linux-kernel - Re: [PATCH v7 00/12] evm: Improve usability of portable signatures

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Date:   Fri, 21 May 2021 13:31:46 -0400
From:   Mimi Zohar <zohar@...ux.ibm.com>
To:     Roberto Sassu <roberto.sassu@...wei.com>,
        "mjg59@...f.ucam.org" <mjg59@...f.ucam.org>
Cc:     "linux-integrity@...r.kernel.org" <linux-integrity@...r.kernel.org>,
        "linux-security-module@...r.kernel.org" 
        <linux-security-module@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v7 00/12] evm: Improve usability of portable signatures

On Fri, 2021-05-21 at 07:07 +0000, Roberto Sassu wrote:
> > From: Mimi Zohar [mailto:zohar@...ux.ibm.com]
> > Sent: Thursday, May 20, 2021 8:56 PM
> > On Fri, 2021-05-14 at 17:27 +0200, Roberto Sassu wrote:
> > > EVM portable signatures are particularly suitable for the protection of
> > > metadata of immutable files where metadata is signed by a software vendor.
> > > They can be used for example in conjunction with an IMA policy that
> > > appraises only executed and memory mapped files.
> > >
> > > However, until now portable signatures can be properly installed only if
> > > the EVM_ALLOW_METADATA_WRITES initialization flag is also set, which
> > > disables metadata verification until an HMAC key is loaded. This will cause
> > > metadata writes to be allowed even in the situations where they shouldn't
> > > (metadata protected by a portable signature is immutable).
> > >
> > > The main reason why setting the flag is necessary is that the operations
> > > necessary to install portable signatures and protected metadata would be
> > > otherwise denied, despite being legitimate, due to the fact that the
> > > decision logic has to avoid an unsafe recalculation of the HMAC that would
> > > make the unsuccessfully verified metadata valid. However, the decision
> > > logic is too coarse, and does not fully take into account all the possible
> > > situations where metadata operations could be allowed.
> > >
> > > For example, if the HMAC key is not loaded and it cannot be loaded in the
> > > future due the EVM_SETUP_COMPLETE flag being set, it wouldn't be a
> > problem
> > > to allow metadata operations, as they wouldn't result in an HMAC being
> > > recalculated.
> > >
> > > This patch set extends the decision logic and adds the necessary exceptions
> > > to use portable signatures without turning off metadata verification and
> > > deprecates the EVM_ALLOW_METADATA_WRITES flag.
> > 
> > Thanks, Roberto.
> > 
> > Applied to: git://git.kernel.org/pub/scm/linux/kernel/git/zohar/linux-
> > integrity.git
> > next-integrity-testing
> 
> Hi Mimi
> 
> could you please take the newer version of patch 5/12, which also adds
> an exception for the INTEGRITY_UNKNOWN error (it occurs when xattrs
> are not supported)?

Thank you for catching it.  I'd appreciate your checking once more. 
FYI, get-lore-mbox.py moved "Cc: stable" to the end.

thanks,

Mimi