linux-kernel - Re: [PATCH v3 1/1] x86/shstk: don't create the shadow stack for PF_USER

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Message-ID: <f071255b-b62b-43c9-b374-d213017dffd5@sirena.org.uk>
Date: Wed, 3 Sep 2025 17:39:52 +0100
From: Mark Brown <broonie@...nel.org>
To: Dave Hansen <dave.hansen@...el.com>
Cc: Oleg Nesterov <oleg@...hat.com>, Borislav Petkov <bp@...en8.de>,
	Dave Hansen <dave.hansen@...ux.intel.com>,
	Deepak Gupta <debug@...osinc.com>, "H. Peter Anvin" <hpa@...or.com>,
	Ingo Molnar <mingo@...nel.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Peter Zijlstra <peterz@...radead.org>,
	Rick Edgecombe <rick.p.edgecombe@...el.com>,
	Sohil Mehta <sohil.mehta@...el.com>,
	Thomas Gleixner <tglx@...utronix.de>, linux-kernel@...r.kernel.org,
	x86@...nel.org
Subject: Re: [PATCH v3 1/1] x86/shstk: don't create the shadow stack for
 PF_USER_WORKERs

On Wed, Sep 03, 2025 at 09:14:30AM -0700, Dave Hansen wrote:
> On 9/3/25 06:42, Oleg Nesterov wrote:

> >  arch/x86/include/asm/shstk.h | 4 ++--
> >  arch/x86/kernel/process.c    | 2 +-
> >  arch/x86/kernel/shstk.c      | 9 +++++++--
> >  3 files changed, 10 insertions(+), 5 deletions(-)

> That's not a great diffstat for a "cleanup". It's also not fixing any
> end-user-visible issues as far as I can tell.

...

> This doesn't clean things up or clarify the situation enough to make me
> want to apply it immediately.

I think the suggestion from one of the earlier discussions that if we
want to do this we roll it into a more general pulling out of shared
shadow stack code into the core makes sense here.  There's clearly a lot
of overlap between the three shadow stack implementations we have, and
an optimisation like this really shouldn't be arch specific.  I do
intend to poke at this whenever my clone3() series goes in.

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