[PATCH v3 4/6] IMA: add policy to measure critical data from kernel components

[Mimi Zohar]

On Thu, 2020-08-27 at 18:57 -0700, Tushar Sugandhi wrote:
> There would be several candidate kernel components suitable for IMA
> measurement. Not all of them would have support for IMA measurement.
> Also, system administrators may not want to measure data for all of
> them, even when they support IMA measurement. An IMA policy specific
> to various kernel components is needed to measure their respective
> critical data.

The base policy rules are wide, but may be constrained by specifying
different options.  For example the builtin policy rules cannot be
written in terms LSM labels, which would constrain them.  A policy rule
may measure all keyrings or may constrain which keyrings need to be
measured.  Measuring critical data is not any different.

Please rewrite the above paragraph accordingly.

> 
> Add a new IMA policy "critical_kernel_data_sources" to support measuring
> various critical kernel components. This policy would enable the
> system administrators to limit the measurement to the components,
> if the components support IMA measurement.

"critical_kernel_data_sources" is really wordy.   Find a better, self
defining term for describing the type of data, one that isn't so wordy,
and reflect it in the code.

> 
> Signed-off-by: Tushar Sugandhi <tusharsu at linux.microsoft.com>
> ---
>  Documentation/ABI/testing/ima_policy |  3 +++
>  security/integrity/ima/ima_policy.c  | 29 +++++++++++++++++++++++++++-
>  2 files changed, 31 insertions(+), 1 deletion(-)
> 
> diff --git a/Documentation/ABI/testing/ima_policy b/Documentation/ABI/testing/ima_policy
> index cd572912c593..7ccdc1964e29 100644
> --- a/Documentation/ABI/testing/ima_policy
> +++ b/Documentation/ABI/testing/ima_policy
> @@ -48,6 +48,9 @@ Description:
>  			template:= name of a defined IMA template type
>  			(eg, ima-ng). Only valid when action is "measure".
>  			pcr:= decimal value
> +			critical_kernel_data_sources:= list of kernel
> +			components (eg, selinux|apparmor|dm-crypt) that
> +			contain data critical to the security of the kernel.

This original policy definition, for the most part, is in Backus–Naur
format.   The keyring names is an exception, because it is not limited
to pre-defined kernel objects.  The critical data hook is measuring
things in kernel memory.  As new calls to measure critical data are
added, new identifiers would be added here.

For example, if SELinux is the first example of measuring critical
data, then the SELinux critical data patch would include
"critical_data:= [selinux]".  Each subsequent critical data being
measured would extend this list.  At the same time, the list of known
"critical data" defined in patch 6/6 would be updated.

Normally a new feature and the first usage of that feature are included
in the same patch set.  Separating them like this makes it difficult to
write, review and upstream.

Mimi