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         if ((old_addr & ~PMD_MASK) || (new_addr & ~PMD_MASK))
 203                 return false;
 204
 205         /*
 206          * The destination pmd shouldn't be established, free_pgtables()
 207          * should have released it.
 208          *
 209          * However, there's a case during execve() where we use mremap
 210          * to move the initial stack, and in that case the target area
 211          * may overlap the source area (always moving down).
 212          *
 213          * If everything is PMD-aligned, that works fine, as moving
 214          * each pmd down will clear the source pmd. But if we first
 215          * have a few 4kB-only pages that get moved down, and then
 216          * hit the "now the rest is PMD-aligned, let's do everything
 217          * one pmd at a time", we will still have the old (now empty
 218          * of any 4kB pages, but still there) PMD in the page table
 219          * tree.
 220          *
 221          * Warn on it once - because we really should try to figure
 222          * out how to do this better - but then say "I won't move
 223          * this pmd".
 224          *
 225          * One alternative might be to just unmap the target pmd at
 226          * this point, and verify that it really is empty. We'll see.
 227          */
 228         if (WARN_ON_ONCE(!pmd_none(*new_pmd)))
 229                 return false;
 230
 231         /*
 232          * We don't have to worry about the ordering of src and dst
 233          * ptlocks because exclusive mmap_lock prevents deadlock.
 234          */
 235         old_ptl = pmd_lock(vma->vm_mm, old_pmd);
 236         new_ptl = pmd_lockptr(mm, new_pmd);
 237         if (new_ptl != old_ptl)
 238                 spin_lock_nested(new_ptl, SINGLE_DEPTH_NESTING);
 239
 240         /* Clear the pmd */
 241         pmd = *old_pmd;
 242         pmd_clear(old_pmd);
 243
 244         VM_BUG_ON(!pmd_none(*new_pmd));
 245
 246         /* Set the new pmd */
 247         set_pmd_at(mm, new_addr, new_pmd, pmd);
 248         flush_tlb_range(vma, old_addr, old_addr + PMD_SIZE);
 249         if (new_ptl != old_ptl)
 250                 spin_unlock(new_ptl);
 251         spin_unlock(old_ptl);
 252
 253         return true;
 254 }
 255 #endif
 256
 257 unsigned long move_page_tables(struct vm_area_struct *vma,
 258                 unsigned long old_addr, struct vm_area_struct *new_vma,
 259                 unsigned long new_addr, unsigned long len,
 260                 bool need_rmap_locks)
 261 {
 262         unsigned long extent, next, old_end;
 263         struct mmu_notifier_range range;
 264         pmd_t *old_pmd, *new_pmd;
 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                         if (need_rmap_locks)
 314                                 take_rmap_locks(vma);
 315                         moved = move_normal_pmd(vma, old_addr, new_addr,
 316                                                 old_pmd, new_pmd);
 317                         if (need_rmap_locks)
 318                                 drop_rmap_locks(vma);
 319                         if (moved)
 320                                 continue;
 321 #endif
 322                 }
 323
 324                 if (pte_alloc(new_vma->vm_mm, new_pmd))
 325                         break;
 326                 move_ptes(vma, old_pmd, old_addr, old_addr + extent, new_vma,
 327                           new_pmd, new_addr, need_rmap_locks);
 328         }
 329
 330         mmu_notifier_invalidate_range_end(&range);
 331
 332         return len + old_addr - old_end;        /* how much done */
 333 }
 334
 335 static unsigned long move_vma(struct vm_area_struct *vma,
 336                 unsigned long old_addr, unsigned long old_len,
 337                 unsigned long new_len, unsigned long new_addr,
 338                 bool *locked, unsigned long flags,
 339                 struct vm_userfaultfd_ctx *uf, struct list_head *uf_unmap)
 340 {
 341         struct mm_struct *mm = vma->vm_mm;
 342         struct vm_area_struct *new_vma;
 343         unsigned long vm_flags = vma->vm_flags;
 344         unsigned long new_pgoff;
 345         unsigned long moved_len;
 346         unsigned long excess = 0;
 347         unsigned long hiwater_vm;
 348         int split = 0;
 349         int err;
 350         bool need_rmap_locks;
 351
 352         /*
 353          * We'd prefer to avoid failure later on in do_munmap:
 354          * which may split one vma into three before unmapping.
 355          */
 356         if (mm->map_count >= sysctl_max_map_count - 3)
 357                 return -ENOMEM;
 358
 359         /*
 360          * Advise KSM to break any KSM pages in the area to be moved:
 361          * it would be confusing if they were to turn up at the new
 362          * location, where they happen to coincide with different KSM
 363          * pages recently unmapped.  But leave vma->vm_flags as it was,
 364          * so KSM can come around to merge on vma and new_vma afterwards.
 365          */
 366         err = ksm_madvise(vma, old_addr, old_addr + old_len,
 367                                                 MADV_UNMERGEABLE, &vm_flags);
 368         if (err)
 369                 return err;
 370
 371         new_pgoff = vma->vm_pgoff + ((old_addr - vma->vm_start) >> PAGE_SHIFT);
 372         new_vma = copy_vma(&vma, new_addr, new_len, new_pgoff,
 373                            &need_rmap_locks);
 374         if (!new_vma)
 375                 return -ENOMEM;
 376
 377         moved_len = move_page_tables(vma, old_addr, new_vma, new_addr, old_len,
 378                                      need_rmap_locks);
 379         if (moved_len < old_len) {
 380                 err = -ENOMEM;
 381         } else if (vma->vm_ops && vma->vm_ops->mremap) {
 382                 err = vma->vm_ops->mremap(new_vma);
 383         }
 384
 385         if (unlikely(err)) {
 386                 /*
 387                  * On error, move entries back from new area to old,
 388                  * which will succeed since page tables still there,
 389                  * and then proceed to unmap new area instead of old.
 390                  */
 391                 move_page_tables(new_vma, new_addr, vma, old_addr, moved_len,
 392                                  true);
 393                 vma = new_vma;
 394                 old_len = new_len;
 395                 old_addr = new_addr;
 396                 new_addr = err;
 397         } else {
 398                 mremap_userfaultfd_prep(new_vma, uf);
 399                 arch_remap(mm, old_addr, old_addr + old_len,
 400                            new_addr, new_addr + new_len);
 401         }
 402
 403         /* Conceal VM_ACCOUNT so old reservation is not undone */
 404         if (vm_flags & VM_ACCOUNT) {
 405                 vma->vm_flags &= ~VM_ACCOUNT;
 406                 excess = vma->vm_end - vma->vm_start - old_len;
 407                 if (old_addr > vma->vm_start &&
 408                     old_addr + old_len < vma->vm_end)
 409                         split = 1;
 410         }
 411
 412         /*
 413          * If we failed to move page tables we still do total_vm increment
 414          * since do_munmap() will decrement it by old_len == new_len.
 415          *
 416          * Since total_vm is about to be raised artificially high for a
 417          * moment, we need to restore high watermark afterwards: if stats
 418          * are taken meanwhile, total_vm and hiwater_vm appear too high.
 419          * If this were a serious issue, we'd add a flag to do_munmap().
 420          */
 421         hiwater_vm = mm->hiwater_vm;
 422         vm_stat_account(mm, vma->vm_flags, new_len >> PAGE_SHIFT);
 423
 424         /* Tell pfnmap has moved from this vma */
 425         if (unlikely(vma->vm_flags & VM_PFNMAP))
 426                 untrack_pfn_moved(vma);
 427
 428         if (unlikely(!err && (flags & MREMAP_DONTUNMAP))) {
 429                 if (vm_flags & VM_ACCOUNT) {
 430                         /* Always put back VM_ACCOUNT since we won't unmap */
 431                         vma->vm_flags |= VM_ACCOUNT;
 432
 433                         vm_acct_memory(new_len >> PAGE_SHIFT);
 434                 }
 435
 436                 /*
 437                  * VMAs can actually be merged back together in copy_vma
 438                  * calling merge_vma. This can happen with anonymous vmas
 439                  * which have not yet been faulted, so if we were to consider
 440                  * this VMA split we'll end up adding VM_ACCOUNT on the
 441                  * next VMA, which is completely unrelated if this VMA
 442                  * was re-merged.
 443                  */
 444                 if (split && new_vma == vma)
 445                         split = 0;
 446
 447                 /* We always clear VM_LOCKED[ONFAULT] on the old vma */
 448                 vma->vm_flags &= VM_LOCKED_CLEAR_MASK;
 449
 450                 /* Because we won't unmap we don't need to touch locked_vm */
 451                 goto out;
 452         }
 453
 454         if (do_munmap(mm, old_addr, old_len, uf_unmap) < 0) {
 455                 /* OOM: unable to split vma, just get accounts right */
 456                 vm_unacct_memory(excess >> PAGE_SHIFT);
 457                 excess = 0;
 458         }
 459
 460         if (vm_flags & VM_LOCKED) {
 461                 mm->locked_vm += new_len >> PAGE_SHIFT;
 462                 *locked = true;
 463         }
 464 out:
 465         mm->hiwater_vm = hiwater_vm;
 466
 467         /* Restore VM_ACCOUNT if one or two pieces of vma left */
 468         if (excess) {
 469                 vma->vm_flags |= VM_ACCOUNT;
 470                 if (split)
 471                         vma->vm_next->vm_flags |= VM_ACCOUNT;
 472         }
 473
 474         return new_addr;
 475 }
 476
 477 static struct vm_area_struct *vma_to_resize(unsigned long addr,
 478         unsigned long old_len, unsigned long new_len, unsigned long flags,
 479         unsigned long *p)
 480 {
 481         struct mm_struct *mm = current->mm;
 482         struct vm_area_struct *vma = find_vma(mm, addr);
 483         unsigned long pgoff;
 484
 485         if (!vma || vma->vm_start > addr)
 486                 return ERR_PTR(-EFAULT);
 487
 488         /*
 489          * !old_len is a special case where an attempt is made to 'duplicate'
 490          * a mapping.  This makes no sense for private mappings as it will
 491          * instead create a fresh/new mapping unrelated to the original.  This
 492          * is contrary to the basic idea of mremap which creates new mappings
 493          * based on the original.  There are no known use cases for this
 494          * behavior.  As a result, fail such attempts.
 495          */
 496         if (!old_len && !(vma->vm_flags & (VM_SHARED | VM_MAYSHARE))) {
 497                 pr_warn_once("%s (%d): attempted to duplicate a private mapping with mremap.  This is not supported.\n", current->comm, current->pid);
 498                 return ERR_PTR(-EINVAL);
 499         }
 500
 501         if (flags & MREMAP_DONTUNMAP && (!vma_is_anonymous(vma) ||
 502                         vma->vm_flags & VM_SHARED))
 503                 return ERR_PTR(-EINVAL);
 504
 505         if (is_vm_hugetlb_page(vma))
 506                 return ERR_PTR(-EINVAL);
 507
 508         /* We can't remap across vm area boundaries */
 509         if (old_len > vma->vm_end - addr)
 510                 return ERR_PTR(-EFAULT);
 511
 512         if (new_len == old_len)
 513                 return vma;
 514
 515         /* Need to be careful about a growing mapping */
 516         pgoff = (addr - vma->vm_start) >> PAGE_SHIFT;
 517         pgoff += vma->vm_pgoff;
 518         if (pgoff + (new_len >> PAGE_SHIFT) < pgoff)
 519                 return ERR_PTR(-EINVAL);
 520
 521         if (vma->vm_flags & (VM_DONTEXPAND | VM_PFNMAP))
 522                 return ERR_PTR(-EFAULT);
 523
 524         if (vma->vm_flags & VM_LOCKED) {
 525                 unsigned long locked, lock_limit;
 526                 locked = mm->locked_vm << PAGE_SHIFT;
 527                 lock_limit = rlimit(RLIMIT_MEMLOCK);
 528                 locked += new_len - old_len;
 529                 if (locked > lock_limit && !capable(CAP_IPC_LOCK))
 530                         return ERR_PTR(-EAGAIN);
 531         }
 532
 533         if (!may_expand_vm(mm, vma->vm_flags,
 534                                 (new_len - old_len) >> PAGE_SHIFT))
 535                 return ERR_PTR(-ENOMEM);
 536
 537         if (vma->vm_flags & VM_ACCOUNT) {
 538                 unsigned long charged = (new_len - old_len) >> PAGE_SHIFT;
 539                 if (security_vm_enough_memory_mm(mm, charged))
 540                         return ERR_PTR(-ENOMEM);
 541                 *p = charged;
 542         }
 543
 544         return vma;
 545 }
 546
 547 static unsigned long mremap_to(unsigned long addr, unsigned long old_len,
 548                 unsigned long new_addr, unsigned long new_len, bool *locked,
 549                 unsigned long flags, struct vm_userfaultfd_ctx *uf,
 550                 struct list_head *uf_unmap_early,
 551                 struct list_head *uf_unmap)
 552 {
 553         struct mm_struct *mm = current->mm;
 554         struct vm_area_struct *vma;
 555         unsigned long ret = -EINVAL;
 556         unsigned long charged = 0;
 557         unsigned long map_flags = 0;
 558
 559         if (offset_in_page(new_addr))
 560                 goto out;
 561
 562         if (new_len > TASK_SIZE || new_addr > TASK_SIZE - new_len)
 563                 goto out;
 564
 565         /* Ensure the old/new locations do not overlap */
 566         if (addr + old_len > new_addr && new_addr + new_len > addr)
 567                 goto out;
 568
 569         /*
 570          * move_vma() need us to stay 4 maps below the threshold, otherwise
 571          * it will bail out at the very beginning.
 572          * That is a problem if we have already unmaped the regions here
 573          * (new_addr, and old_addr), because userspace will not know the
 574          * state of the vma's after it gets -ENOMEM.
 575          * So, to avoid such scenario we can pre-compute if the whole
 576          * operation has high chances to success map-wise.
 577          * Worst-scenario case is when both vma's (new_addr and old_addr) get
 578          * split in 3 before unmaping it.
 579          * That means 2 more maps (1 for each) to the ones we already hold.
 580          * Check whether current map count plus 2 still leads us to 4 maps below
 581          * the threshold, otherwise return -ENOMEM here to be more safe.
 582          */
 583         if ((mm->map_count + 2) >= sysctl_max_map_count - 3)
 584                 return -ENOMEM;
 585
 586         if (flags & MREMAP_FIXED) {
 587                 ret = do_munmap(mm, new_addr, new_len, uf_unmap_early);
 588                 if (ret)
 589                         goto out;
 590         }
 591
 592         if (old_len >= new_len) {
 593                 ret = do_munmap(mm, addr+new_len, old_len - new_len, uf_unmap);
 594                 if (ret && old_len != new_len)
 595                         goto out;
 596                 old_len = new_len;
 597         }
 598
 599         vma = vma_to_resize(addr, old_len, new_len, flags, &charged);
 600         if (IS_ERR(vma)) {
 601                 ret = PTR_ERR(vma);
 602                 goto out;
 603         }
 604
 605         /* MREMAP_DONTUNMAP expands by old_len since old_len == new_len */
 606         if (flags & MREMAP_DONTUNMAP &&
 607                 !may_expand_vm(mm, vma->vm_flags, old_len >> PAGE_SHIFT)) {
 608                 ret = -ENOMEM;
 609                 goto out;
 610         }
 611
 612         if (flags & MREMAP_FIXED)
 613                 map_flags |= MAP_FIXED;
 614
 615         if (vma->vm_flags & VM_MAYSHARE)
 616                 map_flags |= MAP_SHARED;
 617
 618         ret = get_unmapped_area(vma->vm_file, new_addr, new_len, vma->vm_pgoff +
 619                                 ((addr - vma->vm_start) >> PAGE_SHIFT),
 620                                 map_flags);
 621         if (IS_ERR_VALUE(ret))
 622                 goto out1;
 623
 624         /* We got a new mapping */
 625         if (!(flags & MREMAP_FIXED))
 626                 new_addr = ret;
 627
 628         ret = move_vma(vma, addr, old_len, new_len, new_addr, locked, flags, uf,
 629                        uf_unmap);
 630
 631         if (!(offset_in_page(ret)))
 632                 goto out;
 633
 634 out1:
 635         vm_unacct_memory(charged);
 636
 637 out:
 638         return ret;
 639 }
 640
 641 static int vma_expandable(struct vm_area_struct *vma, unsigned long delta)
 642 {
 643         unsigned long end = vma->vm_end + delta;
 644         if (end < vma->vm_end) /* overflow */
 645                 return 0;
 646         if (vma->vm_next && vma->vm_next->vm_start < end) /* intersection */
 647                 return 0;
 648         if (get_unmapped_area(NULL, vma->vm_start, end - vma->vm_start,
 649                               0, MAP_FIXED) & ~PAGE_MASK)
 650                 return 0;
 651         return 1;
 652 }
 653
 654 /*
 655  * Expand (or shrink) an existing mapping, potentially moving it at the
 656  * same time (controlled by the MREMAP_MAYMOVE flag and available VM space)
 657  *
 658  * MREMAP_FIXED option added 5-Dec-1999 by Benjamin LaHaise
 659  * This option implies MREMAP_MAYMOVE.
 660  */
 661 SYSCALL_DEFINE5(mremap, unsigned long, addr, unsigned long, old_len,
 662                 unsigned long, new_len, unsigned long, flags,
 663                 unsigned long, new_addr)
 664 {
 665         struct mm_struct *mm = current->mm;
 666         struct vm_area_struct *vma;
 667         unsigned long ret = -EINVAL;
 668         unsigned long charged = 0;
 669         bool locked = false;
 670         bool downgraded = false;
 671         struct vm_userfaultfd_ctx uf = NULL_VM_UFFD_CTX;
 672         LIST_HEAD(uf_unmap_early);
 673         LIST_HEAD(uf_unmap);
 674
 675         /*
 676          * There is a deliberate asymmetry here: we strip the pointer tag
 677          * from the old address but leave the new address alone. This is
 678          * for consistency with mmap(), where we prevent the creation of
 679          * aliasing mappings in userspace by leaving the tag bits of the
 680          * mapping address intact. A non-zero tag will cause the subsequent
 681          * range checks to reject the address as invalid.
 682          *
 683          * See Documentation/arm64/tagged-address-abi.rst for more information.
 684          */
 685         addr = untagged_addr(addr);
 686
 687         if (flags & ~(MREMAP_FIXED | MREMAP_MAYMOVE | MREMAP_DONTUNMAP))
 688                 return ret;
 689
 690         if (flags & MREMAP_FIXED && !(flags & MREMAP_MAYMOVE))
 691                 return ret;
 692
 693         /*
 694          * MREMAP_DONTUNMAP is always a move and it does not allow resizing
 695          * in the process.
 696          */
 697         if (flags & MREMAP_DONTUNMAP &&
 698                         (!(flags & MREMAP_MAYMOVE) || old_len != new_len))
 699                 return ret;
 700
 701
 702         if (offset_in_page(addr))
 703                 return ret;
 704
 705         old_len = PAGE_ALIGN(old_len);
 706         new_len = PAGE_ALIGN(new_len);
 707
 708         /*
 709          * We allow a zero old-len as a special case
 710          * for DOS-emu "duplicate shm area" thing. But
 711          * a zero new-len is nonsensical.
 712          */
 713         if (!new_len)
 714                 return ret;
 715
 716         if (mmap_write_lock_killable(current->mm))
 717                 return -EINTR;
 718
 719         if (flags & (MREMAP_FIXED | MREMAP_DONTUNMAP)) {
 720                 ret = mremap_to(addr, old_len, new_addr, new_len,
 721                                 &locked, flags, &uf, &uf_unmap_early,
 722                                 &uf_unmap);
 723                 goto out;
 724         }
 725
 726         /*
 727          * Always allow a shrinking remap: that just unmaps
 728          * the unnecessary pages..
 729          * __do_munmap does all the needed commit accounting, and
 730          * downgrades mmap_lock to read if so directed.
 731          */
 732         if (old_len >= new_len) {
 733                 int retval;
 734
 735                 retval = __do_munmap(mm, addr+new_len, old_len - new_len,
 736                                   &uf_unmap, true);
 737                 if (retval < 0 && old_len != new_len) {
 738                         ret = retval;
 739                         goto out;
 740                 /* Returning 1 indicates mmap_lock is downgraded to read. */
 741                 } else if (retval == 1)
 742                         downgraded = true;
 743                 ret = addr;
 744                 goto out;
 745         }
 746
 747         /*
 748          * Ok, we need to grow..
 749          */
 750         vma = vma_to_resize(addr, old_len, new_len, flags, &charged);
 751         if (IS_ERR(vma)) {
 752                 ret = PTR_ERR(vma);
 753                 goto out;
 754         }
 755
 756         /* old_len exactly to the end of the area..
 757          */
 758         if (old_len == vma->vm_end - addr) {
 759                 /* can we just expand the current mapping? */
 760                 if (vma_expandable(vma, new_len - old_len)) {
 761                         int pages = (new_len - old_len) >> PAGE_SHIFT;
 762
 763                         if (vma_adjust(vma, vma->vm_start, addr + new_len,
 764                                        vma->vm_pgoff, NULL)) {
 765                                 ret = -ENOMEM;
 766                                 goto out;
 767                         }
 768
 769                         vm_stat_account(mm, vma->vm_flags, pages);
 770                         if (vma->vm_flags & VM_LOCKED) {
 771                                 mm->locked_vm += pages;
 772                                 locked = true;
 773                                 new_addr = addr;
 774                         }
 775                         ret = addr;
 776                         goto out;
 777                 }
 778         }
 779
 780         /*
 781          * We weren't able to just expand or shrink the area,
 782          * we need to create a new one and move it..
 783          */
 784         ret = -ENOMEM;
 785         if (flags & MREMAP_MAYMOVE) {
 786                 unsigned long map_flags = 0;
 787                 if (vma->vm_flags & VM_MAYSHARE)
 788                         map_flags |= MAP_SHARED;
 789
 790                 new_addr = get_unmapped_area(vma->vm_file, 0, new_len,
 791                                         vma->vm_pgoff +
 792                                         ((addr - vma->vm_start) >> PAGE_SHIFT),
 793                                         map_flags);
 794                 if (IS_ERR_VALUE(new_addr)) {
 795                         ret = new_addr;
 796                         goto out;
 797                 }
 798
 799                 ret = move_vma(vma, addr, old_len, new_len, new_addr,
 800                                &locked, flags, &uf, &uf_unmap);
 801         }
 802 out:
 803         if (offset_in_page(ret)) {
 804                 vm_unacct_memory(charged);
 805                 locked = false;
 806         }
 807         if (downgraded)
 808                 mmap_read_unlock(current->mm);
 809         else
 810                 mmap_write_unlock(current->mm);
 811         if (locked && new_len > old_len)
 812                 mm_populate(new_addr + old_len, new_len - old_len);
 813         userfaultfd_unmap_complete(mm, &uf_unmap_early);
 814         mremap_userfaultfd_complete(&uf, addr, ret, old_len);
 815         userfaultfd_unmap_complete(mm, &uf_unmap);
 816         return ret;
 817 }