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=-15.7 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_CR_TRAILER, INCLUDES_PATCH,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED autolearn=unavailable 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 E6DD3C433E6 for ; Wed, 17 Feb 2021 18:01:06 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id B007064E5F for ; Wed, 17 Feb 2021 18:01:06 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S234708AbhBQSA4 (ORCPT ); Wed, 17 Feb 2021 13:00:56 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:37416 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S234667AbhBQSAs (ORCPT ); Wed, 17 Feb 2021 13:00:48 -0500 Received: from mail.skyhub.de (mail.skyhub.de [IPv6:2a01:4f8:190:11c2::b:1457]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 943A5C061574; Wed, 17 Feb 2021 10:00:08 -0800 (PST) Received: from zn.tnic (p200300ec2f05bb00a5a1b5cb6f03bfce.dip0.t-ipconnect.de [IPv6:2003:ec:2f05:bb00:a5a1:b5cb:6f03:bfce]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.skyhub.de (SuperMail on ZX Spectrum 128k) with ESMTPSA id 37E1F1EC0531; Wed, 17 Feb 2021 19:00:06 +0100 (CET) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=alien8.de; s=dkim; t=1613584806; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: content-transfer-encoding:in-reply-to:in-reply-to: references:references; bh=W/PjtAFD7kN1k373OiTnMpXJo6wSfCFewIb7shmRoAo=; b=eWIvMjcR2w2Szi9tvlUj/PBm2DwWXFJEV6+2klCghZf1r9mpzHJQsSclQG/T7mwfY0uiQo rMtKbbqzVOerG0czLj1WllEinByD4lSHtLn93sBH0+1z7g/qOd18ASqqXmXgniWL7fCCaj U249HiTnjWRQTmgbdVAvXjFEVHgaw54= Date: Wed, 17 Feb 2021 19:00:09 +0100 From: Borislav Petkov To: Joerg Roedel Cc: x86@kernel.org, Joerg Roedel , Andy Lutomirski , stable@vger.kernel.org, hpa@zytor.com, Dave Hansen , Peter Zijlstra , Jiri Slaby , Dan Williams , Tom Lendacky , Juergen Gross , Kees Cook , David Rientjes , Cfir Cohen , Erdem Aktas , Masami Hiramatsu , Mike Stunes , Sean Christopherson , Martin Radev , Arvind Sankar , linux-kernel@vger.kernel.org, kvm@vger.kernel.org, virtualization@lists.linux-foundation.org Subject: Re: [PATCH 2/3] x86/sev-es: Check if regs->sp is trusted before adjusting #VC IST stack Message-ID: <20210217180009.GB6479@zn.tnic> References: <20210217120143.6106-1-joro@8bytes.org> <20210217120143.6106-3-joro@8bytes.org> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: <20210217120143.6106-3-joro@8bytes.org> Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, Feb 17, 2021 at 01:01:42PM +0100, Joerg Roedel wrote: > From: Joerg Roedel > > The code in the NMI handler to adjust the #VC handler IST stack is > needed in case an NMI hits when the #VC handler is still using its IST > stack. > But the check for this condition also needs to look if the regs->sp > value is trusted, meaning it was not set by user-space. Extend the > check to not use regs->sp when the NMI interrupted user-space code or > the SYSCALL gap. > > Reported-by: Andy Lutomirski > Fixes: 315562c9af3d5 ("x86/sev-es: Adjust #VC IST Stack on entering NMI handler") > Cc: stable@vger.kernel.org # 5.10+ > Signed-off-by: Joerg Roedel > --- > arch/x86/kernel/sev-es.c | 4 +++- > 1 file changed, 3 insertions(+), 1 deletion(-) > > diff --git a/arch/x86/kernel/sev-es.c b/arch/x86/kernel/sev-es.c > index 84c1821819af..0df38b185d53 100644 > --- a/arch/x86/kernel/sev-es.c > +++ b/arch/x86/kernel/sev-es.c > @@ -144,7 +144,9 @@ void noinstr __sev_es_ist_enter(struct pt_regs *regs) > old_ist = __this_cpu_read(cpu_tss_rw.x86_tss.ist[IST_INDEX_VC]); > > /* Make room on the IST stack */ > - if (on_vc_stack(regs->sp)) > + if (on_vc_stack(regs->sp) && > + !user_mode(regs) && > + !from_syscall_gap(regs)) Why not add those checks to on_vc_stack() directly? Because in it, you can say: on_vc_stack(): /* user mode rSP is not trusted */ if (user_mode()) return false; /* ditto */ if (ip_within_syscall_gap()) return false; ... ? -- Regards/Gruss, Boris. https://people.kernel.org/tglx/notes-about-netiquette