linux-kernel - Re: [PATCH] mm: Enable MAP_UNINITIALIZED for archs with mmu

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Message-ID: <CAKTCnznyZGLiZPNS151GzsUMApN_SYu3n6xX9E0ceMpq9JNq7w@mail.gmail.com>
Date:	Sat, 25 Feb 2012 09:43:14 +0530
From:	Balbir Singh <bsingharora@...il.com>
To:	Arun Sharma <asharma@...com>
Cc:	linux-kernel@...r.kernel.org, linux-mm@...ck.org,
	akpm@...ux-foundation.org,
	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
Subject: Re: [PATCH] mm: Enable MAP_UNINITIALIZED for archs with mmu

On Sat, Feb 25, 2012 at 12:41 AM, Arun Sharma <asharma@...com> wrote:
> On 2/24/12 6:51 AM, Balbir Singh wrote:
>>
>> On Fri, Feb 24, 2012 at 8:17 AM, KAMEZAWA Hiroyuki
>> <kamezawa.hiroyu@...fujitsu.com>  wrote:
>>>>
>>>> They don't have access to each other's VMAs, but if "accidentally" one
>>>> of them comes across an uninitialized page with data from another task,
>>>> it's not a violation of the security model.
>>
>>
>> Can you expand more on the single address space model?
>
>
> I haven't thought this through yet. But I know that just adding
>
> && (cgroup_task_count() == 1)
>
> to page_needs_clearing() is not going to do it. We'll have to design a new
> mechanism (cgroup_mm_count_all()?) and make sure that it doesn't race with
> fork() and inadvertently expose pages from the new address space to the
> existing one.
>
> A uid based approach such as the one implemented by Davide Libenzi
>
> http://thread.gmane.org/gmane.linux.kernel/548928
> http://thread.gmane.org/gmane.linux.kernel/548926
>
> would probably apply the optimization to more use cases - but conceptually a
> bit more complex. If we go with this more relaxed approach, we'll have to
> design a race-free cgroup_uid_count() based mechanism.

Are you suggesting all processes with the same UID should have access
to each others memory contents?

Balbir
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