linux-kernel - [PATCH 03/10] KVM: SVM: Terminate the VM if a SEV-ES+ guest is run with an invalid VMSA

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Message-ID: <20250219012705.1495231-4-seanjc@google.com>
Date: Tue, 18 Feb 2025 17:26:58 -0800
From: Sean Christopherson <seanjc@...gle.com>
To: Sean Christopherson <seanjc@...gle.com>, Paolo Bonzini <pbonzini@...hat.com>
Cc: kvm@...r.kernel.org, linux-kernel@...r.kernel.org, 
	Naveen N Rao <naveen@...nel.org>, Kim Phillips <kim.phillips@....com>, 
	Tom Lendacky <thomas.lendacky@....com>, Alexey Kardashevskiy <aik@....com>
Subject: [PATCH 03/10] KVM: SVM: Terminate the VM if a SEV-ES+ guest is run
 with an invalid VMSA

Terminate the VM if userspace attempts to run an SEV-SNP (or -ES) vCPU
that has an invalid VMSA.  With SNP's AP Create/Destroy hypercalls, it's
possible for an SNP vCPU to end up with an invalid VMSA, e.g. through a
deliberate Destroy or a failed Create event.  KVM marks the vCPU HALTED so
that *KVM* doesn't run the vCPU, but nothing prevents a misbehaving VMM
from manually making the vCPU RUNNABLE via KVM_SET_MP_STATE.

Fixes: e366f92ea99e ("KVM: SEV: Support SEV-SNP AP Creation NAE event")
Cc: stable@...r.kernel.org
Signed-off-by: Sean Christopherson <seanjc@...gle.com>
---
 arch/x86/kvm/svm/sev.c | 18 +++++++++++++++---
 arch/x86/kvm/svm/svm.c |  7 +++++--
 arch/x86/kvm/svm/svm.h |  2 +-
 3 files changed, 21 insertions(+), 6 deletions(-)

diff --git a/arch/x86/kvm/svm/sev.c b/arch/x86/kvm/svm/sev.c
index 6c6d45e13858..e14a37dbc6ea 100644
--- a/arch/x86/kvm/svm/sev.c
+++ b/arch/x86/kvm/svm/sev.c
@@ -3452,10 +3452,21 @@ void sev_es_unmap_ghcb(struct vcpu_svm *svm)
 	svm->sev_es.ghcb = NULL;
 }
 
-void pre_sev_run(struct vcpu_svm *svm, int cpu)
+int pre_sev_run(struct vcpu_svm *svm, int cpu)
 {
 	struct svm_cpu_data *sd = per_cpu_ptr(&svm_data, cpu);
-	unsigned int asid = sev_get_asid(svm->vcpu.kvm);
+	struct kvm *kvm = svm->vcpu.kvm;
+	unsigned int asid = sev_get_asid(kvm);
+
+	/*
+	 * Terminate the VM if userspace attempts to run the vCPU with an
+	 * invalid VMSA, e.g. if userspace forces the vCPU to be RUNNABLE after
+	 * an SNP AP Destroy event.
+	 */
+	if (sev_es_guest(kvm) && !VALID_PAGE(svm->vmcb->control.vmsa_pa)) {
+		kvm_vm_dead(kvm);
+		return -EIO;
+	}
 
 	/* Assign the asid allocated with this SEV guest */
 	svm->asid = asid;
@@ -3468,11 +3479,12 @@ void pre_sev_run(struct vcpu_svm *svm, int cpu)
 	 */
 	if (sd->sev_vmcbs[asid] == svm->vmcb &&
 	    svm->vcpu.arch.last_vmentry_cpu == cpu)
-		return;
+		return 0;
 
 	sd->sev_vmcbs[asid] = svm->vmcb;
 	svm->vmcb->control.tlb_ctl = TLB_CONTROL_FLUSH_ASID;
 	vmcb_mark_dirty(svm->vmcb, VMCB_ASID);
+	return 0;
 }
 
 #define GHCB_SCRATCH_AREA_LIMIT		(16ULL * PAGE_SIZE)
diff --git a/arch/x86/kvm/svm/svm.c b/arch/x86/kvm/svm/svm.c
index b8aa0f36850f..46e0b65a9fec 100644
--- a/arch/x86/kvm/svm/svm.c
+++ b/arch/x86/kvm/svm/svm.c
@@ -3587,7 +3587,7 @@ static int svm_handle_exit(struct kvm_vcpu *vcpu, fastpath_t exit_fastpath)
 	return svm_invoke_exit_handler(vcpu, exit_code);
 }
 
-static void pre_svm_run(struct kvm_vcpu *vcpu)
+static int pre_svm_run(struct kvm_vcpu *vcpu)
 {
 	struct svm_cpu_data *sd = per_cpu_ptr(&svm_data, vcpu->cpu);
 	struct vcpu_svm *svm = to_svm(vcpu);
@@ -3609,6 +3609,8 @@ static void pre_svm_run(struct kvm_vcpu *vcpu)
 	/* FIXME: handle wraparound of asid_generation */
 	if (svm->current_vmcb->asid_generation != sd->asid_generation)
 		new_asid(svm, sd);
+
+	return 0;
 }
 
 static void svm_inject_nmi(struct kvm_vcpu *vcpu)
@@ -4231,7 +4233,8 @@ static __no_kcsan fastpath_t svm_vcpu_run(struct kvm_vcpu *vcpu,
 	if (force_immediate_exit)
 		smp_send_reschedule(vcpu->cpu);
 
-	pre_svm_run(vcpu);
+	if (pre_svm_run(vcpu))
+		return EXIT_FASTPATH_EXIT_USERSPACE;
 
 	sync_lapic_to_cr8(vcpu);
 
diff --git a/arch/x86/kvm/svm/svm.h b/arch/x86/kvm/svm/svm.h
index 5b159f017055..e51852977b70 100644
--- a/arch/x86/kvm/svm/svm.h
+++ b/arch/x86/kvm/svm/svm.h
@@ -713,7 +713,7 @@ void avic_refresh_virtual_apic_mode(struct kvm_vcpu *vcpu);
 
 /* sev.c */
 
-void pre_sev_run(struct vcpu_svm *svm, int cpu);
+int pre_sev_run(struct vcpu_svm *svm, int cpu);
 void sev_init_vmcb(struct vcpu_svm *svm);
 void sev_vcpu_after_set_cpuid(struct vcpu_svm *svm);
 int sev_es_string_io(struct vcpu_svm *svm, int size, unsigned int port, int in);
-- 
2.48.1.601.g30ceb7b040-goog