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From:   Kees Cook <keescook@chromium.org>
Date:   Thu, 15 Feb 2018 09:58:00 -0800
Message-ID: <CAGXu5jKH1N3nqmRLnRiieGS-YpXj+dptDAB65ZgBWx+Ey3mCdQ@mail.gmail.com>
Subject: Re: [PATCH 2/2] [stable-4.9] x86: fix build warnign with 32-bit PAE
To:     Arnd Bergmann <arnd@arndb.de>
Cc:     "# 3.4.x" <stable@vger.kernel.org>, X86 ML <x86@kernel.org>,
        Dave Hansen <dave.hansen@linux.intel.com>,
        Ben Hutchings <ben.hutchings@codethink.co.uk>,
        Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        Hugh Dickins <hughd@google.com>,
        LKML <linux-kernel@vger.kernel.org>
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On Thu, Feb 15, 2018 at 7:16 AM, Arnd Bergmann <arnd@arndb.de> wrote:
> I ran into a 4.9 build warning in randconfig testing, starting with the
> KAISER patches:
>
> arch/x86/kernel/ldt.c: In function 'alloc_ldt_struct':
> arch/x86/include/asm/pgtable_types.h:208:24: error: large integer implicitly truncated to unsigned type [-Werror=overflow]
>  #define __PAGE_KERNEL  (__PAGE_KERNEL_EXEC | _PAGE_NX)
>                         ^
> arch/x86/kernel/ldt.c:81:6: note: in expansion of macro '__PAGE_KERNEL'
>       __PAGE_KERNEL);
>       ^~~~~~~~~~~~~
>
> I originally ran into this last year when the patches were part of linux-next,
> and tried to work around it by using the proper 'pteval_t' types consistently,
> but that caused additional problems.
>
> This takes a much simpler approach, and makes the argument type of the dummy
> helper always 64-bit, which is wide enough for any page table layout and
> won't hurt since this call is just an empty stub anyway.
>
> Fixes: 8f0baadf2bea ("kaiser: merged update")
> Signed-off-by: Arnd Bergmann <arnd@arndb.de>
> ---
>  include/linux/kaiser.h | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/include/linux/kaiser.h b/include/linux/kaiser.h
> index 58c55b1589d0..b56c19010480 100644
> --- a/include/linux/kaiser.h
> +++ b/include/linux/kaiser.h
> @@ -32,7 +32,7 @@ static inline void kaiser_init(void)
>  {
>  }
>  static inline int kaiser_add_mapping(unsigned long addr,
> -                                    unsigned long size, unsigned long flags)
> +                                    unsigned long size, u64 flags)
>  {
>         return 0;
>  }
> --
> 2.9.0
>

Acked-by: Kees Cook <keescook@chromium.org>

I assume this is needed for 4.4 as well...

-Kees

-- 
Kees Cook
Pixel Security