[PATCH v12 02/10] KVM: VMX: Set guest CET MSRs per KVM and host configuration

Yang Weijiang
2020-05-06T08:19:39Z

CET MSRs pass through guest directly to enhance performance. CET runtime
control settings are stored in MSR_IA32_{U,S}_CET, Shadow Stack Pointer(SSP)
are stored in MSR_IA32_PL{0,1,2,3}_SSP, SSP table base address is stored in
MSR_IA32_INT_SSP_TAB, these MSRs are defined in kernel and re-used here.

MSR_IA32_U_CET and MSR_IA32_PL3_SSP are used for user-mode protection,the MSR
contents are switched between threads during scheduling, it makes sense to pass
through them so that the guest kernel can use xsaves/xrstors to operate them
efficiently. Other MSRs are used for non-user mode protection. See SDM for detailed
info.

The difference between CET VMCS fields and CET MSRs is that,the former are used
during VMEnter/VMExit, whereas the latter are used for CET state storage between
task/thread scheduling.

Co-developed-by: Zhang Yi Z <yi.z.zhang@linux.intel.com>
Signed-off-by: Zhang Yi Z <yi.z.zhang@linux.intel.com>
Signed-off-by: Yang Weijiang <weijiang.yang@intel.com>
---
arch/x86/kvm/vmx/vmx.c | 46 ++++++++++++++++++++++++++++++++++++++++++
arch/x86/kvm/x86.c | 3 +++
2 files changed, 49 insertions(+)

diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c
index d52d470e36b1..97e766875a7e 100644
--- a/arch/x86/kvm/vmx/vmx.c
+++ b/arch/x86/kvm/vmx/vmx.c
@@ -3020,6 +3020,13 @@ void vmx_load_mmu_pgd(struct kvm_vcpu *vcpu, unsigned long cr3)
vmcs_writel(GUEST_CR3, guest_cr3);
}

+static bool is_cet_state_supported(struct kvm_vcpu *vcpu, u32 xss_states)
+{
+ return ((supported_xss & xss_states) &&
+ (guest_cpuid_has(vcpu, X86_FEATURE_SHSTK) ||
+ guest_cpuid_has(vcpu, X86_FEATURE_IBT)));
+}
+
int vmx_set_cr4(struct kvm_vcpu *vcpu, unsigned long cr4)
{
struct vcpu_vmx *vmx = to_vmx(vcpu);
@@ -7098,6 +7105,42 @@ static void update_intel_pt_cfg(struct kvm_vcpu *vcpu)
vmx->pt_desc.ctl_bitmask &= ~(0xfULL << (32 + i * 4));
}

+static void vmx_update_intercept_for_cet_msr(struct kvm_vcpu *vcpu)
+{
+ struct vcpu_vmx *vmx = to_vmx(vcpu);
+ unsigned long *msr_bitmap = vmx->vmcs01.msr_bitmap;
+ bool incpt;
+
+ incpt = !is_cet_state_supported(vcpu, XFEATURE_MASK_CET_USER);
+ /*
+ * U_CET is required for USER CET, and U_CET, PL3_SPP are bound as
+ * one component and controlled by IA32_XSS[bit 11].
+ */
+ vmx_set_intercept_for_msr(msr_bitmap, MSR_IA32_U_CET, MSR_TYPE_RW,
+ incpt);
+ vmx_set_intercept_for_msr(msr_bitmap, MSR_IA32_PL3_SSP, MSR_TYPE_RW,
+ incpt);
+
+ incpt = !is_cet_state_supported(vcpu, XFEATURE_MASK_CET_KERNEL);
+ /*
+ * S_CET is required for KERNEL CET, and PL0_SSP ... PL2_SSP are
+ * bound as one component and controlled by IA32_XSS[bit 12].
+ */
+ vmx_set_intercept_for_msr(msr_bitmap, MSR_IA32_S_CET, MSR_TYPE_RW,
+ incpt);
+ vmx_set_intercept_for_msr(msr_bitmap, MSR_IA32_PL0_SSP, MSR_TYPE_RW,
+ incpt);
+ vmx_set_intercept_for_msr(msr_bitmap, MSR_IA32_PL1_SSP, MSR_TYPE_RW,
+ incpt);
+ vmx_set_intercept_for_msr(msr_bitmap, MSR_IA32_PL2_SSP, MSR_TYPE_RW,
+ incpt);
+
+ incpt |= !guest_cpuid_has(vcpu, X86_FEATURE_SHSTK);
+ /* SSP_TAB is only available for KERNEL SHSTK.*/
+ vmx_set_intercept_for_msr(msr_bitmap, MSR_IA32_INT_SSP_TAB, MSR_TYPE_RW,
+ incpt);
+}
+
static void vmx_cpuid_update(struct kvm_vcpu *vcpu)
{
struct vcpu_vmx *vmx = to_vmx(vcpu);
@@ -7136,6 +7179,9 @@ static void vmx_cpuid_update(struct kvm_vcpu *vcpu)
vmx_set_guest_msr(vmx, msr, enabled ? 0 : TSX_CTRL_RTM_DISABLE);
}
}
+
+ if (supported_xss & (XFEATURE_MASK_CET_KERNEL | XFEATURE_MASK_CET_USER))
+ vmx_update_intercept_for_cet_msr(vcpu);
}

static __init void vmx_set_cpu_caps(void)
diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index c5835f9cb9ad..6390b62c12ed 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -186,6 +186,9 @@ static struct kvm_shared_msrs __percpu *shared_msrs;
| XFEATURE_MASK_BNDCSR | XFEATURE_MASK_AVX512 \
| XFEATURE_MASK_PKRU)

+#define KVM_SUPPORTED_XSS (XFEATURE_MASK_CET_USER | \
+ XFEATURE_MASK_CET_KERNEL)
+
u64 __read_mostly host_efer;
EXPORT_SYMBOL_GPL(host_efer);

--
2.17.2