xref: /openbmc/linux/fs/crypto/inline_crypt.c (revision 21bb8af5)
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 struct fscrypt_blk_crypto_key {
25 	struct blk_crypto_key base;
26 	int num_devs;
27 	struct request_queue *devs[];
28 };
29 
30 static int fscrypt_get_num_devices(struct super_block *sb)
31 {
32 	if (sb->s_cop->get_num_devices)
33 		return sb->s_cop->get_num_devices(sb);
34 	return 1;
35 }
36 
37 static void fscrypt_get_devices(struct super_block *sb, int num_devs,
38 				struct request_queue **devs)
39 {
40 	if (num_devs == 1)
41 		devs[0] = bdev_get_queue(sb->s_bdev);
42 	else
43 		sb->s_cop->get_devices(sb, devs);
44 }
45 
46 static unsigned int fscrypt_get_dun_bytes(const struct fscrypt_info *ci)
47 {
48 	struct super_block *sb = ci->ci_inode->i_sb;
49 	unsigned int flags = fscrypt_policy_flags(&ci->ci_policy);
50 	int ino_bits = 64, lblk_bits = 64;
51 
52 	if (flags & FSCRYPT_POLICY_FLAG_DIRECT_KEY)
53 		return offsetofend(union fscrypt_iv, nonce);
54 
55 	if (flags & FSCRYPT_POLICY_FLAG_IV_INO_LBLK_64)
56 		return sizeof(__le64);
57 
58 	if (flags & FSCRYPT_POLICY_FLAG_IV_INO_LBLK_32)
59 		return sizeof(__le32);
60 
61 	/* Default case: IVs are just the file logical block number */
62 	if (sb->s_cop->get_ino_and_lblk_bits)
63 		sb->s_cop->get_ino_and_lblk_bits(sb, &ino_bits, &lblk_bits);
64 	return DIV_ROUND_UP(lblk_bits, 8);
65 }
66 
67 /*
68  * Log a message when starting to use blk-crypto (native) or blk-crypto-fallback
69  * for an encryption mode for the first time.  This is the blk-crypto
70  * counterpart to the message logged when starting to use the crypto API for the
71  * first time.  A limitation is that these messages don't convey which specific
72  * filesystems or files are using each implementation.  However, *usually*
73  * systems use just one implementation per mode, which makes these messages
74  * helpful for debugging problems where the "wrong" implementation is used.
75  */
76 static void fscrypt_log_blk_crypto_impl(struct fscrypt_mode *mode,
77 					struct request_queue **devs,
78 					int num_devs,
79 					const struct blk_crypto_config *cfg)
80 {
81 	int i;
82 
83 	for (i = 0; i < num_devs; i++) {
84 		if (!IS_ENABLED(CONFIG_BLK_INLINE_ENCRYPTION_FALLBACK) ||
85 		    __blk_crypto_cfg_supported(devs[i]->crypto_profile, cfg)) {
86 			if (!xchg(&mode->logged_blk_crypto_native, 1))
87 				pr_info("fscrypt: %s using blk-crypto (native)\n",
88 					mode->friendly_name);
89 		} else if (!xchg(&mode->logged_blk_crypto_fallback, 1)) {
90 			pr_info("fscrypt: %s using blk-crypto-fallback\n",
91 				mode->friendly_name);
92 		}
93 	}
94 }
95 
96 /* Enable inline encryption for this file if supported. */
97 int fscrypt_select_encryption_impl(struct fscrypt_info *ci)
98 {
99 	const struct inode *inode = ci->ci_inode;
100 	struct super_block *sb = inode->i_sb;
101 	struct blk_crypto_config crypto_cfg;
102 	int num_devs;
103 	struct request_queue **devs;
104 	int i;
105 
106 	/* The file must need contents encryption, not filenames encryption */
107 	if (!S_ISREG(inode->i_mode))
108 		return 0;
109 
110 	/* The crypto mode must have a blk-crypto counterpart */
111 	if (ci->ci_mode->blk_crypto_mode == BLK_ENCRYPTION_MODE_INVALID)
112 		return 0;
113 
114 	/* The filesystem must be mounted with -o inlinecrypt */
115 	if (!(sb->s_flags & SB_INLINECRYPT))
116 		return 0;
117 
118 	/*
119 	 * When a page contains multiple logically contiguous filesystem blocks,
120 	 * some filesystem code only calls fscrypt_mergeable_bio() for the first
121 	 * block in the page. This is fine for most of fscrypt's IV generation
122 	 * strategies, where contiguous blocks imply contiguous IVs. But it
123 	 * doesn't work with IV_INO_LBLK_32. For now, simply exclude
124 	 * IV_INO_LBLK_32 with blocksize != PAGE_SIZE from inline encryption.
125 	 */
126 	if ((fscrypt_policy_flags(&ci->ci_policy) &
127 	     FSCRYPT_POLICY_FLAG_IV_INO_LBLK_32) &&
128 	    sb->s_blocksize != PAGE_SIZE)
129 		return 0;
130 
131 	/*
132 	 * On all the filesystem's devices, blk-crypto must support the crypto
133 	 * configuration that the file would use.
134 	 */
135 	crypto_cfg.crypto_mode = ci->ci_mode->blk_crypto_mode;
136 	crypto_cfg.data_unit_size = sb->s_blocksize;
137 	crypto_cfg.dun_bytes = fscrypt_get_dun_bytes(ci);
138 	num_devs = fscrypt_get_num_devices(sb);
139 	devs = kmalloc_array(num_devs, sizeof(*devs), GFP_KERNEL);
140 	if (!devs)
141 		return -ENOMEM;
142 	fscrypt_get_devices(sb, num_devs, devs);
143 
144 	for (i = 0; i < num_devs; i++) {
145 		if (!blk_crypto_config_supported(devs[i], &crypto_cfg))
146 			goto out_free_devs;
147 	}
148 
149 	fscrypt_log_blk_crypto_impl(ci->ci_mode, devs, num_devs, &crypto_cfg);
150 
151 	ci->ci_inlinecrypt = true;
152 out_free_devs:
153 	kfree(devs);
154 
155 	return 0;
156 }
157 
158 int fscrypt_prepare_inline_crypt_key(struct fscrypt_prepared_key *prep_key,
159 				     const u8 *raw_key,
160 				     const struct fscrypt_info *ci)
161 {
162 	const struct inode *inode = ci->ci_inode;
163 	struct super_block *sb = inode->i_sb;
164 	enum blk_crypto_mode_num crypto_mode = ci->ci_mode->blk_crypto_mode;
165 	int num_devs = fscrypt_get_num_devices(sb);
166 	int queue_refs = 0;
167 	struct fscrypt_blk_crypto_key *blk_key;
168 	int err;
169 	int i;
170 
171 	blk_key = kzalloc(struct_size(blk_key, devs, num_devs), GFP_KERNEL);
172 	if (!blk_key)
173 		return -ENOMEM;
174 
175 	blk_key->num_devs = num_devs;
176 	fscrypt_get_devices(sb, num_devs, blk_key->devs);
177 
178 	err = blk_crypto_init_key(&blk_key->base, raw_key, crypto_mode,
179 				  fscrypt_get_dun_bytes(ci), sb->s_blocksize);
180 	if (err) {
181 		fscrypt_err(inode, "error %d initializing blk-crypto key", err);
182 		goto fail;
183 	}
184 
185 	/*
186 	 * We have to start using blk-crypto on all the filesystem's devices.
187 	 * We also have to save all the request_queue's for later so that the
188 	 * key can be evicted from them.  This is needed because some keys
189 	 * aren't destroyed until after the filesystem was already unmounted
190 	 * (namely, the per-mode keys in struct fscrypt_master_key).
191 	 */
192 	for (i = 0; i < num_devs; i++) {
193 		if (!blk_get_queue(blk_key->devs[i])) {
194 			fscrypt_err(inode, "couldn't get request_queue");
195 			err = -EAGAIN;
196 			goto fail;
197 		}
198 		queue_refs++;
199 
200 		err = blk_crypto_start_using_key(&blk_key->base,
201 						 blk_key->devs[i]);
202 		if (err) {
203 			fscrypt_err(inode,
204 				    "error %d starting to use blk-crypto", err);
205 			goto fail;
206 		}
207 	}
208 	/*
209 	 * Pairs with the smp_load_acquire() in fscrypt_is_key_prepared().
210 	 * I.e., here we publish ->blk_key with a RELEASE barrier so that
211 	 * concurrent tasks can ACQUIRE it.  Note that this concurrency is only
212 	 * possible for per-mode keys, not for per-file keys.
213 	 */
214 	smp_store_release(&prep_key->blk_key, blk_key);
215 	return 0;
216 
217 fail:
218 	for (i = 0; i < queue_refs; i++)
219 		blk_put_queue(blk_key->devs[i]);
220 	kfree_sensitive(blk_key);
221 	return err;
222 }
223 
224 void fscrypt_destroy_inline_crypt_key(struct fscrypt_prepared_key *prep_key)
225 {
226 	struct fscrypt_blk_crypto_key *blk_key = prep_key->blk_key;
227 	int i;
228 
229 	if (blk_key) {
230 		for (i = 0; i < blk_key->num_devs; i++) {
231 			blk_crypto_evict_key(blk_key->devs[i], &blk_key->base);
232 			blk_put_queue(blk_key->devs[i]);
233 		}
234 		kfree_sensitive(blk_key);
235 	}
236 }
237 
238 bool __fscrypt_inode_uses_inline_crypto(const struct inode *inode)
239 {
240 	return inode->i_crypt_info->ci_inlinecrypt;
241 }
242 EXPORT_SYMBOL_GPL(__fscrypt_inode_uses_inline_crypto);
243 
244 static void fscrypt_generate_dun(const struct fscrypt_info *ci, u64 lblk_num,
245 				 u64 dun[BLK_CRYPTO_DUN_ARRAY_SIZE])
246 {
247 	union fscrypt_iv iv;
248 	int i;
249 
250 	fscrypt_generate_iv(&iv, lblk_num, ci);
251 
252 	BUILD_BUG_ON(FSCRYPT_MAX_IV_SIZE > BLK_CRYPTO_MAX_IV_SIZE);
253 	memset(dun, 0, BLK_CRYPTO_MAX_IV_SIZE);
254 	for (i = 0; i < ci->ci_mode->ivsize/sizeof(dun[0]); i++)
255 		dun[i] = le64_to_cpu(iv.dun[i]);
256 }
257 
258 /**
259  * fscrypt_set_bio_crypt_ctx() - prepare a file contents bio for inline crypto
260  * @bio: a bio which will eventually be submitted to the file
261  * @inode: the file's inode
262  * @first_lblk: the first file logical block number in the I/O
263  * @gfp_mask: memory allocation flags - these must be a waiting mask so that
264  *					bio_crypt_set_ctx can't fail.
265  *
266  * If the contents of the file should be encrypted (or decrypted) with inline
267  * encryption, then assign the appropriate encryption context to the bio.
268  *
269  * Normally the bio should be newly allocated (i.e. no pages added yet), as
270  * otherwise fscrypt_mergeable_bio() won't work as intended.
271  *
272  * The encryption context will be freed automatically when the bio is freed.
273  */
274 void fscrypt_set_bio_crypt_ctx(struct bio *bio, const struct inode *inode,
275 			       u64 first_lblk, gfp_t gfp_mask)
276 {
277 	const struct fscrypt_info *ci;
278 	u64 dun[BLK_CRYPTO_DUN_ARRAY_SIZE];
279 
280 	if (!fscrypt_inode_uses_inline_crypto(inode))
281 		return;
282 	ci = inode->i_crypt_info;
283 
284 	fscrypt_generate_dun(ci, first_lblk, dun);
285 	bio_crypt_set_ctx(bio, &ci->ci_enc_key.blk_key->base, dun, gfp_mask);
286 }
287 EXPORT_SYMBOL_GPL(fscrypt_set_bio_crypt_ctx);
288 
289 /* Extract the inode and logical block number from a buffer_head. */
290 static bool bh_get_inode_and_lblk_num(const struct buffer_head *bh,
291 				      const struct inode **inode_ret,
292 				      u64 *lblk_num_ret)
293 {
294 	struct page *page = bh->b_page;
295 	const struct address_space *mapping;
296 	const struct inode *inode;
297 
298 	/*
299 	 * The ext4 journal (jbd2) can submit a buffer_head it directly created
300 	 * for a non-pagecache page.  fscrypt doesn't care about these.
301 	 */
302 	mapping = page_mapping(page);
303 	if (!mapping)
304 		return false;
305 	inode = mapping->host;
306 
307 	*inode_ret = inode;
308 	*lblk_num_ret = ((u64)page->index << (PAGE_SHIFT - inode->i_blkbits)) +
309 			(bh_offset(bh) >> inode->i_blkbits);
310 	return true;
311 }
312 
313 /**
314  * fscrypt_set_bio_crypt_ctx_bh() - prepare a file contents bio for inline
315  *				    crypto
316  * @bio: a bio which will eventually be submitted to the file
317  * @first_bh: the first buffer_head for which I/O will be submitted
318  * @gfp_mask: memory allocation flags
319  *
320  * Same as fscrypt_set_bio_crypt_ctx(), except this takes a buffer_head instead
321  * of an inode and block number directly.
322  */
323 void fscrypt_set_bio_crypt_ctx_bh(struct bio *bio,
324 				  const struct buffer_head *first_bh,
325 				  gfp_t gfp_mask)
326 {
327 	const struct inode *inode;
328 	u64 first_lblk;
329 
330 	if (bh_get_inode_and_lblk_num(first_bh, &inode, &first_lblk))
331 		fscrypt_set_bio_crypt_ctx(bio, inode, first_lblk, gfp_mask);
332 }
333 EXPORT_SYMBOL_GPL(fscrypt_set_bio_crypt_ctx_bh);
334 
335 /**
336  * fscrypt_mergeable_bio() - test whether data can be added to a bio
337  * @bio: the bio being built up
338  * @inode: the inode for the next part of the I/O
339  * @next_lblk: the next file logical block number in the I/O
340  *
341  * When building a bio which may contain data which should undergo inline
342  * encryption (or decryption) via fscrypt, filesystems should call this function
343  * to ensure that the resulting bio contains only contiguous data unit numbers.
344  * This will return false if the next part of the I/O cannot be merged with the
345  * bio because either the encryption key would be different or the encryption
346  * data unit numbers would be discontiguous.
347  *
348  * fscrypt_set_bio_crypt_ctx() must have already been called on the bio.
349  *
350  * This function isn't required in cases where crypto-mergeability is ensured in
351  * another way, such as I/O targeting only a single file (and thus a single key)
352  * combined with fscrypt_limit_io_blocks() to ensure DUN contiguity.
353  *
354  * Return: true iff the I/O is mergeable
355  */
356 bool fscrypt_mergeable_bio(struct bio *bio, const struct inode *inode,
357 			   u64 next_lblk)
358 {
359 	const struct bio_crypt_ctx *bc = bio->bi_crypt_context;
360 	u64 next_dun[BLK_CRYPTO_DUN_ARRAY_SIZE];
361 
362 	if (!!bc != fscrypt_inode_uses_inline_crypto(inode))
363 		return false;
364 	if (!bc)
365 		return true;
366 
367 	/*
368 	 * Comparing the key pointers is good enough, as all I/O for each key
369 	 * uses the same pointer.  I.e., there's currently no need to support
370 	 * merging requests where the keys are the same but the pointers differ.
371 	 */
372 	if (bc->bc_key != &inode->i_crypt_info->ci_enc_key.blk_key->base)
373 		return false;
374 
375 	fscrypt_generate_dun(inode->i_crypt_info, next_lblk, next_dun);
376 	return bio_crypt_dun_is_contiguous(bc, bio->bi_iter.bi_size, next_dun);
377 }
378 EXPORT_SYMBOL_GPL(fscrypt_mergeable_bio);
379 
380 /**
381  * fscrypt_mergeable_bio_bh() - test whether data can be added to a bio
382  * @bio: the bio being built up
383  * @next_bh: the next buffer_head for which I/O will be submitted
384  *
385  * Same as fscrypt_mergeable_bio(), except this takes a buffer_head instead of
386  * an inode and block number directly.
387  *
388  * Return: true iff the I/O is mergeable
389  */
390 bool fscrypt_mergeable_bio_bh(struct bio *bio,
391 			      const struct buffer_head *next_bh)
392 {
393 	const struct inode *inode;
394 	u64 next_lblk;
395 
396 	if (!bh_get_inode_and_lblk_num(next_bh, &inode, &next_lblk))
397 		return !bio->bi_crypt_context;
398 
399 	return fscrypt_mergeable_bio(bio, inode, next_lblk);
400 }
401 EXPORT_SYMBOL_GPL(fscrypt_mergeable_bio_bh);
402 
403 /**
404  * fscrypt_dio_supported() - check whether a DIO (direct I/O) request is
405  *			     supported as far as encryption is concerned
406  * @iocb: the file and position the I/O is targeting
407  * @iter: the I/O data segment(s)
408  *
409  * Return: %true if there are no encryption constraints that prevent DIO from
410  *	   being supported; %false if DIO is unsupported.  (Note that in the
411  *	   %true case, the filesystem might have other, non-encryption-related
412  *	   constraints that prevent DIO from actually being supported.)
413  */
414 bool fscrypt_dio_supported(struct kiocb *iocb, struct iov_iter *iter)
415 {
416 	const struct inode *inode = file_inode(iocb->ki_filp);
417 	const unsigned int blocksize = i_blocksize(inode);
418 
419 	/* If the file is unencrypted, no veto from us. */
420 	if (!fscrypt_needs_contents_encryption(inode))
421 		return true;
422 
423 	/* We only support DIO with inline crypto, not fs-layer crypto. */
424 	if (!fscrypt_inode_uses_inline_crypto(inode))
425 		return false;
426 
427 	/*
428 	 * Since the granularity of encryption is filesystem blocks, the file
429 	 * position and total I/O length must be aligned to the filesystem block
430 	 * size -- not just to the block device's logical block size as is
431 	 * traditionally the case for DIO on many filesystems.
432 	 *
433 	 * We require that the user-provided memory buffers be filesystem block
434 	 * aligned too.  It is simpler to have a single alignment value required
435 	 * for all properties of the I/O, as is normally the case for DIO.
436 	 * Also, allowing less aligned buffers would imply that data units could
437 	 * cross bvecs, which would greatly complicate the I/O stack, which
438 	 * assumes that bios can be split at any bvec boundary.
439 	 */
440 	if (!IS_ALIGNED(iocb->ki_pos | iov_iter_alignment(iter), blocksize))
441 		return false;
442 
443 	return true;
444 }
445 EXPORT_SYMBOL_GPL(fscrypt_dio_supported);
446 
447 /**
448  * fscrypt_limit_io_blocks() - limit I/O blocks to avoid discontiguous DUNs
449  * @inode: the file on which I/O is being done
450  * @lblk: the block at which the I/O is being started from
451  * @nr_blocks: the number of blocks we want to submit starting at @lblk
452  *
453  * Determine the limit to the number of blocks that can be submitted in a bio
454  * targeting @lblk without causing a data unit number (DUN) discontiguity.
455  *
456  * This is normally just @nr_blocks, as normally the DUNs just increment along
457  * with the logical blocks.  (Or the file is not encrypted.)
458  *
459  * In rare cases, fscrypt can be using an IV generation method that allows the
460  * DUN to wrap around within logically contiguous blocks, and that wraparound
461  * will occur.  If this happens, a value less than @nr_blocks will be returned
462  * so that the wraparound doesn't occur in the middle of a bio, which would
463  * cause encryption/decryption to produce wrong results.
464  *
465  * Return: the actual number of blocks that can be submitted
466  */
467 u64 fscrypt_limit_io_blocks(const struct inode *inode, u64 lblk, u64 nr_blocks)
468 {
469 	const struct fscrypt_info *ci;
470 	u32 dun;
471 
472 	if (!fscrypt_inode_uses_inline_crypto(inode))
473 		return nr_blocks;
474 
475 	if (nr_blocks <= 1)
476 		return nr_blocks;
477 
478 	ci = inode->i_crypt_info;
479 	if (!(fscrypt_policy_flags(&ci->ci_policy) &
480 	      FSCRYPT_POLICY_FLAG_IV_INO_LBLK_32))
481 		return nr_blocks;
482 
483 	/* With IV_INO_LBLK_32, the DUN can wrap around from U32_MAX to 0. */
484 
485 	dun = ci->ci_hashed_ino + lblk;
486 
487 	return min_t(u64, nr_blocks, (u64)U32_MAX + 1 - dun);
488 }
489 EXPORT_SYMBOL_GPL(fscrypt_limit_io_blocks);
490