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SubjectRe: [RFC][PATCH v2 02/12] diglim: Basic definitions
Em Mon, 26 Jul 2021 18:36:50 +0200
Roberto Sassu <roberto.sassu@huawei.com> escreveu:

> Introduce the basic definitions, exported to user space, to use digest
> lists. The definitions, added to include/uapi/linux/diglim.h, are
> documented in Documentation/security/diglim/implementation.rst.
>
> Signed-off-by: Roberto Sassu <roberto.sassu@huawei.com>
> ---
> .../security/diglim/implementation.rst | 97 +++++++++++++++++++
> Documentation/security/diglim/index.rst | 1 +
> MAINTAINERS | 2 +
> include/uapi/linux/diglim.h | 51 ++++++++++
> 4 files changed, 151 insertions(+)
> create mode 100644 Documentation/security/diglim/implementation.rst
> create mode 100644 include/uapi/linux/diglim.h
>
> diff --git a/Documentation/security/diglim/implementation.rst b/Documentation/security/diglim/implementation.rst
> new file mode 100644
> index 000000000000..59a180b3bb3f
> --- /dev/null
> +++ b/Documentation/security/diglim/implementation.rst
> @@ -0,0 +1,97 @@
> +.. SPDX-License-Identifier: GPL-2.0
> +
> +Implementation
> +==============
> +
> +This section describes the implementation of DIGLIM.
> +
> +
> +Basic Definitions
> +-----------------
> +
> +This section introduces the basic definitions required to use DIGLIM.
> +
> +
> +Compact Digest List Format
> +~~~~~~~~~~~~~~~~~~~~~~~~~~
> +
> +.. kernel-doc:: include/uapi/linux/diglim.h
> + :identifiers: compact_list_hdr
> +
> +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 DIGLIM 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 DIGLIM 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 which digests have been uploaded to the
> +kernel.
> +
> +
> +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/Documentation/security/diglim/index.rst b/Documentation/security/diglim/index.rst
> index 0fc5ab019bc0..4771134c2f0d 100644
> --- a/Documentation/security/diglim/index.rst
> +++ b/Documentation/security/diglim/index.rst
> @@ -9,3 +9,4 @@ Digest Lists Integrity Module (DIGLIM)
>
> introduction
> architecture
> + implementation
> diff --git a/MAINTAINERS b/MAINTAINERS
> index c914dadd7e65..f61f5239468a 100644
> --- a/MAINTAINERS
> +++ b/MAINTAINERS
> @@ -5458,8 +5458,10 @@ 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/diglim/architecture.rst
> +F: Documentation/security/diglim/implementation.rst
> F: Documentation/security/diglim/index.rst
> F: Documentation/security/diglim/introduction.rst
> +F: include/uapi/linux/diglim.h
>
> DIOLAN U2C-12 I2C DRIVER
> M: Guenter Roeck <linux@roeck-us.net>
> diff --git a/include/uapi/linux/diglim.h b/include/uapi/linux/diglim.h
> new file mode 100644
> index 000000000000..8a33d1f0fefb
> --- /dev/null
> +++ b/include/uapi/linux/diglim.h
> @@ -0,0 +1,51 @@
> +/* 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>
> + *
> + * DIGLIM definitions exported to user space, useful for generating digest
> + * lists.
> + */
> +
> +#ifndef _UAPI__LINUX_DIGLIM_H
> +#define _UAPI__LINUX_DIGLIM_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 - header of the following concatenated digests
> + * @version: version of the digest list
> + * @_reserved: field reserved for future use
> + * @type: type of digest list among enum compact_types
> + * @modifiers: additional attributes among (1 << enum compact_modifiers)
> + * @algo: digest algorithm
> + * @count: number of digests
> + * @datalen: length of concatenated digests
> + *
> + * A digest list is a set of blocks composed by struct compact_list_hdr and
> + * the following concatenated digests.
> + */
> +struct compact_list_hdr {
> + __u8 version;
> + __u8 _reserved;
> + __le16 type;
> + __le16 modifiers;
> + __le16 algo;
> + __le32 count;
> + __le32 datalen;
> +} __packed;
> +#endif /*_UAPI__LINUX_DIGLIM_H*/

Besides Greg's notes, I'm wondering why to enforce a particular
endness here. I mean, this is uAPI. I would expect it to use the
CPU endianness instead, in order to avoid uneeded conversions.

Thanks,
Mauro

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