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From:   Andy Lutomirski <luto@kernel.org>
Date:   Wed, 25 Mar 2020 15:51:52 -0700
Message-ID: <CALCETrUshiLMHyf4DShgDRtCvnzUVyRQgmgCiudvhuhw05cDxg@mail.gmail.com>
Subject: Re: [RFC PATCH 00/12] x86: Trenchboot secure late launch Linux kernel support
To:     Matthew Garrett <mjg59@google.com>
Cc:     Ross Philipson <ross.philipson@oracle.com>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
        "the arch/x86 maintainers" <x86@kernel.org>,
        "open list:DOCUMENTATION" <linux-doc@vger.kernel.org>,
        dpsmith@apertussolutions.com, Thomas Gleixner <tglx@linutronix.de>,
        Ingo Molnar <mingo@redhat.com>, Borislav Petkov <bp@alien8.de>,
        "H. Peter Anvin" <hpa@zytor.com>, trenchboot-devel@googlegroups.com
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On Wed, Mar 25, 2020 at 1:29 PM Matthew Garrett <mjg59@google.com> wrote:
>
> On Wed, Mar 25, 2020 at 12:43 PM Ross Philipson
> <ross.philipson@oracle.com> wrote:
> > To enable the kernel to be launched by GETSEC or SKINIT, a stub must be
> > built into the setup section of the compressed kernel to handle the
> > specific state that the late launch process leaves the BSP. This is a
> > lot like the EFI stub that is found in the same area. Also this stub
> > must measure everything that is going to be used as early as possible.
> > This stub code and subsequent code must also deal with the specific
> > state that the late launch leaves the APs in.
>
> How does this integrate with the EFI entry point? That's the expected
> entry point on most modern x86. What's calling ExitBootServices() in
> this flow, and does the secure launch have to occur after it? It'd be
> a lot easier if you could still use the firmware's TPM code rather
> than carrying yet another copy.

I was wondering why the bootloader was involved at all.  In other
words, could you instead hand off control to the kernel just like
normal and have the kernel itself (in normal code, the EFI stub, or
wherever it makes sense) do the DRTM launch all by itself?  This would
avoid needing to patch bootloaders, to implement this specially for
QEMU -kernel, to get the exact right buy-in from all the cloud
vendors, etc.  It would also give you more flexibility to evolve
exactly what configuration maps to exactly what PCRs in the future.