Re: [PATCH v10 01/26] Documentation/x86: Add CET description

Yu-cheng Yu
2020-05-12T23:20:30Z

On Wed, 2020-04-29 at 16:02 -0700, Yu-cheng Yu wrote:
> On Wed, 2020-04-29 at 15:53 -0700, Dave Hansen wrote:
> > On 4/29/20 3:07 PM, Yu-cheng Yu wrote:
> > > +Note:
> > > + There is no CET-enabling arch_prctl function. By design, CET is enabled
> > > + automatically if the binary and the system can support it.
> >
> > I think Andy and I danced around this last time. Let me try to say it
> > more explicitly.
> >
> > I want CET kernel enabling to able to be disconnected from the on-disk
> > binary. I want a binary compiled with CET to be able to disable it, and
> > I want a binary not compiled with CET to be able to enable it. I want
> > different threads in a process to be able to each have different CET status.
>
> The kernel patches we have now can be modified to support this model. If after
> discussion this is favorable, I will modify code accordingly.

To turn on/off and to lock CET are application-level decisions. The kernel does
not prevent any of those. Should there be a need to provide an arch_prctl() to
turn on CET, it can be added without any conflict to this series.

> > Which JITs was this tested with? I think as a bare minimum we need to
> > know that this design can accommodate _a_ modern JIT. It would be
> > horrible if the browser javascript engines couldn't use this design, for
> > instance.
>
> JIT work is still in progress. When that is available I will test it.

I found CET has been enabled in LLVM JIT, Mesa JIT as well as sljit which is
used by jit. So the current model works with JIT.

Yu-cheng