kprobe/dbi_kprobes_deps.c

   1 /*
   2  *  Dynamic Binary Instrumentation Module based on KProbes
   3  *  modules/kprobe/dbi_kprobes_deps.h
   4  *
   5  * This program is free software; you can redistribute it and/or modify
   6  * it under the terms of the GNU General Public License as published by
   7  * the Free Software Foundation; either version 2 of the License, or
   8  * (at your option) any later version.
   9  *
  10  * This program is distributed in the hope that it will be useful,
  11  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  12  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  13  * GNU General Public License for more details.
  14  *
  15  * You should have received a copy of the GNU General Public License
  16  * along with this program; if not, write to the Free Software
  17  * Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.
  18  *
  19  * Copyright (C) Samsung Electronics, 2006-2010
  20  *
  21  * 2008-2009    Alexey Gerenkov <a.gerenkov@samsung.com> User-Space
  22  *              Probes initial implementation; Support x86/ARM/MIPS for both user and kernel spaces.
  23  * 2010         Ekaterina Gorelkina <e.gorelkina@samsung.com>: redesign module for separating core and arch parts
  24  *
  25
  26  */
  27
  28 #include <linux/module.h>
  29 #include <linux/sched.h>
  30
  31 #include <asm/pgtable.h>
  32
  33 #include "dbi_kprobes_deps.h"
  34 #include "dbi_kdebug.h"
  35
  36
  37 #include <linux/slab.h>
  38
  39 unsigned int *sched_addr;
  40 unsigned int *fork_addr;
  41
  42
  43 #define GUP_FLAGS_WRITE                  0x1
  44 #define GUP_FLAGS_FORCE                  0x2
  45 #define GUP_FLAGS_IGNORE_VMA_PERMISSIONS 0x4
  46 #define GUP_FLAGS_IGNORE_SIGKILL         0x8
  47
  48 #if LINUX_VERSION_CODE > KERNEL_VERSION(2, 6, 29)
  49 struct mm_struct* init_mm_ptr;
  50 struct mm_struct init_mm;
  51 #endif
  52
  53
  54 DECLARE_MOD_CB_DEP(kallsyms_search, unsigned long, const char *name);
  55 DECLARE_MOD_FUNC_DEP(access_process_vm, int, struct task_struct * tsk, unsigned long addr, void *buf, int len, int write);
  56 #if LINUX_VERSION_CODE == KERNEL_VERSION(2, 6, 32)
  57 DECLARE_MOD_FUNC_DEP(copy_to_user_page, void, struct vm_area_struct *vma, struct page *page, unsigned long uaddr, void *dst, const void *src, unsigned long len);
  58 #endif
  59
  60 DECLARE_MOD_FUNC_DEP(find_extend_vma, struct vm_area_struct *, struct mm_struct * mm, unsigned long addr);
  61
  62 #if LINUX_VERSION_CODE <= KERNEL_VERSION(2, 6, 30)
  63 #if LINUX_VERSION_CODE > KERNEL_VERSION(2, 6, 18)
  64 DECLARE_MOD_FUNC_DEP(handle_mm_fault, int, struct mm_struct *mm, struct vm_area_struct *vma, unsigned long address, int write_access);
  65 #endif
  66 #else
  67 DECLARE_MOD_FUNC_DEP(handle_mm_fault, int, struct mm_struct *mm, struct vm_area_struct *vma, unsigned long address, unsigned int flags);
  68 #endif /* LINUX_VERSION_CODE <= KERNEL_VERSION(2, 6, 30) */
  69
  70 DECLARE_MOD_FUNC_DEP(get_gate_vma, struct vm_area_struct *, struct task_struct *tsk);
  71
  72 #ifdef CONFIG_HUGETLB_PAGE
  73 DECLARE_MOD_FUNC_DEP(follow_hugetlb_page, int, struct mm_struct *mm, struct vm_area_struct *vma, struct page **pages, struct vm_area_struct **vmas, unsigned long *position, int *length, int i, int write);
  74 #endif
  75
  76 #ifdef  __HAVE_ARCH_GATE_AREA
  77 DECLARE_MOD_FUNC_DEP(in_gate_area, int, struct task_struct *tsk,unsigned long addr);
  78 #else
  79 DECLARE_MOD_FUNC_DEP(in_gate_area_no_task, int, unsigned long addr);
  80 #endif
  81 DECLARE_MOD_FUNC_DEP(follow_page, \
  82                 struct page *, struct vm_area_struct * vma, \
  83                 unsigned long address, unsigned int foll_flags);
  84 DECLARE_MOD_FUNC_DEP(__flush_anon_page, \
  85                 void, struct vm_area_struct *vma, struct page *page, \
  86                 unsigned long vmaddr);
  87 DECLARE_MOD_FUNC_DEP(vm_normal_page, \
  88                 struct page *, struct vm_area_struct *vma, \
  89                 unsigned long addr, pte_t pte);
  90
  91 DECLARE_MOD_FUNC_DEP(flush_ptrace_access, \
  92                 void, struct vm_area_struct *vma, struct page *page, \
  93                 unsigned long uaddr, void *kaddr, unsigned long len, int write);
  94
  95
  96 #if (LINUX_VERSION_CODE != KERNEL_VERSION(2, 6, 16))
  97 DECLARE_MOD_FUNC_DEP(put_task_struct, \
  98                 void, struct task_struct *tsk);
  99 #else
 100 DECLARE_MOD_FUNC_DEP(put_task_struct, \
 101                 void, struct rcu_head * rhp);
 102 #endif
 103
 104         DECLARE_MOD_DEP_WRAPPER(access_process_vm, int, struct task_struct *tsk, unsigned long addr, void *buf, int len, int write)
 105 IMP_MOD_DEP_WRAPPER (access_process_vm, tsk, addr, buf, len, write)
 106
 107         DECLARE_MOD_DEP_WRAPPER (find_extend_vma, struct vm_area_struct *, struct mm_struct * mm, unsigned long addr)
 108 IMP_MOD_DEP_WRAPPER (find_extend_vma, mm, addr)
 109
 110 #if LINUX_VERSION_CODE <= KERNEL_VERSION(2, 6, 30)
 111 #if LINUX_VERSION_CODE > KERNEL_VERSION(2, 6, 18)
 112         DECLARE_MOD_DEP_WRAPPER (handle_mm_fault, \
 113                         int, struct mm_struct *mm, struct vm_area_struct *vma, unsigned long address, int write_access)
 114 IMP_MOD_DEP_WRAPPER (handle_mm_fault, mm, vma, address, write_access)
 115 #endif
 116 #else
 117         DECLARE_MOD_DEP_WRAPPER (handle_mm_fault, \
 118                         int, struct mm_struct *mm, struct vm_area_struct *vma, unsigned long address, unsigned int flags)
 119 IMP_MOD_DEP_WRAPPER (handle_mm_fault, mm, vma, address, flags)
 120 #endif
 121
 122         DECLARE_MOD_DEP_WRAPPER (get_gate_vma, \
 123                         struct vm_area_struct *, struct task_struct *tsk)
 124 IMP_MOD_DEP_WRAPPER (get_gate_vma, tsk)
 125
 126 #ifdef CONFIG_HUGETLB_PAGE
 127         DECLARE_MOD_DEP_WRAPPER (follow_hugetlb_page, int, struct mm_struct *mm, struct vm_area_struct *vma, struct page **pages, struct vm_area_struct **vmas, unsigned long *position, int *length, int i, int write)
 128         IMP_MOD_DEP_WRAPPER (follow_hugetlb_page, mm, vma, pages, vmas, position, length, i, write)
 129 #endif
 130
 131 #ifdef  __HAVE_ARCH_GATE_AREA
 132         DECLARE_MOD_DEP_WRAPPER (in_gate_area, int, struct task_struct *tsk, unsigned long addr)
 133         IMP_MOD_DEP_WRAPPER (in_gate_area, tsk, addr)
 134 #else
 135         DECLARE_MOD_DEP_WRAPPER (in_gate_area_no_task, int, unsigned long addr)
 136 IMP_MOD_DEP_WRAPPER (in_gate_area_no_task, addr)
 137 #endif
 138
 139 #if (LINUX_VERSION_CODE != KERNEL_VERSION(2, 6, 11))
 140         DECLARE_MOD_DEP_WRAPPER (follow_page, \
 141                         struct page *, struct vm_area_struct * vma, \
 142                         unsigned long address, unsigned int foll_flags)
 143 IMP_MOD_DEP_WRAPPER (follow_page, vma, address, foll_flags)
 144 #endif
 145         DECLARE_MOD_DEP_WRAPPER (__flush_anon_page, \
 146                         void, struct vm_area_struct *vma, \
 147                         struct page *page, unsigned long vmaddr)
 148 IMP_MOD_DEP_WRAPPER (__flush_anon_page, vma, page, vmaddr)
 149
 150         DECLARE_MOD_DEP_WRAPPER(vm_normal_page, \
 151                         struct page *, struct vm_area_struct *vma, \
 152                         unsigned long addr, pte_t pte)
 153 IMP_MOD_DEP_WRAPPER (vm_normal_page, vma, addr, pte)
 154
 155         DECLARE_MOD_DEP_WRAPPER (flush_ptrace_access, \
 156                         void, struct vm_area_struct *vma, struct page *page, \
 157                         unsigned long uaddr, void *kaddr, unsigned long len, int write)
 158 IMP_MOD_DEP_WRAPPER (flush_ptrace_access, vma, page, uaddr, kaddr, len, write)
 159
 160 #if LINUX_VERSION_CODE == KERNEL_VERSION(2, 6, 32)
 161         DECLARE_MOD_DEP_WRAPPER(copy_to_user_page, void, struct vm_area_struct *vma, struct page *page, unsigned long uaddr, void *dst, const void *src, unsigned long len)
 162 IMP_MOD_DEP_WRAPPER (copy_to_user_page, vma, page, uaddr, dst, src, len)
 163 #endif
 164
 165
 166 int init_module_dependencies()
 167 {
 168
 169 #if LINUX_VERSION_CODE > KERNEL_VERSION(2, 6, 29)
 170         init_mm_ptr = (struct mm_struct*) kallsyms_search ("init_mm");
 171         memcmp(init_mm_ptr, &init_mm, sizeof(struct mm_struct));
 172 #endif
 173
 174 #if LINUX_VERSION_CODE > KERNEL_VERSION(2, 6, 18)
 175         INIT_MOD_DEP_VAR(handle_mm_fault, handle_mm_fault);
 176 #endif
 177
 178         INIT_MOD_DEP_VAR(flush_ptrace_access, flush_ptrace_access);
 179         INIT_MOD_DEP_VAR(find_extend_vma, find_extend_vma);
 180         INIT_MOD_DEP_VAR(get_gate_vma, get_gate_vma);
 181
 182 #ifdef CONFIG_HUGETLB_PAGE
 183         INIT_MOD_DEP_VAR(follow_hugetlb_page, follow_hugetlb_page);
 184 #endif
 185
 186 #ifdef  __HAVE_ARCH_GATE_AREA
 187         INIT_MOD_DEP_VAR(in_gate_area, in_gate_area);
 188 #else
 189         INIT_MOD_DEP_VAR(in_gate_area_no_task, in_gate_area_no_task);
 190 #endif
 191         INIT_MOD_DEP_VAR(follow_page, follow_page);
 192
 193         INIT_MOD_DEP_VAR(__flush_anon_page, __flush_anon_page);
 194         INIT_MOD_DEP_VAR(vm_normal_page, vm_normal_page);
 195         INIT_MOD_DEP_VAR(access_process_vm, access_process_vm);
 196
 197 #if (LINUX_VERSION_CODE != KERNEL_VERSION(2, 6, 16))
 198 # if (LINUX_VERSION_CODE < KERNEL_VERSION(2, 6, 11))
 199         INIT_MOD_DEP_VAR(put_task_struct, put_task_struct);
 200 # else
 201         INIT_MOD_DEP_VAR(put_task_struct, __put_task_struct);
 202 # endif
 203 #else /*2.6.16 */
 204         INIT_MOD_DEP_VAR(put_task_struct, __put_task_struct_cb);
 205 #endif
 206
 207
 208 #if (LINUX_VERSION_CODE == KERNEL_VERSION(2, 6, 32))
 209         INIT_MOD_DEP_VAR(copy_to_user_page, copy_to_user_page);
 210 #endif
 211
 212         return 0;
 213 }
 214
 215 #define GUP_FLAGS_WRITE                  0x1
 216 #define GUP_FLAGS_FORCE                  0x2
 217 #define GUP_FLAGS_IGNORE_VMA_PERMISSIONS 0x4
 218 #define GUP_FLAGS_IGNORE_SIGKILL         0x8
 219
 220 #if LINUX_VERSION_CODE > KERNEL_VERSION(2,6,18)
 221 static inline int use_zero_page(struct vm_area_struct *vma)
 222 {
 223         /*
 224          * We don't want to optimize FOLL_ANON for make_pages_present()
 225          * when it tries to page in a VM_LOCKED region. As to VM_SHARED,
 226          * we want to get the page from the page tables to make sure
 227          * that we serialize and update with any other user of that
 228          * mapping.
 229          */
 230         if (vma->vm_flags & (VM_LOCKED | VM_SHARED))
 231                 return 0;
 232         /*
 233          * And if we have a fault routine, it's not an anonymous region.
 234          */
 235         return !vma->vm_ops || !vma->vm_ops->fault;
 236 }
 237
 238 int __get_user_pages_uprobe(struct task_struct *tsk, struct mm_struct *mm,
 239                      unsigned long start, int len, int flags,
 240                 struct page **pages, struct vm_area_struct **vmas)
 241 {
 242         int i;
 243         unsigned int vm_flags = 0;
 244         int write = !!(flags & GUP_FLAGS_WRITE);
 245         int force = !!(flags & GUP_FLAGS_FORCE);
 246         int ignore = !!(flags & GUP_FLAGS_IGNORE_VMA_PERMISSIONS);
 247         int ignore_sigkill = !!(flags & GUP_FLAGS_IGNORE_SIGKILL);
 248
 249         if (len <= 0)
 250                 return 0;
 251         /*
 252          * Require read or write permissions.
 253          * If 'force' is set, we only require the "MAY" flags.
 254          */
 255         vm_flags  = write ? (VM_WRITE | VM_MAYWRITE) : (VM_READ | VM_MAYREAD);
 256         vm_flags &= force ? (VM_MAYREAD | VM_MAYWRITE) : (VM_READ | VM_WRITE);
 257         i = 0;
 258
 259         do {
 260                 struct vm_area_struct *vma;
 261                 unsigned int foll_flags;
 262
 263                 //vma = find_extend_vma(mm, start);
 264                 vma = find_vma(mm, start);
 265                 if (!vma && in_gate_area(tsk, start)) {
 266                         unsigned long pg = start & PAGE_MASK;
 267                         struct vm_area_struct *gate_vma = get_gate_vma(tsk);
 268                         pgd_t *pgd;
 269                         pud_t *pud;
 270                         pmd_t *pmd;
 271                         pte_t *pte;
 272
 273                         /* user gate pages are read-only */
 274                         if (!ignore && write)
 275                                 return i ? : -EFAULT;
 276                         if (pg > TASK_SIZE)
 277                                 pgd = pgd_offset_k(pg);
 278                         else
 279                                 pgd = pgd_offset_gate(mm, pg);
 280                         BUG_ON(pgd_none(*pgd));
 281                         pud = pud_offset(pgd, pg);
 282                         BUG_ON(pud_none(*pud));
 283                         pmd = pmd_offset(pud, pg);
 284                         if (pmd_none(*pmd))
 285                                 return i ? : -EFAULT;
 286                         pte = pte_offset_map(pmd, pg);
 287                         if (pte_none(*pte)) {
 288                                 pte_unmap(pte);
 289                                 return i ? : -EFAULT;
 290                         }
 291                         if (pages) {
 292                                 struct page *page = vm_normal_page(gate_vma, start, *pte);
 293                                 pages[i] = page;
 294                                 if (page)
 295                                         get_page(page);
 296                         }
 297                         pte_unmap(pte);
 298                         if (vmas)
 299                                 vmas[i] = gate_vma;
 300                         i++;
 301                         start += PAGE_SIZE;
 302                         len--;
 303                         continue;
 304                 }
 305
 306                 if (!vma ||
 307                     (vma->vm_flags & (VM_IO | VM_PFNMAP)) ||
 308                     (!ignore && !(vm_flags & vma->vm_flags)))
 309                         return i ? : -EFAULT;
 310
 311                 if (is_vm_hugetlb_page(vma)) {
 312 #if  LINUX_VERSION_CODE <= KERNEL_VERSION(2,6,18)
 313                         i = follow_hugetlb_page(mm, vma, pages, vmas,
 314                                                 &start, &len, i);
 315 #else
 316                         i = follow_hugetlb_page(mm, vma, pages, vmas,
 317                                                 &start, &len, i, write);
 318 #endif
 319                         continue;
 320                 }
 321
 322                 foll_flags = FOLL_TOUCH;
 323                 if (pages)
 324                         foll_flags |= FOLL_GET;
 325
 326 #if LINUX_VERSION_CODE > KERNEL_VERSION(2,6,18)
 327 #if LINUX_VERSION_CODE <= KERNEL_VERSION(2,6,30)
 328                 if (!write && use_zero_page(vma))
 329                   foll_flags |= FOLL_ANON;
 330 #endif
 331 #endif
 332
 333                 do {
 334                         struct page *page;
 335
 336 #if 0
 337                         /*
 338                          * If we have a pending SIGKILL, don't keep faulting
 339                          * pages and potentially allocating memory, unless
 340                          * current is handling munlock--e.g., on exit. In
 341                          * that case, we are not allocating memory.  Rather,
 342                          * we're only unlocking already resident/mapped pages.
 343                          */
 344                         if (unlikely(!ignore_sigkill &&
 345                                         fatal_signal_pending(current)))
 346                                 return i ? i : -ERESTARTSYS;
 347 #endif
 348
 349                         if (write)
 350                                 foll_flags |= FOLL_WRITE;
 351
 352
 353                         //cond_resched();
 354
 355                         DBPRINTF ("pages = %p vma = %p\n", pages, vma);
 356                         while (!(page = follow_page(vma, start, foll_flags))) {
 357                                 int ret;
 358                                 ret = handle_mm_fault(mm, vma, start,
 359                                                 foll_flags & FOLL_WRITE);
 360
 361 #if  LINUX_VERSION_CODE <= KERNEL_VERSION(2,6,18)
 362                                 if (ret & VM_FAULT_WRITE)
 363                                   foll_flags &= ~FOLL_WRITE;
 364
 365                                 switch (ret & ~VM_FAULT_WRITE) {
 366                                 case VM_FAULT_MINOR:
 367                                   tsk->min_flt++;
 368                                   break;
 369                                 case VM_FAULT_MAJOR:
 370                                   tsk->maj_flt++;
 371                                   break;
 372                                 case VM_FAULT_SIGBUS:
 373                                   return i ? i : -EFAULT;
 374                                 case VM_FAULT_OOM:
 375                                   return i ? i : -ENOMEM;
 376                                 default:
 377                                   BUG();
 378                                 }
 379
 380 #else
 381                                 if (ret & VM_FAULT_ERROR) {
 382                                   if (ret & VM_FAULT_OOM)
 383                                     return i ? i : -ENOMEM;
 384                                   else if (ret & VM_FAULT_SIGBUS)
 385                                     return i ? i : -EFAULT;
 386                                   BUG();
 387                                 }
 388                                 if (ret & VM_FAULT_MAJOR)
 389                                   tsk->maj_flt++;
 390                                 else
 391                                   tsk->min_flt++;
 392
 393                                 /*
 394                                  * The VM_FAULT_WRITE bit tells us that
 395                                  * do_wp_page has broken COW when necessary,
 396                                  * even if maybe_mkwrite decided not to set
 397                                  * pte_write. We can thus safely do subsequent
 398                                  * page lookups as if they were reads. But only
 399                                  * do so when looping for pte_write is futile:
 400                                  * in some cases userspace may also be wanting
 401                                  * to write to the gotten user page, which a
 402                                  * read fault here might prevent (a readonly
 403                                  * page might get reCOWed by userspace write).
 404                                  */
 405                                 if ((ret & VM_FAULT_WRITE) &&
 406                                     !(vma->vm_flags & VM_WRITE))
 407                                   foll_flags &= ~FOLL_WRITE;
 408
 409                                 //cond_resched();
 410 #endif
 411
 412                         }
 413
 414                         if (IS_ERR(page))
 415                                 return i ? i : PTR_ERR(page);
 416                         if (pages) {
 417                                 pages[i] = page;
 418
 419 #if  LINUX_VERSION_CODE <= KERNEL_VERSION(2,6,18)
 420                                 flush_anon_page(page, start);
 421 #else
 422                                 flush_anon_page(vma, page, start);
 423 #endif
 424                                 flush_dcache_page(page);
 425                         }
 426                         if (vmas)
 427                                 vmas[i] = vma;
 428                         i++;
 429                         start += PAGE_SIZE;
 430                         len--;
 431                 } while (len && start < vma->vm_end);
 432         } while (len);
 433         return i;
 434 }
 435 #endif
 436
 437
 438 int get_user_pages_uprobe(struct task_struct *tsk, struct mm_struct *mm,
 439                 unsigned long start, int len, int write, int force,
 440                 struct page **pages, struct vm_area_struct **vmas)
 441 {
 442 #if LINUX_VERSION_CODE >= KERNEL_VERSION(2, 6, 29)
 443         int flags = 0;
 444
 445         if (write)
 446                 flags |= GUP_FLAGS_WRITE;
 447         if (force)
 448                 flags |= GUP_FLAGS_FORCE;
 449
 450         return __get_user_pages_uprobe(tsk, mm,
 451                                 start, len, flags,
 452                                 pages, vmas);
 453 #else
 454         return get_user_pages(tsk, mm, start, len, write, force, pages, vmas);
 455 #endif
 456 }
 457
 458
 459 int access_process_vm_atomic(struct task_struct *tsk, unsigned long addr, void *buf, int len, int write)
 460 {
 461         struct mm_struct *mm;
 462         struct vm_area_struct *vma;
 463         void *old_buf = buf;
 464         unsigned long addr1 = addr;
 465         unsigned int* inst_buf = (unsigned int*)old_buf;
 466
 467
 468         mm = get_task_mm(tsk);
 469         if (!mm)
 470                 return 0;
 471
 472         down_read(&mm->mmap_sem);
 473         /* ignore errors, just check how much was successfully transferred */
 474         while (len) {
 475                 int bytes, ret, offset;
 476                 void *maddr;
 477                 struct page *page = NULL;
 478
 479                 ret = get_user_pages_uprobe(tsk, mm, addr, 1,
 480                                 write, 1, &page, &vma);
 481
 482                 if (ret <= 0) {
 483                         /*
 484                          * Check if this is a VM_IO | VM_PFNMAP VMA, which
 485                          * we can access using slightly different code.
 486                          */
 487 #ifdef CONFIG_HAVE_IOREMAP_PROT
 488                         vma = find_vma(mm, addr);
 489                         if (!vma)
 490                                 break;
 491                         if (vma->vm_ops && vma->vm_ops->access)
 492                                 ret = vma->vm_ops->access(vma, addr, buf,
 493                                                           len, write);
 494                         if (ret <= 0)
 495 #endif
 496                                 break;
 497                         bytes = ret;
 498                 } else {
 499                         bytes = len;
 500                         offset = addr & (PAGE_SIZE-1);
 501                         if (bytes > PAGE_SIZE-offset)
 502                                 bytes = PAGE_SIZE-offset;
 503
 504                         maddr = kmap(page);
 505                         if (write) {
 506                                 copy_to_user_page(vma, page, addr,
 507                                                   maddr + offset, buf, bytes);
 508                                 set_page_dirty_lock(page);
 509                         } else {
 510                                 copy_from_user_page(vma, page, addr,
 511                                                     buf, maddr + offset, bytes);
 512                         }
 513                         kunmap(page);
 514                         page_cache_release(page);
 515                 }
 516                 len -= bytes;
 517                 buf += bytes;
 518                 addr += bytes;
 519         }
 520         up_read(&mm->mmap_sem);
 521         mmput(mm);
 522
 523         return buf - old_buf;
 524 }
 525
 526 int page_present (struct mm_struct *mm, unsigned long address)
 527 {
 528         pgd_t *pgd;
 529         pud_t *pud;
 530         pmd_t *pmd;
 531         pte_t *ptep, pte;
 532         unsigned long pfn;
 533
 534         pgd = pgd_offset(mm, address);
 535         if (pgd_none(*pgd) || unlikely(pgd_bad(*pgd)))
 536                 goto out;
 537
 538         pud = pud_offset(pgd, address);
 539         if (pud_none(*pud) || unlikely(pud_bad(*pud)))
 540                 goto out;
 541
 542         pmd = pmd_offset(pud, address);
 543         if (pmd_none(*pmd) || unlikely(pmd_bad(*pmd)))
 544                 goto out;
 545
 546         ptep = pte_offset_map(pmd, address);
 547         if (!ptep)
 548                 goto out;
 549
 550         pte = *ptep;
 551         pte_unmap(ptep);
 552         if (pte_present(pte)) {
 553                 pfn = pte_pfn(pte);
 554                 if (pfn_valid(pfn)) {
 555                         return 1;
 556                 }
 557         }
 558
 559 out:
 560         return 0;
 561 }
 562
 563
 564 EXPORT_SYMBOL_GPL (page_present);
 565 EXPORT_SYMBOL_GPL (get_user_pages_uprobe);
 566 EXPORT_SYMBOL_GPL (access_process_vm_atomic);
 567