KVM: nVMX: Fix memory corruption when using VMCS shadowing

commit 2f1fe81123f59271bddda673b60116bde9660385 upstream.

When freeing the nested resources of a vcpu, there is an assumption that
the vcpu's vmcs01 is the current VMCS on the CPU that executes
nested_release_vmcs12(). If this assumption is violated, the vcpu's
vmcs01 may be made active on multiple CPUs at the same time, in
violation of Intel's specification. Moreover, since the vcpu's vmcs01 is
not VMCLEARed on every CPU on which it is active, it can linger in a
CPU's VMCS cache after it has been freed and potentially
repurposed. Subsequent eviction from the CPU's VMCS cache on a capacity
miss can result in memory corruption.

It is not sufficient for vmx_free_vcpu() to call vmx_load_vmcs01(). If
the vcpu in question was last loaded on a different CPU, it must be
migrated to the current CPU before calling vmx_load_vmcs01().

Signed-off-by: Jim Mattson <jmattson@google.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>

diff --git a/arch/x86/kvm/vmx.c b/arch/x86/kvm/vmx.c
index 82bb49d39fbb0389922e63cbcd393d0f859da503..bb4656ad74809fc62ca52e7aa413712e06059a82 100644 (file)
--- a/arch/x86/kvm/vmx.c
+++ b/arch/x86/kvm/vmx.c
@@ -7578,14 +7578,29 @@ static void vmx_load_vmcs01(struct kvm_vcpu *vcpu)
        put_cpu();
 }
 
+/*
+ * Ensure that the current vmcs of the logical processor is the
+ * vmcs01 of the vcpu before calling free_nested().
+ */
+static void vmx_free_vcpu_nested(struct kvm_vcpu *vcpu)
+{
+       struct vcpu_vmx *vmx = to_vmx(vcpu);
+       int r;
+
+       r = vcpu_load(vcpu);
+       BUG_ON(r);
+       vmx_load_vmcs01(vcpu);
+       free_nested(vmx);
+       vcpu_put(vcpu);
+}
+
 static void vmx_free_vcpu(struct kvm_vcpu *vcpu)
 {
        struct vcpu_vmx *vmx = to_vmx(vcpu);
 
        free_vpid(vmx);
        leave_guest_mode(vcpu);
-       vmx_load_vmcs01(vcpu);
-       free_nested(vmx);
+       vmx_free_vcpu_nested(vcpu);
        free_loaded_vmcs(vmx->loaded_vmcs);
        kfree(vmx->guest_msrs);
        kvm_vcpu_uninit(vcpu);

diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
index a63127acc67d699a7638f6193ba7c89ab5631d98..6103f92387745c2e124deb53102a20395b72530b 100644 (file)
--- a/virt/kvm/kvm_main.c
+++ b/virt/kvm/kvm_main.c
@@ -137,6 +137,7 @@ int vcpu_load(struct kvm_vcpu *vcpu)
        put_cpu();
        return 0;
 }
+EXPORT_SYMBOL_GPL(vcpu_load);
 
 void vcpu_put(struct kvm_vcpu *vcpu)
 {
@@ -146,6 +147,7 @@ void vcpu_put(struct kvm_vcpu *vcpu)
        preempt_enable();
        mutex_unlock(&vcpu->mutex);
 }
+EXPORT_SYMBOL_GPL(vcpu_put);
 
 static void ack_flush(void *_completed)
 {