[v4,15/38] KVM: x86/pmu: Check PMU cpuid configuration from user space

Commit Message

Mingwei Zhang March 24, 2025, 5:30 p.m. UTC

From: Dapeng Mi <[e-mail]>

Check user space's PMU cpuid configuration and filter the invalid
configuration.

Either legacy perf-based vPMU or mediated vPMU needs kernel to support
local APIC, otherwise PMI has no way to be injected into guest. If
kernel doesn't support local APIC, reject user space to enable PMU
cpuid.

User space configured PMU version must be no larger than KVM supported
maximum pmu version for mediated vPMU, otherwise guest may manipulate
some unsupported or unallowed PMU MSRs, this is dangerous and harmful.

If the pmu version is larger than 1 but smaller than 5, CPUID.AH.ECX
must be 0 as well which is required by SDM.

Suggested-by: Zide Chen <[e-mail]>
Signed-off-by: Dapeng Mi <[e-mail]>
Signed-off-by: Mingwei Zhang <[e-mail]>
---
 arch/x86/kvm/cpuid.c | 15 +++++++++++++++
 arch/x86/kvm/pmu.c   |  7 +++++--
 arch/x86/kvm/pmu.h   |  1 +
 3 files changed, 21 insertions(+), 2 deletions(-)

Patch

diff --git a/arch/x86/kvm/cpuid.c b/arch/x86/kvm/cpuid.c
index 8eb3a88707f2..f849ced9deba 100644
--- a/arch/x86/kvm/cpuid.c
+++ b/arch/x86/kvm/cpuid.c
@@ -179,6 +179,21 @@  static int kvm_check_cpuid(struct kvm_vcpu *vcpu)
 			return -EINVAL;
 	}
 
+	best = kvm_find_cpuid_entry(vcpu, 0xa);
+	if (vcpu->kvm->arch.enable_pmu && best) {
+		union cpuid10_eax eax;
+
+		eax.full = best->eax;
+		if (enable_mediated_pmu &&
+		    eax.split.version_id > kvm_pmu_cap.version)
+			return -EINVAL;
+		if (eax.split.version_id > 0 && !vcpu_pmu_can_enable(vcpu))
+			return -EINVAL;
+		if (eax.split.version_id > 1 && eax.split.version_id < 5 &&
+		    best->ecx != 0)
+			return -EINVAL;
+	}
+
 	/*
 	 * Exposing dynamic xfeatures to the guest requires additional
 	 * enabling in the FPU, e.g. to expand the guest XSAVE state size.
diff --git a/arch/x86/kvm/pmu.c b/arch/x86/kvm/pmu.c
index 4f455afe4009..92c742ead663 100644
--- a/arch/x86/kvm/pmu.c
+++ b/arch/x86/kvm/pmu.c
@@ -743,6 +743,10 @@  static void kvm_pmu_reset(struct kvm_vcpu *vcpu)
 	kvm_pmu_call(reset)(vcpu);
 }
 
+inline bool vcpu_pmu_can_enable(struct kvm_vcpu *vcpu)
+{
+	return vcpu->kvm->arch.enable_pmu && lapic_in_kernel(vcpu);
+}
 
 /*
  * Refresh the PMU configuration for the vCPU, e.g. if userspace changes CPUID
@@ -775,8 +779,7 @@  void kvm_pmu_refresh(struct kvm_vcpu *vcpu)
 	pmu->pebs_data_cfg_rsvd = ~0ull;
 	bitmap_zero(pmu->all_valid_pmc_idx, X86_PMC_IDX_MAX);
 
-	if (!vcpu->kvm->arch.enable_pmu ||
-	    (!lapic_in_kernel(vcpu) && enable_mediated_pmu))
+	if (!vcpu_pmu_can_enable(vcpu))
 		return;
 
 	kvm_pmu_call(refresh)(vcpu);
diff --git a/arch/x86/kvm/pmu.h b/arch/x86/kvm/pmu.h
index dd45a0c6be74..e1d0096f249b 100644
--- a/arch/x86/kvm/pmu.h
+++ b/arch/x86/kvm/pmu.h
@@ -284,6 +284,7 @@  void kvm_pmu_cleanup(struct kvm_vcpu *vcpu);
 void kvm_pmu_destroy(struct kvm_vcpu *vcpu);
 int kvm_vm_ioctl_set_pmu_event_filter(struct kvm *kvm, void __user *argp);
 void kvm_pmu_trigger_event(struct kvm_vcpu *vcpu, u64 eventsel);
+bool vcpu_pmu_can_enable(struct kvm_vcpu *vcpu);
 
 bool is_vmware_backdoor_pmc(u32 pmc_idx);