inline_crypt.c

  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/export.h>
 19#include <linux/sched/mm.h>
 20#include <linux/slab.h>
 21#include <linux/uio.h>
 22
 23#include "fscrypt_private.h"
 24
 25static struct block_device **fscrypt_get_devices(struct super_block *sb,
 26						 unsigned int *num_devs)
 27{
 28	struct block_device **devs;
 29
 30	if (sb->s_cop->get_devices) {
 31		devs = sb->s_cop->get_devices(sb, num_devs);
 32		if (devs)
 33			return devs;
 34	}
 35	devs = kmalloc(sizeof(*devs), GFP_KERNEL);
 36	if (!devs)
 37		return ERR_PTR(-ENOMEM);
 38	devs[0] = sb->s_bdev;
 39	*num_devs = 1;
 40	return devs;
 41}
 42
 43static unsigned int fscrypt_get_dun_bytes(const struct fscrypt_inode_info *ci)
 44{
 45	const struct super_block *sb = ci->ci_inode->i_sb;
 46	unsigned int flags = fscrypt_policy_flags(&ci->ci_policy);
 47	int dun_bits;
 48
 49	if (flags & FSCRYPT_POLICY_FLAG_DIRECT_KEY)
 50		return offsetofend(union fscrypt_iv, nonce);
 51
 52	if (flags & FSCRYPT_POLICY_FLAG_IV_INO_LBLK_64)
 53		return sizeof(__le64);
 54
 55	if (flags & FSCRYPT_POLICY_FLAG_IV_INO_LBLK_32)
 56		return sizeof(__le32);
 57
 58	/* Default case: IVs are just the file data unit index */
 59	dun_bits = fscrypt_max_file_dun_bits(sb, ci->ci_data_unit_bits);
 60	return DIV_ROUND_UP(dun_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_inode_info *ci,
 94				   bool is_hw_wrapped_key)
 95{
 96	const struct inode *inode = ci->ci_inode;
 97	struct super_block *sb = inode->i_sb;
 98	struct blk_crypto_config crypto_cfg;
 99	struct block_device **devs;
100	unsigned int num_devs;
101	unsigned int i;
102
103	/* The file must need contents encryption, not filenames encryption */
104	if (!S_ISREG(inode->i_mode))
105		return 0;
106
107	/* The crypto mode must have a blk-crypto counterpart */
108	if (ci->ci_mode->blk_crypto_mode == BLK_ENCRYPTION_MODE_INVALID)
109		return 0;
110
111	/* The filesystem must be mounted with -o inlinecrypt */
112	if (!(sb->s_flags & SB_INLINECRYPT))
113		return 0;
114
115	/*
116	 * When a page contains multiple logically contiguous filesystem blocks,
117	 * some filesystem code only calls fscrypt_mergeable_bio() for the first
118	 * block in the page. This is fine for most of fscrypt's IV generation
119	 * strategies, where contiguous blocks imply contiguous IVs. But it
120	 * doesn't work with IV_INO_LBLK_32. For now, simply exclude
121	 * IV_INO_LBLK_32 with blocksize != PAGE_SIZE from inline encryption.
122	 */
123	if ((fscrypt_policy_flags(&ci->ci_policy) &
124	     FSCRYPT_POLICY_FLAG_IV_INO_LBLK_32) &&
125	    sb->s_blocksize != PAGE_SIZE)
126		return 0;
127
128	/*
129	 * On all the filesystem's block devices, blk-crypto must support the
130	 * crypto configuration that the file would use.
131	 */
132	crypto_cfg.crypto_mode = ci->ci_mode->blk_crypto_mode;
133	crypto_cfg.data_unit_size = 1U << ci->ci_data_unit_bits;
134	crypto_cfg.dun_bytes = fscrypt_get_dun_bytes(ci);
135	crypto_cfg.key_type = is_hw_wrapped_key ?
136		BLK_CRYPTO_KEY_TYPE_HW_WRAPPED : BLK_CRYPTO_KEY_TYPE_RAW;
137
138	devs = fscrypt_get_devices(sb, &num_devs);
139	if (IS_ERR(devs))
140		return PTR_ERR(devs);
141
142	for (i = 0; i < num_devs; i++) {
143		if (!blk_crypto_config_supported(devs[i], &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;
150out_free_devs:
151	kfree(devs);
152
153	return 0;
154}
155
156int fscrypt_prepare_inline_crypt_key(struct fscrypt_prepared_key *prep_key,
157				     const u8 *key_bytes, size_t key_size,
158				     bool is_hw_wrapped,
159				     const struct fscrypt_inode_info *ci)
160{
161	const struct inode *inode = ci->ci_inode;
162	struct super_block *sb = inode->i_sb;
163	enum blk_crypto_mode_num crypto_mode = ci->ci_mode->blk_crypto_mode;
164	enum blk_crypto_key_type key_type = is_hw_wrapped ?
165		BLK_CRYPTO_KEY_TYPE_HW_WRAPPED : BLK_CRYPTO_KEY_TYPE_RAW;
166	struct blk_crypto_key *blk_key;
167	struct block_device **devs;
168	unsigned int num_devs;
169	unsigned int i;
170	int err;
171
172	blk_key = kmalloc(sizeof(*blk_key), GFP_KERNEL);
173	if (!blk_key)
174		return -ENOMEM;
175
176	err = blk_crypto_init_key(blk_key, key_bytes, key_size, key_type,
177				  crypto_mode, fscrypt_get_dun_bytes(ci),
178				  1U << ci->ci_data_unit_bits);
179	if (err) {
180		fscrypt_err(inode, "error %d initializing blk-crypto key", err);
181		goto fail;
182	}
183
184	/* Start using blk-crypto on all the filesystem's block devices. */
185	devs = fscrypt_get_devices(sb, &num_devs);
186	if (IS_ERR(devs)) {
187		err = PTR_ERR(devs);
188		goto fail;
189	}
190	for (i = 0; i < num_devs; i++) {
191		err = blk_crypto_start_using_key(devs[i], blk_key);
192		if (err)
193			break;
194	}
195	kfree(devs);
196	if (err) {
197		fscrypt_err(inode, "error %d starting to use blk-crypto", err);
198		goto fail;
199	}
200
201	/*
202	 * Pairs with the smp_load_acquire() in fscrypt_is_key_prepared().
203	 * I.e., here we publish ->blk_key with a RELEASE barrier so that
204	 * concurrent tasks can ACQUIRE it.  Note that this concurrency is only
205	 * possible for per-mode keys, not for per-file keys.
206	 */
207	smp_store_release(&prep_key->blk_key, blk_key);
208	return 0;
209
210fail:
211	kfree_sensitive(blk_key);
212	return err;
213}
214
215void fscrypt_destroy_inline_crypt_key(struct super_block *sb,
216				      struct fscrypt_prepared_key *prep_key)
217{
218	struct blk_crypto_key *blk_key = prep_key->blk_key;
219	struct block_device **devs;
220	unsigned int num_devs;
221	unsigned int i;
222
223	if (!blk_key)
224		return;
225
226	/* Evict the key from all the filesystem's block devices. */
227	devs = fscrypt_get_devices(sb, &num_devs);
228	if (!IS_ERR(devs)) {
229		for (i = 0; i < num_devs; i++)
230			blk_crypto_evict_key(devs[i], blk_key);
231		kfree(devs);
232	}
233	kfree_sensitive(blk_key);
234}
235
236/*
237 * Ask the inline encryption hardware to derive the software secret from a
238 * hardware-wrapped key.  Returns -EOPNOTSUPP if hardware-wrapped keys aren't
239 * supported on this filesystem or hardware.
240 */
241int fscrypt_derive_sw_secret(struct super_block *sb,
242			     const u8 *wrapped_key, size_t wrapped_key_size,
243			     u8 sw_secret[BLK_CRYPTO_SW_SECRET_SIZE])
244{
245	int err;
246
247	/* The filesystem must be mounted with -o inlinecrypt. */
248	if (!(sb->s_flags & SB_INLINECRYPT)) {
249		fscrypt_warn(NULL,
250			     "%s: filesystem not mounted with inlinecrypt\n",
251			     sb->s_id);
252		return -EOPNOTSUPP;
253	}
254
255	err = blk_crypto_derive_sw_secret(sb->s_bdev, wrapped_key,
256					  wrapped_key_size, sw_secret);
257	if (err == -EOPNOTSUPP)
258		fscrypt_warn(NULL,
259			     "%s: block device doesn't support hardware-wrapped keys\n",
260			     sb->s_id);
261	return err;
262}
263
264bool __fscrypt_inode_uses_inline_crypto(const struct inode *inode)
265{
266	return fscrypt_get_inode_info_raw(inode)->ci_inlinecrypt;
267}
268EXPORT_SYMBOL_GPL(__fscrypt_inode_uses_inline_crypto);
269
270static void fscrypt_generate_dun(const struct fscrypt_inode_info *ci,
271				 u64 lblk_num,
272				 u64 dun[BLK_CRYPTO_DUN_ARRAY_SIZE])
273{
274	u64 index = lblk_num << ci->ci_data_units_per_block_bits;
275	union fscrypt_iv iv;
276	int i;
277
278	fscrypt_generate_iv(&iv, index, ci);
279
280	BUILD_BUG_ON(FSCRYPT_MAX_IV_SIZE > BLK_CRYPTO_MAX_IV_SIZE);
281	memset(dun, 0, BLK_CRYPTO_MAX_IV_SIZE);
282	for (i = 0; i < ci->ci_mode->ivsize/sizeof(dun[0]); i++)
283		dun[i] = le64_to_cpu(iv.dun[i]);
284}
285
286/**
287 * fscrypt_set_bio_crypt_ctx() - prepare a file contents bio for inline crypto
288 * @bio: a bio which will eventually be submitted to the file
289 * @inode: the file's inode
290 * @first_lblk: the first file logical block number in the I/O
291 * @gfp_mask: memory allocation flags - these must be a waiting mask so that
292 *					bio_crypt_set_ctx can't fail.
293 *
294 * If the contents of the file should be encrypted (or decrypted) with inline
295 * encryption, then assign the appropriate encryption context to the bio.
296 *
297 * Normally the bio should be newly allocated (i.e. no pages added yet), as
298 * otherwise fscrypt_mergeable_bio() won't work as intended.
299 *
300 * The encryption context will be freed automatically when the bio is freed.
301 */
302void fscrypt_set_bio_crypt_ctx(struct bio *bio, const struct inode *inode,
303			       u64 first_lblk, gfp_t gfp_mask)
304{
305	const struct fscrypt_inode_info *ci;
306	u64 dun[BLK_CRYPTO_DUN_ARRAY_SIZE];
307
308	if (!fscrypt_inode_uses_inline_crypto(inode))
309		return;
310	ci = fscrypt_get_inode_info_raw(inode);
311
312	fscrypt_generate_dun(ci, first_lblk, dun);
313	bio_crypt_set_ctx(bio, ci->ci_enc_key.blk_key, dun, gfp_mask);
314}
315EXPORT_SYMBOL_GPL(fscrypt_set_bio_crypt_ctx);
316
317/* Extract the inode and logical block number from a buffer_head. */
318static bool bh_get_inode_and_lblk_num(const struct buffer_head *bh,
319				      const struct inode **inode_ret,
320				      u64 *lblk_num_ret)
321{
322	struct folio *folio = bh->b_folio;
323	const struct address_space *mapping;
324	const struct inode *inode;
325
326	/*
327	 * The ext4 journal (jbd2) can submit a buffer_head it directly created
328	 * for a non-pagecache page.  fscrypt doesn't care about these.
329	 */
330	mapping = folio_mapping(folio);
331	if (!mapping)
332		return false;
333	inode = mapping->host;
334
335	*inode_ret = inode;
336	*lblk_num_ret = (folio_pos(folio) + bh_offset(bh)) >> inode->i_blkbits;
337	return true;
338}
339
340/**
341 * fscrypt_set_bio_crypt_ctx_bh() - prepare a file contents bio for inline
342 *				    crypto
343 * @bio: a bio which will eventually be submitted to the file
344 * @first_bh: the first buffer_head for which I/O will be submitted
345 * @gfp_mask: memory allocation flags
346 *
347 * Same as fscrypt_set_bio_crypt_ctx(), except this takes a buffer_head instead
348 * of an inode and block number directly.
349 */
350void fscrypt_set_bio_crypt_ctx_bh(struct bio *bio,
351				  const struct buffer_head *first_bh,
352				  gfp_t gfp_mask)
353{
354	const struct inode *inode;
355	u64 first_lblk;
356
357	if (bh_get_inode_and_lblk_num(first_bh, &inode, &first_lblk))
358		fscrypt_set_bio_crypt_ctx(bio, inode, first_lblk, gfp_mask);
359}
360EXPORT_SYMBOL_GPL(fscrypt_set_bio_crypt_ctx_bh);
361
362/**
363 * fscrypt_mergeable_bio() - test whether data can be added to a bio
364 * @bio: the bio being built up
365 * @inode: the inode for the next part of the I/O
366 * @next_lblk: the next file logical block number in the I/O
367 *
368 * When building a bio which may contain data which should undergo inline
369 * encryption (or decryption) via fscrypt, filesystems should call this function
370 * to ensure that the resulting bio contains only contiguous data unit numbers.
371 * This will return false if the next part of the I/O cannot be merged with the
372 * bio because either the encryption key would be different or the encryption
373 * data unit numbers would be discontiguous.
374 *
375 * fscrypt_set_bio_crypt_ctx() must have already been called on the bio.
376 *
377 * This function isn't required in cases where crypto-mergeability is ensured in
378 * another way, such as I/O targeting only a single file (and thus a single key)
379 * combined with fscrypt_limit_io_blocks() to ensure DUN contiguity.
380 *
381 * Return: true iff the I/O is mergeable
382 */
383bool fscrypt_mergeable_bio(struct bio *bio, const struct inode *inode,
384			   u64 next_lblk)
385{
386	const struct bio_crypt_ctx *bc = bio->bi_crypt_context;
387	const struct fscrypt_inode_info *ci;
388	u64 next_dun[BLK_CRYPTO_DUN_ARRAY_SIZE];
389
390	if (!!bc != fscrypt_inode_uses_inline_crypto(inode))
391		return false;
392	if (!bc)
393		return true;
394	ci = fscrypt_get_inode_info_raw(inode);
395
396	/*
397	 * Comparing the key pointers is good enough, as all I/O for each key
398	 * uses the same pointer.  I.e., there's currently no need to support
399	 * merging requests where the keys are the same but the pointers differ.
400	 */
401	if (bc->bc_key != ci->ci_enc_key.blk_key)
402		return false;
403
404	fscrypt_generate_dun(ci, next_lblk, next_dun);
405	return bio_crypt_dun_is_contiguous(bc, bio->bi_iter.bi_size, next_dun);
406}
407EXPORT_SYMBOL_GPL(fscrypt_mergeable_bio);
408
409/**
410 * fscrypt_mergeable_bio_bh() - test whether data can be added to a bio
411 * @bio: the bio being built up
412 * @next_bh: the next buffer_head for which I/O will be submitted
413 *
414 * Same as fscrypt_mergeable_bio(), except this takes a buffer_head instead of
415 * an inode and block number directly.
416 *
417 * Return: true iff the I/O is mergeable
418 */
419bool fscrypt_mergeable_bio_bh(struct bio *bio,
420			      const struct buffer_head *next_bh)
421{
422	const struct inode *inode;
423	u64 next_lblk;
424
425	if (!bh_get_inode_and_lblk_num(next_bh, &inode, &next_lblk))
426		return !bio->bi_crypt_context;
427
428	return fscrypt_mergeable_bio(bio, inode, next_lblk);
429}
430EXPORT_SYMBOL_GPL(fscrypt_mergeable_bio_bh);
431
432/**
433 * fscrypt_dio_supported() - check whether DIO (direct I/O) is supported on an
434 *			     inode, as far as encryption is concerned
435 * @inode: the inode in question
436 *
437 * Return: %true if there are no encryption constraints that prevent DIO from
438 *	   being supported; %false if DIO is unsupported.  (Note that in the
439 *	   %true case, the filesystem might have other, non-encryption-related
440 *	   constraints that prevent DIO from actually being supported.  Also, on
441 *	   encrypted files the filesystem is still responsible for only allowing
442 *	   DIO when requests are filesystem-block-aligned.)
443 */
444bool fscrypt_dio_supported(struct inode *inode)
445{
446	int err;
447
448	/* If the file is unencrypted, no veto from us. */
449	if (!fscrypt_needs_contents_encryption(inode))
450		return true;
451
452	/*
453	 * We only support DIO with inline crypto, not fs-layer crypto.
454	 *
455	 * To determine whether the inode is using inline crypto, we have to set
456	 * up the key if it wasn't already done.  This is because in the current
457	 * design of fscrypt, the decision of whether to use inline crypto or
458	 * not isn't made until the inode's encryption key is being set up.  In
459	 * the DIO read/write case, the key will always be set up already, since
460	 * the file will be open.  But in the case of statx(), the key might not
461	 * be set up yet, as the file might not have been opened yet.
462	 */
463	err = fscrypt_require_key(inode);
464	if (err) {
465		/*
466		 * Key unavailable or couldn't be set up.  This edge case isn't
467		 * worth worrying about; just report that DIO is unsupported.
468		 */
469		return false;
470	}
471	return fscrypt_inode_uses_inline_crypto(inode);
472}
473EXPORT_SYMBOL_GPL(fscrypt_dio_supported);
474
475/**
476 * fscrypt_limit_io_blocks() - limit I/O blocks to avoid discontiguous DUNs
477 * @inode: the file on which I/O is being done
478 * @lblk: the block at which the I/O is being started from
479 * @nr_blocks: the number of blocks we want to submit starting at @lblk
480 *
481 * Determine the limit to the number of blocks that can be submitted in a bio
482 * targeting @lblk without causing a data unit number (DUN) discontiguity.
483 *
484 * This is normally just @nr_blocks, as normally the DUNs just increment along
485 * with the logical blocks.  (Or the file is not encrypted.)
486 *
487 * In rare cases, fscrypt can be using an IV generation method that allows the
488 * DUN to wrap around within logically contiguous blocks, and that wraparound
489 * will occur.  If this happens, a value less than @nr_blocks will be returned
490 * so that the wraparound doesn't occur in the middle of a bio, which would
491 * cause encryption/decryption to produce wrong results.
492 *
493 * Return: the actual number of blocks that can be submitted
494 */
495u64 fscrypt_limit_io_blocks(const struct inode *inode, u64 lblk, u64 nr_blocks)
496{
497	const struct fscrypt_inode_info *ci;
498	u32 dun;
499
500	if (!fscrypt_inode_uses_inline_crypto(inode))
501		return nr_blocks;
502
503	if (nr_blocks <= 1)
504		return nr_blocks;
505
506	ci = fscrypt_get_inode_info_raw(inode);
507	if (!(fscrypt_policy_flags(&ci->ci_policy) &
508	      FSCRYPT_POLICY_FLAG_IV_INO_LBLK_32))
509		return nr_blocks;
510
511	/* With IV_INO_LBLK_32, the DUN can wrap around from U32_MAX to 0. */
512
513	dun = ci->ci_hashed_ino + lblk;
514
515	return min_t(u64, nr_blocks, (u64)U32_MAX + 1 - dun);
516}
517EXPORT_SYMBOL_GPL(fscrypt_limit_io_blocks);