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.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_inode_info *ci)
43 {
44 const struct super_block *sb = ci->ci_inode->i_sb;
45 unsigned int flags = fscrypt_policy_flags(&ci->ci_policy);
46 int dun_bits;
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 data unit index */
58 dun_bits = fscrypt_max_file_dun_bits(sb, ci->ci_data_unit_bits);
59 return DIV_ROUND_UP(dun_bits, 8);
60 }
61
62 /*
63 * Log a message when starting to use blk-crypto (native) or blk-crypto-fallback
64 * for an encryption mode for the first time. This is the blk-crypto
65 * counterpart to the message logged when starting to use the crypto API for the
66 * first time. A limitation is that these messages don't convey which specific
67 * filesystems or files are using each implementation. However, *usually*
68 * systems use just one implementation per mode, which makes these messages
69 * helpful for debugging problems where the "wrong" implementation is used.
70 */
71 static void fscrypt_log_blk_crypto_impl(struct fscrypt_mode *mode,
72 struct block_device **devs,
73 unsigned int num_devs,
74 const struct blk_crypto_config *cfg)
75 {
76 unsigned int i;
77
78 for (i = 0; i < num_devs; i++) {
79 if (!IS_ENABLED(CONFIG_BLK_INLINE_ENCRYPTION_FALLBACK) ||
80 blk_crypto_config_supported_natively(devs[i], cfg)) {
81 if (!xchg(&mode->logged_blk_crypto_native, 1))
82 pr_info("fscrypt: %s using blk-crypto (native)\n",
83 mode->friendly_name);
84 } else if (!xchg(&mode->logged_blk_crypto_fallback, 1)) {
85 pr_info("fscrypt: %s using blk-crypto-fallback\n",
86 mode->friendly_name);
87 }
88 }
89 }
90
91 /* Enable inline encryption for this file if supported. */
92 int fscrypt_select_encryption_impl(struct fscrypt_inode_info *ci)
93 {
94 const struct inode *inode = ci->ci_inode;
95 struct super_block *sb = inode->i_sb;
96 struct blk_crypto_config crypto_cfg;
97 struct block_device **devs;
98 unsigned int num_devs;
99 unsigned int i;
100
101 /* The file must need contents encryption, not filenames encryption */
102 if (!S_ISREG(inode->i_mode))
103 return 0;
104
105 /* The crypto mode must have a blk-crypto counterpart */
106 if (ci->ci_mode->blk_crypto_mode == BLK_ENCRYPTION_MODE_INVALID)
107 return 0;
108
109 /* The filesystem must be mounted with -o inlinecrypt */
110 if (!(sb->s_flags & SB_INLINECRYPT))
111 return 0;
112
113 /*
114 * When a page contains multiple logically contiguous filesystem blocks,
115 * some filesystem code only calls fscrypt_mergeable_bio() for the first
116 * block in the page. This is fine for most of fscrypt's IV generation
117 * strategies, where contiguous blocks imply contiguous IVs. But it
118 * doesn't work with IV_INO_LBLK_32. For now, simply exclude
119 * IV_INO_LBLK_32 with blocksize != PAGE_SIZE from inline encryption.
120 */
121 if ((fscrypt_policy_flags(&ci->ci_policy) &
122 FSCRYPT_POLICY_FLAG_IV_INO_LBLK_32) &&
123 sb->s_blocksize != PAGE_SIZE)
124 return 0;
125
126 /*
127 * On all the filesystem's block devices, blk-crypto must support the
128 * crypto configuration that the file would use.
129 */
130 crypto_cfg.crypto_mode = ci->ci_mode->blk_crypto_mode;
131 crypto_cfg.data_unit_size = 1U << ci->ci_data_unit_bits;
132 crypto_cfg.dun_bytes = fscrypt_get_dun_bytes(ci);
133
134 devs = fscrypt_get_devices(sb, &num_devs);
135 if (IS_ERR(devs))
136 return PTR_ERR(devs);
137
138 for (i = 0; i < num_devs; i++) {
139 if (!blk_crypto_config_supported(devs[i], &crypto_cfg))
140 goto out_free_devs;
141 }
142
143 fscrypt_log_blk_crypto_impl(ci->ci_mode, devs, num_devs, &crypto_cfg);
144
145 ci->ci_inlinecrypt = true;
146 out_free_devs:
147 kfree(devs);
148
149 return 0;
150 }
151
152 int fscrypt_prepare_inline_crypt_key(struct fscrypt_prepared_key *prep_key,
153 const u8 *raw_key,
154 const struct fscrypt_inode_info *ci)
155 {
156 const struct inode *inode = ci->ci_inode;
157 struct super_block *sb = inode->i_sb;
158 enum blk_crypto_mode_num crypto_mode = ci->ci_mode->blk_crypto_mode;
159 struct blk_crypto_key *blk_key;
160 struct block_device **devs;
161 unsigned int num_devs;
162 unsigned int i;
163 int err;
164
165 blk_key = kmalloc(sizeof(*blk_key), GFP_KERNEL);
166 if (!blk_key)
167 return -ENOMEM;
168
169 err = blk_crypto_init_key(blk_key, raw_key, crypto_mode,
170 fscrypt_get_dun_bytes(ci),
171 1U << ci->ci_data_unit_bits);
172 if (err) {
173 fscrypt_err(inode, "error %d initializing blk-crypto key", err);
174 goto fail;
175 }
176
177 /* Start using blk-crypto on all the filesystem's block devices. */
178 devs = fscrypt_get_devices(sb, &num_devs);
179 if (IS_ERR(devs)) {
180 err = PTR_ERR(devs);
181 goto fail;
182 }
183 for (i = 0; i < num_devs; i++) {
184 err = blk_crypto_start_using_key(devs[i], blk_key);
185 if (err)
186 break;
187 }
188 kfree(devs);
189 if (err) {
190 fscrypt_err(inode, "error %d starting to use blk-crypto", err);
191 goto fail;
192 }
193
194 /*
195 * Pairs with the smp_load_acquire() in fscrypt_is_key_prepared().
196 * I.e., here we publish ->blk_key with a RELEASE barrier so that
197 * concurrent tasks can ACQUIRE it. Note that this concurrency is only
198 * possible for per-mode keys, not for per-file keys.
199 */
200 smp_store_release(&prep_key->blk_key, blk_key);
201 return 0;
202
203 fail:
204 kfree_sensitive(blk_key);
205 return err;
206 }
207
208 void fscrypt_destroy_inline_crypt_key(struct super_block *sb,
209 struct fscrypt_prepared_key *prep_key)
210 {
211 struct blk_crypto_key *blk_key = prep_key->blk_key;
212 struct block_device **devs;
213 unsigned int num_devs;
214 unsigned int i;
215
216 if (!blk_key)
217 return;
218
219 /* Evict the key from all the filesystem's block devices. */
220 devs = fscrypt_get_devices(sb, &num_devs);
221 if (!IS_ERR(devs)) {
222 for (i = 0; i < num_devs; i++)
223 blk_crypto_evict_key(devs[i], blk_key);
224 kfree(devs);
225 }
226 kfree_sensitive(blk_key);
227 }
228
229 bool __fscrypt_inode_uses_inline_crypto(const struct inode *inode)
230 {
231 return inode->i_crypt_info->ci_inlinecrypt;
232 }
233 EXPORT_SYMBOL_GPL(__fscrypt_inode_uses_inline_crypto);
234
235 static void fscrypt_generate_dun(const struct fscrypt_inode_info *ci,
236 u64 lblk_num,
237 u64 dun[BLK_CRYPTO_DUN_ARRAY_SIZE])
238 {
239 u64 index = lblk_num << ci->ci_data_units_per_block_bits;
240 union fscrypt_iv iv;
241 int i;
242
243 fscrypt_generate_iv(&iv, index, 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_inode_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 folio *folio = bh->b_folio;
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 = folio_mapping(folio);
296 if (!mapping)
297 return false;
298 inode = mapping->host;
299
300 *inode_ret = inode;
301 *lblk_num_ret = ((u64)folio->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_inode_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
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