linux-kernel - Re: [PATCH v4 1/3] efi/libstub: Copy confidential computing secret area

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Date:   Wed, 20 Oct 2021 14:11:46 +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>,
        Andrew Scull <ascull@...gle.com>,
        Dave Hansen <dave.hansen@...el.com>,
        "Dr. David Alan Gilbert" <dgilbert@...hat.com>,
        Tobin Feldman-Fitzthum <tobin@...ux.ibm.com>,
        Jim Cadden <jcadden@....com>,
        Daniele Buono <dbuono@...ux.vnet.ibm.com>,
        linux-coco@...ts.linux.dev, linux-security-module@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v4 1/3] efi/libstub: Copy confidential computing secret
 area

On Wed, Oct 20, 2021 at 08:00:28AM -0400, James Bottomley wrote:
> On Wed, 2021-10-20 at 08:39 +0200, Greg KH wrote:
> > On Wed, Oct 20, 2021 at 06:14:06AM +0000, Dov Murik wrote:
> [...]
> > > +	help
> > > +	  Copy memory reserved by EFI for Confidential Computing (coco)
> > > +	  injected secrets, if EFI exposes such a table entry.
> > 
> > Why would you want to "copy" secret memory?
> > 
> > This sounds really odd here, it sounds like you are opening up a
> > security hole.  Are you sure this is the correct text that everyone
> > on the "COCO" group agrees with?
> 
> The way this works is that EFI covers the secret area with a boot time
> handoff block, which means it gets destroyed as soon as
> ExitBootServices is called as a security measure ... if you do nothing
> the secret is shredded.  This means you need to make a copy of it
> before that happens if there are secrets that need to live beyond the
> EFI boot stub.

Ok, but "copy secrets" does sound really odd, so you all need a much
better description here, and hopefully somewhere else in Documentation/
to describe exactly what this new API is and is to be used for.

Otherwise I read this as "hey a backdoor to read the secrets I wasn't
supposed to be able to see!"

thanks,

greg k-h