mm/userfaultfd.c - arm/linux - Git at Google

 /*
  *  mm/userfaultfd.c
  *
  *  Copyright (C) 2015  Red Hat, Inc.
  *
  *  This work is licensed under the terms of the GNU GPL, version 2. See
  *  the COPYING file in the top-level directory.
  */

 #include <linux/mm.h>
 #include <linux/pagemap.h>
 #include <linux/rmap.h>
 #include <linux/swap.h>
 #include <linux/swapops.h>
 #include <linux/userfaultfd_k.h>
 #include <linux/mmu_notifier.h>
 #include <asm/tlbflush.h>
 #include "internal.h"

 static int mcopy_atomic_pte(struct mm_struct *dst_mm,
 			    pmd_t *dst_pmd,
 			    struct vm_area_struct *dst_vma,
 			    unsigned long dst_addr,
 			    unsigned long src_addr,
 			    struct page **pagep)
 {
 	struct mem_cgroup *memcg;
 	pte_t _dst_pte, *dst_pte;
 	spinlock_t *ptl;
 	void *page_kaddr;
 	int ret;
 	struct page *page;

 	if (!*pagep) {
 		ret = -ENOMEM;
 		page = alloc_page_vma(GFP_HIGHUSER_MOVABLE, dst_vma, dst_addr);
 		if (!page)
 			goto out;

 		page_kaddr = kmap_atomic(page);
 		ret = copy_from_user(page_kaddr,
 				     (const void __user *) src_addr,
 				     PAGE_SIZE);
 		kunmap_atomic(page_kaddr);

 		/* fallback to copy_from_user outside mmap_sem */
 		if (unlikely(ret)) {
 			ret = -EFAULT;
 			*pagep = page;
 			/* don't free the page */
 			goto out;
 		}
 	} else {
 		page = *pagep;
 		*pagep = NULL;
 	}

 	/*
 	 * The memory barrier inside __SetPageUptodate makes sure that
 	 * preceeding stores to the page contents become visible before
 	 * the set_pte_at() write.
 	 */
 	__SetPageUptodate(page);

 	ret = -ENOMEM;
 	if (mem_cgroup_try_charge(page, dst_mm, GFP_KERNEL, &memcg, false))
 		goto out_release;

 	_dst_pte = mk_pte(page, dst_vma->vm_page_prot);
 	if (dst_vma->vm_flags & VM_WRITE)
 		_dst_pte = pte_mkwrite(pte_mkdirty(_dst_pte));

 	ret = -EEXIST;
 	dst_pte = pte_offset_map_lock(dst_mm, dst_pmd, dst_addr, &ptl);
 	if (!pte_none(*dst_pte))
 		goto out_release_uncharge_unlock;

 	inc_mm_counter(dst_mm, MM_ANONPAGES);
 	page_add_new_anon_rmap(page, dst_vma, dst_addr, false);
 	mem_cgroup_commit_charge(page, memcg, false, false);
 	lru_cache_add_active_or_unevictable(page, dst_vma);

 	set_pte_at(dst_mm, dst_addr, dst_pte, _dst_pte);

 	/* No need to invalidate - it was non-present before */
 	update_mmu_cache(dst_vma, dst_addr, dst_pte);

 	pte_unmap_unlock(dst_pte, ptl);
 	ret = 0;
 out:
 	return ret;
 out_release_uncharge_unlock:
 	pte_unmap_unlock(dst_pte, ptl);
 	mem_cgroup_cancel_charge(page, memcg, false);
 out_release:
 	page_cache_release(page);
 	goto out;
 }

 static int mfill_zeropage_pte(struct mm_struct *dst_mm,
 			      pmd_t *dst_pmd,
 			      struct vm_area_struct *dst_vma,
 			      unsigned long dst_addr)
 {
 	pte_t _dst_pte, *dst_pte;
 	spinlock_t *ptl;
 	int ret;

 	_dst_pte = pte_mkspecial(pfn_pte(my_zero_pfn(dst_addr),
 					 dst_vma->vm_page_prot));
 	ret = -EEXIST;
 	dst_pte = pte_offset_map_lock(dst_mm, dst_pmd, dst_addr, &ptl);
 	if (!pte_none(*dst_pte))
 		goto out_unlock;
 	set_pte_at(dst_mm, dst_addr, dst_pte, _dst_pte);
 	/* No need to invalidate - it was non-present before */
 	update_mmu_cache(dst_vma, dst_addr, dst_pte);
 	ret = 0;
 out_unlock:
 	pte_unmap_unlock(dst_pte, ptl);
 	return ret;
 }

 static pmd_t *mm_alloc_pmd(struct mm_struct *mm, unsigned long address)
 {
 	pgd_t *pgd;
 	pud_t *pud;
 	pmd_t *pmd = NULL;

 	pgd = pgd_offset(mm, address);
 	pud = pud_alloc(mm, pgd, address);
 	if (pud)
 		/*
 		 * Note that we didn't run this because the pmd was
 		 * missing, the *pmd may be already established and in
 		 * turn it may also be a trans_huge_pmd.
 		 */
 		pmd = pmd_alloc(mm, pud, address);
 	return pmd;
 }

 static __always_inline ssize_t __mcopy_atomic(struct mm_struct *dst_mm,
 					      unsigned long dst_start,
 					      unsigned long src_start,
 					      unsigned long len,
 					      bool zeropage)
 {
 	struct vm_area_struct *dst_vma;
 	ssize_t err;
 	pmd_t *dst_pmd;
 	unsigned long src_addr, dst_addr;
 	long copied;
 	struct page *page;

 	/*
 	 * Sanitize the command parameters:
 	 */
 	BUG_ON(dst_start & ~PAGE_MASK);
 	BUG_ON(len & ~PAGE_MASK);

 	/* Does the address range wrap, or is the span zero-sized? */
 	BUG_ON(src_start + len <= src_start);
 	BUG_ON(dst_start + len <= dst_start);

 	src_addr = src_start;
 	dst_addr = dst_start;
 	copied = 0;
 	page = NULL;
 retry:
 	down_read(&dst_mm->mmap_sem);

 	/*
 	 * Make sure the vma is not shared, that the dst range is
 	 * both valid and fully within a single existing vma.
 	 */
 	err = -EINVAL;
 	dst_vma = find_vma(dst_mm, dst_start);
 	if (!dst_vma || (dst_vma->vm_flags & VM_SHARED))
 		goto out_unlock;
 	if (dst_start < dst_vma->vm_start ||
 	    dst_start + len > dst_vma->vm_end)
 		goto out_unlock;

 	/*
 	 * Be strict and only allow __mcopy_atomic on userfaultfd
 	 * registered ranges to prevent userland errors going
 	 * unnoticed. As far as the VM consistency is concerned, it
 	 * would be perfectly safe to remove this check, but there's
 	 * no useful usage for __mcopy_atomic ouside of userfaultfd
 	 * registered ranges. This is after all why these are ioctls
 	 * belonging to the userfaultfd and not syscalls.
 	 */
 	if (!dst_vma->vm_userfaultfd_ctx.ctx)
 		goto out_unlock;

 	/*
 	 * FIXME: only allow copying on anonymous vmas, tmpfs should
 	 * be added.
 	 */
 	if (dst_vma->vm_ops)
 		goto out_unlock;

 	/*
 	 * Ensure the dst_vma has a anon_vma or this page
 	 * would get a NULL anon_vma when moved in the
 	 * dst_vma.
 	 */
 	err = -ENOMEM;
 	if (unlikely(anon_vma_prepare(dst_vma)))
 		goto out_unlock;

 	while (src_addr < src_start + len) {
 		pmd_t dst_pmdval;

 		BUG_ON(dst_addr >= dst_start + len);

 		dst_pmd = mm_alloc_pmd(dst_mm, dst_addr);
 		if (unlikely(!dst_pmd)) {
 			err = -ENOMEM;
 			break;
 		}

 		dst_pmdval = pmd_read_atomic(dst_pmd);
 		/*
 		 * If the dst_pmd is mapped as THP don't
 		 * override it and just be strict.
 		 */
 		if (unlikely(pmd_trans_huge(dst_pmdval))) {
 			err = -EEXIST;
 			break;
 		}
 		if (unlikely(pmd_none(dst_pmdval)) &&
 		    unlikely(__pte_alloc(dst_mm, dst_pmd, dst_addr))) {
 			err = -ENOMEM;
 			break;
 		}
 		/* If an huge pmd materialized from under us fail */
 		if (unlikely(pmd_trans_huge(*dst_pmd))) {
 			err = -EFAULT;
 			break;
 		}

 		BUG_ON(pmd_none(*dst_pmd));
 		BUG_ON(pmd_trans_huge(*dst_pmd));

 		if (!zeropage)
 			err = mcopy_atomic_pte(dst_mm, dst_pmd, dst_vma,
 					       dst_addr, src_addr, &page);
 		else
 			err = mfill_zeropage_pte(dst_mm, dst_pmd, dst_vma,
 						 dst_addr);

 		cond_resched();

 		if (unlikely(err == -EFAULT)) {
 			void *page_kaddr;

 			up_read(&dst_mm->mmap_sem);
 			BUG_ON(!page);

 			page_kaddr = kmap(page);
 			err = copy_from_user(page_kaddr,
 					     (const void __user *) src_addr,
 					     PAGE_SIZE);
 			kunmap(page);
 			if (unlikely(err)) {
 				err = -EFAULT;
 				goto out;
 			}
 			goto retry;
 		} else
 			BUG_ON(page);

 		if (!err) {
 			dst_addr += PAGE_SIZE;
 			src_addr += PAGE_SIZE;
 			copied += PAGE_SIZE;

 			if (fatal_signal_pending(current))
 				err = -EINTR;
 		}
 		if (err)
 			break;
 	}

 out_unlock:
 	up_read(&dst_mm->mmap_sem);
 out:
 	if (page)
 		page_cache_release(page);
 	BUG_ON(copied < 0);
 	BUG_ON(err > 0);
 	BUG_ON(!copied && !err);
 	return copied ? copied : err;
 }

 ssize_t mcopy_atomic(struct mm_struct *dst_mm, unsigned long dst_start,
 		     unsigned long src_start, unsigned long len)
 {
 	return __mcopy_atomic(dst_mm, dst_start, src_start, len, false);
 }

 ssize_t mfill_zeropage(struct mm_struct *dst_mm, unsigned long start,
 		       unsigned long len)
 {
 	return __mcopy_atomic(dst_mm, start, 0, len, true);
 }
	/*
	* mm/userfaultfd.c
	*
	* Copyright (C) 2015 Red Hat, Inc.
	*
	* This work is licensed under the terms of the GNU GPL, version 2. See
	* the COPYING file in the top-level directory.
	*/

	#include <linux/mm.h>
	#include <linux/pagemap.h>
	#include <linux/rmap.h>
	#include <linux/swap.h>
	#include <linux/swapops.h>
	#include <linux/userfaultfd_k.h>
	#include <linux/mmu_notifier.h>
	#include <asm/tlbflush.h>
	#include "internal.h"

	static int mcopy_atomic_pte(struct mm_struct *dst_mm,
	pmd_t *dst_pmd,
	struct vm_area_struct *dst_vma,
	unsigned long dst_addr,
	unsigned long src_addr,
	struct page **pagep)
	{
	struct mem_cgroup *memcg;
	pte_t _dst_pte, *dst_pte;
	spinlock_t *ptl;
	void *page_kaddr;
	int ret;
	struct page *page;

	if (!*pagep) {
	ret = -ENOMEM;
	page = alloc_page_vma(GFP_HIGHUSER_MOVABLE, dst_vma, dst_addr);
	if (!page)
	goto out;

	page_kaddr = kmap_atomic(page);
	ret = copy_from_user(page_kaddr,
	(const void __user *) src_addr,
	PAGE_SIZE);
	kunmap_atomic(page_kaddr);

	/* fallback to copy_from_user outside mmap_sem */
	if (unlikely(ret)) {
	ret = -EFAULT;
	*pagep = page;
	/* don't free the page */
	goto out;
	}
	} else {
	page = *pagep;
	*pagep = NULL;
	}

	/*
	* The memory barrier inside __SetPageUptodate makes sure that
	* preceeding stores to the page contents become visible before
	* the set_pte_at() write.
	*/
	__SetPageUptodate(page);

	ret = -ENOMEM;
	if (mem_cgroup_try_charge(page, dst_mm, GFP_KERNEL, &memcg, false))
	goto out_release;

	_dst_pte = mk_pte(page, dst_vma->vm_page_prot);
	if (dst_vma->vm_flags & VM_WRITE)
	_dst_pte = pte_mkwrite(pte_mkdirty(_dst_pte));

	ret = -EEXIST;
	dst_pte = pte_offset_map_lock(dst_mm, dst_pmd, dst_addr, &ptl);
	if (!pte_none(*dst_pte))
	goto out_release_uncharge_unlock;

	inc_mm_counter(dst_mm, MM_ANONPAGES);
	page_add_new_anon_rmap(page, dst_vma, dst_addr, false);
	mem_cgroup_commit_charge(page, memcg, false, false);
	lru_cache_add_active_or_unevictable(page, dst_vma);

	set_pte_at(dst_mm, dst_addr, dst_pte, _dst_pte);

	/* No need to invalidate - it was non-present before */
	update_mmu_cache(dst_vma, dst_addr, dst_pte);

	pte_unmap_unlock(dst_pte, ptl);
	ret = 0;
	out:
	return ret;
	out_release_uncharge_unlock:
	pte_unmap_unlock(dst_pte, ptl);
	mem_cgroup_cancel_charge(page, memcg, false);
	out_release:
	page_cache_release(page);
	goto out;
	}

	static int mfill_zeropage_pte(struct mm_struct *dst_mm,
	pmd_t *dst_pmd,
	struct vm_area_struct *dst_vma,
	unsigned long dst_addr)
	{
	pte_t _dst_pte, *dst_pte;
	spinlock_t *ptl;
	int ret;

	_dst_pte = pte_mkspecial(pfn_pte(my_zero_pfn(dst_addr),
	dst_vma->vm_page_prot));
	ret = -EEXIST;
	dst_pte = pte_offset_map_lock(dst_mm, dst_pmd, dst_addr, &ptl);
	if (!pte_none(*dst_pte))
	goto out_unlock;
	set_pte_at(dst_mm, dst_addr, dst_pte, _dst_pte);
	/* No need to invalidate - it was non-present before */
	update_mmu_cache(dst_vma, dst_addr, dst_pte);
	ret = 0;
	out_unlock:
	pte_unmap_unlock(dst_pte, ptl);
	return ret;
	}

	static pmd_t mm_alloc_pmd(struct mm_struct mm, unsigned long address)
	{
	pgd_t *pgd;
	pud_t *pud;
	pmd_t *pmd = NULL;

	pgd = pgd_offset(mm, address);
	pud = pud_alloc(mm, pgd, address);
	if (pud)
	/*
	* Note that we didn't run this because the pmd was
	* missing, the *pmd may be already established and in
	* turn it may also be a trans_huge_pmd.
	*/
	pmd = pmd_alloc(mm, pud, address);
	return pmd;
	}

	static __always_inline ssize_t __mcopy_atomic(struct mm_struct *dst_mm,
	unsigned long dst_start,
	unsigned long src_start,
	unsigned long len,
	bool zeropage)
	{
	struct vm_area_struct *dst_vma;
	ssize_t err;
	pmd_t *dst_pmd;
	unsigned long src_addr, dst_addr;
	long copied;
	struct page *page;

	/*
	* Sanitize the command parameters:
	*/
	BUG_ON(dst_start & ~PAGE_MASK);
	BUG_ON(len & ~PAGE_MASK);

	/* Does the address range wrap, or is the span zero-sized? */
	BUG_ON(src_start + len <= src_start);
	BUG_ON(dst_start + len <= dst_start);

	src_addr = src_start;
	dst_addr = dst_start;
	copied = 0;
	page = NULL;
	retry:
	down_read(&dst_mm->mmap_sem);

	/*
	* Make sure the vma is not shared, that the dst range is
	* both valid and fully within a single existing vma.
	*/
	err = -EINVAL;
	dst_vma = find_vma(dst_mm, dst_start);
	if (!dst_vma \|\| (dst_vma->vm_flags & VM_SHARED))
	goto out_unlock;
	if (dst_start < dst_vma->vm_start \|\|
	dst_start + len > dst_vma->vm_end)
	goto out_unlock;

	/*
	* Be strict and only allow __mcopy_atomic on userfaultfd
	* registered ranges to prevent userland errors going
	* unnoticed. As far as the VM consistency is concerned, it
	* would be perfectly safe to remove this check, but there's
	* no useful usage for __mcopy_atomic ouside of userfaultfd
	* registered ranges. This is after all why these are ioctls
	* belonging to the userfaultfd and not syscalls.
	*/
	if (!dst_vma->vm_userfaultfd_ctx.ctx)
	goto out_unlock;

	/*
	* FIXME: only allow copying on anonymous vmas, tmpfs should
	* be added.
	*/
	if (dst_vma->vm_ops)
	goto out_unlock;

	/*
	* Ensure the dst_vma has a anon_vma or this page
	* would get a NULL anon_vma when moved in the
	* dst_vma.
	*/
	err = -ENOMEM;
	if (unlikely(anon_vma_prepare(dst_vma)))
	goto out_unlock;

	while (src_addr < src_start + len) {
	pmd_t dst_pmdval;

	BUG_ON(dst_addr >= dst_start + len);

	dst_pmd = mm_alloc_pmd(dst_mm, dst_addr);
	if (unlikely(!dst_pmd)) {
	err = -ENOMEM;
	break;
	}

	dst_pmdval = pmd_read_atomic(dst_pmd);
	/*
	* If the dst_pmd is mapped as THP don't
	* override it and just be strict.
	*/
	if (unlikely(pmd_trans_huge(dst_pmdval))) {
	err = -EEXIST;
	break;
	}
	if (unlikely(pmd_none(dst_pmdval)) &&
	unlikely(__pte_alloc(dst_mm, dst_pmd, dst_addr))) {
	err = -ENOMEM;
	break;
	}
	/* If an huge pmd materialized from under us fail */
	if (unlikely(pmd_trans_huge(*dst_pmd))) {
	err = -EFAULT;
	break;
	}

	BUG_ON(pmd_none(*dst_pmd));
	BUG_ON(pmd_trans_huge(*dst_pmd));

	if (!zeropage)
	err = mcopy_atomic_pte(dst_mm, dst_pmd, dst_vma,
	dst_addr, src_addr, &page);
	else
	err = mfill_zeropage_pte(dst_mm, dst_pmd, dst_vma,
	dst_addr);

	cond_resched();

	if (unlikely(err == -EFAULT)) {
	void *page_kaddr;

	up_read(&dst_mm->mmap_sem);
	BUG_ON(!page);

	page_kaddr = kmap(page);
	err = copy_from_user(page_kaddr,
	(const void __user *) src_addr,
	PAGE_SIZE);
	kunmap(page);
	if (unlikely(err)) {
	err = -EFAULT;
	goto out;
	}
	goto retry;
	} else
	BUG_ON(page);

	if (!err) {
	dst_addr += PAGE_SIZE;
	src_addr += PAGE_SIZE;
	copied += PAGE_SIZE;

	if (fatal_signal_pending(current))
	err = -EINTR;
	}
	if (err)
	break;
	}

	out_unlock:
	up_read(&dst_mm->mmap_sem);
	out:
	if (page)
	page_cache_release(page);
	BUG_ON(copied < 0);
	BUG_ON(err > 0);
	BUG_ON(!copied && !err);
	return copied ? copied : err;
	}

	ssize_t mcopy_atomic(struct mm_struct *dst_mm, unsigned long dst_start,
	unsigned long src_start, unsigned long len)
	{
	return __mcopy_atomic(dst_mm, dst_start, src_start, len, false);
	}

	ssize_t mfill_zeropage(struct mm_struct *dst_mm, unsigned long start,
	unsigned long len)
	{
	return __mcopy_atomic(dst_mm, start, 0, len, true);
	}