Re: [PATCH v11 9/9] x86: Disallow vsyscall emulation when CET is enabled

[Yu, Yu-cheng]

On 8/25/2020 2:14 AM, Florian Weimer wrote:
> * Andy Lutomirski:
>
> > On Mon, Aug 24, 2020 at 5:30 PM Yu-cheng Yu <yu-cheng.yu@xxxxxxxxx> wrote:
> > > From: "H.J. Lu" <hjl.tools@xxxxxxxxx>
> > >
> > > Emulation of the legacy vsyscall page is required by some programs built
> > > before 2013.  Newer programs after 2013 don't use it.  Disallow vsyscall
> > > emulation when Control-flow Enforcement (CET) is enabled to enhance
> > > security.
> >
> > NAK.
> >
> > By all means disable execute emulation if CET-IBT is enabled at the
> > time emulation is attempted, and maybe even disable the vsyscall page
> > entirely if you can magically tell that CET-IBT will be enabled when a
> > process starts, but you don't get to just disable it outright on a
> > CET-enabled kernel.
>
> Yeah, we definitely would have to revert/avoid this downstream.  People
> definitely want to run glibc-2.12-era workloads on current kernels.
> Thanks for catching it.

That makes sense.  I will update the patch.

Thanks,
Yu-cheng