Re: [PATCH RFT v9 4/8] fork: Add shadow stack support to clone3()

[Edgecombe, Rick P]

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