mm/mremap.c

   1 // SPDX-License-Identifier: GPL-2.0
   2 /*
   3  *      mm/mremap.c
   4  *
   5  *      (C) Copyright 1996 Linus Torvalds
   6  *
   7  *      Address space accounting code   <alan@lxorguk.ukuu.org.uk>
   8  *      (C) Copyright 2002 Red Hat Inc, All Rights Reserved
   9  */
  10
  11 #include <linux/mm.h>
  12 #include <linux/mm_inline.h>
  13 #include <linux/hugetlb.h>
  14 #include <linux/shm.h>
  15 #include <linux/ksm.h>
  16 #include <linux/mman.h>
  17 #include <linux/swap.h>
  18 #include <linux/capability.h>
  19 #include <linux/fs.h>
  20 #include <linux/swapops.h>
  21 #include <linux/highmem.h>
  22 #include <linux/security.h>
  23 #include <linux/syscalls.h>
  24 #include <linux/mmu_notifier.h>
  25 #include <linux/uaccess.h>
  26 #include <linux/userfaultfd_k.h>
  27 #include <linux/mempolicy.h>
  28
  29 #include <asm/cacheflush.h>
  30 #include <asm/tlb.h>
  31 #include <asm/pgalloc.h>
  32
  33 #include "internal.h"
  34
  35 static pud_t *get_old_pud(struct mm_struct *mm, unsigned long addr)
  36 {
  37         pgd_t *pgd;
  38         p4d_t *p4d;
  39         pud_t *pud;
  40
  41         pgd = pgd_offset(mm, addr);
  42         if (pgd_none_or_clear_bad(pgd))
  43                 return NULL;
  44
  45         p4d = p4d_offset(pgd, addr);
  46         if (p4d_none_or_clear_bad(p4d))
  47                 return NULL;
  48
  49         pud = pud_offset(p4d, addr);
  50         if (pud_none_or_clear_bad(pud))
  51                 return NULL;
  52
  53         return pud;
  54 }
  55
  56 static pmd_t *get_old_pmd(struct mm_struct *mm, unsigned long addr)
  57 {
  58         pud_t *pud;
  59         pmd_t *pmd;
  60
  61         pud = get_old_pud(mm, addr);
  62         if (!pud)
  63                 return NULL;
  64
  65         pmd = pmd_offset(pud, addr);
  66         if (pmd_none(*pmd))
  67                 return NULL;
  68
  69         return pmd;
  70 }
  71
  72 static pud_t *alloc_new_pud(struct mm_struct *mm, struct vm_area_struct *vma,
  73                             unsigned long addr)
  74 {
  75         pgd_t *pgd;
  76         p4d_t *p4d;
  77
  78         pgd = pgd_offset(mm, addr);
  79         p4d = p4d_alloc(mm, pgd, addr);
  80         if (!p4d)
  81                 return NULL;
  82
  83         return pud_alloc(mm, p4d, addr);
  84 }
  85
  86 static pmd_t *alloc_new_pmd(struct mm_struct *mm, struct vm_area_struct *vma,
  87                             unsigned long addr)
  88 {
  89         pud_t *pud;
  90         pmd_t *pmd;
  91
  92         pud = alloc_new_pud(mm, vma, addr);
  93         if (!pud)
  94                 return NULL;
  95
  96         pmd = pmd_alloc(mm, pud, addr);
  97         if (!pmd)
  98                 return NULL;
  99
 100         VM_BUG_ON(pmd_trans_huge(*pmd));
 101
 102         return pmd;
 103 }
 104
 105 static void take_rmap_locks(struct vm_area_struct *vma)
 106 {
 107         if (vma->vm_file)
 108                 i_mmap_lock_write(vma->vm_file->f_mapping);
 109         if (vma->anon_vma)
 110                 anon_vma_lock_write(vma->anon_vma);
 111 }
 112
 113 static void drop_rmap_locks(struct vm_area_struct *vma)
 114 {
 115         if (vma->anon_vma)
 116                 anon_vma_unlock_write(vma->anon_vma);
 117         if (vma->vm_file)
 118                 i_mmap_unlock_write(vma->vm_file->f_mapping);
 119 }
 120
 121 static pte_t move_soft_dirty_pte(pte_t pte)
 122 {
 123         /*
 124          * Set soft dirty bit so we can notice
 125          * in userspace the ptes were moved.
 126          */
 127 #ifdef CONFIG_MEM_SOFT_DIRTY
 128         if (pte_present(pte))
 129                 pte = pte_mksoft_dirty(pte);
 130         else if (is_swap_pte(pte))
 131                 pte = pte_swp_mksoft_dirty(pte);
 132 #endif
 133         return pte;
 134 }
 135
 136 static int move_ptes(struct vm_area_struct *vma, pmd_t *old_pmd,
 137                 unsigned long old_addr, unsigned long old_end,
 138                 struct vm_area_struct *new_vma, pmd_t *new_pmd,
 139                 unsigned long new_addr, bool need_rmap_locks)
 140 {
 141         struct mm_struct *mm = vma->vm_mm;
 142         pte_t *old_pte, *new_pte, pte;
 143         spinlock_t *old_ptl, *new_ptl;
 144         bool force_flush = false;
 145         unsigned long len = old_end - old_addr;
 146         int err = 0;
 147
 148         /*
 149          * When need_rmap_locks is true, we take the i_mmap_rwsem and anon_vma
 150          * locks to ensure that rmap will always observe either the old or the
 151          * new ptes. This is the easiest way to avoid races with
 152          * truncate_pagecache(), page migration, etc...
 153          *
 154          * When need_rmap_locks is false, we use other ways to avoid
 155          * such races:
 156          *
 157          * - During exec() shift_arg_pages(), we use a specially tagged vma
 158          *   which rmap call sites look for using vma_is_temporary_stack().
 159          *
 160          * - During mremap(), new_vma is often known to be placed after vma
 161          *   in rmap traversal order. This ensures rmap will always observe
 162          *   either the old pte, or the new pte, or both (the page table locks
 163          *   serialize access to individual ptes, but only rmap traversal
 164          *   order guarantees that we won't miss both the old and new ptes).
 165          */
 166         if (need_rmap_locks)
 167                 take_rmap_locks(vma);
 168
 169         /*
 170          * We don't have to worry about the ordering of src and dst
 171          * pte locks because exclusive mmap_lock prevents deadlock.
 172          */
 173         old_pte = pte_offset_map_lock(mm, old_pmd, old_addr, &old_ptl);
 174         if (!old_pte) {
 175                 err = -EAGAIN;
 176                 goto out;
 177         }
 178         new_pte = pte_offset_map_nolock(mm, new_pmd, new_addr, &new_ptl);
 179         if (!new_pte) {
 180                 pte_unmap_unlock(old_pte, old_ptl);
 181                 err = -EAGAIN;
 182                 goto out;
 183         }
 184         if (new_ptl != old_ptl)
 185                 spin_lock_nested(new_ptl, SINGLE_DEPTH_NESTING);
 186         flush_tlb_batched_pending(vma->vm_mm);
 187         arch_enter_lazy_mmu_mode();
 188
 189         for (; old_addr < old_end; old_pte++, old_addr += PAGE_SIZE,
 190                                    new_pte++, new_addr += PAGE_SIZE) {
 191                 if (pte_none(ptep_get(old_pte)))
 192                         continue;
 193
 194                 pte = ptep_get_and_clear(mm, old_addr, old_pte);
 195                 /*
 196                  * If we are remapping a valid PTE, make sure
 197                  * to flush TLB before we drop the PTL for the
 198                  * PTE.
 199                  *
 200                  * NOTE! Both old and new PTL matter: the old one
 201                  * for racing with folio_mkclean(), the new one to
 202                  * make sure the physical page stays valid until
 203                  * the TLB entry for the old mapping has been
 204                  * flushed.
 205                  */
 206                 if (pte_present(pte))
 207                         force_flush = true;
 208                 pte = move_pte(pte, old_addr, new_addr);
 209                 pte = move_soft_dirty_pte(pte);
 210                 set_pte_at(mm, new_addr, new_pte, pte);
 211         }
 212
 213         arch_leave_lazy_mmu_mode();
 214         if (force_flush)
 215                 flush_tlb_range(vma, old_end - len, old_end);
 216         if (new_ptl != old_ptl)
 217                 spin_unlock(new_ptl);
 218         pte_unmap(new_pte - 1);
 219         pte_unmap_unlock(old_pte - 1, old_ptl);
 220 out:
 221         if (need_rmap_locks)
 222                 drop_rmap_locks(vma);
 223         return err;
 224 }
 225
 226 #ifndef arch_supports_page_table_move
 227 #define arch_supports_page_table_move arch_supports_page_table_move
 228 static inline bool arch_supports_page_table_move(void)
 229 {
 230         return IS_ENABLED(CONFIG_HAVE_MOVE_PMD) ||
 231                 IS_ENABLED(CONFIG_HAVE_MOVE_PUD);
 232 }
 233 #endif
 234
 235 #ifdef CONFIG_HAVE_MOVE_PMD
 236 static bool move_normal_pmd(struct vm_area_struct *vma, unsigned long old_addr,
 237                   unsigned long new_addr, pmd_t *old_pmd, pmd_t *new_pmd)
 238 {
 239         spinlock_t *old_ptl, *new_ptl;
 240         struct mm_struct *mm = vma->vm_mm;
 241         pmd_t pmd;
 242
 243         if (!arch_supports_page_table_move())
 244                 return false;
 245         /*
 246          * The destination pmd shouldn't be established, free_pgtables()
 247          * should have released it.
 248          *
 249          * However, there's a case during execve() where we use mremap
 250          * to move the initial stack, and in that case the target area
 251          * may overlap the source area (always moving down).
 252          *
 253          * If everything is PMD-aligned, that works fine, as moving
 254          * each pmd down will clear the source pmd. But if we first
 255          * have a few 4kB-only pages that get moved down, and then
 256          * hit the "now the rest is PMD-aligned, let's do everything
 257          * one pmd at a time", we will still have the old (now empty
 258          * of any 4kB pages, but still there) PMD in the page table
 259          * tree.
 260          *
 261          * Warn on it once - because we really should try to figure
 262          * out how to do this better - but then say "I won't move
 263          * this pmd".
 264          *
 265          * One alternative might be to just unmap the target pmd at
 266          * this point, and verify that it really is empty. We'll see.
 267          */
 268         if (WARN_ON_ONCE(!pmd_none(*new_pmd)))
 269                 return false;
 270
 271         /*
 272          * We don't have to worry about the ordering of src and dst
 273          * ptlocks because exclusive mmap_lock prevents deadlock.
 274          */
 275         old_ptl = pmd_lock(vma->vm_mm, old_pmd);
 276         new_ptl = pmd_lockptr(mm, new_pmd);
 277         if (new_ptl != old_ptl)
 278                 spin_lock_nested(new_ptl, SINGLE_DEPTH_NESTING);
 279
 280         /* Clear the pmd */
 281         pmd = *old_pmd;
 282         pmd_clear(old_pmd);
 283
 284         VM_BUG_ON(!pmd_none(*new_pmd));
 285
 286         pmd_populate(mm, new_pmd, pmd_pgtable(pmd));
 287         flush_tlb_range(vma, old_addr, old_addr + PMD_SIZE);
 288         if (new_ptl != old_ptl)
 289                 spin_unlock(new_ptl);
 290         spin_unlock(old_ptl);
 291
 292         return true;
 293 }
 294 #else
 295 static inline bool move_normal_pmd(struct vm_area_struct *vma,
 296                 unsigned long old_addr, unsigned long new_addr, pmd_t *old_pmd,
 297                 pmd_t *new_pmd)
 298 {
 299         return false;
 300 }
 301 #endif
 302
 303 #if CONFIG_PGTABLE_LEVELS > 2 && defined(CONFIG_HAVE_MOVE_PUD)
 304 static bool move_normal_pud(struct vm_area_struct *vma, unsigned long old_addr,
 305                   unsigned long new_addr, pud_t *old_pud, pud_t *new_pud)
 306 {
 307         spinlock_t *old_ptl, *new_ptl;
 308         struct mm_struct *mm = vma->vm_mm;
 309         pud_t pud;
 310
 311         if (!arch_supports_page_table_move())
 312                 return false;
 313         /*
 314          * The destination pud shouldn't be established, free_pgtables()
 315          * should have released it.
 316          */
 317         if (WARN_ON_ONCE(!pud_none(*new_pud)))
 318                 return false;
 319
 320         /*
 321          * We don't have to worry about the ordering of src and dst
 322          * ptlocks because exclusive mmap_lock prevents deadlock.
 323          */
 324         old_ptl = pud_lock(vma->vm_mm, old_pud);
 325         new_ptl = pud_lockptr(mm, new_pud);
 326         if (new_ptl != old_ptl)
 327                 spin_lock_nested(new_ptl, SINGLE_DEPTH_NESTING);
 328
 329         /* Clear the pud */
 330         pud = *old_pud;
 331         pud_clear(old_pud);
 332
 333         VM_BUG_ON(!pud_none(*new_pud));
 334
 335         pud_populate(mm, new_pud, pud_pgtable(pud));
 336         flush_tlb_range(vma, old_addr, old_addr + PUD_SIZE);
 337         if (new_ptl != old_ptl)
 338                 spin_unlock(new_ptl);
 339         spin_unlock(old_ptl);
 340
 341         return true;
 342 }
 343 #else
 344 static inline bool move_normal_pud(struct vm_area_struct *vma,
 345                 unsigned long old_addr, unsigned long new_addr, pud_t *old_pud,
 346                 pud_t *new_pud)
 347 {
 348         return false;
 349 }
 350 #endif
 351
 352 #if defined(CONFIG_TRANSPARENT_HUGEPAGE) && defined(CONFIG_HAVE_ARCH_TRANSPARENT_HUGEPAGE_PUD)
 353 static bool move_huge_pud(struct vm_area_struct *vma, unsigned long old_addr,
 354                           unsigned long new_addr, pud_t *old_pud, pud_t *new_pud)
 355 {
 356         spinlock_t *old_ptl, *new_ptl;
 357         struct mm_struct *mm = vma->vm_mm;
 358         pud_t pud;
 359
 360         /*
 361          * The destination pud shouldn't be established, free_pgtables()
 362          * should have released it.
 363          */
 364         if (WARN_ON_ONCE(!pud_none(*new_pud)))
 365                 return false;
 366
 367         /*
 368          * We don't have to worry about the ordering of src and dst
 369          * ptlocks because exclusive mmap_lock prevents deadlock.
 370          */
 371         old_ptl = pud_lock(vma->vm_mm, old_pud);
 372         new_ptl = pud_lockptr(mm, new_pud);
 373         if (new_ptl != old_ptl)
 374                 spin_lock_nested(new_ptl, SINGLE_DEPTH_NESTING);
 375
 376         /* Clear the pud */
 377         pud = *old_pud;
 378         pud_clear(old_pud);
 379
 380         VM_BUG_ON(!pud_none(*new_pud));
 381
 382         /* Set the new pud */
 383         /* mark soft_ditry when we add pud level soft dirty support */
 384         set_pud_at(mm, new_addr, new_pud, pud);
 385         flush_pud_tlb_range(vma, old_addr, old_addr + HPAGE_PUD_SIZE);
 386         if (new_ptl != old_ptl)
 387                 spin_unlock(new_ptl);
 388         spin_unlock(old_ptl);
 389
 390         return true;
 391 }
 392 #else
 393 static bool move_huge_pud(struct vm_area_struct *vma, unsigned long old_addr,
 394                           unsigned long new_addr, pud_t *old_pud, pud_t *new_pud)
 395 {
 396         WARN_ON_ONCE(1);
 397         return false;
 398
 399 }
 400 #endif
 401
 402 enum pgt_entry {
 403         NORMAL_PMD,
 404         HPAGE_PMD,
 405         NORMAL_PUD,
 406         HPAGE_PUD,
 407 };
 408
 409 /*
 410  * Returns an extent of the corresponding size for the pgt_entry specified if
 411  * valid. Else returns a smaller extent bounded by the end of the source and
 412  * destination pgt_entry.
 413  */
 414 static __always_inline unsigned long get_extent(enum pgt_entry entry,
 415                         unsigned long old_addr, unsigned long old_end,
 416                         unsigned long new_addr)
 417 {
 418         unsigned long next, extent, mask, size;
 419
 420         switch (entry) {
 421         case HPAGE_PMD:
 422         case NORMAL_PMD:
 423                 mask = PMD_MASK;
 424                 size = PMD_SIZE;
 425                 break;
 426         case HPAGE_PUD:
 427         case NORMAL_PUD:
 428                 mask = PUD_MASK;
 429                 size = PUD_SIZE;
 430                 break;
 431         default:
 432                 BUILD_BUG();
 433                 break;
 434         }
 435
 436         next = (old_addr + size) & mask;
 437         /* even if next overflowed, extent below will be ok */
 438         extent = next - old_addr;
 439         if (extent > old_end - old_addr)
 440                 extent = old_end - old_addr;
 441         next = (new_addr + size) & mask;
 442         if (extent > next - new_addr)
 443                 extent = next - new_addr;
 444         return extent;
 445 }
 446
 447 /*
 448  * Attempts to speedup the move by moving entry at the level corresponding to
 449  * pgt_entry. Returns true if the move was successful, else false.
 450  */
 451 static bool move_pgt_entry(enum pgt_entry entry, struct vm_area_struct *vma,
 452                         unsigned long old_addr, unsigned long new_addr,
 453                         void *old_entry, void *new_entry, bool need_rmap_locks)
 454 {
 455         bool moved = false;
 456
 457         /* See comment in move_ptes() */
 458         if (need_rmap_locks)
 459                 take_rmap_locks(vma);
 460
 461         switch (entry) {
 462         case NORMAL_PMD:
 463                 moved = move_normal_pmd(vma, old_addr, new_addr, old_entry,
 464                                         new_entry);
 465                 break;
 466         case NORMAL_PUD:
 467                 moved = move_normal_pud(vma, old_addr, new_addr, old_entry,
 468                                         new_entry);
 469                 break;
 470         case HPAGE_PMD:
 471                 moved = IS_ENABLED(CONFIG_TRANSPARENT_HUGEPAGE) &&
 472                         move_huge_pmd(vma, old_addr, new_addr, old_entry,
 473                                       new_entry);
 474                 break;
 475         case HPAGE_PUD:
 476                 moved = IS_ENABLED(CONFIG_TRANSPARENT_HUGEPAGE) &&
 477                         move_huge_pud(vma, old_addr, new_addr, old_entry,
 478                                       new_entry);
 479                 break;
 480
 481         default:
 482                 WARN_ON_ONCE(1);
 483                 break;
 484         }
 485
 486         if (need_rmap_locks)
 487                 drop_rmap_locks(vma);
 488
 489         return moved;
 490 }
 491
 492 /*
 493  * A helper to check if aligning down is OK. The aligned address should fall
 494  * on *no mapping*. For the stack moving down, that's a special move within
 495  * the VMA that is created to span the source and destination of the move,
 496  * so we make an exception for it.
 497  */
 498 static bool can_align_down(struct vm_area_struct *vma, unsigned long addr_to_align,
 499                             unsigned long mask, bool for_stack)
 500 {
 501         unsigned long addr_masked = addr_to_align & mask;
 502
 503         /*
 504          * If @addr_to_align of either source or destination is not the beginning
 505          * of the corresponding VMA, we can't align down or we will destroy part
 506          * of the current mapping.
 507          */
 508         if (!for_stack && vma->vm_start != addr_to_align)
 509                 return false;
 510
 511         /* In the stack case we explicitly permit in-VMA alignment. */
 512         if (for_stack && addr_masked >= vma->vm_start)
 513                 return true;
 514
 515         /*
 516          * Make sure the realignment doesn't cause the address to fall on an
 517          * existing mapping.
 518          */
 519         return find_vma_intersection(vma->vm_mm, addr_masked, vma->vm_start) == NULL;
 520 }
 521
 522 /* Opportunistically realign to specified boundary for faster copy. */
 523 static void try_realign_addr(unsigned long *old_addr, struct vm_area_struct *old_vma,
 524                              unsigned long *new_addr, struct vm_area_struct *new_vma,
 525                              unsigned long mask, bool for_stack)
 526 {
 527         /* Skip if the addresses are already aligned. */
 528         if ((*old_addr & ~mask) == 0)
 529                 return;
 530
 531         /* Only realign if the new and old addresses are mutually aligned. */
 532         if ((*old_addr & ~mask) != (*new_addr & ~mask))
 533                 return;
 534
 535         /* Ensure realignment doesn't cause overlap with existing mappings. */
 536         if (!can_align_down(old_vma, *old_addr, mask, for_stack) ||
 537             !can_align_down(new_vma, *new_addr, mask, for_stack))
 538                 return;
 539
 540         *old_addr = *old_addr & mask;
 541         *new_addr = *new_addr & mask;
 542 }
 543
 544 unsigned long move_page_tables(struct vm_area_struct *vma,
 545                 unsigned long old_addr, struct vm_area_struct *new_vma,
 546                 unsigned long new_addr, unsigned long len,
 547                 bool need_rmap_locks, bool for_stack)
 548 {
 549         unsigned long extent, old_end;
 550         struct mmu_notifier_range range;
 551         pmd_t *old_pmd, *new_pmd;
 552         pud_t *old_pud, *new_pud;
 553
 554         if (!len)
 555                 return 0;
 556
 557         old_end = old_addr + len;
 558
 559         if (is_vm_hugetlb_page(vma))
 560                 return move_hugetlb_page_tables(vma, new_vma, old_addr,
 561                                                 new_addr, len);
 562
 563         /*
 564          * If possible, realign addresses to PMD boundary for faster copy.
 565          * Only realign if the mremap copying hits a PMD boundary.
 566          */
 567         if (len >= PMD_SIZE - (old_addr & ~PMD_MASK))
 568                 try_realign_addr(&old_addr, vma, &new_addr, new_vma, PMD_MASK,
 569                                  for_stack);
 570
 571         flush_cache_range(vma, old_addr, old_end);
 572         mmu_notifier_range_init(&range, MMU_NOTIFY_UNMAP, 0, vma->vm_mm,
 573                                 old_addr, old_end);
 574         mmu_notifier_invalidate_range_start(&range);
 575
 576         for (; old_addr < old_end; old_addr += extent, new_addr += extent) {
 577                 cond_resched();
 578                 /*
 579                  * If extent is PUD-sized try to speed up the move by moving at the
 580                  * PUD level if possible.
 581                  */
 582                 extent = get_extent(NORMAL_PUD, old_addr, old_end, new_addr);
 583
 584                 old_pud = get_old_pud(vma->vm_mm, old_addr);
 585                 if (!old_pud)
 586                         continue;
 587                 new_pud = alloc_new_pud(vma->vm_mm, vma, new_addr);
 588                 if (!new_pud)
 589                         break;
 590                 if (pud_trans_huge(*old_pud) || pud_devmap(*old_pud)) {
 591                         if (extent == HPAGE_PUD_SIZE) {
 592                                 move_pgt_entry(HPAGE_PUD, vma, old_addr, new_addr,
 593                                                old_pud, new_pud, need_rmap_locks);
 594                                 /* We ignore and continue on error? */
 595                                 continue;
 596                         }
 597                 } else if (IS_ENABLED(CONFIG_HAVE_MOVE_PUD) && extent == PUD_SIZE) {
 598
 599                         if (move_pgt_entry(NORMAL_PUD, vma, old_addr, new_addr,
 600                                            old_pud, new_pud, true))
 601                                 continue;
 602                 }
 603
 604                 extent = get_extent(NORMAL_PMD, old_addr, old_end, new_addr);
 605                 old_pmd = get_old_pmd(vma->vm_mm, old_addr);
 606                 if (!old_pmd)
 607                         continue;
 608                 new_pmd = alloc_new_pmd(vma->vm_mm, vma, new_addr);
 609                 if (!new_pmd)
 610                         break;
 611 again:
 612                 if (is_swap_pmd(*old_pmd) || pmd_trans_huge(*old_pmd) ||
 613                     pmd_devmap(*old_pmd)) {
 614                         if (extent == HPAGE_PMD_SIZE &&
 615                             move_pgt_entry(HPAGE_PMD, vma, old_addr, new_addr,
 616                                            old_pmd, new_pmd, need_rmap_locks))
 617                                 continue;
 618                         split_huge_pmd(vma, old_pmd, old_addr);
 619                 } else if (IS_ENABLED(CONFIG_HAVE_MOVE_PMD) &&
 620                            extent == PMD_SIZE) {
 621                         /*
 622                          * If the extent is PMD-sized, try to speed the move by
 623                          * moving at the PMD level if possible.
 624                          */
 625                         if (move_pgt_entry(NORMAL_PMD, vma, old_addr, new_addr,
 626                                            old_pmd, new_pmd, true))
 627                                 continue;
 628                 }
 629                 if (pmd_none(*old_pmd))
 630                         continue;
 631                 if (pte_alloc(new_vma->vm_mm, new_pmd))
 632                         break;
 633                 if (move_ptes(vma, old_pmd, old_addr, old_addr + extent,
 634                               new_vma, new_pmd, new_addr, need_rmap_locks) < 0)
 635                         goto again;
 636         }
 637
 638         mmu_notifier_invalidate_range_end(&range);
 639
 640         /*
 641          * Prevent negative return values when {old,new}_addr was realigned
 642          * but we broke out of the above loop for the first PMD itself.
 643          */
 644         if (len + old_addr < old_end)
 645                 return 0;
 646
 647         return len + old_addr - old_end;        /* how much done */
 648 }
 649
 650 static unsigned long move_vma(struct vm_area_struct *vma,
 651                 unsigned long old_addr, unsigned long old_len,
 652                 unsigned long new_len, unsigned long new_addr,
 653                 bool *locked, unsigned long flags,
 654                 struct vm_userfaultfd_ctx *uf, struct list_head *uf_unmap)
 655 {
 656         long to_account = new_len - old_len;
 657         struct mm_struct *mm = vma->vm_mm;
 658         struct vm_area_struct *new_vma;
 659         unsigned long vm_flags = vma->vm_flags;
 660         unsigned long new_pgoff;
 661         unsigned long moved_len;
 662         unsigned long account_start = 0;
 663         unsigned long account_end = 0;
 664         unsigned long hiwater_vm;
 665         int err = 0;
 666         bool need_rmap_locks;
 667         struct vma_iterator vmi;
 668
 669         /*
 670          * We'd prefer to avoid failure later on in do_munmap:
 671          * which may split one vma into three before unmapping.
 672          */
 673         if (mm->map_count >= sysctl_max_map_count - 3)
 674                 return -ENOMEM;
 675
 676         if (unlikely(flags & MREMAP_DONTUNMAP))
 677                 to_account = new_len;
 678
 679         if (vma->vm_ops && vma->vm_ops->may_split) {
 680                 if (vma->vm_start != old_addr)
 681                         err = vma->vm_ops->may_split(vma, old_addr);
 682                 if (!err && vma->vm_end != old_addr + old_len)
 683                         err = vma->vm_ops->may_split(vma, old_addr + old_len);
 684                 if (err)
 685                         return err;
 686         }
 687
 688         /*
 689          * Advise KSM to break any KSM pages in the area to be moved:
 690          * it would be confusing if they were to turn up at the new
 691          * location, where they happen to coincide with different KSM
 692          * pages recently unmapped.  But leave vma->vm_flags as it was,
 693          * so KSM can come around to merge on vma and new_vma afterwards.
 694          */
 695         err = ksm_madvise(vma, old_addr, old_addr + old_len,
 696                                                 MADV_UNMERGEABLE, &vm_flags);
 697         if (err)
 698                 return err;
 699
 700         if (vm_flags & VM_ACCOUNT) {
 701                 if (security_vm_enough_memory_mm(mm, to_account >> PAGE_SHIFT))
 702                         return -ENOMEM;
 703         }
 704
 705         vma_start_write(vma);
 706         new_pgoff = vma->vm_pgoff + ((old_addr - vma->vm_start) >> PAGE_SHIFT);
 707         new_vma = copy_vma(&vma, new_addr, new_len, new_pgoff,
 708                            &need_rmap_locks);
 709         if (!new_vma) {
 710                 if (vm_flags & VM_ACCOUNT)
 711                         vm_unacct_memory(to_account >> PAGE_SHIFT);
 712                 return -ENOMEM;
 713         }
 714
 715         moved_len = move_page_tables(vma, old_addr, new_vma, new_addr, old_len,
 716                                      need_rmap_locks, false);
 717         if (moved_len < old_len) {
 718                 err = -ENOMEM;
 719         } else if (vma->vm_ops && vma->vm_ops->mremap) {
 720                 err = vma->vm_ops->mremap(new_vma);
 721         }
 722
 723         if (unlikely(err)) {
 724                 /*
 725                  * On error, move entries back from new area to old,
 726                  * which will succeed since page tables still there,
 727                  * and then proceed to unmap new area instead of old.
 728                  */
 729                 move_page_tables(new_vma, new_addr, vma, old_addr, moved_len,
 730                                  true, false);
 731                 vma = new_vma;
 732                 old_len = new_len;
 733                 old_addr = new_addr;
 734                 new_addr = err;
 735         } else {
 736                 mremap_userfaultfd_prep(new_vma, uf);
 737         }
 738
 739         if (is_vm_hugetlb_page(vma)) {
 740                 clear_vma_resv_huge_pages(vma);
 741         }
 742
 743         /* Conceal VM_ACCOUNT so old reservation is not undone */
 744         if (vm_flags & VM_ACCOUNT && !(flags & MREMAP_DONTUNMAP)) {
 745                 vm_flags_clear(vma, VM_ACCOUNT);
 746                 if (vma->vm_start < old_addr)
 747                         account_start = vma->vm_start;
 748                 if (vma->vm_end > old_addr + old_len)
 749                         account_end = vma->vm_end;
 750         }
 751
 752         /*
 753          * If we failed to move page tables we still do total_vm increment
 754          * since do_munmap() will decrement it by old_len == new_len.
 755          *
 756          * Since total_vm is about to be raised artificially high for a
 757          * moment, we need to restore high watermark afterwards: if stats
 758          * are taken meanwhile, total_vm and hiwater_vm appear too high.
 759          * If this were a serious issue, we'd add a flag to do_munmap().
 760          */
 761         hiwater_vm = mm->hiwater_vm;
 762         vm_stat_account(mm, vma->vm_flags, new_len >> PAGE_SHIFT);
 763
 764         /* Tell pfnmap has moved from this vma */
 765         if (unlikely(vma->vm_flags & VM_PFNMAP))
 766                 untrack_pfn_clear(vma);
 767
 768         if (unlikely(!err && (flags & MREMAP_DONTUNMAP))) {
 769                 /* We always clear VM_LOCKED[ONFAULT] on the old vma */
 770                 vm_flags_clear(vma, VM_LOCKED_MASK);
 771
 772                 /*
 773                  * anon_vma links of the old vma is no longer needed after its page
 774                  * table has been moved.
 775                  */
 776                 if (new_vma != vma && vma->vm_start == old_addr &&
 777                         vma->vm_end == (old_addr + old_len))
 778                         unlink_anon_vmas(vma);
 779
 780                 /* Because we won't unmap we don't need to touch locked_vm */
 781                 return new_addr;
 782         }
 783
 784         vma_iter_init(&vmi, mm, old_addr);
 785         if (do_vmi_munmap(&vmi, mm, old_addr, old_len, uf_unmap, false) < 0) {
 786                 /* OOM: unable to split vma, just get accounts right */
 787                 if (vm_flags & VM_ACCOUNT && !(flags & MREMAP_DONTUNMAP))
 788                         vm_acct_memory(old_len >> PAGE_SHIFT);
 789                 account_start = account_end = 0;
 790         }
 791
 792         if (vm_flags & VM_LOCKED) {
 793                 mm->locked_vm += new_len >> PAGE_SHIFT;
 794                 *locked = true;
 795         }
 796
 797         mm->hiwater_vm = hiwater_vm;
 798
 799         /* Restore VM_ACCOUNT if one or two pieces of vma left */
 800         if (account_start) {
 801                 vma = vma_prev(&vmi);
 802                 vm_flags_set(vma, VM_ACCOUNT);
 803         }
 804
 805         if (account_end) {
 806                 vma = vma_next(&vmi);
 807                 vm_flags_set(vma, VM_ACCOUNT);
 808         }
 809
 810         return new_addr;
 811 }
 812
 813 static struct vm_area_struct *vma_to_resize(unsigned long addr,
 814         unsigned long old_len, unsigned long new_len, unsigned long flags)
 815 {
 816         struct mm_struct *mm = current->mm;
 817         struct vm_area_struct *vma;
 818         unsigned long pgoff;
 819
 820         vma = vma_lookup(mm, addr);
 821         if (!vma)
 822                 return ERR_PTR(-EFAULT);
 823
 824         /*
 825          * !old_len is a special case where an attempt is made to 'duplicate'
 826          * a mapping.  This makes no sense for private mappings as it will
 827          * instead create a fresh/new mapping unrelated to the original.  This
 828          * is contrary to the basic idea of mremap which creates new mappings
 829          * based on the original.  There are no known use cases for this
 830          * behavior.  As a result, fail such attempts.
 831          */
 832         if (!old_len && !(vma->vm_flags & (VM_SHARED | VM_MAYSHARE))) {
 833                 pr_warn_once("%s (%d): attempted to duplicate a private mapping with mremap.  This is not supported.\n", current->comm, current->pid);
 834                 return ERR_PTR(-EINVAL);
 835         }
 836
 837         if ((flags & MREMAP_DONTUNMAP) &&
 838                         (vma->vm_flags & (VM_DONTEXPAND | VM_PFNMAP)))
 839                 return ERR_PTR(-EINVAL);
 840
 841         /* We can't remap across vm area boundaries */
 842         if (old_len > vma->vm_end - addr)
 843                 return ERR_PTR(-EFAULT);
 844
 845         if (new_len == old_len)
 846                 return vma;
 847
 848         /* Need to be careful about a growing mapping */
 849         pgoff = (addr - vma->vm_start) >> PAGE_SHIFT;
 850         pgoff += vma->vm_pgoff;
 851         if (pgoff + (new_len >> PAGE_SHIFT) < pgoff)
 852                 return ERR_PTR(-EINVAL);
 853
 854         if (vma->vm_flags & (VM_DONTEXPAND | VM_PFNMAP))
 855                 return ERR_PTR(-EFAULT);
 856
 857         if (!mlock_future_ok(mm, vma->vm_flags, new_len - old_len))
 858                 return ERR_PTR(-EAGAIN);
 859
 860         if (!may_expand_vm(mm, vma->vm_flags,
 861                                 (new_len - old_len) >> PAGE_SHIFT))
 862                 return ERR_PTR(-ENOMEM);
 863
 864         return vma;
 865 }
 866
 867 static unsigned long mremap_to(unsigned long addr, unsigned long old_len,
 868                 unsigned long new_addr, unsigned long new_len, bool *locked,
 869                 unsigned long flags, struct vm_userfaultfd_ctx *uf,
 870                 struct list_head *uf_unmap_early,
 871                 struct list_head *uf_unmap)
 872 {
 873         struct mm_struct *mm = current->mm;
 874         struct vm_area_struct *vma;
 875         unsigned long ret = -EINVAL;
 876         unsigned long map_flags = 0;
 877
 878         if (offset_in_page(new_addr))
 879                 goto out;
 880
 881         if (new_len > TASK_SIZE || new_addr > TASK_SIZE - new_len)
 882                 goto out;
 883
 884         /* Ensure the old/new locations do not overlap */
 885         if (addr + old_len > new_addr && new_addr + new_len > addr)
 886                 goto out;
 887
 888         /*
 889          * move_vma() need us to stay 4 maps below the threshold, otherwise
 890          * it will bail out at the very beginning.
 891          * That is a problem if we have already unmaped the regions here
 892          * (new_addr, and old_addr), because userspace will not know the
 893          * state of the vma's after it gets -ENOMEM.
 894          * So, to avoid such scenario we can pre-compute if the whole
 895          * operation has high chances to success map-wise.
 896          * Worst-scenario case is when both vma's (new_addr and old_addr) get
 897          * split in 3 before unmapping it.
 898          * That means 2 more maps (1 for each) to the ones we already hold.
 899          * Check whether current map count plus 2 still leads us to 4 maps below
 900          * the threshold, otherwise return -ENOMEM here to be more safe.
 901          */
 902         if ((mm->map_count + 2) >= sysctl_max_map_count - 3)
 903                 return -ENOMEM;
 904
 905         /*
 906          * In mremap_to().
 907          * Move a VMA to another location, check if src addr is sealed.
 908          *
 909          * Place can_modify_mm here because mremap_to()
 910          * does its own checking for address range, and we only
 911          * check the sealing after passing those checks.
 912          *
 913          * can_modify_mm assumes we have acquired the lock on MM.
 914          */
 915         if (unlikely(!can_modify_mm(mm, addr, addr + old_len)))
 916                 return -EPERM;
 917
 918         if (flags & MREMAP_FIXED) {
 919                 /*
 920                  * In mremap_to().
 921                  * VMA is moved to dst address, and munmap dst first.
 922                  * do_munmap will check if dst is sealed.
 923                  */
 924                 ret = do_munmap(mm, new_addr, new_len, uf_unmap_early);
 925                 if (ret)
 926                         goto out;
 927         }
 928
 929         if (old_len > new_len) {
 930                 ret = do_munmap(mm, addr+new_len, old_len - new_len, uf_unmap);
 931                 if (ret)
 932                         goto out;
 933                 old_len = new_len;
 934         }
 935
 936         vma = vma_to_resize(addr, old_len, new_len, flags);
 937         if (IS_ERR(vma)) {
 938                 ret = PTR_ERR(vma);
 939                 goto out;
 940         }
 941
 942         /* MREMAP_DONTUNMAP expands by old_len since old_len == new_len */
 943         if (flags & MREMAP_DONTUNMAP &&
 944                 !may_expand_vm(mm, vma->vm_flags, old_len >> PAGE_SHIFT)) {
 945                 ret = -ENOMEM;
 946                 goto out;
 947         }
 948
 949         if (flags & MREMAP_FIXED)
 950                 map_flags |= MAP_FIXED;
 951
 952         if (vma->vm_flags & VM_MAYSHARE)
 953                 map_flags |= MAP_SHARED;
 954
 955         ret = get_unmapped_area(vma->vm_file, new_addr, new_len, vma->vm_pgoff +
 956                                 ((addr - vma->vm_start) >> PAGE_SHIFT),
 957                                 map_flags);
 958         if (IS_ERR_VALUE(ret))
 959                 goto out;
 960
 961         /* We got a new mapping */
 962         if (!(flags & MREMAP_FIXED))
 963                 new_addr = ret;
 964
 965         ret = move_vma(vma, addr, old_len, new_len, new_addr, locked, flags, uf,
 966                        uf_unmap);
 967
 968 out:
 969         return ret;
 970 }
 971
 972 static int vma_expandable(struct vm_area_struct *vma, unsigned long delta)
 973 {
 974         unsigned long end = vma->vm_end + delta;
 975
 976         if (end < vma->vm_end) /* overflow */
 977                 return 0;
 978         if (find_vma_intersection(vma->vm_mm, vma->vm_end, end))
 979                 return 0;
 980         if (get_unmapped_area(NULL, vma->vm_start, end - vma->vm_start,
 981                               0, MAP_FIXED) & ~PAGE_MASK)
 982                 return 0;
 983         return 1;
 984 }
 985
 986 /*
 987  * Expand (or shrink) an existing mapping, potentially moving it at the
 988  * same time (controlled by the MREMAP_MAYMOVE flag and available VM space)
 989  *
 990  * MREMAP_FIXED option added 5-Dec-1999 by Benjamin LaHaise
 991  * This option implies MREMAP_MAYMOVE.
 992  */
 993 SYSCALL_DEFINE5(mremap, unsigned long, addr, unsigned long, old_len,
 994                 unsigned long, new_len, unsigned long, flags,
 995                 unsigned long, new_addr)
 996 {
 997         struct mm_struct *mm = current->mm;
 998         struct vm_area_struct *vma;
 999         unsigned long ret = -EINVAL;
1000         bool locked = false;
1001         struct vm_userfaultfd_ctx uf = NULL_VM_UFFD_CTX;
1002         LIST_HEAD(uf_unmap_early);
1003         LIST_HEAD(uf_unmap);
1004
1005         /*
1006          * There is a deliberate asymmetry here: we strip the pointer tag
1007          * from the old address but leave the new address alone. This is
1008          * for consistency with mmap(), where we prevent the creation of
1009          * aliasing mappings in userspace by leaving the tag bits of the
1010          * mapping address intact. A non-zero tag will cause the subsequent
1011          * range checks to reject the address as invalid.
1012          *
1013          * See Documentation/arch/arm64/tagged-address-abi.rst for more
1014          * information.
1015          */
1016         addr = untagged_addr(addr);
1017
1018         if (flags & ~(MREMAP_FIXED | MREMAP_MAYMOVE | MREMAP_DONTUNMAP))
1019                 return ret;
1020
1021         if (flags & MREMAP_FIXED && !(flags & MREMAP_MAYMOVE))
1022                 return ret;
1023
1024         /*
1025          * MREMAP_DONTUNMAP is always a move and it does not allow resizing
1026          * in the process.
1027          */
1028         if (flags & MREMAP_DONTUNMAP &&
1029                         (!(flags & MREMAP_MAYMOVE) || old_len != new_len))
1030                 return ret;
1031
1032
1033         if (offset_in_page(addr))
1034                 return ret;
1035
1036         old_len = PAGE_ALIGN(old_len);
1037         new_len = PAGE_ALIGN(new_len);
1038
1039         /*
1040          * We allow a zero old-len as a special case
1041          * for DOS-emu "duplicate shm area" thing. But
1042          * a zero new-len is nonsensical.
1043          */
1044         if (!new_len)
1045                 return ret;
1046
1047         if (mmap_write_lock_killable(current->mm))
1048                 return -EINTR;
1049         vma = vma_lookup(mm, addr);
1050         if (!vma) {
1051                 ret = -EFAULT;
1052                 goto out;
1053         }
1054
1055         if (is_vm_hugetlb_page(vma)) {
1056                 struct hstate *h __maybe_unused = hstate_vma(vma);
1057
1058                 old_len = ALIGN(old_len, huge_page_size(h));
1059                 new_len = ALIGN(new_len, huge_page_size(h));
1060
1061                 /* addrs must be huge page aligned */
1062                 if (addr & ~huge_page_mask(h))
1063                         goto out;
1064                 if (new_addr & ~huge_page_mask(h))
1065                         goto out;
1066
1067                 /*
1068                  * Don't allow remap expansion, because the underlying hugetlb
1069                  * reservation is not yet capable to handle split reservation.
1070                  */
1071                 if (new_len > old_len)
1072                         goto out;
1073         }
1074
1075         if (flags & (MREMAP_FIXED | MREMAP_DONTUNMAP)) {
1076                 ret = mremap_to(addr, old_len, new_addr, new_len,
1077                                 &locked, flags, &uf, &uf_unmap_early,
1078                                 &uf_unmap);
1079                 goto out;
1080         }
1081
1082         /*
1083          * Below is shrink/expand case (not mremap_to())
1084          * Check if src address is sealed, if so, reject.
1085          * In other words, prevent shrinking or expanding a sealed VMA.
1086          *
1087          * Place can_modify_mm here so we can keep the logic related to
1088          * shrink/expand together.
1089          */
1090         if (unlikely(!can_modify_mm(mm, addr, addr + old_len))) {
1091                 ret = -EPERM;
1092                 goto out;
1093         }
1094
1095         /*
1096          * Always allow a shrinking remap: that just unmaps
1097          * the unnecessary pages..
1098          * do_vmi_munmap does all the needed commit accounting, and
1099          * unlocks the mmap_lock if so directed.
1100          */
1101         if (old_len >= new_len) {
1102                 VMA_ITERATOR(vmi, mm, addr + new_len);
1103
1104                 if (old_len == new_len) {
1105                         ret = addr;
1106                         goto out;
1107                 }
1108
1109                 ret = do_vmi_munmap(&vmi, mm, addr + new_len, old_len - new_len,
1110                                     &uf_unmap, true);
1111                 if (ret)
1112                         goto out;
1113
1114                 ret = addr;
1115                 goto out_unlocked;
1116         }
1117
1118         /*
1119          * Ok, we need to grow..
1120          */
1121         vma = vma_to_resize(addr, old_len, new_len, flags);
1122         if (IS_ERR(vma)) {
1123                 ret = PTR_ERR(vma);
1124                 goto out;
1125         }
1126
1127         /* old_len exactly to the end of the area..
1128          */
1129         if (old_len == vma->vm_end - addr) {
1130                 unsigned long delta = new_len - old_len;
1131
1132                 /* can we just expand the current mapping? */
1133                 if (vma_expandable(vma, delta)) {
1134                         long pages = delta >> PAGE_SHIFT;
1135                         VMA_ITERATOR(vmi, mm, vma->vm_end);
1136                         long charged = 0;
1137
1138                         if (vma->vm_flags & VM_ACCOUNT) {
1139                                 if (security_vm_enough_memory_mm(mm, pages)) {
1140                                         ret = -ENOMEM;
1141                                         goto out;
1142                                 }
1143                                 charged = pages;
1144                         }
1145
1146                         /*
1147                          * Function vma_merge_extend() is called on the
1148                          * extension we are adding to the already existing vma,
1149                          * vma_merge_extend() will merge this extension with the
1150                          * already existing vma (expand operation itself) and
1151                          * possibly also with the next vma if it becomes
1152                          * adjacent to the expanded vma and otherwise
1153                          * compatible.
1154                          */
1155                         vma = vma_merge_extend(&vmi, vma, delta);
1156                         if (!vma) {
1157                                 vm_unacct_memory(charged);
1158                                 ret = -ENOMEM;
1159                                 goto out;
1160                         }
1161
1162                         vm_stat_account(mm, vma->vm_flags, pages);
1163                         if (vma->vm_flags & VM_LOCKED) {
1164                                 mm->locked_vm += pages;
1165                                 locked = true;
1166                                 new_addr = addr;
1167                         }
1168                         ret = addr;
1169                         goto out;
1170                 }
1171         }
1172
1173         /*
1174          * We weren't able to just expand or shrink the area,
1175          * we need to create a new one and move it..
1176          */
1177         ret = -ENOMEM;
1178         if (flags & MREMAP_MAYMOVE) {
1179                 unsigned long map_flags = 0;
1180                 if (vma->vm_flags & VM_MAYSHARE)
1181                         map_flags |= MAP_SHARED;
1182
1183                 new_addr = get_unmapped_area(vma->vm_file, 0, new_len,
1184                                         vma->vm_pgoff +
1185                                         ((addr - vma->vm_start) >> PAGE_SHIFT),
1186                                         map_flags);
1187                 if (IS_ERR_VALUE(new_addr)) {
1188                         ret = new_addr;
1189                         goto out;
1190                 }
1191
1192                 ret = move_vma(vma, addr, old_len, new_len, new_addr,
1193                                &locked, flags, &uf, &uf_unmap);
1194         }
1195 out:
1196         if (offset_in_page(ret))
1197                 locked = false;
1198         mmap_write_unlock(current->mm);
1199         if (locked && new_len > old_len)
1200                 mm_populate(new_addr + old_len, new_len - old_len);
1201 out_unlocked:
1202         userfaultfd_unmap_complete(mm, &uf_unmap_early);
1203         mremap_userfaultfd_complete(&uf, addr, ret, old_len);
1204         userfaultfd_unmap_complete(mm, &uf_unmap);
1205         return ret;
1206 }