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 
fscrypt_get_devices(struct super_block * sb,unsigned int * num_devs)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 
fscrypt_get_dun_bytes(const struct fscrypt_info * ci)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  */
fscrypt_log_blk_crypto_impl(struct fscrypt_mode * mode,struct block_device ** devs,unsigned int num_devs,const struct blk_crypto_config * cfg)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. */
fscrypt_select_encryption_impl(struct fscrypt_info * ci)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(bdev_get_queue(devs[i]),
143 						 &crypto_cfg))
144 			goto out_free_devs;
145 	}
146 
147 	fscrypt_log_blk_crypto_impl(ci->ci_mode, devs, num_devs, &crypto_cfg);
148 
149 	ci->ci_inlinecrypt = true;
150 out_free_devs:
151 	kfree(devs);
152 
153 	return 0;
154 }
155 
fscrypt_prepare_inline_crypt_key(struct fscrypt_prepared_key * prep_key,const u8 * raw_key,const struct fscrypt_info * ci)156 int fscrypt_prepare_inline_crypt_key(struct fscrypt_prepared_key *prep_key,
157 				     const u8 *raw_key,
158 				     const struct fscrypt_info *ci)
159 {
160 	const struct inode *inode = ci->ci_inode;
161 	struct super_block *sb = inode->i_sb;
162 	enum blk_crypto_mode_num crypto_mode = ci->ci_mode->blk_crypto_mode;
163 	struct blk_crypto_key *blk_key;
164 	struct block_device **devs;
165 	unsigned int num_devs;
166 	unsigned int i;
167 	int err;
168 
169 	blk_key = kmalloc(sizeof(*blk_key), GFP_KERNEL);
170 	if (!blk_key)
171 		return -ENOMEM;
172 
173 	err = blk_crypto_init_key(blk_key, raw_key, crypto_mode,
174 				  fscrypt_get_dun_bytes(ci), sb->s_blocksize);
175 	if (err) {
176 		fscrypt_err(inode, "error %d initializing blk-crypto key", err);
177 		goto fail;
178 	}
179 
180 	/* Start using blk-crypto on all the filesystem's block devices. */
181 	devs = fscrypt_get_devices(sb, &num_devs);
182 	if (IS_ERR(devs)) {
183 		err = PTR_ERR(devs);
184 		goto fail;
185 	}
186 	for (i = 0; i < num_devs; i++) {
187 		err = blk_crypto_start_using_key(blk_key,
188 						 bdev_get_queue(devs[i]));
189 		if (err)
190 			break;
191 	}
192 	kfree(devs);
193 	if (err) {
194 		fscrypt_err(inode, "error %d starting to use blk-crypto", err);
195 		goto fail;
196 	}
197 
198 	/*
199 	 * Pairs with the smp_load_acquire() in fscrypt_is_key_prepared().
200 	 * I.e., here we publish ->blk_key with a RELEASE barrier so that
201 	 * concurrent tasks can ACQUIRE it.  Note that this concurrency is only
202 	 * possible for per-mode keys, not for per-file keys.
203 	 */
204 	smp_store_release(&prep_key->blk_key, blk_key);
205 	return 0;
206 
207 fail:
208 	kfree_sensitive(blk_key);
209 	return err;
210 }
211 
fscrypt_destroy_inline_crypt_key(struct super_block * sb,struct fscrypt_prepared_key * prep_key)212 void fscrypt_destroy_inline_crypt_key(struct super_block *sb,
213 				      struct fscrypt_prepared_key *prep_key)
214 {
215 	struct blk_crypto_key *blk_key = prep_key->blk_key;
216 	struct block_device **devs;
217 	unsigned int num_devs;
218 	unsigned int i;
219 
220 	if (!blk_key)
221 		return;
222 
223 	/* Evict the key from all the filesystem's block devices. */
224 	devs = fscrypt_get_devices(sb, &num_devs);
225 	if (!IS_ERR(devs)) {
226 		for (i = 0; i < num_devs; i++)
227 			blk_crypto_evict_key(bdev_get_queue(devs[i]), blk_key);
228 		kfree(devs);
229 	}
230 	kfree_sensitive(blk_key);
231 }
232 
__fscrypt_inode_uses_inline_crypto(const struct inode * inode)233 bool __fscrypt_inode_uses_inline_crypto(const struct inode *inode)
234 {
235 	return inode->i_crypt_info->ci_inlinecrypt;
236 }
237 EXPORT_SYMBOL_GPL(__fscrypt_inode_uses_inline_crypto);
238 
fscrypt_generate_dun(const struct fscrypt_info * ci,u64 lblk_num,u64 dun[BLK_CRYPTO_DUN_ARRAY_SIZE])239 static void fscrypt_generate_dun(const struct fscrypt_info *ci, u64 lblk_num,
240 				 u64 dun[BLK_CRYPTO_DUN_ARRAY_SIZE])
241 {
242 	union fscrypt_iv iv;
243 	int i;
244 
245 	fscrypt_generate_iv(&iv, lblk_num, ci);
246 
247 	BUILD_BUG_ON(FSCRYPT_MAX_IV_SIZE > BLK_CRYPTO_MAX_IV_SIZE);
248 	memset(dun, 0, BLK_CRYPTO_MAX_IV_SIZE);
249 	for (i = 0; i < ci->ci_mode->ivsize/sizeof(dun[0]); i++)
250 		dun[i] = le64_to_cpu(iv.dun[i]);
251 }
252 
253 /**
254  * fscrypt_set_bio_crypt_ctx() - prepare a file contents bio for inline crypto
255  * @bio: a bio which will eventually be submitted to the file
256  * @inode: the file's inode
257  * @first_lblk: the first file logical block number in the I/O
258  * @gfp_mask: memory allocation flags - these must be a waiting mask so that
259  *					bio_crypt_set_ctx can't fail.
260  *
261  * If the contents of the file should be encrypted (or decrypted) with inline
262  * encryption, then assign the appropriate encryption context to the bio.
263  *
264  * Normally the bio should be newly allocated (i.e. no pages added yet), as
265  * otherwise fscrypt_mergeable_bio() won't work as intended.
266  *
267  * The encryption context will be freed automatically when the bio is freed.
268  */
fscrypt_set_bio_crypt_ctx(struct bio * bio,const struct inode * inode,u64 first_lblk,gfp_t gfp_mask)269 void fscrypt_set_bio_crypt_ctx(struct bio *bio, const struct inode *inode,
270 			       u64 first_lblk, gfp_t gfp_mask)
271 {
272 	const struct fscrypt_info *ci;
273 	u64 dun[BLK_CRYPTO_DUN_ARRAY_SIZE];
274 
275 	if (!fscrypt_inode_uses_inline_crypto(inode))
276 		return;
277 	ci = inode->i_crypt_info;
278 
279 	fscrypt_generate_dun(ci, first_lblk, dun);
280 	bio_crypt_set_ctx(bio, ci->ci_enc_key.blk_key, dun, gfp_mask);
281 }
282 EXPORT_SYMBOL_GPL(fscrypt_set_bio_crypt_ctx);
283 
284 /* Extract the inode and logical block number from a buffer_head. */
bh_get_inode_and_lblk_num(const struct buffer_head * bh,const struct inode ** inode_ret,u64 * lblk_num_ret)285 static bool bh_get_inode_and_lblk_num(const struct buffer_head *bh,
286 				      const struct inode **inode_ret,
287 				      u64 *lblk_num_ret)
288 {
289 	struct page *page = bh->b_page;
290 	const struct address_space *mapping;
291 	const struct inode *inode;
292 
293 	/*
294 	 * The ext4 journal (jbd2) can submit a buffer_head it directly created
295 	 * for a non-pagecache page.  fscrypt doesn't care about these.
296 	 */
297 	mapping = page_mapping(page);
298 	if (!mapping)
299 		return false;
300 	inode = mapping->host;
301 
302 	*inode_ret = inode;
303 	*lblk_num_ret = ((u64)page->index << (PAGE_SHIFT - inode->i_blkbits)) +
304 			(bh_offset(bh) >> inode->i_blkbits);
305 	return true;
306 }
307 
308 /**
309  * fscrypt_set_bio_crypt_ctx_bh() - prepare a file contents bio for inline
310  *				    crypto
311  * @bio: a bio which will eventually be submitted to the file
312  * @first_bh: the first buffer_head for which I/O will be submitted
313  * @gfp_mask: memory allocation flags
314  *
315  * Same as fscrypt_set_bio_crypt_ctx(), except this takes a buffer_head instead
316  * of an inode and block number directly.
317  */
fscrypt_set_bio_crypt_ctx_bh(struct bio * bio,const struct buffer_head * first_bh,gfp_t gfp_mask)318 void fscrypt_set_bio_crypt_ctx_bh(struct bio *bio,
319 				  const struct buffer_head *first_bh,
320 				  gfp_t gfp_mask)
321 {
322 	const struct inode *inode;
323 	u64 first_lblk;
324 
325 	if (bh_get_inode_and_lblk_num(first_bh, &inode, &first_lblk))
326 		fscrypt_set_bio_crypt_ctx(bio, inode, first_lblk, gfp_mask);
327 }
328 EXPORT_SYMBOL_GPL(fscrypt_set_bio_crypt_ctx_bh);
329 
330 /**
331  * fscrypt_mergeable_bio() - test whether data can be added to a bio
332  * @bio: the bio being built up
333  * @inode: the inode for the next part of the I/O
334  * @next_lblk: the next file logical block number in the I/O
335  *
336  * When building a bio which may contain data which should undergo inline
337  * encryption (or decryption) via fscrypt, filesystems should call this function
338  * to ensure that the resulting bio contains only contiguous data unit numbers.
339  * This will return false if the next part of the I/O cannot be merged with the
340  * bio because either the encryption key would be different or the encryption
341  * data unit numbers would be discontiguous.
342  *
343  * fscrypt_set_bio_crypt_ctx() must have already been called on the bio.
344  *
345  * This function isn't required in cases where crypto-mergeability is ensured in
346  * another way, such as I/O targeting only a single file (and thus a single key)
347  * combined with fscrypt_limit_io_blocks() to ensure DUN contiguity.
348  *
349  * Return: true iff the I/O is mergeable
350  */
fscrypt_mergeable_bio(struct bio * bio,const struct inode * inode,u64 next_lblk)351 bool fscrypt_mergeable_bio(struct bio *bio, const struct inode *inode,
352 			   u64 next_lblk)
353 {
354 	const struct bio_crypt_ctx *bc = bio->bi_crypt_context;
355 	u64 next_dun[BLK_CRYPTO_DUN_ARRAY_SIZE];
356 
357 	if (!!bc != fscrypt_inode_uses_inline_crypto(inode))
358 		return false;
359 	if (!bc)
360 		return true;
361 
362 	/*
363 	 * Comparing the key pointers is good enough, as all I/O for each key
364 	 * uses the same pointer.  I.e., there's currently no need to support
365 	 * merging requests where the keys are the same but the pointers differ.
366 	 */
367 	if (bc->bc_key != inode->i_crypt_info->ci_enc_key.blk_key)
368 		return false;
369 
370 	fscrypt_generate_dun(inode->i_crypt_info, next_lblk, next_dun);
371 	return bio_crypt_dun_is_contiguous(bc, bio->bi_iter.bi_size, next_dun);
372 }
373 EXPORT_SYMBOL_GPL(fscrypt_mergeable_bio);
374 
375 /**
376  * fscrypt_mergeable_bio_bh() - test whether data can be added to a bio
377  * @bio: the bio being built up
378  * @next_bh: the next buffer_head for which I/O will be submitted
379  *
380  * Same as fscrypt_mergeable_bio(), except this takes a buffer_head instead of
381  * an inode and block number directly.
382  *
383  * Return: true iff the I/O is mergeable
384  */
fscrypt_mergeable_bio_bh(struct bio * bio,const struct buffer_head * next_bh)385 bool fscrypt_mergeable_bio_bh(struct bio *bio,
386 			      const struct buffer_head *next_bh)
387 {
388 	const struct inode *inode;
389 	u64 next_lblk;
390 
391 	if (!bh_get_inode_and_lblk_num(next_bh, &inode, &next_lblk))
392 		return !bio->bi_crypt_context;
393 
394 	return fscrypt_mergeable_bio(bio, inode, next_lblk);
395 }
396 EXPORT_SYMBOL_GPL(fscrypt_mergeable_bio_bh);
397 
398 /**
399  * fscrypt_dio_supported() - check whether DIO (direct I/O) is supported on an
400  *			     inode, as far as encryption is concerned
401  * @inode: the inode in question
402  *
403  * Return: %true if there are no encryption constraints that prevent DIO from
404  *	   being supported; %false if DIO is unsupported.  (Note that in the
405  *	   %true case, the filesystem might have other, non-encryption-related
406  *	   constraints that prevent DIO from actually being supported.  Also, on
407  *	   encrypted files the filesystem is still responsible for only allowing
408  *	   DIO when requests are filesystem-block-aligned.)
409  */
fscrypt_dio_supported(struct inode * inode)410 bool fscrypt_dio_supported(struct inode *inode)
411 {
412 	int err;
413 
414 	/* If the file is unencrypted, no veto from us. */
415 	if (!fscrypt_needs_contents_encryption(inode))
416 		return true;
417 
418 	/*
419 	 * We only support DIO with inline crypto, not fs-layer crypto.
420 	 *
421 	 * To determine whether the inode is using inline crypto, we have to set
422 	 * up the key if it wasn't already done.  This is because in the current
423 	 * design of fscrypt, the decision of whether to use inline crypto or
424 	 * not isn't made until the inode's encryption key is being set up.  In
425 	 * the DIO read/write case, the key will always be set up already, since
426 	 * the file will be open.  But in the case of statx(), the key might not
427 	 * be set up yet, as the file might not have been opened yet.
428 	 */
429 	err = fscrypt_require_key(inode);
430 	if (err) {
431 		/*
432 		 * Key unavailable or couldn't be set up.  This edge case isn't
433 		 * worth worrying about; just report that DIO is unsupported.
434 		 */
435 		return false;
436 	}
437 	return fscrypt_inode_uses_inline_crypto(inode);
438 }
439 EXPORT_SYMBOL_GPL(fscrypt_dio_supported);
440 
441 /**
442  * fscrypt_limit_io_blocks() - limit I/O blocks to avoid discontiguous DUNs
443  * @inode: the file on which I/O is being done
444  * @lblk: the block at which the I/O is being started from
445  * @nr_blocks: the number of blocks we want to submit starting at @lblk
446  *
447  * Determine the limit to the number of blocks that can be submitted in a bio
448  * targeting @lblk without causing a data unit number (DUN) discontiguity.
449  *
450  * This is normally just @nr_blocks, as normally the DUNs just increment along
451  * with the logical blocks.  (Or the file is not encrypted.)
452  *
453  * In rare cases, fscrypt can be using an IV generation method that allows the
454  * DUN to wrap around within logically contiguous blocks, and that wraparound
455  * will occur.  If this happens, a value less than @nr_blocks will be returned
456  * so that the wraparound doesn't occur in the middle of a bio, which would
457  * cause encryption/decryption to produce wrong results.
458  *
459  * Return: the actual number of blocks that can be submitted
460  */
fscrypt_limit_io_blocks(const struct inode * inode,u64 lblk,u64 nr_blocks)461 u64 fscrypt_limit_io_blocks(const struct inode *inode, u64 lblk, u64 nr_blocks)
462 {
463 	const struct fscrypt_info *ci;
464 	u32 dun;
465 
466 	if (!fscrypt_inode_uses_inline_crypto(inode))
467 		return nr_blocks;
468 
469 	if (nr_blocks <= 1)
470 		return nr_blocks;
471 
472 	ci = inode->i_crypt_info;
473 	if (!(fscrypt_policy_flags(&ci->ci_policy) &
474 	      FSCRYPT_POLICY_FLAG_IV_INO_LBLK_32))
475 		return nr_blocks;
476 
477 	/* With IV_INO_LBLK_32, the DUN can wrap around from U32_MAX to 0. */
478 
479 	dun = ci->ci_hashed_ino + lblk;
480 
481 	return min_t(u64, nr_blocks, (u64)U32_MAX + 1 - dun);
482 }
483 EXPORT_SYMBOL_GPL(fscrypt_limit_io_blocks);
484