On Tue, 2024-10-01 at 18:33 +0100, Mark Brown wrote:

quoted

quoted

A shadow stack size is more symmetric on the surface, but I'm not sure it
will
be easier for userspace to handle. So I think we should just have a
pointer to
the token. But it will be a usable implementation either way.

My suspicion would be that if we're doing the pivot to a previously used
shadow stack we'd also be pivoting the regular stack along with it which
would face similar issues with having an unusual method for specifying
the stack top so I don't know how much we're really winning.

I'm not so sure. The thing is a regular stack can be re-used in full - just set
the RSP to the end and take advantage of the whole stack. A shadow stack can
only be used where there is a token.

  Like we
both keep saying either of the interfaces works though, it's just a
taste question with both having downsides.

Fair enough.