Re: [PATCH v2 0/4] Static calls

[Andy Lutomirski]

>> On Dec 5, 2018, at 7:04 AM, Josh Poimboeuf <jpoimboe@xxxxxxxxxx> wrote:
>
>
>> Anyway, I have a new objection to Joshâs create_gap proposal: what on
>> Earth will kernel CET do to it?  Maybe my longjmp-like hack is
>> actually better.
>
> Does CET even care about iret?  I assumed it didn't.  If it does, your
> proposal would have the same problem, no?

I think it doesnât, but it doesnât really matter.  The shadow stack looks like:

retaddr of function being poked
call do_int3 + 5

And, to emulate a call, you need to stick a new frame right in the
middle.  At least with a longjmp-like approach, you can clobber the
âcall do_int3 + 5â part and then INCSSP on the way out.  To be fair, I
think this also sucks.

PeterZ, can we abuse NMI to make this problem go away?  I don't
suppose that we have some rule that NMI handlers never wait for other
CPUs to finish doing anything?