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

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Message-ID: <YVV36z4UZaL/vOBI@hirez.programming.kicks-ass.net>
Date:   Thu, 30 Sep 2021 10:40:11 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     Josh Poimboeuf <jpoimboe@...hat.com>
Cc:     Kees Cook <keescook@...omium.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 06:01:57PM -0700, Josh Poimboeuf wrote:

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

Alternatively, can we make /stack go away? AFAICT the semantics of that
are far worse in that it wants the actual kernel stack of a task,
blocked or not, which is a total pain in the arse (not to mention a
giant infoleak and side-channel).

> - 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().

Done that for you :-)