linux-kernel - Re: [PATCH v2 0/2] x86/kexec: UKI Support

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Date:   Tue, 12 Sep 2023 21:25:26 +0200
From:   "Jan Hendrik Farr" <kernel@...rr.cc>
To:     "Baoquan He" <bhe@...hat.com>
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, bhelgaas@...gle.com,
        "Luca Boccassi" <bluca@...ian.org>, lennart@...ttering.net,
        prudo@...hat.com
Subject: Re: [PATCH v2 0/2] x86/kexec: UKI Support

> By the way, could you provide detailed steps about how to test this
> patchset so that people interested can give it a shot?

Sure.

0. Build and run your kernel with my patches.
1. You're gonna need a UKI to kexec. I personally use sbctl or ukify to create them.

sbctl command example (assumes you have the cmdline you want saved in a file called cmdline):
sudo sbctl bundle -k /boot/vmlinuz-6.5.2 -f /boot/initrd.img-6.5.2 -c ./cmdline -s ./uki.efi

ukify command example:
sudo python3 ukify.py build --linux=/boot/vmlinuz-6.5.2 --initrd=/boot/initrd.img-6.5.2 --cmdline <cmdline as string or a filename>

2. If you are running in lockdown mode you'll have to sign the UKI. You can use sbctl, pesign, or sbsign for example.
3. Compile kexec-test (see links below). Simple "gcc main.c -o kexec-test" should work
4. Do the kexec load: ./kexec-text <path to uki>
(this is equivalent to "kexec -a -l <path to UKI>", however that currently complains about not recognizing the format)
5. At this point it's useful to check if the loading succeeded with: "cat /sys/kernel/kexec_loaded" (should return "1")
6. Do a kexec reboot. If you are running systemd, the best way is with: "systemctl kexec". Otherwise you can try "kexec -e", however this will not shut all your services down

If anyone has problems please feel free to ask.

Links:
sbctl: https://github.com/Foxboron/sbctl
ukify: https://github.com/systemd/systemd/tree/main/src/ukify
kexec-test: https://github.com/Cydox/kexec-test/