linux-kernel - [PATCH v2 7/7] KVM: nVMX: Assert that vcpu->mutex is held when accessing secondary VMCSes

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Message-ID: <20240906043413.1049633-8-seanjc@google.com>
Date: Thu,  5 Sep 2024 21:34:13 -0700
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, 
	Nathan Chancellor <nathan@...nel.org>, Chao Gao <chao.gao@...el.com>, 
	Zeng Guang <guang.zeng@...el.com>
Subject: [PATCH v2 7/7] KVM: nVMX: Assert that vcpu->mutex is held when
 accessing secondary VMCSes

Add lockdep assertions in get_vmcs12() and get_shadow_vmcs12() to verify
the vCPU's mutex is held, as the returned VMCS objects are dynamically
allocated/freed when nested VMX is turned on/off, i.e. accessing vmcs12
structures without holding vcpu->mutex is susceptible to use-after-free.

Waive the assertion if the VM is being destroyed, as KVM currently forces
a nested VM-Exit when freeing the vCPU.  If/when that wart is fixed, the
assertion can/should be converted to an unqualified lockdep assertion.
See also https://lore.kernel.org/all/Zsd0TqCeY3B5Sb5b@google.com.

Signed-off-by: Sean Christopherson <seanjc@...gle.com>
---
 arch/x86/kvm/vmx/nested.h | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/arch/x86/kvm/vmx/nested.h b/arch/x86/kvm/vmx/nested.h
index cce4e2aa30fb..668b6c83a373 100644
--- a/arch/x86/kvm/vmx/nested.h
+++ b/arch/x86/kvm/vmx/nested.h
@@ -39,11 +39,17 @@ bool nested_vmx_check_io_bitmaps(struct kvm_vcpu *vcpu, unsigned int port,
 
 static inline struct vmcs12 *get_vmcs12(struct kvm_vcpu *vcpu)
 {
+	lockdep_assert_once(lockdep_is_held(&vcpu->mutex) ||
+			    !refcount_read(&vcpu->kvm->users_count));
+
 	return to_vmx(vcpu)->nested.cached_vmcs12;
 }
 
 static inline struct vmcs12 *get_shadow_vmcs12(struct kvm_vcpu *vcpu)
 {
+	lockdep_assert_once(lockdep_is_held(&vcpu->mutex) ||
+			    !refcount_read(&vcpu->kvm->users_count));
+
 	return to_vmx(vcpu)->nested.cached_shadow_vmcs12;
 }
 
-- 
2.46.0.469.g59c65b2a67-goog