Message-ID: <CAMuHMdX7K-9gXuOM3KkFieM_W2-Sbb3AVZ-sR65abRMdSBux5A@mail.gmail.com>
Date:   Tue, 13 Jun 2023 09:19:32 +0200
From:   Geert Uytterhoeven <geert@...ux-m68k.org>
To:     Rick Edgecombe <rick.p.edgecombe@...el.com>
Cc:     x86@...nel.org, "H . Peter Anvin" <hpa@...or.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, linux-kernel@...r.kernel.org,
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        linux-alpha@...r.kernel.org, linux-snps-arc@...ts.infradead.org,
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        linux-hexagon@...r.kernel.org, linux-ia64@...r.kernel.org,
        loongarch@...ts.linux.dev, linux-m68k@...ts.linux-m68k.org,
        Michal Simek <monstr@...str.eu>,
        Dinh Nguyen <dinguyen@...nel.org>, linux-mips@...r.kernel.org,
        openrisc@...ts.librecores.org, linux-parisc@...r.kernel.org,
        linuxppc-dev@...ts.ozlabs.org, linux-riscv@...ts.infradead.org,
        linux-s390@...r.kernel.org, linux-sh@...r.kernel.org,
        sparclinux@...r.kernel.org, linux-um@...ts.infradead.org,
        Linus Torvalds <torvalds@...uxfoundation.org>
Subject: Re: [PATCH v9 01/42] mm: Rename arch pte_mkwrite()'s to pte_mkwrite_novma()

On Tue, Jun 13, 2023 at 2:13 AM Rick Edgecombe
<rick.p.edgecombe@...el.com> wrote:
> The x86 Shadow stack feature includes a new type of memory called shadow
> stack. This shadow stack memory has some unusual properties, which requires
> some core mm changes to function properly.
>
> One of these unusual properties is that shadow stack memory is writable,
> but only in limited ways. These limits are applied via a specific PTE
> bit combination. Nevertheless, the memory is writable, and core mm code
> will need to apply the writable permissions in the typical paths that
> call pte_mkwrite(). Future patches will make pte_mkwrite() take a VMA, so
> that the x86 implementation of it can know whether to create regular
> writable memory or shadow stack memory.
>
> But there are a couple of challenges to this. Modifying the signatures of
> each arch pte_mkwrite() implementation would be error prone because some
> are generated with macros and would need to be re-implemented. Also, some
> pte_mkwrite() callers operate on kernel memory without a VMA.
>
> So this can be done in a three step process. First pte_mkwrite() can be
> renamed to pte_mkwrite_novma() in each arch, with a generic pte_mkwrite()
> added that just calls pte_mkwrite_novma(). Next callers without a VMA can
> be moved to pte_mkwrite_novma(). And lastly, pte_mkwrite() and all callers
> can be changed to take/pass a VMA.
>
> Start the process by renaming pte_mkwrite() to pte_mkwrite_novma() and
> adding the pte_mkwrite() wrapper in linux/pgtable.h. Apply the same
> pattern for pmd_mkwrite(). Since not all archs have a pmd_mkwrite_novma(),
> create a new arch config HAS_HUGE_PAGE that can be used to tell if
> pmd_mkwrite() should be defined. Otherwise in the !HAS_HUGE_PAGE cases the
> compiler would not be able to find pmd_mkwrite_novma().
>
> No functional change.
>
> Cc: linux-doc@...r.kernel.org
> Cc: linux-kernel@...r.kernel.org
> Cc: linux-alpha@...r.kernel.org
> Cc: linux-snps-arc@...ts.infradead.org
> Cc: linux-arm-kernel@...ts.infradead.org
> Cc: linux-csky@...r.kernel.org
> Cc: linux-hexagon@...r.kernel.org
> Cc: linux-ia64@...r.kernel.org
> Cc: loongarch@...ts.linux.dev
> Cc: linux-m68k@...ts.linux-m68k.org
> Cc: Michal Simek <monstr@...str.eu>
> Cc: Dinh Nguyen <dinguyen@...nel.org>
> Cc: linux-mips@...r.kernel.org
> Cc: openrisc@...ts.librecores.org
> Cc: linux-parisc@...r.kernel.org
> Cc: linuxppc-dev@...ts.ozlabs.org
> Cc: linux-riscv@...ts.infradead.org
> Cc: linux-s390@...r.kernel.org
> Cc: linux-sh@...r.kernel.org
> Cc: sparclinux@...r.kernel.org
> Cc: linux-um@...ts.infradead.org
> Cc: linux-arch@...r.kernel.org
> Cc: linux-mm@...ck.org
> Suggested-by: Linus Torvalds <torvalds@...uxfoundation.org>
> Signed-off-by: Rick Edgecombe <rick.p.edgecombe@...el.com>
> Link: https://lore.kernel.org/lkml/CAHk-=wiZjSu7c9sFYZb3q04108stgHff2wfbokGCCgW7riz+8Q@mail.gmail.com/

>  arch/m68k/include/asm/mcf_pgtable.h          |  2 +-
>  arch/m68k/include/asm/motorola_pgtable.h     |  2 +-
>  arch/m68k/include/asm/sun3_pgtable.h         |  2 +-

Acked-by: Geert Uytterhoeven <geert@...ux-m68k.org>

Gr{oetje,eeting}s,

                        Geert

-- 
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@...ux-m68k.org

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
                                -- Linus Torvalds

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