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From:   Ard Biesheuvel <ardb@kernel.org>
Date:   Wed, 30 Mar 2022 09:12:19 +0200
Message-ID: <CAMj1kXE9WrBOUG6MRQ90cMH_NvvCw_jVCar5Dsj+gkZr1AA0MQ@mail.gmail.com>
Subject: Re: Linux DRTM on UEFI platforms
To:     Matthew Garrett <mjg59@srcf.ucam.org>
Cc:     Daniel Kiper <daniel.kiper@oracle.com>,
        Alec Brown <alec.r.brown@oracle.com>,
        Kanth Ghatraju <kanth.ghatraju@oracle.com>,
        Ross Philipson <ross.philipson@oracle.com>,
        "dpsmith@apertussolutions.com" <dpsmith@apertussolutions.com>,
        "piotr.krol@3mdeb.com" <piotr.krol@3mdeb.com>,
        "krystian.hebel@3mdeb.com" <krystian.hebel@3mdeb.com>,
        "persaur@gmail.com" <persaur@gmail.com>,
        "Yoder, Stuart" <stuart.yoder@arm.com>,
        Andrew Cooper <andrew.cooper3@citrix.com>,
        "michal.zygowski@3mdeb.com" <michal.zygowski@3mdeb.com>,
        James Bottomley <James.Bottomley@hansenpartnership.com>,
        "lukasz@hawrylko.pl" <lukasz@hawrylko.pl>,
        linux-efi <linux-efi@vger.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
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        Kees Cook <keescook@chromium.org>
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On Wed, 30 Mar 2022 at 09:11, Matthew Garrett <mjg59@srcf.ucam.org> wrote:
>
> On Wed, Mar 30, 2022 at 09:02:18AM +0200, Ard Biesheuvel wrote:
>
> > Wouldn't it be better for the secure launch kernel to boot the EFI
> > entrypoint directly? As it happens, I just completed a PoC last week
> > for a minimal implementation of EFI (in Rust) that only carries the
> > pieces that the EFI stub needs to boot Linux. It is currently just a
> > proof of concept that only works on QEMU/arm64, but it should not be
> > too hard to adapt it for x86 and for booting a kernel that has already
> > been loaded to memory.
>
> The EFI stub carries out a bunch of actions that have meaningful
> security impact, and that's material that should be measured. Having the
> secure launch kernel execute the stub without awareness of what it does
> means it would need to measure the code without measuring the state,
> while the goal of DRTM solutions is to measure state rather than the
> code.

But how is that any different from the early kernel code?