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Subject[PATCH v11 7/9] KVM: X86: Add userspace 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.

To correctly read/write the CET MSRs, it's necessary to check
whether the kernel FPU context switch happened and reload guest
FPU context if needed.

Suggested-by: Sean Christopherson <sean.j.christopherson@intel.com>
Signed-off-by: Yang Weijiang <weijiang.yang@intel.com>
---
arch/x86/kvm/vmx/vmx.c | 133 +++++++++++++++++++++++++++++++++++++++++
arch/x86/kvm/x86.c | 11 ++++
2 files changed, 144 insertions(+)

diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c
index 87f101750746..a3d01014b9e7 100644
--- a/arch/x86/kvm/vmx/vmx.c
+++ b/arch/x86/kvm/vmx/vmx.c
@@ -1809,6 +1809,91 @@ static int vmx_get_msr_feature(struct kvm_msr_entry *msr)
}
}

+static void vmx_get_xsave_msr(struct msr_data *msr_info)
+{
+ local_irq_disable();
+ if (test_thread_flag(TIF_NEED_FPU_LOAD))
+ switch_fpu_return();
+ rdmsrl(msr_info->index, msr_info->data);
+ local_irq_enable();
+}
+
+static void vmx_set_xsave_msr(struct msr_data *msr_info)
+{
+ local_irq_disable();
+ if (test_thread_flag(TIF_NEED_FPU_LOAD))
+ switch_fpu_return();
+ wrmsrl(msr_info->index, msr_info->data);
+ local_irq_enable();
+}
+
+#define CET_MSR_RSVD_BITS_1 GENMASK(1, 0)
+#define CET_MSR_RSVD_BITS_2 GENMASK(9, 6)
+
+static bool cet_check_msr_write(struct kvm_vcpu *vcpu,
+ struct msr_data *msr,
+ u64 mask)
+{
+ u64 data = msr->data;
+ u32 high_word = data >> 32;
+
+ if (data & mask)
+ return false;
+
+ if (!is_64_bit_mode(vcpu) && high_word)
+ return false;
+
+ return true;
+}
+
+static bool cet_check_ssp_msr_access(struct kvm_vcpu *vcpu,
+ struct msr_data *msr)
+{
+ u32 index = msr->index;
+
+ if (!boot_cpu_has(X86_FEATURE_SHSTK))
+ return false;
+
+ if (!msr->host_initiated &&
+ !guest_cpuid_has(vcpu, X86_FEATURE_SHSTK))
+ return false;
+
+ if (index == MSR_IA32_INT_SSP_TAB)
+ return true;
+
+ if (index == MSR_IA32_PL3_SSP) {
+ if (!(supported_xss & XFEATURE_MASK_CET_USER))
+ return false;
+ } else if (!(supported_xss & XFEATURE_MASK_CET_KERNEL)) {
+ return false;
+ }
+
+ return true;
+}
+
+static bool cet_check_ctl_msr_access(struct kvm_vcpu *vcpu,
+ struct msr_data *msr)
+{
+ u32 index = msr->index;
+
+ if (!boot_cpu_has(X86_FEATURE_SHSTK) &&
+ !boot_cpu_has(X86_FEATURE_IBT))
+ return false;
+
+ if (!msr->host_initiated &&
+ !guest_cpuid_has(vcpu, X86_FEATURE_SHSTK) &&
+ !guest_cpuid_has(vcpu, X86_FEATURE_IBT))
+ return false;
+
+ if (index == MSR_IA32_U_CET) {
+ if (!(supported_xss & XFEATURE_MASK_CET_USER))
+ return false;
+ } else if (!(supported_xss & XFEATURE_MASK_CET_KERNEL)) {
+ return false;
+ }
+
+ return true;
+}
/*
* Reads an msr value (of 'msr_index') into 'pdata'.
* Returns 0 on success, non-0 otherwise.
@@ -1941,6 +2026,26 @@ 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_check_ctl_msr_access(vcpu, msr_info))
+ return 1;
+ msr_info->data = vmcs_readl(GUEST_S_CET);
+ break;
+ case MSR_IA32_INT_SSP_TAB:
+ if (!cet_check_ssp_msr_access(vcpu, msr_info))
+ return 1;
+ msr_info->data = vmcs_readl(GUEST_INTR_SSP_TABLE);
+ break;
+ case MSR_IA32_U_CET:
+ if (!cet_check_ctl_msr_access(vcpu, msr_info))
+ return 1;
+ vmx_get_xsave_msr(msr_info);
+ break;
+ case MSR_IA32_PL0_SSP ... MSR_IA32_PL3_SSP:
+ if (!cet_check_ssp_msr_access(vcpu, msr_info))
+ return 1;
+ vmx_get_xsave_msr(msr_info);
+ break;
case MSR_TSC_AUX:
if (!msr_info->host_initiated &&
!guest_cpuid_has(vcpu, X86_FEATURE_RDTSCP))
@@ -2197,6 +2302,34 @@ 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_check_ctl_msr_access(vcpu, msr_info))
+ return 1;
+ if (!cet_check_msr_write(vcpu, msr_info, CET_MSR_RSVD_BITS_2))
+ return 1;
+ vmcs_writel(GUEST_S_CET, data);
+ break;
+ case MSR_IA32_INT_SSP_TAB:
+ if (!cet_check_ctl_msr_access(vcpu, msr_info))
+ return 1;
+ if (!is_64_bit_mode(vcpu))
+ return 1;
+ vmcs_writel(GUEST_INTR_SSP_TABLE, data);
+ break;
+ case MSR_IA32_U_CET:
+ if (!cet_check_ctl_msr_access(vcpu, msr_info))
+ return 1;
+ if (!cet_check_msr_write(vcpu, msr_info, CET_MSR_RSVD_BITS_2))
+ return 1;
+ vmx_set_xsave_msr(msr_info);
+ break;
+ case MSR_IA32_PL0_SSP ... MSR_IA32_PL3_SSP:
+ if (!cet_check_ssp_msr_access(vcpu, msr_info))
+ return 1;
+ if (!cet_check_msr_write(vcpu, msr_info, CET_MSR_RSVD_BITS_1))
+ return 1;
+ vmx_set_xsave_msr(msr_info);
+ 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 9654d779bdab..9e89ee6a09e1 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -1229,6 +1229,10 @@ static const u32 msrs_to_save_all[] = {
MSR_ARCH_PERFMON_EVENTSEL0 + 12, MSR_ARCH_PERFMON_EVENTSEL0 + 13,
MSR_ARCH_PERFMON_EVENTSEL0 + 14, MSR_ARCH_PERFMON_EVENTSEL0 + 15,
MSR_ARCH_PERFMON_EVENTSEL0 + 16, MSR_ARCH_PERFMON_EVENTSEL0 + 17,
+
+ 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 u32 msrs_to_save[ARRAY_SIZE(msrs_to_save_all)];
@@ -1504,6 +1508,13 @@ static int __kvm_set_msr(struct kvm_vcpu *vcpu, u32 index, u64 data,
* invokes 64-bit SYSENTER.
*/
data = get_canonical(data, vcpu_virt_addr_bits(vcpu));
+ break;
+ case MSR_IA32_PL0_SSP ... MSR_IA32_PL3_SSP:
+ case MSR_IA32_U_CET:
+ case MSR_IA32_S_CET:
+ case MSR_IA32_INT_SSP_TAB:
+ if (is_noncanonical_address(data, vcpu))
+ return 1;
}

msr.data = data;
--
2.17.2
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