Make PL{0,1,2}_SSP as write-intercepted to detect whether
guest is using these MSRs. Disable intercept to the MSRs
if they're written with non-zero values. KVM does save/
reload for the MSRs only if they're used by guest.
Signed-off-by: Yang Weijiang <weijiang.yang@xxxxxxxxx>
---
arch/x86/include/asm/kvm_host.h | 1 +
arch/x86/kvm/vmx/vmx.c | 34 +++++++++++++++++++++++++++++----
arch/x86/kvm/x86.c | 15 ++++++++++-----
3 files changed, 41 insertions(+), 9 deletions(-)
diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h
index 69cbc9d9b277..c50b555234fb 100644
--- a/arch/x86/include/asm/kvm_host.h
+++ b/arch/x86/include/asm/kvm_host.h
@@ -748,6 +748,7 @@ struct kvm_vcpu_arch {
bool tpr_access_reporting;
bool xsaves_enabled;
bool xfd_no_write_intercept;
+ bool cet_sss_active;
u64 ia32_xss;
u64 microcode_version;
u64 arch_capabilities;
diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c
index cba24acf1a7a..3eb4fe9c9ab6 100644
--- a/arch/x86/kvm/vmx/vmx.c
+++ b/arch/x86/kvm/vmx/vmx.c
@@ -2155,6 +2155,18 @@ static u64 vmx_get_supported_debugctl(struct kvm_vcpu *vcpu, bool host_initiated
return debugctl;
}
+static void vmx_disable_write_intercept_sss_msr(struct kvm_vcpu *vcpu)
+{
+ if (guest_can_use(vcpu, X86_FEATURE_SHSTK)) {
+ vmx_set_intercept_for_msr(vcpu, MSR_IA32_PL0_SSP,
+ MSR_TYPE_RW, false);
+ vmx_set_intercept_for_msr(vcpu, MSR_IA32_PL1_SSP,
+ MSR_TYPE_RW, false);
+ vmx_set_intercept_for_msr(vcpu, MSR_IA32_PL2_SSP,
+ MSR_TYPE_RW, false);
+ }
+}
+
/*
* Writes msr value into the appropriate "register".
* Returns 0 on success, non-0 otherwise.
@@ -2427,7 +2439,16 @@ static int vmx_set_msr(struct kvm_vcpu *vcpu, struct msr_data *msr_info)
#define CET_LEG_BITMAP_BASE(data) ((data) >> 12)
#define CET_EXCLUSIVE_BITS (CET_SUPPRESS | CET_WAIT_ENDBR)
case MSR_IA32_PL0_SSP ... MSR_IA32_PL3_SSP:
- return kvm_set_msr_common(vcpu, msr_info);
+ if (kvm_set_msr_common(vcpu, msr_info))
+ return 1;
+ /*
+ * Write to the base SSP MSRs should happen ahead of toggling
+ * of IA32_S_CET.SH_STK_EN bit.
+ */
+ if (msr_index != MSR_IA32_PL3_SSP && data) {
+ vmx_disable_write_intercept_sss_msr(vcpu);
+ wrmsrl(msr_index, data);
+ }
break;
case MSR_IA32_U_CET:
case MSR_IA32_S_CET:
@@ -7774,12 +7795,17 @@ static void vmx_update_intercept_for_cet_msr(struct kvm_vcpu *vcpu)
MSR_TYPE_RW, false);
vmx_set_intercept_for_msr(vcpu, MSR_IA32_S_CET,
MSR_TYPE_RW, false);
+ /*
+ * Supervisor shadow stack MSRs are intercepted until
+ * they're written by guest, this is designed to
+ * optimize the save/restore overhead.
+ */
vmx_set_intercept_for_msr(vcpu, MSR_IA32_PL0_SSP,
- MSR_TYPE_RW, false);
+ MSR_TYPE_R, false);
vmx_set_intercept_for_msr(vcpu, MSR_IA32_PL1_SSP,
- MSR_TYPE_RW, false);
+ MSR_TYPE_R, false);
vmx_set_intercept_for_msr(vcpu, MSR_IA32_PL2_SSP,
- MSR_TYPE_RW, false);
+ MSR_TYPE_R, false);
vmx_set_intercept_for_msr(vcpu, MSR_IA32_PL3_SSP,
MSR_TYPE_RW, false);
vmx_set_intercept_for_msr(vcpu, MSR_IA32_INT_SSP_TAB,
diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index e200f22cdaad..49049454caf4 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -4051,6 +4051,8 @@ int kvm_set_msr_common(struct kvm_vcpu *vcpu, struct msr_data *msr_info)
if (msr == MSR_IA32_PL0_SSP || msr == MSR_IA32_PL1_SSP ||
msr == MSR_IA32_PL2_SSP) {
vcpu->arch.cet_s_ssp[msr - MSR_IA32_PL0_SSP] = data;
+ if (!vcpu->arch.cet_sss_active && data)
+ vcpu->arch.cet_sss_active = true;
} else if (msr == MSR_IA32_PL3_SSP) {
kvm_set_xsave_msr(msr_info);
}
@@ -11252,7 +11254,8 @@ int kvm_arch_vcpu_ioctl_run(struct kvm_vcpu *vcpu)
kvm_sigset_activate(vcpu);
kvm_run->flags = 0;
kvm_load_guest_fpu(vcpu);
- kvm_reload_cet_supervisor_ssp(vcpu);
+ if (vcpu->arch.cet_sss_active)
+ kvm_reload_cet_supervisor_ssp(vcpu);
kvm_vcpu_srcu_read_lock(vcpu);
if (unlikely(vcpu->arch.mp_state == KVM_MP_STATE_UNINITIALIZED)) {
@@ -11341,7 +11344,8 @@ int kvm_arch_vcpu_ioctl_run(struct kvm_vcpu *vcpu)
r = vcpu_run(vcpu);
out:
- kvm_save_cet_supervisor_ssp(vcpu);
+ if (vcpu->arch.cet_sss_active)
+ kvm_save_cet_supervisor_ssp(vcpu);
kvm_put_guest_fpu(vcpu);
if (kvm_run->kvm_valid_regs)
store_regs(vcpu);
@@ -12430,15 +12434,16 @@ void kvm_arch_sched_in(struct kvm_vcpu *vcpu, int cpu)
pmu->need_cleanup = true;
kvm_make_request(KVM_REQ_PMU, vcpu);
}
-
- kvm_reload_cet_supervisor_ssp(vcpu);
+ if (vcpu->arch.cet_sss_active)
+ kvm_reload_cet_supervisor_ssp(vcpu);
static_call(kvm_x86_sched_in)(vcpu, cpu);
}
void kvm_arch_sched_out(struct kvm_vcpu *vcpu, int cpu)
{
- kvm_save_cet_supervisor_ssp(vcpu);
+ if (vcpu->arch.cet_sss_active)
+ kvm_save_cet_supervisor_ssp(vcpu);
}
void kvm_arch_free_vm(struct kvm *kvm)
--
2.27.0
