From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756952AbaEIQDt (ORCPT ); Fri, 9 May 2014 12:03:49 -0400 Received: from terminus.zytor.com ([198.137.202.10]:48733 "EHLO mail.zytor.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750987AbaEIQDs (ORCPT ); Fri, 9 May 2014 12:03:48 -0400 Message-ID: <536CFC3C.5030706@zytor.com> Date: Fri, 09 May 2014 09:03:08 -0700 From: "H. Peter Anvin" User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:24.0) Gecko/20100101 Thunderbird/24.4.0 MIME-Version: 1.0 To: Boris Ostrovsky CC: tglx@linutronix.de, mingo@redhat.com, linux-kernel@vger.kernel.org, stefani@seibold.net, luto@amacapital.net, konrad.wilk@oracle.com, stable@vger.kernel.org Subject: Re: [PATCH] time: Cast tv_nsec to u64 for proper shifting in update_vsyscall() References: <1399648287-15178-1-git-send-email-boris.ostrovsky@oracle.com> <536CF7B3.4040705@zytor.com> <536CFB79.7030602@oracle.com> In-Reply-To: <536CFB79.7030602@oracle.com> X-Enigmail-Version: 1.6 Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 05/09/2014 08:59 AM, Boris Ostrovsky wrote: > On 05/09/2014 11:43 AM, H. Peter Anvin wrote: >> On 05/09/2014 08:11 AM, Boris Ostrovsky wrote: >>> With tk->wall_to_monotonic.tv_nsec being a 32-bit value on 32-bit >>> systems, (tk->wall_to_monotonic.tv_nsec << tk->shift) in >>> update_vsyscall() >>> may lose upper bits or, worse, add them since compiler will do this: >>> (u64)(tk->wall_to_monotonic.tv_nsec << tk->shift) >>> instead of >>> ((u64)tk->wall_to_monotonic.tv_nsec << tk->shift) >>> >>> So if, for example, tv_nsec is 0x800000 and shift is 8 we will end up >>> with 0xffffffff80000000 instead of 0x80000000. And then we are stuck in >>> the subsequent 'while' loop. >>> >>> We need explicit cast. >>> >>> Signed-off-by: Boris Ostrovsky >>> Acked-by: Konrad Rzeszutek Wilk >>> Cc: stable@vger.kernel.org >> This is needed in stable only for v3.14, right? > > I suspect anything that has commit 650ea024 needs to be fixed. I see > this code, for example, in 3.12 (it used to be in vsyscall_64.c). > But you're talking about 32-bit platforms. Vsyscalls aren't used on x86-32 until 3.14. Am I missing something? -hpa