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=-3.5 required=3.0 tests=DKIM_INVALID,DKIM_SIGNED, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_HELO_NONE, SPF_PASS,URIBL_BLOCKED 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 B8D02C433E1 for ; Fri, 29 May 2020 21:35:16 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 93C8920810 for ; Fri, 29 May 2020 21:35:16 +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="hhUfMFOJ" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728441AbgE2VfM (ORCPT ); Fri, 29 May 2020 17:35:12 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:50536 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1728270AbgE2Ve5 (ORCPT ); Fri, 29 May 2020 17:34:57 -0400 Received: from bombadil.infradead.org (bombadil.infradead.org [IPv6:2607:7c80:54:e::133]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 70E65C08C5D1 for ; Fri, 29 May 2020 14:34:57 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=infradead.org; s=bombadil.20170209; h=Content-Type:MIME-Version:References: Subject:Cc:To:From:Date:Message-ID:Sender:Reply-To:Content-Transfer-Encoding: Content-ID:Content-Description:In-Reply-To; bh=jkfi8De0rOCnIZq+jSVpuHzRxY6NvNqU+eyz6LHLrYQ=; b=hhUfMFOJhzIFo8hVId0+9nc22u CsBbl4d5CuKKRws0AoyFXg1k5zbiZAph9zWm+qukDiQNJCuH8RIFJCiLkIvSZ4nzEt7VCg/Dd1PXc Jm+CBu3luBoOMHfPL/YbwO1Ql5ZUH+u/Ko9TqzxJ97/jeM8N2C4dmGKvsApbhy+4Zn8pKsYSKr/bw LGbTuvD9qcsGsDbwcpXPdGM8OeSIe4btWAqJmMicEW1ORN5CrxNtcrfetcGYO64ApxSpZzPBSYt5i p9hZlxAchgJLakt/0LHUMd2IRhzAQ3iO5YdytpK2koO6L9As76F5+XP+R8IZmp9v899ExEwoS5/pQ yK14ruQw==; Received: from j217100.upc-j.chello.nl ([24.132.217.100] helo=noisy.programming.kicks-ass.net) by bombadil.infradead.org with esmtpsa (Exim 4.92.3 #3 (Red Hat Linux)) id 1jemeJ-0000Kk-Jg; Fri, 29 May 2020 21:34:43 +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 EF8F4306A9D; Fri, 29 May 2020 23:34:41 +0200 (CEST) Received: by hirez.programming.kicks-ass.net (Postfix, from userid 0) id 2CAC120FF0A0D; Fri, 29 May 2020 23:34:41 +0200 (CEST) Message-ID: <20200529213321.069223695@infradead.org> User-Agent: quilt/0.66 Date: Fri, 29 May 2020 23:27:34 +0200 From: Peter Zijlstra To: tglx@linutronix.de, luto@amacapital.net, peterz@infradead.org Cc: linux-kernel@vger.kernel.org, x86@kernel.org, Lai Jiangshan , sean.j.christopherson@intel.com, andrew.cooper3@citrix.com, daniel.thompson@linaro.org, a.darwish@linutronix.de, rostedt@goodmis.org, bigeasy@linutronix.de Subject: [PATCH 06/14] x86/entry, nmi: Disable #DB References: <20200529212728.795169701@infradead.org> MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Instead of playing stupid games with IST stacks, fully disallow #DB during NMIs. There is absolutely no reason to allow them, and killing this saves a heap of trouble. We already disallow #DB on noinstr and CEA, so we can't get #DB before this, and this ensures we can't get it after this either. Signed-off-by: Peter Zijlstra (Intel) --- arch/x86/kernel/nmi.c | 55 ++------------------------------------------------ 1 file changed, 3 insertions(+), 52 deletions(-) --- a/arch/x86/kernel/nmi.c +++ b/arch/x86/kernel/nmi.c @@ -474,40 +474,7 @@ enum nmi_states { }; static DEFINE_PER_CPU(enum nmi_states, nmi_state); static DEFINE_PER_CPU(unsigned long, nmi_cr2); - -#ifdef CONFIG_X86_64 -/* - * In x86_64, we need to handle breakpoint -> NMI -> breakpoint. Without - * some care, the inner breakpoint will clobber the outer breakpoint's - * stack. - * - * If a breakpoint is being processed, and the debug stack is being - * used, if an NMI comes in and also hits a breakpoint, the stack - * pointer will be set to the same fixed address as the breakpoint that - * was interrupted, causing that stack to be corrupted. To handle this - * case, check if the stack that was interrupted is the debug stack, and - * if so, change the IDT so that new breakpoints will use the current - * stack and not switch to the fixed address. On return of the NMI, - * switch back to the original IDT. - */ -static DEFINE_PER_CPU(int, update_debug_stack); - -static noinstr bool is_debug_stack(unsigned long addr) -{ - struct cea_exception_stacks *cs = __this_cpu_read(cea_exception_stacks); - unsigned long top = CEA_ESTACK_TOP(cs, DB); - unsigned long bot = CEA_ESTACK_BOT(cs, DB1); - - if (__this_cpu_read(debug_stack_usage)) - return true; - /* - * Note, this covers the guard page between DB and DB1 as well to - * avoid two checks. But by all means @addr can never point into - * the guard page. - */ - return addr >= bot && addr < top; -} -#endif +static DEFINE_PER_CPU(unsigned long, nmi_dr7); DEFINE_IDTENTRY_NMI(exc_nmi) { @@ -522,18 +489,7 @@ DEFINE_IDTENTRY_NMI(exc_nmi) this_cpu_write(nmi_cr2, read_cr2()); nmi_restart: -#ifdef CONFIG_X86_64 - /* - * If we interrupted a breakpoint, it is possible that - * the nmi handler will have breakpoints too. We need to - * change the IDT such that breakpoints that happen here - * continue to use the NMI stack. - */ - if (unlikely(is_debug_stack(regs->sp))) { - debug_stack_set_zero(); - this_cpu_write(update_debug_stack, 1); - } -#endif + this_cpu_write(nmi_dr7, local_db_save()); nmi_enter(); @@ -544,12 +500,7 @@ DEFINE_IDTENTRY_NMI(exc_nmi) nmi_exit(); -#ifdef CONFIG_X86_64 - if (unlikely(this_cpu_read(update_debug_stack))) { - debug_stack_reset(); - this_cpu_write(update_debug_stack, 0); - } -#endif + local_db_restore(this_cpu_read(nmi_dr7)); if (unlikely(this_cpu_read(nmi_cr2) != read_cr2())) write_cr2(this_cpu_read(nmi_cr2));