From: Mark Rutland <mark.rutland@arm.com>
To: Kees Cook <keescook@chromium.org>
Cc: "Vito Caputo" <vcaputo@pengaru.com>,
"Jann Horn" <jannh@google.com>,
"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>,
"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/$pid/wchan
Date: Mon, 27 Sep 2021 10:03:51 +0100 [thread overview]
Message-ID: <20210927090337.GB1131@C02TD0UTHF1T.local> (raw)
In-Reply-To: <202109240716.A0792BE46@keescook>
On Fri, Sep 24, 2021 at 07:26:22AM -0700, Kees Cook wrote:
> On Fri, Sep 24, 2021 at 02:54:24PM +0100, Mark Rutland wrote:
> > On Thu, Sep 23, 2021 at 06:16:16PM -0700, Kees Cook wrote:
> > > On Thu, Sep 23, 2021 at 05:22:30PM -0700, Vito Caputo wrote:
> > > > Instead of unwinding stacks maybe the kernel should be sticking an
> > > > entrypoint address in the current task struct for get_wchan() to
> > > > access, whenever userspace enters the kernel?
> > >
> > > wchan is supposed to show where the kernel is at the instant the
> > > get_wchan() happens. (i.e. recording it at syscall entry would just
> > > always show syscall entry.)
> >
> > It's supposed to show where a blocked task is blocked; the "wait
> > channel".
> >
> > I'd wanted to remove get_wchan since it requires cross-task stack
> > walking, which is generally painful.
>
> Right -- this is the "fragile" part I'm worried about.
>
> > We could instead have the scheduler entrypoints snapshot their caller
> > into a field in task_struct. If there are sufficiently few callers, that
> > could be an inline wrapper that passes a __func__ string. Otherwise, we
> > still need to symbolize.
>
> Hmm. Does PREEMPT break this?
Within the core scheduler functions interrupts should be disabled, and
as long as we only update task_struct there we shouldn't have a race.
> Can we actually use __builtin_return_address(0) in __schedule?
We'd need to do this in a few entry points above __schedule, since the
currently get_wchan walks until !in_sched_functions(). It should be
possible, though we might need to make sure those the nexus points
aren't inlined.
Thanks,
Mark.
next prev parent reply other threads:[~2021-09-27 9:04 UTC|newest]
Thread overview: 26+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-09-23 23:31 [PATCH] proc: Disable /proc/$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 [this message]
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
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=20210927090337.GB1131@C02TD0UTHF1T.local \
--to=mark.rutland@arm.com \
--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=keescook@chromium.org \
--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=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 \
/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
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
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).