From: Josh Poimboeuf <jpoimboe@redhat.com>
To: Miroslav Benes <mbenes@suse.cz>
Cc: Peter Zijlstra <peterz@infradead.org>,
live-patching@vger.kernel.org, linux-kernel@vger.kernel.org,
Jessica Yu <jeyu@kernel.org>
Subject: Re: [PATCH 0/7] livepatch,module: Remove .klp.arch and module_disable_ro()
Date: Thu, 16 Apr 2020 07:20:51 -0500 [thread overview]
Message-ID: <20200416122051.p3dk5i7h6ty4cwuc@treble> (raw)
In-Reply-To: <alpine.LSU.2.21.2004161136340.10475@pobox.suse.cz>
On Thu, Apr 16, 2020 at 11:45:05AM +0200, Miroslav Benes wrote:
> On Tue, 14 Apr 2020, Josh Poimboeuf wrote:
>
> > On Tue, Apr 14, 2020 at 08:27:26PM +0200, Peter Zijlstra wrote:
> > > On Tue, Apr 14, 2020 at 11:28:36AM -0500, Josh Poimboeuf wrote:
> > > > Better late than never, these patches add simplifications and
> > > > improvements for some issues Peter found six months ago, as part of his
> > > > non-writable text code (W^X) cleanups.
> > >
> > > Excellent stuff, thanks!!
> > >
> > > I'll go brush up these two patches then:
> > >
> > > https://lkml.kernel.org/r/20191018074634.801435443@infradead.org
> > > https://lkml.kernel.org/r/20191018074634.858645375@infradead.org
> >
> > Ah right, I meant to bring that up. I actually played around with those
> > patches. While it would be nice to figure out a way to converge the
> > ftrace module init, I didn't really like the first patch.
> >
> > It bothers me that both the notifiers and the module init() both see the
> > same MODULE_STATE_COMING state, but only in the former case is the text
> > writable.
> >
> > I think it's cognitively simpler if MODULE_STATE_COMING always means the
> > same thing, like the comments imply, "fully formed" and thus
> > not-writable:
> >
> > enum module_state {
> > MODULE_STATE_LIVE, /* Normal state. */
> > MODULE_STATE_COMING, /* Full formed, running module_init. */
> > MODULE_STATE_GOING, /* Going away. */
> > MODULE_STATE_UNFORMED, /* Still setting it up. */
> > };
> >
> > And, it keeps tighter constraints on what a notifier can do, which is a
> > good thing if we can get away with it.
>
> Agreed.
>
> On the other hand, the first patch would remove the tiny race window when
> a module state is still UNFORMED, but the protections are (being) set up.
> Patches 4/7 and 5/7 allow to use memcpy in that case, because it is early.
> But it is in fact not already. I haven't checked yet if it really matters
> somewhere (a race with livepatch running klp_module_coming while another
> module is being loaded or anything like that).
Maybe I'm missing your point, but I don't see any races here.
apply_relocate_add() only writes to the patch module's text, so there
can't be races with other modules.
--
Josh
next prev parent reply other threads:[~2020-04-16 12:21 UTC|newest]
Thread overview: 38+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-04-14 16:28 [PATCH 0/7] livepatch,module: Remove .klp.arch and module_disable_ro() Josh Poimboeuf
2020-04-14 16:28 ` [PATCH 1/7] livepatch: Apply vmlinux-specific KLP relocations early Josh Poimboeuf
2020-04-14 17:44 ` Peter Zijlstra
2020-04-14 18:01 ` Josh Poimboeuf
2020-04-14 19:31 ` Josh Poimboeuf
2020-04-15 14:30 ` Miroslav Benes
2020-04-15 16:29 ` Josh Poimboeuf
2020-04-15 14:34 ` Miroslav Benes
2020-04-15 16:30 ` Josh Poimboeuf
2020-04-14 16:28 ` [PATCH 2/7] livepatch: Remove .klp.arch Josh Poimboeuf
2020-04-15 15:18 ` Jessica Yu
2020-04-14 16:28 ` [PATCH 3/7] livepatch: Prevent module-specific KLP rela sections from referencing vmlinux symbols Josh Poimboeuf
2020-04-14 16:28 ` [PATCH 4/7] s390/module: Use s390_kernel_write() for relocations Josh Poimboeuf
2020-04-16 8:56 ` Miroslav Benes
2020-04-16 12:06 ` Josh Poimboeuf
2020-04-16 13:16 ` Josh Poimboeuf
2020-04-17 1:37 ` Josh Poimboeuf
2020-04-14 16:28 ` [PATCH 5/7] x86/module: Use text_poke() " Josh Poimboeuf
2020-04-14 16:28 ` [PATCH 6/7] livepatch: Remove module_disable_ro() usage Josh Poimboeuf
2020-04-15 15:02 ` Jessica Yu
2020-04-15 16:33 ` Josh Poimboeuf
2020-04-16 9:28 ` Miroslav Benes
2020-04-16 12:10 ` Josh Poimboeuf
2020-04-14 16:28 ` [PATCH 7/7] module: Remove module_disable_ro() Josh Poimboeuf
2020-04-14 18:27 ` [PATCH 0/7] livepatch,module: Remove .klp.arch and module_disable_ro() Peter Zijlstra
2020-04-14 19:08 ` Josh Poimboeuf
2020-04-15 14:24 ` Peter Zijlstra
2020-04-15 16:17 ` Josh Poimboeuf
2020-04-16 15:31 ` Jessica Yu
2020-04-16 15:45 ` Josh Poimboeuf
2020-04-17 8:27 ` Miroslav Benes
2020-04-17 8:50 ` Jessica Yu
2020-04-16 9:45 ` Miroslav Benes
2020-04-16 12:20 ` Josh Poimboeuf [this message]
2020-04-17 9:08 ` Miroslav Benes
2020-04-15 0:57 ` Joe Lawrence
2020-04-15 1:31 ` Josh Poimboeuf
2020-04-15 1:37 ` Joe Lawrence
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