linux-kernel - Re: [PATCH 2/3] binfmt_elf: Verify signature of signed elf binary

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Date:	Mon, 21 Jan 2013 13:30:07 -0500
From:	Mimi Zohar <zohar@...ux.vnet.ibm.com>
To:	Vivek Goyal <vgoyal@...hat.com>
Cc:	"Eric W. Biederman" <ebiederm@...ssion.com>,
	linux-kernel@...r.kernel.org, pjones@...hat.com, hpa@...or.com,
	dhowells@...hat.com, jwboyer@...hat.com
Subject: Re: [PATCH 2/3] binfmt_elf: Verify signature of signed elf binary

On Mon, 2013-01-21 at 11:42 -0500, Vivek Goyal wrote:
> On Tue, Jan 15, 2013 at 11:55:59PM -0500, Mimi Zohar wrote:
> 
> [..]
> > Please remind me why you can't use IMA-appraisal, which was upstreamed
> > in Linux 3.7?  Why another method is needed?
> 
> So is this IMA-appraisal also supports digital signatures? The IMA white
> paper seems to put digital signatures in separate category
> (IMA-Appraisal-Signature-Extension).

The white paper was written a couple of years ago, before either EVM or
IMA-appraisal were upstreamed.

- Linux 3.2: Extended Verification Module (EVM) - protects file metadata from offline modification
- Linux 3.3: Dmitry Kasatkin's digital signature verification for use with EVM/IMA-appraisal.
- Linux 3.7: IMA-appraisal/with digital signatures

> > With IMA-appraisal, there are a couple of issues that would still need
> > to be addressed:
> > - missing the ability to specify the validation method required.

Patches to address this issue are available from linux-integrity-test/
#next-ima-appraise-status and were posted on the LSM mailing list as an
RFC (12/18/2012).  Review of these patches would be appreciated.

> > - modify the ima_appraise_tcb policy policy to require elf executables
> > to be digitally signed.
> 
> For my use case, all executable don't have to be digitally signed. If
> something is digitally signed then do the signature verification.

We already discussed this.  Hard coding policy into the Linux kernel is
wrong.

thanks,

Mimi

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