linux-kernel - Re: [PATCH 10/10] powerpc: remove address space overrides using set

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Date:   Wed, 2 Sep 2020 14:36:46 +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-fsdevel@...r.kernel.org, linux-arch@...r.kernel.org,
        linuxppc-dev@...ts.ozlabs.org, Kees Cook <keescook@...omium.org>,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH 10/10] powerpc: remove address space overrides using
 set_fs()

On Wed, Sep 02, 2020 at 08:15:12AM +0200, Christophe Leroy wrote:
>> -		return 0;
>> -	return (size == 0 || size - 1 <= seg.seg - addr);
>> +	if (addr >= TASK_SIZE_MAX)
>> +		return false;
>> +	if (size == 0)
>> +		return false;
>
> __access_ok() was returning true when size == 0 up to now. Any reason to 
> return false now ?

No, this is accidental and broken.  Can you re-run your benchmark with
this fixed?