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Received-SPF: Pass (protection.outlook.com: domain of amd.com designates 165.204.84.17 as permitted sender) receiver=protection.outlook.com; client-ip=165.204.84.17; helo=SATLEXMB04.amd.com; pr=C Received: from SATLEXMB04.amd.com (165.204.84.17) by MN1PEPF0000ECD4.mail.protection.outlook.com (10.167.242.132) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256) id 15.20.7159.9 via Frontend Transport; Sat, 30 Dec 2023 17:24:46 +0000 Received: from localhost (10.180.168.240) by SATLEXMB04.amd.com (10.181.40.145) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256) id 15.1.2507.34; Sat, 30 Dec 2023 11:24:41 -0600 From: Michael Roth To: CC: , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , Alexey Kardashevskiy Subject: [PATCH v11 10/35] KVM: SEV: Do not intercept accesses to MSR_IA32_XSS for SEV-ES guests Date: Sat, 30 Dec 2023 11:23:26 -0600 Message-ID: <20231230172351.574091-11-michael.roth@amd.com> X-Mailer: git-send-email 2.25.1 In-Reply-To: <20231230172351.574091-1-michael.roth@amd.com> References: <20231230172351.574091-1-michael.roth@amd.com> Precedence: bulk X-Mailing-List: linux-crypto@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 X-ClientProxiedBy: SATLEXMB03.amd.com (10.181.40.144) To SATLEXMB04.amd.com (10.181.40.145) X-EOPAttributedMessage: 0 X-MS-PublicTrafficType: Email X-MS-TrafficTypeDiagnostic: MN1PEPF0000ECD4:EE_|IA0PR12MB7531:EE_ X-MS-Office365-Filtering-Correlation-Id: 4a11e442-b6d0-4604-85f0-08dc095c3818 X-MS-Exchange-SenderADCheck: 1 X-MS-Exchange-AntiSpam-Relay: 0 X-Microsoft-Antispam: BCL:0; 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DIR:OUT; SFP:1101; X-OriginatorOrg: amd.com X-MS-Exchange-CrossTenant-OriginalArrivalTime: 30 Dec 2023 17:24:46.1915 (UTC) X-MS-Exchange-CrossTenant-Network-Message-Id: 4a11e442-b6d0-4604-85f0-08dc095c3818 X-MS-Exchange-CrossTenant-Id: 3dd8961f-e488-4e60-8e11-a82d994e183d X-MS-Exchange-CrossTenant-OriginalAttributedTenantConnectingIp: TenantId=3dd8961f-e488-4e60-8e11-a82d994e183d; Ip=[165.204.84.17]; Helo=[SATLEXMB04.amd.com] X-MS-Exchange-CrossTenant-AuthSource: MN1PEPF0000ECD4.namprd02.prod.outlook.com X-MS-Exchange-CrossTenant-AuthAs: Anonymous X-MS-Exchange-CrossTenant-FromEntityHeader: HybridOnPrem X-MS-Exchange-Transport-CrossTenantHeadersStamped: IA0PR12MB7531 When intercepts are enabled for MSR_IA32_XSS, the host will swap in/out the guest-defined values while context-switching to/from guest mode. However, in the case of SEV-ES, vcpu->arch.guest_state_protected is set, so the guest-defined value is effectively ignored when switching to guest mode with the understanding that the VMSA will handle swapping in/out this register state. However, SVM is still configured to intercept these accesses for SEV-ES guests, so the values in the initial MSR_IA32_XSS are effectively read-only, and a guest will experience undefined behavior if it actually tries to write to this MSR. Fortunately, only CET/shadowstack makes use of this register on SEV-ES-capable systems currently, which isn't yet widely used, but this may become more of an issue in the future. Additionally, enabling intercepts of MSR_IA32_XSS results in #VC exceptions in the guest in certain paths that can lead to unexpected #VC nesting levels. One example is SEV-SNP guests when handling #VC exceptions for CPUID instructions involving leaf 0xD, subleaf 0x1, since they will access MSR_IA32_XSS as part of servicing the CPUID #VC, then generate another #VC when accessing MSR_IA32_XSS, which can lead to guest crashes if an NMI occurs at that point in time. Running perf on a guest while it is issuing such a sequence is one example where these can be problematic. Address this by disabling intercepts of MSR_IA32_XSS for SEV-ES guests if the host/guest configuration allows it. If the host/guest configuration doesn't allow for MSR_IA32_XSS, leave it intercepted so that it can be caught by the existing checks in kvm_{set,get}_msr_common() if the guest still attempts to access it. Fixes: 376c6d285017 ("KVM: SVM: Provide support for SEV-ES vCPU creation/loading") Cc: Alexey Kardashevskiy Suggested-by: Tom Lendacky Signed-off-by: Michael Roth --- arch/x86/kvm/svm/sev.c | 19 +++++++++++++++++++ arch/x86/kvm/svm/svm.c | 1 + arch/x86/kvm/svm/svm.h | 2 +- 3 files changed, 21 insertions(+), 1 deletion(-) diff --git a/arch/x86/kvm/svm/sev.c b/arch/x86/kvm/svm/sev.c index 2efe3ed89808..f99435b6648f 100644 --- a/arch/x86/kvm/svm/sev.c +++ b/arch/x86/kvm/svm/sev.c @@ -2978,6 +2978,25 @@ static void sev_es_vcpu_after_set_cpuid(struct vcpu_svm *svm) set_msr_interception(vcpu, svm->msrpm, MSR_TSC_AUX, v_tsc_aux, v_tsc_aux); } + + /* + * For SEV-ES, accesses to MSR_IA32_XSS should not be intercepted if + * the host/guest supports its use. + * + * guest_can_use() checks a number of requirements on the host/guest to + * ensure that MSR_IA32_XSS is available, but it might report true even + * if X86_FEATURE_XSAVES isn't configured in the guest to ensure host + * MSR_IA32_XSS is always properly restored. For SEV-ES, it is better + * to further check that the guest CPUID actually supports + * X86_FEATURE_XSAVES so that accesses to MSR_IA32_XSS by misbehaved + * guests will still get intercepted and caught in the normal + * kvm_emulate_rdmsr()/kvm_emulated_wrmsr() paths. + */ + if (guest_can_use(vcpu, X86_FEATURE_XSAVES) && + guest_cpuid_has(vcpu, X86_FEATURE_XSAVES)) + set_msr_interception(vcpu, svm->msrpm, MSR_IA32_XSS, 1, 1); + else + set_msr_interception(vcpu, svm->msrpm, MSR_IA32_XSS, 0, 0); } void sev_vcpu_after_set_cpuid(struct vcpu_svm *svm) diff --git a/arch/x86/kvm/svm/svm.c b/arch/x86/kvm/svm/svm.c index b6179696861a..18d55df7fa5f 100644 --- a/arch/x86/kvm/svm/svm.c +++ b/arch/x86/kvm/svm/svm.c @@ -103,6 +103,7 @@ static const struct svm_direct_access_msrs { { .index = MSR_IA32_LASTBRANCHTOIP, .always = false }, { .index = MSR_IA32_LASTINTFROMIP, .always = false }, { .index = MSR_IA32_LASTINTTOIP, .always = false }, + { .index = MSR_IA32_XSS, .always = false }, { .index = MSR_EFER, .always = false }, { .index = MSR_IA32_CR_PAT, .always = false }, { .index = MSR_AMD64_SEV_ES_GHCB, .always = true }, diff --git a/arch/x86/kvm/svm/svm.h b/arch/x86/kvm/svm/svm.h index 9ed9d72546b3..7f1fbd874c45 100644 --- a/arch/x86/kvm/svm/svm.h +++ b/arch/x86/kvm/svm/svm.h @@ -30,7 +30,7 @@ #define IOPM_SIZE PAGE_SIZE * 3 #define MSRPM_SIZE PAGE_SIZE * 2 -#define MAX_DIRECT_ACCESS_MSRS 46 +#define MAX_DIRECT_ACCESS_MSRS 47 #define MSRPM_OFFSETS 32 extern u32 msrpm_offsets[MSRPM_OFFSETS] __read_mostly; extern bool npt_enabled;