mremap.c 22.1 KB
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 101 102 103 104 105 106 107 108 109 110 111 112 113 114 115 116 117 118 119 120 121 122 123 124 125 126 127 128 129 130 131 132 133 134 135 136 137 138 139 140 141 142 143 144 145 146 147 148 149 150 151 152 153 154 155 156 157 158 159 160 161 162 163 164 165 166 167 168 169 170 171 172 173 174 175 176 177 178 179 180 181 182 183 184 185 186 187 188 189 190 191 192 193 194 195 196 197 198 199 200 201 202 203 204 205 206 207 208 209 210 211 212 213 214 215 216 217 218 219 220 221 222 223 224 225 226 227 228 229 230 231 232 233 234 235 236 237 238 239 240 241 242 243 244 245 246 247 248 249 250 251 252 253 254 255 256 257 258 259 260 261 262 263 264 265 266 267 268 269 270 271 272 273 274 275 276 277 278 279 280 281 282 283 284 285 286 287 288 289 290 291 292 293 294 295 296 297 298 299 300 301 302 303 304 305 306 307 308 309 310 311 312 313 314 315 316 317 318 319 320 321 322 323 324 325 326 327 328 329 330 331 332 333 334 335 336 337 338 339 340 341 342 343 344 345 346 347 348 349 350 351 352 353 354 355 356 357 358 359 360 361 362 363 364 365 366 367 368 369 370 371 372 373 374 375 376 377 378 379 380 381 382 383 384 385 386 387 388 389 390 391 392 393 394 395 396 397 398 399 400 401 402 403 404 405 406 407 408 409 410 411 412 413 414 415 416 417 418 419 420 421 422 423 424 425 426 427 428 429 430 431 432 433 434 435 436 437 438 439 440 441 442 443 444 445 446 447 448 449 450 451 452 453 454 455 456 457 458 459 460 461 462 463 464 465 466 467 468 469 470 471 472 473 474 475 476 477 478 479 480 481 482 483 484 485 486 487 488 489 490 491 492 493 494 495 496 497 498 499 500 501 502 503 504 505 506 507 508 509 510 511 512 513 514 515 516 517 518 519 520 521 522 523 524 525 526 527 528 529 530 531 532 533 534 535 536 537 538 539 540 541 542 543 544 545 546 547 548 549 550 551 552 553 554 555 556 557 558 559 560 561 562 563 564 565 566 567 568 569 570 571 572 573 574 575 576 577 578 579 580 581 582 583 584 585 586 587 588 589 590 591 592 593 594 595 596 597 598 599 600 601 602 603 604 605 606 607 608 609 610 611 612 613 614 615 616 617 618 619 620 621 622 623 624 625 626 627 628 629 630 631 632 633 634 635 636 637 638 639 640 641 642 643 644 645 646 647 648 649 650 651 652 653 654 655 656 657 658 659 660 661 662 663 664 665 666 667 668 669 670 671 672 673 674 675 676 677 678 679 680 681 682 683 684 685 686 687 688 689 690 691 692 693 694 695 696 697 698 699 700 701 702 703 704 705 706 707 708 709 710 711 712 713 714 715 716 717 718 719 720 721 722 723 724 725 726 727 728 729 730 731 732 733 734 735 736 737 738 739 740 741 742 743 744 745 746 747 748 749 750 751 752 753 754 755 756 757 758 759 760 761 762 763 764 765 766 767 768 769 770 771 772 773 774 775 776 777 778 779 780 781 782 783 784 785 786 787 788 789 790 791 792 793 794 795 796 797 798 799 800 801 802 803 804 805 806 807 808 809 810 811 812 813 814
// SPDX-License-Identifier: GPL-2.0
/*
 *	mm/mremap.c
 *
 *	(C) Copyright 1996 Linus Torvalds
 *
 *	Address space accounting code	<alan@lxorguk.ukuu.org.uk>
 *	(C) Copyright 2002 Red Hat Inc, All Rights Reserved
 */

#include <linux/mm.h>
#include <linux/hugetlb.h>
#include <linux/shm.h>
#include <linux/ksm.h>
#include <linux/mman.h>
#include <linux/swap.h>
#include <linux/capability.h>
#include <linux/fs.h>
#include <linux/swapops.h>
#include <linux/highmem.h>
#include <linux/security.h>
#include <linux/syscalls.h>
#include <linux/mmu_notifier.h>
#include <linux/uaccess.h>
#include <linux/mm-arch-hooks.h>
#include <linux/userfaultfd_k.h>

#include <asm/cacheflush.h>
#include <asm/tlbflush.h>

#include "internal.h"

static pmd_t *get_old_pmd(struct mm_struct *mm, unsigned long addr)
{
	pgd_t *pgd;
	p4d_t *p4d;
	pud_t *pud;
	pmd_t *pmd;

	pgd = pgd_offset(mm, addr);
	if (pgd_none_or_clear_bad(pgd))
		return NULL;

	p4d = p4d_offset(pgd, addr);
	if (p4d_none_or_clear_bad(p4d))
		return NULL;

	pud = pud_offset(p4d, addr);
	if (pud_none_or_clear_bad(pud))
		return NULL;

	pmd = pmd_offset(pud, addr);
	if (pmd_none(*pmd))
		return NULL;

	return pmd;
}

static pmd_t *alloc_new_pmd(struct mm_struct *mm, struct vm_area_struct *vma,
			    unsigned long addr)
{
	pgd_t *pgd;
	p4d_t *p4d;
	pud_t *pud;
	pmd_t *pmd;

	pgd = pgd_offset(mm, addr);
	p4d = p4d_alloc(mm, pgd, addr);
	if (!p4d)
		return NULL;
	pud = pud_alloc(mm, p4d, addr);
	if (!pud)
		return NULL;

	pmd = pmd_alloc(mm, pud, addr);
	if (!pmd)
		return NULL;

	VM_BUG_ON(pmd_trans_huge(*pmd));

	return pmd;
}

static void take_rmap_locks(struct vm_area_struct *vma)
{
	if (vma->vm_file)
		i_mmap_lock_write(vma->vm_file->f_mapping);
	if (vma->anon_vma)
		anon_vma_lock_write(vma->anon_vma);
}

static void drop_rmap_locks(struct vm_area_struct *vma)
{
	if (vma->anon_vma)
		anon_vma_unlock_write(vma->anon_vma);
	if (vma->vm_file)
		i_mmap_unlock_write(vma->vm_file->f_mapping);
}

static pte_t move_soft_dirty_pte(pte_t pte)
{
	/*
	 * Set soft dirty bit so we can notice
	 * in userspace the ptes were moved.
	 */
#ifdef CONFIG_MEM_SOFT_DIRTY
	if (pte_present(pte))
		pte = pte_mksoft_dirty(pte);
	else if (is_swap_pte(pte))
		pte = pte_swp_mksoft_dirty(pte);
#endif
	return pte;
}

static void 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)
{
	struct mm_struct *mm = vma->vm_mm;
	pte_t *old_pte, *new_pte, pte;
	spinlock_t *old_ptl, *new_ptl;
	bool force_flush = false;
	unsigned long len = old_end - old_addr;

	/*
	 * When need_rmap_locks is true, we take the i_mmap_rwsem and anon_vma
	 * locks to ensure that rmap will always observe either the old or the
	 * new ptes. This is the easiest way to avoid races with
	 * truncate_pagecache(), page migration, etc...
	 *
	 * When need_rmap_locks is false, we use other ways to avoid
	 * such races:
	 *
	 * - During exec() shift_arg_pages(), we use a specially tagged vma
	 *   which rmap call sites look for using vma_is_temporary_stack().
	 *
	 * - During mremap(), new_vma is often known to be placed after vma
	 *   in rmap traversal order. This ensures rmap will always observe
	 *   either the old pte, or the new pte, or both (the page table locks
	 *   serialize access to individual ptes, but only rmap traversal
	 *   order guarantees that we won't miss both the old and new ptes).
	 */
	if (need_rmap_locks)
		take_rmap_locks(vma);

	/*
	 * We don't have to worry about the ordering of src and dst
	 * pte locks because exclusive mmap_lock prevents deadlock.
	 */
	old_pte = pte_offset_map_lock(mm, old_pmd, old_addr, &old_ptl);
	new_pte = pte_offset_map(new_pmd, new_addr);
	new_ptl = pte_lockptr(mm, new_pmd);
	if (new_ptl != old_ptl)
		spin_lock_nested(new_ptl, SINGLE_DEPTH_NESTING);
	flush_tlb_batched_pending(vma->vm_mm);
	arch_enter_lazy_mmu_mode();

	for (; old_addr < old_end; old_pte++, old_addr += PAGE_SIZE,
				   new_pte++, new_addr += PAGE_SIZE) {
		if (pte_none(*old_pte))
			continue;

		pte = ptep_get_and_clear(mm, old_addr, old_pte);
		/*
		 * If we are remapping a valid PTE, make sure
		 * to flush TLB before we drop the PTL for the
		 * PTE.
		 *
		 * NOTE! Both old and new PTL matter: the old one
		 * for racing with page_mkclean(), the new one to
		 * make sure the physical page stays valid until
		 * the TLB entry for the old mapping has been
		 * flushed.
		 */
		if (pte_present(pte))
			force_flush = true;
		pte = move_pte(pte, new_vma->vm_page_prot, old_addr, new_addr);
		pte = move_soft_dirty_pte(pte);
		set_pte_at(mm, new_addr, new_pte, pte);
	}

	arch_leave_lazy_mmu_mode();
	if (force_flush)
		flush_tlb_range(vma, old_end - len, old_end);
	if (new_ptl != old_ptl)
		spin_unlock(new_ptl);
	pte_unmap(new_pte - 1);
	pte_unmap_unlock(old_pte - 1, old_ptl);
	if (need_rmap_locks)
		drop_rmap_locks(vma);
}

#ifdef CONFIG_HAVE_MOVE_PMD
static bool move_normal_pmd(struct vm_area_struct *vma, unsigned long old_addr,
		  unsigned long new_addr, pmd_t *old_pmd, pmd_t *new_pmd)
{
	spinlock_t *old_ptl, *new_ptl;
	struct mm_struct *mm = vma->vm_mm;
	pmd_t pmd;

	/*
	 * The destination pmd shouldn't be established, free_pgtables()
	 * should have released it.
	 *
	 * However, there's a case during execve() where we use mremap
	 * to move the initial stack, and in that case the target area
	 * may overlap the source area (always moving down).
	 *
	 * If everything is PMD-aligned, that works fine, as moving
	 * each pmd down will clear the source pmd. But if we first
	 * have a few 4kB-only pages that get moved down, and then
	 * hit the "now the rest is PMD-aligned, let's do everything
	 * one pmd at a time", we will still have the old (now empty
	 * of any 4kB pages, but still there) PMD in the page table
	 * tree.
	 *
	 * Warn on it once - because we really should try to figure
	 * out how to do this better - but then say "I won't move
	 * this pmd".
	 *
	 * One alternative might be to just unmap the target pmd at
	 * this point, and verify that it really is empty. We'll see.
	 */
	if (WARN_ON_ONCE(!pmd_none(*new_pmd)))
		return false;

	/*
	 * We don't have to worry about the ordering of src and dst
	 * ptlocks because exclusive mmap_lock prevents deadlock.
	 */
	old_ptl = pmd_lock(vma->vm_mm, old_pmd);
	new_ptl = pmd_lockptr(mm, new_pmd);
	if (new_ptl != old_ptl)
		spin_lock_nested(new_ptl, SINGLE_DEPTH_NESTING);

	/* Clear the pmd */
	pmd = *old_pmd;
	pmd_clear(old_pmd);

	VM_BUG_ON(!pmd_none(*new_pmd));

	/* Set the new pmd */
	set_pmd_at(mm, new_addr, new_pmd, pmd);
	flush_tlb_range(vma, old_addr, old_addr + PMD_SIZE);
	if (new_ptl != old_ptl)
		spin_unlock(new_ptl);
	spin_unlock(old_ptl);

	return true;
}
#endif

unsigned long 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)
{
	unsigned long extent, next, old_end;
	struct mmu_notifier_range range;
	pmd_t *old_pmd, *new_pmd;

	old_end = old_addr + len;
	flush_cache_range(vma, old_addr, old_end);

	mmu_notifier_range_init(&range, MMU_NOTIFY_UNMAP, 0, vma, vma->vm_mm,
				old_addr, old_end);
	mmu_notifier_invalidate_range_start(&range);

	for (; old_addr < old_end; old_addr += extent, new_addr += extent) {
		cond_resched();
		next = (old_addr + PMD_SIZE) & PMD_MASK;
		/* even if next overflowed, extent below will be ok */
		extent = next - old_addr;
		if (extent > old_end - old_addr)
			extent = old_end - old_addr;
		next = (new_addr + PMD_SIZE) & PMD_MASK;
		if (extent > next - new_addr)
			extent = next - new_addr;
		old_pmd = get_old_pmd(vma->vm_mm, old_addr);
		if (!old_pmd)
			continue;
		new_pmd = alloc_new_pmd(vma->vm_mm, vma, new_addr);
		if (!new_pmd)
			break;
		if (is_swap_pmd(*old_pmd) || pmd_trans_huge(*old_pmd) || pmd_devmap(*old_pmd)) {
			if (extent == HPAGE_PMD_SIZE) {
				bool moved;
				/* See comment in move_ptes() */
				if (need_rmap_locks)
					take_rmap_locks(vma);
				moved = move_huge_pmd(vma, old_addr, new_addr,
						      old_pmd, new_pmd);
				if (need_rmap_locks)
					drop_rmap_locks(vma);
				if (moved)
					continue;
			}
			split_huge_pmd(vma, old_pmd, old_addr);
			if (pmd_trans_unstable(old_pmd))
				continue;
		} else if (extent == PMD_SIZE) {
#ifdef CONFIG_HAVE_MOVE_PMD
			/*
			 * If the extent is PMD-sized, try to speed the move by
			 * moving at the PMD level if possible.
			 */
			bool moved;

			if (need_rmap_locks)
				take_rmap_locks(vma);
			moved = move_normal_pmd(vma, old_addr, new_addr,
						old_pmd, new_pmd);
			if (need_rmap_locks)
				drop_rmap_locks(vma);
			if (moved)
				continue;
#endif
		}

		if (pte_alloc(new_vma->vm_mm, new_pmd))
			break;
		move_ptes(vma, old_pmd, old_addr, old_addr + extent, new_vma,
			  new_pmd, new_addr, need_rmap_locks);
	}

	mmu_notifier_invalidate_range_end(&range);

	return len + old_addr - old_end;	/* how much done */
}

static unsigned long 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)
{
	struct mm_struct *mm = vma->vm_mm;
	struct vm_area_struct *new_vma;
	unsigned long vm_flags = vma->vm_flags;
	unsigned long new_pgoff;
	unsigned long moved_len;
	unsigned long excess = 0;
	unsigned long hiwater_vm;
	int split = 0;
	int err;
	bool need_rmap_locks;

	/*
	 * We'd prefer to avoid failure later on in do_munmap:
	 * which may split one vma into three before unmapping.
	 */
	if (mm->map_count >= sysctl_max_map_count - 3)
		return -ENOMEM;

	/*
	 * Advise KSM to break any KSM pages in the area to be moved:
	 * it would be confusing if they were to turn up at the new
	 * location, where they happen to coincide with different KSM
	 * pages recently unmapped.  But leave vma->vm_flags as it was,
	 * so KSM can come around to merge on vma and new_vma afterwards.
	 */
	err = ksm_madvise(vma, old_addr, old_addr + old_len,
						MADV_UNMERGEABLE, &vm_flags);
	if (err)
		return err;

	new_pgoff = vma->vm_pgoff + ((old_addr - vma->vm_start) >> PAGE_SHIFT);
	new_vma = copy_vma(&vma, new_addr, new_len, new_pgoff,
			   &need_rmap_locks);
	if (!new_vma)
		return -ENOMEM;

	moved_len = move_page_tables(vma, old_addr, new_vma, new_addr, old_len,
				     need_rmap_locks);
	if (moved_len < old_len) {
		err = -ENOMEM;
	} else if (vma->vm_ops && vma->vm_ops->mremap) {
		err = vma->vm_ops->mremap(new_vma);
	}

	if (unlikely(err)) {
		/*
		 * On error, move entries back from new area to old,
		 * which will succeed since page tables still there,
		 * and then proceed to unmap new area instead of old.
		 */
		move_page_tables(new_vma, new_addr, vma, old_addr, moved_len,
				 true);
		vma = new_vma;
		old_len = new_len;
		old_addr = new_addr;
		new_addr = err;
	} else {
		mremap_userfaultfd_prep(new_vma, uf);
		arch_remap(mm, old_addr, old_addr + old_len,
			   new_addr, new_addr + new_len);
	}

	/* Conceal VM_ACCOUNT so old reservation is not undone */
	if (vm_flags & VM_ACCOUNT) {
		vma->vm_flags &= ~VM_ACCOUNT;
		excess = vma->vm_end - vma->vm_start - old_len;
		if (old_addr > vma->vm_start &&
		    old_addr + old_len < vma->vm_end)
			split = 1;
	}

	/*
	 * If we failed to move page tables we still do total_vm increment
	 * since do_munmap() will decrement it by old_len == new_len.
	 *
	 * Since total_vm is about to be raised artificially high for a
	 * moment, we need to restore high watermark afterwards: if stats
	 * are taken meanwhile, total_vm and hiwater_vm appear too high.
	 * If this were a serious issue, we'd add a flag to do_munmap().
	 */
	hiwater_vm = mm->hiwater_vm;
	vm_stat_account(mm, vma->vm_flags, new_len >> PAGE_SHIFT);

	/* Tell pfnmap has moved from this vma */
	if (unlikely(vma->vm_flags & VM_PFNMAP))
		untrack_pfn_moved(vma);

	if (unlikely(!err && (flags & MREMAP_DONTUNMAP))) {
		if (vm_flags & VM_ACCOUNT) {
			/* Always put back VM_ACCOUNT since we won't unmap */
			vma->vm_flags |= VM_ACCOUNT;

			vm_acct_memory(new_len >> PAGE_SHIFT);
		}

		/*
		 * VMAs can actually be merged back together in copy_vma
		 * calling merge_vma. This can happen with anonymous vmas
		 * which have not yet been faulted, so if we were to consider
		 * this VMA split we'll end up adding VM_ACCOUNT on the
		 * next VMA, which is completely unrelated if this VMA
		 * was re-merged.
		 */
		if (split && new_vma == vma)
			split = 0;

		/* We always clear VM_LOCKED[ONFAULT] on the old vma */
		vma->vm_flags &= VM_LOCKED_CLEAR_MASK;

		/* Because we won't unmap we don't need to touch locked_vm */
		goto out;
	}

	if (do_munmap(mm, old_addr, old_len, uf_unmap) < 0) {
		/* OOM: unable to split vma, just get accounts right */
		vm_unacct_memory(excess >> PAGE_SHIFT);
		excess = 0;
	}

	if (vm_flags & VM_LOCKED) {
		mm->locked_vm += new_len >> PAGE_SHIFT;
		*locked = true;
	}
out:
	mm->hiwater_vm = hiwater_vm;

	/* Restore VM_ACCOUNT if one or two pieces of vma left */
	if (excess) {
		vma->vm_flags |= VM_ACCOUNT;
		if (split)
			vma->vm_next->vm_flags |= VM_ACCOUNT;
	}

	return new_addr;
}

static struct vm_area_struct *vma_to_resize(unsigned long addr,
	unsigned long old_len, unsigned long new_len, unsigned long flags,
	unsigned long *p)
{
	struct mm_struct *mm = current->mm;
	struct vm_area_struct *vma = find_vma(mm, addr);
	unsigned long pgoff;

	if (!vma || vma->vm_start > addr)
		return ERR_PTR(-EFAULT);

	/*
	 * !old_len is a special case where an attempt is made to 'duplicate'
	 * a mapping.  This makes no sense for private mappings as it will
	 * instead create a fresh/new mapping unrelated to the original.  This
	 * is contrary to the basic idea of mremap which creates new mappings
	 * based on the original.  There are no known use cases for this
	 * behavior.  As a result, fail such attempts.
	 */
	if (!old_len && !(vma->vm_flags & (VM_SHARED | VM_MAYSHARE))) {
		pr_warn_once("%s (%d): attempted to duplicate a private mapping with mremap.  This is not supported.\n", current->comm, current->pid);
		return ERR_PTR(-EINVAL);
	}

	if (flags & MREMAP_DONTUNMAP && (!vma_is_anonymous(vma) ||
			vma->vm_flags & VM_SHARED))
		return ERR_PTR(-EINVAL);

	if (is_vm_hugetlb_page(vma))
		return ERR_PTR(-EINVAL);

	/* We can't remap across vm area boundaries */
	if (old_len > vma->vm_end - addr)
		return ERR_PTR(-EFAULT);

	if (new_len == old_len)
		return vma;

	/* Need to be careful about a growing mapping */
	pgoff = (addr - vma->vm_start) >> PAGE_SHIFT;
	pgoff += vma->vm_pgoff;
	if (pgoff + (new_len >> PAGE_SHIFT) < pgoff)
		return ERR_PTR(-EINVAL);

	if (vma->vm_flags & (VM_DONTEXPAND | VM_PFNMAP))
		return ERR_PTR(-EFAULT);

	if (vma->vm_flags & VM_LOCKED) {
		unsigned long locked, lock_limit;
		locked = mm->locked_vm << PAGE_SHIFT;
		lock_limit = rlimit(RLIMIT_MEMLOCK);
		locked += new_len - old_len;
		if (locked > lock_limit && !capable(CAP_IPC_LOCK))
			return ERR_PTR(-EAGAIN);
	}

	if (!may_expand_vm(mm, vma->vm_flags,
				(new_len - old_len) >> PAGE_SHIFT))
		return ERR_PTR(-ENOMEM);

	if (vma->vm_flags & VM_ACCOUNT) {
		unsigned long charged = (new_len - old_len) >> PAGE_SHIFT;
		if (security_vm_enough_memory_mm(mm, charged))
			return ERR_PTR(-ENOMEM);
		*p = charged;
	}

	return vma;
}

static unsigned long 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)
{
	struct mm_struct *mm = current->mm;
	struct vm_area_struct *vma;
	unsigned long ret = -EINVAL;
	unsigned long charged = 0;
	unsigned long map_flags = 0;

	if (offset_in_page(new_addr))
		goto out;

	if (new_len > TASK_SIZE || new_addr > TASK_SIZE - new_len)
		goto out;

	/* Ensure the old/new locations do not overlap */
	if (addr + old_len > new_addr && new_addr + new_len > addr)
		goto out;

	/*
	 * move_vma() need us to stay 4 maps below the threshold, otherwise
	 * it will bail out at the very beginning.
	 * That is a problem if we have already unmaped the regions here
	 * (new_addr, and old_addr), because userspace will not know the
	 * state of the vma's after it gets -ENOMEM.
	 * So, to avoid such scenario we can pre-compute if the whole
	 * operation has high chances to success map-wise.
	 * Worst-scenario case is when both vma's (new_addr and old_addr) get
	 * split in 3 before unmaping it.
	 * That means 2 more maps (1 for each) to the ones we already hold.
	 * Check whether current map count plus 2 still leads us to 4 maps below
	 * the threshold, otherwise return -ENOMEM here to be more safe.
	 */
	if ((mm->map_count + 2) >= sysctl_max_map_count - 3)
		return -ENOMEM;

	if (flags & MREMAP_FIXED) {
		ret = do_munmap(mm, new_addr, new_len, uf_unmap_early);
		if (ret)
			goto out;
	}

	if (old_len >= new_len) {
		ret = do_munmap(mm, addr+new_len, old_len - new_len, uf_unmap);
		if (ret && old_len != new_len)
			goto out;
		old_len = new_len;
	}

	vma = vma_to_resize(addr, old_len, new_len, flags, &charged);
	if (IS_ERR(vma)) {
		ret = PTR_ERR(vma);
		goto out;
	}

	/* MREMAP_DONTUNMAP expands by old_len since old_len == new_len */
	if (flags & MREMAP_DONTUNMAP &&
		!may_expand_vm(mm, vma->vm_flags, old_len >> PAGE_SHIFT)) {
		ret = -ENOMEM;
		goto out;
	}

	if (flags & MREMAP_FIXED)
		map_flags |= MAP_FIXED;

	if (vma->vm_flags & VM_MAYSHARE)
		map_flags |= MAP_SHARED;

	ret = get_unmapped_area(vma->vm_file, new_addr, new_len, vma->vm_pgoff +
				((addr - vma->vm_start) >> PAGE_SHIFT),
				map_flags);
	if (IS_ERR_VALUE(ret))
		goto out1;

	/* We got a new mapping */
	if (!(flags & MREMAP_FIXED))
		new_addr = ret;

	ret = move_vma(vma, addr, old_len, new_len, new_addr, locked, flags, uf,
		       uf_unmap);

	if (!(offset_in_page(ret)))
		goto out;

out1:
	vm_unacct_memory(charged);

out:
	return ret;
}

static int vma_expandable(struct vm_area_struct *vma, unsigned long delta)
{
	unsigned long end = vma->vm_end + delta;
	if (end < vma->vm_end) /* overflow */
		return 0;
	if (vma->vm_next && vma->vm_next->vm_start < end) /* intersection */
		return 0;
	if (get_unmapped_area(NULL, vma->vm_start, end - vma->vm_start,
			      0, MAP_FIXED) & ~PAGE_MASK)
		return 0;
	return 1;
}

/*
 * Expand (or shrink) an existing mapping, potentially moving it at the
 * same time (controlled by the MREMAP_MAYMOVE flag and available VM space)
 *
 * MREMAP_FIXED option added 5-Dec-1999 by Benjamin LaHaise
 * This option implies MREMAP_MAYMOVE.
 */
SYSCALL_DEFINE5(mremap, unsigned long, addr, unsigned long, old_len,
		unsigned long, new_len, unsigned long, flags,
		unsigned long, new_addr)
{
	struct mm_struct *mm = current->mm;
	struct vm_area_struct *vma;
	unsigned long ret = -EINVAL;
	unsigned long charged = 0;
	bool locked = false;
	bool downgraded = false;
	struct vm_userfaultfd_ctx uf = NULL_VM_UFFD_CTX;
	LIST_HEAD(uf_unmap_early);
	LIST_HEAD(uf_unmap);

	/*
	 * There is a deliberate asymmetry here: we strip the pointer tag
	 * from the old address but leave the new address alone. This is
	 * for consistency with mmap(), where we prevent the creation of
	 * aliasing mappings in userspace by leaving the tag bits of the
	 * mapping address intact. A non-zero tag will cause the subsequent
	 * range checks to reject the address as invalid.
	 *
	 * See Documentation/arm64/tagged-address-abi.rst for more information.
	 */
	addr = untagged_addr(addr);

	if (flags & ~(MREMAP_FIXED | MREMAP_MAYMOVE | MREMAP_DONTUNMAP))
		return ret;

	if (flags & MREMAP_FIXED && !(flags & MREMAP_MAYMOVE))
		return ret;

	/*
	 * MREMAP_DONTUNMAP is always a move and it does not allow resizing
	 * in the process.
	 */
	if (flags & MREMAP_DONTUNMAP &&
			(!(flags & MREMAP_MAYMOVE) || old_len != new_len))
		return ret;


	if (offset_in_page(addr))
		return ret;

	old_len = PAGE_ALIGN(old_len);
	new_len = PAGE_ALIGN(new_len);

	/*
	 * We allow a zero old-len as a special case
	 * for DOS-emu "duplicate shm area" thing. But
	 * a zero new-len is nonsensical.
	 */
	if (!new_len)
		return ret;

	if (mmap_write_lock_killable(current->mm))
		return -EINTR;

	if (flags & (MREMAP_FIXED | MREMAP_DONTUNMAP)) {
		ret = mremap_to(addr, old_len, new_addr, new_len,
				&locked, flags, &uf, &uf_unmap_early,
				&uf_unmap);
		goto out;
	}

	/*
	 * Always allow a shrinking remap: that just unmaps
	 * the unnecessary pages..
	 * __do_munmap does all the needed commit accounting, and
	 * downgrades mmap_lock to read if so directed.
	 */
	if (old_len >= new_len) {
		int retval;

		retval = __do_munmap(mm, addr+new_len, old_len - new_len,
				  &uf_unmap, true);
		if (retval < 0 && old_len != new_len) {
			ret = retval;
			goto out;
		/* Returning 1 indicates mmap_lock is downgraded to read. */
		} else if (retval == 1)
			downgraded = true;
		ret = addr;
		goto out;
	}

	/*
	 * Ok, we need to grow..
	 */
	vma = vma_to_resize(addr, old_len, new_len, flags, &charged);
	if (IS_ERR(vma)) {
		ret = PTR_ERR(vma);
		goto out;
	}

	/* old_len exactly to the end of the area..
	 */
	if (old_len == vma->vm_end - addr) {
		/* can we just expand the current mapping? */
		if (vma_expandable(vma, new_len - old_len)) {
			int pages = (new_len - old_len) >> PAGE_SHIFT;

			if (vma_adjust(vma, vma->vm_start, addr + new_len,
				       vma->vm_pgoff, NULL)) {
				ret = -ENOMEM;
				goto out;
			}

			vm_stat_account(mm, vma->vm_flags, pages);
			if (vma->vm_flags & VM_LOCKED) {
				mm->locked_vm += pages;
				locked = true;
				new_addr = addr;
			}
			ret = addr;
			goto out;
		}
	}

	/*
	 * We weren't able to just expand or shrink the area,
	 * we need to create a new one and move it..
	 */
	ret = -ENOMEM;
	if (flags & MREMAP_MAYMOVE) {
		unsigned long map_flags = 0;
		if (vma->vm_flags & VM_MAYSHARE)
			map_flags |= MAP_SHARED;

		new_addr = get_unmapped_area(vma->vm_file, 0, new_len,
					vma->vm_pgoff +
					((addr - vma->vm_start) >> PAGE_SHIFT),
					map_flags);
		if (IS_ERR_VALUE(new_addr)) {
			ret = new_addr;
			goto out;
		}

		ret = move_vma(vma, addr, old_len, new_len, new_addr,
			       &locked, flags, &uf, &uf_unmap);
	}
out:
	if (offset_in_page(ret)) {
		vm_unacct_memory(charged);
		locked = false;
	}
	if (downgraded)
		mmap_read_unlock(current->mm);
	else
		mmap_write_unlock(current->mm);
	if (locked && new_len > old_len)
		mm_populate(new_addr + old_len, new_len - old_len);
	userfaultfd_unmap_complete(mm, &uf_unmap_early);
	mremap_userfaultfd_complete(&uf, addr, ret, old_len);
	userfaultfd_unmap_complete(mm, &uf_unmap);
	return ret;
}