[RFC][PATCH 03/12] digest_lists: Basic definitions

Roberto Sassu
2021-06-25T16:56:43Z

This patch introduces the basic definitions, exported to user space, to use
digest lists. The definitions, added to include/uapi/linux/digest_lists.h,
are documented in Documentation/security/digest_lists.rst.

Signed-off-by: Roberto Sassu <roberto.sassu@huawei.com>
---
Documentation/security/digest_lists.rst | 119 ++++++++++++++++++++++++
MAINTAINERS | 1 +
include/uapi/linux/digest_lists.h | 43 +++++++++
3 files changed, 163 insertions(+)
create mode 100644 include/uapi/linux/digest_lists.h

diff --git a/Documentation/security/digest_lists.rst b/Documentation/security/digest_lists.rst
index 8980be7836f8..995260294783 100644
--- a/Documentation/security/digest_lists.rst
+++ b/Documentation/security/digest_lists.rst
@@ -226,3 +226,122 @@ the digest list) (step 5).

Finally, digests can be searched from user space through a securityfs file
(step 6) or by the kernel itself.
+
+
+Implementation
+==============
+
+This section describes the implementation of Huawei Digest Lists.
+
+
+Basic Definitions
+-----------------
+
+This section introduces the basic definitions required to use digest lists.
+
+
+Compact Digest List Format
+~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+Compact digest lists consist of one or multiple headers defined as:
+
+::
+
+ struct compact_list_hdr {
+ __u8 version;
+ __u8 _reserved;
+ __le16 type;
+ __le16 modifiers;
+ __le16 algo;
+ __le32 count;
+ __le32 datalen;
+ } __packed;
+
+which characterize the subsequent block of concatenated digests.
+
+The ``algo`` field specifies the algorithm used to calculate the digest.
+
+The ``count`` field specifies how many digests are stored in the subsequent
+block of digests.
+
+The ``datalen`` field specifies the length of the subsequent block of
+digests (it is redundant, it is the same as
+``hash_digest_size[algo] * count``).
+
+
+Compact Types
+.............
+
+Digests can be of different types:
+
+- ``COMPACT_PARSER``: digests of executables which are given the ability to
+ parse digest lists not in the compact format and to upload to the kernel
+ the digest list converted to the compact format;
+- ``COMPACT_FILE``: digests of regular files;
+- ``COMPACT_METADATA``: digests of file metadata (e.g. the digest
+ calculated by EVM to verify a portable signature);
+- ``COMPACT_DIGEST_LIST``: digests of digest lists (only used internally by
+ the kernel).
+
+Different users of Huawei Digest Lists might query digests with different
+compact types. For example, IMA would be interested in COMPACT_FILE, as it
+deals with regular files, while EVM would be interested in
+COMPACT_METADATA, as it verifies file metadata.
+
+
+Compact Modifiers
+.................
+
+Digests can also have specific attributes called modifiers (bit position):
+
+- ``COMPACT_MOD_IMMUTABLE``: file content or metadata should not be
+ modifiable.
+
+IMA might use this information to deny open for writing, or EVM to deny
+setxattr operations.
+
+
+Actions
+.......
+
+This section defines a set of possible actions that have been executed on
+the digest lists (bit position):
+
+- ``COMPACT_ACTION_IMA_MEASURED``: the digest list has been measured by
+ IMA;
+- ``COMPACT_ACTION_IMA_APPRAISED``: the digest list has been successfully
+ appraised by IMA;
+- ``COMPACT_ACTION_IMA_APPRAISED_DIGSIG``: the digest list has been
+ successfully appraised by IMA by verifying a digital signature.
+
+This information might help users of Huawei Digest Lists to decide whether
+to use the result of a queried digest.
+
+For example, if a digest belongs to a digest list that was not measured
+before, IMA should ignore the result of the query as the measurement list
+sent to remote verifiers would lack how the database was populated.
+
+
+Compact Digest List Example
+...........................
+
+::
+
+ version: 1, type: 2, modifiers: 0 algo: 4, count: 3, datalen: 96
+ <SHA256 digest1><SHA256 digest2><SHA256 digest3>
+ version: 1, type: 3, modifiers: 1 algo: 6, count: 2, datalen: 128
+ <SHA512 digest1><SHA512 digest2>
+
+This digest list consists of two blocks. The first block contains three
+SHA256 digests of regular files. The second block contains two SHA512
+digests of immutable metadata.
+
+
+Compact Digest List Operations
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+Finally, this section defines the possible operations that can be performed
+with digest lists:
+
+- ``DIGEST_LIST_ADD``: the digest list is being added;
+- ``DIGEST_LIST_DEL``: the digest list is being deleted.
diff --git a/MAINTAINERS b/MAINTAINERS
index cba3d82fee43..ccf555862673 100644
--- a/MAINTAINERS
+++ b/MAINTAINERS
@@ -8387,6 +8387,7 @@ L: linux-integrity@vger.kernel.org
S: Supported
T: git://git.kernel.org/pub/scm/linux/kernel/git/zohar/linux-integrity.git
F: Documentation/security/digest_lists.rst
+F: uapi/linux/digest_lists.h

HUAWEI ETHERNET DRIVER
M: Bin Luo <luobin9@huawei.com>
diff --git a/include/uapi/linux/digest_lists.h b/include/uapi/linux/digest_lists.h
new file mode 100644
index 000000000000..9545a8aaa231
--- /dev/null
+++ b/include/uapi/linux/digest_lists.h
@@ -0,0 +1,43 @@
+/* SPDX-License-Identifier: GPL-2.0 WITH Linux-syscall-note */
+/*
+ * Copyright (C) 2017-2021 Huawei Technologies Duesseldorf GmbH
+ *
+ * Author: Roberto Sassu <roberto.sassu@huawei.com>
+ *
+ * This program is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU General Public License as
+ * published by the Free Software Foundation, version 2 of the
+ * License.
+ *
+ * File: digest_lists.h
+ * Digest list definitions exported to user space.
+ */
+
+#ifndef _UAPI__LINUX_DIGEST_LISTS_H
+#define _UAPI__LINUX_DIGEST_LISTS_H
+
+#include <linux/types.h>
+#include <linux/hash_info.h>
+
+enum compact_types { COMPACT_KEY, COMPACT_PARSER, COMPACT_FILE,
+ COMPACT_METADATA, COMPACT_DIGEST_LIST, COMPACT__LAST };
+
+enum compact_modifiers { COMPACT_MOD_IMMUTABLE, COMPACT_MOD__LAST };
+
+enum compact_actions { COMPACT_ACTION_IMA_MEASURED,
+ COMPACT_ACTION_IMA_APPRAISED,
+ COMPACT_ACTION_IMA_APPRAISED_DIGSIG,
+ COMPACT_ACTION__LAST };
+
+enum ops { DIGEST_LIST_ADD, DIGEST_LIST_DEL, DIGEST_LIST_OP__LAST };
+
+struct compact_list_hdr {
+ __u8 version;
+ __u8 _reserved;
+ __le16 type;
+ __le16 modifiers;
+ __le16 algo;
+ __le32 count;
+ __le32 datalen;
+} __packed;
+#endif
--
2.25.1