fs/ext4/verity.c - linux - Git at Google

 // SPDX-License-Identifier: GPL-2.0
 /*
  * fs/ext4/verity.c: fs-verity support for ext4
  *
  * Copyright 2019 Google LLC
  */

 /*
  * Implementation of fsverity_operations for ext4.
  *
  * ext4 stores the verity metadata (Merkle tree and fsverity_descriptor) past
  * the end of the file, starting at the first 64K boundary beyond i_size.  This
  * approach works because (a) verity files are readonly, and (b) pages fully
  * beyond i_size aren't visible to userspace but can be read/written internally
  * by ext4 with only some relatively small changes to ext4.  This approach
  * avoids having to depend on the EA_INODE feature and on rearchitecturing
  * ext4's xattr support to support paging multi-gigabyte xattrs into memory, and
  * to support encrypting xattrs.  Note that the verity metadata *must* be
  * encrypted when the file is, since it contains hashes of the plaintext data.
  *
  * Using a 64K boundary rather than a 4K one keeps things ready for
  * architectures with 64K pages, and it doesn't necessarily waste space on-disk
  * since there can be a hole between i_size and the start of the Merkle tree.
  */

 #include <linux/quotaops.h>

 #include "ext4.h"
 #include "ext4_extents.h"
 #include "ext4_jbd2.h"

 static inline loff_t ext4_verity_metadata_pos(const struct inode *inode)
 {
 	return round_up(inode->i_size, 65536);
 }

 /*
  * Read some verity metadata from the inode.  __vfs_read() can't be used because
  * we need to read beyond i_size.
  */
 static int pagecache_read(struct inode *inode, void *buf, size_t count,
 			  loff_t pos)
 {
 	while (count) {
 		size_t n = min_t(size_t, count,
 				 PAGE_SIZE - offset_in_page(pos));
 		struct page *page;
 		void *addr;

 		page = read_mapping_page(inode->i_mapping, pos >> PAGE_SHIFT,
 					 NULL);
 		if (IS_ERR(page))
 			return PTR_ERR(page);

 		addr = kmap_atomic(page);
 		memcpy(buf, addr + offset_in_page(pos), n);
 		kunmap_atomic(addr);

 		put_page(page);

 		buf += n;
 		pos += n;
 		count -= n;
 	}
 	return 0;
 }

 /*
  * Write some verity metadata to the inode for FS_IOC_ENABLE_VERITY.
  * kernel_write() can't be used because the file descriptor is readonly.
  */
 static int pagecache_write(struct inode *inode, const void *buf, size_t count,
 			   loff_t pos)
 {
 	if (pos + count > inode->i_sb->s_maxbytes)
 		return -EFBIG;

 	while (count) {
 		size_t n = min_t(size_t, count,
 				 PAGE_SIZE - offset_in_page(pos));
 		struct page *page;
 		void *fsdata;
 		void *addr;
 		int res;

 		res = pagecache_write_begin(NULL, inode->i_mapping, pos, n, 0,
 					    &page, &fsdata);
 		if (res)
 			return res;

 		addr = kmap_atomic(page);
 		memcpy(addr + offset_in_page(pos), buf, n);
 		kunmap_atomic(addr);

 		res = pagecache_write_end(NULL, inode->i_mapping, pos, n, n,
 					  page, fsdata);
 		if (res < 0)
 			return res;
 		if (res != n)
 			return -EIO;

 		buf += n;
 		pos += n;
 		count -= n;
 	}
 	return 0;
 }

 static int ext4_begin_enable_verity(struct file *filp)
 {
 	struct inode *inode = file_inode(filp);
 	const int credits = 2; /* superblock and inode for ext4_orphan_add() */
 	handle_t *handle;
 	int err;

 	if (IS_DAX(inode) || ext4_test_inode_flag(inode, EXT4_INODE_DAX))
 		return -EINVAL;

 	if (ext4_verity_in_progress(inode))
 		return -EBUSY;

 	/*
 	 * Since the file was opened readonly, we have to initialize the jbd
 	 * inode and quotas here and not rely on ->open() doing it.  This must
 	 * be done before evicting the inline data.
 	 */

 	err = ext4_inode_attach_jinode(inode);
 	if (err)
 		return err;

 	err = dquot_initialize(inode);
 	if (err)
 		return err;

 	err = ext4_convert_inline_data(inode);
 	if (err)
 		return err;

 	if (!ext4_test_inode_flag(inode, EXT4_INODE_EXTENTS)) {
 		ext4_warning_inode(inode,
 				   "verity is only allowed on extent-based files");
 		return -EOPNOTSUPP;
 	}

 	/*
 	 * ext4 uses the last allocated block to find the verity descriptor, so
 	 * we must remove any other blocks past EOF which might confuse things.
 	 */
 	err = ext4_truncate(inode);
 	if (err)
 		return err;

 	handle = ext4_journal_start(inode, EXT4_HT_INODE, credits);
 	if (IS_ERR(handle))
 		return PTR_ERR(handle);

 	err = ext4_orphan_add(handle, inode);
 	if (err == 0)
 		ext4_set_inode_state(inode, EXT4_STATE_VERITY_IN_PROGRESS);

 	ext4_journal_stop(handle);
 	return err;
 }

 /*
  * ext4 stores the verity descriptor beginning on the next filesystem block
  * boundary after the Merkle tree.  Then, the descriptor size is stored in the
  * last 4 bytes of the last allocated filesystem block --- which is either the
  * block in which the descriptor ends, or the next block after that if there
  * weren't at least 4 bytes remaining.
  *
  * We can't simply store the descriptor in an xattr because it *must* be
  * encrypted when ext4 encryption is used, but ext4 encryption doesn't encrypt
  * xattrs.  Also, if the descriptor includes a large signature blob it may be
  * too large to store in an xattr without the EA_INODE feature.
  */
 static int ext4_write_verity_descriptor(struct inode *inode, const void *desc,
 					size_t desc_size, u64 merkle_tree_size)
 {
 	const u64 desc_pos = round_up(ext4_verity_metadata_pos(inode) +
 				      merkle_tree_size, i_blocksize(inode));
 	const u64 desc_end = desc_pos + desc_size;
 	const __le32 desc_size_disk = cpu_to_le32(desc_size);
 	const u64 desc_size_pos = round_up(desc_end + sizeof(desc_size_disk),
 					   i_blocksize(inode)) -
 				  sizeof(desc_size_disk);
 	int err;

 	err = pagecache_write(inode, desc, desc_size, desc_pos);
 	if (err)
 		return err;

 	return pagecache_write(inode, &desc_size_disk, sizeof(desc_size_disk),
 			       desc_size_pos);
 }

 static int ext4_end_enable_verity(struct file *filp, const void *desc,
 				  size_t desc_size, u64 merkle_tree_size)
 {
 	struct inode *inode = file_inode(filp);
 	const int credits = 2; /* superblock and inode for ext4_orphan_del() */
 	handle_t *handle;
 	struct ext4_iloc iloc;
 	int err = 0;

 	/*
 	 * If an error already occurred (which fs/verity/ signals by passing
 	 * desc == NULL), then only clean-up is needed.
 	 */
 	if (desc == NULL)
 		goto cleanup;

 	/* Append the verity descriptor. */
 	err = ext4_write_verity_descriptor(inode, desc, desc_size,
 					   merkle_tree_size);
 	if (err)
 		goto cleanup;

 	/*
 	 * Write all pages (both data and verity metadata).  Note that this must
 	 * happen before clearing EXT4_STATE_VERITY_IN_PROGRESS; otherwise pages
 	 * beyond i_size won't be written properly.  For crash consistency, this
 	 * also must happen before the verity inode flag gets persisted.
 	 */
 	err = filemap_write_and_wait(inode->i_mapping);
 	if (err)
 		goto cleanup;

 	/*
 	 * Finally, set the verity inode flag and remove the inode from the
 	 * orphan list (in a single transaction).
 	 */

 	handle = ext4_journal_start(inode, EXT4_HT_INODE, credits);
 	if (IS_ERR(handle)) {
 		err = PTR_ERR(handle);
 		goto cleanup;
 	}

 	err = ext4_orphan_del(handle, inode);
 	if (err)
 		goto stop_and_cleanup;

 	err = ext4_reserve_inode_write(handle, inode, &iloc);
 	if (err)
 		goto stop_and_cleanup;

 	ext4_set_inode_flag(inode, EXT4_INODE_VERITY);
 	ext4_set_inode_flags(inode, false);
 	err = ext4_mark_iloc_dirty(handle, inode, &iloc);
 	if (err)
 		goto stop_and_cleanup;

 	ext4_journal_stop(handle);

 	ext4_clear_inode_state(inode, EXT4_STATE_VERITY_IN_PROGRESS);
 	return 0;

 stop_and_cleanup:
 	ext4_journal_stop(handle);
 cleanup:
 	/*
 	 * Verity failed to be enabled, so clean up by truncating any verity
 	 * metadata that was written beyond i_size (both from cache and from
 	 * disk), removing the inode from the orphan list (if it wasn't done
 	 * already), and clearing EXT4_STATE_VERITY_IN_PROGRESS.
 	 */
 	truncate_inode_pages(inode->i_mapping, inode->i_size);
 	ext4_truncate(inode);
 	ext4_orphan_del(NULL, inode);
 	ext4_clear_inode_state(inode, EXT4_STATE_VERITY_IN_PROGRESS);
 	return err;
 }

 static int ext4_get_verity_descriptor_location(struct inode *inode,
 					       size_t *desc_size_ret,
 					       u64 *desc_pos_ret)
 {
 	struct ext4_ext_path *path;
 	struct ext4_extent *last_extent;
 	u32 end_lblk;
 	u64 desc_size_pos;
 	__le32 desc_size_disk;
 	u32 desc_size;
 	u64 desc_pos;
 	int err;

 	/*
 	 * Descriptor size is in last 4 bytes of last allocated block.
 	 * See ext4_write_verity_descriptor().
 	 */

 	if (!ext4_test_inode_flag(inode, EXT4_INODE_EXTENTS)) {
 		EXT4_ERROR_INODE(inode, "verity file doesn't use extents");
 		return -EFSCORRUPTED;
 	}

 	path = ext4_find_extent(inode, EXT_MAX_BLOCKS - 1, NULL, 0);
 	if (IS_ERR(path))
 		return PTR_ERR(path);

 	last_extent = path[path->p_depth].p_ext;
 	if (!last_extent) {
 		EXT4_ERROR_INODE(inode, "verity file has no extents");
 		ext4_ext_drop_refs(path);
 		kfree(path);
 		return -EFSCORRUPTED;
 	}

 	end_lblk = le32_to_cpu(last_extent->ee_block) +
 		   ext4_ext_get_actual_len(last_extent);
 	desc_size_pos = (u64)end_lblk << inode->i_blkbits;
 	ext4_ext_drop_refs(path);
 	kfree(path);

 	if (desc_size_pos < sizeof(desc_size_disk))
 		goto bad;
 	desc_size_pos -= sizeof(desc_size_disk);

 	err = pagecache_read(inode, &desc_size_disk, sizeof(desc_size_disk),
 			     desc_size_pos);
 	if (err)
 		return err;
 	desc_size = le32_to_cpu(desc_size_disk);

 	/*
 	 * The descriptor is stored just before the desc_size_disk, but starting
 	 * on a filesystem block boundary.
 	 */

 	if (desc_size > INT_MAX || desc_size > desc_size_pos)
 		goto bad;

 	desc_pos = round_down(desc_size_pos - desc_size, i_blocksize(inode));
 	if (desc_pos < ext4_verity_metadata_pos(inode))
 		goto bad;

 	*desc_size_ret = desc_size;
 	*desc_pos_ret = desc_pos;
 	return 0;

 bad:
 	EXT4_ERROR_INODE(inode, "verity file corrupted; can't find descriptor");
 	return -EFSCORRUPTED;
 }

 static int ext4_get_verity_descriptor(struct inode *inode, void *buf,
 				      size_t buf_size)
 {
 	size_t desc_size = 0;
 	u64 desc_pos = 0;
 	int err;

 	err = ext4_get_verity_descriptor_location(inode, &desc_size, &desc_pos);
 	if (err)
 		return err;

 	if (buf_size) {
 		if (desc_size > buf_size)
 			return -ERANGE;
 		err = pagecache_read(inode, buf, desc_size, desc_pos);
 		if (err)
 			return err;
 	}
 	return desc_size;
 }

 static struct page *ext4_read_merkle_tree_page(struct inode *inode,
 					       pgoff_t index,
 					       unsigned long num_ra_pages)
 {
 	DEFINE_READAHEAD(ractl, NULL, inode->i_mapping, index);
 	struct page *page;

 	index += ext4_verity_metadata_pos(inode) >> PAGE_SHIFT;

 	page = find_get_page_flags(inode->i_mapping, index, FGP_ACCESSED);
 	if (!page || !PageUptodate(page)) {
 		if (page)
 			put_page(page);
 		else if (num_ra_pages > 1)
 			page_cache_ra_unbounded(&ractl, num_ra_pages, 0);
 		page = read_mapping_page(inode->i_mapping, index, NULL);
 	}
 	return page;
 }

 static int ext4_write_merkle_tree_block(struct inode *inode, const void *buf,
 					u64 index, int log_blocksize)
 {
 	loff_t pos = ext4_verity_metadata_pos(inode) + (index << log_blocksize);

 	return pagecache_write(inode, buf, 1 << log_blocksize, pos);
 }

 const struct fsverity_operations ext4_verityops = {
 	.begin_enable_verity	= ext4_begin_enable_verity,
 	.end_enable_verity	= ext4_end_enable_verity,
 	.get_verity_descriptor	= ext4_get_verity_descriptor,
 	.read_merkle_tree_page	= ext4_read_merkle_tree_page,
 	.write_merkle_tree_block = ext4_write_merkle_tree_block,
 };
	// SPDX-License-Identifier: GPL-2.0
	/*
	* fs/ext4/verity.c: fs-verity support for ext4
	*
	* Copyright 2019 Google LLC
	*/

	/*
	* Implementation of fsverity_operations for ext4.
	*
	* ext4 stores the verity metadata (Merkle tree and fsverity_descriptor) past
	* the end of the file, starting at the first 64K boundary beyond i_size. This
	* approach works because (a) verity files are readonly, and (b) pages fully
	* beyond i_size aren't visible to userspace but can be read/written internally
	* by ext4 with only some relatively small changes to ext4. This approach
	* avoids having to depend on the EA_INODE feature and on rearchitecturing
	* ext4's xattr support to support paging multi-gigabyte xattrs into memory, and
	* to support encrypting xattrs. Note that the verity metadata must be
	* encrypted when the file is, since it contains hashes of the plaintext data.
	*
	* Using a 64K boundary rather than a 4K one keeps things ready for
	* architectures with 64K pages, and it doesn't necessarily waste space on-disk
	* since there can be a hole between i_size and the start of the Merkle tree.
	*/

	#include <linux/quotaops.h>

	#include "ext4.h"
	#include "ext4_extents.h"
	#include "ext4_jbd2.h"

	static inline loff_t ext4_verity_metadata_pos(const struct inode *inode)
	{
	return round_up(inode->i_size, 65536);
	}

	/*
	* Read some verity metadata from the inode. __vfs_read() can't be used because
	* we need to read beyond i_size.
	*/
	static int pagecache_read(struct inode inode, void buf, size_t count,
	loff_t pos)
	{
	while (count) {
	size_t n = min_t(size_t, count,
	PAGE_SIZE - offset_in_page(pos));
	struct page *page;
	void *addr;

	page = read_mapping_page(inode->i_mapping, pos >> PAGE_SHIFT,
	NULL);
	if (IS_ERR(page))
	return PTR_ERR(page);

	addr = kmap_atomic(page);
	memcpy(buf, addr + offset_in_page(pos), n);
	kunmap_atomic(addr);

	put_page(page);

	buf += n;
	pos += n;
	count -= n;
	}
	return 0;
	}

	/*
	* Write some verity metadata to the inode for FS_IOC_ENABLE_VERITY.
	* kernel_write() can't be used because the file descriptor is readonly.
	*/
	static int pagecache_write(struct inode inode, const void buf, size_t count,
	loff_t pos)
	{
	if (pos + count > inode->i_sb->s_maxbytes)
	return -EFBIG;

	while (count) {
	size_t n = min_t(size_t, count,
	PAGE_SIZE - offset_in_page(pos));
	struct page *page;
	void *fsdata;
	void *addr;
	int res;

	res = pagecache_write_begin(NULL, inode->i_mapping, pos, n, 0,
	&page, &fsdata);
	if (res)
	return res;

	addr = kmap_atomic(page);
	memcpy(addr + offset_in_page(pos), buf, n);
	kunmap_atomic(addr);

	res = pagecache_write_end(NULL, inode->i_mapping, pos, n, n,
	page, fsdata);
	if (res < 0)
	return res;
	if (res != n)
	return -EIO;

	buf += n;
	pos += n;
	count -= n;
	}
	return 0;
	}

	static int ext4_begin_enable_verity(struct file *filp)
	{
	struct inode *inode = file_inode(filp);
	const int credits = 2; /* superblock and inode for ext4_orphan_add() */
	handle_t *handle;
	int err;

	if (IS_DAX(inode) \|\| ext4_test_inode_flag(inode, EXT4_INODE_DAX))
	return -EINVAL;

	if (ext4_verity_in_progress(inode))
	return -EBUSY;

	/*
	* Since the file was opened readonly, we have to initialize the jbd
	* inode and quotas here and not rely on ->open() doing it. This must
	* be done before evicting the inline data.
	*/

	err = ext4_inode_attach_jinode(inode);
	if (err)
	return err;

	err = dquot_initialize(inode);
	if (err)
	return err;

	err = ext4_convert_inline_data(inode);
	if (err)
	return err;

	if (!ext4_test_inode_flag(inode, EXT4_INODE_EXTENTS)) {
	ext4_warning_inode(inode,
	"verity is only allowed on extent-based files");
	return -EOPNOTSUPP;
	}

	/*
	* ext4 uses the last allocated block to find the verity descriptor, so
	* we must remove any other blocks past EOF which might confuse things.
	*/
	err = ext4_truncate(inode);
	if (err)
	return err;

	handle = ext4_journal_start(inode, EXT4_HT_INODE, credits);
	if (IS_ERR(handle))
	return PTR_ERR(handle);

	err = ext4_orphan_add(handle, inode);
	if (err == 0)
	ext4_set_inode_state(inode, EXT4_STATE_VERITY_IN_PROGRESS);

	ext4_journal_stop(handle);
	return err;
	}

	/*
	* ext4 stores the verity descriptor beginning on the next filesystem block
	* boundary after the Merkle tree. Then, the descriptor size is stored in the
	* last 4 bytes of the last allocated filesystem block --- which is either the
	* block in which the descriptor ends, or the next block after that if there
	* weren't at least 4 bytes remaining.
	*
	* We can't simply store the descriptor in an xattr because it must be
	* encrypted when ext4 encryption is used, but ext4 encryption doesn't encrypt
	* xattrs. Also, if the descriptor includes a large signature blob it may be
	* too large to store in an xattr without the EA_INODE feature.
	*/
	static int ext4_write_verity_descriptor(struct inode inode, const void desc,
	size_t desc_size, u64 merkle_tree_size)
	{
	const u64 desc_pos = round_up(ext4_verity_metadata_pos(inode) +
	merkle_tree_size, i_blocksize(inode));
	const u64 desc_end = desc_pos + desc_size;
	const __le32 desc_size_disk = cpu_to_le32(desc_size);
	const u64 desc_size_pos = round_up(desc_end + sizeof(desc_size_disk),
	i_blocksize(inode)) -
	sizeof(desc_size_disk);
	int err;

	err = pagecache_write(inode, desc, desc_size, desc_pos);
	if (err)
	return err;

	return pagecache_write(inode, &desc_size_disk, sizeof(desc_size_disk),
	desc_size_pos);
	}

	static int ext4_end_enable_verity(struct file filp, const void desc,
	size_t desc_size, u64 merkle_tree_size)
	{
	struct inode *inode = file_inode(filp);
	const int credits = 2; /* superblock and inode for ext4_orphan_del() */
	handle_t *handle;
	struct ext4_iloc iloc;
	int err = 0;

	/*
	* If an error already occurred (which fs/verity/ signals by passing
	* desc == NULL), then only clean-up is needed.
	*/
	if (desc == NULL)
	goto cleanup;

	/* Append the verity descriptor. */
	err = ext4_write_verity_descriptor(inode, desc, desc_size,
	merkle_tree_size);
	if (err)
	goto cleanup;

	/*
	* Write all pages (both data and verity metadata). Note that this must
	* happen before clearing EXT4_STATE_VERITY_IN_PROGRESS; otherwise pages
	* beyond i_size won't be written properly. For crash consistency, this
	* also must happen before the verity inode flag gets persisted.
	*/
	err = filemap_write_and_wait(inode->i_mapping);
	if (err)
	goto cleanup;

	/*
	* Finally, set the verity inode flag and remove the inode from the
	* orphan list (in a single transaction).
	*/

	handle = ext4_journal_start(inode, EXT4_HT_INODE, credits);
	if (IS_ERR(handle)) {
	err = PTR_ERR(handle);
	goto cleanup;
	}

	err = ext4_orphan_del(handle, inode);
	if (err)
	goto stop_and_cleanup;

	err = ext4_reserve_inode_write(handle, inode, &iloc);
	if (err)
	goto stop_and_cleanup;

	ext4_set_inode_flag(inode, EXT4_INODE_VERITY);
	ext4_set_inode_flags(inode, false);
	err = ext4_mark_iloc_dirty(handle, inode, &iloc);
	if (err)
	goto stop_and_cleanup;

	ext4_journal_stop(handle);

	ext4_clear_inode_state(inode, EXT4_STATE_VERITY_IN_PROGRESS);
	return 0;

	stop_and_cleanup:
	ext4_journal_stop(handle);
	cleanup:
	/*
	* Verity failed to be enabled, so clean up by truncating any verity
	* metadata that was written beyond i_size (both from cache and from
	* disk), removing the inode from the orphan list (if it wasn't done
	* already), and clearing EXT4_STATE_VERITY_IN_PROGRESS.
	*/
	truncate_inode_pages(inode->i_mapping, inode->i_size);
	ext4_truncate(inode);
	ext4_orphan_del(NULL, inode);
	ext4_clear_inode_state(inode, EXT4_STATE_VERITY_IN_PROGRESS);
	return err;
	}

	static int ext4_get_verity_descriptor_location(struct inode *inode,
	size_t *desc_size_ret,
	u64 *desc_pos_ret)
	{
	struct ext4_ext_path *path;
	struct ext4_extent *last_extent;
	u32 end_lblk;
	u64 desc_size_pos;
	__le32 desc_size_disk;
	u32 desc_size;
	u64 desc_pos;
	int err;

	/*
	* Descriptor size is in last 4 bytes of last allocated block.
	* See ext4_write_verity_descriptor().
	*/

	if (!ext4_test_inode_flag(inode, EXT4_INODE_EXTENTS)) {
	EXT4_ERROR_INODE(inode, "verity file doesn't use extents");
	return -EFSCORRUPTED;
	}

	path = ext4_find_extent(inode, EXT_MAX_BLOCKS - 1, NULL, 0);
	if (IS_ERR(path))
	return PTR_ERR(path);

	last_extent = path[path->p_depth].p_ext;
	if (!last_extent) {
	EXT4_ERROR_INODE(inode, "verity file has no extents");
	ext4_ext_drop_refs(path);
	kfree(path);
	return -EFSCORRUPTED;
	}

	end_lblk = le32_to_cpu(last_extent->ee_block) +
	ext4_ext_get_actual_len(last_extent);
	desc_size_pos = (u64)end_lblk << inode->i_blkbits;
	ext4_ext_drop_refs(path);
	kfree(path);

	if (desc_size_pos < sizeof(desc_size_disk))
	goto bad;
	desc_size_pos -= sizeof(desc_size_disk);

	err = pagecache_read(inode, &desc_size_disk, sizeof(desc_size_disk),
	desc_size_pos);
	if (err)
	return err;
	desc_size = le32_to_cpu(desc_size_disk);

	/*
	* The descriptor is stored just before the desc_size_disk, but starting
	* on a filesystem block boundary.
	*/

	if (desc_size > INT_MAX \|\| desc_size > desc_size_pos)
	goto bad;

	desc_pos = round_down(desc_size_pos - desc_size, i_blocksize(inode));
	if (desc_pos < ext4_verity_metadata_pos(inode))
	goto bad;

	*desc_size_ret = desc_size;
	*desc_pos_ret = desc_pos;
	return 0;

	bad:
	EXT4_ERROR_INODE(inode, "verity file corrupted; can't find descriptor");
	return -EFSCORRUPTED;
	}

	static int ext4_get_verity_descriptor(struct inode inode, void buf,
	size_t buf_size)
	{
	size_t desc_size = 0;
	u64 desc_pos = 0;
	int err;

	err = ext4_get_verity_descriptor_location(inode, &desc_size, &desc_pos);
	if (err)
	return err;

	if (buf_size) {
	if (desc_size > buf_size)
	return -ERANGE;
	err = pagecache_read(inode, buf, desc_size, desc_pos);
	if (err)
	return err;
	}
	return desc_size;
	}

	static struct page ext4_read_merkle_tree_page(struct inode inode,
	pgoff_t index,
	unsigned long num_ra_pages)
	{
	DEFINE_READAHEAD(ractl, NULL, inode->i_mapping, index);
	struct page *page;

	index += ext4_verity_metadata_pos(inode) >> PAGE_SHIFT;

	page = find_get_page_flags(inode->i_mapping, index, FGP_ACCESSED);
	if (!page \|\| !PageUptodate(page)) {
	if (page)
	put_page(page);
	else if (num_ra_pages > 1)
	page_cache_ra_unbounded(&ractl, num_ra_pages, 0);
	page = read_mapping_page(inode->i_mapping, index, NULL);
	}
	return page;
	}

	static int ext4_write_merkle_tree_block(struct inode inode, const void buf,
	u64 index, int log_blocksize)
	{
	loff_t pos = ext4_verity_metadata_pos(inode) + (index << log_blocksize);

	return pagecache_write(inode, buf, 1 << log_blocksize, pos);
	}

	const struct fsverity_operations ext4_verityops = {
	.begin_enable_verity = ext4_begin_enable_verity,
	.end_enable_verity = ext4_end_enable_verity,
	.get_verity_descriptor = ext4_get_verity_descriptor,
	.read_merkle_tree_page = ext4_read_merkle_tree_page,
	.write_merkle_tree_block = ext4_write_merkle_tree_block,
	};