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, 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 released it.
 210          *
 211          * However, there's a case during execve() where we use mremap
 212          * to move the initial stack, and in that case the target area
 213          * may overlap the source area (always moving down).
 214          *
 215          * If everything is PMD-aligned, that works fine, as moving
 216          * each pmd down will clear the source pmd. But if we first
 217          * have a few 4kB-only pages that get moved down, and then
 218          * hit the "now the rest is PMD-aligned, let's do everything
 219          * one pmd at a time", we will still have the old (now empty
 220          * of any 4kB pages, but still there) PMD in the page table
 221          * tree.
 222          *
 223          * Warn on it once - because we really should try to figure
 224          * out how to do this better - but then say "I won't move
 225          * this pmd".
 226          *
 227          * One alternative might be to just unmap the target pmd at
 228          * this point, and verify that it really is empty. We'll see.
 229          */
 230         if (WARN_ON_ONCE(!pmd_none(*new_pmd)))
 231                 return false;
 232
 233         /*
 234          * We don't have to worry about the ordering of src and dst
 235          * ptlocks because exclusive mmap_lock prevents deadlock.
 236          */
 237         old_ptl = pmd_lock(vma->vm_mm, old_pmd);
 238         new_ptl = pmd_lockptr(mm, new_pmd);
 239         if (new_ptl != old_ptl)
 240                 spin_lock_nested(new_ptl, SINGLE_DEPTH_NESTING);
 241
 242         /* Clear the pmd */
 243         pmd = *old_pmd;
 244         pmd_clear(old_pmd);
 245
 246         VM_BUG_ON(!pmd_none(*new_pmd));
 247
 248         /* Set the new pmd */
 249         set_pmd_at(mm, new_addr, new_pmd, pmd);
 250         flush_tlb_range(vma, old_addr, old_addr + PMD_SIZE);
 251         if (new_ptl != old_ptl)
 252                 spin_unlock(new_ptl);
 253         spin_unlock(old_ptl);
 254
 255         return true;
 256 }
 257 #endif
 258
 259 unsigned long move_page_tables(struct vm_area_struct *vma,
 260                 unsigned long old_addr, struct vm_area_struct *new_vma,
 261                 unsigned long new_addr, unsigned long len,
 262                 bool need_rmap_locks)
 263 {
 264         unsigned long extent, next, old_end;
 265         struct mmu_notifier_range range;
 266         pmd_t *old_pmd, *new_pmd;
 267
 268         old_end = old_addr + len;
 269         flush_cache_range(vma, old_addr, old_end);
 270
 271         mmu_notifier_range_init(&range, MMU_NOTIFY_UNMAP, 0, vma, vma->vm_mm,
 272                                 old_addr, old_end);
 273         mmu_notifier_invalidate_range_start(&range);
 274
 275         for (; old_addr < old_end; old_addr += extent, new_addr += extent) {
 276                 cond_resched();
 277                 next = (old_addr + PMD_SIZE) & PMD_MASK;
 278                 /* even if next overflowed, extent below will be ok */
 279                 extent = next - old_addr;
 280                 if (extent > old_end - old_addr)
 281                         extent = old_end - old_addr;
 282                 old_pmd = get_old_pmd(vma->vm_mm, old_addr);
 283                 if (!old_pmd)
 284                         continue;
 285                 new_pmd = alloc_new_pmd(vma->vm_mm, vma, new_addr);
 286                 if (!new_pmd)
 287                         break;
 288                 if (is_swap_pmd(*old_pmd) || pmd_trans_huge(*old_pmd) || pmd_devmap(*old_pmd)) {
 289                         if (extent == HPAGE_PMD_SIZE) {
 290                                 bool moved;
 291                                 /* See comment in move_ptes() */
 292                                 if (need_rmap_locks)
 293                                         take_rmap_locks(vma);
 294                                 moved = move_huge_pmd(vma, old_addr, new_addr,
 295                                                     old_end, old_pmd, new_pmd);
 296                                 if (need_rmap_locks)
 297                                         drop_rmap_locks(vma);
 298                                 if (moved)
 299                                         continue;
 300                         }
 301                         split_huge_pmd(vma, old_pmd, old_addr);
 302                         if (pmd_trans_unstable(old_pmd))
 303                                 continue;
 304                 } else if (extent == PMD_SIZE) {
 305 #ifdef CONFIG_HAVE_MOVE_PMD
 306                         /*
 307                          * If the extent is PMD-sized, try to speed the move by
 308                          * moving at the PMD level if possible.
 309                          */
 310                         bool moved;
 311
 312                         if (need_rmap_locks)
 313                                 take_rmap_locks(vma);
 314                         moved = move_normal_pmd(vma, old_addr, new_addr,
 315                                         old_end, old_pmd, new_pmd);
 316                         if (need_rmap_locks)
 317                                 drop_rmap_locks(vma);
 318                         if (moved)
 319                                 continue;
 320 #endif
 321                 }
 322
 323                 if (pte_alloc(new_vma->vm_mm, new_pmd))
 324                         break;
 325                 next = (new_addr + PMD_SIZE) & PMD_MASK;
 326                 if (extent > next - new_addr)
 327                         extent = next - new_addr;
 328                 move_ptes(vma, old_pmd, old_addr, old_addr + extent, new_vma,
 329                           new_pmd, new_addr, need_rmap_locks);
 330         }
 331
 332         mmu_notifier_invalidate_range_end(&range);
 333
 334         return len + old_addr - old_end;        /* how much done */
 335 }
 336
 337 static unsigned long move_vma(struct vm_area_struct *vma,
 338                 unsigned long old_addr, unsigned long old_len,
 339                 unsigned long new_len, unsigned long new_addr,
 340                 bool *locked, unsigned long flags,
 341                 struct vm_userfaultfd_ctx *uf, struct list_head *uf_unmap)
 342 {
 343         struct mm_struct *mm = vma->vm_mm;
 344         struct vm_area_struct *new_vma;
 345         unsigned long vm_flags = vma->vm_flags;
 346         unsigned long new_pgoff;
 347         unsigned long moved_len;
 348         unsigned long excess = 0;
 349         unsigned long hiwater_vm;
 350         int split = 0;
 351         int err;
 352         bool need_rmap_locks;
 353
 354         /*
 355          * We'd prefer to avoid failure later on in do_munmap:
 356          * which may split one vma into three before unmapping.
 357          */
 358         if (mm->map_count >= sysctl_max_map_count - 3)
 359                 return -ENOMEM;
 360
 361         /*
 362          * Advise KSM to break any KSM pages in the area to be moved:
 363          * it would be confusing if they were to turn up at the new
 364          * location, where they happen to coincide with different KSM
 365          * pages recently unmapped.  But leave vma->vm_flags as it was,
 366          * so KSM can come around to merge on vma and new_vma afterwards.
 367          */
 368         err = ksm_madvise(vma, old_addr, old_addr + old_len,
 369                                                 MADV_UNMERGEABLE, &vm_flags);
 370         if (err)
 371                 return err;
 372
 373         new_pgoff = vma->vm_pgoff + ((old_addr - vma->vm_start) >> PAGE_SHIFT);
 374         new_vma = copy_vma(&vma, new_addr, new_len, new_pgoff,
 375                            &need_rmap_locks);
 376         if (!new_vma)
 377                 return -ENOMEM;
 378
 379         moved_len = move_page_tables(vma, old_addr, new_vma, new_addr, old_len,
 380                                      need_rmap_locks);
 381         if (moved_len < old_len) {
 382                 err = -ENOMEM;
 383         } else if (vma->vm_ops && vma->vm_ops->mremap) {
 384                 err = vma->vm_ops->mremap(new_vma);
 385         }
 386
 387         if (unlikely(err)) {
 388                 /*
 389                  * On error, move entries back from new area to old,
 390                  * which will succeed since page tables still there,
 391                  * and then proceed to unmap new area instead of old.
 392                  */
 393                 move_page_tables(new_vma, new_addr, vma, old_addr, moved_len,
 394                                  true);
 395                 vma = new_vma;
 396                 old_len = new_len;
 397                 old_addr = new_addr;
 398                 new_addr = err;
 399         } else {
 400                 mremap_userfaultfd_prep(new_vma, uf);
 401                 arch_remap(mm, old_addr, old_addr + old_len,
 402                            new_addr, new_addr + new_len);
 403         }
 404
 405         /* Conceal VM_ACCOUNT so old reservation is not undone */
 406         if (vm_flags & VM_ACCOUNT) {
 407                 vma->vm_flags &= ~VM_ACCOUNT;
 408                 excess = vma->vm_end - vma->vm_start - old_len;
 409                 if (old_addr > vma->vm_start &&
 410                     old_addr + old_len < vma->vm_end)
 411                         split = 1;
 412         }
 413
 414         /*
 415          * If we failed to move page tables we still do total_vm increment
 416          * since do_munmap() will decrement it by old_len == new_len.
 417          *
 418          * Since total_vm is about to be raised artificially high for a
 419          * moment, we need to restore high watermark afterwards: if stats
 420          * are taken meanwhile, total_vm and hiwater_vm appear too high.
 421          * If this were a serious issue, we'd add a flag to do_munmap().
 422          */
 423         hiwater_vm = mm->hiwater_vm;
 424         vm_stat_account(mm, vma->vm_flags, new_len >> PAGE_SHIFT);
 425
 426         /* Tell pfnmap has moved from this vma */
 427         if (unlikely(vma->vm_flags & VM_PFNMAP))
 428                 untrack_pfn_moved(vma);
 429
 430         if (unlikely(!err && (flags & MREMAP_DONTUNMAP))) {
 431                 if (vm_flags & VM_ACCOUNT) {
 432                         /* Always put back VM_ACCOUNT since we won't unmap */
 433                         vma->vm_flags |= VM_ACCOUNT;
 434
 435                         vm_acct_memory(new_len >> PAGE_SHIFT);
 436                 }
 437
 438                 /*
 439                  * VMAs can actually be merged back together in copy_vma
 440                  * calling merge_vma. This can happen with anonymous vmas
 441                  * which have not yet been faulted, so if we were to consider
 442                  * this VMA split we'll end up adding VM_ACCOUNT on the
 443                  * next VMA, which is completely unrelated if this VMA
 444                  * was re-merged.
 445                  */
 446                 if (split && new_vma == vma)
 447                         split = 0;
 448
 449                 /* We always clear VM_LOCKED[ONFAULT] on the old vma */
 450                 vma->vm_flags &= VM_LOCKED_CLEAR_MASK;
 451
 452                 /* Because we won't unmap we don't need to touch locked_vm */
 453                 goto out;
 454         }
 455
 456         if (do_munmap(mm, old_addr, old_len, uf_unmap) < 0) {
 457                 /* OOM: unable to split vma, just get accounts right */
 458                 vm_unacct_memory(excess >> PAGE_SHIFT);
 459                 excess = 0;
 460         }
 461
 462         if (vm_flags & VM_LOCKED) {
 463                 mm->locked_vm += new_len >> PAGE_SHIFT;
 464                 *locked = true;
 465         }
 466 out:
 467         mm->hiwater_vm = hiwater_vm;
 468
 469         /* Restore VM_ACCOUNT if one or two pieces of vma left */
 470         if (excess) {
 471                 vma->vm_flags |= VM_ACCOUNT;
 472                 if (split)
 473                         vma->vm_next->vm_flags |= VM_ACCOUNT;
 474         }
 475
 476         return new_addr;
 477 }
 478
 479 static struct vm_area_struct *vma_to_resize(unsigned long addr,
 480         unsigned long old_len, unsigned long new_len, unsigned long flags,
 481         unsigned long *p)
 482 {
 483         struct mm_struct *mm = current->mm;
 484         struct vm_area_struct *vma = find_vma(mm, addr);
 485         unsigned long pgoff;
 486
 487         if (!vma || vma->vm_start > addr)
 488                 return ERR_PTR(-EFAULT);
 489
 490         /*
 491          * !old_len is a special case where an attempt is made to 'duplicate'
 492          * a mapping.  This makes no sense for private mappings as it will
 493          * instead create a fresh/new mapping unrelated to the original.  This
 494          * is contrary to the basic idea of mremap which creates new mappings
 495          * based on the original.  There are no known use cases for this
 496          * behavior.  As a result, fail such attempts.
 497          */
 498         if (!old_len && !(vma->vm_flags & (VM_SHARED | VM_MAYSHARE))) {
 499                 pr_warn_once("%s (%d): attempted to duplicate a private mapping with mremap.  This is not supported.\n", current->comm, current->pid);
 500                 return ERR_PTR(-EINVAL);
 501         }
 502
 503         if (flags & MREMAP_DONTUNMAP && (!vma_is_anonymous(vma) ||
 504                         vma->vm_flags & VM_SHARED))
 505                 return ERR_PTR(-EINVAL);
 506
 507         if (is_vm_hugetlb_page(vma))
 508                 return ERR_PTR(-EINVAL);
 509
 510         /* We can't remap across vm area boundaries */
 511         if (old_len > vma->vm_end - addr)
 512                 return ERR_PTR(-EFAULT);
 513
 514         if (new_len == old_len)
 515                 return vma;
 516
 517         /* Need to be careful about a growing mapping */
 518         pgoff = (addr - vma->vm_start) >> PAGE_SHIFT;
 519         pgoff += vma->vm_pgoff;
 520         if (pgoff + (new_len >> PAGE_SHIFT) < pgoff)
 521                 return ERR_PTR(-EINVAL);
 522
 523         if (vma->vm_flags & (VM_DONTEXPAND | VM_PFNMAP))
 524                 return ERR_PTR(-EFAULT);
 525
 526         if (vma->vm_flags & VM_LOCKED) {
 527                 unsigned long locked, lock_limit;
 528                 locked = mm->locked_vm << PAGE_SHIFT;
 529                 lock_limit = rlimit(RLIMIT_MEMLOCK);
 530                 locked += new_len - old_len;
 531                 if (locked > lock_limit && !capable(CAP_IPC_LOCK))
 532                         return ERR_PTR(-EAGAIN);
 533         }
 534
 535         if (!may_expand_vm(mm, vma->vm_flags,
 536                                 (new_len - old_len) >> PAGE_SHIFT))
 537                 return ERR_PTR(-ENOMEM);
 538
 539         if (vma->vm_flags & VM_ACCOUNT) {
 540                 unsigned long charged = (new_len - old_len) >> PAGE_SHIFT;
 541                 if (security_vm_enough_memory_mm(mm, charged))
 542                         return ERR_PTR(-ENOMEM);
 543                 *p = charged;
 544         }
 545
 546         return vma;
 547 }
 548
 549 static unsigned long mremap_to(unsigned long addr, unsigned long old_len,
 550                 unsigned long new_addr, unsigned long new_len, bool *locked,
 551                 unsigned long flags, struct vm_userfaultfd_ctx *uf,
 552                 struct list_head *uf_unmap_early,
 553                 struct list_head *uf_unmap)
 554 {
 555         struct mm_struct *mm = current->mm;
 556         struct vm_area_struct *vma;
 557         unsigned long ret = -EINVAL;
 558         unsigned long charged = 0;
 559         unsigned long map_flags = 0;
 560
 561         if (offset_in_page(new_addr))
 562                 goto out;
 563
 564         if (new_len > TASK_SIZE || new_addr > TASK_SIZE - new_len)
 565                 goto out;
 566
 567         /* Ensure the old/new locations do not overlap */
 568         if (addr + old_len > new_addr && new_addr + new_len > addr)
 569                 goto out;
 570
 571         /*
 572          * move_vma() need us to stay 4 maps below the threshold, otherwise
 573          * it will bail out at the very beginning.
 574          * That is a problem if we have already unmaped the regions here
 575          * (new_addr, and old_addr), because userspace will not know the
 576          * state of the vma's after it gets -ENOMEM.
 577          * So, to avoid such scenario we can pre-compute if the whole
 578          * operation has high chances to success map-wise.
 579          * Worst-scenario case is when both vma's (new_addr and old_addr) get
 580          * split in 3 before unmaping it.
 581          * That means 2 more maps (1 for each) to the ones we already hold.
 582          * Check whether current map count plus 2 still leads us to 4 maps below
 583          * the threshold, otherwise return -ENOMEM here to be more safe.
 584          */
 585         if ((mm->map_count + 2) >= sysctl_max_map_count - 3)
 586                 return -ENOMEM;
 587
 588         if (flags & MREMAP_FIXED) {
 589                 ret = do_munmap(mm, new_addr, new_len, uf_unmap_early);
 590                 if (ret)
 591                         goto out;
 592         }
 593
 594         if (old_len >= new_len) {
 595                 ret = do_munmap(mm, addr+new_len, old_len - new_len, uf_unmap);
 596                 if (ret && old_len != new_len)
 597                         goto out;
 598                 old_len = new_len;
 599         }
 600
 601         vma = vma_to_resize(addr, old_len, new_len, flags, &charged);
 602         if (IS_ERR(vma)) {
 603                 ret = PTR_ERR(vma);
 604                 goto out;
 605         }
 606
 607         /* MREMAP_DONTUNMAP expands by old_len since old_len == new_len */
 608         if (flags & MREMAP_DONTUNMAP &&
 609                 !may_expand_vm(mm, vma->vm_flags, old_len >> PAGE_SHIFT)) {
 610                 ret = -ENOMEM;
 611                 goto out;
 612         }
 613
 614         if (flags & MREMAP_FIXED)
 615                 map_flags |= MAP_FIXED;
 616
 617         if (vma->vm_flags & VM_MAYSHARE)
 618                 map_flags |= MAP_SHARED;
 619
 620         ret = get_unmapped_area(vma->vm_file, new_addr, new_len, vma->vm_pgoff +
 621                                 ((addr - vma->vm_start) >> PAGE_SHIFT),
 622                                 map_flags);
 623         if (IS_ERR_VALUE(ret))
 624                 goto out1;
 625
 626         /* We got a new mapping */
 627         if (!(flags & MREMAP_FIXED))
 628                 new_addr = ret;
 629
 630         ret = move_vma(vma, addr, old_len, new_len, new_addr, locked, flags, uf,
 631                        uf_unmap);
 632
 633         if (!(offset_in_page(ret)))
 634                 goto out;
 635
 636 out1:
 637         vm_unacct_memory(charged);
 638
 639 out:
 640         return ret;
 641 }
 642
 643 static int vma_expandable(struct vm_area_struct *vma, unsigned long delta)
 644 {
 645         unsigned long end = vma->vm_end + delta;
 646         if (end < vma->vm_end) /* overflow */
 647                 return 0;
 648         if (vma->vm_next && vma->vm_next->vm_start < end) /* intersection */
 649                 return 0;
 650         if (get_unmapped_area(NULL, vma->vm_start, end - vma->vm_start,
 651                               0, MAP_FIXED) & ~PAGE_MASK)
 652                 return 0;
 653         return 1;
 654 }
 655
 656 /*
 657  * Expand (or shrink) an existing mapping, potentially moving it at the
 658  * same time (controlled by the MREMAP_MAYMOVE flag and available VM space)
 659  *
 660  * MREMAP_FIXED option added 5-Dec-1999 by Benjamin LaHaise
 661  * This option implies MREMAP_MAYMOVE.
 662  */
 663 SYSCALL_DEFINE5(mremap, unsigned long, addr, unsigned long, old_len,
 664                 unsigned long, new_len, unsigned long, flags,
 665                 unsigned long, new_addr)
 666 {
 667         struct mm_struct *mm = current->mm;
 668         struct vm_area_struct *vma;
 669         unsigned long ret = -EINVAL;
 670         unsigned long charged = 0;
 671         bool locked = false;
 672         bool downgraded = false;
 673         struct vm_userfaultfd_ctx uf = NULL_VM_UFFD_CTX;
 674         LIST_HEAD(uf_unmap_early);
 675         LIST_HEAD(uf_unmap);
 676
 677         /*
 678          * There is a deliberate asymmetry here: we strip the pointer tag
 679          * from the old address but leave the new address alone. This is
 680          * for consistency with mmap(), where we prevent the creation of
 681          * aliasing mappings in userspace by leaving the tag bits of the
 682          * mapping address intact. A non-zero tag will cause the subsequent
 683          * range checks to reject the address as invalid.
 684          *
 685          * See Documentation/arm64/tagged-address-abi.rst for more information.
 686          */
 687         addr = untagged_addr(addr);
 688
 689         if (flags & ~(MREMAP_FIXED | MREMAP_MAYMOVE | MREMAP_DONTUNMAP))
 690                 return ret;
 691
 692         if (flags & MREMAP_FIXED && !(flags & MREMAP_MAYMOVE))
 693                 return ret;
 694
 695         /*
 696          * MREMAP_DONTUNMAP is always a move and it does not allow resizing
 697          * in the process.
 698          */
 699         if (flags & MREMAP_DONTUNMAP &&
 700                         (!(flags & MREMAP_MAYMOVE) || old_len != new_len))
 701                 return ret;
 702
 703
 704         if (offset_in_page(addr))
 705                 return ret;
 706
 707         old_len = PAGE_ALIGN(old_len);
 708         new_len = PAGE_ALIGN(new_len);
 709
 710         /*
 711          * We allow a zero old-len as a special case
 712          * for DOS-emu "duplicate shm area" thing. But
 713          * a zero new-len is nonsensical.
 714          */
 715         if (!new_len)
 716                 return ret;
 717
 718         if (mmap_write_lock_killable(current->mm))
 719                 return -EINTR;
 720
 721         if (flags & (MREMAP_FIXED | MREMAP_DONTUNMAP)) {
 722                 ret = mremap_to(addr, old_len, new_addr, new_len,
 723                                 &locked, flags, &uf, &uf_unmap_early,
 724                                 &uf_unmap);
 725                 goto out;
 726         }
 727
 728         /*
 729          * Always allow a shrinking remap: that just unmaps
 730          * the unnecessary pages..
 731          * __do_munmap does all the needed commit accounting, and
 732          * downgrades mmap_lock to read if so directed.
 733          */
 734         if (old_len >= new_len) {
 735                 int retval;
 736
 737                 retval = __do_munmap(mm, addr+new_len, old_len - new_len,
 738                                   &uf_unmap, true);
 739                 if (retval < 0 && old_len != new_len) {
 740                         ret = retval;
 741                         goto out;
 742                 /* Returning 1 indicates mmap_lock is downgraded to read. */
 743                 } else if (retval == 1)
 744                         downgraded = true;
 745                 ret = addr;
 746                 goto out;
 747         }
 748
 749         /*
 750          * Ok, we need to grow..
 751          */
 752         vma = vma_to_resize(addr, old_len, new_len, flags, &charged);
 753         if (IS_ERR(vma)) {
 754                 ret = PTR_ERR(vma);
 755                 goto out;
 756         }
 757
 758         /* old_len exactly to the end of the area..
 759          */
 760         if (old_len == vma->vm_end - addr) {
 761                 /* can we just expand the current mapping? */
 762                 if (vma_expandable(vma, new_len - old_len)) {
 763                         int pages = (new_len - old_len) >> PAGE_SHIFT;
 764
 765                         if (vma_adjust(vma, vma->vm_start, addr + new_len,
 766                                        vma->vm_pgoff, NULL)) {
 767                                 ret = -ENOMEM;
 768                                 goto out;
 769                         }
 770
 771                         vm_stat_account(mm, vma->vm_flags, pages);
 772                         if (vma->vm_flags & VM_LOCKED) {
 773                                 mm->locked_vm += pages;
 774                                 locked = true;
 775                                 new_addr = addr;
 776                         }
 777                         ret = addr;
 778                         goto out;
 779                 }
 780         }
 781
 782         /*
 783          * We weren't able to just expand or shrink the area,
 784          * we need to create a new one and move it..
 785          */
 786         ret = -ENOMEM;
 787         if (flags & MREMAP_MAYMOVE) {
 788                 unsigned long map_flags = 0;
 789                 if (vma->vm_flags & VM_MAYSHARE)
 790                         map_flags |= MAP_SHARED;
 791
 792                 new_addr = get_unmapped_area(vma->vm_file, 0, new_len,
 793                                         vma->vm_pgoff +
 794                                         ((addr - vma->vm_start) >> PAGE_SHIFT),
 795                                         map_flags);
 796                 if (IS_ERR_VALUE(new_addr)) {
 797                         ret = new_addr;
 798                         goto out;
 799                 }
 800
 801                 ret = move_vma(vma, addr, old_len, new_len, new_addr,
 802                                &locked, flags, &uf, &uf_unmap);
 803         }
 804 out:
 805         if (offset_in_page(ret)) {
 806                 vm_unacct_memory(charged);
 807                 locked = false;
 808         }
 809         if (downgraded)
 810                 mmap_read_unlock(current->mm);
 811         else
 812                 mmap_write_unlock(current->mm);
 813         if (locked && new_len > old_len)
 814                 mm_populate(new_addr + old_len, new_len - old_len);
 815         userfaultfd_unmap_complete(mm, &uf_unmap_early);
 816         mremap_userfaultfd_complete(&uf, addr, ret, old_len);
 817         userfaultfd_unmap_complete(mm, &uf_unmap);
 818         return ret;
 819 }