linux-kernel - Re: [RFC] module: signature infrastructure

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Date:	Tue, 04 Sep 2012 09:40:48 -0400
From:	Mimi Zohar <zohar@...ux.vnet.ibm.com>
To:	"Kasatkin, Dmitry" <dmitry.kasatkin@...el.com>
Cc:	Rusty Russell <rusty@...tcorp.com.au>,
	David Howells <dhowells@...hat.com>, jmorris@...ei.org,
	keyrings@...ux-nfs.org, linux-security-module@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [RFC] module: signature infrastructure

On Tue, 2012-09-04 at 15:21 +0300, Kasatkin, Dmitry wrote:
> On Tue, Sep 4, 2012 at 3:07 PM, Kasatkin, Dmitry
> <dmitry.kasatkin@...el.com> wrote:
> > Hi,
> >
> > Please read bellow...
> >
> > On Tue, Sep 4, 2012 at 8:55 AM, Rusty Russell <rusty@...tcorp.com.au> wrote:
> >> OK, I took a look at the module.c parts of David and Dmitry's patchsets,
> >> and didn't really like either, but I stole parts of David's to make
> >> this.
> >>
> >> So, here's the module.c part of module signing.  I hope you two got time
> >> to discuss the signature format details?  

The integrity subsystem currently defines 3 extended attribute formats
in security/integrity.h.

enum evm_ima_xattr_type {
        IMA_XATTR_DIGEST = 0x01,
        EVM_XATTR_HMAC,
        EVM_IMA_XATTR_DIGSIG,
};

integrity_digsig_verify() is called to appraise EVM signatures stored as
EVM_IMA_XATTR_DIGSIG.  In Dmitry's patches, this same call is used to
appraise modules.  If you decide to define a new format, it should be
included here as well.

> Mimi suggested a scheme where
> >> the private key would never be saved on disk (even temporarily), but I
> >> didn't see patches.  Frankly it's something we can do later; let's aim
> >> at getting the format right for the next merge window.

Right, the key is a build issue, which doesn't affect the format.

> > In our patches key is stored on the disc in encrypted format...

An updated version of Dmitry's patches are in the 'modsig' branch of
git://git.kernel.org/pub/scm/linux/kernel/git/kasatkin/linux-digsig. For
now, although commit 59f1d53 "modsig: build rules and scripts to
generate keys and sign modules" writes the ephemeral key to disk, it is
encrypted.

thanks,

Mimi

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