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Linux/mm/userfaultfd.c

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

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