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Linux/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/pagemap.h>
 12 #include <linux/rmap.h>
 13 #include <linux/swap.h>
 14 #include <linux/swapops.h>
 15 #include <linux/userfaultfd_k.h>
 16 #include <linux/mmu_notifier.h>
 17 #include <asm/tlbflush.h>
 18 #include "internal.h"
 19 
 20 static int mcopy_atomic_pte(struct mm_struct *dst_mm,
 21                             pmd_t *dst_pmd,
 22                             struct vm_area_struct *dst_vma,
 23                             unsigned long dst_addr,
 24                             unsigned long src_addr,
 25                             struct page **pagep)
 26 {
 27         struct mem_cgroup *memcg;
 28         pte_t _dst_pte, *dst_pte;
 29         spinlock_t *ptl;
 30         void *page_kaddr;
 31         int ret;
 32         struct page *page;
 33 
 34         if (!*pagep) {
 35                 ret = -ENOMEM;
 36                 page = alloc_page_vma(GFP_HIGHUSER_MOVABLE, dst_vma, dst_addr);
 37                 if (!page)
 38                         goto out;
 39 
 40                 page_kaddr = kmap_atomic(page);
 41                 ret = copy_from_user(page_kaddr,
 42                                      (const void __user *) src_addr,
 43                                      PAGE_SIZE);
 44                 kunmap_atomic(page_kaddr);
 45 
 46                 /* fallback to copy_from_user outside mmap_sem */
 47                 if (unlikely(ret)) {
 48                         ret = -EFAULT;
 49                         *pagep = page;
 50                         /* don't free the page */
 51                         goto out;
 52                 }
 53         } else {
 54                 page = *pagep;
 55                 *pagep = NULL;
 56         }
 57 
 58         /*
 59          * The memory barrier inside __SetPageUptodate makes sure that
 60          * preceeding stores to the page contents become visible before
 61          * the set_pte_at() write.
 62          */
 63         __SetPageUptodate(page);
 64 
 65         ret = -ENOMEM;
 66         if (mem_cgroup_try_charge(page, dst_mm, GFP_KERNEL, &memcg, false))
 67                 goto out_release;
 68 
 69         _dst_pte = mk_pte(page, dst_vma->vm_page_prot);
 70         if (dst_vma->vm_flags & VM_WRITE)
 71                 _dst_pte = pte_mkwrite(pte_mkdirty(_dst_pte));
 72 
 73         ret = -EEXIST;
 74         dst_pte = pte_offset_map_lock(dst_mm, dst_pmd, dst_addr, &ptl);
 75         if (!pte_none(*dst_pte))
 76                 goto out_release_uncharge_unlock;
 77 
 78         inc_mm_counter(dst_mm, MM_ANONPAGES);
 79         page_add_new_anon_rmap(page, dst_vma, dst_addr, false);
 80         mem_cgroup_commit_charge(page, memcg, false, false);
 81         lru_cache_add_active_or_unevictable(page, dst_vma);
 82 
 83         set_pte_at(dst_mm, dst_addr, dst_pte, _dst_pte);
 84 
 85         /* No need to invalidate - it was non-present before */
 86         update_mmu_cache(dst_vma, dst_addr, dst_pte);
 87 
 88         pte_unmap_unlock(dst_pte, ptl);
 89         ret = 0;
 90 out:
 91         return ret;
 92 out_release_uncharge_unlock:
 93         pte_unmap_unlock(dst_pte, ptl);
 94         mem_cgroup_cancel_charge(page, memcg, false);
 95 out_release:
 96         put_page(page);
 97         goto out;
 98 }
 99 
100 static int mfill_zeropage_pte(struct mm_struct *dst_mm,
101                               pmd_t *dst_pmd,
102                               struct vm_area_struct *dst_vma,
103                               unsigned long dst_addr)
104 {
105         pte_t _dst_pte, *dst_pte;
106         spinlock_t *ptl;
107         int ret;
108 
109         _dst_pte = pte_mkspecial(pfn_pte(my_zero_pfn(dst_addr),
110                                          dst_vma->vm_page_prot));
111         ret = -EEXIST;
112         dst_pte = pte_offset_map_lock(dst_mm, dst_pmd, dst_addr, &ptl);
113         if (!pte_none(*dst_pte))
114                 goto out_unlock;
115         set_pte_at(dst_mm, dst_addr, dst_pte, _dst_pte);
116         /* No need to invalidate - it was non-present before */
117         update_mmu_cache(dst_vma, dst_addr, dst_pte);
118         ret = 0;
119 out_unlock:
120         pte_unmap_unlock(dst_pte, ptl);
121         return ret;
122 }
123 
124 static pmd_t *mm_alloc_pmd(struct mm_struct *mm, unsigned long address)
125 {
126         pgd_t *pgd;
127         pud_t *pud;
128         pmd_t *pmd = NULL;
129 
130         pgd = pgd_offset(mm, address);
131         pud = pud_alloc(mm, pgd, address);
132         if (pud)
133                 /*
134                  * Note that we didn't run this because the pmd was
135                  * missing, the *pmd may be already established and in
136                  * turn it may also be a trans_huge_pmd.
137                  */
138                 pmd = pmd_alloc(mm, pud, address);
139         return pmd;
140 }
141 
142 static __always_inline ssize_t __mcopy_atomic(struct mm_struct *dst_mm,
143                                               unsigned long dst_start,
144                                               unsigned long src_start,
145                                               unsigned long len,
146                                               bool zeropage)
147 {
148         struct vm_area_struct *dst_vma;
149         ssize_t err;
150         pmd_t *dst_pmd;
151         unsigned long src_addr, dst_addr;
152         long copied;
153         struct page *page;
154 
155         /*
156          * Sanitize the command parameters:
157          */
158         BUG_ON(dst_start & ~PAGE_MASK);
159         BUG_ON(len & ~PAGE_MASK);
160 
161         /* Does the address range wrap, or is the span zero-sized? */
162         BUG_ON(src_start + len <= src_start);
163         BUG_ON(dst_start + len <= dst_start);
164 
165         src_addr = src_start;
166         dst_addr = dst_start;
167         copied = 0;
168         page = NULL;
169 retry:
170         down_read(&dst_mm->mmap_sem);
171 
172         /*
173          * Make sure the vma is not shared, that the dst range is
174          * both valid and fully within a single existing vma.
175          */
176         err = -EINVAL;
177         dst_vma = find_vma(dst_mm, dst_start);
178         if (!dst_vma || (dst_vma->vm_flags & VM_SHARED))
179                 goto out_unlock;
180         if (dst_start < dst_vma->vm_start ||
181             dst_start + len > dst_vma->vm_end)
182                 goto out_unlock;
183 
184         /*
185          * Be strict and only allow __mcopy_atomic on userfaultfd
186          * registered ranges to prevent userland errors going
187          * unnoticed. As far as the VM consistency is concerned, it
188          * would be perfectly safe to remove this check, but there's
189          * no useful usage for __mcopy_atomic ouside of userfaultfd
190          * registered ranges. This is after all why these are ioctls
191          * belonging to the userfaultfd and not syscalls.
192          */
193         if (!dst_vma->vm_userfaultfd_ctx.ctx)
194                 goto out_unlock;
195 
196         /*
197          * FIXME: only allow copying on anonymous vmas, tmpfs should
198          * be added.
199          */
200         if (dst_vma->vm_ops)
201                 goto out_unlock;
202 
203         /*
204          * Ensure the dst_vma has a anon_vma or this page
205          * would get a NULL anon_vma when moved in the
206          * dst_vma.
207          */
208         err = -ENOMEM;
209         if (unlikely(anon_vma_prepare(dst_vma)))
210                 goto out_unlock;
211 
212         while (src_addr < src_start + len) {
213                 pmd_t dst_pmdval;
214 
215                 BUG_ON(dst_addr >= dst_start + len);
216 
217                 dst_pmd = mm_alloc_pmd(dst_mm, dst_addr);
218                 if (unlikely(!dst_pmd)) {
219                         err = -ENOMEM;
220                         break;
221                 }
222 
223                 dst_pmdval = pmd_read_atomic(dst_pmd);
224                 /*
225                  * If the dst_pmd is mapped as THP don't
226                  * override it and just be strict.
227                  */
228                 if (unlikely(pmd_trans_huge(dst_pmdval))) {
229                         err = -EEXIST;
230                         break;
231                 }
232                 if (unlikely(pmd_none(dst_pmdval)) &&
233                     unlikely(__pte_alloc(dst_mm, dst_pmd, dst_addr))) {
234                         err = -ENOMEM;
235                         break;
236                 }
237                 /* If an huge pmd materialized from under us fail */
238                 if (unlikely(pmd_trans_huge(*dst_pmd))) {
239                         err = -EFAULT;
240                         break;
241                 }
242 
243                 BUG_ON(pmd_none(*dst_pmd));
244                 BUG_ON(pmd_trans_huge(*dst_pmd));
245 
246                 if (!zeropage)
247                         err = mcopy_atomic_pte(dst_mm, dst_pmd, dst_vma,
248                                                dst_addr, src_addr, &page);
249                 else
250                         err = mfill_zeropage_pte(dst_mm, dst_pmd, dst_vma,
251                                                  dst_addr);
252 
253                 cond_resched();
254 
255                 if (unlikely(err == -EFAULT)) {
256                         void *page_kaddr;
257 
258                         up_read(&dst_mm->mmap_sem);
259                         BUG_ON(!page);
260 
261                         page_kaddr = kmap(page);
262                         err = copy_from_user(page_kaddr,
263                                              (const void __user *) src_addr,
264                                              PAGE_SIZE);
265                         kunmap(page);
266                         if (unlikely(err)) {
267                                 err = -EFAULT;
268                                 goto out;
269                         }
270                         goto retry;
271                 } else
272                         BUG_ON(page);
273 
274                 if (!err) {
275                         dst_addr += PAGE_SIZE;
276                         src_addr += PAGE_SIZE;
277                         copied += PAGE_SIZE;
278 
279                         if (fatal_signal_pending(current))
280                                 err = -EINTR;
281                 }
282                 if (err)
283                         break;
284         }
285 
286 out_unlock:
287         up_read(&dst_mm->mmap_sem);
288 out:
289         if (page)
290                 put_page(page);
291         BUG_ON(copied < 0);
292         BUG_ON(err > 0);
293         BUG_ON(!copied && !err);
294         return copied ? copied : err;
295 }
296 
297 ssize_t mcopy_atomic(struct mm_struct *dst_mm, unsigned long dst_start,
298                      unsigned long src_start, unsigned long len)
299 {
300         return __mcopy_atomic(dst_mm, dst_start, src_start, len, false);
301 }
302 
303 ssize_t mfill_zeropage(struct mm_struct *dst_mm, unsigned long start,
304                        unsigned long len)
305 {
306         return __mcopy_atomic(dst_mm, start, 0, len, true);
307 }
308 

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