linux-kernel - Re: [RFC PATCH 0/2] ima: uncompressed module appraisal support

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Message-ID: <5c246616-9a3a-3ed2-c1f9-f634cef511c9@linux.vnet.ibm.com>
Date:   Thu, 6 Feb 2020 15:22:04 -0500
From:   Nayna <nayna@...ux.vnet.ibm.com>
To:     Eric Snowberg <eric.snowberg@...cle.com>,
        dmitry.kasatkin@...il.com, jmorris@...ei.org, serge@...lyn.com
Cc:     zohar@...ux.ibm.com, dhowells@...hat.com, geert@...ux-m68k.org,
        gregkh@...uxfoundation.org, nayna@...ux.ibm.com,
        tglx@...utronix.de, bauerman@...ux.ibm.com, mpe@...erman.id.au,
        linux-integrity@...r.kernel.org,
        linux-security-module@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [RFC PATCH 0/2] ima: uncompressed module appraisal support

On 2/6/20 11:42 AM, Eric Snowberg wrote:
> When booting with either "ima_policy=secure_boot module.sig_enforce=1"
> or building a kernel with CONFIG_IMA_ARCH_POLICY and booting with
> "ima_policy=secure_boot", module loading behaves differently based on if
> the module is compressed or not.  Originally when appraising a module
> with ima it had to be uncompressed and ima signed.  Recent changes in 5.4
> have allowed internally signed modules to load [1].  But this only works
> if the internally signed module is compressed.  The uncompressed module
> that is internally signed must still be ima signed. This patch series
> tries to bring the two in line.

We (Mimi and I) have been trying to understand the cover letter. It 
seems "by internally signed" you are referring to modules signed with 
build time generated keys.

Our interpretation of the cover letter is that IMA originally did not 
support appended signatures and now does. Since the modules are signed 
with build time generated keys, the signature verification still fails, 
as the keys are only available on the .builtin keyring and not the .ima 
keyring.

Lastly, there is nothing in these patches that indicate that the kernel 
modules being compressed/uncompressed is related to the signature 
verification.

Thanks & Regards,

      - Nayna