lists  /  announce  owl-users  owl-dev  john-users  john-dev  passwdqc-users  yescrypt  popa3d-users  /  oss-security  kernel-hardening  musl  sabotage  tlsify  passwords  /  crypt-dev  xvendor  /  Bugtraq  Full-Disclosure  linux-kernel  linux-netdev  linux-ext4  linux-hardening  linux-cve-announce  PHC 
Open Source and information security mailing list archives
Hash Suite: Windows password security audit tool. GUI, reports in PDF.
[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]
Date:   Thu, 23 Sep 2021 18:42:04 -0700
From:   Kees Cook <>
To:     Vito Caputo <>
Cc:     Jann Horn <>, Thomas Gleixner <>,
        Josh Poimboeuf <>,
        Ingo Molnar <>, Borislav Petkov <>,
        "H. Peter Anvin" <>, Jens Axboe <>,
        Mark Rutland <>,
        Peter Zijlstra <>,
        Stefan Metzmacher <>,
        Andy Lutomirski <>,
        Lai Jiangshan <>,
        Christian Brauner <>,
        Andrew Morton <>,
        "" <>,
        Daniel Bristot de Oliveira <>,
        Michael WeiƟ 
        Anand K Mistry <>,
        Alexey Gladkov <>,
        Michal Hocko <>, Helge Deller <>,
        Dave Hansen <>,
        Andrea Righi <>,
        Ohhoon Kwon <>,
        Kalesh Singh <>,
        YiFei Zhu <>,
        "Eric W. Biederman" <>,,,,
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 Cook

Powered by blists - more mailing lists