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:

quoted

On 4/29/20 3:07 PM, Yu-cheng Yu wrote:

quoted

+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.

quoted

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