[PATCH 0/7] Kernel Userspace Protection for radix

[Michael Ellerman]

Kees Cook <keescook at chromium.org> writes:
> On Thu, Feb 21, 2019 at 4:09 PM Russell Currey <ruscur at russell.cc> wrote:
>> On Thu, 2019-02-21 at 08:07 -0800, Kees Cook wrote:
>> > On Thu, Feb 21, 2019 at 1:36 AM Russell Currey <ruscur at russell.cc>
>> > wrote:
>> > > The first three patches of these series are from Christophe's work
>> > > and are
>> > > the bare minimum framework needed to implement the support for
>> > > radix.
>> > >
>> > > In patch 3, I have removed from Christophe's patch my
>> > > implementation of
>> > > the 64-bit exception handling code, since we don't have an answer
>> > > for
>> > > making nested exceptions work yet.  This is mentioned in the final
>> > > KUAP
>> > > patch.  Regardless, this is still a significant security
>> > > improvement
>> > > and greatly narrows the attack surface.
>> >
>> > Nice! Am I understanding correctly that with this series powerpc9 and
>> > later, using radix, will pass the lkdtm tests for KUAP and KUEP (i.e.
>> > EXEC_USERSPACE and ACCESS_USERSPACE)?
>>
>> Yes!  We've had execution prevention for a while on radix (which is
>> default on POWER9) since 3b10d0095a1e, the only functional thing this
>> series does is allow disabling it with nosmep.  This series adds access
>> prevention.
>
> Ah-ha; excellent. And CONFIG_PPC_RADIX_MMU is "default y" already. :)

Though on real hardware it doesn't really work yet, at least if there
are any idle states enabled.

Patch under discussion to fix it:

  https://patchwork.ozlabs.org/patch/1038568/


cheers