From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752405AbbIKSAF (ORCPT ); Fri, 11 Sep 2015 14:00:05 -0400 Received: from pandora.arm.linux.org.uk ([78.32.30.218]:41650 "EHLO pandora.arm.linux.org.uk" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751347AbbIKSAC (ORCPT ); Fri, 11 Sep 2015 14:00:02 -0400 Date: Fri, 11 Sep 2015 18:59:51 +0100 From: Russell King - ARM Linux To: Stefano Stabellini Cc: Julien Grall , ian.campbell@citrix.com, Riku Voipio , linux-kernel@vger.kernel.org, xen-devel@lists.xenproject.org, linux-arm-kernel@lists.infradead.org Subject: Re: [PATCH v2] arm/xen: Enable user access to the kernel before issuing a privcmd call Message-ID: <20150911175951.GA21084@n2100.arm.linux.org.uk> References: <1441988759-4572-1-git-send-email-julien.grall@citrix.com> <20150911170027.GX21084@n2100.arm.linux.org.uk> <55F3102B.3090309@citrix.com> <55F31105.6070305@citrix.com> <20150911175107.GY21084@n2100.arm.linux.org.uk> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.5.23 (2014-03-12) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Fri, Sep 11, 2015 at 06:56:50PM +0100, Stefano Stabellini wrote: > On Fri, 11 Sep 2015, Russell King - ARM Linux wrote: > > On Fri, Sep 11, 2015 at 06:36:05PM +0100, Julien Grall wrote: > > > On 11/09/15 18:32, Julien Grall wrote: > > > > On 11/09/15 18:00, Russell King - ARM Linux wrote: > > > >> On Fri, Sep 11, 2015 at 05:25:59PM +0100, Julien Grall wrote: > > > >>> + /* > > > >>> + * Privcmd calls are issued by the userspace. We need to allow the > > > >>> + * kernel to access the userspace memory before issuing the hypercall. > > > >>> + */ > > > >>> + uaccess_enable r4 > > > >>> + > > > >>> + /* r4 is loaded now as we use it as scratch register before */ > > > >>> ldr r4, [sp, #4] > > > >> > > > >> As I mentioned in one of my previous mails, "ip" should be safe to use > > > >> here - it's a caller-corrupted register, just like r0-r3 and lr. So, > > > >> you could do: > > > >> > > > >> ldr r4, [sp, #4] > > > >> + uaccess_enable ip > > > > > > > > The register ip (aka r12) is used to store the hypercall number. So we > > > > can't reuse it as scratch register. > > > > > > > > The easiest one is r4. > > > > > > > >> > > > >> which fractionally tightens the window. > > > >> > > > >> However, there's nothing actually wrong with your version - there's no > > > >> way we could've got this far with sp pointing at userspace. > > > >> > > > >> I'm happy with either version, so: > > > >> > > > >> Acked-by: Russell King > > > >> > > > >> How do you want to handle the patch? I already have some other uaccess > > > >> fixes queued up to send to Linus before the merge window closes. > > > > > > Forgot to answer to this bits. I was thinking to ask Stefano carrying > > > the patch in xentip. Although it won't go until rc1. > > > > > > I don't mind if it's going earlier in Linux/master. > > > > Thanks, I've applied your patch as-is now. > > That's fine by me, the patch looks good. If you'd like your ack on it, please send one, I can still do that. -- FTTC broadband for 0.8mile line: currently at 9.6Mbps down 400kbps up according to speedtest.net.