From owner-svn-src-head@freebsd.org  Sun Jul 29 23:53:12 2018
Return-Path: <owner-svn-src-head@freebsd.org>
Delivered-To: svn-src-head@mailman.ysv.freebsd.org
Received: from mx1.freebsd.org (mx1.freebsd.org [IPv6:2610:1c1:1:606c::19:1])
 by mailman.ysv.freebsd.org (Postfix) with ESMTP id C42F810670F2;
 Sun, 29 Jul 2018 23:53:12 +0000 (UTC)
 (envelope-from kostikbel@gmail.com)
Received: from kib.kiev.ua (kib.kiev.ua [IPv6:2001:470:d5e7:1::1])
 (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits))
 (Client did not present a certificate)
 by mx1.freebsd.org (Postfix) with ESMTPS id 16B087F958;
 Sun, 29 Jul 2018 23:53:11 +0000 (UTC)
 (envelope-from kostikbel@gmail.com)
Received: from tom.home (kib@localhost [127.0.0.1])
 by kib.kiev.ua (8.15.2/8.15.2) with ESMTPS id w6TNr1RI088933
 (version=TLSv1.2 cipher=DHE-RSA-AES256-GCM-SHA384 bits=256 verify=NO);
 Mon, 30 Jul 2018 02:53:04 +0300 (EEST)
 (envelope-from kostikbel@gmail.com)
DKIM-Filter: OpenDKIM Filter v2.10.3 kib.kiev.ua w6TNr1RI088933
Received: (from kostik@localhost)
 by tom.home (8.15.2/8.15.2/Submit) id w6TNr1GN088932;
 Mon, 30 Jul 2018 02:53:01 +0300 (EEST)
 (envelope-from kostikbel@gmail.com)
X-Authentication-Warning: tom.home: kostik set sender to kostikbel@gmail.com
 using -f
Date: Mon, 30 Jul 2018 02:53:01 +0300
From: Konstantin Belousov <kostikbel@gmail.com>
To: Oliver Pinter <oliver.pinter@hardenedbsd.org>
Cc: src-committers@freebsd.org, svn-src-all@freebsd.org,
 svn-src-head@freebsd.org
Subject: Re: svn commit: r336876 - in head/sys: amd64/amd64 amd64/ia32
 amd64/include conf dev/hyperv/vmbus/amd64
Message-ID: <20180729235301.GM40119@kib.kiev.ua>
References: <201807292047.w6TKl0hV004691@repo.freebsd.org>
 <CAPQ4ffsHqf8OiqUF-WBJ_0KbZGgAOs-6npyLjqWYFN+oCq=8Pw@mail.gmail.com>
 <20180729223158.GL40119@kib.kiev.ua>
 <CAPQ4ffsWKQG9vAna9ORefNW1DYBv4=32s0TDLTe+i6BB96vrdw@mail.gmail.com>
MIME-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline
In-Reply-To: <CAPQ4ffsWKQG9vAna9ORefNW1DYBv4=32s0TDLTe+i6BB96vrdw@mail.gmail.com>
User-Agent: Mutt/1.10.1 (2018-07-13)
X-Spam-Status: No, score=-2.0 required=5.0 tests=ALL_TRUSTED,BAYES_00,
 DKIM_ADSP_CUSTOM_MED,FREEMAIL_FROM,NML_ADSP_CUSTOM_MED autolearn=no
 autolearn_force=no version=3.4.1
X-Spam-Checker-Version: SpamAssassin 3.4.1 (2015-04-28) on tom.home
X-BeenThere: svn-src-head@freebsd.org
X-Mailman-Version: 2.1.27
Precedence: list
List-Id: SVN commit messages for the src tree for head/-current
 <svn-src-head.freebsd.org>
List-Unsubscribe: <https://lists.freebsd.org/mailman/options/svn-src-head>,
 <mailto:svn-src-head-request@freebsd.org?subject=unsubscribe>
List-Archive: <http://lists.freebsd.org/pipermail/svn-src-head/>
List-Post: <mailto:svn-src-head@freebsd.org>
List-Help: <mailto:svn-src-head-request@freebsd.org?subject=help>
List-Subscribe: <https://lists.freebsd.org/mailman/listinfo/svn-src-head>,
 <mailto:svn-src-head-request@freebsd.org?subject=subscribe>
X-List-Received-Date: Sun, 29 Jul 2018 23:53:12 -0000

On Mon, Jul 30, 2018 at 01:26:51AM +0200, Oliver Pinter wrote:
> On 7/30/18, Konstantin Belousov <kostikbel@gmail.com> wrote:
> >>         testq   %r9,%r9
> >>         jz      1f
> >>         subq    %rdx,%r8
> >>         movq    %r8,(%r9) << Here you access user-space, with cleared
> >> RFLAGS.AC from the fault handler.
> > How does this instruction access userspace ?  I do not see.
> 
> As far as I remember from 4 years, the r9 may contained a user-space
> address in 10-STABLE
> in the case of starting the init. I've a stac/clac pair in my internal
> version, but I haven't found
> yet the relevant commit message.
This does not make any sense at all.

What could be a use for copyinstr(9) to pass a userspace pointer to
return the copied string' length ? More, kernel must not directly access
userspace, it needs to prepare for these accesses to fault.