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From:   Geert Uytterhoeven <geert@linux-m68k.org>
Date:   Fri, 18 Feb 2022 10:00:39 +0100
Message-ID: <CAMuHMdWMhP5WgZ7CvOz53SyfizaAvLkHbeuds8G+_nZkwzhWWw@mail.gmail.com>
Subject: Re: [PATCH v2 10/18] m68k: fix access_ok for coldfire
To:     Arnd Bergmann <arnd@kernel.org>
Cc:     Linus Torvalds <torvalds@linux-foundation.org>,
        Christoph Hellwig <hch@lst.de>,
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Hi Arnd,

On Wed, Feb 16, 2022 at 2:17 PM Arnd Bergmann <arnd@kernel.org> wrote:
> From: Arnd Bergmann <arnd@arndb.de>
>
> While most m68k platforms use separate address spaces for user
> and kernel space, at least coldfire does not, and the other
> ones have a TASK_SIZE that is less than the entire 4GB address
> range.
>
> Using the default implementation of __access_ok() stops coldfire
> user space from trivially accessing kernel memory.
>
> Signed-off-by: Arnd Bergmann <arnd@arndb.de>

Thanks for your patch!

> --- a/arch/m68k/include/asm/uaccess.h
> +++ b/arch/m68k/include/asm/uaccess.h
> @@ -12,14 +12,21 @@
>  #include <asm/extable.h>
>
>  /* We let the MMU do all checking */
> -static inline int access_ok(const void __user *addr,
> +static inline int access_ok(const void __user *ptr,
>                             unsigned long size)
>  {
> +       unsigned long limit = TASK_SIZE;
> +       unsigned long addr = (unsigned long)ptr;
> +
>         /*
>          * XXX: for !CONFIG_CPU_HAS_ADDRESS_SPACES this really needs to check
>          * for TASK_SIZE!
> +        * Removing this helper is probably sufficient.
>          */

Shouldn't the above comment block be removed completely,
as this is now implemented below?

> -       return 1;
> +       if (IS_ENABLED(CONFIG_CPU_HAS_ADDRESS_SPACES))
> +               return 1;
> +
> +       return (size <= limit) && (addr <= (limit - size));
>  }

Any pesky compilers that warn (or worse with -Werror) about
"condition always true" for TASK_SIZE = 0xFFFFFFFFUL?

Gr{oetje,eeting}s,

                        Geert

--
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@linux-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