From: Petr Mladek <pmladek@suse.com>
To: Jessica Yu <jeyu@redhat.com>
Cc: Josh Poimboeuf <jpoimboe@redhat.com>,
Miroslav Benes <mbenes@suse.cz>, Jiri Kosina <jikos@kernel.org>,
Chris J Arges <chris.j.arges@canonical.com>,
Eugene Shatokhin <eugene.shatokhin@rosalab.ru>,
live-patching@vger.kernel.org, x86@kernel.org,
linux-kernel@vger.kernel.org
Subject: Re: [PATCH 0/2] Fix issue with alternatives/paravirt patches
Date: Thu, 7 Jul 2016 17:56:33 +0200 [thread overview]
Message-ID: <20160707155633.GC3556@pathway.suse.cz> (raw)
In-Reply-To: <1467772500-26092-1-git-send-email-jeyu@redhat.com>
On Tue 2016-07-05 22:34:58, Jessica Yu wrote:
> Hi,
>
> A few months ago, Chris Arges reported a bug involving alternatives/paravirt
> patching that was discussed here [1] and here [2]. To briefly summarize the
> bug, patch modules that contained .altinstructions or .parainstructions
> sections would break because these alternative/paravirt patches would be
> applied first by the module loader (see x86 module_finalize()), then
> livepatch would later clobber these patches when applying per-object
> relocations. This lead to crashes and unpredictable behavior.
>
> One conclusion we reached from our last discussion was that we will
> need to introduce some arch-specific code to address this problem.
> This patchset presents a possible fix for the bug by adding a new
> arch-specific arch_klp_init_object_loaded() function that by default
> does nothing but can be overridden by different arches.
>
> To fix this issue for x86, since we can access a patch module's Elf
> sections through mod->klp_info, we can simply delay the calls to
> apply_paravirt() and apply_alternatives() to arch_klp_init_object_loaded(),
> which is called after relocations have been written for an object.
> In addition, for patch modules, .parainstructions and .altinstructions are
> prefixed by ".klp.arch.${objname}" so that the module loader ignores them
> and livepatch can apply them manually.
The solution looks correct to me. The fun will be how to generate
the sections. If I get this correctly, it is not enough to rename
the existing ones. Instead, we need to split .parainstructions
and .altinstructions sections into per-object ones.
I wonder if there is a plan for this. Especially I am interested
into the patches created from sources ;-) I wonder if we could add
a tag somewhere and improve the build infrastructure.
Best Regards,
Petr
next prev parent reply other threads:[~2016-07-07 15:56 UTC|newest]
Thread overview: 15+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-07-06 2:34 [PATCH 0/2] Fix issue with alternatives/paravirt patches Jessica Yu
2016-07-06 2:34 ` [PATCH 1/2] livepatch: use arch_klp_init_object_loaded() to finish arch-specific tasks Jessica Yu
2016-07-06 2:35 ` [PATCH 2/2] livepatch/x86: apply alternatives and paravirt patches after relocations Jessica Yu
2016-07-08 15:44 ` Josh Poimboeuf
2016-07-07 15:56 ` Petr Mladek [this message]
2016-07-07 22:53 ` [PATCH 0/2] Fix issue with alternatives/paravirt patches Josh Poimboeuf
2016-07-12 11:55 ` Miroslav Benes
2016-07-12 14:01 ` Josh Poimboeuf
2016-07-13 1:18 ` Jessica Yu
2016-07-07 23:51 ` Jessica Yu
2016-07-08 5:22 ` [PATCH 0/2] " Christopher Arges
2016-07-08 16:57 ` Jessica Yu
2016-07-12 12:06 ` [PATCH 0/2] " Miroslav Benes
2016-07-21 5:10 ` Jessica Yu
2016-07-21 8:48 ` Miroslav Benes
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