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 vma_is_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_lock 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, pmd_t *old_pmd, pmd_t *new_pmd)
 197 {
 198         spinlock_t *old_ptl, *new_ptl;
 199         struct mm_struct *mm = vma->vm_mm;
 200         pmd_t pmd;
 201
 202         /*
 203          * The destination pmd shouldn't be established, free_pgtables()
 204          * should have released it.
 205          *
 206          * However, there's a case during execve() where we use mremap
 207          * to move the initial stack, and in that case the target area
 208          * may overlap the source area (always moving down).
 209          *
 210          * If everything is PMD-aligned, that works fine, as moving
 211          * each pmd down will clear the source pmd. But if we first
 212          * have a few 4kB-only pages that get moved down, and then
 213          * hit the "now the rest is PMD-aligned, let's do everything
 214          * one pmd at a time", we will still have the old (now empty
 215          * of any 4kB pages, but still there) PMD in the page table
 216          * tree.
 217          *
 218          * Warn on it once - because we really should try to figure
 219          * out how to do this better - but then say "I won't move
 220          * this pmd".
 221          *
 222          * One alternative might be to just unmap the target pmd at
 223          * this point, and verify that it really is empty. We'll see.
 224          */
 225         if (WARN_ON_ONCE(!pmd_none(*new_pmd)))
 226                 return false;
 227
 228         /*
 229          * We don't have to worry about the ordering of src and dst
 230          * ptlocks because exclusive mmap_lock prevents deadlock.
 231          */
 232         old_ptl = pmd_lock(vma->vm_mm, old_pmd);
 233         new_ptl = pmd_lockptr(mm, new_pmd);
 234         if (new_ptl != old_ptl)
 235                 spin_lock_nested(new_ptl, SINGLE_DEPTH_NESTING);
 236
 237         /* Clear the pmd */
 238         pmd = *old_pmd;
 239         pmd_clear(old_pmd);
 240
 241         VM_BUG_ON(!pmd_none(*new_pmd));
 242
 243         /* Set the new pmd */
 244         set_pmd_at(mm, new_addr, new_pmd, pmd);
 245         flush_tlb_range(vma, old_addr, old_addr + PMD_SIZE);
 246         if (new_ptl != old_ptl)
 247                 spin_unlock(new_ptl);
 248         spin_unlock(old_ptl);
 249
 250         return true;
 251 }
 252 #endif
 253
 254 unsigned long move_page_tables(struct vm_area_struct *vma,
 255                 unsigned long old_addr, struct vm_area_struct *new_vma,
 256                 unsigned long new_addr, unsigned long len,
 257                 bool need_rmap_locks)
 258 {
 259         unsigned long extent, next, old_end;
 260         struct mmu_notifier_range range;
 261         pmd_t *old_pmd, *new_pmd;
 262
 263         if (!len)
 264                 return 0;
 265
 266         old_end = old_addr + len;
 267         flush_cache_range(vma, old_addr, old_end);
 268
 269         mmu_notifier_range_init(&range, MMU_NOTIFY_UNMAP, 0, vma, vma->vm_mm,
 270                                 old_addr, old_end);
 271         mmu_notifier_invalidate_range_start(&range);
 272
 273         for (; old_addr < old_end; old_addr += extent, new_addr += extent) {
 274                 cond_resched();
 275                 next = (old_addr + PMD_SIZE) & PMD_MASK;
 276                 /* even if next overflowed, extent below will be ok */
 277                 extent = next - old_addr;
 278                 if (extent > old_end - old_addr)
 279                         extent = old_end - old_addr;
 280                 next = (new_addr + PMD_SIZE) & PMD_MASK;
 281                 if (extent > next - new_addr)
 282                         extent = next - new_addr;
 283                 old_pmd = get_old_pmd(vma->vm_mm, old_addr);
 284                 if (!old_pmd)
 285                         continue;
 286                 new_pmd = alloc_new_pmd(vma->vm_mm, vma, new_addr);
 287                 if (!new_pmd)
 288                         break;
 289                 if (is_swap_pmd(*old_pmd) || pmd_trans_huge(*old_pmd) || pmd_devmap(*old_pmd)) {
 290                         if (extent == HPAGE_PMD_SIZE) {
 291                                 bool moved;
 292                                 /* See comment in move_ptes() */
 293                                 if (need_rmap_locks)
 294                                         take_rmap_locks(vma);
 295                                 moved = move_huge_pmd(vma, old_addr, new_addr,
 296                                                       old_pmd, new_pmd);
 297                                 if (need_rmap_locks)
 298                                         drop_rmap_locks(vma);
 299                                 if (moved)
 300                                         continue;
 301                         }
 302                         split_huge_pmd(vma, old_pmd, old_addr);
 303                         if (pmd_trans_unstable(old_pmd))
 304                                 continue;
 305                 } else if (extent == PMD_SIZE) {
 306 #ifdef CONFIG_HAVE_MOVE_PMD
 307                         /*
 308                          * If the extent is PMD-sized, try to speed the move by
 309                          * moving at the PMD level if possible.
 310                          */
 311                         bool moved;
 312
 313                         take_rmap_locks(vma);
 314                         moved = move_normal_pmd(vma, old_addr, new_addr,
 315                                                 old_pmd, new_pmd);
 316                         drop_rmap_locks(vma);
 317                         if (moved)
 318                                 continue;
 319 #endif
 320                 }
 321
 322                 if (pte_alloc(new_vma->vm_mm, new_pmd))
 323                         break;
 324                 move_ptes(vma, old_pmd, old_addr, old_addr + extent, new_vma,
 325                           new_pmd, new_addr, need_rmap_locks);
 326         }
 327
 328         mmu_notifier_invalidate_range_end(&range);
 329
 330         return len + old_addr - old_end;        /* how much done */
 331 }
 332
 333 static unsigned long move_vma(struct vm_area_struct *vma,
 334                 unsigned long old_addr, unsigned long old_len,
 335                 unsigned long new_len, unsigned long new_addr,
 336                 bool *locked, unsigned long flags,
 337                 struct vm_userfaultfd_ctx *uf, struct list_head *uf_unmap)
 338 {
 339         struct mm_struct *mm = vma->vm_mm;
 340         struct vm_area_struct *new_vma;
 341         unsigned long vm_flags = vma->vm_flags;
 342         unsigned long new_pgoff;
 343         unsigned long moved_len;
 344         unsigned long excess = 0;
 345         unsigned long hiwater_vm;
 346         int split = 0;
 347         int err;
 348         bool need_rmap_locks;
 349
 350         /*
 351          * We'd prefer to avoid failure later on in do_munmap:
 352          * which may split one vma into three before unmapping.
 353          */
 354         if (mm->map_count >= sysctl_max_map_count - 3)
 355                 return -ENOMEM;
 356
 357         /*
 358          * Advise KSM to break any KSM pages in the area to be moved:
 359          * it would be confusing if they were to turn up at the new
 360          * location, where they happen to coincide with different KSM
 361          * pages recently unmapped.  But leave vma->vm_flags as it was,
 362          * so KSM can come around to merge on vma and new_vma afterwards.
 363          */
 364         err = ksm_madvise(vma, old_addr, old_addr + old_len,
 365                                                 MADV_UNMERGEABLE, &vm_flags);
 366         if (err)
 367                 return err;
 368
 369         new_pgoff = vma->vm_pgoff + ((old_addr - vma->vm_start) >> PAGE_SHIFT);
 370         new_vma = copy_vma(&vma, new_addr, new_len, new_pgoff,
 371                            &need_rmap_locks);
 372         if (!new_vma)
 373                 return -ENOMEM;
 374
 375         moved_len = move_page_tables(vma, old_addr, new_vma, new_addr, old_len,
 376                                      need_rmap_locks);
 377         if (moved_len < old_len) {
 378                 err = -ENOMEM;
 379         } else if (vma->vm_ops && vma->vm_ops->mremap) {
 380                 err = vma->vm_ops->mremap(new_vma);
 381         }
 382
 383         if (unlikely(err)) {
 384                 /*
 385                  * On error, move entries back from new area to old,
 386                  * which will succeed since page tables still there,
 387                  * and then proceed to unmap new area instead of old.
 388                  */
 389                 move_page_tables(new_vma, new_addr, vma, old_addr, moved_len,
 390                                  true);
 391                 vma = new_vma;
 392                 old_len = new_len;
 393                 old_addr = new_addr;
 394                 new_addr = err;
 395         } else {
 396                 mremap_userfaultfd_prep(new_vma, uf);
 397                 arch_remap(mm, old_addr, old_addr + old_len,
 398                            new_addr, new_addr + new_len);
 399         }
 400
 401         /* Conceal VM_ACCOUNT so old reservation is not undone */
 402         if (vm_flags & VM_ACCOUNT) {
 403                 vma->vm_flags &= ~VM_ACCOUNT;
 404                 excess = vma->vm_end - vma->vm_start - old_len;
 405                 if (old_addr > vma->vm_start &&
 406                     old_addr + old_len < vma->vm_end)
 407                         split = 1;
 408         }
 409
 410         /*
 411          * If we failed to move page tables we still do total_vm increment
 412          * since do_munmap() will decrement it by old_len == new_len.
 413          *
 414          * Since total_vm is about to be raised artificially high for a
 415          * moment, we need to restore high watermark afterwards: if stats
 416          * are taken meanwhile, total_vm and hiwater_vm appear too high.
 417          * If this were a serious issue, we'd add a flag to do_munmap().
 418          */
 419         hiwater_vm = mm->hiwater_vm;
 420         vm_stat_account(mm, vma->vm_flags, new_len >> PAGE_SHIFT);
 421
 422         /* Tell pfnmap has moved from this vma */
 423         if (unlikely(vma->vm_flags & VM_PFNMAP))
 424                 untrack_pfn_moved(vma);
 425
 426         if (unlikely(!err && (flags & MREMAP_DONTUNMAP))) {
 427                 if (vm_flags & VM_ACCOUNT) {
 428                         /* Always put back VM_ACCOUNT since we won't unmap */
 429                         vma->vm_flags |= VM_ACCOUNT;
 430
 431                         vm_acct_memory(new_len >> PAGE_SHIFT);
 432                 }
 433
 434                 /*
 435                  * VMAs can actually be merged back together in copy_vma
 436                  * calling merge_vma. This can happen with anonymous vmas
 437                  * which have not yet been faulted, so if we were to consider
 438                  * this VMA split we'll end up adding VM_ACCOUNT on the
 439                  * next VMA, which is completely unrelated if this VMA
 440                  * was re-merged.
 441                  */
 442                 if (split && new_vma == vma)
 443                         split = 0;
 444
 445                 /* We always clear VM_LOCKED[ONFAULT] on the old vma */
 446                 vma->vm_flags &= VM_LOCKED_CLEAR_MASK;
 447
 448                 /* Because we won't unmap we don't need to touch locked_vm */
 449                 goto out;
 450         }
 451
 452         if (do_munmap(mm, old_addr, old_len, uf_unmap) < 0) {
 453                 /* OOM: unable to split vma, just get accounts right */
 454                 vm_unacct_memory(excess >> PAGE_SHIFT);
 455                 excess = 0;
 456         }
 457
 458         if (vm_flags & VM_LOCKED) {
 459                 mm->locked_vm += new_len >> PAGE_SHIFT;
 460                 *locked = true;
 461         }
 462 out:
 463         mm->hiwater_vm = hiwater_vm;
 464
 465         /* Restore VM_ACCOUNT if one or two pieces of vma left */
 466         if (excess) {
 467                 vma->vm_flags |= VM_ACCOUNT;
 468                 if (split)
 469                         vma->vm_next->vm_flags |= VM_ACCOUNT;
 470         }
 471
 472         return new_addr;
 473 }
 474
 475 static struct vm_area_struct *vma_to_resize(unsigned long addr,
 476         unsigned long old_len, unsigned long new_len, unsigned long flags,
 477         unsigned long *p)
 478 {
 479         struct mm_struct *mm = current->mm;
 480         struct vm_area_struct *vma = find_vma(mm, addr);
 481         unsigned long pgoff;
 482
 483         if (!vma || vma->vm_start > addr)
 484                 return ERR_PTR(-EFAULT);
 485
 486         /*
 487          * !old_len is a special case where an attempt is made to 'duplicate'
 488          * a mapping.  This makes no sense for private mappings as it will
 489          * instead create a fresh/new mapping unrelated to the original.  This
 490          * is contrary to the basic idea of mremap which creates new mappings
 491          * based on the original.  There are no known use cases for this
 492          * behavior.  As a result, fail such attempts.
 493          */
 494         if (!old_len && !(vma->vm_flags & (VM_SHARED | VM_MAYSHARE))) {
 495                 pr_warn_once("%s (%d): attempted to duplicate a private mapping with mremap.  This is not supported.\n", current->comm, current->pid);
 496                 return ERR_PTR(-EINVAL);
 497         }
 498
 499         if (flags & MREMAP_DONTUNMAP && (!vma_is_anonymous(vma) ||
 500                         vma->vm_flags & VM_SHARED))
 501                 return ERR_PTR(-EINVAL);
 502
 503         if (is_vm_hugetlb_page(vma))
 504                 return ERR_PTR(-EINVAL);
 505
 506         /* We can't remap across vm area boundaries */
 507         if (old_len > vma->vm_end - addr)
 508                 return ERR_PTR(-EFAULT);
 509
 510         if (new_len == old_len)
 511                 return vma;
 512
 513         /* Need to be careful about a growing mapping */
 514         pgoff = (addr - vma->vm_start) >> PAGE_SHIFT;
 515         pgoff += vma->vm_pgoff;
 516         if (pgoff + (new_len >> PAGE_SHIFT) < pgoff)
 517                 return ERR_PTR(-EINVAL);
 518
 519         if (vma->vm_flags & (VM_DONTEXPAND | VM_PFNMAP))
 520                 return ERR_PTR(-EFAULT);
 521
 522         if (vma->vm_flags & VM_LOCKED) {
 523                 unsigned long locked, lock_limit;
 524                 locked = mm->locked_vm << PAGE_SHIFT;
 525                 lock_limit = rlimit(RLIMIT_MEMLOCK);
 526                 locked += new_len - old_len;
 527                 if (locked > lock_limit && !capable(CAP_IPC_LOCK))
 528                         return ERR_PTR(-EAGAIN);
 529         }
 530
 531         if (!may_expand_vm(mm, vma->vm_flags,
 532                                 (new_len - old_len) >> PAGE_SHIFT))
 533                 return ERR_PTR(-ENOMEM);
 534
 535         if (vma->vm_flags & VM_ACCOUNT) {
 536                 unsigned long charged = (new_len - old_len) >> PAGE_SHIFT;
 537                 if (security_vm_enough_memory_mm(mm, charged))
 538                         return ERR_PTR(-ENOMEM);
 539                 *p = charged;
 540         }
 541
 542         return vma;
 543 }
 544
 545 static unsigned long mremap_to(unsigned long addr, unsigned long old_len,
 546                 unsigned long new_addr, unsigned long new_len, bool *locked,
 547                 unsigned long flags, struct vm_userfaultfd_ctx *uf,
 548                 struct list_head *uf_unmap_early,
 549                 struct list_head *uf_unmap)
 550 {
 551         struct mm_struct *mm = current->mm;
 552         struct vm_area_struct *vma;
 553         unsigned long ret = -EINVAL;
 554         unsigned long charged = 0;
 555         unsigned long map_flags = 0;
 556
 557         if (offset_in_page(new_addr))
 558                 goto out;
 559
 560         if (new_len > TASK_SIZE || new_addr > TASK_SIZE - new_len)
 561                 goto out;
 562
 563         /* Ensure the old/new locations do not overlap */
 564         if (addr + old_len > new_addr && new_addr + new_len > addr)
 565                 goto out;
 566
 567         /*
 568          * move_vma() need us to stay 4 maps below the threshold, otherwise
 569          * it will bail out at the very beginning.
 570          * That is a problem if we have already unmaped the regions here
 571          * (new_addr, and old_addr), because userspace will not know the
 572          * state of the vma's after it gets -ENOMEM.
 573          * So, to avoid such scenario we can pre-compute if the whole
 574          * operation has high chances to success map-wise.
 575          * Worst-scenario case is when both vma's (new_addr and old_addr) get
 576          * split in 3 before unmaping it.
 577          * That means 2 more maps (1 for each) to the ones we already hold.
 578          * Check whether current map count plus 2 still leads us to 4 maps below
 579          * the threshold, otherwise return -ENOMEM here to be more safe.
 580          */
 581         if ((mm->map_count + 2) >= sysctl_max_map_count - 3)
 582                 return -ENOMEM;
 583
 584         if (flags & MREMAP_FIXED) {
 585                 ret = do_munmap(mm, new_addr, new_len, uf_unmap_early);
 586                 if (ret)
 587                         goto out;
 588         }
 589
 590         if (old_len >= new_len) {
 591                 ret = do_munmap(mm, addr+new_len, old_len - new_len, uf_unmap);
 592                 if (ret && old_len != new_len)
 593                         goto out;
 594                 old_len = new_len;
 595         }
 596
 597         vma = vma_to_resize(addr, old_len, new_len, flags, &charged);
 598         if (IS_ERR(vma)) {
 599                 ret = PTR_ERR(vma);
 600                 goto out;
 601         }
 602
 603         /* MREMAP_DONTUNMAP expands by old_len since old_len == new_len */
 604         if (flags & MREMAP_DONTUNMAP &&
 605                 !may_expand_vm(mm, vma->vm_flags, old_len >> PAGE_SHIFT)) {
 606                 ret = -ENOMEM;
 607                 goto out;
 608         }
 609
 610         if (flags & MREMAP_FIXED)
 611                 map_flags |= MAP_FIXED;
 612
 613         if (vma->vm_flags & VM_MAYSHARE)
 614                 map_flags |= MAP_SHARED;
 615
 616         ret = get_unmapped_area(vma->vm_file, new_addr, new_len, vma->vm_pgoff +
 617                                 ((addr - vma->vm_start) >> PAGE_SHIFT),
 618                                 map_flags);
 619         if (IS_ERR_VALUE(ret))
 620                 goto out1;
 621
 622         /* We got a new mapping */
 623         if (!(flags & MREMAP_FIXED))
 624                 new_addr = ret;
 625
 626         ret = move_vma(vma, addr, old_len, new_len, new_addr, locked, flags, uf,
 627                        uf_unmap);
 628
 629         if (!(offset_in_page(ret)))
 630                 goto out;
 631
 632 out1:
 633         vm_unacct_memory(charged);
 634
 635 out:
 636         return ret;
 637 }
 638
 639 static int vma_expandable(struct vm_area_struct *vma, unsigned long delta)
 640 {
 641         unsigned long end = vma->vm_end + delta;
 642         if (end < vma->vm_end) /* overflow */
 643                 return 0;
 644         if (vma->vm_next && vma->vm_next->vm_start < end) /* intersection */
 645                 return 0;
 646         if (get_unmapped_area(NULL, vma->vm_start, end - vma->vm_start,
 647                               0, MAP_FIXED) & ~PAGE_MASK)
 648                 return 0;
 649         return 1;
 650 }
 651
 652 /*
 653  * Expand (or shrink) an existing mapping, potentially moving it at the
 654  * same time (controlled by the MREMAP_MAYMOVE flag and available VM space)
 655  *
 656  * MREMAP_FIXED option added 5-Dec-1999 by Benjamin LaHaise
 657  * This option implies MREMAP_MAYMOVE.
 658  */
 659 SYSCALL_DEFINE5(mremap, unsigned long, addr, unsigned long, old_len,
 660                 unsigned long, new_len, unsigned long, flags,
 661                 unsigned long, new_addr)
 662 {
 663         struct mm_struct *mm = current->mm;
 664         struct vm_area_struct *vma;
 665         unsigned long ret = -EINVAL;
 666         unsigned long charged = 0;
 667         bool locked = false;
 668         bool downgraded = false;
 669         struct vm_userfaultfd_ctx uf = NULL_VM_UFFD_CTX;
 670         LIST_HEAD(uf_unmap_early);
 671         LIST_HEAD(uf_unmap);
 672
 673         /*
 674          * There is a deliberate asymmetry here: we strip the pointer tag
 675          * from the old address but leave the new address alone. This is
 676          * for consistency with mmap(), where we prevent the creation of
 677          * aliasing mappings in userspace by leaving the tag bits of the
 678          * mapping address intact. A non-zero tag will cause the subsequent
 679          * range checks to reject the address as invalid.
 680          *
 681          * See Documentation/arm64/tagged-address-abi.rst for more information.
 682          */
 683         addr = untagged_addr(addr);
 684
 685         if (flags & ~(MREMAP_FIXED | MREMAP_MAYMOVE | MREMAP_DONTUNMAP))
 686                 return ret;
 687
 688         if (flags & MREMAP_FIXED && !(flags & MREMAP_MAYMOVE))
 689                 return ret;
 690
 691         /*
 692          * MREMAP_DONTUNMAP is always a move and it does not allow resizing
 693          * in the process.
 694          */
 695         if (flags & MREMAP_DONTUNMAP &&
 696                         (!(flags & MREMAP_MAYMOVE) || old_len != new_len))
 697                 return ret;
 698
 699
 700         if (offset_in_page(addr))
 701                 return ret;
 702
 703         old_len = PAGE_ALIGN(old_len);
 704         new_len = PAGE_ALIGN(new_len);
 705
 706         /*
 707          * We allow a zero old-len as a special case
 708          * for DOS-emu "duplicate shm area" thing. But
 709          * a zero new-len is nonsensical.
 710          */
 711         if (!new_len)
 712                 return ret;
 713
 714         if (mmap_write_lock_killable(current->mm))
 715                 return -EINTR;
 716
 717         if (flags & (MREMAP_FIXED | MREMAP_DONTUNMAP)) {
 718                 ret = mremap_to(addr, old_len, new_addr, new_len,
 719                                 &locked, flags, &uf, &uf_unmap_early,
 720                                 &uf_unmap);
 721                 goto out;
 722         }
 723
 724         /*
 725          * Always allow a shrinking remap: that just unmaps
 726          * the unnecessary pages..
 727          * __do_munmap does all the needed commit accounting, and
 728          * downgrades mmap_lock to read if so directed.
 729          */
 730         if (old_len >= new_len) {
 731                 int retval;
 732
 733                 retval = __do_munmap(mm, addr+new_len, old_len - new_len,
 734                                   &uf_unmap, true);
 735                 if (retval < 0 && old_len != new_len) {
 736                         ret = retval;
 737                         goto out;
 738                 /* Returning 1 indicates mmap_lock is downgraded to read. */
 739                 } else if (retval == 1)
 740                         downgraded = true;
 741                 ret = addr;
 742                 goto out;
 743         }
 744
 745         /*
 746          * Ok, we need to grow..
 747          */
 748         vma = vma_to_resize(addr, old_len, new_len, flags, &charged);
 749         if (IS_ERR(vma)) {
 750                 ret = PTR_ERR(vma);
 751                 goto out;
 752         }
 753
 754         /* old_len exactly to the end of the area..
 755          */
 756         if (old_len == vma->vm_end - addr) {
 757                 /* can we just expand the current mapping? */
 758                 if (vma_expandable(vma, new_len - old_len)) {
 759                         int pages = (new_len - old_len) >> PAGE_SHIFT;
 760
 761                         if (vma_adjust(vma, vma->vm_start, addr + new_len,
 762                                        vma->vm_pgoff, NULL)) {
 763                                 ret = -ENOMEM;
 764                                 goto out;
 765                         }
 766
 767                         vm_stat_account(mm, vma->vm_flags, pages);
 768                         if (vma->vm_flags & VM_LOCKED) {
 769                                 mm->locked_vm += pages;
 770                                 locked = true;
 771                                 new_addr = addr;
 772                         }
 773                         ret = addr;
 774                         goto out;
 775                 }
 776         }
 777
 778         /*
 779          * We weren't able to just expand or shrink the area,
 780          * we need to create a new one and move it..
 781          */
 782         ret = -ENOMEM;
 783         if (flags & MREMAP_MAYMOVE) {
 784                 unsigned long map_flags = 0;
 785                 if (vma->vm_flags & VM_MAYSHARE)
 786                         map_flags |= MAP_SHARED;
 787
 788                 new_addr = get_unmapped_area(vma->vm_file, 0, new_len,
 789                                         vma->vm_pgoff +
 790                                         ((addr - vma->vm_start) >> PAGE_SHIFT),
 791                                         map_flags);
 792                 if (IS_ERR_VALUE(new_addr)) {
 793                         ret = new_addr;
 794                         goto out;
 795                 }
 796
 797                 ret = move_vma(vma, addr, old_len, new_len, new_addr,
 798                                &locked, flags, &uf, &uf_unmap);
 799         }
 800 out:
 801         if (offset_in_page(ret)) {
 802                 vm_unacct_memory(charged);
 803                 locked = false;
 804         }
 805         if (downgraded)
 806                 mmap_read_unlock(current->mm);
 807         else
 808                 mmap_write_unlock(current->mm);
 809         if (locked && new_len > old_len)
 810                 mm_populate(new_addr + old_len, new_len - old_len);
 811         userfaultfd_unmap_complete(mm, &uf_unmap_early);
 812         mremap_userfaultfd_complete(&uf, addr, ret, old_len);
 813         userfaultfd_unmap_complete(mm, &uf_unmap);
 814         return ret;
 815 }