| // SPDX-License-Identifier: GPL-2.0 |
| /* |
| * fs/verity/verify.c: 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) |
| { |
| 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); |
| 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 |
| * |
| * 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; |
| |
| req = ahash_request_alloc(vi->tree_params.hash_alg->tfm, GFP_NOFS); |
| if (unlikely(!req)) |
| return false; |
| |
| valid = verify_page(inode, vi, req, page); |
| |
| ahash_request_free(req); |
| |
| return valid; |
| } |
| EXPORT_SYMBOL_GPL(fsverity_verify_page); |
| |
| #ifdef CONFIG_BLOCK |
| /** |
| * fsverity_verify_bio() - verify a 'read' bio that has just completed |
| * |
| * 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; |
| struct ahash_request *req; |
| struct bio_vec *bv; |
| struct bvec_iter_all iter_all; |
| |
| req = ahash_request_alloc(vi->tree_params.hash_alg->tfm, GFP_NOFS); |
| if (unlikely(!req)) { |
| bio_for_each_segment_all(bv, bio, iter_all) |
| SetPageError(bv->bv_page); |
| return; |
| } |
| |
| bio_for_each_segment_all(bv, bio, iter_all) { |
| struct page *page = bv->bv_page; |
| |
| if (!PageError(page) && !verify_page(inode, vi, req, page)) |
| SetPageError(page); |
| } |
| |
| ahash_request_free(req); |
| } |
| EXPORT_SYMBOL_GPL(fsverity_verify_bio); |
| #endif /* CONFIG_BLOCK */ |
| |
| /** |
| * fsverity_enqueue_verify_work() - enqueue work on the fs-verity workqueue |
| * |
| * 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; |
| } |