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Date: Mon, 27 Sep 2021 09:16:17 +0000 From: David Laight <David.Laight@...LAB.COM> To: 'Mark Rutland' <mark.rutland@....com>, Kees Cook <keescook@...omium.org> CC: Vito Caputo <vcaputo@...garu.com>, Jann Horn <jannh@...gle.com>, "Thomas Gleixner" <tglx@...utronix.de>, Josh Poimboeuf <jpoimboe@...hat.com>, "Ingo Molnar" <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>, "H. Peter Anvin" <hpa@...or.com>, Jens Axboe <axboe@...nel.dk>, Peter Zijlstra <peterz@...radead.org>, Stefan Metzmacher <metze@...ba.org>, Andy Lutomirski <luto@...nel.org>, Lai Jiangshan <laijs@...ux.alibaba.com>, Christian Brauner <christian.brauner@...ntu.com>, Andrew Morton <akpm@...ux-foundation.org>, "Kenta.Tada@...y.com" <Kenta.Tada@...y.com>, Daniel Bristot de Oliveira <bristot@...hat.com>, Michael Weiß <michael.weiss@...ec.fraunhofer.de>, Anand K Mistry <amistry@...gle.com>, Alexey Gladkov <legion@...nel.org>, Michal Hocko <mhocko@...e.com>, "Helge Deller" <deller@....de>, Dave Hansen <dave.hansen@...ux.intel.com>, "Andrea Righi" <andrea.righi@...onical.com>, Ohhoon Kwon <ohoono.kwon@...sung.com>, Kalesh Singh <kaleshsingh@...gle.com>, YiFei Zhu <yifeifz2@...inois.edu>, "Eric W. Biederman" <ebiederm@...ssion.com>, "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>, "x86@...nel.org" <x86@...nel.org>, "linux-fsdevel@...r.kernel.org" <linux-fsdevel@...r.kernel.org>, "linux-hardening@...r.kernel.org" <linux-hardening@...r.kernel.org> Subject: RE: [PATCH] proc: Disable /proc/$pid/wchan From: Mark Rutland > Sent: 24 September 2021 14:54 > > 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. > > 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. It ought to be something stashed in the 'wait_queue_head'. Perhaps defaulting to the address/name of the function that initialised it. That would be much nearer the original (pre Linux) semantics. David - Registered Address Lakeside, Bramley Road, Mount Farm, Milton Keynes, MK1 1PT, UK Registration No: 1397386 (Wales)
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