linux-kernel - Re: [RFC PATCH v2] x86/boot: add .sbat section to the bzImage

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Message-ID: <CAMw=ZnSHDYrLXoad=d_O_qAsurqv196z3Fc3VRAJXSsJNVXdPw@mail.gmail.com>
Date:   Fri, 21 Jul 2023 13:40:14 +0100
From:   Luca Boccassi <bluca@...ian.org>
To:     James Bottomley <James.Bottomley@...senpartnership.com>
Cc:     Eric Snowberg <eric.snowberg@...cle.com>,
        Ard Biesheuvel <ardb@...nel.org>,
        Daniel P. Berrangé <berrange@...hat.com>,
        Emanuele Giuseppe Esposito <eesposit@...hat.com>,
        "x86@...nel.org" <x86@...nel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        "lennart@...ttering.net" <lennart@...ttering.net>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        "H. Peter Anvin" <hpa@...or.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Masahiro Yamada <masahiroy@...nel.org>,
        Alexander Potapenko <glider@...gle.com>,
        Nick Desaulniers <ndesaulniers@...gle.com>,
        Vitaly Kuznetsov <vkuznets@...hat.com>,
        open list <linux-kernel@...r.kernel.org>,
        "linux-efi@...r.kernel.org" <linux-efi@...r.kernel.org>,
        "keyrings@...r.kernel.org" <keyrings@...r.kernel.org>,
        Jarkko Sakkinen <jarkko@...nel.org>
Subject: Re: [RFC PATCH v2] x86/boot: add .sbat section to the bzImage

On Fri, 21 Jul 2023 at 12:24, James Bottomley
<James.Bottomley@...senpartnership.com> wrote:
>
> On Fri, 2023-07-21 at 09:55 +0100, Luca Boccassi wrote:
> > On Fri, 21 Jul 2023 at 02:49, Eric Snowberg
> > <eric.snowberg@...cle.com> wrote:
> > > > On Jul 20, 2023, at 1:16 PM, Luca Boccassi <bluca@...ian.org>
> > > > wrote:
> > > > On Thu, 20 Jul 2023 at 18:11, Eric Snowberg
> > > > <eric.snowberg@...cle.com> wrote:
> [...]
> > > > > I agree with James in the previous thread;  adding the SBAT
> > > > > section to the kernel should be handled by the signing tools.
> > > > > It really doesn't need to be included in the mainline kernel
> > > > > code. I also agree with the sentiment that mainline and the
> > > > > stable branches should not have SBAT versions attached
> > > > > to them. These are things distros should be responsible for
> > > > > including in their kernel if they want to have SBAT support.
> > > >
> > > > Why would 'signing tools' handle that? It's just a text-based PE
> > > > section, it doesn't require access to private key materials to be
> > > > handled, nor it has any relationship with signing.
> > >
> > > There is a relationship, the sbat information within the signed
> > > file can be used for revocation in lieu of revoking the hash or
> > > signing certificate at a later time.
> >
> > No, it is completely disjoint. In fact, the kernel doesn't even have
> > to be signed at all, but it still _must_ have a .sbat section when it
> > is used in a UKI.
>
> Just a minute, this is wrong.  I was talking to Peter after all of this
> blew up about how we handle signed kernels with no sbat (since we need
> that still to work for developers who sign their own kernels).  I
> thought he was planning to require an sbat section for all EFI
> binaries, but he says that's not true.  The current way shim does the
> sbat check is that if the section doesn't exist the binary is processed
> as having an empty sbat section (i.e. no sbat level checking will be
> done because there's no named sbat level for anything and it will just
> work) and they're planning to keep it that way so that a signed but no
> sbat kernel will always "just work" without any special key handling in
> shim.  So if we're planning to keep this no-sbat case in discrete
> kernels, even when the shim verifier checks sbat, the UKI kernel will
> need to work for this case as well.

Are you sure that's not just about local signing? IE, MoK vs embedded
cert auth flow? As far as I know, the plan for the 3rd party CA flow
is to eventually (very eventually) require it. I might have missed
some development ofc.