fs/proc/kcore.c

   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/notifier.h>
  22 #include <linux/vmalloc.h>
  23 #include <linux/highmem.h>
  24 #include <linux/printk.h>
  25 #include <linux/bootmem.h>
  26 #include <linux/init.h>
  27 #include <linux/slab.h>
  28 #include <linux/uaccess.h>
  29 #include <asm/io.h>
  30 #include <linux/list.h>
  31 #include <linux/ioport.h>
  32 #include <linux/memory.h>
  33 #include <linux/sched/task.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         if (!memmap_valid_within(pfn, p, page_zone(p)))
 196                 return 1;
 197
 198         ent = kmalloc(sizeof(*ent), GFP_KERNEL);
 199         if (!ent)
 200                 return -ENOMEM;
 201         ent->addr = (unsigned long)page_to_virt(p);
 202         ent->size = nr_pages << PAGE_SHIFT;
 203
 204         if (!virt_addr_valid(ent->addr))
 205                 goto free_out;
 206
 207         /* cut not-mapped area. ....from ppc-32 code. */
 208         if (ULONG_MAX - ent->addr < ent->size)
 209                 ent->size = ULONG_MAX - ent->addr;
 210
 211         /*
 212          * We've already checked virt_addr_valid so we know this address
 213          * is a valid pointer, therefore we can check against it to determine
 214          * if we need to trim
 215          */
 216         if (VMALLOC_START > ent->addr) {
 217                 if (VMALLOC_START - ent->addr < ent->size)
 218                         ent->size = VMALLOC_START - ent->addr;
 219         }
 220
 221         ent->type = KCORE_RAM;
 222         list_add_tail(&ent->list, head);
 223
 224         if (!get_sparsemem_vmemmap_info(ent, head)) {
 225                 list_del(&ent->list);
 226                 goto free_out;
 227         }
 228
 229         return 0;
 230 free_out:
 231         kfree(ent);
 232         return 1;
 233 }
 234
 235 static int kcore_ram_list(struct list_head *list)
 236 {
 237         int nid, ret;
 238         unsigned long end_pfn;
 239
 240         /* Not inialized....update now */
 241         /* find out "max pfn" */
 242         end_pfn = 0;
 243         for_each_node_state(nid, N_MEMORY) {
 244                 unsigned long node_end;
 245                 node_end = node_end_pfn(nid);
 246                 if (end_pfn < node_end)
 247                         end_pfn = node_end;
 248         }
 249         /* scan 0 to max_pfn */
 250         ret = walk_system_ram_range(0, end_pfn, list, kclist_add_private);
 251         if (ret)
 252                 return -ENOMEM;
 253         return 0;
 254 }
 255 #endif /* CONFIG_HIGHMEM */
 256
 257 static int kcore_update_ram(void)
 258 {
 259         LIST_HEAD(list);
 260         LIST_HEAD(garbage);
 261         int nphdr;
 262         size_t phdrs_len, notes_len, data_offset;
 263         struct kcore_list *tmp, *pos;
 264         int ret = 0;
 265
 266         down_write(&kclist_lock);
 267         if (!xchg(&kcore_need_update, 0))
 268                 goto out;
 269
 270         ret = kcore_ram_list(&list);
 271         if (ret) {
 272                 /* Couldn't get the RAM list, try again next time. */
 273                 WRITE_ONCE(kcore_need_update, 1);
 274                 list_splice_tail(&list, &garbage);
 275                 goto out;
 276         }
 277
 278         list_for_each_entry_safe(pos, tmp, &kclist_head, list) {
 279                 if (pos->type == KCORE_RAM || pos->type == KCORE_VMEMMAP)
 280                         list_move(&pos->list, &garbage);
 281         }
 282         list_splice_tail(&list, &kclist_head);
 283
 284         proc_root_kcore->size = get_kcore_size(&nphdr, &phdrs_len, &notes_len,
 285                                                &data_offset);
 286
 287 out:
 288         up_write(&kclist_lock);
 289         list_for_each_entry_safe(pos, tmp, &garbage, list) {
 290                 list_del(&pos->list);
 291                 kfree(pos);
 292         }
 293         return ret;
 294 }
 295
 296 static void append_kcore_note(char *notes, size_t *i, const char *name,
 297                               unsigned int type, const void *desc,
 298                               size_t descsz)
 299 {
 300         struct elf_note *note = (struct elf_note *)&notes[*i];
 301
 302         note->n_namesz = strlen(name) + 1;
 303         note->n_descsz = descsz;
 304         note->n_type = type;
 305         *i += sizeof(*note);
 306         memcpy(&notes[*i], name, note->n_namesz);
 307         *i = ALIGN(*i + note->n_namesz, 4);
 308         memcpy(&notes[*i], desc, descsz);
 309         *i = ALIGN(*i + descsz, 4);
 310 }
 311
 312 static ssize_t
 313 read_kcore(struct file *file, char __user *buffer, size_t buflen, loff_t *fpos)
 314 {
 315         char *buf = file->private_data;
 316         size_t phdrs_offset, notes_offset, data_offset;
 317         size_t phdrs_len, notes_len;
 318         struct kcore_list *m;
 319         size_t tsz;
 320         int nphdr;
 321         unsigned long start;
 322         size_t orig_buflen = buflen;
 323         int ret = 0;
 324
 325         down_read(&kclist_lock);
 326
 327         get_kcore_size(&nphdr, &phdrs_len, &notes_len, &data_offset);
 328         phdrs_offset = sizeof(struct elfhdr);
 329         notes_offset = phdrs_offset + phdrs_len;
 330
 331         /* ELF file header. */
 332         if (buflen && *fpos < sizeof(struct elfhdr)) {
 333                 struct elfhdr ehdr = {
 334                         .e_ident = {
 335                                 [EI_MAG0] = ELFMAG0,
 336                                 [EI_MAG1] = ELFMAG1,
 337                                 [EI_MAG2] = ELFMAG2,
 338                                 [EI_MAG3] = ELFMAG3,
 339                                 [EI_CLASS] = ELF_CLASS,
 340                                 [EI_DATA] = ELF_DATA,
 341                                 [EI_VERSION] = EV_CURRENT,
 342                                 [EI_OSABI] = ELF_OSABI,
 343                         },
 344                         .e_type = ET_CORE,
 345                         .e_machine = ELF_ARCH,
 346                         .e_version = EV_CURRENT,
 347                         .e_phoff = sizeof(struct elfhdr),
 348                         .e_flags = ELF_CORE_EFLAGS,
 349                         .e_ehsize = sizeof(struct elfhdr),
 350                         .e_phentsize = sizeof(struct elf_phdr),
 351                         .e_phnum = nphdr,
 352                 };
 353
 354                 tsz = min_t(size_t, buflen, sizeof(struct elfhdr) - *fpos);
 355                 if (copy_to_user(buffer, (char *)&ehdr + *fpos, tsz)) {
 356                         ret = -EFAULT;
 357                         goto out;
 358                 }
 359
 360                 buffer += tsz;
 361                 buflen -= tsz;
 362                 *fpos += tsz;
 363         }
 364
 365         /* ELF program headers. */
 366         if (buflen && *fpos < phdrs_offset + phdrs_len) {
 367                 struct elf_phdr *phdrs, *phdr;
 368
 369                 phdrs = kzalloc(phdrs_len, GFP_KERNEL);
 370                 if (!phdrs) {
 371                         ret = -ENOMEM;
 372                         goto out;
 373                 }
 374
 375                 phdrs[0].p_type = PT_NOTE;
 376                 phdrs[0].p_offset = notes_offset;
 377                 phdrs[0].p_filesz = notes_len;
 378
 379                 phdr = &phdrs[1];
 380                 list_for_each_entry(m, &kclist_head, list) {
 381                         phdr->p_type = PT_LOAD;
 382                         phdr->p_flags = PF_R | PF_W | PF_X;
 383                         phdr->p_offset = kc_vaddr_to_offset(m->addr) + data_offset;
 384                         if (m->type == KCORE_REMAP)
 385                                 phdr->p_vaddr = (size_t)m->vaddr;
 386                         else
 387                                 phdr->p_vaddr = (size_t)m->addr;
 388                         if (m->type == KCORE_RAM || m->type == KCORE_REMAP)
 389                                 phdr->p_paddr = __pa(m->addr);
 390                         else if (m->type == KCORE_TEXT)
 391                                 phdr->p_paddr = __pa_symbol(m->addr);
 392                         else
 393                                 phdr->p_paddr = (elf_addr_t)-1;
 394                         phdr->p_filesz = phdr->p_memsz = m->size;
 395                         phdr->p_align = PAGE_SIZE;
 396                         phdr++;
 397                 }
 398
 399                 tsz = min_t(size_t, buflen, phdrs_offset + phdrs_len - *fpos);
 400                 if (copy_to_user(buffer, (char *)phdrs + *fpos - phdrs_offset,
 401                                  tsz)) {
 402                         kfree(phdrs);
 403                         ret = -EFAULT;
 404                         goto out;
 405                 }
 406                 kfree(phdrs);
 407
 408                 buffer += tsz;
 409                 buflen -= tsz;
 410                 *fpos += tsz;
 411         }
 412
 413         /* ELF note segment. */
 414         if (buflen && *fpos < notes_offset + notes_len) {
 415                 struct elf_prstatus prstatus = {};
 416                 struct elf_prpsinfo prpsinfo = {
 417                         .pr_sname = 'R',
 418                         .pr_fname = "vmlinux",
 419                 };
 420                 char *notes;
 421                 size_t i = 0;
 422
 423                 strlcpy(prpsinfo.pr_psargs, saved_command_line,
 424                         sizeof(prpsinfo.pr_psargs));
 425
 426                 notes = kzalloc(notes_len, GFP_KERNEL);
 427                 if (!notes) {
 428                         ret = -ENOMEM;
 429                         goto out;
 430                 }
 431
 432                 append_kcore_note(notes, &i, CORE_STR, NT_PRSTATUS, &prstatus,
 433                                   sizeof(prstatus));
 434                 append_kcore_note(notes, &i, CORE_STR, NT_PRPSINFO, &prpsinfo,
 435                                   sizeof(prpsinfo));
 436                 append_kcore_note(notes, &i, CORE_STR, NT_TASKSTRUCT, current,
 437                                   arch_task_struct_size);
 438                 /*
 439                  * vmcoreinfo_size is mostly constant after init time, but it
 440                  * can be changed by crash_save_vmcoreinfo(). Racing here with a
 441                  * panic on another CPU before the machine goes down is insanely
 442                  * unlikely, but it's better to not leave potential buffer
 443                  * overflows lying around, regardless.
 444                  */
 445                 append_kcore_note(notes, &i, VMCOREINFO_NOTE_NAME, 0,
 446                                   vmcoreinfo_data,
 447                                   min(vmcoreinfo_size, notes_len - i));
 448
 449                 tsz = min_t(size_t, buflen, notes_offset + notes_len - *fpos);
 450                 if (copy_to_user(buffer, notes + *fpos - notes_offset, tsz)) {
 451                         kfree(notes);
 452                         ret = -EFAULT;
 453                         goto out;
 454                 }
 455                 kfree(notes);
 456
 457                 buffer += tsz;
 458                 buflen -= tsz;
 459                 *fpos += tsz;
 460         }
 461
 462         /*
 463          * Check to see if our file offset matches with any of
 464          * the addresses in the elf_phdr on our list.
 465          */
 466         start = kc_offset_to_vaddr(*fpos - data_offset);
 467         if ((tsz = (PAGE_SIZE - (start & ~PAGE_MASK))) > buflen)
 468                 tsz = buflen;
 469
 470         m = NULL;
 471         while (buflen) {
 472                 /*
 473                  * If this is the first iteration or the address is not within
 474                  * the previous entry, search for a matching entry.
 475                  */
 476                 if (!m || start < m->addr || start >= m->addr + m->size) {
 477                         list_for_each_entry(m, &kclist_head, list) {
 478                                 if (start >= m->addr &&
 479                                     start < m->addr + m->size)
 480                                         break;
 481                         }
 482                 }
 483
 484                 if (&m->list == &kclist_head) {
 485                         if (clear_user(buffer, tsz)) {
 486                                 ret = -EFAULT;
 487                                 goto out;
 488                         }
 489                         m = NULL;       /* skip the list anchor */
 490                 } else if (!pfn_is_ram(__pa(start) >> PAGE_SHIFT)) {
 491                         if (clear_user(buffer, tsz)) {
 492                                 ret = -EFAULT;
 493                                 goto out;
 494                         }
 495                 } else if (m->type == KCORE_VMALLOC) {
 496                         vread(buf, (char *)start, tsz);
 497                         /* we have to zero-fill user buffer even if no read */
 498                         if (copy_to_user(buffer, buf, tsz)) {
 499                                 ret = -EFAULT;
 500                                 goto out;
 501                         }
 502                 } else if (m->type == KCORE_USER) {
 503                         /* User page is handled prior to normal kernel page: */
 504                         if (copy_to_user(buffer, (char *)start, tsz)) {
 505                                 ret = -EFAULT;
 506                                 goto out;
 507                         }
 508                 } else {
 509                         if (kern_addr_valid(start)) {
 510                                 /*
 511                                  * Using bounce buffer to bypass the
 512                                  * hardened user copy kernel text checks.
 513                                  */
 514                                 if (probe_kernel_read(buf, (void *) start, tsz)) {
 515                                         if (clear_user(buffer, tsz)) {
 516                                                 ret = -EFAULT;
 517                                                 goto out;
 518                                         }
 519                                 } else {
 520                                         if (copy_to_user(buffer, buf, tsz)) {
 521                                                 ret = -EFAULT;
 522                                                 goto out;
 523                                         }
 524                                 }
 525                         } else {
 526                                 if (clear_user(buffer, tsz)) {
 527                                         ret = -EFAULT;
 528                                         goto out;
 529                                 }
 530                         }
 531                 }
 532                 buflen -= tsz;
 533                 *fpos += tsz;
 534                 buffer += tsz;
 535                 start += tsz;
 536                 tsz = (buflen > PAGE_SIZE ? PAGE_SIZE : buflen);
 537         }
 538
 539 out:
 540         up_read(&kclist_lock);
 541         if (ret)
 542                 return ret;
 543         return orig_buflen - buflen;
 544 }
 545
 546 static int open_kcore(struct inode *inode, struct file *filp)
 547 {
 548         if (!capable(CAP_SYS_RAWIO))
 549                 return -EPERM;
 550
 551         filp->private_data = kmalloc(PAGE_SIZE, GFP_KERNEL);
 552         if (!filp->private_data)
 553                 return -ENOMEM;
 554
 555         if (kcore_need_update)
 556                 kcore_update_ram();
 557         if (i_size_read(inode) != proc_root_kcore->size) {
 558                 inode_lock(inode);
 559                 i_size_write(inode, proc_root_kcore->size);
 560                 inode_unlock(inode);
 561         }
 562         return 0;
 563 }
 564
 565 static int release_kcore(struct inode *inode, struct file *file)
 566 {
 567         kfree(file->private_data);
 568         return 0;
 569 }
 570
 571 static const struct file_operations proc_kcore_operations = {
 572         .read           = read_kcore,
 573         .open           = open_kcore,
 574         .release        = release_kcore,
 575         .llseek         = default_llseek,
 576 };
 577
 578 /* just remember that we have to update kcore */
 579 static int __meminit kcore_callback(struct notifier_block *self,
 580                                     unsigned long action, void *arg)
 581 {
 582         switch (action) {
 583         case MEM_ONLINE:
 584         case MEM_OFFLINE:
 585                 kcore_need_update = 1;
 586                 break;
 587         }
 588         return NOTIFY_OK;
 589 }
 590
 591 static struct notifier_block kcore_callback_nb __meminitdata = {
 592         .notifier_call = kcore_callback,
 593         .priority = 0,
 594 };
 595
 596 static struct kcore_list kcore_vmalloc;
 597
 598 #ifdef CONFIG_ARCH_PROC_KCORE_TEXT
 599 static struct kcore_list kcore_text;
 600 /*
 601  * If defined, special segment is used for mapping kernel text instead of
 602  * direct-map area. We need to create special TEXT section.
 603  */
 604 static void __init proc_kcore_text_init(void)
 605 {
 606         kclist_add(&kcore_text, _text, _end - _text, KCORE_TEXT);
 607 }
 608 #else
 609 static void __init proc_kcore_text_init(void)
 610 {
 611 }
 612 #endif
 613
 614 #if defined(CONFIG_MODULES) && defined(MODULES_VADDR)
 615 /*
 616  * MODULES_VADDR has no intersection with VMALLOC_ADDR.
 617  */
 618 struct kcore_list kcore_modules;
 619 static void __init add_modules_range(void)
 620 {
 621         if (MODULES_VADDR != VMALLOC_START && MODULES_END != VMALLOC_END) {
 622                 kclist_add(&kcore_modules, (void *)MODULES_VADDR,
 623                         MODULES_END - MODULES_VADDR, KCORE_VMALLOC);
 624         }
 625 }
 626 #else
 627 static void __init add_modules_range(void)
 628 {
 629 }
 630 #endif
 631
 632 static int __init proc_kcore_init(void)
 633 {
 634         proc_root_kcore = proc_create("kcore", S_IRUSR, NULL,
 635                                       &proc_kcore_operations);
 636         if (!proc_root_kcore) {
 637                 pr_err("couldn't create /proc/kcore\n");
 638                 return 0; /* Always returns 0. */
 639         }
 640         /* Store text area if it's special */
 641         proc_kcore_text_init();
 642         /* Store vmalloc area */
 643         kclist_add(&kcore_vmalloc, (void *)VMALLOC_START,
 644                 VMALLOC_END - VMALLOC_START, KCORE_VMALLOC);
 645         add_modules_range();
 646         /* Store direct-map area from physical memory map */
 647         kcore_update_ram();
 648         register_hotmemory_notifier(&kcore_callback_nb);
 649
 650         return 0;
 651 }
 652 fs_initcall(proc_kcore_init);