linux-hardening - Re: [PATCH v2 0/6] wchan: Fix ORC support and leaky fallback

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Date:   Wed, 29 Sep 2021 18:01:57 -0700
From:   Josh Poimboeuf <jpoimboe@...hat.com>
To:     Kees Cook <keescook@...omium.org>
Cc:     Peter Zijlstra <peterz@...radead.org>,
        kernel test robot <oliver.sang@...el.com>,
        Vito Caputo <vcaputo@...garu.com>,
        Jann Horn <jannh@...gle.com>, Ingo Molnar <mingo@...hat.com>,
        Juri Lelli <juri.lelli@...hat.com>,
        Vincent Guittot <vincent.guittot@...aro.org>,
        Dietmar Eggemann <dietmar.eggemann@....com>,
        Steven Rostedt <rostedt@...dmis.org>,
        Ben Segall <bsegall@...gle.com>, Mel Gorman <mgorman@...e.de>,
        Daniel Bristot de Oliveira <bristot@...hat.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Christian Brauner <christian.brauner@...ntu.com>,
        Anand K Mistry <amistry@...gle.com>,
        "Kenta.Tada@...y.com" <Kenta.Tada@...y.com>,
        Alexey Gladkov <legion@...nel.org>,
        Michael Weiß <michael.weiss@...ec.fraunhofer.de>,
        Michal Hocko <mhocko@...e.com>, Helge Deller <deller@....de>,
        Qi Zheng <zhengqi.arch@...edance.com>,
        "Tobin C. Harding" <me@...in.cc>,
        Tycho Andersen <tycho@...ho.pizza>,
        Thomas Gleixner <tglx@...utronix.de>,
        Borislav Petkov <bp@...en8.de>,
        "H. Peter Anvin" <hpa@...or.com>,
        Mark Rutland <mark.rutland@....com>,
        Jens Axboe <axboe@...nel.dk>,
        Stefan Metzmacher <metze@...ba.org>,
        Lai Jiangshan <laijs@...ux.alibaba.com>,
        Andy Lutomirski <luto@...nel.org>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        "Eric W. Biederman" <ebiederm@...ssion.com>,
        Ohhoon Kwon <ohoono.kwon@...sung.com>,
        Kalesh Singh <kaleshsingh@...gle.com>,
        YiFei Zhu <yifeifz2@...inois.edu>,
        linux-kernel@...r.kernel.org, linux-fsdevel@...r.kernel.org,
        linux-hardening@...r.kernel.org, x86@...nel.org
Subject: Re: [PATCH v2 0/6] wchan: Fix ORC support and leaky fallback

On Wed, Sep 29, 2021 at 03:02:12PM -0700, Kees Cook wrote:
> Hi,
> 
> This attempts to solve the issues from the discussion here[1]. Specifically:
> 
> 1) wchan leaking raw addresses since 152c432b128c (v5.12).
> 
> patch 1 fixes this with a revert.
> 
> 2) wchan has been broken under ORC, seen as a failure to stack walk
>    resulting in _usually_ a 0 value, since ee9f8fce9964 (v4.14).
> 
> patches 2-5 fixes this with Qi Zheng's new get_wchan() and changes to
> the /proc code to use the new helper suggested by Peter to do the stack
> walk only if the process can be kept blocked:
> https://lore.kernel.org/lkml/20210929194026.GA4323@worktop.programming.kicks-ass.net/
> 
> Peter, can you take this via -tip?

It all looks sane to me.  Thanks for cleaning up this mess.

- Should we use a similar sched wrapper for /proc/$pid/stack to make its
  raciness go away?

- At the risk of triggering a much larger patch set, I suspect
  get_wchan() can be made generic ;-)  It's just a glorified wrapper
  around stack_trace_save_tsk().

Regardless:

Acked-by: Josh Poimboeuf <jpoimboe@...hat.com>

-- 
Josh