Re: [RFC PATCH v9 05/27] x86/cet/shstk: Add Kconfig option for user-mode Shadow Stack protection

[Dave Hansen]

On 3/6/20 10:37 AM, Yu-cheng Yu wrote:
> We used to do this for CET instructions, but after adding kernel-mode
> instructions and inserting ENDBR's, the code becomes cluttered.  I also
> found an earlier discussion on the ENDBR:
> 
> https://lore.kernel.org/lkml/CALCETrVRH8LeYoo7V1VBPqg4WS0Enxtizt=T7dPvgoeWfJrdzA@xxxxxxxxxxxxxx/
> 
> It makes sense to let the user know early on that the system cannot support
> CET and cannot build a CET-enabled kernel.
> 
> One thing we can do is to disable CET in Kconfig and not in kernel
> build, which I will do in the next version.

I'll go on the record and say I think we should allow building
CET-enabled kernels on old toolchains.  We need it for build test
coverage.  We can spit out a warning, but we need to allow building it.

Andy L, do you have any heartburn with that?