From: Jann Horn <jannh@google.com>
To: Vito Caputo <vcaputo@pengaru.com>
Cc: "Kees Cook" <keescook@chromium.org>,
"Thomas Gleixner" <tglx@linutronix.de>,
"Josh Poimboeuf" <jpoimboe@redhat.com>,
"Ingo Molnar" <mingo@redhat.com>,
"Borislav Petkov" <bp@alien8.de>,
"H. Peter Anvin" <hpa@zytor.com>, "Jens Axboe" <axboe@kernel.dk>,
"Mark Rutland" <mark.rutland@arm.com>,
"Peter Zijlstra" <peterz@infradead.org>,
"Stefan Metzmacher" <metze@samba.org>,
"Andy Lutomirski" <luto@kernel.org>,
"Lai Jiangshan" <laijs@linux.alibaba.com>,
"Christian Brauner" <christian.brauner@ubuntu.com>,
"Andrew Morton" <akpm@linux-foundation.org>,
"Kenta.Tada@sony.com" <Kenta.Tada@sony.com>,
"Daniel Bristot de Oliveira" <bristot@redhat.com>,
"Michael Weiß" <michael.weiss@aisec.fraunhofer.de>,
"Anand K Mistry" <amistry@google.com>,
"Alexey Gladkov" <legion@kernel.org>,
"Michal Hocko" <mhocko@suse.com>, "Helge Deller" <deller@gmx.de>,
"Dave Hansen" <dave.hansen@linux.intel.com>,
"Andrea Righi" <andrea.righi@canonical.com>,
"Ohhoon Kwon" <ohoono.kwon@samsung.com>,
"Kalesh Singh" <kaleshsingh@google.com>,
"YiFei Zhu" <yifeifz2@illinois.edu>,
"Eric W. Biederman" <ebiederm@xmission.com>,
linux-kernel@vger.kernel.org, x86@kernel.org,
linux-fsdevel@vger.kernel.org, linux-hardening@vger.kernel.org
Subject: Re: [PATCH] proc: Disable /proc/$pid/wchan
Date: Fri, 24 Sep 2021 02:08:45 +0200 [thread overview]
Message-ID: <CAG48ez0Rtv5kqHWw368Ym3GkKodPA+JETOAN+=c2KPa3opENSA@mail.gmail.com> (raw)
In-Reply-To: <20210923234917.pqrxwoq7yqnvfpwu@shells.gnugeneration.com>
On Fri, Sep 24, 2021 at 1:59 AM Vito Caputo <vcaputo@pengaru.com> wrote:
> On Thu, Sep 23, 2021 at 04:31:05PM -0700, Kees Cook wrote:
> > The /proc/$pid/wchan file has been broken by default on x86_64 for 4
> > years now[1]. As this remains a potential leak of either kernel
> > addresses (when symbolization fails) or limited observation of kernel
> > function progress, just remove the contents for good.
> >
> > Unconditionally set the contents to "0" and also mark the wchan
> > field in /proc/$pid/stat with 0.
> >
> > This leaves kernel/sched/fair.c as the only user of get_wchan(). But
> > again, since this was broken for 4 years, was this profiling logic
> > actually doing anything useful?
> >
> > [1] https://lore.kernel.org/lkml/20210922001537.4ktg3r2ky3b3r6yp@treble/
> >
> > Cc: Josh Poimboeuf <jpoimboe@redhat.com>
> > Cc: Vito Caputo <vcaputo@pengaru.com>
> > Signed-off-by: Kees Cook <keescook@chromium.org>
> <snip>
>
>
> Please don't deliberately break WCHANs wholesale. This is a very
> useful tool for sysadmins to get a vague sense of where processes are
> spending time in the kernel on production systems without affecting
> performance or having to restart things under instrumentation.
Wouldn't /proc/$pid/stack be more useful for that anyway? As long as
you have root privileges, you can read that to get the entire stack,
not just a single method name.
(By the way, I guess that might be an alternative to ripping wchan out
completely - require CAP_SYS_ADMIN like for /proc/$pid/stack?)
next prev parent reply other threads:[~2021-09-24 0:09 UTC|newest]
Thread overview: 26+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-09-23 23:31 [PATCH] proc: Disable /proc/$pid/wchan Kees Cook
2021-09-23 23:38 ` Kees Cook
2021-09-24 13:31 ` Peter Zijlstra
2021-09-23 23:49 ` Vito Caputo
2021-09-24 0:08 ` Jann Horn [this message]
2021-09-24 0:22 ` Vito Caputo
2021-09-24 1:16 ` Kees Cook
2021-09-24 1:34 ` Vito Caputo
2021-09-24 1:42 ` Kees Cook
2021-09-24 13:54 ` Mark Rutland
2021-09-24 14:26 ` Kees Cook
2021-09-27 9:03 ` Mark Rutland
2021-09-27 18:07 ` Kees Cook
2021-09-27 20:50 ` Josh Poimboeuf
2021-09-29 18:54 ` Kees Cook
2021-09-29 19:00 ` Mark Brown
2021-09-29 19:26 ` Kees Cook
2021-09-29 19:40 ` Peter Zijlstra
2021-09-29 21:10 ` Josh Poimboeuf
2021-09-27 9:16 ` David Laight
2021-09-29 8:48 ` Peter Zijlstra
2021-09-24 2:13 ` Andrew Morton
2021-09-24 6:04 ` Kees Cook
2021-09-24 13:29 ` Peter Zijlstra
2021-09-30 18:05 ` Stephen Brennan
2021-09-30 18:12 ` Kees Cook
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