Adding upstream version 5.10.209.upstream/5.10.209upstream

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>

1 files changed, 815 insertions, 0 deletions

diff --git a/mm/mremap.c b/mm/mremap.c
new file mode 100644
index 000000000..3334c4022
--- /dev/null
+++ b/mm/mremap.c
@@ -0,0 +1,815 @@
+// 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;
+
+	if (!len)
+		return 0;
+
+	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;
+
+			take_rmap_locks(vma);
+			moved = move_normal_pmd(vma, old_addr, new_addr,
+						old_pmd, new_pmd);
+			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;
+}