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