HIGHMEM is special because part of memory is _invisible_ from the kernel.)
124  */
125 static int kcore_ram_list(struct list_head *head)
126 {
127 	struct kcore_list *ent;
128 
129 	ent = kmalloc(sizeof(*ent), GFP_KERNEL);
130 	if (!ent)
131 		return -ENOMEM;
132 	ent->addr = (unsigned long)__va(0);
133 	ent->size = max_low_pfn << PAGE_SHIFT;
134 	ent->type = KCORE_RAM;
135 	list_add(&ent->list, head);
136 	return 0;
137 }
138 
139 #else /* !CONFIG_HIGHMEM */
140 
141 #ifdef CONFIG_SPARSEMEM_VMEMMAP
142 /* calculate vmemmap's address from given system ram pfn and register it */
143 static int
144 get_sparsemem_vmemmap_info(struct kcore_list *ent, struct list_head *head)
145 {
146 	unsigned long pfn = __pa(ent->addr) >> PAGE_SHIFT;
147 	unsigned long nr_pages = ent->size >> PAGE_SHIFT;
148 	unsigned long start, end;
149 	struct kcore_list *vmm, *tmp;
150 
151 
152 	start = ((unsigned long)pfn_to_page(pfn)) & PAGE_MASK;
153 	end = ((unsigned long)pfn_to_page(pfn + nr_pages)) - 1;
154 	end = PAGE_ALIGN(end);
155 	/* overlap check (because we have to align page */
156 	list_for_each_entry(tmp, head, list) {
157 		if (tmp->type != KCORE_VMEMMAP)
158 			continue;
159 		if (start < tmp->addr + tmp->size)
160 			if (end > tmp->addr)
161 				end = tmp->addr;
162 	}
163 	if (start < end) {
164 		vmm = kmalloc(sizeof(*vmm), GFP_KERNEL);
165 		if (!vmm)
166 			return 0;
167 		vmm->addr = start;
168 		vmm->size = end - start;
169 		vmm->type = KCORE_VMEMMAP;
170 		list_add_tail(&vmm->list, head);
171 	}
172 	return 1;
173 
174 }
175 #else
176 static int
177 get_sparsemem_vmemmap_info(struct kcore_list *ent, struct list_head *head)
178 {
179 	return 1;
180 }
181 
182 #endif
183 
184 static int
185 kclist_add_private(unsigned long pfn, unsigned long nr_pages, void *arg)
186 {
187 	struct list_head *head = (struct list_head *)arg;
188 	struct kcore_list *ent;
189 	struct page *p;
190 
191 	if (!pfn_valid(pfn))
192 		return 1;
193 
194 	p = pfn_to_page(pfn);
195 
196 	ent = kmalloc(sizeof(*ent), GFP_KERNEL);
197 	if (!ent)
198 		return -ENOMEM;
199 	ent->addr = (unsigned long)page_to_virt(p);
200 	ent->size = nr_pages << PAGE_SHIFT;
201 
202 	if (!virt_addr_valid(ent->addr))
203 		goto free_out;
204 
205 	/* cut not-mapped area. ....from ppc-32 code. */
206 	if (ULONG_MAX - ent->addr < ent->size)
207 		ent->size = ULONG_MAX - ent->addr;
208 
209 	/*
210 	 * We've already checked virt_addr_valid so we know this address
211 	 * is a valid pointer, therefore we can check against it to determine
212 	 * if we need to trim
213 	 */
214 	if (VMALLOC_START > ent->addr) {
215 		if (VMALLOC_START - ent->addr < ent->size)
216 			ent->size = VMALLOC_START - ent->addr;
217 	}
218 
219 	ent->type = KCORE_RAM;
220 	list_add_tail(&ent->list, head);
221 
222 	if (!get_sparsemem_vmemmap_info(ent, head)) {
223 		list_del(&ent->list);
224 		goto free_out;
225 	}
226 
227 	return 0;
228 free_out:
229 	kfree(ent);
230 	return 1;
231 }
232 
233 static int kcore_ram_list(struct list_head *list)
234 {
235 	int nid, ret;
236 	unsigned long end_pfn;
237 
238 	/* Not inialized....update now */
239 	/* find out "max pfn" */
240 	end_pfn = 0;
241 	for_each_node_state(nid, N_MEMORY) {
242 		unsigned long node_end;
243 		node_end = node_end_pfn(nid);
244 		if (end_pfn < node_end)
245 			end_pfn = node_end;
246 	}
247 	/* scan 0 to max_pfn */
248 	ret = walk_system_ram_range(0, end_pfn, list, kclist_add_private);
249 	if (ret)
250 		return -ENOMEM;
251 	return 0;
252 }
253 #endif /* CONFIG_HIGHMEM */
254 
255 static int kcore_update_ram(void)
256 {
257 	LIST_HEAD(list);
258 	LIST_HEAD(garbage);
259 	int nphdr;
260 	size_t phdrs_len, notes_len, data_offset;
261 	struct kcore_list *tmp, *pos;
262 	int ret = 0;
263 
264 	down_write(&kclist_lock);
265 	if (!xchg(&kcore_need_update, 0))
266 		goto out;
267 
268 	ret = kcore_ram_list(&list);
269 	if (ret) {
270 		/* Couldn't get the RAM list, try again next time. */
271 		WRITE_ONCE(kcore_need_update, 1);
272 		list_splice_tail(&list, &garbage);
273 		goto out;
274 	}
275 
276 	list_for_each_entry_safe(pos, tmp, &kclist_head, list) {
277 		if (pos->type == KCORE_RAM || pos->type == KCORE_VMEMMAP)
278 			list_move(&pos->list, &garbage);
279 	}
280 	list_splice_tail(&list, &kclist_head);
281 
282 	proc_root_kcore->size = get_kcore_size(&nphdr, &phdrs_len, &notes_len,
283 					       &data_offset);
284 
285 out:
286 	up_write(&kclist_lock);
287 	list_for_each_entry_safe(pos, tmp, &garbage, list) {
288 		list_del(&pos->list);
289 		kfree(pos);
290 	}
291 	return ret;
292 }
293 
294 static void append_kcore_note(char *notes, size_t *i, const char *name,
295 			      unsigned int type, const void *desc,
296 			      size_t descsz)
297 {
298 	struct elf_note *note = (struct elf_note *)&notes[*i];
299 
300 	note->n_namesz = strlen(name) + 1;
301 	note->n_descsz = descsz;
302 	note->n_type = type;
303 	*i += sizeof(*note);
304 	memcpy(&notes[*i], name, note->n_namesz);
305 	*i = ALIGN(*i + note->n_namesz, 4);
306 	memcpy(&notes[*i], desc, descsz);
307 	*i = ALIGN(*i + descsz, 4);
308 }
309 
310 static ssize_t
311 read_kcore(struct file *file, char __user *buffer, size_t buflen, loff_t *fpos)
312 {
313 	char *buf = file->private_data;
314 	size_t phdrs_offset, notes_offset, data_offset;
315 	size_t page_offline_frozen = 1;
316 	size_t phdrs_len, notes_len;
317 	struct kcore_list *m;
318 	size_t tsz;
319 	int nphdr;
320 	unsigned long start;
321 	size_t orig_buflen = buflen;
322 	int ret = 0;
323 
324 	down_read(&kclist_lock);
325 	/*
326 	 * Don't race against drivers that set PageOffline() and expect no
327 	 * further page access.
328 	 */
329 	page_offline_freeze();
330 
331 	get_kcore_size(&nphdr, &phdrs_len, &notes_len, &data_offset);
332 	phdrs_offset = sizeof(struct elfhdr);
333 	notes_offset = phdrs_offset + phdrs_len;
334 
335 	/* ELF file header. */
336 	if (buflen && *fpos < sizeof(struct elfhdr)) {
337 		struct elfhdr ehdr = {
338 			.e_ident = {
339 				[EI_MAG0] = ELFMAG0,
340 				[EI_MAG1] = ELFMAG1,
341 				[EI_MAG2] = ELFMAG2,
342 				[EI_MAG3] = ELFMAG3,
343 				[EI_CLASS] = ELF_CLASS,
344 				[EI_DATA] = ELF_DATA,
345 				[EI_VERSION] = EV_CURRENT,
346 				[EI_OSABI] = ELF_OSABI,
347 			},
348 			.e_type = ET_CORE,
349 			.e_machine = ELF_ARCH,
350 			.e_version = EV_CURRENT,
351 			.e_phoff = sizeof(struct elfhdr),
352 			.e_flags = ELF_CORE_EFLAGS,
353 			.e_ehsize = sizeof(struct elfhdr),
354 			.e_phentsize = sizeof(struct elf_phdr),
355 			.e_phnum = nphdr,
356 		};
357 
358 		tsz = min_t(size_t, buflen, sizeof(struct elfhdr) - *fpos);
359 		if (copy_to_user(buffer, (char *)&ehdr + *fpos, tsz)) {
360 			ret = -EFAULT;
361 			goto out;
362 		}
363 
364 		buffer += tsz;
365 		buflen -= tsz;
366 		*fpos += tsz;
367 	}
368 
369 	/* ELF program headers. */
370 	if (buflen && *fpos < phdrs_offset + phdrs_len) {
371 		struct elf_phdr *phdrs, *phdr;
372 
373 		phdrs = kzalloc(phdrs_len, GFP_KERNEL);
374 		if (!phdrs) {
375 			ret = -ENOMEM;
376 			goto out;
377 		}
378 
379 		phdrs[0].p_type = PT_NOTE;
380 		phdrs[0].p_offset = notes_offset;
381 		phdrs[0].p_filesz = notes_len;
382 
383 		phdr = &phdrs[1];
384 		list_for_each_entry(m, &kclist_head, list) {
385 			phdr->p_type = PT_LOAD;
386 			phdr->p_flags = PF_R | PF_W | PF_X;
387 			phdr->p_offset = kc_vaddr_to_offset(m->addr) + data_offset;
388 			phdr->p_vaddr = (size_t)m->addr;
389 			if (m->type == KCORE_RAM)
390 				phdr->p_paddr = __pa(m->addr);
391 			else if (m->type == KCORE_TEXT)
392 				phdr->p_paddr = __pa_symbol(m->addr);
393 			else
394 				phdr->p_paddr = (elf_addr_t)-1;
395 			phdr->p_filesz = phdr->p_memsz = m->size;
396 			phdr->p_align = PAGE_SIZE;
397 			phdr++;
398 		}
399 
400 		tsz = min_t(size_t, buflen, phdrs_offset + phdrs_len - *fpos);
401 		if (copy_to_user(buffer, (char *)phdrs + *fpos - phdrs_offset,
402 				 tsz)) {
403 			kfree(phdrs);
404 			ret = -EFAULT;
405 			goto out;
406 		}
407 		kfree(phdrs);
408 
409 		buffer += tsz;
410 		buflen -= tsz;
411 		*fpos += tsz;
412 	}
413 
414 	/* ELF note segment. */
415 	if (buflen && *fpos < notes_offset + notes_len) {
416 		struct elf_prstatus prstatus = {};
417 		struct elf_prpsinfo prpsinfo = {
418 			.pr_sname = 'R',
419 			.pr_fname = "vmlinux",
420 		};
421 		char *notes;
422 		size_t i = 0;
423 
424 		strlcpy(prpsinfo.pr_psargs, saved_command_line,
425 			sizeof(prpsinfo.pr_psargs));
426 
427 		notes = kzalloc(notes_len, GFP_KERNEL);
428 		if (!notes) {
429 			ret = -ENOMEM;
430 			goto out;
431 		}
432 
433 		append_kcore_note(notes, &i, CORE_STR, NT_PRSTATUS, &prstatus,
434 				  sizeof(prstatus));
435 		append_kcore_note(notes, &i, CORE_STR, NT_PRPSINFO, &prpsinfo,
436 				  sizeof(prpsinfo));
437 		append_kcore_note(notes, &i, CORE_STR, NT_TASKSTRUCT, current,
438 				  arch_task_struct_size);
439 		/*
440 		 * vmcoreinfo_size is mostly constant after init time, but it
441 		 * can be changed by crash_save_vmcoreinfo(). Racing here with a
442 		 * panic on another CPU before the machine goes down is insanely
443 		 * unlikely, but it's better to not leave potential buffer
444 		 * overflows lying around, regardless.
445 		 */
446 		append_kcore_note(notes, &i, VMCOREINFO_NOTE_NAME, 0,
447 				  vmcoreinfo_data,
448 				  min(vmcoreinfo_size, notes_len - i));
449 
450 		tsz = min_t(size_t, buflen, notes_offset + notes_len - *fpos);
451 		if (copy_to_user(buffer, notes + *fpos - notes_offset, tsz)) {
452 			kfree(notes);
453 			ret = -EFAULT;
454 			goto out;
455 		}
456 		kfree(notes);
457 
458 		buffer += tsz;
459 		buflen -= tsz;
460 		*fpos += tsz;
461 	}
462 
463 	/*
464 	 * Check to see if our file offset matches with any of
465 	 * the addresses in the elf_phdr on our list.
466 	 */
467 	start = kc_offset_to_vaddr(*fpos - data_offset);
468 	if ((tsz = (PAGE_SIZE - (start & ~PAGE_MASK))) > buflen)
469 		tsz = buflen;
470 
471 	m = NULL;
472 	while (buflen) {
473 		struct page *page;
474 		unsigned long pfn;
475 
476 		/*
477 		 * If this is the first iteration or the address is not within
478 		 * the previous entry, search for a matching entry.
479 		 */
480 		if (!m || start < m->addr || start >= m->addr + m->size) {
481 			struct kcore_list *iter;
482 
483 			m = NULL;
484 			list_for_each_entry(iter, &kclist_head, list) {
485 				if (start >= iter->addr &&
486 				    start < iter->addr + iter->size) {
487 					m = iter;
488 					break;
489 				}
490 			}
491 		}
492 
493 		if (page_offline_frozen++ % MAX_ORDER_NR_PAGES == 0) {
494 			page_offline_thaw();
495 			cond_resched();
496 			page_offline_freeze();
497 		}
498 
499 		if (!m) {
500 			if (clear_user(buffer, tsz)) {
501 				ret = -EFAULT;
502 				goto out;
503 			}
504 			goto skip;
505 		}
506 
507 		switch (m->type) {
508 		case KCORE_VMALLOC:
509 			vread(buf, (char *)start, tsz);
510 			/* we have to zero-fill user buffer even if no read */
511 			if (copy_to_user(buffer, buf, tsz)) {
512 				ret = -EFAULT;
513 				goto out;
514 			}
515 			break;
516 		case KCORE_USER:
517 			/* User page is handled prior to normal kernel page: */
518 			if (copy_to_user(buffer, (char *)start, tsz)) {
519 				ret = -EFAULT;
520 				goto out;
521 			}
522 			break;
523 		case KCORE_RAM:
524 			pfn = __pa(start) >> PAGE_SHIFT;
525 			page = pfn_to_online_page(pfn);
526 
527 			/*
528 			 * Don't read offline sections, logically offline pages
529 			 * (e.g., inflated in a balloon), hwpoisoned pages,
530 			 * and explicitly excluded physical ranges.
531 			 */
532 			if (!page || PageOffline(page) ||
533 			    is_page_hwpoison(page) || !pfn_is_ram(pfn)) {
534 				if (clear_user(buffer, tsz)) {
535 					ret = -EFAULT;
536 					goto out;
537 				}
538 				break;
539 			}
540 			fallthrough;
541 		case KCORE_VMEMMAP:
542 		case KCORE_TEXT:
543 			/*
544 			 * Using bounce buffer to bypass the
545 			 * hardened user copy kernel text checks.
546 			 */
547 			if (copy_from_kernel_nofault(buf, (void *)start, tsz)) {
548 				if (clear_user(buffer, tsz)) {
549 					ret = -EFAULT;
550 					goto out;
551 				}
552 			} else {
553 				if (copy_to_user(buffer, buf, tsz)) {
554 					ret = -EFAULT;
555 					goto out;
556 				}
557 			}
558 			break;
559 		default:
560 			pr_warn_once("Unhandled KCORE type: %d\n", m->type);
561 			if (clear_user(buffer, tsz)) {
562 				ret = -EFAULT;
563 				goto out;
564 			}
565 		}
566 skip:
567 		buflen -= tsz;
568 		*fpos += tsz;
569 		buffer += tsz;
570 		start += tsz;
571 		tsz = (buflen > PAGE_SIZE ? PAGE_SIZE : buflen);
572 	}
573 
574 out:
575 	page_offline_thaw();
576 	up_read(&kclist_lock);
577 	if (ret)
578 		return ret;
579 	return orig_buflen - buflen;
580 }
581 
582 static int open_kcore(struct inode *inode, struct file *filp)
583 {
584 	int ret = security_locked_down(LOCKDOWN_KCORE);
585 
586 	if (!capable(CAP_SYS_RAWIO))
587 		return -EPERM;
588 
589 	if (ret)
590 		return ret;
591 
592 	filp->private_data = kmalloc(PAGE_SIZE, GFP_KERNEL);
593 	if (!filp->private_data)
594 		return -ENOMEM;
595 
596 	if (kcore_need_update)
597 		kcore_update_ram();
598 	if (i_size_read(inode) != proc_root_kcore->size) {
599 		inode_lock(inode);
600 		i_size_write(inode, proc_root_kcore->size);
601 		inode_unlock(inode);
602 	}
603 	return 0;
604 }
605 
606 static int release_kcore(struct inode *inode, struct file *file)
607 {
608 	kfree(file->private_data);
609 	return 0;
610 }
611 
612 static const struct proc_ops kcore_proc_ops = {
613 	.proc_read	= read_kcore,
614 	.proc_open	= open_kcore,
615 	.proc_release	= release_kcore,
616 	.proc_lseek	= default_llseek,
617 };
618 
619 /* just remember that we have to update kcore */
620 static int __meminit kcore_callback(struct notifier_block *self,
621 				    unsigned long action, void *arg)
622 {
623 	switch (action) {
624 	case MEM_ONLINE:
625 	case MEM_OFFLINE:
626 		kcore_need_update = 1;
627 		break;
628 	}
629 	return NOTIFY_OK;
630 }
631 
632 
633 static struct kcore_list kcore_vmalloc;
634 
635 #ifdef CONFIG_ARCH_PROC_KCORE_TEXT
636 static struct kcore_list kcore_text;
637 /*
638  * If defined, special segment is used for mapping kernel text instead of
639  * direct-map area. We need to create special TEXT section.
640  */
641 static void __init proc_kcore_text_init(void)
642 {
643 	kclist_add(&kcore_text, _text, _end - _text, KCORE_TEXT);
644 }
645 #else
646 static void __init proc_kcore_text_init(void)
647 {
648 }
649 #endif
650 
651 #if defined(CONFIG_MODULES) && defined(MODULES_VADDR)
652 /*
653  * MODULES_VADDR has no intersection with VMALLOC_ADDR.
654  */
655 static struct kcore_list kcore_modules;
656 static void __init add_modules_range(void)
657 {
658 	if (MODULES_VADDR != VMALLOC_START && MODULES_END != VMALLOC_END) {
659 		kclist_add(&kcore_modules, (void *)MODULES_VADDR,
660 			MODULES_END - MODULES_VADDR, KCORE_VMALLOC);
661 	}
662 }
663 #else
664 static void __init add_modules_range(void)
665 {
666 }
667 #endif
668 
669 static int __init proc_kcore_init(void)
670 {
671 	proc_root_kcore = proc_create("kcore", S_IRUSR, NULL, &kcore_proc_ops);
672 	if (!proc_root_kcore) {
673 		pr_err("couldn't create /proc/kcore\n");
674 		return 0; /* Always returns 0. */
675 	}
676 	/* Store text area if it's special */
677 	proc_kcore_text_init();
678 	/* Store vmalloc area */
679 	kclist_add(&kcore_vmalloc, (void *)VMALLOC_START,
680 		VMALLOC_END - VMALLOC_START, KCORE_VMALLOC);
681 	add_modules_range();
682 	/* Store direct-map area from physical memory map */
683 	kcore_update_ram();
684 	hotplug_memory_notifier(kcore_callback, DEFAULT_CALLBACK_PRI);
685 
686 	return 0;
687 }
688 fs_initcall(proc_kcore_init);
689