On Fri, 2021-01-22 at 15:24 -0500, Paul Moore wrote: > On Thu, Jan 14, 2021 at 2:15 PM Lakshmi Ramasubramanian > <nramas@xxxxxxxxxxxxxxxxxxx> 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@xxxxxxxxxxxxxxxxxxx> > > Suggested-by: Stephen Smalley <stephen.smalley.work@xxxxxxxxx> > > Acked-by: Paul Moore <paul@xxxxxxxxxxxxxx> > > Reviewed-by: Tyler Hicks <tyhicks@xxxxxxxxxxxxxxxxxxx> > > --- > > 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 > > Hi Mimi, > > Just checking as I didn't see a reply to this from you in my inbox, > you merged this into the IMA linux-next branch, yes? The patches are first staged in the linux-integrity #next-integrity- testing branch, before being staged in the #next-integrity branch, which is picked up by linux-next. Sorry, they've been staged in the next-integrity-testing branch, but are now next-integrity. Mim
