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

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Message-ID: <8de54fe0-4be9-5624-dd1d-d95d792e933d@csgroup.eu>
Date:   Wed, 2 Sep 2020 15:24:39 +0200
From:   Christophe Leroy <christophe.leroy@...roup.eu>
To:     David Laight <David.Laight@...LAB.COM>,
        'Christoph Hellwig' <hch@....de>
Cc:     Linus Torvalds <torvalds@...ux-foundation.org>,
        Al Viro <viro@...iv.linux.org.uk>,
        Michael Ellerman <mpe@...erman.id.au>,
        "x86@...nel.org" <x86@...nel.org>,
        "linux-fsdevel@...r.kernel.org" <linux-fsdevel@...r.kernel.org>,
        "linux-arch@...r.kernel.org" <linux-arch@...r.kernel.org>,
        "linuxppc-dev@...ts.ozlabs.org" <linuxppc-dev@...ts.ozlabs.org>,
        Kees Cook <keescook@...omium.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 10/10] powerpc: remove address space overrides using
 set_fs()



Le 02/09/2020 à 15:13, David Laight a écrit :
> From: Christoph Hellwig
>> Sent: 02 September 2020 13:37
>>
>> 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?
> 
> Is TASK_SIZE_MASK defined such that you can do:
> 
> 	return (addr | size) < TASK_SIZE_MAX) || !size;

TASK_SIZE_MAX will usually be 0xc0000000

With:
addr = 0x80000000;
size = 0x80000000;

I expect it to fail ....

With the formula you propose it will succeed, won't it ?

Christophe