// 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 <linux/blk-crypto.h>
#include <linux/blkdev.h>
#include <linux/buffer_head.h>
#include <linux/sched/mm.h>
#include <linux/slab.h>
#include <linux/uio.h>
#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 folio *folio = bh->b_folio;
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 = folio_mapping(folio);
if (!mapping)
return false;
inode = mapping->host;
*inode_ret = inode;
*lblk_num_ret = ((u64)folio->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);
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