linux-kernel - Re: [PATCH 5/6] x86/shstk: don't create the shadow stack for PF_USER

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Message-ID: <78b04d05b94b605f287b9a594cd2aa9f1cda10df.camel@intel.com>
Date: Thu, 14 Aug 2025 22:43:45 +0000
From: "Edgecombe, Rick P" <rick.p.edgecombe@...el.com>
To: "broonie@...nel.org" <broonie@...nel.org>
CC: "debug@...osinc.com" <debug@...osinc.com>, "mingo@...nel.org"
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Subject: Re: [PATCH 5/6] x86/shstk: don't create the shadow stack for
 PF_USER_WORKERs

On Thu, 2025-08-14 at 19:33 +0100, Mark Brown wrote:
> > How about just adding the 'minimal' condition to:
> >  	if (clone_flags & CLONE_VFORK) {
> >  		shstk->base = 0;
> >  		shstk->size = 0;
> >  		return 0;
> >  	}
> > ...then update all the comments where vfork is called out as the only case
> > that
> > does this?
> 
> Perhaps we should factor the logic for deciding if we need to allocate a
> userspace shadow stack out into the arch independent code and do
> something like set a flag in kernel_clone_args that the arches can
> check?  I think the logic is the same for all arches at the minute and
> don't see a reason why it'd diverge.

Sounds good. Like a little start to this:
https://lore.kernel.org/lkml/20241010-shstk_converge-v1-0-631beca676e7@rivosinc.com/

>   That'd collide a bit with my
> clone3() series, there's some overlap there with that creating another
> reason why the decision would change.  Reducing the duplication would be
> nice.

Argh, I need to test the latest of that still.