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 B8ABDEB64D7 for ; Fri, 23 Jun 2023 21:11:55 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S232193AbjFWVLy (ORCPT ); Fri, 23 Jun 2023 17:11:54 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:48868 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S231129AbjFWVLx (ORCPT ); Fri, 23 Jun 2023 17:11:53 -0400 Received: from mail-yw1-x1149.google.com (mail-yw1-x1149.google.com [IPv6:2607:f8b0:4864:20::1149]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id C7BC31706 for ; Fri, 23 Jun 2023 14:11:48 -0700 (PDT) Received: by mail-yw1-x1149.google.com with SMTP id 00721157ae682-570553a18deso14186587b3.2 for ; Fri, 23 Jun 2023 14:11:48 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=20221208; t=1687554708; x=1690146708; h=cc:to:from:subject:message-id:references:mime-version:in-reply-to :date:from:to:cc:subject:date:message-id:reply-to; bh=rpF0hJJdSCbzsXPIoBpV2pAuOEkgh57lqkiUh3PViIQ=; b=Z2ZG8+JWQ/AJEglu3wNgXco8+XmzhLq2CVJ2un8X+jEC+3HIrxT1tq0nbdYwA8Yrra ndGsZbgjYCE2or+YVhgaK34KNqyP+BZltg/k7bG1CQ7krFyzsAMtsUfExcZONQWH8tM0 mmLPIUk1rGspZgW4B/QCWLv+rbhntlGzHyylQ58aOfoOqPsqEq+bEIDBtBFYqLsEtSBa 3MkjAF3TlyU50oTblmp4WpT3CnLH9UMvqJLErd6Jb/WLqZvdTJB1UrgFCezn1PWExIaV B4BV0ZalGq26K8w4IDfwQ+48wzsItvYJLFdKx2B6szRpKm6c5CynAEU+NTJptX86hOfq ZvlA== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20221208; t=1687554708; x=1690146708; h=cc:to:from:subject:message-id:references:mime-version:in-reply-to :date:x-gm-message-state:from:to:cc:subject:date:message-id:reply-to; bh=rpF0hJJdSCbzsXPIoBpV2pAuOEkgh57lqkiUh3PViIQ=; b=DcPVN4g7+WBq2A99jZhJhE9zoKs8+F82WxQGgH74pL4ci49xierNfiTCul3unO1KBn jl6SIqXKZW81Ty2QCfGNQVToxQOpas1U9fOpyxqFJvu4H7s8pODKRyXHrMDoXYI0P1hW yPMhZTJPTPqkcFwtSsg6INCHnN0oL6yPe4+Cq/Glwk8EOBa6AmBpaHOIF7blYLy+mT0o aX/FpBZq67SXA1hY5simfYoaxkg/iIu+wAW7U+LoyvWinnePlPB0oLXvYbPDU0w472Iu y2qFf4CdslY7CyJza9kKhhRDefv8qGGSeMR9w61jHj42+FmbjzJbRz823ftRuGlU1Viz kobg== X-Gm-Message-State: AC+VfDyJ+9kCmleF8S01+YRvX9frRIUp0ipYciaYmN2TJXn9+uU+j2RM cC5MrjcdidzSXde3fpoh1DaSzqMOMMo= X-Google-Smtp-Source: ACHHUZ5jEXzf8lMdetFcA8JZhGt4cfiznO7FQIC6B5UL1to8romdSXGDf1QhqaDKP3d0XURqDXrADMLBEqA= X-Received: from zagreus.c.googlers.com ([fda3:e722:ac3:cc00:7f:e700:c0a8:5c37]) (user=seanjc job=sendgmr) by 2002:a81:b710:0:b0:565:9f59:664f with SMTP id v16-20020a81b710000000b005659f59664fmr9910110ywh.6.1687554707928; Fri, 23 Jun 2023 14:11:47 -0700 (PDT) Date: Fri, 23 Jun 2023 14:11:46 -0700 In-Reply-To: <20230524155339.415820-5-john.allen@amd.com> Mime-Version: 1.0 References: <20230524155339.415820-1-john.allen@amd.com> <20230524155339.415820-5-john.allen@amd.com> Message-ID: Subject: Re: [RFC PATCH v2 4/6] KVM: SVM: Save shadow stack host state on VMRUN From: Sean Christopherson To: John Allen Cc: kvm@vger.kernel.org, linux-kernel@vger.kernel.org, pbonzini@redhat.com, weijiang.yang@intel.com, rick.p.edgecombe@intel.com, x86@kernel.org, thomas.lendacky@amd.com, bp@alien8.de Content-Type: text/plain; charset="us-ascii" Precedence: bulk List-ID: X-Mailing-List: kvm@vger.kernel.org On Wed, May 24, 2023, John Allen wrote: > When running as an SEV-ES guest, the PL0_SSP, PL1_SSP, PL2_SSP, PL3_SSP, > and U_CET fields in the VMCB save area are type B, meaning the host > state is automatically loaded on a VMEXIT, but is not saved on a VMRUN. > The other shadow stack MSRs, S_CET, SSP, and ISST_ADDR are type A, > meaning they are loaded on VMEXIT and saved on VMRUN. Manually save the > type B host MSR values before VMRUN. > > Signed-off-by: John Allen > --- > arch/x86/kvm/svm/sev.c | 13 +++++++++++++ > 1 file changed, 13 insertions(+) > > diff --git a/arch/x86/kvm/svm/sev.c b/arch/x86/kvm/svm/sev.c > index c25aeb550cd9..03dd68bddd51 100644 > --- a/arch/x86/kvm/svm/sev.c > +++ b/arch/x86/kvm/svm/sev.c > @@ -3028,6 +3028,19 @@ void sev_es_prepare_switch_to_guest(struct sev_es_save_area *hostsa) > > /* MSR_IA32_XSS is restored on VMEXIT, save the currnet host value */ > hostsa->xss = host_xss; > + > + if (boot_cpu_has(X86_FEATURE_SHSTK)) { > + /* > + * MSR_IA32_U_CET, MSR_IA32_PL0_SSP, MSR_IA32_PL1_SSP, > + * MSR_IA32_PL2_SSP, and MSR_IA32_PL3_SSP are restored on > + * VMEXIT, save the current host values. > + */ > + rdmsrl(MSR_IA32_U_CET, hostsa->u_cet); > + rdmsrl(MSR_IA32_PL0_SSP, hostsa->vmpl0_ssp); > + rdmsrl(MSR_IA32_PL1_SSP, hostsa->vmpl1_ssp); > + rdmsrl(MSR_IA32_PL2_SSP, hostsa->vmpl2_ssp); > + rdmsrl(MSR_IA32_PL3_SSP, hostsa->vmpl3_ssp); Heh, can you send a patch to fix the names for the PLx_SSP fields? They should be ->plN_ssp, not ->vmplN_ssp. As for the values themselves, the kernel doesn't support Supervisor Shadow Stacks (SSS), so PL0-2_SSP are guaranteed to be zero. And if/when SSS support is added, I doubt the kernel will ever use PL1_SSP or PL2_SSP, so those can probably be ignored entirely, and PL0_SSP might be constant per task? In other words, I don't see any reason to try and track the host values for support that doesn't exist, just do what VMX does for BNDCFGS and yell if the MSRs are non-zero. Though for SSS it probably makes sense for KVM to refuse to load (KVM continues on for BNDCFGS because it's a pretty safe assumption that the kernel won't regain MPX supported). E.g. in rough pseudocode if (boot_cpu_has(X86_FEATURE_SHSTK)) { rdmsrl(MSR_IA32_PLx_SSP, host_plx_ssp); if (WARN_ON_ONCE(host_pl0_ssp || host_pl1_ssp || host_pl2_ssp)) return -EIO; }