1 // SPDX-License-Identifier: GPL-2.0 2 /* 3 * Inline encryption support for fscrypt 4 * 5 * Copyright 2019 Google LLC 6 */ 7 8 /* 9 * With "inline encryption", the block layer handles the decryption/encryption 10 * as part of the bio, instead of the filesystem doing the crypto itself via 11 * crypto API. See Documentation/block/inline-encryption.rst. fscrypt still 12 * provides the key and IV to use. 13 */ 14 15 #include <linux/blk-crypto-profile.h> 16 #include <linux/blkdev.h> 17 #include <linux/buffer_head.h> 18 #include <linux/sched/mm.h> 19 #include <linux/slab.h> 20 #include <linux/uio.h> 21 22 #include "fscrypt_private.h" 23 24 static struct block_device **fscrypt_get_devices(struct super_block *sb, 25 unsigned int *num_devs) 26 { 27 struct block_device **devs; 28 29 if (sb->s_cop->get_devices) { 30 devs = sb->s_cop->get_devices(sb, num_devs); 31 if (devs) 32 return devs; 33 } 34 devs = kmalloc(sizeof(*devs), GFP_KERNEL); 35 if (!devs) 36 return ERR_PTR(-ENOMEM); 37 devs[0] = sb->s_bdev; 38 *num_devs = 1; 39 return devs; 40 } 41 42 static unsigned int fscrypt_get_dun_bytes(const struct fscrypt_info *ci) 43 { 44 struct super_block *sb = ci->ci_inode->i_sb; 45 unsigned int flags = fscrypt_policy_flags(&ci->ci_policy); 46 int ino_bits = 64, lblk_bits = 64; 47 48 if (flags & FSCRYPT_POLICY_FLAG_DIRECT_KEY) 49 return offsetofend(union fscrypt_iv, nonce); 50 51 if (flags & FSCRYPT_POLICY_FLAG_IV_INO_LBLK_64) 52 return sizeof(__le64); 53 54 if (flags & FSCRYPT_POLICY_FLAG_IV_INO_LBLK_32) 55 return sizeof(__le32); 56 57 /* Default case: IVs are just the file logical block number */ 58 if (sb->s_cop->get_ino_and_lblk_bits) 59 sb->s_cop->get_ino_and_lblk_bits(sb, &ino_bits, &lblk_bits); 60 return DIV_ROUND_UP(lblk_bits, 8); 61 } 62 63 /* 64 * Log a message when starting to use blk-crypto (native) or blk-crypto-fallback 65 * for an encryption mode for the first time. This is the blk-crypto 66 * counterpart to the message logged when starting to use the crypto API for the 67 * first time. A limitation is that these messages don't convey which specific 68 * filesystems or files are using each implementation. However, *usually* 69 * systems use just one implementation per mode, which makes these messages 70 * helpful for debugging problems where the "wrong" implementation is used. 71 */ 72 static void fscrypt_log_blk_crypto_impl(struct fscrypt_mode *mode, 73 struct block_device **devs, 74 unsigned int num_devs, 75 const struct blk_crypto_config *cfg) 76 { 77 unsigned int i; 78 79 for (i = 0; i < num_devs; i++) { 80 struct request_queue *q = bdev_get_queue(devs[i]); 81 82 if (!IS_ENABLED(CONFIG_BLK_INLINE_ENCRYPTION_FALLBACK) || 83 __blk_crypto_cfg_supported(q->crypto_profile, cfg)) { 84 if (!xchg(&mode->logged_blk_crypto_native, 1)) 85 pr_info("fscrypt: %s using blk-crypto (native)\n", 86 mode->friendly_name); 87 } else if (!xchg(&mode->logged_blk_crypto_fallback, 1)) { 88 pr_info("fscrypt: %s using blk-crypto-fallback\n", 89 mode->friendly_name); 90 } 91 } 92 } 93 94 /* Enable inline encryption for this file if supported. */ 95 int fscrypt_select_encryption_impl(struct fscrypt_info *ci) 96 { 97 const struct inode *inode = ci->ci_inode; 98 struct super_block *sb = inode->i_sb; 99 struct blk_crypto_config crypto_cfg; 100 struct block_device **devs; 101 unsigned int num_devs; 102 unsigned int i; 103 104 /* The file must need contents encryption, not filenames encryption */ 105 if (!S_ISREG(inode->i_mode)) 106 return 0; 107 108 /* The crypto mode must have a blk-crypto counterpart */ 109 if (ci->ci_mode->blk_crypto_mode == BLK_ENCRYPTION_MODE_INVALID) 110 return 0; 111 112 /* The filesystem must be mounted with -o inlinecrypt */ 113 if (!(sb->s_flags & SB_INLINECRYPT)) 114 return 0; 115 116 /* 117 * When a page contains multiple logically contiguous filesystem blocks, 118 * some filesystem code only calls fscrypt_mergeable_bio() for the first 119 * block in the page. This is fine for most of fscrypt's IV generation 120 * strategies, where contiguous blocks imply contiguous IVs. But it 121 * doesn't work with IV_INO_LBLK_32. For now, simply exclude 122 * IV_INO_LBLK_32 with blocksize != PAGE_SIZE from inline encryption. 123 */ 124 if ((fscrypt_policy_flags(&ci->ci_policy) & 125 FSCRYPT_POLICY_FLAG_IV_INO_LBLK_32) && 126 sb->s_blocksize != PAGE_SIZE) 127 return 0; 128 129 /* 130 * On all the filesystem's block devices, blk-crypto must support the 131 * crypto configuration that the file would use. 132 */ 133 crypto_cfg.crypto_mode = ci->ci_mode->blk_crypto_mode; 134 crypto_cfg.data_unit_size = sb->s_blocksize; 135 crypto_cfg.dun_bytes = fscrypt_get_dun_bytes(ci); 136 137 devs = fscrypt_get_devices(sb, &num_devs); 138 if (IS_ERR(devs)) 139 return PTR_ERR(devs); 140 141 for (i = 0; i < num_devs; i++) { 142 if (!blk_crypto_config_supported(devs[i], &crypto_cfg)) 143 goto out_free_devs; 144 } 145 146 fscrypt_log_blk_crypto_impl(ci->ci_mode, devs, num_devs, &crypto_cfg); 147 148 ci->ci_inlinecrypt = true; 149 out_free_devs: 150 kfree(devs); 151 152 return 0; 153 } 154 155 int fscrypt_prepare_inline_crypt_key(struct fscrypt_prepared_key *prep_key, 156 const u8 *raw_key, 157 const struct fscrypt_info *ci) 158 { 159 const struct inode *inode = ci->ci_inode; 160 struct super_block *sb = inode->i_sb; 161 enum blk_crypto_mode_num crypto_mode = ci->ci_mode->blk_crypto_mode; 162 struct blk_crypto_key *blk_key; 163 struct block_device **devs; 164 unsigned int num_devs; 165 unsigned int i; 166 int err; 167 168 blk_key = kmalloc(sizeof(*blk_key), GFP_KERNEL); 169 if (!blk_key) 170 return -ENOMEM; 171 172 err = blk_crypto_init_key(blk_key, raw_key, crypto_mode, 173 fscrypt_get_dun_bytes(ci), sb->s_blocksize); 174 if (err) { 175 fscrypt_err(inode, "error %d initializing blk-crypto key", err); 176 goto fail; 177 } 178 179 /* Start using blk-crypto on all the filesystem's block devices. */ 180 devs = fscrypt_get_devices(sb, &num_devs); 181 if (IS_ERR(devs)) { 182 err = PTR_ERR(devs); 183 goto fail; 184 } 185 for (i = 0; i < num_devs; i++) { 186 err = blk_crypto_start_using_key(devs[i], blk_key); 187 if (err) 188 break; 189 } 190 kfree(devs); 191 if (err) { 192 fscrypt_err(inode, "error %d starting to use blk-crypto", err); 193 goto fail; 194 } 195 196 /* 197 * Pairs with the smp_load_acquire() in fscrypt_is_key_prepared(). 198 * I.e., here we publish ->blk_key with a RELEASE barrier so that 199 * concurrent tasks can ACQUIRE it. Note that this concurrency is only 200 * possible for per-mode keys, not for per-file keys. 201 */ 202 smp_store_release(&prep_key->blk_key, blk_key); 203 return 0; 204 205 fail: 206 kfree_sensitive(blk_key); 207 return err; 208 } 209 210 void fscrypt_destroy_inline_crypt_key(struct super_block *sb, 211 struct fscrypt_prepared_key *prep_key) 212 { 213 struct blk_crypto_key *blk_key = prep_key->blk_key; 214 struct block_device **devs; 215 unsigned int num_devs; 216 unsigned int i; 217 218 if (!blk_key) 219 return; 220 221 /* Evict the key from all the filesystem's block devices. */ 222 devs = fscrypt_get_devices(sb, &num_devs); 223 if (!IS_ERR(devs)) { 224 for (i = 0; i < num_devs; i++) 225 blk_crypto_evict_key(devs[i], blk_key); 226 kfree(devs); 227 } 228 kfree_sensitive(blk_key); 229 } 230 231 bool __fscrypt_inode_uses_inline_crypto(const struct inode *inode) 232 { 233 return inode->i_crypt_info->ci_inlinecrypt; 234 } 235 EXPORT_SYMBOL_GPL(__fscrypt_inode_uses_inline_crypto); 236 237 static void fscrypt_generate_dun(const struct fscrypt_info *ci, u64 lblk_num, 238 u64 dun[BLK_CRYPTO_DUN_ARRAY_SIZE]) 239 { 240 union fscrypt_iv iv; 241 int i; 242 243 fscrypt_generate_iv(&iv, lblk_num, ci); 244 245 BUILD_BUG_ON(FSCRYPT_MAX_IV_SIZE > BLK_CRYPTO_MAX_IV_SIZE); 246 memset(dun, 0, BLK_CRYPTO_MAX_IV_SIZE); 247 for (i = 0; i < ci->ci_mode->ivsize/sizeof(dun[0]); i++) 248 dun[i] = le64_to_cpu(iv.dun[i]); 249 } 250 251 /** 252 * fscrypt_set_bio_crypt_ctx() - prepare a file contents bio for inline crypto 253 * @bio: a bio which will eventually be submitted to the file 254 * @inode: the file's inode 255 * @first_lblk: the first file logical block number in the I/O 256 * @gfp_mask: memory allocation flags - these must be a waiting mask so that 257 * bio_crypt_set_ctx can't fail. 258 * 259 * If the contents of the file should be encrypted (or decrypted) with inline 260 * encryption, then assign the appropriate encryption context to the bio. 261 * 262 * Normally the bio should be newly allocated (i.e. no pages added yet), as 263 * otherwise fscrypt_mergeable_bio() won't work as intended. 264 * 265 * The encryption context will be freed automatically when the bio is freed. 266 */ 267 void fscrypt_set_bio_crypt_ctx(struct bio *bio, const struct inode *inode, 268 u64 first_lblk, gfp_t gfp_mask) 269 { 270 const struct fscrypt_info *ci; 271 u64 dun[BLK_CRYPTO_DUN_ARRAY_SIZE]; 272 273 if (!fscrypt_inode_uses_inline_crypto(inode)) 274 return; 275 ci = inode->i_crypt_info; 276 277 fscrypt_generate_dun(ci, first_lblk, dun); 278 bio_crypt_set_ctx(bio, ci->ci_enc_key.blk_key, dun, gfp_mask); 279 } 280 EXPORT_SYMBOL_GPL(fscrypt_set_bio_crypt_ctx); 281 282 /* Extract the inode and logical block number from a buffer_head. */ 283 static bool bh_get_inode_and_lblk_num(const struct buffer_head *bh, 284 const struct inode **inode_ret, 285 u64 *lblk_num_ret) 286 { 287 struct page *page = bh->b_page; 288 const struct address_space *mapping; 289 const struct inode *inode; 290 291 /* 292 * The ext4 journal (jbd2) can submit a buffer_head it directly created 293 * for a non-pagecache page. fscrypt doesn't care about these. 294 */ 295 mapping = page_mapping(page); 296 if (!mapping) 297 return false; 298 inode = mapping->host; 299 300 *inode_ret = inode; 301 *lblk_num_ret = ((u64)page->index << (PAGE_SHIFT - inode->i_blkbits)) + 302 (bh_offset(bh) >> inode->i_blkbits); 303 return true; 304 } 305 306 /** 307 * fscrypt_set_bio_crypt_ctx_bh() - prepare a file contents bio for inline 308 * crypto 309 * @bio: a bio which will eventually be submitted to the file 310 * @first_bh: the first buffer_head for which I/O will be submitted 311 * @gfp_mask: memory allocation flags 312 * 313 * Same as fscrypt_set_bio_crypt_ctx(), except this takes a buffer_head instead 314 * of an inode and block number directly. 315 */ 316 void fscrypt_set_bio_crypt_ctx_bh(struct bio *bio, 317 const struct buffer_head *first_bh, 318 gfp_t gfp_mask) 319 { 320 const struct inode *inode; 321 u64 first_lblk; 322 323 if (bh_get_inode_and_lblk_num(first_bh, &inode, &first_lblk)) 324 fscrypt_set_bio_crypt_ctx(bio, inode, first_lblk, gfp_mask); 325 } 326 EXPORT_SYMBOL_GPL(fscrypt_set_bio_crypt_ctx_bh); 327 328 /** 329 * fscrypt_mergeable_bio() - test whether data can be added to a bio 330 * @bio: the bio being built up 331 * @inode: the inode for the next part of the I/O 332 * @next_lblk: the next file logical block number in the I/O 333 * 334 * When building a bio which may contain data which should undergo inline 335 * encryption (or decryption) via fscrypt, filesystems should call this function 336 * to ensure that the resulting bio contains only contiguous data unit numbers. 337 * This will return false if the next part of the I/O cannot be merged with the 338 * bio because either the encryption key would be different or the encryption 339 * data unit numbers would be discontiguous. 340 * 341 * fscrypt_set_bio_crypt_ctx() must have already been called on the bio. 342 * 343 * This function isn't required in cases where crypto-mergeability is ensured in 344 * another way, such as I/O targeting only a single file (and thus a single key) 345 * combined with fscrypt_limit_io_blocks() to ensure DUN contiguity. 346 * 347 * Return: true iff the I/O is mergeable 348 */ 349 bool fscrypt_mergeable_bio(struct bio *bio, const struct inode *inode, 350 u64 next_lblk) 351 { 352 const struct bio_crypt_ctx *bc = bio->bi_crypt_context; 353 u64 next_dun[BLK_CRYPTO_DUN_ARRAY_SIZE]; 354 355 if (!!bc != fscrypt_inode_uses_inline_crypto(inode)) 356 return false; 357 if (!bc) 358 return true; 359 360 /* 361 * Comparing the key pointers is good enough, as all I/O for each key 362 * uses the same pointer. I.e., there's currently no need to support 363 * merging requests where the keys are the same but the pointers differ. 364 */ 365 if (bc->bc_key != inode->i_crypt_info->ci_enc_key.blk_key) 366 return false; 367 368 fscrypt_generate_dun(inode->i_crypt_info, next_lblk, next_dun); 369 return bio_crypt_dun_is_contiguous(bc, bio->bi_iter.bi_size, next_dun); 370 } 371 EXPORT_SYMBOL_GPL(fscrypt_mergeable_bio); 372 373 /** 374 * fscrypt_mergeable_bio_bh() - test whether data can be added to a bio 375 * @bio: the bio being built up 376 * @next_bh: the next buffer_head for which I/O will be submitted 377 * 378 * Same as fscrypt_mergeable_bio(), except this takes a buffer_head instead of 379 * an inode and block number directly. 380 * 381 * Return: true iff the I/O is mergeable 382 */ 383 bool fscrypt_mergeable_bio_bh(struct bio *bio, 384 const struct buffer_head *next_bh) 385 { 386 const struct inode *inode; 387 u64 next_lblk; 388 389 if (!bh_get_inode_and_lblk_num(next_bh, &inode, &next_lblk)) 390 return !bio->bi_crypt_context; 391 392 return fscrypt_mergeable_bio(bio, inode, next_lblk); 393 } 394 EXPORT_SYMBOL_GPL(fscrypt_mergeable_bio_bh); 395 396 /** 397 * fscrypt_dio_supported() - check whether DIO (direct I/O) is supported on an 398 * inode, as far as encryption is concerned 399 * @inode: the inode in question 400 * 401 * Return: %true if there are no encryption constraints that prevent DIO from 402 * being supported; %false if DIO is unsupported. (Note that in the 403 * %true case, the filesystem might have other, non-encryption-related 404 * constraints that prevent DIO from actually being supported. Also, on 405 * encrypted files the filesystem is still responsible for only allowing 406 * DIO when requests are filesystem-block-aligned.) 407 */ 408 bool fscrypt_dio_supported(struct inode *inode) 409 { 410 int err; 411 412 /* If the file is unencrypted, no veto from us. */ 413 if (!fscrypt_needs_contents_encryption(inode)) 414 return true; 415 416 /* 417 * We only support DIO with inline crypto, not fs-layer crypto. 418 * 419 * To determine whether the inode is using inline crypto, we have to set 420 * up the key if it wasn't already done. This is because in the current 421 * design of fscrypt, the decision of whether to use inline crypto or 422 * not isn't made until the inode's encryption key is being set up. In 423 * the DIO read/write case, the key will always be set up already, since 424 * the file will be open. But in the case of statx(), the key might not 425 * be set up yet, as the file might not have been opened yet. 426 */ 427 err = fscrypt_require_key(inode); 428 if (err) { 429 /* 430 * Key unavailable or couldn't be set up. This edge case isn't 431 * worth worrying about; just report that DIO is unsupported. 432 */ 433 return false; 434 } 435 return fscrypt_inode_uses_inline_crypto(inode); 436 } 437 EXPORT_SYMBOL_GPL(fscrypt_dio_supported); 438 439 /** 440 * fscrypt_limit_io_blocks() - limit I/O blocks to avoid discontiguous DUNs 441 * @inode: the file on which I/O is being done 442 * @lblk: the block at which the I/O is being started from 443 * @nr_blocks: the number of blocks we want to submit starting at @lblk 444 * 445 * Determine the limit to the number of blocks that can be submitted in a bio 446 * targeting @lblk without causing a data unit number (DUN) discontiguity. 447 * 448 * This is normally just @nr_blocks, as normally the DUNs just increment along 449 * with the logical blocks. (Or the file is not encrypted.) 450 * 451 * In rare cases, fscrypt can be using an IV generation method that allows the 452 * DUN to wrap around within logically contiguous blocks, and that wraparound 453 * will occur. If this happens, a value less than @nr_blocks will be returned 454 * so that the wraparound doesn't occur in the middle of a bio, which would 455 * cause encryption/decryption to produce wrong results. 456 * 457 * Return: the actual number of blocks that can be submitted 458 */ 459 u64 fscrypt_limit_io_blocks(const struct inode *inode, u64 lblk, u64 nr_blocks) 460 { 461 const struct fscrypt_info *ci; 462 u32 dun; 463 464 if (!fscrypt_inode_uses_inline_crypto(inode)) 465 return nr_blocks; 466 467 if (nr_blocks <= 1) 468 return nr_blocks; 469 470 ci = inode->i_crypt_info; 471 if (!(fscrypt_policy_flags(&ci->ci_policy) & 472 FSCRYPT_POLICY_FLAG_IV_INO_LBLK_32)) 473 return nr_blocks; 474 475 /* With IV_INO_LBLK_32, the DUN can wrap around from U32_MAX to 0. */ 476 477 dun = ci->ci_hashed_ino + lblk; 478 479 return min_t(u64, nr_blocks, (u64)U32_MAX + 1 - dun); 480 } 481 EXPORT_SYMBOL_GPL(fscrypt_limit_io_blocks); 482