linux-kernel - [PATCH v4 08/20] KVM:x86: Report KVM supported CET MSRs as to-be-saved

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Message-Id: <20230721030352.72414-9-weijiang.yang@intel.com>
Date:   Thu, 20 Jul 2023 23:03:40 -0400
From:   Yang Weijiang <weijiang.yang@...el.com>
To:     seanjc@...gle.com, pbonzini@...hat.com, peterz@...radead.org,
        john.allen@....com, kvm@...r.kernel.org,
        linux-kernel@...r.kernel.org
Cc:     rick.p.edgecombe@...el.com, chao.gao@...el.com,
        binbin.wu@...ux.intel.com, weijiang.yang@...el.com
Subject: [PATCH v4 08/20] KVM:x86: Report KVM supported CET MSRs as to-be-saved

Add all CET MSRs including the synthesized GUEST_SSP to report list.
PL{0,1,2}_SSP are independent to host XSAVE management with later
patches. MSR_IA32_U_CET and MSR_IA32_PL3_SSP are XSAVE-managed on
host side. MSR_IA32_S_CET/MSR_IA32_INT_SSP_TAB/MSR_KVM_GUEST_SSP
are not XSAVE-managed.

When CET IBT/SHSTK are enumerated to guest, both user and supervisor
modes should be supported for architechtural integrity, i.e., two
modes are supported as both or neither.

Signed-off-by: Yang Weijiang <weijiang.yang@...el.com>
---
 arch/x86/include/uapi/asm/kvm_para.h |  1 +
 arch/x86/kvm/x86.c                   | 10 ++++++++++
 arch/x86/kvm/x86.h                   | 10 ++++++++++
 3 files changed, 21 insertions(+)

diff --git a/arch/x86/include/uapi/asm/kvm_para.h b/arch/x86/include/uapi/asm/kvm_para.h
index 6e64b27b2c1e..7af465e4e0bd 100644
--- a/arch/x86/include/uapi/asm/kvm_para.h
+++ b/arch/x86/include/uapi/asm/kvm_para.h
@@ -58,6 +58,7 @@
 #define MSR_KVM_ASYNC_PF_INT	0x4b564d06
 #define MSR_KVM_ASYNC_PF_ACK	0x4b564d07
 #define MSR_KVM_MIGRATION_CONTROL	0x4b564d08
+#define MSR_KVM_GUEST_SSP	0x4b564d09
 
 struct kvm_steal_time {
 	__u64 steal;
diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index be76ac6bbb21..59e961a88b75 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -1463,6 +1463,9 @@ static const u32 msrs_to_save_base[] = {
 
 	MSR_IA32_XFD, MSR_IA32_XFD_ERR,
 	MSR_IA32_XSS,
+	MSR_IA32_U_CET, MSR_IA32_S_CET,
+	MSR_IA32_PL0_SSP, MSR_IA32_PL1_SSP, MSR_IA32_PL2_SSP,
+	MSR_IA32_PL3_SSP, MSR_IA32_INT_SSP_TAB, MSR_KVM_GUEST_SSP,
 };
 
 static const u32 msrs_to_save_pmu[] = {
@@ -7215,6 +7218,13 @@ static void kvm_probe_msr_to_save(u32 msr_index)
 		if (!kvm_caps.supported_xss)
 			return;
 		break;
+	case MSR_IA32_U_CET:
+	case MSR_IA32_S_CET:
+	case MSR_KVM_GUEST_SSP:
+	case MSR_IA32_PL0_SSP ... MSR_IA32_INT_SSP_TAB:
+		if (!kvm_is_cet_supported())
+			return;
+		break;
 	default:
 		break;
 	}
diff --git a/arch/x86/kvm/x86.h b/arch/x86/kvm/x86.h
index 82e3dafc5453..6e6292915f8c 100644
--- a/arch/x86/kvm/x86.h
+++ b/arch/x86/kvm/x86.h
@@ -362,6 +362,16 @@ static inline bool kvm_mpx_supported(void)
 		== (XFEATURE_MASK_BNDREGS | XFEATURE_MASK_BNDCSR);
 }
 
+#define CET_XSTATE_MASK (XFEATURE_MASK_CET_USER)
+/*
+ * Shadow Stack and Indirect Branch Tracking feature enabling depends on
+ * whether host side CET user xstate bit is supported or not.
+ */
+static inline bool kvm_is_cet_supported(void)
+{
+	return (kvm_caps.supported_xss & CET_XSTATE_MASK) == CET_XSTATE_MASK;
+}
+
 extern unsigned int min_timer_period_us;
 
 extern bool enable_vmware_backdoor;
-- 
2.27.0