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 14:56:36 -0700 [thread overview]
Message-ID: <CAKwvOdmyEoBJCGEERUB1Vjzgw6bZpmopGzyhTecCJBMjjd_fbg@mail.gmail.com> (raw)
In-Reply-To: <CAKwvOdk26WrqF7Ni0DP+KYEp7LCtfhTemG5RBYFwR02_VRc=6Q@mail.gmail.com>
On Thu, Jul 26, 2018 at 9:59 AM Nick Desaulniers
<ndesaulniers@google.com> wrote:
>
> 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;
> }
> }
What are folks thoughts on this:
1. create function show_symbols_for_perf() that replaces
kallsyms_show_value(), maybe in linux/ftrace.c (since linux/ftrace.h
is included in kernel/trace/trace_printk.c and kernel/kallsyms.c).
2. use new show_symbols_for_perf() in kernel/kallsyms.c and
kernel/trace/trace_printk.c
Where the implementation of show_symbols_for_perf() is
kallsyms_show_value() implementation-wise (just renamed since it's no
longer kallsyms specific). Does that make sense, or should I just
send a patch? Does it make sense to check whether
kernel/trace/trace_printk.c#t_show() should print an address based on
the same checks done in kallsyms_show_value()?
--
Thanks,
~Nick Desaulniers
next prev parent reply other threads:[~2018-07-26 21:56 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
2018-07-26 21:56 ` Nick Desaulniers [this message]
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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