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

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Message-ID: <0999160fd5282ac129aab300b667af35d7251582.camel@intel.com>
Date: Tue, 1 Oct 2024 23:03:10 +0000
From: "Edgecombe, Rick P" <rick.p.edgecombe@...el.com>
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Subject: Re: [PATCH RFT v9 4/8] fork: Add shadow stack support to clone3()

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.