linux-kernel - Re: [PATCH RFC 0/3] arm64/gcs: Allow reuse of user managed shadow stacks

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Message-ID: <04dc6271e11b453204255779fcd3c29573c9c296.camel@intel.com>
Date: Fri, 26 Sep 2025 15:39:46 +0000
From: "Edgecombe, Rick P" <rick.p.edgecombe@...el.com>
To: "yury.khrustalev@....com" <yury.khrustalev@....com>
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Subject: Re: [PATCH RFC 0/3] arm64/gcs: Allow reuse of user managed shadow
 stacks

On Fri, 2025-09-26 at 16:07 +0100, Yury Khrustalev wrote:
> > I think we should see a fuller solution from the glibc side before
> > adding new
> > kernel features like this. (apologies if I missed it).
> 
> What do you mean by "a fuller solution from the glibc side"? A
> solution
> for re-using shadow stacks? 

I mean some code or a fuller explained solution that uses this new
kernel functionality. I think the scheme that Florian suggested in the
thread linked above (longjmp() to the start of the stack) will have
trouble if the thread pivots to a new shadow stack before exiting (e.g.
ucontext).

> Right now Glibc cannot do anything about
> shadow stacks for new threads because clone3 interface doesn't allow
> it.

If you enable WRSS (or the arm equivalent) you can re-use shadow stacks
today by writing a token.