Message-ID: <903062f7b2e2709ae0e4416545ffadd91c132676.camel@huaweicloud.com>
Subject: Re: [RFC PATCH v9 10/16] dm-verity: consume root hash digest and
 signature data via LSM hook
From:   Roberto Sassu <roberto.sassu@huaweicloud.com>
To:     Fan Wu <wufan@linux.microsoft.com>
Cc:     corbet@lwn.net, zohar@linux.ibm.com, jmorris@namei.org,
        serge@hallyn.com, tytso@mit.edu, ebiggers@kernel.org,
        axboe@kernel.dk, agk@redhat.com, snitzer@kernel.org,
        eparis@redhat.com, paul@paul-moore.com, linux-doc@vger.kernel.org,
        linux-integrity@vger.kernel.org,
        linux-security-module@vger.kernel.org,
        linux-fscrypt@vger.kernel.org, linux-block@vger.kernel.org,
        dm-devel@redhat.com, linux-audit@redhat.com,
        roberto.sassu@huawei.com, linux-kernel@vger.kernel.org,
        Deven Bowers <deven.desai@linux.microsoft.com>
Date:   Thu, 02 Feb 2023 09:21:24 +0100
In-Reply-To: <20230201232639.GB9075@linuxonhyperv3.guj3yctzbm1etfxqx2vob5hsef.xx.internal.cloudapp.net>
References: <1675119451-23180-1-git-send-email-wufan@linux.microsoft.com>
         <1675119451-23180-11-git-send-email-wufan@linux.microsoft.com>
         <4f029a41d80d883d9b4729cbc85211955c9efe8e.camel@huaweicloud.com>
         <20230201232639.GB9075@linuxonhyperv3.guj3yctzbm1etfxqx2vob5hsef.xx.internal.cloudapp.net>
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On Wed, 2023-02-01 at 15:26 -0800, Fan Wu wrote:
> On Tue, Jan 31, 2023 at 02:22:01PM +0100, Roberto Sassu wrote:
> > On Mon, 2023-01-30 at 14:57 -0800, Fan Wu wrote:
> > > From: Deven Bowers <deven.desai@linux.microsoft.com>
> > > 
> > > dm-verity provides a strong guarantee of a block device's integrity. As
> > > a generic way to check the integrity of a block device, it provides
> > > those integrity guarantees to its higher layers, including the filesystem
> > > level.
> > 
> > I think you could reuse most of is_trusted_verity_target(), in
> > particular dm_verity_get_root_digest().
> > 
> > And probably, the previous patch is not necessary.
> > 
> > Roberto
> > 
> Thanks for the info. This function seems could be used to get the roothash
> but for saving the signature we still need the hook function in the previous
> patch.

Uhm, look at the LoadPin case. It does not need to temporarily store
the root digest in a security blob. It evaluates it directly.

Well, ok, dm_verity_loadpin_is_bdev_trusted() looks for trusted digests
in the dm_verity_loadpin_trusted_root_digests list. So, something
equivalent needs to be made for IPE (or you just get the digest).
However, I find not introducing new hooks and evaluating the
information directly more efficient.

Roberto