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    SubjectRe: [PATCH] x86/mm: Disable W^X detection and enforcement on 32-bit
    On Sat, 24 Sept 2022 at 00:17, Dave Hansen <dave.hansen@linux.intel.com> wrote:
    >
    > The 32-bit code is in a weird spot. Some 32-bit builds (non-PAE) do not
    > even have NX support. Even PAE builds that support NX have to contend
    > with things like EFI data and code mixed in the same pages where W+X
    > is unavoidable.
    >
    > The folks still running X86_32=y kernels are unlikely to care much about
    > NX. That combined with the fundamental inability fix _all_ of the W+X
    > things means this code had little value on X86_32=y. Disable the checks.
    >
    > Reported-by: Guenter Roeck <linux@roeck-us.net>
    > Signed-off-by: Dave Hansen <dave.hansen@linux.intel.com>
    > Cc: Ard Biesheuvel <ardb@kernel.org>
    > Cc: Darren Hart <dvhart@infradead.org>
    > Cc: Andy Shevchenko <andy@infradead.org>
    > Cc: Thomas Gleixner <tglx@linutronix.de>
    > Cc: Ingo Molnar <mingo@redhat.com>
    > Cc: Borislav Petkov <bp@alien8.de>
    > Cc: x86@kernel.org
    > Cc: linux-efi@vger.kernel.org
    > Cc: "H. Peter Anvin" <hpa@zytor.com>
    > Cc: Kees Cook <keescook@chromium.org>
    > Link: https://lore.kernel.org/all/CAMj1kXHcF_iK_g0OZSkSv56Wmr=eQGQwNstcNjLEfS=mm7a06w@mail.gmail.com/

    Acked-by: Ard Biesheuvel <ardb@kernel.org>

    > ---
    > arch/x86/mm/pat/set_memory.c | 8 ++++++++
    > 1 file changed, 8 insertions(+)
    >
    > diff --git a/arch/x86/mm/pat/set_memory.c b/arch/x86/mm/pat/set_memory.c
    > index 20b1e24baa85..efe882c753ca 100644
    > --- a/arch/x86/mm/pat/set_memory.c
    > +++ b/arch/x86/mm/pat/set_memory.c
    > @@ -587,6 +587,14 @@ static inline pgprot_t verify_rwx(pgprot_t old, pgprot_t new, unsigned long star
    > {
    > unsigned long end;
    >
    > + /*
    > + * 32-bit has some unfixable W+X issues, like EFI code
    > + * and writeable data being in the same page. Disable
    > + * detection and enforcement there.
    > + */
    > + if (IS_ENABLED(CONFIG_X86_32))
    > + return new;
    > +
    > /* Only enforce when NX is supported: */
    > if (!(__supported_pte_mask & _PAGE_NX))
    > return new;
    > --
    > 2.34.1
    >

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