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_sem prevents deadlock.
 150          */
 151         old_pte = pte_offset_map_lock(mm, old_pmd, old_addr, &old_ptl);
 152         new_pte = pte_offset_map(new_pmd, new_addr);
 153         new_ptl = pte_lockptr(mm, new_pmd);
 154         if (new_ptl != old_ptl)
 155                 spin_lock_nested(new_ptl, SINGLE_DEPTH_NESTING);
 156         flush_tlb_batched_pending(vma->vm_mm);
 157         arch_enter_lazy_mmu_mode();
 158
 159         for (; old_addr < old_end; old_pte++, old_addr += PAGE_SIZE,
 160                                    new_pte++, new_addr += PAGE_SIZE) {
 161                 if (pte_none(*old_pte))
 162                         continue;
 163
 164                 pte = ptep_get_and_clear(mm, old_addr, old_pte);
 165                 /*
 166                  * If we are remapping a valid PTE, make sure
 167                  * to flush TLB before we drop the PTL for the
 168                  * PTE.
 169                  *
 170                  * NOTE! Both old and new PTL matter: the old one
 171                  * for racing with page_mkclean(), the new one to
 172                  * make sure the physical page stays valid until
 173                  * the TLB entry for the old mapping has been
 174                  * flushed.
 175                  */
 176                 if (pte_present(pte))
 177                         force_flush = true;
 178                 pte = move_pte(pte, new_vma->vm_page_prot, old_addr, new_addr);
 179                 pte = move_soft_dirty_pte(pte);
 180                 set_pte_at(mm, new_addr, new_pte, pte);
 181         }
 182
 183         arch_leave_lazy_mmu_mode();
 184         if (force_flush)
 185                 flush_tlb_range(vma, old_end - len, old_end);
 186         if (new_ptl != old_ptl)
 187                 spin_unlock(new_ptl);
 188         pte_unmap(new_pte - 1);
 189         pte_unmap_unlock(old_pte - 1, old_ptl);
 190         if (need_rmap_locks)
 191                 drop_rmap_locks(vma);
 192 }
 193
 194 #ifdef CONFIG_HAVE_MOVE_PMD
 195 static bool move_normal_pmd(struct vm_area_struct *vma, unsigned long old_addr,
 196                   unsigned long new_addr, unsigned long old_end,
 197                   pmd_t *old_pmd, pmd_t *new_pmd)
 198 {
 199         spinlock_t *old_ptl, *new_ptl;
 200         struct mm_struct *mm = vma->vm_mm;
 201         pmd_t pmd;
 202
 203         if ((old_addr & ~PMD_MASK) || (new_addr & ~PMD_MASK)
 204             || old_end - old_addr < PMD_SIZE)
 205                 return false;
 206
 207         /*
 208          * The destination pmd shouldn't be established, free_pgtables()
 209          * should have release it.
 210          */
 211         if (WARN_ON(!pmd_none(*new_pmd)))
 212                 return false;
 213
 214         /*
 215          * We don't have to worry about the ordering of src and dst
 216          * ptlocks because exclusive mmap_sem prevents deadlock.
 217          */
 218         old_ptl = pmd_lock(vma->vm_mm, old_pmd);
 219         new_ptl = pmd_lockptr(mm, new_pmd);
 220         if (new_ptl != old_ptl)
 221                 spin_lock_nested(new_ptl, SINGLE_DEPTH_NESTING);
 222
 223         /* Clear the pmd */
 224         pmd = *old_pmd;
 225         pmd_clear(old_pmd);
 226
 227         VM_BUG_ON(!pmd_none(*new_pmd));
 228
 229         /* Set the new pmd */
 230         set_pmd_at(mm, new_addr, new_pmd, pmd);
 231         flush_tlb_range(vma, old_addr, old_addr + PMD_SIZE);
 232         if (new_ptl != old_ptl)
 233                 spin_unlock(new_ptl);
 234         spin_unlock(old_ptl);
 235
 236         return true;
 237 }
 238 #endif
 239
 240 unsigned long move_page_tables(struct vm_area_struct *vma,
 241                 unsigned long old_addr, struct vm_area_struct *new_vma,
 242                 unsigned long new_addr, unsigned long len,
 243                 bool need_rmap_locks)
 244 {
 245         unsigned long extent, next, old_end;
 246         struct mmu_notifier_range range;
 247         pmd_t *old_pmd, *new_pmd;
 248
 249         old_end = old_addr + len;
 250         flush_cache_range(vma, old_addr, old_end);
 251
 252         mmu_notifier_range_init(&range, MMU_NOTIFY_UNMAP, 0, vma, vma->vm_mm,
 253                                 old_addr, old_end);
 254         mmu_notifier_invalidate_range_start(&range);
 255
 256         for (; old_addr < old_end; old_addr += extent, new_addr += extent) {
 257                 cond_resched();
 258                 next = (old_addr + PMD_SIZE) & PMD_MASK;
 259                 /* even if next overflowed, extent below will be ok */
 260                 extent = next - old_addr;
 261                 if (extent > old_end - old_addr)
 262                         extent = old_end - old_addr;
 263                 old_pmd = get_old_pmd(vma->vm_mm, old_addr);
 264                 if (!old_pmd)
 265                         continue;
 266                 new_pmd = alloc_new_pmd(vma->vm_mm, vma, new_addr);
 267                 if (!new_pmd)
 268                         break;
 269                 if (is_swap_pmd(*old_pmd) || pmd_trans_huge(*old_pmd)) {
 270                         if (extent == HPAGE_PMD_SIZE) {
 271                                 bool moved;
 272                                 /* See comment in move_ptes() */
 273                                 if (need_rmap_locks)
 274                                         take_rmap_locks(vma);
 275                                 moved = move_huge_pmd(vma, old_addr, new_addr,
 276                                                     old_end, old_pmd, new_pmd);
 277                                 if (need_rmap_locks)
 278                                         drop_rmap_locks(vma);
 279                                 if (moved)
 280                                         continue;
 281                         }
 282                         split_huge_pmd(vma, old_pmd, old_addr);
 283                         if (pmd_trans_unstable(old_pmd))
 284                                 continue;
 285                 } else if (extent == PMD_SIZE) {
 286 #ifdef CONFIG_HAVE_MOVE_PMD
 287                         /*
 288                          * If the extent is PMD-sized, try to speed the move by
 289                          * moving at the PMD level if possible.
 290                          */
 291                         bool moved;
 292
 293                         if (need_rmap_locks)
 294                                 take_rmap_locks(vma);
 295                         moved = move_normal_pmd(vma, old_addr, new_addr,
 296                                         old_end, old_pmd, new_pmd);
 297                         if (need_rmap_locks)
 298                                 drop_rmap_locks(vma);
 299                         if (moved)
 300                                 continue;
 301 #endif
 302                 }
 303
 304                 if (pte_alloc(new_vma->vm_mm, new_pmd))
 305                         break;
 306                 next = (new_addr + PMD_SIZE) & PMD_MASK;
 307                 if (extent > next - new_addr)
 308                         extent = next - new_addr;
 309                 move_ptes(vma, old_pmd, old_addr, old_addr + extent, new_vma,
 310                           new_pmd, new_addr, need_rmap_locks);
 311         }
 312
 313         mmu_notifier_invalidate_range_end(&range);
 314
 315         return len + old_addr - old_end;        /* how much done */
 316 }
 317
 318 static unsigned long move_vma(struct vm_area_struct *vma,
 319                 unsigned long old_addr, unsigned long old_len,
 320                 unsigned long new_len, unsigned long new_addr,
 321                 bool *locked, unsigned long flags,
 322                 struct vm_userfaultfd_ctx *uf, struct list_head *uf_unmap)
 323 {
 324         struct mm_struct *mm = vma->vm_mm;
 325         struct vm_area_struct *new_vma;
 326         unsigned long vm_flags = vma->vm_flags;
 327         unsigned long new_pgoff;
 328         unsigned long moved_len;
 329         unsigned long excess = 0;
 330         unsigned long hiwater_vm;
 331         int split = 0;
 332         int err;
 333         bool need_rmap_locks;
 334
 335         /*
 336          * We'd prefer to avoid failure later on in do_munmap:
 337          * which may split one vma into three before unmapping.
 338          */
 339         if (mm->map_count >= sysctl_max_map_count - 3)
 340                 return -ENOMEM;
 341
 342         /*
 343          * Advise KSM to break any KSM pages in the area to be moved:
 344          * it would be confusing if they were to turn up at the new
 345          * location, where they happen to coincide with different KSM
 346          * pages recently unmapped.  But leave vma->vm_flags as it was,
 347          * so KSM can come around to merge on vma and new_vma afterwards.
 348          */
 349         err = ksm_madvise(vma, old_addr, old_addr + old_len,
 350                                                 MADV_UNMERGEABLE, &vm_flags);
 351         if (err)
 352                 return err;
 353
 354         new_pgoff = vma->vm_pgoff + ((old_addr - vma->vm_start) >> PAGE_SHIFT);
 355         new_vma = copy_vma(&vma, new_addr, new_len, new_pgoff,
 356                            &need_rmap_locks);
 357         if (!new_vma)
 358                 return -ENOMEM;
 359
 360         moved_len = move_page_tables(vma, old_addr, new_vma, new_addr, old_len,
 361                                      need_rmap_locks);
 362         if (moved_len < old_len) {
 363                 err = -ENOMEM;
 364         } else if (vma->vm_ops && vma->vm_ops->mremap) {
 365                 err = vma->vm_ops->mremap(new_vma);
 366         }
 367
 368         if (unlikely(err)) {
 369                 /*
 370                  * On error, move entries back from new area to old,
 371                  * which will succeed since page tables still there,
 372                  * and then proceed to unmap new area instead of old.
 373                  */
 374                 move_page_tables(new_vma, new_addr, vma, old_addr, moved_len,
 375                                  true);
 376                 vma = new_vma;
 377                 old_len = new_len;
 378                 old_addr = new_addr;
 379                 new_addr = err;
 380         } else {
 381                 mremap_userfaultfd_prep(new_vma, uf);
 382                 arch_remap(mm, old_addr, old_addr + old_len,
 383                            new_addr, new_addr + new_len);
 384         }
 385
 386         /* Conceal VM_ACCOUNT so old reservation is not undone */
 387         if (vm_flags & VM_ACCOUNT) {
 388                 vma->vm_flags &= ~VM_ACCOUNT;
 389                 excess = vma->vm_end - vma->vm_start - old_len;
 390                 if (old_addr > vma->vm_start &&
 391                     old_addr + old_len < vma->vm_end)
 392                         split = 1;
 393         }
 394
 395         /*
 396          * If we failed to move page tables we still do total_vm increment
 397          * since do_munmap() will decrement it by old_len == new_len.
 398          *
 399          * Since total_vm is about to be raised artificially high for a
 400          * moment, we need to restore high watermark afterwards: if stats
 401          * are taken meanwhile, total_vm and hiwater_vm appear too high.
 402          * If this were a serious issue, we'd add a flag to do_munmap().
 403          */
 404         hiwater_vm = mm->hiwater_vm;
 405         vm_stat_account(mm, vma->vm_flags, new_len >> PAGE_SHIFT);
 406
 407         /* Tell pfnmap has moved from this vma */
 408         if (unlikely(vma->vm_flags & VM_PFNMAP))
 409                 untrack_pfn_moved(vma);
 410
 411         if (unlikely(!err && (flags & MREMAP_DONTUNMAP))) {
 412                 if (vm_flags & VM_ACCOUNT) {
 413                         /* Always put back VM_ACCOUNT since we won't unmap */
 414                         vma->vm_flags |= VM_ACCOUNT;
 415
 416                         vm_acct_memory(vma_pages(new_vma));
 417                 }
 418
 419                 /* We always clear VM_LOCKED[ONFAULT] on the old vma */
 420                 vma->vm_flags &= VM_LOCKED_CLEAR_MASK;
 421
 422                 /* Because we won't unmap we don't need to touch locked_vm */
 423                 goto out;
 424         }
 425
 426         if (do_munmap(mm, old_addr, old_len, uf_unmap) < 0) {
 427                 /* OOM: unable to split vma, just get accounts right */
 428                 vm_unacct_memory(excess >> PAGE_SHIFT);
 429                 excess = 0;
 430         }
 431
 432         if (vm_flags & VM_LOCKED) {
 433                 mm->locked_vm += new_len >> PAGE_SHIFT;
 434                 *locked = true;
 435         }
 436 out:
 437         mm->hiwater_vm = hiwater_vm;
 438
 439         /* Restore VM_ACCOUNT if one or two pieces of vma left */
 440         if (excess) {
 441                 vma->vm_flags |= VM_ACCOUNT;
 442                 if (split)
 443                         vma->vm_next->vm_flags |= VM_ACCOUNT;
 444         }
 445
 446         return new_addr;
 447 }
 448
 449 static struct vm_area_struct *vma_to_resize(unsigned long addr,
 450         unsigned long old_len, unsigned long new_len, unsigned long flags,
 451         unsigned long *p)
 452 {
 453         struct mm_struct *mm = current->mm;
 454         struct vm_area_struct *vma = find_vma(mm, addr);
 455         unsigned long pgoff;
 456
 457         if (!vma || vma->vm_start > addr)
 458                 return ERR_PTR(-EFAULT);
 459
 460         /*
 461          * !old_len is a special case where an attempt is made to 'duplicate'
 462          * a mapping.  This makes no sense for private mappings as it will
 463          * instead create a fresh/new mapping unrelated to the original.  This
 464          * is contrary to the basic idea of mremap which creates new mappings
 465          * based on the original.  There are no known use cases for this
 466          * behavior.  As a result, fail such attempts.
 467          */
 468         if (!old_len && !(vma->vm_flags & (VM_SHARED | VM_MAYSHARE))) {
 469                 pr_warn_once("%s (%d): attempted to duplicate a private mapping with mremap.  This is not supported.\n", current->comm, current->pid);
 470                 return ERR_PTR(-EINVAL);
 471         }
 472
 473         if (flags & MREMAP_DONTUNMAP && (!vma_is_anonymous(vma) ||
 474                         vma->vm_flags & VM_SHARED))
 475                 return ERR_PTR(-EINVAL);
 476
 477         if (is_vm_hugetlb_page(vma))
 478                 return ERR_PTR(-EINVAL);
 479
 480         /* We can't remap across vm area boundaries */
 481         if (old_len > vma->vm_end - addr)
 482                 return ERR_PTR(-EFAULT);
 483
 484         if (new_len == old_len)
 485                 return vma;
 486
 487         /* Need to be careful about a growing mapping */
 488         pgoff = (addr - vma->vm_start) >> PAGE_SHIFT;
 489         pgoff += vma->vm_pgoff;
 490         if (pgoff + (new_len >> PAGE_SHIFT) < pgoff)
 491                 return ERR_PTR(-EINVAL);
 492
 493         if (vma->vm_flags & (VM_DONTEXPAND | VM_PFNMAP))
 494                 return ERR_PTR(-EFAULT);
 495
 496         if (vma->vm_flags & VM_LOCKED) {
 497                 unsigned long locked, lock_limit;
 498                 locked = mm->locked_vm << PAGE_SHIFT;
 499                 lock_limit = rlimit(RLIMIT_MEMLOCK);
 500                 locked += new_len - old_len;
 501                 if (locked > lock_limit && !capable(CAP_IPC_LOCK))
 502                         return ERR_PTR(-EAGAIN);
 503         }
 504
 505         if (!may_expand_vm(mm, vma->vm_flags,
 506                                 (new_len - old_len) >> PAGE_SHIFT))
 507                 return ERR_PTR(-ENOMEM);
 508
 509         if (vma->vm_flags & VM_ACCOUNT) {
 510                 unsigned long charged = (new_len - old_len) >> PAGE_SHIFT;
 511                 if (security_vm_enough_memory_mm(mm, charged))
 512                         return ERR_PTR(-ENOMEM);
 513                 *p = charged;
 514         }
 515
 516         return vma;
 517 }
 518
 519 static unsigned long mremap_to(unsigned long addr, unsigned long old_len,
 520                 unsigned long new_addr, unsigned long new_len, bool *locked,
 521                 unsigned long flags, struct vm_userfaultfd_ctx *uf,
 522                 struct list_head *uf_unmap_early,
 523                 struct list_head *uf_unmap)
 524 {
 525         struct mm_struct *mm = current->mm;
 526         struct vm_area_struct *vma;
 527         unsigned long ret = -EINVAL;
 528         unsigned long charged = 0;
 529         unsigned long map_flags = 0;
 530
 531         if (offset_in_page(new_addr))
 532                 goto out;
 533
 534         if (new_len > TASK_SIZE || new_addr > TASK_SIZE - new_len)
 535                 goto out;
 536
 537         /* Ensure the old/new locations do not overlap */
 538         if (addr + old_len > new_addr && new_addr + new_len > addr)
 539                 goto out;
 540
 541         /*
 542          * move_vma() need us to stay 4 maps below the threshold, otherwise
 543          * it will bail out at the very beginning.
 544          * That is a problem if we have already unmaped the regions here
 545          * (new_addr, and old_addr), because userspace will not know the
 546          * state of the vma's after it gets -ENOMEM.
 547          * So, to avoid such scenario we can pre-compute if the whole
 548          * operation has high chances to success map-wise.
 549          * Worst-scenario case is when both vma's (new_addr and old_addr) get
 550          * split in 3 before unmaping it.
 551          * That means 2 more maps (1 for each) to the ones we already hold.
 552          * Check whether current map count plus 2 still leads us to 4 maps below
 553          * the threshold, otherwise return -ENOMEM here to be more safe.
 554          */
 555         if ((mm->map_count + 2) >= sysctl_max_map_count - 3)
 556                 return -ENOMEM;
 557
 558         if (flags & MREMAP_FIXED) {
 559                 ret = do_munmap(mm, new_addr, new_len, uf_unmap_early);
 560                 if (ret)
 561                         goto out;
 562         }
 563
 564         if (old_len >= new_len) {
 565                 ret = do_munmap(mm, addr+new_len, old_len - new_len, uf_unmap);
 566                 if (ret && old_len != new_len)
 567                         goto out;
 568                 old_len = new_len;
 569         }
 570
 571         vma = vma_to_resize(addr, old_len, new_len, flags, &charged);
 572         if (IS_ERR(vma)) {
 573                 ret = PTR_ERR(vma);
 574                 goto out;
 575         }
 576
 577         /* MREMAP_DONTUNMAP expands by old_len since old_len == new_len */
 578         if (flags & MREMAP_DONTUNMAP &&
 579                 !may_expand_vm(mm, vma->vm_flags, old_len >> PAGE_SHIFT)) {
 580                 ret = -ENOMEM;
 581                 goto out;
 582         }
 583
 584         if (flags & MREMAP_FIXED)
 585                 map_flags |= MAP_FIXED;
 586
 587         if (vma->vm_flags & VM_MAYSHARE)
 588                 map_flags |= MAP_SHARED;
 589
 590         ret = get_unmapped_area(vma->vm_file, new_addr, new_len, vma->vm_pgoff +
 591                                 ((addr - vma->vm_start) >> PAGE_SHIFT),
 592                                 map_flags);
 593         if (IS_ERR_VALUE(ret))
 594                 goto out1;
 595
 596         /* We got a new mapping */
 597         if (!(flags & MREMAP_FIXED))
 598                 new_addr = ret;
 599
 600         ret = move_vma(vma, addr, old_len, new_len, new_addr, locked, flags, uf,
 601                        uf_unmap);
 602
 603         if (!(offset_in_page(ret)))
 604                 goto out;
 605
 606 out1:
 607         vm_unacct_memory(charged);
 608
 609 out:
 610         return ret;
 611 }
 612
 613 static int vma_expandable(struct vm_area_struct *vma, unsigned long delta)
 614 {
 615         unsigned long end = vma->vm_end + delta;
 616         if (end < vma->vm_end) /* overflow */
 617                 return 0;
 618         if (vma->vm_next && vma->vm_next->vm_start < end) /* intersection */
 619                 return 0;
 620         if (get_unmapped_area(NULL, vma->vm_start, end - vma->vm_start,
 621                               0, MAP_FIXED) & ~PAGE_MASK)
 622                 return 0;
 623         return 1;
 624 }
 625
 626 /*
 627  * Expand (or shrink) an existing mapping, potentially moving it at the
 628  * same time (controlled by the MREMAP_MAYMOVE flag and available VM space)
 629  *
 630  * MREMAP_FIXED option added 5-Dec-1999 by Benjamin LaHaise
 631  * This option implies MREMAP_MAYMOVE.
 632  */
 633 SYSCALL_DEFINE5(mremap, unsigned long, addr, unsigned long, old_len,
 634                 unsigned long, new_len, unsigned long, flags,
 635                 unsigned long, new_addr)
 636 {
 637         struct mm_struct *mm = current->mm;
 638         struct vm_area_struct *vma;
 639         unsigned long ret = -EINVAL;
 640         unsigned long charged = 0;
 641         bool locked = false;
 642         bool downgraded = false;
 643         struct vm_userfaultfd_ctx uf = NULL_VM_UFFD_CTX;
 644         LIST_HEAD(uf_unmap_early);
 645         LIST_HEAD(uf_unmap);
 646
 647         /*
 648          * There is a deliberate asymmetry here: we strip the pointer tag
 649          * from the old address but leave the new address alone. This is
 650          * for consistency with mmap(), where we prevent the creation of
 651          * aliasing mappings in userspace by leaving the tag bits of the
 652          * mapping address intact. A non-zero tag will cause the subsequent
 653          * range checks to reject the address as invalid.
 654          *
 655          * See Documentation/arm64/tagged-address-abi.rst for more information.
 656          */
 657         addr = untagged_addr(addr);
 658
 659         if (flags & ~(MREMAP_FIXED | MREMAP_MAYMOVE | MREMAP_DONTUNMAP))
 660                 return ret;
 661
 662         if (flags & MREMAP_FIXED && !(flags & MREMAP_MAYMOVE))
 663                 return ret;
 664
 665         /*
 666          * MREMAP_DONTUNMAP is always a move and it does not allow resizing
 667          * in the process.
 668          */
 669         if (flags & MREMAP_DONTUNMAP &&
 670                         (!(flags & MREMAP_MAYMOVE) || old_len != new_len))
 671                 return ret;
 672
 673
 674         if (offset_in_page(addr))
 675                 return ret;
 676
 677         old_len = PAGE_ALIGN(old_len);
 678         new_len = PAGE_ALIGN(new_len);
 679
 680         /*
 681          * We allow a zero old-len as a special case
 682          * for DOS-emu "duplicate shm area" thing. But
 683          * a zero new-len is nonsensical.
 684          */
 685         if (!new_len)
 686                 return ret;
 687
 688         if (down_write_killable(&current->mm->mmap_sem))
 689                 return -EINTR;
 690
 691         if (flags & (MREMAP_FIXED | MREMAP_DONTUNMAP)) {
 692                 ret = mremap_to(addr, old_len, new_addr, new_len,
 693                                 &locked, flags, &uf, &uf_unmap_early,
 694                                 &uf_unmap);
 695                 goto out;
 696         }
 697
 698         /*
 699          * Always allow a shrinking remap: that just unmaps
 700          * the unnecessary pages..
 701          * __do_munmap does all the needed commit accounting, and
 702          * downgrades mmap_sem to read if so directed.
 703          */
 704         if (old_len >= new_len) {
 705                 int retval;
 706
 707                 retval = __do_munmap(mm, addr+new_len, old_len - new_len,
 708                                   &uf_unmap, true);
 709                 if (retval < 0 && old_len != new_len) {
 710                         ret = retval;
 711                         goto out;
 712                 /* Returning 1 indicates mmap_sem is downgraded to read. */
 713                 } else if (retval == 1)
 714                         downgraded = true;
 715                 ret = addr;
 716                 goto out;
 717         }
 718
 719         /*
 720          * Ok, we need to grow..
 721          */
 722         vma = vma_to_resize(addr, old_len, new_len, flags, &charged);
 723         if (IS_ERR(vma)) {
 724                 ret = PTR_ERR(vma);
 725                 goto out;
 726         }
 727
 728         /* old_len exactly to the end of the area..
 729          */
 730         if (old_len == vma->vm_end - addr) {
 731                 /* can we just expand the current mapping? */
 732                 if (vma_expandable(vma, new_len - old_len)) {
 733                         int pages = (new_len - old_len) >> PAGE_SHIFT;
 734
 735                         if (vma_adjust(vma, vma->vm_start, addr + new_len,
 736                                        vma->vm_pgoff, NULL)) {
 737                                 ret = -ENOMEM;
 738                                 goto out;
 739                         }
 740
 741                         vm_stat_account(mm, vma->vm_flags, pages);
 742                         if (vma->vm_flags & VM_LOCKED) {
 743                                 mm->locked_vm += pages;
 744                                 locked = true;
 745                                 new_addr = addr;
 746                         }
 747                         ret = addr;
 748                         goto out;
 749                 }
 750         }
 751
 752         /*
 753          * We weren't able to just expand or shrink the area,
 754          * we need to create a new one and move it..
 755          */
 756         ret = -ENOMEM;
 757         if (flags & MREMAP_MAYMOVE) {
 758                 unsigned long map_flags = 0;
 759                 if (vma->vm_flags & VM_MAYSHARE)
 760                         map_flags |= MAP_SHARED;
 761
 762                 new_addr = get_unmapped_area(vma->vm_file, 0, new_len,
 763                                         vma->vm_pgoff +
 764                                         ((addr - vma->vm_start) >> PAGE_SHIFT),
 765                                         map_flags);
 766                 if (IS_ERR_VALUE(new_addr)) {
 767                         ret = new_addr;
 768                         goto out;
 769                 }
 770
 771                 ret = move_vma(vma, addr, old_len, new_len, new_addr,
 772                                &locked, flags, &uf, &uf_unmap);
 773         }
 774 out:
 775         if (offset_in_page(ret)) {
 776                 vm_unacct_memory(charged);
 777                 locked = 0;
 778         }
 779         if (downgraded)
 780                 up_read(&current->mm->mmap_sem);
 781         else
 782                 up_write(&current->mm->mmap_sem);
 783         if (locked && new_len > old_len)
 784                 mm_populate(new_addr + old_len, new_len - old_len);
 785         userfaultfd_unmap_complete(mm, &uf_unmap_early);
 786         mremap_userfaultfd_complete(&uf, addr, new_addr, old_len);
 787         userfaultfd_unmap_complete(mm, &uf_unmap);
 788         return ret;
 789 }