1 // SPDX-License-Identifier: GPL-2.0
2 /*
3 * mm/mremap.c
4 *
5 * (C) Copyright 1996 Linus Torvalds
6 *
7 * Address space accounting code <alan@lxorguk.ukuu.org.uk>
8 * (C) Copyright 2002 Red Hat Inc, All Rights Reserved
9 */
10
11 #include <linux/mm.h>
12 #include <linux/hugetlb.h>
13 #include <linux/shm.h>
14 #include <linux/ksm.h>
15 #include <linux/mman.h>
16 #include <linux/swap.h>
17 #include <linux/capability.h>
18 #include <linux/fs.h>
19 #include <linux/swapops.h>
20 #include <linux/highmem.h>
21 #include <linux/security.h>
22 #include <linux/syscalls.h>
23 #include <linux/mmu_notifier.h>
24 #include <linux/uaccess.h>
25 #include <linux/mm-arch-hooks.h>
26 #include <linux/userfaultfd_k.h>
27
28 #include <asm/cacheflush.h>
29 #include <asm/tlbflush.h>
30
31 #include "internal.h"
32
get_old_pmd(struct mm_struct * mm,unsigned long addr)33 static pmd_t *get_old_pmd(struct mm_struct *mm, unsigned long addr)
34 {
35 pgd_t *pgd;
36 p4d_t *p4d;
37 pud_t *pud;
38 pmd_t *pmd;
39
40 pgd = pgd_offset(mm, addr);
41 if (pgd_none_or_clear_bad(pgd))
42 return NULL;
43
44 p4d = p4d_offset(pgd, addr);
45 if (p4d_none_or_clear_bad(p4d))
46 return NULL;
47
48 pud = pud_offset(p4d, addr);
49 if (pud_none_or_clear_bad(pud))
50 return NULL;
51
52 pmd = pmd_offset(pud, addr);
53 if (pmd_none(*pmd))
54 return NULL;
55
56 return pmd;
57 }
58
alloc_new_pmd(struct mm_struct * mm,struct vm_area_struct * vma,unsigned long addr)59 static pmd_t *alloc_new_pmd(struct mm_struct *mm, struct vm_area_struct *vma,
60 unsigned long addr)
61 {
62 pgd_t *pgd;
63 p4d_t *p4d;
64 pud_t *pud;
65 pmd_t *pmd;
66
67 pgd = pgd_offset(mm, addr);
68 p4d = p4d_alloc(mm, pgd, addr);
69 if (!p4d)
70 return NULL;
71 pud = pud_alloc(mm, p4d, addr);
72 if (!pud)
73 return NULL;
74
75 pmd = pmd_alloc(mm, pud, addr);
76 if (!pmd)
77 return NULL;
78
79 VM_BUG_ON(pmd_trans_huge(*pmd));
80
81 return pmd;
82 }
83
take_rmap_locks(struct vm_area_struct * vma)84 static void take_rmap_locks(struct vm_area_struct *vma)
85 {
86 if (vma->vm_file)
87 i_mmap_lock_write(vma->vm_file->f_mapping);
88 if (vma->anon_vma)
89 anon_vma_lock_write(vma->anon_vma);
90 }
91
drop_rmap_locks(struct vm_area_struct * vma)92 static void drop_rmap_locks(struct vm_area_struct *vma)
93 {
94 if (vma->anon_vma)
95 anon_vma_unlock_write(vma->anon_vma);
96 if (vma->vm_file)
97 i_mmap_unlock_write(vma->vm_file->f_mapping);
98 }
99
move_soft_dirty_pte(pte_t pte)100 static pte_t move_soft_dirty_pte(pte_t pte)
101 {
102 /*
103 * Set soft dirty bit so we can notice
104 * in userspace the ptes were moved.
105 */
106 #ifdef CONFIG_MEM_SOFT_DIRTY
107 if (pte_present(pte))
108 pte = pte_mksoft_dirty(pte);
109 else if (is_swap_pte(pte))
110 pte = pte_swp_mksoft_dirty(pte);
111 #endif
112 return pte;
113 }
114
move_ptes(struct vm_area_struct * vma,pmd_t * old_pmd,unsigned long old_addr,unsigned long old_end,struct vm_area_struct * new_vma,pmd_t * new_pmd,unsigned long new_addr,bool need_rmap_locks)115 static void move_ptes(struct vm_area_struct *vma, pmd_t *old_pmd,
116 unsigned long old_addr, unsigned long old_end,
117 struct vm_area_struct *new_vma, pmd_t *new_pmd,
118 unsigned long new_addr, bool need_rmap_locks)
119 {
120 struct mm_struct *mm = vma->vm_mm;
121 pte_t *old_pte, *new_pte, pte;
122 spinlock_t *old_ptl, *new_ptl;
123 bool force_flush = false;
124 unsigned long len = old_end - old_addr;
125
126 /*
127 * When need_rmap_locks is true, we take the i_mmap_rwsem and anon_vma
128 * locks to ensure that rmap will always observe either the old or the
129 * new ptes. This is the easiest way to avoid races with
130 * truncate_pagecache(), page migration, etc...
131 *
132 * When need_rmap_locks is false, we use other ways to avoid
133 * such races:
134 *
135 * - During exec() shift_arg_pages(), we use a specially tagged vma
136 * which rmap call sites look for using vma_is_temporary_stack().
137 *
138 * - During mremap(), new_vma is often known to be placed after vma
139 * in rmap traversal order. This ensures rmap will always observe
140 * either the old pte, or the new pte, or both (the page table locks
141 * serialize access to individual ptes, but only rmap traversal
142 * order guarantees that we won't miss both the old and new ptes).
143 */
144 if (need_rmap_locks)
145 take_rmap_locks(vma);
146
147 /*
148 * We don't have to worry about the ordering of src and dst
149 * pte locks because exclusive mmap_lock prevents deadlock.
150 */
151 old_pte = pte_offset_map_lock(mm, old_pmd, old_addr, &old_ptl);
152 new_pte = pte_offset_map(new_pmd, new_addr);
153 new_ptl = pte_lockptr(mm, new_pmd);
154 if (new_ptl != old_ptl)
155 spin_lock_nested(new_ptl, SINGLE_DEPTH_NESTING);
156 flush_tlb_batched_pending(vma->vm_mm);
157 arch_enter_lazy_mmu_mode();
158
159 for (; old_addr < old_end; old_pte++, old_addr += PAGE_SIZE,
160 new_pte++, new_addr += PAGE_SIZE) {
161 if (pte_none(*old_pte))
162 continue;
163
164 pte = ptep_get_and_clear(mm, old_addr, old_pte);
165 /*
166 * If we are remapping a valid PTE, make sure
167 * to flush TLB before we drop the PTL for the
168 * PTE.
169 *
170 * NOTE! Both old and new PTL matter: the old one
171 * for racing with page_mkclean(), the new one to
172 * make sure the physical page stays valid until
173 * the TLB entry for the old mapping has been
174 * flushed.
175 */
176 if (pte_present(pte))
177 force_flush = true;
178 pte = move_pte(pte, new_vma->vm_page_prot, old_addr, new_addr);
179 pte = move_soft_dirty_pte(pte);
180 set_pte_at(mm, new_addr, new_pte, pte);
181 }
182
183 arch_leave_lazy_mmu_mode();
184 if (force_flush)
185 flush_tlb_range(vma, old_end - len, old_end);
186 if (new_ptl != old_ptl)
187 spin_unlock(new_ptl);
188 pte_unmap(new_pte - 1);
189 pte_unmap_unlock(old_pte - 1, old_ptl);
190 if (need_rmap_locks)
191 drop_rmap_locks(vma);
192 }
193
194 #ifdef CONFIG_HAVE_MOVE_PMD
move_normal_pmd(struct vm_area_struct * vma,unsigned long old_addr,unsigned long new_addr,pmd_t * old_pmd,pmd_t * new_pmd)195 static bool move_normal_pmd(struct vm_area_struct *vma, unsigned long old_addr,
196 unsigned long new_addr, pmd_t *old_pmd, pmd_t *new_pmd)
197 {
198 spinlock_t *old_ptl, *new_ptl;
199 struct mm_struct *mm = vma->vm_mm;
200 pmd_t pmd;
201
202 /*
203 * The destination pmd shouldn't be established, free_pgtables()
204 * should have released it.
205 *
206 * However, there's a case during execve() where we use mremap
207 * to move the initial stack, and in that case the target area
208 * may overlap the source area (always moving down).
209 *
210 * If everything is PMD-aligned, that works fine, as moving
211 * each pmd down will clear the source pmd. But if we first
212 * have a few 4kB-only pages that get moved down, and then
213 * hit the "now the rest is PMD-aligned, let's do everything
214 * one pmd at a time", we will still have the old (now empty
215 * of any 4kB pages, but still there) PMD in the page table
216 * tree.
217 *
218 * Warn on it once - because we really should try to figure
219 * out how to do this better - but then say "I won't move
220 * this pmd".
221 *
222 * One alternative might be to just unmap the target pmd at
223 * this point, and verify that it really is empty. We'll see.
224 */
225 if (WARN_ON_ONCE(!pmd_none(*new_pmd)))
226 return false;
227
228 /*
229 * We don't have to worry about the ordering of src and dst
230 * ptlocks because exclusive mmap_lock prevents deadlock.
231 */
232 old_ptl = pmd_lock(vma->vm_mm, old_pmd);
233 new_ptl = pmd_lockptr(mm, new_pmd);
234 if (new_ptl != old_ptl)
235 spin_lock_nested(new_ptl, SINGLE_DEPTH_NESTING);
236
237 /* Clear the pmd */
238 pmd = *old_pmd;
239 pmd_clear(old_pmd);
240
241 VM_BUG_ON(!pmd_none(*new_pmd));
242
243 /* Set the new pmd */
244 set_pmd_at(mm, new_addr, new_pmd, pmd);
245 flush_tlb_range(vma, old_addr, old_addr + PMD_SIZE);
246 if (new_ptl != old_ptl)
247 spin_unlock(new_ptl);
248 spin_unlock(old_ptl);
249
250 return true;
251 }
252 #endif
253
move_page_tables(struct vm_area_struct * vma,unsigned long old_addr,struct vm_area_struct * new_vma,unsigned long new_addr,unsigned long len,bool need_rmap_locks)254 unsigned long move_page_tables(struct vm_area_struct *vma,
255 unsigned long old_addr, struct vm_area_struct *new_vma,
256 unsigned long new_addr, unsigned long len,
257 bool need_rmap_locks)
258 {
259 unsigned long extent, next, old_end;
260 struct mmu_notifier_range range;
261 pmd_t *old_pmd, *new_pmd;
262
263 if (!len)
264 return 0;
265
266 old_end = old_addr + len;
267 flush_cache_range(vma, old_addr, old_end);
268
269 mmu_notifier_range_init(&range, MMU_NOTIFY_UNMAP, 0, vma, vma->vm_mm,
270 old_addr, old_end);
271 mmu_notifier_invalidate_range_start(&range);
272
273 for (; old_addr < old_end; old_addr += extent, new_addr += extent) {
274 cond_resched();
275 next = (old_addr + PMD_SIZE) & PMD_MASK;
276 /* even if next overflowed, extent below will be ok */
277 extent = next - old_addr;
278 if (extent > old_end - old_addr)
279 extent = old_end - old_addr;
280 next = (new_addr + PMD_SIZE) & PMD_MASK;
281 if (extent > next - new_addr)
282 extent = next - new_addr;
283 old_pmd = get_old_pmd(vma->vm_mm, old_addr);
284 if (!old_pmd)
285 continue;
286 new_pmd = alloc_new_pmd(vma->vm_mm, vma, new_addr);
287 if (!new_pmd)
288 break;
289 if (is_swap_pmd(*old_pmd) || pmd_trans_huge(*old_pmd) || pmd_devmap(*old_pmd)) {
290 if (extent == HPAGE_PMD_SIZE) {
291 bool moved;
292 /* See comment in move_ptes() */
293 if (need_rmap_locks)
294 take_rmap_locks(vma);
295 moved = move_huge_pmd(vma, old_addr, new_addr,
296 old_pmd, new_pmd);
297 if (need_rmap_locks)
298 drop_rmap_locks(vma);
299 if (moved)
300 continue;
301 }
302 split_huge_pmd(vma, old_pmd, old_addr);
303 if (pmd_trans_unstable(old_pmd))
304 continue;
305 } else if (extent == PMD_SIZE) {
306 #ifdef CONFIG_HAVE_MOVE_PMD
307 /*
308 * If the extent is PMD-sized, try to speed the move by
309 * moving at the PMD level if possible.
310 */
311 bool moved;
312
313 take_rmap_locks(vma);
314 moved = move_normal_pmd(vma, old_addr, new_addr,
315 old_pmd, new_pmd);
316 drop_rmap_locks(vma);
317 if (moved)
318 continue;
319 #endif
320 }
321
322 if (pte_alloc(new_vma->vm_mm, new_pmd))
323 break;
324 move_ptes(vma, old_pmd, old_addr, old_addr + extent, new_vma,
325 new_pmd, new_addr, need_rmap_locks);
326 }
327
328 mmu_notifier_invalidate_range_end(&range);
329
330 return len + old_addr - old_end; /* how much done */
331 }
332
move_vma(struct vm_area_struct * vma,unsigned long old_addr,unsigned long old_len,unsigned long new_len,unsigned long new_addr,bool * locked,unsigned long flags,struct vm_userfaultfd_ctx * uf,struct list_head * uf_unmap)333 static unsigned long move_vma(struct vm_area_struct *vma,
334 unsigned long old_addr, unsigned long old_len,
335 unsigned long new_len, unsigned long new_addr,
336 bool *locked, unsigned long flags,
337 struct vm_userfaultfd_ctx *uf, struct list_head *uf_unmap)
338 {
339 struct mm_struct *mm = vma->vm_mm;
340 struct vm_area_struct *new_vma;
341 unsigned long vm_flags = vma->vm_flags;
342 unsigned long new_pgoff;
343 unsigned long moved_len;
344 unsigned long excess = 0;
345 unsigned long hiwater_vm;
346 int split = 0;
347 int err;
348 bool need_rmap_locks;
349
350 /*
351 * We'd prefer to avoid failure later on in do_munmap:
352 * which may split one vma into three before unmapping.
353 */
354 if (mm->map_count >= sysctl_max_map_count - 3)
355 return -ENOMEM;
356
357 /*
358 * Advise KSM to break any KSM pages in the area to be moved:
359 * it would be confusing if they were to turn up at the new
360 * location, where they happen to coincide with different KSM
361 * pages recently unmapped. But leave vma->vm_flags as it was,
362 * so KSM can come around to merge on vma and new_vma afterwards.
363 */
364 err = ksm_madvise(vma, old_addr, old_addr + old_len,
365 MADV_UNMERGEABLE, &vm_flags);
366 if (err)
367 return err;
368
369 new_pgoff = vma->vm_pgoff + ((old_addr - vma->vm_start) >> PAGE_SHIFT);
370 new_vma = copy_vma(&vma, new_addr, new_len, new_pgoff,
371 &need_rmap_locks);
372 if (!new_vma)
373 return -ENOMEM;
374
375 moved_len = move_page_tables(vma, old_addr, new_vma, new_addr, old_len,
376 need_rmap_locks);
377 if (moved_len < old_len) {
378 err = -ENOMEM;
379 } else if (vma->vm_ops && vma->vm_ops->mremap) {
380 err = vma->vm_ops->mremap(new_vma);
381 }
382
383 if (unlikely(err)) {
384 /*
385 * On error, move entries back from new area to old,
386 * which will succeed since page tables still there,
387 * and then proceed to unmap new area instead of old.
388 */
389 move_page_tables(new_vma, new_addr, vma, old_addr, moved_len,
390 true);
391 vma = new_vma;
392 old_len = new_len;
393 old_addr = new_addr;
394 new_addr = err;
395 } else {
396 mremap_userfaultfd_prep(new_vma, uf);
397 arch_remap(mm, old_addr, old_addr + old_len,
398 new_addr, new_addr + new_len);
399 }
400
401 /* Conceal VM_ACCOUNT so old reservation is not undone */
402 if (vm_flags & VM_ACCOUNT) {
403 vma->vm_flags &= ~VM_ACCOUNT;
404 excess = vma->vm_end - vma->vm_start - old_len;
405 if (old_addr > vma->vm_start &&
406 old_addr + old_len < vma->vm_end)
407 split = 1;
408 }
409
410 /*
411 * If we failed to move page tables we still do total_vm increment
412 * since do_munmap() will decrement it by old_len == new_len.
413 *
414 * Since total_vm is about to be raised artificially high for a
415 * moment, we need to restore high watermark afterwards: if stats
416 * are taken meanwhile, total_vm and hiwater_vm appear too high.
417 * If this were a serious issue, we'd add a flag to do_munmap().
418 */
419 hiwater_vm = mm->hiwater_vm;
420 vm_stat_account(mm, vma->vm_flags, new_len >> PAGE_SHIFT);
421
422 /* Tell pfnmap has moved from this vma */
423 if (unlikely(vma->vm_flags & VM_PFNMAP))
424 untrack_pfn_moved(vma);
425
426 if (unlikely(!err && (flags & MREMAP_DONTUNMAP))) {
427 if (vm_flags & VM_ACCOUNT) {
428 /* Always put back VM_ACCOUNT since we won't unmap */
429 vma->vm_flags |= VM_ACCOUNT;
430
431 vm_acct_memory(new_len >> PAGE_SHIFT);
432 }
433
434 /*
435 * VMAs can actually be merged back together in copy_vma
436 * calling merge_vma. This can happen with anonymous vmas
437 * which have not yet been faulted, so if we were to consider
438 * this VMA split we'll end up adding VM_ACCOUNT on the
439 * next VMA, which is completely unrelated if this VMA
440 * was re-merged.
441 */
442 if (split && new_vma == vma)
443 split = 0;
444
445 /* We always clear VM_LOCKED[ONFAULT] on the old vma */
446 vma->vm_flags &= VM_LOCKED_CLEAR_MASK;
447
448 /* Because we won't unmap we don't need to touch locked_vm */
449 goto out;
450 }
451
452 if (do_munmap(mm, old_addr, old_len, uf_unmap) < 0) {
453 /* OOM: unable to split vma, just get accounts right */
454 vm_unacct_memory(excess >> PAGE_SHIFT);
455 excess = 0;
456 }
457
458 if (vm_flags & VM_LOCKED) {
459 mm->locked_vm += new_len >> PAGE_SHIFT;
460 *locked = true;
461 }
462 out:
463 mm->hiwater_vm = hiwater_vm;
464
465 /* Restore VM_ACCOUNT if one or two pieces of vma left */
466 if (excess) {
467 vma->vm_flags |= VM_ACCOUNT;
468 if (split)
469 vma->vm_next->vm_flags |= VM_ACCOUNT;
470 }
471
472 return new_addr;
473 }
474
vma_to_resize(unsigned long addr,unsigned long old_len,unsigned long new_len,unsigned long flags,unsigned long * p)475 static struct vm_area_struct *vma_to_resize(unsigned long addr,
476 unsigned long old_len, unsigned long new_len, unsigned long flags,
477 unsigned long *p)
478 {
479 struct mm_struct *mm = current->mm;
480 struct vm_area_struct *vma = find_vma(mm, addr);
481 unsigned long pgoff;
482
483 if (!vma || vma->vm_start > addr)
484 return ERR_PTR(-EFAULT);
485
486 /*
487 * !old_len is a special case where an attempt is made to 'duplicate'
488 * a mapping. This makes no sense for private mappings as it will
489 * instead create a fresh/new mapping unrelated to the original. This
490 * is contrary to the basic idea of mremap which creates new mappings
491 * based on the original. There are no known use cases for this
492 * behavior. As a result, fail such attempts.
493 */
494 if (!old_len && !(vma->vm_flags & (VM_SHARED | VM_MAYSHARE))) {
495 pr_warn_once("%s (%d): attempted to duplicate a private mapping with mremap. This is not supported.\n", current->comm, current->pid);
496 return ERR_PTR(-EINVAL);
497 }
498
499 if (flags & MREMAP_DONTUNMAP && (!vma_is_anonymous(vma) ||
500 vma->vm_flags & VM_SHARED))
501 return ERR_PTR(-EINVAL);
502
503 if (is_vm_hugetlb_page(vma))
504 return ERR_PTR(-EINVAL);
505
506 /* We can't remap across vm area boundaries */
507 if (old_len > vma->vm_end - addr)
508 return ERR_PTR(-EFAULT);
509
510 if (new_len == old_len)
511 return vma;
512
513 /* Need to be careful about a growing mapping */
514 pgoff = (addr - vma->vm_start) >> PAGE_SHIFT;
515 pgoff += vma->vm_pgoff;
516 if (pgoff + (new_len >> PAGE_SHIFT) < pgoff)
517 return ERR_PTR(-EINVAL);
518
519 if (vma->vm_flags & (VM_DONTEXPAND | VM_PFNMAP))
520 return ERR_PTR(-EFAULT);
521
522 if (vma->vm_flags & VM_LOCKED) {
523 unsigned long locked, lock_limit;
524 locked = mm->locked_vm << PAGE_SHIFT;
525 lock_limit = rlimit(RLIMIT_MEMLOCK);
526 locked += new_len - old_len;
527 if (locked > lock_limit && !capable(CAP_IPC_LOCK))
528 return ERR_PTR(-EAGAIN);
529 }
530
531 if (!may_expand_vm(mm, vma->vm_flags,
532 (new_len - old_len) >> PAGE_SHIFT))
533 return ERR_PTR(-ENOMEM);
534
535 if (vma->vm_flags & VM_ACCOUNT) {
536 unsigned long charged = (new_len - old_len) >> PAGE_SHIFT;
537 if (security_vm_enough_memory_mm(mm, charged))
538 return ERR_PTR(-ENOMEM);
539 *p = charged;
540 }
541
542 return vma;
543 }
544
mremap_to(unsigned long addr,unsigned long old_len,unsigned long new_addr,unsigned long new_len,bool * locked,unsigned long flags,struct vm_userfaultfd_ctx * uf,struct list_head * uf_unmap_early,struct list_head * uf_unmap)545 static unsigned long mremap_to(unsigned long addr, unsigned long old_len,
546 unsigned long new_addr, unsigned long new_len, bool *locked,
547 unsigned long flags, struct vm_userfaultfd_ctx *uf,
548 struct list_head *uf_unmap_early,
549 struct list_head *uf_unmap)
550 {
551 struct mm_struct *mm = current->mm;
552 struct vm_area_struct *vma;
553 unsigned long ret = -EINVAL;
554 unsigned long charged = 0;
555 unsigned long map_flags = 0;
556
557 if (offset_in_page(new_addr))
558 goto out;
559
560 if (new_len > TASK_SIZE || new_addr > TASK_SIZE - new_len)
561 goto out;
562
563 /* Ensure the old/new locations do not overlap */
564 if (addr + old_len > new_addr && new_addr + new_len > addr)
565 goto out;
566
567 /*
568 * move_vma() need us to stay 4 maps below the threshold, otherwise
569 * it will bail out at the very beginning.
570 * That is a problem if we have already unmaped the regions here
571 * (new_addr, and old_addr), because userspace will not know the
572 * state of the vma's after it gets -ENOMEM.
573 * So, to avoid such scenario we can pre-compute if the whole
574 * operation has high chances to success map-wise.
575 * Worst-scenario case is when both vma's (new_addr and old_addr) get
576 * split in 3 before unmaping it.
577 * That means 2 more maps (1 for each) to the ones we already hold.
578 * Check whether current map count plus 2 still leads us to 4 maps below
579 * the threshold, otherwise return -ENOMEM here to be more safe.
580 */
581 if ((mm->map_count + 2) >= sysctl_max_map_count - 3)
582 return -ENOMEM;
583
584 if (flags & MREMAP_FIXED) {
585 ret = do_munmap(mm, new_addr, new_len, uf_unmap_early);
586 if (ret)
587 goto out;
588 }
589
590 if (old_len >= new_len) {
591 ret = do_munmap(mm, addr+new_len, old_len - new_len, uf_unmap);
592 if (ret && old_len != new_len)
593 goto out;
594 old_len = new_len;
595 }
596
597 vma = vma_to_resize(addr, old_len, new_len, flags, &charged);
598 if (IS_ERR(vma)) {
599 ret = PTR_ERR(vma);
600 goto out;
601 }
602
603 /* MREMAP_DONTUNMAP expands by old_len since old_len == new_len */
604 if (flags & MREMAP_DONTUNMAP &&
605 !may_expand_vm(mm, vma->vm_flags, old_len >> PAGE_SHIFT)) {
606 ret = -ENOMEM;
607 goto out;
608 }
609
610 if (flags & MREMAP_FIXED)
611 map_flags |= MAP_FIXED;
612
613 if (vma->vm_flags & VM_MAYSHARE)
614 map_flags |= MAP_SHARED;
615
616 ret = get_unmapped_area(vma->vm_file, new_addr, new_len, vma->vm_pgoff +
617 ((addr - vma->vm_start) >> PAGE_SHIFT),
618 map_flags);
619 if (IS_ERR_VALUE(ret))
620 goto out1;
621
622 /* We got a new mapping */
623 if (!(flags & MREMAP_FIXED))
624 new_addr = ret;
625
626 ret = move_vma(vma, addr, old_len, new_len, new_addr, locked, flags, uf,
627 uf_unmap);
628
629 if (!(offset_in_page(ret)))
630 goto out;
631
632 out1:
633 vm_unacct_memory(charged);
634
635 out:
636 return ret;
637 }
638
vma_expandable(struct vm_area_struct * vma,unsigned long delta)639 static int vma_expandable(struct vm_area_struct *vma, unsigned long delta)
640 {
641 unsigned long end = vma->vm_end + delta;
642 if (end < vma->vm_end) /* overflow */
643 return 0;
644 if (vma->vm_next && vma->vm_next->vm_start < end) /* intersection */
645 return 0;
646 if (get_unmapped_area(NULL, vma->vm_start, end - vma->vm_start,
647 0, MAP_FIXED) & ~PAGE_MASK)
648 return 0;
649 return 1;
650 }
651
652 /*
653 * Expand (or shrink) an existing mapping, potentially moving it at the
654 * same time (controlled by the MREMAP_MAYMOVE flag and available VM space)
655 *
656 * MREMAP_FIXED option added 5-Dec-1999 by Benjamin LaHaise
657 * This option implies MREMAP_MAYMOVE.
658 */
SYSCALL_DEFINE5(mremap,unsigned long,addr,unsigned long,old_len,unsigned long,new_len,unsigned long,flags,unsigned long,new_addr)659 SYSCALL_DEFINE5(mremap, unsigned long, addr, unsigned long, old_len,
660 unsigned long, new_len, unsigned long, flags,
661 unsigned long, new_addr)
662 {
663 struct mm_struct *mm = current->mm;
664 struct vm_area_struct *vma;
665 unsigned long ret = -EINVAL;
666 unsigned long charged = 0;
667 bool locked = false;
668 bool downgraded = false;
669 struct vm_userfaultfd_ctx uf = NULL_VM_UFFD_CTX;
670 LIST_HEAD(uf_unmap_early);
671 LIST_HEAD(uf_unmap);
672
673 /*
674 * There is a deliberate asymmetry here: we strip the pointer tag
675 * from the old address but leave the new address alone. This is
676 * for consistency with mmap(), where we prevent the creation of
677 * aliasing mappings in userspace by leaving the tag bits of the
678 * mapping address intact. A non-zero tag will cause the subsequent
679 * range checks to reject the address as invalid.
680 *
681 * See Documentation/arm64/tagged-address-abi.rst for more information.
682 */
683 addr = untagged_addr(addr);
684
685 if (flags & ~(MREMAP_FIXED | MREMAP_MAYMOVE | MREMAP_DONTUNMAP))
686 return ret;
687
688 if (flags & MREMAP_FIXED && !(flags & MREMAP_MAYMOVE))
689 return ret;
690
691 /*
692 * MREMAP_DONTUNMAP is always a move and it does not allow resizing
693 * in the process.
694 */
695 if (flags & MREMAP_DONTUNMAP &&
696 (!(flags & MREMAP_MAYMOVE) || old_len != new_len))
697 return ret;
698
699
700 if (offset_in_page(addr))
701 return ret;
702
703 old_len = PAGE_ALIGN(old_len);
704 new_len = PAGE_ALIGN(new_len);
705
706 /*
707 * We allow a zero old-len as a special case
708 * for DOS-emu "duplicate shm area" thing. But
709 * a zero new-len is nonsensical.
710 */
711 if (!new_len)
712 return ret;
713
714 if (mmap_write_lock_killable(current->mm))
715 return -EINTR;
716
717 if (flags & (MREMAP_FIXED | MREMAP_DONTUNMAP)) {
718 ret = mremap_to(addr, old_len, new_addr, new_len,
719 &locked, flags, &uf, &uf_unmap_early,
720 &uf_unmap);
721 goto out;
722 }
723
724 /*
725 * Always allow a shrinking remap: that just unmaps
726 * the unnecessary pages..
727 * __do_munmap does all the needed commit accounting, and
728 * downgrades mmap_lock to read if so directed.
729 */
730 if (old_len >= new_len) {
731 int retval;
732
733 retval = __do_munmap(mm, addr+new_len, old_len - new_len,
734 &uf_unmap, true);
735 if (retval < 0 && old_len != new_len) {
736 ret = retval;
737 goto out;
738 /* Returning 1 indicates mmap_lock is downgraded to read. */
739 } else if (retval == 1)
740 downgraded = true;
741 ret = addr;
742 goto out;
743 }
744
745 /*
746 * Ok, we need to grow..
747 */
748 vma = vma_to_resize(addr, old_len, new_len, flags, &charged);
749 if (IS_ERR(vma)) {
750 ret = PTR_ERR(vma);
751 goto out;
752 }
753
754 /* old_len exactly to the end of the area..
755 */
756 if (old_len == vma->vm_end - addr) {
757 /* can we just expand the current mapping? */
758 if (vma_expandable(vma, new_len - old_len)) {
759 int pages = (new_len - old_len) >> PAGE_SHIFT;
760
761 if (vma_adjust(vma, vma->vm_start, addr + new_len,
762 vma->vm_pgoff, NULL)) {
763 ret = -ENOMEM;
764 goto out;
765 }
766
767 vm_stat_account(mm, vma->vm_flags, pages);
768 if (vma->vm_flags & VM_LOCKED) {
769 mm->locked_vm += pages;
770 locked = true;
771 new_addr = addr;
772 }
773 ret = addr;
774 goto out;
775 }
776 }
777
778 /*
779 * We weren't able to just expand or shrink the area,
780 * we need to create a new one and move it..
781 */
782 ret = -ENOMEM;
783 if (flags & MREMAP_MAYMOVE) {
784 unsigned long map_flags = 0;
785 if (vma->vm_flags & VM_MAYSHARE)
786 map_flags |= MAP_SHARED;
787
788 new_addr = get_unmapped_area(vma->vm_file, 0, new_len,
789 vma->vm_pgoff +
790 ((addr - vma->vm_start) >> PAGE_SHIFT),
791 map_flags);
792 if (IS_ERR_VALUE(new_addr)) {
793 ret = new_addr;
794 goto out;
795 }
796
797 ret = move_vma(vma, addr, old_len, new_len, new_addr,
798 &locked, flags, &uf, &uf_unmap);
799 }
800 out:
801 if (offset_in_page(ret)) {
802 vm_unacct_memory(charged);
803 locked = false;
804 }
805 if (downgraded)
806 mmap_read_unlock(current->mm);
807 else
808 mmap_write_unlock(current->mm);
809 if (locked && new_len > old_len)
810 mm_populate(new_addr + old_len, new_len - old_len);
811 userfaultfd_unmap_complete(mm, &uf_unmap_early);
812 mremap_userfaultfd_complete(&uf, addr, ret, old_len);
813 userfaultfd_unmap_complete(mm, &uf_unmap);
814 return ret;
815 }
816