Live-Patching Archive on lore.kernel.org
 help / color / Atom feed
From: Petr Mladek <pmladek@suse.com>
To: Josh Poimboeuf <jpoimboe@redhat.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 15:52:59 +0200
Message-ID: <20190905135259.7obdymb7c2wdgafw@pathway.suse.cz> (raw)
In-Reply-To: <20190905131502.mgiaplb3grlxsahp@treble>

On Thu 2019-09-05 08:15:02, Josh Poimboeuf wrote:
> On Thu, Sep 05, 2019 at 08:08:32AM -0500, Josh Poimboeuf wrote:
> > 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.
> 
> Obviously some functions may use more than one jump label so this isn't
> exactly bulletproof math.  But it gives a rough idea of how widespread
> they are.

It looks scary. I just wonder why we have never met this problem during
last few years.

My only guess is that most of these functions are either in core
kernel or in code that we do not livepatch.

I do not want to say that we should ignore it. I want to
understand the cost and impact of the various approaches.

Regards,
Petr

  reply index

Thread overview: 44+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-07-19 12:28 [RFC PATCH 0/2] " 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
2019-09-05 13:15                               ` Josh Poimboeuf
2019-09-05 13:52                                 ` Petr Mladek [this message]
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 publically 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=20190905135259.7obdymb7c2wdgafw@pathway.suse.cz \
    --to=pmladek@suse.com \
    --cc=jikos@kernel.org \
    --cc=joe.lawrence@redhat.com \
    --cc=jpoimboe@redhat.com \
    --cc=linux-kernel@vger.kernel.org \
    --cc=live-patching@vger.kernel.org \
    --cc=mbenes@suse.cz \
    /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

Live-Patching Archive on lore.kernel.org

Archives are clonable:
	git clone --mirror https://lore.kernel.org/live-patching/0 live-patching/git/0.git

	# If you have public-inbox 1.1+ installed, you may
	# initialize and index your mirror using the following commands:
	public-inbox-init -V2 live-patching live-patching/ https://lore.kernel.org/live-patching \
		live-patching@vger.kernel.org
	public-inbox-index live-patching

Example config snippet for mirrors

Newsgroup available over NNTP:
	nntp://nntp.lore.kernel.org/org.kernel.vger.live-patching


AGPL code for this site: git clone https://public-inbox.org/public-inbox.git