On 2/9/22 19:57, Sasha Levin wrote:
From: Sean Christopherson seanjc@google.com
[ Upstream commit d6e656cd266cdcc95abd372c7faef05bee271d1a ]
WARN if KVM attempts to allocate a shadow VMCS for vmcs02. KVM emulates VMCS shadowing but doesn't virtualize it, i.e. KVM should never allocate a "real" shadow VMCS for L2.
The previous code WARNed but continued anyway with the allocation, presumably in an attempt to avoid NULL pointer dereference. However, alloc_vmcs (and hence alloc_shadow_vmcs) can fail, and indeed the sole caller does:
if (enable_shadow_vmcs && !alloc_shadow_vmcs(vcpu)) goto out_shadow_vmcs;
which makes it not a useful attempt.
Signed-off-by: Sean Christopherson seanjc@google.com Message-Id: 20220125220527.2093146-1-seanjc@google.com Signed-off-by: Paolo Bonzini pbonzini@redhat.com Signed-off-by: Sasha Levin sashal@kernel.org
arch/x86/kvm/vmx/nested.c | 22 ++++++++++++---------- 1 file changed, 12 insertions(+), 10 deletions(-)
diff --git a/arch/x86/kvm/vmx/nested.c b/arch/x86/kvm/vmx/nested.c index 0c2389d0fdafe..0734a98eaaad1 100644 --- a/arch/x86/kvm/vmx/nested.c +++ b/arch/x86/kvm/vmx/nested.c @@ -4786,18 +4786,20 @@ static struct vmcs *alloc_shadow_vmcs(struct kvm_vcpu *vcpu) struct loaded_vmcs *loaded_vmcs = vmx->loaded_vmcs; /*
* We should allocate a shadow vmcs for vmcs01 only when L1* executes VMXON and free it when L1 executes VMXOFF.* As it is invalid to execute VMXON twice, we shouldn't reach* here when vmcs01 already have an allocated shadow vmcs.
* KVM allocates a shadow VMCS only when L1 executes VMXON and frees it* when L1 executes VMXOFF or the vCPU is forced out of nested* operation. VMXON faults if the CPU is already post-VMXON, so it* should be impossible to already have an allocated shadow VMCS. KVM* doesn't support virtualization of VMCS shadowing, so vmcs01 should* always be the loaded VMCS.
- WARN_ON(loaded_vmcs == &vmx->vmcs01 && loaded_vmcs->shadow_vmcs);
- if (WARN_ON(loaded_vmcs != &vmx->vmcs01 || loaded_vmcs->shadow_vmcs))
return loaded_vmcs->shadow_vmcs;- loaded_vmcs->shadow_vmcs = alloc_vmcs(true);
- if (loaded_vmcs->shadow_vmcs)
vmcs_clear(loaded_vmcs->shadow_vmcs);
- if (!loaded_vmcs->shadow_vmcs) {
loaded_vmcs->shadow_vmcs = alloc_vmcs(true);if (loaded_vmcs->shadow_vmcs)vmcs_clear(loaded_vmcs->shadow_vmcs);- } return loaded_vmcs->shadow_vmcs; }
NACK