[PATCH v12 06/10] KVM: x86: Add userspace access interface for CET MSRs

Yang Weijiang
2020-05-06T08:19:47Z

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/include/uapi/asm/kvm_para.h | 7 +-
arch/x86/kvm/vmx/vmx.c | 148 +++++++++++++++++++++++++++
arch/x86/kvm/x86.c | 4 +
3 files changed, 156 insertions(+), 3 deletions(-)

diff --git a/arch/x86/include/uapi/asm/kvm_para.h b/arch/x86/include/uapi/asm/kvm_para.h
index 2a8e0b6b9805..211bba6f7d8a 100644
--- a/arch/x86/include/uapi/asm/kvm_para.h
+++ b/arch/x86/include/uapi/asm/kvm_para.h
@@ -46,10 +46,11 @@
/* Custom MSRs falls in the range 0x4b564d00-0x4b564dff */
#define MSR_KVM_WALL_CLOCK_NEW 0x4b564d00
#define MSR_KVM_SYSTEM_TIME_NEW 0x4b564d01
-#define MSR_KVM_ASYNC_PF_EN 0x4b564d02
-#define MSR_KVM_STEAL_TIME 0x4b564d03
-#define MSR_KVM_PV_EOI_EN 0x4b564d04
+#define MSR_KVM_ASYNC_PF_EN 0x4b564d02
+#define MSR_KVM_STEAL_TIME 0x4b564d03
+#define MSR_KVM_PV_EOI_EN 0x4b564d04
#define MSR_KVM_POLL_CONTROL 0x4b564d05
+#define MSR_KVM_GUEST_SSP 0x4b564d06

struct kvm_steal_time {
__u64 steal;
diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c
index 7137e252ab38..7f3a65ee64c5 100644
--- a/arch/x86/kvm/vmx/vmx.c
+++ b/arch/x86/kvm/vmx/vmx.c
@@ -1777,6 +1777,94 @@ 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(2, 0)
+#define CET_MSR_RSVD_BITS_2 GENMASK(9, 6)
+
+static bool cet_check_msr_valid(struct kvm_vcpu *vcpu,
+ struct msr_data *msr, u64 rsvd_bits)
+{
+ u64 data = msr->data;
+ u32 index = msr->index;
+
+ if ((index == MSR_IA32_PL0_SSP || index == MSR_IA32_PL1_SSP ||
+ index == MSR_IA32_PL2_SSP || index == MSR_IA32_PL3_SSP ||
+ index == MSR_IA32_INT_SSP_TAB || index == MSR_KVM_GUEST_SSP) &&
+ is_noncanonical_address(data, vcpu))
+ return false;
+
+ if ((index == MSR_IA32_S_CET || index == MSR_IA32_U_CET) &&
+ data & MSR_IA32_CET_ENDBR_EN) {
+ u64 bitmap_base = data >> 12;
+
+ if (is_noncanonical_address(bitmap_base, vcpu))
+ return false;
+ }
+
+ return !(data & rsvd_bits);
+}
+
+static bool cet_check_ssp_msr_accessible(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_KVM_GUEST_SSP)
+ return msr->host_initiated &&
+ guest_cpuid_has(vcpu, X86_FEATURE_SHSTK);
+
+ if (index == MSR_IA32_INT_SSP_TAB)
+ return true;
+
+ if (index == MSR_IA32_PL3_SSP)
+ return supported_xss & XFEATURE_MASK_CET_USER;
+
+ return supported_xss & XFEATURE_MASK_CET_KERNEL;
+}
+
+static bool cet_check_ctl_msr_accessible(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)
+ return supported_xss & XFEATURE_MASK_CET_USER;
+
+ return supported_xss & XFEATURE_MASK_CET_KERNEL;
+}
/*
* Reads an msr value (of 'msr_index') into 'pdata'.
* Returns 0 on success, non-0 otherwise.
@@ -1909,6 +1997,31 @@ 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_KVM_GUEST_SSP:
+ if (!cet_check_ssp_msr_accessible(vcpu, msr_info))
+ return 1;
+ msr_info->data = vmcs_readl(GUEST_SSP);
+ break;
+ case MSR_IA32_S_CET:
+ if (!cet_check_ctl_msr_accessible(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_accessible(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_accessible(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_accessible(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))
@@ -2165,6 +2278,41 @@ 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_KVM_GUEST_SSP:
+ if (!cet_check_ssp_msr_accessible(vcpu, msr_info))
+ return 1;
+ if (!cet_check_msr_valid(vcpu, msr_info, CET_MSR_RSVD_BITS_1))
+ return 1;
+ vmcs_writel(GUEST_SSP, data);
+ break;
+ case MSR_IA32_S_CET:
+ if (!cet_check_ctl_msr_accessible(vcpu, msr_info))
+ return 1;
+ if (!cet_check_msr_valid(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_accessible(vcpu, msr_info))
+ return 1;
+ if (!cet_check_msr_valid(vcpu, msr_info, 0))
+ return 1;
+ vmcs_writel(GUEST_INTR_SSP_TABLE, data);
+ break;
+ case MSR_IA32_U_CET:
+ if (!cet_check_ctl_msr_accessible(vcpu, msr_info))
+ return 1;
+ if (!cet_check_msr_valid(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_accessible(vcpu, msr_info))
+ return 1;
+ if (!cet_check_msr_valid(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 50f80dcab3a9..1ba91101e6e6 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -1228,6 +1228,10 @@ 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)];
--
2.17.2