linux-kernel - Re: [PATCH 0/3] Allow access to confidential computing secret area in SEV guests

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Date:   Thu, 2 Sep 2021 18:09:55 +0200
From:   Greg KH <gregkh@...uxfoundation.org>
To:     James Bottomley <jejb@...ux.ibm.com>
Cc:     Dov Murik <dovmurik@...ux.ibm.com>, linux-efi@...r.kernel.org,
        Borislav Petkov <bp@...e.de>,
        Ashish Kalra <ashish.kalra@....com>,
        Brijesh Singh <brijesh.singh@....com>,
        Tom Lendacky <thomas.lendacky@....com>,
        Ard Biesheuvel <ardb@...nel.org>,
        James Morris <jmorris@...ei.org>,
        "Serge E. Hallyn" <serge@...lyn.com>,
        Andi Kleen <ak@...ux.intel.com>,
        "Dr. David Alan Gilbert" <dgilbert@...hat.com>,
        Tobin Feldman-Fitzthum <tobin@...ux.ibm.com>,
        Jim Cadden <jcadden@....com>, linux-coco@...ts.linux.dev,
        linux-security-module@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 0/3] Allow access to confidential computing secret area
 in SEV guests

On Thu, Sep 02, 2021 at 08:19:51AM -0700, James Bottomley wrote:
> On Thu, 2021-09-02 at 17:05 +0200, Greg KH wrote:
> > On Thu, Sep 02, 2021 at 07:35:10AM -0700, James Bottomley wrote:
> > > On Thu, 2021-09-02 at 14:57 +0200, Greg KH wrote:
> > > [...]
> > > > Wait, why are you using securityfs for this?
> > > > 
> > > > securityfs is for LSMs to use. 
> > > 
> > > No it isn't ... at least not exclusively; we use it for non LSM
> > > security purposes as well, like for the TPM BIOS log and for
> > > IMA.  What makes you think we should start restricting securityfs
> > > to LSMs only?  That's not been the policy up to now.
> > 
> > Well that was the original intent of the filesystem when it was
> > created, but I guess it's really up to the LSM maintainers now what
> > they want it for.
> > 
> > > >  If you want your own filesystem to play around with stuff like
> > > > this, great, write your own, it's only 200 lines or less these
> > > > days.  We used to do it all the time until people realized they
> > > > should just use sysfs for driver stuff.
> > > 
> > > This is a security purpose (injected key retrieval), so securityfs
> > > seems to be the best choice.  It's certainly possible to create a
> > > new filesystem, but I really think things with a security purpose
> > > should use securityfs so people know where to look for them.
> > 
> > knowing where to look should not be an issue, as that should be
> > documented in Documentation/ABI/ anyway, right?
> > 
> > It's just the overlap / overreach of using an existing filesystem for
> > things that don't seem to be LSM-related that feels odd to me.
> > 
> > Why not just make a cocofs if those people want a filesystem
> > interface?
> > It's 200 lines or so these days, if not less, and that way you only
> > mount what you actually need for the system.
> 
> Secrets transfer is actually broader than confidential computing,
> although confidential computing is a first proposed use, so I think
> cocofs would be too narrow.
> 
> > Why force this into securityfs if it doesn't have to be?
> 
> It's not being forced.  Secrets transfer is a security function in the
> same way the bios log is.

Is the bios log in securityfs today?

Anyway, it's up to the securityfs maintainer (i.e. not me), but
personally, I think this should be a separate filesystem as that would
probably make things easier in the long run...

good luck!

greg k-h