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

 // SPDX-License-Identifier: GPL-2.0
 /*
  * Data verification functions, i.e. hooks for ->readpages()
  *
  * Copyright 2019 Google LLC
  */

 #include "fsverity_private.h"

 #include <crypto/hash.h>
 #include <linux/bio.h>
 #include <linux/ratelimit.h>

 static struct workqueue_struct *fsverity_read_workqueue;

 /**
  * hash_at_level() - compute the location of the block's hash at the given level
  *
  * @params:	(in) the Merkle tree parameters
  * @dindex:	(in) the index of the data block being verified
  * @level:	(in) the level of hash we want (0 is leaf level)
  * @hindex:	(out) the index of the hash block containing the wanted hash
  * @hoffset:	(out) the byte offset to the wanted hash within the hash block
  */
 static void hash_at_level(const struct merkle_tree_params *params,
 			  pgoff_t dindex, unsigned int level, pgoff_t *hindex,
 			  unsigned int *hoffset)
 {
 	pgoff_t position;

 	/* Offset of the hash within the level's region, in hashes */
 	position = dindex >> (level * params->log_arity);

 	/* Index of the hash block in the tree overall */
 	*hindex = params->level_start[level] + (position >> params->log_arity);

 	/* Offset of the wanted hash (in bytes) within the hash block */
 	*hoffset = (position & ((1 << params->log_arity) - 1)) <<
 		   (params->log_blocksize - params->log_arity);
 }

 static inline int cmp_hashes(const struct fsverity_info *vi,
 			     const u8 *want_hash, const u8 *real_hash,
 			     pgoff_t index, int level)
 {
 	const unsigned int hsize = vi->tree_params.digest_size;

 	if (memcmp(want_hash, real_hash, hsize) == 0)
 		return 0;

 	fsverity_err(vi->inode,
 		     "FILE CORRUPTED! index=%lu, level=%d, want_hash=%s:%*phN, real_hash=%s:%*phN",
 		     index, level,
 		     vi->tree_params.hash_alg->name, hsize, want_hash,
 		     vi->tree_params.hash_alg->name, hsize, real_hash);
 	return -EBADMSG;
 }

 /*
  * Verify a single data page against the file's Merkle tree.
  *
  * In principle, we need to verify the entire path to the root node.  However,
  * for efficiency the filesystem may cache the hash pages.  Therefore we need
  * only ascend the tree until an already-verified page is seen, as indicated by
  * the PageChecked bit being set; then verify the path to that page.
  *
  * This code currently only supports the case where the verity block size is
  * equal to PAGE_SIZE.  Doing otherwise would be possible but tricky, since we
  * wouldn't be able to use the PageChecked bit.
  *
  * Note that multiple processes may race to verify a hash page and mark it
  * Checked, but it doesn't matter; the result will be the same either way.
  *
  * Return: true if the page is valid, else false.
  */
 static bool verify_page(struct inode *inode, const struct fsverity_info *vi,
 			struct ahash_request *req, struct page *data_page,
 			unsigned long level0_ra_pages)
 {
 	const struct merkle_tree_params *params = &vi->tree_params;
 	const unsigned int hsize = params->digest_size;
 	const pgoff_t index = data_page->index;
 	int level;
 	u8 _want_hash[FS_VERITY_MAX_DIGEST_SIZE];
 	const u8 *want_hash;
 	u8 real_hash[FS_VERITY_MAX_DIGEST_SIZE];
 	struct page *hpages[FS_VERITY_MAX_LEVELS];
 	unsigned int hoffsets[FS_VERITY_MAX_LEVELS];
 	int err;

 	if (WARN_ON_ONCE(!PageLocked(data_page) || PageUptodate(data_page)))
 		return false;

 	pr_debug_ratelimited("Verifying data page %lu...\n", index);

 	/*
 	 * Starting at the leaf level, ascend the tree saving hash pages along
 	 * the way until we find a verified hash page, indicated by PageChecked;
 	 * or until we reach the root.
 	 */
 	for (level = 0; level < params->num_levels; level++) {
 		pgoff_t hindex;
 		unsigned int hoffset;
 		struct page *hpage;

 		hash_at_level(params, index, level, &hindex, &hoffset);

 		pr_debug_ratelimited("Level %d: hindex=%lu, hoffset=%u\n",
 				     level, hindex, hoffset);

 		hpage = inode->i_sb->s_vop->read_merkle_tree_page(inode, hindex,
 				level == 0 ? level0_ra_pages : 0);
 		if (IS_ERR(hpage)) {
 			err = PTR_ERR(hpage);
 			fsverity_err(inode,
 				     "Error %d reading Merkle tree page %lu",
 				     err, hindex);
 			goto out;
 		}

 		if (PageChecked(hpage)) {
 			memcpy_from_page(_want_hash, hpage, hoffset, hsize);
 			want_hash = _want_hash;
 			put_page(hpage);
 			pr_debug_ratelimited("Hash page already checked, want %s:%*phN\n",
 					     params->hash_alg->name,
 					     hsize, want_hash);
 			goto descend;
 		}
 		pr_debug_ratelimited("Hash page not yet checked\n");
 		hpages[level] = hpage;
 		hoffsets[level] = hoffset;
 	}

 	want_hash = vi->root_hash;
 	pr_debug("Want root hash: %s:%*phN\n",
 		 params->hash_alg->name, hsize, want_hash);
 descend:
 	/* Descend the tree verifying hash pages */
 	for (; level > 0; level--) {
 		struct page *hpage = hpages[level - 1];
 		unsigned int hoffset = hoffsets[level - 1];

 		err = fsverity_hash_page(params, inode, req, hpage, real_hash);
 		if (err)
 			goto out;
 		err = cmp_hashes(vi, want_hash, real_hash, index, level - 1);
 		if (err)
 			goto out;
 		SetPageChecked(hpage);
 		memcpy_from_page(_want_hash, hpage, hoffset, hsize);
 		want_hash = _want_hash;
 		put_page(hpage);
 		pr_debug("Verified hash page at level %d, now want %s:%*phN\n",
 			 level - 1, params->hash_alg->name, hsize, want_hash);
 	}

 	/* Finally, verify the data page */
 	err = fsverity_hash_page(params, inode, req, data_page, real_hash);
 	if (err)
 		goto out;
 	err = cmp_hashes(vi, want_hash, real_hash, index, -1);
 out:
 	for (; level > 0; level--)
 		put_page(hpages[level - 1]);

 	return err == 0;
 }

 /**
  * fsverity_verify_page() - verify a data page
  * @page: the page to verity
  *
  * Verify a page that has just been read from a verity file.  The page must be a
  * pagecache page that is still locked and not yet uptodate.
  *
  * Return: true if the page is valid, else false.
  */
 bool fsverity_verify_page(struct page *page)
 {
 	struct inode *inode = page->mapping->host;
 	const struct fsverity_info *vi = inode->i_verity_info;
 	struct ahash_request *req;
 	bool valid;

 	/* This allocation never fails, since it's mempool-backed. */
 	req = fsverity_alloc_hash_request(vi->tree_params.hash_alg, GFP_NOFS);

 	valid = verify_page(inode, vi, req, page, 0);

 	fsverity_free_hash_request(vi->tree_params.hash_alg, req);

 	return valid;
 }
 EXPORT_SYMBOL_GPL(fsverity_verify_page);

 #ifdef CONFIG_BLOCK
 /**
  * fsverity_verify_bio() - verify a 'read' bio that has just completed
  * @bio: the bio to verify
  *
  * Verify a set of pages that have just been read from a verity file.  The pages
  * must be pagecache pages that are still locked and not yet uptodate.  If a
  * page fails verification, then bio->bi_status is set to an error status.
  *
  * This is a helper function for use by the ->readpages() method of filesystems
  * that issue bios to read data directly into the page cache.  Filesystems that
  * populate the page cache without issuing bios (e.g. non block-based
  * filesystems) must instead call fsverity_verify_page() directly on each page.
  * All filesystems must also call fsverity_verify_page() on holes.
  */
 void fsverity_verify_bio(struct bio *bio)
 {
 	struct inode *inode = bio_first_page_all(bio)->mapping->host;
 	const struct fsverity_info *vi = inode->i_verity_info;
 	const struct merkle_tree_params *params = &vi->tree_params;
 	struct ahash_request *req;
 	struct bio_vec *bv;
 	struct bvec_iter_all iter_all;
 	unsigned long max_ra_pages = 0;

 	/* This allocation never fails, since it's mempool-backed. */
 	req = fsverity_alloc_hash_request(params->hash_alg, GFP_NOFS);

 	if (bio->bi_opf & REQ_RAHEAD) {
 		/*
 		 * If this bio is for data readahead, then we also do readahead
 		 * of the first (largest) level of the Merkle tree.  Namely,
 		 * when a Merkle tree page is read, we also try to piggy-back on
 		 * some additional pages -- up to 1/4 the number of data pages.
 		 *
 		 * This improves sequential read performance, as it greatly
 		 * reduces the number of I/O requests made to the Merkle tree.
 		 */
 		bio_for_each_segment_all(bv, bio, iter_all)
 			max_ra_pages++;
 		max_ra_pages /= 4;
 	}

 	bio_for_each_segment_all(bv, bio, iter_all) {
 		struct page *page = bv->bv_page;
 		unsigned long level0_index = page->index >> params->log_arity;
 		unsigned long level0_ra_pages =
 			min(max_ra_pages, params->level0_blocks - level0_index);

 		if (!verify_page(inode, vi, req, page, level0_ra_pages)) {
 			bio->bi_status = BLK_STS_IOERR;
 			break;
 		}
 	}

 	fsverity_free_hash_request(params->hash_alg, req);
 }
 EXPORT_SYMBOL_GPL(fsverity_verify_bio);
 #endif /* CONFIG_BLOCK */

 /**
  * fsverity_enqueue_verify_work() - enqueue work on the fs-verity workqueue
  * @work: the work to enqueue
  *
  * Enqueue verification work for asynchronous processing.
  */
 void fsverity_enqueue_verify_work(struct work_struct *work)
 {
 	queue_work(fsverity_read_workqueue, work);
 }
 EXPORT_SYMBOL_GPL(fsverity_enqueue_verify_work);

 int __init fsverity_init_workqueue(void)
 {
 	/*
 	 * Use an unbound workqueue to allow bios to be verified in parallel
 	 * even when they happen to complete on the same CPU.  This sacrifices
 	 * locality, but it's worthwhile since hashing is CPU-intensive.
 	 *
 	 * Also use a high-priority workqueue to prioritize verification work,
 	 * which blocks reads from completing, over regular application tasks.
 	 */
 	fsverity_read_workqueue = alloc_workqueue("fsverity_read_queue",
 						  WQ_UNBOUND | WQ_HIGHPRI,
 						  num_online_cpus());
 	if (!fsverity_read_workqueue)
 		return -ENOMEM;
 	return 0;
 }

 void __init fsverity_exit_workqueue(void)
 {
 	destroy_workqueue(fsverity_read_workqueue);
 	fsverity_read_workqueue = NULL;
 }
	// SPDX-License-Identifier: GPL-2.0
	/*
	* Data verification functions, i.e. hooks for ->readpages()
	*
	* Copyright 2019 Google LLC
	*/

	#include "fsverity_private.h"

	#include <crypto/hash.h>
	#include <linux/bio.h>
	#include <linux/ratelimit.h>

	static struct workqueue_struct *fsverity_read_workqueue;

	/**
	* hash_at_level() - compute the location of the block's hash at the given level
	*
	* @params: (in) the Merkle tree parameters
	* @dindex: (in) the index of the data block being verified
	* @level: (in) the level of hash we want (0 is leaf level)
	* @hindex: (out) the index of the hash block containing the wanted hash
	* @hoffset: (out) the byte offset to the wanted hash within the hash block
	*/
	static void hash_at_level(const struct merkle_tree_params *params,
	pgoff_t dindex, unsigned int level, pgoff_t *hindex,
	unsigned int *hoffset)
	{
	pgoff_t position;

	/* Offset of the hash within the level's region, in hashes */
	position = dindex >> (level * params->log_arity);

	/* Index of the hash block in the tree overall */
	*hindex = params->level_start[level] + (position >> params->log_arity);

	/* Offset of the wanted hash (in bytes) within the hash block */
	*hoffset = (position & ((1 << params->log_arity) - 1)) <<
	(params->log_blocksize - params->log_arity);
	}

	static inline int cmp_hashes(const struct fsverity_info *vi,
	const u8 want_hash, const u8 real_hash,
	pgoff_t index, int level)
	{
	const unsigned int hsize = vi->tree_params.digest_size;

	if (memcmp(want_hash, real_hash, hsize) == 0)
	return 0;

	fsverity_err(vi->inode,
	"FILE CORRUPTED! index=%lu, level=%d, want_hash=%s:%phN, real_hash=%s:%phN",
	index, level,
	vi->tree_params.hash_alg->name, hsize, want_hash,
	vi->tree_params.hash_alg->name, hsize, real_hash);
	return -EBADMSG;
	}

	/*
	* Verify a single data page against the file's Merkle tree.
	*
	* In principle, we need to verify the entire path to the root node. However,
	* for efficiency the filesystem may cache the hash pages. Therefore we need
	* only ascend the tree until an already-verified page is seen, as indicated by
	* the PageChecked bit being set; then verify the path to that page.
	*
	* This code currently only supports the case where the verity block size is
	* equal to PAGE_SIZE. Doing otherwise would be possible but tricky, since we
	* wouldn't be able to use the PageChecked bit.
	*
	* Note that multiple processes may race to verify a hash page and mark it
	* Checked, but it doesn't matter; the result will be the same either way.
	*
	* Return: true if the page is valid, else false.
	*/
	static bool verify_page(struct inode inode, const struct fsverity_info vi,
	struct ahash_request req, struct page data_page,
	unsigned long level0_ra_pages)
	{
	const struct merkle_tree_params *params = &vi->tree_params;
	const unsigned int hsize = params->digest_size;
	const pgoff_t index = data_page->index;
	int level;
	u8 _want_hash[FS_VERITY_MAX_DIGEST_SIZE];
	const u8 *want_hash;
	u8 real_hash[FS_VERITY_MAX_DIGEST_SIZE];
	struct page *hpages[FS_VERITY_MAX_LEVELS];
	unsigned int hoffsets[FS_VERITY_MAX_LEVELS];
	int err;

	if (WARN_ON_ONCE(!PageLocked(data_page) \|\| PageUptodate(data_page)))
	return false;

	pr_debug_ratelimited("Verifying data page %lu...\n", index);

	/*
	* Starting at the leaf level, ascend the tree saving hash pages along
	* the way until we find a verified hash page, indicated by PageChecked;
	* or until we reach the root.
	*/
	for (level = 0; level < params->num_levels; level++) {
	pgoff_t hindex;
	unsigned int hoffset;
	struct page *hpage;

	hash_at_level(params, index, level, &hindex, &hoffset);

	pr_debug_ratelimited("Level %d: hindex=%lu, hoffset=%u\n",
	level, hindex, hoffset);

	hpage = inode->i_sb->s_vop->read_merkle_tree_page(inode, hindex,
	level == 0 ? level0_ra_pages : 0);
	if (IS_ERR(hpage)) {
	err = PTR_ERR(hpage);
	fsverity_err(inode,
	"Error %d reading Merkle tree page %lu",
	err, hindex);
	goto out;
	}

	if (PageChecked(hpage)) {
	memcpy_from_page(_want_hash, hpage, hoffset, hsize);
	want_hash = _want_hash;
	put_page(hpage);
	pr_debug_ratelimited("Hash page already checked, want %s:%*phN\n",
	params->hash_alg->name,
	hsize, want_hash);
	goto descend;
	}
	pr_debug_ratelimited("Hash page not yet checked\n");
	hpages[level] = hpage;
	hoffsets[level] = hoffset;
	}

	want_hash = vi->root_hash;
	pr_debug("Want root hash: %s:%*phN\n",
	params->hash_alg->name, hsize, want_hash);
	descend:
	/* Descend the tree verifying hash pages */
	for (; level > 0; level--) {
	struct page *hpage = hpages[level - 1];
	unsigned int hoffset = hoffsets[level - 1];

	err = fsverity_hash_page(params, inode, req, hpage, real_hash);
	if (err)
	goto out;
	err = cmp_hashes(vi, want_hash, real_hash, index, level - 1);
	if (err)
	goto out;
	SetPageChecked(hpage);
	memcpy_from_page(_want_hash, hpage, hoffset, hsize);
	want_hash = _want_hash;
	put_page(hpage);
	pr_debug("Verified hash page at level %d, now want %s:%*phN\n",
	level - 1, params->hash_alg->name, hsize, want_hash);
	}

	/* Finally, verify the data page */
	err = fsverity_hash_page(params, inode, req, data_page, real_hash);
	if (err)
	goto out;
	err = cmp_hashes(vi, want_hash, real_hash, index, -1);
	out:
	for (; level > 0; level--)
	put_page(hpages[level - 1]);

	return err == 0;
	}

	/**
	* fsverity_verify_page() - verify a data page
	* @page: the page to verity
	*
	* Verify a page that has just been read from a verity file. The page must be a
	* pagecache page that is still locked and not yet uptodate.
	*
	* Return: true if the page is valid, else false.
	*/
	bool fsverity_verify_page(struct page *page)
	{
	struct inode *inode = page->mapping->host;
	const struct fsverity_info *vi = inode->i_verity_info;
	struct ahash_request *req;
	bool valid;

	/* This allocation never fails, since it's mempool-backed. */
	req = fsverity_alloc_hash_request(vi->tree_params.hash_alg, GFP_NOFS);

	valid = verify_page(inode, vi, req, page, 0);

	fsverity_free_hash_request(vi->tree_params.hash_alg, req);

	return valid;
	}
	EXPORT_SYMBOL_GPL(fsverity_verify_page);

	#ifdef CONFIG_BLOCK
	/**
	* fsverity_verify_bio() - verify a 'read' bio that has just completed
	* @bio: the bio to verify
	*
	* Verify a set of pages that have just been read from a verity file. The pages
	* must be pagecache pages that are still locked and not yet uptodate. If a
	* page fails verification, then bio->bi_status is set to an error status.
	*
	* This is a helper function for use by the ->readpages() method of filesystems
	* that issue bios to read data directly into the page cache. Filesystems that
	* populate the page cache without issuing bios (e.g. non block-based
	* filesystems) must instead call fsverity_verify_page() directly on each page.
	* All filesystems must also call fsverity_verify_page() on holes.
	*/
	void fsverity_verify_bio(struct bio *bio)
	{
	struct inode *inode = bio_first_page_all(bio)->mapping->host;
	const struct fsverity_info *vi = inode->i_verity_info;
	const struct merkle_tree_params *params = &vi->tree_params;
	struct ahash_request *req;
	struct bio_vec *bv;
	struct bvec_iter_all iter_all;
	unsigned long max_ra_pages = 0;

	/* This allocation never fails, since it's mempool-backed. */
	req = fsverity_alloc_hash_request(params->hash_alg, GFP_NOFS);

	if (bio->bi_opf & REQ_RAHEAD) {
	/*
	* If this bio is for data readahead, then we also do readahead
	* of the first (largest) level of the Merkle tree. Namely,
	* when a Merkle tree page is read, we also try to piggy-back on
	* some additional pages -- up to 1/4 the number of data pages.
	*
	* This improves sequential read performance, as it greatly
	* reduces the number of I/O requests made to the Merkle tree.
	*/
	bio_for_each_segment_all(bv, bio, iter_all)
	max_ra_pages++;
	max_ra_pages /= 4;
	}

	bio_for_each_segment_all(bv, bio, iter_all) {
	struct page *page = bv->bv_page;
	unsigned long level0_index = page->index >> params->log_arity;
	unsigned long level0_ra_pages =
	min(max_ra_pages, params->level0_blocks - level0_index);

	if (!verify_page(inode, vi, req, page, level0_ra_pages)) {
	bio->bi_status = BLK_STS_IOERR;
	break;
	}
	}

	fsverity_free_hash_request(params->hash_alg, req);
	}
	EXPORT_SYMBOL_GPL(fsverity_verify_bio);
	#endif /* CONFIG_BLOCK */

	/**
	* fsverity_enqueue_verify_work() - enqueue work on the fs-verity workqueue
	* @work: the work to enqueue
	*
	* Enqueue verification work for asynchronous processing.
	*/
	void fsverity_enqueue_verify_work(struct work_struct *work)
	{
	queue_work(fsverity_read_workqueue, work);
	}
	EXPORT_SYMBOL_GPL(fsverity_enqueue_verify_work);

	int __init fsverity_init_workqueue(void)
	{
	/*
	* Use an unbound workqueue to allow bios to be verified in parallel
	* even when they happen to complete on the same CPU. This sacrifices
	* locality, but it's worthwhile since hashing is CPU-intensive.
	*
	* Also use a high-priority workqueue to prioritize verification work,
	* which blocks reads from completing, over regular application tasks.
	*/
	fsverity_read_workqueue = alloc_workqueue("fsverity_read_queue",
	WQ_UNBOUND \| WQ_HIGHPRI,
	num_online_cpus());
	if (!fsverity_read_workqueue)
	return -ENOMEM;
	return 0;
	}

	void __init fsverity_exit_workqueue(void)
	{
	destroy_workqueue(fsverity_read_workqueue);
	fsverity_read_workqueue = NULL;
	}