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
mcopy_atomic_pte(struct mm_struct * dst_mm,pmd_t * dst_pmd,struct vm_area_struct * dst_vma,unsigned long dst_addr,unsigned long src_addr,struct page ** pagep)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
mfill_zeropage_pte(struct mm_struct * dst_mm,pmd_t * dst_pmd,struct vm_area_struct * dst_vma,unsigned long dst_addr)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
mm_alloc_pmd(struct mm_struct * mm,unsigned long address)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 */
__mcopy_atomic_hugetlb(struct mm_struct * dst_mm,struct vm_area_struct * dst_vma,unsigned long dst_start,unsigned long src_start,unsigned long len,bool zeropage)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
mfill_atomic_pte(struct mm_struct * dst_mm,pmd_t * dst_pmd,struct vm_area_struct * dst_vma,unsigned long dst_addr,unsigned long src_addr,struct page ** page,bool zeropage)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
__mcopy_atomic(struct mm_struct * dst_mm,unsigned long dst_start,unsigned long src_start,unsigned long len,bool zeropage,bool * mmap_changing)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
mcopy_atomic(struct mm_struct * dst_mm,unsigned long dst_start,unsigned long src_start,unsigned long len,bool * mmap_changing)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
mfill_zeropage(struct mm_struct * dst_mm,unsigned long start,unsigned long len,bool * mmap_changing)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
