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=-2.1 required=3.0 tests=DKIM_INVALID,DKIM_SIGNED, 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 51008C41514 for ; Fri, 23 Aug 2019 09:37:05 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 2679121726 for ; Fri, 23 Aug 2019 09:37:05 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=fail reason="signature verification failed" (2048-bit key) header.d=infradead.org header.i=@infradead.org header.b="QYnL2t5M" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1733243AbfHWJhE (ORCPT ); Fri, 23 Aug 2019 05:37:04 -0400 Received: from merlin.infradead.org ([205.233.59.134]:36708 "EHLO merlin.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1725857AbfHWJhD (ORCPT ); Fri, 23 Aug 2019 05:37:03 -0400 DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=infradead.org; s=merlin.20170209; h=In-Reply-To:Content-Type:MIME-Version: References:Message-ID:Subject:Cc:To:From:Date:Sender:Reply-To: Content-Transfer-Encoding:Content-ID:Content-Description:Resent-Date: Resent-From:Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID:List-Id: List-Help:List-Unsubscribe:List-Subscribe:List-Post:List-Owner:List-Archive; bh=npY3kxMBkpg6StNbFZw2v3WvWnwH4EGOxrS2hJvkUAQ=; b=QYnL2t5MsjdvI+dwV/uz9x/ny w4l7H3zbjU9ULp8rqmNsdkMzJefwulHzT674UaVXVW2ZOxGNk2IPoyDOVYwxdlw2/cUrKB2IuCmzk UFf3j6w6pZBxPDIBCztDYsTGYBwpd2G/WFNNpuW/cqSeOLJdLz2CvmEqnVpO7gFMO3i7gP79I0hrQ PnrgbnRKx5QW5wmGNN0cHJoBXpzj4VZ/EfwacdpQ1zfnNaHhHt6Bv/aWXHXIiY6jseD6krryICT92 bfZ6I3NLzuSNC85WpvHObD0w9bp2jOXxOTUBKMCaXC47F2BAJ83x4nEeaGSMW+OLfKDn7VfnST5Xb njK0EEvPQ==; Received: from j217100.upc-j.chello.nl ([24.132.217.100] helo=noisy.programming.kicks-ass.net) by merlin.infradead.org with esmtpsa (Exim 4.92 #3 (Red Hat Linux)) id 1i15zt-0007yJ-1Y; Fri, 23 Aug 2019 09:36:41 +0000 Received: from hirez.programming.kicks-ass.net (hirez.programming.kicks-ass.net [192.168.1.225]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (Client did not present a certificate) by noisy.programming.kicks-ass.net (Postfix) with ESMTPS id A175E307603; Fri, 23 Aug 2019 11:36:05 +0200 (CEST) Received: by hirez.programming.kicks-ass.net (Postfix, from userid 1000) id DEFD920BF0F18; Fri, 23 Aug 2019 11:36:37 +0200 (CEST) Date: Fri, 23 Aug 2019 11:36:37 +0200 From: Peter Zijlstra To: Song Liu Cc: linux-kernel@vger.kernel.org, linux-mm@kvack.org, kernel-team@fb.com, stable@vger.kernel.org, Thomas Gleixner , Dave Hansen , Steven Rostedt , Andy Lutomirski Subject: Re: [PATCH] x86/mm: Do not split_large_page() for set_kernel_text_rw() Message-ID: <20190823093637.GH2369@hirez.programming.kicks-ass.net> References: <20190823052335.572133-1-songliubraving@fb.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20190823052335.572133-1-songliubraving@fb.com> User-Agent: Mutt/1.10.1 (2018-07-13) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 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.