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/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/mm-arch-hooks.h>
  26 #include <linux/userfaultfd_k.h>
  27
  28 #include <asm/cacheflush.h>
  29 #include <asm/tlbflush.h>
  30
  31 #include "internal.h"
  32
  33 static pmd_t *get_old_pmd(struct mm_struct *mm, unsigned long addr)
  34 {
  35         pgd_t *pgd;
  36         p4d_t *p4d;
  37         pud_t *pud;
  38         pmd_t *pmd;
  39
  40         pgd = pgd_offset(mm, addr);
  41         if (pgd_none_or_clear_bad(pgd))
  42                 return NULL;
  43
  44         p4d = p4d_offset(pgd, addr);
  45         if (p4d_none_or_clear_bad(p4d))
  46                 return NULL;
  47
  48         pud = pud_offset(p4d, addr);
  49         if (pud_none_or_clear_bad(pud))
  50                 return NULL;
  51
  52         pmd = pmd_offset(pud, addr);
  53         if (pmd_none(*pmd))
  54                 return NULL;
  55
  56         return pmd;
  57 }
  58
  59 static pmd_t *alloc_new_pmd(struct mm_struct *mm, struct vm_area_struct *vma,
  60                             unsigned long addr)
  61 {
  62         pgd_t *pgd;
  63         p4d_t *p4d;
  64         pud_t *pud;
  65         pmd_t *pmd;
  66
  67         pgd = pgd_offset(mm, addr);
  68         p4d = p4d_alloc(mm, pgd, addr);
  69         if (!p4d)
  70                 return NULL;
  71         pud = pud_alloc(mm, p4d, addr);
  72         if (!pud)
  73                 return NULL;
  74
  75         pmd = pmd_alloc(mm, pud, addr);
  76         if (!pmd)
  77                 return NULL;
  78
  79         VM_BUG_ON(pmd_trans_huge(*pmd));
  80
  81         return pmd;
  82 }
  83
  84 static void take_rmap_locks(struct vm_area_struct *vma)
  85 {
  86         if (vma->vm_file)
  87                 i_mmap_lock_write(vma->vm_file->f_mapping);
  88         if (vma->anon_vma)
  89                 anon_vma_lock_write(vma->anon_vma);
  90 }
  91
  92 static void drop_rmap_locks(struct vm_area_struct *vma)
  93 {
  94         if (vma->anon_vma)
  95                 anon_vma_unlock_write(vma->anon_vma);
  96         if (vma->vm_file)
  97                 i_mmap_unlock_write(vma->vm_file->f_mapping);
  98 }
  99
 100 static pte_t move_soft_dirty_pte(pte_t pte)
 101 {
 102         /*
 103          * Set soft dirty bit so we can notice
 104          * in userspace the ptes were moved.
 105          */
 106 #ifdef CONFIG_MEM_SOFT_DIRTY
 107         if (pte_present(pte))
 108                 pte = pte_mksoft_dirty(pte);
 109         else if (is_swap_pte(pte))
 110                 pte = pte_swp_mksoft_dirty(pte);
 111 #endif
 112         return pte;
 113 }
 114
 115 static void move_ptes(struct vm_area_struct *vma, pmd_t *old_pmd,
 116                 unsigned long old_addr, unsigned long old_end,
 117                 struct vm_area_struct *new_vma, pmd_t *new_pmd,
 118                 unsigned long new_addr, bool need_rmap_locks)
 119 {
 120         struct mm_struct *mm = vma->vm_mm;
 121         pte_t *old_pte, *new_pte, pte;
 122         spinlock_t *old_ptl, *new_ptl;
 123         bool force_flush = false;
 124         unsigned long len = old_end - old_addr;
 125
 126         /*
 127          * When need_rmap_locks is true, we take the i_mmap_rwsem and anon_vma
 128          * locks to ensure that rmap will always observe either the old or the
 129          * new ptes. This is the easiest way to avoid races with
 130          * truncate_pagecache(), page migration, etc...
 131          *
 132          * When need_rmap_locks is false, we use other ways to avoid
 133          * such races:
 134          *
 135          * - During exec() shift_arg_pages(), we use a specially tagged vma
 136          *   which rmap call sites look for using is_vma_temporary_stack().
 137          *
 138          * - During mremap(), new_vma is often known to be placed after vma
 139          *   in rmap traversal order. This ensures rmap will always observe
 140          *   either the old pte, or the new pte, or both (the page table locks
 141          *   serialize access to individual ptes, but only rmap traversal
 142          *   order guarantees that we won't miss both the old and new ptes).
 143          */
 144         if (need_rmap_locks)
 145                 take_rmap_locks(vma);
 146
 147         /*
 148          * We don't have to worry about the ordering of src and dst
 149          * pte locks because exclusive mmap_sem prevents deadlock.
 150          */
 151         old_pte = pte_offset_map_lock(mm, old_pmd, old_addr, &old_ptl);
 152         new_pte = pte_offset_map(new_pmd, new_addr);
 153         new_ptl = pte_lockptr(mm, new_pmd);
 154         if (new_ptl != old_ptl)
 155                 spin_lock_nested(new_ptl, SINGLE_DEPTH_NESTING);
 156         flush_tlb_batched_pending(vma->vm_mm);
 157         arch_enter_lazy_mmu_mode();
 158
 159         for (; old_addr < old_end; old_pte++, old_addr += PAGE_SIZE,
 160                                    new_pte++, new_addr += PAGE_SIZE) {
 161                 if (pte_none(*old_pte))
 162                         continue;
 163
 164                 pte = ptep_get_and_clear(mm, old_addr, old_pte);
 165                 /*
 166                  * If we are remapping a valid PTE, make sure
 167                  * to flush TLB before we drop the PTL for the
 168                  * PTE.
 169                  *
 170                  * NOTE! Both old and new PTL matter: the old one
 171                  * for racing with page_mkclean(), the new one to
 172                  * make sure the physical page stays valid until
 173                  * the TLB entry for the old mapping has been
 174                  * flushed.
 175                  */
 176                 if (pte_present(pte))
 177                         force_flush = true;
 178                 pte = move_pte(pte, new_vma->vm_page_prot, old_addr, new_addr);
 179                 pte = move_soft_dirty_pte(pte);
 180                 set_pte_at(mm, new_addr, new_pte, pte);
 181         }
 182
 183         arch_leave_lazy_mmu_mode();
 184         if (force_flush)
 185                 flush_tlb_range(vma, old_end - len, old_end);
 186         if (new_ptl != old_ptl)
 187                 spin_unlock(new_ptl);
 188         pte_unmap(new_pte - 1);
 189         pte_unmap_unlock(old_pte - 1, old_ptl);
 190         if (need_rmap_locks)
 191                 drop_rmap_locks(vma);
 192 }
 193
 194 #ifdef CONFIG_HAVE_MOVE_PMD
 195 static bool move_normal_pmd(struct vm_area_struct *vma, unsigned long old_addr,
 196                   unsigned long new_addr, unsigned long old_end,
 197                   pmd_t *old_pmd, pmd_t *new_pmd)
 198 {
 199         spinlock_t *old_ptl, *new_ptl;
 200         struct mm_struct *mm = vma->vm_mm;
 201         pmd_t pmd;
 202
 203         if ((old_addr & ~PMD_MASK) || (new_addr & ~PMD_MASK)
 204             || old_end - old_addr < PMD_SIZE)
 205                 return false;
 206
 207         /*
 208          * The destination pmd shouldn't be established, free_pgtables()
 209          * should have release it.
 210          */
 211         if (WARN_ON(!pmd_none(*new_pmd)))
 212                 return false;
 213
 214         /*
 215          * We don't have to worry about the ordering of src and dst
 216          * ptlocks because exclusive mmap_sem prevents deadlock.
 217          */
 218         old_ptl = pmd_lock(vma->vm_mm, old_pmd);
 219         new_ptl = pmd_lockptr(mm, new_pmd);
 220         if (new_ptl != old_ptl)
 221                 spin_lock_nested(new_ptl, SINGLE_DEPTH_NESTING);
 222
 223         /* Clear the pmd */
 224         pmd = *old_pmd;
 225         pmd_clear(old_pmd);
 226
 227         VM_BUG_ON(!pmd_none(*new_pmd));
 228
 229         /* Set the new pmd */
 230         set_pmd_at(mm, new_addr, new_pmd, pmd);
 231         flush_tlb_range(vma, old_addr, old_addr + PMD_SIZE);
 232         if (new_ptl != old_ptl)
 233                 spin_unlock(new_ptl);
 234         spin_unlock(old_ptl);
 235
 236         return true;
 237 }
 238 #endif
 239
 240 unsigned long move_page_tables(struct vm_area_struct *vma,
 241                 unsigned long old_addr, struct vm_area_struct *new_vma,
 242                 unsigned long new_addr, unsigned long len,
 243                 bool need_rmap_locks)
 244 {
 245         unsigned long extent, next, old_end;
 246         struct mmu_notifier_range range;
 247         pmd_t *old_pmd, *new_pmd;
 248
 249         old_end = old_addr + len;
 250         flush_cache_range(vma, old_addr, old_end);
 251
 252         mmu_notifier_range_init(&range, MMU_NOTIFY_UNMAP, 0, vma, vma->vm_mm,
 253                                 old_addr, old_end);
 254         mmu_notifier_invalidate_range_start(&range);
 255
 256         for (; old_addr < old_end; old_addr += extent, new_addr += extent) {
 257                 cond_resched();
 258                 next = (old_addr + PMD_SIZE) & PMD_MASK;
 259                 /* even if next overflowed, extent below will be ok */
 260                 extent = next - old_addr;
 261                 if (extent > old_end - old_addr)
 262                         extent = old_end - old_addr;
 263                 old_pmd = get_old_pmd(vma->vm_mm, old_addr);
 264                 if (!old_pmd)
 265                         continue;
 266                 new_pmd = alloc_new_pmd(vma->vm_mm, vma, new_addr);
 267                 if (!new_pmd)
 268                         break;
 269                 if (is_swap_pmd(*old_pmd) || pmd_trans_huge(*old_pmd) || pmd_devmap(*old_pmd)) {
 270                         if (extent == HPAGE_PMD_SIZE) {
 271                                 bool moved;
 272                                 /* See comment in move_ptes() */
 273                                 if (need_rmap_locks)
 274                                         take_rmap_locks(vma);
 275                                 moved = move_huge_pmd(vma, old_addr, new_addr,
 276                                                     old_end, old_pmd, new_pmd);
 277                                 if (need_rmap_locks)
 278                                         drop_rmap_locks(vma);
 279                                 if (moved)
 280                                         continue;
 281                         }
 282                         split_huge_pmd(vma, old_pmd, old_addr);
 283                         if (pmd_trans_unstable(old_pmd))
 284                                 continue;
 285                 } else if (extent == PMD_SIZE) {
 286 #ifdef CONFIG_HAVE_MOVE_PMD
 287                         /*
 288                          * If the extent is PMD-sized, try to speed the move by
 289                          * moving at the PMD level if possible.
 290                          */
 291                         bool moved;
 292
 293                         if (need_rmap_locks)
 294                                 take_rmap_locks(vma);
 295                         moved = move_normal_pmd(vma, old_addr, new_addr,
 296                                         old_end, old_pmd, new_pmd);
 297                         if (need_rmap_locks)
 298                                 drop_rmap_locks(vma);
 299                         if (moved)
 300                                 continue;
 301 #endif
 302                 }
 303
 304                 if (pte_alloc(new_vma->vm_mm, new_pmd))
 305                         break;
 306                 next = (new_addr + PMD_SIZE) & PMD_MASK;
 307                 if (extent > next - new_addr)
 308                         extent = next - new_addr;
 309                 move_ptes(vma, old_pmd, old_addr, old_addr + extent, new_vma,
 310                           new_pmd, new_addr, need_rmap_locks);
 311         }
 312
 313         mmu_notifier_invalidate_range_end(&range);
 314
 315         return len + old_addr - old_end;        /* how much done */
 316 }
 317
 318 static unsigned long move_vma(struct vm_area_struct *vma,
 319                 unsigned long old_addr, unsigned long old_len,
 320                 unsigned long new_len, unsigned long new_addr,
 321                 bool *locked, struct vm_userfaultfd_ctx *uf,
 322                 struct list_head *uf_unmap)
 323 {
 324         struct mm_struct *mm = vma->vm_mm;
 325         struct vm_area_struct *new_vma;
 326         unsigned long vm_flags = vma->vm_flags;
 327         unsigned long new_pgoff;
 328         unsigned long moved_len;
 329         unsigned long excess = 0;
 330         unsigned long hiwater_vm;
 331         int split = 0;
 332         int err;
 333         bool need_rmap_locks;
 334
 335         /*
 336          * We'd prefer to avoid failure later on in do_munmap:
 337          * which may split one vma into three before unmapping.
 338          */
 339         if (mm->map_count >= sysctl_max_map_count - 3)
 340                 return -ENOMEM;
 341
 342         /*
 343          * Advise KSM to break any KSM pages in the area to be moved:
 344          * it would be confusing if they were to turn up at the new
 345          * location, where they happen to coincide with different KSM
 346          * pages recently unmapped.  But leave vma->vm_flags as it was,
 347          * so KSM can come around to merge on vma and new_vma afterwards.
 348          */
 349         err = ksm_madvise(vma, old_addr, old_addr + old_len,
 350                                                 MADV_UNMERGEABLE, &vm_flags);
 351         if (err)
 352                 return err;
 353
 354         new_pgoff = vma->vm_pgoff + ((old_addr - vma->vm_start) >> PAGE_SHIFT);
 355         new_vma = copy_vma(&vma, new_addr, new_len, new_pgoff,
 356                            &need_rmap_locks);
 357         if (!new_vma)
 358                 return -ENOMEM;
 359
 360         moved_len = move_page_tables(vma, old_addr, new_vma, new_addr, old_len,
 361                                      need_rmap_locks);
 362         if (moved_len < old_len) {
 363                 err = -ENOMEM;
 364         } else if (vma->vm_ops && vma->vm_ops->mremap) {
 365                 err = vma->vm_ops->mremap(new_vma);
 366         }
 367
 368         if (unlikely(err)) {
 369                 /*
 370                  * On error, move entries back from new area to old,
 371                  * which will succeed since page tables still there,
 372                  * and then proceed to unmap new area instead of old.
 373                  */
 374                 move_page_tables(new_vma, new_addr, vma, old_addr, moved_len,
 375                                  true);
 376                 vma = new_vma;
 377                 old_len = new_len;
 378                 old_addr = new_addr;
 379                 new_addr = err;
 380         } else {
 381                 mremap_userfaultfd_prep(new_vma, uf);
 382                 arch_remap(mm, old_addr, old_addr + old_len,
 383                            new_addr, new_addr + new_len);
 384         }
 385
 386         /* Conceal VM_ACCOUNT so old reservation is not undone */
 387         if (vm_flags & VM_ACCOUNT) {
 388                 vma->vm_flags &= ~VM_ACCOUNT;
 389                 excess = vma->vm_end - vma->vm_start - old_len;
 390                 if (old_addr > vma->vm_start &&
 391                     old_addr + old_len < vma->vm_end)
 392                         split = 1;
 393         }
 394
 395         /*
 396          * If we failed to move page tables we still do total_vm increment
 397          * since do_munmap() will decrement it by old_len == new_len.
 398          *
 399          * Since total_vm is about to be raised artificially high for a
 400          * moment, we need to restore high watermark afterwards: if stats
 401          * are taken meanwhile, total_vm and hiwater_vm appear too high.
 402          * If this were a serious issue, we'd add a flag to do_munmap().
 403          */
 404         hiwater_vm = mm->hiwater_vm;
 405         vm_stat_account(mm, vma->vm_flags, new_len >> PAGE_SHIFT);
 406
 407         /* Tell pfnmap has moved from this vma */
 408         if (unlikely(vma->vm_flags & VM_PFNMAP))
 409                 untrack_pfn_moved(vma);
 410
 411         if (do_munmap(mm, old_addr, old_len, uf_unmap) < 0) {
 412                 /* OOM: unable to split vma, just get accounts right */
 413                 vm_unacct_memory(excess >> PAGE_SHIFT);
 414                 excess = 0;
 415         }
 416         mm->hiwater_vm = hiwater_vm;
 417
 418         /* Restore VM_ACCOUNT if one or two pieces of vma left */
 419         if (excess) {
 420                 vma->vm_flags |= VM_ACCOUNT;
 421                 if (split)
 422                         vma->vm_next->vm_flags |= VM_ACCOUNT;
 423         }
 424
 425         if (vm_flags & VM_LOCKED) {
 426                 mm->locked_vm += new_len >> PAGE_SHIFT;
 427                 *locked = true;
 428         }
 429
 430         return new_addr;
 431 }
 432
 433 static struct vm_area_struct *vma_to_resize(unsigned long addr,
 434         unsigned long old_len, unsigned long new_len, unsigned long *p)
 435 {
 436         struct mm_struct *mm = current->mm;
 437         struct vm_area_struct *vma = find_vma(mm, addr);
 438         unsigned long pgoff;
 439
 440         if (!vma || vma->vm_start > addr)
 441                 return ERR_PTR(-EFAULT);
 442
 443         /*
 444          * !old_len is a special case where an attempt is made to 'duplicate'
 445          * a mapping.  This makes no sense for private mappings as it will
 446          * instead create a fresh/new mapping unrelated to the original.  This
 447          * is contrary to the basic idea of mremap which creates new mappings
 448          * based on the original.  There are no known use cases for this
 449          * behavior.  As a result, fail such attempts.
 450          */
 451         if (!old_len && !(vma->vm_flags & (VM_SHARED | VM_MAYSHARE))) {
 452                 pr_warn_once("%s (%d): attempted to duplicate a private mapping with mremap.  This is not supported.\n", current->comm, current->pid);
 453                 return ERR_PTR(-EINVAL);
 454         }
 455
 456         if (is_vm_hugetlb_page(vma))
 457                 return ERR_PTR(-EINVAL);
 458
 459         /* We can't remap across vm area boundaries */
 460         if (old_len > vma->vm_end - addr)
 461                 return ERR_PTR(-EFAULT);
 462
 463         if (new_len == old_len)
 464                 return vma;
 465
 466         /* Need to be careful about a growing mapping */
 467         pgoff = (addr - vma->vm_start) >> PAGE_SHIFT;
 468         pgoff += vma->vm_pgoff;
 469         if (pgoff + (new_len >> PAGE_SHIFT) < pgoff)
 470                 return ERR_PTR(-EINVAL);
 471
 472         if (vma->vm_flags & (VM_DONTEXPAND | VM_PFNMAP))
 473                 return ERR_PTR(-EFAULT);
 474
 475         if (vma->vm_flags & VM_LOCKED) {
 476                 unsigned long locked, lock_limit;
 477                 locked = mm->locked_vm << PAGE_SHIFT;
 478                 lock_limit = rlimit(RLIMIT_MEMLOCK);
 479                 locked += new_len - old_len;
 480                 if (locked > lock_limit && !capable(CAP_IPC_LOCK))
 481                         return ERR_PTR(-EAGAIN);
 482         }
 483
 484         if (!may_expand_vm(mm, vma->vm_flags,
 485                                 (new_len - old_len) >> PAGE_SHIFT))
 486                 return ERR_PTR(-ENOMEM);
 487
 488         if (vma->vm_flags & VM_ACCOUNT) {
 489                 unsigned long charged = (new_len - old_len) >> PAGE_SHIFT;
 490                 if (security_vm_enough_memory_mm(mm, charged))
 491                         return ERR_PTR(-ENOMEM);
 492                 *p = charged;
 493         }
 494
 495         return vma;
 496 }
 497
 498 static unsigned long mremap_to(unsigned long addr, unsigned long old_len,
 499                 unsigned long new_addr, unsigned long new_len, bool *locked,
 500                 struct vm_userfaultfd_ctx *uf,
 501                 struct list_head *uf_unmap_early,
 502                 struct list_head *uf_unmap)
 503 {
 504         struct mm_struct *mm = current->mm;
 505         struct vm_area_struct *vma;
 506         unsigned long ret = -EINVAL;
 507         unsigned long charged = 0;
 508         unsigned long map_flags;
 509
 510         if (offset_in_page(new_addr))
 511                 goto out;
 512
 513         if (new_len > TASK_SIZE || new_addr > TASK_SIZE - new_len)
 514                 goto out;
 515
 516         /* Ensure the old/new locations do not overlap */
 517         if (addr + old_len > new_addr && new_addr + new_len > addr)
 518                 goto out;
 519
 520         /*
 521          * move_vma() need us to stay 4 maps below the threshold, otherwise
 522          * it will bail out at the very beginning.
 523          * That is a problem if we have already unmaped the regions here
 524          * (new_addr, and old_addr), because userspace will not know the
 525          * state of the vma's after it gets -ENOMEM.
 526          * So, to avoid such scenario we can pre-compute if the whole
 527          * operation has high chances to success map-wise.
 528          * Worst-scenario case is when both vma's (new_addr and old_addr) get
 529          * split in 3 before unmaping it.
 530          * That means 2 more maps (1 for each) to the ones we already hold.
 531          * Check whether current map count plus 2 still leads us to 4 maps below
 532          * the threshold, otherwise return -ENOMEM here to be more safe.
 533          */
 534         if ((mm->map_count + 2) >= sysctl_max_map_count - 3)
 535                 return -ENOMEM;
 536
 537         ret = do_munmap(mm, new_addr, new_len, uf_unmap_early);
 538         if (ret)
 539                 goto out;
 540
 541         if (old_len >= new_len) {
 542                 ret = do_munmap(mm, addr+new_len, old_len - new_len, uf_unmap);
 543                 if (ret && old_len != new_len)
 544                         goto out;
 545                 old_len = new_len;
 546         }
 547
 548         vma = vma_to_resize(addr, old_len, new_len, &charged);
 549         if (IS_ERR(vma)) {
 550                 ret = PTR_ERR(vma);
 551                 goto out;
 552         }
 553
 554         map_flags = MAP_FIXED;
 555         if (vma->vm_flags & VM_MAYSHARE)
 556                 map_flags |= MAP_SHARED;
 557
 558         ret = get_unmapped_area(vma->vm_file, new_addr, new_len, vma->vm_pgoff +
 559                                 ((addr - vma->vm_start) >> PAGE_SHIFT),
 560                                 map_flags);
 561         if (offset_in_page(ret))
 562                 goto out1;
 563
 564         ret = move_vma(vma, addr, old_len, new_len, new_addr, locked, uf,
 565                        uf_unmap);
 566         if (!(offset_in_page(ret)))
 567                 goto out;
 568 out1:
 569         vm_unacct_memory(charged);
 570
 571 out:
 572         return ret;
 573 }
 574
 575 static int vma_expandable(struct vm_area_struct *vma, unsigned long delta)
 576 {
 577         unsigned long end = vma->vm_end + delta;
 578         if (end < vma->vm_end) /* overflow */
 579                 return 0;
 580         if (vma->vm_next && vma->vm_next->vm_start < end) /* intersection */
 581                 return 0;
 582         if (get_unmapped_area(NULL, vma->vm_start, end - vma->vm_start,
 583                               0, MAP_FIXED) & ~PAGE_MASK)
 584                 return 0;
 585         return 1;
 586 }
 587
 588 /*
 589  * Expand (or shrink) an existing mapping, potentially moving it at the
 590  * same time (controlled by the MREMAP_MAYMOVE flag and available VM space)
 591  *
 592  * MREMAP_FIXED option added 5-Dec-1999 by Benjamin LaHaise
 593  * This option implies MREMAP_MAYMOVE.
 594  */
 595 SYSCALL_DEFINE5(mremap, unsigned long, addr, unsigned long, old_len,
 596                 unsigned long, new_len, unsigned long, flags,
 597                 unsigned long, new_addr)
 598 {
 599         struct mm_struct *mm = current->mm;
 600         struct vm_area_struct *vma;
 601         unsigned long ret = -EINVAL;
 602         unsigned long charged = 0;
 603         bool locked = false;
 604         bool downgraded = false;
 605         struct vm_userfaultfd_ctx uf = NULL_VM_UFFD_CTX;
 606         LIST_HEAD(uf_unmap_early);
 607         LIST_HEAD(uf_unmap);
 608
 609         /*
 610          * There is a deliberate asymmetry here: we strip the pointer tag
 611          * from the old address but leave the new address alone. This is
 612          * for consistency with mmap(), where we prevent the creation of
 613          * aliasing mappings in userspace by leaving the tag bits of the
 614          * mapping address intact. A non-zero tag will cause the subsequent
 615          * range checks to reject the address as invalid.
 616          *
 617          * See Documentation/arm64/tagged-address-abi.rst for more information.
 618          */
 619         addr = untagged_addr(addr);
 620
 621         if (flags & ~(MREMAP_FIXED | MREMAP_MAYMOVE))
 622                 return ret;
 623
 624         if (flags & MREMAP_FIXED && !(flags & MREMAP_MAYMOVE))
 625                 return ret;
 626
 627         if (offset_in_page(addr))
 628                 return ret;
 629
 630         old_len = PAGE_ALIGN(old_len);
 631         new_len = PAGE_ALIGN(new_len);
 632
 633         /*
 634          * We allow a zero old-len as a special case
 635          * for DOS-emu "duplicate shm area" thing. But
 636          * a zero new-len is nonsensical.
 637          */
 638         if (!new_len)
 639                 return ret;
 640
 641         if (down_write_killable(&current->mm->mmap_sem))
 642                 return -EINTR;
 643
 644         if (flags & MREMAP_FIXED) {
 645                 ret = mremap_to(addr, old_len, new_addr, new_len,
 646                                 &locked, &uf, &uf_unmap_early, &uf_unmap);
 647                 goto out;
 648         }
 649
 650         /*
 651          * Always allow a shrinking remap: that just unmaps
 652          * the unnecessary pages..
 653          * __do_munmap does all the needed commit accounting, and
 654          * downgrades mmap_sem to read if so directed.
 655          */
 656         if (old_len >= new_len) {
 657                 int retval;
 658
 659                 retval = __do_munmap(mm, addr+new_len, old_len - new_len,
 660                                   &uf_unmap, true);
 661                 if (retval < 0 && old_len != new_len) {
 662                         ret = retval;
 663                         goto out;
 664                 /* Returning 1 indicates mmap_sem is downgraded to read. */
 665                 } else if (retval == 1)
 666                         downgraded = true;
 667                 ret = addr;
 668                 goto out;
 669         }
 670
 671         /*
 672          * Ok, we need to grow..
 673          */
 674         vma = vma_to_resize(addr, old_len, new_len, &charged);
 675         if (IS_ERR(vma)) {
 676                 ret = PTR_ERR(vma);
 677                 goto out;
 678         }
 679
 680         /* old_len exactly to the end of the area..
 681          */
 682         if (old_len == vma->vm_end - addr) {
 683                 /* can we just expand the current mapping? */
 684                 if (vma_expandable(vma, new_len - old_len)) {
 685                         int pages = (new_len - old_len) >> PAGE_SHIFT;
 686
 687                         if (vma_adjust(vma, vma->vm_start, addr + new_len,
 688                                        vma->vm_pgoff, NULL)) {
 689                                 ret = -ENOMEM;
 690                                 goto out;
 691                         }
 692
 693                         vm_stat_account(mm, vma->vm_flags, pages);
 694                         if (vma->vm_flags & VM_LOCKED) {
 695                                 mm->locked_vm += pages;
 696                                 locked = true;
 697                                 new_addr = addr;
 698                         }
 699                         ret = addr;
 700                         goto out;
 701                 }
 702         }
 703
 704         /*
 705          * We weren't able to just expand or shrink the area,
 706          * we need to create a new one and move it..
 707          */
 708         ret = -ENOMEM;
 709         if (flags & MREMAP_MAYMOVE) {
 710                 unsigned long map_flags = 0;
 711                 if (vma->vm_flags & VM_MAYSHARE)
 712                         map_flags |= MAP_SHARED;
 713
 714                 new_addr = get_unmapped_area(vma->vm_file, 0, new_len,
 715                                         vma->vm_pgoff +
 716                                         ((addr - vma->vm_start) >> PAGE_SHIFT),
 717                                         map_flags);
 718                 if (offset_in_page(new_addr)) {
 719                         ret = new_addr;
 720                         goto out;
 721                 }
 722
 723                 ret = move_vma(vma, addr, old_len, new_len, new_addr,
 724                                &locked, &uf, &uf_unmap);
 725         }
 726 out:
 727         if (offset_in_page(ret)) {
 728                 vm_unacct_memory(charged);
 729                 locked = 0;
 730         }
 731         if (downgraded)
 732                 up_read(&current->mm->mmap_sem);
 733         else
 734                 up_write(&current->mm->mmap_sem);
 735         if (locked && new_len > old_len)
 736                 mm_populate(new_addr + old_len, new_len - old_len);
 737         userfaultfd_unmap_complete(mm, &uf_unmap_early);
 738         mremap_userfaultfd_complete(&uf, addr, new_addr, old_len);
 739         userfaultfd_unmap_complete(mm, &uf_unmap);
 740         return ret;
 741 }