linux-kernel - Re: net: atm: Spectre v1 fix introduced bug in bcb964012d1b in -stable

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Date:   Mon, 20 May 2019 11:54:59 -0500
From:   "Gustavo A. R. Silva" <gustavo@...eddedor.com>
To:     Pavel Machek <pavel@...x.de>
Cc:     stable@...nel.org, kernel list <linux-kernel@...r.kernel.org>,
        davem@...emloft.net, gregkh@...uxfoundation.org
Subject: Re: net: atm: Spectre v1 fix introduced bug in bcb964012d1b in
 -stable



On 5/20/19 11:15 AM, Pavel Machek wrote:
> On Mon 2019-05-20 09:15:50, Gustavo A. R. Silva wrote:
>>
>>
>> On 5/20/19 7:40 AM, Pavel Machek wrote:
>>>
>>> In lecd_attach, if arg is < 0, it was treated as 0. Spectre v1 fix
>>> changed that. Bug does not exist in mainline AFAICT.
>>>
>>
>> NACK
>>
>> array_index_nospec() macro returns zero if *arg* is out of bounds.
> 
> No, it does not. Take a look:
> 
> #define array_index_nospec(index, size)
> ...
>         (typeof(_i)) (_i & _mask);
> })
> 	

Tell me more about that _mask.

Also, don't ignore the backward compatibility; otherwise you
would be forking your own kernel.

--
Gustavo