Messages in this thread | | | Subject | Re: [PATCH v10 8/8] selinux: include a consumer of the new IMA critical data hook | From | Lakshmi Ramasubramanian <> | Date | Tue, 12 Jan 2021 10:25:11 -0800 |
| |
On 1/12/21 8:27 AM, Paul Moore wrote: > On Thu, Jan 7, 2021 at 11:07 PM Tushar Sugandhi > <tusharsu@linux.microsoft.com> wrote: >> From: Lakshmi Ramasubramanian <nramas@linux.microsoft.com> >> >> 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> >> Reviewed-by: Tyler Hicks <tyhicks@linux.microsoft.com> >> --- >> Documentation/ABI/testing/ima_policy | 3 +- >> security/selinux/Makefile | 2 + >> security/selinux/ima.c | 64 ++++++++++++++++++++++++++++ >> security/selinux/include/ima.h | 24 +++++++++++ >> security/selinux/include/security.h | 3 +- >> security/selinux/ss/services.c | 64 ++++++++++++++++++++++++---- >> 6 files changed, 149 insertions(+), 11 deletions(-) >> create mode 100644 security/selinux/ima.c >> create mode 100644 security/selinux/include/ima.h > > I remain concerned about the possibility of bypassing a measurement by > tampering with the time, but I appear to be the only one who is > worried about this so I'm not going to block this patch on those > grounds. > > Acked-by: Paul Moore <paul@paul-moore.com>
Thanks Paul.
-lakshmi
| |