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From: Kees Cook <keescook@chromium.org>
To: Andrew Morton <akpm@linux-foundation.org>
Cc: "Thomas Gleixner" <tglx@linutronix.de>,
	"Josh Poimboeuf" <jpoimboe@redhat.com>,
	"Vito Caputo" <vcaputo@pengaru.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>,
	"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: Thu, 23 Sep 2021 23:04:11 -0700	[thread overview]
Message-ID: <202109232301.B0B9753D@keescook> (raw)
In-Reply-To: <20210923191306.664d39866761778a4a6ea56c@linux-foundation.org>

On Thu, Sep 23, 2021 at 07:13:06PM -0700, Andrew Morton wrote:
> On Thu, 23 Sep 2021 16:31:05 -0700 Kees Cook <keescook@chromium.org> wrote:
> 
> > The /proc/$pid/wchan file has been broken by default on x86_64 for 4
> > years now[1].
> 
> [1] is hard to decrypt.  I think it would be better if this changelog
> were to describe the problem directly, completely and succinctly?
> 
> > As this remains a potential leak of either kernel
> > addresses (when symbolization fails) or limited observation of kernel
> > function progress, just remove the contents for good.
> > 
> > Unconditionally set the contents to "0" and also mark the wchan
> > field in /proc/$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?
> 
> Agree that returning a hard-wired "0\n" is the way to go.

I must NAK my own patch. ;) It looks like this would be a breaking
userspace-visible change[1].

We need to fix the two bugs though:

1) wchan broken under ORC (patch exists in the thread at [1])

2) wchan leaking raw addresses (152c432b128c needs reverting from v5.12 and later)

-Kees

[1] https://lore.kernel.org/lkml/20210924054647.v6x6risoa4jhuu6s@shells.gnugeneration.com

-- 
Kees Cook

  reply	other threads:[~2021-09-24  6:04 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
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 [this message]
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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