linux-kernel - Re: [PATCH v6 02/20] liveupdate: luo

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

Message-ID: <CA+CK2bBEs2nr0TmsaV18S-xJTULkobYgv0sU9=RCdReiS0CbPQ@mail.gmail.com>
Date: Mon, 17 Nov 2025 13:29:47 -0500
From: Pasha Tatashin <pasha.tatashin@...een.com>
To: Mike Rapoport <rppt@...nel.org>
Cc: pratyush@...nel.org, jasonmiu@...gle.com, graf@...zon.com, 
	dmatlack@...gle.com, 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 02/20] liveupdate: luo_core: integrate with KHO

On Sun, Nov 16, 2025 at 2:16 PM Mike Rapoport <rppt@...nel.org> wrote:
>
> On Sun, Nov 16, 2025 at 09:55:30AM -0500, Pasha Tatashin wrote:
> > On Sun, Nov 16, 2025 at 7:43 AM Mike Rapoport <rppt@...nel.org> wrote:
> > >
> > > > +static int __init liveupdate_early_init(void)
> > > > +{
> > > > +     int err;
> > > > +
> > > > +     err = luo_early_startup();
> > > > +     if (err) {
> > > > +             pr_err("The incoming tree failed to initialize properly [%pe], disabling live update\n",
> > > > +                    ERR_PTR(err));
> > >
> > > How do we report this to the userspace?
> > > I think the decision what to do in this case belongs there. Even if it's
> > > down to choosing between plain kexec and full reboot, it's still a policy
> > > that should be implemented in userspace.
> >
> > I agree that policy belongs in userspace, and that is how we designed
> > it. In this specific failure case (ABI mismatch or corrupt FDT), the
> > preserved state is unrecoverable by the kernel. We cannot parse the
> > incoming data, so we cannot offer it to userspace.
> >
> > We report this state by not registering the /dev/liveupdate device.
> > When the userspace agent attempts to initialize, it receives ENOENT.
> > At that point, the agent exercises its policy:
> >
> > - Check dmesg for the specific error and report the failure to the
> > fleet control plane.
>
> Hmm, this is not nice. I think we still should register /dev/liveupdate and
> let userspace discover this error via /dev/liveupdate ABIs.

Not registering the device is the correct approach here for two reasons:

1. This follows the standard Linux driver pattern. If a driver fails
to initialize its underlying resources (hardware, firmware, or in this
case, the incoming FDT), it does not register a character device.
2. Registering a "zombie" device that exists solely to return errors
adds significant complexity. We would need to introduce a specific
"broken" state to the state machine and add checks to IOCTLs to reject
commands with a specific error code.

Pasha