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 <asm/tlb.h>
  20 #include "internal.h"
  21
  22 static __always_inline
  23 struct vm_area_struct *find_dst_vma(struct mm_struct *dst_mm,
  24                                     unsigned long dst_start,
  25                                     unsigned long len)
  26 {
  27         /*
  28          * Make sure that the dst range is both valid and fully within a
  29          * single existing vma.
  30          */
  31         struct vm_area_struct *dst_vma;
  32
  33         dst_vma = find_vma(dst_mm, dst_start);
  34         if (!dst_vma)
  35                 return NULL;
  36
  37         if (dst_start < dst_vma->vm_start ||
  38             dst_start + len > dst_vma->vm_end)
  39                 return NULL;
  40
  41         /*
  42          * Check the vma is registered in uffd, this is required to
  43          * enforce the VM_MAYWRITE check done at uffd registration
  44          * time.
  45          */
  46         if (!dst_vma->vm_userfaultfd_ctx.ctx)
  47                 return NULL;
  48
  49         return dst_vma;
  50 }
  51
  52 /*
  53  * Install PTEs, to map dst_addr (within dst_vma) to page.
  54  *
  55  * This function handles both MCOPY_ATOMIC_NORMAL and _CONTINUE for both shmem
  56  * and anon, and for both shared and private VMAs.
  57  */
  58 int mfill_atomic_install_pte(struct mm_struct *dst_mm, pmd_t *dst_pmd,
  59                              struct vm_area_struct *dst_vma,
  60                              unsigned long dst_addr, struct page *page,
  61                              bool newly_allocated, bool wp_copy)
  62 {
  63         int ret;
  64         pte_t _dst_pte, *dst_pte;
  65         bool writable = dst_vma->vm_flags & VM_WRITE;
  66         bool vm_shared = dst_vma->vm_flags & VM_SHARED;
  67         bool page_in_cache = page_mapping(page);
  68         spinlock_t *ptl;
  69         struct folio *folio;
  70         struct inode *inode;
  71         pgoff_t offset, max_off;
  72
  73         _dst_pte = mk_pte(page, dst_vma->vm_page_prot);
  74         _dst_pte = pte_mkdirty(_dst_pte);
  75         if (page_in_cache && !vm_shared)
  76                 writable = false;
  77
  78         /*
  79          * Always mark a PTE as write-protected when needed, regardless of
  80          * VM_WRITE, which the user might change.
  81          */
  82         if (wp_copy) {
  83                 _dst_pte = pte_mkuffd_wp(_dst_pte);
  84                 writable = false;
  85         }
  86
  87         if (writable)
  88                 _dst_pte = pte_mkwrite(_dst_pte);
  89         else
  90                 /*
  91                  * We need this to make sure write bit removed; as mk_pte()
  92                  * could return a pte with write bit set.
  93                  */
  94                 _dst_pte = pte_wrprotect(_dst_pte);
  95
  96         dst_pte = pte_offset_map_lock(dst_mm, dst_pmd, dst_addr, &ptl);
  97
  98         if (vma_is_shmem(dst_vma)) {
  99                 /* serialize against truncate with the page table lock */
 100                 inode = dst_vma->vm_file->f_inode;
 101                 offset = linear_page_index(dst_vma, dst_addr);
 102                 max_off = DIV_ROUND_UP(i_size_read(inode), PAGE_SIZE);
 103                 ret = -EFAULT;
 104                 if (unlikely(offset >= max_off))
 105                         goto out_unlock;
 106         }
 107
 108         ret = -EEXIST;
 109         /*
 110          * We allow to overwrite a pte marker: consider when both MISSING|WP
 111          * registered, we firstly wr-protect a none pte which has no page cache
 112          * page backing it, then access the page.
 113          */
 114         if (!pte_none_mostly(*dst_pte))
 115                 goto out_unlock;
 116
 117         folio = page_folio(page);
 118         if (page_in_cache) {
 119                 /* Usually, cache pages are already added to LRU */
 120                 if (newly_allocated)
 121                         folio_add_lru(folio);
 122                 page_add_file_rmap(page, dst_vma, false);
 123         } else {
 124                 page_add_new_anon_rmap(page, dst_vma, dst_addr);
 125                 folio_add_lru_vma(folio, dst_vma);
 126         }
 127
 128         /*
 129          * Must happen after rmap, as mm_counter() checks mapping (via
 130          * PageAnon()), which is set by __page_set_anon_rmap().
 131          */
 132         inc_mm_counter(dst_mm, mm_counter(page));
 133
 134         set_pte_at(dst_mm, dst_addr, dst_pte, _dst_pte);
 135
 136         /* No need to invalidate - it was non-present before */
 137         update_mmu_cache(dst_vma, dst_addr, dst_pte);
 138         ret = 0;
 139 out_unlock:
 140         pte_unmap_unlock(dst_pte, ptl);
 141         return ret;
 142 }
 143
 144 static int mcopy_atomic_pte(struct mm_struct *dst_mm,
 145                             pmd_t *dst_pmd,
 146                             struct vm_area_struct *dst_vma,
 147                             unsigned long dst_addr,
 148                             unsigned long src_addr,
 149                             struct page **pagep,
 150                             bool wp_copy)
 151 {
 152         void *page_kaddr;
 153         int ret;
 154         struct page *page;
 155
 156         if (!*pagep) {
 157                 ret = -ENOMEM;
 158                 page = alloc_page_vma(GFP_HIGHUSER_MOVABLE, dst_vma, dst_addr);
 159                 if (!page)
 160                         goto out;
 161
 162                 page_kaddr = kmap_local_page(page);
 163                 /*
 164                  * The read mmap_lock is held here.  Despite the
 165                  * mmap_lock being read recursive a deadlock is still
 166                  * possible if a writer has taken a lock.  For example:
 167                  *
 168                  * process A thread 1 takes read lock on own mmap_lock
 169                  * process A thread 2 calls mmap, blocks taking write lock
 170                  * process B thread 1 takes page fault, read lock on own mmap lock
 171                  * process B thread 2 calls mmap, blocks taking write lock
 172                  * process A thread 1 blocks taking read lock on process B
 173                  * process B thread 1 blocks taking read lock on process A
 174                  *
 175                  * Disable page faults to prevent potential deadlock
 176                  * and retry the copy outside the mmap_lock.
 177                  */
 178                 pagefault_disable();
 179                 ret = copy_from_user(page_kaddr,
 180                                      (const void __user *) src_addr,
 181                                      PAGE_SIZE);
 182                 pagefault_enable();
 183                 kunmap_local(page_kaddr);
 184
 185                 /* fallback to copy_from_user outside mmap_lock */
 186                 if (unlikely(ret)) {
 187                         ret = -ENOENT;
 188                         *pagep = page;
 189                         /* don't free the page */
 190                         goto out;
 191                 }
 192
 193                 flush_dcache_page(page);
 194         } else {
 195                 page = *pagep;
 196                 *pagep = NULL;
 197         }
 198
 199         /*
 200          * The memory barrier inside __SetPageUptodate makes sure that
 201          * preceding stores to the page contents become visible before
 202          * the set_pte_at() write.
 203          */
 204         __SetPageUptodate(page);
 205
 206         ret = -ENOMEM;
 207         if (mem_cgroup_charge(page_folio(page), dst_mm, GFP_KERNEL))
 208                 goto out_release;
 209
 210         ret = mfill_atomic_install_pte(dst_mm, dst_pmd, dst_vma, dst_addr,
 211                                        page, true, wp_copy);
 212         if (ret)
 213                 goto out_release;
 214 out:
 215         return ret;
 216 out_release:
 217         put_page(page);
 218         goto out;
 219 }
 220
 221 static int mfill_zeropage_pte(struct mm_struct *dst_mm,
 222                               pmd_t *dst_pmd,
 223                               struct vm_area_struct *dst_vma,
 224                               unsigned long dst_addr)
 225 {
 226         pte_t _dst_pte, *dst_pte;
 227         spinlock_t *ptl;
 228         int ret;
 229         pgoff_t offset, max_off;
 230         struct inode *inode;
 231
 232         _dst_pte = pte_mkspecial(pfn_pte(my_zero_pfn(dst_addr),
 233                                          dst_vma->vm_page_prot));
 234         dst_pte = pte_offset_map_lock(dst_mm, dst_pmd, dst_addr, &ptl);
 235         if (dst_vma->vm_file) {
 236                 /* the shmem MAP_PRIVATE case requires checking the i_size */
 237                 inode = dst_vma->vm_file->f_inode;
 238                 offset = linear_page_index(dst_vma, dst_addr);
 239                 max_off = DIV_ROUND_UP(i_size_read(inode), PAGE_SIZE);
 240                 ret = -EFAULT;
 241                 if (unlikely(offset >= max_off))
 242                         goto out_unlock;
 243         }
 244         ret = -EEXIST;
 245         if (!pte_none(*dst_pte))
 246                 goto out_unlock;
 247         set_pte_at(dst_mm, dst_addr, dst_pte, _dst_pte);
 248         /* No need to invalidate - it was non-present before */
 249         update_mmu_cache(dst_vma, dst_addr, dst_pte);
 250         ret = 0;
 251 out_unlock:
 252         pte_unmap_unlock(dst_pte, ptl);
 253         return ret;
 254 }
 255
 256 /* Handles UFFDIO_CONTINUE for all shmem VMAs (shared or private). */
 257 static int mcontinue_atomic_pte(struct mm_struct *dst_mm,
 258                                 pmd_t *dst_pmd,
 259                                 struct vm_area_struct *dst_vma,
 260                                 unsigned long dst_addr,
 261                                 bool wp_copy)
 262 {
 263         struct inode *inode = file_inode(dst_vma->vm_file);
 264         pgoff_t pgoff = linear_page_index(dst_vma, dst_addr);
 265         struct folio *folio;
 266         struct page *page;
 267         int ret;
 268
 269         ret = shmem_get_folio(inode, pgoff, &folio, SGP_NOALLOC);
 270         /* Our caller expects us to return -EFAULT if we failed to find folio */
 271         if (ret == -ENOENT)
 272                 ret = -EFAULT;
 273         if (ret)
 274                 goto out;
 275         if (!folio) {
 276                 ret = -EFAULT;
 277                 goto out;
 278         }
 279
 280         page = folio_file_page(folio, pgoff);
 281         if (PageHWPoison(page)) {
 282                 ret = -EIO;
 283                 goto out_release;
 284         }
 285
 286         ret = mfill_atomic_install_pte(dst_mm, dst_pmd, dst_vma, dst_addr,
 287                                        page, false, wp_copy);
 288         if (ret)
 289                 goto out_release;
 290
 291         folio_unlock(folio);
 292         ret = 0;
 293 out:
 294         return ret;
 295 out_release:
 296         folio_unlock(folio);
 297         folio_put(folio);
 298         goto out;
 299 }
 300
 301 static pmd_t *mm_alloc_pmd(struct mm_struct *mm, unsigned long address)
 302 {
 303         pgd_t *pgd;
 304         p4d_t *p4d;
 305         pud_t *pud;
 306
 307         pgd = pgd_offset(mm, address);
 308         p4d = p4d_alloc(mm, pgd, address);
 309         if (!p4d)
 310                 return NULL;
 311         pud = pud_alloc(mm, p4d, address);
 312         if (!pud)
 313                 return NULL;
 314         /*
 315          * Note that we didn't run this because the pmd was
 316          * missing, the *pmd may be already established and in
 317          * turn it may also be a trans_huge_pmd.
 318          */
 319         return pmd_alloc(mm, pud, address);
 320 }
 321
 322 #ifdef CONFIG_HUGETLB_PAGE
 323 /*
 324  * __mcopy_atomic processing for HUGETLB vmas.  Note that this routine is
 325  * called with mmap_lock held, it will release mmap_lock before returning.
 326  */
 327 static __always_inline ssize_t __mcopy_atomic_hugetlb(struct mm_struct *dst_mm,
 328                                               struct vm_area_struct *dst_vma,
 329                                               unsigned long dst_start,
 330                                               unsigned long src_start,
 331                                               unsigned long len,
 332                                               enum mcopy_atomic_mode mode,
 333                                               bool wp_copy)
 334 {
 335         int vm_shared = dst_vma->vm_flags & VM_SHARED;
 336         ssize_t err;
 337         pte_t *dst_pte;
 338         unsigned long src_addr, dst_addr;
 339         long copied;
 340         struct page *page;
 341         unsigned long vma_hpagesize;
 342         pgoff_t idx;
 343         u32 hash;
 344         struct address_space *mapping;
 345
 346         /*
 347          * There is no default zero huge page for all huge page sizes as
 348          * supported by hugetlb.  A PMD_SIZE huge pages may exist as used
 349          * by THP.  Since we can not reliably insert a zero page, this
 350          * feature is not supported.
 351          */
 352         if (mode == MCOPY_ATOMIC_ZEROPAGE) {
 353                 mmap_read_unlock(dst_mm);
 354                 return -EINVAL;
 355         }
 356
 357         src_addr = src_start;
 358         dst_addr = dst_start;
 359         copied = 0;
 360         page = NULL;
 361         vma_hpagesize = vma_kernel_pagesize(dst_vma);
 362
 363         /*
 364          * Validate alignment based on huge page size
 365          */
 366         err = -EINVAL;
 367         if (dst_start & (vma_hpagesize - 1) || len & (vma_hpagesize - 1))
 368                 goto out_unlock;
 369
 370 retry:
 371         /*
 372          * On routine entry dst_vma is set.  If we had to drop mmap_lock and
 373          * retry, dst_vma will be set to NULL and we must lookup again.
 374          */
 375         if (!dst_vma) {
 376                 err = -ENOENT;
 377                 dst_vma = find_dst_vma(dst_mm, dst_start, len);
 378                 if (!dst_vma || !is_vm_hugetlb_page(dst_vma))
 379                         goto out_unlock;
 380
 381                 err = -EINVAL;
 382                 if (vma_hpagesize != vma_kernel_pagesize(dst_vma))
 383                         goto out_unlock;
 384
 385                 vm_shared = dst_vma->vm_flags & VM_SHARED;
 386         }
 387
 388         /*
 389          * If not shared, ensure the dst_vma has a anon_vma.
 390          */
 391         err = -ENOMEM;
 392         if (!vm_shared) {
 393                 if (unlikely(anon_vma_prepare(dst_vma)))
 394                         goto out_unlock;
 395         }
 396
 397         while (src_addr < src_start + len) {
 398                 BUG_ON(dst_addr >= dst_start + len);
 399
 400                 /*
 401                  * Serialize via vma_lock and hugetlb_fault_mutex.
 402                  * vma_lock ensures the dst_pte remains valid even
 403                  * in the case of shared pmds.  fault mutex prevents
 404                  * races with other faulting threads.
 405                  */
 406                 idx = linear_page_index(dst_vma, dst_addr);
 407                 mapping = dst_vma->vm_file->f_mapping;
 408                 hash = hugetlb_fault_mutex_hash(mapping, idx);
 409                 mutex_lock(&hugetlb_fault_mutex_table[hash]);
 410                 hugetlb_vma_lock_read(dst_vma);
 411
 412                 err = -ENOMEM;
 413                 dst_pte = huge_pte_alloc(dst_mm, dst_vma, dst_addr, vma_hpagesize);
 414                 if (!dst_pte) {
 415                         hugetlb_vma_unlock_read(dst_vma);
 416                         mutex_unlock(&hugetlb_fault_mutex_table[hash]);
 417                         goto out_unlock;
 418                 }
 419
 420                 if (mode != MCOPY_ATOMIC_CONTINUE &&
 421                     !huge_pte_none_mostly(huge_ptep_get(dst_pte))) {
 422                         err = -EEXIST;
 423                         hugetlb_vma_unlock_read(dst_vma);
 424                         mutex_unlock(&hugetlb_fault_mutex_table[hash]);
 425                         goto out_unlock;
 426                 }
 427
 428                 err = hugetlb_mcopy_atomic_pte(dst_mm, dst_pte, dst_vma,
 429                                                dst_addr, src_addr, mode, &page,
 430                                                wp_copy);
 431
 432                 hugetlb_vma_unlock_read(dst_vma);
 433                 mutex_unlock(&hugetlb_fault_mutex_table[hash]);
 434
 435                 cond_resched();
 436
 437                 if (unlikely(err == -ENOENT)) {
 438                         mmap_read_unlock(dst_mm);
 439                         BUG_ON(!page);
 440
 441                         err = copy_huge_page_from_user(page,
 442                                                 (const void __user *)src_addr,
 443                                                 vma_hpagesize / PAGE_SIZE,
 444                                                 true);
 445                         if (unlikely(err)) {
 446                                 err = -EFAULT;
 447                                 goto out;
 448                         }
 449                         mmap_read_lock(dst_mm);
 450
 451                         dst_vma = NULL;
 452                         goto retry;
 453                 } else
 454                         BUG_ON(page);
 455
 456                 if (!err) {
 457                         dst_addr += vma_hpagesize;
 458                         src_addr += vma_hpagesize;
 459                         copied += vma_hpagesize;
 460
 461                         if (fatal_signal_pending(current))
 462                                 err = -EINTR;
 463                 }
 464                 if (err)
 465                         break;
 466         }
 467
 468 out_unlock:
 469         mmap_read_unlock(dst_mm);
 470 out:
 471         if (page)
 472                 put_page(page);
 473         BUG_ON(copied < 0);
 474         BUG_ON(err > 0);
 475         BUG_ON(!copied && !err);
 476         return copied ? copied : err;
 477 }
 478 #else /* !CONFIG_HUGETLB_PAGE */
 479 /* fail at build time if gcc attempts to use this */
 480 extern ssize_t __mcopy_atomic_hugetlb(struct mm_struct *dst_mm,
 481                                       struct vm_area_struct *dst_vma,
 482                                       unsigned long dst_start,
 483                                       unsigned long src_start,
 484                                       unsigned long len,
 485                                       enum mcopy_atomic_mode mode,
 486                                       bool wp_copy);
 487 #endif /* CONFIG_HUGETLB_PAGE */
 488
 489 static __always_inline ssize_t mfill_atomic_pte(struct mm_struct *dst_mm,
 490                                                 pmd_t *dst_pmd,
 491                                                 struct vm_area_struct *dst_vma,
 492                                                 unsigned long dst_addr,
 493                                                 unsigned long src_addr,
 494                                                 struct page **page,
 495                                                 enum mcopy_atomic_mode mode,
 496                                                 bool wp_copy)
 497 {
 498         ssize_t err;
 499
 500         if (mode == MCOPY_ATOMIC_CONTINUE) {
 501                 return mcontinue_atomic_pte(dst_mm, dst_pmd, dst_vma, dst_addr,
 502                                             wp_copy);
 503         }
 504
 505         /*
 506          * The normal page fault path for a shmem will invoke the
 507          * fault, fill the hole in the file and COW it right away. The
 508          * result generates plain anonymous memory. So when we are
 509          * asked to fill an hole in a MAP_PRIVATE shmem mapping, we'll
 510          * generate anonymous memory directly without actually filling
 511          * the hole. For the MAP_PRIVATE case the robustness check
 512          * only happens in the pagetable (to verify it's still none)
 513          * and not in the radix tree.
 514          */
 515         if (!(dst_vma->vm_flags & VM_SHARED)) {
 516                 if (mode == MCOPY_ATOMIC_NORMAL)
 517                         err = mcopy_atomic_pte(dst_mm, dst_pmd, dst_vma,
 518                                                dst_addr, src_addr, page,
 519                                                wp_copy);
 520                 else
 521                         err = mfill_zeropage_pte(dst_mm, dst_pmd,
 522                                                  dst_vma, dst_addr);
 523         } else {
 524                 err = shmem_mfill_atomic_pte(dst_mm, dst_pmd, dst_vma,
 525                                              dst_addr, src_addr,
 526                                              mode != MCOPY_ATOMIC_NORMAL,
 527                                              wp_copy, page);
 528         }
 529
 530         return err;
 531 }
 532
 533 static __always_inline ssize_t __mcopy_atomic(struct mm_struct *dst_mm,
 534                                               unsigned long dst_start,
 535                                               unsigned long src_start,
 536                                               unsigned long len,
 537                                               enum mcopy_atomic_mode mcopy_mode,
 538                                               atomic_t *mmap_changing,
 539                                               __u64 mode)
 540 {
 541         struct vm_area_struct *dst_vma;
 542         ssize_t err;
 543         pmd_t *dst_pmd;
 544         unsigned long src_addr, dst_addr;
 545         long copied;
 546         struct page *page;
 547         bool wp_copy;
 548
 549         /*
 550          * Sanitize the command parameters:
 551          */
 552         BUG_ON(dst_start & ~PAGE_MASK);
 553         BUG_ON(len & ~PAGE_MASK);
 554
 555         /* Does the address range wrap, or is the span zero-sized? */
 556         BUG_ON(src_start + len <= src_start);
 557         BUG_ON(dst_start + len <= dst_start);
 558
 559         src_addr = src_start;
 560         dst_addr = dst_start;
 561         copied = 0;
 562         page = NULL;
 563 retry:
 564         mmap_read_lock(dst_mm);
 565
 566         /*
 567          * If memory mappings are changing because of non-cooperative
 568          * operation (e.g. mremap) running in parallel, bail out and
 569          * request the user to retry later
 570          */
 571         err = -EAGAIN;
 572         if (mmap_changing && atomic_read(mmap_changing))
 573                 goto out_unlock;
 574
 575         /*
 576          * Make sure the vma is not shared, that the dst range is
 577          * both valid and fully within a single existing vma.
 578          */
 579         err = -ENOENT;
 580         dst_vma = find_dst_vma(dst_mm, dst_start, len);
 581         if (!dst_vma)
 582                 goto out_unlock;
 583
 584         err = -EINVAL;
 585         /*
 586          * shmem_zero_setup is invoked in mmap for MAP_ANONYMOUS|MAP_SHARED but
 587          * it will overwrite vm_ops, so vma_is_anonymous must return false.
 588          */
 589         if (WARN_ON_ONCE(vma_is_anonymous(dst_vma) &&
 590             dst_vma->vm_flags & VM_SHARED))
 591                 goto out_unlock;
 592
 593         /*
 594          * validate 'mode' now that we know the dst_vma: don't allow
 595          * a wrprotect copy if the userfaultfd didn't register as WP.
 596          */
 597         wp_copy = mode & UFFDIO_COPY_MODE_WP;
 598         if (wp_copy && !(dst_vma->vm_flags & VM_UFFD_WP))
 599                 goto out_unlock;
 600
 601         /*
 602          * If this is a HUGETLB vma, pass off to appropriate routine
 603          */
 604         if (is_vm_hugetlb_page(dst_vma))
 605                 return  __mcopy_atomic_hugetlb(dst_mm, dst_vma, dst_start,
 606                                                src_start, len, mcopy_mode,
 607                                                wp_copy);
 608
 609         if (!vma_is_anonymous(dst_vma) && !vma_is_shmem(dst_vma))
 610                 goto out_unlock;
 611         if (!vma_is_shmem(dst_vma) && mcopy_mode == MCOPY_ATOMIC_CONTINUE)
 612                 goto out_unlock;
 613
 614         /*
 615          * Ensure the dst_vma has a anon_vma or this page
 616          * would get a NULL anon_vma when moved in the
 617          * dst_vma.
 618          */
 619         err = -ENOMEM;
 620         if (!(dst_vma->vm_flags & VM_SHARED) &&
 621             unlikely(anon_vma_prepare(dst_vma)))
 622                 goto out_unlock;
 623
 624         while (src_addr < src_start + len) {
 625                 pmd_t dst_pmdval;
 626
 627                 BUG_ON(dst_addr >= dst_start + len);
 628
 629                 dst_pmd = mm_alloc_pmd(dst_mm, dst_addr);
 630                 if (unlikely(!dst_pmd)) {
 631                         err = -ENOMEM;
 632                         break;
 633                 }
 634
 635                 dst_pmdval = pmdp_get_lockless(dst_pmd);
 636                 /*
 637                  * If the dst_pmd is mapped as THP don't
 638                  * override it and just be strict.
 639                  */
 640                 if (unlikely(pmd_trans_huge(dst_pmdval))) {
 641                         err = -EEXIST;
 642                         break;
 643                 }
 644                 if (unlikely(pmd_none(dst_pmdval)) &&
 645                     unlikely(__pte_alloc(dst_mm, dst_pmd))) {
 646                         err = -ENOMEM;
 647                         break;
 648                 }
 649                 /* If an huge pmd materialized from under us fail */
 650                 if (unlikely(pmd_trans_huge(*dst_pmd))) {
 651                         err = -EFAULT;
 652                         break;
 653                 }
 654
 655                 BUG_ON(pmd_none(*dst_pmd));
 656                 BUG_ON(pmd_trans_huge(*dst_pmd));
 657
 658                 err = mfill_atomic_pte(dst_mm, dst_pmd, dst_vma, dst_addr,
 659                                        src_addr, &page, mcopy_mode, wp_copy);
 660                 cond_resched();
 661
 662                 if (unlikely(err == -ENOENT)) {
 663                         void *page_kaddr;
 664
 665                         mmap_read_unlock(dst_mm);
 666                         BUG_ON(!page);
 667
 668                         page_kaddr = kmap_local_page(page);
 669                         err = copy_from_user(page_kaddr,
 670                                              (const void __user *) src_addr,
 671                                              PAGE_SIZE);
 672                         kunmap_local(page_kaddr);
 673                         if (unlikely(err)) {
 674                                 err = -EFAULT;
 675                                 goto out;
 676                         }
 677                         flush_dcache_page(page);
 678                         goto retry;
 679                 } else
 680                         BUG_ON(page);
 681
 682                 if (!err) {
 683                         dst_addr += PAGE_SIZE;
 684                         src_addr += PAGE_SIZE;
 685                         copied += PAGE_SIZE;
 686
 687                         if (fatal_signal_pending(current))
 688                                 err = -EINTR;
 689                 }
 690                 if (err)
 691                         break;
 692         }
 693
 694 out_unlock:
 695         mmap_read_unlock(dst_mm);
 696 out:
 697         if (page)
 698                 put_page(page);
 699         BUG_ON(copied < 0);
 700         BUG_ON(err > 0);
 701         BUG_ON(!copied && !err);
 702         return copied ? copied : err;
 703 }
 704
 705 ssize_t mcopy_atomic(struct mm_struct *dst_mm, unsigned long dst_start,
 706                      unsigned long src_start, unsigned long len,
 707                      atomic_t *mmap_changing, __u64 mode)
 708 {
 709         return __mcopy_atomic(dst_mm, dst_start, src_start, len,
 710                               MCOPY_ATOMIC_NORMAL, mmap_changing, mode);
 711 }
 712
 713 ssize_t mfill_zeropage(struct mm_struct *dst_mm, unsigned long start,
 714                        unsigned long len, atomic_t *mmap_changing)
 715 {
 716         return __mcopy_atomic(dst_mm, start, 0, len, MCOPY_ATOMIC_ZEROPAGE,
 717                               mmap_changing, 0);
 718 }
 719
 720 ssize_t mcopy_continue(struct mm_struct *dst_mm, unsigned long start,
 721                        unsigned long len, atomic_t *mmap_changing)
 722 {
 723         return __mcopy_atomic(dst_mm, start, 0, len, MCOPY_ATOMIC_CONTINUE,
 724                               mmap_changing, 0);
 725 }
 726
 727 void uffd_wp_range(struct mm_struct *dst_mm, struct vm_area_struct *dst_vma,
 728                    unsigned long start, unsigned long len, bool enable_wp)
 729 {
 730         struct mmu_gather tlb;
 731         pgprot_t newprot;
 732
 733         if (enable_wp)
 734                 newprot = vm_get_page_prot(dst_vma->vm_flags & ~(VM_WRITE));
 735         else
 736                 newprot = vm_get_page_prot(dst_vma->vm_flags);
 737
 738         tlb_gather_mmu(&tlb, dst_mm);
 739         change_protection(&tlb, dst_vma, start, start + len, newprot,
 740                           enable_wp ? MM_CP_UFFD_WP : MM_CP_UFFD_WP_RESOLVE);
 741         tlb_finish_mmu(&tlb);
 742 }
 743
 744 int mwriteprotect_range(struct mm_struct *dst_mm, unsigned long start,
 745                         unsigned long len, bool enable_wp,
 746                         atomic_t *mmap_changing)
 747 {
 748         struct vm_area_struct *dst_vma;
 749         unsigned long page_mask;
 750         int err;
 751
 752         /*
 753          * Sanitize the command parameters:
 754          */
 755         BUG_ON(start & ~PAGE_MASK);
 756         BUG_ON(len & ~PAGE_MASK);
 757
 758         /* Does the address range wrap, or is the span zero-sized? */
 759         BUG_ON(start + len <= start);
 760
 761         mmap_read_lock(dst_mm);
 762
 763         /*
 764          * If memory mappings are changing because of non-cooperative
 765          * operation (e.g. mremap) running in parallel, bail out and
 766          * request the user to retry later
 767          */
 768         err = -EAGAIN;
 769         if (mmap_changing && atomic_read(mmap_changing))
 770                 goto out_unlock;
 771
 772         err = -ENOENT;
 773         dst_vma = find_dst_vma(dst_mm, start, len);
 774
 775         if (!dst_vma)
 776                 goto out_unlock;
 777         if (!userfaultfd_wp(dst_vma))
 778                 goto out_unlock;
 779         if (!vma_can_userfault(dst_vma, dst_vma->vm_flags))
 780                 goto out_unlock;
 781
 782         if (is_vm_hugetlb_page(dst_vma)) {
 783                 err = -EINVAL;
 784                 page_mask = vma_kernel_pagesize(dst_vma) - 1;
 785                 if ((start & page_mask) || (len & page_mask))
 786                         goto out_unlock;
 787         }
 788
 789         uffd_wp_range(dst_mm, dst_vma, start, len, enable_wp);
 790
 791         err = 0;
 792 out_unlock:
 793         mmap_read_unlock(dst_mm);
 794         return err;
 795 }