Re: [PATCH v8 31/33] x86/fred: BUG() when ERETU with %rsp not equal to that when the ring 3 event was just delivered

[H. Peter Anvin]

On 6/5/23 07:15, Thomas Gleixner wrote:
> On Mon, Apr 10 2023 at 01:14, Xin Li wrote:
> > A FRED stack frame generated by a ring 3 event should never be messed up, and
> > the first thing we must make sure is that at the time an ERETU instruction is
> > executed, %rsp must have the same address as that when the user level event
> > was just delivered.
> >
> > However we don't want to bother the normal code path of ERETU because it's on
> > the hotest code path, a good choice is to do this check when ERETU
> > faults.
>
> Which might be not catching bugs where the wrong frame makes ERETU not
> fault.
>
> We have CONFIG_DEBUG_ENTRY for catching this at the proper place.

This is true, but this BUG() is a cheap test on a slow path, and thus 
can be included in production code.

	-hpa