Re: [PATCH v10 13/40] arm64/mm: Map pages for guarded control stack

[Catalin Marinas]

On Tue, Aug 20, 2024 at 04:28:21PM +0100, Mark Brown wrote:
> On Tue, Aug 20, 2024 at 03:59:21PM +0100, Catalin Marinas wrote:
> > On Mon, Aug 19, 2024 at 05:33:24PM +0100, Mark Brown wrote:
> > > On Mon, Aug 19, 2024 at 10:10:36AM +0100, Catalin Marinas wrote:
> > > > Is there any arch restriction with setting BTI and GCS? It doesn't make
> > > > sense but curious if it matters. We block the exec permission anyway
> > > > (unless the BTI pages moved to PIE as well, I don't remember).
> 
> > > As you say BTI should be meaningless for a non-executable page like GCS,
> > > I'm not aware of any way in which it matters.  BTI is separate to PIE.
> 
> > My thoughts were whether we can get rid of this hunk entirely by
> > handling it in the core code. We'd allow BTI if one wants such useless
> > combination but clear VM_MAYEXEC in the core code (and ignore VM_SHARED
> > since you can't set it anyway).
> 
> I have to admit that the BTI because I was shoving _EXEC in there rather
> than because it specifically needed to be blocked.  So change the check
> for VM_SHARED to a VM_WARN_ON(), and leave the _EXEC check for now
> pending the above core change?

Yes, sounds good.

-- 
Catalin