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(new_len >> PAGE_SHIFT);
 417                 }
 418
 419                 /*
 420                  * VMAs can actually be merged back together in copy_vma
 421                  * calling merge_vma. This can happen with anonymous vmas
 422                  * which have not yet been faulted, so if we were to consider
 423                  * this VMA split we'll end up adding VM_ACCOUNT on the
 424                  * next VMA, which is completely unrelated if this VMA
 425                  * was re-merged.
 426                  */
 427                 if (split && new_vma == vma)
 428                         split = 0;
 429
 430                 /* We always clear VM_LOCKED[ONFAULT] on the old vma */
 431                 vma->vm_flags &= VM_LOCKED_CLEAR_MASK;
 432
 433                 /* Because we won't unmap we don't need to touch locked_vm */
 434                 goto out;
 435         }
 436
 437         if (do_munmap(mm, old_addr, old_len, uf_unmap) < 0) {
 438                 /* OOM: unable to split vma, just get accounts right */
 439                 vm_unacct_memory(excess >> PAGE_SHIFT);
 440                 excess = 0;
 441         }
 442
 443         if (vm_flags & VM_LOCKED) {
 444                 mm->locked_vm += new_len >> PAGE_SHIFT;
 445                 *locked = true;
 446         }
 447 out:
 448         mm->hiwater_vm = hiwater_vm;
 449
 450         /* Restore VM_ACCOUNT if one or two pieces of vma left */
 451         if (excess) {
 452                 vma->vm_flags |= VM_ACCOUNT;
 453                 if (split)
 454                         vma->vm_next->vm_flags |= VM_ACCOUNT;
 455         }
 456
 457         return new_addr;
 458 }
 459
 460 static struct vm_area_struct *vma_to_resize(unsigned long addr,
 461         unsigned long old_len, unsigned long new_len, unsigned long flags,
 462         unsigned long *p)
 463 {
 464         struct mm_struct *mm = current->mm;
 465         struct vm_area_struct *vma = find_vma(mm, addr);
 466         unsigned long pgoff;
 467
 468         if (!vma || vma->vm_start > addr)
 469                 return ERR_PTR(-EFAULT);
 470
 471         /*
 472          * !old_len is a special case where an attempt is made to 'duplicate'
 473          * a mapping.  This makes no sense for private mappings as it will
 474          * instead create a fresh/new mapping unrelated to the original.  This
 475          * is contrary to the basic idea of mremap which creates new mappings
 476          * based on the original.  There are no known use cases for this
 477          * behavior.  As a result, fail such attempts.
 478          */
 479         if (!old_len && !(vma->vm_flags & (VM_SHARED | VM_MAYSHARE))) {
 480                 pr_warn_once("%s (%d): attempted to duplicate a private mapping with mremap.  This is not supported.\n", current->comm, current->pid);
 481                 return ERR_PTR(-EINVAL);
 482         }
 483
 484         if (flags & MREMAP_DONTUNMAP && (!vma_is_anonymous(vma) ||
 485                         vma->vm_flags & VM_SHARED))
 486                 return ERR_PTR(-EINVAL);
 487
 488         if (is_vm_hugetlb_page(vma))
 489                 return ERR_PTR(-EINVAL);
 490
 491         /* We can't remap across vm area boundaries */
 492         if (old_len > vma->vm_end - addr)
 493                 return ERR_PTR(-EFAULT);
 494
 495         if (new_len == old_len)
 496                 return vma;
 497
 498         /* Need to be careful about a growing mapping */
 499         pgoff = (addr - vma->vm_start) >> PAGE_SHIFT;
 500         pgoff += vma->vm_pgoff;
 501         if (pgoff + (new_len >> PAGE_SHIFT) < pgoff)
 502                 return ERR_PTR(-EINVAL);
 503
 504         if (vma->vm_flags & (VM_DONTEXPAND | VM_PFNMAP))
 505                 return ERR_PTR(-EFAULT);
 506
 507         if (vma->vm_flags & VM_LOCKED) {
 508                 unsigned long locked, lock_limit;
 509                 locked = mm->locked_vm << PAGE_SHIFT;
 510                 lock_limit = rlimit(RLIMIT_MEMLOCK);
 511                 locked += new_len - old_len;
 512                 if (locked > lock_limit && !capable(CAP_IPC_LOCK))
 513                         return ERR_PTR(-EAGAIN);
 514         }
 515
 516         if (!may_expand_vm(mm, vma->vm_flags,
 517                                 (new_len - old_len) >> PAGE_SHIFT))
 518                 return ERR_PTR(-ENOMEM);
 519
 520         if (vma->vm_flags & VM_ACCOUNT) {
 521                 unsigned long charged = (new_len - old_len) >> PAGE_SHIFT;
 522                 if (security_vm_enough_memory_mm(mm, charged))
 523                         return ERR_PTR(-ENOMEM);
 524                 *p = charged;
 525         }
 526
 527         return vma;
 528 }
 529
 530 static unsigned long mremap_to(unsigned long addr, unsigned long old_len,
 531                 unsigned long new_addr, unsigned long new_len, bool *locked,
 532                 unsigned long flags, struct vm_userfaultfd_ctx *uf,
 533                 struct list_head *uf_unmap_early,
 534                 struct list_head *uf_unmap)
 535 {
 536         struct mm_struct *mm = current->mm;
 537         struct vm_area_struct *vma;
 538         unsigned long ret = -EINVAL;
 539         unsigned long charged = 0;
 540         unsigned long map_flags = 0;
 541
 542         if (offset_in_page(new_addr))
 543                 goto out;
 544
 545         if (new_len > TASK_SIZE || new_addr > TASK_SIZE - new_len)
 546                 goto out;
 547
 548         /* Ensure the old/new locations do not overlap */
 549         if (addr + old_len > new_addr && new_addr + new_len > addr)
 550                 goto out;
 551
 552         /*
 553          * move_vma() need us to stay 4 maps below the threshold, otherwise
 554          * it will bail out at the very beginning.
 555          * That is a problem if we have already unmaped the regions here
 556          * (new_addr, and old_addr), because userspace will not know the
 557          * state of the vma's after it gets -ENOMEM.
 558          * So, to avoid such scenario we can pre-compute if the whole
 559          * operation has high chances to success map-wise.
 560          * Worst-scenario case is when both vma's (new_addr and old_addr) get
 561          * split in 3 before unmaping it.
 562          * That means 2 more maps (1 for each) to the ones we already hold.
 563          * Check whether current map count plus 2 still leads us to 4 maps below
 564          * the threshold, otherwise return -ENOMEM here to be more safe.
 565          */
 566         if ((mm->map_count + 2) >= sysctl_max_map_count - 3)
 567                 return -ENOMEM;
 568
 569         if (flags & MREMAP_FIXED) {
 570                 ret = do_munmap(mm, new_addr, new_len, uf_unmap_early);
 571                 if (ret)
 572                         goto out;
 573         }
 574
 575         if (old_len >= new_len) {
 576                 ret = do_munmap(mm, addr+new_len, old_len - new_len, uf_unmap);
 577                 if (ret && old_len != new_len)
 578                         goto out;
 579                 old_len = new_len;
 580         }
 581
 582         vma = vma_to_resize(addr, old_len, new_len, flags, &charged);
 583         if (IS_ERR(vma)) {
 584                 ret = PTR_ERR(vma);
 585                 goto out;
 586         }
 587
 588         /* MREMAP_DONTUNMAP expands by old_len since old_len == new_len */
 589         if (flags & MREMAP_DONTUNMAP &&
 590                 !may_expand_vm(mm, vma->vm_flags, old_len >> PAGE_SHIFT)) {
 591                 ret = -ENOMEM;
 592                 goto out;
 593         }
 594
 595         if (flags & MREMAP_FIXED)
 596                 map_flags |= MAP_FIXED;
 597
 598         if (vma->vm_flags & VM_MAYSHARE)
 599                 map_flags |= MAP_SHARED;
 600
 601         ret = get_unmapped_area(vma->vm_file, new_addr, new_len, vma->vm_pgoff +
 602                                 ((addr - vma->vm_start) >> PAGE_SHIFT),
 603                                 map_flags);
 604         if (IS_ERR_VALUE(ret))
 605                 goto out1;
 606
 607         /* We got a new mapping */
 608         if (!(flags & MREMAP_FIXED))
 609                 new_addr = ret;
 610
 611         ret = move_vma(vma, addr, old_len, new_len, new_addr, locked, flags, uf,
 612                        uf_unmap);
 613
 614         if (!(offset_in_page(ret)))
 615                 goto out;
 616
 617 out1:
 618         vm_unacct_memory(charged);
 619
 620 out:
 621         return ret;
 622 }
 623
 624 static int vma_expandable(struct vm_area_struct *vma, unsigned long delta)
 625 {
 626         unsigned long end = vma->vm_end + delta;
 627         if (end < vma->vm_end) /* overflow */
 628                 return 0;
 629         if (vma->vm_next && vma->vm_next->vm_start < end) /* intersection */
 630                 return 0;
 631         if (get_unmapped_area(NULL, vma->vm_start, end - vma->vm_start,
 632                               0, MAP_FIXED) & ~PAGE_MASK)
 633                 return 0;
 634         return 1;
 635 }
 636
 637 /*
 638  * Expand (or shrink) an existing mapping, potentially moving it at the
 639  * same time (controlled by the MREMAP_MAYMOVE flag and available VM space)
 640  *
 641  * MREMAP_FIXED option added 5-Dec-1999 by Benjamin LaHaise
 642  * This option implies MREMAP_MAYMOVE.
 643  */
 644 SYSCALL_DEFINE5(mremap, unsigned long, addr, unsigned long, old_len,
 645                 unsigned long, new_len, unsigned long, flags,
 646                 unsigned long, new_addr)
 647 {
 648         struct mm_struct *mm = current->mm;
 649         struct vm_area_struct *vma;
 650         unsigned long ret = -EINVAL;
 651         unsigned long charged = 0;
 652         bool locked = false;
 653         bool downgraded = false;
 654         struct vm_userfaultfd_ctx uf = NULL_VM_UFFD_CTX;
 655         LIST_HEAD(uf_unmap_early);
 656         LIST_HEAD(uf_unmap);
 657
 658         /*
 659          * There is a deliberate asymmetry here: we strip the pointer tag
 660          * from the old address but leave the new address alone. This is
 661          * for consistency with mmap(), where we prevent the creation of
 662          * aliasing mappings in userspace by leaving the tag bits of the
 663          * mapping address intact. A non-zero tag will cause the subsequent
 664          * range checks to reject the address as invalid.
 665          *
 666          * See Documentation/arm64/tagged-address-abi.rst for more information.
 667          */
 668         addr = untagged_addr(addr);
 669
 670         if (flags & ~(MREMAP_FIXED | MREMAP_MAYMOVE | MREMAP_DONTUNMAP))
 671                 return ret;
 672
 673         if (flags & MREMAP_FIXED && !(flags & MREMAP_MAYMOVE))
 674                 return ret;
 675
 676         /*
 677          * MREMAP_DONTUNMAP is always a move and it does not allow resizing
 678          * in the process.
 679          */
 680         if (flags & MREMAP_DONTUNMAP &&
 681                         (!(flags & MREMAP_MAYMOVE) || old_len != new_len))
 682                 return ret;
 683
 684
 685         if (offset_in_page(addr))
 686                 return ret;
 687
 688         old_len = PAGE_ALIGN(old_len);
 689         new_len = PAGE_ALIGN(new_len);
 690
 691         /*
 692          * We allow a zero old-len as a special case
 693          * for DOS-emu "duplicate shm area" thing. But
 694          * a zero new-len is nonsensical.
 695          */
 696         if (!new_len)
 697                 return ret;
 698
 699         if (down_write_killable(&current->mm->mmap_sem))
 700                 return -EINTR;
 701
 702         if (flags & (MREMAP_FIXED | MREMAP_DONTUNMAP)) {
 703                 ret = mremap_to(addr, old_len, new_addr, new_len,
 704                                 &locked, flags, &uf, &uf_unmap_early,
 705                                 &uf_unmap);
 706                 goto out;
 707         }
 708
 709         /*
 710          * Always allow a shrinking remap: that just unmaps
 711          * the unnecessary pages..
 712          * __do_munmap does all the needed commit accounting, and
 713          * downgrades mmap_sem to read if so directed.
 714          */
 715         if (old_len >= new_len) {
 716                 int retval;
 717
 718                 retval = __do_munmap(mm, addr+new_len, old_len - new_len,
 719                                   &uf_unmap, true);
 720                 if (retval < 0 && old_len != new_len) {
 721                         ret = retval;
 722                         goto out;
 723                 /* Returning 1 indicates mmap_sem is downgraded to read. */
 724                 } else if (retval == 1)
 725                         downgraded = true;
 726                 ret = addr;
 727                 goto out;
 728         }
 729
 730         /*
 731          * Ok, we need to grow..
 732          */
 733         vma = vma_to_resize(addr, old_len, new_len, flags, &charged);
 734         if (IS_ERR(vma)) {
 735                 ret = PTR_ERR(vma);
 736                 goto out;
 737         }
 738
 739         /* old_len exactly to the end of the area..
 740          */
 741         if (old_len == vma->vm_end - addr) {
 742                 /* can we just expand the current mapping? */
 743                 if (vma_expandable(vma, new_len - old_len)) {
 744                         int pages = (new_len - old_len) >> PAGE_SHIFT;
 745
 746                         if (vma_adjust(vma, vma->vm_start, addr + new_len,
 747                                        vma->vm_pgoff, NULL)) {
 748                                 ret = -ENOMEM;
 749                                 goto out;
 750                         }
 751
 752                         vm_stat_account(mm, vma->vm_flags, pages);
 753                         if (vma->vm_flags & VM_LOCKED) {
 754                                 mm->locked_vm += pages;
 755                                 locked = true;
 756                                 new_addr = addr;
 757                         }
 758                         ret = addr;
 759                         goto out;
 760                 }
 761         }
 762
 763         /*
 764          * We weren't able to just expand or shrink the area,
 765          * we need to create a new one and move it..
 766          */
 767         ret = -ENOMEM;
 768         if (flags & MREMAP_MAYMOVE) {
 769                 unsigned long map_flags = 0;
 770                 if (vma->vm_flags & VM_MAYSHARE)
 771                         map_flags |= MAP_SHARED;
 772
 773                 new_addr = get_unmapped_area(vma->vm_file, 0, new_len,
 774                                         vma->vm_pgoff +
 775                                         ((addr - vma->vm_start) >> PAGE_SHIFT),
 776                                         map_flags);
 777                 if (IS_ERR_VALUE(new_addr)) {
 778                         ret = new_addr;
 779                         goto out;
 780                 }
 781
 782                 ret = move_vma(vma, addr, old_len, new_len, new_addr,
 783                                &locked, flags, &uf, &uf_unmap);
 784         }
 785 out:
 786         if (offset_in_page(ret)) {
 787                 vm_unacct_memory(charged);
 788                 locked = 0;
 789         }
 790         if (downgraded)
 791                 up_read(&current->mm->mmap_sem);
 792         else
 793                 up_write(&current->mm->mmap_sem);
 794         if (locked && new_len > old_len)
 795                 mm_populate(new_addr + old_len, new_len - old_len);
 796         userfaultfd_unmap_complete(mm, &uf_unmap_early);
 797         mremap_userfaultfd_complete(&uf, addr, ret, old_len);
 798         userfaultfd_unmap_complete(mm, &uf_unmap);
 799         return ret;
 800 }