From: Eric Biggers <ebiggers@xxxxxxxxxx>
Document the format of verity files on ext4, and the corresponding inode
and superblock flags.
Reviewed-by: Theodore Ts'o <tytso@xxxxxxx>
Signed-off-by: Eric Biggers <ebiggers@xxxxxxxxxx>
---
Documentation/filesystems/ext4/inodes.rst | 6 ++-
Documentation/filesystems/ext4/overview.rst | 1 +
Documentation/filesystems/ext4/super.rst | 2 +
Documentation/filesystems/ext4/verity.rst | 41 +++++++++++++++++++++
4 files changed, 48 insertions(+), 2 deletions(-)
create mode 100644 Documentation/filesystems/ext4/verity.rst
diff --git a/Documentation/filesystems/ext4/inodes.rst b/Documentation/filesystems/ext4/inodes.rst
index 6bd35e506b6fd..e851e6ca31fa0 100644
--- a/Documentation/filesystems/ext4/inodes.rst
+++ b/Documentation/filesystems/ext4/inodes.rst
@@ -277,6 +277,8 @@ The ``i_flags`` field is a combination of these values:
- This is a huge file (EXT4\_HUGE\_FILE\_FL).
* - 0x80000
- Inode uses extents (EXT4\_EXTENTS\_FL).
+ * - 0x100000
+ - Verity protected file (EXT4\_VERITY\_FL).
* - 0x200000
- Inode stores a large extended attribute value in its data blocks
(EXT4\_EA\_INODE\_FL).
@@ -299,9 +301,9 @@ The ``i_flags`` field is a combination of these values:
- Reserved for ext4 library (EXT4\_RESERVED\_FL).
* -
- Aggregate flags:
- * - 0x4BDFFF
+ * - 0x705BDFFF
- User-visible flags.
- * - 0x4B80FF
+ * - 0x604BC0FF
- User-modifiable flags. Note that while EXT4\_JOURNAL\_DATA\_FL and
EXT4\_EXTENTS\_FL can be set with setattr, they are not in the kernel's
EXT4\_FL\_USER\_MODIFIABLE mask, since it needs to handle the setting of
diff --git a/Documentation/filesystems/ext4/overview.rst b/Documentation/filesystems/ext4/overview.rst
index cbab18baba121..123ebfde47ee1 100644
--- a/Documentation/filesystems/ext4/overview.rst
+++ b/Documentation/filesystems/ext4/overview.rst
@@ -24,3 +24,4 @@ order.
.. include:: bigalloc.rst
.. include:: inlinedata.rst
.. include:: eainode.rst
+.. include:: verity.rst
diff --git a/Documentation/filesystems/ext4/super.rst b/Documentation/filesystems/ext4/super.rst
index 04ff079a2acf8..6eae920548278 100644
--- a/Documentation/filesystems/ext4/super.rst
+++ b/Documentation/filesystems/ext4/super.rst
@@ -696,6 +696,8 @@ the following:
(RO\_COMPAT\_READONLY)
* - 0x2000
- Filesystem tracks project quotas. (RO\_COMPAT\_PROJECT)
+ * - 0x8000
+ - Verity inodes may be present on the filesystem. (RO\_COMPAT\_VERITY)
.. _super_def_hash:
diff --git a/Documentation/filesystems/ext4/verity.rst b/Documentation/filesystems/ext4/verity.rst
new file mode 100644
index 0000000000000..3e4c0ee0e0683
--- /dev/null
+++ b/Documentation/filesystems/ext4/verity.rst
@@ -0,0 +1,41 @@
+.. SPDX-License-Identifier: GPL-2.0
+
+Verity files
+------------
+
+ext4 supports fs-verity, which is a filesystem feature that provides
+Merkle tree based hashing for individual readonly files. Most of
+fs-verity is common to all filesystems that support it; see
+:ref:`Documentation/filesystems/fsverity.rst <fsverity>` for the
+fs-verity documentation. However, the on-disk layout of the verity
+metadata is filesystem-specific. On ext4, the verity metadata is
+stored after the end of the file data itself, in the following format:
+
+- Zero-padding to the next 65536-byte boundary. This padding need not
+ actually be allocated on-disk, i.e. it may be a hole.
+
+- The Merkle tree, as documented in
+ :ref:`Documentation/filesystems/fsverity.rst
+ <fsverity_merkle_tree>`, with the tree levels stored in order from
+ root to leaf, and the tree blocks within each level stored in their
+ natural order.
+
+- Zero-padding to the next filesystem block boundary.
+
+- The verity descriptor, as documented in
+ :ref:`Documentation/filesystems/fsverity.rst <fsverity_descriptor>`,
+ with optionally appended signature blob.
+
+- Zero-padding to the next offset that is 4 bytes before a filesystem
+ block boundary.
+
+- The size of the verity descriptor in bytes, as a 4-byte little
+ endian integer.
+
+Verity inodes have EXT4_VERITY_FL set, and they must use extents, i.e.
+EXT4_EXTENTS_FL must be set and EXT4_INLINE_DATA_FL must be clear.
+They can have EXT4_ENCRYPT_FL set, in which case the verity metadata
+is encrypted as well as the data itself.
+
+Verity files cannot have blocks allocated past the end of the verity
+metadata.
--
2.22.0
