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

[zhong jiang <zhongjiang@huawei.com>]

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.
>
>>> 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.
>
 I have no a simple way to fix. Do you any suggestion. or you can send
 a patch for me ?

 Thanks
 zhongjiang