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

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Message-ID: <c644d64b-f7d0-47de-b5ba-ae2ac1b46e1b@sirena.org.uk>
Date: Fri, 16 Aug 2024 11:51:57 +0100
From: Mark Brown <broonie@...nel.org>
To: Catalin Marinas <catalin.marinas@....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 09:44:46AM +0100, Catalin Marinas wrote:

> We could, in theory, consume this token in the parent before the child
> mm is created. The downside is that if a parent forks multiple
> processes using the same shadow stack, it will have to set the token
> each time. I'd be fine with this, that's really only for the mostly
> theoretical case where one doesn't use CLONE_VM and still want a
> separate stack and shadow stack.

I originally implemented things that way but people did complain about
the !CLONE_VM case, which does TBH seem reasonable.  Note that the
parent won't as standard be able to set the token again - since the
shadow stack is not writable to userspace by default it'd instead need
to allocate a whole new shadow stack for each child.

I change back to parsing the token in the parent but I don't want to end
up in a cycle of bouncing between the two implementations depending on
who's reviewed the most recent version.

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