From: Mauro Carvalho Chehab [mailto:mchehab+huawei@kernel.org]
Sent: Wednesday, July 28, 2021 2:47 PM
Em Mon, 26 Jul 2021 18:36:59 +0200
Roberto Sassu [off-list ref] escreveu:

quoted

Add more information about remote attestation with IMA and DIGLIM in
Documentation/security/diglim/remote_attestation.rst.

Signed-off-by: Roberto Sassu <roberto.sassu@huawei.com>
---
 Documentation/security/diglim/index.rst       |  1 +
 .../security/diglim/remote_attestation.rst    | 87 +++++++++++++++++++
 MAINTAINERS                                   |  1 +
 3 files changed, 89 insertions(+)
 create mode 100644 Documentation/security/diglim/remote_attestation.rst

diff --git a/Documentation/security/diglim/index.rst

b/Documentation/security/diglim/index.rst

quoted

index 4771134c2f0d..0f28c5ad71c0 100644

--- a/Documentation/security/diglim/index.rst
+++ b/Documentation/security/diglim/index.rst

@@ -10,3 +10,4 @@ Digest Lists Integrity Module (DIGLIM)
    introduction
    architecture
    implementation
+   remote_attestation

diff --git a/Documentation/security/diglim/remote_attestation.rst

b/Documentation/security/diglim/remote_attestation.rst

quoted

new file mode 100644
index 000000000000..83fd7581c460

--- /dev/null
+++ b/Documentation/security/diglim/remote_attestation.rst

@@ -0,0 +1,87 @@
+.. SPDX-License-Identifier: GPL-2.0
+
+Remote Attestation
+==================
+
+When a digest list is added or deleted through the ``digest_list_add`` or
+``digest_list_del`` interfaces, its buffer is sent to the IMA function
+``ima_measure_critical_data()``. The primary reason for it is to calculate
+the buffer digest, so that the digest list itself is searchable in the hash
+table.
+
+``ima_measure_critical_data()`` can be also used to create a new
+measurement entry each time this function is called, if there is an
+appropriate rule in the IMA policy. Given that this function is called
+during an addition or deletion of a digest list, a remote verifier can
+infer from the measurement list precise information about what has been
+uploaded to the kernel.
+
+To enable this functionality, the following rule must be added to the IMA
+policy:
+
+::

As commented on other patches at this series, you can merge :: at the
previous text line, e. g.:

	policy::

does the same as:

	policy:

	::

but it is nicer for text-only readers, IMO.

Ok, will change in the next version of the patch set.

Thanks

Roberto

HUAWEI TECHNOLOGIES Duesseldorf GmbH, HRB 56063
Managing Director: Li Peng, Li Jian, Shi Yanli

quoted

+
+ measure func=CRITICAL_DATA label=diglim
+
+
+When a file is uploaded, the workflow and the resulting IMA measurement
+list are:
+
+.. code-block:: bash
+
+ # echo $PWD/0-file_list-compact-cat >

/sys/kernel/security/integrity/diglim/digest_list_add

quoted

+ # echo $PWD/0-file_list-compact-cat >

/sys/kernel/security/integrity/diglim/digest_list_del

quoted

+ # cat /sys/kernel/security/integrity/ima/ascii_runtime_measurements
+ ...
+ 10 <template digest> ima-buf sha256:<buffer digest> add_file_0-file_list-

compact-cat <buffer>

quoted

+ 10 <template digest> ima-buf sha256:<buffer digest> del_file_0-file_list-

compact-cat <buffer>

quoted

+
+When a buffer is uploaded, the workflow and the resulting IMA

measurement

quoted

+list are:
+
+.. code-block:: bash
+
+ # echo 0-file_list-compact-cat >

/sys/kernel/security/integrity/diglim/digest_label

quoted

+ # cat 0-file_list-compact-cat >

/sys/kernel/security/integrity/diglim/digest_list_add

quoted

+ # echo 0-file_list-compact-cat >

/sys/kernel/security/integrity/diglim/digest_label

quoted

+ # cat 0-file_list-compact-cat >

/sys/kernel/security/integrity/diglim/digest_list_del

quoted

+ # cat /sys/kernel/security/integrity/ima/ascii_runtime_measurements
+ ...
+ 10 <template digest> ima-buf sha256:<buffer digest> add_buffer_0-

file_list-compact-cat <buffer>

quoted

+ 10 <template digest> ima-buf sha256:<buffer digest> del_buffer_0-file_list-

compact-cat <buffer>

quoted

+
+In the second case, the digest list label must be set explicitly, as the
+kernel cannot determine it by itself (in the first case it is derived from
+the name of the file uploaded).
+
+The confirmation that the digest list has been processed by IMA can be
+obtained by reading the ASCII representation of the digest list:
+
+.. code-block:: bash
+
+ # cat /sys/kernel/security/integrity/diglim/digest_lists_loaded/sha256-

<digest list digest>-0-file_list-compact-cat.ascii

quoted

+ actions: 1, version: 1, algo: sha256, type: 2, modifiers: 1, count: 1, datalen:

32

quoted

+

87e5bd81850e11eeec2d3bb696b626b2a7f45673241cbbd64769c83580432869

quoted

+
+In this output, ``actions`` is set to 1

(``COMPACT_ACTION_IMA_MEASURED``

quoted

+bit set).
+
+
+DIGLIM guarantees that the information reported in the IMA measurement

list

quoted

+is complete. If digest list loading is not recorded, digest query results
+are ignored by IMA. If the addition was recorded, deletion can be

performed

quoted

+only if also the deletion is recorded. This can be seen in the following
+sequence of commands:
+
+.. code-block:: bash
+
+ # echo 0-file_list-compact-cat >

/sys/kernel/security/integrity/diglim/digest_label

quoted

+ # cat 0-file_list-compact-cat >

/sys/kernel/security/integrity/diglim/digest_list_add

quoted

+ # echo 0-file_list-compact-cat >

/sys/kernel/security/integrity/diglim/digest_label

quoted

+ # /tmp/cat 0-file_list-compact-cat >

/sys/kernel/security/integrity/diglim/digest_list_del

quoted

+ diglim: actions mismatch, add: 1, del: 0
+ diglim: unable to upload generated digest list
+ /tmp/cat: write error: Invalid argument
+
+Digest list measurement is avoided with the execution of ``/tmp/cat``, for
+which a dont_measure rule was previously added in the IMA policy.

diff --git a/MAINTAINERS b/MAINTAINERS
index 0672128fae7f..a7c502685109 100644
--- a/MAINTAINERS
+++ b/MAINTAINERS

@@ -5461,6 +5461,7 @@ F:

	Documentation/security/diglim/architecture.rst

quoted

 F:	Documentation/security/diglim/implementation.rst
 F:	Documentation/security/diglim/index.rst
 F:	Documentation/security/diglim/introduction.rst
+F:	Documentation/security/diglim/remote_attestation.rst
 F:	include/linux/diglim.h
 F:	include/uapi/linux/diglim.h
 F:	security/integrity/diglim/diglim.h