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=-10.5 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH, MAILING_LIST_MULTI,MENTIONS_GIT_HOSTING,SPF_HELO_NONE,SPF_PASS, UNPARSEABLE_RELAY,USER_AGENT_SANE_1 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 1235DC2BA19 for ; Mon, 6 Apr 2020 14:51:46 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id D927E206C0 for ; Mon, 6 Apr 2020 14:51:45 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=oracle.com header.i=@oracle.com header.b="Ri0l9h8p" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728780AbgDFOvo (ORCPT ); Mon, 6 Apr 2020 10:51:44 -0400 Received: from userp2120.oracle.com ([156.151.31.85]:34624 "EHLO userp2120.oracle.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1728776AbgDFOvo (ORCPT ); Mon, 6 Apr 2020 10:51:44 -0400 Received: from pps.filterd (userp2120.oracle.com [127.0.0.1]) by userp2120.oracle.com (8.16.0.42/8.16.0.42) with SMTP id 036EmsmR135008; Mon, 6 Apr 2020 14:51:29 GMT DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=oracle.com; h=subject : from : to : cc : references : message-id : date : mime-version : in-reply-to : content-type : content-transfer-encoding; s=corp-2020-01-29; bh=TSq08w3zBJ3WXbaxngAG7bWBdNx8iSe5Zcj/t0FI1rw=; b=Ri0l9h8ptsXQDNmrdV0oqlk3PhIRtpT+VA3DLBFX1F3ehnf8e2VpCGQ/3OJbFrQQ+3lM oZ6RuOzs06z/VuyoWfJWZifIbj4OH5tfzLnYxxbd4eBuWgEvL+lTXkEj0i1D7YoHH0PL Br3BDVsun96eWccBnYX2kuQB1UR4MB1ri8cMKWmdudOwV4mshQM1kZuSq3mp+pMs7hru sXffiZevQIyatQWu18WKnaSbQGyEX2EKs45/As/oeHD0MqoazoMTw0fo+I17IbNsUiD0 w71ktjB+SGvoi10WBOh9OlBi46u37S9k7RZwD2EuxQQZfLWaheodP/VZwK5wJeUtr/mv gQ== Received: from userp3030.oracle.com (userp3030.oracle.com [156.151.31.80]) by userp2120.oracle.com with ESMTP id 306jvmy8su-1 (version=TLSv1.2 cipher=ECDHE-RSA-AES256-GCM-SHA384 bits=256 verify=OK); Mon, 06 Apr 2020 14:51:29 +0000 Received: from pps.filterd (userp3030.oracle.com [127.0.0.1]) by userp3030.oracle.com (8.16.0.42/8.16.0.42) with SMTP id 036ElDtv100043; Mon, 6 Apr 2020 14:51:29 GMT Received: from aserv0121.oracle.com (aserv0121.oracle.com [141.146.126.235]) by userp3030.oracle.com with ESMTP id 3073qd9kvb-1 (version=TLSv1.2 cipher=ECDHE-RSA-AES256-GCM-SHA384 bits=256 verify=OK); Mon, 06 Apr 2020 14:51:28 +0000 Received: from abhmp0007.oracle.com (abhmp0007.oracle.com [141.146.116.13]) by aserv0121.oracle.com (8.14.4/8.13.8) with ESMTP id 036EpRta018224; Mon, 6 Apr 2020 14:51:27 GMT Received: from linux-1.home (/92.157.90.160) by default (Oracle Beehive Gateway v4.0) with ESMTP ; Mon, 06 Apr 2020 07:51:27 -0700 Subject: Re: [PATCH 4/7] objtool: Add support for return trampoline call From: Alexandre Chartre To: Peter Zijlstra Cc: x86@kernel.org, linux-kernel@vger.kernel.org, jpoimboe@redhat.com, jthierry@redhat.com, tglx@linutronix.de References: <20200402082220.808-1-alexandre.chartre@oracle.com> <20200402082220.808-5-alexandre.chartre@oracle.com> <20200402152717.GE20730@hirez.programming.kicks-ass.net> <94272807-23c0-3eae-8312-9488607186ca@oracle.com> Message-ID: <8a33ffae-1926-9c0c-35b2-8276c49cfe5a@oracle.com> Date: Mon, 6 Apr 2020 16:55:52 +0200 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.2.0 MIME-Version: 1.0 In-Reply-To: <94272807-23c0-3eae-8312-9488607186ca@oracle.com> Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-US Content-Transfer-Encoding: 8bit X-Proofpoint-Virus-Version: vendor=nai engine=6000 definitions=9582 signatures=668685 X-Proofpoint-Spam-Details: rule=notspam policy=default score=0 phishscore=0 mlxscore=0 mlxlogscore=999 spamscore=0 bulkscore=0 adultscore=0 malwarescore=0 suspectscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.12.0-2003020000 definitions=main-2004060123 X-Proofpoint-Virus-Version: vendor=nai engine=6000 definitions=9582 signatures=668685 X-Proofpoint-Spam-Details: rule=notspam policy=default score=0 phishscore=0 suspectscore=0 mlxlogscore=999 mlxscore=0 bulkscore=0 adultscore=0 priorityscore=1501 lowpriorityscore=0 clxscore=1015 malwarescore=0 impostorscore=0 spamscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.12.0-2003020000 definitions=main-2004060123 Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 4/6/20 4:34 PM, Alexandre Chartre wrote: > > On 4/2/20 5:27 PM, Peter Zijlstra wrote: >> On Thu, Apr 02, 2020 at 10:22:17AM +0200, Alexandre Chartre wrote: >>> With retpoline, the return instruction is used to branch to an address >>> stored on the stack. So, unlike a regular return instruction, when a >>> retpoline return instruction is reached the stack has been modified >>> compared to what we have when the function was entered. >>> >>> Provide the mechanism to explicitly call-out such return instruction >>> so that objtool can correctly handle them. >> >> https://lkml.kernel.org/r/20200331222703.GH2452@worktop.programming.kicks-ass.net >> >> And also, the split out version: >> >>    https://git.kernel.org/pub/scm/linux/kernel/git/peterz/queue.git/commit/?h=core/objtool&id=ec9d9549901dfd2ff411676dfc624e50219e4d5a >> > > HINT_RET_OFFSET works fine when an immediate value is pushed on the > stack. However if the value is pushed from a callee-saved register > (%rbp, %rbx, %r12-%r15) then we still have a "return with modified > stack frame" warning. That's because objtool checks callee-saved > registers pushed/popped on the stack, and we have retpoline functions > built for each register (see arch/x86/lib/retpoline.S) > > So that's why I also added a bool to has_modified_stack_frame() to > no check registers: > > @@ -1432,7 +1478,8 @@ static bool is_fentry_call(struct instruction *insn) >      return false; >  } > > -static bool has_modified_stack_frame(struct insn_state *state) > +static bool has_modified_stack_frame(struct insn_state *state, > +                     bool check_registers) >  { >      int i; > > @@ -1442,6 +1489,9 @@ static bool has_modified_stack_frame(struct insn_state *state) >          state->drap) >          return true; > > +    if (!check_registers) > +        return false; > + >      for (i = 0; i < CFI_NUM_REGS; i++) >          if (state->regs[i].base != initial_func_cfi.regs[i].base || >              state->regs[i].offset != initial_func_cfi.regs[i].offset) > > Here is a simple change on top of the UNWIND_HINT_RET_OFFSET patch to prevent this problem: diff --git a/tools/objtool/check.c b/tools/objtool/check.c index dbb2b2187037..97db8f49e06f 100644 --- a/tools/objtool/check.c +++ b/tools/objtool/check.c @@ -1390,6 +1390,14 @@ static bool has_modified_stack_frame(struct instruction *insn, if (state->stack_size != initial_func_cfi.cfa.offset + ret_offset) return true; + /* + * If there is a ret offset hint then don't check registers + * because a callee-saved register might have been pushed on + * the stack. + */ + if (ret_offset) + return false; + for (i = 0; i < CFI_NUM_REGS; i++) { if (state->regs[i].base != initial_func_cfi.regs[i].base || state->regs[i].offset != initial_func_cfi.regs[i].offset) alex.