linux-kernel - Re: [PATCH 0/2] Avoid crashes by early (boot) consoles using init memory

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <d5bb87b5-1b9e-c5b0-500e-ab165f9b342a@redhat.com>
Date:   Sat, 15 Jul 2017 07:05:35 +0200
From:   "Fabio M. Di Nitto" <fdinitto@...hat.com>
To:     Petr Mladek <pmladek@...e.com>
Cc:     Sergey Senozhatsky <sergey.senozhatsky@...il.com>,
        Steven Rostedt <rostedt@...dmis.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Matt Redfearn <matt.redfearn@...tec.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Jiri Slaby <jslaby@...e.com>,
        "David S. Miller" <davem@...emloft.net>,
        Alan Cox <gnomes@...rguk.ukuu.org.uk>,
        linux-serial@...r.kernel.org, linux-kernel@...r.kernel.org,
        Sergey Senozhatsky <sergey.senozhatsky.work@...il.com>
Subject: Re: [PATCH 0/2] Avoid crashes by early (boot) consoles using init
 memory

On 7/14/2017 4:37 PM, Petr Mladek wrote:
> On Fri 2017-07-14 14:57:45, Fabio M. Di Nitto wrote:
>> Hi Petr,
>>
>> On 7/14/2017 2:51 PM, Petr Mladek wrote:
>>> Some early consoles have code and data in the init section. It makes some
>>> sense but this might cause problems when they are not replaced by
>>> the real console in time. The two patches fix the safequard and
>>> help to avoid the problems.
>>>
>>> I though about removing keep_bootcon option completely. But it is useful
>>> at least for now.
>>
>> Let´s just keep in mind that keep_bootcon was introduced only to debug
>> issues (read crashes or hangs) that could happen between disabling
>> bootconsole and enabling the real console. It shouldn´t be used for
>> anything else really.
> 
> This was my initial replay as well. But then I realized that
> it was a bad idea to use a freed code and data to debug any other
> issue. It would just create crazy issues on its own.

Perhaps some changes that were made later in the code introduced this
behavior. I honestly didn´t check. It´s been just so long ago :-)

> 
> I tried to google 'keep_bootcon'. It found several links to strange
> crashes related to this option. Maybe I was not patient enough but
> I did not find any page where this option was suggested and helped.

It´s in Documentation/admin-guide/kernel-parameters.txt. It´s also rare
that consoles are not working or something is crashing in that small
window, so I am not entirely surprised that there are few to none
references of users using it.

> 
> I still think that the option makes some sense but only when
> it does not cause more breakages on its own.

agreed.

Cheers
Fabio

> 
>> If the new code can replace keep_bootcon, by all mean, go for it :-)
> 
> keep_bootcon stays usable for most early consoles. We print a warning
> when an unusable console is disabled too early. Also there is a
> comment how to fix it.
> 
> Best Regards,
> Petr
>