linux-kernel - Re: [RESENT PATCH] x86/mem: fix the offset overflow when read/write mem

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Message-ID: <591277AE.80908@huawei.com>
Date:   Wed, 10 May 2017 10:15:10 +0800
From:   Xishi Qiu <qiuxishi@...wei.com>
To:     Rik van Riel <riel@...hat.com>
CC:     zhong jiang <zhongjiang@...wei.com>,
        David Rientjes <rientjes@...gle.com>,
        Bjorn Helgaas <bhelgaas@...gle.com>,
        Yoshinori Sato <ysato@...rs.sourceforge.jp>,
        Rich Felker <dalias@...c.org>,
        Andrew Morton <akpm@...ux-foundation.org>, <arnd@...db.de>,
        <hannes@...xchg.org>, <kirill@...temov.name>,
        <mgorman@...hsingularity.net>, <hughd@...gle.com>,
        <linux-mm@...ck.org>, <linux-kernel@...r.kernel.org>
Subject: Re: [RESENT PATCH] x86/mem: fix the offset overflow when read/write
 mem

On 2017/5/9 23:46, Rik van Riel wrote:

> On Thu, 2017-05-04 at 10:28 +0800, zhong jiang wrote:
>> On 2017/5/4 2:46, Rik van Riel wrote:
> 
>>> However, it is not as easy as simply checking the
>>> end against __pa(high_memory). Some systems have
>>> non-contiguous physical memory ranges, with gaps
>>> of invalid addresses in-between.
>>
>>  The invalid physical address means that it is used as
>>  io mapped. not in system ram region. /dev/mem is not
>>  access to them , is it right?
> 
> Not necessarily. Some systems simply have large
> gaps in physical memory access. Their memory map
> may look like this:
> 
> |MMMMMM|IO|MMMM|..................|MMMMMMMM|
> 
> Where M is memory, IO is IO space, and the
> dots are simply a gap in physical address
> space with no valid accesses at all.
>

Hi Rik,

Do you mean IO space is allowed to access from mmap /dev/mem?

Thanks,
Xishi Qiu

 
>>> At that point, is the complexity so much that it no
>>> longer makes sense to try to protect against root
>>> crashing the system?
>>>
>>
>>  your suggestion is to let the issue along without any protection.
>>  just root user know what they are doing.
> 
> Well, root already has other ways to crash the system.
> 
> Implementing validation on /dev/mem may make sense if
> it can be done in a simple way, but may not be worth
> it if it becomes too complex.
>