From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Message-ID: <536CFB79.7030602@oracle.com> Date: Fri, 09 May 2014 11:59:53 -0400 From: Boris Ostrovsky MIME-Version: 1.0 To: "H. Peter Anvin" 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> In-Reply-To: <536CF7B3.4040705@zytor.com> Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: 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). -boris