From: Petr Mladek <pmladek@suse.com>
To: Jessica Yu <jeyu@kernel.org>
Cc: 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, jpoimboe@redhat.com,
live-patching@vger.kernel.org
Subject: Re: [PATCH v3 5/6] x86/ftrace: Use text_poke()
Date: Fri, 18 Oct 2019 15:40:58 +0200 [thread overview]
Message-ID: <20191018134058.7zyls4746wpa7jy5@pathway.suse.cz> (raw)
In-Reply-To: <20191018130342.GA4625@linux-8ccs>
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.
We would still need special delayed handling for the module-specific
elf sections. Also we still would not need to clear the modifications
in these sections when the livepatched object gets unloaded.
I am afraid that the real difference might come when we split
the livepatch into per-livepatched object modules. This would
move the complexity to another parts of the code ;-) I am
unable to say what approach is easier and more safe to maintain
at the moment.
Best Regards,
Petr
next prev parent reply other threads:[~2019-10-18 13:41 UTC|newest]
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 ` [PATCH v3 5/6] x86/ftrace: Use text_poke() 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 [this message]
2019-10-21 14:14 ` Jessica Yu
2019-10-21 15:31 ` Josh Poimboeuf
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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