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=-2.2 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,USER_AGENT_SANE_1 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 6281FC2BB55 for ; Wed, 15 Apr 2020 10:08:51 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 4375220768 for ; Wed, 15 Apr 2020 10:08:51 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2896200AbgDOKIs (ORCPT ); Wed, 15 Apr 2020 06:08:48 -0400 Received: from foss.arm.com ([217.140.110.172]:41338 "EHLO foss.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S2896152AbgDOKIp (ORCPT ); Wed, 15 Apr 2020 06:08:45 -0400 Received: from usa-sjc-imap-foss1.foss.arm.com (unknown [10.121.207.14]) by usa-sjc-mx-foss1.foss.arm.com (Postfix) with ESMTP id 748491063; Wed, 15 Apr 2020 03:08:44 -0700 (PDT) Received: from gaia (unknown [172.31.20.19]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id 9E1BF3F68F; Wed, 15 Apr 2020 03:08:43 -0700 (PDT) Date: Wed, 15 Apr 2020 11:08:37 +0100 From: Catalin Marinas To: Will Deacon Cc: Vincenzo Frascino , Mark Rutland , linux-arm-kernel@lists.infradead.org, stable@vger.kernel.org Subject: Re: [PATCH 1/5] arm64: vdso: don't free unallocated pages Message-ID: <20200415100836.GB6526@gaia> References: <20200414104252.16061-1-mark.rutland@arm.com> <20200414104252.16061-2-mark.rutland@arm.com> <20200414132751.GF2486@C02TD0UTHF1T.local> <8681c958-0fd9-130e-f7bb-99bfd3a027cb@arm.com> <20200414151033.GA30288@willie-the-truck> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20200414151033.GA30288@willie-the-truck> User-Agent: Mutt/1.10.1 (2018-07-13) Sender: stable-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: stable@vger.kernel.org On Tue, Apr 14, 2020 at 04:10:35PM +0100, Will Deacon wrote: > On Tue, Apr 14, 2020 at 03:53:45PM +0100, Vincenzo Frascino wrote: > > On 4/14/20 2:27 PM, Mark Rutland wrote: > > > On Tue, Apr 14, 2020 at 01:50:38PM +0100, Vincenzo Frascino wrote: > > >> On 4/14/20 11:42 AM, Mark Rutland wrote: > > >>> The aarch32_vdso_pages[] array never has entries allocated in the C_VVAR > > >>> or C_VDSO slots, and as the array is zero initialized these contain > > >>> NULL. > > >>> > > >>> However in __aarch32_alloc_vdso_pages() when > > >>> aarch32_alloc_kuser_vdso_page() fails we attempt to free the page whose > > >>> struct page is at NULL, which is obviously nonsensical. > > >> > > >> Could you please explain why do you think that free(NULL) is "nonsensical"? > > > > > > Regardless of the below, can you please explain why it is sensical? I'm > > > struggling to follow your argument here. > > > > free(NULL) is a no-operation ("no action occurs") according to the C standard > > (ISO-IEC 9899 paragraph 7.20.3.2). Hence this should not cause any bug if the > > allocator is correctly implemented. From what I can see the implementation of > > the page allocator honors this assumption. > > > > Since you say it is a bug (providing evidence), we might have to investigate > > because probably there is an issue somewhere else. > > Not sure why you feel the need to throw the C standard around -- the patch > from Mark looks obviously like the right thing to do to me, so: > > Acked-by: Will Deacon > > Catalin -- please take this one as a fix so that I can queue the rest of > the patches for 5.8 once it's hit mainline. I queued this patch for -rc2. Thanks. -- Catalin