mm/userfaultfd.c

   1 // SPDX-License-Identifier: GPL-2.0-only
   2 /*
   3  *  mm/userfaultfd.c
   4  *
   5  *  Copyright (C) 2015  Red Hat, Inc.
   6  */
   7
   8 #include <linux/mm.h>
   9 #include <linux/sched/signal.h>
  10 #include <linux/pagemap.h>
  11 #include <linux/rmap.h>
  12 #include <linux/swap.h>
  13 #include <linux/swapops.h>
  14 #include <linux/userfaultfd_k.h>
  15 #include <linux/mmu_notifier.h>
  16 #include <linux/hugetlb.h>
  17 #include <linux/shmem_fs.h>
  18 #include <asm/tlbflush.h>
  19 #include "internal.h"
  20
  21 static __always_inline
  22 struct vm_area_struct *find_dst_vma(struct mm_struct *dst_mm,
  23                                     unsigned long dst_start,
  24                                     unsigned long len)
  25 {
  26         /*
  27          * Make sure that the dst range is both valid and fully within a
  28          * single existing vma.
  29          */
  30         struct vm_area_struct *dst_vma;
  31
  32         dst_vma = find_vma(dst_mm, dst_start);
  33         if (!dst_vma)
  34                 return NULL;
  35
  36         if (dst_start < dst_vma->vm_start ||
  37             dst_start + len > dst_vma->vm_end)
  38                 return NULL;
  39
  40         /*
  41          * Check the vma is registered in uffd, this is required to
  42          * enforce the VM_MAYWRITE check done at uffd registration
  43          * time.
  44          */
  45         if (!dst_vma->vm_userfaultfd_ctx.ctx)
  46                 return NULL;
  47
  48         return dst_vma;
  49 }
  50
  51 static int mcopy_atomic_pte(struct mm_struct *dst_mm,
  52                             pmd_t *dst_pmd,
  53                             struct vm_area_struct *dst_vma,
  54                             unsigned long dst_addr,
  55                             unsigned long src_addr,
  56                             struct page **pagep,
  57                             bool wp_copy)
  58 {
  59         struct mem_cgroup *memcg;
  60         pte_t _dst_pte, *dst_pte;
  61         spinlock_t *ptl;
  62         void *page_kaddr;
  63         int ret;
  64         struct page *page;
  65         pgoff_t offset, max_off;
  66         struct inode *inode;
  67
  68         if (!*pagep) {
  69                 ret = -ENOMEM;
  70                 page = alloc_page_vma(GFP_HIGHUSER_MOVABLE, dst_vma, dst_addr);
  71                 if (!page)
  72                         goto out;
  73
  74                 page_kaddr = kmap_atomic(page);
  75                 ret = copy_from_user(page_kaddr,
  76                                      (const void __user *) src_addr,
  77                                      PAGE_SIZE);
  78                 kunmap_atomic(page_kaddr);
  79
  80                 /* fallback to copy_from_user outside mmap_sem */
  81                 if (unlikely(ret)) {
  82                         ret = -ENOENT;
  83                         *pagep = page;
  84                         /* don't free the page */
  85                         goto out;
  86                 }
  87         } else {
  88                 page = *pagep;
  89                 *pagep = NULL;
  90         }
  91
  92         /*
  93          * The memory barrier inside __SetPageUptodate makes sure that
  94          * preceding stores to the page contents become visible before
  95          * the set_pte_at() write.
  96          */
  97         __SetPageUptodate(page);
  98
  99         ret = -ENOMEM;
 100         if (mem_cgroup_try_charge(page, dst_mm, GFP_KERNEL, &memcg, false))
 101                 goto out_release;
 102
 103         _dst_pte = pte_mkdirty(mk_pte(page, dst_vma->vm_page_prot));
 104         if (dst_vma->vm_flags & VM_WRITE) {
 105                 if (wp_copy)
 106                         _dst_pte = pte_mkuffd_wp(_dst_pte);
 107                 else
 108                         _dst_pte = pte_mkwrite(_dst_pte);
 109         }
 110
 111         dst_pte = pte_offset_map_lock(dst_mm, dst_pmd, dst_addr, &ptl);
 112         if (dst_vma->vm_file) {
 113                 /* the shmem MAP_PRIVATE case requires checking the i_size */
 114                 inode = dst_vma->vm_file->f_inode;
 115                 offset = linear_page_index(dst_vma, dst_addr);
 116                 max_off = DIV_ROUND_UP(i_size_read(inode), PAGE_SIZE);
 117                 ret = -EFAULT;
 118                 if (unlikely(offset >= max_off))
 119                         goto out_release_uncharge_unlock;
 120         }
 121         ret = -EEXIST;
 122         if (!pte_none(*dst_pte))
 123                 goto out_release_uncharge_unlock;
 124
 125         inc_mm_counter(dst_mm, MM_ANONPAGES);
 126         page_add_new_anon_rmap(page, dst_vma, dst_addr, false);
 127         mem_cgroup_commit_charge(page, memcg, false, false);
 128         lru_cache_add_active_or_unevictable(page, dst_vma);
 129
 130         set_pte_at(dst_mm, dst_addr, dst_pte, _dst_pte);
 131
 132         /* No need to invalidate - it was non-present before */
 133         update_mmu_cache(dst_vma, dst_addr, dst_pte);
 134
 135         pte_unmap_unlock(dst_pte, ptl);
 136         ret = 0;
 137 out:
 138         return ret;
 139 out_release_uncharge_unlock:
 140         pte_unmap_unlock(dst_pte, ptl);
 141         mem_cgroup_cancel_charge(page, memcg, false);
 142 out_release:
 143         put_page(page);
 144         goto out;
 145 }
 146
 147 static int mfill_zeropage_pte(struct mm_struct *dst_mm,
 148                               pmd_t *dst_pmd,
 149                               struct vm_area_struct *dst_vma,
 150                               unsigned long dst_addr)
 151 {
 152         pte_t _dst_pte, *dst_pte;
 153         spinlock_t *ptl;
 154         int ret;
 155         pgoff_t offset, max_off;
 156         struct inode *inode;
 157
 158         _dst_pte = pte_mkspecial(pfn_pte(my_zero_pfn(dst_addr),
 159                                          dst_vma->vm_page_prot));
 160         dst_pte = pte_offset_map_lock(dst_mm, dst_pmd, dst_addr, &ptl);
 161         if (dst_vma->vm_file) {
 162                 /* the shmem MAP_PRIVATE case requires checking the i_size */
 163                 inode = dst_vma->vm_file->f_inode;
 164                 offset = linear_page_index(dst_vma, dst_addr);
 165                 max_off = DIV_ROUND_UP(i_size_read(inode), PAGE_SIZE);
 166                 ret = -EFAULT;
 167                 if (unlikely(offset >= max_off))
 168                         goto out_unlock;
 169         }
 170         ret = -EEXIST;
 171         if (!pte_none(*dst_pte))
 172                 goto out_unlock;
 173         set_pte_at(dst_mm, dst_addr, dst_pte, _dst_pte);
 174         /* No need to invalidate - it was non-present before */
 175         update_mmu_cache(dst_vma, dst_addr, dst_pte);
 176         ret = 0;
 177 out_unlock:
 178         pte_unmap_unlock(dst_pte, ptl);
 179         return ret;
 180 }
 181
 182 static pmd_t *mm_alloc_pmd(struct mm_struct *mm, unsigned long address)
 183 {
 184         pgd_t *pgd;
 185         p4d_t *p4d;
 186         pud_t *pud;
 187
 188         pgd = pgd_offset(mm, address);
 189         p4d = p4d_alloc(mm, pgd, address);
 190         if (!p4d)
 191                 return NULL;
 192         pud = pud_alloc(mm, p4d, address);
 193         if (!pud)
 194                 return NULL;
 195         /*
 196          * Note that we didn't run this because the pmd was
 197          * missing, the *pmd may be already established and in
 198          * turn it may also be a trans_huge_pmd.
 199          */
 200         return pmd_alloc(mm, pud, address);
 201 }
 202
 203 #ifdef CONFIG_HUGETLB_PAGE
 204 /*
 205  * __mcopy_atomic processing for HUGETLB vmas.  Note that this routine is
 206  * called with mmap_sem held, it will release mmap_sem before returning.
 207  */
 208 static __always_inline ssize_t __mcopy_atomic_hugetlb(struct mm_struct *dst_mm,
 209                                               struct vm_area_struct *dst_vma,
 210                                               unsigned long dst_start,
 211                                               unsigned long src_start,
 212                                               unsigned long len,
 213                                               bool zeropage)
 214 {
 215         int vm_alloc_shared = dst_vma->vm_flags & VM_SHARED;
 216         int vm_shared = dst_vma->vm_flags & VM_SHARED;
 217         ssize_t err;
 218         pte_t *dst_pte;
 219         unsigned long src_addr, dst_addr;
 220         long copied;
 221         struct page *page;
 222         unsigned long vma_hpagesize;
 223         pgoff_t idx;
 224         u32 hash;
 225         struct address_space *mapping;
 226
 227         /*
 228          * There is no default zero huge page for all huge page sizes as
 229          * supported by hugetlb.  A PMD_SIZE huge pages may exist as used
 230          * by THP.  Since we can not reliably insert a zero page, this
 231          * feature is not supported.
 232          */
 233         if (zeropage) {
 234                 up_read(&dst_mm->mmap_sem);
 235                 return -EINVAL;
 236         }
 237
 238         src_addr = src_start;
 239         dst_addr = dst_start;
 240         copied = 0;
 241         page = NULL;
 242         vma_hpagesize = vma_kernel_pagesize(dst_vma);
 243
 244         /*
 245          * Validate alignment based on huge page size
 246          */
 247         err = -EINVAL;
 248         if (dst_start & (vma_hpagesize - 1) || len & (vma_hpagesize - 1))
 249                 goto out_unlock;
 250
 251 retry:
 252         /*
 253          * On routine entry dst_vma is set.  If we had to drop mmap_sem and
 254          * retry, dst_vma will be set to NULL and we must lookup again.
 255          */
 256         if (!dst_vma) {
 257                 err = -ENOENT;
 258                 dst_vma = find_dst_vma(dst_mm, dst_start, len);
 259                 if (!dst_vma || !is_vm_hugetlb_page(dst_vma))
 260                         goto out_unlock;
 261
 262                 err = -EINVAL;
 263                 if (vma_hpagesize != vma_kernel_pagesize(dst_vma))
 264                         goto out_unlock;
 265
 266                 vm_shared = dst_vma->vm_flags & VM_SHARED;
 267         }
 268
 269         /*
 270          * If not shared, ensure the dst_vma has a anon_vma.
 271          */
 272         err = -ENOMEM;
 273         if (!vm_shared) {
 274                 if (unlikely(anon_vma_prepare(dst_vma)))
 275                         goto out_unlock;
 276         }
 277
 278         while (src_addr < src_start + len) {
 279                 pte_t dst_pteval;
 280
 281                 BUG_ON(dst_addr >= dst_start + len);
 282
 283                 /*
 284                  * Serialize via i_mmap_rwsem and hugetlb_fault_mutex.
 285                  * i_mmap_rwsem ensures the dst_pte remains valid even
 286                  * in the case of shared pmds.  fault mutex prevents
 287                  * races with other faulting threads.
 288                  */
 289                 mapping = dst_vma->vm_file->f_mapping;
 290                 i_mmap_lock_read(mapping);
 291                 idx = linear_page_index(dst_vma, dst_addr);
 292                 hash = hugetlb_fault_mutex_hash(mapping, idx);
 293                 mutex_lock(&hugetlb_fault_mutex_table[hash]);
 294
 295                 err = -ENOMEM;
 296                 dst_pte = huge_pte_alloc(dst_mm, dst_addr, vma_hpagesize);
 297                 if (!dst_pte) {
 298                         mutex_unlock(&hugetlb_fault_mutex_table[hash]);
 299                         i_mmap_unlock_read(mapping);
 300                         goto out_unlock;
 301                 }
 302
 303                 err = -EEXIST;
 304                 dst_pteval = huge_ptep_get(dst_pte);
 305                 if (!huge_pte_none(dst_pteval)) {
 306                         mutex_unlock(&hugetlb_fault_mutex_table[hash]);
 307                         i_mmap_unlock_read(mapping);
 308                         goto out_unlock;
 309                 }
 310
 311                 err = hugetlb_mcopy_atomic_pte(dst_mm, dst_pte, dst_vma,
 312                                                 dst_addr, src_addr, &page);
 313
 314                 mutex_unlock(&hugetlb_fault_mutex_table[hash]);
 315                 i_mmap_unlock_read(mapping);
 316                 vm_alloc_shared = vm_shared;
 317
 318                 cond_resched();
 319
 320                 if (unlikely(err == -ENOENT)) {
 321                         up_read(&dst_mm->mmap_sem);
 322                         BUG_ON(!page);
 323
 324                         err = copy_huge_page_from_user(page,
 325                                                 (const void __user *)src_addr,
 326                                                 vma_hpagesize / PAGE_SIZE,
 327                                                 true);
 328                         if (unlikely(err)) {
 329                                 err = -EFAULT;
 330                                 goto out;
 331                         }
 332                         down_read(&dst_mm->mmap_sem);
 333
 334                         dst_vma = NULL;
 335                         goto retry;
 336                 } else
 337                         BUG_ON(page);
 338
 339                 if (!err) {
 340                         dst_addr += vma_hpagesize;
 341                         src_addr += vma_hpagesize;
 342                         copied += vma_hpagesize;
 343
 344                         if (fatal_signal_pending(current))
 345                                 err = -EINTR;
 346                 }
 347                 if (err)
 348                         break;
 349         }
 350
 351 out_unlock:
 352         up_read(&dst_mm->mmap_sem);
 353 out:
 354         if (page) {
 355                 /*
 356                  * We encountered an error and are about to free a newly
 357                  * allocated huge page.
 358                  *
 359                  * Reservation handling is very subtle, and is different for
 360                  * private and shared mappings.  See the routine
 361                  * restore_reserve_on_error for details.  Unfortunately, we
 362                  * can not call restore_reserve_on_error now as it would
 363                  * require holding mmap_sem.
 364                  *
 365                  * If a reservation for the page existed in the reservation
 366                  * map of a private mapping, the map was modified to indicate
 367                  * the reservation was consumed when the page was allocated.
 368                  * We clear the PagePrivate flag now so that the global
 369                  * reserve count will not be incremented in free_huge_page.
 370                  * The reservation map will still indicate the reservation
 371                  * was consumed and possibly prevent later page allocation.
 372                  * This is better than leaking a global reservation.  If no
 373                  * reservation existed, it is still safe to clear PagePrivate
 374                  * as no adjustments to reservation counts were made during
 375                  * allocation.
 376                  *
 377                  * The reservation map for shared mappings indicates which
 378                  * pages have reservations.  When a huge page is allocated
 379                  * for an address with a reservation, no change is made to
 380                  * the reserve map.  In this case PagePrivate will be set
 381                  * to indicate that the global reservation count should be
 382                  * incremented when the page is freed.  This is the desired
 383                  * behavior.  However, when a huge page is allocated for an
 384                  * address without a reservation a reservation entry is added
 385                  * to the reservation map, and PagePrivate will not be set.
 386                  * When the page is freed, the global reserve count will NOT
 387                  * be incremented and it will appear as though we have leaked
 388                  * reserved page.  In this case, set PagePrivate so that the
 389                  * global reserve count will be incremented to match the
 390                  * reservation map entry which was created.
 391                  *
 392                  * Note that vm_alloc_shared is based on the flags of the vma
 393                  * for which the page was originally allocated.  dst_vma could
 394                  * be different or NULL on error.
 395                  */
 396                 if (vm_alloc_shared)
 397                         SetPagePrivate(page);
 398                 else
 399                         ClearPagePrivate(page);
 400                 put_page(page);
 401         }
 402         BUG_ON(copied < 0);
 403         BUG_ON(err > 0);
 404         BUG_ON(!copied && !err);
 405         return copied ? copied : err;
 406 }
 407 #else /* !CONFIG_HUGETLB_PAGE */
 408 /* fail at build time if gcc attempts to use this */
 409 extern ssize_t __mcopy_atomic_hugetlb(struct mm_struct *dst_mm,
 410                                       struct vm_area_struct *dst_vma,
 411                                       unsigned long dst_start,
 412                                       unsigned long src_start,
 413                                       unsigned long len,
 414                                       bool zeropage);
 415 #endif /* CONFIG_HUGETLB_PAGE */
 416
 417 static __always_inline ssize_t mfill_atomic_pte(struct mm_struct *dst_mm,
 418                                                 pmd_t *dst_pmd,
 419                                                 struct vm_area_struct *dst_vma,
 420                                                 unsigned long dst_addr,
 421                                                 unsigned long src_addr,
 422                                                 struct page **page,
 423                                                 bool zeropage,
 424                                                 bool wp_copy)
 425 {
 426         ssize_t err;
 427
 428         /*
 429          * The normal page fault path for a shmem will invoke the
 430          * fault, fill the hole in the file and COW it right away. The
 431          * result generates plain anonymous memory. So when we are
 432          * asked to fill an hole in a MAP_PRIVATE shmem mapping, we'll
 433          * generate anonymous memory directly without actually filling
 434          * the hole. For the MAP_PRIVATE case the robustness check
 435          * only happens in the pagetable (to verify it's still none)
 436          * and not in the radix tree.
 437          */
 438         if (!(dst_vma->vm_flags & VM_SHARED)) {
 439                 if (!zeropage)
 440                         err = mcopy_atomic_pte(dst_mm, dst_pmd, dst_vma,
 441                                                dst_addr, src_addr, page,
 442                                                wp_copy);
 443                 else
 444                         err = mfill_zeropage_pte(dst_mm, dst_pmd,
 445                                                  dst_vma, dst_addr);
 446         } else {
 447                 VM_WARN_ON_ONCE(wp_copy);
 448                 if (!zeropage)
 449                         err = shmem_mcopy_atomic_pte(dst_mm, dst_pmd,
 450                                                      dst_vma, dst_addr,
 451                                                      src_addr, page);
 452                 else
 453                         err = shmem_mfill_zeropage_pte(dst_mm, dst_pmd,
 454                                                        dst_vma, dst_addr);
 455         }
 456
 457         return err;
 458 }
 459
 460 static __always_inline ssize_t __mcopy_atomic(struct mm_struct *dst_mm,
 461                                               unsigned long dst_start,
 462                                               unsigned long src_start,
 463                                               unsigned long len,
 464                                               bool zeropage,
 465                                               bool *mmap_changing,
 466                                               __u64 mode)
 467 {
 468         struct vm_area_struct *dst_vma;
 469         ssize_t err;
 470         pmd_t *dst_pmd;
 471         unsigned long src_addr, dst_addr;
 472         long copied;
 473         struct page *page;
 474         bool wp_copy;
 475
 476         /*
 477          * Sanitize the command parameters:
 478          */
 479         BUG_ON(dst_start & ~PAGE_MASK);
 480         BUG_ON(len & ~PAGE_MASK);
 481
 482         /* Does the address range wrap, or is the span zero-sized? */
 483         BUG_ON(src_start + len <= src_start);
 484         BUG_ON(dst_start + len <= dst_start);
 485
 486         src_addr = src_start;
 487         dst_addr = dst_start;
 488         copied = 0;
 489         page = NULL;
 490 retry:
 491         down_read(&dst_mm->mmap_sem);
 492
 493         /*
 494          * If memory mappings are changing because of non-cooperative
 495          * operation (e.g. mremap) running in parallel, bail out and
 496          * request the user to retry later
 497          */
 498         err = -EAGAIN;
 499         if (mmap_changing && READ_ONCE(*mmap_changing))
 500                 goto out_unlock;
 501
 502         /*
 503          * Make sure the vma is not shared, that the dst range is
 504          * both valid and fully within a single existing vma.
 505          */
 506         err = -ENOENT;
 507         dst_vma = find_dst_vma(dst_mm, dst_start, len);
 508         if (!dst_vma)
 509                 goto out_unlock;
 510
 511         err = -EINVAL;
 512         /*
 513          * shmem_zero_setup is invoked in mmap for MAP_ANONYMOUS|MAP_SHARED but
 514          * it will overwrite vm_ops, so vma_is_anonymous must return false.
 515          */
 516         if (WARN_ON_ONCE(vma_is_anonymous(dst_vma) &&
 517             dst_vma->vm_flags & VM_SHARED))
 518                 goto out_unlock;
 519
 520         /*
 521          * validate 'mode' now that we know the dst_vma: don't allow
 522          * a wrprotect copy if the userfaultfd didn't register as WP.
 523          */
 524         wp_copy = mode & UFFDIO_COPY_MODE_WP;
 525         if (wp_copy && !(dst_vma->vm_flags & VM_UFFD_WP))
 526                 goto out_unlock;
 527
 528         /*
 529          * If this is a HUGETLB vma, pass off to appropriate routine
 530          */
 531         if (is_vm_hugetlb_page(dst_vma))
 532                 return  __mcopy_atomic_hugetlb(dst_mm, dst_vma, dst_start,
 533                                                 src_start, len, zeropage);
 534
 535         if (!vma_is_anonymous(dst_vma) && !vma_is_shmem(dst_vma))
 536                 goto out_unlock;
 537
 538         /*
 539          * Ensure the dst_vma has a anon_vma or this page
 540          * would get a NULL anon_vma when moved in the
 541          * dst_vma.
 542          */
 543         err = -ENOMEM;
 544         if (!(dst_vma->vm_flags & VM_SHARED) &&
 545             unlikely(anon_vma_prepare(dst_vma)))
 546                 goto out_unlock;
 547
 548         while (src_addr < src_start + len) {
 549                 pmd_t dst_pmdval;
 550
 551                 BUG_ON(dst_addr >= dst_start + len);
 552
 553                 dst_pmd = mm_alloc_pmd(dst_mm, dst_addr);
 554                 if (unlikely(!dst_pmd)) {
 555                         err = -ENOMEM;
 556                         break;
 557                 }
 558
 559                 dst_pmdval = pmd_read_atomic(dst_pmd);
 560                 /*
 561                  * If the dst_pmd is mapped as THP don't
 562                  * override it and just be strict.
 563                  */
 564                 if (unlikely(pmd_trans_huge(dst_pmdval))) {
 565                         err = -EEXIST;
 566                         break;
 567                 }
 568                 if (unlikely(pmd_none(dst_pmdval)) &&
 569                     unlikely(__pte_alloc(dst_mm, dst_pmd))) {
 570                         err = -ENOMEM;
 571                         break;
 572                 }
 573                 /* If an huge pmd materialized from under us fail */
 574                 if (unlikely(pmd_trans_huge(*dst_pmd))) {
 575                         err = -EFAULT;
 576                         break;
 577                 }
 578
 579                 BUG_ON(pmd_none(*dst_pmd));
 580                 BUG_ON(pmd_trans_huge(*dst_pmd));
 581
 582                 err = mfill_atomic_pte(dst_mm, dst_pmd, dst_vma, dst_addr,
 583                                        src_addr, &page, zeropage, wp_copy);
 584                 cond_resched();
 585
 586                 if (unlikely(err == -ENOENT)) {
 587                         void *page_kaddr;
 588
 589                         up_read(&dst_mm->mmap_sem);
 590                         BUG_ON(!page);
 591
 592                         page_kaddr = kmap(page);
 593                         err = copy_from_user(page_kaddr,
 594                                              (const void __user *) src_addr,
 595                                              PAGE_SIZE);
 596                         kunmap(page);
 597                         if (unlikely(err)) {
 598                                 err = -EFAULT;
 599                                 goto out;
 600                         }
 601                         goto retry;
 602                 } else
 603                         BUG_ON(page);
 604
 605                 if (!err) {
 606                         dst_addr += PAGE_SIZE;
 607                         src_addr += PAGE_SIZE;
 608                         copied += PAGE_SIZE;
 609
 610                         if (fatal_signal_pending(current))
 611                                 err = -EINTR;
 612                 }
 613                 if (err)
 614                         break;
 615         }
 616
 617 out_unlock:
 618         up_read(&dst_mm->mmap_sem);
 619 out:
 620         if (page)
 621                 put_page(page);
 622         BUG_ON(copied < 0);
 623         BUG_ON(err > 0);
 624         BUG_ON(!copied && !err);
 625         return copied ? copied : err;
 626 }
 627
 628 ssize_t mcopy_atomic(struct mm_struct *dst_mm, unsigned long dst_start,
 629                      unsigned long src_start, unsigned long len,
 630                      bool *mmap_changing, __u64 mode)
 631 {
 632         return __mcopy_atomic(dst_mm, dst_start, src_start, len, false,
 633                               mmap_changing, mode);
 634 }
 635
 636 ssize_t mfill_zeropage(struct mm_struct *dst_mm, unsigned long start,
 637                        unsigned long len, bool *mmap_changing)
 638 {
 639         return __mcopy_atomic(dst_mm, start, 0, len, true, mmap_changing, 0);
 640 }
 641
 642 int mwriteprotect_range(struct mm_struct *dst_mm, unsigned long start,
 643                         unsigned long len, bool enable_wp, bool *mmap_changing)
 644 {
 645         struct vm_area_struct *dst_vma;
 646         pgprot_t newprot;
 647         int err;
 648
 649         /*
 650          * Sanitize the command parameters:
 651          */
 652         BUG_ON(start & ~PAGE_MASK);
 653         BUG_ON(len & ~PAGE_MASK);
 654
 655         /* Does the address range wrap, or is the span zero-sized? */
 656         BUG_ON(start + len <= start);
 657
 658         down_read(&dst_mm->mmap_sem);
 659
 660         /*
 661          * If memory mappings are changing because of non-cooperative
 662          * operation (e.g. mremap) running in parallel, bail out and
 663          * request the user to retry later
 664          */
 665         err = -EAGAIN;
 666         if (mmap_changing && READ_ONCE(*mmap_changing))
 667                 goto out_unlock;
 668
 669         err = -ENOENT;
 670         dst_vma = find_dst_vma(dst_mm, start, len);
 671         /*
 672          * Make sure the vma is not shared, that the dst range is
 673          * both valid and fully within a single existing vma.
 674          */
 675         if (!dst_vma || (dst_vma->vm_flags & VM_SHARED))
 676                 goto out_unlock;
 677         if (!userfaultfd_wp(dst_vma))
 678                 goto out_unlock;
 679         if (!vma_is_anonymous(dst_vma))
 680                 goto out_unlock;
 681
 682         if (enable_wp)
 683                 newprot = vm_get_page_prot(dst_vma->vm_flags & ~(VM_WRITE));
 684         else
 685                 newprot = vm_get_page_prot(dst_vma->vm_flags);
 686
 687         change_protection(dst_vma, start, start + len, newprot,
 688                           enable_wp ? MM_CP_UFFD_WP : MM_CP_UFFD_WP_RESOLVE);
 689
 690         err = 0;
 691 out_unlock:
 692         up_read(&dst_mm->mmap_sem);
 693         return err;
 694 }