1 // SPDX-License-Identifier: GPL-2.0 2 /* 3 * fs/verity/verify.c: data verification functions, i.e. hooks for ->readpages() 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 { 89 const struct merkle_tree_params *params = &vi->tree_params; 90 const unsigned int hsize = params->digest_size; 91 const pgoff_t index = data_page->index; 92 int level; 93 u8 _want_hash[FS_VERITY_MAX_DIGEST_SIZE]; 94 const u8 *want_hash; 95 u8 real_hash[FS_VERITY_MAX_DIGEST_SIZE]; 96 struct page *hpages[FS_VERITY_MAX_LEVELS]; 97 unsigned int hoffsets[FS_VERITY_MAX_LEVELS]; 98 int err; 99 100 if (WARN_ON_ONCE(!PageLocked(data_page) || PageUptodate(data_page))) 101 return false; 102 103 pr_debug_ratelimited("Verifying data page %lu...\n", index); 104 105 /* 106 * Starting at the leaf level, ascend the tree saving hash pages along 107 * the way until we find a verified hash page, indicated by PageChecked; 108 * or until we reach the root. 109 */ 110 for (level = 0; level < params->num_levels; level++) { 111 pgoff_t hindex; 112 unsigned int hoffset; 113 struct page *hpage; 114 115 hash_at_level(params, index, level, &hindex, &hoffset); 116 117 pr_debug_ratelimited("Level %d: hindex=%lu, hoffset=%u\n", 118 level, hindex, hoffset); 119 120 hpage = inode->i_sb->s_vop->read_merkle_tree_page(inode, 121 hindex); 122 if (IS_ERR(hpage)) { 123 err = PTR_ERR(hpage); 124 fsverity_err(inode, 125 "Error %d reading Merkle tree page %lu", 126 err, hindex); 127 goto out; 128 } 129 130 if (PageChecked(hpage)) { 131 extract_hash(hpage, hoffset, hsize, _want_hash); 132 want_hash = _want_hash; 133 put_page(hpage); 134 pr_debug_ratelimited("Hash page already checked, want %s:%*phN\n", 135 params->hash_alg->name, 136 hsize, want_hash); 137 goto descend; 138 } 139 pr_debug_ratelimited("Hash page not yet checked\n"); 140 hpages[level] = hpage; 141 hoffsets[level] = hoffset; 142 } 143 144 want_hash = vi->root_hash; 145 pr_debug("Want root hash: %s:%*phN\n", 146 params->hash_alg->name, hsize, want_hash); 147 descend: 148 /* Descend the tree verifying hash pages */ 149 for (; level > 0; level--) { 150 struct page *hpage = hpages[level - 1]; 151 unsigned int hoffset = hoffsets[level - 1]; 152 153 err = fsverity_hash_page(params, inode, req, hpage, real_hash); 154 if (err) 155 goto out; 156 err = cmp_hashes(vi, want_hash, real_hash, index, level - 1); 157 if (err) 158 goto out; 159 SetPageChecked(hpage); 160 extract_hash(hpage, hoffset, hsize, _want_hash); 161 want_hash = _want_hash; 162 put_page(hpage); 163 pr_debug("Verified hash page at level %d, now want %s:%*phN\n", 164 level - 1, params->hash_alg->name, hsize, want_hash); 165 } 166 167 /* Finally, verify the data page */ 168 err = fsverity_hash_page(params, inode, req, data_page, real_hash); 169 if (err) 170 goto out; 171 err = cmp_hashes(vi, want_hash, real_hash, index, -1); 172 out: 173 for (; level > 0; level--) 174 put_page(hpages[level - 1]); 175 176 return err == 0; 177 } 178 179 /** 180 * fsverity_verify_page() - verify a data page 181 * 182 * Verify a page that has just been read from a verity file. The page must be a 183 * pagecache page that is still locked and not yet uptodate. 184 * 185 * Return: true if the page is valid, else false. 186 */ 187 bool fsverity_verify_page(struct page *page) 188 { 189 struct inode *inode = page->mapping->host; 190 const struct fsverity_info *vi = inode->i_verity_info; 191 struct ahash_request *req; 192 bool valid; 193 194 req = ahash_request_alloc(vi->tree_params.hash_alg->tfm, GFP_NOFS); 195 if (unlikely(!req)) 196 return false; 197 198 valid = verify_page(inode, vi, req, page); 199 200 ahash_request_free(req); 201 202 return valid; 203 } 204 EXPORT_SYMBOL_GPL(fsverity_verify_page); 205 206 #ifdef CONFIG_BLOCK 207 /** 208 * fsverity_verify_bio() - verify a 'read' bio that has just completed 209 * 210 * Verify a set of pages that have just been read from a verity file. The pages 211 * must be pagecache pages that are still locked and not yet uptodate. Pages 212 * that fail verification are set to the Error state. Verification is skipped 213 * for pages already in the Error state, e.g. due to fscrypt decryption failure. 214 * 215 * This is a helper function for use by the ->readpages() method of filesystems 216 * that issue bios to read data directly into the page cache. Filesystems that 217 * populate the page cache without issuing bios (e.g. non block-based 218 * filesystems) must instead call fsverity_verify_page() directly on each page. 219 * All filesystems must also call fsverity_verify_page() on holes. 220 */ 221 void fsverity_verify_bio(struct bio *bio) 222 { 223 struct inode *inode = bio_first_page_all(bio)->mapping->host; 224 const struct fsverity_info *vi = inode->i_verity_info; 225 struct ahash_request *req; 226 struct bio_vec *bv; 227 struct bvec_iter_all iter_all; 228 229 req = ahash_request_alloc(vi->tree_params.hash_alg->tfm, GFP_NOFS); 230 if (unlikely(!req)) { 231 bio_for_each_segment_all(bv, bio, iter_all) 232 SetPageError(bv->bv_page); 233 return; 234 } 235 236 bio_for_each_segment_all(bv, bio, iter_all) { 237 struct page *page = bv->bv_page; 238 239 if (!PageError(page) && !verify_page(inode, vi, req, page)) 240 SetPageError(page); 241 } 242 243 ahash_request_free(req); 244 } 245 EXPORT_SYMBOL_GPL(fsverity_verify_bio); 246 #endif /* CONFIG_BLOCK */ 247 248 /** 249 * fsverity_enqueue_verify_work() - enqueue work on the fs-verity workqueue 250 * 251 * Enqueue verification work for asynchronous processing. 252 */ 253 void fsverity_enqueue_verify_work(struct work_struct *work) 254 { 255 queue_work(fsverity_read_workqueue, work); 256 } 257 EXPORT_SYMBOL_GPL(fsverity_enqueue_verify_work); 258 259 int __init fsverity_init_workqueue(void) 260 { 261 /* 262 * Use an unbound workqueue to allow bios to be verified in parallel 263 * even when they happen to complete on the same CPU. This sacrifices 264 * locality, but it's worthwhile since hashing is CPU-intensive. 265 * 266 * Also use a high-priority workqueue to prioritize verification work, 267 * which blocks reads from completing, over regular application tasks. 268 */ 269 fsverity_read_workqueue = alloc_workqueue("fsverity_read_queue", 270 WQ_UNBOUND | WQ_HIGHPRI, 271 num_online_cpus()); 272 if (!fsverity_read_workqueue) 273 return -ENOMEM; 274 return 0; 275 } 276 277 void __init fsverity_exit_workqueue(void) 278 { 279 destroy_workqueue(fsverity_read_workqueue); 280 fsverity_read_workqueue = NULL; 281 } 282