From: Eric Biggers Subject: [RFC PATCH 02/10] fs-verity: add data verification hooks for ->readpages() Date: Fri, 24 Aug 2018 09:16:34 -0700 Message-ID: <20180824161642.1144-3-ebiggers@kernel.org> References: <20180824161642.1144-1-ebiggers@kernel.org> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Cc: Dmitry Kasatkin , Michael Halcrow , linux-kernel@vger.kernel.org, linux-fscrypt@vger.kernel.org, linux-integrity@vger.kernel.org, Mimi Zohar , Victor Hsieh To: linux-fsdevel@vger.kernel.org, linux-ext4@vger.kernel.org, linux-f2fs-devel@lists.sourceforge.net Return-path: In-Reply-To: <20180824161642.1144-1-ebiggers@kernel.org> List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: linux-f2fs-devel-bounces@lists.sourceforge.net List-Id: linux-ext4.vger.kernel.org From: Eric Biggers 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. Signed-off-by: Eric Biggers --- fs/verity/Makefile | 2 +- fs/verity/fsverity_private.h | 3 + fs/verity/setup.c | 26 ++- fs/verity/verify.c | 310 +++++++++++++++++++++++++++++++++++ include/linux/fsverity.h | 23 +++ 5 files changed, 362 insertions(+), 2 deletions(-) create mode 100644 fs/verity/verify.c diff --git a/fs/verity/Makefile b/fs/verity/Makefile index 39e123805c827..a6c7cefb61ab7 100644 --- a/fs/verity/Makefile +++ b/fs/verity/Makefile @@ -1,3 +1,3 @@ obj-$(CONFIG_FS_VERITY) += fsverity.o -fsverity-y := hash_algs.o setup.o +fsverity-y := hash_algs.o setup.o verify.o diff --git a/fs/verity/fsverity_private.h b/fs/verity/fsverity_private.h index a18ff645695f4..c553f99dc4973 100644 --- a/fs/verity/fsverity_private.h +++ b/fs/verity/fsverity_private.h @@ -96,4 +96,7 @@ static inline bool set_fsverity_info(struct inode *inode, return true; } +/* verify.c */ +extern struct workqueue_struct *fsverity_read_workqueue; + #endif /* _FSVERITY_PRIVATE_H */ diff --git a/fs/verity/setup.c b/fs/verity/setup.c index e675c52898d5b..84cc2edeca25b 100644 --- a/fs/verity/setup.c +++ b/fs/verity/setup.c @@ -824,18 +824,42 @@ EXPORT_SYMBOL_GPL(fsverity_full_i_size); static int __init fsverity_module_init(void) { + int err; + + /* + * 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. + */ + err = -ENOMEM; + fsverity_read_workqueue = alloc_workqueue("fsverity_read_queue", + WQ_UNBOUND | WQ_HIGHPRI, + num_online_cpus()); + if (!fsverity_read_workqueue) + goto error; + + err = -ENOMEM; fsverity_info_cachep = KMEM_CACHE(fsverity_info, SLAB_RECLAIM_ACCOUNT); if (!fsverity_info_cachep) - return -ENOMEM; + goto error_free_workqueue; fsverity_check_hash_algs(); pr_debug("Initialized fs-verity\n"); return 0; + +error_free_workqueue: + destroy_workqueue(fsverity_read_workqueue); +error: + return err; } static void __exit fsverity_module_exit(void) { + destroy_workqueue(fsverity_read_workqueue); kmem_cache_destroy(fsverity_info_cachep); fsverity_exit_hash_algs(); } diff --git a/fs/verity/verify.c b/fs/verity/verify.c new file mode 100644 index 0000000000000..1452dd05f75d3 --- /dev/null +++ b/fs/verity/verify.c @@ -0,0 +1,310 @@ +// SPDX-License-Identifier: GPL-2.0 +/* + * fs/verity/verify.c: fs-verity data verification functions, + * i.e. hooks for ->readpages() + * + * Copyright (C) 2018 Google LLC + * + * Originally written by Jaegeuk Kim and Michael Halcrow; + * heavily rewritten by Eric Biggers. + */ + +#include "fsverity_private.h" + +#include +#include +#include +#include +#include + +struct workqueue_struct *fsverity_read_workqueue; + +/** + * hash_at_level() - compute the location of the block's hash at the given level + * + * @vi: (in) the file's verity info + * @dindex: (in) the index of the data block being verified + * @level: (in) the level of hash we want + * @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 fsverity_info *vi, pgoff_t dindex, + unsigned int level, pgoff_t *hindex, + unsigned int *hoffset) +{ + pgoff_t hoffset_in_lvl; + + /* + * Compute the offset of the hash within the level's region, in hashes. + * For example, with 4096-byte blocks and 32-byte hashes, there are + * 4096/32 = 128 = 2^7 hashes per hash block, i.e. log_arity = 7. Then, + * if the data block index is 65668 and we want the level 1 hash, it is + * located at 65668 >> 7 = 513 hashes into the level 1 region. + */ + hoffset_in_lvl = dindex >> (level * vi->log_arity); + + /* + * Compute the index of the hash block containing the wanted hash. + * Continuing the above example, the block would be at index 513 >> 7 = + * 4 within the level 1 region. To this we'd add the index at which the + * level 1 region starts. + */ + *hindex = vi->hash_lvl_region_idx[level] + + (hoffset_in_lvl >> vi->log_arity); + + /* + * Finally, compute the index of the hash within the block rather than + * the region, and multiply by the hash size to turn it into a byte + * offset. Continuing the above example, the hash would be at byte + * offset (513 & ((1 << 7) - 1)) * 32 = 32 within the block. + */ + *hoffset = (hoffset_in_lvl & ((1 << vi->log_arity) - 1)) * + vi->hash_alg->digest_size; +} + +/* 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 int hash_page(const struct fsverity_info *vi, struct ahash_request *req, + struct page *page, u8 *out) +{ + struct scatterlist sg[3]; + DECLARE_CRYPTO_WAIT(wait); + int err; + + sg_init_table(sg, 1); + sg_set_page(&sg[0], page, PAGE_SIZE, 0); + + ahash_request_set_callback(req, CRYPTO_TFM_REQ_MAY_SLEEP | + CRYPTO_TFM_REQ_MAY_BACKLOG, + crypto_req_done, &wait); + ahash_request_set_crypt(req, sg, out, PAGE_SIZE); + + err = crypto_ahash_import(req, vi->hashstate); + if (err) + return err; + + return crypto_wait_req(crypto_ahash_finup(req), &wait); +} + +static inline int compare_hashes(const u8 *want_hash, const u8 *real_hash, + int digest_size, struct inode *inode, + pgoff_t index, int level, const char *algname) +{ + if (memcmp(want_hash, real_hash, digest_size) == 0) + return 0; + + pr_warn_ratelimited("VERIFICATION FAILURE! ino=%lu, index=%lu, level=%d, want_hash=%s:%*phN, real_hash=%s:%*phN\n", + inode->i_ino, index, level, + algname, digest_size, want_hash, + algname, digest_size, 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. But as an + * optimization, we cache the hash pages in the file's page cache, similar to + * data pages. Therefore, we can stop verifying as soon as a verified hash page + * is seen while ascending the tree. + * + * Note that unlike data pages, hash pages are marked Uptodate *before* they are + * verified; instead, the Checked bit is set on hash pages that have been + * verified. Multiple tasks may race to verify a hash page and mark it Checked, + * but it doesn't matter. The use of the Checked bit also implies that the hash + * block size must equal PAGE_SIZE (for now). + */ +static bool verify_page(struct inode *inode, const struct fsverity_info *vi, + struct ahash_request *req, struct page *data_page) +{ + pgoff_t index = data_page->index; + int level = 0; + u8 _want_hash[FS_VERITY_MAX_DIGEST_SIZE]; + const u8 *want_hash = NULL; + u8 real_hash[FS_VERITY_MAX_DIGEST_SIZE]; + struct page *hpages[FS_VERITY_MAX_LEVELS]; + unsigned int hoffsets[FS_VERITY_MAX_LEVELS]; + int err; + + /* The page must not be unlocked until verification has completed. */ + if (WARN_ON_ONCE(!PageLocked(data_page))) + return false; + + /* + * Since ->i_size is overridden with ->data_i_size, and fs-verity avoids + * recursing into itself when reading hash pages, we shouldn't normally + * get here with a page beyond ->data_i_size. But, it can happen if a + * read is issued at or beyond EOF since the VFS doesn't check i_size + * before calling ->readpage(). Thus, just skip verification if the + * page is beyond ->data_i_size. + */ + if (index >= (vi->data_i_size + PAGE_SIZE - 1) >> PAGE_SHIFT) { + pr_debug("Page %lu is in metadata region\n", index); + return true; + } + + pr_debug_ratelimited("Verifying data page %lu...\n", index); + + /* + * Starting at the leaves, 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 < vi->depth; level++) { + pgoff_t hindex; + unsigned int hoffset; + struct page *hpage; + + hash_at_level(vi, index, level, &hindex, &hoffset); + + pr_debug_ratelimited("Level %d: hindex=%lu, hoffset=%u\n", + level, hindex, hoffset); + + hpage = read_mapping_page(inode->i_mapping, hindex, NULL); + if (IS_ERR(hpage)) { + err = PTR_ERR(hpage); + goto out; + } + + if (PageChecked(hpage)) { + extract_hash(hpage, hoffset, vi->hash_alg->digest_size, + _want_hash); + want_hash = _want_hash; + put_page(hpage); + pr_debug_ratelimited("Hash page already checked, want %s:%*phN\n", + vi->hash_alg->name, + vi->hash_alg->digest_size, + want_hash); + break; + } + pr_debug_ratelimited("Hash page not yet checked\n"); + hpages[level] = hpage; + hoffsets[level] = hoffset; + } + + if (!want_hash) { + want_hash = vi->root_hash; + pr_debug("Want root hash: %s:%*phN\n", vi->hash_alg->name, + vi->hash_alg->digest_size, want_hash); + } + + /* Descend the tree verifying hash pages */ + for (; level > 0; level--) { + struct page *hpage = hpages[level - 1]; + unsigned int hoffset = hoffsets[level - 1]; + + err = hash_page(vi, req, hpage, real_hash); + if (err) + goto out; + err = compare_hashes(want_hash, real_hash, + vi->hash_alg->digest_size, + inode, index, level - 1, + vi->hash_alg->name); + if (err) + goto out; + SetPageChecked(hpage); + extract_hash(hpage, hoffset, vi->hash_alg->digest_size, + _want_hash); + want_hash = _want_hash; + put_page(hpage); + pr_debug("Verified hash page at level %d, now want %s:%*phN\n", + level - 1, vi->hash_alg->name, + vi->hash_alg->digest_size, want_hash); + } + + /* Finally, verify the data page */ + err = hash_page(vi, req, data_page, real_hash); + if (err) + goto out; + err = compare_hashes(want_hash, real_hash, vi->hash_alg->digest_size, + inode, index, -1, vi->hash_alg->name); +out: + for (; level > 0; level--) + put_page(hpages[level - 1]); + if (err) { + pr_warn_ratelimited("Error verifying page; ino=%lu, index=%lu (err=%d)\n", + inode->i_ino, data_page->index, err); + return false; + } + return true; +} + +/** + * fsverity_verify_page - verify a data page + * + * Verify a page that has just been read from a file against that file's Merkle + * tree. The page is assumed to be a pagecache page. + * + * Return: true if the page is valid, else false. + */ +bool fsverity_verify_page(struct page *data_page) +{ + struct inode *inode = data_page->mapping->host; + const struct fsverity_info *vi = get_fsverity_info(inode); + struct ahash_request *req; + bool valid; + + req = ahash_request_alloc(vi->hash_alg->tfm, GFP_KERNEL); + if (unlikely(!req)) + return false; + + valid = verify_page(inode, vi, req, data_page); + + ahash_request_free(req); + + return valid; +} +EXPORT_SYMBOL_GPL(fsverity_verify_page); + +/** + * fsverity_verify_bio - verify a 'read' bio that has just completed + * + * Verify a set of pages that have just been read from a file against that + * file's Merkle tree. The pages are assumed to be pagecache pages. 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. + */ +void fsverity_verify_bio(struct bio *bio) +{ + struct inode *inode = bio_first_page_all(bio)->mapping->host; + const struct fsverity_info *vi = get_fsverity_info(inode); + struct ahash_request *req; + struct bio_vec *bv; + int i; + + req = ahash_request_alloc(vi->hash_alg->tfm, GFP_KERNEL); + if (unlikely(!req)) { + bio_for_each_segment_all(bv, bio, i) + SetPageError(bv->bv_page); + return; + } + + bio_for_each_segment_all(bv, bio, i) { + 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); + +/** + * 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); diff --git a/include/linux/fsverity.h b/include/linux/fsverity.h index 3af55241046aa..56341f10aa965 100644 --- a/include/linux/fsverity.h +++ b/include/linux/fsverity.h @@ -28,6 +28,11 @@ extern int fsverity_prepare_getattr(struct inode *inode); extern void fsverity_cleanup_inode(struct inode *inode); extern loff_t fsverity_full_i_size(const struct inode *inode); +/* verify.c */ +extern bool fsverity_verify_page(struct page *page); +extern void fsverity_verify_bio(struct bio *bio); +extern void fsverity_enqueue_verify_work(struct work_struct *work); + #else /* !__FS_HAS_VERITY */ /* setup.c */ @@ -57,6 +62,24 @@ static inline loff_t fsverity_full_i_size(const struct inode *inode) return i_size_read(inode); } +/* verify.c */ + +static inline bool fsverity_verify_page(struct page *page) +{ + WARN_ON(1); + return false; +} + +static inline void fsverity_verify_bio(struct bio *bio) +{ + WARN_ON(1); +} + +static inline void fsverity_enqueue_verify_work(struct work_struct *work) +{ + WARN_ON(1); +} + #endif /* !__FS_HAS_VERITY */ #endif /* _LINUX_FSVERITY_H */ -- 2.18.0 ------------------------------------------------------------------------------ Check out the vibrant tech community on one of the world's most engaging tech sites, Slashdot.org! http://sdm.link/slashdot