From: Josh Poimboeuf <jpoimboe@redhat.com>
To: Petr Mladek <pmladek@suse.com>
Cc: jikos@kernel.org, Joe Lawrence <joe.lawrence@redhat.com>,
Miroslav Benes <mbenes@suse.cz>,
linux-kernel@vger.kernel.org, live-patching@vger.kernel.org
Subject: Re: [RFC PATCH 2/2] livepatch: Clear relocation targets on a module removal
Date: Thu, 5 Sep 2019 08:08:32 -0500 [thread overview]
Message-ID: <20190905130832.dznviqrrg6lfrxvx@treble> (raw)
In-Reply-To: <20190905110955.wl4lwjbnpqybhkcn@pathway.suse.cz>
On Thu, Sep 05, 2019 at 01:09:55PM +0200, Petr Mladek wrote:
> > I don't have a number, but it's very common to patch a function which
> > uses jump labels or alternatives.
>
> Really? My impression is that both alternatives and jump_labels
> are used in hot paths. I would expect them mostly in core code
> that is always loaded.
>
> Alternatives are often used in assembly that we are not able
> to livepatch anyway.
>
> Or are they spread widely via some macros or inlined functions?
Jump labels are used everywhere. Looking at vmlinux.o in my kernel:
Relocation section [19621] '.rela__jump_table' for section [19620] '__jump_table' at offset 0x197873c8 contains 11913 entries:
Each jump label entry has 3 entries, so 11913/3 = 3971 jump labels.
$ readelf -s vmlinux.o |grep FUNC |wc -l
46902
3971/46902 = ~8.5%
~8.5% of functions use jump labels.
> > > + How often new problematic features appear?
> >
> > I'm not exactly sure what you mean, but it seems that anytime we add a
> > new feature, we have to try to wrap our heads around how it interacts
> > with the weirdness of late module patching.
>
> I agree that we need to think about it and it makes complications.
> Anyway, I think that these are never the biggest problems.
>
> I would be more concerned about arch-specific features that might need
> special handling in the livepatch code. Everyone talks only about
> alternatives and jump_labels that were added long time ago.
Jump labels have been around for many years, but we somehow missed
implementing klp.arch for them. As I said this resulted in panics.
There may be other similar cases lurking, both in x86 and other arches.
It's not a comforting thought!
And each case requires special klp code in addition to the real code.
--
Josh
next prev parent reply other threads:[~2019-09-05 13:08 UTC|newest]
Thread overview: 44+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-07-19 12:28 [RFC PATCH 0/2] livepatch: Clear relocation targets on a module removal Miroslav Benes
2019-07-19 12:28 ` [PATCH 1/2] livepatch: Nullify obj->mod in klp_module_coming()'s error path Miroslav Benes
2019-07-28 19:45 ` Josh Poimboeuf
2019-08-19 11:26 ` Petr Mladek
2019-07-19 12:28 ` [RFC PATCH 2/2] livepatch: Clear relocation targets on a module removal Miroslav Benes
2019-07-22 9:33 ` Petr Mladek
2019-08-14 12:33 ` Miroslav Benes
2019-07-28 20:04 ` Josh Poimboeuf
2019-08-14 11:06 ` Miroslav Benes
2019-08-14 15:12 ` Josh Poimboeuf
2019-08-16 9:46 ` Petr Mladek
2019-08-22 22:36 ` Josh Poimboeuf
2019-08-23 8:13 ` Petr Mladek
2019-08-26 14:54 ` Josh Poimboeuf
2019-08-27 15:05 ` Joe Lawrence
2019-08-27 15:37 ` Josh Poimboeuf
2019-09-02 16:13 ` Miroslav Benes
2019-09-02 17:05 ` Joe Lawrence
2019-09-03 13:02 ` Miroslav Benes
2019-09-04 8:49 ` Petr Mladek
2019-09-04 16:26 ` Joe Lawrence
2019-09-05 2:50 ` Josh Poimboeuf
2019-09-05 11:09 ` Petr Mladek
2019-09-05 11:19 ` Jiri Kosina
2019-09-05 13:23 ` Josh Poimboeuf
2019-09-05 13:31 ` Jiri Kosina
2019-09-05 13:42 ` Josh Poimboeuf
2019-09-05 11:39 ` Joe Lawrence
2019-09-05 13:08 ` Josh Poimboeuf [this message]
2019-09-05 13:15 ` Josh Poimboeuf
2019-09-05 13:52 ` Petr Mladek
2019-09-05 14:28 ` Josh Poimboeuf
2019-09-05 12:03 ` Miroslav Benes
2019-09-05 12:35 ` Josh Poimboeuf
2019-09-05 12:49 ` Miroslav Benes
2019-09-05 11:52 ` Miroslav Benes
2019-09-05 2:32 ` Josh Poimboeuf
2019-09-05 12:16 ` Miroslav Benes
2019-09-05 12:54 ` Josh Poimboeuf
2019-09-06 12:51 ` Miroslav Benes
2019-09-06 15:38 ` Joe Lawrence
2019-09-06 16:45 ` Josh Poimboeuf
2019-08-26 13:44 ` Nicolai Stange
2019-08-26 15:02 ` Josh Poimboeuf
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