linux-kernel - Re: [RFC PATCH 2/2] livepatch: Clear relocation targets on a module removal

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Message-ID: <20190905023202.ed7fecc22xze4pwj@treble>
Date:   Wed, 4 Sep 2019 21:32:02 -0500
From:   Josh Poimboeuf <jpoimboe@...hat.com>
To:     Miroslav Benes <mbenes@...e.cz>
Cc:     Joe Lawrence <joe.lawrence@...hat.com>,
        Petr Mladek <pmladek@...e.com>, jikos@...nel.org,
        linux-kernel@...r.kernel.org, live-patching@...r.kernel.org
Subject: Re: [RFC PATCH 2/2] livepatch: Clear relocation targets on a module
 removal

On Tue, Sep 03, 2019 at 03:02:34PM +0200, Miroslav Benes wrote:
> On Mon, 2 Sep 2019, Joe Lawrence wrote:
> 
> > On 9/2/19 12:13 PM, Miroslav Benes wrote:
> > >> I can easily foresee more problems like those in the future.  Going
> > >> forward we have to always keep track of which special sections are
> > >> needed for which architectures.  Those special sections can change over
> > >> time, or can simply be overlooked for a given architecture.  It's
> > >> fragile.
> > > 
> > > Indeed. It bothers me a lot. Even x86 "port" is not feature complete in
> > > this regard (jump labels, alternatives,...) and who knows what lurks in
> > > the corners of the other architectures we support.
> > > 
> > > So it is in itself reason enough to do something about late module
> > > patching.
> > > 
> > 
> > Hi Miroslav,
> > 
> > I was tinkering with the "blue-sky" ideas that I mentioned to Josh the other
> > day.
> 
> > I dunno if you had a chance to look at what removing that code looks
> > like, but I can continue to flesh out that idea if it looks interesting:
> 
> Unfortunately no and I don't think I'll come up with something useful 
> before LPC, so anything is really welcome.
> 
> > 
> >   https://github.com/joe-lawrence/linux/tree/blue-sky

I like this a lot.

> > A full demo would require packaging up replacement .ko's with a livepatch, as
> > well as "blacklisting" those deprecated .kos, etc.  But that's all I had time
> > to cook up last week before our holiday weekend here.
> 
> Frankly, I'm not sure about this approach. I'm kind of torn. The current 
> solution is far from ideal, but I'm not excited about the other options 
> either. It seems like the choice is basically between "general but 
> technically complicated fragile solution with nontrivial maintenance 
> burden", or "something safer and maybe cleaner, but limiting for 
> users/distros". Of course it depends on whether the limitation is even 
> real and how big it is. Unfortunately we cannot quantify it much and that 
> is probably why our opinions (in the email thread) differ.

How would this option be "limiting for users/distros"?  If the packaging
part of the solution is done correctly then I don't see how it would be
limiting.

-- 
Josh