linux-kernel - Re: [PATCH v2 10/18] m68k: fix access

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Date:   Fri, 18 Feb 2022 10:24:50 +0100
From:   Arnd Bergmann <arnd@...nel.org>
To:     Geert Uytterhoeven <geert@...ux-m68k.org>
Cc:     Linus Torvalds <torvalds@...ux-foundation.org>,
        Christoph Hellwig <hch@....de>,
        Linux-Arch <linux-arch@...r.kernel.org>,
        Linux MM <linux-mm@...ck.org>,
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Subject: Re: [PATCH v2 10/18] m68k: fix access_ok for coldfire

On Fri, Feb 18, 2022 at 10:00 AM Geert Uytterhoeven
<geert@...ux-m68k.org> wrote:
> >  /* 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?

Yes, obviously. Fixed now.

> > -       return 1;
> > +       if (IS_ENABLED(CONFIG_CPU_HAS_ADDRESS_SPACES))
> > +               return 1;

I just noticed this should have the same change that I made for the
generic version, changed it now to

+       if (IS_ENABLED(CONFIG_CPU_HAS_ADDRESS_SPACES) ||
+           !IS_ENABLED(CONFIG_MMU))

This is gone again after the cleanup patch, when the generic version
is used instead.

> > +       return (size <= limit) && (addr <= (limit - size));
> >  }
>
> Any pesky compilers that warn (or worse with -Werror) about
> "condition always true" for TASK_SIZE = 0xFFFFFFFFUL?

No, using a local variable avoids this warning.

        Arnd