From mboxrd@z Thu Jan  1 00:00:00 1970
From: qiuxishi@huawei.com (Xishi Qiu)
Date: Thu, 14 Jan 2016 21:06:08 +0800
Subject: Have any influence on set_memory_** about below patch ??
In-Reply-To: <56979621.1060102@huawei.com>
References: <5693A740.7070408@huawei.com> <20160111133145.GM6499@leverpostej>
 <569454F6.1060207@huawei.com> <20160112111531.GA4858@leverpostej>
 <5696272E.8090408@huawei.com> <20160113111806.GC23370@leverpostej>
 <56979621.1060102@huawei.com>
Message-ID: <56979D40.4060602@huawei.com>
To: linux-arm-kernel@lists.infradead.org
List-Id: linux-arm-kernel.lists.infradead.org

On 2016/1/14 20:35, Xishi Qiu wrote:

> On 2016/1/13 19:18, Mark Rutland wrote:
> 
>> On Wed, Jan 13, 2016 at 06:30:06PM +0800, Xishi Qiu wrote:
>>> Hi Mark,
>>>
>>> If I create swapper page tables by 4kb, not large page, then I use
>>> set_memory_ro() to change the pate table flag, does it have the problem
>>> too?
>>
>> The splitting/merging problem would not apply.
>>
>> However, you're going to waste a reasonable amount of memory by not
>> using section mappings in the swapper, and we gain additional complexity
>> in the page table setup code (which is shared with others things that
>> want section mappings).
>>
>> What are you exactly actually trying to achieve?
>>
> 
> If module allocates some pages and save data on them, and the data will
> not be changed during the module running. So we want to use set_memory_ro()
> to increase the security. If the data is changed, we can catch someone.
> 
>> What memory do you want to mark RO, and why?
>>
> 
> The key data, and it will not be changed during the running time.
> 
>> >From a previous discussion [1], we figured out alternative approaches
>> for common cases. Do none of those work for your case?
>>
> 
> I have not read the patchset carefully, could you tell me the general meaning
> of the approaches?
> 

Hi Mark,

Is the two approaches like following?
1. use create_mapping to map the data in read only, then use fixmap to create a
temp page table, and change the data when necessary.
2. use vmalloc, then we can use set_memory_ro to change the page table prot.

Thanks,
Xishi Qiu

> Thanks,
> Xishi Qiu
> 
>> Thanks,
>> Mark.
>>
>> [1] http://lists.infradead.org/pipermail/linux-arm-kernel/2016-January/397320.html
>>
>> .
>>
> 
>