[PATCH v9 4/7] KVM: VMX: Load CET states on vmentry/vmexit

[Yang Weijiang]

"Load {guest,host} CET state" bit controls whether guest/host
CET states will be loaded at VM entry/exit. Before doing that,
KVM needs to check if CET can be enabled both on host and guest.

Note:
1)The processor does not allow CR4.CET to be set if CR0.WP = 0,
  similarly, it does not allow CR0.WP to be cleared while CR4.CET = 1.
  In either case, KVM would inject #GP to guest.

2)SHSTK and IBT features share one control MSR:
  MSR_IA32_{U,S}_CET, which means it's difficult to hide
  one feature from another in the case of SHSTK != IBT,
  after discussed in community, it's agreed to allow Guest
  control two features independently as it won't introduce
  security hole.

Co-developed-by: Zhang Yi Z <yi.z.zhang@xxxxxxxxxxxxxxx>
Signed-off-by: Zhang Yi Z <yi.z.zhang@xxxxxxxxxxxxxxx>
Signed-off-by: Yang Weijiang <weijiang.yang@xxxxxxxxx>
---
 arch/x86/kvm/vmx/capabilities.h | 10 ++++++
 arch/x86/kvm/vmx/vmx.c          | 56 +++++++++++++++++++++++++++++++--
 arch/x86/kvm/x86.c              |  3 ++
 3 files changed, 67 insertions(+), 2 deletions(-)

diff --git a/arch/x86/kvm/vmx/capabilities.h b/arch/x86/kvm/vmx/capabilities.h
index 7aa69716d516..4a67d35a42a2 100644
--- a/arch/x86/kvm/vmx/capabilities.h
+++ b/arch/x86/kvm/vmx/capabilities.h
@@ -106,6 +106,16 @@ static inline bool vmx_mpx_supported(void)
 		(vmcs_config.vmentry_ctrl & VM_ENTRY_LOAD_BNDCFGS);
 }
 
+static inline bool cpu_has_load_guest_cet_states_ctrl(void)
+{
+	return ((vmcs_config.vmentry_ctrl) & VM_ENTRY_LOAD_GUEST_CET_STATE);
+}
+
+static inline bool cpu_has_load_host_cet_states_ctrl(void)
+{
+	return ((vmcs_config.vmexit_ctrl) & VM_EXIT_LOAD_HOST_CET_STATE);
+}
+
 static inline bool cpu_has_vmx_tpr_shadow(void)
 {
 	return vmcs_config.cpu_based_exec_ctrl & CPU_BASED_TPR_SHADOW;
diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c
index 61fc846c7ef3..95063cc7da89 100644
--- a/arch/x86/kvm/vmx/vmx.c
+++ b/arch/x86/kvm/vmx/vmx.c
@@ -44,6 +44,7 @@
 #include <asm/spec-ctrl.h>
 #include <asm/virtext.h>
 #include <asm/vmx.h>
+#include <asm/cet.h>
 
 #include "capabilities.h"
 #include "cpuid.h"
@@ -2445,7 +2446,8 @@ static __init int setup_vmcs_config(struct vmcs_config *vmcs_conf,
 	      VM_EXIT_LOAD_IA32_EFER |
 	      VM_EXIT_CLEAR_BNDCFGS |
 	      VM_EXIT_PT_CONCEAL_PIP |
-	      VM_EXIT_CLEAR_IA32_RTIT_CTL;
+	      VM_EXIT_CLEAR_IA32_RTIT_CTL |
+	      VM_EXIT_LOAD_HOST_CET_STATE;
 	if (adjust_vmx_controls(min, opt, MSR_IA32_VMX_EXIT_CTLS,
 				&_vmexit_control) < 0)
 		return -EIO;
@@ -2469,7 +2471,8 @@ static __init int setup_vmcs_config(struct vmcs_config *vmcs_conf,
 	      VM_ENTRY_LOAD_IA32_EFER |
 	      VM_ENTRY_LOAD_BNDCFGS |
 	      VM_ENTRY_PT_CONCEAL_PIP |
-	      VM_ENTRY_LOAD_IA32_RTIT_CTL;
+	      VM_ENTRY_LOAD_IA32_RTIT_CTL |
+	      VM_ENTRY_LOAD_GUEST_CET_STATE;
 	if (adjust_vmx_controls(min, opt, MSR_IA32_VMX_ENTRY_CTLS,
 				&_vmentry_control) < 0)
 		return -EIO;
@@ -3027,6 +3030,25 @@ void vmx_set_cr3(struct kvm_vcpu *vcpu, unsigned long cr3)
 	vmcs_writel(GUEST_CR3, guest_cr3);
 }
 
+bool is_cet_bit_allowed(struct kvm_vcpu *vcpu)
+{
+	u64 kvm_xss = kvm_supported_xss();
+	unsigned long cr0;
+	bool cet_allowed;
+
+	cr0 = kvm_read_cr0(vcpu);
+
+	/* Right now, only user-mode CET is supported.*/
+	cet_allowed = (kvm_xss & XFEATURE_MASK_CET_USER) &&
+		      (guest_cpuid_has(vcpu, X86_FEATURE_SHSTK) ||
+		      guest_cpuid_has(vcpu, X86_FEATURE_IBT));
+
+	if ((cr0 & X86_CR0_WP) && cet_allowed)
+		return true;
+
+	return false;
+}
+
 int vmx_set_cr4(struct kvm_vcpu *vcpu, unsigned long cr4)
 {
 	struct vcpu_vmx *vmx = to_vmx(vcpu);
@@ -3067,6 +3089,9 @@ int vmx_set_cr4(struct kvm_vcpu *vcpu, unsigned long cr4)
 			return 1;
 	}
 
+	if ((cr4 & X86_CR4_CET) && !is_cet_bit_allowed(vcpu))
+		return 1;
+
 	if (vmx->nested.vmxon && !nested_cr4_valid(vcpu, cr4))
 		return 1;
 
@@ -3930,6 +3955,12 @@ void vmx_set_constant_host_state(struct vcpu_vmx *vmx)
 
 	if (cpu_has_load_ia32_efer())
 		vmcs_write64(HOST_IA32_EFER, host_efer);
+
+	if (cpu_has_load_host_cet_states_ctrl()) {
+		vmcs_writel(HOST_S_CET, 0);
+		vmcs_writel(HOST_INTR_SSP_TABLE, 0);
+		vmcs_writel(HOST_SSP, 0);
+	}
 }
 
 void set_cr4_guest_host_mask(struct vcpu_vmx *vmx)
@@ -6499,7 +6530,9 @@ bool __vmx_vcpu_run(struct vcpu_vmx *vmx, unsigned long *regs, bool launched);
 static void vmx_vcpu_run(struct kvm_vcpu *vcpu)
 {
 	struct vcpu_vmx *vmx = to_vmx(vcpu);
+	u64 kvm_xss = kvm_supported_xss();
 	unsigned long cr3, cr4;
+	bool cet_allowed;
 
 	/* Record the guest's net vcpu time for enforced NMI injections. */
 	if (unlikely(!enable_vnmi &&
@@ -6530,6 +6563,25 @@ static void vmx_vcpu_run(struct kvm_vcpu *vcpu)
 		vmx->loaded_vmcs->host_state.cr3 = cr3;
 	}
 
+	/* Right now, only user-mode CET is supported.*/
+	cet_allowed = (kvm_xss & XFEATURE_MASK_CET_USER) &&
+		      (guest_cpuid_has(vcpu, X86_FEATURE_SHSTK) ||
+		      guest_cpuid_has(vcpu, X86_FEATURE_IBT));
+
+	if (cpu_has_load_guest_cet_states_ctrl() && cet_allowed)
+		vmcs_set_bits(VM_ENTRY_CONTROLS,
+			      VM_ENTRY_LOAD_GUEST_CET_STATE);
+	else
+		vmcs_clear_bits(VM_ENTRY_CONTROLS,
+				VM_ENTRY_LOAD_GUEST_CET_STATE);
+
+	if (cpu_has_load_host_cet_states_ctrl() && cet_allowed)
+		vmcs_set_bits(VM_EXIT_CONTROLS,
+			      VM_EXIT_LOAD_HOST_CET_STATE);
+	else
+		vmcs_clear_bits(VM_EXIT_CONTROLS,
+				VM_EXIT_LOAD_HOST_CET_STATE);
+
 	cr4 = cr4_read_shadow();
 	if (unlikely(cr4 != vmx->loaded_vmcs->host_state.cr4)) {
 		vmcs_writel(HOST_CR4, cr4);
diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index a9b1140d0508..b27d97eaec24 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -788,6 +788,9 @@ int kvm_set_cr0(struct kvm_vcpu *vcpu, unsigned long cr0)
 	if (!(cr0 & X86_CR0_PG) && kvm_read_cr4_bits(vcpu, X86_CR4_PCIDE))
 		return 1;
 
+	if (!(cr0 & X86_CR0_WP) && kvm_read_cr4_bits(vcpu, X86_CR4_CET))
+		return 1;
+
 	kvm_x86_ops->set_cr0(vcpu, cr0);
 
 	if ((cr0 ^ old_cr0) & X86_CR0_PG) {
-- 
2.17.2