Received-SPF: pass (google.com: domain of linux-kernel+bounces-39566-linux.lists.archive=gmail.com@vger.kernel.org designates 2604:1380:4601:e00::3 as permitted sender) client-ip=2604:1380:4601:e00::3;
Date: Fri, 26 Jan 2024 11:17:24 +0800
From: Chao Gao <chao.gao@intel.com>
To: Yang Weijiang <weijiang.yang@intel.com>
CC: <seanjc@google.com>, <pbonzini@redhat.com>, <dave.hansen@intel.com>,
	<kvm@vger.kernel.org>, <linux-kernel@vger.kernel.org>, <x86@kernel.org>,
	<yuan.yao@linux.intel.com>, <peterz@infradead.org>,
	<rick.p.edgecombe@intel.com>, <mlevitsk@redhat.com>, <john.allen@amd.com>
Subject: Re: [PATCH v9 21/27] KVM: x86: Save and reload SSP to/from SMRAM
Message-ID: <ZbMkRKyhy3jdiuzx@chao-email>
References: <20240124024200.102792-1-weijiang.yang@intel.com>
 <20240124024200.102792-22-weijiang.yang@intel.com>
Content-Type: text/plain; charset="us-ascii"
Content-Disposition: inline
In-Reply-To: <20240124024200.102792-22-weijiang.yang@intel.com>
Precedence: bulk
MIME-Version: 1.0
X-MS-Exchange-AntiSpam-MessageData-ChunkCount: 1
X-MS-Exchange-AntiSpam-MessageData-0: =?us-ascii?Q?pjB8YFvyGaLMiVir5NaA9AQrom7fJXVkWZkvJ12mFgiLRDK79OXAMWtVAoQd?=
 =?us-ascii?Q?UVOLjl2pXjdCYqDBgz0AidGasQB89kRezTPzWpcW0vI7KALmlGykDY/XMOC3?=
 =?us-ascii?Q?OUjkHKNcdhi5RBHfkUXY8NV9g1o2fBSwK76SqsM2DE1hGSKIcuLpcWz4zm/A?=
 =?us-ascii?Q?O7TjrAWvaRSWele+NXaQ4ZpIePFJoWbWSPaDj/f5ekj8OcxJQGSQrbZ1f2BM?=
 =?us-ascii?Q?1E+YKteY9moCnNb/66/PB8zoWdgnqcOWddPNQqX1E6EpAHaQ+YVEwqAF4UMj?=
 =?us-ascii?Q?Lpmhy+jl+O76c5tEYJCHFyKitK5UKHAxSNHEDZQ+NAToZeGjSOAw8p7vDJyv?=
 =?us-ascii?Q?H+gZc1+aZB8F73Qk1HNi2hhw+sZbgOGE3EWg70OHoU7yNpHFiM2hDpxcHIuH?=
 =?us-ascii?Q?EqHJHBXPDJgLRaBEJYTG7gWMhVlsYjRYADAxcgVpHdxT2wBCqBzoub/YKk5D?=
 =?us-ascii?Q?H/SFQSjTFlBoJd/O+KGNzuqXWTlSXBUy+xD+8iS787FR6VuZIe+/arqfinTR?=
 =?us-ascii?Q?NCRCpY3zS0AP3IkkylYnuMBuM3HrqL40B71tx5ocFGzcpa2lxAEoaLmrD94L?=
 =?us-ascii?Q?fXm4bpIeIwv/5ED5A6owYdGqFdh7CqdD9kjQdeLiKRxTkOCnG4qdtBzmh4Na?=
 =?us-ascii?Q?AqF+KT3Iz10G8XjKsF+FDtneNLgLiJD+XcKatuegLTrXuncQ2qMcxsERLexx?=
 =?us-ascii?Q?0FS30AxaNVW5Y9xYApdBrWbpiOCnnYqNkygWXiLfLQDDOJh4a2tCT07cXHxk?=
 =?us-ascii?Q?+Eyojar3qyPTLxgkKBnG9yZfk8XxGtHXAeWGje0AC/pWYptQjd/yfDIMNo9+?=
 =?us-ascii?Q?ekbw+WrghyqQ6ONC+wNj7QimO4VeosCAshPS2XpRKvw+m+2QB2Z7ccy2njqE?=
 =?us-ascii?Q?MxVq38ioOoV4buNF/AUi0Zcb745pqNCJVADkzHGgSCPTIHgapSMQ1W2A+oTt?=
 =?us-ascii?Q?77yzdAtsyjLy7xTBncdSgCvmNCiWImQqG45WgZZEm1ufCvUYP87YL9PTXWps?=
 =?us-ascii?Q?qNwZKGPOzQxMSVaTIqTs1lLI1yNuCf76KqvpK+yurZSB2ydstHzFvOee6WU1?=
 =?us-ascii?Q?zqZaV0bzrUBpSGGoiwstrSR678TXMHbqQTBn+9LNGEcs7svTtlwa5AEeipwI?=
 =?us-ascii?Q?WMdcnzWAJEBcamUFy16xGCNgcx86IDbSWDNfSy8rgfzFpU8ARv8JCOm/Yyxv?=
 =?us-ascii?Q?h6PXgLEu65+EleVqAEUg0XndRApD9fJ+rnqARPk01B6lzKz0o7gBHu6HI3Tg?=
 =?us-ascii?Q?L8zEbIci2t0qKjiWi89Nq8Qh86ycaPQARvlR45moHSvznAU9fY/FqXXmbWOj?=
 =?us-ascii?Q?SvXnTFiOzLiMdPxEGcbeopVuZ8YrInE00o1g02Rm/CK1aNjFmdkHy+zcvp3q?=
 =?us-ascii?Q?XhzVcHBUyzt4dQp5P9dJeSFrb1evC5ObYMIyKSSepfWZXeFVlPN+mb4kiL9K?=
 =?us-ascii?Q?dD43ja/Ak6Nl8NGNczfX+A5yYHm4GDa1yQkV01zqlZjxVy93CWeg3XHI3acf?=
 =?us-ascii?Q?aCrGI1tsJKWIKdbMltIxigyVG51OqnO1J9M7c/sdxaAg8mpnE3m77NZXTVSp?=
 =?us-ascii?Q?Y9V/AVrK5Cl1tErgT0Z1Ywv4wPXYi4cCMjtXfW0X?=
X-MS-Exchange-CrossTenant-Network-Message-Id: 2f799347-dcf1-4391-c576-08dc1e1d570d
X-MS-Exchange-CrossTenant-AuthSource: DS0PR11MB8665.namprd11.prod.outlook.com
X-MS-Exchange-CrossTenant-AuthAs: Internal
X-MS-Exchange-CrossTenant-OriginalArrivalTime: 26 Jan 2024 03:17:35.0063
 (UTC)
X-MS-Exchange-CrossTenant-FromEntityHeader: Hosted
X-MS-Exchange-CrossTenant-Id: 46c98d88-e344-4ed4-8496-4ed7712e255d
X-MS-Exchange-CrossTenant-MailboxType: HOSTED
X-MS-Exchange-CrossTenant-UserPrincipalName: f7cd0r453XN5JZaSSNvO+9vCm+3ONl34+LJSwh+4k/mox+HArgiFpxIqPJfh5JuWO39eHvRnbY302yno4cBzxQ==
X-MS-Exchange-Transport-CrossTenantHeadersStamped: PH8PR11MB6879
X-OriginatorOrg: intel.com

On Tue, Jan 23, 2024 at 06:41:54PM -0800, Yang Weijiang wrote:
>Save CET SSP to SMRAM on SMI and reload it on RSM. KVM emulates HW arch
>behavior when guest enters/leaves SMM mode,i.e., save registers to SMRAM
>at the entry of SMM and reload them at the exit to SMM. Per SDM, SSP is
>one of such registers on 64-bit Arch, and add the support for SSP. Note,
>on 32-bit Arch, SSP is not defined in SMRAM, so fail 32-bit CET guest
>launch.
>
>Suggested-by: Sean Christopherson <seanjc@google.com>
>Suggested-by: Chao Gao <chao.gao@intel.com>
>Signed-off-by: Yang Weijiang <weijiang.yang@intel.com>
>Reviewed-by: Maxim Levitsky <mlevitsk@redhat.com>
>---
> arch/x86/kvm/cpuid.c | 11 +++++++++++
> arch/x86/kvm/smm.c   |  8 ++++++++
> arch/x86/kvm/smm.h   |  2 +-
> 3 files changed, 20 insertions(+), 1 deletion(-)
>
>diff --git a/arch/x86/kvm/cpuid.c b/arch/x86/kvm/cpuid.c
>index 3ab133530573..95233b0879a3 100644
>--- a/arch/x86/kvm/cpuid.c
>+++ b/arch/x86/kvm/cpuid.c
>@@ -149,6 +149,17 @@ static int kvm_check_cpuid(struct kvm_vcpu *vcpu,
> 		if (vaddr_bits != 48 && vaddr_bits != 57 && vaddr_bits != 0)
> 			return -EINVAL;
> 	}
>+	/*
>+	 * Prevent 32-bit guest launch if shadow stack is exposed as SSP
>+	 * state is not defined for 32-bit SMRAM.
>+	 */
>+	best = cpuid_entry2_find(entries, nent, 0x80000001,
>+				 KVM_CPUID_INDEX_NOT_SIGNIFICANT);
>+	if (best && !(best->edx & F(LM))) {
>+		best = cpuid_entry2_find(entries, nent, 0x7, 0);
>+		if (best && (best->ecx & F(SHSTK)))

F(LM) and F(SHSTK) are kernel-defined feature bits; they are not
bit masks defined by the CPU. You can use cpuid_entry_has() instead.

Shouldn't we do this only if SMM is supported, i.e., when

static_call(kvm_x86_has_emulated_msr)(kvm, MSR_IA32_SMBASE) is true.

>+			return -EINVAL;
>+	}

> 
> 	/*
> 	 * Exposing dynamic xfeatures to the guest requires additional
>diff --git a/arch/x86/kvm/smm.c b/arch/x86/kvm/smm.c
>index 45c855389ea7..7aac9c54c353 100644
>--- a/arch/x86/kvm/smm.c
>+++ b/arch/x86/kvm/smm.c
>@@ -275,6 +275,10 @@ static void enter_smm_save_state_64(struct kvm_vcpu *vcpu,
> 	enter_smm_save_seg_64(vcpu, &smram->gs, VCPU_SREG_GS);
> 
> 	smram->int_shadow = static_call(kvm_x86_get_interrupt_shadow)(vcpu);
>+
>+	if (guest_can_use(vcpu, X86_FEATURE_SHSTK))
>+		KVM_BUG_ON(kvm_msr_read(vcpu, MSR_KVM_SSP, &smram->ssp),
>+			   vcpu->kvm);
> }
> #endif
> 
>@@ -564,6 +568,10 @@ static int rsm_load_state_64(struct x86_emulate_ctxt *ctxt,
> 	static_call(kvm_x86_set_interrupt_shadow)(vcpu, 0);
> 	ctxt->interruptibility = (u8)smstate->int_shadow;
> 
>+	if (guest_can_use(vcpu, X86_FEATURE_SHSTK))
>+		KVM_BUG_ON(kvm_msr_write(vcpu, MSR_KVM_SSP, smstate->ssp),
>+			   vcpu->kvm);
>+
> 	return X86EMUL_CONTINUE;
> }
> #endif
>diff --git a/arch/x86/kvm/smm.h b/arch/x86/kvm/smm.h
>index a1cf2ac5bd78..1e2a3e18207f 100644
>--- a/arch/x86/kvm/smm.h
>+++ b/arch/x86/kvm/smm.h
>@@ -116,8 +116,8 @@ struct kvm_smram_state_64 {
> 	u32 smbase;
> 	u32 reserved4[5];
> 
>-	/* ssp and svm_* fields below are not implemented by KVM */
> 	u64 ssp;
>+	/* svm_* fields below are not implemented by KVM */
> 	u64 svm_guest_pat;
> 	u64 svm_host_efer;
> 	u64 svm_host_cr4;
>-- 
>2.39.3
>