// SPDX-License-Identifier: GPL-2.0 /* * Inline encryption support for fscrypt * * Copyright 2019 Google LLC */ /* * With "inline encryption", the block layer handles the decryption/encryption * as part of the bio, instead of the filesystem doing the crypto itself via * crypto API. See Documentation/block/inline-encryption.rst. fscrypt still * provides the key and IV to use. */ #include #include #include #include #include #include #include "fscrypt_private.h" static struct block_device **fscrypt_get_devices(struct super_block *sb, unsigned int *num_devs) { struct block_device **devs; if (sb->s_cop->get_devices) { devs = sb->s_cop->get_devices(sb, num_devs); if (devs) return devs; } devs = kmalloc(sizeof(*devs), GFP_KERNEL); if (!devs) return ERR_PTR(-ENOMEM); devs[0] = sb->s_bdev; *num_devs = 1; return devs; } static unsigned int fscrypt_get_dun_bytes(const struct fscrypt_inode_info *ci) { const struct super_block *sb = ci->ci_inode->i_sb; unsigned int flags = fscrypt_policy_flags(&ci->ci_policy); int dun_bits; if (flags & FSCRYPT_POLICY_FLAG_DIRECT_KEY) return offsetofend(union fscrypt_iv, nonce); if (flags & FSCRYPT_POLICY_FLAG_IV_INO_LBLK_64) return sizeof(__le64); if (flags & FSCRYPT_POLICY_FLAG_IV_INO_LBLK_32) return sizeof(__le32); /* Default case: IVs are just the file data unit index */ dun_bits = fscrypt_max_file_dun_bits(sb, ci->ci_data_unit_bits); return DIV_ROUND_UP(dun_bits, 8); } /* * Log a message when starting to use blk-crypto (native) or blk-crypto-fallback * for an encryption mode for the first time. This is the blk-crypto * counterpart to the message logged when starting to use the crypto API for the * first time. A limitation is that these messages don't convey which specific * filesystems or files are using each implementation. However, *usually* * systems use just one implementation per mode, which makes these messages * helpful for debugging problems where the "wrong" implementation is used. */ static void fscrypt_log_blk_crypto_impl(struct fscrypt_mode *mode, struct block_device **devs, unsigned int num_devs, const struct blk_crypto_config *cfg) { unsigned int i; for (i = 0; i < num_devs; i++) { if (!IS_ENABLED(CONFIG_BLK_INLINE_ENCRYPTION_FALLBACK) || blk_crypto_config_supported_natively(devs[i], cfg)) { if (!xchg(&mode->logged_blk_crypto_native, 1)) pr_info("fscrypt: %s using blk-crypto (native)\n", mode->friendly_name); } else if (!xchg(&mode->logged_blk_crypto_fallback, 1)) { pr_info("fscrypt: %s using blk-crypto-fallback\n", mode->friendly_name); } } } /* Enable inline encryption for this file if supported. */ int fscrypt_select_encryption_impl(struct fscrypt_inode_info *ci) { const struct inode *inode = ci->ci_inode; struct super_block *sb = inode->i_sb; struct blk_crypto_config crypto_cfg; struct block_device **devs; unsigned int num_devs; unsigned int i; /* The file must need contents encryption, not filenames encryption */ if (!S_ISREG(inode->i_mode)) return 0; /* The crypto mode must have a blk-crypto counterpart */ if (ci->ci_mode->blk_crypto_mode == BLK_ENCRYPTION_MODE_INVALID) return 0; /* The filesystem must be mounted with -o inlinecrypt */ if (!(sb->s_flags & SB_INLINECRYPT)) return 0; /* * When a page contains multiple logically contiguous filesystem blocks, * some filesystem code only calls fscrypt_mergeable_bio() for the first * block in the page. This is fine for most of fscrypt's IV generation * strategies, where contiguous blocks imply contiguous IVs. But it * doesn't work with IV_INO_LBLK_32. For now, simply exclude * IV_INO_LBLK_32 with blocksize != PAGE_SIZE from inline encryption. */ if ((fscrypt_policy_flags(&ci->ci_policy) & FSCRYPT_POLICY_FLAG_IV_INO_LBLK_32) && sb->s_blocksize != PAGE_SIZE) return 0; /* * On all the filesystem's block devices, blk-crypto must support the * crypto configuration that the file would use. */ crypto_cfg.crypto_mode = ci->ci_mode->blk_crypto_mode; crypto_cfg.data_unit_size = 1U << ci->ci_data_unit_bits; crypto_cfg.dun_bytes = fscrypt_get_dun_bytes(ci); devs = fscrypt_get_devices(sb, &num_devs); if (IS_ERR(devs)) return PTR_ERR(devs); for (i = 0; i < num_devs; i++) { if (!blk_crypto_config_supported(devs[i], &crypto_cfg)) goto out_free_devs; } fscrypt_log_blk_crypto_impl(ci->ci_mode, devs, num_devs, &crypto_cfg); ci->ci_inlinecrypt = true; out_free_devs: kfree(devs); return 0; } int fscrypt_prepare_inline_crypt_key(struct fscrypt_prepared_key *prep_key, const u8 *raw_key, const struct fscrypt_inode_info *ci) { const struct inode *inode = ci->ci_inode; struct super_block *sb = inode->i_sb; enum blk_crypto_mode_num crypto_mode = ci->ci_mode->blk_crypto_mode; struct blk_crypto_key *blk_key; struct block_device **devs; unsigned int num_devs; unsigned int i; int err; blk_key = kmalloc(sizeof(*blk_key), GFP_KERNEL); if (!blk_key) return -ENOMEM; err = blk_crypto_init_key(blk_key, raw_key, crypto_mode, fscrypt_get_dun_bytes(ci), 1U << ci->ci_data_unit_bits); if (err) { fscrypt_err(inode, "error %d initializing blk-crypto key", err); goto fail; } /* Start using blk-crypto on all the filesystem's block devices. */ devs = fscrypt_get_devices(sb, &num_devs); if (IS_ERR(devs)) { err = PTR_ERR(devs); goto fail; } for (i = 0; i < num_devs; i++) { err = blk_crypto_start_using_key(devs[i], blk_key); if (err) break; } kfree(devs); if (err) { fscrypt_err(inode, "error %d starting to use blk-crypto", err); goto fail; } /* * Pairs with the smp_load_acquire() in fscrypt_is_key_prepared(). * I.e., here we publish ->blk_key with a RELEASE barrier so that * concurrent tasks can ACQUIRE it. Note that this concurrency is only * possible for per-mode keys, not for per-file keys. */ smp_store_release(&prep_key->blk_key, blk_key); return 0; fail: kfree_sensitive(blk_key); return err; } void fscrypt_destroy_inline_crypt_key(struct super_block *sb, struct fscrypt_prepared_key *prep_key) { struct blk_crypto_key *blk_key = prep_key->blk_key; struct block_device **devs; unsigned int num_devs; unsigned int i; if (!blk_key) return; /* Evict the key from all the filesystem's block devices. */ devs = fscrypt_get_devices(sb, &num_devs); if (!IS_ERR(devs)) { for (i = 0; i < num_devs; i++) blk_crypto_evict_key(devs[i], blk_key); kfree(devs); } kfree_sensitive(blk_key); } bool __fscrypt_inode_uses_inline_crypto(const struct inode *inode) { return inode->i_crypt_info->ci_inlinecrypt; } EXPORT_SYMBOL_GPL(__fscrypt_inode_uses_inline_crypto); static void fscrypt_generate_dun(const struct fscrypt_inode_info *ci, u64 lblk_num, u64 dun[BLK_CRYPTO_DUN_ARRAY_SIZE]) { u64 index = lblk_num << ci->ci_data_units_per_block_bits; union fscrypt_iv iv; int i; fscrypt_generate_iv(&iv, index, ci); BUILD_BUG_ON(FSCRYPT_MAX_IV_SIZE > BLK_CRYPTO_MAX_IV_SIZE); memset(dun, 0, BLK_CRYPTO_MAX_IV_SIZE); for (i = 0; i < ci->ci_mode->ivsize/sizeof(dun[0]); i++) dun[i] = le64_to_cpu(iv.dun[i]); } /** * fscrypt_set_bio_crypt_ctx() - prepare a file contents bio for inline crypto * @bio: a bio which will eventually be submitted to the file * @inode: the file's inode * @first_lblk: the first file logical block number in the I/O * @gfp_mask: memory allocation flags - these must be a waiting mask so that * bio_crypt_set_ctx can't fail. * * If the contents of the file should be encrypted (or decrypted) with inline * encryption, then assign the appropriate encryption context to the bio. * * Normally the bio should be newly allocated (i.e. no pages added yet), as * otherwise fscrypt_mergeable_bio() won't work as intended. * * The encryption context will be freed automatically when the bio is freed. */ void fscrypt_set_bio_crypt_ctx(struct bio *bio, const struct inode *inode, u64 first_lblk, gfp_t gfp_mask) { const struct fscrypt_inode_info *ci; u64 dun[BLK_CRYPTO_DUN_ARRAY_SIZE]; if (!fscrypt_inode_uses_inline_crypto(inode)) return; ci = inode->i_crypt_info; fscrypt_generate_dun(ci, first_lblk, dun); bio_crypt_set_ctx(bio, ci->ci_enc_key.blk_key, dun, gfp_mask); } EXPORT_SYMBOL_GPL(fscrypt_set_bio_crypt_ctx); /* Extract the inode and logical block number from a buffer_head. */ static bool bh_get_inode_and_lblk_num(const struct buffer_head *bh, const struct inode **inode_ret, u64 *lblk_num_ret) { struct page *page = bh->b_page; const struct address_space *mapping; const struct inode *inode; /* * The ext4 journal (jbd2) can submit a buffer_head it directly created * for a non-pagecache page. fscrypt doesn't care about these. */ mapping = page_mapping(page); if (!mapping) return false; inode = mapping->host; *inode_ret = inode; *lblk_num_ret = ((u64)page->index << (PAGE_SHIFT - inode->i_blkbits)) + (bh_offset(bh) >> inode->i_blkbits); return true; } /** * fscrypt_set_bio_crypt_ctx_bh() - prepare a file contents bio for inline * crypto * @bio: a bio which will eventually be submitted to the file * @first_bh: the first buffer_head for which I/O will be submitted * @gfp_mask: memory allocation flags * * Same as fscrypt_set_bio_crypt_ctx(), except this takes a buffer_head instead * of an inode and block number directly. */ void fscrypt_set_bio_crypt_ctx_bh(struct bio *bio, const struct buffer_head *first_bh, gfp_t gfp_mask) { const struct inode *inode; u64 first_lblk; if (bh_get_inode_and_lblk_num(first_bh, &inode, &first_lblk)) fscrypt_set_bio_crypt_ctx(bio, inode, first_lblk, gfp_mask); } EXPORT_SYMBOL_GPL(fscrypt_set_bio_crypt_ctx_bh); /** * fscrypt_mergeable_bio() - test whether data can be added to a bio * @bio: the bio being built up * @inode: the inode for the next part of the I/O * @next_lblk: the next file logical block number in the I/O * * When building a bio which may contain data which should undergo inline * encryption (or decryption) via fscrypt, filesystems should call this function * to ensure that the resulting bio contains only contiguous data unit numbers. * This will return false if the next part of the I/O cannot be merged with the * bio because either the encryption key would be different or the encryption * data unit numbers would be discontiguous. * * fscrypt_set_bio_crypt_ctx() must have already been called on the bio. * * This function isn't required in cases where crypto-mergeability is ensured in * another way, such as I/O targeting only a single file (and thus a single key) * combined with fscrypt_limit_io_blocks() to ensure DUN contiguity. * * Return: true iff the I/O is mergeable */ bool fscrypt_mergeable_bio(struct bio *bio, const struct inode *inode, u64 next_lblk) { const struct bio_crypt_ctx *bc = bio->bi_crypt_context; u64 next_dun[BLK_CRYPTO_DUN_ARRAY_SIZE]; if (!!bc != fscrypt_inode_uses_inline_crypto(inode)) return false; if (!bc) return true; /* * Comparing the key pointers is good enough, as all I/O for each key * uses the same pointer. I.e., there's currently no need to support * merging requests where the keys are the same but the pointers differ. */ if (bc->bc_key != inode->i_crypt_info->ci_enc_key.blk_key) return false; fscrypt_generate_dun(inode->i_crypt_info, next_lblk, next_dun); return bio_crypt_dun_is_contiguous(bc, bio->bi_iter.bi_size, next_dun); } EXPORT_SYMBOL_GPL(fscrypt_mergeable_bio); /** * fscrypt_mergeable_bio_bh() - test whether data can be added to a bio * @bio: the bio being built up * @next_bh: the next buffer_head for which I/O will be submitted * * Same as fscrypt_mergeable_bio(), except this takes a buffer_head instead of * an inode and block number directly. * * Return: true iff the I/O is mergeable */ bool fscrypt_mergeable_bio_bh(struct bio *bio, const struct buffer_head *next_bh) { const struct inode *inode; u64 next_lblk; if (!bh_get_inode_and_lblk_num(next_bh, &inode, &next_lblk)) return !bio->bi_crypt_context; return fscrypt_mergeable_bio(bio, inode, next_lblk); } EXPORT_SYMBOL_GPL(fscrypt_mergeable_bio_bh); /** * fscrypt_dio_supported() - check whether DIO (direct I/O) is supported on an * inode, as far as encryption is concerned * @inode: the inode in question * * Return: %true if there are no encryption constraints that prevent DIO from * being supported; %false if DIO is unsupported. (Note that in the * %true case, the filesystem might have other, non-encryption-related * constraints that prevent DIO from actually being supported. Also, on * encrypted files the filesystem is still responsible for only allowing * DIO when requests are filesystem-block-aligned.) */ bool fscrypt_dio_supported(struct inode *inode) { int err; /* If the file is unencrypted, no veto from us. */ if (!fscrypt_needs_contents_encryption(inode)) return true; /* * We only support DIO with inline crypto, not fs-layer crypto. * * To determine whether the inode is using inline crypto, we have to set * up the key if it wasn't already done. This is because in the current * design of fscrypt, the decision of whether to use inline crypto or * not isn't made until the inode's encryption key is being set up. In * the DIO read/write case, the key will always be set up already, since * the file will be open. But in the case of statx(), the key might not * be set up yet, as the file might not have been opened yet. */ err = fscrypt_require_key(inode); if (err) { /* * Key unavailable or couldn't be set up. This edge case isn't * worth worrying about; just report that DIO is unsupported. */ return false; } return fscrypt_inode_uses_inline_crypto(inode); } EXPORT_SYMBOL_GPL(fscrypt_dio_supported); /** * fscrypt_limit_io_blocks() - limit I/O blocks to avoid discontiguous DUNs * @inode: the file on which I/O is being done * @lblk: the block at which the I/O is being started from * @nr_blocks: the number of blocks we want to submit starting at @lblk * * Determine the limit to the number of blocks that can be submitted in a bio * targeting @lblk without causing a data unit number (DUN) discontiguity. * * This is normally just @nr_blocks, as normally the DUNs just increment along * with the logical blocks. (Or the file is not encrypted.) * * In rare cases, fscrypt can be using an IV generation method that allows the * DUN to wrap around within logically contiguous blocks, and that wraparound * will occur. If this happens, a value less than @nr_blocks will be returned * so that the wraparound doesn't occur in the middle of a bio, which would * cause encryption/decryption to produce wrong results. * * Return: the actual number of blocks that can be submitted */ u64 fscrypt_limit_io_blocks(const struct inode *inode, u64 lblk, u64 nr_blocks) { const struct fscrypt_inode_info *ci; u32 dun; if (!fscrypt_inode_uses_inline_crypto(inode)) return nr_blocks; if (nr_blocks <= 1) return nr_blocks; ci = inode->i_crypt_info; if (!(fscrypt_policy_flags(&ci->ci_policy) & FSCRYPT_POLICY_FLAG_IV_INO_LBLK_32)) return nr_blocks; /* With IV_INO_LBLK_32, the DUN can wrap around from U32_MAX to 0. */ dun = ci->ci_hashed_ino + lblk; return min_t(u64, nr_blocks, (u64)U32_MAX + 1 - dun); } EXPORT_SYMBOL_GPL(fscrypt_limit_io_blocks);