From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from aserp1040.oracle.com ([141.146.126.69]:25201 "EHLO aserp1040.oracle.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751729AbaJXPFM (ORCPT ); Fri, 24 Oct 2014 11:05:12 -0400 Message-ID: <544A6A6B.3040602@oracle.com> Date: Fri, 24 Oct 2014 11:04:11 -0400 From: Sasha Levin MIME-Version: 1.0 Subject: Re: drivers: random: Shift out-of-bounds in _mix_pool_bytes References: <1413802499-17928-1-git-send-email-a.ryabinin@samsung.com> <5444EBFA.5030103@samsung.com> <20141020124929.GA23177@thunk.org> <54451501.2070700@samsung.com> <5445179A.4080804@redhat.com> <20141020141635.GA4499@thunk.org> <20141024100108.GF12706@worktop.programming.kicks-ass.net> <544A52D7.6000202@oracle.com> <20141024134205.GB21513@worktop.programming.kicks-ass.net> In-Reply-To: <20141024134205.GB21513@worktop.programming.kicks-ass.net> Content-Type: text/plain; charset=windows-1252 Content-Transfer-Encoding: 8bit Sender: linux-kbuild-owner@vger.kernel.org List-ID: To: Peter Zijlstra Cc: Theodore Ts'o , Daniel Borkmann , Andrey Ryabinin , Andrew Morton , Thomas Gleixner , Ingo Molnar , "H. Peter Anvin" , Michal Marek , x86@kernel.org, linux-kbuild@vger.kernel.org, linux-kernel@vger.kernel.org, Andreas Dilger , Dmitry Vyukov , Konstantin Khlebnikov On 10/24/2014 09:42 AM, Peter Zijlstra wrote: > On Fri, Oct 24, 2014 at 09:23:35AM -0400, Sasha Levin wrote: >> >> i >> 32 may happen to be "i", but is there anything that prevents the compiler >> from returning, let's say, 42? > > Not really, although gcc seems to opt for the 'sane' option and emit the > instruction and let the arch figure out how to deal with it. Hence the > 'fun' difference between x86 and ARM. It's interesting how many different views on undefined behaviour there are between kernel folks. Everything between Ted Ts'o saying that GCC can launch nethack on oversized shifts, to DaveM saying he will file a GCC bug if the behaviour isn't sane w.r.t to memcpy(). Thanks, Sasha