Mainline kernel now supports supervisor IBT for kernel code,
to make s-IBT work in guest(nested guest), pass through
MSR_IA32_S_CET to guest(nested guest) if host kernel and KVM
enabled IBT. Note, s-IBT can work independent to host xsaves
support because guest MSR_IA32_S_CET can be stored/loaded from
specific VMCS field.
Signed-off-by: Yang Weijiang <weijiang.yang@xxxxxxxxx>
---
arch/x86/kvm/cpuid.h | 5 +++++
arch/x86/kvm/vmx/nested.c | 3 +++
arch/x86/kvm/vmx/vmx.c | 27 ++++++++++++++++++++++++---
arch/x86/kvm/x86.c | 13 ++++++++++++-
4 files changed, 44 insertions(+), 4 deletions(-)
diff --git a/arch/x86/kvm/cpuid.h b/arch/x86/kvm/cpuid.h
index ac72aabba981..c67c1e2fc11a 100644
--- a/arch/x86/kvm/cpuid.h
+++ b/arch/x86/kvm/cpuid.h
@@ -230,4 +230,9 @@ static __always_inline bool guest_pv_has(struct kvm_vcpu *vcpu,
return vcpu->arch.pv_cpuid.features & (1u << kvm_feature);
}
+static __always_inline bool cet_kernel_ibt_supported(void)
+{
+ return HAS_KERNEL_IBT && kvm_cpu_cap_has(X86_FEATURE_IBT);
+}
+
#endif
diff --git a/arch/x86/kvm/vmx/nested.c b/arch/x86/kvm/vmx/nested.c
index f31f3d394507..d394136891d0 100644
--- a/arch/x86/kvm/vmx/nested.c
+++ b/arch/x86/kvm/vmx/nested.c
@@ -688,6 +688,9 @@ static inline bool nested_vmx_prepare_msr_bitmap(struct kvm_vcpu *vcpu,
nested_vmx_set_intercept_for_msr(vmx, msr_bitmap_l1, msr_bitmap_l0,
MSR_IA32_U_CET, MSR_TYPE_RW);
+ nested_vmx_set_intercept_for_msr(vmx, msr_bitmap_l1, msr_bitmap_l0,
+ MSR_IA32_S_CET, MSR_TYPE_RW);
+
nested_vmx_set_intercept_for_msr(vmx, msr_bitmap_l1, msr_bitmap_l0,
MSR_IA32_PL3_SSP, MSR_TYPE_RW);
diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c
index 00782d1750a5..6e7e596c0147 100644
--- a/arch/x86/kvm/vmx/vmx.c
+++ b/arch/x86/kvm/vmx/vmx.c
@@ -585,6 +585,7 @@ static bool is_valid_passthrough_msr(u32 msr)
return true;
case MSR_IA32_U_CET:
case MSR_IA32_PL3_SSP:
+ case MSR_IA32_S_CET:
return true;
}
@@ -1773,7 +1774,8 @@ static int vmx_get_msr_feature(struct kvm_msr_entry *msr)
static bool cet_is_msr_accessible(struct kvm_vcpu *vcpu,
struct msr_data *msr)
{
- if (!kvm_cet_user_supported())
+ if (!kvm_cet_user_supported() &&
+ !cet_kernel_ibt_supported())
return false;
if (msr->host_initiated)
@@ -1783,6 +1785,10 @@ static bool cet_is_msr_accessible(struct kvm_vcpu *vcpu,
!guest_cpuid_has(vcpu, X86_FEATURE_IBT))
return false;
+ if (msr->index == MSR_IA32_S_CET &&
+ guest_cpuid_has(vcpu, X86_FEATURE_IBT))
+ return true;
+
if ((msr->index == MSR_IA32_PL3_SSP ||
msr->index == MSR_KVM_GUEST_SSP) &&
!guest_cpuid_has(vcpu, X86_FEATURE_SHSTK))
@@ -1933,10 +1939,13 @@ static int vmx_get_msr(struct kvm_vcpu *vcpu, struct msr_data *msr_info)
case MSR_IA32_U_CET:
case MSR_IA32_PL3_SSP:
case MSR_KVM_GUEST_SSP:
+ case MSR_IA32_S_CET:
if (!cet_is_msr_accessible(vcpu, msr_info))
return 1;
if (msr_info->index == MSR_KVM_GUEST_SSP)
msr_info->data = vmcs_readl(GUEST_SSP);
+ else if (msr_info->index == MSR_IA32_S_CET)
+ msr_info->data = vmcs_readl(GUEST_S_CET);
else
kvm_get_xsave_msr(msr_info);
break;
@@ -2273,12 +2282,16 @@ static int vmx_set_msr(struct kvm_vcpu *vcpu, struct msr_data *msr_info)
vmx->pt_desc.guest.addr_a[index / 2] = data;
break;
case MSR_IA32_U_CET:
+ case MSR_IA32_S_CET:
if (!cet_is_msr_accessible(vcpu, msr_info))
return 1;
if ((data & GENMASK(9, 6)) ||
is_noncanonical_address(data, vcpu))
return 1;
- kvm_set_xsave_msr(msr_info);
+ if (msr_index == MSR_IA32_S_CET)
+ vmcs_writel(GUEST_S_CET, data);
+ else
+ kvm_set_xsave_msr(msr_info);
break;
case MSR_IA32_PL3_SSP:
case MSR_KVM_GUEST_SSP:
@@ -7615,6 +7628,9 @@ static void vmx_update_intercept_for_cet_msr(struct kvm_vcpu *vcpu)
incpt |= !guest_cpuid_has(vcpu, X86_FEATURE_SHSTK);
vmx_set_intercept_for_msr(vcpu, MSR_IA32_PL3_SSP, MSR_TYPE_RW, incpt);
+
+ incpt |= !guest_cpuid_has(vcpu, X86_FEATURE_IBT);
+ vmx_set_intercept_for_msr(vcpu, MSR_IA32_S_CET, MSR_TYPE_RW, incpt);
}
static void vmx_vcpu_after_set_cpuid(struct kvm_vcpu *vcpu)
@@ -7680,7 +7696,7 @@ static void vmx_vcpu_after_set_cpuid(struct kvm_vcpu *vcpu)
/* Refresh #PF interception to account for MAXPHYADDR changes. */
vmx_update_exception_bitmap(vcpu);
- if (kvm_cet_user_supported())
+ if (kvm_cet_user_supported() || cet_kernel_ibt_supported())
vmx_update_intercept_for_cet_msr(vcpu);
}
@@ -7743,6 +7759,11 @@ static __init void vmx_set_cpu_caps(void)
kvm_cpu_cap_clear(X86_FEATURE_SHSTK);
#endif
+#ifndef CONFIG_X86_KERNEL_IBT
+ if (boot_cpu_has(X86_FEATURE_IBT))
+ kvm_cpu_cap_clear(X86_FEATURE_IBT);
+#endif
+
}
static void vmx_request_immediate_exit(struct kvm_vcpu *vcpu)
diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index fe049d0e5ecc..c0118b33806a 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -1463,6 +1463,7 @@ static const u32 msrs_to_save_all[] = {
MSR_IA32_XFD, MSR_IA32_XFD_ERR,
MSR_IA32_XSS,
MSR_IA32_U_CET, MSR_IA32_PL3_SSP, MSR_KVM_GUEST_SSP,
+ MSR_IA32_S_CET,
};
static u32 msrs_to_save[ARRAY_SIZE(msrs_to_save_all)];
@@ -6823,6 +6824,10 @@ static void kvm_init_msr_list(void)
if (!kvm_cet_user_supported())
continue;
break;
+ case MSR_IA32_S_CET:
+ if (!cet_kernel_ibt_supported())
+ continue;
+ break;
default:
break;
}
@@ -11830,7 +11835,13 @@ int kvm_arch_hardware_setup(void *opaque)
/* Update CET features now as kvm_caps.supported_xss is finalized. */
if (!kvm_cet_user_supported()) {
kvm_cpu_cap_clear(X86_FEATURE_SHSTK);
- kvm_cpu_cap_clear(X86_FEATURE_IBT);
+ /* If CET user bit is disabled due to cmdline option such as
+ * noxsaves, but kernel IBT is on, this means we can expose
+ * kernel IBT alone to guest since CET user mode msrs are not
+ * passed through to guest.
+ */
+ if (!cet_kernel_ibt_supported())
+ kvm_cpu_cap_clear(X86_FEATURE_IBT);
}
/*
--
2.27.0
