From owner-freebsd-security@FreeBSD.ORG  Sun Jun 18 10:09:20 2006
Return-Path: <owner-freebsd-security@FreeBSD.ORG>
X-Original-To: freebsd-security@freebsd.org
Delivered-To: freebsd-security@freebsd.org
Received: from mx1.FreeBSD.org (mx1.freebsd.org [216.136.204.125])
	by hub.freebsd.org (Postfix) with ESMTP id CD86216A506
	for <freebsd-security@freebsd.org>;
	Sun, 18 Jun 2006 10:09:20 +0000 (UTC)
	(envelope-from arne_woerner@yahoo.com)
Received: from web30303.mail.mud.yahoo.com (web30303.mail.mud.yahoo.com
	[68.142.200.96]) by mx1.FreeBSD.org (Postfix) with SMTP id 5A4C343D45
	for <freebsd-security@freebsd.org>;
	Sun, 18 Jun 2006 10:09:20 +0000 (GMT)
	(envelope-from arne_woerner@yahoo.com)
Received: (qmail 95687 invoked by uid 60001); 18 Jun 2006 10:09:19 -0000
DomainKey-Signature: a=rsa-sha1; q=dns; c=nofws; s=s1024; d=yahoo.com;
	h=Message-ID:Received:Date:From:Subject:To:In-Reply-To:MIME-Version:Content-Type:Content-Transfer-Encoding;
	b=nTAoVk2Q/0LIOPzsE23TVWwakqdil0xwNcD9v9t3t5mF/e3ldwxtLAbkXTDVCjqmX6eIdnZA41BrfidKtpmzvAv6xvTP2SUU0YiBZiitjbfeoKsonSPRnTFcNmEysf2q8F91fevf2vSg0yHhA7GlIYwqSuNAEcm0IUPaUkXVn2o=
	; 
Message-ID: <20060618100919.95685.qmail@web30303.mail.mud.yahoo.com>
Received: from [213.54.64.243] by web30303.mail.mud.yahoo.com via HTTP;
	Sun, 18 Jun 2006 03:09:19 PDT
Date: Sun, 18 Jun 2006 03:09:19 -0700 (PDT)
From: "R. B. Riddick" <arne_woerner@yahoo.com>
To: Nick Borisov <neiro21@gmail.com>, freebsd-security@freebsd.org
In-Reply-To: <3bcb4e3f0606180127m3c4fdb13n2b42deb881b7bdc6@mail.gmail.com>
MIME-Version: 1.0
Content-Type: text/plain; charset=iso-8859-1
Content-Transfer-Encoding: 8bit
Cc: 
Subject: Re: memory pages nulling when releasing
X-BeenThere: freebsd-security@freebsd.org
X-Mailman-Version: 2.1.5
Precedence: list
List-Id: "Security issues \[members-only posting\]"
	<freebsd-security.freebsd.org>
List-Unsubscribe: <http://lists.freebsd.org/mailman/listinfo/freebsd-security>, 
	<mailto:freebsd-security-request@freebsd.org?subject=unsubscribe>
List-Archive: <http://lists.freebsd.org/pipermail/freebsd-security>
List-Post: <mailto:freebsd-security@freebsd.org>
List-Help: <mailto:freebsd-security-request@freebsd.org?subject=help>
List-Subscribe: <http://lists.freebsd.org/mailman/listinfo/freebsd-security>, 
	<mailto:freebsd-security-request@freebsd.org?subject=subscribe>
X-List-Received-Date: Sun, 18 Jun 2006 10:09:20 -0000

--- Nick Borisov <neiro21@gmail.com> wrote:
> Could you tell me if FreeBSD supports memory page nulling when
> releasing it to prevent unauthorized access to data left in the page
> after it's allocated again.
> If it does, what sys calls etc provide that?
> IMHO this is an important issue when operating data with different
> sensivity levels.
>
It is important, that no user process can look at non-shared (mmap(2) /
MAP_SHARED) pages in main memory that were used by another process before.

I think FreeBSD does it as follows (but I am not sure):

1. If a page is allocated for a process it is either overwritten with zeroes
(0x00) (e. g. in case of a page for the stack segment of a process) or it is
overwritten with the bytes of an executable or another file or so...

2. For maximum performance the system keeps a bunch of "pre-zero-ed" pages, so
that the OS is quite fast, when a process wants pages for data (malloc(3)) or
for stack.

Here is my "proof": :-)
% vmstat -s | grep zero
  3840247 zero fill pages zeroed
   844738 zero fill pages prezeroed

-Arne


__________________________________________________
Do You Yahoo!?
Tired of spam?  Yahoo! Mail has the best spam protection around 
http://mail.yahoo.com