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

[Thomas Gleixner]

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.

Thanks,

        tglx