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