mm/userfaultfd.c

   1 /*
   2  *  mm/userfaultfd.c
   3  *
   4  *  Copyright (C) 2015  Red Hat, Inc.
   5  *
   6  *  This work is licensed under the terms of the GNU GPL, version 2. See
   7  *  the COPYING file in the top-level directory.
   8  */
   9
  10 #include <linux/mm.h>
  11 #include <linux/sched/signal.h>
  12 #include <linux/pagemap.h>
  13 #include <linux/rmap.h>
  14 #include <linux/swap.h>
  15 #include <linux/swapops.h>
  16 #include <linux/userfaultfd_k.h>
  17 #include <linux/mmu_notifier.h>
  18 #include <linux/hugetlb.h>
  19 #include <linux/pagemap.h>
  20 #include <linux/shmem_fs.h>
  21 #include <asm/tlbflush.h>
  22 #include "internal.h"
  23
  24 static int mcopy_atomic_pte(struct mm_struct *dst_mm,
  25                             pmd_t *dst_pmd,
  26                             struct vm_area_struct *dst_vma,
  27                             unsigned long dst_addr,
  28                             unsigned long src_addr,
  29                             struct page **pagep)
  30 {
  31         struct mem_cgroup *memcg;
  32         pte_t _dst_pte, *dst_pte;
  33         spinlock_t *ptl;
  34         void *page_kaddr;
  35         int ret;
  36         struct page *page;
  37
  38         if (!*pagep) {
  39                 ret = -ENOMEM;
  40                 page = alloc_page_vma(GFP_HIGHUSER_MOVABLE, dst_vma, dst_addr);
  41                 if (!page)
  42                         goto out;
  43
  44                 page_kaddr = kmap_atomic(page);
  45                 ret = copy_from_user(page_kaddr,
  46                                      (const void __user *) src_addr,
  47                                      PAGE_SIZE);
  48                 kunmap_atomic(page_kaddr);
  49
  50                 /* fallback to copy_from_user outside mmap_sem */
  51                 if (unlikely(ret)) {
  52                         ret = -EFAULT;
  53                         *pagep = page;
  54                         /* don't free the page */
  55                         goto out;
  56                 }
  57         } else {
  58                 page = *pagep;
  59                 *pagep = NULL;
  60         }
  61
  62         /*
  63          * The memory barrier inside __SetPageUptodate makes sure that
  64          * preceeding stores to the page contents become visible before
  65          * the set_pte_at() write.
  66          */
  67         __SetPageUptodate(page);
  68
  69         ret = -ENOMEM;
  70         if (mem_cgroup_try_charge(page, dst_mm, GFP_KERNEL, &memcg, false))
  71                 goto out_release;
  72
  73         _dst_pte = mk_pte(page, dst_vma->vm_page_prot);
  74         if (dst_vma->vm_flags & VM_WRITE)
  75                 _dst_pte = pte_mkwrite(pte_mkdirty(_dst_pte));
  76
  77         ret = -EEXIST;
  78         dst_pte = pte_offset_map_lock(dst_mm, dst_pmd, dst_addr, &ptl);
  79         if (!pte_none(*dst_pte))
  80                 goto out_release_uncharge_unlock;
  81
  82         inc_mm_counter(dst_mm, MM_ANONPAGES);
  83         page_add_new_anon_rmap(page, dst_vma, dst_addr, false);
  84         mem_cgroup_commit_charge(page, memcg, false, false);
  85         lru_cache_add_active_or_unevictable(page, dst_vma);
  86
  87         set_pte_at(dst_mm, dst_addr, dst_pte, _dst_pte);
  88
  89         /* No need to invalidate - it was non-present before */
  90         update_mmu_cache(dst_vma, dst_addr, dst_pte);
  91
  92         pte_unmap_unlock(dst_pte, ptl);
  93         ret = 0;
  94 out:
  95         return ret;
  96 out_release_uncharge_unlock:
  97         pte_unmap_unlock(dst_pte, ptl);
  98         mem_cgroup_cancel_charge(page, memcg, false);
  99 out_release:
 100         put_page(page);
 101         goto out;
 102 }
 103
 104 static int mfill_zeropage_pte(struct mm_struct *dst_mm,
 105                               pmd_t *dst_pmd,
 106                               struct vm_area_struct *dst_vma,
 107                               unsigned long dst_addr)
 108 {
 109         pte_t _dst_pte, *dst_pte;
 110         spinlock_t *ptl;
 111         int ret;
 112
 113         _dst_pte = pte_mkspecial(pfn_pte(my_zero_pfn(dst_addr),
 114                                          dst_vma->vm_page_prot));
 115         ret = -EEXIST;
 116         dst_pte = pte_offset_map_lock(dst_mm, dst_pmd, dst_addr, &ptl);
 117         if (!pte_none(*dst_pte))
 118                 goto out_unlock;
 119         set_pte_at(dst_mm, dst_addr, dst_pte, _dst_pte);
 120         /* No need to invalidate - it was non-present before */
 121         update_mmu_cache(dst_vma, dst_addr, dst_pte);
 122         ret = 0;
 123 out_unlock:
 124         pte_unmap_unlock(dst_pte, ptl);
 125         return ret;
 126 }
 127
 128 static pmd_t *mm_alloc_pmd(struct mm_struct *mm, unsigned long address)
 129 {
 130         pgd_t *pgd;
 131         pud_t *pud;
 132         pmd_t *pmd = NULL;
 133
 134         pgd = pgd_offset(mm, address);
 135         pud = pud_alloc(mm, pgd, address);
 136         if (pud)
 137                 /*
 138                  * Note that we didn't run this because the pmd was
 139                  * missing, the *pmd may be already established and in
 140                  * turn it may also be a trans_huge_pmd.
 141                  */
 142                 pmd = pmd_alloc(mm, pud, address);
 143         return pmd;
 144 }
 145
 146 #ifdef CONFIG_HUGETLB_PAGE
 147 /*
 148  * __mcopy_atomic processing for HUGETLB vmas.  Note that this routine is
 149  * called with mmap_sem held, it will release mmap_sem before returning.
 150  */
 151 static __always_inline ssize_t __mcopy_atomic_hugetlb(struct mm_struct *dst_mm,
 152                                               struct vm_area_struct *dst_vma,
 153                                               unsigned long dst_start,
 154                                               unsigned long src_start,
 155                                               unsigned long len,
 156                                               bool zeropage)
 157 {
 158         int vm_alloc_shared = dst_vma->vm_flags & VM_SHARED;
 159         int vm_shared = dst_vma->vm_flags & VM_SHARED;
 160         ssize_t err;
 161         pte_t *dst_pte;
 162         unsigned long src_addr, dst_addr;
 163         long copied;
 164         struct page *page;
 165         struct hstate *h;
 166         unsigned long vma_hpagesize;
 167         pgoff_t idx;
 168         u32 hash;
 169         struct address_space *mapping;
 170
 171         /*
 172          * There is no default zero huge page for all huge page sizes as
 173          * supported by hugetlb.  A PMD_SIZE huge pages may exist as used
 174          * by THP.  Since we can not reliably insert a zero page, this
 175          * feature is not supported.
 176          */
 177         if (zeropage) {
 178                 up_read(&dst_mm->mmap_sem);
 179                 return -EINVAL;
 180         }
 181
 182         src_addr = src_start;
 183         dst_addr = dst_start;
 184         copied = 0;
 185         page = NULL;
 186         vma_hpagesize = vma_kernel_pagesize(dst_vma);
 187
 188         /*
 189          * Validate alignment based on huge page size
 190          */
 191         err = -EINVAL;
 192         if (dst_start & (vma_hpagesize - 1) || len & (vma_hpagesize - 1))
 193                 goto out_unlock;
 194
 195 retry:
 196         /*
 197          * On routine entry dst_vma is set.  If we had to drop mmap_sem and
 198          * retry, dst_vma will be set to NULL and we must lookup again.
 199          */
 200         if (!dst_vma) {
 201                 err = -ENOENT;
 202                 dst_vma = find_vma(dst_mm, dst_start);
 203                 if (!dst_vma || !is_vm_hugetlb_page(dst_vma))
 204                         goto out_unlock;
 205                 /*
 206                  * Only allow __mcopy_atomic_hugetlb on userfaultfd
 207                  * registered ranges.
 208                  */
 209                 if (!dst_vma->vm_userfaultfd_ctx.ctx)
 210                         goto out_unlock;
 211
 212                 if (dst_start < dst_vma->vm_start ||
 213                     dst_start + len > dst_vma->vm_end)
 214                         goto out_unlock;
 215
 216                 err = -EINVAL;
 217                 if (vma_hpagesize != vma_kernel_pagesize(dst_vma))
 218                         goto out_unlock;
 219
 220                 vm_shared = dst_vma->vm_flags & VM_SHARED;
 221         }
 222
 223         if (WARN_ON(dst_addr & (vma_hpagesize - 1) ||
 224                     (len - copied) & (vma_hpagesize - 1)))
 225                 goto out_unlock;
 226
 227         /*
 228          * If not shared, ensure the dst_vma has a anon_vma.
 229          */
 230         err = -ENOMEM;
 231         if (!vm_shared) {
 232                 if (unlikely(anon_vma_prepare(dst_vma)))
 233                         goto out_unlock;
 234         }
 235
 236         h = hstate_vma(dst_vma);
 237
 238         while (src_addr < src_start + len) {
 239                 pte_t dst_pteval;
 240
 241                 BUG_ON(dst_addr >= dst_start + len);
 242                 VM_BUG_ON(dst_addr & ~huge_page_mask(h));
 243
 244                 /*
 245                  * Serialize via hugetlb_fault_mutex
 246                  */
 247                 idx = linear_page_index(dst_vma, dst_addr);
 248                 mapping = dst_vma->vm_file->f_mapping;
 249                 hash = hugetlb_fault_mutex_hash(h, dst_mm, dst_vma, mapping,
 250                                                                 idx, dst_addr);
 251                 mutex_lock(&hugetlb_fault_mutex_table[hash]);
 252
 253                 err = -ENOMEM;
 254                 dst_pte = huge_pte_alloc(dst_mm, dst_addr, huge_page_size(h));
 255                 if (!dst_pte) {
 256                         mutex_unlock(&hugetlb_fault_mutex_table[hash]);
 257                         goto out_unlock;
 258                 }
 259
 260                 err = -EEXIST;
 261                 dst_pteval = huge_ptep_get(dst_pte);
 262                 if (!huge_pte_none(dst_pteval)) {
 263                         mutex_unlock(&hugetlb_fault_mutex_table[hash]);
 264                         goto out_unlock;
 265                 }
 266
 267                 err = hugetlb_mcopy_atomic_pte(dst_mm, dst_pte, dst_vma,
 268                                                 dst_addr, src_addr, &page);
 269
 270                 mutex_unlock(&hugetlb_fault_mutex_table[hash]);
 271                 vm_alloc_shared = vm_shared;
 272
 273                 cond_resched();
 274
 275                 if (unlikely(err == -EFAULT)) {
 276                         up_read(&dst_mm->mmap_sem);
 277                         BUG_ON(!page);
 278
 279                         err = copy_huge_page_from_user(page,
 280                                                 (const void __user *)src_addr,
 281                                                 pages_per_huge_page(h), true);
 282                         if (unlikely(err)) {
 283                                 err = -EFAULT;
 284                                 goto out;
 285                         }
 286                         down_read(&dst_mm->mmap_sem);
 287
 288                         dst_vma = NULL;
 289                         goto retry;
 290                 } else
 291                         BUG_ON(page);
 292
 293                 if (!err) {
 294                         dst_addr += vma_hpagesize;
 295                         src_addr += vma_hpagesize;
 296                         copied += vma_hpagesize;
 297
 298                         if (fatal_signal_pending(current))
 299                                 err = -EINTR;
 300                 }
 301                 if (err)
 302                         break;
 303         }
 304
 305 out_unlock:
 306         up_read(&dst_mm->mmap_sem);
 307 out:
 308         if (page) {
 309                 /*
 310                  * We encountered an error and are about to free a newly
 311                  * allocated huge page.
 312                  *
 313                  * Reservation handling is very subtle, and is different for
 314                  * private and shared mappings.  See the routine
 315                  * restore_reserve_on_error for details.  Unfortunately, we
 316                  * can not call restore_reserve_on_error now as it would
 317                  * require holding mmap_sem.
 318                  *
 319                  * If a reservation for the page existed in the reservation
 320                  * map of a private mapping, the map was modified to indicate
 321                  * the reservation was consumed when the page was allocated.
 322                  * We clear the PagePrivate flag now so that the global
 323                  * reserve count will not be incremented in free_huge_page.
 324                  * The reservation map will still indicate the reservation
 325                  * was consumed and possibly prevent later page allocation.
 326                  * This is better than leaking a global reservation.  If no
 327                  * reservation existed, it is still safe to clear PagePrivate
 328                  * as no adjustments to reservation counts were made during
 329                  * allocation.
 330                  *
 331                  * The reservation map for shared mappings indicates which
 332                  * pages have reservations.  When a huge page is allocated
 333                  * for an address with a reservation, no change is made to
 334                  * the reserve map.  In this case PagePrivate will be set
 335                  * to indicate that the global reservation count should be
 336                  * incremented when the page is freed.  This is the desired
 337                  * behavior.  However, when a huge page is allocated for an
 338                  * address without a reservation a reservation entry is added
 339                  * to the reservation map, and PagePrivate will not be set.
 340                  * When the page is freed, the global reserve count will NOT
 341                  * be incremented and it will appear as though we have leaked
 342                  * reserved page.  In this case, set PagePrivate so that the
 343                  * global reserve count will be incremented to match the
 344                  * reservation map entry which was created.
 345                  *
 346                  * Note that vm_alloc_shared is based on the flags of the vma
 347                  * for which the page was originally allocated.  dst_vma could
 348                  * be different or NULL on error.
 349                  */
 350                 if (vm_alloc_shared)
 351                         SetPagePrivate(page);
 352                 else
 353                         ClearPagePrivate(page);
 354                 put_page(page);
 355         }
 356         BUG_ON(copied < 0);
 357         BUG_ON(err > 0);
 358         BUG_ON(!copied && !err);
 359         return copied ? copied : err;
 360 }
 361 #else /* !CONFIG_HUGETLB_PAGE */
 362 /* fail at build time if gcc attempts to use this */
 363 extern ssize_t __mcopy_atomic_hugetlb(struct mm_struct *dst_mm,
 364                                       struct vm_area_struct *dst_vma,
 365                                       unsigned long dst_start,
 366                                       unsigned long src_start,
 367                                       unsigned long len,
 368                                       bool zeropage);
 369 #endif /* CONFIG_HUGETLB_PAGE */
 370
 371 static __always_inline ssize_t __mcopy_atomic(struct mm_struct *dst_mm,
 372                                               unsigned long dst_start,
 373                                               unsigned long src_start,
 374                                               unsigned long len,
 375                                               bool zeropage)
 376 {
 377         struct vm_area_struct *dst_vma;
 378         ssize_t err;
 379         pmd_t *dst_pmd;
 380         unsigned long src_addr, dst_addr;
 381         long copied;
 382         struct page *page;
 383
 384         /*
 385          * Sanitize the command parameters:
 386          */
 387         BUG_ON(dst_start & ~PAGE_MASK);
 388         BUG_ON(len & ~PAGE_MASK);
 389
 390         /* Does the address range wrap, or is the span zero-sized? */
 391         BUG_ON(src_start + len <= src_start);
 392         BUG_ON(dst_start + len <= dst_start);
 393
 394         src_addr = src_start;
 395         dst_addr = dst_start;
 396         copied = 0;
 397         page = NULL;
 398 retry:
 399         down_read(&dst_mm->mmap_sem);
 400
 401         /*
 402          * Make sure the vma is not shared, that the dst range is
 403          * both valid and fully within a single existing vma.
 404          */
 405         err = -ENOENT;
 406         dst_vma = find_vma(dst_mm, dst_start);
 407         if (!dst_vma)
 408                 goto out_unlock;
 409         /*
 410          * Be strict and only allow __mcopy_atomic on userfaultfd
 411          * registered ranges to prevent userland errors going
 412          * unnoticed. As far as the VM consistency is concerned, it
 413          * would be perfectly safe to remove this check, but there's
 414          * no useful usage for __mcopy_atomic ouside of userfaultfd
 415          * registered ranges. This is after all why these are ioctls
 416          * belonging to the userfaultfd and not syscalls.
 417          */
 418         if (!dst_vma->vm_userfaultfd_ctx.ctx)
 419                 goto out_unlock;
 420
 421         if (dst_start < dst_vma->vm_start ||
 422             dst_start + len > dst_vma->vm_end)
 423                 goto out_unlock;
 424
 425         err = -EINVAL;
 426         /*
 427          * shmem_zero_setup is invoked in mmap for MAP_ANONYMOUS|MAP_SHARED but
 428          * it will overwrite vm_ops, so vma_is_anonymous must return false.
 429          */
 430         if (WARN_ON_ONCE(vma_is_anonymous(dst_vma) &&
 431             dst_vma->vm_flags & VM_SHARED))
 432                 goto out_unlock;
 433
 434         /*
 435          * If this is a HUGETLB vma, pass off to appropriate routine
 436          */
 437         if (is_vm_hugetlb_page(dst_vma))
 438                 return  __mcopy_atomic_hugetlb(dst_mm, dst_vma, dst_start,
 439                                                 src_start, len, zeropage);
 440
 441         if (!vma_is_anonymous(dst_vma) && !vma_is_shmem(dst_vma))
 442                 goto out_unlock;
 443
 444         /*
 445          * Ensure the dst_vma has a anon_vma or this page
 446          * would get a NULL anon_vma when moved in the
 447          * dst_vma.
 448          */
 449         err = -ENOMEM;
 450         if (vma_is_anonymous(dst_vma) && unlikely(anon_vma_prepare(dst_vma)))
 451                 goto out_unlock;
 452
 453         while (src_addr < src_start + len) {
 454                 pmd_t dst_pmdval;
 455
 456                 BUG_ON(dst_addr >= dst_start + len);
 457
 458                 dst_pmd = mm_alloc_pmd(dst_mm, dst_addr);
 459                 if (unlikely(!dst_pmd)) {
 460                         err = -ENOMEM;
 461                         break;
 462                 }
 463
 464                 dst_pmdval = pmd_read_atomic(dst_pmd);
 465                 /*
 466                  * If the dst_pmd is mapped as THP don't
 467                  * override it and just be strict.
 468                  */
 469                 if (unlikely(pmd_trans_huge(dst_pmdval))) {
 470                         err = -EEXIST;
 471                         break;
 472                 }
 473                 if (unlikely(pmd_none(dst_pmdval)) &&
 474                     unlikely(__pte_alloc(dst_mm, dst_pmd, dst_addr))) {
 475                         err = -ENOMEM;
 476                         break;
 477                 }
 478                 /* If an huge pmd materialized from under us fail */
 479                 if (unlikely(pmd_trans_huge(*dst_pmd))) {
 480                         err = -EFAULT;
 481                         break;
 482                 }
 483
 484                 BUG_ON(pmd_none(*dst_pmd));
 485                 BUG_ON(pmd_trans_huge(*dst_pmd));
 486
 487                 if (vma_is_anonymous(dst_vma)) {
 488                         if (!zeropage)
 489                                 err = mcopy_atomic_pte(dst_mm, dst_pmd, dst_vma,
 490                                                        dst_addr, src_addr,
 491                                                        &page);
 492                         else
 493                                 err = mfill_zeropage_pte(dst_mm, dst_pmd,
 494                                                          dst_vma, dst_addr);
 495                 } else {
 496                         err = -EINVAL; /* if zeropage is true return -EINVAL */
 497                         if (likely(!zeropage))
 498                                 err = shmem_mcopy_atomic_pte(dst_mm, dst_pmd,
 499                                                              dst_vma, dst_addr,
 500                                                              src_addr, &page);
 501                 }
 502
 503                 cond_resched();
 504
 505                 if (unlikely(err == -EFAULT)) {
 506                         void *page_kaddr;
 507
 508                         up_read(&dst_mm->mmap_sem);
 509                         BUG_ON(!page);
 510
 511                         page_kaddr = kmap(page);
 512                         err = copy_from_user(page_kaddr,
 513                                              (const void __user *) src_addr,
 514                                              PAGE_SIZE);
 515                         kunmap(page);
 516                         if (unlikely(err)) {
 517                                 err = -EFAULT;
 518                                 goto out;
 519                         }
 520                         goto retry;
 521                 } else
 522                         BUG_ON(page);
 523
 524                 if (!err) {
 525                         dst_addr += PAGE_SIZE;
 526                         src_addr += PAGE_SIZE;
 527                         copied += PAGE_SIZE;
 528
 529                         if (fatal_signal_pending(current))
 530                                 err = -EINTR;
 531                 }
 532                 if (err)
 533                         break;
 534         }
 535
 536 out_unlock:
 537         up_read(&dst_mm->mmap_sem);
 538 out:
 539         if (page)
 540                 put_page(page);
 541         BUG_ON(copied < 0);
 542         BUG_ON(err > 0);
 543         BUG_ON(!copied && !err);
 544         return copied ? copied : err;
 545 }
 546
 547 ssize_t mcopy_atomic(struct mm_struct *dst_mm, unsigned long dst_start,
 548                      unsigned long src_start, unsigned long len)
 549 {
 550         return __mcopy_atomic(dst_mm, dst_start, src_start, len, false);
 551 }
 552
 553 ssize_t mfill_zeropage(struct mm_struct *dst_mm, unsigned long start,
 554                        unsigned long len)
 555 {
 556         return __mcopy_atomic(dst_mm, start, 0, len, true);
 557 }