linux-kernel - Re: [PATCH v9 6/7] ima: support fs-verity file digest based version 3 signatures

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Message-ID: <e223929f4fbbfcba51b8cc9dda6a07ace12f5dd8.camel@linux.ibm.com>
Date:   Fri, 06 May 2022 07:34:52 -0400
From:   Mimi Zohar <zohar@...ux.ibm.com>
To:     Stefan Berger <stefanb@...ux.ibm.com>,
        linux-integrity@...r.kernel.org
Cc:     Eric Biggers <ebiggers@...nel.org>, linux-fscrypt@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v9 6/7] ima: support fs-verity file digest based version
 3 signatures

On Thu, 2022-05-05 at 13:12 -0400, Stefan Berger wrote:
> 
> On 5/5/22 08:31, Mimi Zohar wrote:
> > IMA may verify a file's integrity against a "good" value stored in the
> > 'security.ima' xattr or as an appended signature, based on policy.  When
> > the "good value" is stored in the xattr, the xattr may contain a file
> > hash or signature.  In either case, the "good" value is preceded by a
> > header.  The first byte of the xattr header indicates the type of data
> > - hash, signature - stored in the xattr.  To support storing fs-verity
> > signatures in the 'security.ima' xattr requires further differentiating
> > the fs-verity signature from the existing IMA signature.
> > 
> > In addition the signatures stored in 'security.ima' xattr, need to be
> > disambiguated.  Instead of directly signing the fs-verity digest, a new
> > signature format version 3 is defined as the hash of the ima_file_id
> > structure, which identifies the type of signature and the digest.
> > 
> > The IMA policy defines "which" files are to be measured, verified, and/or
> > audited.  For those files being verified, the policy rules indicate "how"
> > the file should be verified.  For example to require a file be signed,
> > the appraise policy rule must include the 'appraise_type' option.
> > 
> > 	appraise_type:= [imasig] | [imasig|modsig] | [sigv3]
> >             where 'imasig' is the original or signature format v2 (default),
> >             where 'modsig' is an appended signature,
> >             where 'sigv3' is the signature format v3.
> > 
> > The policy rule must also indicate the type of digest, if not the IMA
> > default, by first specifying the digest type:
> > 
> > 	digest_type:= [verity]
> > 
> > The following policy rule requires fsverity signatures.  The rule may be
> > constrained, for example based on a fsuuid or LSM label.
> > 
> >        appraise func=BPRM_CHECK digest_type=verity appraise_type=sigv3
> > 
> > Signed-off-by: Mimi Zohar <zohar@...ux.ibm.com>
> 
> Acked-by: Stefan Berger <stefanb@...ux.ibm.com>

Thanks, Stefan!

This patch set is now queued in the next-integrity-testing branch,
waiting additional review/tags. 

thanks,

Mimi