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 arch_enter_lazy_mmu_mode(); 156 157 for (; old_addr < old_end; old_pte++, old_addr += PAGE_SIZE, 158 new_pte++, new_addr += PAGE_SIZE) { 159 if (pte_none(*old_pte)) 160 continue; 161 162 pte = ptep_get_and_clear(mm, old_addr, old_pte); 163 /* 164 * If we are remapping a dirty PTE, make sure 165 * to flush TLB before we drop the PTL for the 166 * old PTE or we may race with page_mkclean(). 167 * 168 * This check has to be done after we removed the 169 * old PTE from page tables or another thread may 170 * dirty it after the check and before the removal. 171 */ 172 if (pte_present(pte) && pte_dirty(pte)) 173 force_flush = true; 174 pte = move_pte(pte, new_vma->vm_page_prot, old_addr, new_addr); 175 pte = move_soft_dirty_pte(pte); 176 set_pte_at(mm, new_addr, new_pte, pte); 177 } 178 179 arch_leave_lazy_mmu_mode(); 180 if (new_ptl != old_ptl) 181 spin_unlock(new_ptl); 182 pte_unmap(new_pte - 1); 183 if (force_flush) 184 flush_tlb_range(vma, old_end - len, old_end); 185 else 186 *need_flush = true; 187 pte_unmap_unlock(old_pte - 1, old_ptl); 188 if (need_rmap_locks) 189 drop_rmap_locks(vma); 190 } 191 192 #define LATENCY_LIMIT (64 * PAGE_SIZE) 193 194 unsigned long move_page_tables(struct vm_area_struct *vma, 195 unsigned long old_addr, struct vm_area_struct *new_vma, 196 unsigned long new_addr, unsigned long len, 197 bool need_rmap_locks) 198 { 199 unsigned long extent, next, old_end; 200 pmd_t *old_pmd, *new_pmd; 201 bool need_flush = false; 202 unsigned long mmun_start; /* For mmu_notifiers */ 203 unsigned long mmun_end; /* For mmu_notifiers */ 204 205 old_end = old_addr + len; 206 flush_cache_range(vma, old_addr, old_end); 207 208 mmun_start = old_addr; 209 mmun_end = old_end; 210 mmu_notifier_invalidate_range_start(vma->vm_mm, mmun_start, mmun_end); 211 212 for (; old_addr < old_end; old_addr += extent, new_addr += extent) { 213 cond_resched(); 214 next = (old_addr + PMD_SIZE) & PMD_MASK; 215 /* even if next overflowed, extent below will be ok */ 216 extent = next - old_addr; 217 if (extent > old_end - old_addr) 218 extent = old_end - old_addr; 219 old_pmd = get_old_pmd(vma->vm_mm, old_addr); 220 if (!old_pmd) 221 continue; 222 new_pmd = alloc_new_pmd(vma->vm_mm, vma, new_addr); 223 if (!new_pmd) 224 break; 225 if (pmd_trans_huge(*old_pmd)) { 226 if (extent == HPAGE_PMD_SIZE) { 227 bool moved; 228 /* See comment in move_ptes() */ 229 if (need_rmap_locks) 230 take_rmap_locks(vma); 231 moved = move_huge_pmd(vma, old_addr, new_addr, 232 old_end, old_pmd, new_pmd, 233 &need_flush); 234 if (need_rmap_locks) 235 drop_rmap_locks(vma); 236 if (moved) 237 continue; 238 } 239 split_huge_pmd(vma, old_pmd, old_addr); 240 if (pmd_trans_unstable(old_pmd)) 241 continue; 242 } 243 if (pte_alloc(new_vma->vm_mm, new_pmd, new_addr)) 244 break; 245 next = (new_addr + PMD_SIZE) & PMD_MASK; 246 if (extent > next - new_addr) 247 extent = next - new_addr; 248 if (extent > LATENCY_LIMIT) 249 extent = LATENCY_LIMIT; 250 move_ptes(vma, old_pmd, old_addr, old_addr + extent, new_vma, 251 new_pmd, new_addr, need_rmap_locks, &need_flush); 252 } 253 if (need_flush) 254 flush_tlb_range(vma, old_end-len, old_addr); 255 256 mmu_notifier_invalidate_range_end(vma->vm_mm, mmun_start, mmun_end); 257 258 return len + old_addr - old_end; /* how much done */ 259 } 260 261 static unsigned long move_vma(struct vm_area_struct *vma, 262 unsigned long old_addr, unsigned long old_len, 263 unsigned long new_len, unsigned long new_addr, 264 bool *locked, struct vm_userfaultfd_ctx *uf, 265 struct list_head *uf_unmap) 266 { 267 struct mm_struct *mm = vma->vm_mm; 268 struct vm_area_struct *new_vma; 269 unsigned long vm_flags = vma->vm_flags; 270 unsigned long new_pgoff; 271 unsigned long moved_len; 272 unsigned long excess = 0; 273 unsigned long hiwater_vm; 274 int split = 0; 275 int err; 276 bool need_rmap_locks; 277 278 /* 279 * We'd prefer to avoid failure later on in do_munmap: 280 * which may split one vma into three before unmapping. 281 */ 282 if (mm->map_count >= sysctl_max_map_count - 3) 283 return -ENOMEM; 284 285 /* 286 * Advise KSM to break any KSM pages in the area to be moved: 287 * it would be confusing if they were to turn up at the new 288 * location, where they happen to coincide with different KSM 289 * pages recently unmapped. But leave vma->vm_flags as it was, 290 * so KSM can come around to merge on vma and new_vma afterwards. 291 */ 292 err = ksm_madvise(vma, old_addr, old_addr + old_len, 293 MADV_UNMERGEABLE, &vm_flags); 294 if (err) 295 return err; 296 297 new_pgoff = vma->vm_pgoff + ((old_addr - vma->vm_start) >> PAGE_SHIFT); 298 new_vma = copy_vma(&vma, new_addr, new_len, new_pgoff, 299 &need_rmap_locks); 300 if (!new_vma) 301 return -ENOMEM; 302 303 moved_len = move_page_tables(vma, old_addr, new_vma, new_addr, old_len, 304 need_rmap_locks); 305 if (moved_len < old_len) { 306 err = -ENOMEM; 307 } else if (vma->vm_ops && vma->vm_ops->mremap) { 308 err = vma->vm_ops->mremap(new_vma); 309 } 310 311 if (unlikely(err)) { 312 /* 313 * On error, move entries back from new area to old, 314 * which will succeed since page tables still there, 315 * and then proceed to unmap new area instead of old. 316 */ 317 move_page_tables(new_vma, new_addr, vma, old_addr, moved_len, 318 true); 319 vma = new_vma; 320 old_len = new_len; 321 old_addr = new_addr; 322 new_addr = err; 323 } else { 324 mremap_userfaultfd_prep(new_vma, uf); 325 arch_remap(mm, old_addr, old_addr + old_len, 326 new_addr, new_addr + new_len); 327 } 328 329 /* Conceal VM_ACCOUNT so old reservation is not undone */ 330 if (vm_flags & VM_ACCOUNT) { 331 vma->vm_flags &= ~VM_ACCOUNT; 332 excess = vma->vm_end - vma->vm_start - old_len; 333 if (old_addr > vma->vm_start && 334 old_addr + old_len < vma->vm_end) 335 split = 1; 336 } 337 338 /* 339 * If we failed to move page tables we still do total_vm increment 340 * since do_munmap() will decrement it by old_len == new_len. 341 * 342 * Since total_vm is about to be raised artificially high for a 343 * moment, we need to restore high watermark afterwards: if stats 344 * are taken meanwhile, total_vm and hiwater_vm appear too high. 345 * If this were a serious issue, we'd add a flag to do_munmap(). 346 */ 347 hiwater_vm = mm->hiwater_vm; 348 vm_stat_account(mm, vma->vm_flags, new_len >> PAGE_SHIFT); 349 350 /* Tell pfnmap has moved from this vma */ 351 if (unlikely(vma->vm_flags & VM_PFNMAP)) 352 untrack_pfn_moved(vma); 353 354 if (do_munmap(mm, old_addr, old_len, uf_unmap) < 0) { 355 /* OOM: unable to split vma, just get accounts right */ 356 vm_unacct_memory(excess >> PAGE_SHIFT); 357 excess = 0; 358 } 359 mm->hiwater_vm = hiwater_vm; 360 361 /* Restore VM_ACCOUNT if one or two pieces of vma left */ 362 if (excess) { 363 vma->vm_flags |= VM_ACCOUNT; 364 if (split) 365 vma->vm_next->vm_flags |= VM_ACCOUNT; 366 } 367 368 if (vm_flags & VM_LOCKED) { 369 mm->locked_vm += new_len >> PAGE_SHIFT; 370 *locked = true; 371 } 372 373 return new_addr; 374 } 375 376 static struct vm_area_struct *vma_to_resize(unsigned long addr, 377 unsigned long old_len, unsigned long new_len, unsigned long *p) 378 { 379 struct mm_struct *mm = current->mm; 380 struct vm_area_struct *vma = find_vma(mm, addr); 381 unsigned long pgoff; 382 383 if (!vma || vma->vm_start > addr) 384 return ERR_PTR(-EFAULT); 385 386 if (is_vm_hugetlb_page(vma)) 387 return ERR_PTR(-EINVAL); 388 389 /* We can't remap across vm area boundaries */ 390 if (old_len > vma->vm_end - addr) 391 return ERR_PTR(-EFAULT); 392 393 if (new_len == old_len) 394 return vma; 395 396 /* Need to be careful about a growing mapping */ 397 pgoff = (addr - vma->vm_start) >> PAGE_SHIFT; 398 pgoff += vma->vm_pgoff; 399 if (pgoff + (new_len >> PAGE_SHIFT) < pgoff) 400 return ERR_PTR(-EINVAL); 401 402 if (vma->vm_flags & (VM_DONTEXPAND | VM_PFNMAP)) 403 return ERR_PTR(-EFAULT); 404 405 if (vma->vm_flags & VM_LOCKED) { 406 unsigned long locked, lock_limit; 407 locked = mm->locked_vm << PAGE_SHIFT; 408 lock_limit = rlimit(RLIMIT_MEMLOCK); 409 locked += new_len - old_len; 410 if (locked > lock_limit && !capable(CAP_IPC_LOCK)) 411 return ERR_PTR(-EAGAIN); 412 } 413 414 if (!may_expand_vm(mm, vma->vm_flags, 415 (new_len - old_len) >> PAGE_SHIFT)) 416 return ERR_PTR(-ENOMEM); 417 418 if (vma->vm_flags & VM_ACCOUNT) { 419 unsigned long charged = (new_len - old_len) >> PAGE_SHIFT; 420 if (security_vm_enough_memory_mm(mm, charged)) 421 return ERR_PTR(-ENOMEM); 422 *p = charged; 423 } 424 425 return vma; 426 } 427 428 static unsigned long mremap_to(unsigned long addr, unsigned long old_len, 429 unsigned long new_addr, unsigned long new_len, bool *locked, 430 struct vm_userfaultfd_ctx *uf, 431 struct list_head *uf_unmap) 432 { 433 struct mm_struct *mm = current->mm; 434 struct vm_area_struct *vma; 435 unsigned long ret = -EINVAL; 436 unsigned long charged = 0; 437 unsigned long map_flags; 438 439 if (offset_in_page(new_addr)) 440 goto out; 441 442 if (new_len > TASK_SIZE || new_addr > TASK_SIZE - new_len) 443 goto out; 444 445 /* Ensure the old/new locations do not overlap */ 446 if (addr + old_len > new_addr && new_addr + new_len > addr) 447 goto out; 448 449 ret = do_munmap(mm, new_addr, new_len, NULL); 450 if (ret) 451 goto out; 452 453 if (old_len >= new_len) { 454 ret = do_munmap(mm, addr+new_len, old_len - new_len, uf_unmap); 455 if (ret && old_len != new_len) 456 goto out; 457 old_len = new_len; 458 } 459 460 vma = vma_to_resize(addr, old_len, new_len, &charged); 461 if (IS_ERR(vma)) { 462 ret = PTR_ERR(vma); 463 goto out; 464 } 465 466 map_flags = MAP_FIXED; 467 if (vma->vm_flags & VM_MAYSHARE) 468 map_flags |= MAP_SHARED; 469 470 ret = get_unmapped_area(vma->vm_file, new_addr, new_len, vma->vm_pgoff + 471 ((addr - vma->vm_start) >> PAGE_SHIFT), 472 map_flags); 473 if (offset_in_page(ret)) 474 goto out1; 475 476 ret = move_vma(vma, addr, old_len, new_len, new_addr, locked, uf, 477 uf_unmap); 478 if (!(offset_in_page(ret))) 479 goto out; 480 out1: 481 vm_unacct_memory(charged); 482 483 out: 484 return ret; 485 } 486 487 static int vma_expandable(struct vm_area_struct *vma, unsigned long delta) 488 { 489 unsigned long end = vma->vm_end + delta; 490 if (end < vma->vm_end) /* overflow */ 491 return 0; 492 if (vma->vm_next && vma->vm_next->vm_start < end) /* intersection */ 493 return 0; 494 if (get_unmapped_area(NULL, vma->vm_start, end - vma->vm_start, 495 0, MAP_FIXED) & ~PAGE_MASK) 496 return 0; 497 return 1; 498 } 499 500 /* 501 * Expand (or shrink) an existing mapping, potentially moving it at the 502 * same time (controlled by the MREMAP_MAYMOVE flag and available VM space) 503 * 504 * MREMAP_FIXED option added 5-Dec-1999 by Benjamin LaHaise 505 * This option implies MREMAP_MAYMOVE. 506 */ 507 SYSCALL_DEFINE5(mremap, unsigned long, addr, unsigned long, old_len, 508 unsigned long, new_len, unsigned long, flags, 509 unsigned long, new_addr) 510 { 511 struct mm_struct *mm = current->mm; 512 struct vm_area_struct *vma; 513 unsigned long ret = -EINVAL; 514 unsigned long charged = 0; 515 bool locked = false; 516 struct vm_userfaultfd_ctx uf = NULL_VM_UFFD_CTX; 517 LIST_HEAD(uf_unmap); 518 519 if (flags & ~(MREMAP_FIXED | MREMAP_MAYMOVE)) 520 return ret; 521 522 if (flags & MREMAP_FIXED && !(flags & MREMAP_MAYMOVE)) 523 return ret; 524 525 if (offset_in_page(addr)) 526 return ret; 527 528 old_len = PAGE_ALIGN(old_len); 529 new_len = PAGE_ALIGN(new_len); 530 531 /* 532 * We allow a zero old-len as a special case 533 * for DOS-emu "duplicate shm area" thing. But 534 * a zero new-len is nonsensical. 535 */ 536 if (!new_len) 537 return ret; 538 539 if (down_write_killable(¤t->mm->mmap_sem)) 540 return -EINTR; 541 542 if (flags & MREMAP_FIXED) { 543 ret = mremap_to(addr, old_len, new_addr, new_len, 544 &locked, &uf, &uf_unmap); 545 goto out; 546 } 547 548 /* 549 * Always allow a shrinking remap: that just unmaps 550 * the unnecessary pages.. 551 * do_munmap does all the needed commit accounting 552 */ 553 if (old_len >= new_len) { 554 ret = do_munmap(mm, addr+new_len, old_len - new_len, &uf_unmap); 555 if (ret && old_len != new_len) 556 goto out; 557 ret = addr; 558 goto out; 559 } 560 561 /* 562 * Ok, we need to grow.. 563 */ 564 vma = vma_to_resize(addr, old_len, new_len, &charged); 565 if (IS_ERR(vma)) { 566 ret = PTR_ERR(vma); 567 goto out; 568 } 569 570 /* old_len exactly to the end of the area.. 571 */ 572 if (old_len == vma->vm_end - addr) { 573 /* can we just expand the current mapping? */ 574 if (vma_expandable(vma, new_len - old_len)) { 575 int pages = (new_len - old_len) >> PAGE_SHIFT; 576 577 if (vma_adjust(vma, vma->vm_start, addr + new_len, 578 vma->vm_pgoff, NULL)) { 579 ret = -ENOMEM; 580 goto out; 581 } 582 583 vm_stat_account(mm, vma->vm_flags, pages); 584 if (vma->vm_flags & VM_LOCKED) { 585 mm->locked_vm += pages; 586 locked = true; 587 new_addr = addr; 588 } 589 ret = addr; 590 goto out; 591 } 592 } 593 594 /* 595 * We weren't able to just expand or shrink the area, 596 * we need to create a new one and move it.. 597 */ 598 ret = -ENOMEM; 599 if (flags & MREMAP_MAYMOVE) { 600 unsigned long map_flags = 0; 601 if (vma->vm_flags & VM_MAYSHARE) 602 map_flags |= MAP_SHARED; 603 604 new_addr = get_unmapped_area(vma->vm_file, 0, new_len, 605 vma->vm_pgoff + 606 ((addr - vma->vm_start) >> PAGE_SHIFT), 607 map_flags); 608 if (offset_in_page(new_addr)) { 609 ret = new_addr; 610 goto out; 611 } 612 613 ret = move_vma(vma, addr, old_len, new_len, new_addr, 614 &locked, &uf, &uf_unmap); 615 } 616 out: 617 if (offset_in_page(ret)) { 618 vm_unacct_memory(charged); 619 locked = 0; 620 } 621 up_write(¤t->mm->mmap_sem); 622 if (locked && new_len > old_len) 623 mm_populate(new_addr + old_len, new_len - old_len); 624 mremap_userfaultfd_complete(&uf, addr, new_addr, old_len); 625 userfaultfd_unmap_complete(mm, &uf_unmap); 626 return ret; 627 } 628