> On Thursday 30 August 2007 23:50:21
Valdis.Kletnieks@vt.edu wrote:
>
>> On Thu, 30 Aug 2007 23:41:09 +0200, Clemens Kolbitsch said:
>>
>>> On Thursday 30 August 2007 23:34:52 you wrote:
>>>
>>>> On Thu, 30 Aug 2007, Clemens Kolbitsch wrote:
>>>>
>>>>> is there no way to tell the kernel, that a certain mapping must not
>>>>> be removed, no matter what (except of course an explicit call to
>>>>> sys_unmap, of course)?
>>>>>
>>>> I don't seem to get what is the issue here. Your mapping is not
>>>> removed, only the VMAs are merged together into one larger VMA if they
>>>> have neighbouring address ranges and compatible protection bits. See
>>>> vma_merge().
>>>>
>>> the thing is that they are not. the kernel chooses to REPLACE my mapping.
>>>
>>> consider the user-space code:
>>>
>>> mmap(0xaaaa0000, 0x3000, MAP_FIXED, ...);
>>> mmap(0xaaaa1000, 0x4000, MAP_FIXED, ...);
>>>
>>> here, the second call to mmap will shorten the first mapping to 0x1000
>>> bytes and create one big vma with size 0x5000 bytes.
>>>
>>> is there a way to tell it that the second mmap MUST fail?
>>>
>> There's an LSM exit point for mmap, you could perhaps do something there.
>>
>> What are you trying to achieve by forcing the second one to fail?
>>
>
> puh... that is a good question :-)
>
> I'm writing my master's thesis on a new model of memory protection and need to
> have every memory mapping in userspace duplicated. I also have kind of a
> second PGD/PTD that allows finding this mirrored mapping.
>
> However, as the number of original mappings grows, I suddenly have the problem
> that the kernel tries to allocate a new mapping and picks the address of a
> mirrored memory page, which it shouldn't.
>
> Honestly, I don't understand why it does so,
