linux-kernel - Re: [PATCH 0/1] x86/kexec: UKI support

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Date:   Thu, 14 Sep 2023 10:48:55 +0200
From:   Lennart Poettering <mzxreary@...inter.de>
To:     Jan Hendrik Farr <kernel@...rr.cc>
Cc:     Jarkko Sakkinen <jarkko@...nel.org>, linux-kernel@...r.kernel.org,
        kexec@...ts.infradead.org, x86@...nel.org, tglx@...utronix.de,
        dhowells@...hat.com, vgoyal@...hat.com, keyrings@...r.kernel.org,
        akpm@...ux-foundation.org, Baoquan He <bhe@...hat.com>,
        bhelgaas@...gle.com, Luca Boccassi <bluca@...ian.org>
Subject: Re: [PATCH 0/1] x86/kexec: UKI support

On Di, 12.09.23 17:32, Jan Hendrik Farr (kernel@...rr.cc) wrote:

> >> The format itself is rather simple. It's just a PE file (as required
> >> by the UEFI spec) that contains a small stub application in the .text,
> >> .data, etc sections that is responsible for invoking the contained
> >> kernel and initrd with the contained cmdline. The kernel image is
> >> placed into a .kernel section, the initrd into a .initrd section, and
> >> the cmdline into a .cmdline section in the PE executable.
> >
> > How does this interact with the existing EFI stub support in
> > linux?
>
> It doesn't. During normal boot of a UKI the stub in it is used
> (systemd-stub, see:
> https://www.freedesktop.org/software/systemd/man/systemd-stub.html). The
> kernel's own EFI stub will still be in the binary inside the .linux
> section but not used.

That's not true actually, if the inner kernel supports the EFI stub
then systemd-stub actually defers to that for kernel execution. It's
more portable that way, since the kernel then deals with the
differences in the boot protocol on different architectures.

Lennart

--
Lennart Poettering, Berlin