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

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Message-ID: <CAKTCnzn-reG4bLmyWNYPELYs-9M3ZShEYeOix_OcnPow-w8PNg@mail.gmail.com>
Date:	Thu, 23 Feb 2012 13:15:30 +0530
From:	Balbir Singh <bsingharora@...il.com>
To:	Arun Sharma <asharma@...com>
Cc:	linux-kernel@...r.kernel.org, linux-mm@...ck.org,
	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>,
	akpm@...ux-foundation.org
Subject: Re: [PATCH] mm: Enable MAP_UNINITIALIZED for archs with mmu

On Thu, Jan 19, 2012 at 12:21 AM, Arun Sharma <asharma@...com> wrote:
>
> This enables malloc optimizations where we might
> madvise(..,MADV_DONTNEED) a page only to fault it
> back at a different virtual address.
>
> To ensure that we don't leak sensitive data to
> unprivileged processes, we enable this optimization
> only for pages that are reused within a memory
> cgroup.
>

So the assumption is that only apps that have access to each others
VMA's will run in this cgroup?

> The idea is to make this opt-in both at the mmap()
> level and cgroup level so the default behavior is
> unchanged after the patch.
>

Sorry, I am not convinced we need to do this

1. I know that zeroing out memory is expensive, but building a
potential loop hole is not a good idea
2. How do we ensure that tasks in a cgroup should be allowed to reuse
memory uninitialized, how does the cgroup admin know what she is
getting into?

So I am going to NACK this.

Balbir
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