linux-kernel - Re: [PATCH v6 18/20] selftests/liveupdate: Add kexec-based selftest for session lifecycle

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite for Android: free password hash cracker in your pocket

[<prev] [next>] [<thread-prev] [day] [month] [year] [list]

Message-ID: <CA+CK2bBoantuwMxqe1=PnRO+RX86Qo0epf89kbmZx5z8i2ivLQ@mail.gmail.com>
Date: Wed, 19 Nov 2025 17:12:24 -0500
From: Pasha Tatashin <pasha.tatashin@...een.com>
To: David Matlack <dmatlack@...gle.com>
Cc: pratyush@...nel.org, jasonmiu@...gle.com, graf@...zon.com, rppt@...nel.org, 
	rientjes@...gle.com, corbet@....net, rdunlap@...radead.org, 
	ilpo.jarvinen@...ux.intel.com, kanie@...ux.alibaba.com, ojeda@...nel.org, 
	aliceryhl@...gle.com, masahiroy@...nel.org, akpm@...ux-foundation.org, 
	tj@...nel.org, yoann.congal@...le.fr, mmaurer@...gle.com, 
	roman.gushchin@...ux.dev, chenridong@...wei.com, axboe@...nel.dk, 
	mark.rutland@....com, jannh@...gle.com, vincent.guittot@...aro.org, 
	hannes@...xchg.org, dan.j.williams@...el.com, david@...hat.com, 
	joel.granados@...nel.org, rostedt@...dmis.org, anna.schumaker@...cle.com, 
	song@...nel.org, linux@...ssschuh.net, linux-kernel@...r.kernel.org, 
	linux-doc@...r.kernel.org, linux-mm@...ck.org, gregkh@...uxfoundation.org, 
	tglx@...utronix.de, mingo@...hat.com, bp@...en8.de, 
	dave.hansen@...ux.intel.com, x86@...nel.org, hpa@...or.com, rafael@...nel.org, 
	dakr@...nel.org, bartosz.golaszewski@...aro.org, cw00.choi@...sung.com, 
	myungjoo.ham@...sung.com, yesanishhere@...il.com, Jonathan.Cameron@...wei.com, 
	quic_zijuhu@...cinc.com, aleksander.lobakin@...el.com, ira.weiny@...el.com, 
	andriy.shevchenko@...ux.intel.com, leon@...nel.org, lukas@...ner.de, 
	bhelgaas@...gle.com, wagi@...nel.org, djeffery@...hat.com, 
	stuart.w.hayes@...il.com, ptyadav@...zon.de, lennart@...ttering.net, 
	brauner@...nel.org, linux-api@...r.kernel.org, linux-fsdevel@...r.kernel.org, 
	saeedm@...dia.com, ajayachandra@...dia.com, jgg@...dia.com, parav@...dia.com, 
	leonro@...dia.com, witu@...dia.com, hughd@...gle.com, skhawaja@...gle.com, 
	chrisl@...nel.org
Subject: Re: [PATCH v6 18/20] selftests/liveupdate: Add kexec-based selftest
 for session lifecycle

On Wed, Nov 19, 2025 at 4:20 PM David Matlack <dmatlack@...gle.com> wrote:
>
> On 2025-11-15 06:34 PM, Pasha Tatashin wrote:
>
> > diff --git a/tools/testing/selftests/liveupdate/do_kexec.sh b/tools/testing/selftests/liveupdate/do_kexec.sh
> > new file mode 100755
> > index 000000000000..3c7c6cafbef8
> > --- /dev/null
> > +++ b/tools/testing/selftests/liveupdate/do_kexec.sh
> > @@ -0,0 +1,16 @@
> > +#!/bin/sh
> > +# SPDX-License-Identifier: GPL-2.0
> > +set -e
> > +
> > +# Use $KERNEL and $INITRAMFS to pass custom Kernel and optional initramfs
>
> It'd be nice to use proper command line options for KERNEL and INITRAMFS
> instead of relying on environment variables.

Now that tests and do_kexec are separate, I do not think we should
complicate do_kexec.sh to support every possible environment. On most
modern distros kexec is managed via systemd, and the load and reboot
commands are going to be handled through systemd. do_kexec.sh is meant
for a very simplistic environment such as with busybox rootfs to
perform selftests.

> e.g.
>
>   ./do_kexec.sh -k <kernel> -i <initramfs>
>
> > +
> > +KERNEL="${KERNEL:-/boot/bzImage}"
> > +set -- -l -s --reuse-cmdline "$KERNEL"
>
> I've observed --reuse-cmdline causing overload of the kernel command
> line when doing repeated kexecs, since it includes the built-in command
> line (CONFIG_CMDLINE) which then also gets added by the next kernel
> during boot.

There is a problem with CONFIG_CMDLINE + KEXEC, ideally, it should be
addressed in the kernel

>
> Should we have something like this instead?
>
> diff --git a/tools/testing/selftests/liveupdate/do_kexec.sh b/tools/testing/selftests/liveupdate/do_kexec.sh
> index 3c7c6cafbef8..2590a870993d 100755
> --- a/tools/testing/selftests/liveupdate/do_kexec.sh
> +++ b/tools/testing/selftests/liveupdate/do_kexec.sh
> @@ -4,8 +4,16 @@ set -e
>
>  # Use $KERNEL and $INITRAMFS to pass custom Kernel and optional initramfs
>
> +# Determine the boot command line we need to pass to the kexec kernel.  Note
> +# that the kernel will append to it its builtin command line, so make sure we
> +# subtract the builtin command to avoid accumulating kernel parameters and
> +# eventually overflowing the command line.
> +full_cmdline=$(cat /proc/cmdline)
> +builtin_cmdline=$(zcat /proc/config.gz|grep CONFIG_CMDLINE=|cut -f2 -d\")

This also implies we have /proc/config.gz or CONFIG_IKCONFIG_PROC ...

> +cmdline=${full_cmdline/$builtin_cmdline /}
> +
>  KERNEL="${KERNEL:-/boot/bzImage}"
> -set -- -l -s --reuse-cmdline "$KERNEL"
> +set -- -l -s --command-line="${cmdline}" "$KERNEL"
>
>  INITRAMFS="${INITRAMFS:-/boot/initramfs}"
>  if [ -f "$INITRAMFS" ]; then
>
> > +
> > +INITRAMFS="${INITRAMFS:-/boot/initramfs}"
> > +if [ -f "$INITRAMFS" ]; then
> > +    set -- "$@" --initrd="$INITRAMFS"
> > +fi
> > +
> > +kexec "$@"
> > +kexec -e
>
> Consider separating the kexec load into its own script, in case systems have
> their own ways of shutting down for kexec.

I think, if do_kexec.sh does not work (load + reboot), the user should
use whatever the standard way on a distro to do kexec.

>
> e.g. a kexec_load.sh script that does everything that do_kexec.sh does execpt
> the `kexec -e`. Then do_kexec.sh just calls kexec_load.sh and kexec -e.