linux-kernel - Re: [PATCH] nommu arch dont zero the anonymous mapping by adding UNINITIALIZE flag

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Message-ID: <15938.1175253862@redhat.com>
Date:	Fri, 30 Mar 2007 12:24:22 +0100
From:	David Howells <dhowells@...hat.com>
To:	"Aubrey Li" <aubreylee@...il.com>
Cc:	vapier.adi@...il.com, jie.zhang@...log.com, bryan.wu@...log.com,
	"Andrew Morton" <akpm@...ux-foundation.org>,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] nommu arch dont zero the anonymous mapping by adding UNINITIALIZE flag 

Aubrey Li <aubreylee@...il.com> wrote:

> malloc() allocates size bytes and returns a pointer to the allocated memory.
> ****The memory is not cleared.****

But this is *not* malloc().  It's mmap().  Are you prepared to guarantee that
there are no applications out there that don't rely on anon mmap() giving
zeroed memory?

The MMU-mode clearing is done for security reasons - there shouldn't be any
leakage between processes, and because the zero page can just be faulted in.

Personally, I'd prefer to maintain compatibility with MMU-mode wherever
possible, but I'm happy with overrides like the MAP_UNINITIALISED flag
suggested.

David
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