On 2020-11-04 4:31 p.m., Mimi Zohar wrote:
Hi Tushar,
Measuring "critical kernel data" is not a new infrastructure, simply a
new IMA hook. Please update the above Subject line to "support for
measuring critical kernel data".
Thanks a lot. Will update.
On Sun, 2020-11-01 at 14:26 -0800, Tushar Sugandhi wrote:
There are several kernel subsystems that contain critical data which if
accidentally or maliciously altered, can compromise the integrity of the
system. Examples of such subsystems would include LSMs like SELinux, or
AppArmor; or device-mapper targets like dm-crypt, dm-verity etc.
"critical data" in this context is kernel subsystem specific information
that is stored in kernel memory. Examples of critical data could be
kernel in-memory r/o structures, hash of the memory structures, or
data that represents a linux kernel subsystem state.
This is a bit better, but needs to be much clearer. Please define
"critical data", not by example, but by describing "what" critical
kernel data is. "There are several kernel subsystems ...." is an
example of "how" it would be used, not a definition. Without a clear
definition it will become a dumping ground for measuring anything
anyone wants to measure. As a result, it may be abused.
Good point. I will come up with a better definition.
This patch set defines a new IMA hook namely CRITICAL_DATA, and a
function ima_measure_critical_data() - to measure the critical data.
The name of the IMA hook is ima_measure_critical_data. This is similar
to the LSM hooks, which are prefixed with "security_". (For a full
list of LSM hooks, refer to lsm_hook_defs.h.)
Thanks for the clarification. I will update this description.
Kernel subsystems can use this functionality, to take advantage of IMA's
measuring and quoting abilities - thus ultimately enabling remote
attestation for the subsystem specific information stored in the kernel
memory.
The functionality is generic enough to measure the data of any kernel
subsystem at run-time. To ensure that only data from supported sources
are measured, the kernel subsystem needs to be added to a compile-time
list of supported sources (an "allowed list of components"). IMA
validates the source passed to ima_measure_critical_data() against this
allowed list at run-time.
Yes, this new feature is generic, but one of the main goals of IMA is
to measure and attest to the integrity of the system, not to measure
and attest to random things.
Ok. I will update the above paragraph accordingly.
System administrators may want to pick and choose which kernel
subsystem information they would want to enable for measurements,
quoting, and remote attestation. To enable that, a new IMA policy is
introduced.
^may want to limit the critical data being measured, quoted and
attested.
^ a new IMA policy condition is defined.
Sounds good. Will update.
This patch set also addresses the need for the kernel subsystems to
measure their data before a custom IMA policy is loaded - by providing
a builtin IMA policy.
^for measuring kernel critical data early, before a custom IMA policy
...
Sounds good. Will update.
And lastly, the use of the overall functionality is demonstrated by
measuring the kernel in-memory data for one such subsystem - SeLinux.
The purpose isn't to demonstrate the "overall functionality", but to
provide an initial caller of the new IMA hook.
Fair point. Will change the description accordingly.
~Tushar
thanks,
Mimi
