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_SIGNED, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_PASS,T_DKIM_INVALID, USER_AGENT_MUTT autolearn=ham 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 5FD39C43334 for ; Thu, 6 Sep 2018 08:43:07 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 0AC602075B for ; Thu, 6 Sep 2018 08:43:07 +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="j+NR29/u" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 0AC602075B Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=infradead.org Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=linux-kernel-owner@vger.kernel.org Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728180AbeIFNR0 (ORCPT ); Thu, 6 Sep 2018 09:17:26 -0400 Received: from bombadil.infradead.org ([198.137.202.133]:37012 "EHLO bombadil.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1728034AbeIFNR0 (ORCPT ); Thu, 6 Sep 2018 09:17:26 -0400 DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=infradead.org; s=bombadil.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=I2m1nJpxwolK6Ba/t22GmwAF/t69Hse/lOxUqR6MY4o=; b=j+NR29/ux8yOkc6iH/+tknb/W f+BW7V0QOoy8oXCSPm6DimqxSHFuFRgC8YpdOtcuHsD3drlkQdMZu94K+9ctY9EDVcW7XV7L6b8SN EHqY5AqoPeb/ctjZr8ntO95pTBR7Z2KsGkHKmTIS/yFjNZ9gkAQfJC0RNIMwiuw7uAESpfFQvmN2V QFwq9BftK46rTHWarkVpLi1pKQ0yPmY3l8sOBIdduHiHz7doBtFO55L7yg3jklsNyCwa648obMC2Y pkoJWO4tCRFsyEvzx/cFS4eMC3Pb9pOBe0pxRtHsRlcwKfgh0IG5yl002V/qSYLqKRS20JPfbCgMo frVkP61SQ==; Received: from j217100.upc-j.chello.nl ([24.132.217.100] helo=hirez.programming.kicks-ass.net) by bombadil.infradead.org with esmtpsa (Exim 4.90_1 #2 (Red Hat Linux)) id 1fxpsR-0002rE-Cv; Thu, 06 Sep 2018 08:42:59 +0000 Received: by hirez.programming.kicks-ass.net (Postfix, from userid 1000) id F184A202547F9; Thu, 6 Sep 2018 10:42:56 +0200 (CEST) Date: Thu, 6 Sep 2018 10:42:56 +0200 From: Peter Zijlstra To: Nadav Amit Cc: Thomas Gleixner , LKML , Ingo Molnar , X86 ML , Arnd Bergmann , linux-arch , Dave Hansen , Jiri Kosina , Andy Lutomirski , Masami Hiramatsu , Kees Cook Subject: Re: [PATCH v2 0/6] x86/alternatives: text_poke() fixes Message-ID: <20180906084256.GE24142@hirez.programming.kicks-ass.net> References: <20180902173224.30606-1-namit@vmware.com> <20180905185617.GC24082@hirez.programming.kicks-ass.net> <8D3CE999-6D3A-4984-934A-634BDD8AC25A@vmware.com> <6B256AB7-0158-47DF-B2D5-4C835579F3A3@vmware.com> <20180906081300.GF24082@hirez.programming.kicks-ass.net> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20180906081300.GF24082@hirez.programming.kicks-ass.net> User-Agent: Mutt/1.10.0 (2018-05-17) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, Sep 06, 2018 at 10:13:00AM +0200, Peter Zijlstra wrote: > No, you got it the first time. There are in fact more fixmap abusers; > see drivers/acpi/apei/ghes.c. Also, as long as set_fixmap() allows > overwriting a _PAGE_PRESENT pte and has that dodgy > __flush_tlb_one_kernel() in it, the broken remains (and can return). > > So we need to fix fixmap, to either disallow overwriting a _PAGE_PRESENT > pte, or to issue a full TLB invalidate. > > Either fix will terminally break GHES, but that's OK, they've known > about this issue since 2015 and haven't cared, so I can't be bothered > about them. Worse, when I boot with the below patch in, I get hits on text_poke (we knew about this), but I also get hits from: release_ds_buffer() Because PEBS/BTS hardware write through the page-tables (I know right), their buffers need to be in the PTI user map, and we do that by mapping the pages in the CAE, and that uses fixmap. --- diff --git a/arch/x86/mm/init_64.c b/arch/x86/mm/init_64.c index dd519f372169..20dcd6fa690e 100644 --- a/arch/x86/mm/init_64.c +++ b/arch/x86/mm/init_64.c @@ -259,9 +259,16 @@ static pte_t *fill_pte(pmd_t *pmd, unsigned long vaddr) static void __set_pte_vaddr(pud_t *pud, unsigned long vaddr, pte_t new_pte) { pmd_t *pmd = fill_pmd(pud, vaddr); - pte_t *pte = fill_pte(pmd, vaddr); + pte_t *ptep = fill_pte(pmd, vaddr); - set_pte(pte, new_pte); + pte_t pte = *ptep; + + set_pte(ptep, new_pte); + + WARN((pte_val(pte) & _PAGE_PRESENT) && (pte_val(pte) != pte_val(new_pte)), + "set_fixmap(%d, %lx), was: %lx", + (int)__virt_to_fix(vaddr), + pte_val(new_pte), pte_val(pte)); /* * It's enough to flush this one mapping.