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
 24static 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
 42static 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 */
 72static 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		if (!IS_ENABLED(CONFIG_BLK_INLINE_ENCRYPTION_FALLBACK) ||
 81		    blk_crypto_config_supported_natively(devs[i], cfg)) {
 82			if (!xchg(&mode->logged_blk_crypto_native, 1))
 83				pr_info("fscrypt: %s using blk-crypto (native)\n",
 84					mode->friendly_name);
 85		} else if (!xchg(&mode->logged_blk_crypto_fallback, 1)) {
 86			pr_info("fscrypt: %s using blk-crypto-fallback\n",
 87				mode->friendly_name);
 88		}
 89	}
 90}
 91
 92/* Enable inline encryption for this file if supported. */
 93int fscrypt_select_encryption_impl(struct fscrypt_info *ci)
 94{
 95	const struct inode *inode = ci->ci_inode;
 96	struct super_block *sb = inode->i_sb;
 97	struct blk_crypto_config crypto_cfg;
 98	struct block_device **devs;
 99	unsigned int num_devs;
100	unsigned int i;
101
102	/* The file must need contents encryption, not filenames encryption */
103	if (!S_ISREG(inode->i_mode))
104		return 0;
105
106	/* The crypto mode must have a blk-crypto counterpart */
107	if (ci->ci_mode->blk_crypto_mode == BLK_ENCRYPTION_MODE_INVALID)
108		return 0;
109
110	/* The filesystem must be mounted with -o inlinecrypt */
111	if (!(sb->s_flags & SB_INLINECRYPT))
112		return 0;
113
114	/*
115	 * When a page contains multiple logically contiguous filesystem blocks,
116	 * some filesystem code only calls fscrypt_mergeable_bio() for the first
117	 * block in the page. This is fine for most of fscrypt's IV generation
118	 * strategies, where contiguous blocks imply contiguous IVs. But it
119	 * doesn't work with IV_INO_LBLK_32. For now, simply exclude
120	 * IV_INO_LBLK_32 with blocksize != PAGE_SIZE from inline encryption.
121	 */
122	if ((fscrypt_policy_flags(&ci->ci_policy) &
123	     FSCRYPT_POLICY_FLAG_IV_INO_LBLK_32) &&
124	    sb->s_blocksize != PAGE_SIZE)
125		return 0;
126
127	/*
128	 * On all the filesystem's block devices, blk-crypto must support the
129	 * crypto configuration that the file would use.
130	 */
131	crypto_cfg.crypto_mode = ci->ci_mode->blk_crypto_mode;
132	crypto_cfg.data_unit_size = sb->s_blocksize;
133	crypto_cfg.dun_bytes = fscrypt_get_dun_bytes(ci);
134
135	devs = fscrypt_get_devices(sb, &num_devs);
136	if (IS_ERR(devs))
137		return PTR_ERR(devs);
138
139	for (i = 0; i < num_devs; i++) {
140		if (!blk_crypto_config_supported(devs[i], &crypto_cfg))
141			goto out_free_devs;
142	}
143
144	fscrypt_log_blk_crypto_impl(ci->ci_mode, devs, num_devs, &crypto_cfg);
145
146	ci->ci_inlinecrypt = true;
147out_free_devs:
148	kfree(devs);
149
150	return 0;
151}
152
153int fscrypt_prepare_inline_crypt_key(struct fscrypt_prepared_key *prep_key,
154				     const u8 *raw_key,
155				     const struct fscrypt_info *ci)
156{
157	const struct inode *inode = ci->ci_inode;
158	struct super_block *sb = inode->i_sb;
159	enum blk_crypto_mode_num crypto_mode = ci->ci_mode->blk_crypto_mode;
160	struct blk_crypto_key *blk_key;
161	struct block_device **devs;
162	unsigned int num_devs;
163	unsigned int i;
164	int err;
165
166	blk_key = kmalloc(sizeof(*blk_key), GFP_KERNEL);
167	if (!blk_key)
168		return -ENOMEM;
169
170	err = blk_crypto_init_key(blk_key, raw_key, crypto_mode,
171				  fscrypt_get_dun_bytes(ci), sb->s_blocksize);
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
203fail:
204	kfree_sensitive(blk_key);
205	return err;
206}
207
208void 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
229bool __fscrypt_inode_uses_inline_crypto(const struct inode *inode)
230{
231	return inode->i_crypt_info->ci_inlinecrypt;
232}
233EXPORT_SYMBOL_GPL(__fscrypt_inode_uses_inline_crypto);
234
235static void fscrypt_generate_dun(const struct fscrypt_info *ci, u64 lblk_num,
236				 u64 dun[BLK_CRYPTO_DUN_ARRAY_SIZE])
237{
238	union fscrypt_iv iv;
239	int i;
240
241	fscrypt_generate_iv(&iv, lblk_num, ci);
242
243	BUILD_BUG_ON(FSCRYPT_MAX_IV_SIZE > BLK_CRYPTO_MAX_IV_SIZE);
244	memset(dun, 0, BLK_CRYPTO_MAX_IV_SIZE);
245	for (i = 0; i < ci->ci_mode->ivsize/sizeof(dun[0]); i++)
246		dun[i] = le64_to_cpu(iv.dun[i]);
247}
248
249/**
250 * fscrypt_set_bio_crypt_ctx() - prepare a file contents bio for inline crypto
251 * @bio: a bio which will eventually be submitted to the file
252 * @inode: the file's inode
253 * @first_lblk: the first file logical block number in the I/O
254 * @gfp_mask: memory allocation flags - these must be a waiting mask so that
255 *					bio_crypt_set_ctx can't fail.
256 *
257 * If the contents of the file should be encrypted (or decrypted) with inline
258 * encryption, then assign the appropriate encryption context to the bio.
259 *
260 * Normally the bio should be newly allocated (i.e. no pages added yet), as
261 * otherwise fscrypt_mergeable_bio() won't work as intended.
262 *
263 * The encryption context will be freed automatically when the bio is freed.
264 */
265void fscrypt_set_bio_crypt_ctx(struct bio *bio, const struct inode *inode,
266			       u64 first_lblk, gfp_t gfp_mask)
267{
268	const struct fscrypt_info *ci;
269	u64 dun[BLK_CRYPTO_DUN_ARRAY_SIZE];
270
271	if (!fscrypt_inode_uses_inline_crypto(inode))
272		return;
273	ci = inode->i_crypt_info;
274
275	fscrypt_generate_dun(ci, first_lblk, dun);
276	bio_crypt_set_ctx(bio, ci->ci_enc_key.blk_key, dun, gfp_mask);
277}
278EXPORT_SYMBOL_GPL(fscrypt_set_bio_crypt_ctx);
279
280/* Extract the inode and logical block number from a buffer_head. */
281static bool bh_get_inode_and_lblk_num(const struct buffer_head *bh,
282				      const struct inode **inode_ret,
283				      u64 *lblk_num_ret)
284{
285	struct page *page = bh->b_page;
286	const struct address_space *mapping;
287	const struct inode *inode;
288
289	/*
290	 * The ext4 journal (jbd2) can submit a buffer_head it directly created
291	 * for a non-pagecache page.  fscrypt doesn't care about these.
292	 */
293	mapping = page_mapping(page);
294	if (!mapping)
295		return false;
296	inode = mapping->host;
297
298	*inode_ret = inode;
299	*lblk_num_ret = ((u64)page->index << (PAGE_SHIFT - inode->i_blkbits)) +
300			(bh_offset(bh) >> inode->i_blkbits);
301	return true;
302}
303
304/**
305 * fscrypt_set_bio_crypt_ctx_bh() - prepare a file contents bio for inline
306 *				    crypto
307 * @bio: a bio which will eventually be submitted to the file
308 * @first_bh: the first buffer_head for which I/O will be submitted
309 * @gfp_mask: memory allocation flags
310 *
311 * Same as fscrypt_set_bio_crypt_ctx(), except this takes a buffer_head instead
312 * of an inode and block number directly.
313 */
314void fscrypt_set_bio_crypt_ctx_bh(struct bio *bio,
315				  const struct buffer_head *first_bh,
316				  gfp_t gfp_mask)
317{
318	const struct inode *inode;
319	u64 first_lblk;
320
321	if (bh_get_inode_and_lblk_num(first_bh, &inode, &first_lblk))
322		fscrypt_set_bio_crypt_ctx(bio, inode, first_lblk, gfp_mask);
323}
324EXPORT_SYMBOL_GPL(fscrypt_set_bio_crypt_ctx_bh);
325
326/**
327 * fscrypt_mergeable_bio() - test whether data can be added to a bio
328 * @bio: the bio being built up
329 * @inode: the inode for the next part of the I/O
330 * @next_lblk: the next file logical block number in the I/O
331 *
332 * When building a bio which may contain data which should undergo inline
333 * encryption (or decryption) via fscrypt, filesystems should call this function
334 * to ensure that the resulting bio contains only contiguous data unit numbers.
335 * This will return false if the next part of the I/O cannot be merged with the
336 * bio because either the encryption key would be different or the encryption
337 * data unit numbers would be discontiguous.
338 *
339 * fscrypt_set_bio_crypt_ctx() must have already been called on the bio.
340 *
341 * This function isn't required in cases where crypto-mergeability is ensured in
342 * another way, such as I/O targeting only a single file (and thus a single key)
343 * combined with fscrypt_limit_io_blocks() to ensure DUN contiguity.
344 *
345 * Return: true iff the I/O is mergeable
346 */
347bool fscrypt_mergeable_bio(struct bio *bio, const struct inode *inode,
348			   u64 next_lblk)
349{
350	const struct bio_crypt_ctx *bc = bio->bi_crypt_context;
351	u64 next_dun[BLK_CRYPTO_DUN_ARRAY_SIZE];
352
353	if (!!bc != fscrypt_inode_uses_inline_crypto(inode))
354		return false;
355	if (!bc)
356		return true;
357
358	/*
359	 * Comparing the key pointers is good enough, as all I/O for each key
360	 * uses the same pointer.  I.e., there's currently no need to support
361	 * merging requests where the keys are the same but the pointers differ.
362	 */
363	if (bc->bc_key != inode->i_crypt_info->ci_enc_key.blk_key)
364		return false;
365
366	fscrypt_generate_dun(inode->i_crypt_info, next_lblk, next_dun);
367	return bio_crypt_dun_is_contiguous(bc, bio->bi_iter.bi_size, next_dun);
368}
369EXPORT_SYMBOL_GPL(fscrypt_mergeable_bio);
370
371/**
372 * fscrypt_mergeable_bio_bh() - test whether data can be added to a bio
373 * @bio: the bio being built up
374 * @next_bh: the next buffer_head for which I/O will be submitted
375 *
376 * Same as fscrypt_mergeable_bio(), except this takes a buffer_head instead of
377 * an inode and block number directly.
378 *
379 * Return: true iff the I/O is mergeable
380 */
381bool fscrypt_mergeable_bio_bh(struct bio *bio,
382			      const struct buffer_head *next_bh)
383{
384	const struct inode *inode;
385	u64 next_lblk;
386
387	if (!bh_get_inode_and_lblk_num(next_bh, &inode, &next_lblk))
388		return !bio->bi_crypt_context;
389
390	return fscrypt_mergeable_bio(bio, inode, next_lblk);
391}
392EXPORT_SYMBOL_GPL(fscrypt_mergeable_bio_bh);
393
394/**
395 * fscrypt_dio_supported() - check whether DIO (direct I/O) is supported on an
396 *			     inode, as far as encryption is concerned
397 * @inode: the inode in question
398 *
399 * Return: %true if there are no encryption constraints that prevent DIO from
400 *	   being supported; %false if DIO is unsupported.  (Note that in the
401 *	   %true case, the filesystem might have other, non-encryption-related
402 *	   constraints that prevent DIO from actually being supported.  Also, on
403 *	   encrypted files the filesystem is still responsible for only allowing
404 *	   DIO when requests are filesystem-block-aligned.)
405 */
406bool fscrypt_dio_supported(struct inode *inode)
407{
408	int err;
409
410	/* If the file is unencrypted, no veto from us. */
411	if (!fscrypt_needs_contents_encryption(inode))
412		return true;
413
414	/*
415	 * We only support DIO with inline crypto, not fs-layer crypto.
416	 *
417	 * To determine whether the inode is using inline crypto, we have to set
418	 * up the key if it wasn't already done.  This is because in the current
419	 * design of fscrypt, the decision of whether to use inline crypto or
420	 * not isn't made until the inode's encryption key is being set up.  In
421	 * the DIO read/write case, the key will always be set up already, since
422	 * the file will be open.  But in the case of statx(), the key might not
423	 * be set up yet, as the file might not have been opened yet.
424	 */
425	err = fscrypt_require_key(inode);
426	if (err) {
427		/*
428		 * Key unavailable or couldn't be set up.  This edge case isn't
429		 * worth worrying about; just report that DIO is unsupported.
430		 */
431		return false;
432	}
433	return fscrypt_inode_uses_inline_crypto(inode);
434}
435EXPORT_SYMBOL_GPL(fscrypt_dio_supported);
436
437/**
438 * fscrypt_limit_io_blocks() - limit I/O blocks to avoid discontiguous DUNs
439 * @inode: the file on which I/O is being done
440 * @lblk: the block at which the I/O is being started from
441 * @nr_blocks: the number of blocks we want to submit starting at @lblk
442 *
443 * Determine the limit to the number of blocks that can be submitted in a bio
444 * targeting @lblk without causing a data unit number (DUN) discontiguity.
445 *
446 * This is normally just @nr_blocks, as normally the DUNs just increment along
447 * with the logical blocks.  (Or the file is not encrypted.)
448 *
449 * In rare cases, fscrypt can be using an IV generation method that allows the
450 * DUN to wrap around within logically contiguous blocks, and that wraparound
451 * will occur.  If this happens, a value less than @nr_blocks will be returned
452 * so that the wraparound doesn't occur in the middle of a bio, which would
453 * cause encryption/decryption to produce wrong results.
454 *
455 * Return: the actual number of blocks that can be submitted
456 */
457u64 fscrypt_limit_io_blocks(const struct inode *inode, u64 lblk, u64 nr_blocks)
458{
459	const struct fscrypt_info *ci;
460	u32 dun;
461
462	if (!fscrypt_inode_uses_inline_crypto(inode))
463		return nr_blocks;
464
465	if (nr_blocks <= 1)
466		return nr_blocks;
467
468	ci = inode->i_crypt_info;
469	if (!(fscrypt_policy_flags(&ci->ci_policy) &
470	      FSCRYPT_POLICY_FLAG_IV_INO_LBLK_32))
471		return nr_blocks;
472
473	/* With IV_INO_LBLK_32, the DUN can wrap around from U32_MAX to 0. */
474
475	dun = ci->ci_hashed_ino + lblk;
476
477	return min_t(u64, nr_blocks, (u64)U32_MAX + 1 - dun);
478}
479EXPORT_SYMBOL_GPL(fscrypt_limit_io_blocks);