linux-kernel - Re: [PATCH 14/14] powerpc: remove address space overrides using set

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Message-ID: <e7d2d231-5658-a4d3-0495-2af62f34aa34@csgroup.eu>
Date:   Thu, 3 Sep 2020 17:43:25 +0200
From:   Christophe Leroy <christophe.leroy@...roup.eu>
To:     Christoph Hellwig <hch@....de>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Al Viro <viro@...iv.linux.org.uk>,
        Michael Ellerman <mpe@...erman.id.au>, x86@...nel.org
Cc:     linux-arch@...r.kernel.org, Kees Cook <keescook@...omium.org>,
        linux-kernel@...r.kernel.org, Luis Chamberlain <mcgrof@...nel.org>,
        linux-fsdevel@...r.kernel.org, linuxppc-dev@...ts.ozlabs.org,
        Alexey Dobriyan <adobriyan@...il.com>
Subject: Re: [PATCH 14/14] powerpc: remove address space overrides using
 set_fs()



Le 03/09/2020 à 16:22, Christoph Hellwig a écrit :
> Stop providing the possibility to override the address space using
> set_fs() now that there is no need for that any more.
> 
> Signed-off-by: Christoph Hellwig <hch@....de>
> ---


>   
> -static inline int __access_ok(unsigned long addr, unsigned long size,
> -			mm_segment_t seg)
> +static inline bool __access_ok(unsigned long addr, unsigned long size)
>   {
> -	if (addr > seg.seg)
> -		return 0;
> -	return (size == 0 || size - 1 <= seg.seg - addr);
> +	if (addr >= TASK_SIZE_MAX)
> +		return false;
> +	return size == 0 || size <= TASK_SIZE_MAX - addr;
>   }

You don't need to test size == 0 anymore. It used to be necessary 
because of the 'size - 1', as size is unsigned.

Now you can directly do

	return size <= TASK_SIZE_MAX - addr;

If size is 0, this will always be true (because you already know that 
addr is not >= TASK_SIZE_MAX

Christophe