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From: Josh Poimboeuf <jpoimboe@redhat.com>
To: Petr Mladek <pmladek@suse.com>
Cc: Jessica Yu <jeyu@kernel.org>, Miroslav Benes <mbenes@suse.cz>,
	Peter Zijlstra <peterz@infradead.org>,
	Steven Rostedt <rostedt@goodmis.org>,
	Joe Lawrence <joe.lawrence@redhat.com>,
	x86@kernel.org, linux-kernel@vger.kernel.org,
	mhiramat@kernel.org, bristot@redhat.com, jbaron@akamai.com,
	torvalds@linux-foundation.org, tglx@linutronix.de,
	mingo@kernel.org, namit@vmware.com, hpa@zytor.com,
	luto@kernel.org, ard.biesheuvel@linaro.org,
	live-patching@vger.kernel.org
Subject: Re: [PATCH v3 5/6] x86/ftrace: Use text_poke()
Date: Mon, 21 Oct 2019 10:31:01 -0500
Message-ID: <20191021153101.y6ik56564er6jra5@treble> (raw)
In-Reply-To: <20191018134058.7zyls4746wpa7jy5@pathway.suse.cz>

On Fri, Oct 18, 2019 at 03:40:58PM +0200, Petr Mladek wrote:
> On Fri 2019-10-18 15:03:42, Jessica Yu wrote:
> > +++ Miroslav Benes [16/10/19 15:29 +0200]:
> > > On Wed, 16 Oct 2019, Miroslav Benes wrote:
> > > Thinking about it more... crazy idea. I think we could leverage these new
> > > ELF .text per vmlinux/module sections for the reinvention I was talking
> > > about. If we teach module loader to relocate (and apply alternatives and
> > > so on, everything in arch-specific module_finalize()) not the whole module
> > > in case of live patch modules, but separate ELF .text sections, it could
> > > solve the issue with late module patching we have. It is a variation on
> > > Steven's idea. When live patch module is loaded, only its section for
> > > present modules would be processed. Then whenever a to-be-patched module
> > > is loaded, its .text section in all present patch module would be
> > > processed.
> > > 
> > > The upside is that almost no work would be required on patch modules
> > > creation side. The downside is that klp_modinfo must stay. Module loader
> > > needs to be hacked a lot in both cases. So it remains to be seen which
> > > idea is easier to implement.
> > > 
> > > Jessica, do you think it would be feasible?
> > 
> > I think that does sound feasible. I'm trying to visualize how that
> > would look. I guess there would need to be various livepatching hooks
> > called during the different stages (apply_relocate_add(),
> > module_finalize(), module_enable_ro/x()).
> > 
> > So maybe something like the following?
> > 
> > When a livepatch module loads:
> >    apply_relocate_add()
> >        klp hook: apply .klp.rela.$objname relocations *only* for
> >        already loaded modules
> >    module_finalize()
> >        klp hook: apply .klp.arch.$objname changes for already loaded modules
> >    module_enable_ro()
> >        klp hook: only enable ro/x for .klp.text.$objname for already
> >        loaded modules
> 
> Just for record. We should also set ro for the not-yet used
> .klp.text.$objname at this stage so that it can't be modified
> easily "by accident".
> 
> 
> > When a to-be-patched module loads:
> >    apply_relocate_add()
> >        klp hook: for each patch module that patches the coming
> >        module, apply .klp.rela.$objname relocations for this object
> >    module_finalize()
> >        klp hook: for each patch module that patches the coming
> >        module, apply .klp.arch.$objname changes for this object
> >    module_enable_ro()
> >        klp hook: for each patch module, apply ro/x permissions for
> >        .klp.text.$objname for this object
> > 
> > Then, in klp_module_coming, we only need to do the callbacks and
> > enable the patch, and get rid of the module_disable_ro->apply
> > relocs->module_enable_ro block.
> > 
> > Does that sound like what you had in mind or am I totally off?
> 
> Makes sense to me.
> 
> Well, I wonder if it is really any better from what we have now.

AFAICT, this would still have a lot of the same problems we have today.
It has a lot of complexity.  It needs arch-specific livepatch code and
sections, and introduces special cases in the module code.

I'd much prefer the proposal from LPC to have per-module live patches.
It's simpler and has less things that can go wrong IMO.

-- 
Josh


  parent reply index

Thread overview: 45+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
     [not found] <20191007081945.10951536.8@infradead.org>
     [not found] ` <20191008104335.6fcd78c9@gandalf.local.home>
     [not found]   ` <20191009224135.2dcf7767@oasis.local.home>
     [not found]     ` <20191010092054.GR2311@hirez.programming.kicks-ass.net>
     [not found]       ` <20191010091956.48fbcf42@gandalf.local.home>
     [not found]         ` <20191010140513.GT2311@hirez.programming.kicks-ass.net>
     [not found]           ` <20191010115449.22044b53@gandalf.local.home>
     [not found]             ` <20191010172819.GS2328@hirez.programming.kicks-ass.net>
     [not found]               ` <20191011125903.GN2359@hirez.programming.kicks-ass.net>
     [not found]                 ` <20191015130739.GA23565@linux-8ccs>
     [not found]                   ` <20191015135634.GK2328@hirez.programming.kicks-ass.net>
2019-10-15 14:13                     ` Miroslav Benes
2019-10-15 15:06                       ` Joe Lawrence
2019-10-15 15:31                         ` Jessica Yu
2019-10-15 22:17                           ` Joe Lawrence
2019-10-15 22:27                             ` Steven Rostedt
2019-10-16  7:42                               ` Peter Zijlstra
2019-10-16 10:15                                 ` Miroslav Benes
2019-10-21 15:05                                 ` Josh Poimboeuf
2020-01-20 16:50                                   ` Josh Poimboeuf
2020-01-21  8:35                                     ` Miroslav Benes
2020-01-21 16:10                                       ` Josh Poimboeuf
2020-01-22 10:09                                         ` Miroslav Benes
2020-01-22 21:42                                           ` Josh Poimboeuf
2020-01-28  9:28                                             ` Miroslav Benes
2020-01-28 15:00                                               ` Josh Poimboeuf
2020-01-28 15:40                                                 ` Petr Mladek
2020-01-28 17:02                                                   ` Josh Poimboeuf
2020-01-29  0:46                                                     ` Jiri Kosina
2020-01-29  2:17                                                       ` Josh Poimboeuf
2020-01-29  3:14                                                         ` Jiri Kosina
2020-01-29 12:28                                                     ` Miroslav Benes
2020-01-29 15:59                                                       ` Josh Poimboeuf
2020-01-30  9:53                                                         ` Petr Mladek
2020-01-30 14:17                                                           ` Josh Poimboeuf
2020-01-31  7:17                                                             ` Petr Mladek
2020-01-22 12:15                                         ` Miroslav Benes
2020-01-22 15:05                                           ` Miroslav Benes
2020-01-22 22:03                                             ` Josh Poimboeuf
2020-01-23 10:19                                               ` Martin Jambor
2019-10-16  7:49                               ` Peter Zijlstra
2019-10-16 10:20                                 ` Miroslav Benes
2019-10-16 13:29                                   ` Miroslav Benes
2019-10-18 13:03                                     ` Jessica Yu
2019-10-18 13:40                                       ` Petr Mladek
2019-10-21 14:14                                         ` Jessica Yu
2019-10-21 15:31                                         ` Josh Poimboeuf [this message]
2019-10-22  8:27                                       ` Miroslav Benes
2019-10-22 14:31                                         ` Josh Poimboeuf
2019-10-23  9:04                                           ` Miroslav Benes
2019-10-16  6:51                         ` Miroslav Benes
2019-10-16  9:23                           ` Peter Zijlstra
2019-10-16  9:36                             ` Jessica Yu
2019-10-16  9:51                               ` Peter Zijlstra
2019-10-16 12:39                           ` Peter Zijlstra
2019-10-22  8:45                             ` Miroslav Benes

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