// SPDX-License-Identifier: GPL-2.0 /* * Data verification functions, i.e. hooks for ->readpages() * * Copyright 2019 Google LLC */ #include "fsverity_private.h" #include #include #include 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 a high-priority workqueue to prioritize verification work, which * blocks reads from completing, over regular application tasks. * * For performance reasons, don't use an unbound workqueue. Using an * unbound workqueue for crypto operations causes excessive scheduler * latency on ARM64. */ fsverity_read_workqueue = alloc_workqueue("fsverity_read_queue", 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; }