linux-kernel - Re: [PATCH RFC v2 02/29] x86: Create CONFIG_MITIGATION_ADDRESS_SPACE

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Message-ID: <CA+i-1C06Sunj0BmFON=MbWBK6ZDt_=K4P3BHChRBYyxXqEkQ2g@mail.gmail.com>
Date: Wed, 5 Mar 2025 14:12:25 +0100
From: Brendan Jackman <jackmanb@...gle.com>
To: Mike Rapoport <rppt@...nel.org>
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	Junaid Shahid <junaids@...gle.com>
Subject: Re: [PATCH RFC v2 02/29] x86: Create CONFIG_MITIGATION_ADDRESS_SPACE_ISOLATION

On Sat, Mar 01, 2025 at 09:23:51AM +0200, Mike Rapoport wrote:
> Hi Brendan,
>
> On Fri, Jan 10, 2025 at 06:40:28PM +0000, Brendan Jackman wrote:
> > Currently a nop config. Keeping as a separate commit for easy review of
> > the boring bits. Later commits will use and enable this new config.
> >
> > This config is only added for non-UML x86_64 as other architectures do
> > not yet have pending implementations. It also has somewhat artificial
> > dependencies on !PARAVIRT and !KASAN which are explained in the Kconfig
> > file.
> >
> > Co-developed-by: Junaid Shahid <junaids@...gle.com>
> > Signed-off-by: Junaid Shahid <junaids@...gle.com>
> > Signed-off-by: Brendan Jackman <jackmanb@...gle.com>
> > ---
> >  arch/alpha/include/asm/Kbuild      |  1 +
> >  arch/arc/include/asm/Kbuild        |  1 +
> >  arch/arm/include/asm/Kbuild        |  1 +
> >  arch/arm64/include/asm/Kbuild      |  1 +
> >  arch/csky/include/asm/Kbuild       |  1 +
> >  arch/hexagon/include/asm/Kbuild    |  1 +
> >  arch/loongarch/include/asm/Kbuild  |  3 +++
> >  arch/m68k/include/asm/Kbuild       |  1 +
> >  arch/microblaze/include/asm/Kbuild |  1 +
> >  arch/mips/include/asm/Kbuild       |  1 +
> >  arch/nios2/include/asm/Kbuild      |  1 +
> >  arch/openrisc/include/asm/Kbuild   |  1 +
> >  arch/parisc/include/asm/Kbuild     |  1 +
> >  arch/powerpc/include/asm/Kbuild    |  1 +
> >  arch/riscv/include/asm/Kbuild      |  1 +
> >  arch/s390/include/asm/Kbuild       |  1 +
> >  arch/sh/include/asm/Kbuild         |  1 +
> >  arch/sparc/include/asm/Kbuild      |  1 +
> >  arch/um/include/asm/Kbuild         |  2 +-
> >  arch/x86/Kconfig                   | 14 ++++++++++++++
> >  arch/xtensa/include/asm/Kbuild     |  1 +
> >  include/asm-generic/asi.h          |  5 +++++
> >  22 files changed, 41 insertions(+), 1 deletion(-)
>
> I don't think this all is needed. You can put asi.h with stubs used outside
> of arch/x86 in include/linux and save you the hassle of updating every
> architecture.

...

> If you expect other architectures might implement ASI the config would better
> fit into init/Kconfig or mm/Kconfig and in arch/x86/Kconfig will define
> ARCH_HAS_MITIGATION_ADDRESS_SPACE_ISOLATION.

...

> > +++ b/include/asm-generic/asi.h
> > @@ -0,0 +1,5 @@
> > +/* SPDX-License-Identifier: GPL-2.0 */
> > +#ifndef __ASM_GENERIC_ASI_H
> > +#define __ASM_GENERIC_ASI_H
> > +
> > +#endif
>
> IMHO it should be include/linux/asi.h, with something like
>
> #infdef __LINUX_ASI_H
> #define __LINUX_ASI_H
>
> #ifdef CONFIG_MITIGATION_ADDRESS_SPACE_ISOLATION
>
> #include <asm/asi.h>
>
> #else /* CONFIG_MITIGATION_ADDRESS_SPACE_ISOLATION */
>
> /* stubs for functions used outside arch/ */
>
> #endif /* CONFIG_MITIGATION_ADDRESS_SPACE_ISOLATION */
>
> #endif /* __LINUX_ASI_H */

Thanks Mike! That does indeed look way tidier. I'll try to adopt it.