Messages in this thread | | | Subject | Re: [PATCH] selinux: include a consumer of the new IMA critical data hook | From | Lakshmi Ramasubramanian <> | Date | Thu, 14 Jan 2021 12:01:26 -0800 |
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On 1/14/21 11:58 AM, Tyler Hicks wrote: > On 2021-01-14 14:29:09, Paul Moore wrote: >> On Thu, Jan 14, 2021 at 2:15 PM Lakshmi Ramasubramanian >> <nramas@linux.microsoft.com> wrote: >>> >>> SELinux stores the active policy in memory, so the changes to this data >>> at runtime would have an impact on the security guarantees provided >>> by SELinux. Measuring in-memory SELinux policy through IMA subsystem >>> provides a secure way for the attestation service to remotely validate >>> the policy contents at runtime. >>> >>> Measure the hash of the loaded policy by calling the IMA hook >>> ima_measure_critical_data(). Since the size of the loaded policy >>> can be large (several MB), measure the hash of the policy instead of >>> the entire policy to avoid bloating the IMA log entry. >>> >>> To enable SELinux data measurement, the following steps are required: >>> >>> 1, Add "ima_policy=critical_data" to the kernel command line arguments >>> to enable measuring SELinux data at boot time. >>> For example, >>> BOOT_IMAGE=/boot/vmlinuz-5.10.0-rc1+ root=UUID=fd643309-a5d2-4ed3-b10d-3c579a5fab2f ro nomodeset security=selinux ima_policy=critical_data >>> >>> 2, Add the following rule to /etc/ima/ima-policy >>> measure func=CRITICAL_DATA label=selinux >>> >>> Sample measurement of the hash of SELinux policy: >>> >>> To verify the measured data with the current SELinux policy run >>> the following commands and verify the output hash values match. >>> >>> sha256sum /sys/fs/selinux/policy | cut -d' ' -f 1 >>> >>> grep "selinux-policy-hash" /sys/kernel/security/integrity/ima/ascii_runtime_measurements | tail -1 | cut -d' ' -f 6 >>> >>> Note that the actual verification of SELinux policy would require loading >>> the expected policy into an identical kernel on a pristine/known-safe >>> system and run the sha256sum /sys/kernel/selinux/policy there to get >>> the expected hash. >>> >>> Signed-off-by: Lakshmi Ramasubramanian <nramas@linux.microsoft.com> >>> Suggested-by: Stephen Smalley <stephen.smalley.work@gmail.com> >>> Acked-by: Paul Moore <paul@paul-moore.com> >>> Reviewed-by: Tyler Hicks <tyhicks@linux.microsoft.com> >>> --- >>> Documentation/ABI/testing/ima_policy | 3 +- >>> security/selinux/Makefile | 2 + >>> security/selinux/ima.c | 44 +++++++++++++++++++ >>> security/selinux/include/ima.h | 24 +++++++++++ >>> security/selinux/include/security.h | 3 +- >>> security/selinux/ss/services.c | 64 ++++++++++++++++++++++++---- >>> 6 files changed, 129 insertions(+), 11 deletions(-) >>> create mode 100644 security/selinux/ima.c >>> create mode 100644 security/selinux/include/ima.h >> >> I think this has changed enough that keeping the "Acked-by" and >> "Reviewed-by" tags is probably not a good choice. I took a quick look >> and this still looks okay from a SELinux perspective, I'll leave Mimi >> to comment on it from a IMA perspective.
Thanks for reviewing the change Paul.
>> >> Unless Tyler has reviewed this version prior to your posting, it might >> be a good idea to remove his "Reviewed-by" unless he has a chance to >> look this over again before it is merged. > > Thanks for calling this out. I hadn't reviewed it prior to the posting > but I was keeping an eye on the thread. > > This new revision still looks good to me and I like the idea of > controlling re-measurements via policy. So, > > Reviewed-by: Tyler Hicks <tyhicks@linux.microsoft.com>
Thanks for the quick response Tyler.
-lakshmi
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