Re: [PATCH] killswitch: add per-function short-circuit mitigation primitive

[Greg KH <gregkh@linuxfoundation.org>]

On Thu, May 07, 2026 at 09:40:44AM -0400, Sasha Levin wrote:
> On Thu, May 07, 2026 at 12:47:43PM +0200, Greg KH wrote:
> > > +	atomic_long_t		retval;
> > 
> > Why is this an atomic value?  Shouldn't it be whatever the userspace
> > return type is?
> 
> The return register is `long` on every arch.
> 
> While testing this, I added the ability to modify the return value after we
> create a killswitch, and figured that it could be a useful thing to keep in the
> code.
> 
> But then I got worried about a race between a user changing the return value of
> the killswitch and some program trying to execute the code, and getting some
> combination of the old and the new return value.
> 
> Is that a real concern? I'm not sure - but making this atomic was cheap enough.

I don't think that a combination should matter all that much here, but
at least it makes sense now.  You might want to document that somewhere
here.

thanks,

greg k-h