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

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Date:   Thu, 14 Sep 2023 14:52:26 +0300
From:   "Jarkko Sakkinen" <jarkko@...nel.org>
To:     "Lennart Poettering" <mzxreary@...inter.de>,
        "Jan Hendrik Farr" <kernel@...rr.cc>
Cc:     <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 Thu Sep 14, 2023 at 11:48 AM EEST, Lennart Poettering wrote:
> 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.

OK, that's nice.

> Lennart
>
> --
> Lennart Poettering, Berlin

BR, Jarkko