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=-3.9 required=3.0 tests=BAYES_00,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 C633AC433E2 for ; Fri, 28 Aug 2020 02:14:37 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 9FF08207DF for ; Fri, 28 Aug 2020 02:14:37 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=ellerman.id.au header.i=@ellerman.id.au header.b="fZT1Uatx" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728048AbgH1COg (ORCPT ); Thu, 27 Aug 2020 22:14:36 -0400 Received: from ozlabs.org ([203.11.71.1]:44905 "EHLO ozlabs.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726147AbgH1COd (ORCPT ); Thu, 27 Aug 2020 22:14:33 -0400 Received: from authenticated.ozlabs.org (localhost [127.0.0.1]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange ECDHE (P-256) server-signature RSA-PSS (4096 bits) server-digest SHA256) (No client certificate requested) by mail.ozlabs.org (Postfix) with ESMTPSA id 4Bd37p4dhPz9sR4; Fri, 28 Aug 2020 12:14:30 +1000 (AEST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=ellerman.id.au; s=201909; t=1598580871; bh=zbHgIvSOOwfYmIlGTu8/cRu0o1U+KPvxZ9Z4EaG6Y68=; h=From:To:Cc:Subject:In-Reply-To:References:Date:From; b=fZT1UatxE65b4IK+nS5xatGzpt4kggDVd1Z9XNbtxcIct8c2jMff2m7GoIPfkRFKf e3KIDQkGIKSCX9Wg+jPcc2d4SW6VQB71b4tl6kF74KWF0iinTMKGk1EgqDZ3PbGt7Y ETeG5sqhwCmC9EqHW9ZF0U8FkKZToMDtKFtKbzOd7iO5egiyY+IrN/+LHUv02qichU jQazusCluSR1RV8SJ9n8FiUwy939+1UFUtd8WmcmV18EzI/59OuynEbPf7EVJGqvlU 8oOZTWqyyARF/BclDpEuy3AAkBF06zUl14nSriPGqog2lMqQCzqPVfRRM5rZD555Fj 0Tu7O8vYbf82w== From: Michael Ellerman To: Dmitry Safonov <0x7f454c46@gmail.com> Cc: Christophe Leroy , Benjamin Herrenschmidt , Paul Mackerras , nathanl@linux.ibm.com, linux-arch , Arnd Bergmann , open list , Andy Lutomirski , Thomas Gleixner , Vincenzo Frascino , linuxppc-dev@lists.ozlabs.org, Will Deacon Subject: Re: [PATCH v8 2/8] powerpc/vdso: Remove __kernel_datapage_offset and simplify __get_datapage() In-Reply-To: References: <0d2201efe3c7727f2acc718aefd7c5bb22c66c57.1588079622.git.christophe.leroy@c-s.fr> <87wo34tbas.fsf@mpe.ellerman.id.au> <2f9b7d02-9e2f-4724-2608-c5573f6507a2@csgroup.eu> <6862421a-5a14-2e38-b825-e39e6ad3d51d@csgroup.eu> <87imd5h5kb.fsf@mpe.ellerman.id.au> Date: Fri, 28 Aug 2020 12:14:28 +1000 Message-ID: <87a6yf34aj.fsf@mpe.ellerman.id.au> MIME-Version: 1.0 Content-Type: text/plain Sender: linux-arch-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-arch@vger.kernel.org Dmitry Safonov <0x7f454c46@gmail.com> writes: > Hello, > > On Wed, 26 Aug 2020 at 15:39, Michael Ellerman wrote: >> Christophe Leroy writes: > [..] >> > arch_remap() gets replaced by vdso_remap() >> > >> > For arch_unmap(), I'm wondering how/what other architectures do, because >> > powerpc seems to be the only one to erase the vdso context pointer when >> > unmapping the vdso. >> >> Yeah. The original unmap/remap stuff was added for CRIU, which I thought >> people tested on other architectures (more than powerpc even). >> >> Possibly no one really cares about vdso unmap though, vs just moving the >> vdso. >> >> We added a test for vdso unmap recently because it happened to trigger a >> KAUP failure, and someone actually hit it & reported it. > > You right, CRIU cares much more about moving vDSO. > It's done for each restoree and as on most setups vDSO is premapped and > used by the application - it's actively tested. > Speaking about vDSO unmap - that's concerning only for heterogeneous C/R, > i.e when an application is migrated from a system that uses vDSO to the one > which doesn't - it's much rare scenario. > (for arm it's !CONFIG_VDSO, for x86 it's `vdso=0` boot parameter) Ah OK that explains it. The case we hit of VDSO unmapping was some strange "library OS" thing which had explicitly unmapped the VDSO, so also very rare. > Looking at the code, it seems quite easy to provide/maintain .close() for > vm_special_mapping. A bit harder to add a test from CRIU side > (as glibc won't know on restore that it can't use vdso anymore), > but totally not impossible. > >> Running that test on arm64 segfaults: >> >> # ./sigreturn_vdso >> VDSO is at 0xffff8191f000-0xffff8191ffff (4096 bytes) >> Signal delivered OK with VDSO mapped >> VDSO moved to 0xffff8191a000-0xffff8191afff (4096 bytes) >> Signal delivered OK with VDSO moved >> Unmapped VDSO >> Remapped the stack executable >> [ 48.556191] potentially unexpected fatal signal 11. >> [ 48.556752] CPU: 0 PID: 140 Comm: sigreturn_vdso Not tainted 5.9.0-rc2-00057-g2ac69819ba9e #190 >> [ 48.556990] Hardware name: linux,dummy-virt (DT) >> [ 48.557336] pstate: 60001000 (nZCv daif -PAN -UAO BTYPE=--) >> [ 48.557475] pc : 0000ffff8191a7bc >> [ 48.557603] lr : 0000ffff8191a7bc >> [ 48.557697] sp : 0000ffffc13c9e90 >> [ 48.557873] x29: 0000ffffc13cb0e0 x28: 0000000000000000 >> [ 48.558201] x27: 0000000000000000 x26: 0000000000000000 >> [ 48.558337] x25: 0000000000000000 x24: 0000000000000000 >> [ 48.558754] x23: 0000000000000000 x22: 0000000000000000 >> [ 48.558893] x21: 00000000004009b0 x20: 0000000000000000 >> [ 48.559046] x19: 0000000000400ff0 x18: 0000000000000000 >> [ 48.559180] x17: 0000ffff817da300 x16: 0000000000412010 >> [ 48.559312] x15: 0000000000000000 x14: 000000000000001c >> [ 48.559443] x13: 656c626174756365 x12: 7865206b63617473 >> [ 48.559625] x11: 0000000000000003 x10: 0101010101010101 >> [ 48.559828] x9 : 0000ffff818afda8 x8 : 0000000000000081 >> [ 48.559973] x7 : 6174732065687420 x6 : 64657070616d6552 >> [ 48.560115] x5 : 000000000e0388bd x4 : 000000000040135d >> [ 48.560270] x3 : 0000000000000000 x2 : 0000000000000001 >> [ 48.560412] x1 : 0000000000000003 x0 : 00000000004120b8 >> Segmentation fault >> # >> >> So I think we need to keep the unmap hook. Maybe it should be handled by >> the special_mapping stuff generically. > > I'll cook a patch for vm_special_mapping if you don't mind :-) That would be great, thanks! cheers