linux-kernel - Re: [PATCH v2] module: kallsyms: Ensure preemption in add_kallsyms() with PREEMPT

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Date:   Thu, 7 Jul 2022 17:57:50 +0100
From:   Aaron Tomlin <atomlin@...hat.com>
To:     Luis Chamberlain <mcgrof@...nel.org>
Cc:     rostedt@...dmis.org, cl@...ux.com, pmladek@...e.com,
        mbenes@...e.cz, christophe.leroy@...roup.eu,
        akpm@...ux-foundation.org, linux-kernel@...r.kernel.org,
        linux-modules@...r.kernel.org, atomlin@...mlin.com,
        ghalat@...hat.com, oleksandr@...alenko.name, neelx@...hat.com,
        daniel.thompson@...aro.org, hch@...radead.org, tglx@...utronix.de,
        linux-rt-users@...r.kernel.org
Subject: Re: [PATCH v2] module: kallsyms: Ensure preemption in add_kallsyms()
 with PREEMPT_RT

On Wed 2022-07-06 10:58 -0700, Luis Chamberlain wrote:
> Hey Aaron, thanks again!

Hi Luis,

No problem :)

> On Mon, Jul 04, 2022 at 05:17:53PM +0100, Aaron Tomlin wrote:
> > To disable preemption in the context of add_kallsyms() is incorrect.
> 
> Why, what broke? Did this used to work? Was the commit in question a
> regression then? Clarifying all this will help a lot.

Sorry for the confusion! If I understand correctly, nothing broke
intrinsically.

Rather with commit 08126db5ff73 ("module: kallsyms: Fix suspicious rcu
usage") under PREEMPT_RT=y, by disabling preemption, I introduced an
unbounded latency since the loop is not fixed which is generally frowned
upon. So, I would say this was a regression since earlier preemption was
not disabled and we would dereference RCU-protected pointers explicitly
i.e. without using the more appropriate rcu_dereference() family
of primitives. That being said, these pointers cannot change in this
context as explained previously.

Would the above be suitable - just to confirm before I send another
iteration?

Kind regards,

-- 
Aaron Tomlin