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=-2.3 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,USER_AGENT_SANE_2 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 E3486C3A59F for ; Mon, 26 Aug 2019 11:33:12 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id BC22521852 for ; Mon, 26 Aug 2019 11:33:12 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1730261AbfHZLdM (ORCPT ); Mon, 26 Aug 2019 07:33:12 -0400 Received: from mail.kernel.org ([198.145.29.99]:51902 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727017AbfHZLdM (ORCPT ); Mon, 26 Aug 2019 07:33:12 -0400 Received: from gandalf.local.home (cpe-66-24-58-225.stny.res.rr.com [66.24.58.225]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPSA id 42DD9217F5; Mon, 26 Aug 2019 11:33:10 +0000 (UTC) Date: Mon, 26 Aug 2019 07:33:08 -0400 From: Steven Rostedt To: Peter Zijlstra Cc: Song Liu , linux-kernel@vger.kernel.org, linux-mm@kvack.org, kernel-team@fb.com, stable@vger.kernel.org, Thomas Gleixner , Dave Hansen , Andy Lutomirski , Nadav Amit , Daniel Bristot de Oliveira Subject: Re: [PATCH] x86/mm: Do not split_large_page() for set_kernel_text_rw() Message-ID: <20190826073308.6e82589d@gandalf.local.home> In-Reply-To: <20190823093637.GH2369@hirez.programming.kicks-ass.net> References: <20190823052335.572133-1-songliubraving@fb.com> <20190823093637.GH2369@hirez.programming.kicks-ass.net> X-Mailer: Claws Mail 3.17.3 (GTK+ 2.24.32; x86_64-pc-linux-gnu) MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Sender: stable-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: stable@vger.kernel.org On Fri, 23 Aug 2019 11:36:37 +0200 Peter Zijlstra wrote: > On Thu, Aug 22, 2019 at 10:23:35PM -0700, Song Liu wrote: > > As 4k pages check was removed from cpa [1], set_kernel_text_rw() leads to > > split_large_page() for all kernel text pages. This means a single kprobe > > will put all kernel text in 4k pages: > > > > root@ ~# grep ffff81000000- /sys/kernel/debug/page_tables/kernel > > 0xffffffff81000000-0xffffffff82400000 20M ro PSE x pmd > > > > root@ ~# echo ONE_KPROBE >> /sys/kernel/debug/tracing/kprobe_events > > root@ ~# echo 1 > /sys/kernel/debug/tracing/events/kprobes/enable > > > > root@ ~# grep ffff81000000- /sys/kernel/debug/page_tables/kernel > > 0xffffffff81000000-0xffffffff82400000 20M ro x pte > > > > To fix this issue, introduce CPA_FLIP_TEXT_RW to bypass "Text RO" check > > in static_protections(). > > > > Two helper functions set_text_rw() and set_text_ro() are added to flip > > _PAGE_RW bit for kernel text. > > > > [1] commit 585948f4f695 ("x86/mm/cpa: Avoid the 4k pages check completely") > > ARGH; so this is because ftrace flips the whole kernel range to RW and > back for giggles? I'm thinking _that_ is a bug, it's a clear W^X > violation. Since ftrace did this way before text_poke existed and way before anybody cared (back in 2007), it's not really a bug. Anyway, I believe Nadav has some patches that converts ftrace to use the shadow page modification trick somewhere. Or we also need the text_poke batch processing (did that get upstream?). Mapping in 40,000 pages one at a time is noticeable from a human stand point. -- Steve