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Subject: Re: [PATCH 06/21] powerpc: Avoid comparison of unsigned long >= 0 in
 __access_ok
To:     Mathieu Malaterre <malat@debian.org>,
        Michael Ellerman <mpe@ellerman.id.au>
Cc:     linux-kernel@vger.kernel.org, Paul Mackerras <paulus@samba.org>,
        Jiri Slaby <jslaby@suse.com>, linuxppc-dev@lists.ozlabs.org
References: <20180225172236.29650-1-malat@debian.org>
 <20180225172236.29650-7-malat@debian.org>
From:   Christophe LEROY <christophe.leroy@c-s.fr>
Message-ID: <8862c1e1-d161-3410-1b2a-502ad06cef57@c-s.fr>
Date:   Mon, 26 Feb 2018 07:34:59 +0100
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Le 25/02/2018 à 18:22, Mathieu Malaterre a écrit :
> Rewrite check size - 1 <= Y as size < Y since `size` is unsigned value.
> Fix warning (treated as error in W=1):
> 
>    CC      arch/powerpc/kernel/signal_32.o
> In file included from ./include/linux/uaccess.h:14:0,
>                   from ./include/asm-generic/termios-base.h:8,
>                   from ./arch/powerpc/include/asm/termios.h:20,
>                   from ./include/uapi/linux/termios.h:6,
>                   from ./include/linux/tty.h:7,
>                   from arch/powerpc/kernel/signal_32.c:36:
> ./include/asm-generic/termios-base.h: In function ‘user_termio_to_kernel_termios’:
> ./arch/powerpc/include/asm/uaccess.h:52:35: error: comparison of unsigned expression >= 0 is always true [-Werror=type-limits]
>     (((size) == 0) || (((size) - 1) <= ((segment).seg - (addr)))))
>                                     ^
> ./arch/powerpc/include/asm/uaccess.h:58:3: note: in expansion of macro ‘__access_ok’
>     __access_ok((__force unsigned long)(addr), (size), get_fs()))
>     ^~~~~~~~~~~
> ./arch/powerpc/include/asm/uaccess.h:262:6: note: in expansion of macro ‘access_ok’
>    if (access_ok(VERIFY_READ, __gu_addr, (size)))   \
>        ^~~~~~~~~
> ./arch/powerpc/include/asm/uaccess.h:80:2: note: in expansion of macro ‘__get_user_check’
>    __get_user_check((x), (ptr), sizeof(*(ptr)))
>    ^~~~~~~~~~~~~~~~
> ./include/asm-generic/termios-base.h:36:6: note: in expansion of macro ‘get_user’
>    if (get_user(termios->c_line, &termio->c_line) < 0)
>        ^~~~~~~~
> [...]
> cc1: all warnings being treated as errors
> 
> Signed-off-by: Mathieu Malaterre <malat@debian.org>
> ---
>   arch/powerpc/include/asm/uaccess.h | 2 +-
>   1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/arch/powerpc/include/asm/uaccess.h b/arch/powerpc/include/asm/uaccess.h
> index 51bfeb8777f0..fadc406bd39d 100644
> --- a/arch/powerpc/include/asm/uaccess.h
> +++ b/arch/powerpc/include/asm/uaccess.h
> @@ -49,7 +49,7 @@
>   
>   #define __access_ok(addr, size, segment)	\
>   	(((addr) <= (segment).seg) &&		\
> -	 (((size) == 0) || (((size) - 1) <= ((segment).seg - (addr)))))
> +	 (((size) == 0) || ((size) < ((segment).seg - (addr)))))

IIUC, ((2 - 1) <= 1) is the same as (2 < 1) ?????

Christophe

>   
>   #endif
>   
>