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From: Nick Desaulniers <ndesaulniers@google.com>
To: rostedt@goodmis.org
Cc: salyzyn@android.com, LKML <linux-kernel@vger.kernel.org>,
	mingo@redhat.com, kernel-team@android.com,
	stable@vger.kernel.org
Subject: Re: [PATCH] tracing: do not leak kernel addresses
Date: Thu, 26 Jul 2018 09:59:38 -0700	[thread overview]
Message-ID: <CAKwvOdk26WrqF7Ni0DP+KYEp7LCtfhTemG5RBYFwR02_VRc=6Q@mail.gmail.com> (raw)
In-Reply-To: <20180726123719.0db9dca0@gandalf.local.home>

On Thu, Jul 26, 2018 at 9:37 AM Steven Rostedt <rostedt@goodmis.org> wrote:
>
> On Thu, 26 Jul 2018 09:32:07 -0700
> Nick Desaulniers <ndesaulniers@google.com> wrote:
>
> > On Thu, Jul 26, 2018 at 8:22 AM Steven Rostedt <rostedt@goodmis.org> wrote:
> > >
> > > On Thu, 26 Jul 2018 08:14:08 -0700
> > > Mark Salyzyn <salyzyn@android.com> wrote:
> > >
> > > > Thank you Steve, much appreciated feedback, I have asked the security
> > > > developers to keep this in mind and come up with a correct fix.
> > > >
> > > > The correct fix that meets your guidelines would _not_ be suitable for
> > > > stable due to the invasiveness it sounds, only for the latest will such
> > > > a rework make sense. As such, the fix proposed in this patch is the only
> > > > one that meets the bar for stable patch simplicity, and merely(!) needs
> > > > to state that if the fix is taken, perf and trace are broken.
> > > >
> > > > Posting this patch publicly on the lists, that may never be applied, may
> > > > be the limit of our responsibility for a fix to stable kernel releases,
> > > > to be optionally applied by vendors concerned with this CVE criteria?
> > > >
> > >
> > > The patch breaks the code it touches. It makes it useless.
> >
> > Doesn't that depend on kptr_restrict, or would it be broken if
> > kptr_restrict was set to 0?
>
> Is that what governs the output of kallsyms?

From my workstation:

$ cat /proc/kallsyms

prints a bunch of zero'd out addresses, while

$ sudo !!

prints out actual addresses.  Looking at kernel/kallsyms.c, it seems
that there's no use of %pK, but kallsyms_show_value() switches on
kptr_restrict (and additional values):

/*
 * We show kallsyms information even to normal users if we've enabled
 * kernel profiling and are explicitly not paranoid (so kptr_restrict
 * is clear, and sysctl_perf_event_paranoid isn't set).
 *
 * Otherwise, require CAP_SYSLOG (assuming kptr_restrict isn't set to
 * block even that).
 */
int kallsyms_show_value(void)
{
        switch (kptr_restrict) {
        case 0:
                if (kallsyms_for_perf())
                        return 1;
        /* fallthrough */
        case 1:
                if (has_capability_noaudit(current, CAP_SYSLOG))
                        return 1;
        /* fallthrough */
        default:
                return 0;
        }
}


-- 
Thanks,
~Nick Desaulniers

  reply	other threads:[~2018-07-26 16:59 UTC|newest]

Thread overview: 26+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2018-07-25 20:22 [PATCH] tracing: do not leak kernel addresses Mark Salyzyn
2018-07-25 21:14 ` Nick Desaulniers
2018-07-26  1:07 ` Steven Rostedt
2018-07-26 15:14   ` Mark Salyzyn
2018-07-26 15:22     ` Steven Rostedt
2018-07-26 16:32       ` Nick Desaulniers
2018-07-26 16:37         ` Steven Rostedt
2018-07-26 16:59           ` Nick Desaulniers [this message]
2018-07-26 21:56             ` Nick Desaulniers
2018-07-26 15:31     ` Greg KH
2018-07-26 16:52       ` Nick Desaulniers
2018-07-26 22:15         ` Steven Rostedt
2018-07-27 12:07           ` Jordan Glover
2018-07-27 13:40             ` Jann Horn
2018-07-27 13:47               ` Steven Rostedt
2018-07-27 18:13                 ` Nick Desaulniers
2018-07-27 18:31                   ` Steven Rostedt
     [not found]                     ` <CAMx4XWv3OazvURuN1XU2+5C5tNDzPuTniMn_T=XTA4P8_uwS_A@mail.gmail.com>
2018-07-27 18:47                       ` Jann Horn
2018-07-27 18:58                         ` Jann Horn
2018-07-27 19:54                           ` Theodore Y. Ts'o
2018-07-27 20:11                             ` Steven Rostedt
2018-07-27 20:21                               ` Theodore Y. Ts'o
2018-07-27 20:53                                 ` Steven Rostedt
2018-07-27 22:05                                 ` Sandeep Patil
2018-07-28  0:04                                   ` Theodore Y. Ts'o
2018-07-30 14:35                                     ` Sandeep Patil

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