Loading...
Note: File does not exist in v3.1.
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
20static 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;
90out:
91 return ret;
92out_release_uncharge_unlock:
93 pte_unmap_unlock(dst_pte, ptl);
94 mem_cgroup_cancel_charge(page, memcg, false);
95out_release:
96 put_page(page);
97 goto out;
98}
99
100static 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;
119out_unlock:
120 pte_unmap_unlock(dst_pte, ptl);
121 return ret;
122}
123
124static 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
142static __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;
169retry:
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
286out_unlock:
287 up_read(&dst_mm->mmap_sem);
288out:
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
297ssize_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
303ssize_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}