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))
  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);
  80         mem_cgroup_commit_charge(page, memcg, 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);
  95 out_release:
  96         page_cache_release(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_vma, dst_pmd,
 234                                          dst_addr))) {
 235                         err = -ENOMEM;
 236                         break;
 237                 }
 238                 /* If an huge pmd materialized from under us fail */
 239                 if (unlikely(pmd_trans_huge(*dst_pmd))) {
 240                         err = -EFAULT;
 241                         break;
 242                 }
 243
 244                 BUG_ON(pmd_none(*dst_pmd));
 245                 BUG_ON(pmd_trans_huge(*dst_pmd));
 246
 247                 if (!zeropage)
 248                         err = mcopy_atomic_pte(dst_mm, dst_pmd, dst_vma,
 249                                                dst_addr, src_addr, &page);
 250                 else
 251                         err = mfill_zeropage_pte(dst_mm, dst_pmd, dst_vma,
 252                                                  dst_addr);
 253
 254                 cond_resched();
 255
 256                 if (unlikely(err == -EFAULT)) {
 257                         void *page_kaddr;
 258
 259                         up_read(&dst_mm->mmap_sem);
 260                         BUG_ON(!page);
 261
 262                         page_kaddr = kmap(page);
 263                         err = copy_from_user(page_kaddr,
 264                                              (const void __user *) src_addr,
 265                                              PAGE_SIZE);
 266                         kunmap(page);
 267                         if (unlikely(err)) {
 268                                 err = -EFAULT;
 269                                 goto out;
 270                         }
 271                         goto retry;
 272                 } else
 273                         BUG_ON(page);
 274
 275                 if (!err) {
 276                         dst_addr += PAGE_SIZE;
 277                         src_addr += PAGE_SIZE;
 278                         copied += PAGE_SIZE;
 279
 280                         if (fatal_signal_pending(current))
 281                                 err = -EINTR;
 282                 }
 283                 if (err)
 284                         break;
 285         }
 286
 287 out_unlock:
 288         up_read(&dst_mm->mmap_sem);
 289 out:
 290         if (page)
 291                 page_cache_release(page);
 292         BUG_ON(copied < 0);
 293         BUG_ON(err > 0);
 294         BUG_ON(!copied && !err);
 295         return copied ? copied : err;
 296 }
 297
 298 ssize_t mcopy_atomic(struct mm_struct *dst_mm, unsigned long dst_start,
 299                      unsigned long src_start, unsigned long len)
 300 {
 301         return __mcopy_atomic(dst_mm, dst_start, src_start, len, false);
 302 }
 303
 304 ssize_t mfill_zeropage(struct mm_struct *dst_mm, unsigned long start,
 305                        unsigned long len)
 306 {
 307         return __mcopy_atomic(dst_mm, start, 0, len, true);
 308 }