On Thu, Jul 26, 2018 at 9:37 AM Steven Rostedt <rostedt@xxxxxxxxxxx> wrote:
>
> On Thu, 26 Jul 2018 09:32:07 -0700
> Nick Desaulniers <ndesaulniers@xxxxxxxxxx> wrote:
>
> > On Thu, Jul 26, 2018 at 8:22 AM Steven Rostedt <rostedt@xxxxxxxxxxx> wrote:
> > >
> > > On Thu, 26 Jul 2018 08:14:08 -0700
> > > Mark Salyzyn <salyzyn@xxxxxxxxxxx> 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
