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 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 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: + +:: + + 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 + # echo $PWD/0-file_list-compact-cat > /sys/kernel/security/integrity/diglim/digest_list_del + # 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> + 10 <template digest> ima-buf sha256:<buffer digest> del_file_0-file_list-compact-cat <buffer> + +When a buffer is uploaded, the workflow and the resulting IMA measurement +list are: + +.. code-block:: bash + + # echo 0-file_list-compact-cat > /sys/kernel/security/integrity/diglim/digest_label + # cat 0-file_list-compact-cat > /sys/kernel/security/integrity/diglim/digest_list_add + # echo 0-file_list-compact-cat > /sys/kernel/security/integrity/diglim/digest_label + # cat 0-file_list-compact-cat > /sys/kernel/security/integrity/diglim/digest_list_del + # 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> + 10 <template digest> ima-buf sha256:<buffer digest> del_buffer_0-file_list-compact-cat <buffer> + +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 + actions: 1, version: 1, algo: sha256, type: 2, modifiers: 1, count: 1, datalen: 32 + 87e5bd81850e11eeec2d3bb696b626b2a7f45673241cbbd64769c83580432869 + +In this output, ``actions`` is set to 1 (``COMPACT_ACTION_IMA_MEASURED`` +bit set). + + +DIGLIM guarantees that the information reported in the IMA measurement list +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 +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 + # cat 0-file_list-compact-cat > /sys/kernel/security/integrity/diglim/digest_list_add + # echo 0-file_list-compact-cat > /sys/kernel/security/integrity/diglim/digest_label + # /tmp/cat 0-file_list-compact-cat > /sys/kernel/security/integrity/diglim/digest_list_del + 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 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