Keys created or updated in the system are currently not measured.
Therefore an attestation service, for instance, would not be able to
attest whether or not the trusted keys keyring(s), for instance, contain
only known good (trusted) keys.
IMA measures system files, command line arguments passed to kexec,
boot aggregate, etc. It can be used to measure keys as well.
But there is no mechanism available in the kernel for IMA to
know when a key is created or updated.
This change aims to address measuring keys created or updated
in the system:
To achieve the above the following changes have been made:
- Added a new IMA hook namely, ima_post_key_create_or_update, which
measures the key. This IMA hook is called from key_create_or_update
function. The key measurement can be controlled through IMA policy.
A new IMA policy function KEY_CHECK has been added to measure keys.
# measure keys loaded onto any keyring
measure func=KEY_CHECK
Testing performed:
* Booted the kernel with this change.
* When KEY_CHECK policy is set IMA measures keys loaded
onto any keyring.
* Keys are not measured when KEY_CHECK is not set.
* Added a new key to a keyring.
=> Added keys to .ima and .evm keyrings.
* Added the same key again.
=> Add the same key to .ima and .evm keyrings.
Change Log:
v6:
=> Rebased the changes to v5.4-rc7
=> Renamed KEYRING_CHECK to KEY_CHECK per Mimi's suggestion.
=> Excluded the patches that add support for limiting key
measurement to specific keyrings ("keyrings=" option
for "measure func=KEY_CHECK" in the IMA policy).
Also, excluded the patches that add support for deferred
processing of keys (queue support).
These patches will be added in separate patch sets later.
v5:
=> Reorganized the patches to add measurement of keys through
the IMA hook without any queuing and then added queuing support.
=> Updated the queuing functions to minimize code executed inside mutex.
=> Process queued keys after custom IMA policies have been applied.
v4:
=> Rebased the changes to v5.4-rc3
=> Applied the following dependent patch set first
and then added new changes.
https://lore.kernel.org/linux-integrity/1572492694-6520-1-git-send-email-zohar@xxxxxxxxxxxxx
=> Refactored the patch set to separate out changes related to
func KEYRING_CHECK and options keyrings into different patches.
=> Moved the functions to queue and dequeue keys for measurement
from ima_queue.c to a new file ima_asymmetric_keys.c.
=> Added a new config namely CONFIG_IMA_MEASURE_ASYMMETRIC_KEYS
to compile ima_asymmetric_keys.c
v3:
=> Added KEYRING_CHECK for measuring keys. This can optionally specify
keyrings to measure.
=> Updated ima_get_action() and related functions to return
the keyrings if specified in the policy.
=> process_buffer_measurement() function is updated to take keyring
as a parameter. The key will be measured if the policy includes
the keyring in the list of measured keyrings. If the policy does not
specify any keyrings then all keys are measured.
v2:
=> Per suggestion from Mimi reordered the patch set to first
enable measuring keys added or updated in the system.
And, then scope the measurement to keys added to
builtin_trusted_keys keyring through ima policy.
=> Removed security_key_create_or_update function and instead
call ima hook, to measure the key, directly from
key_create_or_update function.
v1:
=> LSM function for key_create_or_update. It calls ima.
=> Added ima hook for measuring keys
=> ima measures keys based on ima policy.
v0:
=> Added LSM hook for key_create_or_update.
=> Measure keys added to builtin or secondary trusted keys keyring.
Lakshmi Ramasubramanian (3):
IMA: Add KEY_CHECK func to measure keys
IMA: Define an IMA hook to measure keys
KEYS: Call the IMA hook to measure keys
Documentation/ABI/testing/ima_policy | 6 ++-
include/linux/ima.h | 13 +++++
security/integrity/ima/Kconfig | 14 ++++++
security/integrity/ima/Makefile | 1 +
security/integrity/ima/ima.h | 1 +
security/integrity/ima/ima_asymmetric_keys.c | 51 ++++++++++++++++++++
security/integrity/ima/ima_main.c | 7 +++
security/integrity/ima/ima_policy.c | 4 +-
security/keys/key.c | 9 ++++
9 files changed, 104 insertions(+), 2 deletions(-)
create mode 100644 security/integrity/ima/ima_asymmetric_keys.c
--
2.17.1
