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Subject[PATCH v11 2/9] KVM: VMX: Set guest CET MSRs per KVM and host configuration
Date
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 | 40 ++++++++++++++++++++++++++++++++++++++++
1 file changed, 40 insertions(+)

diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c
index 860e5f4a9f7b..1aca468d9a10 100644
--- a/arch/x86/kvm/vmx/vmx.c
+++ b/arch/x86/kvm/vmx/vmx.c
@@ -3033,6 +3033,13 @@ void vmx_set_cr3(struct kvm_vcpu *vcpu, unsigned long cr3)
vmcs_writel(GUEST_CR3, guest_cr3);
}

+static bool is_cet_mode_allowed(struct kvm_vcpu *vcpu, u32 mode_mask)
+{
+ return ((supported_xss & mode_mask) &&
+ (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);
@@ -7064,6 +7071,35 @@ 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 flag;
+
+ flag = !is_cet_mode_allowed(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, flag);
+ vmx_set_intercept_for_msr(msr_bitmap, MSR_IA32_PL3_SSP, MSR_TYPE_RW, flag);
+
+ flag = !is_cet_mode_allowed(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, flag);
+ vmx_set_intercept_for_msr(msr_bitmap, MSR_IA32_PL0_SSP, MSR_TYPE_RW, flag);
+ vmx_set_intercept_for_msr(msr_bitmap, MSR_IA32_PL1_SSP, MSR_TYPE_RW, flag);
+ vmx_set_intercept_for_msr(msr_bitmap, MSR_IA32_PL2_SSP, MSR_TYPE_RW, flag);
+
+ flag |= !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, flag);
+}
+
static void vmx_cpuid_update(struct kvm_vcpu *vcpu)
{
struct vcpu_vmx *vmx = to_vmx(vcpu);
@@ -7102,6 +7138,10 @@ static void vmx_cpuid_update(struct kvm_vcpu *vcpu)
vmx_set_guest_msr(vmx, msr, enabled ? 0 : TSX_CTRL_RTM_DISABLE);
}
}
+
+ if (guest_cpuid_has(vcpu, X86_FEATURE_SHSTK) ||
+ guest_cpuid_has(vcpu, X86_FEATURE_IBT))
+ vmx_update_intercept_for_cet_msr(vcpu);
}

static __init void vmx_set_cpu_caps(void)
--
2.17.2
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