1 /*
2 * mm/mremap.c
3 *
4 * (C) Copyright 1996 Linus Torvalds
5 *
6 * Address space accounting code <alan@lxorguk.ukuu.org.uk>
7 * (C) Copyright 2002 Red Hat Inc, All Rights Reserved
8 */
9
10 #include <linux/mm.h>
11 #include <linux/hugetlb.h>
12 #include <linux/shm.h>
13 #include <linux/ksm.h>
14 #include <linux/mman.h>
15 #include <linux/swap.h>
16 #include <linux/capability.h>
17 #include <linux/fs.h>
18 #include <linux/swapops.h>
19 #include <linux/highmem.h>
20 #include <linux/security.h>
21 #include <linux/syscalls.h>
22 #include <linux/mmu_notifier.h>
23 #include <linux/sched/sysctl.h>
24 #include <linux/uaccess.h>
25
26 #include <asm/cacheflush.h>
27 #include <asm/tlbflush.h>
28
29 #include "internal.h"
30
get_old_pmd(struct mm_struct * mm,unsigned long addr)31 static pmd_t *get_old_pmd(struct mm_struct *mm, unsigned long addr)
32 {
33 pgd_t *pgd;
34 pud_t *pud;
35 pmd_t *pmd;
36
37 pgd = pgd_offset(mm, addr);
38 if (pgd_none_or_clear_bad(pgd))
39 return NULL;
40
41 pud = pud_offset(pgd, addr);
42 if (pud_none_or_clear_bad(pud))
43 return NULL;
44
45 pmd = pmd_offset(pud, addr);
46 if (pmd_none(*pmd))
47 return NULL;
48
49 return pmd;
50 }
51
alloc_new_pmd(struct mm_struct * mm,struct vm_area_struct * vma,unsigned long addr)52 static pmd_t *alloc_new_pmd(struct mm_struct *mm, struct vm_area_struct *vma,
53 unsigned long addr)
54 {
55 pgd_t *pgd;
56 pud_t *pud;
57 pmd_t *pmd;
58
59 pgd = pgd_offset(mm, addr);
60 pud = pud_alloc(mm, pgd, addr);
61 if (!pud)
62 return NULL;
63
64 pmd = pmd_alloc(mm, pud, addr);
65 if (!pmd)
66 return NULL;
67
68 VM_BUG_ON(pmd_trans_huge(*pmd));
69
70 return pmd;
71 }
72
move_soft_dirty_pte(pte_t pte)73 static pte_t move_soft_dirty_pte(pte_t pte)
74 {
75 /*
76 * Set soft dirty bit so we can notice
77 * in userspace the ptes were moved.
78 */
79 #ifdef CONFIG_MEM_SOFT_DIRTY
80 if (pte_present(pte))
81 pte = pte_mksoft_dirty(pte);
82 else if (is_swap_pte(pte))
83 pte = pte_swp_mksoft_dirty(pte);
84 else if (pte_file(pte))
85 pte = pte_file_mksoft_dirty(pte);
86 #endif
87 return pte;
88 }
89
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)90 static void move_ptes(struct vm_area_struct *vma, pmd_t *old_pmd,
91 unsigned long old_addr, unsigned long old_end,
92 struct vm_area_struct *new_vma, pmd_t *new_pmd,
93 unsigned long new_addr, bool need_rmap_locks)
94 {
95 struct address_space *mapping = NULL;
96 struct anon_vma *anon_vma = NULL;
97 struct mm_struct *mm = vma->vm_mm;
98 pte_t *old_pte, *new_pte, pte;
99 spinlock_t *old_ptl, *new_ptl;
100
101 /*
102 * When need_rmap_locks is true, we take the i_mmap_mutex and anon_vma
103 * locks to ensure that rmap will always observe either the old or the
104 * new ptes. This is the easiest way to avoid races with
105 * truncate_pagecache(), page migration, etc...
106 *
107 * When need_rmap_locks is false, we use other ways to avoid
108 * such races:
109 *
110 * - During exec() shift_arg_pages(), we use a specially tagged vma
111 * which rmap call sites look for using is_vma_temporary_stack().
112 *
113 * - During mremap(), new_vma is often known to be placed after vma
114 * in rmap traversal order. This ensures rmap will always observe
115 * either the old pte, or the new pte, or both (the page table locks
116 * serialize access to individual ptes, but only rmap traversal
117 * order guarantees that we won't miss both the old and new ptes).
118 */
119 if (need_rmap_locks) {
120 if (vma->vm_file) {
121 mapping = vma->vm_file->f_mapping;
122 mutex_lock(&mapping->i_mmap_mutex);
123 }
124 if (vma->anon_vma) {
125 anon_vma = vma->anon_vma;
126 anon_vma_lock_write(anon_vma);
127 }
128 }
129
130 /*
131 * We don't have to worry about the ordering of src and dst
132 * pte locks because exclusive mmap_sem prevents deadlock.
133 */
134 old_pte = pte_offset_map_lock(mm, old_pmd, old_addr, &old_ptl);
135 new_pte = pte_offset_map(new_pmd, new_addr);
136 new_ptl = pte_lockptr(mm, new_pmd);
137 if (new_ptl != old_ptl)
138 spin_lock_nested(new_ptl, SINGLE_DEPTH_NESTING);
139 arch_enter_lazy_mmu_mode();
140
141 for (; old_addr < old_end; old_pte++, old_addr += PAGE_SIZE,
142 new_pte++, new_addr += PAGE_SIZE) {
143 if (pte_none(*old_pte))
144 continue;
145 pte = ptep_get_and_clear(mm, old_addr, old_pte);
146 pte = move_pte(pte, new_vma->vm_page_prot, old_addr, new_addr);
147 pte = move_soft_dirty_pte(pte);
148 set_pte_at(mm, new_addr, new_pte, pte);
149 }
150
151 arch_leave_lazy_mmu_mode();
152 if (new_ptl != old_ptl)
153 spin_unlock(new_ptl);
154 pte_unmap(new_pte - 1);
155 pte_unmap_unlock(old_pte - 1, old_ptl);
156 if (anon_vma)
157 anon_vma_unlock_write(anon_vma);
158 if (mapping)
159 mutex_unlock(&mapping->i_mmap_mutex);
160 }
161
162 #define LATENCY_LIMIT (64 * PAGE_SIZE)
163
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)164 unsigned long move_page_tables(struct vm_area_struct *vma,
165 unsigned long old_addr, struct vm_area_struct *new_vma,
166 unsigned long new_addr, unsigned long len,
167 bool need_rmap_locks)
168 {
169 unsigned long extent, next, old_end;
170 pmd_t *old_pmd, *new_pmd;
171 bool need_flush = false;
172 unsigned long mmun_start; /* For mmu_notifiers */
173 unsigned long mmun_end; /* For mmu_notifiers */
174
175 old_end = old_addr + len;
176 flush_cache_range(vma, old_addr, old_end);
177
178 mmun_start = old_addr;
179 mmun_end = old_end;
180 mmu_notifier_invalidate_range_start(vma->vm_mm, mmun_start, mmun_end);
181
182 for (; old_addr < old_end; old_addr += extent, new_addr += extent) {
183 cond_resched();
184 next = (old_addr + PMD_SIZE) & PMD_MASK;
185 /* even if next overflowed, extent below will be ok */
186 extent = next - old_addr;
187 if (extent > old_end - old_addr)
188 extent = old_end - old_addr;
189 old_pmd = get_old_pmd(vma->vm_mm, old_addr);
190 if (!old_pmd)
191 continue;
192 new_pmd = alloc_new_pmd(vma->vm_mm, vma, new_addr);
193 if (!new_pmd)
194 break;
195 if (pmd_trans_huge(*old_pmd)) {
196 int err = 0;
197 if (extent == HPAGE_PMD_SIZE) {
198 VM_BUG_ON_VMA(vma->vm_file || !vma->anon_vma,
199 vma);
200 /* See comment in move_ptes() */
201 if (need_rmap_locks)
202 anon_vma_lock_write(vma->anon_vma);
203 err = move_huge_pmd(vma, new_vma, old_addr,
204 new_addr, old_end,
205 old_pmd, new_pmd);
206 if (need_rmap_locks)
207 anon_vma_unlock_write(vma->anon_vma);
208 }
209 if (err > 0) {
210 need_flush = true;
211 continue;
212 } else if (!err) {
213 split_huge_page_pmd(vma, old_addr, old_pmd);
214 }
215 VM_BUG_ON(pmd_trans_huge(*old_pmd));
216 }
217 if (pmd_none(*new_pmd) && __pte_alloc(new_vma->vm_mm, new_vma,
218 new_pmd, new_addr))
219 break;
220 next = (new_addr + PMD_SIZE) & PMD_MASK;
221 if (extent > next - new_addr)
222 extent = next - new_addr;
223 if (extent > LATENCY_LIMIT)
224 extent = LATENCY_LIMIT;
225 move_ptes(vma, old_pmd, old_addr, old_addr + extent,
226 new_vma, new_pmd, new_addr, need_rmap_locks);
227 need_flush = true;
228 }
229 if (likely(need_flush))
230 flush_tlb_range(vma, old_end-len, old_addr);
231
232 mmu_notifier_invalidate_range_end(vma->vm_mm, mmun_start, mmun_end);
233
234 return len + old_addr - old_end; /* how much done */
235 }
236
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)237 static unsigned long move_vma(struct vm_area_struct *vma,
238 unsigned long old_addr, unsigned long old_len,
239 unsigned long new_len, unsigned long new_addr, bool *locked)
240 {
241 struct mm_struct *mm = vma->vm_mm;
242 struct vm_area_struct *new_vma;
243 unsigned long vm_flags = vma->vm_flags;
244 unsigned long new_pgoff;
245 unsigned long moved_len;
246 unsigned long excess = 0;
247 unsigned long hiwater_vm;
248 int split = 0;
249 int err;
250 bool need_rmap_locks;
251
252 /*
253 * We'd prefer to avoid failure later on in do_munmap:
254 * which may split one vma into three before unmapping.
255 */
256 if (mm->map_count >= sysctl_max_map_count - 3)
257 return -ENOMEM;
258
259 /*
260 * Advise KSM to break any KSM pages in the area to be moved:
261 * it would be confusing if they were to turn up at the new
262 * location, where they happen to coincide with different KSM
263 * pages recently unmapped. But leave vma->vm_flags as it was,
264 * so KSM can come around to merge on vma and new_vma afterwards.
265 */
266 err = ksm_madvise(vma, old_addr, old_addr + old_len,
267 MADV_UNMERGEABLE, &vm_flags);
268 if (err)
269 return err;
270
271 new_pgoff = vma->vm_pgoff + ((old_addr - vma->vm_start) >> PAGE_SHIFT);
272 new_vma = copy_vma(&vma, new_addr, new_len, new_pgoff,
273 &need_rmap_locks);
274 if (!new_vma)
275 return -ENOMEM;
276
277 moved_len = move_page_tables(vma, old_addr, new_vma, new_addr, old_len,
278 need_rmap_locks);
279 if (moved_len < old_len) {
280 /*
281 * On error, move entries back from new area to old,
282 * which will succeed since page tables still there,
283 * and then proceed to unmap new area instead of old.
284 */
285 move_page_tables(new_vma, new_addr, vma, old_addr, moved_len,
286 true);
287 vma = new_vma;
288 old_len = new_len;
289 old_addr = new_addr;
290 new_addr = -ENOMEM;
291 }
292
293 /* Conceal VM_ACCOUNT so old reservation is not undone */
294 if (vm_flags & VM_ACCOUNT) {
295 vma->vm_flags &= ~VM_ACCOUNT;
296 excess = vma->vm_end - vma->vm_start - old_len;
297 if (old_addr > vma->vm_start &&
298 old_addr + old_len < vma->vm_end)
299 split = 1;
300 }
301
302 /*
303 * If we failed to move page tables we still do total_vm increment
304 * since do_munmap() will decrement it by old_len == new_len.
305 *
306 * Since total_vm is about to be raised artificially high for a
307 * moment, we need to restore high watermark afterwards: if stats
308 * are taken meanwhile, total_vm and hiwater_vm appear too high.
309 * If this were a serious issue, we'd add a flag to do_munmap().
310 */
311 hiwater_vm = mm->hiwater_vm;
312 vm_stat_account(mm, vma->vm_flags, vma->vm_file, new_len>>PAGE_SHIFT);
313
314 if (do_munmap(mm, old_addr, old_len) < 0) {
315 /* OOM: unable to split vma, just get accounts right */
316 vm_unacct_memory(excess >> PAGE_SHIFT);
317 excess = 0;
318 }
319 mm->hiwater_vm = hiwater_vm;
320
321 /* Restore VM_ACCOUNT if one or two pieces of vma left */
322 if (excess) {
323 vma->vm_flags |= VM_ACCOUNT;
324 if (split)
325 vma->vm_next->vm_flags |= VM_ACCOUNT;
326 }
327
328 if (vm_flags & VM_LOCKED) {
329 mm->locked_vm += new_len >> PAGE_SHIFT;
330 *locked = true;
331 }
332
333 return new_addr;
334 }
335
vma_to_resize(unsigned long addr,unsigned long old_len,unsigned long new_len,unsigned long * p)336 static struct vm_area_struct *vma_to_resize(unsigned long addr,
337 unsigned long old_len, unsigned long new_len, unsigned long *p)
338 {
339 struct mm_struct *mm = current->mm;
340 struct vm_area_struct *vma = find_vma(mm, addr);
341
342 if (!vma || vma->vm_start > addr)
343 goto Efault;
344
345 if (is_vm_hugetlb_page(vma))
346 goto Einval;
347
348 /* We can't remap across vm area boundaries */
349 if (old_len > vma->vm_end - addr)
350 goto Efault;
351
352 /* Need to be careful about a growing mapping */
353 if (new_len > old_len) {
354 unsigned long pgoff;
355
356 if (vma->vm_flags & (VM_DONTEXPAND | VM_PFNMAP))
357 goto Efault;
358 pgoff = (addr - vma->vm_start) >> PAGE_SHIFT;
359 pgoff += vma->vm_pgoff;
360 if (pgoff + (new_len >> PAGE_SHIFT) < pgoff)
361 goto Einval;
362 }
363
364 if (vma->vm_flags & VM_LOCKED) {
365 unsigned long locked, lock_limit;
366 locked = mm->locked_vm << PAGE_SHIFT;
367 lock_limit = rlimit(RLIMIT_MEMLOCK);
368 locked += new_len - old_len;
369 if (locked > lock_limit && !capable(CAP_IPC_LOCK))
370 goto Eagain;
371 }
372
373 if (!may_expand_vm(mm, (new_len - old_len) >> PAGE_SHIFT))
374 goto Enomem;
375
376 if (vma->vm_flags & VM_ACCOUNT) {
377 unsigned long charged = (new_len - old_len) >> PAGE_SHIFT;
378 if (security_vm_enough_memory_mm(mm, charged))
379 goto Efault;
380 *p = charged;
381 }
382
383 return vma;
384
385 Efault: /* very odd choice for most of the cases, but... */
386 return ERR_PTR(-EFAULT);
387 Einval:
388 return ERR_PTR(-EINVAL);
389 Enomem:
390 return ERR_PTR(-ENOMEM);
391 Eagain:
392 return ERR_PTR(-EAGAIN);
393 }
394
mremap_to(unsigned long addr,unsigned long old_len,unsigned long new_addr,unsigned long new_len,bool * locked)395 static unsigned long mremap_to(unsigned long addr, unsigned long old_len,
396 unsigned long new_addr, unsigned long new_len, bool *locked)
397 {
398 struct mm_struct *mm = current->mm;
399 struct vm_area_struct *vma;
400 unsigned long ret = -EINVAL;
401 unsigned long charged = 0;
402 unsigned long map_flags;
403
404 if (new_addr & ~PAGE_MASK)
405 goto out;
406
407 if (new_len > TASK_SIZE || new_addr > TASK_SIZE - new_len)
408 goto out;
409
410 /* Check if the location we're moving into overlaps the
411 * old location at all, and fail if it does.
412 */
413 if ((new_addr <= addr) && (new_addr+new_len) > addr)
414 goto out;
415
416 if ((addr <= new_addr) && (addr+old_len) > new_addr)
417 goto out;
418
419 ret = do_munmap(mm, new_addr, new_len);
420 if (ret)
421 goto out;
422
423 if (old_len >= new_len) {
424 ret = do_munmap(mm, addr+new_len, old_len - new_len);
425 if (ret && old_len != new_len)
426 goto out;
427 old_len = new_len;
428 }
429
430 vma = vma_to_resize(addr, old_len, new_len, &charged);
431 if (IS_ERR(vma)) {
432 ret = PTR_ERR(vma);
433 goto out;
434 }
435
436 map_flags = MAP_FIXED;
437 if (vma->vm_flags & VM_MAYSHARE)
438 map_flags |= MAP_SHARED;
439
440 ret = get_unmapped_area(vma->vm_file, new_addr, new_len, vma->vm_pgoff +
441 ((addr - vma->vm_start) >> PAGE_SHIFT),
442 map_flags);
443 if (ret & ~PAGE_MASK)
444 goto out1;
445
446 ret = move_vma(vma, addr, old_len, new_len, new_addr, locked);
447 if (!(ret & ~PAGE_MASK))
448 goto out;
449 out1:
450 vm_unacct_memory(charged);
451
452 out:
453 return ret;
454 }
455
vma_expandable(struct vm_area_struct * vma,unsigned long delta)456 static int vma_expandable(struct vm_area_struct *vma, unsigned long delta)
457 {
458 unsigned long end = vma->vm_end + delta;
459 if (end < vma->vm_end) /* overflow */
460 return 0;
461 if (vma->vm_next && vma->vm_next->vm_start < end) /* intersection */
462 return 0;
463 if (get_unmapped_area(NULL, vma->vm_start, end - vma->vm_start,
464 0, MAP_FIXED) & ~PAGE_MASK)
465 return 0;
466 return 1;
467 }
468
469 /*
470 * Expand (or shrink) an existing mapping, potentially moving it at the
471 * same time (controlled by the MREMAP_MAYMOVE flag and available VM space)
472 *
473 * MREMAP_FIXED option added 5-Dec-1999 by Benjamin LaHaise
474 * This option implies MREMAP_MAYMOVE.
475 */
SYSCALL_DEFINE5(mremap,unsigned long,addr,unsigned long,old_len,unsigned long,new_len,unsigned long,flags,unsigned long,new_addr)476 SYSCALL_DEFINE5(mremap, unsigned long, addr, unsigned long, old_len,
477 unsigned long, new_len, unsigned long, flags,
478 unsigned long, new_addr)
479 {
480 struct mm_struct *mm = current->mm;
481 struct vm_area_struct *vma;
482 unsigned long ret = -EINVAL;
483 unsigned long charged = 0;
484 bool locked = false;
485
486 if (flags & ~(MREMAP_FIXED | MREMAP_MAYMOVE))
487 return ret;
488
489 if (flags & MREMAP_FIXED && !(flags & MREMAP_MAYMOVE))
490 return ret;
491
492 if (addr & ~PAGE_MASK)
493 return ret;
494
495 old_len = PAGE_ALIGN(old_len);
496 new_len = PAGE_ALIGN(new_len);
497
498 /*
499 * We allow a zero old-len as a special case
500 * for DOS-emu "duplicate shm area" thing. But
501 * a zero new-len is nonsensical.
502 */
503 if (!new_len)
504 return ret;
505
506 down_write(¤t->mm->mmap_sem);
507
508 if (flags & MREMAP_FIXED) {
509 ret = mremap_to(addr, old_len, new_addr, new_len,
510 &locked);
511 goto out;
512 }
513
514 /*
515 * Always allow a shrinking remap: that just unmaps
516 * the unnecessary pages..
517 * do_munmap does all the needed commit accounting
518 */
519 if (old_len >= new_len) {
520 ret = do_munmap(mm, addr+new_len, old_len - new_len);
521 if (ret && old_len != new_len)
522 goto out;
523 ret = addr;
524 goto out;
525 }
526
527 /*
528 * Ok, we need to grow..
529 */
530 vma = vma_to_resize(addr, old_len, new_len, &charged);
531 if (IS_ERR(vma)) {
532 ret = PTR_ERR(vma);
533 goto out;
534 }
535
536 /* old_len exactly to the end of the area..
537 */
538 if (old_len == vma->vm_end - addr) {
539 /* can we just expand the current mapping? */
540 if (vma_expandable(vma, new_len - old_len)) {
541 int pages = (new_len - old_len) >> PAGE_SHIFT;
542
543 if (vma_adjust(vma, vma->vm_start, addr + new_len,
544 vma->vm_pgoff, NULL)) {
545 ret = -ENOMEM;
546 goto out;
547 }
548
549 vm_stat_account(mm, vma->vm_flags, vma->vm_file, pages);
550 if (vma->vm_flags & VM_LOCKED) {
551 mm->locked_vm += pages;
552 locked = true;
553 new_addr = addr;
554 }
555 ret = addr;
556 goto out;
557 }
558 }
559
560 /*
561 * We weren't able to just expand or shrink the area,
562 * we need to create a new one and move it..
563 */
564 ret = -ENOMEM;
565 if (flags & MREMAP_MAYMOVE) {
566 unsigned long map_flags = 0;
567 if (vma->vm_flags & VM_MAYSHARE)
568 map_flags |= MAP_SHARED;
569
570 new_addr = get_unmapped_area(vma->vm_file, 0, new_len,
571 vma->vm_pgoff +
572 ((addr - vma->vm_start) >> PAGE_SHIFT),
573 map_flags);
574 if (new_addr & ~PAGE_MASK) {
575 ret = new_addr;
576 goto out;
577 }
578
579 ret = move_vma(vma, addr, old_len, new_len, new_addr, &locked);
580 }
581 out:
582 if (ret & ~PAGE_MASK)
583 vm_unacct_memory(charged);
584 up_write(¤t->mm->mmap_sem);
585 if (locked && new_len > old_len)
586 mm_populate(new_addr + old_len, new_len - old_len);
587 return ret;
588 }
589