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

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Date:   Thu, 3 Sep 2020 17:49:09 +0200
From:   Christoph Hellwig <hch@....de>
To:     Christophe Leroy <christophe.leroy@...roup.eu>
Cc:     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,
        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()

On Thu, Sep 03, 2020 at 05:43:25PM +0200, Christophe Leroy wrote:
>
>
> 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

True.  What do you think of Linus' comment about always using the
ppc32 version on ppc64 as well with this?