From 8a1d0f9cacc997bedc017056a94f35dc823394ed Mon Sep 17 00:00:00 2001 From: Eric Biggers Date: Mon, 22 Jul 2019 09:26:22 -0700 Subject: fs-verity: add data verification hooks for ->readpages() Add functions that verify data pages that have been read from a fs-verity file, against that file's Merkle tree. These will be called from filesystems' ->readpage() and ->readpages() methods. Since data verification can block, a workqueue is provided for these methods to enqueue verification work from their bio completion callback. See the "Verifying data" section of Documentation/filesystems/fsverity.rst for more information. Reviewed-by: Theodore Ts'o Reviewed-by: Jaegeuk Kim Signed-off-by: Eric Biggers --- fs/verity/Makefile | 3 +- fs/verity/fsverity_private.h | 5 + fs/verity/init.c | 8 ++ fs/verity/open.c | 6 + fs/verity/verify.c | 275 +++++++++++++++++++++++++++++++++++++++++++ 5 files changed, 296 insertions(+), 1 deletion(-) create mode 100644 fs/verity/verify.c (limited to 'fs/verity') diff --git a/fs/verity/Makefile b/fs/verity/Makefile index e6a8951c493a..7fa628cd5eba 100644 --- a/fs/verity/Makefile +++ b/fs/verity/Makefile @@ -2,4 +2,5 @@ obj-$(CONFIG_FS_VERITY) += hash_algs.o \ init.o \ - open.o + open.o \ + verify.o diff --git a/fs/verity/fsverity_private.h b/fs/verity/fsverity_private.h index c79746ff335e..eaa2b3b93bbf 100644 --- a/fs/verity/fsverity_private.h +++ b/fs/verity/fsverity_private.h @@ -134,5 +134,10 @@ void fsverity_set_info(struct inode *inode, struct fsverity_info *vi); void fsverity_free_info(struct fsverity_info *vi); int __init fsverity_init_info_cache(void); +void __init fsverity_exit_info_cache(void); + +/* verify.c */ + +int __init fsverity_init_workqueue(void); #endif /* _FSVERITY_PRIVATE_H */ diff --git a/fs/verity/init.c b/fs/verity/init.c index fff1fd634335..b593805aafcc 100644 --- a/fs/verity/init.c +++ b/fs/verity/init.c @@ -41,7 +41,15 @@ static int __init fsverity_init(void) if (err) return err; + err = fsverity_init_workqueue(); + if (err) + goto err_exit_info_cache; + pr_debug("Initialized fs-verity\n"); return 0; + +err_exit_info_cache: + fsverity_exit_info_cache(); + return err; } late_initcall(fsverity_init) diff --git a/fs/verity/open.c b/fs/verity/open.c index 2cb2fe8082bf..3636a1ed8e2c 100644 --- a/fs/verity/open.c +++ b/fs/verity/open.c @@ -337,3 +337,9 @@ int __init fsverity_init_info_cache(void) return -ENOMEM; return 0; } + +void __init fsverity_exit_info_cache(void) +{ + kmem_cache_destroy(fsverity_info_cachep); + fsverity_info_cachep = NULL; +} diff --git a/fs/verity/verify.c b/fs/verity/verify.c new file mode 100644 index 000000000000..62ab8f6a8ea1 --- /dev/null +++ b/fs/verity/verify.c @@ -0,0 +1,275 @@ +// 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 +#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) +{ + 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; +} -- cgit