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authorEric Biggers <ebiggers@google.com>2019-10-25 00:54:36 +0300
committerEric Biggers <ebiggers@google.com>2019-11-06 23:34:36 +0300
commitb103fb7653fff09e7a6fb6ba9398a41584e7ae36 (patch)
tree76a36a85c9d27f1a8e58e6cbf751844958ab1867 /fs/crypto/keysetup.c
parentff73c2c016f8569b728eb1e9ebfab383545e4d65 (diff)
downloadlinux-b103fb7653fff09e7a6fb6ba9398a41584e7ae36.tar.xz
fscrypt: add support for IV_INO_LBLK_64 policies
Inline encryption hardware compliant with the UFS v2.1 standard or with the upcoming version of the eMMC standard has the following properties: (1) Per I/O request, the encryption key is specified by a previously loaded keyslot. There might be only a small number of keyslots. (2) Per I/O request, the starting IV is specified by a 64-bit "data unit number" (DUN). IV bits 64-127 are assumed to be 0. The hardware automatically increments the DUN for each "data unit" of configurable size in the request, e.g. for each filesystem block. Property (1) makes it inefficient to use the traditional fscrypt per-file keys. Property (2) precludes the use of the existing DIRECT_KEY fscrypt policy flag, which needs at least 192 IV bits. Therefore, add a new fscrypt policy flag IV_INO_LBLK_64 which causes the encryption to modified as follows: - The encryption keys are derived from the master key, encryption mode number, and filesystem UUID. - The IVs are chosen as (inode_number << 32) | file_logical_block_num. For filenames encryption, file_logical_block_num is 0. Since the file nonces aren't used in the key derivation, many files may share the same encryption key. This is much more efficient on the target hardware. Including the inode number in the IVs and mixing the filesystem UUID into the keys ensures that data in different files is nevertheless still encrypted differently. Additionally, limiting the inode and block numbers to 32 bits and placing the block number in the low bits maintains compatibility with the 64-bit DUN convention (property (2) above). Since this scheme assumes that inode numbers are stable (which may preclude filesystem shrinking) and that inode and file logical block numbers are at most 32-bit, IV_INO_LBLK_64 will only be allowed on filesystems that meet these constraints. These are acceptable limitations for the cases where this format would actually be used. Note that IV_INO_LBLK_64 is an on-disk format, not an implementation. This patch just adds support for it using the existing filesystem layer encryption. A later patch will add support for inline encryption. Reviewed-by: Paul Crowley <paulcrowley@google.com> Co-developed-by: Satya Tangirala <satyat@google.com> Signed-off-by: Satya Tangirala <satyat@google.com> Signed-off-by: Eric Biggers <ebiggers@google.com>
Diffstat (limited to 'fs/crypto/keysetup.c')
-rw-r--r--fs/crypto/keysetup.c45
1 files changed, 35 insertions, 10 deletions
diff --git a/fs/crypto/keysetup.c b/fs/crypto/keysetup.c
index 28bc2da9be3c..f577bb6613f9 100644
--- a/fs/crypto/keysetup.c
+++ b/fs/crypto/keysetup.c
@@ -114,40 +114,54 @@ int fscrypt_set_derived_key(struct fscrypt_info *ci, const u8 *derived_key)
return PTR_ERR(tfm);
ci->ci_ctfm = tfm;
+ ci->ci_owns_key = true;
return 0;
}
static int setup_per_mode_key(struct fscrypt_info *ci,
- struct fscrypt_master_key *mk)
+ struct fscrypt_master_key *mk,
+ struct crypto_skcipher **tfms,
+ u8 hkdf_context, bool include_fs_uuid)
{
+ const struct inode *inode = ci->ci_inode;
+ const struct super_block *sb = inode->i_sb;
struct fscrypt_mode *mode = ci->ci_mode;
u8 mode_num = mode - available_modes;
struct crypto_skcipher *tfm, *prev_tfm;
u8 mode_key[FSCRYPT_MAX_KEY_SIZE];
+ u8 hkdf_info[sizeof(mode_num) + sizeof(sb->s_uuid)];
+ unsigned int hkdf_infolen = 0;
int err;
- if (WARN_ON(mode_num >= ARRAY_SIZE(mk->mk_mode_keys)))
+ if (WARN_ON(mode_num > __FSCRYPT_MODE_MAX))
return -EINVAL;
/* pairs with cmpxchg() below */
- tfm = READ_ONCE(mk->mk_mode_keys[mode_num]);
+ tfm = READ_ONCE(tfms[mode_num]);
if (likely(tfm != NULL))
goto done;
BUILD_BUG_ON(sizeof(mode_num) != 1);
+ BUILD_BUG_ON(sizeof(sb->s_uuid) != 16);
+ BUILD_BUG_ON(sizeof(hkdf_info) != 17);
+ hkdf_info[hkdf_infolen++] = mode_num;
+ if (include_fs_uuid) {
+ memcpy(&hkdf_info[hkdf_infolen], &sb->s_uuid,
+ sizeof(sb->s_uuid));
+ hkdf_infolen += sizeof(sb->s_uuid);
+ }
err = fscrypt_hkdf_expand(&mk->mk_secret.hkdf,
- HKDF_CONTEXT_PER_MODE_KEY,
- &mode_num, sizeof(mode_num),
+ hkdf_context, hkdf_info, hkdf_infolen,
mode_key, mode->keysize);
if (err)
return err;
- tfm = fscrypt_allocate_skcipher(mode, mode_key, ci->ci_inode);
+ tfm = fscrypt_allocate_skcipher(mode, mode_key, inode);
memzero_explicit(mode_key, mode->keysize);
if (IS_ERR(tfm))
return PTR_ERR(tfm);
/* pairs with READ_ONCE() above */
- prev_tfm = cmpxchg(&mk->mk_mode_keys[mode_num], NULL, tfm);
+ prev_tfm = cmpxchg(&tfms[mode_num], NULL, tfm);
if (prev_tfm != NULL) {
crypto_free_skcipher(tfm);
tfm = prev_tfm;
@@ -178,7 +192,19 @@ static int fscrypt_setup_v2_file_key(struct fscrypt_info *ci,
ci->ci_mode->friendly_name);
return -EINVAL;
}
- return setup_per_mode_key(ci, mk);
+ return setup_per_mode_key(ci, mk, mk->mk_direct_tfms,
+ HKDF_CONTEXT_DIRECT_KEY, false);
+ } else if (ci->ci_policy.v2.flags &
+ FSCRYPT_POLICY_FLAG_IV_INO_LBLK_64) {
+ /*
+ * IV_INO_LBLK_64: encryption keys are derived from (master_key,
+ * mode_num, filesystem_uuid), and inode number is included in
+ * the IVs. This format is optimized for use with inline
+ * encryption hardware compliant with the UFS or eMMC standards.
+ */
+ return setup_per_mode_key(ci, mk, mk->mk_iv_ino_lblk_64_tfms,
+ HKDF_CONTEXT_IV_INO_LBLK_64_KEY,
+ true);
}
err = fscrypt_hkdf_expand(&mk->mk_secret.hkdf,
@@ -302,8 +328,7 @@ static void put_crypt_info(struct fscrypt_info *ci)
if (ci->ci_direct_key)
fscrypt_put_direct_key(ci->ci_direct_key);
- else if (ci->ci_ctfm != NULL &&
- !fscrypt_is_direct_key_policy(&ci->ci_policy))
+ else if (ci->ci_owns_key)
crypto_free_skcipher(ci->ci_ctfm);
key = ci->ci_master_key;