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