Re: [PATCH 1/6] IMA: Allow EVM validation on appraisal even without a symmetric key

[Mimi Zohar <zohar@linux.vnet.ibm.com>]

On Mon, 2017-10-02 at 10:02 -0700, Matthew Garrett wrote:
> On Sat, Sep 30, 2017 at 7:08 PM, Mimi Zohar <zohar@linux.vnet.ibm.com> wrote:
> > On Wed, 2017-09-27 at 15:16 -0700, Matthew Garrett wrote:
> >> A reasonable configuration is to use IMA to appraise a subset of files
> >> (based on user, security label or other features supported by IMA) but
> >> to also want to use EVM to validate not only the state of the IMA hash
> >> but also additional metadata on the file. Right now this is only
> >> possible if a symmetric key has been loaded, which may not be desirable
> >> in all cases (eg, one where EVM digital signatures are shipped to end
> >> systems rather than EVM HMACs being generated locally).
> >
> > Commit 26ddabfe96bb "evm: enable EVM when X509 certificate is loaded"
> > already allows EVM to be enabled without loading a symmetric key.
> 
> This only seems to be set if CONFIG_EVM_LOAD_X509 is set. Should there
> be some sort of callback to set this if a key is loaded onto the evm
> keyring at runtime?

Currently writing 1 to the securityfs file causes the EVM key to be
loaded.  I would extend the existing evm_write_key().  Writing 2, for
example, might skip attempting to load the EVM key.  You'll probably
want to make sure that a public key has been loaded first.

Mimi