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=-0.9 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI, SPF_HELO_NONE,SPF_PASS autolearn=no 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 69CD7C54FCB for ; Thu, 23 Apr 2020 18:10:46 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 4AA7220776 for ; Thu, 23 Apr 2020 18:10:46 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (1024-bit key) header.d=redhat.com header.i=@redhat.com header.b="P0dGg6Vc" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1729995AbgDWSKq (ORCPT ); Thu, 23 Apr 2020 14:10:46 -0400 Received: from us-smtp-delivery-1.mimecast.com ([207.211.31.120]:27023 "EHLO us-smtp-1.mimecast.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1730221AbgDWSKp (ORCPT ); Thu, 23 Apr 2020 14:10:45 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1587665444; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: in-reply-to:in-reply-to:references:references; bh=2yRJCnoX8qkbcjYUfFVSZLzSknvTSyY8JodZRku30p4=; b=P0dGg6VcMTXKlmW7BqEo4Vgz8l15DjI5ZC9YCF5oFhV5eN2BKTwQSZvk6ZQZHRedXeNbE+ V0ORJCgCxl+qzaN/ldBt9DUAWj7k1XaPWj6a4c3VykKruf/vydN2xKdrsI0lzRtuoofVak LcjM+WLTO3Sv3PwyUi1o1IBH02RnvUs= Received: from mimecast-mx01.redhat.com (mimecast-mx01.redhat.com [209.132.183.4]) (Using TLS) by relay.mimecast.com with ESMTP id us-mta-455-ssTxrkrmM5-MnUXBiq4--A-1; Thu, 23 Apr 2020 14:10:38 -0400 X-MC-Unique: ssTxrkrmM5-MnUXBiq4--A-1 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 mimecast-mx01.redhat.com (Postfix) with ESMTPS id 1A8B78005BA; Thu, 23 Apr 2020 18:10:37 +0000 (UTC) Received: from treble (ovpn-118-207.rdu2.redhat.com [10.10.118.207]) by smtp.corp.redhat.com (Postfix) with ESMTPS id CEEF25C1BE; Thu, 23 Apr 2020 18:10:32 +0000 (UTC) Date: Thu, 23 Apr 2020 13:10:30 -0500 From: Josh Poimboeuf To: Miroslav Benes Cc: Gerald Schaefer , live-patching@vger.kernel.org, linux-kernel@vger.kernel.org, Peter Zijlstra , Jessica Yu , linux-s390@vger.kernel.org, heiko.carstens@de.ibm.com, Vasily Gorbik , Joe Lawrence Subject: Re: [PATCH v2 6/9] s390/module: Use s390_kernel_write() for late relocations Message-ID: <20200423181030.b5mircvgc7zmqacr@treble> References: <18266eb2c2c9a2ce0033426837d89dcb363a85d3.1587131959.git.jpoimboe@redhat.com> <20200422164037.7edd21ea@thinkpad> <20200422172126.743908f5@thinkpad> <20200422194605.n77t2wtx5fomxpyd@treble> <20200423141834.234ed0bc@thinkpad> <20200423141228.sjvnxwdqlzoyqdwg@treble> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: <20200423141228.sjvnxwdqlzoyqdwg@treble> X-Scanned-By: MIMEDefang 2.79 on 10.5.11.16 Sender: live-patching-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: live-patching@vger.kernel.org On Thu, Apr 23, 2020 at 09:12:28AM -0500, Josh Poimboeuf wrote: > > > this is strange. While I would have expected an exception similar to > > > this, it really should have happened on the "sturg" instruction which > > > does the DAT-off store in s390_kernel_write(), and certainly not with > > > an ID of 0004 (protection). However, in your case, it happens on a > > > normal store instruction, with 0004 indicating a protection exception. > > > > > > This is more like what I would expect e.g. in the case where you do > > > _not_ use the s390_kernel_write() function for RO module text patching, > > > but rather normal memory access. So I am pretty sure that this is not > > > related to the s390_kernel_write(), but some other issue, maybe some > > > place left where you still use normal memory access? > > > > The call trace above also suggests that it is not a late relocation, no? > > The path is from KLP module init function through klp_enable_patch. It should > > mean that the to-be-patched object is loaded (it must be a module thanks > > to a check klp_init_object_loaded(), vmlinux relocations were processed > > earlier in apply_relocations()). > > > > However, the KLP module state here must be COMING, so s390_kernel_write() > > should be used. What are we missing? > > I'm also scratching my head. It _should_ be using s390_kernel_write() > based on the module state, but I don't see that on the stack trace. > > This trace (and Gerald's comment) seem to imply it's using > __builtin_memcpy(), which might expected for UNFORMED state. > > Weird... Mystery solved: $ CROSS_COMPILE=s390x-linux-gnu- scripts/faddr2line vmlinux apply_rela+0x16a/0x520 apply_rela+0x16a/0x520: apply_rela at arch/s390/kernel/module.c:336 which corresponds to the following code in apply_rela(): case R_390_PLTOFF64: /* 16 bit offset from GOT to PLT. */ if (info->plt_initialized == 0) { unsigned int *ip; ip = me->core_layout.base + me->arch.plt_offset + info->plt_offset; ip[0] = 0x0d10e310; /* basr 1,0 */ ip[1] = 0x100a0004; /* lg 1,10(1) */ Notice how it's writing directly to text... oops. -- Josh