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Open Source and information security mailing list archives
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Date: Thu, 23 Sep 2021 18:42:04 -0700 From: Kees Cook <keescook@...omium.org> To: Vito Caputo <vcaputo@...garu.com> Cc: 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>, Mark Rutland <mark.rutland@....com>, 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, x86@...nel.org, linux-fsdevel@...r.kernel.org, linux-hardening@...r.kernel.org Subject: Re: [PATCH] proc: Disable /proc/$pid/wchan On Thu, Sep 23, 2021 at 06:34:08PM -0700, Vito Caputo 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.) > > > > And you have the syscall # onhand when performing the syscall entry, > no? > > The point is, if the alternative is to always get 0 from > /proc/PID/wchan when a process is sitting in ioctl(), I'd be perfectly > happy to get back sys_ioctl. I'm under the impression there's quite a > bit of vendor-specific flexibility here in terms of how precise WCHAN > is. Oh, yeah, if you're happy with syscall-level granularity, that'd be totally fine by me too. > If it's possible to preserve the old WCHAN precision I'm all for it. > But if we've become so paranoid about leaking anything about the > kernel to userspace that this is untenable, even if it just spits out > the syscall being performed that has value. I'd like to find a middle ground -- wchan has always seemed like a info leak, even with only symbols. And it doesn't help that walking the stack from outside the current task is difficult. :) -Kees -- Kees Cook
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