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 Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 69FE5C636CC for ; Tue, 7 Feb 2023 13:14:18 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S232601AbjBGNOR (ORCPT ); Tue, 7 Feb 2023 08:14:17 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:59992 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S232545AbjBGNOA (ORCPT ); Tue, 7 Feb 2023 08:14:00 -0500 Received: from sin.source.kernel.org (sin.source.kernel.org [IPv6:2604:1380:40e1:4800::1]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 7A51C27D6B for ; Tue, 7 Feb 2023 05:13:36 -0800 (PST) Received: from smtp.kernel.org (relay.kernel.org [52.25.139.140]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by sin.source.kernel.org (Postfix) with ESMTPS id 0A343CE1DB1 for ; Tue, 7 Feb 2023 13:13:19 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 27A54C433EF; Tue, 7 Feb 2023 13:13:15 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linuxfoundation.org; s=korg; t=1675775596; bh=+4MgNm7jobg0Th/28M5WXMhfu5tTKoujsHCRE8soPbk=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=GzKgPP3tFAwIqoS4rSv2LJrgETu/dDYA2WiWJZk9V9uIYVETiviTBl/62fNXmxHgi lIConoCKT9P+m1pPdlLdroKar5zq2fyRrV+xCOV81TfGMMXTyXYieAmLqDpHiB5Vb2 jlotG0mmEWKbpWCeSRV4qPtVIWt6efdWqe21n5vw= From: Greg Kroah-Hartman To: stable@vger.kernel.org Cc: Greg Kroah-Hartman , patches@lists.linux.dev, Alexey Kardashevskiy , Joerg Roedel , "Borislav Petkov (AMD)" Subject: [PATCH 5.15 093/120] x86/debug: Fix stack recursion caused by wrongly ordered DR7 accesses Date: Tue, 7 Feb 2023 13:57:44 +0100 Message-Id: <20230207125622.729221154@linuxfoundation.org> X-Mailer: git-send-email 2.39.1 In-Reply-To: <20230207125618.699726054@linuxfoundation.org> References: <20230207125618.699726054@linuxfoundation.org> User-Agent: quilt/0.67 MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: X-Mailing-List: stable@vger.kernel.org From: Joerg Roedel commit 9d2c7203ffdb846399b82b0660563c89e918c751 upstream. In kernels compiled with CONFIG_PARAVIRT=n, the compiler re-orders the DR7 read in exc_nmi() to happen before the call to sev_es_ist_enter(). This is problematic when running as an SEV-ES guest because in this environment the DR7 read might cause a #VC exception, and taking #VC exceptions is not safe in exc_nmi() before sev_es_ist_enter() has run. The result is stack recursion if the NMI was caused on the #VC IST stack, because a subsequent #VC exception in the NMI handler will overwrite the stack frame of the interrupted #VC handler. As there are no compiler barriers affecting the ordering of DR7 reads/writes, make the accesses to this register volatile, forbidding the compiler to re-order them. [ bp: Massage text, make them volatile too, to make sure some aggressive compiler optimization pass doesn't discard them. ] Fixes: 315562c9af3d ("x86/sev-es: Adjust #VC IST Stack on entering NMI handler") Reported-by: Alexey Kardashevskiy Signed-off-by: Joerg Roedel Signed-off-by: Borislav Petkov (AMD) Cc: stable@vger.kernel.org Link: https://lore.kernel.org/r/20230127035616.508966-1-aik@amd.com Signed-off-by: Greg Kroah-Hartman --- arch/x86/include/asm/debugreg.h | 26 ++++++++++++++++++++++++-- 1 file changed, 24 insertions(+), 2 deletions(-) --- a/arch/x86/include/asm/debugreg.h +++ b/arch/x86/include/asm/debugreg.h @@ -39,7 +39,20 @@ static __always_inline unsigned long nat asm("mov %%db6, %0" :"=r" (val)); break; case 7: - asm("mov %%db7, %0" :"=r" (val)); + /* + * Apply __FORCE_ORDER to DR7 reads to forbid re-ordering them + * with other code. + * + * This is needed because a DR7 access can cause a #VC exception + * when running under SEV-ES. Taking a #VC exception is not a + * safe thing to do just anywhere in the entry code and + * re-ordering might place the access into an unsafe location. + * + * This happened in the NMI handler, where the DR7 read was + * re-ordered to happen before the call to sev_es_ist_enter(), + * causing stack recursion. + */ + asm volatile("mov %%db7, %0" : "=r" (val) : __FORCE_ORDER); break; default: BUG(); @@ -66,7 +79,16 @@ static __always_inline void native_set_d asm("mov %0, %%db6" ::"r" (value)); break; case 7: - asm("mov %0, %%db7" ::"r" (value)); + /* + * Apply __FORCE_ORDER to DR7 writes to forbid re-ordering them + * with other code. + * + * While is didn't happen with a DR7 write (see the DR7 read + * comment above which explains where it happened), add the + * __FORCE_ORDER here too to avoid similar problems in the + * future. + */ + asm volatile("mov %0, %%db7" ::"r" (value), __FORCE_ORDER); break; default: BUG();