linux-kernel - Re: [PATCH 6/6] ima: Support appended signatures for appraisal

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Message-Id: <CDEBC6BB-7178-4891-9743-DD2B70328FCC@linux.vnet.ibm.com>
Date:   Wed, 26 Apr 2017 18:18:34 -0400
From:   Mehmet Kayaalp <mkayaalp@...ux.vnet.ibm.com>
To:     Thiago Jung Bauermann <bauerman@...ux.vnet.ibm.com>
Cc:     kbuild test robot <lkp@...el.com>, kbuild-all@...org,
        LSM <linux-security-module@...r.kernel.org>,
        linux-ima-devel@...ts.sourceforge.net,
        keyrings <keyrings@...r.kernel.org>,
        linux-crypto@...r.kernel.org,
        kernel <linux-kernel@...r.kernel.org>,
        Mimi Zohar <zohar@...ux.vnet.ibm.com>,
        Dmitry Kasatkin <dmitry.kasatkin@...il.com>,
        David Howells <dhowells@...hat.com>,
        Herbert Xu <herbert@...dor.apana.org.au>,
        "David S. Miller" <davem@...emloft.net>,
        Claudio Carvalho <cclaudio@...ux.vnet.ibm.com>
Subject: Re: [PATCH 6/6] ima: Support appended signatures for appraisal


> On Apr 20, 2017, at 7:41 PM, Thiago Jung Bauermann <bauerman@...ux.vnet.ibm.com> wrote:
> 
> This patch introduces the appended_imasig keyword to the IMA policy syntax
> to specify that a given hook should expect the file to have the IMA
> signature appended to it. Here is how it can be used in a rule:
> 
> appraise func=KEXEC_KERNEL_CHECK appraise_type=appended_imasig
> appraise func=KEXEC_KERNEL_CHECK appraise_type=appended_imasig|imasig
> 
> In the second form, IMA will accept either an appended signature or a
> signature stored in the extended attribute. In that case, it will first
> check whether there is an appended signature, and if not it will read it
> from the extended attribute.
> 
> The format of the appended signature is the same used for signed kernel
> modules. This means that the file can be signed with the scripts/sign-file
> tool, with a command line such as this:

I would suggest naming the appraise_type as modsig (or some variant) to clarify
that the format is defined by how module signatures are handled. Maybe we'd like 
to define a different appended/inline signature format for IMA in the future.

-Mehmet