fs/proc/kcore.c

   1 /*
   2  *      fs/proc/kcore.c kernel ELF core dumper
   3  *
   4  *      Modelled on fs/exec.c:aout_core_dump()
   5  *      Jeremy Fitzhardinge <jeremy@sw.oz.au>
   6  *      ELF version written by David Howells <David.Howells@nexor.co.uk>
   7  *      Modified and incorporated into 2.3.x by Tigran Aivazian <tigran@veritas.com>
   8  *      Support to dump vmalloc'd areas (ELF only), Tigran Aivazian <tigran@veritas.com>
   9  *      Safe accesses to vmalloc/direct-mapped discontiguous areas, Kanoj Sarcar <kanoj@sgi.com>
  10  */
  11
  12 #include <linux/mm.h>
  13 #include <linux/proc_fs.h>
  14 #include <linux/kcore.h>
  15 #include <linux/user.h>
  16 #include <linux/capability.h>
  17 #include <linux/elf.h>
  18 #include <linux/elfcore.h>
  19 #include <linux/notifier.h>
  20 #include <linux/vmalloc.h>
  21 #include <linux/highmem.h>
  22 #include <linux/printk.h>
  23 #include <linux/bootmem.h>
  24 #include <linux/init.h>
  25 #include <linux/slab.h>
  26 #include <linux/uaccess.h>
  27 #include <asm/io.h>
  28 #include <linux/list.h>
  29 #include <linux/ioport.h>
  30 #include <linux/memory.h>
  31 #include <linux/sched/task.h>
  32 #include <asm/sections.h>
  33 #include "internal.h"
  34
  35 #define CORE_STR "CORE"
  36
  37 #ifndef ELF_CORE_EFLAGS
  38 #define ELF_CORE_EFLAGS 0
  39 #endif
  40
  41 static struct proc_dir_entry *proc_root_kcore;
  42
  43
  44 #ifndef kc_vaddr_to_offset
  45 #define kc_vaddr_to_offset(v) ((v) - PAGE_OFFSET)
  46 #endif
  47 #ifndef kc_offset_to_vaddr
  48 #define kc_offset_to_vaddr(o) ((o) + PAGE_OFFSET)
  49 #endif
  50
  51 /* An ELF note in memory */
  52 struct memelfnote
  53 {
  54         const char *name;
  55         int type;
  56         unsigned int datasz;
  57         void *data;
  58 };
  59
  60 static LIST_HEAD(kclist_head);
  61 static DEFINE_RWLOCK(kclist_lock);
  62 static int kcore_need_update = 1;
  63
  64 void
  65 kclist_add(struct kcore_list *new, void *addr, size_t size, int type)
  66 {
  67         new->addr = (unsigned long)addr;
  68         new->size = size;
  69         new->type = type;
  70
  71         write_lock(&kclist_lock);
  72         list_add_tail(&new->list, &kclist_head);
  73         write_unlock(&kclist_lock);
  74 }
  75
  76 static size_t get_kcore_size(int *nphdr, size_t *elf_buflen)
  77 {
  78         size_t try, size;
  79         struct kcore_list *m;
  80
  81         *nphdr = 1; /* PT_NOTE */
  82         size = 0;
  83
  84         list_for_each_entry(m, &kclist_head, list) {
  85                 try = kc_vaddr_to_offset((size_t)m->addr + m->size);
  86                 if (try > size)
  87                         size = try;
  88                 *nphdr = *nphdr + 1;
  89         }
  90         *elf_buflen =   sizeof(struct elfhdr) +
  91                         (*nphdr + 2)*sizeof(struct elf_phdr) +
  92                         3 * ((sizeof(struct elf_note)) +
  93                              roundup(sizeof(CORE_STR), 4)) +
  94                         roundup(sizeof(struct elf_prstatus), 4) +
  95                         roundup(sizeof(struct elf_prpsinfo), 4) +
  96                         roundup(arch_task_struct_size, 4);
  97         *elf_buflen = PAGE_ALIGN(*elf_buflen);
  98         return size + *elf_buflen;
  99 }
 100
 101 static void free_kclist_ents(struct list_head *head)
 102 {
 103         struct kcore_list *tmp, *pos;
 104
 105         list_for_each_entry_safe(pos, tmp, head, list) {
 106                 list_del(&pos->list);
 107                 kfree(pos);
 108         }
 109 }
 110 /*
 111  * Replace all KCORE_RAM/KCORE_VMEMMAP information with passed list.
 112  */
 113 static void __kcore_update_ram(struct list_head *list)
 114 {
 115         int nphdr;
 116         size_t size;
 117         struct kcore_list *tmp, *pos;
 118         LIST_HEAD(garbage);
 119
 120         write_lock(&kclist_lock);
 121         if (kcore_need_update) {
 122                 list_for_each_entry_safe(pos, tmp, &kclist_head, list) {
 123                         if (pos->type == KCORE_RAM
 124                                 || pos->type == KCORE_VMEMMAP)
 125                                 list_move(&pos->list, &garbage);
 126                 }
 127                 list_splice_tail(list, &kclist_head);
 128         } else
 129                 list_splice(list, &garbage);
 130         kcore_need_update = 0;
 131         proc_root_kcore->size = get_kcore_size(&nphdr, &size);
 132         write_unlock(&kclist_lock);
 133
 134         free_kclist_ents(&garbage);
 135 }
 136
 137
 138 #ifdef CONFIG_HIGHMEM
 139 /*
 140  * If no highmem, we can assume [0...max_low_pfn) continuous range of memory
 141  * because memory hole is not as big as !HIGHMEM case.
 142  * (HIGHMEM is special because part of memory is _invisible_ from the kernel.)
 143  */
 144 static int kcore_update_ram(void)
 145 {
 146         LIST_HEAD(head);
 147         struct kcore_list *ent;
 148         int ret = 0;
 149
 150         ent = kmalloc(sizeof(*ent), GFP_KERNEL);
 151         if (!ent)
 152                 return -ENOMEM;
 153         ent->addr = (unsigned long)__va(0);
 154         ent->size = max_low_pfn << PAGE_SHIFT;
 155         ent->type = KCORE_RAM;
 156         list_add(&ent->list, &head);
 157         __kcore_update_ram(&head);
 158         return ret;
 159 }
 160
 161 #else /* !CONFIG_HIGHMEM */
 162
 163 #ifdef CONFIG_SPARSEMEM_VMEMMAP
 164 /* calculate vmemmap's address from given system ram pfn and register it */
 165 static int
 166 get_sparsemem_vmemmap_info(struct kcore_list *ent, struct list_head *head)
 167 {
 168         unsigned long pfn = __pa(ent->addr) >> PAGE_SHIFT;
 169         unsigned long nr_pages = ent->size >> PAGE_SHIFT;
 170         unsigned long start, end;
 171         struct kcore_list *vmm, *tmp;
 172
 173
 174         start = ((unsigned long)pfn_to_page(pfn)) & PAGE_MASK;
 175         end = ((unsigned long)pfn_to_page(pfn + nr_pages)) - 1;
 176         end = PAGE_ALIGN(end);
 177         /* overlap check (because we have to align page */
 178         list_for_each_entry(tmp, head, list) {
 179                 if (tmp->type != KCORE_VMEMMAP)
 180                         continue;
 181                 if (start < tmp->addr + tmp->size)
 182                         if (end > tmp->addr)
 183                                 end = tmp->addr;
 184         }
 185         if (start < end) {
 186                 vmm = kmalloc(sizeof(*vmm), GFP_KERNEL);
 187                 if (!vmm)
 188                         return 0;
 189                 vmm->addr = start;
 190                 vmm->size = end - start;
 191                 vmm->type = KCORE_VMEMMAP;
 192                 list_add_tail(&vmm->list, head);
 193         }
 194         return 1;
 195
 196 }
 197 #else
 198 static int
 199 get_sparsemem_vmemmap_info(struct kcore_list *ent, struct list_head *head)
 200 {
 201         return 1;
 202 }
 203
 204 #endif
 205
 206 static int
 207 kclist_add_private(unsigned long pfn, unsigned long nr_pages, void *arg)
 208 {
 209         struct list_head *head = (struct list_head *)arg;
 210         struct kcore_list *ent;
 211
 212         ent = kmalloc(sizeof(*ent), GFP_KERNEL);
 213         if (!ent)
 214                 return -ENOMEM;
 215         ent->addr = (unsigned long)__va((pfn << PAGE_SHIFT));
 216         ent->size = nr_pages << PAGE_SHIFT;
 217
 218         /* Sanity check: Can happen in 32bit arch...maybe */
 219         if (ent->addr < (unsigned long) __va(0))
 220                 goto free_out;
 221
 222         /* cut not-mapped area. ....from ppc-32 code. */
 223         if (ULONG_MAX - ent->addr < ent->size)
 224                 ent->size = ULONG_MAX - ent->addr;
 225
 226         /* cut when vmalloc() area is higher than direct-map area */
 227         if (VMALLOC_START > (unsigned long)__va(0)) {
 228                 if (ent->addr > VMALLOC_START)
 229                         goto free_out;
 230                 if (VMALLOC_START - ent->addr < ent->size)
 231                         ent->size = VMALLOC_START - ent->addr;
 232         }
 233
 234         ent->type = KCORE_RAM;
 235         list_add_tail(&ent->list, head);
 236
 237         if (!get_sparsemem_vmemmap_info(ent, head)) {
 238                 list_del(&ent->list);
 239                 goto free_out;
 240         }
 241
 242         return 0;
 243 free_out:
 244         kfree(ent);
 245         return 1;
 246 }
 247
 248 static int kcore_update_ram(void)
 249 {
 250         int nid, ret;
 251         unsigned long end_pfn;
 252         LIST_HEAD(head);
 253
 254         /* Not inialized....update now */
 255         /* find out "max pfn" */
 256         end_pfn = 0;
 257         for_each_node_state(nid, N_MEMORY) {
 258                 unsigned long node_end;
 259                 node_end = node_end_pfn(nid);
 260                 if (end_pfn < node_end)
 261                         end_pfn = node_end;
 262         }
 263         /* scan 0 to max_pfn */
 264         ret = walk_system_ram_range(0, end_pfn, &head, kclist_add_private);
 265         if (ret) {
 266                 free_kclist_ents(&head);
 267                 return -ENOMEM;
 268         }
 269         __kcore_update_ram(&head);
 270         return ret;
 271 }
 272 #endif /* CONFIG_HIGHMEM */
 273
 274 /*****************************************************************************/
 275 /*
 276  * determine size of ELF note
 277  */
 278 static int notesize(struct memelfnote *en)
 279 {
 280         int sz;
 281
 282         sz = sizeof(struct elf_note);
 283         sz += roundup((strlen(en->name) + 1), 4);
 284         sz += roundup(en->datasz, 4);
 285
 286         return sz;
 287 } /* end notesize() */
 288
 289 /*****************************************************************************/
 290 /*
 291  * store a note in the header buffer
 292  */
 293 static char *storenote(struct memelfnote *men, char *bufp)
 294 {
 295         struct elf_note en;
 296
 297 #define DUMP_WRITE(addr,nr) do { memcpy(bufp,addr,nr); bufp += nr; } while(0)
 298
 299         en.n_namesz = strlen(men->name) + 1;
 300         en.n_descsz = men->datasz;
 301         en.n_type = men->type;
 302
 303         DUMP_WRITE(&en, sizeof(en));
 304         DUMP_WRITE(men->name, en.n_namesz);
 305
 306         /* XXX - cast from long long to long to avoid need for libgcc.a */
 307         bufp = (char*) roundup((unsigned long)bufp,4);
 308         DUMP_WRITE(men->data, men->datasz);
 309         bufp = (char*) roundup((unsigned long)bufp,4);
 310
 311 #undef DUMP_WRITE
 312
 313         return bufp;
 314 } /* end storenote() */
 315
 316 /*
 317  * store an ELF coredump header in the supplied buffer
 318  * nphdr is the number of elf_phdr to insert
 319  */
 320 static void elf_kcore_store_hdr(char *bufp, int nphdr, int dataoff)
 321 {
 322         struct elf_prstatus prstatus;   /* NT_PRSTATUS */
 323         struct elf_prpsinfo prpsinfo;   /* NT_PRPSINFO */
 324         struct elf_phdr *nhdr, *phdr;
 325         struct elfhdr *elf;
 326         struct memelfnote notes[3];
 327         off_t offset = 0;
 328         struct kcore_list *m;
 329
 330         /* setup ELF header */
 331         elf = (struct elfhdr *) bufp;
 332         bufp += sizeof(struct elfhdr);
 333         offset += sizeof(struct elfhdr);
 334         memcpy(elf->e_ident, ELFMAG, SELFMAG);
 335         elf->e_ident[EI_CLASS]  = ELF_CLASS;
 336         elf->e_ident[EI_DATA]   = ELF_DATA;
 337         elf->e_ident[EI_VERSION]= EV_CURRENT;
 338         elf->e_ident[EI_OSABI] = ELF_OSABI;
 339         memset(elf->e_ident+EI_PAD, 0, EI_NIDENT-EI_PAD);
 340         elf->e_type     = ET_CORE;
 341         elf->e_machine  = ELF_ARCH;
 342         elf->e_version  = EV_CURRENT;
 343         elf->e_entry    = 0;
 344         elf->e_phoff    = sizeof(struct elfhdr);
 345         elf->e_shoff    = 0;
 346         elf->e_flags    = ELF_CORE_EFLAGS;
 347         elf->e_ehsize   = sizeof(struct elfhdr);
 348         elf->e_phentsize= sizeof(struct elf_phdr);
 349         elf->e_phnum    = nphdr;
 350         elf->e_shentsize= 0;
 351         elf->e_shnum    = 0;
 352         elf->e_shstrndx = 0;
 353
 354         /* setup ELF PT_NOTE program header */
 355         nhdr = (struct elf_phdr *) bufp;
 356         bufp += sizeof(struct elf_phdr);
 357         offset += sizeof(struct elf_phdr);
 358         nhdr->p_type    = PT_NOTE;
 359         nhdr->p_offset  = 0;
 360         nhdr->p_vaddr   = 0;
 361         nhdr->p_paddr   = 0;
 362         nhdr->p_filesz  = 0;
 363         nhdr->p_memsz   = 0;
 364         nhdr->p_flags   = 0;
 365         nhdr->p_align   = 0;
 366
 367         /* setup ELF PT_LOAD program header for every area */
 368         list_for_each_entry(m, &kclist_head, list) {
 369                 phdr = (struct elf_phdr *) bufp;
 370                 bufp += sizeof(struct elf_phdr);
 371                 offset += sizeof(struct elf_phdr);
 372
 373                 phdr->p_type    = PT_LOAD;
 374                 phdr->p_flags   = PF_R|PF_W|PF_X;
 375                 phdr->p_offset  = kc_vaddr_to_offset(m->addr) + dataoff;
 376                 phdr->p_vaddr   = (size_t)m->addr;
 377                 if (m->type == KCORE_RAM || m->type == KCORE_TEXT)
 378                         phdr->p_paddr   = __pa(m->addr);
 379                 else
 380                         phdr->p_paddr   = (elf_addr_t)-1;
 381                 phdr->p_filesz  = phdr->p_memsz = m->size;
 382                 phdr->p_align   = PAGE_SIZE;
 383         }
 384
 385         /*
 386          * Set up the notes in similar form to SVR4 core dumps made
 387          * with info from their /proc.
 388          */
 389         nhdr->p_offset  = offset;
 390
 391         /* set up the process status */
 392         notes[0].name = CORE_STR;
 393         notes[0].type = NT_PRSTATUS;
 394         notes[0].datasz = sizeof(struct elf_prstatus);
 395         notes[0].data = &prstatus;
 396
 397         memset(&prstatus, 0, sizeof(struct elf_prstatus));
 398
 399         nhdr->p_filesz  = notesize(&notes[0]);
 400         bufp = storenote(&notes[0], bufp);
 401
 402         /* set up the process info */
 403         notes[1].name   = CORE_STR;
 404         notes[1].type   = NT_PRPSINFO;
 405         notes[1].datasz = sizeof(struct elf_prpsinfo);
 406         notes[1].data   = &prpsinfo;
 407
 408         memset(&prpsinfo, 0, sizeof(struct elf_prpsinfo));
 409         prpsinfo.pr_state       = 0;
 410         prpsinfo.pr_sname       = 'R';
 411         prpsinfo.pr_zomb        = 0;
 412
 413         strcpy(prpsinfo.pr_fname, "vmlinux");
 414         strlcpy(prpsinfo.pr_psargs, saved_command_line, sizeof(prpsinfo.pr_psargs));
 415
 416         nhdr->p_filesz  += notesize(&notes[1]);
 417         bufp = storenote(&notes[1], bufp);
 418
 419         /* set up the task structure */
 420         notes[2].name   = CORE_STR;
 421         notes[2].type   = NT_TASKSTRUCT;
 422         notes[2].datasz = arch_task_struct_size;
 423         notes[2].data   = current;
 424
 425         nhdr->p_filesz  += notesize(&notes[2]);
 426         bufp = storenote(&notes[2], bufp);
 427
 428 } /* end elf_kcore_store_hdr() */
 429
 430 /*****************************************************************************/
 431 /*
 432  * read from the ELF header and then kernel memory
 433  */
 434 static ssize_t
 435 read_kcore(struct file *file, char __user *buffer, size_t buflen, loff_t *fpos)
 436 {
 437         char *buf = file->private_data;
 438         ssize_t acc = 0;
 439         size_t size, tsz;
 440         size_t elf_buflen;
 441         int nphdr;
 442         unsigned long start;
 443
 444         read_lock(&kclist_lock);
 445         size = get_kcore_size(&nphdr, &elf_buflen);
 446
 447         if (buflen == 0 || *fpos >= size) {
 448                 read_unlock(&kclist_lock);
 449                 return 0;
 450         }
 451
 452         /* trim buflen to not go beyond EOF */
 453         if (buflen > size - *fpos)
 454                 buflen = size - *fpos;
 455
 456         /* construct an ELF core header if we'll need some of it */
 457         if (*fpos < elf_buflen) {
 458                 char * elf_buf;
 459
 460                 tsz = elf_buflen - *fpos;
 461                 if (buflen < tsz)
 462                         tsz = buflen;
 463                 elf_buf = kzalloc(elf_buflen, GFP_ATOMIC);
 464                 if (!elf_buf) {
 465                         read_unlock(&kclist_lock);
 466                         return -ENOMEM;
 467                 }
 468                 elf_kcore_store_hdr(elf_buf, nphdr, elf_buflen);
 469                 read_unlock(&kclist_lock);
 470                 if (copy_to_user(buffer, elf_buf + *fpos, tsz)) {
 471                         kfree(elf_buf);
 472                         return -EFAULT;
 473                 }
 474                 kfree(elf_buf);
 475                 buflen -= tsz;
 476                 *fpos += tsz;
 477                 buffer += tsz;
 478                 acc += tsz;
 479
 480                 /* leave now if filled buffer already */
 481                 if (buflen == 0)
 482                         return acc;
 483         } else
 484                 read_unlock(&kclist_lock);
 485
 486         /*
 487          * Check to see if our file offset matches with any of
 488          * the addresses in the elf_phdr on our list.
 489          */
 490         start = kc_offset_to_vaddr(*fpos - elf_buflen);
 491         if ((tsz = (PAGE_SIZE - (start & ~PAGE_MASK))) > buflen)
 492                 tsz = buflen;
 493
 494         while (buflen) {
 495                 struct kcore_list *m;
 496
 497                 read_lock(&kclist_lock);
 498                 list_for_each_entry(m, &kclist_head, list) {
 499                         if (start >= m->addr && start < (m->addr+m->size))
 500                                 break;
 501                 }
 502                 read_unlock(&kclist_lock);
 503
 504                 if (&m->list == &kclist_head) {
 505                         if (clear_user(buffer, tsz))
 506                                 return -EFAULT;
 507                 } else if (m->type == KCORE_VMALLOC) {
 508                         vread(buf, (char *)start, tsz);
 509                         /* we have to zero-fill user buffer even if no read */
 510                         if (copy_to_user(buffer, buf, tsz))
 511                                 return -EFAULT;
 512                 } else {
 513                         if (kern_addr_valid(start)) {
 514                                 unsigned long n;
 515
 516                                 /*
 517                                  * Using bounce buffer to bypass the
 518                                  * hardened user copy kernel text checks.
 519                                  */
 520                                 memcpy(buf, (char *) start, tsz);
 521                                 n = copy_to_user(buffer, buf, tsz);
 522                                 /*
 523                                  * We cannot distinguish between fault on source
 524                                  * and fault on destination. When this happens
 525                                  * we clear too and hope it will trigger the
 526                                  * EFAULT again.
 527                                  */
 528                                 if (n) {
 529                                         if (clear_user(buffer + tsz - n,
 530                                                                 n))
 531                                                 return -EFAULT;
 532                                 }
 533                         } else {
 534                                 if (clear_user(buffer, tsz))
 535                                         return -EFAULT;
 536                         }
 537                 }
 538                 buflen -= tsz;
 539                 *fpos += tsz;
 540                 buffer += tsz;
 541                 acc += tsz;
 542                 start += tsz;
 543                 tsz = (buflen > PAGE_SIZE ? PAGE_SIZE : buflen);
 544         }
 545
 546         return acc;
 547 }
 548
 549
 550 static int open_kcore(struct inode *inode, struct file *filp)
 551 {
 552         if (!capable(CAP_SYS_RAWIO))
 553                 return -EPERM;
 554
 555         filp->private_data = kmalloc(PAGE_SIZE, GFP_KERNEL);
 556         if (!filp->private_data)
 557                 return -ENOMEM;
 558
 559         if (kcore_need_update)
 560                 kcore_update_ram();
 561         if (i_size_read(inode) != proc_root_kcore->size) {
 562                 inode_lock(inode);
 563                 i_size_write(inode, proc_root_kcore->size);
 564                 inode_unlock(inode);
 565         }
 566         return 0;
 567 }
 568
 569 static int release_kcore(struct inode *inode, struct file *file)
 570 {
 571         kfree(file->private_data);
 572         return 0;
 573 }
 574
 575 static const struct file_operations proc_kcore_operations = {
 576         .read           = read_kcore,
 577         .open           = open_kcore,
 578         .release        = release_kcore,
 579         .llseek         = default_llseek,
 580 };
 581
 582 /* just remember that we have to update kcore */
 583 static int __meminit kcore_callback(struct notifier_block *self,
 584                                     unsigned long action, void *arg)
 585 {
 586         switch (action) {
 587         case MEM_ONLINE:
 588         case MEM_OFFLINE:
 589                 write_lock(&kclist_lock);
 590                 kcore_need_update = 1;
 591                 write_unlock(&kclist_lock);
 592         }
 593         return NOTIFY_OK;
 594 }
 595
 596 static struct notifier_block kcore_callback_nb __meminitdata = {
 597         .notifier_call = kcore_callback,
 598         .priority = 0,
 599 };
 600
 601 static struct kcore_list kcore_vmalloc;
 602
 603 #ifdef CONFIG_ARCH_PROC_KCORE_TEXT
 604 static struct kcore_list kcore_text;
 605 /*
 606  * If defined, special segment is used for mapping kernel text instead of
 607  * direct-map area. We need to create special TEXT section.
 608  */
 609 static void __init proc_kcore_text_init(void)
 610 {
 611         kclist_add(&kcore_text, _text, _end - _text, KCORE_TEXT);
 612 }
 613 #else
 614 static void __init proc_kcore_text_init(void)
 615 {
 616 }
 617 #endif
 618
 619 #if defined(CONFIG_MODULES) && defined(MODULES_VADDR)
 620 /*
 621  * MODULES_VADDR has no intersection with VMALLOC_ADDR.
 622  */
 623 struct kcore_list kcore_modules;
 624 static void __init add_modules_range(void)
 625 {
 626         if (MODULES_VADDR != VMALLOC_START && MODULES_END != VMALLOC_END) {
 627                 kclist_add(&kcore_modules, (void *)MODULES_VADDR,
 628                         MODULES_END - MODULES_VADDR, KCORE_VMALLOC);
 629         }
 630 }
 631 #else
 632 static void __init add_modules_range(void)
 633 {
 634 }
 635 #endif
 636
 637 static int __init proc_kcore_init(void)
 638 {
 639         proc_root_kcore = proc_create("kcore", S_IRUSR, NULL,
 640                                       &proc_kcore_operations);
 641         if (!proc_root_kcore) {
 642                 pr_err("couldn't create /proc/kcore\n");
 643                 return 0; /* Always returns 0. */
 644         }
 645         /* Store text area if it's special */
 646         proc_kcore_text_init();
 647         /* Store vmalloc area */
 648         kclist_add(&kcore_vmalloc, (void *)VMALLOC_START,
 649                 VMALLOC_END - VMALLOC_START, KCORE_VMALLOC);
 650         add_modules_range();
 651         /* Store direct-map area from physical memory map */
 652         kcore_update_ram();
 653         register_hotmemory_notifier(&kcore_callback_nb);
 654
 655         return 0;
 656 }
 657 fs_initcall(proc_kcore_init);