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/uaccess.h> 24 #include <linux/mm-arch-hooks.h> 25 #include <linux/userfaultfd_k.h> 26 27 #include <asm/cacheflush.h> 28 #include <asm/tlbflush.h> 29 30 #include "internal.h" 31 32 static pmd_t *get_old_pmd(struct mm_struct *mm, unsigned long addr) 33 { 34 pgd_t *pgd; 35 p4d_t *p4d; 36 pud_t *pud; 37 pmd_t *pmd; 38 39 pgd = pgd_offset(mm, addr); 40 if (pgd_none_or_clear_bad(pgd)) 41 return NULL; 42 43 p4d = p4d_offset(pgd, addr); 44 if (p4d_none_or_clear_bad(p4d)) 45 return NULL; 46 47 pud = pud_offset(p4d, addr); 48 if (pud_none_or_clear_bad(pud)) 49 return NULL; 50 51 pmd = pmd_offset(pud, addr); 52 if (pmd_none(*pmd)) 53 return NULL; 54 55 return pmd; 56 } 57 58 static pmd_t *alloc_new_pmd(struct mm_struct *mm, struct vm_area_struct *vma, 59 unsigned long addr) 60 { 61 pgd_t *pgd; 62 p4d_t *p4d; 63 pud_t *pud; 64 pmd_t *pmd; 65 66 pgd = pgd_offset(mm, addr); 67 p4d = p4d_alloc(mm, pgd, addr); 68 if (!p4d) 69 return NULL; 70 pud = pud_alloc(mm, p4d, addr); 71 if (!pud) 72 return NULL; 73 74 pmd = pmd_alloc(mm, pud, addr); 75 if (!pmd) 76 return NULL; 77 78 VM_BUG_ON(pmd_trans_huge(*pmd)); 79 80 return pmd; 81 } 82 83 static void take_rmap_locks(struct vm_area_struct *vma) 84 { 85 if (vma->vm_file) 86 i_mmap_lock_write(vma->vm_file->f_mapping); 87 if (vma->anon_vma) 88 anon_vma_lock_write(vma->anon_vma); 89 } 90 91 static void drop_rmap_locks(struct vm_area_struct *vma) 92 { 93 if (vma->anon_vma) 94 anon_vma_unlock_write(vma->anon_vma); 95 if (vma->vm_file) 96 i_mmap_unlock_write(vma->vm_file->f_mapping); 97 } 98 99 static pte_t move_soft_dirty_pte(pte_t pte) 100 { 101 /* 102 * Set soft dirty bit so we can notice 103 * in userspace the ptes were moved. 104 */ 105 #ifdef CONFIG_MEM_SOFT_DIRTY 106 if (pte_present(pte)) 107 pte = pte_mksoft_dirty(pte); 108 else if (is_swap_pte(pte)) 109 pte = pte_swp_mksoft_dirty(pte); 110 #endif 111 return pte; 112 } 113 114 static void move_ptes(struct vm_area_struct *vma, pmd_t *old_pmd, 115 unsigned long old_addr, unsigned long old_end, 116 struct vm_area_struct *new_vma, pmd_t *new_pmd, 117 unsigned long new_addr, bool need_rmap_locks, bool *need_flush) 118 { 119 struct mm_struct *mm = vma->vm_mm; 120 pte_t *old_pte, *new_pte, pte; 121 spinlock_t *old_ptl, *new_ptl; 122 bool force_flush = false; 123 unsigned long len = old_end - old_addr; 124 125 /* 126 * When need_rmap_locks is true, we take the i_mmap_rwsem and anon_vma 127 * locks to ensure that rmap will always observe either the old or the 128 * new ptes. This is the easiest way to avoid races with 129 * truncate_pagecache(), page migration, etc... 130 * 131 * When need_rmap_locks is false, we use other ways to avoid 132 * such races: 133 * 134 * - During exec() shift_arg_pages(), we use a specially tagged vma 135 * which rmap call sites look for using is_vma_temporary_stack(). 136 * 137 * - During mremap(), new_vma is often known to be placed after vma 138 * in rmap traversal order. This ensures rmap will always observe 139 * either the old pte, or the new pte, or both (the page table locks 140 * serialize access to individual ptes, but only rmap traversal 141 * order guarantees that we won't miss both the old and new ptes). 142 */ 143 if (need_rmap_locks) 144 take_rmap_locks(vma); 145 146 /* 147 * We don't have to worry about the ordering of src and dst 148 * pte locks because exclusive mmap_sem prevents deadlock. 149 */ 150 old_pte = pte_offset_map_lock(mm, old_pmd, old_addr, &old_ptl); 151 new_pte = pte_offset_map(new_pmd, new_addr); 152 new_ptl = pte_lockptr(mm, new_pmd); 153 if (new_ptl != old_ptl) 154 spin_lock_nested(new_ptl, SINGLE_DEPTH_NESTING); 155 flush_tlb_batched_pending(vma->vm_mm); 156 arch_enter_lazy_mmu_mode(); 157 158 for (; old_addr < old_end; old_pte++, old_addr += PAGE_SIZE, 159 new_pte++, new_addr += PAGE_SIZE) { 160 if (pte_none(*old_pte)) 161 continue; 162 163 pte = ptep_get_and_clear(mm, old_addr, old_pte); 164 /* 165 * If we are remapping a dirty PTE, make sure 166 * to flush TLB before we drop the PTL for the 167 * old PTE or we may race with page_mkclean(). 168 * 169 * This check has to be done after we removed the 170 * old PTE from page tables or another thread may 171 * dirty it after the check and before the removal. 172 */ 173 if (pte_present(pte) && pte_dirty(pte)) 174 force_flush = true; 175 pte = move_pte(pte, new_vma->vm_page_prot, old_addr, new_addr); 176 pte = move_soft_dirty_pte(pte); 177 set_pte_at(mm, new_addr, new_pte, pte); 178 } 179 180 arch_leave_lazy_mmu_mode(); 181 if (new_ptl != old_ptl) 182 spin_unlock(new_ptl); 183 pte_unmap(new_pte - 1); 184 if (force_flush) 185 flush_tlb_range(vma, old_end - len, old_end); 186 else 187 *need_flush = true; 188 pte_unmap_unlock(old_pte - 1, old_ptl); 189 if (need_rmap_locks) 190 drop_rmap_locks(vma); 191 } 192 193 #define LATENCY_LIMIT (64 * PAGE_SIZE) 194 195 unsigned long move_page_tables(struct vm_area_struct *vma, 196 unsigned long old_addr, struct vm_area_struct *new_vma, 197 unsigned long new_addr, unsigned long len, 198 bool need_rmap_locks) 199 { 200 unsigned long extent, next, old_end; 201 pmd_t *old_pmd, *new_pmd; 202 bool need_flush = false; 203 unsigned long mmun_start; /* For mmu_notifiers */ 204 unsigned long mmun_end; /* For mmu_notifiers */ 205 206 old_end = old_addr + len; 207 flush_cache_range(vma, old_addr, old_end); 208 209 mmun_start = old_addr; 210 mmun_end = old_end; 211 mmu_notifier_invalidate_range_start(vma->vm_mm, mmun_start, mmun_end); 212 213 for (; old_addr < old_end; old_addr += extent, new_addr += extent) { 214 cond_resched(); 215 next = (old_addr + PMD_SIZE) & PMD_MASK; 216 /* even if next overflowed, extent below will be ok */ 217 extent = next - old_addr; 218 if (extent > old_end - old_addr) 219 extent = old_end - old_addr; 220 old_pmd = get_old_pmd(vma->vm_mm, old_addr); 221 if (!old_pmd) 222 continue; 223 new_pmd = alloc_new_pmd(vma->vm_mm, vma, new_addr); 224 if (!new_pmd) 225 break; 226 if (pmd_trans_huge(*old_pmd)) { 227 if (extent == HPAGE_PMD_SIZE) { 228 bool moved; 229 /* See comment in move_ptes() */ 230 if (need_rmap_locks) 231 take_rmap_locks(vma); 232 moved = move_huge_pmd(vma, old_addr, new_addr, 233 old_end, old_pmd, new_pmd, 234 &need_flush); 235 if (need_rmap_locks) 236 drop_rmap_locks(vma); 237 if (moved) 238 continue; 239 } 240 split_huge_pmd(vma, old_pmd, old_addr); 241 if (pmd_trans_unstable(old_pmd)) 242 continue; 243 } 244 if (pte_alloc(new_vma->vm_mm, new_pmd, new_addr)) 245 break; 246 next = (new_addr + PMD_SIZE) & PMD_MASK; 247 if (extent > next - new_addr) 248 extent = next - new_addr; 249 if (extent > LATENCY_LIMIT) 250 extent = LATENCY_LIMIT; 251 move_ptes(vma, old_pmd, old_addr, old_addr + extent, new_vma, 252 new_pmd, new_addr, need_rmap_locks, &need_flush); 253 } 254 if (need_flush) 255 flush_tlb_range(vma, old_end-len, old_addr); 256 257 mmu_notifier_invalidate_range_end(vma->vm_mm, mmun_start, mmun_end); 258 259 return len + old_addr - old_end; /* how much done */ 260 } 261 262 static unsigned long move_vma(struct vm_area_struct *vma, 263 unsigned long old_addr, unsigned long old_len, 264 unsigned long new_len, unsigned long new_addr, 265 bool *locked, struct vm_userfaultfd_ctx *uf, 266 struct list_head *uf_unmap) 267 { 268 struct mm_struct *mm = vma->vm_mm; 269 struct vm_area_struct *new_vma; 270 unsigned long vm_flags = vma->vm_flags; 271 unsigned long new_pgoff; 272 unsigned long moved_len; 273 unsigned long excess = 0; 274 unsigned long hiwater_vm; 275 int split = 0; 276 int err; 277 bool need_rmap_locks; 278 279 /* 280 * We'd prefer to avoid failure later on in do_munmap: 281 * which may split one vma into three before unmapping. 282 */ 283 if (mm->map_count >= sysctl_max_map_count - 3) 284 return -ENOMEM; 285 286 /* 287 * Advise KSM to break any KSM pages in the area to be moved: 288 * it would be confusing if they were to turn up at the new 289 * location, where they happen to coincide with different KSM 290 * pages recently unmapped. But leave vma->vm_flags as it was, 291 * so KSM can come around to merge on vma and new_vma afterwards. 292 */ 293 err = ksm_madvise(vma, old_addr, old_addr + old_len, 294 MADV_UNMERGEABLE, &vm_flags); 295 if (err) 296 return err; 297 298 new_pgoff = vma->vm_pgoff + ((old_addr - vma->vm_start) >> PAGE_SHIFT); 299 new_vma = copy_vma(&vma, new_addr, new_len, new_pgoff, 300 &need_rmap_locks); 301 if (!new_vma) 302 return -ENOMEM; 303 304 moved_len = move_page_tables(vma, old_addr, new_vma, new_addr, old_len, 305 need_rmap_locks); 306 if (moved_len < old_len) { 307 err = -ENOMEM; 308 } else if (vma->vm_ops && vma->vm_ops->mremap) { 309 err = vma->vm_ops->mremap(new_vma); 310 } 311 312 if (unlikely(err)) { 313 /* 314 * On error, move entries back from new area to old, 315 * which will succeed since page tables still there, 316 * and then proceed to unmap new area instead of old. 317 */ 318 move_page_tables(new_vma, new_addr, vma, old_addr, moved_len, 319 true); 320 vma = new_vma; 321 old_len = new_len; 322 old_addr = new_addr; 323 new_addr = err; 324 } else { 325 mremap_userfaultfd_prep(new_vma, uf); 326 arch_remap(mm, old_addr, old_addr + old_len, 327 new_addr, new_addr + new_len); 328 } 329 330 /* Conceal VM_ACCOUNT so old reservation is not undone */ 331 if (vm_flags & VM_ACCOUNT) { 332 vma->vm_flags &= ~VM_ACCOUNT; 333 excess = vma->vm_end - vma->vm_start - old_len; 334 if (old_addr > vma->vm_start && 335 old_addr + old_len < vma->vm_end) 336 split = 1; 337 } 338 339 /* 340 * If we failed to move page tables we still do total_vm increment 341 * since do_munmap() will decrement it by old_len == new_len. 342 * 343 * Since total_vm is about to be raised artificially high for a 344 * moment, we need to restore high watermark afterwards: if stats 345 * are taken meanwhile, total_vm and hiwater_vm appear too high. 346 * If this were a serious issue, we'd add a flag to do_munmap(). 347 */ 348 hiwater_vm = mm->hiwater_vm; 349 vm_stat_account(mm, vma->vm_flags, new_len >> PAGE_SHIFT); 350 351 /* Tell pfnmap has moved from this vma */ 352 if (unlikely(vma->vm_flags & VM_PFNMAP)) 353 untrack_pfn_moved(vma); 354 355 if (do_munmap(mm, old_addr, old_len, uf_unmap) < 0) { 356 /* OOM: unable to split vma, just get accounts right */ 357 vm_unacct_memory(excess >> PAGE_SHIFT); 358 excess = 0; 359 } 360 mm->hiwater_vm = hiwater_vm; 361 362 /* Restore VM_ACCOUNT if one or two pieces of vma left */ 363 if (excess) { 364 vma->vm_flags |= VM_ACCOUNT; 365 if (split) 366 vma->vm_next->vm_flags |= VM_ACCOUNT; 367 } 368 369 if (vm_flags & VM_LOCKED) { 370 mm->locked_vm += new_len >> PAGE_SHIFT; 371 *locked = true; 372 } 373 374 return new_addr; 375 } 376 377 static struct vm_area_struct *vma_to_resize(unsigned long addr, 378 unsigned long old_len, unsigned long new_len, unsigned long *p) 379 { 380 struct mm_struct *mm = current->mm; 381 struct vm_area_struct *vma = find_vma(mm, addr); 382 unsigned long pgoff; 383 384 if (!vma || vma->vm_start > addr) 385 return ERR_PTR(-EFAULT); 386 387 if (is_vm_hugetlb_page(vma)) 388 return ERR_PTR(-EINVAL); 389 390 /* We can't remap across vm area boundaries */ 391 if (old_len > vma->vm_end - addr) 392 return ERR_PTR(-EFAULT); 393 394 if (new_len == old_len) 395 return vma; 396 397 /* Need to be careful about a growing mapping */ 398 pgoff = (addr - vma->vm_start) >> PAGE_SHIFT; 399 pgoff += vma->vm_pgoff; 400 if (pgoff + (new_len >> PAGE_SHIFT) < pgoff) 401 return ERR_PTR(-EINVAL); 402 403 if (vma->vm_flags & (VM_DONTEXPAND | VM_PFNMAP)) 404 return ERR_PTR(-EFAULT); 405 406 if (vma->vm_flags & VM_LOCKED) { 407 unsigned long locked, lock_limit; 408 locked = mm->locked_vm << PAGE_SHIFT; 409 lock_limit = rlimit(RLIMIT_MEMLOCK); 410 locked += new_len - old_len; 411 if (locked > lock_limit && !capable(CAP_IPC_LOCK)) 412 return ERR_PTR(-EAGAIN); 413 } 414 415 if (!may_expand_vm(mm, vma->vm_flags, 416 (new_len - old_len) >> PAGE_SHIFT)) 417 return ERR_PTR(-ENOMEM); 418 419 if (vma->vm_flags & VM_ACCOUNT) { 420 unsigned long charged = (new_len - old_len) >> PAGE_SHIFT; 421 if (security_vm_enough_memory_mm(mm, charged)) 422 return ERR_PTR(-ENOMEM); 423 *p = charged; 424 } 425 426 return vma; 427 } 428 429 static unsigned long mremap_to(unsigned long addr, unsigned long old_len, 430 unsigned long new_addr, unsigned long new_len, bool *locked, 431 struct vm_userfaultfd_ctx *uf, 432 struct list_head *uf_unmap_early, 433 struct list_head *uf_unmap) 434 { 435 struct mm_struct *mm = current->mm; 436 struct vm_area_struct *vma; 437 unsigned long ret = -EINVAL; 438 unsigned long charged = 0; 439 unsigned long map_flags; 440 441 if (offset_in_page(new_addr)) 442 goto out; 443 444 if (new_len > TASK_SIZE || new_addr > TASK_SIZE - new_len) 445 goto out; 446 447 /* Ensure the old/new locations do not overlap */ 448 if (addr + old_len > new_addr && new_addr + new_len > addr) 449 goto out; 450 451 ret = do_munmap(mm, new_addr, new_len, uf_unmap_early); 452 if (ret) 453 goto out; 454 455 if (old_len >= new_len) { 456 ret = do_munmap(mm, addr+new_len, old_len - new_len, uf_unmap); 457 if (ret && old_len != new_len) 458 goto out; 459 old_len = new_len; 460 } 461 462 vma = vma_to_resize(addr, old_len, new_len, &charged); 463 if (IS_ERR(vma)) { 464 ret = PTR_ERR(vma); 465 goto out; 466 } 467 468 map_flags = MAP_FIXED; 469 if (vma->vm_flags & VM_MAYSHARE) 470 map_flags |= MAP_SHARED; 471 472 ret = get_unmapped_area(vma->vm_file, new_addr, new_len, vma->vm_pgoff + 473 ((addr - vma->vm_start) >> PAGE_SHIFT), 474 map_flags); 475 if (offset_in_page(ret)) 476 goto out1; 477 478 ret = move_vma(vma, addr, old_len, new_len, new_addr, locked, uf, 479 uf_unmap); 480 if (!(offset_in_page(ret))) 481 goto out; 482 out1: 483 vm_unacct_memory(charged); 484 485 out: 486 return ret; 487 } 488 489 static int vma_expandable(struct vm_area_struct *vma, unsigned long delta) 490 { 491 unsigned long end = vma->vm_end + delta; 492 if (end < vma->vm_end) /* overflow */ 493 return 0; 494 if (vma->vm_next && vma->vm_next->vm_start < end) /* intersection */ 495 return 0; 496 if (get_unmapped_area(NULL, vma->vm_start, end - vma->vm_start, 497 0, MAP_FIXED) & ~PAGE_MASK) 498 return 0; 499 return 1; 500 } 501 502 /* 503 * Expand (or shrink) an existing mapping, potentially moving it at the 504 * same time (controlled by the MREMAP_MAYMOVE flag and available VM space) 505 * 506 * MREMAP_FIXED option added 5-Dec-1999 by Benjamin LaHaise 507 * This option implies MREMAP_MAYMOVE. 508 */ 509 SYSCALL_DEFINE5(mremap, unsigned long, addr, unsigned long, old_len, 510 unsigned long, new_len, unsigned long, flags, 511 unsigned long, new_addr) 512 { 513 struct mm_struct *mm = current->mm; 514 struct vm_area_struct *vma; 515 unsigned long ret = -EINVAL; 516 unsigned long charged = 0; 517 bool locked = false; 518 struct vm_userfaultfd_ctx uf = NULL_VM_UFFD_CTX; 519 LIST_HEAD(uf_unmap_early); 520 LIST_HEAD(uf_unmap); 521 522 if (flags & ~(MREMAP_FIXED | MREMAP_MAYMOVE)) 523 return ret; 524 525 if (flags & MREMAP_FIXED && !(flags & MREMAP_MAYMOVE)) 526 return ret; 527 528 if (offset_in_page(addr)) 529 return ret; 530 531 old_len = PAGE_ALIGN(old_len); 532 new_len = PAGE_ALIGN(new_len); 533 534 /* 535 * We allow a zero old-len as a special case 536 * for DOS-emu "duplicate shm area" thing. But 537 * a zero new-len is nonsensical. 538 */ 539 if (!new_len) 540 return ret; 541 542 if (down_write_killable(¤t->mm->mmap_sem)) 543 return -EINTR; 544 545 if (flags & MREMAP_FIXED) { 546 ret = mremap_to(addr, old_len, new_addr, new_len, 547 &locked, &uf, &uf_unmap_early, &uf_unmap); 548 goto out; 549 } 550 551 /* 552 * Always allow a shrinking remap: that just unmaps 553 * the unnecessary pages.. 554 * do_munmap does all the needed commit accounting 555 */ 556 if (old_len >= new_len) { 557 ret = do_munmap(mm, addr+new_len, old_len - new_len, &uf_unmap); 558 if (ret && old_len != new_len) 559 goto out; 560 ret = addr; 561 goto out; 562 } 563 564 /* 565 * Ok, we need to grow.. 566 */ 567 vma = vma_to_resize(addr, old_len, new_len, &charged); 568 if (IS_ERR(vma)) { 569 ret = PTR_ERR(vma); 570 goto out; 571 } 572 573 /* old_len exactly to the end of the area.. 574 */ 575 if (old_len == vma->vm_end - addr) { 576 /* can we just expand the current mapping? */ 577 if (vma_expandable(vma, new_len - old_len)) { 578 int pages = (new_len - old_len) >> PAGE_SHIFT; 579 580 if (vma_adjust(vma, vma->vm_start, addr + new_len, 581 vma->vm_pgoff, NULL)) { 582 ret = -ENOMEM; 583 goto out; 584 } 585 586 vm_stat_account(mm, vma->vm_flags, pages); 587 if (vma->vm_flags & VM_LOCKED) { 588 mm->locked_vm += pages; 589 locked = true; 590 new_addr = addr; 591 } 592 ret = addr; 593 goto out; 594 } 595 } 596 597 /* 598 * We weren't able to just expand or shrink the area, 599 * we need to create a new one and move it.. 600 */ 601 ret = -ENOMEM; 602 if (flags & MREMAP_MAYMOVE) { 603 unsigned long map_flags = 0; 604 if (vma->vm_flags & VM_MAYSHARE) 605 map_flags |= MAP_SHARED; 606 607 new_addr = get_unmapped_area(vma->vm_file, 0, new_len, 608 vma->vm_pgoff + 609 ((addr - vma->vm_start) >> PAGE_SHIFT), 610 map_flags); 611 if (offset_in_page(new_addr)) { 612 ret = new_addr; 613 goto out; 614 } 615 616 ret = move_vma(vma, addr, old_len, new_len, new_addr, 617 &locked, &uf, &uf_unmap); 618 } 619 out: 620 if (offset_in_page(ret)) { 621 vm_unacct_memory(charged); 622 locked = 0; 623 } 624 up_write(¤t->mm->mmap_sem); 625 if (locked && new_len > old_len) 626 mm_populate(new_addr + old_len, new_len - old_len); 627 userfaultfd_unmap_complete(mm, &uf_unmap_early); 628 mremap_userfaultfd_complete(&uf, addr, new_addr, old_len); 629 userfaultfd_unmap_complete(mm, &uf_unmap); 630 return ret; 631 } 632