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 /* Extract a hash from a hash page */ 43 static void extract_hash(struct page *hpage, unsigned int hoffset, 44 unsigned int hsize, u8 *out) 45 { 46 void *virt = kmap_atomic(hpage); 47 48 memcpy(out, virt + hoffset, hsize); 49 kunmap_atomic(virt); 50 } 51 52 static inline int cmp_hashes(const struct fsverity_info *vi, 53 const u8 *want_hash, const u8 *real_hash, 54 pgoff_t index, int level) 55 { 56 const unsigned int hsize = vi->tree_params.digest_size; 57 58 if (memcmp(want_hash, real_hash, hsize) == 0) 59 return 0; 60 61 fsverity_err(vi->inode, 62 "FILE CORRUPTED! index=%lu, level=%d, want_hash=%s:%*phN, real_hash=%s:%*phN", 63 index, level, 64 vi->tree_params.hash_alg->name, hsize, want_hash, 65 vi->tree_params.hash_alg->name, hsize, real_hash); 66 return -EBADMSG; 67 } 68 69 /* 70 * Verify a single data page against the file's Merkle tree. 71 * 72 * In principle, we need to verify the entire path to the root node. However, 73 * for efficiency the filesystem may cache the hash pages. Therefore we need 74 * only ascend the tree until an already-verified page is seen, as indicated by 75 * the PageChecked bit being set; then verify the path to that page. 76 * 77 * This code currently only supports the case where the verity block size is 78 * equal to PAGE_SIZE. Doing otherwise would be possible but tricky, since we 79 * wouldn't be able to use the PageChecked bit. 80 * 81 * Note that multiple processes may race to verify a hash page and mark it 82 * Checked, but it doesn't matter; the result will be the same either way. 83 * 84 * Return: true if the page is valid, else false. 85 */ 86 static bool verify_page(struct inode *inode, const struct fsverity_info *vi, 87 struct ahash_request *req, struct page *data_page, 88 unsigned long level0_ra_pages) 89 { 90 const struct merkle_tree_params *params = &vi->tree_params; 91 const unsigned int hsize = params->digest_size; 92 const pgoff_t index = data_page->index; 93 int level; 94 u8 _want_hash[FS_VERITY_MAX_DIGEST_SIZE]; 95 const u8 *want_hash; 96 u8 real_hash[FS_VERITY_MAX_DIGEST_SIZE]; 97 struct page *hpages[FS_VERITY_MAX_LEVELS]; 98 unsigned int hoffsets[FS_VERITY_MAX_LEVELS]; 99 int err; 100 101 if (WARN_ON_ONCE(!PageLocked(data_page) || PageUptodate(data_page))) 102 return false; 103 104 pr_debug_ratelimited("Verifying data page %lu...\n", index); 105 106 /* 107 * Starting at the leaf level, ascend the tree saving hash pages along 108 * the way until we find a verified hash page, indicated by PageChecked; 109 * or until we reach the root. 110 */ 111 for (level = 0; level < params->num_levels; level++) { 112 pgoff_t hindex; 113 unsigned int hoffset; 114 struct page *hpage; 115 116 hash_at_level(params, index, level, &hindex, &hoffset); 117 118 pr_debug_ratelimited("Level %d: hindex=%lu, hoffset=%u\n", 119 level, hindex, hoffset); 120 121 hpage = inode->i_sb->s_vop->read_merkle_tree_page(inode, hindex, 122 level == 0 ? level0_ra_pages : 0); 123 if (IS_ERR(hpage)) { 124 err = PTR_ERR(hpage); 125 fsverity_err(inode, 126 "Error %d reading Merkle tree page %lu", 127 err, hindex); 128 goto out; 129 } 130 131 if (PageChecked(hpage)) { 132 extract_hash(hpage, hoffset, hsize, _want_hash); 133 want_hash = _want_hash; 134 put_page(hpage); 135 pr_debug_ratelimited("Hash page already checked, want %s:%*phN\n", 136 params->hash_alg->name, 137 hsize, want_hash); 138 goto descend; 139 } 140 pr_debug_ratelimited("Hash page not yet checked\n"); 141 hpages[level] = hpage; 142 hoffsets[level] = hoffset; 143 } 144 145 want_hash = vi->root_hash; 146 pr_debug("Want root hash: %s:%*phN\n", 147 params->hash_alg->name, hsize, want_hash); 148 descend: 149 /* Descend the tree verifying hash pages */ 150 for (; level > 0; level--) { 151 struct page *hpage = hpages[level - 1]; 152 unsigned int hoffset = hoffsets[level - 1]; 153 154 err = fsverity_hash_page(params, inode, req, hpage, real_hash); 155 if (err) 156 goto out; 157 err = cmp_hashes(vi, want_hash, real_hash, index, level - 1); 158 if (err) 159 goto out; 160 SetPageChecked(hpage); 161 extract_hash(hpage, hoffset, hsize, _want_hash); 162 want_hash = _want_hash; 163 put_page(hpage); 164 pr_debug("Verified hash page at level %d, now want %s:%*phN\n", 165 level - 1, params->hash_alg->name, hsize, want_hash); 166 } 167 168 /* Finally, verify the data page */ 169 err = fsverity_hash_page(params, inode, req, data_page, real_hash); 170 if (err) 171 goto out; 172 err = cmp_hashes(vi, want_hash, real_hash, index, -1); 173 out: 174 for (; level > 0; level--) 175 put_page(hpages[level - 1]); 176 177 return err == 0; 178 } 179 180 /** 181 * fsverity_verify_page() - verify a data page 182 * @page: the page to verity 183 * 184 * Verify a page that has just been read from a verity file. The page must be a 185 * pagecache page that is still locked and not yet uptodate. 186 * 187 * Return: true if the page is valid, else false. 188 */ 189 bool fsverity_verify_page(struct page *page) 190 { 191 struct inode *inode = page->mapping->host; 192 const struct fsverity_info *vi = inode->i_verity_info; 193 struct ahash_request *req; 194 bool valid; 195 196 /* This allocation never fails, since it's mempool-backed. */ 197 req = fsverity_alloc_hash_request(vi->tree_params.hash_alg, GFP_NOFS); 198 199 valid = verify_page(inode, vi, req, page, 0); 200 201 fsverity_free_hash_request(vi->tree_params.hash_alg, req); 202 203 return valid; 204 } 205 EXPORT_SYMBOL_GPL(fsverity_verify_page); 206 207 #ifdef CONFIG_BLOCK 208 /** 209 * fsverity_verify_bio() - verify a 'read' bio that has just completed 210 * @bio: the bio to verify 211 * 212 * Verify a set of pages that have just been read from a verity file. The pages 213 * must be pagecache pages that are still locked and not yet uptodate. Pages 214 * that fail verification are set to the Error state. Verification is skipped 215 * for pages already in the Error state, e.g. due to fscrypt decryption failure. 216 * 217 * This is a helper function for use by the ->readahead() method of filesystems 218 * that issue bios to read data directly into the page cache. Filesystems that 219 * populate the page cache without issuing bios (e.g. non block-based 220 * filesystems) must instead call fsverity_verify_page() directly on each page. 221 * All filesystems must also call fsverity_verify_page() on holes. 222 */ 223 void fsverity_verify_bio(struct bio *bio) 224 { 225 struct inode *inode = bio_first_page_all(bio)->mapping->host; 226 const struct fsverity_info *vi = inode->i_verity_info; 227 const struct merkle_tree_params *params = &vi->tree_params; 228 struct ahash_request *req; 229 struct bio_vec *bv; 230 struct bvec_iter_all iter_all; 231 unsigned long max_ra_pages = 0; 232 233 /* This allocation never fails, since it's mempool-backed. */ 234 req = fsverity_alloc_hash_request(params->hash_alg, GFP_NOFS); 235 236 if (bio->bi_opf & REQ_RAHEAD) { 237 /* 238 * If this bio is for data readahead, then we also do readahead 239 * of the first (largest) level of the Merkle tree. Namely, 240 * when a Merkle tree page is read, we also try to piggy-back on 241 * some additional pages -- up to 1/4 the number of data pages. 242 * 243 * This improves sequential read performance, as it greatly 244 * reduces the number of I/O requests made to the Merkle tree. 245 */ 246 bio_for_each_segment_all(bv, bio, iter_all) 247 max_ra_pages++; 248 max_ra_pages /= 4; 249 } 250 251 bio_for_each_segment_all(bv, bio, iter_all) { 252 struct page *page = bv->bv_page; 253 unsigned long level0_index = page->index >> params->log_arity; 254 unsigned long level0_ra_pages = 255 min(max_ra_pages, params->level0_blocks - level0_index); 256 257 if (!PageError(page) && 258 !verify_page(inode, vi, req, page, level0_ra_pages)) 259 SetPageError(page); 260 } 261 262 fsverity_free_hash_request(params->hash_alg, req); 263 } 264 EXPORT_SYMBOL_GPL(fsverity_verify_bio); 265 #endif /* CONFIG_BLOCK */ 266 267 /** 268 * fsverity_enqueue_verify_work() - enqueue work on the fs-verity workqueue 269 * @work: the work to enqueue 270 * 271 * Enqueue verification work for asynchronous processing. 272 */ 273 void fsverity_enqueue_verify_work(struct work_struct *work) 274 { 275 queue_work(fsverity_read_workqueue, work); 276 } 277 EXPORT_SYMBOL_GPL(fsverity_enqueue_verify_work); 278 279 int __init fsverity_init_workqueue(void) 280 { 281 /* 282 * Use an unbound workqueue to allow bios to be verified in parallel 283 * even when they happen to complete on the same CPU. This sacrifices 284 * locality, but it's worthwhile since hashing is CPU-intensive. 285 * 286 * Also use a high-priority workqueue to prioritize verification work, 287 * which blocks reads from completing, over regular application tasks. 288 */ 289 fsverity_read_workqueue = alloc_workqueue("fsverity_read_queue", 290 WQ_UNBOUND | WQ_HIGHPRI, 291 num_online_cpus()); 292 if (!fsverity_read_workqueue) 293 return -ENOMEM; 294 return 0; 295 } 296 297 void __init fsverity_exit_workqueue(void) 298 { 299 destroy_workqueue(fsverity_read_workqueue); 300 fsverity_read_workqueue = NULL; 301 } 302