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 #include <linux/mm.h>
  39
  40 unsigned int *sched_addr;
  41 unsigned int *fork_addr;
  42
  43
  44 #define GUP_FLAGS_WRITE                  0x1
  45 #define GUP_FLAGS_FORCE                  0x2
  46 #define GUP_FLAGS_IGNORE_VMA_PERMISSIONS 0x4
  47 #define GUP_FLAGS_IGNORE_SIGKILL         0x8
  48
  49 #if LINUX_VERSION_CODE > KERNEL_VERSION(2, 6, 29)
  50 struct mm_struct* init_mm_ptr;
  51 struct mm_struct init_mm;
  52 #endif
  53
  54
  55 DECLARE_MOD_CB_DEP(kallsyms_search, unsigned long, const char *name);
  56 DECLARE_MOD_FUNC_DEP(access_process_vm, int, struct task_struct * tsk, unsigned long addr, void *buf, int len, int write);
  57 #if LINUX_VERSION_CODE >= KERNEL_VERSION(2, 6, 32)
  58 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);
  59 #endif
  60
  61 DECLARE_MOD_FUNC_DEP(find_extend_vma, struct vm_area_struct *, struct mm_struct * mm, unsigned long addr);
  62
  63 #if LINUX_VERSION_CODE <= KERNEL_VERSION(2, 6, 30)
  64 #if LINUX_VERSION_CODE > KERNEL_VERSION(2, 6, 18)
  65 DECLARE_MOD_FUNC_DEP(handle_mm_fault, int, struct mm_struct *mm, struct vm_area_struct *vma, unsigned long address, int write_access);
  66 #endif
  67 #else
  68 DECLARE_MOD_FUNC_DEP(handle_mm_fault, int, struct mm_struct *mm, struct vm_area_struct *vma, unsigned long address, unsigned int flags);
  69 #endif /* LINUX_VERSION_CODE <= KERNEL_VERSION(2, 6, 30) */
  70
  71 DECLARE_MOD_FUNC_DEP(get_gate_vma, struct vm_area_struct *, struct task_struct *tsk);
  72
  73 #ifdef CONFIG_HUGETLB_PAGE
  74 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);
  75 #endif
  76
  77 #ifdef  __HAVE_ARCH_GATE_AREA
  78 DECLARE_MOD_FUNC_DEP(in_gate_area, int, struct task_struct *tsk,unsigned long addr);
  79 #else
  80 DECLARE_MOD_FUNC_DEP(in_gate_area_no_task, int, unsigned long addr);
  81 #endif
  82 DECLARE_MOD_FUNC_DEP(follow_page, \
  83                 struct page *, struct vm_area_struct * vma, \
  84                 unsigned long address, unsigned int foll_flags);
  85 DECLARE_MOD_FUNC_DEP(__flush_anon_page, \
  86                 void, struct vm_area_struct *vma, struct page *page, \
  87                 unsigned long vmaddr);
  88 DECLARE_MOD_FUNC_DEP(vm_normal_page, \
  89                 struct page *, struct vm_area_struct *vma, \
  90                 unsigned long addr, pte_t pte);
  91
  92 DECLARE_MOD_FUNC_DEP(flush_ptrace_access, \
  93                 void, struct vm_area_struct *vma, struct page *page, \
  94                 unsigned long uaddr, void *kaddr, unsigned long len, int write);
  95
  96
  97 #if (LINUX_VERSION_CODE != KERNEL_VERSION(2, 6, 16))
  98 DECLARE_MOD_FUNC_DEP(put_task_struct, \
  99                 void, struct task_struct *tsk);
 100 #else
 101 DECLARE_MOD_FUNC_DEP(put_task_struct, \
 102                 void, struct rcu_head * rhp);
 103 #endif
 104
 105         DECLARE_MOD_DEP_WRAPPER(access_process_vm, int, struct task_struct *tsk, unsigned long addr, void *buf, int len, int write)
 106 IMP_MOD_DEP_WRAPPER (access_process_vm, tsk, addr, buf, len, write)
 107
 108         DECLARE_MOD_DEP_WRAPPER (find_extend_vma, struct vm_area_struct *, struct mm_struct * mm, unsigned long addr)
 109 IMP_MOD_DEP_WRAPPER (find_extend_vma, mm, addr)
 110
 111 #if LINUX_VERSION_CODE <= KERNEL_VERSION(2, 6, 30)
 112 #if LINUX_VERSION_CODE > KERNEL_VERSION(2, 6, 18)
 113         DECLARE_MOD_DEP_WRAPPER (handle_mm_fault, \
 114                         int, struct mm_struct *mm, struct vm_area_struct *vma, unsigned long address, int write_access)
 115 IMP_MOD_DEP_WRAPPER (handle_mm_fault, mm, vma, address, write_access)
 116 #endif
 117 #else
 118         DECLARE_MOD_DEP_WRAPPER (handle_mm_fault, \
 119                         int, struct mm_struct *mm, struct vm_area_struct *vma, unsigned long address, unsigned int flags)
 120 IMP_MOD_DEP_WRAPPER (handle_mm_fault, mm, vma, address, flags)
 121 #endif
 122
 123         DECLARE_MOD_DEP_WRAPPER (get_gate_vma, \
 124                         struct vm_area_struct *, struct task_struct *tsk)
 125 IMP_MOD_DEP_WRAPPER (get_gate_vma, tsk)
 126
 127 #ifdef CONFIG_HUGETLB_PAGE
 128         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)
 129         IMP_MOD_DEP_WRAPPER (follow_hugetlb_page, mm, vma, pages, vmas, position, length, i, write)
 130 #endif
 131
 132 #ifdef  __HAVE_ARCH_GATE_AREA
 133         DECLARE_MOD_DEP_WRAPPER (in_gate_area, int, struct task_struct *tsk, unsigned long addr)
 134         IMP_MOD_DEP_WRAPPER (in_gate_area, tsk, addr)
 135 #else
 136         DECLARE_MOD_DEP_WRAPPER (in_gate_area_no_task, int, unsigned long addr)
 137 IMP_MOD_DEP_WRAPPER (in_gate_area_no_task, addr)
 138 #endif
 139
 140 #if (LINUX_VERSION_CODE != KERNEL_VERSION(2, 6, 11))
 141         DECLARE_MOD_DEP_WRAPPER (follow_page, \
 142                         struct page *, struct vm_area_struct * vma, \
 143                         unsigned long address, unsigned int foll_flags)
 144 IMP_MOD_DEP_WRAPPER (follow_page, vma, address, foll_flags)
 145 #endif
 146         DECLARE_MOD_DEP_WRAPPER (__flush_anon_page, \
 147                         void, struct vm_area_struct *vma, \
 148                         struct page *page, unsigned long vmaddr)
 149 IMP_MOD_DEP_WRAPPER (__flush_anon_page, vma, page, vmaddr)
 150
 151         DECLARE_MOD_DEP_WRAPPER(vm_normal_page, \
 152                         struct page *, struct vm_area_struct *vma, \
 153                         unsigned long addr, pte_t pte)
 154 IMP_MOD_DEP_WRAPPER (vm_normal_page, vma, addr, pte)
 155
 156         DECLARE_MOD_DEP_WRAPPER (flush_ptrace_access, \
 157                         void, struct vm_area_struct *vma, struct page *page, \
 158                         unsigned long uaddr, void *kaddr, unsigned long len, int write)
 159 IMP_MOD_DEP_WRAPPER (flush_ptrace_access, vma, page, uaddr, kaddr, len, write)
 160
 161 #if LINUX_VERSION_CODE >= KERNEL_VERSION(2, 6, 32)
 162         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)
 163 IMP_MOD_DEP_WRAPPER (copy_to_user_page, vma, page, uaddr, dst, src, len)
 164 #endif
 165
 166
 167 int init_module_dependencies()
 168 {
 169
 170 #if LINUX_VERSION_CODE > KERNEL_VERSION(2, 6, 29)
 171         init_mm_ptr = (struct mm_struct*) kallsyms_search ("init_mm");
 172         memcmp(init_mm_ptr, &init_mm, sizeof(struct mm_struct));
 173 #endif
 174
 175 #if LINUX_VERSION_CODE > KERNEL_VERSION(2, 6, 18)
 176         INIT_MOD_DEP_VAR(handle_mm_fault, handle_mm_fault);
 177 #endif
 178
 179         INIT_MOD_DEP_VAR(flush_ptrace_access, flush_ptrace_access);
 180         INIT_MOD_DEP_VAR(find_extend_vma, find_extend_vma);
 181         INIT_MOD_DEP_VAR(get_gate_vma, get_gate_vma);
 182
 183 #ifdef CONFIG_HUGETLB_PAGE
 184         INIT_MOD_DEP_VAR(follow_hugetlb_page, follow_hugetlb_page);
 185 #endif
 186
 187 #ifdef  __HAVE_ARCH_GATE_AREA
 188         INIT_MOD_DEP_VAR(in_gate_area, in_gate_area);
 189 #else
 190         INIT_MOD_DEP_VAR(in_gate_area_no_task, in_gate_area_no_task);
 191 #endif
 192         INIT_MOD_DEP_VAR(follow_page, follow_page);
 193
 194         INIT_MOD_DEP_VAR(__flush_anon_page, __flush_anon_page);
 195         INIT_MOD_DEP_VAR(vm_normal_page, vm_normal_page);
 196         INIT_MOD_DEP_VAR(access_process_vm, access_process_vm);
 197
 198 #if (LINUX_VERSION_CODE != KERNEL_VERSION(2, 6, 16))
 199 # if (LINUX_VERSION_CODE < KERNEL_VERSION(2, 6, 11))
 200         INIT_MOD_DEP_VAR(put_task_struct, put_task_struct);
 201 # else
 202         INIT_MOD_DEP_VAR(put_task_struct, __put_task_struct);
 203 # endif
 204 #else /*2.6.16 */
 205         INIT_MOD_DEP_VAR(put_task_struct, __put_task_struct_cb);
 206 #endif
 207
 208
 209 // for 2.6.32.9-iboot (tegra-froyo)
 210 #if (LINUX_VERSION_CODE >= KERNEL_VERSION(2, 6, 32))
 211         INIT_MOD_DEP_VAR(copy_to_user_page, copy_to_user_page);
 212 #endif
 213
 214         return 0;
 215 }
 216
 217 #define GUP_FLAGS_WRITE                  0x1
 218 #define GUP_FLAGS_FORCE                  0x2
 219 #define GUP_FLAGS_IGNORE_VMA_PERMISSIONS 0x4
 220 #define GUP_FLAGS_IGNORE_SIGKILL         0x8
 221
 222 #if LINUX_VERSION_CODE > KERNEL_VERSION(2,6,18)
 223 static inline int use_zero_page(struct vm_area_struct *vma)
 224 {
 225         /*
 226          * We don't want to optimize FOLL_ANON for make_pages_present()
 227          * when it tries to page in a VM_LOCKED region. As to VM_SHARED,
 228          * we want to get the page from the page tables to make sure
 229          * that we serialize and update with any other user of that
 230          * mapping.
 231          */
 232         if (vma->vm_flags & (VM_LOCKED | VM_SHARED))
 233                 return 0;
 234         /*
 235          * And if we have a fault routine, it's not an anonymous region.
 236          */
 237         return !vma->vm_ops || !vma->vm_ops->fault;
 238 }
 239
 240 int __get_user_pages_uprobe(struct task_struct *tsk, struct mm_struct *mm,
 241                      unsigned long start, int len, int flags,
 242                 struct page **pages, struct vm_area_struct **vmas)
 243 {
 244         int i;
 245         unsigned int vm_flags = 0;
 246         int write = !!(flags & GUP_FLAGS_WRITE);
 247         int force = !!(flags & GUP_FLAGS_FORCE);
 248         int ignore = !!(flags & GUP_FLAGS_IGNORE_VMA_PERMISSIONS);
 249         int ignore_sigkill = !!(flags & GUP_FLAGS_IGNORE_SIGKILL);
 250
 251         if (len <= 0)
 252                 return 0;
 253         /*
 254          * Require read or write permissions.
 255          * If 'force' is set, we only require the "MAY" flags.
 256          */
 257         vm_flags  = write ? (VM_WRITE | VM_MAYWRITE) : (VM_READ | VM_MAYREAD);
 258         vm_flags &= force ? (VM_MAYREAD | VM_MAYWRITE) : (VM_READ | VM_WRITE);
 259         i = 0;
 260
 261         do {
 262                 struct vm_area_struct *vma;
 263                 unsigned int foll_flags;
 264
 265                 vma = find_vma(mm, start);
 266                 if (!vma && in_gate_area(tsk, start)) {
 267                         unsigned long pg = start & PAGE_MASK;
 268                         struct vm_area_struct *gate_vma = get_gate_vma(tsk);
 269                         pgd_t *pgd;
 270                         pud_t *pud;
 271                         pmd_t *pmd;
 272                         pte_t *pte;
 273
 274                         /* user gate pages are read-only */
 275                         if (!ignore && write)
 276                                 return i ? : -EFAULT;
 277                         if (pg > TASK_SIZE)
 278                                 pgd = pgd_offset_k(pg);
 279                         else
 280                                 pgd = pgd_offset_gate(mm, pg);
 281                         BUG_ON(pgd_none(*pgd));
 282                         pud = pud_offset(pgd, pg);
 283                         BUG_ON(pud_none(*pud));
 284                         pmd = pmd_offset(pud, pg);
 285                         if (pmd_none(*pmd))
 286                                 return i ? : -EFAULT;
 287                         pte = pte_offset_map(pmd, pg);
 288                         if (pte_none(*pte)) {
 289                                 pte_unmap(pte);
 290                                 return i ? : -EFAULT;
 291                         }
 292                         if (pages) {
 293                                 struct page *page = vm_normal_page(gate_vma, start, *pte);
 294                                 pages[i] = page;
 295                                 if (page)
 296                                         get_page(page);
 297                         }
 298                         pte_unmap(pte);
 299                         if (vmas)
 300                                 vmas[i] = gate_vma;
 301                         i++;
 302                         start += PAGE_SIZE;
 303                         len--;
 304                         continue;
 305                 }
 306
 307                 if (!vma ||
 308                     (vma->vm_flags & (VM_IO | VM_PFNMAP)) ||
 309                     (!ignore && !(vm_flags & vma->vm_flags)))
 310                         return i ? : -EFAULT;
 311
 312                 if (is_vm_hugetlb_page(vma)) {
 313 #if  LINUX_VERSION_CODE <= KERNEL_VERSION(2,6,18)
 314                         i = follow_hugetlb_page(mm, vma, pages, vmas,
 315                                                 &start, &len, i);
 316 #else
 317                         i = follow_hugetlb_page(mm, vma, pages, vmas,
 318                                                 &start, &len, i, write);
 319 #endif
 320                         continue;
 321                 }
 322
 323                 foll_flags = FOLL_TOUCH;
 324                 if (pages)
 325                         foll_flags |= FOLL_GET;
 326
 327 #if LINUX_VERSION_CODE > KERNEL_VERSION(2,6,18)
 328 #if LINUX_VERSION_CODE <= KERNEL_VERSION(2,6,30)
 329                 if (!write && use_zero_page(vma))
 330                   foll_flags |= FOLL_ANON;
 331 #endif
 332 #endif
 333
 334                 do {
 335                         struct page *page;
 336
 337 #if 0
 338                         /*
 339                          * If we have a pending SIGKILL, don't keep faulting
 340                          * pages and potentially allocating memory, unless
 341                          * current is handling munlock--e.g., on exit. In
 342                          * that case, we are not allocating memory.  Rather,
 343                          * we're only unlocking already resident/mapped pages.
 344                          */
 345                         if (unlikely(!ignore_sigkill &&
 346                                         fatal_signal_pending(current)))
 347                                 return i ? i : -ERESTARTSYS;
 348 #endif
 349
 350                         if (write)
 351                                 foll_flags |= FOLL_WRITE;
 352
 353
 354                         //cond_resched();
 355
 356                         DBPRINTF ("pages = %p vma = %p\n", pages, vma);
 357                         while (!(page = follow_page(vma, start, foll_flags))) {
 358                                 int ret;
 359                                 ret = handle_mm_fault(mm, vma, start,
 360                                                 foll_flags & FOLL_WRITE);
 361
 362 #if  LINUX_VERSION_CODE <= KERNEL_VERSION(2,6,18)
 363                                 if (ret & VM_FAULT_WRITE)
 364                                   foll_flags &= ~FOLL_WRITE;
 365
 366                                 switch (ret & ~VM_FAULT_WRITE) {
 367                                 case VM_FAULT_MINOR:
 368                                   tsk->min_flt++;
 369                                   break;
 370                                 case VM_FAULT_MAJOR:
 371                                   tsk->maj_flt++;
 372                                   break;
 373                                 case VM_FAULT_SIGBUS:
 374                                   return i ? i : -EFAULT;
 375                                 case VM_FAULT_OOM:
 376                                   return i ? i : -ENOMEM;
 377                                 default:
 378                                   BUG();
 379                                 }
 380
 381 #else
 382                                 if (ret & VM_FAULT_ERROR) {
 383                                   if (ret & VM_FAULT_OOM)
 384                                     return i ? i : -ENOMEM;
 385                                   else if (ret & VM_FAULT_SIGBUS)
 386                                     return i ? i : -EFAULT;
 387                                   BUG();
 388                                 }
 389                                 if (ret & VM_FAULT_MAJOR)
 390                                   tsk->maj_flt++;
 391                                 else
 392                                   tsk->min_flt++;
 393
 394                                 /*
 395                                  * The VM_FAULT_WRITE bit tells us that
 396                                  * do_wp_page has broken COW when necessary,
 397                                  * even if maybe_mkwrite decided not to set
 398                                  * pte_write. We can thus safely do subsequent
 399                                  * page lookups as if they were reads. But only
 400                                  * do so when looping for pte_write is futile:
 401                                  * in some cases userspace may also be wanting
 402                                  * to write to the gotten user page, which a
 403                                  * read fault here might prevent (a readonly
 404                                  * page might get reCOWed by userspace write).
 405                                  */
 406                                 if ((ret & VM_FAULT_WRITE) &&
 407                                     !(vma->vm_flags & VM_WRITE))
 408                                   foll_flags &= ~FOLL_WRITE;
 409
 410                                 //cond_resched();
 411 #endif
 412
 413                         }
 414
 415                         if (IS_ERR(page))
 416                                 return i ? i : PTR_ERR(page);
 417                         if (pages) {
 418                                 pages[i] = page;
 419
 420 #if  LINUX_VERSION_CODE <= KERNEL_VERSION(2,6,18)
 421                                 flush_anon_page(page, start);
 422 #else
 423                                 flush_anon_page(vma, page, start);
 424 #endif
 425                                 flush_dcache_page(page);
 426                         }
 427                         if (vmas)
 428                                 vmas[i] = vma;
 429                         i++;
 430                         start += PAGE_SIZE;
 431                         len--;
 432                 } while (len && start < vma->vm_end);
 433         } while (len);
 434         return i;
 435 }
 436 #endif
 437
 438
 439 int get_user_pages_uprobe(struct task_struct *tsk, struct mm_struct *mm,
 440                 unsigned long start, int len, int write, int force,
 441                 struct page **pages, struct vm_area_struct **vmas)
 442 {
 443 #if LINUX_VERSION_CODE >= KERNEL_VERSION(2, 6, 29)
 444         int flags = 0;
 445
 446         if (write)
 447                 flags |= GUP_FLAGS_WRITE;
 448         if (force)
 449                 flags |= GUP_FLAGS_FORCE;
 450
 451         return __get_user_pages_uprobe(tsk, mm,
 452                                 start, len, flags,
 453                                 pages, vmas);
 454 #else
 455         return get_user_pages(tsk, mm, start, len, write, force, pages, vmas);
 456 #endif
 457 }
 458
 459
 460 int access_process_vm_atomic(struct task_struct *tsk, unsigned long addr, void *buf, int len, int write)
 461 {
 462         struct mm_struct *mm;
 463         struct vm_area_struct *vma;
 464         void *old_buf = buf;
 465         unsigned long addr1 = addr;
 466         unsigned int* inst_buf = (unsigned int*)old_buf;
 467
 468
 469         mm = get_task_mm(tsk);
 470         if (!mm)
 471                 return 0;
 472
 473         /* down_read(&mm->mmap_sem); */
 474         /* ignore errors, just check how much was successfully transferred */
 475         while (len) {
 476                 int bytes, ret, offset;
 477                 void *maddr;
 478                 struct page *page = NULL;
 479
 480                 ret = get_user_pages_uprobe(tsk, mm, addr, 1,
 481                                 write, 1, &page, &vma);
 482
 483                 if (ret <= 0) {
 484                         /*
 485                          * Check if this is a VM_IO | VM_PFNMAP VMA, which
 486                          * we can access using slightly different code.
 487                          */
 488 #ifdef CONFIG_HAVE_IOREMAP_PROT
 489                         vma = find_vma(mm, addr);
 490                         if (!vma)
 491                                 break;
 492                         if (vma->vm_ops && vma->vm_ops->access)
 493                                 ret = vma->vm_ops->access(vma, addr, buf,
 494                                                           len, write);
 495                         if (ret <= 0)
 496 #endif
 497                                 break;
 498                         bytes = ret;
 499                 } else {
 500                         bytes = len;
 501                         offset = addr & (PAGE_SIZE-1);
 502                         if (bytes > PAGE_SIZE-offset)
 503                                 bytes = PAGE_SIZE-offset;
 504
 505                         maddr = kmap(page);
 506                         if (write) {
 507                                 copy_to_user_page(vma, page, addr,
 508                                                   maddr + offset, buf, bytes);
 509                                 set_page_dirty_lock(page);
 510                         } else {
 511                                 copy_from_user_page(vma, page, addr,
 512                                                     buf, maddr + offset, bytes);
 513                         }
 514                         kunmap(page);
 515                         page_cache_release(page);
 516                 }
 517                 len -= bytes;
 518                 buf += bytes;
 519                 addr += bytes;
 520         }
 521         /* up_read(&mm->mmap_sem); */
 522         mmput(mm);
 523
 524         return buf - old_buf;
 525 }
 526
 527 int page_present (struct mm_struct *mm, unsigned long address)
 528 {
 529         pgd_t *pgd;
 530         pud_t *pud;
 531         pmd_t *pmd;
 532         pte_t *ptep, pte;
 533         unsigned long pfn;
 534
 535         pgd = pgd_offset(mm, address);
 536         if (pgd_none(*pgd) || unlikely(pgd_bad(*pgd)))
 537                 goto out;
 538
 539         pud = pud_offset(pgd, address);
 540         if (pud_none(*pud) || unlikely(pud_bad(*pud)))
 541                 goto out;
 542
 543         pmd = pmd_offset(pud, address);
 544         if (pmd_none(*pmd) || unlikely(pmd_bad(*pmd)))
 545                 goto out;
 546
 547         ptep = pte_offset_map(pmd, address);
 548         if (!ptep)
 549                 goto out;
 550
 551         pte = *ptep;
 552         pte_unmap(ptep);
 553         if (pte_present(pte)) {
 554                 pfn = pte_pfn(pte);
 555                 if (pfn_valid(pfn)) {
 556                         return 1;
 557                 }
 558         }
 559
 560 out:
 561         return 0;
 562 }
 563
 564
 565 EXPORT_SYMBOL_GPL (page_present);
 566 EXPORT_SYMBOL_GPL (get_user_pages_uprobe);
 567 EXPORT_SYMBOL_GPL (access_process_vm_atomic);
 568