linux-kernel.vger.kernel.org archive mirror
 help / color / mirror / Atom feed
From: Kees Cook <keescook@chromium.org>
To: Josh Poimboeuf <jpoimboe@redhat.com>
Cc: "Mark Rutland" <mark.rutland@arm.com>,
	"Vito Caputo" <vcaputo@pengaru.com>,
	"Jann Horn" <jannh@google.com>,
	"Thomas Gleixner" <tglx@linutronix.de>,
	"Ingo Molnar" <mingo@redhat.com>,
	"Borislav Petkov" <bp@alien8.de>,
	"H. Peter Anvin" <hpa@zytor.com>, "Jens Axboe" <axboe@kernel.dk>,
	"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>,
	"Qi Zheng" <zhengqi.arch@bytedance.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: Wed, 29 Sep 2021 11:54:55 -0700	[thread overview]
Message-ID: <202109291152.681444A135@keescook> (raw)
In-Reply-To: <20210927205056.jjdlkof5w6fs5wzw@treble>

On Mon, Sep 27, 2021 at 01:50:56PM -0700, Josh Poimboeuf wrote:
> On Mon, Sep 27, 2021 at 11:07:27AM -0700, Kees Cook wrote:
> > On Mon, Sep 27, 2021 at 10:03:51AM +0100, Mark Rutland wrote:
> > > On Fri, Sep 24, 2021 at 07:26:22AM -0700, Kees Cook wrote:
> > > > On Fri, Sep 24, 2021 at 02:54:24PM +0100, Mark Rutland wrote:
> > > > > On Thu, Sep 23, 2021 at 06:16:16PM -0700, Kees Cook wrote:
> > > > > > On Thu, Sep 23, 2021 at 05:22:30PM -0700, Vito Caputo wrote:
> > > > > > > Instead of unwinding stacks maybe the kernel should be sticking an
> > > > > > > entrypoint address in the current task struct for get_wchan() to
> > > > > > > access, whenever userspace enters the kernel?
> > > > > > 
> > > > > > wchan is supposed to show where the kernel is at the instant the
> > > > > > get_wchan() happens. (i.e. recording it at syscall entry would just
> > > > > > always show syscall entry.)
> > > > > 
> > > > > It's supposed to show where a blocked task is blocked; the "wait
> > > > > channel".
> > > > > 
> > > > > I'd wanted to remove get_wchan since it requires cross-task stack
> > > > > walking, which is generally painful.
> > > > 
> > > > Right -- this is the "fragile" part I'm worried about.
> > 
> > I'd like to clarify this concern first -- is the proposed fix actually
> > fragile? Because I think we'd be better off just restoring behavior than
> > trying to invent new behavior...
> > 
> > i.e. Josh, Jann, do you see any issues with Qi Zheng's fix here:
> > https://lore.kernel.org/all/20210924062006.231699-4-keescook@chromium.org/
> 
> Even with that patch, it doesn't lock the task's runqueue before reading
> the stack, so there's still the possibility of the task running on
> another CPU and the unwinder going off the rails a bit, which might be
> used by an attacker in creative ways similar to the /proc/<pid>/stack
> vulnerability Jann mentioned earlier.

Since I think we're considering get_wchan() to be slow-path, can we just
lock the runqueue and use arch_stack_walk_reliable()?

-- 
Kees Cook

  reply	other threads:[~2021-09-29 18:55 UTC|newest]

Thread overview: 26+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-09-23 23:31 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 [this message]
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

Reply instructions:

You may reply publicly to this message via plain-text email
using any one of the following methods:

* Save the following mbox file, import it into your mail client,
  and reply-to-all from there: mbox

  Avoid top-posting and favor interleaved quoting:
  https://en.wikipedia.org/wiki/Posting_style#Interleaved_style

* Reply using the --to, --cc, and --in-reply-to
  switches of git-send-email(1):

  git send-email \
    --in-reply-to=202109291152.681444A135@keescook \
    --to=keescook@chromium.org \
    --cc=Kenta.Tada@sony.com \
    --cc=akpm@linux-foundation.org \
    --cc=amistry@google.com \
    --cc=andrea.righi@canonical.com \
    --cc=axboe@kernel.dk \
    --cc=bp@alien8.de \
    --cc=bristot@redhat.com \
    --cc=christian.brauner@ubuntu.com \
    --cc=dave.hansen@linux.intel.com \
    --cc=deller@gmx.de \
    --cc=ebiederm@xmission.com \
    --cc=hpa@zytor.com \
    --cc=jannh@google.com \
    --cc=jpoimboe@redhat.com \
    --cc=kaleshsingh@google.com \
    --cc=laijs@linux.alibaba.com \
    --cc=legion@kernel.org \
    --cc=linux-fsdevel@vger.kernel.org \
    --cc=linux-hardening@vger.kernel.org \
    --cc=linux-kernel@vger.kernel.org \
    --cc=luto@kernel.org \
    --cc=mark.rutland@arm.com \
    --cc=metze@samba.org \
    --cc=mhocko@suse.com \
    --cc=michael.weiss@aisec.fraunhofer.de \
    --cc=mingo@redhat.com \
    --cc=ohoono.kwon@samsung.com \
    --cc=peterz@infradead.org \
    --cc=tglx@linutronix.de \
    --cc=vcaputo@pengaru.com \
    --cc=x86@kernel.org \
    --cc=yifeifz2@illinois.edu \
    --cc=zhengqi.arch@bytedance.com \
    --subject='Re: [PATCH] proc: Disable /proc/$pid/wchan' \
    /path/to/YOUR_REPLY

  https://kernel.org/pub/software/scm/git/docs/git-send-email.html

* If your mail client supports setting the In-Reply-To header
  via mailto: links, try the mailto: link

This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).