1 // SPDX-License-Identifier: GPL-2.0 2 /* 3 * Data verification functions, i.e. hooks for ->readahead() 4 * 5 * Copyright 2019 Google LLC 6 */ 7 8 #include "fsverity_private.h" 9 10 #include <crypto/hash.h> 11 #include <linux/bio.h> 12 #include <linux/ratelimit.h> 13 14 static struct workqueue_struct *fsverity_read_workqueue; 15 16 /** 17 * hash_at_level() - compute the location of the block's hash at the given level 18 * 19 * @params: (in) the Merkle tree parameters 20 * @dindex: (in) the index of the data block being verified 21 * @level: (in) the level of hash we want (0 is leaf level) 22 * @hindex: (out) the index of the hash block containing the wanted hash 23 * @hoffset: (out) the byte offset to the wanted hash within the hash block 24 */ 25 static void hash_at_level(const struct merkle_tree_params *params, 26 pgoff_t dindex, unsigned int level, pgoff_t *hindex, 27 unsigned int *hoffset) 28 { 29 pgoff_t position; 30 31 /* Offset of the hash within the level's region, in hashes */ 32 position = dindex >> (level * params->log_arity); 33 34 /* Index of the hash block in the tree overall */ 35 *hindex = params->level_start[level] + (position >> params->log_arity); 36 37 /* Offset of the wanted hash (in bytes) within the hash block */ 38 *hoffset = (position & ((1 << params->log_arity) - 1)) << 39 (params->log_blocksize - params->log_arity); 40 } 41 42 static inline int cmp_hashes(const struct fsverity_info *vi, 43 const u8 *want_hash, const u8 *real_hash, 44 pgoff_t index, int level) 45 { 46 const unsigned int hsize = vi->tree_params.digest_size; 47 48 if (memcmp(want_hash, real_hash, hsize) == 0) 49 return 0; 50 51 fsverity_err(vi->inode, 52 "FILE CORRUPTED! index=%lu, level=%d, want_hash=%s:%*phN, real_hash=%s:%*phN", 53 index, level, 54 vi->tree_params.hash_alg->name, hsize, want_hash, 55 vi->tree_params.hash_alg->name, hsize, real_hash); 56 return -EBADMSG; 57 } 58 59 /* 60 * Verify a single data page against the file's Merkle tree. 61 * 62 * In principle, we need to verify the entire path to the root node. However, 63 * for efficiency the filesystem may cache the hash pages. Therefore we need 64 * only ascend the tree until an already-verified page is seen, as indicated by 65 * the PageChecked bit being set; then verify the path to that page. 66 * 67 * This code currently only supports the case where the verity block size is 68 * equal to PAGE_SIZE. Doing otherwise would be possible but tricky, since we 69 * wouldn't be able to use the PageChecked bit. 70 * 71 * Note that multiple processes may race to verify a hash page and mark it 72 * Checked, but it doesn't matter; the result will be the same either way. 73 * 74 * Return: true if the page is valid, else false. 75 */ 76 static bool verify_page(struct inode *inode, const struct fsverity_info *vi, 77 struct ahash_request *req, struct page *data_page, 78 unsigned long level0_ra_pages) 79 { 80 const struct merkle_tree_params *params = &vi->tree_params; 81 const unsigned int hsize = params->digest_size; 82 const pgoff_t index = data_page->index; 83 int level; 84 u8 _want_hash[FS_VERITY_MAX_DIGEST_SIZE]; 85 const u8 *want_hash; 86 u8 real_hash[FS_VERITY_MAX_DIGEST_SIZE]; 87 struct page *hpages[FS_VERITY_MAX_LEVELS]; 88 unsigned int hoffsets[FS_VERITY_MAX_LEVELS]; 89 int err; 90 91 if (WARN_ON_ONCE(!PageLocked(data_page) || PageUptodate(data_page))) 92 return false; 93 94 pr_debug_ratelimited("Verifying data page %lu...\n", index); 95 96 /* 97 * Starting at the leaf level, ascend the tree saving hash pages along 98 * the way until we find a verified hash page, indicated by PageChecked; 99 * or until we reach the root. 100 */ 101 for (level = 0; level < params->num_levels; level++) { 102 pgoff_t hindex; 103 unsigned int hoffset; 104 struct page *hpage; 105 106 hash_at_level(params, index, level, &hindex, &hoffset); 107 108 pr_debug_ratelimited("Level %d: hindex=%lu, hoffset=%u\n", 109 level, hindex, hoffset); 110 111 hpage = inode->i_sb->s_vop->read_merkle_tree_page(inode, hindex, 112 level == 0 ? level0_ra_pages : 0); 113 if (IS_ERR(hpage)) { 114 err = PTR_ERR(hpage); 115 fsverity_err(inode, 116 "Error %d reading Merkle tree page %lu", 117 err, hindex); 118 goto out; 119 } 120 121 if (PageChecked(hpage)) { 122 memcpy_from_page(_want_hash, hpage, hoffset, hsize); 123 want_hash = _want_hash; 124 put_page(hpage); 125 pr_debug_ratelimited("Hash page already checked, want %s:%*phN\n", 126 params->hash_alg->name, 127 hsize, want_hash); 128 goto descend; 129 } 130 pr_debug_ratelimited("Hash page not yet checked\n"); 131 hpages[level] = hpage; 132 hoffsets[level] = hoffset; 133 } 134 135 want_hash = vi->root_hash; 136 pr_debug("Want root hash: %s:%*phN\n", 137 params->hash_alg->name, hsize, want_hash); 138 descend: 139 /* Descend the tree verifying hash pages */ 140 for (; level > 0; level--) { 141 struct page *hpage = hpages[level - 1]; 142 unsigned int hoffset = hoffsets[level - 1]; 143 144 err = fsverity_hash_page(params, inode, req, hpage, real_hash); 145 if (err) 146 goto out; 147 err = cmp_hashes(vi, want_hash, real_hash, index, level - 1); 148 if (err) 149 goto out; 150 SetPageChecked(hpage); 151 memcpy_from_page(_want_hash, hpage, hoffset, hsize); 152 want_hash = _want_hash; 153 put_page(hpage); 154 pr_debug("Verified hash page at level %d, now want %s:%*phN\n", 155 level - 1, params->hash_alg->name, hsize, want_hash); 156 } 157 158 /* Finally, verify the data page */ 159 err = fsverity_hash_page(params, inode, req, data_page, real_hash); 160 if (err) 161 goto out; 162 err = cmp_hashes(vi, want_hash, real_hash, index, -1); 163 out: 164 for (; level > 0; level--) 165 put_page(hpages[level - 1]); 166 167 return err == 0; 168 } 169 170 /** 171 * fsverity_verify_page() - verify a data page 172 * @page: the page to verity 173 * 174 * Verify a page that has just been read from a verity file. The page must be a 175 * pagecache page that is still locked and not yet uptodate. 176 * 177 * Return: true if the page is valid, else false. 178 */ 179 bool fsverity_verify_page(struct page *page) 180 { 181 struct inode *inode = page->mapping->host; 182 const struct fsverity_info *vi = inode->i_verity_info; 183 struct ahash_request *req; 184 bool valid; 185 186 /* This allocation never fails, since it's mempool-backed. */ 187 req = fsverity_alloc_hash_request(vi->tree_params.hash_alg, GFP_NOFS); 188 189 valid = verify_page(inode, vi, req, page, 0); 190 191 fsverity_free_hash_request(vi->tree_params.hash_alg, req); 192 193 return valid; 194 } 195 EXPORT_SYMBOL_GPL(fsverity_verify_page); 196 197 #ifdef CONFIG_BLOCK 198 /** 199 * fsverity_verify_bio() - verify a 'read' bio that has just completed 200 * @bio: the bio to verify 201 * 202 * Verify a set of pages that have just been read from a verity file. The pages 203 * must be pagecache pages that are still locked and not yet uptodate. If a 204 * page fails verification, then bio->bi_status is set to an error status. 205 * 206 * This is a helper function for use by the ->readahead() method of filesystems 207 * that issue bios to read data directly into the page cache. Filesystems that 208 * populate the page cache without issuing bios (e.g. non block-based 209 * filesystems) must instead call fsverity_verify_page() directly on each page. 210 * All filesystems must also call fsverity_verify_page() on holes. 211 */ 212 void fsverity_verify_bio(struct bio *bio) 213 { 214 struct inode *inode = bio_first_page_all(bio)->mapping->host; 215 const struct fsverity_info *vi = inode->i_verity_info; 216 const struct merkle_tree_params *params = &vi->tree_params; 217 struct ahash_request *req; 218 struct bio_vec *bv; 219 struct bvec_iter_all iter_all; 220 unsigned long max_ra_pages = 0; 221 222 /* This allocation never fails, since it's mempool-backed. */ 223 req = fsverity_alloc_hash_request(params->hash_alg, GFP_NOFS); 224 225 if (bio->bi_opf & REQ_RAHEAD) { 226 /* 227 * If this bio is for data readahead, then we also do readahead 228 * of the first (largest) level of the Merkle tree. Namely, 229 * when a Merkle tree page is read, we also try to piggy-back on 230 * some additional pages -- up to 1/4 the number of data pages. 231 * 232 * This improves sequential read performance, as it greatly 233 * reduces the number of I/O requests made to the Merkle tree. 234 */ 235 bio_for_each_segment_all(bv, bio, iter_all) 236 max_ra_pages++; 237 max_ra_pages /= 4; 238 } 239 240 bio_for_each_segment_all(bv, bio, iter_all) { 241 struct page *page = bv->bv_page; 242 unsigned long level0_index = page->index >> params->log_arity; 243 unsigned long level0_ra_pages = 244 min(max_ra_pages, params->level0_blocks - level0_index); 245 246 if (!verify_page(inode, vi, req, page, level0_ra_pages)) { 247 bio->bi_status = BLK_STS_IOERR; 248 break; 249 } 250 } 251 252 fsverity_free_hash_request(params->hash_alg, req); 253 } 254 EXPORT_SYMBOL_GPL(fsverity_verify_bio); 255 #endif /* CONFIG_BLOCK */ 256 257 /** 258 * fsverity_enqueue_verify_work() - enqueue work on the fs-verity workqueue 259 * @work: the work to enqueue 260 * 261 * Enqueue verification work for asynchronous processing. 262 */ 263 void fsverity_enqueue_verify_work(struct work_struct *work) 264 { 265 queue_work(fsverity_read_workqueue, work); 266 } 267 EXPORT_SYMBOL_GPL(fsverity_enqueue_verify_work); 268 269 int __init fsverity_init_workqueue(void) 270 { 271 /* 272 * Use an unbound workqueue to allow bios to be verified in parallel 273 * even when they happen to complete on the same CPU. This sacrifices 274 * locality, but it's worthwhile since hashing is CPU-intensive. 275 * 276 * Also use a high-priority workqueue to prioritize verification work, 277 * which blocks reads from completing, over regular application tasks. 278 */ 279 fsverity_read_workqueue = alloc_workqueue("fsverity_read_queue", 280 WQ_UNBOUND | WQ_HIGHPRI, 281 num_online_cpus()); 282 if (!fsverity_read_workqueue) 283 return -ENOMEM; 284 return 0; 285 } 286 287 void __init fsverity_exit_workqueue(void) 288 { 289 destroy_workqueue(fsverity_read_workqueue); 290 fsverity_read_workqueue = NULL; 291 } 292