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Subject[PATCH v8 7/7] KVM: X86: Add user-space access interface for CET MSRs
Date
There're two different places storing Guest CET states, states
managed with XSAVES/XRSTORS, as restored/saved
in previous patch, can be read/write directly from/to the MSRs.
For those stored in VMCS fields, they're access via vmcs_read/
vmcs_write.

Signed-off-by: Yang Weijiang <weijiang.yang@intel.com>
---
arch/x86/kvm/vmx/vmx.c | 140 +++++++++++++++++++++++++++++++++++++++++
arch/x86/kvm/x86.c | 3 +
2 files changed, 143 insertions(+)

diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c
index bfb1b922a9ac..71aba264b5d2 100644
--- a/arch/x86/kvm/vmx/vmx.c
+++ b/arch/x86/kvm/vmx/vmx.c
@@ -1671,6 +1671,98 @@ static int vmx_get_msr_feature(struct kvm_msr_entry *msr)
return 0;
}

+#define CET_MSR_RSVD_BITS_1 0x3
+#define CET_MSR_RSVD_BITS_2 (0xF << 6)
+
+static bool cet_msr_write_allowed(struct kvm_vcpu *vcpu, struct msr_data *msr)
+{
+ u32 index = msr->index;
+ u64 data = msr->data;
+ u32 high_word = data >> 32;
+
+ if ((index == MSR_IA32_U_CET || index == MSR_IA32_S_CET) &&
+ (data & CET_MSR_RSVD_BITS_2))
+ return false;
+
+ if (is_64_bit_mode(vcpu)) {
+ if (is_noncanonical_address(data & PAGE_MASK, vcpu))
+ return false;
+ else if ((index == MSR_IA32_PL0_SSP ||
+ index == MSR_IA32_PL1_SSP ||
+ index == MSR_IA32_PL2_SSP ||
+ index == MSR_IA32_PL3_SSP) &&
+ (data & CET_MSR_RSVD_BITS_1))
+ return false;
+ } else {
+ if (msr->index == MSR_IA32_INT_SSP_TAB)
+ return false;
+ else if ((index == MSR_IA32_U_CET ||
+ index == MSR_IA32_S_CET ||
+ index == MSR_IA32_PL0_SSP ||
+ index == MSR_IA32_PL1_SSP ||
+ index == MSR_IA32_PL2_SSP ||
+ index == MSR_IA32_PL3_SSP) &&
+ (high_word & ~0ul))
+ return false;
+ }
+
+ return true;
+}
+
+static bool cet_msr_access_allowed(struct kvm_vcpu *vcpu, struct msr_data *msr)
+{
+ u64 kvm_xss;
+ u32 index = msr->index;
+
+ if (is_guest_mode(vcpu))
+ return false;
+
+ kvm_xss = kvm_supported_xss();
+
+ switch (index) {
+ case MSR_IA32_PL0_SSP ... MSR_IA32_PL3_SSP:
+ if (!boot_cpu_has(X86_FEATURE_SHSTK))
+ return false;
+ if (!msr->host_initiated) {
+ if (!guest_cpuid_has(vcpu, X86_FEATURE_SHSTK))
+ return false;
+ } else {
+ if (index == MSR_IA32_PL3_SSP) {
+ if (!(kvm_xss & XFEATURE_MASK_CET_USER))
+ return false;
+ } else {
+ if (!(kvm_xss & XFEATURE_MASK_CET_KERNEL))
+ return false;
+ }
+ }
+ break;
+ case MSR_IA32_U_CET:
+ case MSR_IA32_S_CET:
+ if (!boot_cpu_has(X86_FEATURE_SHSTK) &&
+ !boot_cpu_has(X86_FEATURE_IBT))
+ return false;
+
+ if (!msr->host_initiated) {
+ if (!guest_cpuid_has(vcpu, X86_FEATURE_SHSTK) &&
+ !guest_cpuid_has(vcpu, X86_FEATURE_IBT))
+ return false;
+ } else if (index == MSR_IA32_U_CET &&
+ !(kvm_xss & XFEATURE_MASK_CET_USER))
+ return false;
+ break;
+ case MSR_IA32_INT_SSP_TAB:
+ if (!boot_cpu_has(X86_FEATURE_SHSTK))
+ return false;
+
+ if (!msr->host_initiated &&
+ !guest_cpuid_has(vcpu, X86_FEATURE_SHSTK))
+ return false;
+ break;
+ default:
+ return false;
+ }
+ return true;
+}
/*
* Reads an msr value (of 'msr_index') into 'pdata'.
* Returns 0 on success, non-0 otherwise.
@@ -1788,6 +1880,26 @@ static int vmx_get_msr(struct kvm_vcpu *vcpu, struct msr_data *msr_info)
else
msr_info->data = vmx->pt_desc.guest.addr_a[index / 2];
break;
+ case MSR_IA32_S_CET:
+ if (!cet_msr_access_allowed(vcpu, msr_info))
+ return 1;
+ msr_info->data = vmcs_readl(GUEST_S_CET);
+ break;
+ case MSR_IA32_INT_SSP_TAB:
+ if (!cet_msr_access_allowed(vcpu, msr_info))
+ return 1;
+ msr_info->data = vmcs_readl(GUEST_INTR_SSP_TABLE);
+ break;
+ case MSR_IA32_U_CET:
+ if (!cet_msr_access_allowed(vcpu, msr_info))
+ return 1;
+ rdmsrl(MSR_IA32_U_CET, msr_info->data);
+ break;
+ case MSR_IA32_PL0_SSP ... MSR_IA32_PL3_SSP:
+ if (!cet_msr_access_allowed(vcpu, msr_info))
+ return 1;
+ rdmsrl(msr_info->index, msr_info->data);
+ break;
case MSR_TSC_AUX:
if (!msr_info->host_initiated &&
!guest_cpuid_has(vcpu, X86_FEATURE_RDTSCP))
@@ -2039,6 +2151,34 @@ static int vmx_set_msr(struct kvm_vcpu *vcpu, struct msr_data *msr_info)
else
vmx->pt_desc.guest.addr_a[index / 2] = data;
break;
+ case MSR_IA32_S_CET:
+ if (!cet_msr_access_allowed(vcpu, msr_info))
+ return 1;
+ if (!cet_msr_write_allowed(vcpu, msr_info))
+ return 1;
+ vmcs_writel(GUEST_S_CET, data);
+ break;
+ case MSR_IA32_INT_SSP_TAB:
+ if (!cet_msr_access_allowed(vcpu, msr_info))
+ return 1;
+ if (!cet_msr_write_allowed(vcpu, msr_info))
+ return 1;
+ vmcs_writel(GUEST_INTR_SSP_TABLE, data);
+ break;
+ case MSR_IA32_U_CET:
+ if (!cet_msr_access_allowed(vcpu, msr_info))
+ return 1;
+ if (!cet_msr_write_allowed(vcpu, msr_info))
+ return 1;
+ wrmsrl(MSR_IA32_U_CET, data);
+ break;
+ case MSR_IA32_PL0_SSP ... MSR_IA32_PL3_SSP:
+ if (!cet_msr_access_allowed(vcpu, msr_info))
+ return 1;
+ if (!cet_msr_write_allowed(vcpu, msr_info))
+ return 1;
+ wrmsrl(msr_info->index, data);
+ break;
case MSR_TSC_AUX:
if (!msr_info->host_initiated &&
!guest_cpuid_has(vcpu, X86_FEATURE_RDTSCP))
diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index 6275a75d5802..1bbe4550da90 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -1143,6 +1143,9 @@ static u32 msrs_to_save[] = {
MSR_IA32_RTIT_ADDR1_A, MSR_IA32_RTIT_ADDR1_B,
MSR_IA32_RTIT_ADDR2_A, MSR_IA32_RTIT_ADDR2_B,
MSR_IA32_RTIT_ADDR3_A, MSR_IA32_RTIT_ADDR3_B,
+ 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,
};

static unsigned num_msrs_to_save;
--
2.17.2
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