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Subject: Re: [PATCH 14/14] powerpc: remove address space overrides using
 set_fs()
To: Christoph Hellwig <hch@lst.de>,
 Linus Torvalds <torvalds@linux-foundation.org>,
 Al Viro <viro@zeniv.linux.org.uk>, Michael Ellerman <mpe@ellerman.id.au>,
 x86@kernel.org
References: <20200903142242.925828-1-hch@lst.de>
 <20200903142242.925828-15-hch@lst.de>
From: Christophe Leroy <christophe.leroy@csgroup.eu>
Message-ID: <e7d2d231-5658-a4d3-0495-2af62f34aa34@csgroup.eu>
Date: Thu, 3 Sep 2020 17:43:25 +0200
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Cc: linux-arch@vger.kernel.org, Kees Cook <keescook@chromium.org>,
 linux-kernel@vger.kernel.org, Luis Chamberlain <mcgrof@kernel.org>,
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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@lst.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