From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-6.0 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,SPF_PASS,USER_AGENT_NEOMUTT autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 6ECBCC43381 for ; Thu, 7 Mar 2019 16:50:28 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 3F45220840 for ; Thu, 7 Mar 2019 16:50:28 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726305AbfCGQu0 (ORCPT ); Thu, 7 Mar 2019 11:50:26 -0500 Received: from mx1.redhat.com ([209.132.183.28]:41728 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726161AbfCGQu0 (ORCPT ); Thu, 7 Mar 2019 11:50:26 -0500 Received: from smtp.corp.redhat.com (int-mx06.intmail.prod.int.phx2.redhat.com [10.5.11.16]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mx1.redhat.com (Postfix) with ESMTPS id 2B9F6285C7; Thu, 7 Mar 2019 16:50:25 +0000 (UTC) Received: from treble (ovpn-120-61.rdu2.redhat.com [10.10.120.61]) by smtp.corp.redhat.com (Postfix) with ESMTPS id 3487D5C1B5; Thu, 7 Mar 2019 16:50:23 +0000 (UTC) Date: Thu, 7 Mar 2019 10:50:21 -0600 From: Josh Poimboeuf To: Peter Zijlstra Cc: torvalds@linux-foundation.org, tglx@linutronix.de, hpa@zytor.com, julien.thierry@arm.com, will.deacon@arm.com, luto@amacapital.net, mingo@kernel.org, catalin.marinas@arm.com, james.morse@arm.com, valentin.schneider@arm.com, brgerst@gmail.com, luto@kernel.org, bp@alien8.de, dvlasenk@redhat.com, linux-kernel@vger.kernel.org, dvyukov@google.com, rostedt@goodmis.org Subject: Re: [PATCH 00/20] objtool: UACCESS validation v3 Message-ID: <20190307165021.nforh2xvvznb56j3@treble> References: <20190307114511.870090179@infradead.org> <20190307120317.GD32477@hirez.programming.kicks-ass.net> <20190307125526.GB32534@hirez.programming.kicks-ass.net> <20190307131312.GC32534@hirez.programming.kicks-ass.net> <20190307164705.qbu4ytdfdmsighas@treble> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: <20190307164705.qbu4ytdfdmsighas@treble> User-Agent: NeoMutt/20180716 X-Scanned-By: MIMEDefang 2.79 on 10.5.11.16 X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.5.110.30]); Thu, 07 Mar 2019 16:50:25 +0000 (UTC) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, Mar 07, 2019 at 10:47:05AM -0600, Josh Poimboeuf wrote: > On Thu, Mar 07, 2019 at 02:13:12PM +0100, Peter Zijlstra wrote: > > On Thu, Mar 07, 2019 at 01:55:26PM +0100, Peter Zijlstra wrote: > > > On Thu, Mar 07, 2019 at 01:03:17PM +0100, Peter Zijlstra wrote: > > > > > > > > 01be 20d3: 31 c0 xor %eax,%eax > > > > 01c0 20d5: 4c 39 eb cmp %r13,%rbx > > > > 01c3 20d8: 77 08 ja 20e2 <__do_sys_waitid+0x1cd> > > > > randconfig-build/kernel/exit.o: warning: objtool: __do_sys_waitid()+0x1c3: (branch) > > > > > > 01cd 20e2: 83 f0 01 xor $0x1,%eax > > > > 01d0 20e5: 48 89 c2 mov %rax,%rdx > > > > 01d3 20e8: 83 e2 01 and $0x1,%edx > > > > 01d6 20eb: 48 83 c2 02 add $0x2,%rdx > > > > 01da 20ef: 48 ff 04 d5 00 00 00 incq 0x0(,%rdx,8) > > > > 01e1 20f6: 00 > > > > 01de 20f3: R_X86_64_32S _ftrace_branch+0x148 > > > > 01e2 20f7: 84 c0 test %al,%al > > > > 01e4 20f9: 75 2d jne 2128 <__do_sys_waitid+0x213> > > > > > > we do not take this branch and fall-through. > > > > And that is the error, I think. We should've taken it and went to: > > > > return -EFAULT; > > > > because: > > > > +1be xor %eax,%eax eax=0 > > +1cd xor $0x1,%eax eax=1 > > +1e2 test %al,%al 1&1==1 -> ZF=0 > > +1e4 jnz > > > > Is an unconditional code sequence, but there's no way objtool can do > > that without becoming a full blown interpreter :/ > > > > > > 0213 2128: 49 c7 c7 f2 ff ff ff mov $0xfffffffffffffff2,%r15 > > > > ffffffffffffe0eb } > > > > 021a 212f: 48 8d 65 d8 lea -0x28(%rbp),%rsp > > > > 021e 2133: 4c 89 f8 mov %r15,%rax > > > > 0221 2136: 5b pop %rbx > > > > 0222 2137: 41 5c pop %r12 > > > > 0224 2139: 41 5d pop %r13 > > > > 0226 213b: 41 5e pop %r14 > > > > 0228 213d: 41 5f pop %r15 > > > > 022a 213f: 5d pop %rbp > > > > 022b 2140: c3 retq > > This "fixes" it, and also seems to help -Os make much code: much *smaller* code > > diff --git a/include/linux/compiler.h b/include/linux/compiler.h > index 445348facea9..8de63db58fdd 100644 > --- a/include/linux/compiler.h > +++ b/include/linux/compiler.h > @@ -67,7 +67,7 @@ void ftrace_likely_update(struct ftrace_likely_data *f, int val, > .line = __LINE__, \ > }; \ > ______r = !!(cond); \ > - ______f.miss_hit[______r]++; \ > + if (______r) ______f.miss_hit[1]++; else ______f.miss_hit[0]++; \ > ______r; \ > })) > #endif /* CONFIG_PROFILE_ALL_BRANCHES */ -- Josh