Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1760587AbcJ1T3I (ORCPT ); Fri, 28 Oct 2016 15:29:08 -0400 Received: from youngberry.canonical.com ([91.189.89.112]:56345 "EHLO youngberry.canonical.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1756516AbcJ1T3H (ORCPT ); Fri, 28 Oct 2016 15:29:07 -0400 Subject: Re: [PATCH] ipc/sem: ensure we left shift a ULL rather than a 32 bit integer To: Manfred Spraul , Andrew Morton , Davidlohr Bueso , Peter Zijlstra , Ingo Molnar , Nikolay Borisov References: <20161028181129.7311-1-colin.king@canonical.com> <8570d3d4-aeaf-7d2e-7d04-3234264959fd@colorfullife.com> Cc: linux-kernel@vger.kernel.org From: Colin Ian King Message-ID: <86085f85-e60f-8942-ccdd-a545a7c949ce@canonical.com> Date: Fri, 28 Oct 2016 20:29:03 +0100 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:45.0) Gecko/20100101 Thunderbird/45.3.0 MIME-Version: 1.0 In-Reply-To: <8570d3d4-aeaf-7d2e-7d04-3234264959fd@colorfullife.com> Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1127 Lines: 34 On 28/10/16 20:21, Manfred Spraul wrote: > Hi Colin, > > On 10/28/2016 08:11 PM, Colin King wrote: >> From: Colin Ian King >> >> The left shift amount is sop->sem_num % 64, which is up to 63, so >> ensure we are shifting a ULL rather than a 32 bit value. > Good catch, thanks. >> CoverityScan CID#1372862 "Bad bit shift operation" >> >> Fixes: 7c24530cb4e3c0ae ("ipc/sem: optimize perform_atomic_semop()") >> Signed-off-by: Colin Ian King >> --- >> ipc/sem.c | 2 +- >> 1 file changed, 1 insertion(+), 1 deletion(-) >> >> diff --git a/ipc/sem.c b/ipc/sem.c >> index ebd18a7..ca4aa23 100644 >> --- a/ipc/sem.c >> +++ b/ipc/sem.c >> @@ -1839,7 +1839,7 @@ SYSCALL_DEFINE4(semtimedop, int, semid, struct >> sembuf __user *, tsops, >> max = 0; >> for (sop = sops; sop < sops + nsops; sop++) { >> - unsigned long mask = 1 << ((sop->sem_num) % BITS_PER_LONG); >> + unsigned long mask = 1ULL << ((sop->sem_num) % BITS_PER_LONG); >> > Why 1ULL? Is 1UL not sufficient? For example, 1UL i386 is 32 bits, where as 1ULL is 64. > > -- > Manfred