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

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