All of lore.kernel.org
 help / color / mirror / Atom feed
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

  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

Reply instructions:

You may reply publicly to this message via plain-text email
using any one of the following methods:

* Save the following mbox file, import it into your mail client,
  and reply-to-all from there: mbox

  Avoid top-posting and favor interleaved quoting:
  https://en.wikipedia.org/wiki/Posting_style#Interleaved_style

* Reply using the --to, --cc, and --in-reply-to
  switches of git-send-email(1):

  git send-email \
    --in-reply-to=20190905130832.dznviqrrg6lfrxvx@treble \
    --to=jpoimboe@redhat.com \
    --cc=jikos@kernel.org \
    --cc=joe.lawrence@redhat.com \
    --cc=linux-kernel@vger.kernel.org \
    --cc=live-patching@vger.kernel.org \
    --cc=mbenes@suse.cz \
    --cc=pmladek@suse.com \
    /path/to/YOUR_REPLY

  https://kernel.org/pub/software/scm/git/docs/git-send-email.html

* If your mail client supports setting the In-Reply-To header
  via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line before the message body. 
This is an external index of several public inboxes,
see mirroring instructions on how to clone and mirror
all data and code used by this external index.