linux-kernel - Re: [PATCH RFT v8 4/9] fork: Add shadow stack support to clone3()

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Message-ID: <830e96b4-8e35-4b80-a32f-1b500febaee5@sirena.org.uk>
Date: Fri, 16 Aug 2024 18:17:17 +0100
From: Mark Brown <broonie@...nel.org>
To: Jann Horn <jannh@...gle.com>
Cc: "Edgecombe, Rick P" <rick.p.edgecombe@...el.com>,
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Subject: Re: [PATCH RFT v8 4/9] fork: Add shadow stack support to clone3()

On Fri, Aug 16, 2024 at 07:08:09PM +0200, Jann Horn wrote:

> Yeah, having a FOLL_FORCE write in clone3 would be a weakness for
> userspace CFI and probably make it possible to violate mseal()
> restrictions that are supposed to enforce that address space regions
> are read-only.

Note that this will only happen for shadow stack pages (with the new
version) and only for a valid token at the specific address.  mseal()ing
a shadow stack to be read only is hopefully not going to go terribly
well for userspace.

> Though, did anyone in the thread yet suggest that you could do this
> before the child process has fully materialized but after the child MM
> has been set up? Somewhere in copy_process() between copy_mm() and the
> "/* No more failure paths after this point. */" comment?

Yes, I'e got a version that does that waiting to go pending some
discussion on if we even do the check for the token in the child mm.

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