From ea08eeccae9297f7aabd2ef7f0c2517ac4549acc Mon Sep 17 00:00:00 2001
From: hc <hc@nodka.com>
Date: Tue, 20 Feb 2024 01:18:26 +0000
Subject: [PATCH] write in 30M

---
 kernel/Documentation/filesystems/fscrypt.rst |  119 +++++++++++++++++++++++++++++++++--------------------------
 1 files changed, 67 insertions(+), 52 deletions(-)

diff --git a/kernel/Documentation/filesystems/fscrypt.rst b/kernel/Documentation/filesystems/fscrypt.rst
index 7f9a372..936fae0 100644
--- a/kernel/Documentation/filesystems/fscrypt.rst
+++ b/kernel/Documentation/filesystems/fscrypt.rst
@@ -176,11 +176,11 @@
 
 Each encrypted directory tree is protected by a *master key*.  Master
 keys can be up to 64 bytes long, and must be at least as long as the
-greater of the key length needed by the contents and filenames
-encryption modes being used.  For example, if AES-256-XTS is used for
-contents encryption, the master key must be 64 bytes (512 bits).  Note
-that the XTS mode is defined to require a key twice as long as that
-required by the underlying block cipher.
+greater of the security strength of the contents and filenames
+encryption modes being used.  For example, if any AES-256 mode is
+used, the master key must be at least 256 bits, i.e. 32 bytes.  A
+stricter requirement applies if the key is used by a v1 encryption
+policy and AES-256-XTS is used; such keys must be 64 bytes.
 
 To "unlock" an encrypted directory tree, userspace must provide the
 appropriate master key.  There can be any number of master keys, each
@@ -366,8 +366,8 @@
 -------------------
 
 For file contents, each filesystem block is encrypted independently.
-Currently, only the case where the filesystem block size is equal to
-the system's page size (usually 4096 bytes) is supported.
+Starting from Linux kernel 5.5, encryption of filesystems with block
+size less than system's page size is supported.
 
 Each block's IV is set to the logical block number within the file as
 a little endian number, except that:
@@ -436,9 +436,9 @@
 
 The FS_IOC_SET_ENCRYPTION_POLICY ioctl sets an encryption policy on an
 empty directory or verifies that a directory or regular file already
-has the specified encryption policy.  It takes in a pointer to a
-:c:type:`struct fscrypt_policy_v1` or a :c:type:`struct
-fscrypt_policy_v2`, defined as follows::
+has the specified encryption policy.  It takes in a pointer to
+struct fscrypt_policy_v1 or struct fscrypt_policy_v2, defined as
+follows::
 
     #define FSCRYPT_POLICY_V1               0
     #define FSCRYPT_KEY_DESCRIPTOR_SIZE     8
@@ -464,11 +464,11 @@
 
 This structure must be initialized as follows:
 
-- ``version`` must be FSCRYPT_POLICY_V1 (0) if the struct is
-  :c:type:`fscrypt_policy_v1` or FSCRYPT_POLICY_V2 (2) if the struct
-  is :c:type:`fscrypt_policy_v2`.  (Note: we refer to the original
-  policy version as "v1", though its version code is really 0.)  For
-  new encrypted directories, use v2 policies.
+- ``version`` must be FSCRYPT_POLICY_V1 (0) if
+  struct fscrypt_policy_v1 is used or FSCRYPT_POLICY_V2 (2) if
+  struct fscrypt_policy_v2 is used. (Note: we refer to the original
+  policy version as "v1", though its version code is really 0.)
+  For new encrypted directories, use v2 policies.
 
 - ``contents_encryption_mode`` and ``filenames_encryption_mode`` must
   be set to constants from ``<linux/fscrypt.h>`` which identify the
@@ -508,9 +508,9 @@
   replaced with ``master_key_identifier``, which is longer and cannot
   be arbitrarily chosen.  Instead, the key must first be added using
   `FS_IOC_ADD_ENCRYPTION_KEY`_.  Then, the ``key_spec.u.identifier``
-  the kernel returned in the :c:type:`struct fscrypt_add_key_arg` must
-  be used as the ``master_key_identifier`` in the :c:type:`struct
-  fscrypt_policy_v2`.
+  the kernel returned in the struct fscrypt_add_key_arg must
+  be used as the ``master_key_identifier`` in
+  struct fscrypt_policy_v2.
 
 If the file is not yet encrypted, then FS_IOC_SET_ENCRYPTION_POLICY
 verifies that the file is an empty directory.  If so, the specified
@@ -590,7 +590,7 @@
 The FS_IOC_GET_ENCRYPTION_POLICY_EX ioctl retrieves the encryption
 policy, if any, for a directory or regular file.  No additional
 permissions are required beyond the ability to open the file.  It
-takes in a pointer to a :c:type:`struct fscrypt_get_policy_ex_arg`,
+takes in a pointer to struct fscrypt_get_policy_ex_arg,
 defined as follows::
 
     struct fscrypt_get_policy_ex_arg {
@@ -637,9 +637,8 @@
 encryption policy, if any, for a directory or regular file.  However,
 unlike `FS_IOC_GET_ENCRYPTION_POLICY_EX`_,
 FS_IOC_GET_ENCRYPTION_POLICY only supports the original policy
-version.  It takes in a pointer directly to a :c:type:`struct
-fscrypt_policy_v1` rather than a :c:type:`struct
-fscrypt_get_policy_ex_arg`.
+version.  It takes in a pointer directly to struct fscrypt_policy_v1
+rather than struct fscrypt_get_policy_ex_arg.
 
 The error codes for FS_IOC_GET_ENCRYPTION_POLICY are the same as those
 for FS_IOC_GET_ENCRYPTION_POLICY_EX, except that
@@ -680,8 +679,7 @@
 encrypted using that key appear "unlocked", i.e. in plaintext form.
 It can be executed on any file or directory on the target filesystem,
 but using the filesystem's root directory is recommended.  It takes in
-a pointer to a :c:type:`struct fscrypt_add_key_arg`, defined as
-follows::
+a pointer to struct fscrypt_add_key_arg, defined as follows::
 
     struct fscrypt_add_key_arg {
             struct fscrypt_key_specifier key_spec;
@@ -710,17 +708,16 @@
             __u8 raw[];
     };
 
-:c:type:`struct fscrypt_add_key_arg` must be zeroed, then initialized
+struct fscrypt_add_key_arg must be zeroed, then initialized
 as follows:
 
 - If the key is being added for use by v1 encryption policies, then
   ``key_spec.type`` must contain FSCRYPT_KEY_SPEC_TYPE_DESCRIPTOR, and
   ``key_spec.u.descriptor`` must contain the descriptor of the key
   being added, corresponding to the value in the
-  ``master_key_descriptor`` field of :c:type:`struct
-  fscrypt_policy_v1`.  To add this type of key, the calling process
-  must have the CAP_SYS_ADMIN capability in the initial user
-  namespace.
+  ``master_key_descriptor`` field of struct fscrypt_policy_v1.
+  To add this type of key, the calling process must have the
+  CAP_SYS_ADMIN capability in the initial user namespace.
 
   Alternatively, if the key is being added for use by v2 encryption
   policies, then ``key_spec.type`` must contain
@@ -737,12 +734,13 @@
 
 - ``key_id`` is 0 if the raw key is given directly in the ``raw``
   field.  Otherwise ``key_id`` is the ID of a Linux keyring key of
-  type "fscrypt-provisioning" whose payload is a :c:type:`struct
-  fscrypt_provisioning_key_payload` whose ``raw`` field contains the
-  raw key and whose ``type`` field matches ``key_spec.type``.  Since
-  ``raw`` is variable-length, the total size of this key's payload
-  must be ``sizeof(struct fscrypt_provisioning_key_payload)`` plus the
-  raw key size.  The process must have Search permission on this key.
+  type "fscrypt-provisioning" whose payload is
+  struct fscrypt_provisioning_key_payload whose ``raw`` field contains
+  the raw key and whose ``type`` field matches ``key_spec.type``.
+  Since ``raw`` is variable-length, the total size of this key's
+  payload must be ``sizeof(struct fscrypt_provisioning_key_payload)``
+  plus the raw key size.  The process must have Search permission on
+  this key.
 
   Most users should leave this 0 and specify the raw key directly.
   The support for specifying a Linux keyring key is intended mainly to
@@ -860,8 +858,8 @@
 encryption key from the filesystem, and possibly removes the key
 itself.  It can be executed on any file or directory on the target
 filesystem, but using the filesystem's root directory is recommended.
-It takes in a pointer to a :c:type:`struct fscrypt_remove_key_arg`,
-defined as follows::
+It takes in a pointer to struct fscrypt_remove_key_arg, defined
+as follows::
 
     struct fscrypt_remove_key_arg {
             struct fscrypt_key_specifier key_spec;
@@ -956,8 +954,8 @@
 The FS_IOC_GET_ENCRYPTION_KEY_STATUS ioctl retrieves the status of a
 master encryption key.  It can be executed on any file or directory on
 the target filesystem, but using the filesystem's root directory is
-recommended.  It takes in a pointer to a :c:type:`struct
-fscrypt_get_key_status_arg`, defined as follows::
+recommended.  It takes in a pointer to
+struct fscrypt_get_key_status_arg, defined as follows::
 
     struct fscrypt_get_key_status_arg {
             /* input */
@@ -1052,9 +1050,9 @@
 - Direct I/O is not supported on encrypted files.  Attempts to use
   direct I/O on such files will fall back to buffered I/O.
 
-- The fallocate operations FALLOC_FL_COLLAPSE_RANGE,
-  FALLOC_FL_INSERT_RANGE, and FALLOC_FL_ZERO_RANGE are not supported
-  on encrypted files and will fail with EOPNOTSUPP.
+- The fallocate operations FALLOC_FL_COLLAPSE_RANGE and
+  FALLOC_FL_INSERT_RANGE are not supported on encrypted files and will
+  fail with EOPNOTSUPP.
 
 - Online defragmentation of encrypted files is not supported.  The
   EXT4_IOC_MOVE_EXT and F2FS_IOC_MOVE_RANGE ioctls will fail with
@@ -1148,17 +1146,17 @@
 Encryption context
 ------------------
 
-An encryption policy is represented on-disk by a :c:type:`struct
-fscrypt_context_v1` or a :c:type:`struct fscrypt_context_v2`.  It is
-up to individual filesystems to decide where to store it, but normally
-it would be stored in a hidden extended attribute.  It should *not* be
+An encryption policy is represented on-disk by
+struct fscrypt_context_v1 or struct fscrypt_context_v2.  It is up to
+individual filesystems to decide where to store it, but normally it
+would be stored in a hidden extended attribute.  It should *not* be
 exposed by the xattr-related system calls such as getxattr() and
 setxattr() because of the special semantics of the encryption xattr.
 (In particular, there would be much confusion if an encryption policy
 were to be added to or removed from anything other than an empty
 directory.)  These structs are defined as follows::
 
-    #define FS_KEY_DERIVATION_NONCE_SIZE 16
+    #define FSCRYPT_FILE_NONCE_SIZE 16
 
     #define FSCRYPT_KEY_DESCRIPTOR_SIZE  8
     struct fscrypt_context_v1 {
@@ -1167,7 +1165,7 @@
             u8 filenames_encryption_mode;
             u8 flags;
             u8 master_key_descriptor[FSCRYPT_KEY_DESCRIPTOR_SIZE];
-            u8 nonce[FS_KEY_DERIVATION_NONCE_SIZE];
+            u8 nonce[FSCRYPT_FILE_NONCE_SIZE];
     };
 
     #define FSCRYPT_KEY_IDENTIFIER_SIZE  16
@@ -1178,7 +1176,7 @@
             u8 flags;
             u8 __reserved[4];
             u8 master_key_identifier[FSCRYPT_KEY_IDENTIFIER_SIZE];
-            u8 nonce[FS_KEY_DERIVATION_NONCE_SIZE];
+            u8 nonce[FSCRYPT_FILE_NONCE_SIZE];
     };
 
 The context structs contain the same information as the corresponding
@@ -1203,6 +1201,18 @@
 buffer.  Some filesystems, such as UBIFS, already use temporary
 buffers regardless of encryption.  Other filesystems, such as ext4 and
 F2FS, have to allocate bounce pages specially for encryption.
+
+Fscrypt is also able to use inline encryption hardware instead of the
+kernel crypto API for en/decryption of file contents.  When possible,
+and if directed to do so (by specifying the 'inlinecrypt' mount option
+for an ext4/F2FS filesystem), it adds encryption contexts to bios and
+uses blk-crypto to perform the en/decryption instead of making use of
+the above read/write path changes.  Of course, even if directed to
+make use of inline encryption, fscrypt will only be able to do so if
+either hardware inline encryption support is available for the
+selected encryption algorithm or CONFIG_BLK_INLINE_ENCRYPTION_FALLBACK
+is selected.  If neither is the case, fscrypt will fall back to using
+the above mentioned read/write path changes for en/decryption.
 
 Filename hashing and encoding
 -----------------------------
@@ -1237,8 +1247,8 @@
 filesystem-specific hash(es) needed for directory lookups.  This
 allows the filesystem to still, with a high degree of confidence, map
 the filename given in ->lookup() back to a particular directory entry
-that was previously listed by readdir().  See :c:type:`struct
-fscrypt_nokey_name` in the source for more details.
+that was previously listed by readdir().  See
+struct fscrypt_nokey_name in the source for more details.
 
 Note that the precise way that filenames are presented to userspace
 without the key is subject to change in the future.  It is only meant
@@ -1250,11 +1260,14 @@
 
 To test fscrypt, use xfstests, which is Linux's de facto standard
 filesystem test suite.  First, run all the tests in the "encrypt"
-group on the relevant filesystem(s).  For example, to test ext4 and
+group on the relevant filesystem(s).  One can also run the tests
+with the 'inlinecrypt' mount option to test the implementation for
+inline encryption support.  For example, to test ext4 and
 f2fs encryption using `kvm-xfstests
 <https://github.com/tytso/xfstests-bld/blob/master/Documentation/kvm-quickstart.md>`_::
 
     kvm-xfstests -c ext4,f2fs -g encrypt
+    kvm-xfstests -c ext4,f2fs -g encrypt -m inlinecrypt
 
 UBIFS encryption can also be tested this way, but it should be done in
 a separate command, and it takes some time for kvm-xfstests to set up
@@ -1276,6 +1289,7 @@
 kvm-xfstests, use the "encrypt" filesystem configuration::
 
     kvm-xfstests -c ext4/encrypt,f2fs/encrypt -g auto
+    kvm-xfstests -c ext4/encrypt,f2fs/encrypt -g auto -m inlinecrypt
 
 Because this runs many more tests than "-g encrypt" does, it takes
 much longer to run; so also consider using `gce-xfstests
@@ -1283,3 +1297,4 @@
 instead of kvm-xfstests::
 
     gce-xfstests -c ext4/encrypt,f2fs/encrypt -g auto
+    gce-xfstests -c ext4/encrypt,f2fs/encrypt -g auto -m inlinecrypt

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