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- // 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);
- }
- /* Extract a hash from a hash page */
- static void extract_hash(struct page *hpage, unsigned int hoffset,
- unsigned int hsize, u8 *out)
- {
- void *virt = kmap_atomic(hpage);
- memcpy(out, virt + hoffset, hsize);
- kunmap_atomic(virt);
- }
- 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)) {
- extract_hash(hpage, hoffset, hsize, _want_hash);
- 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);
- extract_hash(hpage, hoffset, hsize, _want_hash);
- 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. Pages
- * that fail verification are set to the Error state. Verification is skipped
- * for pages already in the Error state, e.g. due to fscrypt decryption failure.
- *
- * 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 (!PageError(page) &&
- !verify_page(inode, vi, req, page, level0_ra_pages))
- SetPageError(page);
- }
- 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;
- }
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