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=-12.8 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH, MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED, USER_AGENT_GIT 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 A04E3C433DF for ; Fri, 9 Oct 2020 14:42:33 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 4E9AD2087D for ; Fri, 9 Oct 2020 14:42:33 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (1024-bit key) header.d=suse.com header.i=@suse.com header.b="hWIW3Uxj" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2388973AbgJIOmc (ORCPT ); Fri, 9 Oct 2020 10:42:32 -0400 Received: from mx2.suse.de ([195.135.220.15]:46028 "EHLO mx2.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S2387662AbgJIOmb (ORCPT ); Fri, 9 Oct 2020 10:42:31 -0400 X-Virus-Scanned: by amavisd-new at test-mx.suse.de DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=suse.com; s=susede1; t=1602254550; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version: content-transfer-encoding:content-transfer-encoding; bh=Mf9G95BFIif8P4JOo8vFEGHaFCuDzB5d2ITiJa6fvhQ=; b=hWIW3UxjjlHedkBjscX2/oMZBiqp8cMgbM5bV0NCuQYPfsNOtHucN61nhTHeTWM/sa/i8N bFbDMkKpRE+iGrAeCuYdUClZo3vcbJlPsqnB+JDYS54Jzgb0ekl4iudUBLU/kUI503bLol WkWWXUua7KDrPPiTrIomxXNLksFUXZo= Received: from relay2.suse.de (unknown [195.135.221.27]) by mx2.suse.de (Postfix) with ESMTP id E8F0CAE2C; Fri, 9 Oct 2020 14:42:29 +0000 (UTC) From: Juergen Gross To: xen-devel@lists.xenproject.org, x86@kernel.org, linux-kernel@vger.kernel.org Cc: Juergen Gross , Thomas Gleixner , Ingo Molnar , Borislav Petkov , "H. Peter Anvin" , Andy Lutomirski Subject: [PATCH] x86/alternative: don't call text_poke() in lazy TLB mode Date: Fri, 9 Oct 2020 16:42:25 +0200 Message-Id: <20201009144225.12019-1-jgross@suse.com> X-Mailer: git-send-email 2.26.2 MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org When running in lazy TLB mode the currently active page tables might be the ones of a previous process, e.g. when running a kernel thread. This can be problematic in case kernel code is being modified via text_poke() in a kernel thread, and on another processor exit_mmap() is active for the process which was running on the first cpu before the kernel thread. As text_poke() is using a temporary address space and the former address space (obtained via cpu_tlbstate.loaded_mm) is restored afterwards, there is a race possible in case the cpu on which exit_mmap() is running wants to make sure there are no stale references to that address space on any cpu active (this e.g. is required when running as a Xen PV guest, where this problem has been observed and analyzed). In order to avoid that, drop off TLB lazy mode before switching to the temporary address space. Fixes: cefa929c034eb5d ("x86/mm: Introduce temporary mm structs") Signed-off-by: Juergen Gross --- arch/x86/kernel/alternative.c | 9 +++++++++ 1 file changed, 9 insertions(+) diff --git a/arch/x86/kernel/alternative.c b/arch/x86/kernel/alternative.c index cdaab30880b9..cd6be6f143e8 100644 --- a/arch/x86/kernel/alternative.c +++ b/arch/x86/kernel/alternative.c @@ -807,6 +807,15 @@ static inline temp_mm_state_t use_temporary_mm(struct mm_struct *mm) temp_mm_state_t temp_state; lockdep_assert_irqs_disabled(); + + /* + * Make sure not to be in TLB lazy mode, as otherwise we'll end up + * with a stale address space WITHOUT being in lazy mode after + * restoring the previous mm. + */ + if (this_cpu_read(cpu_tlbstate.is_lazy)) + leave_mm(smp_processor_id()); + temp_state.mm = this_cpu_read(cpu_tlbstate.loaded_mm); switch_mm_irqs_off(NULL, mm, current); -- 2.26.2