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 16E01ECE58E for ; Thu, 17 Oct 2019 14:28:31 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id E7C0620820 for ; Thu, 17 Oct 2019 14:28:30 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2440088AbfJQO23 (ORCPT ); Thu, 17 Oct 2019 10:28:29 -0400 Received: from mx1.redhat.com ([209.132.183.28]:55396 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1731664AbfJQO23 (ORCPT ); Thu, 17 Oct 2019 10:28:29 -0400 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 34890307D985; Thu, 17 Oct 2019 14:28:29 +0000 (UTC) Received: from dhcp-27-174.brq.redhat.com (unknown [10.43.17.44]) by smtp.corp.redhat.com (Postfix) with SMTP id 5859D5C1B5; Thu, 17 Oct 2019 14:28:27 +0000 (UTC) Received: by dhcp-27-174.brq.redhat.com (nbSMTP-1.00) for uid 1000 oleg@redhat.com; Thu, 17 Oct 2019 16:28:27 +0200 (CEST) Date: Thu, 17 Oct 2019 16:28:24 +0200 From: Oleg Nesterov To: Song Liu Cc: open list , "linux-mm@kvack.org" , "akpm@linux-foundation.org" , "matthew.wilcox@oracle.com" , Kernel Team , "william.kucharski@oracle.com" , "Kirill A . Shutemov" , Srikar Dronamraju Subject: Re: [PATCH 4/4] uprobe: only do FOLL_SPLIT_PMD for uprobe register Message-ID: <20191017142824.GA453@redhat.com> References: <20191016073731.4076725-1-songliubraving@fb.com> <20191016073731.4076725-5-songliubraving@fb.com> <20191016121031.GA31585@redhat.com> <20191017084714.GB17513@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.5.24 (2015-08-30) 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 [10.5.110.48]); Thu, 17 Oct 2019 14:28:29 +0000 (UTC) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 10/17, Song Liu wrote: > > > > On Oct 17, 2019, at 1:47 AM, Oleg Nesterov wrote: > > > > On 10/16, Song Liu wrote: > >> > >>> On Oct 16, 2019, at 5:10 AM, Oleg Nesterov wrote: > >>> > >>>> @@ -489,6 +492,9 @@ int uprobe_write_opcode(struct arch_uprobe *auprobe, struct mm_struct *mm, > >>>> if (ret <= 0) > >>>> goto put_old; > >>>> > >>>> + WARN(!is_register && PageCompound(old_page), > >>>> + "uprobe unregister should never work on compound page\n"); > >>> > >>> But this can happen with the change above. You can't know if *vaddr was > >>> previously changed by install_breakpoint() or not. > >> > >>> If not, verify_opcode() should likely save us, but we can't rely on it. > >>> Say, someone can write "int3" into vm_file at uprobe->offset. > >> > >> I think this won't really happen. With is_register == false, we already > >> know opcode is not "int3", so current call must be from set_orig_insn(). > >> Therefore, old_page must be installed by uprobe, and cannot be compound. > >> > >> The other way is not guaranteed. With is_register == true, it is still > >> possible current call is from set_orig_insn(). However, we do not rely > >> on this path. > > > > Quite contrary. > > > > When is_register == true we know that a) the caller is install_breakpoint() > > and b) the original insn is NOT int3 unless this page was alreadt COW'ed by > > userspace, say, by gdb. > > > > If is_register == false we only know that the caller is remove_breakpoint(). > > We can't know if this page was COW'ed by uprobes or userspace, we can not > > know if the insn we are going to replace is int3 or not, thus we can not > > assume that verify_opcode() will fail and save us. > > So the case we worry about is: > old_page is COW by user space, no, in this case the page shouldn't be huge, > target insn is int3, and it is a huge page; > then uprobe calls remove_breakpoint(); Yes, > Yeah, I guess this could happen. Yes, > For the fix, I guess return -Esomething in such case should be sufficient? this is what I tried to suggest from the very beginning. Oleg.